Maintenance REINVENTING THE WHEEL

As the modern design evolved, belts became integral. They are rubber-coated layers of synthetics or steel wire between the tread and carcass. Structurally they help tires keep their shape. They brace the tread, relieve the circumferential inflation-pressure stress on the radial cords and protect the carcass from road hazard damage.

If the other components of a tire were not fatigued or accidentally damaged, the tire would last as long as the tread. Thicker treads can be used underground because speed restrictions keep the temperatures low and the temperature of the road surface is even and moderate. The current trend in underground tire design is toward more tread, using more cut-resistant rubber compounds in a smooth pattern. The practice of restoring the tread when 15% to 20% is left is losing favor and thicker tread tires are being run out to destruction without retreading. The Trout Lake mine in Flin Flon, Man., for example, uses this method.

The tire life is affected by other factors. John McClure of United Tire has a formula showing how the performance of a tire is affected under varying conditions. A factor for each of nine conditions is selected and the multiplied result indicates what proportion to expect of the tire’s life (see accompanying table). — (TABLE TO COME) —

The example illustrates how tire life is influenced by the environment and the treatment it receives. Operations dependent on mobile equipment for production know the need for preventive maintenance for tires. This means routine inspection so that the air pressure is kept correct, that all damage that could shorten the tire life is repaired, and that the tread depth is monitored to prevent the tire from being run too far before it is replaced or recapped.

While the tire life and reliability on production equipment absorbs attention, service equipment is very often forgotten or ignored and spends much of its life unnecessarily immobile because of tire failures. This is a sign of a deficient maintenance program. Service equipment should be treated the same as production equipment. It should run when it is needed. Routine inspections and servicing, once established, should come after emergencies in priority. In other words, they should never be postponed or bypassed. The inspection checklists should ask for specific response on air pressure, treadwear measure, tire damage, and rim damage. The specification of tires, as with all production equipment, should be a serious decision; agreements should be reached between operations and maintenance when the initial purchase is made. Too often, tires on new service vehicles are not designed for the application.

There is ongoing research into the components and functions of tires. Many trucks have tire-pressure-monitoring systems. Future development will make it simpler and bring the price down. We cannot wait for these improvements. We can make a large contribution in reducing breakdowns in any operation that uses tires by following a program along the lines outlined. Keith Bowley is a Toronto-based maintenance consultant.

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