Precision valve casting (investment casting lost wax casting) process

Valve precision casting

One of the methods of valve casting is precision casting. Precision casting is a special casting method compared to the traditional casting process. It can obtain relatively accurate shapes and high casting accuracy. The more common method is: first design and make a mold according to product requirements (with very small margin or no margin), use casting method to cast wax to obtain the original wax mold; repeat coating and sanding on the wax mold Process, harden the shell and dry; then melt the wax mold inside to dewax and obtain a cavity; roast the shell to obtain sufficient strength and air permeability; cast the required metal materials; clear the sand after shelling , So as to obtain high-precision finished products. According to product needs or heat treatment and cold processing.

1. What is precision casting of stainless steel valve

In the production of stainless steel valves, some valves have strange structures and shapes that cannot be produced by processes such as bending pipes. In order to produce products with such irregular shapes (hollow or solid inside), a wax mold is used to make a sand mold. →The process of filling and forming liquid materials. Advantages: Various styles of products can be made according to different wax patterns.

Second, the precision casting process

1. Make molds according to different shapes of products. The mold is divided into upper and lower concave molds, which are completed through comprehensive processes such as turning, planing, milling, erosion, and electric spark. The shape and size of the pits are consistent with the half of the product. Because the wax mold is mainly used for industrial wax molding, the aluminum alloy material with low melting point, low hardness, low requirement, cheaper price and lighter weight is used as the mold.

2. Use aluminum alloy molds to produce a large number of industrial wax solid core models. Under normal circumstances, an industrial wax solid core model can only correspond to a blank product.

3. Refine the margin around the wax mold. After deburring, stick multiple single wax molds on the pre-prepared die (also called group tree). This die is also an industrial wax solid produced by wax molds. Core model. (It looks like a tree)

4. Coat multiple wax molds fixed on the die with industrial glue and spray the first layer of fine sand (a kind of refractory sand, high temperature resistance, usually silica sand). The sand particles are very small and fine, so as to ensure that the surface of the final blank is as smooth as possible.

5. Let the wax mold sprayed with the first layer of fine sand be air-dried naturally at the set room temperature (or constant temperature), but it cannot affect the shape of the internal wax mold. The natural air-drying time depends on the complexity of the product itself, generally fine The first air-drying time of the casting is about 5-8 hours.

6. After the first sand blasting and natural air drying, continue to apply industrial glue (silicon soluble slurry) on the surface of the wax mold, and spray the second layer of sand. The particle size of the second layer of sand is larger than that of the previous first layer of sand. The big ones come, the rough ones come. After spraying the second layer of sand, let the wax mold dry naturally at the set constant temperature.

7. After the second sand blasting and natural air drying, proceed to the third sand blasting, the fourth sand blasting, and the fifth sand blasting in sequence. Requirements:-Adjust the number of sandblasting according to product surface requirements, size, and weight. Under normal circumstances, the number of sandblasting is 3-7 times. -The grit size of each blasting process is different. Usually, the grit of the later process is coarser than that of the previous process, and the air-drying time is different. Generally, the production cycle of sanding on a complete wax mold is about 3 to 4 days.

8. Before the baking process, the wax mold that has completed the sandblasting process is evenly coated with a layer of white industrial latex (silicon soluble slurry) to bond and solidify the sand mold and seal the wax mold. Preparation for the baking process. At the same time, after the baking process, the brittleness of the sand mold can be improved, which is convenient for breaking the sand layer and taking out the blank.

9. Baking process Put the wax mold fixed on the die head and complete the sandblasting and air-drying process into a special metal closed oven for heating (usually a kerosene-burning steam furnace). Because the melting point of industrial wax is not high, the temperature is about 150 ゜, the wax mold is melted by heat to form wax and flow out along the gate. This process is dewaxing. The wax model after dewaxing is just an empty sand shell. The key to precision casting is to use this empty sand shell. (Generally, this kind of wax can be used repeatedly, but these waxes must be re-filtered, otherwise the unclean wax will affect the surface quality of the blank, such as surface sand holes, pitting, and also affect the shrinkage rate of the precision casting product).

10. Baking the sand shell In order to make the dewaxed sand shell stronger and stable, the sand shell must be baked before pouring the stainless steel water, usually in a high temperature (about 1000 ゜) stove. .

11. Pour the stainless steel water that has been dissolved into liquid at high temperature into the sand shell after dewaxing. The liquid stainless steel water fills the space formed by the previous wax mold until it is completely filled, including the middle part of the die.

12. As materials of different compositions are mixed in the stainless steel boiler, the factory must check the percentage of material. Then adjust the interpretation according to the required ratio, such as adding those elements to achieve the desired effect.

13. After the liquid stainless steel water is cooled and solidified, the outermost sand shell is broken with the help of mechanical tools or manpower, and the solid stainless steel product exposed is the shape of the original wax mold, which is the final required blank. Then it will be cut one by one, separated and then rough ground into a single blank

14. Inspection of the blank: The blank with blisters and pores on the surface must be repaired with argon arc, and when the waste is cleaned, it should be returned to the furnace.

15. Cleaning the blanks: The blanks that have passed the inspection must go through the cleaning process.

16. Carry out other process processing until the finished valve.