Kennecott Utah Copper's Bingham Canyon mine, just outside Salt Lake City, is the world's largest man-made excavation—2½ miles across and ¾ of a mile deep. So, if you're the Goodyear Tire & Rubber Co., and you want to make a really big product announcement to the mining industry, what more appropriate place than Bingham Canyon? Thus, on a sun-baked day in late July, Goodyear's off-the-road tire folks took customers, dealers and equipment makers into the mine to see the new product, which the company considers as revolutionary as its first radial tire.
Six of the "new products" were installed on a 240-ton haul truck and looked nearly like those enormous 12-foot-diameter tires that Kennecott uses on its mining trucks. But, said Goodyear, despite appearances, the new product being announced is not a tire. It is, instead, a Two-Piece Assembly (TPA). And, sure enough, on closer examination, the TPA did have a slightly different look than a conventional mining tire, with a large tread-shoulder that formed a precise, circular seam just where it intersected the sidewall.
The "two pieces" of the TPA are its casing and its tread belt. The casing is constructed much like a big, beefy mining tire, except that its outer diameter, instead of carrying a thick band of tread, is a smooth surface into which are molded ½-inch-deep circumferential grooves, each several inches wide.
The TPA's second component, the tread belt, is just that, an approximately 8-inch-thick belt of specially compounded rubber that has a deep, mining-tire-like tread molded into its outer surface. But molded into the tread belt's inner surface are ribs that fit exactly into the grooves of the casing's outer diameter. Slip the tread belt over the casing, allowing the ribs and grooves to engage, inflate the casing to lock the two components together, and the new 45R57 TPA is ready to roll under a mining truck.
After three years of testing 51-inch-rim-size TPAs, Goodyear is convinced that the interface of the two components, casing and tread belt, works flawlessly.
We asked global sales and marketing manager, Steve Bausch, if Goodyear makes stringent demands about maintaining air pressure to keep the two pieces locked together. Nothing out of the ordinary, he said. Just monitor pressure as with a conventional tire to ensure optimum performance and life. During testing, says Bausch, TPAs were run with pressures far lower than tires would ever be allowed to operate in a mine, and the integrity of the interface was unaffected.
Because the tread belt and casing don't form an integral assembly, says Goodyear, cracks in the tread belt can't migrate into the casing, nor can air migrate from the casing into the belt package. And, says the company, less heat is transferred from the tread belt into the casing, compared to conventional tires, potentially allowing faster speeds and heavier loads.
According to Goodyear's Perry Martenny, who has a Ph.D. in polymer physics, the new TPA is "more radial than a radial." Its simple design, he says, prevents outside-diameter growth and provides an 11-percent greater footprint than conventional 57-inch tires. The result, says Martenny, is more uniform pressure distribution and, subsequently, greater traction and flotation.
Tom Walker, general manager of Goodyear's off-the-road tire group, makes the point that the TPA also offers tread-design flexibility. If a mine goes from dry, hard conditions in the summer, to wet and soft in the winter, he says, the TPA's tread belt can be swapped to optimize the tread pattern for specific conditions.
Also, says Walker, if the tread belt sustains a mortal wound from a sharp rock or railroad spike, the entire assembly need not be discarded, as might be required with a conventional tire. In this instance, he says, replacing just the tread belt (in a fraction of the time required for replacing a conventional tire) restores the assembly. And if the sidewall is damaged beyond repair, then the tread belt can be removed and reused, conserving resources.
Yet another significant advantage of the TPA concept, says Walker, is easier storage and shipping, always a problem with conventional 45R57 tires. For shipping and storage, the tread belt can be folded and the casing deflated.
So, how much will this innovation cost you? Goodyear hedges on specifics, but seems anxious to help mines perform head-to-head comparisons that analyze overall costs between conventional tires and the TPA.