Jun 14, 2022
Before going into detail, the following potential stumbling blocks should be pointed out:
Here are the repair instructions:
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.
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.
Clean out the area to be patched with compressed air, followed by washing it with denatured alcohol (isopropanol) or hexane.
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.
Cut several pieces of the supplied rubber stock in the shape of the patch area, slightly larger.
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.
Repeat step 6 until the patch area is filled up, plus at least 3 mm oversize on top.
Place heating platen on top of the patch, strap tightly to the roll body. Ensure the platen rests firmly on the 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.
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.