The main feature of defects is cracks
- Casting crack: It is a kind of crack formed at higher temperature. It is easy to appear when the volume shrinkage of the casting is large and the thermal expansion coefficient is large.
- Heat treatment cracks: due to heat treatment over-burning or overheating, often appear transcrystalline cracks.
Causes of cracks:
- The design of the casting structure is unreasonable, there are sharp corners, and the thickness of the wall varies greatly. If cracks occur in this case, the structural design of the casting should be improved to avoid sharp corners, and the wall thickness should be uniform and smooth transition.
- Poor concession of sand mold (core) can also cause cracks. Measures should be taken to increase the concession of the sand mold (core).
- Local overheating of the mold will cause cracks. It is necessary to ensure that all parts of the casting solidify at the same time or sequentially, and improve the design of the gating system.
- If the pouring temperature is too high, cracks will also occur, so the pouring temperature should be appropriately lowered.
- When removing the casting from the mold too early, the thermal correction method should be used when the casting is deformed. The cooling time of the mold should be controlled.
- After the heat treatment is overheated and the cooling rate is over-excited, cracks will be generated. The thermal correction method is used when the casting is deformed. Correctly control the heat treatment temperature and reduce the quenching cooling rate.
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