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Good sand molding performance
Dec 05, 2018

The quality of the sand and core sand directly affects the quality of the casting. The poor quality of the sand can cause defects such as pores, sand holes, sand sticks and sand inclusions. Good molding sand should have the following properties:

1) Breathable type

After the high-temperature metal liquid is poured into the mold, the mold is filled with a large amount of gas, and these gases must be smoothly discharged from the mold. The sand-like property of allowing gas to pass through is called gas permeability. Otherwise, the casting will have defects such as pores and insufficient pouring. The gas permeability of the mold is affected by factors such as particle size, clay content, moisture content and sand compactness. The finer the grain size of the sand, the higher the clay and moisture content, the higher the sand compaction, the worse the gas permeability.

2) Strength

The ability of sand to resist external damage is called strength. The molding sand must have sufficient strength to not cause collapse during molding, handling, and boxing, and will not damage the surface of the mold during casting. The strength of the molding sand should not be too high, otherwise the castings will be defective due to the decrease in gas permeability and concession.

3) Fire resistance

The high-temperature metal liquid is poured into the mold to have a strong thermal effect on the mold, so the molding sand should have the ability to resist high-temperature heat, that is, fire resistance. If the fire resistance of the modeling material is poor, the casting is prone to stick sand. The more SiO2 content in the molding sand, the larger the molding sand particles and the better the fire resistance.

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