Rotary die cutter cylinders have traditionally been constructed with bearer rings mounted at each end of each cylinder body. These rings are run against rings on the adjacent cylinder and maintain a fixed center-distance between the cutting cylinders. The bearings supporting one of the cylinders are mounted in eccentric housings which, when rotated, provide a means to move one set of bearer rings mounted on the same cylinder against the adjacent cylinder bearer rings with some degree of force. An adjusting screw, anchored to the frame at one end, is typically used to actuate the rotation of the eccentric.
Working clearance is needed around the eccentrics in their frame support bores, and backlash is required in the threads of the adjusting screw to provide lubrication and prevent sliding surfaces from seizing. The action of forcing the rotary die cutter cylinder bearer rings against each other tends to maintain a fixed cylinder-to-cylinder center distance, neutralizes working clearance and backlash looseness, and prevents cylinder separation due to cutting load impact and cylinder bounce. Cylinder bounce increases die knife wear and makes it necessary for the die knife to run at a greater average distance to the anvil cylinder, thereby cutting down on die cutter ability to cut thinner and softer products cleanly.
The maintenance of a stable cylinder center-distance is required since this distance determines the die knife height relative to the anvil cylinder. The die knife is adjusted to "kiss contact" the anvil cylinder for proper cutting. The bearer rings are undesirable because they prevent this center-distance adjustment, cause center-distance variations due to surface imperfections, cause the rotary die cutting cylinders to be longer by the width of the bearer rings which adds to objectionable cylinder deflection and substantially increases the load on the cylinder bearings resulting in shorter bearing life.
In the prior art bearer rings fix center-distance, and any needed change in die knife height due to wear or manufacturing irregularities must be accommodated with shims between the die knife and the die cylinder surface. The use of shims to obtain the proper knife height is an arduous undertaking. Commercial shims are limited to 0.0005 increments. Shims are not commercially available to provide fine height corrections of 0.0001 or 0.0002 inch which are the increments of correction most often desired.
A knife which has been shimmed too high will be damaged by hitting against the anvil cylinder causing rapid cutting edge deterioration. Also, the loading of the bearer rings against each other induces undesirable cylinder bowing which increases the difficulty of obtaining correct die knife height, and any hard foreign material or surface irregularities on the bearer ring will cause undesirable center-distance and therefore die knife height variations. The combination of the above factors causes excessive die knife wear which increases the amount of nonproductive time required for die replacement and shimming, thereby reducing overall productivity.
Therefore, in addition to the elimination of bearer rings, the objectives of this invention are to provide for precise, infinitely variable center-distance adjustability of rotary die cutter cylinders, and at the same time to minimize cylinder bounce.