Retreading is the generic term for tyre reconditioning which extends the useful life of a worn tyre for its original purpose by the addition of new material.
In the majority of cases the tread rubber is the only part of a tyre to wear away. The structure of the tyre remains intact. As the tyre construction has been produced to be capable of more than one life, to use this potential by replacing the worn tread makes sound environmental and economic sense. Whilst a car tyre is retreaded only once, commercial vehicle tyres are often retreaded two or three times and aircraft tyres many times.
After Initial Inspection of the worn casing to judge its acceptability for processing, the remaining unwanted old tread is removed. This process is called BUFFING and it provides a profile and surface texture in preparation for the application of a new tread.
SECONDARY INSPECTION then takes place during which time any necessary correction work is carried out prior to continuation of the process.
The application of a new tread and sometimes sidewall veneer is the next stage. This is called the building process. There are two main ways of building a retreaded tyre. With the hot cure or mould cure process, uncured tread rubber is applied to the casing, usually using a strip-winding machine. In the cold cure or pre-cure method a pre-cured tread strip is applied to the casing. When the operator is satisfied that all criteria have been met the built tyre then moves on to the curing operation.
CURING or VULCANISATION can also be carried out in different ways. The hot cure process uses an individual curing matrix (known as a mould), similar to that used to cure new tyres. In the pre-cure process, however, the tyres are cured in an autoclave (curing chamber). Car tyres are retreaded exclusively using the hot cure process. Commercial vehicle tyres can be retreaded using either process. During the curing process the physical properties of the tread change and the newly applied material forms a permanent chemical bond with the existing casing.
After curing, a FINAL INSPECTION is made to rule out any defect which would impair serviceability or the safety of the user. Unacceptable tyres are rejected and scrapped.