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.
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.)
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.
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.
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.