Defects and solutions of silica sol wax loss casting process

Defects and solutions of silica sol wax loss casting process

Defect 1: Casting shrinkage

The main reasons are casting shrinkage caused by alloy solidification shrinkage and the absorption of a large amount of oxygen, nitrogen, etc. in the air during alloy dissolution, which releases gas during alloy solidification and causes casting shrinkage.

Solution:

1) Place the storage ball.

2) Bold the diameter of the sprue or reduce the length of the sprue.

3) Increase the amount of metal used.

4) Use the following methods to prevent dents in the direction of the casting path in the

organization.

a. Place a cooling channel at the root of the casting channel.

b. To prevent the melted metal from vertically impacting the mold cavity, the sprue should be curved.

c. Place the casting channel diagonally.

Defect 2: Rough and unclean surface of castings

The rough and melted metal on the surface of the mold cavity undergoes a chemical reaction with the surface, mainly reflecting the following situations.

1) The embedded material has coarse particles and is not delicate after stirring.

2) After solidification, the embedded material is directly placed in the Maofu furnace for roasting, resulting in excessive moisture.

3) The heating rate of roasting is too fast, resulting in expansion differences at different positions in the mold cavity, causing the surface inside the mold cavity to peel off.

4) The highest temperature of roasting is too high or the roasting time is too long, causing the surface inside the mold to be too dry.

5) The melting temperature of the metal or the roasting temperature of the casting ring is too high, causing a reaction between the metal and the mold cavity, and the surface of the casting burns and adheres to the embedded material.

6) Insufficient roasting of the mold causes decomposition of the embedded material when the melted metal is cast in, resulting in a significant amount of gas and the formation of pitting on the surface of the casting.

7) After the molten metal is cast in, it causes local temperatures in the mold cavity to be too high, resulting in local roughness on the surface of the casting.

Solution:

a. Do not over melt the metal.

b. The roasting temperature of the mold should not be too high.

c. The roasting temperature of the mold should not be too low (the roasting temperature of phosphate embedded materials is between 800 ° C and 900 ° C).

d. To avoid the occurrence of indentations in the direction of the casting channel in the organization.

e. Apply a liquid on the wax mold to prevent burning and sticking.

Defect three: Casting cracking defect

There are two main reasons. Firstly, casting defects (seams) are usually caused by the rapid solidification of the metal in that area; The second is cracking caused by high temperature.

1) For the casting joints caused by rapid solidification of metals, they can be solved by controlling the casting time and solidification time. Factors related to casting time: the shape of the wax mold. The quantity of thickness cast. Casting pressure (casting machine). Permeability of embedded materials. Factors related to solidification time: the shape of the wax shape. The highest roasting temperature of the casting ring. The type of embedded material. The type of metal. The temperature of casting.

2) The cracking caused by high temperature is related to the mechanical properties of the metal and embedded materials. The following situations are prone to cracking: high casting temperature is prone to cracking; High strength embedded materials are prone to cracking; Nickel and cobalt alloys with low elongation are prone to cracking.

Solution:

Use low strength embedded materials; Try to reduce the casting temperature of the metal as much as possible; Do not use materials with low ductility. A brittle alloy.

Defect 4: Spherical protrusion defect

Mainly caused by the residual air (bubbles) remaining on the surface of the wax after mixing the embedded materials.

1) True air conditioners and embedded materials have better effects after vacuum embedding.

2) Spray surfactant onto the wax surface before embedding (such as Nissin's castmate)

3) First, apply the embedding material onto the wax mold.

4) Use pressure embedding method to extrude bubbles.

5) Pay attention to the direction of the wax pattern when embedding, and there should be no depression below the connection between the wax pattern and the casting channel.

6) Prevent the inclusion of bubbles during embedding. Casting ring and casting seat. The buffer paper must be tightly sealed; The embedded material needs to be poured along the inner wall of the casting ring (using a shaker).

7) After filling the casting ring, it must not be shaken again.

Defect 5: Flash defects in castings

Mainly due to cracking of the casting ring, molten metal flows into the cracks in the mold cavity.

Solution:

1) Change the embedding conditions: Use high-strength embedding materials. The strength of gypsum embedded materials is lower than that of phosphate embedded materials, so caution should be exercised when using them. Try to use ring casting as much as possible. When casting without a ring, the ring is prone to cracking, so it needs to be noted.

2) Baking conditions: Do not directly roast the embedded material after it has solidified (it should be roasted several hours later). It should be slowly heated up. Immediately cast after roasting, do not repeatedly roast the casting ring.

Precision machining