Do-it-yourself molding mixture for casting

Molding sands for casting

Foundry production is a fairly simple and widespread technological process for producing castings of various sizes and shapes. The production of parts by casting is practiced in the automotive industry, machine tool industry, carriage building and many other branches of mechanical engineering. To produce hollow or multi-hole castings, core and molding mixtures of various compositions are used. The use of sand-clay forms in mass production is economically justified.

The composition of the mixtures depends on:

• molding method:
  manual;
• machine;
• metal type:
  steel;
• cast iron;
• non-ferrous metal and its alloys;

• type of production:
  single;
• serial;
• mass;

• casting type;
• technological equipment.

The materials used to produce molding sands are divided into the following groups:

• sandstone;
• various types of clay;
• auxiliary: binding materials;
• non-stick lubricants and coatings;
• fireproof;
• special.

Clay sands can contain up to 50% clay. They are divided according to the amount of clay content into:

• skinny – up to 10%;
• bold – up to 20%;
• fatty – up to 30%;
• very fatty – up to 50%.

Quartz sands are also used. The silicate base allows you to take a melt into shape, the temperature of which reaches 1700C.

Producing high quality castings requires the use of non-stick coatings and fine materials to prevent the formation of pores in the form.

Definitions

There are several types of sand; to understand the essence of the issue qualitatively, it is necessary to familiarize yourself with the main differences:

natural sand. A material that has a free-flowing state, while it is inorganic. The grains reach a size of 5 mm. Sand is obtained due to the natural crushing of rocks. It is obtained by extracting it from sand deposits or mixed with gravel;

Natural

• special equipment for enrichment can be used;
• crushed. The grain size does not differ and is less than 5 mm. Manufactured by humans using special crushing and grinding equipment. Obtained by crushing rocks;

Crushed

fractional. This is homogeneous sand that has been previously divided into 2 or more fractions. For this purpose, special sifting equipment is used;

Fractional

screenings from crushing. Product of inorganic origin, grain size up to 5 mm. It is obtained by sifting out destroyed mountain rocks. It is a secondary product in the production of crushed stone and some types of metals. Also obtained from certain non-metallic minerals.

Types of alloys

Bronze contains copper and alloying additives (beryllium, lead, aluminum, silicon and tin). All its alloys also contain components such as zinc, phosphorus, etc. In addition to bronze, the modern industrial industry is engaged in the production of other alloys from copper - constantan, copel, nickel silver, cupronickel, brass, etc.

The amount and type of alloying components in a bronze alloy determines its chemical and physical characteristics, as well as the color of the material.

Brands of bronze alloys, the melting point of which lies in the range from 930 to 1140 degrees Celsius, have their own markings. , bronze-based alloys

People learned to combine tin with copper to produce bronze a long time ago. Tin makes the material stronger and also reduces its melting temperature. A striking example of this type of alloy is bell bronze. It contains twenty percent tin and eighty percent copper. However, products made on the basis of bell bronze are characterized by high fragility.

Read also: Circuit diagram of an AC welding machine

Tin-free bronzes, as the name suggests, do not contain tin. Such alloys today are classified into separate categories of bronzes:

1. Beryllium is the strongest and has many characteristics superior to steel;
2. Silicon-zinc - have increased resistance to abrasion (the advantage of such bronzes of this group is that when molten they have high fluidity);
3. Based on aluminum and copper, they have high anti-corrosion protection and excellent anti-friction properties.

Currently, the most common bronzes are those containing tin. For the purposes of marking the material, regardless of the composition, the designation “Br” is used, after which the additives used and their content in the material are indicated. For example, you can decipher the bronze “BR OTSSNZ-7−4−2-. This tin alloy contains tin, zinc, lead and nickel. The numbers indicate their percentage in bronze. The composition of any brand of bronze may contain other elements having the following designations:

1. A - aluminum alloys;
2. B - beryllium-based alloys;
3. F - ordinary iron;
4. K - silicon element;
5. Mts - ordinary manganese;
6. F - phosphorus.

• sifted quartz sand in quantity to fill our mold and sprues. Let's take sand as an integer part - unit (1) or 100% for ease of calculation;
• bentonite clay. We will need 0.15-0.20 (15-20%) of the total mass of sand;
• water. The moisture content of the mixture should be about 0.06 (6%) of the total mass of sand + clay (yes, I took sand as a whole part, and now the whole part is sand + clay).

First, mix sifted sand with sifted clay.

Mix well and dry. Otherwise, if you do this at the same time as water, you will suffer trying to break up lumps of raw clay.

It is convenient to use a spray bottle to moisten the mixture. It will allow the moisture to be evenly distributed, but if it is not there, then just add water a little at a time.

Allow sufficient time to stir the mixture. It should turn out homogeneous and be completely moistened with water (those 6 percent are more than enough for this)

Once everything is funny, our mixture is almost ready to be molded! You just need to let it brew so that the moisture is distributed evenly. Leave the mixture alone for 1 hour or even 2. This is what is good about this mixture - it is easy to make and there is no need to rush anywhere, and if the proportions are not met, this can always be corrected by adding the missing part of sand or clay.

After an hour, the mixture significantly changes its properties for the better - it sticks less to your hands and retains its shape well if you squeeze a handful into a fist (This, by the way, is a popular way to check the quality of the mixture - take a handful of the resulting mixture in your hand and squeeze it. And when When you open your hand, the mixture should follow the curves of your fingers and palm. Then try to break it in half. If the lump breaks exactly in half and does not crumble, that’s what we need)

Now let's move on to the molding process.

Place the prepared frame on a flat surface and pour the mixture into the mold. Don't rush to fall asleep all at once. Add a third and compact it so that the sand fills all corners of the mold. First I make a sandy bottom - I fill it with sand, tamp it, and then I fill the entire mold without tamping and press the model into the loose sand. Before installing the model, it would be a good idea to sprinkle it with talcum powder so that it does not stick to the mixture. I compact it with my fingers along the perimeter and add more mixture as needed. It would be easier if the model was divided in half, but that's another story. We have a specific example. Therefore, the sequence is exactly like this. It is convenient to tamp with a small wooden block - it is strong and heavy enough for a comfortable process. Then use the same block to level the surface. The model should be filled exactly in the center, as it has roundings. To prevent the form from collapsing when removing it, I had to strain a little, but I managed. You can do it too!

When the first half of the mold is compacted and leveled, tap the mold with the same block to loosen it slightly and try to remove it. Everything came out well, and did the form print as it should? Okay, then it’s time to return the model to the mold and use a brush with talcum powder or graphite over the entire surface area of ​​the mold, including the model. This is necessary to ensure that the second half of the mold does not stick to the model and the lower half of the mold.

The second part is easier to tamp - just add sand and tamp evenly until the whole thing is filled.

It is important to remember that if the compaction is insufficient and the mixture remains loose, it will collapse before casting or during the pouring process. If you tamp too hard, the sand will be compressed and the gas permeability of the mold will be poor, which can lead to casting failure, since vapors and gases will be poorly removed from the mold during the casting process.

Properties

The main characteristics of this building material include:

• strength - the mixture has a high density and is practically indestructible;
• plasticity - the mass has a tendency to deform, this is due to the presence of clay inclusions;
• fluidity - the mixture has the ability to be evenly distributed inside the container or casting box;
• gas permeability - the material is able to “get rid” of excess air and gases that are formed during pouring;
• fire resistance – molding sand has increased resistance to high temperatures.

In addition, its main properties include:

• uniformity;
• high sorption capacity;
• chemical resistance;
• increased flowability and porosity of the structure.

In addition, the molding material is divided into two types (denoted by the letters A and B). The first category includes the variety with a large residue on the outermost upper sieve, and on the lower one - category B. Natural and enriched sands are also distinguished. The latter are obtained through special processing, removing clay and unnecessary impurities from natural sand.

CASTING MODELS

Based on drawings and casting technologies developed by a technologist or designer, an experienced modeler makes a model of a part from wood, metal or plastic or polystyrene foam.
The metal shrinks during the cooling process, and crystallization may be heterogeneous due to uneven cooling. Thus, the model should be slightly larger than the finished casting, using the so-called metal shrinkage factor. Different shrinkage rates are used for different metals. During the molding process, models leave imprint cavities in the sand, into which a sand core is placed. Such rods are sometimes reinforced with wire reinforcements, which are used to create cavities that cannot be formed by the main model, such as internal valve passages or cooling spots in engine blocks.

The gating system for the entry of metal into the mold cavities is a guide and includes a funnel and sprues that maintain a good pressure of liquid metal for more uniform filling of the mold cavity. The gas and steam generated during casting escape through permeable sands or through risers, which are made either in the model itself or in the form of separate parts.

Flasks for molding materials Two or more flasks are used for molding. The flasks are made in the form of boxes that can be connected to each other and fastened together. The model is recessed into the lower part of the flask up to its widest cross section. Then the upper part of the model is mounted. The upper part is attached to the lower part of the flask with clamps and the molding mixture is added there and compacted so that it completely covers the model. Sprues and thrusts are installed in the required places. Then the flask is halved and the model, wooden sprues and stops are removed from it.

METAL COOLING

To control the crystallization of the metal structure, metal plates and refrigerators can be placed in the mold. Accordingly, rapid local cooling forms a more detailed metal structure in these places. In black casting, the effect is similar to hardening the metal in a forge. In other metals, condensers can be used to control the directional solidification of the casting. By controlling the cooling method of the casting, internal voids or porosity within the casting can be prevented.

PRODUCTION

Rods are used to create cavities in castings, such as for coolant in engine blocks and cylinder heads. Typically, casting cores are placed in the mold after the model is removed. After drying, the flask with the mold is placed on the foundry platform to be filled with molten metal, usually steel, bronze, brass, aluminum, magnesium and zinc. After filling with liquid metal, the flasks are not touched until the casting has cooled. After knocking out the casting, the cores are removed from the casting. The metal of the sprues and profits must be separated from the casting by any means. Various heat treatments can be used to relieve stress from initial cooling and add hardness in the case of water or oil quenching. The casting surface can be further hardened by shot peening, which adds resistance to cracking and stretches and smoothes out rough surfaces.

TECHNOLOGY DEVELOPMENT

To make it possible to remove the model without violating the integrity of the molding sand, all parts of the model must be pre-calculated by the technologist and have significant parts for installing the rods. A slight slope should be used on surfaces perpendicular to the parting line to allow the model to be removed from the mold. This requirement also applies to rods, since they must be removed from the cavities they form. The vents and risers must be located so as to ensure optimal flow of metal into the mold and gases from it in order to avoid underfilling of the casting.

Methods of casting into the ground

There are two methods of casting in sand molds, the first is using “raw” sand, the so-called raw molds, and the second is the liquid glass method. Wet Molds Wet sand is used to make a mold in a flask. The name comes from the fact that wet sand is used in the molding process. “Raw sand” is a mixture of: -siliceous sand (SiO2), or chromium sand (FeCr2O), or zirconium sand (ZrSiO4), from 75 to 85%, and other components, including graphite, clay from 5 to 11%, water from 2 to 4%, other inorganic elements from 3 to 5%, anthracite up to 1%. There are many molding mixtures with clay, but they all differ in the plastic properties of the mixture, the quality of the surface, as well as the possibility of using molten metal in casting in relation to the throughput for the release of gases. Graphite, as a rule, is contained in a ratio of no more than 5%; it partially burns upon contact with molten metal with the formation and release of organic gases. Raw mixtures are generally not used for casting non-ferrous metals, since raw molds lead to strong oxidation, especially for copper and bronze casting. Raw sand molds are not used for aluminum casting. For aluminum casting, higher quality molding mixtures are used. The choice of sand for molding depends on the temperature of pouring the metal. The pouring temperature of copper, steel and cast iron is higher than other metals, therefore, clay is not further regenerated from exposure to high temperatures. For pouring cast iron and iron-based steel, they usually work with quartz sand - it is relatively inexpensive compared to other sands. Since the clay burns out, a new portion of clay and some of the old sand are added to a new portion of the sand mixture. Silicon is undesirable in sand because The grains of quartz sand tend to explode when exposed to high temperatures during pouring. These particles are suspended in the air, which can lead to silicosis in workers. The foundry has active ventilation to collect dust. Fine sawdust (wood flour) is added to create space, when burned, for the sand grains to expand without deforming the shape.

TRANSPORTATION AND STORAGE

5.1. Molding sands are transported in accordance with the rules for the transportation of goods in force for this type of transport, the technical conditions for loading and securing goods, approved by the Ministry of Railways and GOST 22235.

The bags are packaged in accordance with GOST 26663, GOST 24597, GOST 21650 and GOST 22477.

5.3. It is allowed, by agreement between the manufacturer and the consumer, to transport molding sands with a mass fraction of moisture less than 0.5% in cement hoppers and cement tanks.

5.4. Frozen molding sands are unloaded using thermal and mechanical means of restoring flowability.

5.5. Molding sands with a mass fraction of moisture over 0.5% are stored separately by grade, with a mass fraction of moisture up to 0.5% - separately by grade in covered warehouses or bunkers.

INFORMATION DATA

1. DEVELOPED AND INTRODUCED TC 252 “Foundry”

2. APPROVED AND ENTERED INTO EFFECT by Resolution of the Committee for Standardization and Metrology of the USSR dated December 28, 1991 No. 2263

3. INSTEAD GOST 2138-84

4. REFERENCE REGULATIVE AND TECHNICAL DOCUMENTS

5. REPUBLICATION. July 2005

XTS casting

Aluminum casting is the process of producing aluminum products by pouring (casting) molten metal into a special mold. This form is called a “casting mold”. The working part of the casting mold is a cavity in which the liquid metal cools and solidifies, obtaining the appearance of the final product. Aluminum has an important property for casting - fluidity, that is, the ability to take the configuration of the casting mold. Fluidity depends on the properties of the metal: chemical composition and structure. It is known that it is not pure metal that has good casting properties, but its alloys.

There are many types of casting aluminum alloys, the most widely used are:

• casting into the ground;
• casting in CTS molds (sand casting);
• casting into a free metal mold (mold);
• injection molding;
• centrifugal casting.

Casting into CTS molds (molds based on a cold-hardening mixture) is a relatively simple and technologically advanced method for producing castings. It allows the production of castings with a complex mold parting plane and undercuts on the surface. The surface is of good quality and requires virtually no further processing. High precision allows you to give minimal allowances for machining, and many surfaces can be obtained immediately without processing.

In-ground casting and HTS casting

The closest alternative to sand casting is to cast aluminum in the ground at a very low cost per kilogram of casting. Many factories successfully use this technology. It is suitable for rough workpieces that are then fully processed (or when quality is not an issue). Processing when casting in the ground is expensive: allowances are given at least 5 mm (sometimes up to 40 mm), almost all surfaces of the part are processed. The mixture introduced into the metal spoils the tool; pores and cavities are often opened during processing. Sometimes a half-processed part has to be welded directly on the machine or sent for scrap due to revealed defects.

Casting into molds based on CTS makes it possible to obtain precise and high-quality surfaces. Some surfaces can be left untreated (if the accuracy of LT4 and the roughness of Rz80 are sufficient). Where processing is necessary, allowances can reach 1-3 mm. The less “extra” metal there is in a casting, the more technologically advanced it turns out to be. A lighter and thinner casting is denser, so the likelihood of shells and pores opening during processing is an order of magnitude lower. The smaller mass of the casting allows you to set the cost of casting close to the cost of casting in the ground, although the cost per kilogram of casting will be different.

The final cost of the cast part turns out to be comparable, despite the fact that the price per kg when casting into CTS molds is higher than when casting into the ground. And if we take into account the significant reduction in the number of defects, the reduction in hours for processing the part and the increase in tool life, for many cast parts this type of casting turns out to be more profitable.

Differences between casting in molds based on CTS and casting in the ground:

• there are no sagging or deviations from linear dimensions;
• it is possible to obtain finishing surfaces without treatment (hydrodynamic, working surfaces of molds, blades, etc.);
• minimum allowances are given on the surfaces to be processed (2-5 mm);
• casting pores and cavities are practically absent;
• The casting weight is lower due to smaller allowances and better surface quality.

Equipment for casting CTS

For casting into CTS molds, flask casting equipment made of MDF, model plastics or composite materials is used. For large series, equipment made of aluminum or other metals is used. Modeling equipment follows the shape of the casting, taking into account casting shrinkage. Its production on CNC machines and the selection of molding technology make it possible to obtain curved surfaces that do not require additional processing. The result is castings with accuracy class LT3-LT4, which corresponds to an error of 0.2-0.5 mm. After impregnation with a reinforcing compound, the pattern equipment can withstand several thousand removals. Simple forms consist of two half-forms. To decorate the internal cavities, core boxes are made.

Scope of application

Possessing unique characteristics, quartz sand has found wide application in human life and is used in the following areas:

• used in construction for the manufacture of various types of decorative plasters, dry mixes, as well as for the creation of self-leveling floors;
• for casting heat-resistant molds in the metallurgical field;
• for swimming pools as a filter material;
• for football fields as a covering;
• in the production of glass, fiberglass;
• in the production of building materials - for the production of sand-lime bricks, paving stones, refractory concrete;
• in the agro-industrial sector as an additive to animal feed;
• in the production of electrical fuses, since quartz is a dielectric material;
• for creativity and drawing, in landscape design;
• when preparing mixtures for the production of high-strength reinforced concrete.

Quartz sand is included in modern road pavements, since silicon dioxide is durable and abrasion-resistant, which allows the asphalt surface to be durable and reliable, despite the huge weight load and high traffic. Most types of dishes that are on the shelves are made using quartz sand. The mineral additive of fine-grained quartz allows it to be added to porcelain, earthenware and ordinary glass, which gives these materials increased strength and shine. Quartz is also added in the manufacture of technical glass, as well as window and automobile types; it is used to produce laboratory glassware that is resistant to heat and chemical environments, and is also added to the composition of the mass intended for the production of ceramic finishing tiles.

But that's not all. Quartz sand is an integral component used in the production of optical lenses, making these products smooth, transparent and durable to use. Due to its ability to retain heat, quartz sand is used for industrial and domestic needs. With his participation, electric heating devices are manufactured - quartz is included with an incandescent spiral system, which quickly heats up and maintains the required temperature for a long time.

Engraving work and grinding of surfaces, as well as processing of stone, metal or durable polymers cannot be done without the use of quartz sand, which is used in the sandblasting technique for processing materials. The essence of the process is that sharp-angled rock particles, mixed with an air flow, are supplied under a certain pressure to the surface being processed, which is polished and becomes perfectly clean and smooth.

The well-known ability of quartz sand to absorb various substances is used to filter water in hydraulic structures of various types and purposes. In addition, the adsorbing properties are used in the food industry, as well as in the production of filter equipment.

To learn how to choose the right quartz sand for a pool, watch the following video.

Casting using gasified models - casting with loss of foam

Lost wax casting refers to those casting methods that are high-tech and more economical. The essence of the technology is lost wax casting, but in a permanent form. Translated from English - casting with loss of foam.

Gas casting models

The casting model when casting using gasified models is made of expanded polystyrene (foam plastic). Small models are made in aluminum molds using the foaming method at a temperature of about 130C followed by cooling. Polystyrene molds are cast using precision casting. Their use makes it possible to produce several thousand foam models in a short time.

Large models, castings of which can reach several tons and single copies are cut from slabs according to a template manually using nichrome wire under tension or on engraving and milling machines with PU.

The finished model is coated with paint and a fire-resistant compound on top.

Forming operation

The finished model of simple-shaped castings with a gas-permeable and fire-resistant shell is sent for molding. It is installed in the flask and filled with molding sand. Compaction occurs on a vibrating table. The flask is closed with lids and the gating system bowl is installed.

For models with complex casting geometry, the molding operation is performed by vacuuming. Cover the flask with plastic film. To prevent the destruction of the model, a reduced pressure (vacuum) of minus 4-5 Pa is created in the mold.

The molding operation of large-sized models is carried out using bulk or liquid mixtures.

Fill

Molten metal is poured into a mold. At this time, expanded polystyrene begins to gasify. Its gasification temperature is 560C. Gradually the molten metal fills the mold. The resulting gases are removed by a vacuum system. In its absence, the working area in the workshop becomes smoky, exceeding the permissible values ​​by tens of times.

After the part has cooled and hardened, the flask is turned over and the molding mixture is separated from the casting. If an ordinary molding mixture was used, then the separation occurs on knockout grids.

Advantages of the gasified casting method

The main advantage of this casting method is considered to be the high quality of the resulting castings, comparable to those cast in a mold or lined mold. This is achieved by the absence of a prefabricated uniform.

Modern production uses water-based non-stick coatings for:

• casting of large and medium-sized samples or parts in small-scale production;

• castings of parts whose weight reaches 50 kg, having a complex configuration, with the presentation of increased dimensions in terms of accuracy, in serial and large-scale production.

This method is used to cast parts from: all grades of steel, cast iron, copper and its alloys (brass, bronze), aluminum and its alloys (casting grades). Almost 90% of the resulting products do not require subsequent mechanical processing.

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Published:
2017.11.14

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Rules for receiving quartz, river and alluvial sand

Quartz, river, alluvial sand and crushing screenings must be assessed before shipment to the consumer, and additional samples are taken upon delivery of the cargo. For this purpose, special tests are carried out, and the technical control service is responsible for the reception.

So samples are taken from each production line, then it is determined whether the sand is suitable for construction or whether the sand is suitable for sandblasting or if there are any deviations from the norm.

When carrying out control, the following is revealed:

• grain composition;
• the presence of clay and its quantity in pieces;
• amount of dusty residues and clay components;
• absence of foreign impurities and debris.

Periodic monitoring is carried out to determine changes in rocks over a certain period of time:

• once every 3 months - the density of the embankment is determined; if necessary, testing under certain humidity conditions is possible. The presence of harmful, organic additives and their quantity are revealed;
• once a year or when the composition of the rock changes, it is necessary to check the density of the grains and the amount of minerals contained, mainly harmful ones. The strength grade and effectiveness of radionuclides are determined.

Radionuclide studies cannot be carried out within the enterprise, so samples are taken to specialized research institutions. They must be accredited by regulatory authorities.

If geological analysis data is not available, radioactivity assessments can be made immediately after mining. An expressive option is used, based on the alluvium map. Preparation for examination samples is carried out on the basis of GOST 8735.

When delivering by rail or sea, a batch is a simultaneous quantity of cargo sent. During delivery, all material delivered during the day is taken into account.

Why do you need a passport for sand GOST 8736 93

The consumer may require a passport for sand GOST 8736 93 issued to the enterprise and technical documentation for the batch. To obtain information about the quality of the product, samples should be taken, their quantity depends on the order:

• for batches up to 350 m3, the number of samples is 10;
• orders of 350 – 700 m3 can be subject to 15 samples;
• over 700 m3, samples should be taken from 20 different locations.

The price per m3 of sand GOST 8736 93 is approximately 500 rubles, but the cost varies greatly depending on the quality of the product, the remoteness of the quarry and the premium of the manufacturer and intermediary. Thus, river sand GOST 8736 93 is slightly more expensive than screenings after crushing.

Also, coarse sand is somewhat cheaper than fine sand, and not every manufacturer separates the fraction.

Earth casting is an affordable way to produce castings

Earth casting technology

To obtain a casting of a simple shape with small reliefs, solid models are used. If you need to obtain a casting of a more complex configuration, then split molds are used. When producing sand molds for casting in the ground, special boxes (flasks) are used that do not have a bottom or a lid. These form the mold into which the casting is performed. Boxes are most often made of cast iron, steel, aluminum, and wooden ones are used much less often.

To place an order for casting in the ground, contact the sales department by phone numbers listed on the “Contacts” page.

Peculiarities

The essence of sand casting technology is to create parts by pouring molten metal into a disposable mold made from sand-based molding sand. The technological process of creating castings consists of a chain of actions required for the manufacture of an injection mold and its assembly.

The production of foundry molds is called molding, and involves several necessary elements:

1. Molding sand required to create a casting mold. As a rule, this is quartz sand and a clay or resinous substance that has increased thermal resistance. When making an injection mold, the wet molding mixture is compacted by compression or shaking to maintain the required shape.

2. Foundry flask, or molding container. Serves to fix the mold mixture during its transportation and pouring with metal. When casting in sand molds, holes are made in the walls of the flask to facilitate drying and release of gases during the process of pouring metal.

3. Foundry model. With its help, when casting in sand molds, cavities are created with shapes and sizes corresponding to the design of the casting being created.

BRANDS

1.1. Molding sands, depending on the mass fraction of the clay component (particles of clay materials and fragments of quartz grains and other minerals less than 0.02 mm in size), are divided into quartz (K), lean (T) and fatty (F).

Quartz and lean foundry sands are divided into groups depending on the mass fraction of the clay component, silicon dioxide, uniformity coefficient and average grain size, fat - on the wet compressive strength and average grain size.

1.2. Quartz sands contain up to 2.0% clay component.

Groups of quartz sands are given in table. — .

Table 1

table 2

Table 3

Table 4

1.3. Skinny sands contain from 2.0% to 12.0% clay component.

Groups of lean sands are given in Table. — .

Table 5

Table 6

Table 7

1.4. Fat sands contain from 12.0% to 50.0% clay component.

Groups of fatty sands are given in table. And .

1.5. The designation of grades of quartz and lean sands consists of group designations based on the mass fraction of the clay component, the mass fraction of silicon dioxide, uniformity coefficient and average grain size.

Example.

2K1O302 - quartz foundry sand with a mass fraction of clay component from 0.2% to 0.5%, a mass fraction of silicon dioxide of at least 99.0%, a uniformity coefficient from 60.0% to 70.0% and an average grain size from 0 .19 to 0.23 mm.

(Amendment).

1.6. The designation of fatty sand grades consists of group designations based on wet compressive strength and average grain size.

Example.

Zh2016 is a fatty molding sand with a wet compressive strength of 0.05 to 0.08 MPa and an average grain size of 0.14 to 0.18 mm.

Non-stick coatings

To improve the surface cleanliness of castings, non-stick coatings - paints - are applied to the working surfaces of the molds and cores. The coating is a mixture of dust-like refractory material with water and binders. The applied layers of paint reduce the roughness of the forms and close the pores between the grains of sand. As a result, the surface of the casting is smoother and cleaner, without burning.

Iron casting molds are coated with carbon-containing coatings consisting of graphite, bentonite, water and other substances.

Non-stick mixtures for steel castings include dusted quartz, zircon, magnesite, and for castings made of non-ferrous metals, fine talc. Coatings are applied to both hot and cold molds. Coatings are also used for surface modification and alloying.