Five Reasons Slitting Knives Chip (and How to Fix Each One)

1. The gap and overlap are wrong

Top and bottom knives in a shear slitter work like scissors. If the side load is too high or the overlap too deep, the edges touch under pressure and micro-chips appear within hours. Check the setup sheet: for film, overlap is typically 0.5–1.0 mm; for foil, less. If your knives chip at regular intervals around the circumference, suspect the setup before the steel.

2. The hardness was chosen too high

Every extra point of HRC buys wear life and sells toughness. At HRC 62, SKD-11 wears beautifully but chips on any shock. Dropping to HRC 58–60 often ends chipping overnight, at the cost of some wear life. If your line has vibration, splice joints, or occasional foreign objects, specify the lower end of the hardness window.

3. The edge angle is too sharp for the material

A 20° edge cuts film beautifully and chips on the first staple. A 45° edge survives cardboard and needs more cutting force. The sharper the edge, the more carefully the machine must be set. When a customer sends a chipped blade, we measure the edge angle first — it tells us whether the blade was made for a different job than the one it died on.

4. Foreign objects in the web

Staples in recycled paper, weld splatter in foil, knots in board, grit in recycled film — none of these are the blade's fault, and no hardness survives them. The fix is upstream: metal detectors on recycled lines, edge guides, and realistic expectations. If foreign objects are routine on your line, tell us and we will deliberately under-harden to give you a blade that rolls over instead of chipping out.

5. Mounting runout

A knife mounted with 0.05 mm of runout hammers its edge against the bottom knife once per revolution. Check the shaft, the spacers and the locking nut before blaming the blade. We hold concentricity to 0.01 mm at the factory; the remaining runout budget belongs to your machine.