2) Strength The ability of the sand to resist external force damage is called strength. 4) Plasticity refers to the ability of the molding sand to deform under the action of external force and to maintain the existing shape completely after removing the external force.. If the fire resistance of the molding material is poor, the casting is prone to sticky sand. 3) Fire resistance High-temperature metal liquids have a strong thermal effect on the mold after pouring, so the molding sand must have the ability to resist high-temperature thermal effects, that is, fire resistance. The more SiO2 content in the molding sand, the larger the molding sand particles, the better the fire resistance.
The performance of the sand that allows gas to pass through is called breathability. The strength of the molding sand should not be too high, otherwise the castings will be defective due to the decrease in air permeability and yield. The yield of molding sand is not good, and castings are prone to internal stress or cracking. 5) Concession When the casting is condensed, the volume shrinks, and the molding sand should have a certain ability to be compressed, called concession. The finer the particle size of the sand, the higher the clay and moisture content, the higher the compactness of the sand mold, the worse the air permeability.
Adding wood chips and other materials to the molding sand can improve the yield. The molding sand must have sufficient strength to prevent CNC machining collapse during molding, handling, and boxing, and it will not damage the surface of the mold during pouring. These gases must be smoothly discharged from the mold. The tighter the molding sand, the worse the concession. The air permeability of the mold is affected by factors such as the particle size, clay content, moisture content, and compactness of the mold. The plasticity of the molding material is good, the molding operation is convenient, and the sand shape made is accurate in shape and clear in outline. Otherwise, it will cause defects such as porosity and insufficient pouring in the casting.1) Breathable type After high-temperature molten metal is poured into the mold, the mold is filled with a large amount of gas