Defect 1: Casting shrinkage cavity

The main reasons are the shrinkage caused by alloy solidification, which leads to casting shrinkage, and the absorption of a large amount of oxygen, nitrogen, and other gases from the air during alloy dissolution. Gas release during alloy solidification causes casting shrinkage.

Solution:

1) Place the storage golden ball.

2) Increase the diameter of the casting channel or decrease the length of the casting channel.

3) Increase the amount of metal used.

4) Use the following methods to prevent dents from appearing in the direction of the casting channel.

a. Place a cooling channel at the base 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: Surface roughness and roughness of castings

The rough surface of the mold cavity and the chemical reaction between the melted metal and the mold cavity surface mainly reflect the following situations.

1) The particles of the embedding material are coarse and not delicate after mixing.

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

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

4) The highest temperature for roasting is too high or the roasting time is too long, causing the inner surface of the mold to become 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 is burnt with embedded material.

6) Insufficient roasting of the mold can cause decomposition of the embedded material when the melted metal is cast, 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 the local temperature in the mold cavity to be too high, resulting in local roughness on the surface of the casting.

Solution:

a. Do not excessively melt the metal.

b. The baking 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 material is 800-900 degrees).

d. Avoid the occurrence of dents in the direction of the casting channel in the organization.

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

Defect 3: Cracking defect in castings

There are two main reasons, one is that the metal in this area usually solidifies too quickly, resulting in casting defects (joints); The second is cracking caused by high temperature.

1) The casting joints caused by rapid solidification of metals can be solved by controlling the casting time and solidification time. The relevant factor of casting time: the shape of the wax pattern. The quantity of thickness cast. Casting pressure (casting machine). Breathability of the embedding material. The related factors of solidification time: the shape of the wax type. The highest roasting temperature for casting rings. Types of embedded materials. Types of metals. The temperature of casting.

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

Solution:

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

Defect 4: Spherical protrusion defect

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

1) Real air conditioning and embedding materials have better effects after vacuum embedding.

2) Spray surfactants (such as Castmate from Nisshin Corporation) onto the surface of the wax before embedding

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

4) Using the method of pressure embedding to extrude bubbles.

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

6) Prevent the inclusion of air bubbles during embedding. Casting ring and casting seat. Buffer paper must be tightly sealed; It is necessary to pour embedding material along the inner wall of the casting ring (using a shaking machine).

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

Defect 5: Flying edge defect of castings

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

Solution:

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

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