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Causes and prevention methods of common defects in castings-Chapter Two

Update:13 Apr 2019
Summary:

Shrinkage hole Characteristics: The shrinkage hole is a […]

Shrinkage hole

Characteristics: The shrinkage hole is a surface roughened hole existing on the surface or inside of the casting, and the slight shrinkage hole is a plurality of small shrinkage holes which are dispersed, that is, the shrinkage, shrinkage or shrinkage of the crystal grains. It often occurs near the casting sprue, the root of the riser, the thick part, the thick and thin transition of the wall and the thick place with a large plane.

Reason for formation:

1. The mold working temperature control does not meet the directional solidification requirements.

2. The paint selection is improper, and the thickness of the paint layer in different parts is not well controlled.

3. The position of the casting in the mold is not properly designed.

4. The design of the riser failed to achieve full complementation.

5. The pouring temperature is too low or too high.

Control method:

1. Increase the temperature of the abrasive.

2. Adjust the thickness of the coating layer, the coating should be evenly sprayed, and the coating should not form part of the coating when it is applied.

3. Locally heat the mold or partially heat it with a heat insulating material.

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

5. Design the heat sink on the mold, or accelerate the cooling rate in the local area by water, etc., or spray water and spray outside the mold.

6. Use a detachable chiller block and place it in the cavity in turn to avoid insufficient cooling of the chill block itself during continuous production.

7. Design a pressurizing device on the mold riser.

8. The design of the gating system should be accurate and the appropriate pouring temperature should be selected.

Third, slag hole (flux slag or metal oxide slag)

Characteristics: The slag hole is a bright hole or a dark hole on the casting. All or part of the hole is filled with slag, the shape is irregular, and the small-point flux slag is not easy to find. After the slag is removed, the hole is smooth and generally distributed. In the lower part of the pouring position, near the ingate or at the corner of the casting, the oxide slag is mostly distributed in the form of a mesh on the surface of the casting near the inner runner, sometimes in the form of flakes, or wrinkled irregular clouds, or formed into sheets. The interlayer is present in the interior of the casting in the form of a floc, which is often broken from the interlayer when the fracture is broken. The oxide is one of the roots of the crack in the casting.

Reason for formation:

The slag hole is mainly caused by the alloy smelting process and the casting process (including the incorrect design of the casting system), the mold itself does not cause slag holes, and the metal mold is one of the effective methods to avoid slag holes.

Control method:

1. The gating system is set up correctly or a cast fiber filter is used.

2, using the oblique casting method.

3. Choose flux and strictly control quality.

If you are interested ,you may visit our chapter one here.Chapter three here .