The Reason & Solution of Porosity Defects

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In the proportion of defects castings, air holes caused by casting rejection is still relatively large. One of the common defects of castings in foundry production, which is a cavity formed by gas accumulation on the surface, under the skin, and in the interior of the casting. The hole wall is smooth, the shape and size of the position are no rules, different type, different reasons. 

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Forming reasons : 

1, The preheat temperature of the mold is not correct, because in the pouring process the liquid metal passes through the gating system to cool too quickly.

2, The design of the mold is not correct, resulting in gas discharge can not be smooth.

3, Materials (paint) is not very good, poor exhaust of the paint itself, and even paint itself volatile or decomposed gas.

4, The mold cavity surface itself has holes, pits and other liquid metal into the hole, the pit, gas rapid expansion of compressed liquid metal, formation of choking.

5, Mold cavity is not promptly clean up the surface corrosion.

6, Sand core storage improper storage.

7, Not too good or not enough dosage or improper operation, etc.

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Prevent method: 

1, Mold should be fully pre heating to reduce the sand moisture, paint (graphite) particle size should not be too fine, air permeability should be good. Inoculation ferrosilicon need to preheat and baking.

2, The use of inclined casting method.

3, Raw materials should be stored in ventilated and dry place and to preheat before using.

4, Under the premise of ensuring the ball, it should be slightly reduced the amount of magnesium residues, select the better effect of the oxygen (magnesium).

5, To prevent the precipitation of gas. Increase the cooling rate of castings, increase the pressure of the external atmosphere, etc..

6, Control pouring temperature , should not be too high.

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