Cat 627G push-pull scrapers

By: Geoff Ashcroft, Photography by: Geoff Ashcroft


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Motor scrapers continue to be the most cost-effective means of moving muck – but if you really want to make the dirt fly, your scraper needs to have two engines. We look at Cat’s push-pull system using a pair of twin-engined 627Gs.

  • Can move a lot of load in a short time
  • Plenty of power
  • Cost-effective working
  • Work in less favourable conditions
  • Solid construction

As well as being effective, the push-pull system is one of the most logistically simple to operate. It's essentially a two-man team that fills, hauls, empties and returns to the cut together. It relies on having two sharp operators capable of linking two machines nose-to-tail at full-throttle.

Engine and power

Cat offers single-engined scrapers with an auger or integral elevator - and both these versions can self-load.

But single-engined open bowl scrapers need a helping hand to maximise output potential, and a D8-sezed dozer or maybe larger, is enough to drastically reduce filling times in the cut.

If you're on shallow gradients of up to 7% with low rolling resistance and good under-foot conditions, they'll be working efficiently with just the one engine. But slopes much steeper than this and optimum hauling speeds drop while muck shifting costs go up.

It's at this point, that you really need two engines.

The twin-engined scraper gets a leading power plant that drives the front axle and also powers the machine's steering and hydraulic systems. The second engine - located in the tail - is the less powerful package, only driving the back wheels.

Bringing two engines into play gives you a four-wheel drive machine that can handle much higher rolling resistances, poorer underfoot conditions and far steeper gradients.

So why not use the same engine at both ends?

It's a pivot steer machine, so too much grunt pushing from the back would soon have the front-end out of control. Cat says you only need full power from the rear engine to give extra performance in the cut - but it's also helpful to reach top speeds sooner when sprinting out of the cut and charging down the haul road.

There are two throttle pedals in the cab, so a bit of "heel and toe" can be used to apply more or less power to the axle that needs it.

These machines can also be push-loaded, which increases flexibility when working as part of a mixed scraper fleet. The use of a push-pull attachment allows machines like these to work in pairs, joining nose-to-tail through the cut to apply the combined power of all four engines onto one cutting edge at a time.

Performance and handling

Buried in the nose is a 15-litre straight-six turbocharged and intercooled diesel engine. It's Cat's electronically managed C15 engine with Acert technology that pumps out 365hp.

In the tail is a smaller, lighter, nine-litre C9 engine. It's another six-pot, but supplies just 266hp to the back wheels through a four-speed powershift transmission.

Cat's push-pull attachment sees a hydraulically raised and lowered bail bar on the front of each scraper. It's a solid cast iron loop, beneath which is a spring-loaded cushion plate.
At the rear, there's a huge hook above the rear push-block. Above the rear hook is a heavy frame that protects the radiator of the rear engine.

In practice, the first scraper draws into the cut and starts to load itself, while the following machine slides up behind and drops its bail bar over the hook to couple up on the move. The second scraper then starts to push the first one, using its cushion plate, and speeding up the loading cycle.

As the first scraper's bowl is filled and raised clear of the ground, the following machine lowers its bowl to join the cut where the first one left off. The first scraper then uses its total laden weight to pull the one behind, using the bail bar and hook.

When both are full, the second machine raises its bail bar and uncouples, allowing both outfits to head down the haul road to the dump site.

The result is phenomenal muck shifting performance, and combined effort from both machines eliminates the need for a dozer at the cut area. When linked together, and putting all available horsepower through one cutting edge, both scrapers can be loaded in about 45 seconds.

But these machines can be used gently, and with a fair degree of finesse, to level and tidy the ground too. By raising the apron and bringing the ejector plate to the front of the bowl, the cutting edge can be used as a blade, skimming and trimming the surface.

Instrumentation

The arrival of clever electronic management systems for the engines and drive trains means there's just one gear selector lever.

There's one steering wheel, one multi-function joystick controller and one diff-lock button that engages both axle locks - though it's replicated in two places on the floor, to give choice of left or right-foot operation depending on how you've got the seat positioned. But there are two foot operated throttles.

The right-hand throttle pedal controls the front engine, and there's a button on the main console that needs to be pressed to start engine number two.

The multi-function joystick opens and closes the front apron to determine soil flow into the bowl, raises and lowers the cutting height of the bowl, and offers progressive control of the ejector plate for unloading.

In addition, there are two thumb-operated buttons on the face of the joystick. These are used to lock the transmission in gear to help with maintaining loading and unloading speeds and prevent unwanted gear changes from the 627G's eight-speed powershift box, and the second button brings the cushion hitch into play.

The cushion hitch is a shock absorption system that is incorporated into a parallelogram-type linkage, which nestles in the gooseneck - the latter connects the two halves of the scraper together and creates the pivot steering system that gives this 15m long brute the ability to turn on itself.

On full-lock - either left or right - it is possible to almost tuck the front wheels underneath the neck for immense manoeuvrability.

See a range of scrapers for sale.

Read in-depth machinery reviews in the latest issue of Deals On Wheels magazine, on sale now.

 

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