Productivity Guide: Hydraulic excavators >25 to 30 metric tons
| June 12, 2007 |
There are no hard-and-fast acquisition rules for excavators, but if you’re a contractor in North America, odds are you cut your business teeth on machines in the 12- to 24-metric-ton classes. Once your business is established and growing, it’s likely you’ll begin to take on larger jobs or perhaps move into new applications that require excavators with a bit more oomph. If that’s the case, then machines in the 29-to 46-metric-ton range are the logical size extension for the excavators in your fleet. These machines are typically classified as “medium” size excavators by North American OEMs.
Machines in the >25-to 30-metric-ton class are on the heavy end of this category, making them an ideal fit for contractors who need an extra edge in horsepower and lifting ability, says Peter Robson product marketing manager, Komatsu. “In addition to increased lift capacity or bucket digging forces, excavators in this size class are highly maneuverable for their size,” he explains. “They’re also relatively easy to transport in most areas of the United States. Some regions now have a 70,000- or 80,000-pound weight limit – you’re still ok moving these machines on a regular lowboy trailer, but you will probably need to obtain a width permit since they’re over the 8-foot, 6-inch limit.”
Four to five passes is optimal production in truck-loading applications.
Onboard ECMs simplify operator tasks and machine capabilities
Excavators in this class are typically used in heavy construction applications such as site development, road building and underground utilities work. “These excavators will use a large variety of bucket types and sizes, dependant on what the contractor’s particular application is,” says Jason Bowers, product manager, Caterpillar. “Most models in this class will be spec’d with buckets ranging from 0.9- to 3-yard capacities, depending on how the machine is configured. The most popular buckets we see are from 42 to 54 inches wide and have capacities around 2 yards.”
Bowers also notes attachment use remains strong with excavators in this class, with the most commonly used units being hammers, vibratory plate compactors and hydraulic thumbs. To assist in efficient attachment use, Bowers says that you can spec hydraulic quick couplers and various attachment control systems to ensure easy change-outs and optimal performance. “Caterpillar offers a factory-installed hydraulic quick coupler, which allows you to change buckets or tools quickly without having to exit the cab,” he notes. “Our Tool Control System is also optional. It’s designed for contractors using multiple hydro-mechanical attachments and allows up to five different attachments to be programmed into the machine via the in-cab monitor. The system remembers each attachment’s hydraulic flows and pressures and automatically adjusts machine performance to meet that tool’s requirements when it’s installed on the machine.”
Case has also incorporated electronic systems into its excavators in this class. “Our on-board ECM records real-time operating information that gives contractors an easy way to track the machine’s productivity,” says David Wolf, marketing manager, Case Construction Equipment. “You can quickly learn how many hours the machine was operated in specific modes, how long it has been idling and how many times it has gone over relief.”
Wolf says this information can be broken down to determine where productivity lapses are occurring. “If the machine’s going over relief fairly often, then a different bucket might penetrate the soil better and ease that additional strain on the excavator,” he notes. “If the controller tells you the machine is sitting idle too long, you can examine its support equipment to see if you’re staging trucks correctly, for example. Or perhaps the excavator is filling trucks that take dirt to dozers spreading the material out. Maybe there’s a problem with a haul route or the dozers aren’t working at optimal speed. So there’s a lot of information available at your fingertips to help you fine tune not just your excavator operations but many different aspects of your business as well.”
Material density the no. 1 criterion for bucket selection
Standard rules of gauging productivity with excavators in the >25- to 30-metric-tons class depends heavily on the application at hand. Mike Boyle, product manager, John Deere Construction Machinery, suggests tracking the number of feet of pipe in the ground per day in utility/underground applications. “Truck loading – which is how many of the excavators in this class are used – can be tracked by several methods,” he explains. “You can simply tally the number of trucks loaded per day, or dig a little deeper and track the number of yards of dirt moved per gallon of fuel burned by the excavator.”
Regardless of the method selected, Boyle stresses it’s important to analyze each job to determine its low-versus-high-production scenarios. “You need to examine its location and terrain,” he adds, “and plan how you’re going to organize the jobsite.” But if you’re not meeting your pre-set goals, don’t be afraid to change machines, personnel, or working procedures. “Many times the problem is something simple,” he notes. “Maybe blading your haul road lead would to faster truck cycle times, or perhaps the trucks aren’t properly positioned for speedy loading by the excavator.”
“These machines work well with all on-highway dump trucks,” says Robson. “In most cases the only real production question you’ll face is how many passes you want to make to load a dump bed.”
If you’re consistently truck loading – say for a week at a stretch – Robson says you need to make certain your bucket selection is made with material density foremost in mind. “That’s the easiest way to ensure you’re loading trucks in a minimal amount of time,” he says. “If you’re trying to load trucks with a 24-inch bucket and light material, you’re going to lose money. That’s why I always tell contractors it’s a good idea to have two or three different size buckets on hand when you’re operating excavators in this size class. These extra buckets allow you to meet a variety of jobsite and soil conditions and remain productive regardless.”
Four to five passes is the optimal number for loading a Class 8 dump efficiently, says Brian Black, North American product manager, Terex. “Any fewer or more are inefficient,” he adds. “Fewer passes means you’re overtaxing the machine. Any more and you’re wasting fuel and time – probably due to a bucket that’s too small for the task.”
There are intangibles Black says you must monitor as well to ensure efficient excavator operations. “An operator’s confidence and ability to get the most out of each machine can pay huge dividends in productivity,” Black notes. “Make sure your operators understand the versatility and key performance features and capabilities of the machine. But be aware all machines are different and operator overconfidence can result in increased maintenance costs and accidents. Routinely exceeding machine performance limits invariably leads to premature wear and eventual component failures.”
OEMs report the most popular buckets for machines in this class are typically from 42 to 54 inches wide and have 2 yard capacities.
Proper use in digging applications ensures boom and stick life
Once you’re in the dirt, following established operational procedures can pay dividends in meeting deadlines and extending the excavator’s working life. Regardless of what type of attachment you’re putting on an excavator, be sure to properly match its size to the machine you’re running, cautions Wolf. “You don’t want to have too large a bucket on a long arm or a coupler with too large an attachment – both cases put too much weight too far out on the machine. You’ll lose productivity, and the further you get out with the extra weight will make the excavator more tippy.”
When excavating, don’t dig over the machine’s final drives. “You should always dig over the idler end of the final drive,” Robson cautions. “Otherwise a lot of the shock loads generated by the digging process can be passed through the tracks into the final drives and damage them.”
Corner loading the excavator’s boom and arm – using the bucket as a pry to pull an object out of the ground, is also a bad idea. “An operator would be better off breaking up the object with a hammer attachment rather than using the bucket as a pry,” Wolf explains. “Use the bucket to pry objects loose generates twisting motions on the boom and arm. In turn, these motions place lateral stress loads on these structures that they are not designed to withstand. Using the bucket as a pry will come back to haunt you in the form of stress cracks and premature structural failure.”
There’s a prying variation that Wolf often sees and warns against as well. This time it’s operators who extend the excavator’s boom and arm all the way out, hook the bucket onto an object and then try to pull it out of the ground by reversing the tracks. “This is bad for a machine all the way around,” Wolf says. “It places an incredible amount of stress on the excavator’s frame and final drives – and way too much stress on the boom and arm.”
Cat’s Bowers says it’s not common to see operators boom down with a bucket to drive an object into the ground, but it does happen and it’s never good for the boom, stick or the bucket. “I sometimes see operators using the swing function and bucket to demolish buildings, trees or other structures,” he adds. “These actions seriously damage the longevity not just of the excavator’s digging geometry, but of the machine in general.”
As a basic rule of thumb, it’s best to remember that an excavator’s boom and stick are set up to dig in a straight line, Wolf adds. “Any other type of motion is detrimental.”
What if you suspect there has been damage to your excavator’s boom or arm? Paint cracks along weld lines are a sure indicator of metal fatigue. “Inspection of high-risk/high-stress areas on your excavator should be part of your regular maintenance process,” Robson says. “It’s an easy way to look for early signs of fatigue. If you find evidence of metal stress at an early stage, the problem can easily be rectified. But if you wait a month – or two – the fatigue gets worse and eventually you end up with a catastrophic failure. So I’d recommend taking a close look over the arm and boom structures to look for paint cracks at least once a week.”
When spec’ing tracks, go as narrow as possible
Selecting the proper style and width tracks for your excavator is another way to ensure a productive, profitable machine for your business. There are typically two to three different track widths offered for excavators in this class. Generally speaking, you should always spec the narrowest track you feel the machine can get by with.
There are several reasons for choosing narrower tracks whenever possible. The first is cost: Narrower tracks simply cost less than wider versions – and are cheaper to replace over the life of the machine. Then there are transportation concerns. Wider tracks can be the difference between hauling the excavator without a special permit on a standard lowboy trailer or having to obtain special transport permits and specialized equipment to move the machine.
“You’re going to have better turning capabilities with a narrower track because you don’t have as wide a footprint,” adds Reece Norwood, product manager, Kobelco North America. “And a narrow track places reduced power requirements on the excavator’s final drives. This is simple physics: There is less mass the engine has to move and that puts less strain on the powertrain as a whole.”
Finally, Norwood says, a narrower track is better in rock or jagged material because it will track better over this type of terrain and you won’t have any flexing when the track is on uneven footing.
Despite the numerous advantages narrow tracks have, there are valid reasons to spec wider excavator tracks. Although wider tracks increase a machine’s overall weight, they also slightly reduce the machine’s overall ground pressure. This will give you better flotation, a definite plus when working in sloppy or sensitive ground conditions. Wider tracks also give you a more stable machine if you have to do a lot of lifting over the track.
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