Defect 1: casting shrinkage cavity

The main reasons are that the casting shrinkage cavity is produced by the solidification shrinkage of the alloy, and a large amount of oxygen and nitrogen in the air are absorbed when the alloy is dissolved, and the casting shrinkage cavity is caused by the gas released during the solidification of the alloy.

Solution:

1) Place the gold storage ball.

2) Increase the diameter of the runner or reduce the length of the runner.

3) Increase the amount of metal.

4) The following methods shall be adopted to prevent the depression of the structure in the direction of the casting channel.

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

b. In order to prevent the molten metal from hitting the cavity vertically, the runner shall be arc-shaped.

c. Place the runner diagonally.

Defect 2: rough and rough casting surface

The rough and melted metal on the cavity surface reacts with the cavity surface, which mainly reflects the following conditions.

1) The particles of the embedded material are coarse and not fine after mixing.

2) After curing, the embedded material is directly put into the Maofu furnace for roasting, and the moisture is too much.

3) The heating rate of baking is too fast, and the expansion difference occurs at different positions in the cavity, which makes the surface of the cavity peel off.

4) The maximum baking temperature is too high or the baking time is too long, which makes the cavity surface too dry.

5) The melting temperature of the metal or the roasting temperature of the casting ring is too high, so that the metal reacts with the mold cavity, and the embedded material is burnt on the surface of the casting.

6) The baking of the casting mold is not sufficient. When the molten metal is cast in, it will cause the decomposition of the embedded material, generate more gas, and produce pockmarks on the surface of the casting.

7) After the molten metal is cast in, the local temperature in the mold cavity is too high, and the surface of the casting is locally rough.

Solution:

a. Do not over melt the metal.

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

c. The baking temperature of the mold should not be too low (the baking temperature of the phosphate embedded material is 800-900 degrees).

d. Avoid the phenomenon that the structure faces the direction of the runner.

e. The wax mold is coated with a liquid to prevent burning.

Defect 3: Cracking of casting

There are two major reasons. One is that the casting defects (joints) are usually caused by the rapid solidification of the metal there; Second, cracks caused by high temperature.

1) The casting joint caused by the rapid solidification of metal can be solved by controlling the casting time and solidification time. Related factors of casting time: shape of wax mold. The number of thicknesses cast. Casting pressure (casting machine). Air permeability of embedded materials. Related factors of solidification time: shape of wax mold. Maximum roasting temperature of casting ring. Type of embedded material. Type of metal. Casting temperature.

2) Cracking due to high temperature is related to the mechanical properties of metal and embedded materials. Cracking is easy to occur under the following conditions: high casting temperature is easy to generate cracking; High strength embedded materials are easy to crack; Nickel and cobalt alloys with small extensibility are prone to cracking.

Solution:

Use low strength embedding materials; Reduce the casting temperature of metal as much as possible; Do not use the one with small ductility. A relatively brittle alloy.

Defect 4: spherical protrusion defect

It is mainly caused by the residual air (bubbles) remaining on the surface of the wax mold after the mixing of the embedding material.

1) Real air conditioner and embedding material, the effect is better after vacuum embedding.

2) Spray surfactant on the surface of wax type before embedding (e.g. castmate of Rijin company)

3) First, the embedding material is coated on the wax mold.

4) The method of pressure embedding was used to extrude bubbles.

5) Pay attention to the direction of the wax mold during embedding. There shall be no depression below the connection between the wax mold and the casting channel.

6) Prevent air bubbles from being mixed during embedding. Casting ring and casting seat. The buffer paper shall be tightly sealed; The embedded material shall be poured along the inner wall of the casting ring (using a vibrating machine).

7) Do not vibrate after filling the casting ring.

Defect 5: Flash defect of casting

It is mainly because the casting ring is cracked and the molten metal flows into the crack of the mold cavity.

Solution:

1) Change the embedding conditions: use the embedding materials with high strength. The strength of gypsum embedded materials is lower than that of phosphate embedded materials, so it should be used with caution. Try to use ring casting. When casting without ring, the casting ring is easy to crack, so it needs to be noted.

2) Roasting conditions: do not directly roast the embedded material after curing (it should be roasted after several hours). The temperature shall be raised slowly. Cast immediately after baking. Do not bake the casting ring repeatedly.