Rough working conditions, dirt roads and huge haulage trucks are characteristics of open-cast mining. No matter if a mine is located in Australia, Colombia or Sweden, or whether iron ore or coal is being extracted, the process imposes immense loads and stress on production vehicles. Although the tires mounted on massive trucks are specifically designed to cope with mine-site conditions, it's impossible to completely avoid tire incidents that require repairs-generally performed by technicians using specialized equipment, consumables, tools and systems solutions from companies such as REMA TIP TOP. This allows repairs to be carried out quickly and reliably, minimizing expensive downtime that cuts into production revenues.


The largest tires used on ultra-class haul trucks are nearly 14 ft (4.27 m) tall and weigh approximately 12,500 lb (5,700 kg), with nominal load ratings in excess of 100 mt. A new giant tire’s five-figure price tag makes a compelling argument for repair instead of replacement in most cases.
 

At almost every large-scale surface mine in the world, trucks and operators work around the clock to move extracted raw materials from point A to point B, carrying payloads up to 400 tons. The largest trucks use tires that are more than 4 m in diameter, weigh up to 6 tons and cost, depending on the size and type, about €35,000 apiece. Tire repair rather than replacement is an attractive option for mine operators, because repair costs are typically 10%–15% of the price of a new tire. In addition, fabrication of a single giant off-the-road (OTR) tire requires tons of natural rubber, but only a few kilograms of rubber are needed for a repair. At one large mine in Australia's Hunter Valley, New South Wales, for example, it's common to encounter between 200 and 300 damaged OTR tires each month. Thus, repairing rather than replacing a tire makes sound economic sense-assuming the damage is repairable.

Transporting damaged giant tires to a local tire service operation only makes sense when the service shop is located nearby; repairs are usually carried out on-site by mobile service providers dispatched from a central location.

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It takes only a few kilograms of filler rubber to make most repairs; fabrication of a new giant OTR tire requires tons of material.

Lose Air, Lose a Tire

Damage generally occurs at three different places on a tire: the tread, the tire's shoulder or the sidewall. Most damage to OTR tires is due to penetration by stones or rock splinters encountered on haul roads or loading and dumping areas. Fist-sized stones that become jammed in the tread profile work their way into the tread with every revolution of the wheel, even though that tread may be up to 140 mm thick. When the stone eventually penetrates the carcass, the breach causes a gradual loss of air (slow puncture), usually leading to sidewall or shoulder cracks and eventually to total destruction of the tire if not caught in time. To avoid this, Tire Pressure Monitoring Systems (TPMS) are available from various suppliers that employ sensors installed on the tire to provide early warning of air pressure loss or overheating.

Damage generally occurs at three different places on a tire: the tread, the tire's shoulder or the sidewall. Most damage to OTR tires is due to penetration by stones or rock splinters encountered on haul roads or loading and dumping areas. Fist-sized stones that become jammed in the tread profile work their way into the tread with every revolution of the wheel, even though that tread may be up to 140 mm thick. When the stone eventually penetrates the carcass, the breach causes a gradual loss of air (slow puncture), usually leading to sidewall or shoulder cracks and eventually to total destruction of the tire if not caught in time. To avoid this, Tire Pressure Monitoring Systems (TPMS) are available from various suppliers that employ sensors installed on the tire to provide early warning of air pressure loss or overheating.

To start the repair process, the damaged tire is cleaned and thoroughly inspected to assess the extent of damage. Loose rubber and damaged carcass wires are removed when present. The damaged area is then roughened and a reinforcement patch is placed in position. The damaged area is filled with repair rubber; severe damage may require as much as 12 kg of filler. This step is followed by vulcanization, which can be either a one-step or two-step process, each with specific advantages and disadvantages. 

One Step or Two?

As might be expected, a one-step process vulcanizes the damaged area and the patch in a single step. For a tire with sidewall damage this means, for example, that it can be put back in service after 10 to 12 hours for vulcanization and two to three hours for cooling. During a two-step process, only the damaged area undergoes hot vulcanization; the reinforcement patch is cold-vulcanized. This process takes longer but is easier on the tire because heat is only applied to the damaged area. Something else that sets the two methods apart is the price of the equipment. The large autoclaves and vulcanizing equipment necessary for the one-step process are considerably more expensive than machines such as REMA TIP TOP's Thermopress, designed for two-step vulcanization. However, what counts most is the quality of the resulting repair-equally good for both systems.

Because the quality of a tire repair is independent of the process chosen, the decisive factor is the effectiveness of the complete OTR tire repair system and its compatible consumables, such as reinforcement patches, repair rubber and tools, and vulcanizing solutions. REMA TIP TOP's experts regularly visit OTR tire repair workshops around the world to acquire first-hand information on trends and nature of tire damage and resultant repair work, along with workshop needs. This information is then applied to continually optimize and extend the company's product portfolio. REMA TIP TOP places particular emphasis on workshop audits and training-because quick, professional repairs to these huge tires can take place only when technicians are trained to effectively and efficiently handle the tools and equipment needed for the process.

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