4A – Web Starts with CD Error

The web enters a downstream process with errors from upstream causes.

  • Loss of CD position at trimming, slitting, coating, printing, laminating, winding, and other CD registered processes.
  • Scratching and abrasion of web or roller (or bar).
  • Need to add automatic guiding to compensate for CD errors.
  • Observe the centerline and sidewall errors of input unwinding rolls.
  • Draw a line around a roller in a CD position near the web’s edge, then observe whether the web edge holds or varies in CD position relative to the line.
  • Monitor the actuation of an automatic web guide.

(Note: In sensing or observing only one edge, it may be difficult to distinguish between CD shifts and web width change without observing the other edge simultaneously.

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4B – CD Shifts Between Rollers

The web shifts to left or right versus centerline in the span between rollers.

  • Loss of lateral registration at slitting, coating, printing, laminating, winding, and other CD position sensitive processes.
  • Wrinkling, creasing, and possibly web breaks.
  • Draw a line on the roller where the web edge runs and note if the web moves relative to the line.
  • Use an edge sensor or line sensor from an automatic web guide to monitor the web’s lateral position.
  • Monitor an automatic web guide actuator motion to determine the shifting of the web entering guide.

(Note: CD shifting relative to a CD position could be caused by CD shifting or width change.)

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4C – Web Converges Between Rollers

The web edges shift towards the machine centerline in the span between rollers.

  • Troughing in the converging span.
  • Web buckles, forming MD wrinkles and creases.
  • Width losses from fold over.
  • Measure the web width on the upstream roller in a span and again at the downstream roller to see if web width has decreased.
  • Use two edge sensors to monitor the web’s width.
  • Look for wrinkles that form, but do not shift their CD position. They may wander slightly, but will not have a trend to walk in one direction.
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4D – CD Slips/Shifts on Rollers

CD slipping/shifting on rollers is a change in the web’s lateral position during the contact wrap angle.

  • Scratching, abrasion (of web or roller)
  • Unpredictable tracking
  • Unpredictable web guiding
  • Failure to spread wrinkle-prone web or slit strands

Note: One benefit of webs slipping laterally on a roller – No wrinkles due to lack of friction.

  • Draw a line on the roller where the web edge runs. Observe whether the web moves relative to the line between initial and final contact.
  • Use dual edge sensors to monitor the web’s incoming and outgoing position relative to centerline.
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4E – CD Errors in Rolls

Layers within a winding, wound, or unwinding roll are not aligned to each other or the core.

  • Roll sidewall alignment is out of specification.
  • Laterally shifted layers are easily damage in roll handling
  • CD shifted layers in the roll create problems for the roll customer’s process.
  • CD shifted layers in the rolls required automatic guiding at the roll customer’s process.
  • Scratching, abrasion
  • For gross sidewall errors, simply measure the variation in position of layers to a straight edge.
  • For small sidewall errors, use a dial indicator or profilometer to measure layer position relative to a straight reference.
  • Unwind a roll without web guiding and measure the edge position with an edge sensor.
  • With an automatically guided unwind, monitor the guide’s actuator position as filtered indicator of unwinding roll lateral errors.
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