New era of mine haul truck giants

Diesel Progress North American Edition, March, 1999 by Mike Mercer

Haul truck capacity breaks through 300.ton mark; are 400-, 450, or even 500-ton trucks just around the corner?

"Too much is never enough" is a phrase that fits the rigid frame mine haul truck market. Over the last 30 years, haul truck size has grown remarkably and as the trucks have grown, the development time between each new generation of giants has shortened.

The newest vehicles, haul trucks in the 320- to 360-ton capacity range, are clearly the new benchmark, which begs the question: are 400-, 450- or even 500-ton monsters around the corner?

While no manufacturer appears willing to go that far, most agree that, based on past experience, it is plausible that such trucks may eventually be seen rumbling around mine sites, given some advances in the technology of tires, engines and drivetrains.

"Manufacturers cannot build larger capacity trucks just for the sake of building a larger truck," said Glen Carlson, senior product specialist at Komatsu Mining Systems. "The end goal is always a higher efficiency more economical truck."

The beginning of the dramatic growth spurt in haul trucks began in the mid-1960s. Prior to that, mechanical drive trucks were the standard and they grew appreciably from 27 to 35 tons in the 1950s to 60 to 70 tons by the end of the decade.

But in the '60s came d.c. diesel electric drives, a technology borrowed from locomotive markets, and truck size, which grew incrementally before then, began to advance in leaps and bounds, from 85 tons to 200 tons and more by the end of the 1970s. By the mid-1980s, 240-ton haul trucks were the standard. Mechanical drive configurations also grew, mirroring their electric drive counterparts.

As early as 1973 Terex developed a three-axle, 350-ton hauler, but the drivetrain and tire technology didn't allow it to operate effectively and economically, rendering it an interesting aberration.

Until 1996, that is, when Komatsu Mining Systems introduced the Haulpak 930E, a 320-ton a.c. electric drive truck. More recently, Liebherr has introduced its T282, 360-ton diesel a.c. electric truck (see story elsewhere in this issue). In addition Caterpillar has unveiled its latest entry in to the haul truck market, the mechanical drive 797 haul truck, which has a rated capacity of 360 tons and later this year, Terex Mining Systems will introduce a 340-ton truck, the MT5500.

Mine superintendents are always looking to lower the cost per ton equation. To be financially successful, a mine must move a high volume of material at low cost. Several factors affect cost per ton, only one of which is the haul track. Other costs that are factored in include fuel, tires, maintenance and operators.

Considering that most mines are year-round operations, with machines running as much as 23 hours a day, it's easy to see how reducing the cost per ton can yield significant financial dividends.

As a result, Komatsu found significant interest in its 930E truck, which went into production in June of 1997. "To date, we have over 100 units of the 930E operating in the field," said Carlson. Komatsu's haul truck line incorporates six models, two mechanical drive units and four diesel electrics, including the 930E.

The 930E truck is powered by a MTU/DDC 16V-4000 diesel rated 2700 brake hp at 1900 rpm. The engine drives a GE GTA-34 alternator with integral 2500 cfm cooling fan. The alternator provides power to the GD 85 electric traction wheel motors. According to Komatsu, wheel motor application depends upon gross vehicle weight, haul road grade, haul road length, rolling resistance and other parameters that must be analyzed for each individual application.

There are several design challenges to manufacturing larger trucks, Carlson said, including engine horsepower that fits into truck's envelope, finding tires that are matched to the vehicle's intended use and terrain and an efficient drive system.

Another consideration is, while somewhat mundane, important nonetheless: shipping the truck to the customer. When dealing with vehicles and components of this size, the ability to deliver them to a customer is important. In Komatsu's case, it means shipping from its Peoria, Ill., facilities to mines in the far-flung reaches of South America, Indonesia, Canada and the U.S. "From day one of the design process, the shipping envelope was a consideration," said Carlson. "As a manufacturer we have to consider the cost of shipping and assembling a truck on site.

"In the end however, a mine has to recognize if a larger truck is compatible with its infrastructure," continued Carlson. "Any new truck must be an improvement over its predecessor in terms of reliability, production efficiency and economics."

Changes in tire technology have also been one of many key factors in the emergence of the new generation of haul trucks. Tires have increased in size over the years as the trucks themselves have grown, but there is a limit to how big a tire can be in order for it to be shipped to the manufacturer or user.

"There are certain rates for shipping the fires and obviously as tire size increases, shipping costs go up," said Vickie L. Johnson, Michelin's marketing manager for North American earthmover tires. "Figuring into that cost are the special hauling permits required for transporting the tires over public roads. Along with the economic costs, there is also a point where the tires are just physically too large to ship.