Edge cracks are caused at the paper mill by the slitter when slitting rolls to size for offset web printers. The result is small cracks, or tears no longer than an inch that appear randomly on the edges of a paper reel. They are usually closer to the core.
What causes edge cracks?
There are two causes. The first is due to uneven paper caliper and strength.
The second is that the setting of the slitter at the paper mill. The slitter is set too deep or too shallow against the cutting anvil. In the case of edge cracks, if the slitter is too deep, it will cause a sawing effect. Combined with tension it will cause slight tears, or edge cracks.
The same principle applies to running a slitter on a web press. Here are the optimum depths and angles to run a slitter for paper.
The optimum depth of a slitter against an anvil is .06" for paper. But this can depend on the type of paper being slit. Anything outside of this range will cause edge cuts.
How to detect edge cracks on press.
Since this is a paper defect, they are difficult to prove after a web break. And to receive compensation from a paper mill company requires evidence. Therefore detection systems have been made to see them before the web passes through the offset press and breaks.
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| Edge crack detection principle |
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