Machine tool bed casting composition of phosphorus content in liquid iron in phosphorus content: high, make solidification range expansion, at the same time, low melting phosphorus eutectic in the final setting time do not supply, as well as the casting shell becomes weaker, so increased the shrinkage hole, shrinkage resulting tendency. Control of phosphorus content less than 0.08% general factory.

Machine tool castings of carbon equivalent carbon content: improve, increase the graphitizing expansion, can reduce shrinkage. In addition, increasing the carbon equivalent and can improve the ductile iron mobility, in favor of feeding. The production of high quality castings experience formula for C%+1/7Si%>39%. But with the increase of carbon equivalent, should not make the cause of casting graphite floating and other defects.