Artic ejector trucks for the tough going

In tough conditions, nothing beats an articulated dump truck for hauling. Well, almost nothing. In some situations, an articulated ejector truck beats a standard articulated truck hands down.

The Caterpillar 730 model and 740 model ejector trucks are based on the equivalent models of the standard Cat articulated truck range. However, as Perth-based Ertech Pty Ltd has discovered, the ejectors offer even greater versatility and, in many of Ertech?s operations, the ejectors have become the company?s trucks of first choice.

Ertech is an engineering contracting and project management group; its annual turnover exceeds $200 million and its contracts include everything from roadwork to mines tailing dam construction.

Currently, the company has quite a few Cat articulated trucks in its fleet, including standard articulated units, six Cat 740 ejectors and another two ejectors on order, so company staff are well placed to know which truck suits which application best.

According to Stephen Eardley, the company?s construction manager, in many instances the Cat ejector trucks have a distinct advantage.

?An ejector truck allows us to dump material on the run, and in the right situation that can save us 20 to 30 seconds per bank cubic metre,? said Mr Eardley. ?And that means we save on fuel as well as time,? he said.

Improved cycle times is one thing, but on ejectors the truck bodies effectively clean themselves during unloading, and that feature is important to Ertech for safety reasons.

?We often need to handle sticky clays,? Mr Eardley said. ?In a conventional articulated truck, with a hoisted body, that sort of material can really build up, to the point where its weight can affect the truck?s stability when unloading.?

With an ejector truck, the load is dumped from the rear without raising the body, so the truck can work safely on inclines, side slopes and in very soft conditions. The truck also comes into its own on sites where overhead obstacles such as conveyors, hoppers, power lines or bridges would interfere with dumping from hoisted truck bodies.

Another benefit of the ejectors? self-cleaning feature is that virtually no carry-back occurs from one load cycle to the next, so payload and productivity are maximised while fuel consumption and the cost per tonne are kept to a minimum.

Ertech currently has Caterpillar 740 articulated ejector trucks working at BHP Billiton?s Ravensthorpe and Xstrata?s Sinclair nickel projects in Western Australia, and BHP Billiton?s copper-uranium Olympic Dam mine in South Australia.

Mr Eardley said that the trucks are especially useful for Ertech?s construction of the mine tailings dams. Often the clay in the lining wall of a dam is just three or four metres thick – too narrow for a dozer to run behind a truck spreading and compacting the material as it is dumped. With the ejector truck, the material can be run in, in a consistent lift thickness as the truck moves along the wall alignment, eliminating the need for further spreading prior to compaction with a roller or grader.

Ertech is also finding the Cat ejectors perfect for placing base course rock in road construction. On many sites, the trucks placing base course are not allowed to run directly on the subgrade.

However, with an ejector truck this is not an issue. A truck can be reversed along the road formation, discharging an even layer of material onto the subgrade before the wheels pass over it.

Caterpillar articulated ejector trucks are available in two models: the 730 model with a 28.1 tonne payload and the 740 model with a 38 tonne payload.

The bodies of Caterpillar ejectors are designed to be exceptionally durable. The body base and sides are made from thick, high-yield, hardened steel and the ejector top rails are made from high-strength alloy steel. For optimum durability and wear life, the ejector body is designed to work in applications where any rocks carried are smaller than 150mm in diameter.

The ejector blade is made from high-strength steel and uses technology similar to that proven in Cat wheel tractor-scrapers. A three-stage, high-speed, double-acting cylinder operates the blade. The cylinder is specifically designed for horizontal mounting and smooth load ejection. It is centrally supported and nitride-hardened to ensure a long service life.

Typical eject and retract times on the 730 model are 12 seconds and 15 seconds respectively. On the 740 model the same times are 14 seconds and 24 seconds. A load can be ejected on the move or statically.

The 730 and 740 are fitted with the wellproven Cat C11 ACERT and C15 ACERT engines respectively, to meet EPA Tier 3 and EU Stage IIIa engine exhaust emission regulations.

Both models have electronically controlled transmissions designed specifically for articulated truck applications and feature anti-hunt strategy for speed continuity. Other drivetrain features include:
? Controlled throttle shifting, which significantly reduces power train stress and clutch wear by controlling engine speed, torque converter lock-up and transmission clutch engagements.
? Engine overspeed inhibitor, which shifts the transmission up one gear at specified revs. If the transmission is in its highest gear, torque converter lock-up disengages.
? Directional shift management, which regulates engine speed to prevent damage caused by high-speed directional changes.
? On-the-move inter-axle and cross-axle differential lock system, with fast engagement and disengagement.
? Optimum tractor trailer torque distribution, for better traction in poor ground.
The larger 740 model has a Caterpillar engine compression brake for increased braking on downhill grades. It has very fast response time and produces no additional heat, so it can be used continuously.

For fast and convenient servicing, the lubrication and service points are all grouped, and the front-hinged hood is raised electrically for safe and easy no-tools access to the engine compartment.

To lower maintenance costs and downtime, Cat ejectors have long engine oil change and hydraulic oil change intervals, extended life coolant and adjustment-free wheel bearings.

The cabin of a Cat ejector is centrally mounted. It provides a spacious and quiet work environment with exceptional all-around viewing through a curved, one-piece, fully wiped windshield. An adjustable Cat comfort air suspension seat, easy-to-read instruments, ergonomically placed controls and an electronic monitoring system further enhance operator comfort and productivity. A full-size training seat is also included.

Source: Caterpillar Australia

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