Casting process flow

The main process of sand casting is as follows:

Mould making part: Make moulds according to the requirements of drawings. Generally, wooden molds can be used for single-piece production, plastic molds and metal molds can be used for mass production, and templates can be used for mass casting.

2. Sand mixing stage: according to the requirements of sand mold manufacturing and different types of castings, qualified molding sand is prepared for modeling.

3. Modeling (core making) stage: including modeling (forming the cavity of the casting with molding sand), core making (forming the internal shape of the casting) and mold matching (putting the core into the cavity and closing the upper and lower sand boxes). Modeling is the key link in casting.

4. Melting stage: prepare the chemical composition according to the required metal composition, and select a suitable melting furnace to melt the alloy material to form qualified liquid metal (including qualified composition and temperature).

5. Pouring stage: the qualified molten metal is poured into the sand box with the mold. The pouring stage is dangerous, so pay special attention to it.

6. Cleaning stage: after the molten metal is poured and solidified, the molding sand is removed, and the gate and other accessories are knocked out to form the required castings.

Extended data

summary

The basic raw materials for making sand molds are casting sand and sand binder. The most commonly used casting sand is siliceous sand. When the high temperature performance of silica sand can't meet the use requirements, special sand such as zircon sand, chromite sand and corundum sand is used. In order to make the sand mold and core have certain strength and not be deformed or damaged when transporting, molding and pouring liquid metal, it is generally necessary to add molding sand binder during casting to bond loose sand particles to form molding sand. Clay is the most widely used binder for molding sand, and various drying oil or semi-drying oil, water-soluble silicates or phosphates and various synthetic resins can also be used as binders for molding sand. The external sand mold used for sand casting can be divided into three types: clay wet sand mold, clay dry sand mold and chemically hardened sand mold according to the binder used for molding sand and the way to establish strength.

Clay wet sand

Clay and proper amount of water are used as the main binder of molding sand, and the sand mold is directly molded and poured in wet state after it is made. Green mold casting has a long history and is widely used. The strength of green sand depends on the clay slurry mixed by clay and water in a certain proportion. Once the sand is mixed evenly, it has a certain strength, and after being compacted into a sand mold, it can meet the requirements of modeling and pouring. Therefore, the clay content and moisture in molding sand are very important technological factors.

A casting method uses molding sand and core sand as molding materials to make molds, and liquid metal fills the molds under the action of gravity to produce castings. Steel, iron and most nonferrous alloy castings can be obtained by sand casting. Because the molding materials used in sand casting are cheap and easy to obtain, and the mold is simple to manufacture, it can adapt to the single piece production, batch production and batch production of castings. For a long time, it has been a basic working procedure in foundry production.

The mold used in sand casting usually consists of an external sand mold and a core. In order to improve the surface quality of castings, a layer of paint is often painted on the surface of sand molds and cores. The main components of the coating are powdery materials and binders with high fire resistance and good high-temperature chemical stability, and convenient carriers (water or other solvents) and various additives are added.

The advantages of clay green sand casting are: ① rich clay resources and low price. ② After proper sand treatment, most of the used clay wet sand can be recycled. (3) The manufacturing cycle of the mold is short and the working efficiency is high. ④ Mixed sand can be used for a long time. ⑤ After the sand mold is compacted, it can still bear a small amount of deformation without being damaged, which is very beneficial to mold pulling and core lowering. The disadvantages are as follows: ① When mixing sand, it is necessary to coat the surface of sand particles with sticky clay slurry and use high-power sand mixing equipment with kneading function, otherwise good quality molding sand can not be obtained. (2) Due to the high strength of mixed molding sand, it is not easy to flow and compact during modeling, manual modeling is laborious and requires certain skills, and the equipment for machine modeling is complex and huge. ③ The rigidity of the mold is not high, and the dimensional accuracy of the casting is poor. ④ Casting is prone to sand washing, sand inclusion, porosity and other defects.

The wet water content of molding sand used to make this kind of sand mold with clay dry sand mold is slightly higher than that used in wet sand mold.

Clay sand core A simple sand core made of clay sand.

Baidu Encyclopedia: Sand Casting