The performance of aluminum alloy roll casting.
After the high-temperature molten metal is poured into the mold, the mold is filled with a large amount of gas. These gases must be smoothly discharged from the mold. This type of sand, which allows the gas to permeate, is called breathability. Otherwise, it will cause defects such as blowholes and lack of pouring in the castings. The permeability of the mold is influenced by factors such as sand particle size, clay content, moisture content and sand compaction. The finer the sand particle size, the higher the clay and moisture content, the higher the sand compaction, and the worse the air permeability.
The ability of sand to resist external forces is called strength. The sand must have enough strength to not cause collapse during modeling, handling, and boxing, and it will not damage the mold surface when poured. The strength of the sand should not be too high, otherwise it will cause the defects of the casting due to the decrease of air permeability and concession.
The high-temperature metal liquid has a strong thermal effect on the mold after it is poured. Therefore, the mold sand has the ability to resist high-temperature heat, that is, fire resistance. If the molding material is poor in fire resistance, castings tend to produce sticky sand. The more SiO2 content in the sand, the larger sand particles, the better the fire resistance.
The finger sand deforms under the action of external force, and can completely maintain the existing shape after removing the external force. The molding material has good plasticity, convenient molding operation, and the sand shape formed has an accurate shape and clear outline.
When the casting is condensing, the volume shrinks. The sand should have a certain ability to be compressed, which is called concession. The concession of sand is not good, and castings are prone to internal stress or cracking. The tighter the sand, the worse the concession. Adding sawdust and other materials in the sand can improve concession.