Busting up reinforced concrete or hard rock is a pretty straightforward demolition application. If you’re tasked with concrete or rock removal on your jobsite, hammers and breakers in the 5,000- to 7,000-pound classes are the ideal attachment choice, particularly if you use excavators between 25 and 45 metric tons.
Hammer and breaker attachments are built tough to withstand their grueling work. But there is almost no application-driven variation in these classes. Any hammer spec’d in the 5,000- to 7,000-pound classes will be suitable for heavy rock and concrete demolition.
Beyond that, specific application requirements can be addressed with some variations in a hammer’s configuration, says Tom Witt, sales manager, BTI. “Box type (enclosed) hammer housings with narrow frontheads are an advantage in trenching and other close-quarter applications,” he notes. “And if you’re regularly working in abusive or abrasive conditions, it’s a good idea to spec a hammer with extra protection for the front head area of the breaker, where the hammer’s chisel is mounted. Extra front head protection can reduce hammer wear and maintenance, and extend its overall service life.”
Another spec’ing possibility is rock hooks, particularly when breaking boulders, according to Al Springer, national sales manager, Allied Construction Products. “Rock hooks welded to the bottom of a hammer’s housing make the operator more productive and protect its front head.”
Springer explains that boulders are rarely positioned so an operator can effectively place the hammer and begin breaking. “Rock hooks allow you to roll a boulder or turn it to the optimum breaking position,” he says. “They also allow you to use the hammer to rake boulders out of a pile without risking damage to the attachment. And they can easily be hard-faced or replaced when they wear.”
Two basic hammer types dominate North American market
Although exterior hammer variations are relatively minor, there are a couple of significant design differences found internally. There are two distinctly different styles of actuating hammers in these classes: gas-assisted and fully hydraulic operation. Gas-assist hammers use a gas-filled chamber that is compressed by the piston and acts a spring to drive the piston home. Although they also contain nitrogen chambers, fully hydraulic hammers use only hydraulic oil acting directly on the piston for initiating impact blows.
“Hydraulic oil is the primary mechanism for generating impact energy in our hammers,” explains John Knott, hydraulic products specialist, Atlas-Copco. “Nitrogen gas is contained in a diaphragm type accumulator that helps to maintain hydraulic pressure through the impact stroke and reduce hydraulic pulsations to the carrier. Nitrogen gas does not act directly on the piston.”
Proponents of nitrogen-charged hammers say the spring-like, downward force generated by the gas allows their chisels to hit harder than those on hydraulically operated units, letting them break rock or concrete more effectively. Manufacturers who market hydraulically actuated hammers say their designs are simpler, and more durable and reliable over the long haul since there is less chance of nitrogen loss.
Match numbers for effective hammer performance
While hammers in these classes are designed for use on one type of machine – excavators – they still must be able to work with any manufacturer’s model, as well as on machines of different sizes. All hammers require that the host excavator have an auxiliary hydraulic system on board, often referred to as the extra, or third-spool hydraulic valve.
“Before a hammer is installed, you need to run a flow test on the excavator,” says Charles Corriher, president, Construction Attachments. “A flow meter will accurately tell you the machine’s hydraulic pressures and flow rates. That will give you a realistic picture of how that machine is performing, and enable you to make an informed decision when you’re spec’ing a hammer.”
In fact, Corriher says, even if you’re already running hammers on your excavators, it’s a good idea to periodically run a flow meter test. “Again, you can verify that your excavator’s hydraulic system is performing at peak pressures and flows,” he says. “I would recommend doing these tests at least once per work season to make sure you’re getting the best possible performance from your hammer.”
“If you’re using excavators 25 metric tons and up, there’s usually adequate hydraulic and lift capacity to run and carry these hammers,” Knott says. “In many cases, spec’ing a hammer is a simple matter of making sure its flow and pressure requirements match those put out by your excavator. Remember that for peak performance, you want to try and run a hammer as close to its maximum flow rate as possible. They’re designed to run at full power without harming their internal components.”
Correctly plumbing and mounting a breaker cannot be overemphasized, Corriher says. “An improperly plumbed excavator will cause several problems,” he notes. “It can create overheating of the hydraulic system and it will cause downtime if the hoses are not adequately attached to the excavator. You also need to decide if you want the unit’s mounting bracket to be used in conjunction with a quick coupler. In either case, you need to ensure that the hammer is mounted correctly. A poorly mounted hammer will not perform well and becomes a safety issue to boot.”
Another important factor to consider, according to Ryan Murphy, product manager, Indeco, is whether or not you intend to use other attachments besides a hammer or breaker. “A hammer requires only single direction flow of auxiliary hydraulics – oil in and oil out in one direction,” he says. “Other attachments such as a hydraulic thumb, crusher or shear require bi-directional flow, for opening and closing. If a contractor wishes to use his excavator as a carrier for multiple attachments, then the variety and hydraulic requirements of those attachments need to be considered.”
It’s also a good idea to pay attention to shock absorption, says Bill Papineau, engineering manager mounting/hydraulics, NPK. “All hammers generate high vibration loads, which are transmitted through the boom structure to the carbody and cab of the excavator,” he notes. “Spec’ing good shock absorbing mounts protects the carrier from these shocks. This can reduce maintenance demands and greatly reduce operator fatigue.”
You also need to make certain your machine can handle the hammer being considered, Knott suggests. “The carrier must be large enough for stable operation when breaking or moving around a jobsite,” he says.
Volume and time the best measures of productivity
Calculating productivity with a hammer or breaker can be difficult due to the vastly differing nature of jobsites and applications they’re used in. Further complicating productivity guidelines is the fact that an operator can encounter numerous variables on a jobsite while using a hammer. As Corriher points out, it’s not unusual for a hammer operator to encounter widely different levels of resistance in a single vein of rock.
Still, Murphy thinks you can apply some general guidelines to accurately measure hammer productivity. Again, it all boils down to application. “If a building project is delayed until a rock ledge or slab is removed, then obviously, time is the only yardstick,” he notes. “If the breaker is being used in a secondary application, reducing oversize, for example, then material volume can be a good measuring tool.” Over time, Murphy says, all the variables that effect production must be considered, including regular maintenance and downtime.
One of the best ways to ensure good hammer and breaker productivity is to instill good work habits in your operators, says Gary Hesseltine, vice president, marketing, Tramac. “For all the abuse they take, hammers are pretty picky pieces of equipment,” Hesseltine says. “They don’t handle lateral (side-to-side) stresses well. That’s why it’s important to always position the breaker perpendicular (straight on) to the material being broken.”
All hammers require sufficient pressure against the chisel to allow the transmissions of energy to flow through the tool to the material being broken. At the same time, remember that as an excavator arm travels downward, it follows a curved path, which will change the hammer’s original position. “Remembering the importance of perpendicular positioning, it’s also important that the applied pressure follows the tool,” Hesseltine says. “Failure to do so will lead to reduced hammer performance and premature tool failure.”
If you’re not putting the correct amount of applied pressure on the hammer, the tool will dance around on top of the material, rather than sending energy into the rock or concrete. “But,” says Hesseltine, “applied pressure should not lift the carrier off the ground. If it does, then when the tool cuts through the material, the excavator will drop suddenly and harmful shock loads will be transmitted through the chisel, the hammer and the excavator.”
Avoid blank firing and continuous operation to extend hammer life
If there’s a cardinal rule of hammer use, it has to be avoid blank-firing the hammer at all times. Blank firing occurs when the hammer is operating and the tool is not preloaded against the piston or extended out of the hammer’s housing. You can tell a hammer is blank firing by the distinctive metallic ringing noise it will give. Your operators should be watchful when the tools breaks through or slips off the material being broken. They should stop the hammer immediately when this happens to avoid blank firing.
Blank-firing a hammer or breaker allows its piston to strike the chisel shank with full impact. This action, in turn, forces the tool against the retainers, piston chuck housing, tie rods and the breaker itself. Since there is no material present to absorb that impact energy, the shock waves will bounce back up the tool in violent pulses, meeting other energy waves traveling down the tool. These energy collisions will create a disorganized mass of energy that will cause extensive damage to the tool and other hammer components.
Some applications are more prone to blank firing than others. Springer says contractors breaking walls, overhead or light concrete or reducing oversize rock are particularly vulnerable to blank firing. “If you’re working in these applications, I’d recommend spec’ing a hammer with a select start function,” he advised. “In these applications, you simply cannot apply sufficient pressure against the chisel to eliminate blank firing. Therefore, you need the hammer to fire with very little applied pressure – just enough to cock the piston.”
Springer says a selection start system allows you to choose the proper setting of the hammer to match the material or the application at hand. “Our Easy Start mode allows the hammer to fire with very little applied pressure,” he says. “The alternate Auto Shut-Off mode will let the hammer begin work only when full downpressure is applied (when the tool is pushed up against the piston). As breaking occurs and downpressure diminishes, the hammer will switch off automatically before a blank fire can occur.”
Another good piece of advice is to train your operators to avoid hammering at a single area for too long. “Our recommendation is to hit a particular area for 15 to 20 seconds,” notes Knott. “If, in that time, you don’t see some sort of crack or fissure forming in the material being broken up, you should pick up the hammer and move it to another position.”
“If you hammer in one spot too long without any work being done, you can put too much energy – in the form of heat – into the tool bit,” Knott explains. “This excessive heat buildup can destroy the heat treatment, or the hardness, of the bit. In many cases, you’ll see almost immediate bit failure. I’ve seen operators take new hammers, hit in granite without repositioning and just peel the point away. This isn’t anything that reflects the quality of the bit. It’s pure physics – the bit just can’t withstand that kind of energy.”
Never use the tool or the breaker as a lifting device, Hesseltine says, and never use it to pry rock or concrete. “Also remember not to fire the hammer with the excavator’s cylinders at the ends of their stroke. They cannot handle the hammer’s heavy vibrations in that position.”
Ratings controversy continues unabated
One problem with predicting and comparing hammer productivity is that current industry rating systems are extremely fluid right now. That’s because the industry as a whole has yet to settle on a universal rating system for hammers and breakers.
Currently, the industry uses a system developed by the Construction Industry Manufacturers Association’s Mounted Breakers Manufacturers Bureau. (Both MBMB and CIMA are now part of the Association of Equipment Manufacturers, which is why the current rating system is often referred to as both “CIMA” or “AEM” numbers.)
This rating system is intended to provide contractors with an energy rating, reflected as the amount of foot-pounds delivered per blow by a hammer’s tool. But some hammer manufacturers are claiming their competitors have found ways to tweak the test and obtain much higher foot-pound measurements than intended. Smaller hammer manufacturers complain the AEM test is expensive and its results are inconclusive. Others maintain AEM favors nitrogen-charged hammers. And still other OEMs say there’s nothing wrong with the ratings and they should be left alone. Recently, some OEMs have stopped publishing their AEM ratings altogether.
“The AEM rating system was developed to address inaccuracies in the old ‘Energy Class’ rating system,” Knott says. “If done properly, ‘Energy Class’ represents calculated impact energy based on the energy going into the hammer as hydraulic oil flow and pressure. Manufacturers often inflated the calculated values to the next higher energy class, for instance, from 850 foot-pounds class to the 1,000 foot-pounds class. The AEM rating system shows the energy available to do the work at the tool tip. We publish both numbers for our hammers, but think that AEM’s a good way to do it, as it really describes what is truly happening and what energy is available.”
But many OEMs say Energy Class ratings were approximate, and some manufacturers weren’t honest about their energy class ratings. They claim some manufacturers manipulated those numbers and bumped their hammers up a class or two. Some AEM rating system supporters charge manufacturers were claiming energy class outputs higher than the amount of energy (in terms of hydraulic pressure and flow) going into the hammer.
“The problem with the old energy classification system is that these numbers are, and were, ‘made up’ by the hammer manufacturers,” Springer says. “Contractors need to ask dealers or OEMs how an energy class number was calculated. What makes a hammer fit into the 5,000-foot-pound class and not the 4,000-foot-pound class?”
AEM ratings, which require expensive testing equipment and independent, third-party verification, were intended to bring hammer energy rating numbers back in line. But many say AEM isn’t foolproof – and worse, that the numbers the test generates are meaningless.
“The AEM tool energy measurement system is a laboratory test conducted in a utopian environment,” Murphy explains. “Each manufacturer is able to optimize their tool energy outputs by creating flows and pressures at the highest tolerable ends of their published specifications.” This, he says, is the loophole that has allowed some manufacturers to inflate their performance rating numbers. But, he says, “If breakers are continuously operated at those test flows and pressures in the field, they will fail in the course of normal use.”
“I think the AEM rating system is totally worthless,” Corriher says. “It was developed by big hammer manufacturers to hold smaller OEMs down. It’s not only an expensive test to conduct, but they want to sell AEM specs to municipalities as a scientific system, then have those municipalities require that all hammers purchased be AEM rated.”
Corriher says AEM numbers are vague, and he’d like to return to the old Energy Classification system. “Hammers should be rated in foot-pounds,” he says. “That number tells a contractor how much energy that particular hammer generates to break rock or concrete. It’s just like looking at the horsepower rating on an engine. The more foot-pounds or the more horsepower a hammer or engine has, the more it’s going to be able to do. It’s a direct, exact indication of power.”
“The AEM tool energy testing system does not measure efficiency or productivity, and provides a contractor with no valuable metric for making a wise business decision in evaluating breakers,” Murphy argues. “So, it’s really further clouded the issue it was meant to clarify. Production is the reason that a contractor buys a breaker … It is a solution to a problem. The productivity of that contractor’s equipment over time is the best metric for measurement, and there may be no clear way to measure this.”
Tom Witt disagrees. “The AEM rating is the best overall method available to measure the impact power of breakers in a specific class,” he says. “It measures the shock wave generated by the hammer that is critical to meeting the breaking threshold of the material being struck.”
But, Witt adds, AEM isn’t perfect. “Frequency (blows per minute) of the impact will drastically affect different materials that are being broken,” he notes. “So the AEM system does have some flaws.”
This dispute isn’t likely to be resolved any time soon. For now, Knott suggests asking for as much information as possible on any hammer you’re considering. “I’d ask for AEM numbers, old Energy Class numbers, product specifications – all of it,” he says. “For now, that’s the only way you can compare and contrast these attachments to see if they will perform like you want them to.”