In recent ten years, based on the research on the development of grinding ball materials at home and abroad, China has developed a kind of ductile iron material to make ball mill grinding balls, which has achieved remarkable results. Among them, Si Mn alloyed ductile iron grinding balls and isothermal quenched ductile iron grinding balls are representative. Spheroidal graphite cast iron grinding balls can be produced by sand coating process of iron mould, oil quenching and tempering, water based quenching and tempering or isothermal heat treatment process. As the carbon in the nodular cast iron grinding ball exists in the form of spherical graphite, the stress concentration phenomenon is effectively avoided, so it has better impact toughness. Through reasonable chemical composition, effective inoculation spheroidizing and heat treatment process to adjust the matrix structure, the comprehensive mechanical properties of ductile iron matrix can be better.
There is a large amount of spherical graphite in the grinding ball of nodular cast iron, which is conducive to reducing the impact of external forces on the matrix and absorbing a large amount of impact energy. At the same time, spherical graphite is conducive to terminating the extension and expansion of microcracks in the matrix structure, and has a good anti crushing ability. Therefore, the spheroidization rate and spheroidization grade of nodular cast iron grinding balls are required to be high. The better the graphite grade is, the better the performance of nodular cast iron grinding balls will be.
Si Mn alloyed spheroidal graphite cast iron grinding balls adjust graphite spheroidizing and quenching properties by adding silicon manganese alloy, so that the spheroidal graphite cast iron grinding balls have higher hardness and impact toughness indexes under the premise of ensuring lower cost.
At present, the quenching media used for the heat treatment of nodular cast iron grinding balls include oil quenching, salt bath quenching and water-based quenching. Both oil quenching and salt bath quenching have certain pollution to the environment, and a large number of environmental protection equipment needs to be invested to ensure that the pollution is reduced to the lowest level. Water based quenching is relatively more environmentally friendly.