WEAR OF MILL COMPONENTS DURING THE BALL MILLING OF CALCIUM-CARBONATE

Calcium-containing minerals, such as calcium carbonate, compact into a hard cake during ball milling. This protective cake guards the walls of the pot. The balls, however, are left unprotected to collide violently with one another. The potential for contamination through wear is high. Rates of wear in 1-liter capacity ball mills of either enstatite porcelain (MgSiO3) or stainless steel have been studied during prolonged grinding for 1000 hr. The brittle enstatite balls wore at a rate ∼250 times faster than those of the ductile steel. The steel mill contaminated the charge of calcium carbonate at a rate of ∼0.4 g Fe per 1000 hr at two different initial loadings: 660 and 10mg of calcium carbonate per cm2 of pot wall. Provided that the charge of powder is sufficient to prevent the balls colliding directly with the walls of the pot then the rate of wear is nearly independent of the loading. One concludes that the steel mill is to be recommended for maintaining a cleaner milled product. The physicochemical stresses in the wearing surfaces of the enstatite balls were severe enough to induce phase changes and chemical disproportionation with the production of quartz. © 1979.