Ball Mill For Grinding Lime Mortar. Ball Mill is a type of grinder used to grind materials into extremely fine powder for use in mineral dressing processes. It works on the principle of impact: size reduction is done by impact as the balls drop from near the top of the shell. It is of welded steel construction, having an internal diameter of 12 inch x 13.5 inch long (volume 1 cu.ft.) and is made of 5/16 inch thick steel plate. The drum is supported on heavy duty ball bearings on the two ends. It has an opening of 4 inch width along the full length of the drum. An air and water tight cover is provided to close the opening after the specimen has been but inside the drum. The speed of rotation is 28-30 r.p.m. The pug mill has an arrangement for being held in any position. A revolution counter for recording the revolutions of the mill is fixed on the machine. Twelve 3/4 inch dia steel balls are also supplied with the unit. It is fitted with a 1/2 H.P. electric motor to operate on single phase, 220/230 volts A.C. supply & same model with three phase 440 volt is also available.