News & Events

Causes and prevention methods of common defects in castings

Update:23 Mar 2019

First: Hole with air (bubble, pupil, air pocket) Charac […]


Hole with air (bubble, pupil, air pocket)

Characteristics: The pores are holes existing on the surface or inside of the casting, which are round, elliptical or irregular. Sometimes a plurality of pores form an air mass, and the skin is generally pear-shaped. The shape of the pupil is irregular and the surface is rough. The air pocket is a concave surface of the casting and the surface is smooth. The visual inspection of the open hole reveals that the subcutaneous stomata can only be found after mechanical processing.

Reason for formation:

1. The mold preheating temperature is too low, and the liquid metal cools too quickly when it passes through the pouring system.

2. The mold exhaust design is poor, and the gas cannot be discharged smoothly.

3, the coating is not good, its own poor venting, and even its own volatilization or decomposition of gas.

4. There are holes and pits on the surface of the mold cavity. After the liquid metal is injected, the gas in the hole and the pit rapidly expands and compresses the liquid metal to form the pupil.

5. The surface of the mold cavity is rusted and not cleaned.

6. Raw materials (sand core) are improperly stored and are not preheated before use.

7, the deoxidizer is not good, or the amount is not enough or improper operation.

Prevention method:

1. The mold should be fully preheated. The particle size of the coating (graphite) should not be too fine and the gas permeability should be good.

2. Cast using a tilt casting method.

3. Raw materials should be stored in a ventilated and dry place, and should be preheated when used.

4. Select a deoxidizer (magnesium) with good deoxidation effect.

5. The pouring temperature should not be too high.


Chapter Two and Chapter three here.