Back in Black

CW shows how, with proper care, retread tyres can be as good as new

New rubber is applied to the carcass. Glue is used as a primary bond prior to autoclaving.
New rubber is applied to the carcass. Glue is used as a primary bond prior to autoclaving.
Removing tread impurities and preparing the carcass is a  hands on job.
Removing tread impurities and preparing the carcass is a hands on job.
After the retreading process,  looks and perform just like their new counterparts.
After the retreading process, looks and perform just like their new counterparts.

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Some months ago, we took a look at the retreading process. Once again, as the desert sun is still scorching the sand, we thought we would take another look, and include some details on how best to care for the only contact your fleet has with the road.

Both in Europe and the US it is extremely common to find tyres that have been given a second life through a process known as ‘retreading’, or ‘remoulding’. Strict EU legislation ensures that the quality of the refurbished products remains comparable to brand new products.

In fact, some tyre casings in the UK get re-used several times over, and in the US a law was introduced that required the use of retread tyres on government vehicles such as school buses in order to reduce costs and waste.

With this in mind, it surprised us to find out that the use of retread tyres is not popular in the GCC, even on heavy roadgoing trucks, where fleet managers generally drive costs down to the last dirham.

In fact, it seems that the majority of fleet managers didn’t even realise that retreads were available in the GCC, or that they are even legal. One myth that surrounds retread tyres is that they are more likely to fail than new rubber.

While it is true that a lack of regulation has hampered the trade – essentially anybody with a sander and a stack of old tyres could set up a retread company – but now some firms have invested in modern technology which would comply with the latest international guidelines.

This increases the cost, but the finished product is still a lot cheaper than a new tyre.

According to Uday Kumar, factory manager at Al Dobowi, a tyre dealer and retread franchise owner in Dubai, there is no problem with the rubber.

“Our plant is built to EC 109 standard. There is no requirement to build to EC Standards here, but it gives people confidence” he said. The operation is a franchise from Bandag, a company owned by Bridgestone and operated in the UAE by Al Dobowi.

The first step is to pick a decent, premium-brand carcass. This is not too hard in the UAE, as there are vast reserves of discarded stocks to choose from. From these mountains, selected tyres are brought to the depot and the retreading process begins.

First, the tyre is placed on a dolly and hit with a ‘hammer’ – a special tool that quickly ensures there are no broken belts.

Kumar said, “We select the best [casing] by look, we inspect the crown and the tyre wall. Inside and outside and everywhere. With the hammer test, there are several layers of steel belts and they should be intact.”

This preliminary inspection is used mainly to screen out the many unusable casings before the next stage, which is an automatic buffing machine which boasts a CNC-controlled laser.

Laser shearography, as it is known, measures the shape of the tyre when it is under stress.

Once the tyre is mounted on the machine, the beam scans the shape, and calculates exactly how much tread the old tyre has left, and how much it needs to buff off. After the computations are complete, the wheel spins, and a buffer cleans the walls before taking off the old tread.

In a short time, the machine leaves the old carcass devoid of tread, but with a surface rough enough to bond the new mould on to it later.

Next, the laser scans the subject again, and an operator makes a manual note of the dimensions, which are displayed on a computer screen.

Out of interest, this modern device offers a far more accurate way of sanding down the treads than has been offered before
in the region, and it is said to be the first of its type anywhere in the UAE.

The next stage takes place in an old tiled office, that houses another complex machine. This equipment analyses the casing, but this time using ultrasonic sound waves to determine the condition of the casing. Essentially it is doing the same job as the man with the hammer but it is, of course, far more accurate.

The installation divides the casing into several different areas, each marked by a different colour. Using this as a reference, a graph is produced on a computer screen, with sound waves scrolling across it, very similar to the readout on an oscilloscope, or even a heartbeat monitor.

This not only provides detailed information about the condition of the carcass, but is necessary to meet EU 109 production standards.

After this, the tyre moves on to a machine called a ‘skiver’. This device is necessary to gouge out any pocks. Un-vulcanised rubber is then used to repair these marks, while anything else, such as punctures, are fixed. After this the casing is put in a wrap and it is then ready to have the new tread applied.

“The rubber cement is just to hold the tread rubber until curing. After that it is totally different and uses a chemical process with the heat” Kumar said.

“We have various types of design, for on-road, off-road or a combination. We have treads for the cement industry and for the quarry industry. All of the machines that you see here are brought in from Belgium” he pointed out.

Tread building
Applying the tread is a process known as building. In Europe you need to remove the original numbers on the sidewall, but there is no need to do that here, although the firm does stamp its brand on the tyre wall.

“Then we put the production date on the tyre. It is not a legal requirement, it is only for our identification. You will know when they are produced. We keep records about every tyre, through every step of the process,” Kumar explained.

“There are two envelopes. The point of enveloping is that the tread will be compressed onto the casing until curing.”

“The tyre will be inspected again, and the final thing to do is the date stamp” he concluded.

Interestingly, the new tread arrives in flat strips which are then pressed on to the tyre to form the new rolling surface. The rubbers then cure together in a tube-shaped machine known as an ‘autoclave’ with nineteen other tyres on a rack.

Although the autoclave maintains a temperature of around 100 degrees, the process is known as ‘cold curing’, as ‘hot curing’, a different method not employed by this plant, uses higher temperatures.

With earthmover tyres process remains the same, but on a bigger scale. Most of the time the tyre is not available for retreading, as the sidewalls burst long before the tread is worn out.

Once curing is complete, the tyre is subjected to a final internal and external inspection. Once the technician is satisfied, it receives the factory’s unique date code stamped into the tyre wall, while the finished product then gets a coating of black on the tyre wall.

It’s a complex and thorough process that ensures the quality of retread tyres remains at the highest levels. And, with the ecological and economical benefits retread tyres offer, fleet managers would be well advised to look at just how much money can be saved by using them.

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