Knowing the symptoms of unnecessary blade wear can mean the difference of thousands of dollars a year in blade replacements, blade sharpening expenses, and downtime incurred from removing and replacing blades. By identifying simple wear patterns on your upper and lower knife blades, you can find clues that will help you optimize the life of your blade and reduce your maintenance budget.
The first step is to determine what a healthy blade looks like. Healthy blade wear can be identified in the wear band as a smooth, straight, plane surface that is normal and uniform. Any other type of wear will indicate a problem. There are typically four major types of unnecessary wear issues: elliptical, concave, burrs or chips in wear, and smooth or rounded blades that are too dull for a proper slit. Each type of blade wear has its own cause and solution.
An elliptical wear pattern on the upper or lower blade suggests extreme run-out of that blade. The run-out is caused by an inconsistent contact point between the upper and lower blade as the lower blade oscillates back and forth or up and down. All slitter blades have some level of run-out that contributes to blade wear. A small amount of run-out may be acceptable at slower speeds, but causes more aggressive blade wear at higher speeds.
Solution—Make sure your upper and lower blades are attached in a way that does not allow them to oscillate from side-to-side or up and down. You can maintain the ideal geometric settings of the upper blade by incorporating an in-house sharpening system that keeps the upper blade in the cartridge during the sharpening process, which reduces variability of remounting the blade.
When you see a concave wear ring around the blade, it is typically caused by excessive side-load established during operator set up, vibration from the speed of the material running between the blades, or from excessive run-out. Side-load, the most common cause, is the amount of force used to get the upper and lower blade to come into contact. Side-load is often determined by operator instinct, where the operator has a tendency to increase side-load whenever a slitting issue is encountered or an adjustment is desired. This can lead to excessive side-load, which actually makes your slit quality worse and degrades blade life.