Calender Fabric Issues Affecting overall Calendered Rubber Gauge

The following relates to fabric calenders, both textile and steel cord only.

Localized cord disturbance in cord distribution does not usually affect fabric weight, whereas overall cord distribution problems can affect fabric weight, sheet gauge, and quality.

For example, an incorrect cord distribution that has a light weight center and heavy outer edges is due to:

• reduced average EPI (Ends per Inch) in the center of the fabric and
• increased EPI on the outer edges

How can this happen? -I’ve got a scanner!!

First, off:

• Weight samples alone do not distinguish between cord & gum
• Thickness samples alone do not distinguish between cord & gum
• Thickness & weight still do not distinguish between cord & gum
• Cord count must always be considered

A scanner is an excellent tool for the operator but is not necessarily recommended for control.

Here’s the problem

Many 4 Roll Calenders have space limitations that have prevented the use of on-calender gauges on the top gum wall. Historically this has necessitated the use of on-calender gauges on the lower gum wall and an overall scanner with math derivation of the top gum profile. This has lead to many calenders producing off-spec material that had a flat weight & thickness profile. Cords tend to bunch on the outer edges and have reduced EPI (Ends Per Inch) in the center.

The scanner cannot distinguish cord from gum & hence adjusts C/A (Cross Axis) or R/S (Roll Straightening) and fills in the center with rubber at the expenses of the outer edge zones. The result is a final fabric profile with edges that have high EPI count and low rubber insulation and centers that are the reverse, i.e. low EPI and heavy rubber gauge. Yet the scanner profile will indicate all is well. Even though the scanner may indicate an overall profile that is within spec, the edges may be out of spec, with excessive cord EPI distribution, and low rubber insulation thickness, while the center is out of spec with low EPI and heavy rubber gauge.

Technology is available to solve this problem. The small size and high accuracy of modern on-calender gauges permits using 3 gauges on the top and bottom gum walls, 6 total, to assure a flat sheet. Visit the FACTS website and search out our ON-CAL3 gauging system.

Since both top and bottom gum walls are now precisely controlled and assured to be flat and on spec, the scanner will provide a more accurate representation of the profile. Heavy edges for example, would indicate cord distribution problems.