Ceramic foundry sand for core making

The hydraulic main control valve, a component of an excavator, is a complex hydraulic component. It mainly serves to transmit the pressure oil discharged by the pump to different executing components according to specific instructions. In this way, the excavator can complete various actions. The material of the main control valve is Ductile iron, with a complex internal structure. The core molding of the control valve is precise work, ceramic foundry sand is a good choice for core making.

In the past, foundries often used low-cost silica sand for core making. The technology of casting is resin-coated sand production. However, silica sand is of high thermal expansion rate and low refractory temperature. The castings will get defects such as deformation, sand sticking, core breakage, and veins. Some manufacturers also adopt chromium ore sand or zircon sand as core sand materials. But these two types of casting sand are both natural ores. They are granular shapes with a large angular coefficient and poor flowability. During the process of core making, the angular sand leads to an uneven and loose sand core structure. It is not easy to clean the molding sand after casting either. The expansion rate and thermal conductivity of zircon sand are both good, but the cost is too high. It‘s not so worth adopting.

Using ceramic foundry sand for core making can avoid the above situation.

Firstly, the thermal expansion rate of ceramic sand is small. The casting temperature of molten iron steel can reach 1350-1400 °. In this case, the coefficient of thermal expansion of ceramic sand is 0.13%, which is much less than 1.5% of silica sand and 0.4% of chromite sand. Therefore, the core molding is not easily deformed. Thus it can improve the accuracy and yield of the casting.

Secondly, the strength of ceramic foundry sand is high. After coating, it has good tensile strength and bending strength. Combined with the special micro bead shape of ceramic sand, it is easier to maintain the integrity and density of the sand core. So it improves the smoothness and surface quality of the inner wall of the casting.

Then, ceramic foundry sand is made by the electric melting of refractory grade bauxite. It can resist high refractory temperatures and get stable physical and chemical properties. Therefore, it can withstand the high-temperature impact of molten steel pouring and prevent sand sticking caused by the reaction between the steel liquid.

Finally, the shape of ceramic foundry sand is a smooth microsphere shaped with a low angular coefficient and good fluidity. The space between spherical particles is large. As a result, the permeability is better than that of irregular silica sand, chromium ore sand, and zircon sand. The spherical structure of pearl sand also has the characteristics of good flowability and collapsibility, making it easy to clean and recover.

All in all, ceramic foundry sand is more suitable for complex precision component casting. It has advantages that other casting sand does not have. So it greatly improves the efficiency and quality of the casting.