Rotary knife paper trimmer with long life shearing surfaces for trimming

Abstract

Significant improvements in the life of cutting knife blades and the quality of shearing of thick multiple sheet and shingled paper products are produced in a paper trimming system having two circular rotatable knives mounted to overlap at a shearing station through which the paper products are passed. Thin steel annular disc cutting blades with teeth about the outer circumference are significantly improved in life by eliminating the effects of blade warping and non-continuous mating contact with a bed knife cutting surface in an adjacent shearing relationship that is not broken by intervention of sheared paper or out of round knife surfaces or by deflection of the cutting blade away from mating surface contact by the pressure of thick or shingled paper products. Friction and wear is reduced by inclination of the cutting blade to prevent continuous rubbing against sheared paper edges. These problems are resolved by dishing and mounting the thin flexible annular disc cutting knife at a small angle away from perpendicular to the axes of rotation of the knives and by supporting its outer circumference to prevent deflection away from mating contact with the bed knife cutting surface. Thus, the cutting edges between the two rotary knives remain in continuous contact to produce clean cuts without raggedness in the presence of heavy loading from thick many paged paper products even when shingled to present a succession of step function increases of cutting loads.