Casting plant. State and prospects of foundry production in Russia

In September, business meetings between Dutch companies and Russian potential partners took place in the Urals. Partnerships were proposed for various industries: metallurgy, mechanical engineering, agriculture, food industry. The crisis disasters that affected the Urals, like all regions of the Russian Federation, did not frighten European industrialists. And this is a good sign!

Despite the fact that the Urals are in decline today, we need to think about the future, says Marina Bogdanova, business development manager at GEMCO CAST METAL TECHNOLOGY. - When the economy starts to develop again, it may already be too late. In Russia, the foundry industry is represented mainly by foundries that are part of engineering and other manufacturing corporations and holdings, and a relatively small number of independent foundries. In this situation, foundry production for the company as a whole is often perceived as auxiliary, and therefore “eating up” the company’s funds. Hence the residual sign of capital investment in development. Over the course of decades, this approach has led to almost universal moral and technical obsolescence of equipment and technologies. Point-by-point attempts to improve and modernize do not give the desired effect.

As a result, in the industry as a whole we have high-cost, inefficient, poorly organized production, which weighs heavily on the shoulders of companies. Meanwhile, everything should be the other way around. Foundry production is a business where you can and should make money. How to make this possible? Naturally, serious capital investments are required. But besides this, and no less important, we need a highly professional approach to mastering such tools. Purchasing new equipment is not everything; here you need to solve a complex of problems. Namely, the choice of equipment should be optimal, so as not to spend extra money on excess capacity, and at the same time not create a shortage of capacity. It is necessary to build an optimal production scheme and optimally organize the production process. This will significantly reduce costs, make it possible to recoup capital investments within 4-5 years, and bring production to the level of an independent business that brings good profits. Today, the winner in the market is the one who offers high quality at a low price. However, this task is not an easy one. GEMCO, which has a staff of professionals who have accumulated relevant experience and knowledge, knows how to achieve such a combination.

Marina, what, first of all, does a production worker really care about: profit or quality?

This issue cannot be divided. These two concepts depend on each other. They are inseparable. If a company produces low-quality products, then what benefits are we talking about? The owner of the company can increase quality, at the initial stage at a loss, and establish himself. Or maybe lower it, but there is a risk of losing customers. The profitability of an enterprise depends on sales volume. You made a successful batch, they bought it from you - you have proven yourself. This is how business connections are built. Quality - reputation - sales - benefits .

Russia has long been among the countries where any activity is specific. This requires a special approach. However, the Dutch are no strangers - they know how to professionally and effectively make a Russian company a leader.

What tools does the company offer to solve problems in foundry production?

Our company is engaged in foundry production: ferrous and non-ferrous. The activities of GEMCO CAST METAL TECHNOLOGY are divided into three components. Engineering: includes the development of a foundry project and the stages of its implementation. Contracting: general contracting. Foundry consulting, which can be operational or strategic. Operational is a marketing research on customers, a comparative analysis of production efficiency. This may include technical and commercial audits required for mergers and acquisitions. Operations consulting involves developing methods to improve production. When an enterprise has been operating for a certain time, it is necessary to periodically monitor production efficiency.

We are talking again about strategic planning, the absence of which our entrepreneurs often sin. In this case, precisely calculated technical and economic aspects are simply necessary. After all, in order to get the expected result, you need to act correctly at each stage.

Marina, your company is called unique. For what?

There are companies on the market that provide only engineering, or only consulting, or specializing in the supply of equipment. What makes GEMCO unique is that we provide a comprehensive approach. And our customers will confirm to you our accuracy and responsibility.

Tell us your step-by-step approach to the project

First, you need to consider aspects of the future project that the company is going to release. Based on them, a production concept is made, the technical part is drawn up and preliminary layout is carried out. Then the project begins to be filled with the necessary equipment according to needs. There is no point in installing equipment that cannot support production volumes or that will not be used 100%.

Next, we calculate resource costs: how much gas, water, energy, raw materials are needed, how many people should service the line. This is the concept. After completing the above work, we calculate how much the entire project will cost.

For example, what specific advantage can you give to the customer’s company?

For example, creating a team. It is very important. If a company does not have a team, it is doomed to failure. Uniting technologists, metallurgists, and working operators is not an easy matter. Let’s say the company has been using the “casting in the ground” technology for a long time and the management decided to introduce a new product. And for this we need another technology that has not yet been mastered. It is we who will carry out the transfer of technology: we will select personnel according to professional requirements, determine the responsibilities for each team member, train and, most importantly, monitor the implementation of the process.

What is the current state of the foundry industry in the Netherlands?

To answer this question, you need to trace the situation ten years ago. During this period of time, major changes occurred. Some businesses closed, many were moved to new locations. Over the past 10 years, there has been a tendency to concentrate on narrow-range products. Now in Russia the same topic is just beginning. There are many such industries in the Russian Federation. Now the attitude towards foundry production is as auxiliary, as ballast, but everything must change.

In the Netherlands, the crisis is almost over. This is not to say that everything is great, because... there are problems that require solutions. Many companies have suspended operations. And, interestingly, part of the vacated market has already been occupied. Roughly, everything will return to normal in about two years. But for Russia the time frame is longer. And if we knew the answer to the question “When will the crisis end?” - they wouldn’t tell it to anyone, but use it for themselves. In the Netherlands this is several months, for Russia it is years. There are still banking problems and bureaucratic barriers, but it is the task of the state to create conditions. in which people wanted to do something.

You held meetings with Ural businessmen, but now the situation is so unstable. Do you think today is the time for new projects?

There is a concentration of such companies in Chelyabinsk, but today a serious modernization of production is needed. Management understands this and is working in this direction. Unfortunately, the process takes longer than we would like.

GEMCO CAST METAL TECHNOLOGY's early activities were related to the manufacture of equipment for foundries, but practice has shown that it is necessary to focus on intellectual activity. There is such a thing in business - finding your niche. We found her. It is important that there are people who will help you professionally understand the issues of applying the most economically and technically effective production solutions, make the optimal selection of equipment, determine the technological process and movement of materials, and effectively use investment capital. I would like to emphasize that we will provide a realistic overview of the required investment and project timeline; We will give an objective definition of the price level of products and financial indicators.

1.1 Basic concepts and definitions

Foundry, or casting, is a method of producing 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 of various shapes, intended for the production of casting halves 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 at 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. A regular closed or open profit can only work 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, which are not subject to high requirements in terms of 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 trowel 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 compact the mixture around the model 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).

The RemMechService company is a manufacturing company whose activities include the production of parts for various purposes, machine components and mechanisms, as well as their mechanical processing. To manufacture parts, we use various structural materials - rubber and polymers, steel, non-ferrous metals and their alloys. Among other things, our company accepts orders for the production of molded rubber products. You can order the production of the following rubber products:

1. Mold products:

• spare parts for machines and mechanisms;
• rings of various sections;
• plates and plates for various purposes.
2. Non-shaped products:
• Seals for various purposes;
• rugs;
• gaskets;
• tubes.

Material for the manufacture of molded rubber products

Rubber is an elastic material obtained from natural or synthetic rubber by vulcanization: the rubber is mixed with a vulcanizing component, most often sulfur, and heated. According to their purpose, rubber is divided into:

• oil and petrol resistant;
• acid-resistant;
• aggressive;
• heat resistant;
• heat resistant;
• ozone resistant;
• conductive.

According to the degree of vulcanization, rubber is divided into three types:

• soft, which contains up to 3% sulfur;
• semi-solid, with sulfur content up to 30%;
• solid, the sulfur concentration in which exceeds 30%.

Our company uses only high-quality natural and artificial materials in the rubber molding production process:

• rubbers (nitrile butadiene rubber, fluorine rubber, etc.);
• latex;
• polyamides;
• silicone;

Technology for the production of molded rubber products

The basic processes for processing rubber into products are:

• preparation of rubber mixtures;
• casting of products;
• curing.

In the process of preparing mixtures, all powder components are dried and sifted in order to free the mixture from large inclusions and foreign objects, the ingress of which into the mixture leads to a decrease in mechanical strength and defective products. The rubber is steamed, crushed, and then, using rollers, it is given the necessary plasticity. Then, using rollers or special mixers, the powder components and rubber are thoroughly mixed. Next, the resulting mass is sent for processing into semi-finished or finished products.

There are four types of processing of rubber compounds:

• calendering;
• continuous extrusion;
• injection molding;
• pressing.

1. The process of calendering is the sheeting of a rubber mixture to obtain raw rubber in sheets or strips with a thickness of 0.5 mm to 7 mm. Special machines - calenders - are a three- or four-roll stand of a sheet rolling mill. In a three-roll calender, the rubber mixture passing between the upper and middle rolls (their temperature is 60-90 degrees) is heated, envelops the middle roll and is discharged into the gap between the middle and lower rolls, the temperature of which is 15 degrees. The main requirements for the calendering process are good surface quality, uniformity of gauge along the length and width of the web, winding of the canvas with minimal fluctuation in the rolling width. Calendering produces both smooth and profiled rubber sheets. Also, using a universal sheet-coating calender, textiles are covered or coated with a thin layer of rubber mixture; the process proceeds in the same way as calendering of rubber compounds.

2. Continuous extrusion (extrusion, extrusion) is the process of extruding raw rubber, in which the heated rubber mixture is pushed through a profiling hole (mouthpiece) and profiled blanks are formed. Tubes, strips, cords and other products are made in this way. The temperature of the rubber compound plays a significant role in the continuous extrusion process:

• for warm feed worm machines it should be within 40-80 degrees (if it changes, the extrusion process is disrupted and workpieces of the wrong profile are obtained);
• for cold feed worm machines – 18-23 degrees, which greatly simplifies temperature control;
• in worm-type syringes - cold and hot feed machines, the supplied mixture is squeezed out through the profile hole of the head using a worm. In syringe presses, the mixture is forced by a plunger through a mouthpiece under pressure. Syringe presses, unlike syringe machines, are periodic mechanisms and cannot provide a continuous process. In turn, worm machines can be assembled into mechanical or automated production lines.

3. Rubber injection molding is the process of injecting a heated rubber mixture into a prepared pre-closed mold, after which the mixture is vulcanized and rubber with predetermined properties is obtained. Such casting is one of the most progressive processes for processing rubber into products, which is especially appropriate for the mass production of homogeneous products with complex configurations. Injection molding is a cyclical process. Rubber compounds for injection molding can be based on isoprene and siloxane rubbers, polychlororelen, butyl rubber, styrene butadiene rubber, nitrile butadiene rubber or natural rubber. The mixtures must have a high vulcanization rate and at the same time have high resistance to scorching. Rubber injection molding has a number of advantages over other methods: by closing the mold before injecting the prepared rubber mixture, products are obtained with a smooth surface, without burrs and flash, which do not require additional processing, and the amount of production waste is reduced.

4. The pressing method is one of the most common methods for producing products from rubber compounds. Hot pressing technology is quite simple and does not require complex expensive equipment. The raw rubber mixture is placed into the internal cavity of the mold, heated to 130-200 degrees, manually, then under the required pressure the mixture is shaped into the internal cavity of the mold. To obtain high-quality monolithic products, it is necessary to remove moisture and volatile substances from the mold. What is needed is the so-called pressing process: a short-term opening of the mold followed by its closure. Next comes the vulcanization stage: the rubber mixture loses fluidity, becomes strong and elastic. The duration of vulcanization in the process of hot pressing of rubber can significantly exceed the duration of the cycle of filling the mold with the rubber mixture and giving it the required shape.

Quality control of rubber molding

Thanks to the availability of modern equipment and qualified personnel, all molded rubber products are manufactured in accordance with international and domestic standards. Quality department specialists constantly monitor the quality of input raw materials and finished products; compliance with the required standards of each batch of cast rubber products is confirmed by a passport of the finished product.

How to order and buy molded rubber products?

We accept orders for the production of both serial and single cast rubber products. To order rubber casting, the customer must provide a drawing or sketch of the part (photo) indicating all the required dimensions and tolerances, and data on the loads tested, operating conditions (temperature, pressure, working environment, etc.). If such documentation is not available, our specialists will assist in preparing the design documentation based on the customer’s requirements.

To place an order for the manufacture of molded rubber products, you need to fill out the feedback form or send drawings by email [email protected].

Rubber molding

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 are 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 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. The 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 of cast workpieces has led to in-depth scientific research into the properties of liquid metals, the 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 machining allowances due to very accurate dimensions and high surface finish, which was necessary due to the extremely difficult machinability of all heat-resistant alloys based 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 narrowest point is the 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,

Another important achievement in the technology of producing high-quality castings, developed and implemented during the development of shaped casting from new alloys of non-ferrous metals, is the principle of directional solidification of castings. 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 principles of 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 higher education. 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 correspond to the advanced achievements of scientific and technological progress. Their result, in particular, was the creation of modern die casting and injection molding shops 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-slips, through holes and looseness are not allowed in castings. Surfaces that are bases for machining , must not have sagging or damage. Allowable 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. The need for heat treatment is 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, various methods of casting into one-time and reusable molds are used.

CLASSIFICATION OF CASTINGS

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

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 of 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 processed surfaces, purpose and special technical requirements, castings are divided into 5-6 complex groups (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. A quantitative assessment of the kinetics is very difficult due to the uncertainty of the equations that describe the time 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 possible more complete accounting and assessment 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 the 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 of technological operations of 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 diagrams of the state 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 the general rule of alloy melting technology 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, various types of melting furnaces are used in the workshops for blank and shaped casting of non-ferrous metals.

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 method of converting electrical energy into heat. 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. The 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 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 are created by a vertical-slot gating system. 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 mold is filled below the flooded level and the hot metal continuously flows 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). The composition of the mixture for medium and large molds: 30% gypsum, 60% sand, 10% asbestos, 40-50% water. The mixture for making rods contains 50% gypsum, 40% sand, 10% asbestos, 40-50% water, 1-2% slaked lime is added to the mixture. the strength of the forms is achieved through the hydration of anhydrous or semi-aqueous gypsum. To reduce strength and increase gas permeability, raw gypsum forms 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 for days in air. 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 in shell molds, the same gating systems and temperature conditions are used as when casting in sand molds.

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 mold cavity 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 hardening 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 rate of solidification 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 The radius of curvature must be at least 3 mm. Holes with a diameter of more than 8 mm for small castings, 10 mm for medium ones and 12 mm for large ones are made with rods. The optimal ratio of the hole depth to its diameter is 0.7-1. 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. A distinctive feature of this casting method is the 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 the 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. Increased pressure contributes to better nutrition of 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 a minimum pitch of 1 mm and a diameter of 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

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