Excavators: Brain, Brawn & Power
By David GodkinEquipment
Designing excavators is a balancing act
They’re big. They’re powerful. They’re smarter than ever. How to manage all the brawn and brainpower in a large construction excavator continues to challenge equipment manufacturers. And it’s not all just about engines and hydraulics.
Product manager Joel Escalante pulls no punches when talking about Volvo’s EC480 excavator in road construction, mass earth movement or demolition. He thinks his machine is at the top of the list for strength and durability – not just because engineers have focused on the gauge or quality of steel used in the machine, but “putting the steel where it counts.” For instance, Volvo places more steel at the lower frames of the 480’s car body and front idlers, which Escalante tells us increases the machine’s robustness and lowers its centre of gravity for greater stability.
“(Other machines) can lift more along the crawler frame, but when they swing, they get into trouble. In our machine, because we put the steel down at the bottom, it allows the operator to carry the weight across 360 degrees without any problems,” says Escalante.
Equally important is increasing robustness along the boom and arm. “It’s not by welding plates around it like our competitors do, but by increasing the thickness of steel at special areas, such as the end of the boom where the arm connects to the boom and where the boom connects to the mainframe on the machine.” But don’t you risk making it too heavy? Good question, Escalante observes.
“The engineering balances the harmonics of the motion of that attachment so that it doesn’t affect the functioning of the operator as he’s digging. The attachment doesn’t offset the way the machine moves by my making it tippy, for example,” he says.
Machine longevity, meantime, is enhanced with a cab made of high-gauge extruded steel pillars instead of welded steel and at the front end where the frame is plugged to prevent ingress of dirt. “We pay attention to detail,” says Escalante, pointing to caulking at the welds around the inside of the EC480’s door frames to prevent water ingress and corrosion.
This is something overlooked in many other designs, Escalante says. “The difference between our machines and the competition is that our machine is built to live longer. It’s bullet-proof.”
The Volvo EC48OD features a Volvo D13-T4 (A) engine, breakout power of 310.6 kN, with up to 15 per cent increased boom down speed and two-pump flow for bucket in. It boasts an additional 196 mm of ground clearance and operating weights of 47.9 to 50.5 metric tons.
The undercarriage on Caterpillar’s 390FL “is heavy, it’s wide, very durable,” says Kent Pellegrini, product application specialist for Excavators at Cat. Ditto the Cat 374 and 390’s boom and stick, which have castings and forgings at high-stress areas including the boom nose, boom foot, boom cylinder and stick foot. While careful to guard some of the machine’s design secrets, Pellegrini cites the “underbelly wrap” which “in certain areas” of the machine is reinforced with welded side plate. This is designed to address swing inertia, “and that’s because we carry such a big bucket.”
“The higher capacity the bucket you carry, the more stress you’re going to put on the boom and stick. The swing inertia has an impact on boom life, not so much the operator digging,” says Pellegrini.
Hyundai takes a slightly different approach to ensure undercarriage durability, using low-stress, high-strength steel “integrally welded” to form a stronger, more durable upper and lower frame,” says Steve DePriest, sales product trainer for Hyundai Construction Equipment Americas. Hyundai also employs sealing and lubricating rollers and idlers in its R-series excavators for “a maintenance-free undercarriage.” Like other manufacturers, Hyundai mitigates enormous forces and wear at the centre joint using swing motors.
“Two motors working in unison prevent too much stress on a single motor,” DePriest explains.” Using two swing motors evens the weight pulling on the teeth.”
Any manufacturer worth its salt field tests all of this, running an excavator through its paces under different loads and working conditions. The bar has been raised even higher now that international Roll Over Protection Standards (ROPS) are a reality. Cat’s Pellegrini says earlier cabs had enormous aesthetic appeal, with “curved windows and siding to give it a more bubble-look appeal.” If all those lovely contours don’t hold up under a ROPS crush test, what does?
“A welded ROPS, very heavy…Our cabs are really built stout on all four posts. If something like a rock falls off a cliff onto the cab, that’s what’s needed.”
Volvo made a case for its heavy excavators’ ability to change from a low to high arm; this is due to the pin dimensions at the boom which allow change up to a shorter or longer arm to meet different applications. Other machines may “have to exchange the entire front, change the boom along with the arm, instead of the arm alone,” says Escalante.
For his part, Pellegrini says Cat had a good reason for abandoning that approach in favour of heavy-duty boom and arms. “That way we can cover a multitude of applications. When you have multiple boom and stick offerings, it can get really convoluted and a customer can get confused.”
The 90-tonne 390FL Cat Excavator features a 524 HP Cat C18 ACERT engine, with a net power rating of 391 kW, a maximum forward reach of 17,250 mm, maximum digging depth of 11,800 mm and maximum drawbar pull of 132,637 lb. It delivers significantly lower fuel consumption than the 390D model.
Just as important as horsepower is engine torque, i.e. delivering the highest torque at the lowest RPM so that you consume less fuel and increase the engine’s longevity. But that’s not all, says Pellegrini. You need to run higher engine horsepower, lower engine RPM, increase pump displacement and minimize production loss.
Another factor, DePriest adds, is how engine horsepower is used. Hyundai swears by the Eco standard and power settings on its excavators which “control the RPM so if full engine power is not needed, it can be turned down for the application.” Power boost is another standard feature on Hyundai 9-Series excavators, says DePriest, which provides 10 per cent additional hydraulic power to break out a load or start the lift, again, with more precise control.
“Improved pump flow control reduces flow when controls are not being used. In other words, it delivers power when and where it’s needed, which maximizes productivity while keeping fuel consumption low.”
The Hyundai 9 Series also includes as standard arm-in and boom-down flow regeneration, “and improved control-valve technology and auto boom swing priority,” he adds. “These make it easier for any operator to be more productive, whatever their application.”
The cab is very quiet. “Some seasoned operators say they miss louder operating noises because they use engine sound as a guide for operation,” says DePriest. “We actually hear some say that the machines are too quiet!”
DePriest believes operators will continue to be drawn by the ease of operation of its excavators.
As for all those buttons and switches the operator is facing, the R520LC-9A’s cluster monitor “is very intuitive – like a tablet computer – so we usually get high marks for ease of use,” says DePriest.
The Hyundai R520LC-9A has a 263-kW Tier 4 Interim Cummins QSX11.9 engine, maximum reach at ground level of 12.4 m, maximum digging depth of 7,590 mm, bucket breakout force of 253 kN and operating weight of 52 metric tons.
It’s a subject that too often overlooked: dust and vibration. “You touch a very sensitive point,” says Escalante. “Every component in a machine is vulnerable to dust. There is no electronic system out there that is bullet-proof.” For its part, Volvo seals all connectors and covers any harness entry way with panels across its entire heavy product line. “You seal them not only to avoid dust, but to avoid water.”
Heavy equipment sometimes finds itself in very harsh environments, according to Pellegrini. “Say, you go into an ammonium nitrate facility where you have a lot of airborne particles. Those are not only contaminants, they’re corrosive.” Fluid film to seal electronic components is the usual solution. “But if we have a customer that’s going into a facility like that, then we’ll seal it in the factory and protect the entire machine.”
In a 2013 study published at the Faculty of Mechanical Engineering in Poland, engineers discovered that vibration problems frequently occur in high-performance machines like bucket wheel excavators. The report concluded the reasons for this are “various and difficult to investigate… If undetected at the design stage, they can lead to serious problems in operation such as excessive vibration, cracks, deformations, wear and mechanical failure.”
Manufacturers continue to tackle the problem on the ground, and with success. Viscous rubber cab mounts on CAT’s 390FL dampen vibrations and sound levels for greater operator comfort while thick steel tubing along the bottom reduces vibration and fatigue. Hyundai performs thousands of hours of endurance testing on its machines to reduce dust and vibration under “extreme temperatures and cycles,” says DePriest.
The bottom line is that engineers have provided cab operators with a great place to work – auto climate cabs that are comfortable summer and winter. “It keeps it kind of like your house,” says Pellegrini. “You set the thermostat” and the automatic climate controls look after the rest. The air cooled and air heated seats don’t hurt either, he adds.
David Godkin is a B.C.-based freelance writer and editor