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CASE STUDY: HITACHI TRUCK

Dump truck manufacturer switches from aluminum bronze to ToughMet® for kingpin bushings and gains threefold increase in service life.

Some of the world's largest mobile machinery is used in surface mining. Dump trucks, for example, can be bigger than a house, weigh around 180 tons and carry a payload of 250 tons or more. Needless to say, engineered components in these trucks have to be extremely rugged to withstand the high loads and harsh environments encountered. Furthermore, maintenance is difficult on such large equipment and downtime is extremely costly. As a result, reliabilty and long service intervals are critical to productivity and the customer's bottom line.

Hitachi Truck manufactures a range of dump trucks, the most recent being the EH5000 model. An area of dump truck design that has traditionally been problematic is the upper and lower kingpin spindle bushings on the front suspension. These bushings can wear, leading to slackness in the steering and, ultimately, damage to other components. Replacing these bushings is not a simple matter, especially if the repair must be carried out in the field.

The Challenge
Hitachi Truck was using a lubricated steel bushing on a steel kingpin, but if the lubrication became marginal, the resulting steel-on-steel arrangement would begin to gall. A change to aluminum bronze overcame the galling problems, but these bearings suffered from high wear rates. Brush Wellman's ToughMet, a pinodal alloy of copper, nickel and tin, was directly substituted for aluminum bronze in the bushings with no additional modifications required.

The result of switching to ToughMet
Extensive testing was done on a test rig built by Hitachi Truck that replicated one side of the front suspensions of a large dump truck. Using this rig, field conditions were simulated and bushing life predicted., Remarkably, the test showed that ToughMet exhibited one-third the wear rate of aluminum bronze, which translated directly to a three-fold increase in the service interval of the vehicle. Additionally, Hitachi Truck found no overall cost premium for this substituition. In, fact, the company is realizing specific competitive advantages as a result, including improved supply chain management, shorter lead times and the aability to maintain lower inventories.

Mac Knight, the Senior Design Engineer at Hitachi Truck, says, "The combination of the excellent bearing properties of ToughMet and the way in which Brush Wellman is prepared to deliver the sizes and quantities we need when we need them, means that we are far better off with ToughMet than we were with aluminum bronze. Our cusotmers also appreciate the extended service intervals because downtime on dump trucks is hugely expensive for mine operators."

Today, ToughMet is specified as kingpin bushings on every EH5000 as well as the new 4500s (280 ton) and the 700 through 1100 series (36-66 tons).

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