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When a haul truck or grader stops moving, a company stops making money. Site profitability is directly related to equipment mobility. This is true in all major earthmoving applications, from residential construction in the Southeastern U.S. to large-scale surface mining in Northern Canada.
To help ensure continual equipment mobility, many site managers and maintenance personnel scrutinize every aspect of their machines looking for ways to limit downtime and maximize productivity. Few components are as closely monitored as those directly responsible for mobility – the tires. In rough conditions at large sites, poor tire selection and maintenance can cost a company tens of thousands of dollars a year–per machine.
Maintenance managers who understand the basics behind earthmover tire management are better equipped to keep their machines running at optimal performance longer.There are several factors that affect profitability and mobility. They can be subdivided into three categories – 1) factors that lower the life-cycle cost of the tires themselves, such as wear and damage resistance, 2) factors that increase equipment productivity, such as reduced downtime and productivity, and 3) factors that affect the operator’s ability to do his job, such as comfort and safety.
Life-Cycle Costs
The true cost of a tire should not be measured by the sticker price. A radial tire that costs twice as much as a bias-ply tire but lasts four times longer provides more value when all factors are considered.
By selecting higher quality tires, end users can help minimize lifecycle costs associated with unnecessary flat repairs, unplanned downtime, lost productivity, cut tires and rapid tread wear. Tires are an investment, especially in very rough environments, where users often have to scrap tires prior to complete wear life. In those instances, heavier duty tires should be considered. In almost all situations, it pays to invest in radial tires.
Equipment Productivity
The impact that a tire program has on equipment productivity is less visible than actual tire costs. However, a machine that runs more efficiently has a direct effect on a company’s profitability. By matching the right tread, rubber compound and air pressure to the job at hand, operators can often improve traction, gas mileage and up time on their machines–all of which improve productivity and widen profit margins.
Tire manufacturers are continually developing the latest technologies, including new tires and procedures, to help end users best manage all of the factors involved in tire performance.
Operator Productivity
The least visible impact that tires can have is found in the driver’s seat–the equipment operator. A more comfortable ride allows operators to work with more efficiency and confidence for longer periods of time. Tires that are designed for a specific machine in given work conditions, and that are properly inflated and maintained, can make a noticeable difference to the machine’s operator.
Safety
Safety is a direct result of best practices. The Michelin Earthmover group has published seven steps to promote tire safety:
1. Properly secure tires during storage, transporting and mounting to avoid falling or rolling.
2. Continually monitor and maintain inflation pressures to optimize performance in any given operating conditions.
3. Store tires away from bad weather or hydrocarbons that can degrade the rubber and increase the likelihood of tire failure.
4. Continually check the condition of the wheels and wheel equipment to make sure they are clean and corrosion free.
5. Keep a safe distance from tires during inflation.
6. Never weld near tires or apply heat to wheels, nuts or studs.
7. Always refer to technical documentation published by the manufacturer before working with any tire.
What is a Tire?
While all tires were similar a hundred years ago, today there are drastic differences, especially tires designed for extreme conditions, such as those found at a construction site, rock quarry or mining operation. Differences include factors like construction type (radial, bias-ply, solid), the size of the tire, tread patterns and tread depths, and the chemical makeup of the rubber components.
Tire Construction
In the 1940s, almost all construction, mining and quarry equipment ran on bias ply tires. A bias ply tire is made up of textile plies, usually nylon or rayon, crisscrossed on top of one another and bonded together by a rubber compound. This design is prone to damage from poor heat conduction and punctures. In addition, sidewall distortion can lead to uneven wear and reduced adhesion between plies.
In 1959, Michelin brought radial tire technology to the heavy equipment market. The biggest difference between a radial and a bias ply tire is that the sidewall of a radial is separate from the crown, allowing each component to work independently, and thereby enhance performance. In a Michelin radial tire, metallic casing plies hold the sidewall and the crown together and reinforce the strength of the tire. In addition, the metal allows for greater heat dispersion and impact resistance. Since the sidewalls can flex independently of the crown, a Michelin radial tire offers exceptional operator comfort without compromising stability.
To improve upon the radial design, modern Michelin radials incorporate a special butyl rubber layer that eliminates the need for a tube in the tire. Tubeless earthmoving tires provide several advantages by eliminating the risk of nipping of the inner tube and of trapped air between the tire and inner tube. In addition, when a puncture does occur, there is less likelihood of a sudden deflation due to a punctured tube. With a tubeless tire, air loss is slower, allowing an operator more time to reach the repair workshop.
Tire Size and Aspect Ratio
In the past five years, a new class of vehicle has emerged–the ultra-class haul truck. Some of these trucks can carry a payload as heavy as 400 tons–with the total vehicle weighing more than 700 tons. This has driven the development of a new class of tire. In 1998, Michelin introduced a new tire architecture–the 80 series mining tire, in which the height of the sidewall is 80 percent of the tire’s width. This wider tire made it possible to increase the load carried–and allowed truck manufacturers to develop the ultra-class haul truck. Currently the largest Michelin 80 series tire stands more than 13-feet tall and can carry 99-metric tons.
Tread Pattern and Depth
Every worksite is different–with unique demands and conditions that must be addressed. The tread pattern and depth of a tire determine how it will interact with the landscape. These can influence how much traction and adherence a tire can have along with how much resistance to damage the tire can have.
Rubber Compounds
Another element of a tire is the chemical makeup of the rubber compounds. Similar to tread pattern and depth, the selection of rubber compound is determined by the application and worksite conditions. Softer compounds are usually used where vehicles need to move faster for longer periods of time on well-maintained roads. Harder compounds are used in extreme conditions where cuts, abrasions and tears are more of a concern. Michelin uses up to six different rubber compounds to develop tires that meet specific needs.
Tire Maintenance
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