Causes and Preventive Measures of common defects in castings (1)

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There will be various shortcomings in the casting process, so we need to know where are the causes of these shortcomings? And what are the ways to prevent these shortcomings? Today, Wuxi Hong Ming Casting Co., Ltd. sorted out the reasons and ways to prevent these shortcomings, which are mainly summarized in the following six aspects:

Stomata (bubbles, choke holes, air pockets)

Characteristics: Pores are holes that exist on the surface or inside the casting, which are round, oval or irregular, sometimes multiple pores form an air mass, and the skin is generally pear-shaped. The shape of the choke hole is irregular, and the appearance is rough, and the air socket is a concave piece of the casting surface, and the appearance is smooth. The appearance of open holes can be found, and the subcutaneous pores can be found after mechanical processing.

The cause of composition:

1. The preheating temperature of the mold is too low, and the liquid metal cools too fast when passing through the pouring system.

2, mold exhaust planning is poor, the gas can not be smoothly discharged.

3, the paint is not good, its own exhaust is not safe, and even its own volatilization or differentiation of gas.

4. There are holes and pits on the surface of the mold cavity. After the liquid metal is injected into the holes and pits, the gas at the holes and pits rapidly expands and compacts the liquid metal, forming choke holes.

5. The mold cavity is corroded and not cleaned.

6. Raw materials (sand core) are not stored properly and have not been preheated before use.

7, the deoxidizer is not safe, or the amount is not enough or the operation is not appropriate.

Prevention measures:

1, the mold should be fully preheated, the particle size of the paint (graphite) should not be too fine, good air permeability.

2. Use inclined pouring method to pour.

3, raw materials should be stored in a ventilated dry place, use to preheat.

4, pouring temperature should not be too high.

shrinkage

Features: The shrinkage hole is a kind of rough appearance hole existing on the surface or inside the casting, the fine shrinkage hole is a lot of scattered small shrinkage holes, that is, the shrinkage hole or the shrinkage grain is coarse. It often occurs near the runner in the casting, at the root of the riser, at most of the thickness, at the thickness of the wall and at the thickness with a large flat surface.

The cause of composition:

1, the mold operating temperature control does not meet the requirements of directional condensation.

2, paint selection is not good, different parts of the coating layer thickness control is not good.

3, the position of the casting in the mold is not properly planned.

4, the pouring gate planning failed to achieve the role of full feeding.

5, casting temperature is too low or too high.

Prevention and treatment measures:

1, improve the grinding tool temperature.

2, adjust the thickness of the coating layer, the coating spray should be uniform, and the coating can not form part of the coating accumulation phenomenon.

3, the mold is partially heated or partially insulated with insulation materials.

4, the hot section is inlaid with copper block, and the part is chilled.

5. Plan the heat sink on the mold, or accelerate the cooling speed in some areas through water, or spray water outside the mold.

6, with removable cold block, placed in the cavity in turn, to prevent the continuous production of the cold block itself cooling is not sufficient.

7, mold riser planning pressure equipment.

8, the pouring system planning should be accurate, select the appropriate pouring temperature.

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