Factors affecting the cutting quality:

When there is a slitting problem, the first thing to do is to check the edges. At the most common slit thicknesses, a 30X microscope is ideal for this purpose. Usually there is a notch and a broken area at the edge.

If the line between the score and the fracture is straight, and the fracture is clean, then it is a good edge. If the line is uneven or the fracture is rough, it is a bad edge.

Some slitting problems can be attributed to poor metal quality; however, problems caused by other variables and factors are more common in the slitting process. Slicing involves many variables, most of which can be controlled. In order to achieve a good slitting effect, every controllable variable must be controlled.

If the line between the notch on the edge and the break is clean, then it’s a good edge. If the lines are not flat or the broken lines are rough, it is a bad edge, caused by the improper setting of the cutter.

Tool clearance. Horizontal knife clearance is the most important of these variables. The gap is almost always set to 10% of the metal thickness. For example, a 0.008" gap is used to cut 0.080" thick metal. There are some metal thicknesses and types that just fit the 10% rule. However, 10% is rarely the correct clearance.

The thinner the metal, the harder it is to achieve the correct clearance. Conversely, on thicker metals, the old rules are less applicable. The new slot metals are designed for a specific purpose and have vastly different mechanical properties than the old low-tech metals. This is true whether you are cutting steel, aluminum, copper, brass, composites or any new design metal. Every metal has an optimal gap, and even the same metal form different sources or thicknesses may require different gaps.

Excessive vertical knife clearance or overlap can be the culprit for many strip defects, including edge waves, crossbows, arcs and deep knife marks. It can also damage tools such as knives and stripping rings, and even wear down the slitter.

Horizontal knife clearance is the most important coil slitting variable that you can adjust to improve slitting edge quality.