Score slitting; Five factors to consider
Score slitting, often referred to as “crush” slitting in international markets, is a common method of separating the web. Basically, a hardened steel disk is pressed against a rotating, hardened steel cylinder, creating a crushing nip into which the material is directed. The resultant nip force exceeds the ultimate yield of the material, and the material is severed along the nip line. Changing slit widths is relatively easy because only the slitter is repositioned over the fixed anvil roll. That’s all there is to it. Simple, or so it seems.
Slit-edge quality is variable and depends on the material being slit, the blade-edge profile, blade-edge finish and anvil smoothness. Because slitting is a “crushing” action in the nip between the slitter blade and the anvil surface, it’s generally considered the dustiest of the slitting methods, delivering the poorest edge quality.
Under a microscope, the resultant edge is ragged and frequently displays a ridge formed by material that has been displaced by the blade tip. Extremely dense or thick materials might require nip forces beyond the yield strength of the blade steel, making score slitting impractical.
Score-slitting variables can be separated into at least five different factors that affect the performance of the process. They include:
- Web material characteristics
Nip forces (their extent and effect on the blade and anvil roll)
Blade tip profiles
Metallurgy of the slitter blades and anvil rolls
Mounting geometry of the blade relative to the anvil roll
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