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June 22, 2005
The open nip is a major cause of poor slitting
THE NIP MUST BE CLOSED. In the rotary shear process, materials are slit in the nip between two overlapping, hardened metal disks that create stress in the shear mode sufficient to sever the product.
This is in contrast to compressive stress when crush/score slitting or tensile stress when razor slitting. The characteristics of the blade's extreme edges determine the sharpness and should not be confused with the grind angle or cross-sectional profile of the slitting blades. All slitting blades must have sharp edges, but profiles can vary widely and still meet the criteria for sharp blades. A sharp blade has an edge that is uncompromised at its extreme perimeter. The adjacent surfaces (blade rim and blade contact face) must meet in a perfect intersection with no chamfer at the corner, no radius, no burrs, no chips, or any other flaws that prevent perfect contact between the extreme edges of the mating shear blades. An open nip, no matter how microscopically minute, results when the extreme edges of both blades do not meet. That open nip is a major cause of poor slitting.
Any thoughts?
Posted by Reiny Schable at June 22, 2005 02:45 PM
Comments
I was at a newspaper printer recently and they were advised by the press mfgr to run the blades (shear)with about 3-6 thou gap. No Nip!? Needless to say they were tearing the web not cutting. Why is there such notions going around from people that build presses and other machines, I wonder?
Posted by: mike flannigan at July 15, 2005 05:23 PM
