A retreaded tyre is a tyre whose worn tread has been replaced with new material showing characteristics similar to the original. The raw material employed in this process is recovered from worn tyres whose structural features have remained unchanged. The tyre’s integrity is tested through careful selection. Tyres can be retreaded because they have a longer life cycle than their treads.
The retreading process
The retreading process has to comply with specific regulations: UN/ECE Regulation 108 (passenger cars) and UN/ECE Regulation 109 (commercial vehicles).
Tyre retreading is accomplished through following steps:
1- Primary inspection
Tyres that are suitable for retreading undergo several tests to prove fit for a new life.
The first check is a tactile / visual inspection, conducted by a qualified specialist who thoroughly controls the tyre internally and externally using special tools. Man-conducted inspection is complemented with instrumental inspection, performed through various technologies, such as shearography.
After the first check, the tyre is now buffed, namely its worn tread is removed and the surface is prepared so as to allow receiving a new tread. This operation is performed with special machinery.
|3- Casing inspection and repair
Further inspection of the casing is performed to allow possible repairs.
|4- Rubber cement application
A layer of liquid rubber is applied to prepare the tread area for application of new material.
5- New tread application
The aforementioned procedures apply to both hot and cold retreading. Here is where the systems differ:
The tyre casing is placed in a full circle mold and a new layer of uncured rubber is applied to the casing in a continuous ribbon.
A prevulcanized tread with design is applied on the tyre. The tread comes in strips or prepared rings. Besides flat strips, strips with “flaps” (also known as “wings”) are also available, intended to envelop the shoulders of the tyre.
In the hot cure process, the prepared casing, built up with uncured rubber, is placed into a mold bearing the final tread design. Time, temperature and pressure regulating devices are placed inside the press.
Curing temperature oscillates between 150° and 160° C. Curing pressure is around 14 – 16 atm. After the cure cycle is completed – cure time varies according to tyre size and tread depth – the air inside the press is let out and the tyre can be removed from the mold.
The tyre is placed in a rubber curing bag called envelope; the envelope is then vacuum-sealed.
The tyre is then placed in a heated autoclave to be vulcanized. The vulcanization process takes approximately 2,5 – 3 hours to complete and requires a temperature of about 110° C.
7- Final inspection and finish
The retreaded tyre is subjected to a final inspection internally and externally, then it is trimmed and painted.
The finished tyre is now ready for a second life.