Process for Stainless Steel Precision Casting

2022-07-06

Process for Stainless Steel Precision Casting First. What is stainless steel precision casting?

In the production of stainless steel products, the shape of some products is strange, therefore, for the production of this kind of irregular shape (hollow or solid internal) products, a technology of fillingmoulding by wax mould → sand mould→ liquid material is used.

Advantages: A variety of products can be made based on different wax mould, which can save materials. It is easy to process, compared with sand casting and other processes, this technology has higher precision and lower surface roughness.

Second.  Process of Precision Casting 

1. Make mould according to different shapes of products. Mould is divided into mould with upper and lower concave, through the comprehensive process of turning, planing, milling, etching, electric spark and so on, the mould can be completed. The shape and size of pits are consistent with half of the product. Because the wax mould is mainly used for industrial wax pressing, the aluminum alloy material with low melting point, low hardness and light weight is selected to make mould.

2.A large number of industrial wax solid core models are produced by aluminum alloy mould. Under normal circumstances, an industrial wax solid core model can only correspond to a casting product.

3.The allowance around the wax mould is refined, and after deburring, multiple single wax mould are glued to the pre-prepared mould head (also known as tuple tree) which is also an industrial wax solid core model produced by the wax mould.（It looks like a tree on appearance） 

4. The multiple wax mould that have been fixed on the mould head are coated with industrial glue and sprayed with the first layer of fine sand (a kind of fire sand with high temperature resistant, it is usually silica sand), because the sand particles are very small and fine, it can ensure that the final surface of the casting is as smooth as possible.

5.  At the set room temperature (or constant temperature), the wax mould sprayed with the first layer of fine sand can be air-dried naturally, but it can not affect the shape change of the internal wax mould. The natural air drying time depends on the internal complexity of the product itself. Generally, the first air drying time of precision castings is about 5-8 hours.

6. After the first sand spraying and natural air drying, continue to apply industrial glue (silica slurry) on the surface of the waxmould, and spray a second layer of sand, the second layer of sand particle size is larger and coarser than the previous first layer of sand. After spraying the second layer of sand, the wax mould is also allowed to air dry under the set constant temperature.

7.After the second sand blasting and natural air drying, the third sand blasting, the fourth sand blasting, the fifth sand blasting and other work sequences will be carried out by analogy. Requirements: - It is necessary to adjust the number of sandblasting according to the product surface requirements, volume size, weight and so on. Under normal circumstances, the number of sandblasting is 3-7 times. - The size of sand in each sandblasting process is different. Usually, the sand in the later process is thicker than that in the previous process, and the length of air drying time is also different. Generally, the production cycle of a complete waxmould sand is about 3~4 days.

8.The waxmould that has completed the sandblasting process is uniformly coated with a layer of white industrial latex (silicon slurry) before the baking process to bond and solidify the sandmould and seal the waxmould, so as to prepare for the later baking process. At the same time, after the baking process, it can also improve the brittleness of the sandmould, which is easy to break the sand layer, take out the casting.

9.Baking Process.  The waxmould fixed on themould head and completed the sandblasting air drying process is heated in a special metal closed oven. Because the melting point of industrial wax is not high, the temperature is about 150℃, when the waxmould is hot to form wax water, it will flow out along the sprue, this process is dewaxing. The dewaxed waxmould is just an empty sand shell. The key to precision casting is to use this empty sand shell. （Generally, this wax can be used repeatedly, but this wax must be re-filtered, otherwise, unclean wax will affect the surface quality of the casting, such as surface sand holes, pitting, which also affects the shrinkage rate of the investment casting products）.

10. Sand shell Baking. To make the dewaxed sand shell more solid and stable, the sand shell must be baked before pouring stainless steel water, it is often baked in the furnace at high temperature(about 1000 ℃)  .

11. Pour the liquid stainless steel water that has been dissolved at high temperature into the dewaxed sand shell. The liquid stainless steel water fills the space of the waxmould until it is completely filled, including the middle of themould head. 

12. Since there will be different components of the stainless steel boiler materials mixed, the factory must test the material percentage. Then it is necessary to adjust the proportions as needed, such as adding aspects to achieve the desired effect.

13. After liquid stainless steel is cooled and solidified, the outermost sand shell is broken up by mechanical tools or human labor, at this time, the solid stainless steel product is the shape of the original waxmould, which is the final casting required. Then it will be cut, separated and roughed into a single casting one by one.

14. Inspection of casting: The casting with trachoma and air hole on the surface must be repaired and welded with argon arc, and the serious waste products shall be re-furnace after cleaning.

15.casting Cleaning. The casting that passes the inspection must go through the cleaning process.

16.  It is necessary to perform other processing procedures until finished product.