6A – Buckled Web in Spans

The web is out of plane in the span between rollers.

  • Amplitude of buckling is enough to contact nozzles or slots.
  • Amplitude of buckling moves web out of the field of view of camera or laser inspection systems.
  • The angled web is tilted relative to the Z-direction measurement, causing thickness gauges to read too high.
  • Buckled shape is locked in if present during curing, drying, or quenching process.
  • Distance between web edges is smaller than the width of material.
  • Moving troughs can cause variation of edge position.
  • Span buckling (a.k.a., troughing) is a pre-cursor or warning of imminent wrinkling, usually on the roller at the downstream end of the troughing span.
  • Visual inspection viewing web with low angled lighting.
  • A low angle line scan laser can highlight troughing severity.
  • Count troughs. Observe the web from one side with a low angle of incidence and estimate troughing amplitude.
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6B – Buckles on Rollers

All or a portion of the width of the web is under MD or CD compression and buckling as it passes over a roller, through a nip point, or into a winding roll.

  • Creases
  • Web breaks
  • Coating and laminating defects (including uncoated areas, bubbles, and delamination)
  • Winding defects
  • Most wrinkles are measured by viewing or counting the creases in the web.
  • For all wrinkling defects (i.e., buckling on rollers), observe and note 1) the angle and position any troughs in the span immediately upstream of where the wrinkles form, 2) the angle and crossweb position of the wrinkles, and 3) whether the wrinkle shifts or walks laterally.
  • View wrinkling in high speed processes by projecting a visible laser beam crossweb at a small spacing above the roller’s surface. Any wrinkling that buckling into the laser’s path will reflect the laser light for easy observation.
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6C – Buckles in Rolls

Portions of the roll are visibly wavy or corrugated.

The outer surface of the roll may not be a perfect cylinder or the end of the roll layers may not form perfect circular rings.

  • CD buckles may become permanent deformations in the web and create functional or optical defects in final products, especially in laminated or coated products.
  • CD buckles in PSA products can create air gaps in the roll’s inner layers, creating visual and functional defects where the gaps form.
  • MD buckles may become permanent deformations in the web and create functional or optical defects in final products, especially in laminated or coated products.
  • Buckles in the roll do not pass esthetic quality needs (i.e., the rolls look bad).
  • Buckles may form permanent distortion in the web upon unwinding.
  • In slitter rewinding, one severely buckles roll may disturb winding quality of the entire set from tension variations or upsetting forces and contact load from a shared winding nip roller.
  • Slip knots (a.k.a., convolution buckles) may lead to wrinkling and creases in the web.
  • CD buckles in rolls are measured by direct observation. They may appear as CD ridges in the roll, sometimes visible at the outside of the full roll, but commonly only seen in layers near the core. From an end view, the CD ridges will form starring, spoking, or wavy ring patterns as several layers will buckle as a set, nesting upon each other.
  • Note width and radial positions where CD buckles occur – Full width vs. in specific lanes across the roll’s width, throughout the roll or only in specific radial positions, such as in layers near the core or at the roll’s outer diameter layers.
  • Direction observation of MD buckled ridges.
  • Note if the MD buckles have a uniform or variable pitch or CD wavelength.
  • Note if the MD buckles form across a portion or the entire width of the roll.
  • Note if the MD buckles appear throughout the roll or only in radial zones (e.g., only in the roll’s outside layers).
  • Note if the MD buckles are in the roll immediately after winding or either develop later or increase over time.
  • Note if MD buckles are seasonal or align with humidity variations.
  • Observe surface imperfections while winding.
  • Note if surface imperfections change with winding additional layers.
  • Note the position of surface imperfections, both their CD and radial position within the roll. Unwind the roll to see if the slip knot was initiated by surface debris or other surface imperfection.
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