Points to pay attention to in the design of support rollers for slit coating

Processors and equipment manufacturers alike look to steel backup rolls to improve runout (TIR) and mitigate heat transfer issues. Steel rolls have been successful in some cases in laboratories or narrow production systems. However, in most cases steel rolls are not as forgiving as elastomer rolls and have therefore not been accepted for production. We expect this to change as the technology matures.

Elastomeric rolls have been improved over the past few years to achieve an exact roll-to-lip configuration that is close to what the coating absolutely needs. When specifying elastomeric rolls, the following need to be carefully considered:

• Runout tolerance

• Release properties

• Spreads heat

• Hardness

• Uniformity of hardness

• Rolling deformation (bow)

• Resistant to paint or cleaning agents

We see this most notably in the use of rollers covered with polyurethane or Viton, with a diameter of approximately 300 mm and a hardness of up to 90 durometer, Shore A. Runout tolerances of 0.0005 inches and better are being achieved.

Elastomeric rolls will deform for a given width of the web, and rolls need to be supplied to match the variation in web width. A spare volume is also necessary because corruption often occurs.