Choosing shear blade profiles

In shear slitting, blade profile is one of the most frequently asked questions. While slit-edge quality is the result of many factors, blade profile is one of the factors most frequently changed in an attempt to improve slit quality. Often, a profile change does not yield the expected results because the shearing mechanism itself is not well understood.

This article looks at how profile affects shear slitting. Profile is defined as the cross-sectional shape of the blade tip, including the region beyond the actual cutting edge. This discussion is, however, limited to the portion of the blade profile that actually engages the web in the slitting process. Shear slitting, by definition, is the vertical displacement of the material as it enters a shearing nip between two opposing edges. The opposing edges can be two straight blades, as in a guillotine, or two rotating disks, as in the familiar web-slitting machine. These edges are usually in contact, however, some distance, as determined by the web characteristics, may separate them.

“Gap slitting” of metals is one example. Because the upper blade projects through the web during slitting, its profile is of great importance. Any damage to the web along the slit edge is, to a great extent, a result of the upper blade’s profile. As blade profile angles are gradually increased from “square” to acutely pointed, the material deflection path gradually changes from a vertical (shear stress) displacement to a lateral (tensile stress) displacement. Thus, the shearing mechanism gradually changes from a pure shearing action and merges into a “slicing” or “cutting” action as the blade profile narrows.

In this article, we'll address:

The effect of web materials on slitting quality
Minimizing web damage
Tangent slitting blade profiles
Wrap slitting blade profiles
Lower slitter ring considerations