The quality of molding sand and core sand has a direct impact on the quality of castings. Poor quality of molding sand will cause defects of castings such as porosity, sand hole, sand sticking and sand inclusion. Outstanding molding sand shall have the following functions:

1) air permeability type

After the high temperature liquid metal is poured into the mold, the mold is filled with a large amount of gas, which must be discharged smoothly from the mold. The function of molding sand which can let the gas through is called permeability. Otherwise, the casting will suffer from porosity and lack of pouring. The permeability of the mold is affected by the grain size, clay content, moisture content and compactness of the sand mold. The finer the grain size of sand, the higher the clay and moisture content, the higher the compactness of sand mold, the worse the permeability

2) strength

Strength is the ability of molding sand to resist external force damage. Molding sand must have enough high strength to avoid collapse in the process of molding, handling and closing, and the surface of the mold will not be damaged during pouring. The strength of molding sand should not be too high, or the casting will have defects due to the decrease of permeability and concession.

3) fire resistance

High temperature liquid metal has a strong thermal effect on the mold after pouring, so the molding sand must have the ability of resisting high temperature thermal effect, that is, fire resistance. If the fire resistance of molding data is poor, the casting is prone to sand sticking. The more SiO2 content in molding sand, the larger molding sand particles, the better fire resistance.

4) plasticity

It refers to the ability of molding sand to deform under the action of external force and keep its shape completely after removing the external force. The plasticity of modeling data is good, the modeling operation is convenient, and the shape of the sand mold made is accurate and clear.

5) concession

When the casting condenses, the volume shrinks, and the molding sand should have certain ability to be shrunk, which is called concession. The yield of molding sand is not good, and the casting is easy to crack or internal stress. The more compact the molding sand, the worse the concession. Adding sawdust and other materials to molding sand can improve the concentricity.

Article source: Zhongshan Jinlei Electronic Technology Co., Ltdhttp://www.jinleidj.com/