The topic of retreading has been receiving a lot of attention due to discussions about conservation of resources and sustainability. The editors of AutoRäderReifen-Gummibereifung would like to raise awareness of specialized tyre dealers, transport companies, forwarding agents and drivers to take more care of tyres as a safety-relevant component. Thus, the editors decided to document different types of carcass damages and to get an analysis of those from experts at the tyre manufacturer Bridgestone. Stefan Lamp, Head of Product Management Commercial, and Marcel Münzing, Technical Engineer Quality Assurance, offered their expertise concerning individual damages and provided valuable hints for further procedures. The editors are very thankful for a trustful cooperation and the outstanding commitment.
We are going to present several images of damages and to give tips how to prevent them in the future in our multi-part series. Our collection will also be useful in consultation sessions between specialized tyre dealers and commercial end-users or fleet operators. Modern tyres for commercial vehicles offer a high-performance potential when combined with optimum conditions of use and adequate maintenance. Moreover, retreading will enable full economic efficiency.
Maintaining carcasses
There is a difference between cold and hot retreading in retreading. Both procedures need usable carcasses. Before retreading, the carcasses get assessed. Several damages are already noticeable during visual inspection. Deeper damages and cuts of the tyres are discovered with shearography as second important step of quality control. In the meantime, all the retreading companies with a high level of quality awareness make use of shearography in order to find defects within the carcass. Furthermore, production capacities are used in an efficient way, as damaged carcasses are already excluded before retreading.
In general, retreaded tyres can be used in all axle positions and in all areas of use from long-distance traffic via regional and city traffic up to construction areas. Only the quality of the carcasses and thus, the one of the retreaded tyres is essential for the area the tyre is to be used in or it would be most suitable to be used. If the carcass disposes of quality 1, it can be used in long-distance traffic without limitations, whereas quality 3 is only suitable for construction areas.
DOT age
There has again and again been the question whether there is to be a maximum limit for the purchase of truck and bus tyres. Generally speaking, there are no age limitations, as it always depends on the condition of the carcass. Thus, carcasses are bought based on a classification system: The axle position of the used tyres is less relevant, but it plays a bigger role with regard to the brand of the manufacturer (tier 1, 2, 3). Use, tyre size, tyre maintenance and recutting are further categories.
There are different types of information from the retreading companies: Depending on the company, carcasses older than 5 years do not get purchased. In other cases, there are different levels of assessment depending on the age of the carcasses. As a consequence, carcasses up to the age of six years get quality 1, carcasses up to 7 years quality 2 and up to eight years quality 3. After being excluded because of age the carcasses move into qualified disposal.
Nail hole damages
In the case of nail hole damages, a nail or screw mostly enters the area completely up to a maximum of 8mm of the belt package. The retreading person can usually grind the area, fill it with extruder rubber and close it with a repair plaster via hot vulcanization in autoclaves.
Two possibilities are available for professional repair. With an entering angle of a maximum of 15°: cleaning and closing with a mini combination of 8mm via cold vulcanization. With an entering angle over 15°: cleaning and closing with 8-mm Rema Stem and 8-mm UP patch via cold vulcanization.
