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So long as flat belts were the established driving medium, it was customary to equip the fixed roll with a large pulley, and the movable or spring roll with a smaller one-generally one-half the diameter of the large one. The large pulley was designed to carry the full amount of power needed to drive both rolls, which of course relegated the smaller one to the status of an idling pulley; its sole purpose was to bring the spring roll up to speed, and to maintain that speed during idling periods.
There was a logical purpose behind this arrangement. Because of the variables involved, it would be the exception, rather than the rule, if both roll faces ran at exactly the same speed under no-Ioad conditions, and if this "slip" between faces continued when the rolls were loaded, wear on the shell faces would be greatly accelerated. The large-and-small pulley set-up permits the material to "gear" the shell faces together so that the speeds are the same, and any compensation that might be required in surface speeds is taken care of by belt slippage on the small pulley.
When the multiple V -belt drive carne into its own, and line-shaft transmission was replaced by individual motor drives, an improved driving arrangement for crushing 1'0115 was developed. V-belt sheaves of equal size were installed on both 1'0115, and the load was divided between two motors. With this system, any speed compensation which may be required is taken care of automatically by increased slip of whichever motor happens to be driving the 1'011 with highest no-Ioad peripheral speed.
Although crushing rolls fitted with corrugated shells have been used in some special applications for secondary crushing, they are essentially a fine-reduction crusher, and as such are always fitted with smooth-face shells. The maximum one-way dimension of feed size is established by that point at which the 1'0115 will nip the feed. This, in turn, depends upon the coefficient of friction of the material, the diameter of the rolls, and the spacing between roll faces. |
