The conditions under which earthmover tyres operate are very hostile and they can be damaged, sometimes severely. This damage is however not always beyond repair.
Subject to certain conditions, earthmover tyres can, in fact, be repaired. Right from the design stage, the possibility of repairing MICHELIN earthmover
tyres is included in the design specification.
Note: While repairs to smaller earthmover tyres pose no particular problem, on the other hand, repairing very large tyres (over 57”) is more difficult.
For these sizes, the manufacturer’s assistance is essential.
Repairing a tyre will save the tyre from scrap.
Repairs are therefore an essential factor to achieve cost-savings on the tyre budget. They also contribute to environmental conservation by postponing scrapping.
Repair operations demand a thorough knowledge of the recommended procedures and proven skill; they must be carried out by trained personnel.
Not all damage is repairable. Tyre manufacturers and in particular MICHELIN publishes information to assist with repairs (notably the maximum dimensions of repairable damage).
When a repair is performed according to the proper procedures, it does not affect the safety of the tyre.
The products required
For cold cure repairs. A cold-repair (not requiring an external heat source) is carried out with cold cure products and rubber solution. Mushroom-type repair patches present the advantage of blocking the perforation channel.
Patches and cold cure products can also be used.
For hot cure repairs.
The products required for a hot repair include:
- a patch of the appropriate type and size for the damage;
- rubber for filling in the damage, known as “filler rubber”;
- rubber known as “bonding or liaison rubber” which, once mixed with the filling rubber, ensures proper cohesion between the repair products and the tyre; - Rubber solution, to facilitate the curing.
It is imperative to use products that are compatible with one another. We strongly recommend that only products made by the same manufacturer are used together.
For hot repairs, check that the products used are suitable for the temperatures reached during the curing of the repair.
The feasibility of repairing a tyre, and the products to use, depend on the size, nature and position of the damage. The repair dimensions are measured after the damaged area has been prepared for repair (cleaned). The measurement of the dimensions of the damage determines whether the tyre is acceptable for repair, and the choice of the method and materials that will be used for the repair.
The repairable damage limits for MICHELIN tyres are indicated in the document “Size limits of prepared damages”.
Check that the repair is feasible: that the unprepared damage lies within the limits for repairable damage and that it is situated on a repairable part of the tyre.
Preparation of the damage
Clean the damaged area properly (on the interior and exterior of the tyre).
Checking after preparation
Measure the dimensions of the damage after preparation and check that they lie within the tolerances given by the tyre manufacturer.
Preparation of repair products
Prepare the repair products in accordance with the dimensions of the damage and the method used.
The patch (or the cold cure product) is positioned on the inner surface of the tyre.
To repair damage on the outside of the tyre, the rubber preparation is applied on the outer surface of the damage.
Depending on the method chosen, the curing (chemical joining the different components) is carried out:
- in an oven;
- in a hot chamber;
- in an autoclave;
- by section heating
In all events, the curing must be performed with pressure on the repair.
For checking and preparing damage:
- a pocket lamp;
- circlip pliers;
- a rapid air grinder (for the cables);
- a slow air grinder (for the rubber);
- a set of suitable milling-cutters or grinding discs;
- cutting pliers;
- a tape-measure;
- grease chalk.
For the repair:
The tools depend on the method chosen.
Precautions to be observed
The following safety rules must be followed for the protection of operators, tyres and the environment.
During tyre handling operations, all operators must wear gloves, protective glasses and safety shoes.
The repair workshop must be well ventilated and equipped with a dust extractor.
Securing the tyre to be repaired
The tyre must be fixed to prevent it from rolling or falling over.
During tyre-handling and repair operations, the operator must check to ensure the tyre(s) are secure, and correct if necessary This should be done each time the tyre is turned around or over.
All repair operations must be carried out on demounted tyres.
Do not repair tyres showing damage such as:
- exposed or deformed bead wire
- separation of rubber or fabric
- damage by oil, grease or corrosive materials
- irregular marks or mottling of the inner rubber caused by operating when underinflated
- damage outside the tolerated limits (see the instructions for earthmover repair limits)
MICHELIN training module
MICHELIN has developed a specific training module for tyre repair. Your usual MICHELIN representative would be happy to present it to you.