At initial inspection a visual and tactile examination of the casing takes place. Thereafter a non-destructive shearography test or scan is completed. This test detects inherent separations in the carcass that are otherwise invisible and would remain undetected by the naked eye. If accepted, it will then go through the complete retread process.
The buffing process removes the remaining tread and sidewall rubber to predetermined dimensions by means of high speed revolving rasps and brushes. The machinery used in this process is computer-controlled so that the exact dimensions are achieved. This ensures that the buffed casing is an exact fit for the matrix of mould for which it is destined.
The granular residue and dust that is produced during this process is extracted by means of high powered fans and collected in large hoppers for recycling. Most of this material is processed into cushion backing for the carpet industry.
To locate any minute holes in the inner wall, the casing is subject to a penetration detection process whereby high voltage electricity is passed through the tyre while it is rotated. If a minute hole is located, an arc will be produced which stops the machine and identifies the location for a repair to be made. Larger holes in the casing are filled with compound and patched to rebuild the integral strength. Finally, the prepared casing is sprayed with a water-based adhesive, ready for the building process.
In the precure system, the tread rubber has already been vulcanised with the new tread design. The buffed tire has a thin layer of cushion gum wrapped around the tread area and the precured tread is then applied. The cushion gum bonds the precured tread to the tyre. The tyre is then placed in a curing chamber and the precured tread becomes adhered to the tyre through a vulcanising process that is very similar to the one used in new tyre construction.
In the mold cure system, unvulcanised tread rubber is applied to the buffed tyre. The tyre is then placed into a rigid mold which contains the tread design in the tread area. The mold is heated and the rubber in the tread area vulcanises and adheres to the tyre with the new tread design molded in. Again, this vulcanisation process is very similar to that used in new tyre construction.
Please note: Both systems require a combination of time, heat and pressure to create the vulcanisation of the new rubber to the tread area of the tyre.
During curing, the newly-built tyre is placed in a hot, segmented, radial matrix or mold in a curing chamber. The tyre is heated for up to 95 minutes at 150 degrees Celcius, while it is inflated to 200 psi. The combination of heat, time and pressure ensures that the new rubber is correctly vulcanised and produces the exact tread patterns and depths required from the mold. This is the same process as used for the production of new tyres.
The retreaded tyre is subjected to a final inspection. This inspection ensures that only tyres that meet industry quality standards are allowed to leave the retread plant.
Trimming And Painting
The retreaded tyre that successfully has passed the final inspection is trimmed to remove any excess rubber and painted. It is then ready to return to full service and a second (or third) life as a safe and economical alternative to high-priced new tyres.
Nail Hole And Section Repairs
If and when required, nail holes and section repairs are performed within the retread industry repair guidelines.