What Is Sand Casting?

Sand casting refers to the casting method used to produce castings in sand molds. Steel, iron and most nonferrous alloy castings can be obtained by sand casting. Because the molding materials used for sand casting are cheap and easy to obtain, the mold is easy to manufacture, and it can adapt to the single-piece production, batch production and mass production of castings.

The materials used to make sand molds are called modeling materials. The materials used to make sand molds are conventionally called molding sands, and the molding materials used to make sand cores are called core sands. Usually sand is made of raw sand (mountain sand or river sand), clay and water in a certain proportion, of which clay is about 9%, water is about 6%, and the rest is raw sand. Sometimes small amounts of additives such as pulverized coal, vegetable oil, and wood chips are added to improve the performance of molding sand and core sand.

The quality of molding sand and core sand directly affects the quality of castings. Poor quality of molding sand will cause defects such as porosity, trachoma, sticky sand, and sand inclusion in the casting. Good molding sand should have the following properties:

1) Breathable

After the high temperature metal liquid is poured into the mold, the mold is filled with a large amount of gas, and these gases must be smoothly discharged from the mold. The property of the sand that allows gas to pass is called permeability. Otherwise, it will cause defects such as porosity and insufficient pouring. The permeability of the mold is affected by the sand particle size, clay content, moisture content, and sand compactness. The finer the sand size, the higher the clay and moisture content, the higher the compactness of the sand mold, and the worse the air permeability

2) Strength

The ability of molding sand to resist external force damage is called strength. The molding sand must have high enough strength to not cause collapse during molding, handling, and box closing, and it will not damage the surface of the mold during pouring. The strength of the molding sand should not be too high, otherwise the casting will have defects due to the decrease in air permeability and concession.

3) Fire resistance

After the high-temperature metal liquid is poured, it has a strong thermal effect on the mold, so the molding sand must have the ability to resist the high-temperature thermal effect, that is, fire resistance. If the fire resistance of the molding material is poor, the casting is prone to sticky sand. The more SiO2 content in the molding sand, the larger the molding sand particles, and the better the fire resistance.

4) Plasticity

The ability of the finger sand to deform under the action of external force and to maintain the existing shape completely after removing the external force. The plasticity of the molding material is good, the molding operation is convenient, and the shape of the sand mold is accurate and the outline is clear.

5) Concession

When the casting is condensing, the volume shrinks, and the molding sand should have a certain ability to be compressed, which is called concession. Mold sand has poor concession, and castings are prone to internal stress or cracking. The tighter the molding sand, the worse the concession. Adding wood dust and other materials to the molding sand can improve the yield.

The characteristics of the chemically hardened sand casting process are:

The strength of the chemically hardened sand mold is much higher than that of the clay sand mold, and after the sand mold is made to have a relatively high strength, the film is removed, and no mold modification is required. Therefore, the mold can accurately reflect the size and contour of the pattern, and it is not easy to deform in the subsequent process. The obtained casting has high dimensional accuracy.

Because the viscosity of the binder and hardener used is not high, it is easy to mix with the sand particles. The sand mixing equipment has a light structure, low power and high productivity, and the sand processing work can be simplified.

The mixed molding sand has good fluidity before hardening, and the molding sand is easy to be compacted when modeling, so there is no need for a large and complicated molding machine.

When modeling with chemically hardened sand, pattern materials such as wood, plastic and metal can be selected according to production requirements.

The content of binder in chemically hardened sand is much lower than that of clay sand, and there is no powdery auxiliary material. If raw sand with the same particle size is used, the gap between the sand particles is much larger than that of clay sand. In order to prevent the metal from penetrating between the sand particles during casting, the surface of the sand mold or core should be coated with high-quality paint.

The chemically hardened sand with water glass as a binder has low cost and no odor in the working environment during use. However, the molding sand is not easy to disintegrate after the casting metal is cast; the used old sand cannot be directly recycled and must be recycled, and the regeneration of water glass sand is more difficult.

The cost of chemically hardened sand using resin as a binder is relatively high, but the casting is easy to separate from the molding sand after pouring, the workload of casting cleaning is reduced, and most of the used sand can be recycled and reused.

Crusher wear-resistant parts of sand casting are still very common in China, such as jaw plate, high chromium plate hammer, crushing wall, rolling wall, etc., because in the crusher equipment, as a relatively large wear-resistant casting, Relatively speaking, the accuracy is not very high. Especially for jaws, the finished products are hardly polished by a lathe. Broken walls, mortar walls, rolls and other parts are only required to be polished by a lathe, so they are particularly suitable for sand casting Because of the sand casting of jaw plate, high chromium plate hammer, crushing wall, rolling wall, roller skin, etc., the wear parts of these crushing equipment are more than 20% more durable than other products such as lost foam casting process. However, lost foam casting has high dimensional accuracy, small machining allowance, convenient dry sand dropping, reduced cleaning and grinding workload by more than 50%, and saved labor costs, so the price of lost foam casting is relatively low.

Sand casting is a type of casting process. The mold used for sand casting is generally composed of a combination of an outer sand mold and a core. Because the molding materials used for sand casting are cheap and easy to obtain, the mold is easy to manufacture, and it can adapt to the single-piece production, batch production and mass production of castings. At present, internationally, in the production of all castings, 60 to 70% of the castings are produced with sand molds, and about 70% of them are produced with clay sand molds.

The main reasons are: compared with other casting methods, the cost of sand casting is low, the production process is simple,

More than 80% of the products in the foundry industry are completed by sand casting, so the casting we usually refer to is generally sand casting, that is, sand casting.

During the "Eighth Five-Year Plan" period, casting was highly valued by the former Ministry of Mechanical and Electrical Engineering, and it invested the largest loan for special technological reform and research expenses since the founding of the People's Republic of China, which supported the development and development of products in the casting machinery industry. "Manufacturing of large-scale shot blasting machine", "Vertical partless boxless injection molding machine", "Research and development of water glass sand used sand recycling equipment", "Metal mold casting equipment" and so on have been developed and applied successively.

During the "Ninth Five-Year Plan" period, the foundry industry undertook and completed the task of "Complete technology and equipment for refined and efficient modeling and cleaning of passenger car casting blanks", and "the development and development of efficient continuous shot blasting and cleaning lines for cylinder bodies" also achieved complete success. In 1999, the national high-level gas-impact molding line project was successfully completed.

During the Tenth Five-Year Plan period, the average annual growth of the main economic indicators of the foundry industry is more than 30%, which is higher than the average growth rate of the machine tool industry. In particular, the profit growth is faster, and the average annual profit growth is as high as 46%. High market sales level. In addition, the resin sand casting complete set of equipment can basically meet the domestic market demand, which has changed the situation of relying mainly on imports in the past; it has been able to produce a high level of automatic casting production line, which can partially replace imports, and partially solve the car engine Casting blanks such as cylinder blocks and cylinder heads must also be imported; high-level automatic core making machines, automatic casting cleaning machines, automatic sand processing machines, large-scale automatic die-casting machines, and precision casting equipment such as casting machinery can basically be produced in China . It should be said that the product level of the foundry machinery industry has greatly improved during the Tenth Five-Year Plan period, laying a good foundation for the further development of China's foundry machinery industry in the future.

During the "Eleventh Five-Year Plan" period, the casting industry will continue to maintain a relatively high growth rate under the stimulation of huge market demand. As the technological level of foundry machinery products is still far from the market demand, there is huge development potential and expansion space for the development of the industry, which brings opportunities for the rapid growth of the foundry machinery industry.

During the "Twelfth Five-Year Plan" period, the entire foundry industry must pay special attention to new casting techniques and new materials. The price of casting materials remains high, and the precision casting industry must develop new and alternative low-cost new materials quickly. The continuous improvement of customer requirements has driven us to raise the level of craftsmanship; the rising cost of human resources, we must work harder, develop more, and invest more in precision casting equipment! For example, China Foundry Association China Foundry Association and

Sand casting is the most popular and simplest type of casting that has been used for centuries. Sand casting is used to make large parts such as gray cast iron, ductile iron, stainless steel and other types of steel. The main steps include painting, mold, core making, modeling, melting and pouring, cleaning, etc.

mapping

The traditional method is to obtain the foundry drawings and send them to the foundry. This process can be done in the quote. Today, more and more customers and foundries use computer-aided design instead.

Mold:

In sand casting, the mold is made of wood or other metal materials. In this process, we ask our engineers to make the mold size slightly larger than the finished product, and the difference is called the shrinkage margin. The purpose is to apply molten metal to the mold to ensure that the molten metal solidifies and shrinks, thereby preventing voids during the casting process.

Core:

The core is made by placing resin grit in a mold to form a casting on the inner surface. The void between the core and the mold eventually becomes a casting.

forming

A pair of molds needs to be prepared during the smelting process. Molding usually involves the support frame of the mold, the mold is pulled out to separate it during the casting process, the previously placed core is melted in the mold and the mold mouth is closed.

clean

The purpose of cleaning is to remove grit, sand and excess metal from the casting. Welding, de-sanding can improve the surface appearance of the casting. Burnt out sand and scale are removed to improve the surface appearance of the casting. Excess metal and other risers were removed. A further step of welding and sanding. Finally, check its defects and comprehensive quality.

sort out

Reprocess before shipping. According to the requirements of different customers, we can do heat treatment, surface treatment, additional inspection, etc. for them.

Selection of casting position for sand casting

(1) The important machined surface of the casting shall be facing downward or on the side.

(2) The wide plane of the casting shall face downward.

(3) The thin-walled part with a large area should be placed in the lower part of the mold or in a vertical and inclined position.

(4) For castings that are prone to shrinkage, the thicker section should be placed on the top or side.

(5) The number of cores should be reduced as much as possible, and it is easy to place, fix and exhaust.

Selection of mold parting surface for sand casting

1) It is easy to lift the mold and simplify the modeling process.

(1) The selection of the parting surface should avoid living blocks and cores as much as possible in order to simplify the molding, modeling, and closing processes.

(2) In order to facilitate the ejection of the mold, the parting surface should be selected from the largest section of the casting.

(3) The parting surface should be as straight as possible and the number should be small.

(4) Try to make the casting only have a parting surface, so that the two-box model with simple modeling process can be used.

2) Try to put the important machining surface or most of the machining surface and machining reference surface of the casting in the same sand box.

3) Try to keep the cavity and main core in the lower box ^[1]