Slitter Savvy: Visual Roll Defects & Remedies

Published: August 01, 2001

Poor starts: There are obvious differences in appearance between the paper near the core and the remainder of the roll.

Remedies:

• Tighten web before fastening to core
• Start with web straight on cores
• Use good quality, properly stored cores
• Start with proper tension, nip and/or torque.

Splices: These necessary evils normally are due to web breaks or cutting out defective material in a parent roll. Most customers will allow up to three splices in a roll of wound material but will not allow rolls with splices near the core or near the full roll. They also insist that splices be made and marked properly. Bad rolls contain numerous splices, poorly made splices, or unmarked splices.

Remedies:

• Reduce bad material in parent roll to a minimum.
• Determine if web breaks are due to defects in material or winder and correct problem.

Starred rolls: In these rolls the ends have a star pattern due to the shifting of the layers of web in localized bands starting at or near the core and continuing out toward the outer wraps. These localized shifts cause a star pattern that is symmetrical, but frequently one or more rays of the star are missing.

Remedies:

• Wind tight at the start and then gradually soften roll hardness as diameter increases.
• Keep cross-caliper variation to a minimum.
• Oscillate before slitting.
• Provide for proper handling and transporting of rolls.

Offsets and Interweaving: Offsets are defined as an abrupt change in the position of the edge of the web. Interweaving is often caused by severe offsets in the rolls that are wound side by side on a winder.

Remedies:

• Be sure that core shaft and cores are securely retained.
• Check oscillation speed relative to web speed or binding in oscillation mechanism.
• Correct abrupt changes in speed or tension.
• Check for binding or other reasons for abrupt changes in nip load.
• Do not increase tension, nip, or torque during the winding operation.

Dished rolls: Dished rolls are defined as rolls that are wound with progressive edge misalignment that may be convex or concave. This curvature occurs while the rolls are winding.

Remedies:

• Make sure cores are firmly retained during winding.
• Achieve a good, hard start at the core.
• Ensure the roll hardness does not increase during winding.
• Check for machine misalignment.

Telescoped rolls: In telescoped rolls, a curvature occurs while handling or unwinding the rolls of web material.

Remedies:

• Wind tighter rolls with a good, hard start and decrease roll hardness.
• Unwind with less tension.

Core offsets: The cores extend inside or out of the sides of the rolls.

Remedies:

• Be sure cores are aligned with slitters.
• Securely retain cores and fasten webs securely to the cores.

Trim wound in rolls: This is caused when the winder trim is not collected into the trim removal system and follows the web into the winding roll.

Remedies:

• Check to ensure the air velocity at intake of trim removal system is greater than winding speed.
• Check to ensure laminator air flow at trim nozzles.
• Check edge guide unwinding roll or be sure that offsets are not greater than trim width.

Slitter rings: Concentric ring patterns on the edges of the roll give the roll edge the appearance of a target. This defect is very common on winders with mandrel-mounted bottom knives after the mandrel has been reground one or more times.

Remedies:

• Ensure that run out of bottom knives after grinding does not exceed the thickness of the webs.
• Check to be sure that bottom knives have a close sliding fit with mandrel.
• On individually driven bottom knives, check run out of drive shafts.

Other Slitter Defects

• Excessive slitter dust is caused by dull slitter blades, excessive overspeed of bottom knifes, and/or worn slitter bearings.

• Nicked blades cause roll edges to have small and very short pieces of web protruding from the smooth roll edge. Nicked blades are commonly caused by engaging top blades on top of bottom knives or improper storing or handling of the slitter knives.

• Scalloped edges are defined as rolls in which the slit web width increases and decreases during the winding process. This is normally caused by excessive slitter runout, insufficient side pressure on shear slitters, or slitters that are not securely retained during the slitting process.

• High edges are common when dull razor slitters are used in razor-type slitting. It is corrected by replacing the razor knives or by moving the razor to obtain a new cutting point on the blade. This defect also can be minimized by oscillating the razor blade to vary the cutting point on the blade during winding.

• Scalloped edges are defined as rolls in which the slit web width increases and decreases during the winding process. This is normally caused by excessive slitter runout, insufficient side pressure on shear slitters, or slitters that are not securely retained during the slitting process.

• High edges are common when dull razor slitters are used in razor-type slitting. It is corrected by replacing the razor knives or by moving the razor to obtain a new cutting point on the blade. This defect also can be minimized by oscillating the razor blade to vary the cutting point on the blade during winding.