Gray iron casting

The basic characteristics of gray iron castings are: high clay content, low moisture, and low amount of pulverized coal.
The basic feature of high density molding sand for gray iron castings is that the amount of pulverized coal added is also low. Therefore, the following points should be grasped during sand mixing.
① Clay content and mud content. The strength of molding sand with high clay content also increases with the increase of specific pressure, and the effective bentonite is usually controlled at 7%~10%. The sum of effective clay and dead clay in molding sand is equivalent to the mud content
The mud volume is generally controlled at 12%~16%. If the mud content is too high or too low, all performance indexes of molding sand will be affected.
② Moisture. The water content in the sand produced by lost foam casting is the main factor that determines the plasticity and adhesion of clay. When the water content is too high, it is easy to bow | stick t, the binding force deteriorates, the fluidity of molding sand decreases, and the uniformity of molding sand is not obtained
Mold density. When the water content is too low, the molding sand is not easy to mix, the strength of the molding sand is low, the brittleness is large, and the mold liftoff is poor, which is easy to cause the sand sticking defect of the casting. Generally, the moisture content shall be controlled at 10% higher than the moisture content at the peak value of wet compression strength
③ Original sand grain size. The density of sand mold is high during high-density molding and the expansion is large during pouring. Therefore, the original sand size should not be too concentrated. The original sand particles are circular or polygonal. Generally, three-screen sand or four-screen sand is selected.