SAND CASTING EQUIPMENT.

1、the causes of casting shrinkage and countermeasures
The main cause of alloy solidification shrinkage casting shrinkage, and alloy dissolution absorbed a large amount of oxygen in the air, nitrogen, etc., when the alloy solidification gas caused by casting shrinkage
Solutions.
1.1 Place the gold storage ball
1.2 thicken the diameter of the casting channel or shorten the length of the casting channel
1.3 increase the amount of metal
1.4 Use the following methods to prevent depression in the direction of the casting channel
1.41 in the root of the casting channel placed cooling channel
1.42 To prevent the molten metal from hitting the cavity vertically, the casting channel should be curved
1.43 Placement of the casting channel in an oblique direction

2、The reason for the rough surface of the casting is not polished
The surface of the cavity is rough and the molten metal has a chemical reaction with the surface of the cavity, mainly reflecting the following situations
2.11 embedding material particles coarse, not fine after mixing
2.12 After curing, the embedded material is directly put into the Mofo furnace and roasted, and there is too much moisture.
2.13 The heating speed of the accompanying firing is too fast, and the expansion difference is produced in different positions in the cavity, so that the inner surface of the cavity flakes off.
2.14 The maximum temperature of roasting is too high or the roasting time is too long, so that the inner surface of the cavity is too dry, etc.
2.15 The melting temperature of the metal or the baking temperature of the cast ring is too high, so that the metal reacts with the cavity, and the surface of the casting burns sticky embedded material
2.16 The baking of the casting is not sufficient, the melted metal cast into, causing the decomposition of the embedding material, more gas occurs, the surface of the casting produces pockmarks
2.17 molten metal cast into the cavity, resulting in the local temperature is too high, the surface of the casting produces local roughness
Solution
2.21 Do not over-melt the metal
2.22 The baking temperature of the casting should not be too high
2.23 The baking temperature of the mold should not be too low (the baking temperature of phosphate embedded material is 800 ℃ -900 ℃)
2.24 Avoid the phenomenon of depression in the direction of the casting channel
2.25 in the wax type coated with a liquid to prevent burning stick

3、The reason for cracking of castings
There are two main reasons
3.1 Usually because the metal solidifies too quickly, resulting in casting defects (seams)
For metal solidification too fast, the casting seam, can be solved by controlling the casting time and solidification time.
Factors related to the casting time, the shape of the wax model, the number of coarse and fine castings, the casting pressure (casting machine), the permeability of the embedding material, factors related to the solidification time: the shape of the wax model, the maximum baking temperature of the cast ring, the type of embedding material, the type of metal, the casting temperature
3.2 Cracking due to high temperature.
Cracking due to high temperature is related to the mechanical properties of the metal and the embedded material. The following cases are prone to cracking: high casting temperature is prone to cracking, high strength embedding material is prone to cracking, and nickel branding alloy and cobalt branding alloy with low extensibility are prone to cracking.
Solutions: Use low strength embedding materials; minimize the casting temperature of the metal; do not use brittle alloys with low ductility.

4、The cause of spherical protrusion and countermeasures
It is mainly caused by the residual air bubbles staying on the surface of the wax type after blending the embedding material.
4.1 Vacuum blending and embedding material, the effect is better after using vacuum embedding
4.2 Spray surfactant on the surface of wax type before embedding (e.g. Nissin''''s)
4.3 Coating the embedding material on the wax first
4.4 Use pressure embedding method to squeeze out the air bubbles
4.5 Pay attention to the direction of the wax pattern when embedding, and do not have depressions under the connection between the wax pattern and the casting channel
4.6 Prevent air bubbles from being mixed in the embedding. Casting ring and casting seat. The buffer paper should be tightly closed, and it should be filled with embedding material along the inner wall of the casting ring (using a vibrating machine)
4.7 Do not shake again after filling the cast ring

5、How the flying edge of the casting is formed
Mainly due to the cracking of the casting ring, the molten metal flows into the crack of the cavity
Solution
5.1 change the embedding conditions: the use of higher strength embedding material. The strength of gypsum-like embedding material is lower than that of phosphate embedding material, so the use of caution. Try to use a ring casting. Casting without a ring, the cast ring is easy to produce cracking, so need to pay attention to
5.2 baking conditions: do not bake directly after the curing of the embedding material (should be baked after a few hours) should slowly increase the temperature. Casting immediately after roasting, do not repeat the roasting of the cast ring

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