The Anaconda concentrating plant

When it was decided to remodel the Anaconda concentrating plant, it was not known whether, pebbles or steel balls should be used for grinding. To provide for this uncertainty a compromise was effected. The mills were made 10 by 4 ft. and built sufficiently strong for steel balls in case balls were used. Each mill was equipped with a 225-hp. motor directly connected through a flexible coupling. The mill filled with pebbles takes from 95 to 115 hp. to operate. In case steel balls were used it was planned to put in a false wood lining back of the steel lining in the cylindrical part of the mill to reduce the effective diameter of the mill.

This latter plan was finally adopted, and the Hardinge mills will be equipped with the false wood lining, 15 in. thick, in the cylindrical part of the mill, and a Cascade steel lining. With this form of lining, the mill is virtually 7% by 6 ft. and requires about 225 hp. when loaded with steel balls.

Fig. 21 gives the details of the lining. This lining was designed by the American Manganese Steel Co.

Jay A. Carpenter in describing the ore treatment at the West End mill, Tonopah, Nev. 1 says:

"Six tons of manganoid-steel balls were substituted for the 6-ton load of Danish pebbles in the 5 by 15-ft. tube mill. There was a sharp increase in the power required for the mill, but less power per ton ground.

The saving of power was overbalanced by the greater cost per ton for crease in the power required for the mill, but less power per ton ground. The saving of power was overbalanced by the greater cost per ton for the steel balls. Later, the mill was reduced to 3-ft. diameter, and charged with steel balls, resulting in a considerable increase of tonnage and decrease in the power required for the mill over the use of Danish pebbles in the 5-ft. mill. On account of a saving of 33 per cent, in power per ton ground, the test is being continued over a long period to determine the consumption of steel balls under the favorable conditions of the 3-ft. diameter mill."

With the increased use of steel balls in the tube mill inventors have given us every form of grinder that they could think of. We have dumb-bells and dumb-bells with rings around the shank; the concave balls already described ; then we have short and long cylinders of steel; and next we will probably have the hollow steel ball offering less weight with greater grinding surface than the solid balls.

The preceding table will give an idea of the character and cost per ton of the grinding surfaces used at various mills.