Ten step procedure for patch repair of rubber roll covers

Before going into detail, the following potential stumbling blocks should be pointed out:

• Must have a heating platen available that puts out about 160°C, to be firmly strapped (with tension) to the roll body on top of the patch.
• Must have a Dremel tool or equivalent (high-speed rotary cutter); some uncured, un-vulcanized rubber stock.

Here are the repair instructions:

Step 1 - Prepare tack cement

From the uncured rubber package, weigh up approx 250g and cut into small pieces. Stir into 250 ml of MEK (methyl-ethyl-ketone, sold by its chemical name) until completely dissolved. Place this tack cement into a tin can or glass jar, seal tightly and refrigerate until - 30 min prior to use. Caution - MEK is a skin irritant, handle with protective gloves and safety goggles.

Step 2 - Dremel

Dremel out the damaged area to generate a symmetrical shape (circle or oval). Undercut the area to be patched, i.e. go deeper into the side walls, so that it looks something like a letter 'C' lying down. That configuration will allow a good bond.

Step 3 - Clean and wash

Clean out the area to be patched with compressed air, followed by washing it with denatured alcohol (isopropanol) or hexane.

Step 4 - Apply tack cement

Apply two (2) coats of the tack cement (made in step 1) in the prepared, clean opening. Allow 15-30 minutes drying time between coats.

Step 5 - Cut rubber stock

Cut several pieces of the supplied rubber stock in the shape of the patch area, slightly larger.

Step 6 - Insert rubber stock

Wash one (1) side with MEK, lay into patch opening (surface should not be soaking wet but does not necessarily have to be completely dry; the intent is to provide good tack.) Push down firmly. Use a pin to pick and remove any air bubbles.

Step 7 - Fill patch area

Repeat step 6 until the patch area is filled up, plus at least 3 mm oversize on top.

Step 8 - Affix heating platen

Place heating platen on top of the patch, strap tightly to the roll body. Ensure the platen rests firmly on the patch.

Step 9 - Heat patch

Heat at 160°C for 6-8 hours if the patch depth is < 10 mm; heat for 10-12 hours if depth is > 12 mm.

Step 10 - Sand patch

Remove platen. After cool-down, hand-sand the patched area. Drill through-hole(s) if so desired.

That's it!

The trick is not to try to rush the job; take your time and be sure the patch area is kept clean.

For assistance with roll cover repairs, contact your Valmet representative or your local Valmet roll shop.