Vacu-Lug Tyres Ltd
Gonerby Hill Foot
Grantham
Lincolnshire
NG31 8HE

What is retreading?

‘Retreading’ means taking a worn casing of good structural quality and putting it through a process which completely renews the tread of the tyre and sometimes the sidewall rubber. The rebuilt tyre is then subjected to a curing process where the new rubber is vulcanised to the casing and the tread pattern is formed.

Over the years tyre manufacturers have invested heavily in product development to deliver tyres that not only have a ‘first life’ but are also designed to perform equally as well in subsequent second and even third lives. Stronger casings, improved re-manufacturing techniques, a variety of specialist rubber compounds, coupled with the need to recycle and reduce the negative impact on the environment has lead to a sustained growth in the retread industry.

A retread tyre starts life as a worn tyre, where perhaps the tread is down to 2-3 mm and may have been previously re-grooved, or one that's been punctured and needs a repair. The first part of the process is to inspect the tyre to see whether it meets with our stringent quality guidelines.

	Initial inspection At initial inspection a visual and tactile examination of the casing takes place, then a non destructive shearography test or scan is completed. This detects inherent separations in the carcass that are otherwise invisible and would remain undetected by the naked eye. If accepted after this stage it will then go through the complete retread process.
	Buffing 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 exact dimensions are achieved in order that the buffed carcass 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.
	Preparation After buffing the carcass to be prepared to accept the building compound. Firstly, in order to locate any minute holes in the inner wall, the carcass 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.
	Building The new tread is applied or stitched to the carcass using a patented computer-controlled process. A continuous strip of premium rubber compound is wrapped around the tyre while it revolves on an inflatable chuck. The whole process is controlled to ensure the correct amount of rubber is applied to form the exact profile and volume of the tread pattern required for the matrix to which it is destined. The fact that there is no join ensures the tyre is perfectly balanced for service.
	Curing During curing, the “built” tyre is placed in a hot, segmented, radial matrix or mould within a curing press. The tyre is heated for up to 95 minutes at 150 decrees Celcius, whilst inflated to 200psi with the use of an internal bladder placed within the carcase. 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 mould. This is the same process as used for the production of new tyres.
	Final inspection Once the cured tyres have been deflated, removed from the press and have cooled and been trimmed, they are ready for the final inspection process. This involves three further examinations. The first is a visual and tactile examination, where the trained eye will spot imperfections in the tread pattern or sidewall. Secondly, the tyre goes through an inflation test where it is rapidly inflated to 110 psi over a five second period. Any imperfections in the tyre or weaknesses in the casing will cause the tyre to violently explode. Finally, the tyre goes through another scanning process known as shearography, which can detect even minor separations or porosity which are invisible to the naked eye but which would nevertheless cause the tyre to fail prematurely during service.