Foundry production of non-ferrous metals. Lecture notes on the discipline "Foundry"

Foundry is one of the industries whose main products are those used in mechanical engineering. There are many factories of this specialization in Russia. Some of these enterprises have small capacities, others can be considered real industrial giants. Further in the article we will look at what are the largest foundry and mechanical plants in Russia on the market (with addresses and descriptions), and what specific products they produce.

Products produced by LMZ

Of course, such enterprises are a vital part of the national economy. Foundries in Russia produce a huge number of different products. For example, castings, ingots, and ingots are produced in the workshops of such enterprises. Finished products are also produced at enterprises in this industry. These could be, for example, grates, sewer hatches, bells, etc.

Iron foundries in Russia supply their products, as already mentioned, mainly to enterprises in the mechanical engineering industry. Up to 50% of the equipment produced by such factories is made from cast billets. Of course, companies of other specializations can also be LMZ partners.

Main problems of the industry

The situation with foundry production in the Russian Federation today is, unfortunately, difficult. After the collapse of the USSR, the country's engineering industry fell into almost complete decline. Accordingly, the demand for shaped casting products has also decreased significantly. Later, sanctions and outflow of investment had a negative impact on the development of LMZ. However, despite this, Russian foundries continue to exist, supply high-quality products to the market and even increase production rates.

The main problem of enterprises of this specialization in the Russian Federation for many years has been the need for modernization. However, the implementation of new technologies also requires additional costs. Unfortunately, in most cases, such companies still have to buy the equipment necessary for modernization abroad for a lot of money.

List of the largest foundries in Russia

Today in the Russian Federation, about 2,000 enterprises are engaged in the production of shaped products from cast iron, steel, aluminum, etc. The largest foundries in Russia are:

• Balashikhinsky.
• Kamensk-Uralsky.
• Taganrog.
• "KAMAZ".
• Cherepovetsky.
• Balezinsky.

KULZ

This enterprise was founded in Kamensk-Uralsky during the war - in 1942. At that time Balashikhinsky was evacuated here foundry. Later, the facilities of this enterprise were returned to their place. In Kamensk-Uralsk, its own foundry began to operate.

During the Soviet era, KULZ products were focused mainly on the country's military-industrial complex. In the 90s, during the conversion period, the enterprise was repurposed to produce consumer goods.

Today KULZ is engaged in the production of shaped casting blanks intended for both military equipment, and for civilians. In total, the company produces 150 types of products. The plant supplies the market with brake systems and wheels for aircraft, radio components, blanks made of biometal and metal-ceramics, etc. The head office of KULZ is located at the following address: Kamensk-Uralsky, st. Ryabova, 6.

BLMZ

Almost all foundries in Russia, the list of which was provided above, were put into operation in the last century. BLMZ is no exception in this regard. This company, the oldest in the country, was founded in 1932. Its first products were spoked wheels for aircraft. In 1935, the plant mastered technologies for the production of shaped aluminum products and in the post-war period, the enterprise specialized mainly in the production of take-off and landing devices for aircraft. In 1966, products made from titanium alloys began to be produced here.

During the collapse of the USSR, the Balashikha plant managed to maintain the main direction of its activity. In the early 2000s, the company actively updated its technical fleet. In 2010, the plant began developing new production areas in order to expand the range of products.

Since 2015 BLMZ, together with scientific complex Soyuz began implementing a project to produce gas turbine units with a capacity of up to 30 MW. The office of the BLMZ company is located at the address: Balashikha, Entuziastov Highway, 4.

Taganrog Foundry

The main office of this company can be found at the following address: Taganrog, Severnaya Square, 3. TLMZ was founded quite recently - in 2015. However, today its capacity is already about 13 thousand tons per year. This became possible thanks to the use the latest equipment And innovative technologies. Currently, Taganrog LMZ is the most modern enterprise foundry industry in the country.

TLMZ was built for just a few months. In total, about 500 million rubles were spent during this time. The enterprise purchased components for the main production line from Danish companies. The stoves at the plant are Turkish. All other equipment is made in Germany. Today, 90% of the Taganrog plant's products are supplied to the domestic market.

The largest foundries in Russia: ChLMZ

The decision to build the Cherepovets enterprise was made in 1950. Since 1951, the plant began producing spare parts for road construction machines and tractors. In all subsequent years, until perestroika, the enterprise was constantly modernized and expanded. In 2000, the plant management chose the following strategic directions of production:

• production of furnace rollers for metallurgical plants;
• production of furnaces for machine-building enterprises;
• pump casting for the chemical industry;
• production of radiator heaters for furnaces.

Today ChLMZ is one of the main Russian manufacturers similar products. His partners are not only machine-building enterprises, but also light industry, housing and communal services. The office of this company is located at: Cherepovets, st. Construction industry, 12.

Balezinsky foundry

This largest enterprise was founded in 1948. Initially it was called the “Liteyshchik” artel. In the first years of its existence, the plant specialized mainly in the production of aluminum cookware. A year later, the company began producing cast iron. The artel was renamed the Balezinsky LMZ in 1956. Today this plant produces about 400 types of a wide variety of products. Its main activity is the production of oven castings, tableware and baking molds. Company address: Balezin, st. K. Marx, 77.

Foundry plant "KAMAZ"

This company operates in Naberezhnye Chelny. Its production capacity is 245 thousand castings per year. The KamAZ foundry produces products from high-strength cast iron, gray, with vermicular graphite. This enterprise was built in 1975. The first product of the plant was aluminum castings 83 titles. In 1976, the enterprise mastered the production of cast iron and steel products. Initially, the plant was part of the well-known joint stock company"KAMAZ". In 1997, it gained independent status. However, in 2002, the enterprise again became part of KamAZ OJSC. This plant is located at the address: Naberezhnye Chelny, Avtozavodsky Avenue, 2.

Nizhny Novgorod enterprise OJSC LMZ

The main product of JSC Foundry and Mechanical Plant (Russia, Nizhny Novgorod) is cast iron pipeline fittings. The products produced by this enterprise are used in the transportation of gas, steam, oil, water, fuel oil, and oils. The plant began its activities in 1969. At that time it was one of the workshops of the Gorky Flax Association. Today, its partners are many mechanical engineering, housing and communal services and water supply enterprises.

Instead of a conclusion

The well-being of the entire country as a whole largely depends on how smoothly and stably the Russian foundries described above will function. Without the products manufactured by these companies, domestic enterprises of mechanical engineering, metallurgy, light industry, etc. will not be able to operate. Therefore, paying maximum attention to the development, reconstruction and modernization of these and other foundries, providing them with comprehensive support, including at the state level, of course , necessary and very important.

Foundry production is one of the oldest crafts mastered by mankind. The first casting material was bronze. In ancient times, bronzes were complex alloys based on copper with additives of tin (5-7%), zinc (3-5%), antimony and lead (1-3%) with admixtures of arsenic, sulfur, silver (tenths of a percent). The origin of bronze smelting and the production of cast products from it (weapons, jewelry, dishes, etc.) in different regions dates back to the 3rd-7th millennium BC. Apparently, the smelting of native silver, gold and their alloys was mastered almost simultaneously. In the territory where the Eastern Slavs lived, a developed foundry craft appeared in the first centuries AD. e.

The main methods of producing castings from bronze and alloys of silver and gold were casting ij stone molds and casting on wax. Stone forms were made from soft limestone rocks, in which a working cavity was cut out. Typically, stone molds were poured open, so that one side of the product, formed by the open surface of the melt, was flat. When casting on wax, wax models were first made as exact copies of future products. These models were immersed in a liquid clay solution, which was then dried and fired. The wax burned out, and the melt was poured into the resulting cavity.

A big step forward in the development of bronze casting was made when the casting of bells and cannons began (XV-XVI centuries). The skill and art of Russian craftsmen who made unique bronze castings are widely known - the “Tsar Cannon” weighing 40 tons (Andrei Chokhov, 1586), and the “Tsar Bell” weighing 200 tons (Ivan and Mikhail Motorin, 1736).

Bronze and later brass have been the main material for the production of artistic castings, monuments and sculptures for many centuries. A bronze sculpture of the Roman emperor Marcus Aurelius (2nd century AD) has survived to this day. Monuments cast in bronze to Peter 1 in Leningrad (1775) and the monument “Millennium of Russia” in Novgorod (1862) became world famous. In our time, a cast bronze monument to Yuri Dolgoruky, the founder of Moscow, was made (1954).

In the 18th century The new foundry material, cast iron, which served as the basis for the development of the machine industry in the first half of the 19th century, took first place in terms of mass production and versatility. By the beginning of the 20th century. foundry production of non-ferrous metals and alloys consisted of producing shaped castings from tin bronzes and brass and ingots from copper, bronze and brass. Shaped castings were made only by casting in sand molds (at that time they said and wrote “earth molds”, “casting in the ground”). Ingots weighing no more than 200 kg were produced by casting into cast iron molds.

The next stage in the development of foundry production of non-ferrous metals and alloys began around 1910-1920, when new alloys were developed, primarily based on aluminum and, somewhat later, based on magnesium. At the same time, the development of shaped and blank casting from special bronzes and brasses - aluminum, silicon, manganese, nickel, as well as the development of the production of ingots from nickel and its alloys began. In 1920-1930 Zinc alloys are created for injection molding. In 1930-1940 Shaped casting from nickel alloys is being developed. Period 1950-1970 was marked by the development of technology for melting and casting titanium and its alloys, uranium and other radioactive metals, zirconium and alloys based on it, molybdenum, tungsten, chromium, niobium, beryllium and rare earth metals.

The development of new alloys required a radical restructuring of smelting technology and melting equipment, the use of new molding materials and new methods for making molds. The mass nature of production contributed to the development of new principles for organizing production, based on extensive mechanization and automation of the processes of manufacturing molds and cores, melting, pouring molds, and processing castings.

The need to ensure high quality castings has led to deep scientific research properties of liquid metals, processes of interaction of melts with gases, refractory materials, slags and fluxes, refining processes from inclusions and gases, crystallization processes of metal alloys at very low and very high cooling rates, filling processes

foundries X molds with a melt, solidification of castings with accompanying phenomena - volumetric and linear shrinkage, the emergence of different structures, segregation, stresses. These studies began in 1930-1940. acad. A. A. Bochvar, who laid the foundations of the theory of casting properties of alloys.

Since 1920-1930 Electric furnaces - resistance, induction channel and crucible - are widely used for melting non-ferrous metals and alloys. Melting of refractory metals was practically possible only by using an arc discharge in a vacuum and electron beam heating. Plasma melting is currently being developed, and laser beam melting is next.

In 1940-1950 There was a massive transition from sand casting to metal casting - chill molds (aluminum alloys, magnesium and copper) to pressure casting (zinc, aluminum, magnesium alloys, brass). During these same years, in connection with the production of cast turbine blades from heat-resistant nickel alloys, the ancient method of wax casting, called precision casting and now called lost-wax casting, was revived on a new basis. This method ensured the production of castings with very small allowances for machining due to very precise dimensions and high surface finish, which was necessary due to the extremely difficult machinability of all heat-resistant alloys on nickel and cobalt bases.

In blank casting (production of ingots for subsequent deformation for the purpose of manufacturing semi-finished products) in 1920-1930. Instead of cast iron, water-cooled molds began to be widely used. In the 1940-1950s. semi-continuous and continuous casting of ingots from aluminum, magnesium, copper and nickel alloys is being introduced.

In 1930-1940 There have been fundamental changes in the principles of constructing the technology of pouring molds and solidifying castings. These changes were due to both the sharp difference in the properties of new casting alloys from the properties of traditional gray cast iron and tin bronze (formation of strong oxide films, large volumetric shrinkage, crystallization interval changing from alloy to alloy), and the increased level of requirements for castings in terms of strength, density and homogeneity.

Designs of new expanding gating systems were developed in contrast to the old tapering ones. In expanding systems, the cross-sectional areas of the channels increase from the riser to the feeder gates, so that the most bottleneck is the cross section of the riser at the transition to the slag collector. In this case, the first portions of metal flowing from the riser into the slag, which cannot be filled, flow of the melt from the slag into the gates occurs under the influence of a very small pressure in the unfilled slag. This small pressure creates a correspondingly small linear velocity of the melt entering the mold cavity. The melt streams in the mold do not break into droplets and do not capture air; but the oxide film on the surface of the melt in the mold is destroyed, the melt is not contaminated with films. Due to these advantages of expanding gating systems, they are currently used to produce critical castings from all alloys,

To others important achievement In the technology for producing high-quality castings, the principle of directional solidification of castings was developed and implemented during the development of shaped casting from new alloys of non-ferrous metals. The experience gained in producing castings from traditional, “old” casting alloys - gray cast iron and tin bronze - indicated that it is necessary to disperse the supply of the melt into the casting mold, ensuring, first of all, reliable filling of the mold cavity and preventing its local heating. The volume of gray cast iron almost does not change during crystallization, and therefore castings from this alloy are practically not affected by shrinkage porosity or shell `i`e and do not need gains.

“Old” tin bronzes with 8-10% tin had a very long crystallization interval, therefore, when casting in sand molds, all volumetric shrinkage in the castings manifested itself in the form of fine scattered porosity, indistinguishable to the naked eye. The impression was created that the metal in the casting is dense and that using the experience of producing cast iron castings, with the supply of metal to its thin parts, is also justified in the case of casting bronze products. Profits like technological tides on castings simply did not exist. The mold provided only a vent - a vertical channel from the mold cavity, the appearance of a melt in which served as a sign of filling the casting mold.

To obtain high-quality castings from new alloys, it turned out to be necessary to carry out directional solidification from thin parts, which naturally harden first, to more massive ones and then to profits. In this case, the loss in volume during crystallization of each previously solidified area is replenished with melt from the area that has not yet begun to solidify, and, finally, from the gains that are the last to solidify. Such directed solidification requires a very competent choice of the location for supplying the melt to the mold. It is impossible to supply the melt to the thinnest section of the mold; it is more rational to supply the liquid metal near the profit so that this part of the mold heats up during filling. To create directional solidification, it is necessary to intentionally freeze those parts of the mold where solidification should occur faster. This is achieved using refrigerators in sand molds or special cooling in metal molds. Where hardening should take place last, the mold is deliberately insulated or heated.

The principle of directional solidification, realized and formulated during the development of the production of castings from aluminum and magnesium alloys, is now absolutely mandatory for obtaining high-quality castings from any alloys.

The development of the scientific basis for melting alloys of non-ferrous metals, their crystallization, and the development of technology for producing shaped castings and ingots is the merit of a large group of scientists, many of whom were closely associated with high school. These primarily include A. A. Bochvar, S. M. Voronov, I. E. Gorshkov, I. F. Kolobnev, N. V. Okromeshko, A. G. Spassky, M. V. Sharov.

Scientific developments and production processes in the field of foundry production of non-ferrous metals in our country corresponds to advanced achievements scientific and technological progress. Their result, in particular, was the creation modern workshops chill casting and injection molding at the Volzhsky Automobile Plant and a number of other enterprises. At the Zavolzhsky Motor Plant, large injection molding machines with a mold locking force of 35 MN are successfully operating, which produce cylinder blocks made of aluminum alloys for the Volga car. The Altai Motor Plant has mastered an automated line for producing injection molded castings. In the Soviet Union, for the first time in the world, the process of continuous casting of aluminum alloy ingots into an electromagnetic crystallizer was developed and mastered. This method significantly improves the quality of ingots and reduces the amount of waste in the form of chips during turning.

The main task facing the foundry industry in our country is a significant overall improvement in the quality of castings, which should find expression in reducing wall thickness, reducing allowances for machining and for gating-feeding systems while maintaining the proper performance properties of products. The final result of this work)) should be to meet the increased needs of mechanical engineering with the required quantity of castings without a significant increase in the total output of castings by weight.

The problem of improving the quality of castings is closely related to the problem of economical use of metal. When applied to non-ferrous metals, both of these problems become particularly acute. Due to the depletion of rich deposits of non-ferrous metals, the cost of their production is constantly and significantly increasing. Now non-ferrous metals are five to ten or more times more expensive than cast iron and carbon steel. Therefore, economical use of non-ferrous metals, reduction of losses, and reasonable use of waste are an indispensable condition for the development of foundry production.

In industry, the share of non-ferrous metal alloys obtained by processing waste - trimmings, shavings, various scrap and slags - is constantly increasing. These alloys contain an increased amount of various impurities that can reduce their technological properties and performance characteristics of products. Therefore, extensive research is currently underway to develop methods for refining such melts and developing technology for producing high-quality cast billets.

REQUIREMENTS FOR CASTINGS

Castings from alloys of non-ferrous metals must have a certain chemical composition, a given level of mechanical properties, the necessary dimensional accuracy and surface cleanliness without external and internal defects. Cracks, non-slates, through holes and looseness are not allowed in castings. Surfaces that are bases for machining , must not have sagging or damage.Acceptable defects, their number, detection methods and correction methods are regulated by industry standards (OST) and technical specifications.

The castings are supplied with the sprues cut off and the sprues cut off. Trimming and stumping areas on untreated surfaces are cleaned flush. Correction of defects by welding and impregnation is allowed. Necessity heat treatment determined by technical conditions.

The dimensional accuracy of castings must meet the requirements of OST 1.41154-72. Tolerances, which include the sum of all deviations from the dimensions of the drawing that occur at various stages of casting production, except for deviations due to the presence of casting slopes, must correspond to one of seven accuracy classes (Table 20). In each accuracy class, all tolerances for any size of one type (D, T or M) are equal for a given casting and are set according to the largest overall dimension.

The processed surfaces of castings must have an allowance for machining. The minimum allowance must be greater than the tolerance. The amount of allowance is determined by the overall dimensions and accuracy class of the castings.

The surface cleanliness of castings must correspond to the specified roughness class. It depends on the method of making castings, the materials used to make molds, the quality of surface preparation of models, molds and molds. To obtain castings that meet the above requirements, use various ways casting into one-time and reusable molds.

CLASSIFICATION OF CASTINGS

According to the service conditions, regardless of the manufacturing method, castings are divided into three groups: general, responsible and special responsible appointment.

The general purpose group includes castings for parts not designed for strength. Their configuration and dimensions are determined only by design and technological considerations. Such castings are not subjected to X-ray inspection.

Castings for critical purposes are used for the manufacture of parts designed for strength and operating under static loads. They undergo selective X-ray inspection.

The group of especially critical purposes includes castings for parts designed for strength and operating under cyclic and dynamic loads. They are subjected to individual X-ray inspection, fluorescence inspection and eddy current inspection.

Depending on the volume of acceptance tests, industry standards OST11.90021-71, OST 1.90016-72, OST1.90248-77 provide for the division of castings from non-ferrous metal alloys into three groups.

Group 1 includes castings whose mechanical properties are monitored selectively on samples cut from the body of control castings, with simultaneous testing of mechanical properties on separately cast samples from each cast or piece-by-piece testing on samples cut from blanks cast to each casting, as well as piece-by-piece testing density control (x-ray).

Group II includes castings, the mechanical properties of which are determined on separately cast samples or on samples cut from blanks cast to the casting, and, at the request of the consumer plant, on samples cut from castings (selectively), as well as piece-by-piece or selective control for the density of castings by X-ray method. (For castings of group IIa, density control is not performed).

Group III consists of castings in which only hardness is controlled. At the request of the consumer plant, mechanical properties are monitored on separately cast samples.

The assignment of castings to the appropriate group is made by the designer and specified in the drawing.

Depending on the manufacturing method, surface configuration, masses of maximum geometric size, wall thickness, characteristics of mortars, ribs, thickenings, holes, number of rods, nature of machining and roughness of machined surfaces, purpose and special technical requirements the division of castings into 5-6 complex groups is provided (casting in sand molds and under pressure - 6 groups; casting in chill molds, lost wax and shell molds - 5 groups). In this case, the number of matching features should be at least five or four for six or five complexity groups, respectively. If there is a smaller number of matching features, a method of grouping them is used by sequentially assigning them starting from higher complexity groups towards lower ones and stopping at the complexity group at which the required number of conditionally matching features is achieved. If the number of features in two groups is equal, it is difficult to assign the casting to the group in which the feature “surface configuration” was used to determine it.

BASICS OF MELTING TECHNOLOGY

Having information about the properties of materials and their interactions with gases and refractory materials, it is possible to create a scientifically based smelting technology. The development of smelting technology for a specific situation includes the choice of a melting unit, the type of energy, the choice of furnace lining material, and the determination of the required composition of the atmosphere in the furnace during smelting. When creating technology, they decide on ways to prevent possible contamination of the melt and methods for refining it. The need for deoxidation and modification of the alloy is also considered.

A very important issue is the correct choice of charge materials, i.e. those materials that are subject to fusion. When creating technologies, they also provide for a reduction in the consumption of metals, auxiliary materials, energy, and labor. These issues can only be resolved in a very specific situation.

It should be borne in mind that the above information about the properties of metals and ongoing processes related to the conditions of a “pure” experiment, when the influence of other processes was deliberately minimized. In a real situation, this influence can significantly change individual properties. In addition, in a real situation, the melt as a system is never in equilibrium with the environment; it turns out to be either oversaturated or undersaturated. In this regard, the kinetic side of the process becomes of great importance. Quantification kinetics is very difficult due to the uncertainty of the equations describing in time the processes of gas saturation, degassing, interaction with the lining, etc. Therefore, in the end it turns out that for a correct judgment about the phenomena occurring during melting, not only quantitative calculations of individual processes are important, but also more complete accounting and evaluation of the largest number of these processes.

DEVELOPMENT OF MELTING TECHNOLOGY

The starting points when creating a technology for melting a metal or alloy are its composition, which includes the base, alloying components and impurities, and a given level of mechanical and other properties of the alloy in the casting. In addition, the quantitative demand for melt per unit time is taken into account. The type of melting furnace is selected based on the melting temperature of the main component of the alloy and the chemical activity of both it and all alloying components and the most harmful impurities; at the same time, the issue of the furnace lining material is resolved.

In most cases, melting is carried out in air. If interaction with air is limited to the formation of compounds insoluble in the melt on the surface and the resulting film of these compounds significantly slows down further interaction, then usually no measures are taken to suppress such interaction. In this case, smelting is carried out in direct contact of the melt with the atmosphere. This is done in the preparation of most aluminum, zinc, and tin-lead alloys. If the resulting film of insoluble compounds is fragile and unable to protect the melt from further interaction (magnesium

and its alloys), then take special measures using fluxes or a protective atmosphere.

Protection of the melt from interaction with gases is absolutely necessary if the gas dissolves in the liquid metal. They mainly strive to prevent the interaction of the melt with oxygen. This applies to the melting of nickel-based alloys and copper alloys capable of dissolving oxygen, where the melts are necessarily protected from interaction with the furnace atmosphere. Protection of the melt is achieved primarily by the use of slags, fluxes and other protective coatings. If such measures turn out to be insufficient or impossible, resort to smelting in an atmosphere of protective or inert gases. Finally, melting is used in a vacuum, i.e., at a gas pressure reduced to a certain level. In some cases, to reduce the intensity of interaction of the melt with oxygen, additives of beryllium (hundredths of a percent in aluminum-magnesium and magnesium alloys), silicon and aluminum (tenths of a percent in brass) are introduced into it.

Despite the protection, metal melts are still contaminated with various impurities above permissible limit. Often, charge materials contain too many impurities. Therefore, during melting, melts are often refined - purified from soluble and insoluble impurities, as well as deoxidized - removed dissolved oxygen. Many alloys find application in a modified state, when they acquire a fine-crystalline structure and higher mechanical or technological properties. The modification operation is carried out as one of the last stages of the smelting process immediately before casting. When developing a smelting technology, it is taken into account that the mass of the resulting liquid metal will always be slightly less than the mass of the metal charge due to metal losses in the slag and waste losses. These losses amount to 2-5% in total, and the greater the mass of a single melt, the lower the losses.

Slag, which always appears on the surface of the melt, is a complex system of alloy solutions and mixtures of oxides of the main component of the alloy, alloying components and impurities. In addition, the slag necessarily contains oxides from the smelting furnace lining. Such primary slag naturally occurring on the melt can be completely liquid, partially liquid (curdled) and solid. In addition to oxides, slags always contain some amount of free metal. In liquid and curdled slags, free metal is found in the form of separate drops - beads. If the oxides that make up the slag are below their melting point, then they are solid. When stirring the melt and attempting to remove slag from it, these oxides, often in the form of a film, are mixed into the melt. Thus, despite the refractoriness of the oxides, the formed and removed slag has a liquid consistency, which is due to the large amount of trapped melt. In such slag, the amount of free metal is about 50% of the total mass of the removed slag, while in truly liquid slag its content does not exceed 10-30%.

The loss of metals during waste smelting is determined by their evaporation and interaction with the lining, expressed in its metallization.

The metal contained in the slag can be returned to production. This is most simply achieved in relation to a free metal that is not bound into any compounds. Crushing and sieving the slag allows you to return 70-80% of the free metal. The remaining slag is a high-quality metallurgical raw material, and it is sent to metallurgical plants to isolate the most valuable components.

When determining metal losses during melting for waste and with slag, one must not forget about the contamination of charge materials with foreign non-metallic impurities and inclusions in the form of oil residues, emulsion, water, slag, molding and core mixtures. If the work is not done carefully, the mass of these impurities is automatically counted as the mass of the metal being melted, and the result is an unreasonably inflated value of losses during melting.

An important aspect of the technology is the temperature regime of smelting, the order of loading charge materials and the introduction of individual alloy components, the sequence technological operations metallurgical processing of the melt. Melting is always carried out in a preheated furnace, the temperature in which should be 100-200 ° C higher than the melting point of the main component of the alloy. It is advisable that all materials loaded into the oven be heated to 150-200°C so that no moisture remains in them. The first charge material that makes up the largest share in the sample is loaded into the melting furnace. When preparing an alloy from pure metals, the main component of the alloy is always loaded first. If smelting is carried out using slags and fluxes, they are usually poured on top of the loaded metal charge. If production conditions allow, a new melt is started, leaving a certain amount of melt from the previous melt in the furnace. Loading the charge into a liquid bath significantly speeds up the smelting process and reduces metal losses. First, a more refractory charge is loaded into the liquid bath. Periodically add fresh slag or flux and, if necessary, remove the old one. If the technology requires deoxidation of the melt (removal of dissolved oxygen), then it is carried out in such a way as to avoid the formation of difficult-to-remove and harmful non-metallic inclusions in the melt and to ensure reliable removal of deoxidation products (see below). Lastly, volatile and chemically active components of the alloy are introduced into the melt to reduce their losses. Then the melt is refined. Immediately before casting, the melt is modified.

It is advisable to determine the conditions for introducing individual types of charge or alloy components into a liquid bath by comparing the melting temperature of the loaded material and its density with the melting temperature and density of the alloy. It is also necessary to know at least double state diagrams of the main component of the alloy with alloying components, impurities and modifying additives.

In the vast majority of cases, all alloying components and impurities are dissolved in the liquid base of the alloy, so that the melt can be considered a solution. However, the preparation and formation of such a solution is carried out in different ways. If the next solid additive has a higher melting temperature than the melt, then only the usual dissolution of a solid into a liquid is possible. This requires active forced mixing. The specified refractory additive may have a density lower than the density of the melt, and in this case it will float on the surface, where it can oxidize and become entangled in slag. This raises the danger of not meeting the specified alloy composition. If such a “light” additive has a lower melting point than the melt, it goes into a liquid state and therefore its further dissolution in the melt is significantly facilitated. In some cases, in order to avoid oxidation and loss, such additives are introduced into the melt using a so-called bell - a perforated glass into which the added additive is placed, and then immersed in the melt. If the additive is heavier than the melt, it sinks to the bottom of the liquid bath, so it is unlikely to oxidize. However, it is difficult to monitor the dissolution of such additives, especially if they are more refractory than the melt. Sufficiently long and thorough mixing of the entire mass of the melt is necessary to ensure complete dissolution.

Alloys are often used to prepare alloys. This is the name given to intermediate alloys, usually consisting of the main component of the working alloy with one or more alloying components, but in significantly higher contents than in the working alloy. The use of ligatures has to be resorted to in cases where the introduction of the additive component in its pure form is difficult for various reasons. Such reasons may be the duration of the dissolution process, losses from oxidation, evaporation, and slag formation.

Ligatures are also used when introducing chemically active additives, which in free form in air can interact with oxygen and nitrogen. Alloys are also widely used in cases where a pure additive element is too expensive or is not available at all, but the production of alloy alloys has already been mastered, they are available and quite cheap.

Finally, it is advisable to use alloys when it is necessary to introduce very small additives into the alloy. The amount of pure additive can be only a few hundred grams per several hundred kilograms of melt. It is almost impossible to reliably introduce such a small amount of alloying component due to various types of losses and uneven distribution. The use of a ligature, which is introduced in a much larger quantity, eliminates these difficulties.

It should be noted that general rule technology for melting alloys is to keep the process time as short as possible. This helps reduce energy costs, metal losses, and contamination of the melt with gases and impurities. At the same time, it must be borne in mind that in order to completely dissolve all components and average the composition of the alloy, it is necessary to “boil” the melt - hold it at the highest permissible temperature for 10-15 minutes.

CLASSIFICATION OF MELTING FURNACES

Depending on the scale of production, the requirements for the quality of the melted metal and a number of other factors, non-ferrous metals are used in blank and shaped casting shops Various types melting furnaces.

Based on the type of energy used for melting alloys, all melting furnaces are divided into fuel and electric. Fuel furnaces are divided into crucible, reverberatory and shaft-bath furnaces. Electric furnaces are classified depending on the conversion method electrical energy to thermal. Foundries use resistance, induction, electric arc, electron beam and plasma furnaces.

In electric resistance furnaces, heating and melting of the charge is carried out due to thermal energy supplied from electric heating elements installed in the roof or walls of the melting furnace. These furnaces are used for melting aluminum, magnesium, zinc, tin and lead alloys.

Based on their operating principle and design, induction furnaces are divided into crucible and channel furnaces. Crucible furnaces, depending on the frequency of the supply current, are classified into furnaces with increased [(0.15-10)-10^6 per/s] and industrial frequency (50 per/s).

Regardless of the frequency of the supply current, the operating principle of all induction crucible furnaces is based on the induction of electromagnetic energy in the heated metal (Foucault currents) and its conversion into heat. When melting in metal or other crucibles made of electrically conductive materials, thermal energy is also transferred to the heated metal by the walls of the crucible. Induction crucible furnaces are used for melting aluminum, magnesium, copper, nickel alloys, as well as steels and cast irons.

Channel induction furnaces are used for melting aluminum, copper, nickel and zinc alloys. In addition to melting furnaces, induction channel mixers are also used, which serve for refining and maintaining the temperature of the liquid metal at a given level. Melting and casting complexes, consisting of a melting furnace - mixer - casting machine, are used for casting ingots from aluminum, magnesium and copper alloys using a continuous method. The principle of thermal operation of channel induction furnaces is similar to the principle of operation of a power electric current transformer, which, as is known, consists of a primary coil, a magnetic circuit and a secondary coil. The role of the secondary coil in the furnace is played by a short-circuited channel filled with liquid metal. When current is passed through the furnace inductor (primary coil), a large electric current is induced in a channel filled with liquid metal, which heats the liquid metal contained in it. Thermal energy, released in the channel, heats and melts the metal located above the channel in the furnace bath.

Electric arc furnaces, based on the principle of heat transfer from an electric arc to the heated metal, are divided into direct and indirect heating furnaces.

In indirect heating furnaces, most of the thermal energy from the hot arc is transferred to the heated metal by radiation, and in direct heating furnaces - by radiation and thermal conductivity. Indirect furnaces are currently used to a limited extent. Direct action furnaces (electric arc vacuum furnaces with a consumable electrode) are used for melting refractory, chemically active metals and alloys, as well as alloy steels, nickel and other alloys. According to their design and operating principle, direct electric arc furnaces are divided into two groups: furnaces for melting in a scull crucible and furnaces for melting in a mold or crystallizer.

Electron beam melting furnaces are used for melting refractory and chemically active metals and alloys based on niobium, titanium, zirconium, molybdenum, tungsten, as well as for a number of steel grades and other alloys. The principle of electron beam heating is based on the conversion of the kinetic energy of the electron flow into thermal energy when they meet the surface of the heated charge. The release of thermal energy occurs in a thin surface layer of the metal. Heating and melting are carried out in vacuum at a residual pressure of 1.3-10^-3 Pa. Electron beam melting is used to produce ingots and shaped castings. With electron beam melting, it is possible to significantly overheat the liquid metal and keep it in a liquid state for a long time. This advantage allows you to effectively refine the melt and clean it from a number of impurities. Using electron beam

Metal melts can remove all impurities whose vapor pressure significantly exceeds the vapor pressure of the base metal. High temperature and deep vacuum also help clean the metal from impurities due to the thermal dissociation of nitride oxides and other compounds found in the metal. Electroslag remelting furnace ESR according to the principle of operation It is an indirect heating resistance furnace, in which the heat source is a bath of molten slag of a given chemical composition. The metal to be melted in the form of a consumable electrode is immersed in a layer (bath) of liquid electrically conductive slag. An electric current is passed through the consumable electrode and the slag. The slag is heated, the end of the consumable electrode is melted and drops of liquid metal, passing through a layer of chemically active slag, are cleaned as a result of contact with it and are formed in the mold in the form of an ingot. The slag protects the liquid metal from interaction with the air atmosphere. ESR furnaces are mainly used to produce ingots from high-quality steels, heat-resistant, stainless and other alloys. The ESR method is also used for the production of large shaped castings: crankshafts, housings, fittings and other products.

In plasma melting furnaces, the source of thermal energy is a flow of ionized gas heated to a high temperature (plasma arc), which, upon contact with the metal, heats and melts it. To obtain a plasma flow, melting furnaces are equipped with special devices - plasmatrons. The plasma method of heating and melting alloys is used in bath-type furnaces, in melting plants for producing ingots in a crystallizer and for melting metals in a skull crucible.

Bath-type plasma furnaces are mainly used for melting steels and nickel-based alloys. Plasma furnaces for melting in a crystallizer can be used to produce ingots of steel, beryllium, molybdenum, niobium, titanium and other metals. Plasma furnaces for melting in a skull crucible are designed for shaped casting of steels, refractory and chemically active metals.

PRODUCTION OF ALUMINUM ALLOY CASTINGS

Sand casting

Of the above methods of casting in one-time molds, the most widely used in the manufacture of castings from aluminum alloys is casting in wet sand molds. This is due to the low density of the alloys, the small force effect of the metal on the mold and low casting temperatures (680-800C).

For the manufacture of sand molds, molding and core mixtures are used, prepared from quartz and clay sands (GOST 2138-74), molding clays (GOST 3226-76), binders and auxiliary materials. The creation of cavities in castings is carried out using cores, manufactured mainly using hot (220-300 ° C) core boxes. For this purpose, clad quartz sand or a mixture of sand with thermosetting resin and catalyst is used. For the production of rods, single-position sand-shooting machines and installations, as well as multi-position carousel installations, are widely used. Drying rods are made using shaking, sand-blowing and sand-shooting machines or manually from mixtures with oil (4ГУ, С) or water-soluble binders. The duration of drying (from 3 to 12 hours) depends on the weight and size of the rod and is usually determined experimentally. The drying temperature is prescribed depending on the nature of the binder: for oil-based binders 250-280 °C, and for water-soluble binders 160-200 °C. For the manufacture of large massive rods, cold hardening mixtures (CMC) or liquid self-hardening mixtures (LCS) are increasingly being used. Cold-hardening mixtures contain synthetic resins as a binder, and the cold-hardening catalyst is usually phosphoric acid. LCS mixtures contain a surfactant that promotes foam formation.

The rods are connected into nodes by gluing or by pouring aluminum melts into special holes in the symbolic parts. Shrinkage of the alloy during cooling provides the necessary strength of the connection.

Smooth filling of casting molds without shocks or swirls is ensured by the use of expanding gating systems with the ratio of cross-sectional areas of the main elements Fst: Fshp: Fpit 1:2:3; 1:2:4; 1:3:6, respectively, for the lower, slotted or multi-tiered supply of metal to the mold cavity. The rate of rise of the metal in the cavity of the casting mold should not exceed 4.5/6, where 6 is the prevailing thickness of the walls of the casting, cm. The minimum rate of rise of the metal in the mold (cm/s) is determined by the formula of A. A. Lebedev Vmin = 3/§ .

The type of gating system is selected taking into account the dimensions of the casting, the complexity of its configuration and location in the mold. Pouring molds for castings of complex configurations of small height is carried out, as a rule, using lower gating systems. For large casting heights and thin walls, it is preferable to use vertical slot or combined gating systems. Molds for small-sized castings can be filled through the upper gating systems. In this case, the height of the fall of the metal scab into the mold cavity should not exceed 80 mm.

To reduce the speed of movement of the melt upon entering the mold cavity and to better separate the oxide films and slag inclusions suspended in it, additional hydraulic resistance is introduced into the gating systems - meshes are installed (metal or fiberglass) or poured through granular filters.

Sprues (feeders), as a rule, are brought to thin sections (walls) of castings distributed along the perimeter, taking into account the convenience of their subsequent separation during processing. The supply of metal to massive units is unacceptable, since it causes the formation of shrinkage cavities, macro-looseness and shrinkage “dips” on the surface of the castings. In cross-section, the gating channels most often have a rectangular shape with the wide side measuring 15-20 mm and the narrow side 5-7 mm.

Alloys with a narrow crystallization range (AL2, AL4, AL), AL34, AK9, AL25, ALZO) are prone to the formation of concentrated shrinkage cavities in the thermal units of castings. To bring these shells beyond the castings, the installation of massive profits is widely used. For thin-walled (4-5 mm) and small castings, the profit mass is 2-3 times the mass of the castings, for thick-walled ones it is up to 1.5 times. The profit height is chosen depending on the height of the casting. If the height is less than 150 mm, the height of the profit Nprib is taken equal to the height of the casting Notl. For higher castings, the ratio Nprib/Notl is taken equal to 0.3–0.5. The ratio between the height of the profit and its thickness is on average 2-3. The greatest application in the casting of aluminum alloys is found in upper open profits of round or oval cross-section; In most cases, side profits are closed. To increase the efficiency of the profits, they are insulated, filled with hot metal, and topped up. Insulation is usually carried out by sticking asbestos sheets onto the surface of the mold, followed by drying with a gas flame. Alloys with a wide crystallization range (AL1, AL7, AL8, AL19, ALZZ) are prone to the formation of scattered shrinkage porosity. Impregnation of shrinkage pores with the help of profits is ineffective. Therefore, when making castings from the listed alloys, it is not recommended to use the installation of massive profits. To obtain high-quality castings, directional crystallization is carried out, widely using for this purpose the installation of refrigerators made of cast iron and aluminum alloys. Optimal conditions for directional crystallization, a vertical-slot gating system is created. To prevent gas evolution during crystallization and prevent the formation of gas-shrinkage porosity in thick-walled castings, crystallization under a pressure of 0.4-0.5 MPa is widely used. To do this, casting molds are placed in autoclaves before pouring, they are filled with metal and the castings are crystallized under air pressure. To produce large-sized (up to 2-3 m in height) thin-walled castings, a casting method with sequentially directed solidification is used. The essence of the method is the sequential crystallization of the casting from bottom to top. To do this, the casting mold is placed on the table of a hydraulic lift and metal tubes with a diameter of 12-20 mm, heated to 500-700 °C, are lowered into it, performing the function of risers. The tubes are fixedly fixed in the sprue bowl and the holes in them are closed with stoppers. After filling the sprue bowl with the melt, the stoppers are lifted and the alloy flows through tubes into gating wells connected to the mold cavity by slotted sprues (feeders). After the melt level in the wells rises 20-30 mm above the lower end of the tubes, the hydraulic table lowering mechanism is turned on. The lowering speed is taken such that the form is filled to the flooded level and hot metal continuously flowed into the upper parts of the mold. This ensures directional solidification and allows complex castings to be produced without shrinkage defects.

Sand molds are poured with metal from ladles lined with refractory material. Before filling with metal, ladles with fresh lining are dried and calcined at 780-800 °C to remove moisture. Before pouring, I maintain the melt temperature at 720-780 °C. Molds for thin-walled castings are filled with melts heated to 730-750 °C, and for thick-walled ones to 700-720 °C.

Casting in plaster molds

Casting in plaster molds is used in cases where increased demands are placed on castings in terms of accuracy, surface cleanliness and reproduction of the smallest relief details. Compared to sand gypsum molds, they have higher strength, dimensional accuracy, better resistance to high temperatures, and make it possible to produce castings of complex configurations with a wall thickness of 1.5 mm according to the 5-6th accuracy class. Molds are made using wax or metal (brass, steel) chrome-plated models with a taper in external dimensions of no more than 30" and in internal dimensions from 30" to 3°. Model plates are made of aluminum alloys. To facilitate the removal of models from the molds, their surface is coated with a thin layer of kerosene-stearine grease.

Small and medium-sized molds for complex thin-walled castings are made from a mixture consisting of 80% gypsum, 20% quartz sand or asbestos and 60-70% water (by weight of the dry mixture). Composition of the mixture for medium and large forms: 30% gypsum, 60% sand, 10% asbestos, 40-50% water. The mixture for making rods contains 50% gypsum, 40% sand, 10% asbestos, 40-50% water. To slow down the setting, 1-2% slaked lime is introduced into the mixture. The required strength of the forms is achieved by hydrating anhydrous or semi-aqueous gypsum. To reduce strength and increase gas permeability, raw gypsum molds are subjected to hydrothermal treatment - kept in an autoclave for 6-10 hours under a water vapor pressure of 0.13-0.14 MPa, and then in air for 24 hours. After this, the forms are subjected to stepwise drying at 350-500 °C.

A feature of gypsum molds is their low thermal conductivity. This circumstance makes it difficult to obtain dense castings from aluminum alloys with a wide crystallization range. Therefore, the main task when developing a gating system for gypsum molds is to prevent the formation of shrinkage cavities, looseness, oxide films, hot cracks and underfilling of thin walls. This is achieved by using expanding gating systems (Fst: Fshl: EFpit == 1: 2: 4), ensuring low speed of movement of melts in the mold cavity, directed solidification of thermal units towards profits using refrigerators, increasing mold compliance due to increasing the content of quartz sand in the mixture. Thin-walled castings are poured into molds heated to 100--200 °C using vacuum suction, which allows filling cavities up to 0.2 mm thick. Thick-walled (more than 10 mm) castings are produced by pouring molds in autoclaves. Crystallization of the metal in this case is carried out under a pressure of 0.4-0.5 MPa.

Shell casting

It is advisable to use shell casting for serial and large-scale production of castings of limited sizes with increased surface cleanliness, greater dimensional accuracy and less machining than sand casting.

Shell molds are made using hot (250-300 °C) metal (steel, cast iron) equipment using the bunker method. Modeling equipment is made according to 4-5th accuracy classes with molding slopes from 0.5 to 1.5%. The shells are made of two layers: the first layer is from a mixture with 6-10% thermosetting resin, the second is from a mixture with 2% resin. For better removal of the shell, before filling the molding mixture, the model plate is covered with a thin layer of release emulsion (5% silicone liquid No. 5; 3% laundry soap; 92% water).

For the manufacture of shell molds, fine-grained quartz sands containing at least 96% silica are used. The connection of the halves is carried out by gluing on special pin presses. Glue composition: 40% MF17 resin; 60% marshalite and 1.5% aluminum chloride (hardening catalyst). The assembled molds are poured in containers. When casting into shell molds, the same gating systems and temperature conditions, as in sand casting.

The low rate of metal crystallization in shell molds and the smaller possibilities for creating directional crystallization lead to the production of castings with lower properties than when casting in raw sand molds.

Lost wax casting

Lost wax casting is used to produce castings with increased accuracy (3-5th class) and surface cleanliness (4-6th roughness class), for which this method is the only possible or optimal one.

Models in most cases are made from paste-like paraffin-stearin (1: 1) compositions by pressing into metal molds (cast and prefabricated) on stationary or rotary installations. When producing complex castings larger than 200 mm in size, in order to avoid model deformation, substances are introduced into the model mass that increase their softening (melting) temperature.

A suspension of hydrolyzed ethyl silicate (30-40%) and dusted quartz (70-60%) is used as a refractory coating in the manufacture of ceramic molds. The model blocks are covered with calcined sand 1KO16A or 1K025A. Each layer of coating is dried in air for 10-12 hours or in an atmosphere containing ammonia vapor for 0.5-1 hours. The required strength of the ceramic mold is achieved with a shell thickness of 4-6 mm (4-6 layers of refractory coating). To ensure smooth filling of the mold, expanding gating systems are used to supply metal to thick sections and massive units. The castings are usually fed from a massive riser through thickened sprues (feeders). For complex castings, it is allowed to use massive profits to feed the upper massive units with the obligatory filling of them from the riser.

Melting of models from molds is carried out in hot (85-90 C) water, acidified with hydrochloric acid (0.5-1 cm3 per liter of water) to prevent saponification of stearin. After melting the models, the ceramic molds are dried at 150-170 °C for 1-2 hours, placed in containers, filled with dry filler and calcined at 600-700 °C for 5-8 hours. Pouring is carried out in cold and heated molds. The heating temperature (50-300 °C) of the molds is determined by the thickness of the casting walls. Filling the molds with metal is carried out in the usual way, as well as using vacuum or centrifugal force. Most aluminum alloys are heated to 720-750 °C before pouring.

Chill casting

Chill casting is the main method of serial and mass production of castings from aluminum alloys, which makes it possible to obtain castings of 4-6 accuracy classes with a surface roughness Rz = 50-20 and a minimum wall thickness of 3-4 mm. When casting in a chill mold, along with defects caused by high speeds of movement of the melt in the cavity of the mold and non-compliance with the requirements of directional solidification (gas porosity, oxide films, shrinkage looseness), the main types of casting defects are underfilling and cracks. The appearance of cracks is caused by difficult shrinkage. Cracks occur especially often in castings made from alloys with a wide crystallization range and having large linear shrinkage (1.25-1.35%). Prevention of the formation of these defects is achieved by various technological methods.

In order to ensure a smooth, quiet flow of metal into the cavity of the casting mold, reliable separation of slag and oxide films formed in the metal during the melting process and movement along the gating channels, and to prevent their formation in the casting mold, when casting into a chill mold, expanding gating molds are used systems with bottom, slot and multi-tiered supply of metal to thin sections of castings. In the case of supplying metal to thick sections, provision must be made for feeding the supply site by installing a supply boss (profit). All elements of the gating systems are located along the die connector. The following ratios of the cross-sectional areas of the gating channels are recommended: for small castings EFst: EFshl: EFpit = 1: 2: 3; for large castings EFst: EFsh: EFpit = 1: 3: 6.

To reduce the rate of melt flow into the mold cavity, curved risers, fiberglass or metal meshes, and granular filters are used. The quality of aluminum alloy castings depends on the rate of rise of the melt in the cavity of the casting mold. This speed must be sufficient to guarantee the filling of thin sections of castings under conditions of increased heat dissipation and at the same time not cause underfilling due to incomplete release of air and gases through the ventilation ducts and profits, turbulence and gushing of the melt during the transition from narrow sections to wide ones. The rate of rise of the metal in the mold cavity when casting in a chill mold is assumed to be slightly higher than when casting in sand molds. The minimum permissible lifting speed is calculated using the formulas of A. A. Lebedev and N. M. Galdin (see section “Sand Casting”).

To obtain dense castings, directed solidification is created, as in sand casting, by properly positioning the casting in the mold and adjusting the heat dissipation. As a rule, massive (thick) casting units are located in the upper part of the mold. This makes it possible to compensate for the reduction in their volume during solidification directly from the profits installed above them. Regulating the intensity of heat removal in order to create directional solidification is carried out by cooling or insulating various sections of the casting mold. To locally increase heat removal, inserts made of heat-conducting copper are widely used, they provide for an increase in the cooling surface of the chill mold due to fins, and carry out local cooling of the chill molds with compressed air or water. To reduce the intensity of heat removal, a layer of paint 0.1-0.5 mm thick is applied to the working surface of the chill mold. For this purpose, a layer of paint 1-1.5 mm thick is applied to the surface of the gating channels and profits. Slowing down the cooling of the metal in the mold can also be achieved through local thickening of the die walls, the use of various coatings with low thermal conductivity, and insulation of the mold with asbestos stickers. Painting the working surface of the chill mold improves the appearance of the castings, helps eliminate gas holes and non-sheets on their surface and increases the durability of the chill molds. Before painting, the chill molds are heated to 100-120 °C. An excessively high heating temperature is undesirable, since this reduces the rate of solidification of castings and the service life of the die. Heating reduces the temperature difference between the casting and the mold and the expansion of the mold due to its heating by the casting metal. As a result, tensile stresses in the casting, which cause cracks, are reduced. However, heating the mold alone is not enough to eliminate the possibility of cracks. Timely removal of the casting from the mold is necessary. The casting should be removed from the die before the moment when its temperature becomes equal to the temperature of the die and the shrinkage stress reaches its greatest value. Usually the casting is removed at the moment when it is so strong that it can be moved without destruction (450-500 ° C). At this point, the gating system has not yet acquired sufficient strength and is destroyed by light impacts. The duration of holding the casting in the mold is determined by the solidification rate and depends on the temperature of the metal, the temperature of the mold and the pouring speed. Aluminum alloys, depending on the composition and complexity of the casting configuration, are poured into chill molds at 680-750 °C. The weight filling speed is 0.15-3 kg/s. Castings with thin walls are poured at higher speeds than with thick ones.

To eliminate metal adhesion, increase service life and facilitate removal, metal rods are lubricated during operation. The most common lubricant is a water-graphite suspension (3-5% graphite).

Parts of the molds that create the external outlines of the castings are made of gray cast iron. The wall thickness of the molds is determined depending on the wall thickness of the castings in accordance with the recommendations of GOST 16237-70. Internal cavities in castings are made using metal (steel) and sand rods. Sand rods are used to form complex cavities that cannot be made with metal rods. To facilitate the removal of castings from the molds, the outer surfaces of the castings must have a casting slope of 30" to 3° towards the connector. The internal surfaces of castings made with metal rods must have a slope of at least 6°. Sharp transitions from thick sections to thin sections are not allowed in castings . Curvature radii must be at least 3 mm. Holes with a diameter of more than 8 mm for small castings, 10 mm for medium and 12 mm for large ones are made with rods. The optimal ratio of the depth of the hole to its diameter is 0.7-1. The amount of allowance for processing when Chill casting costs two times less than sand casting.

Air and gases are removed from the die cavity using ventilation channels placed in the parting plane and plugs placed in the walls near the deep cavities.

In modern foundries, chill molds are installed on single-position or multi-position semi-automatic casting machines, in which the closing and opening of the chill mold, installation and removal of cores, ejection and removal of the casting from the mold are automated. There is also automatic control of the heating temperature of the chill mold. Filling of chill molds on machines is carried out using dispensers.

To improve the filling of the thin cavities of the molds and remove air and gases released during the destruction of the binders, the molds are evacuated and filled under low pressure or using centrifugal force.

Squeeze casting

Squeeze casting is a type of chill casting. It is intended for the production of large-sized panel-type castings (2500x1400 mm) with a wall thickness of 2-3 mm (Fig. 63). For this purpose, metal half-forms are used, which are mounted on specialized casting and pressing machines with one-sided or two-sided approach of the half-forms. Distinctive feature This casting method involves forced filling of the mold cavity with a wide flow of melt as the mold halves approach each other. The casting mold does not contain elements of a conventional gating system. Using this method, castings are made from AL2, AL4, AL9, AL34 alloys, which have a narrow crystallization range.

^The permissible rate of rise of the melt in the working area of ​​the mold cavity when casting panels from aluminum alloys should be in the range of 0.5-0.7 m/s. A lower speed can lead to non-filling of thin sections of castings; an excessively high speed can lead to defects of a hydrodynamic nature: waviness, uneven surfaces of castings, the capture of air bubbles, erosion of sand cores and the formation of cracks due to flow rupture. Metal is poured into metal receptacles heated to 250--350 °C. The melt cooling rate is regulated by applying the mold cavity to the working surface

thermal insulation coating of various thicknesses (0.05-1 mm). Overheating of alloys before pouring should not exceed 15-20° above the liquidus temperature. The duration of the approach of the half-forms is 5-3 s.

Low pressure casting

Low pressure casting is another variation of die casting. It is used in the manufacture of large-sized thin-walled castings from aluminum alloys with a narrow crystallization range (AL2, AL4, AL9, AL34). As with chill casting, the outer surfaces of the castings are made with a metal mold, and the internal cavities are made with metal or sand rods.

To make the rods, use a mixture consisting of 55% 1K016A quartz sand; 13.5% semi-fat sand P01; 27% pulverized quartz; 0.8% pectin glue; 3.2% tar M and 0.5% kerosene. This mixture does not form a mechanical burn. Filling of molds with metal is carried out by the pressure of compressed dried air (18-80 kPa) supplied to the surface of the melt in a crucible heated to 720-750 °C. Under the influence of this pressure, the melt is forced out of the crucible into the metal pipe, and from it into the manifold of the gating system and further into the cavity of the casting mold. The advantage of low-pressure casting is the ability to automatically control the rate of rise of the metal in the mold cavity, which makes it possible to obtain thin-walled castings of higher quality than when casting under the influence of gravity.

Crystallization of alloys in a mold is carried out under a pressure of 10-30 kPa before the formation of a solid metal crust and 50-80 kPa after the formation of a crust.

Denser aluminum alloy castings are produced by low-pressure backpressure casting. Filling the mold cavity during backpressure casting is carried out due to the difference in pressure in the crucible and in the mold (10-60 kPa). Crystallization of the metal in the mold is carried out under a pressure of 0.4-0.5 MPa. This prevents the release of hydrogen dissolved in the metal and the formation of gas pores. High blood pressure contributes to better nutrition massive casting units. Otherwise, back pressure casting technology is no different from low pressure casting technology.

Back pressure casting successfully combines the advantages of low pressure casting and pressure crystallization.

Injection molding

By injection molding from aluminum alloys AL2, ALZ, AL1, ALO, AL11, AL13, AL22, AL28, AL32, AL34, complex configuration castings of 1-3 accuracy classes are produced with wall thicknesses from 1 mm and above, cast holes with a diameter of up to 1.2 mm,

cast external and internal threads with minimal step 1 mm and diameter 6 mm. The surface cleanliness of such castings corresponds to roughness classes 5–8. The production of such castings is carried out on machines with cold horizontal or vertical pressing chambers, with a specific pressing pressure of 30-70 MPa. Preference is given to machines with a horizontal pressing chamber.

The dimensions and weight of castings are limited by the capabilities of injection molding machines: the volume of the pressing chamber, the specific pressing pressure (p) and the locking force (0). The projection area (F) of the casting, sprue channels and pressing chamber onto the movable plate of the mold should not exceed the values ​​​​determined by the formula F = 0.85 0/r.

To avoid unfilled forms and unfilled sheets, the wall thickness of olives made of aluminum alloys is determined taking into account their surface area:

Surface area

castings, cm2 Up to 25 25-150 150-250 250-500 Above 500

Wall thickness, mm. 1-2 1.5-3 2-4 2.5-6 3-8

The optimal slope values ​​for external surfaces are 45"; for internal surfaces 1°. The minimum radius of curvature is 0.5-1" mm. Holes larger than 2.5 mm in diameter are made by casting. Castings made of aluminum alloys, as a rule, are machined only along the seating surfaces. The processing allowance is assigned taking into account the dimensions of the casting and ranges from 0.3 to 1 mm.

Various materials are used to make molds. Parts of the molds in contact with liquid metal are made of steels ZH2V8, 4Х8В2, 4ХВ2С, fastening plates and matrix cages are made of steels 35, 45, 50, pins, bushings and guide columns are made of steel U8A.

The supply of metal to the mold cavity is carried out using external and internal gating systems. Feeders are brought to the casting area to be machined. Their thickness is determined depending on the thickness of the casting wall at the point of supply and the specified nature of filling the mold. This dependence is determined by the ratio of the thickness of the Feeder to the thickness of the casting wall. Smooth filling of molds, without turbulence or air entrapment, occurs if the ratio is close to unity. For castings with a wall thickness of up to 2 mm, the feeders have a thickness of 0.8 mm; with a wall thickness of 3 mm, the thickness of the feeders is 1.2 mm; with a wall thickness of 4-6 mm-2 mm.

To receive the first portion of the melt, enriched with air inclusions, special washing tanks are placed near the mold cavity, the volume of which can reach 20-40% of the casting volume. The washers are connected to the mold cavity by channels whose thickness is equal to the thickness of the feeders. Air and gas are removed from the mold cavity through special ventilation channels and gaps between the rods (ejectors) and the mold matrix. Ventilation channels are made in the plane of the connector on the stationary part of the mold, as well as along the movable rods and ejectors. The depth of the ventilation channels when casting aluminum alloys is taken to be 0.05-0.15 mm, and the width is 10-30 mm in order to improve the ventilation of the molds; the cavities of the washers are connected to the atmosphere by thin channels (0.2-0.5 mm).

The main defects of castings obtained by injection molding are air (gas) subcortical porosity, caused by air entrapment at high speeds of metal inlet into the mold cavity, and shrinkage porosity (or cavities) in thermal units. The formation of these defects is greatly influenced by the parameters of the casting technology - pressing speed, pressing pressure, and thermal conditions of the mold.

The pressing speed determines the mode of filling the mold. The higher the pressing speed, the higher the speed the melt moves through the gating channels, the higher the speed of inlet of the melt into the mold cavity. High pressing speeds contribute to better filling of thin and elongated cavities. At the same time, they cause the metal to trap air and form subcortical porosity. When casting aluminum alloys, high pressing speeds are used only for the production of complex thin-walled castings. Pressure has a great influence on the quality of castings. As it increases, the density of the castings increases.

The magnitude of the pressing pressure is usually limited by the magnitude of the locking force of the machine, which must exceed the pressure exerted by the metal on the movable matrix (pF). Therefore, local pre-pressing of thick-walled castings, known as the “Ashigai process,” is gaining great interest. The low speed of metal inlet into the cavity of the molds through large-section feeders and the effective pre-pressing of the crystallizing melt using a double plunger make it possible to obtain dense castings.

The quality of castings is also significantly influenced by the temperature of the alloy and mold. When producing thick-walled castings of simple configuration, the melt is poured at a temperature 20-30 °C below the liquidus temperature. Thin-walled castings require the use of a melt superheated above the liquidus temperature by 10-15 °C. To reduce the magnitude of shrinkage stresses and prevent the formation of cracks in castings, the molds are heated before pouring. The following heating temperatures are recommended:

Casting wall thickness, mm 1 - 2 2-3 3-5 5-8

Heating temperature

molds, °C 250-280 200-250 160-200 120-160

The stability of the thermal regime is ensured by heating (electric) or cooling (water) of the molds.

To protect the working surface of the molds from sticking and erosive effects of the melt, to reduce friction when removing the cores and to facilitate the removal of castings, the molds are lubricated. For this purpose, fatty (oil with graphite or aluminum powder) or aqueous (salt solutions, aqueous preparations based on colloidal graphite) lubricants are used.

The density of aluminum alloy castings increases significantly when casting with vacuum molds. To do this, the mold is placed in a sealed casing, in which the necessary vacuum is created. Good results can be obtained using the "oxygen process". To do this, the air in the mold cavity is replaced with oxygen. At high rates of metal inlet into the mold cavity, causing the capture of oxygen by the melt, subcortical porosity does not form in the castings, since all the trapped oxygen is spent on the formation of finely dispersed aluminum oxides, which do not noticeably affect the mechanical properties of the castings. Such castings can be subjected to heat treatment.

Quality control of castings and correction of their defects

Depending on the technical requirements, castings made of aluminum alloys can be subjected to various types of inspection: X-ray, gamma flaw detection or ultrasonic to detect internal defects; markings to determine dimensional deviations; luminescent for detecting surface cracks; hydro- or pneumatic control to assess tightness. The frequency of the listed types of control is stipulated by technical conditions or determined by the department of the chief metallurgist of the plant. Identified defects, if permitted by technical specifications, are eliminated by welding or impregnation. Argon-arc welding is used for welding underfills, cavities, and loose cracks. Before welding, the defective area is cut so that the walls of the recesses have a slope of 30-42. The castings are subjected to local or general heating to 300-350C. Local heating is carried out with an oxygen-acetylene flame, general heating is carried out in chamber furnaces. Welding is carried out with the same alloys from which the castings are made, using a non-consumable tungsten electrode with a diameter of 2-6 mm at an argon flow rate of 5-12 l/min. The welding current strength is usually 25-40 A per 1 mm of electrode diameter.

Porosity in castings is eliminated by impregnation with bakelite varnish, asphalt varnish, drying oil or liquid glass. Impregnation is carried out in special boilers under a pressure of 490-590 kPa with preliminary exposure of the castings in a rarefied atmosphere (1.3-6.5 kPa). The temperature of the impregnating liquid is maintained at 100°C. After impregnation, the castings are dried at 65-200°C, during which the impregnating liquid hardens, and re-inspected.

Bibliography

1. Casting alloys and technologies for their smelting in mechanical engineering. M.: Mechanical engineering. 1984.
2. Theory of foundry processes. L.: Mechanical engineering. 1976.
3. Castings from aluminum alloys. M.: Mechanical engineering. 1970.
4. Production of castings from non-ferrous metal alloys. M.: Metallurgy. 1986.
5. Production of cast aluminum parts. M.: Metallurgy. 1979.
6. Aluminum alloys. Directory. M.: Metallurgy. 1983.

Foundries in Russia are enterprises that produce castings - shaped parts and blanks - by filling casting molds with liquid alloys. The main consumers of foundry products are enterprises of the machine-building complex (up to 70% of all cast billets produced), and the metallurgical industry (up to 20%). About 10% of products produced by casting are sanitary fittings.

Casting is the optimal way to produce workpieces of complex geometry that are as close in configuration as possible to finished products, which is not always possible to achieve by other methods (forging, welding, etc.). During the casting process, products of the most varied thickness (from 0.5 to 500 mm), length (from several cm to 20 m) and weight (from several grams to 300 tons) are obtained. Small allowances are an advantageous feature of casting blanks, which allows reducing the cost of finished products by reducing metal consumption and the cost of machining products. Over half of the parts used in modern industrial equipment, made by casting.

The main types of raw materials in foundry production are:

• gray cast iron (up to 75%);
• steel – carbon and alloy (20%);
• malleable cast iron (3%);
• non-ferrous alloys - aluminum, magnesium, zinc copper (2%).

The casting process is carried out in a variety of ways, which are classified:

1) according to the method of filling molds:

• conventional casting;
• casting with insulation;
• injection molding;
• centrifugal casting;

2) according to the method of manufacturing casting molds:

• in one-time molds (sand, shell), designed to produce only one casting;
• in reusable molds (ceramic or clay-sand) that can withstand up to 150 pours;
• into permanent metal molds (for example, chill molds) that can withstand several thousand pours.

The most common method is sand casting (up to 80% by weight of all castings carried out in the world). The technology of this type of casting includes:

• preparation of materials;
• preparation of molding and core mixtures;
• creating forms and cores;
• suspending cores and assembling molds;
• melting metal and pouring it into molds;
• cooling the metal and knocking out the finished casting;
• cleaning of the casting, its heat treatment and finishing.

The first Russian foundry (the so-called “cannon hut”) appeared in Moscow in 1479. Under Ivan the Terrible, foundries appeared in Kashira, Tula and other cities. During the reign of Peter I, the production of castings was mastered in almost the entire state - in the Urals, in the southern and northern parts of the country. In the 17th century, Russia began to export iron castings. Remarkable examples of Russian foundry art are the 40-ton “Tsar Cannon”, cast by A. Chokhov in 1586, the “Tsar Bell” weighing over 200 tons, created in 1735 by I.F. and M.I. Matorin. In 1873, workers at the Perm plant cast a steam hammer weighing 650 tons, which is one of the largest castings in the world.

FOUNDRY, one of the technological processes for producing a product by filling a pre-prepared mold with molten metal, in which the metal hardens. The importance of foundry production in mechanical engineering is characterized by the fact that more than 75% by weight of all parts of machines and tools are cast. The production of parts by casting is not only a simple and therefore cheap method, but often with very complex designs and large dimensions of the parts - it is the only one. The foundry process can also produce products from metals that cannot be forged. In foundry production, machine parts are manufactured individually, in batches, and in some cases in mass quantities.

Foundry materials are: casting materials (cast iron, steel, copper and its alloys, aluminum and its alloys, etc.); molding materials (sand, clay, etc.); auxiliary materials: fuel, refractory materials, fluxes, etc. The main operations in foundry production are as follows: 1) preparation of molding earth, 2) making a mold (molding), 3) melting metal, 4) assembling and pouring the mold, 5) releasing the casting from molds (knocking out), 6) casting cleaning (cutting, cleaning and trimming), 7) heat treatment (annealing or complete heat treatment).

Making molds (molding). In foundry production, the following are used: temporary molds, mainly made of clay and sand, and permanent metal molds, Ch. arr. of steel. During solidification, the metal decreases in volume (shrinkage phenomenon), so the mold is made larger in size than the product by the amount of shrinkage. The phenomenon of shrinkage affects the strength of the casting, and sometimes even its integrity, when, for example, the molding mass (rods) surrounded by liquid metal is too strong and unyielding, and the casting metal contracts as it solidifies. Therefore, in temporary molds, the molding compound must be used. pliable; with permanent molds, it is necessary (depending on the rate of solidification of the metal) to throw out products from them in a timely manner, which is achieved by very precise (in time) action of the appropriate mechanisms.

Constant forms were developed by ch. arr. for casting non-ferrous metals having a low melting point, and partly for cast iron; For steel, permanent forms are rarely used, since it is very difficult (even for cast iron) to select a metal that can withstand repeated heating and cooling. Casting into permanent molds with metal cones of aluminum alloys has become especially widespread. Permanent molds include the so-called long-life molds, proposed and patented by Holley Carburettor Co., Detroit. They are made from very durable fire-resistant material. The whole difficulty of making these forms lies in finding the appropriate material (kaolin, magnesia, bauxite) and connecting it well with the cast iron shell. The surface of the refractory layer can be adjusted until it wears out, after which the refractory layer is applied again. Cast iron and other metals (except steel) are cast into such molds. There is no bleaching of the cast iron and the casting is well processed.

Temporary molds are made using models or templates, which are an exact copy of the casting (increased by the amount of shrinkage), and flasks - rectangular or square (less often round) boxes without a bottom or lid. The flasks serve to give strength to the molding material and to use as little molding soil as possible during molding. Much less often, molding is done in the soil without flasks or with only one upper flask.

Schematically, the process of making molds is as follows. 1) Half of the model is placed on a sub-model plate (Fig. 1). 2) The lower half of the flask is placed on the slab and covered with a few mm of model soil (Fig. 2), lightly compacted around the model (in most cases by hand); after this, filling soil is poured into the flask (to the top or more), which is then compacted b. or m. greatly depending on the size and nature of the casting; the form is ventilated (pierced in several places with a hairpin).

3) The filled flask is turned over together with the model board (Fig. 3); the fake board is removed; The surface of the lower flask is sprinkled with separating sand. 4) On the lower half of the model, place the upper half of the model, covered with a layer of model sand, and the upper flask (Fig. 4), into which the sprue and butt models are placed (Fig. 5). 5) After compacting the filling soil, the flasks are separated and the models are removed from each half. 6) A rod is inserted into the lower mold freed from the model (Fig. 6), which is prepared separately. 7) The lower flask with the rod is covered with the upper flask (Fig. 7); the assembled flasks are loaded, i.e., a weight is placed on the upper flask to protect it from floating when the mold is filled with liquid metal.

Methods for filling flasks with molding material and compacting it are shown in Fig. 8.

Molding machines are divided into three main types: pressing, shaking and sand-throwing. Each molding machine is equipped with devices for releasing the model from the flask. The main methods for releasing the model from the flasks are shown in Fig. 9.

In accordance with the methods for releasing models from flasks, molding machines are also divided into subgroups: 1) machines with lifting flasks, 2) machines with a rotating plate and 3) machines with a broaching plate.

In fig. 10 shows an ordinary pressing (with manual pressing from below) molding machine; in fig. Figure 11 shows one of the newest types of shaking-press machines of the Nichols system, operating with compressed air.

The model plate of this machine is mounted on the model B holder; the flask (not shown in the diagram) is connected either to the model plate or to frame E, which serves as a support for the flask. Place valve handle N to the right. Shaking occurs; in this case, the air passes inside piston B under piston A, which carries the model plate. The lifting of the piston is controlled automatically by raising the windows F by the lower edge of the piston. Through these windows, air flows into piston B and into the atmosphere. During shaking, the traverses H with the pressing block stand above the flask.

Then the valve handle N is turned to the left. Then the air goes through another wire under piston B and lifts both pistons with the model plate, frames D and E and a shaken flask filled with sand and presses the latter against the press block, which is how compaction is achieved. Turn handle N again to the middle position, which opens the outlet of the press cylinder. Both pistons A and B, the model holder D with the model plate and the frame E supporting the flask fall down, and in addition to the press piston B, round rods G serve as guides. During movement, the rods G are stopped by pawls C at a known height so that frame E with the finished shape stops while B-A-D system with the model plate continue moving down; in this case, the model is pulled out of the mold. After pumping out the traverse with the press block, it is easy to remove the mold. To ensure precise vertical movement of the model D holder, there are four guide rods M in the shaking table. The rods G in the lower position are immersed in an oil bath, as well as the guides M, in order to ensure good lubrication and a smooth fall of the frame E, for which purpose the pawl C is turned to the right by moving the foot lever. On the frame E you can attach a broaching plate, on which the flask is already placed like this , so that with a tall model with steep walls, work using the pulling method. In both cases, a vibrator on frame D helps remove the model. In fig. Figure 12 shows one of the many designs of a sand blower - the latest molding machine, which simultaneously fills the flask with molding earth and compacts the latter by the action of centrifugal force.

The molding material is transferred via an elevator to a shaking chute, then to a belt, which transfers it to the sand thrower head; here the earth is picked up by a rapidly rotating bucket of the working head, which cuts off a portion of the earth from the total amount and, with enormous speed (12-18 m/sec), directs the earth into the flask, where it is compacted. The main advantage of the sand blower compared to other types of molding machines is that it is not associated with a certain size of the flask, as is the case in other molding machines, and therefore only the sand blower solves the problem of mechanizing the work of filling the flasks with molding material and compacting the latter in foundries, where individual work predominates. In addition, the sand blower has extremely high productivity.

The internal outlines of a part, voids, etc. are obtained using rods or cones, which are prepared separately from the molds in the so-called. core boxes. Since during the pouring process the cones are in most cases surrounded by molten metal, the issue of proper ventilation becomes extremely important: the gas permeability of the cones must be significantly higher than the gas permeability of the form itself. In fig. Figure 13 shows a drawing of a core (half of a core box).

To increase the gas permeability of the rod, a wax cord (cement) is placed inside it, the wax of which will melt during drying, leaving so. free passage for gas. To increase the resistance of the rod to the action of a column of molten metal, the rod is equipped with a special metal frame. For the production of such critical and complex castings, such as car blocks, radiators, etc., the so-called. oil rods, which are prepared in most cases from pure quartz sand with the addition of various binders for binding; Of these, linseed oil should be considered the best, but bean oil, maize oil, molasses, dextrin, gluten, etc. are also used. With the help of cones, you can obtain not only the internal, but also the external outline of the part ( flaskless molding). Many factories in America use this method, omitting all forming work and replacing it with core work, which does not require particularly skilled labor.

The manufactured forms are dusted with finely ground coal or graphite, or painted with a specially made mass ( beluga or paint), which is a very liquid mixture of refractory clay, flour and glue; When finishing molds for iron casting, fine graphite or coke is added to such a mass. Smoothing the surface of the mold with a smoothing iron is prohibited. After finishing, the mold is either placed in the dryer (more often) and collected for pouring, or (less often) it enters the pouring process in a raw form - wet casting. Drying of molds for different metals is carried out at different temperatures: for steel 500-600°C, for cast iron 200-300°C, for non-ferrous metals 150-250°C. Permanent and long-term molds are always slightly heated before casting (up to 75-100°C); then, for subsequent castings, on the contrary, they are cooled so that their temperature does not exceed 75-100°C. Particular care should be given to the issue of drying the rods, for which dryers are successfully used continuous action, allowing you to regulate the drying temperature within strictly defined limits with a fluctuation of ±5°C. Since the wet mold is more pliable than the dry one, often many castings that fail in the dry form succeed in the wet form. However, the green form requires special attention to the composition of the molding mass (large porosity is needed to remove not only gases released from the metal, but also water vapor) and proper compaction of the form. Do not over-compact (“ring”) and do not fill the molding mass too loosely (otherwise the liquid metal will wash away the walls of the mold) - a task that can only be solved by a very experienced worker.

Melting metal. Casting materials must have the following properties: a) fluidity, i.e. the ability of molten metal to fill the mold; b) minimal shrinkage, i.e. the ability of the casting to retain its shape; c) the least tendency to segregation; d) possibly low melting point. Almost all industrial metals(with the exception of aluminum) in their pure form do not satisfy these conditions: for example, iron has a very high melting point and has insignificant fluidity and high shrinkage; Copper, although it does not have a very high melting point, but due to its excessively high tendency to dissolve gases, obtaining dense, bubble-free castings is very difficult and requires special conditions to avoid defective castings. Admixtures of other metals and metalloids to the base metal (iron, copper, etc.) significantly improve casting qualities in the sense of lowering the melting point, reducing the shrinkage coefficient, etc. An admixture of carbon to iron in an amount of 1.7% or higher lowers the temperature iron melting from 1528°C to 1135°C, shrinkage coefficient - from 2% to 1%; an admixture of zinc or tin to copper and aluminum significantly improves their casting qualities. Aluminum-copper and aluminum-silicon alloys have the best casting qualities. Steel for castings is used in two types: with a C content of 0.15 to 0.18% (tensile strength 36 kg/mm ​​2) and from 0.30 to 0.35% (54 kg/mm ​​2); Mn< 0,6-0,8%, Si < 0,20%; S и Р обыкновенно менее 0,05%. Этот состав обеспечивает плотность отливки. Специальные стали для литья применяются редко. В табл. 1 приводятся наиболее употребительные литейные сплавы алюминия.

To obtain a casting of the required qualities at the lowest cost, you need to know under what conditions the casting will work, what qualities will be required from it, and what changes will occur in the metal when it is remelted. Based on this, a calculation of the charge is made. In addition to the original casting materials, the charge also includes waste foundry(srues, blowouts, rejected castings, splashes from casting ladles, etc.) and scrap metal.

Below is an example of a numerical calculation of a charge (according to Moldenka) of acid-resistant gray cast iron (Table 2).

It is required to calculate the mixture of the following composition: 3.25% C, 1.53% Si, 1.25% Mn, 0.20% P, 0.05% S. For the calculation, certain values ​​of element loss during melting in a cupola furnace are taken. The task is to determine the relative quantities in which the cast irons of the groups must be mixedI,II and III to obtain a mixture of composition (in%): 1.82 Si, 1.91 Mn, 0.1 P, 0.016 S.

To do this, on the M axesn-Si (Fig. 14) we set aside the corresponding contents of Si and Mn; By connecting the points corresponding to the three cast irons (foundry lines 4, 5 and 6), we see that the point of the average composition of the required mixture is located inside the triangle I-II-III, which indicates the possibility of preparing the required mixture from these 3 types of cast iron. We connect the vertices of the triangle I-II-III to point O and continue the straight lines IO,IIO and IIIO until they intersect with the opposite sides of the triangle at points a, b and c.

Then we take an arbitrary straight line O 2 O 1 (Fig. 15), divided into 100 equal parts (100%), and at the ends of this straight line we draw straight lines 0 2 K and 0 1 L, parallel to each other, at an arbitrary angle. From point O 1, lay off the segments O 1 l, O 1 lI, O 1 III, equalO.I.OII, OIII. In the same way, from point O 2 we lay off straight lines O 2 a, O 2b and O 2 c, respectively equal to Oa, Ob and Os. Connecting points a with I, b withII and c with III, we will immediately read on the straight line O 2 O 1 that cast iron I should be taken 34%, cast ironII - 51% and cast iron III - 15%. Consequently, every 150 kg of charge will consist of 34 kg of cast iron I, 51 kg of cast iron II, 15 kg of cast iron III; 30 kg of your own scrap and 20 kg of purchased scrap.

For melting various metals, furnaces of various designs are used: for melting steel - open-hearth furnaces (acidic and basic), small Bessemer furnaces (for example, Tropenas, Robert); cast iron - cupola furnaces, reverberatory furnaces and crucible installations; for aluminum, copper and their alloys - various designs crucible, flame and electric furnaces. The cupola melting process is the most economical and therefore the most common; the use of crucibles is limited by the high cost of the process and the extreme inconvenience of producing castings (for example, steel shaped castings) from crucibles. Flame furnaces for non-ferrous casting are inconvenient because the oxidizing effect of the flame spoils the quality of the metal, and the metal oxides released in the room have a harmful effect on the health of workers; in addition, it is required that the pouring temperature of non-ferrous metals be within very narrow, predetermined limits (for example, for aluminum 700 ± 20 ° C). Recently, electric furnaces have become widespread various systems for melting ch. arr. steel and non-ferrous metals. The main advantage of electric furnaces is their indifference to the chemical reactions that take place during smelting, and, as a result, cleaner metal; then the ability to regulate, within a very wide range, the degree of overheating of the metal, its lower waste, etc. To melt cast iron, the use of electricity is much more expensive than melting in cupola furnaces, and therefore is relatively rare and only in the form of a combined process: cupola-electric furnace or cupola-furnace. Bessemer-electric furnace, in accordance with special requirements, presented by production. When melting non-ferrous metals in electric furnaces, the waste is reduced: for example, the waste of brass in crucibles is 4-6%, in electric furnaces 0.5-1.5%. In table Table 3 shows comparative data on the cost of melting 1 ton of brass in crucibles and electric furnaces of the Ajax system.

Casting technique. The supply of molten metal to the mold is one of the most important operations in foundry production; metal, perfectly composed (by analysis), molten and deoxidized according to all the best instructions, b. spoiled by inept putting it into shape. First of all, it is necessary to ensure that the stream of metal entering the mold is continuous and completely fills the channels supplying the metal to the mold. To do this, it is necessary to correctly calculate the mutual ratio of the cross sections of the gate, slag catcher and feeders (Fig. 16); So, with a gate diameter of 20 mm, the cross-sectional area of ​​the gate = 315 mm 2, the area of ​​the slag catcher should be taken smaller, namely 255 mm 2, and the sum of the areas of the feeders should not exceed 170 mm 2.

In fig. 17-22 show examples of correct and incorrect installations of gates, slag traps and feeders.

Fig. 17, 18 and 19 give examples correct installation, fig. 20 - incorrect installation because the cross-section of the sprue is too small and during casting the metal will not completely fill the slag trap, as a result of which slag will fall into the mold and spoil the casting. In fig. Figure 21 shows an incorrect installation: the sprue is placed directly above the feeder, the slag directly enters the mold. In fig. 22 the sprue is shifted and placed directly above the feeder, the slag falls into the mold. To avoid shrinkage cavities, two stops are placed in steel castings. Profits in steel castings take up about 25-30% of the weight of the casting. Small steel castings, cast iron (except for very critical ones) and non-ferrous castings are cast without profit. Filling molds requires some skill. Metal cannot be poured into the sprue with interruptions in the flow. In some cases, when high pressure is required, they try to direct a stream of steel from the ladle directly into the sprue, thus creating. strike of steel. The pouring of steel is considered complete when the metal appears in profit. At this point, in large castings, it is preferable to add metal in the margins, rather than through the sprue. That. a hot profit is created, feeding the casting (while reducing the volume of solidifying metal) from above, but not from below (which is harmful). It is recommended to deoxidize the finished metal with silica spigel before release. This additive makes the metal calmer and it pours well. Shrinkage cavities form in the thickest parts of the castings. The common view that the presence of shrinkage bubbles in castings reduces the strength of the metal is not always correct: a bubble enclosed in the metal is a sphere (like a dome) with regularly arranged crystals and exhibits significant resistance to destruction, especially crushing. Forging this bubble by forging forms a fold, the presence of which certainly weakens the metal. To avoid the formation of shrinkage bubbles, centrifugal casting and pressure casting are used.

Centrifugal casting involves introducing molten metal into a rapidly rotating metal mold, where centrifugal force causes it to adhere to the outer surface of the rotating mold. That. you can prepare a variety of bodies of rotation. The operating diagram of a centrifugal casting machine is shown in Fig. 23.

The form is cylinder A. By means of handle C, form A can be made. moved back (on the drawing - to the right). A piston at the end of the spindle with a cooling ribbed surface F forms the rear wall of the mold. At the beginning of the casting, mold A is pressed completely tightly against body B, after which ladle B filled with molten metal is rolled into mold D, which is simultaneously set into rotation. By turning handwheel E, molten metal is poured into the mold. As soon as the metal hardens, mold A is moved to the right onto the piston, which squeezes out the casting. The method of centrifugal casting in the manufacture of cast iron pipes has become particularly widespread. The material from which molds for centrifugal castings are prepared is selected especially carefully depending on the operating conditions of the centrifugal casting machine. For molds with a high degree of heating, cast iron, due to its tendency to grow (increase in volume with repeated heating), is not recommended; the use of steel gives better results. Molds without lining, heated or cooled by water, can be made of steel, but their service life is short. Therefore, it is preferable to make molds from nichrome (60% Ni and 40% Cr) or from Becket metal, as well as from an alloy of the following composition: 80% Ni and 20% Cr. This alloy can withstand prolonged and repeated temperature loads in excess of 1370°C. The essential requirement is that steel molds do not have cavities closer than 3 mm from the inner surface of the mold, and that this surface is completely smooth; The wall thickness is chosen so that during casting the mold does not heat up above the critical point of the given metal.

In injection molding, molten metal is injected under high pressure into a metal mold, resulting in parts that are so precisely sized that they require no further machining. This represents particularly significant benefits when mass production small parts requiring high precision (for example, meter parts, small machine parts). The most important industrial alloys for die casting are zinc, aluminum and, to some extent, copper alloys. In table 4 shows the characteristics various alloys, used for injection moldings.

The machines used for injection molding are divided into two main groups. 1) For alloys with a low melting point, piston machines are used (Fig. 24).

The liquid metal bath contains a pump driven by a lever or compressed air. When the piston moves down, the metal is pressed into the mold through the nozzle. Piston machines for alloys with a higher melting point (aluminum, etc.) turned out to be unsuitable: the metal hardens between the piston and the cylinder walls, which causes frequent cleaning and a sharp increase in overhead costs. 2) For refractory alloys, therefore, machines are used (Figs. 25 and 26) equipped with a special scoop (gooseneck), which, with the help of a special device, each time captures a strictly required portion of the metal; the metal is exposed to compressed air only in this scoop on a relatively small surface, thereby avoiding excessive oxidation of the metal.

Knocking out castings. The quickest release of the poured product from the molds has a significant impact on its integrity. It should also be borne in mind that a hot casting can easily be deformed by an awkward blow when being released from the mold. It is especially important to quickly release the central bumps of castings. For this purpose, when cones are made, part of the frame, which is the skeleton of the cone, is brought out through the “sign” so that after pouring with a sledgehammer, the cone can easily be knocked out along this protruding part and thereby allow the casting to contract freely during its further cooling.

The operation of knocking out flasks in modern foundries is completely mechanized. The simplest device for this purpose is to have a vibrator suspended from a pneumatic lift using a special device. attached to the flask, which at the same time rises slightly; After this, the vibrator is activated, and after a few seconds the flask is emptied. With another method of knocking out, the flasks are placed on a grid, which is set into an oscillatory motion with the help of cams; the earth from the flasks falls through the bars. To prevent hot soil from falling onto the soil conveyor belt in too large a mass, two feed rollers are installed under the grate, which evenly feed it onto the conveyor. Knocking out the rods is done either manually or using a water jet high pressure, or on specially designed pneumatic vibrator machines (Fig. 27) of the Stoney system.

Castings from the trolley are installed in special machine holders using an air lift located at each machine. Then the vibrator is activated, and the rods are knocked out for 3-6 seconds.

Casting cleaning. When removed from the mold, the casting has a number of bosses (sprues, thrusts and protrusions), which are unnecessary according to the product drawing, but necessary during production. The earth adhering to the casting, the sprues and the thrusts are removed by cutting off, and the profits by cutting off. A cleaned casting with profits is called black, and without profits - trimmed, or clean. Cast iron b. hours are left without pruning. Cleaning castings in some cases encounters difficulties, for example, during metal explosions, a “clog” occurs in the casting if the torn mass is not carried to the profit or vent; if the sprue is positioned incorrectly, the cutter can break out the sprue with the casting process; in this case, it is better to send the casting with the sprue for trimming; when removing deep cones, it is very difficult to select a thin cone from a long pipe; in this case, shifting the frame during the solidification of the metal can not only help maintain the integrity of the casting, but also facilitate knockout. Cleaning the outer surface of castings from burnt earth is carried out in modern foundries in rotating drums or with a stream of sand in sandblasting machines and chambers. The first method is mainly common in America, the second - in Europe. The disadvantage of the method of cleaning castings in ordinary drums is the large expenditure of labor and time for manual loading and unloading. A significant simplification is obtained if continuous drums are used instead of ordinary drums (Fig. 28).

The drum has internal and external cavities. The castings enter the internal cavity of the rotating drum from the right side. Hardened cast-iron sprockets enter there from the outer cavity through special slots. By moving slowly towards the opposite end of the drum, the casting has time to clean itself. Before reaching the end of the drum, the cast iron sprockets fall through small slots from the inner to the outer cavity of the drum, from where they are transmitted through spiral guides to the head of the drum. Castings that are more complex, when cleaning in drums one could be afraid of a large percentage of defects due to breakage and which are subject to significant mechanical processing, are cleaned in continuous sandblasting chambers. The method of hydraulic cleaning of castings, first successfully used at the Allis Chalmers Co. plant, turned out to be very successful. (Millwaukee): Cleaning time has been reduced from hours to minutes. The device is used for cleaning turbine wheels, gasometer cylinders and similar heavy castings. Cleaning of castings is carried out in a closed concrete chamber (Fig. 29), located in the middle of the casting room.

The internal dimensions of the chamber are 10370x18725x6100 mm. The thickness of the concrete walls is 305 mm. To protect the walls from the eroding effect of water, they are covered with steel plates. Inside the chamber there are two turntables with a diameter of 3050 mm (lifts 100 tons) and 6100 mm (300 tons). Both circles rotate on ball bearings and are driven by 25 and 35 HP motors. The service room is located in one of the corners of the chamber. There are 2 devices installed with three nozzles located at equal heights. Nozzles m.b. placed at any height. The nozzle for the larger table has a diameter of 27 mm, for the smaller one - 16 mm. The pump with a capacity of 3500 l/min is driven by a 300 HP motor. With two simultaneously operating nozzles, the water pressure is 28 atm. The dirt resulting from cleaning settles in two receptacles under the floor, from which it is continuously removed using an elevator. The earth is separated from the water, brought to 7% humidity and put back into production. The advantage of this cleaning method is its low cost, complete absence of dust, and also the fact that the rod frames do not deteriorate and can be used again.

Heat treatment. After cleaning, the casting is sometimes subjected to heat treatment. Cast steel and malleable cast iron must be annealed. Regarding cast iron, it has now been proven that it can. subjected to heat treatment similar to steel, and the ferrite-graphite-cementite structure of cast iron transforms into a pearlite-graphite structure with an increase in mechanical properties (elongation up to 8%, tensile strength up to 40-45 kg/mm ​​2). Heat treatment is especially facilitated by casting cast iron into permanent molds. Bronze casting can also be used in many cases. improved by heat treatment. Aluminum casting is always hardened at 500±10°C and tempered at 140±10°C.

Basic principles of foundry design. When designing a new foundry, you first have to take into account the location of the main metalworking shops and choose a location for the foundry in such a way as to be able to most easily and cheaply deliver castings to the processing shops. Foundry work program determined with the most accurate details possible, both in quantitative and weight terms, and in dimensional terms, which will make it possible to select the most suitable equipment for a given case and the most appropriate technological process. The foundry calculation scheme in this case is reduced to the following. Having a precise program of work, they compile an album of moldings, which will also give the basic principles for organizing individual operations technological process and the number of flasks required for the production and their types, as well as the required amount of molding materials, and therefore the power of the agricultural device. Having received it like this. arr. approximate data on the consumption of raw materials, on the size of the required space, begin to clarify individual operations of the production process, its possible mechanization as a whole or in individual parts. Various options for calculating the relative position of individual foundry shops will make it possible to most expediently resolve the issue of organizing a given production process. If the program does not m.b. defined with b. or with acceptable accuracy, then it is necessary to calculate the main and auxiliary workshops of the foundry using the so-called coefficients. In fig. 30 shows the usual types of foundry buildings;

fig. A - gray cast iron foundry for individual casting; B - malleable cast iron foundry with installation of flame furnaces; B - shaped steel foundry with open hearth furnace department; G - shaped steel with converters; D - steel foundry with electric furnaces.

Occupational hazards and safety precautions. All production processes taking place in foundries are associated with the occurrence of certain occupational hazards. Thus, during the preparation and processing of molding materials, knocking out, cutting and cleaning of castings, a huge amount of dust is generated (from 20 to 180 mg/m3). Proper ventilation must be installed to control dust pollution; Particularly favorable in this regard is the use of a hydraulic method for cleaning castings. During molding work, in cases where molding is carried out on the foundry floor, workers are forced to keep their body bent, often in a very unnatural position, which can lead to curvature of the skeletal bones. These hazards are eliminated during work on molding machines. Low temperature in foundries winter time(often below 0°C), high dampness, always cold and often frozen earthen floors cause frequent colds among molders, especially rheumatism. When servicing melting machines, workers are exposed to the harmful effects of sudden temperature fluctuations. When casting, molten metals release harmful gases. Of the latter, the following are of greatest importance: carbon monoxide, sulfur dioxide and zinc oxide. The concentration of CO in the air of foundries fluctuates on average within the range of 0.03-0.05 mg/l, reaching 0.21-0.32 mg/l at certain moments of casting above the flasks. (The Institute of Occupational Safety and Health has set a standard of 0.02 mg/l.) The amount of sulfur dioxide (SO 2) in the air of foundries, depending on the type of metal and coke used, reaches 0.045-0.15 mg/l (standard 0.02- 0.04 mg/l). Inhalation of zinc oxide vapors in copper foundries causes attacks of foundry fever in workers. When manually filling the charge into melting machines, when pouring metal into flasks manually, extremely high muscle tension is observed, which, due to the high temperature of the work, causes very debilitating sweating. These hazards are eliminated by the use of conveyors, mechanization of loading furnaces and transport, as well as pneumatic knocking out of flasks.

The largest number of accidents in iron and copper foundries occurs from burns from molten and hot metal during manual handling or delivery. Especially serious consequences entails contact of molten metal or slag with moisture (explosions). To eliminate these phenomena, it is necessary to have smooth paths made of brick, concrete, reinforced concrete, etc. in places not occupied by molding, and the main passage should be. not already 2 m; d.b. the flow of people with empty ladles and molten metal is correctly organized; places where castings and slag are poured must be dry; buckets d.b. well dried and heated; Ladle casings should have small holes to remove vapors from the coating, etc. Workers handling molten metal should b. equipped with proper protective clothing, goggles, respirators, etc., and the shirt should not be tucked into pants and pants into boots, and the brim of the hat should not be tucked into pants. bent down. Hand molding is accompanied by a large number of pins on the iron pins present in the old molding soil. The remedy is to pass the earth through a magnetic separator. When carrying ladles with molten metal, their center of gravity must be below the axis of rotation (up to 50 mm) to avoid tipping over. All chains, ropes and rockers must be tested to full load at least once every 2 months and thoroughly inspected at least once every 2 weeks. All machines must be equipped with reliable guards for hazardous areas.

To legally regulate working conditions in foundries, the People's Commissariat of Labor issued a number of mandatory decrees. This primarily includes the “Safety Rules for Work in Iron and Copper Foundries”; resolutions on limiting the use of labor of women and adolescents in the most harmful and hazardous work in foundries; decisions on shortened working hours and additional leave for certain categories of workers (copper foundries, sandblasters, etc.).

1.1 Basic concepts and definitions

Foundry, or casting, is a method of making a workpiece or finished product by pouring molten metal into a cavity of a given configuration and then solidifying it.

Blanks or products obtained by casting are called castings.

The cavity filled with liquid metal during casting is called a casting mold.

The purpose of the casting mold is as follows.

1. Providing the necessary configuration and dimensions of the casting.

2. Ensuring the specified dimensional accuracy and surface quality of the casting.

3. Ensuring a certain cooling rate of the poured metal, facilitating the formation of the required alloy structure and the quality of the castings.

Based on the degree of use, forms are divided into one-time, semi-permanent and permanent.

Single-use molds are used to produce only one casting; they are made from quartz sand, the grains of which are connected by some kind of binder.

Semi-permanent forms – These are forms in which several castings are obtained (up to 10-20); such forms are made of ceramics.

Permanent forms – molds in which from several tens to several hundred thousand castings are obtained. Such forms are usually made of cast iron or steel.

The main task of foundry production is to produce castings with the shape and surface dimensions as close as possible to similar parameters of the finished part in order to reduce the labor intensity of subsequent machining. The main advantage of forming blanks by casting is the ability to obtain blanks of almost any complexity of various weights directly from liquid metal.

The cost of cast products is often much less than products made by other methods, however, not any alloys are suitable for casting, but only those that have good casting properties. The main casting properties are:

1. Fluidity - the ability of liquid metal to fill a casting mold, accurately repeating its configuration.

The higher the fluidity, the better the casting alloy. In steel and cast iron, this property decreases with increasing sulfur content and increases with increasing phosphorus and silicon content. Overheating the alloy above its melting point increases its fluidity.

Fluidity is assessed by the length of the path traveled by the liquid metal before solidification. Silumins, gray cast iron, and silicon brass have high fluidity (>700 mm); carbon steels, white cast iron, aluminum-copper and aluminum-magnesium alloys have medium fluidity (350-340 mm); magnesium alloys have low fluidity.

2. Shrinkage – reduction in the size of the casting during the transition of the metal from a liquid to a solid state. The less shrinkage, the better the casting alloy. A distinction is made between volumetric shrinkage (reduction in volume) and linear shrinkage (reduction in linear dimensions). This property depends mainly on the chemical composition of the alloy. Approximately linear shrinkage is 1% for cast iron and 2% for steel and non-ferrous. Of course, each specific grade of casting alloy has its own shrinkage value.

3. Tendency to segregation. Liquation is the name given to chemical heterogeneity throughout the volume of a casting. The less tendency of a cast alloy to segregate, the better it is.

Many different alloys are used in foundry production. The most common is gray cast iron, from which about 75% of castings (by weight) are made in domestic mechanical engineering, about 20% from steel, 3% from malleable cast iron, and about 2% of cast parts are made from non-ferrous metal alloys.

There are two ways to pour metal into molds.

1. Conventional pouring, in which the metal fills the mold freely under the influence of gravity. This method includes casting in sand-clay molds.

2. Special casting methods, there are about 15 of them, the main ones are:

· injection molding;

· centrifugal casting;

· die casting (in metal molds);

· casting into shell molds;

· casting using lost wax, burnt out or dissolved models.

Casting in sand-clay molds is the main method of producing castings. This method produces cast parts of both simple and complex shapes, the largest castings that cannot be obtained by other methods.

The use of special casting methods makes it possible to reduce defects in foundry production. When casting into metal molds, centrifugal casting ensures the production of high-precision castings. Along with this, special casting methods are applicable only for products of relatively small sizes (weight up to 300 kg).

To make a casting mold, you must have a model kit. In general, a model kit consists of a model, a core box and models of gating system elements.

The model is a prototype of the future casting; with the help of the model, mainly its external configuration is formed. The model differs from the casting in the material, the presence of rod marks (if the casting is hollow and a rod is needed to form the cavity), the presence of a connector (if molding is carried out using a split model), and dimensions that exceed the corresponding dimensions of the casting by the amount of linear shrinkage of the alloy.

A core box is a part of a model kit designed for making a core. The rod, in turn, is necessary to form the internal configuration of the casting (to produce holes).

The gating system is a set of channels in the casting mold that supply molten metal, trap slag and non-metallic inclusions, remove gases from the mold, and also supply the casting with liquid metal during its crystallization.

1.2 Technology for producing castings

The technological process for producing castings in sand-clay molds includes molding, i.e. preparing half-molds and cores; assembly of casting molds; melt pouring, knocking out and cleaning of castings.

For the manufacture of foundry molds from molding sands, model-flask equipment is used. It includes models, model tiles, core boxes, etc.

To facilitate the study of the casting manufacturing process, let us consider the technological process diagram (Fig. 1).

Based on the drawing of the part (Fig. 1, a), the foundry technologist develops a drawing of the model and the core box. In the model shop, according to these drawings, a model (Fig. 1, b) and a core box (Fig. 1, c) are made, taking into account allowances for machining and shrinkage of the alloy during cooling. In order to obtain supporting surfaces for installing rods, rod marks were made on the models. A rod is molded along the core box (Fig. 1, d), which is intended to form an internal cavity in the casting.

To fill the mold with metal, there is a gating system consisting of a bowl, a riser, a slag trap, feeders and vents (Fig. 1, e). During assembly, a rod is installed in the lower half-form, then both half-forms are connected and loaded with ballast. The assembled casting mold is shown in Fig. 1, d.

In the melting department, metal is melted and poured into molds. The cooled casting is knocked out of the mold and transferred to the cleaning and trimming department, where it is cleaned of the molding core mixture and the remains of the sprue, bays, etc. are chopped off.

Models are devices with the help of which impressions are obtained in the molding sand - cavities corresponding to the external configuration of the castings. Holes and cavities inside the castings are formed using rods installed in the mold during their assembly.

The dimensions of the model are larger than the corresponding dimensions of the casting by the amount of linear shrinkage of the alloy, which is 1.5-2% for carbon steel, 0.8-1.2% for cast iron, 1-1.5% for bronzes and brasses, etc. d. To facilitate the manufacture of models from the molding mixture during molding, the walls of the models should have molding slopes (for wooden models 1-3 0, for metal ones 1-2 0) At the joints, make smooth joints with a radius R = (1/5 - 1/ 3) average thickness of the contact walls.

The advantage of wooden models is low cost and ease of manufacture, the disadvantage is fragility. Models are painted red for cast iron castings and blue for steel castings. The rod signs are painted black.

Metal models are most often made from aluminum alloys. These alloys are light, do not oxidize, and are easy to cut.

Machine molding usually uses metal pattern tooling with the installation of the pattern with the installation of the pattern and gating system on a metal pattern plate.

The cores are formed in wooden or metal core boxes.

Molding, as a rule, is carried out in flasks - strong and rigid. metal boxes various shapes, intended for the production of foundry half-molds from the molding sand by compacting it.

For the manufacture of casting molds and cores, mixtures of natural sands and clays with the addition of the required amount of water are used. The quality, composition and properties of materials and mixtures depend on their service conditions in the gating mold.

Molding and core mixtures must have the following properties:

– strength (to maintain integrity during assembly, transportation, mechanical impact);

– gas permeability;

– fire resistance (in contact with metal it should not melt, sinter, burn to the casting, or soften);

– plasticity (retains its shape after removing the load);

– non-adherence of the mixture to the model, core box and in the parting plane of the mold;

– non-hygroscopic;

– thermal conductivity;

– ease of removal of the mixture when cleaning castings;

– durability, i.e. the ability of mixtures to retain properties after repeated use;

- cheap.

Fresh molding materials, i.e. sand and clay, require an average of 0.5 - 1 ton per 1 ton of casting, while the consumption of mixtures for the manufacture of molds and cores is 4 - 7 tons. The main part in the mixtures is waste molding materials , fresh materials serve only to replace the sand grains turning into dust and to fulfill the binding properties of the clays.

The grain part of the sand should consist predominantly of quartz grains (SiO 2) in the best types of sand the content of SiO 2 is ³ 97%, in the worst the content of SiO 2 is ³ 90%.

The clayey part of sand conventionally includes all particles contained in it with a size of less than 0.022 mm.

Molding clays are sands containing more than 50% clay substances. Clays are divided into ordinary molding clays and bektonite clays. Bectonite clays include clays consisting mainly of montmoriglionite crystals. This material swells strongly in water, which increases the binding properties of clays. Bectonite is used for the manufacture of forms and cores that are not subject to drying.

Ordinary molding clays consist mainly of kaolin crystals Al 2 O 3 · 2SiO 2 · 2H 2, which do not exhibit intracrystalline swelling.

For steel casting, the most refractory clay with high thermochemical stability is taken - at least 1580 ° C, for cast iron - with an average resistance of at least 1350 ° C, for non-ferrous casting the thermochemical stability of clays is not limited.

For the production of molding and core mixtures, in addition to sand and clay, organic and inorganic binding materials are used. Organic binders burn and decompose when high temperatures. These materials include linseed oil, drying oil, crepetel (vegetable oil, rosin, white alcohol), peat and wood pitch, rosin, pectin glue, molasses and a number of others. Cement and liquid glass are used as inorganic binders.

In foundries that have mechanized soil preparation, they use a single molding mixture. In workshops with a lesser degree of mechanization, facing and filling mixtures are used; the former are of higher quality and serve to form an internal layer in contact with the casting.

Materials for the rods - rod mixtures - are selected depending on the configuration of the rods and their location in the mold. They must have high strength, have sufficient flexibility so as not to interfere with metal shrinkage, and good gas permeability. In the production of castings from steel and cast iron, high-quality sand-oil-resin mixtures (pure quartz sand and a polymer binder - resin or liquid glass) are used to prepare such rods. Less critical rods with a thicker cross-section are made from mixtures consisting of 91-97% SiO 2 and 3-4% clay with the addition of liquid glass or other binders. For massive rods, lower quality mixtures are used, made from 30-70% SiO 2, 20-60% recycled earth and 7-10% clay, which is the main binder.

To prevent burning and improve the surface cleanliness of castings, molds and cores are coated with a thin layer of non-stick materials. For raw forms, non-stick materials are dusts, which are powdered graphite (for cast iron castings) and powdered quartz (for steel castings). Non-stick paints are prepared for dry molds. Paints are aqueous suspensions of the same materials: graphite (for cast iron), quartz (for steel) with binders. Paints are applied to hot forms and cores that have not had time to cool after drying.

1.3 Gating systems

The purpose of the gating system is to ensure a smooth, shock-free supply of metal into the mold, regulate thermophysical phenomena in the mold to obtain a high-quality casting, and protect the mold from slag inclusions getting into it. The elements of a normal gating system are a gating bowl 1, a riser 2, a slag catcher 3, and feeders 4 that supply metal directly to the casting. When pouring, the entire gating system must be filled with liquid metal to prevent slag and atmospheric air from being sucked into the mold.

When producing castings from steel, ductile iron and some alloys of non-ferrous metals with relatively large shrinkage, the gating system feeds them with liquid metal during the solidification process.

There is a certain ratio between the cross-sectional areas of all channels of the gating system, in which each subsequent element, starting with the funnel, passes less metal than the previous one. In the production of castings, when selecting the cross-section of gating system elements, one should be guided by the following rule: F riser > F slag trap > SF feeders. For cast iron castings weighing up to 1 ton SF feeders: F slag catcher: F riser = 1:1.1:1.15; for cast iron castings weighing more than 1 ton, the area ratio is 1:1.2:1.4; for steel casting – 1:1.4:1.6 tons. In this case, the total cross-sectional area of ​​the feeders is determined by the following relationship:

, m 2 ,

where Q is the mass of the casting and profit, kg,

r - density of the casting material, kg/m 3,

m = 0.4-0.6 – outflow coefficient,

t = 4-9 s – mold filling time,

g = 9.81 m/s 2 – gravitational acceleration,

H – average pressure, m (height of the liquid metal column in the mold, measured from the top edge of the funnel to the center of mass of the casting).

In other words, the gating system is locked and creates conditions under which slag does not pass through the funnel and air is not sucked in because it is constantly filled with metal and the riser tapering towards the bottom restrains the pressure. At the same time, the gates (feeders) are not able to pass through all the metal coming from the riser; the slag film on the surface of the metal rises to the top of the slag catcher, and only pure metal goes into the casting through the gates.

To remove air from the mold, as well as to monitor the filling of the mold with metal, vertical channels (protrusions) are installed on the upper parts of the castings. When casting from steel, aluminum alloys, and some types of bronze, which are characterized by high shrinkage, the stops are replaced with profits. Their main purpose is to feed the casting with liquid metal during its crystallization to prevent the formation of shrinkage cavities in the areas of the castings that are the last to solidify. Regular closed or open profit can only act if it is located above the casting. The volume of metal in the profit must provide the necessary ferrostatic pressure on the casting metal.

Forming methods

Manual molding is mainly used to produce individual, both small and large, complex castings.

Open soil molding is carried out for non-critical castings with a flat surface, for example, slabs that are not subject to high requirements By appearance and surface quality.

This forming can be done on a soft bed or on a hard bed.

When molding on a soft bed (Fig. 2), a hole 150-200 mm deep is dug in the earthen floor of the workshop and a soft bed is prepared in it from a loose filling mixture and a layer of facing mixture 10-15 mm thick is placed on top of it. After leveling with a smoothing iron and checking the horizontal surface of the bed using a spirit level 3, model 4 is pressed into it by hand. To do this, place the model on the surface of the mixture and push it down with hammer blows through a plank, then the mixture around the model is compacted with a tamper, cut off the excess mixture, cut out the sprue bowl 1 and the channel on the left 2 for filling the mold with metal, and on the right there is a drain channel 5 for draining excess metal. To remove gases from the mold, 6 channels are pierced with gaskets. After this, carefully wet the edges of the mold near the model and remove it. If defects are found, they are corrected, the surface of the mold is coated with dust and filled with metal.

If the casting is heavy, make a hard bed under it (Fig. 3), dig a hole 300–500 deep mm greater than the height of the model, a layer of burnt coke 100 thick is placed on the bottom mm, Two pipes are installed obliquely on the sides to remove gases and the mixture is filled.

The first few layers are 50–70 mm densely packed with tampers, the next layers are filled looser, and the last 100–120 mm leave without compaction, slightly leveling the surface with a trowel. In the prepared bed, make frequent pricks with a strangler until the coke layer is formed and cover the surface with a layer of facing mixture 15–20 mm thick. mm. The model is deposited on this mixture depending on the design - half if it is detachable, or all if it is one-piece. After this, check the density of the mixture around the model and tamp it down if weak spots are found, and then the entire surface around the half-model is smoothed and sprinkled with dry fine sand to eliminate sticking to the upper half-mold.

When making the upper half of the mold, first the upper half is placed on the lower half of the model exactly along the tenons, then the models of the riser and supports are placed. After this, the model is covered with a facing mixture and the entire volume is filled with the filling mixture, and then punctures are made with a gas outlet. The position of the flask in relation to the bottom of the mold is fixed by driving pegs in all four corners.

Now remove the flask and place it on the floor, first turning it 180°. Carefully remove both halves of the model, smooth out the damaged areas, cover the cavities of the half-molds with dust, install a rod in the lower half-mold, place the flask half-mold on the ground exactly along the boundaries of the driven pegs, put the sprue bowl in place and load weights onto the upper surface of the mold to prevent the danger of lifting it poured metal, to avoid burns near the place where the mold is poured.

Molding in flasks

Molding in flasks is most widely used in foundries. Depending on the design of the models, conditions and nature of production, it has many varieties. Let's look at the most typical of them.

In Fig. Figure 4 shows molding using a split model. The part being cast (Fig. 4, A) molded according to a model with signs for the rod forming a cavity in the casting (Fig. 4, b). On shield 1 (Fig. 4, V) first install half of the model 2, and then the flask 4, The model is dusted with a thin layer of dust and covered with a facing mixture, and then the entire flask is filled with a filling mixture. After this, excess mixture is removed from the upper side and gas outlet channels 3 are punctured. Then the half-mold is turned 180° and placed on

shield (Fig. 4, d). After this, the surface of the connector is sprinkled with release sand. The top 5 is placed on the lower half of the model, strictly centering it along the tenons, then the flask is aged 6, models of riser 7 and thrusts 8 and fill them in the same order as the lower half of the mold. Then the upper surface is smoothed, the channels are pricked, the outlines of the sprue bowl are drawn, and the models of the riser 7 and thrusts are extracted 8. Then the upper half-mold is removed and rotated 180°. Models are removed from both halves of the mold, the damaged areas are smoothed, sprinkled with dust, the rod is installed in the lower half of the mold, covered with the upper half of the mold and the mold is fastened or loaded for pouring metal (Fig. 4, d).

Molding in two flasks according to the one-piece model is shown in Fig. 5. Model of the molded part (Fig. 5, A) without the lower rod sign, they are placed on the shield (Fig. 5, b), covered with facing, and then filled with the filling mixture and the excess is raked from above. When the mixture falls under the model, the half-mold is rotated 180° (Fig. 5, V) and cut out the mixture along line 3-4 . Smooth the entire surface of the connector, sprinkle it with release sand and put rod mark 2 in place , they place the upper flask, models of the riser and vents, fill it with molding sand, open the mold, remove the model, finish it, sprinkle it with dust, place the core, cover it with the upper half-mold, load it and place it under pouring (Fig. 5, G).