Written: Marek Bernaciak
Bonding of conveyor belts and rubber linings
with PKT adhesive
Introduction
This study is intended as a guide for those who wish to carry out cold bonding of industrial rubber conveyor belts and rubber to metal bonding, for example in the manufacture of bumpers or rubber linings. Proxima Adhesives offers a special high-strength adhesive, MONOLITH PKT, for this purpose, which enables flexible and durable joints to be made.
General notes on rubber bonding
As an adhesive substrate, rubber is a specific substrate. It oxidises easily and covers itself with a passive layer of brittle ‘crust’. This process is very rapid under atmospheric conditions, especially when the rubber is exposed to ozone and sunlight.
Therefore, the basic operation when bonding rubber is to remove the oxidised layer using wire brushes, scrapers, coarse sandpaper or other mechanical means.
Bonding rubber conveyor belts
Bonding rubber conveyor belts with adhesive is probably the most common method, both for bonding new belts and in emergency situations. It allows a joint to be made that is resistant to weathering, repeated bending and scraping.
The basis of a good splice is
- Correctly cut and align the tape,
- Apply the adhesive in accordance with the technical data sheet,
- Apply sufficient pressure and leave the bonded tape in place until the adhesive is fully cured.
Preparing the tape for bonding
Before applying the adhesive, the following operations must be carried out:
- Cut the tape at a 60° angle with an allowance of approximately 1.5 tape widths.
- Both ends of the tape should be staggered so that any scrapers do not catch and tear the splice. The number of steps should be equal to the number of plies minus one (see sketch).
Once properly trimmed, care should be taken to ensure that the adhesive surfaces are well roughened using tools such as rotary wire brushes.
Applying the adhesive
MONOLITH PKT adhesive must first be thoroughly mixed with the amount of hardener supplied. If only part of the adhesive is to be used, weigh out the appropriate amount of adhesive using an accurate scale. Do not measure the amount of adhesive by eye. An error can significantly reduce the strength of the bond.
The mixed adhesive should be applied to the surface of the tape to be bonded using short bristle brushes. The first layer of adhesive should be allowed to dry more than the second (see Technical Data Sheet). If the substrate is very absorbent, apply three coats of adhesive. The first two coats should be thoroughly dry.
The last layer of adhesive should only be allowed to dry to the so-called dry touch, i.e. to the point where touching the finger causes only slight adhesion of the finger to the adhesive (the adhesive does not stick to the finger).
It is then necessary to press the two parts of the tape together using a thick (preferably 2-3 cm) plywood or even steel plate (8-12 mm). Press the two parts together with a roller (8-16 mm) or a heavy hammer (approx. 2 kg). Accuracy of pressing is essential for a good bond.
Bonding rubber flooring
The bonding of rubber linings is typically used in the following types of structures:
- Chemical resistant linings for tanks, gutters,
- Abrasion resistant lining of chutes, cyclones,
- Lining of drive drums in mining belt conveyors, etc,
- Manufacture of bumpers or their components
Preparation of the rubber surface
Thoroughly grind the metal (usually steel) to white metal, leaving as rough a surface as possible. If only part of the steel structure is to be rubber lined, sand the adjacent area as well (approx. 100 mm from the proposed rubber edge). Then apply PKT Metal Primer to the entire sandblasted metal surface. If no primer is available, MONOLITH PKT Adhesive mixed with hardener according to the technical data sheet can be used to prime the steel).
Applying the adhesive
We do not apply the adhesive until it has been thoroughly mixed with the hardener. We try to use the entire batch of mixed adhesive within the time specified in the technical data sheet.
Bonding to rubber is applied in the same way as for conveyor belts.
Glue on steel is applied similarly, except that the first layer of glue is dried very thoroughly. This may mean that the drying time is twice as long as for rubber. Always use a short bristle brush to apply the adhesive.
Tip
Our data reflect the current state of chemistry and technology and do not claim to be exhaustive. The best safeguard against possible errors, for which we cannot accept any responsibility, is to carry out your own tests. In this way, the variable data, which depend on the application, working method and materials, will be confirmed in each case under specific conditions.
