Defects and solutions of silicon sol-lost wax casting process

Defect 1: casting shrinkage cavity

The main reason is that the alloy solidifies and contracts, which causes the casting shrinkage cavity and absorbs a large amount of oxygen and nitrogen in the air when the alloy is dissolved.

Solution:

1) place the gold ball.

2) the diameter of the thickened casting channel or the length of the shorter casting channel.

3) increase the amount of metal used.

4) the following methods are adopted to prevent the organization from pitting in the direction of the casting channel.

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

B. to prevent the molten metal from hitting the cavity vertically, the casting channel should be curved.

C. oblique placement of casting channel.

Defect 2: rough and dirty surface of casting

The surface of the cavity is rough and the molten metal reacts with the surface of the cavity.

1) the embedded particles are thick and not delicate after stirring.

2) directly put the embedded material into the maofu furnace to roast after curing, with too much water.

3) the heating rate of roasting is too fast, and the expansion difference in different positions of the cavity causes the inner surface of the cavity to peel off.

4) the highest temperature of roasting is too high or the roasting time is too long, which makes the inner surface of the cavity too dry.

5) the melting temperature of the metal or the roasting temperature of the casting ring is too high, which causes the metal to react with the cavity, and the surface of the casting is burnt with the embedding material.

6) insufficient roasting of the casting type, when molten metal is cast, the decomposition of the buried material will be caused, more gas will be generated, and flax will be produced on the casting surface.

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

Solution:

Don't overmelt metal.

B. The roasting temperature of casting type should not be too high.

C. The roasting temperature of casting type should not be too low (the roasting temperature of phosphate embedding material is 800-900 degrees).

D. Avoid pitting in the direction of casting channel.

E. Apply a coating on the wax pattern to prevent burning of sticky liquid.

Defect 3: cracks occur in the casting

There are two main reasons. First, the casting defect (joint) is usually caused by the rapid solidification of the metal at the place.Second, the cracking caused by high temperature.

1) for casting joints caused by too fast solidification of metal, it can be solved by controlling the casting time and solidification time.Factors related to casting time: waxy shape.The amount of thickness cast.Casting pressure (casting machine).The permeability of the buried material.Factors related to solidification time: waxy shape.The highest roasting temperature of the cast ring.Type of embedding material.The type of metal.Casting temperature.

2) cracking caused by high temperature is related to mechanical properties of metal and embedded materials.Cracks are easy to occur in the following situations: cracks are easy to occur when the casting temperature is high;High strength embedding material is easy to crack.Nickel alloy and cobalt alloy with small elongation are easy to crack.

Solution:

Use of low strength embedding material;Minimize the casting temperature of metal;Small malleability is not used.Brittle alloy.

Defect 4: bulbous protuberance defect

It is mainly caused by the residual air (air bubbles) remaining on the waxy surface after the embedding material is mixed.

1) vacuum mixing and embedding material, the effect of vacuum embedding is better.

2) surfactant in waxy surface-jet interface before embedding (such as the castmate of Nikko solar)

3) cover the embedding material on the wax pattern first.

4) use the method of pressurized embedding to squeeze out the bubbles.

5) pay attention to the direction of the wax pattern when embedding, and there should be no dent at the bottom of the connection between the wax pattern and the casting channel.

6) prevent the inclusion of air bubbles in the embedding process.Cast ring and stand.The buffer paper needs to be closed;The inner wall of the cast ring shall be filled with embedded materials (using oscillators).

7) no further shock after filling the casting ring.

Defect 5: casting flanging defect

Mainly due to the cracks in the cast ring, molten metal flows into the cracks in the cavity.

Solution:

1) change the embedding conditions: use high strength embedding materials.The strength of gypsum cladding material is lower than that of phosphate cladding material.Use circular casting as much as possible.When cast without the ring, the ring is easy to crack, so note.

2) conditions of roasting: do not directly roasting the buried material after curing (it should be roasting after several hours).The temperature should rise slowly.Cast immediately after roasting, do not repeat roasting ring.