How to ensure the quality of foundry sand
In the process of casting at high temperature, due to the thermal expansion of molding sand, it is easy to cause a small change in the size of molding sand, thus affecting the dimensional accuracy, appearance and performance of castings. At the same time, if the thermal expansion coefficient of molding sand is too large, it will cause sand inclusion, scab, rat tail and other casting defects. All kinds of factors make foundry enterprises more cautious in choosing molding sand, not only considering the coefficient of thermal expansion of molding sand, but also considering the cost of molding sand.
The basic requirements of foundry sand are: high purity and cleanliness; high fire resistance and thermal stability; suitable particle shape and composition; not easy to be wetted by liquid metal; and low price. In addition, the particle shape and composition of foundry sand have an influence on the fluidity, compactness, air permeability, strength and permeability of liquid metal, which is an important index of foundry sand quality.
In the early days, most of the natural silica sand containing clay, that is, mountain sand and river sand, have good plasticity, but now the emergence of foundry sand can be said to be a better substitute, its characteristics and quality are relatively good, and it has a good prospect in the future trend.