Slitting Education and Information

What slitting equipment is right for my process?
Specifying the web slitting needs of your process takes three easy steps.

Step 1 – Define Your Slitting Process Needs

Slitting is the process of dividing a web into two or more strands or narrower webs, typically using mechanical knives to focus a load onto a small volume of material, creating a controlled zone of fracture in a machine direction line.   

Trimming – Two slitting positions near either edge of a wide web. Trimming is needed to create a final web of a set width from a too wide or width varying input material. Trimming is used to remove ragged, uncoated, damaged, or out-of-spec material.

Splitting – Slitting in a position near the center of a wide web to create two webs. Splitting is often done at the end of wide processes to reduce the width of winding rolls.

Multiple Strand Slitting – Using several slitting positions to combine splitting and trimming, creating two or more downstream strands of desired width. In many web making processes, such at paper mill, film orientation, and blown film lines, trimming and splitting are combined to create two webs of desired width prior to winding. In slitter rewinders, the web is slitting into anywhere from two to over one hundred individual strands.

Do you have a specialty slitting need?

Lateral Oscillation Slitting – Usually combined with trimming, lateral oscillation is the intentional shifting two or more slitting positions to create a wave profile in the slit web. Most often, lateral oscillation creates a triangle wave shape web followed by automatic winder guiding to reduce wound roll stress and diameter variations from long-term thick lanes in a web from paper or film making or coating. Straight-sided rolls wound downstream of lateral oscillation will have less roll defects and reduced bagginess.

Edge Positioning – Using one or more slitting positions to create a highly accurate and precisely web edge position. Where is may be difficult to use an automatic web guide to position a web to a precision of less than +/- 1 or 2 mils (+/- 25 to 50 microns), the position of a web’s edge immediately downstream of a  slitting system can meet this specification.

Stripe or Registration Slitting – Using a slitting position to make an edge in an accurate and precise position relative to a feature on the web, such as a coated or printed pattern or stripe. 

Gapping –Using two closely spaced slitting positions to take a narrow strand of web out from between two

Do you have a non-traditional slitting need?

Crosscut Slitting – Using a slitting system to cut a product in the crossweb direction, such as to sever a web at a winder or unwinder roll transfer or to create cut-to-length web sheets. Many cross-cut processes don’t use slitting, instead severing a web with a full-width serrated blade or guillotine.

Scoring – Using a slitting system to cut through one layer of a laminate or to make a controlled depth cut or deep scratch in the surface of a web to aide subsequent delaminating or tearing.

List all the known materials that you will be slitting, including single layer webs, coated webs, laminate webs, and spliced webs (including splicing tape).

If the product range is too broad, one slitting system may not meet the needs for all products. Sometimes the most difficult extreme is slitting through a lap-splice where the web is temporarily double thickness plus splicing tape.

What are the slitting process speeds?
Increased process speeds will require an increased strain rate to fracture the web in a shorter time period. Most materials will act like a harder material when strain rates are increased, requiring more applied force or smaller focus of force into stress to reach the necessary fracture stresses. Higher slitting speeds will also lead to more heat generation, quicker blade wear, and possibly more deflection from the higher loads.

What are your slit dimensional tolerances?

Slit width is defined by the relative position of two simultaneous and adjacent slitting positions. Slit width is usually defined as a target width with plus and minus tolerance values. A slit width tolerance may be symmetrical, such as 6 inches +/- 0.125”, or assymetrical, such ast 1.000”, +0.010”/-0.002”.

Beside slit width, many products have dimensional requirements of the structure of each slit edges. Every slitting process creates two new web edges. The quality of each slit edge may include the accurate and precise position of the new edge (which affects the slit width), the sharpness or geometry of the edge and adjacent web, the size and volume of particles or dust, and any fracture, scratching, abrasion or smearing web surface coatings (if present).

Debris and particles are often created by fracture and abrasion.

Any fracture process will likely have a kerf, a volume of material that turns to dust or particles, especially when fracturing thicker and more brittle materials. Mechanical fracture creates particles when the propagating cracks split and rejoins with themselves. Kerf and slitting fracture dust and particles are minimized by focusing the slitting stresses to as small as volume of material as possible. Shear slitting and its stresses focused between two sharp knives usually creates less dust than crush slitting with its larger fracture zone created by the duller knife and the flat anvil roller.

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