Roller Crushers *

Abstract

The paper describes roller crushers used for the reduction of ore, stone, coal, or chemical preparations of similar densities. Single-roll breakers developed originally for the crushing of coal, have been applied for the reduction of semi-hard slippery materials such as phosphate, gypsum, shale, and certain limestones. Two-roller crushers are the most numerous class and their growth from the early Cornish type to the modern high-speed rolls of great size and capacity is illustrated. Three-roller mills have not proved very successful in this particular field of service. Two examples are described and their defects explained. Four-roller machines have proved useful for the crushing of coal and some of the chemical products. Six-roller crushers are not very common. Two examples are shown and reasons are given for their restricted application. Two special types of roller crushers are also discussed, namely Taylor's three-stage coal breaker and the “Simplex” machine comprising two rollers and an intervening rotary disk.

The factors which influence the performance of the rolls are examined in detail and a formula for obtaining their capacity is given. The correlation of the angle of nip and the feed size, and their effect on the diameter of smooth rolls, is emphasized. A time factor diagram is given to show the reason why rolls of large diameter can be run with advantage at the higher circumferential speeds. Figures covering normal power consumption are specified.