A continuously running ball mill was invented in Germany in 1891. Balls are used as grinders. The balls are of different sizes. The large ones are about 10–15cm, the small ones about 25mm. In grinding, the mill can contain up to 82% balls and 18% grindable material. The most common type of mill is an overflow mill in which ground ore sludge flows over the edge of the mill. The first mills installed in the old concentration plant in 1928 were peripheral discharge mills. In them, the ore sludge was discharged through port openings equally spaced around the mill periphery.
Ball mills were mainly used in Outokumpu, in the old concentration plant. In 1939, when the Mökkivaara mine was opened, rod mills were installed in the old concentration plant to increase grinding capacity.
Outokummun vanhalla rikastamolla käytettiin pääasiallisesti kuulamyllyjä. Vuonna 1939 kun Mökkivaaran kuilu aloitti tuotannon, hankittiin vanhalle rikastamolle tankomyllyjä jauhatuskapasiteetin lisäämiseksi.
The first mills used in the old concentration plant were peripheral discharge mills. In the photo, the mills are inside the boxes to prevent the ore sludge from splashing from the outlets.
