Tyre Retreading


Retreading is an economical form of tyre recycling; this is done by reconditioning old tyres, using new materials so the tyre is again fit for its original use.

Generally, the tyre treads are the only part to wear away, the structure of the tyre is therefore fundamentally still intact. Nowadays the vast majority of tyres are actually manufactured to have more than one life, therefore tyre retreading makes sound and economic sense.

Car tyres can be retreaded once, whereas commercials vehicles can often be retreaded two or three times, and aircraft tyres can be retreaded many, many times. On average, manufacturing a retreaded tyre will use 4.5 gallons less oil than manufacturing a new one, retreaded tyres therefore also help to save valuable natural resources. For commercial tyres this is estimated to be around 15 gallons per tyre, which is a huge saving.

The Retreading Process

After the tyre has been initially inspected to judge whether it is acceptable to be processed, all remaining unwanted tread will be removed. This is called buffing and is done to provide a good surface texture in preparation for the application of the new tread.


A secondary inspection then takes place, this ensures that all necessary correction work has been performed.


After the tyre has passed a secondary inspection, the tyre building process is then performed which involves the application of the new tread and occasionally the sidewall veneer. This has then to go through further inspection by the operator to ensure that it is fit for use.


The curing/vulcanization process is then carried out. This can be done in one of two ways; either a mould, also known as an individual curing matrix is applied or the process will be completed in an autoclave which is normally used for commercial tyres as it can hold a number of tyres at once. Throughout the curing process the actual physical properties of the tyres tread changes; this newly made material then forms a permanent chemical bond with the existing tyre casing.

A final inspection is then carried out to ensure there are no defects which may affect the tyres safety or performance. Any with defects are immediately disposed of.



The Legal Requirement

Tyre retreading must be carried out in accordance with EC regulations 108 (for cars) and 109 (for commercial vehicles).

 Retreading Process

Initial Inspection

 

Each tyre received in a retread plant is subjected to a rigorous visual inspection. Inspectors are assisted by the use of non-destructive sophisticated inspection equipment.
We also purchase a new machine (Inspection Spreader).This Inspection Spreader designed to detect pinholes, nail holes, cuts, cracks, porosity,etc,Automatic tyre rotation stop when penetration detected with sparks.

Buffing

 

The tyre’s old tread is mechanically removed on high speed buffers. Today’s buffers are extremely accurate and will remove the proper amount of old rubber while turning the tyre to an exact specified diameter and radius.

Skiving & Repairing

 

With advances in state-of-the-art repair materials and repair methods, many of these tyres can be routinely repaired and in most cases can be retreaded when the original tread is worn off. The repair station is where any surface injury is treated using effective material and tools for grinding and patching.

Cementing & Filling

 

Even in small injuries it is critical that the injury is cleaned and filled. If this is not done, severe rust, separation and steel cable looseness could take tyre out of service. The injury should be inspected, and then cleaned out with a carbide cutter. After cementing the injury, a vulcanizing rubber stem should be applied to “fill” the injury. This would create a permanent repair that maximizes tyre life.

Building

 

In the pre-cure system, the tread rubber has already been vulcanized with the new tread pattern design. The buffed tyre needs a thin layer of cushion gum to be wrapped around its crown area. The pre-cured tread rubber is then applied with the building machine. This is called the building process.

Enveloping, Rim Mounting & Double Envelope System

  

a) The built tyres are then mounted with envelops and rims to prepare them for curing.
b) For enveloping, tyres are first fitted an outer envelope at the envelope-mounting table before the inner envelope is fitted into them. The enveloped tyres are then vacuumed out for preparation prior to curing. Modern plants have their casings hoisted by monorail systems.

Curing by Chamber (Precure)


 

The Precure Tread system is a process by which a tread pattern is fully cured or vulcanized into the tread by using a press. The tread is then vulcanized onto a tire casing using a bonding layer of uncured natural rubber. The tyre is vulcanized with heat, time and pressure in a curing chamber that bonds the tread to the casing. This thin layer called precure cushion or bonding gum. Cold retreading was then a term used to describe a process in which the final curing of retread is done at temperature lower than 115c.

Hot Process (Hotcure)

This system is similar to the technology of new tyre manufacturing.
Hot retreading is the term used to describe the retreading process in which the curing of retread is done at a temperature of above 140c. It employs a steel or aluminum mold with a tread design cast or machined into it.

Final Inspection (Presure Test) & Painting



  • Tyre inflation pre-set at 2, 4 & 8 bar (max) for a better QC inspection.
  • Enclosed by steel cage as safety protection.
  • Testing cycle ended automatically to reduce supervision work.
  • Well lighted within the cage for better visual inspection.
The retreaded tyre is subjected to a final inspection. This inspection insures that only tyres that meet industry quality standards are allowed to leave the retread plant.
All retreaded tyres are encouraged to be returned with the sidewalls painted using a light coat of black tyre paint.