The job of a hydraulic hammer is easy to understand. “It has to break the material under it without breaking itself,” says Donald Dennis, product support manager for Caterpillar Impact Products.
Manufacturers have solved this dilemma by designing hammers so the critical parts that wear can be replaced easily. Rebuilds are a part of the hammer life. The contractor who knows what needs to be maintained and scheduled plus how to use the hammer correctly can extend its life. Conversely, the contractor or operator who ignores the hammer’s maintenance can destroy a healthy hammer in a single shift.
The bushing and the bit
The two most critical wear items of the hammer are the tool or bit that delivers the impacts to the material, be it a chisel or moil point or other design, and the lower tool bushings that hold the tool in correct alignment with the piston.
“The internal piston directly strikes the top of the tool and you have to have good linear alignment between those two components,” says Kevin Loomis, hydraulic applications manager for Atlas Copco Construction Tools. “That’s why bushing wear is important. As your bushing wears, your tool can cock to the side and then you’re not hitting the top of the tool square. You’re point loading and that can chip the tool or the piston.”
As a result, checking the clearance between the tool shaft and the internal diameter of the bushing is an important part of any hammer’s regular maintenance checks. Some models will have graduated wear marks etched into the edge of the bushing for easy visual inspections and some manufacturers provide gauges to check this gap; but they all have specs and need to be monitored closely to prevent expensive damage to the hammer’s internal parts.
Typically the tip of the tool will wear down, shortening its length to the point where it needs replacing. But an often overlooked measurement, says Loomis, is the diameter of the tool shaft. “If the shaft of the tool wears out, that can also give you side to side movement, even though your bushing may be within 50 percent of spec,” he says.
Rebuildable vs. consumable
In considering the owning and operating costs of a hammer, Dennis says it’s a good idea to distinguish between consumable and rebuildable wear parts. Consumables would be things like the tool or bit (what Cat calls the ground-engaging tools or GET) and the lower tool bushing. These aren’t rebuildable and there isn’t a fixed schedule for replacing consumable items. You inspect and replace them when they’re worn. “Every hammer owner has a different utilization rate,” Dennis says, “but consumable items can account for up to 50 percent of a hammer’s owning and operating annual cost.”
The other items that are often replaced during a scheduled rebuild are the seals and O rings (if equipped) and other soft parts. The upper bushing may also need to be replaced although these don’t wear out as fast as the lower bushing. With the hammer disassembled it’s a good time to do a thorough inspection as well. You’ll want to inspect internal components such as tie rods, piston cylinder and spools and measure the shank/tool stops and accumulator diaphragm. Inspect the cradle and exterior wear parts as well, including external accumulators used on direct acting designs to protect carrier hydraulic circuits from hammer pulsation.
The time it takes to do a rebuild varies. Some of the smaller hammers with new technology can be rebuilt much faster – and in fact most of the emphasis with hammers being introduced into the marketplace now is on making them easier and quicker to rebuild. Manufacturers are doing this with slip-fit lower bushings, quick-change tool retaining systems, the elimination of tie rods and a general reduction of parts, particularly in the smaller hammer sizes. Even if your current hammers are just a year or two old, you may be surprised at how far the technology has evolved in such a short time. “With the slip-fit lower bushings we’ve taken a replacement procedure that used to take four to 10 hours and reduced it to 30 minutes for pressed in bushings,” Dennis says.
On more traditional small hammers a rebuild typically takes up to six hours of shop time. And for the jumbo sized hammers used in high volume quarry and demolition work you’re looking at up to 20 hours of labor.
When to rebuild
It’s time to rebuild your hammer anytime the bushing wears beyond spec or you see oil leaking down the shaft of the tool, says Tom Witt, director of sales at Breaker Technology.
When this happens varies widely and is influenced by the size of the breaker, the application, the quality of the maintenance and the skill of the operator. “The parts can last from one week to literally one year,” says Philip M. Paranic at Allied Construction Products.
The smaller hammers usually have double the life between rebuilds as the larger units, says Witt. On average, he says, small breakers are rebuilt between 1,200 and 1,500 hours. Midsize units will last 800 to 1,200 hours between rebuilds and the larger units may go 500 to 800 hours.
Just keep in mind, says Loomis, that it’s like asking how long a set of brake pads last. “We advise people that at the six-month mark they should be looking at replacing the lower bushing. At the one-year mark, if you haven’t already done so, the breaker should be torn down, resealed and completely rebushed.”
All hydraulic or nitrogen gas assist
In terms of wear and rebuildable or consumable parts, there isn’t much difference between all-hydraulic and nitrogen-gas-assist breakers. The one major difference is that the nitrogen-gas-assist hammers have upper gas seals in the cylinder that are critical to hammer operations, says Paranic. As these seals fatigue in the field, a gradual loss of gas occurs along with a slight decrease in hammer performance, says Steve Kubish at NPK. But the gas heads can be recharged with the kits sold with the hammer and the hammer performance is controlled by the users’ recharging frequency or until these seals are replaced during regular scheduled maintenance.
On hydraulic breakers that use a bladder-style accumulator to assist in piston impact, when the rubber bladder fails performance drops considerably and the hammer becomes non-functional. And running a hammer with a blown accumulator can potentially damage the carrier’s hydraulics, Kubish says.
With good maintenance practices and proper operation, hammers, even some of the bigger ones, can last for eight years or more, says Tim Atchley, technical support manager for Ingersoll Rand Construction Technologies’ attachments division (which sells the green Tramac branded hammers).
“The strike pistons are a serviceable item and will wear out and be replaced,” Atchley says. “The usual life span is seven to eight years. It’s a high-dollar item but it can be replaced. If you’ve maintained your bushing wear diameters and kept the alignments good, the cylinder will last forever.” Other rebuildable parts include the front guide that houses the bushings and the cradle. In quarry applications, OEMs recommend you move rock with the cradle rather than the tool. “So every second or third rebuild you may want to do some buildup on the cradle,” Atchley says.
Dealer or do it yourself?
It is possible for contractors to do their own rebuilds, but in most cases inadvisable. “It’s a matter of the contractor’s time and good use of his money,” says Dennis. “These are finely machined pieces of equipment. You need a clean environment with proper shop tools, cleaning equipment and stands for faster servicing as well as overhead cranes for handling heavy components.”
High torque wrenches, some with 18-to-1 torque multipliers, are needed for disassembly of tie rods, Atchley says, in addition to bearing presses, hammer stands and other equipment. When contractors who lack this equipment try to do the work themselves, they’re often forced to use cruder, field expedient methods. These methods often take a lot longer than using specialized tools and increase the chances of damaging the hammer. “Hammers have heat treated components,” Atchley says. “Anytime you start using welding equipment or try to air-arc stuff out you’re going to destroy the integrity of the housing. I see it a lot; people try to repair everything themselves and cause major damage.”
Metric lift eyes to pull heavy components out of their casings are another tool, Loomis adds, that few contractors are going to have on hand. Major rebuilds may also involve fairly sophisticated processes including machining, precision welding and polishing, Paranic says. And dealer or factory rebuilds usually give you the extra assurance of a limited warranty as well.
Dealers or factory service personnel are also better trained to spot small problems before they become big ones, says Mark Kitson, product manager for JCB attachments in the United Kingdom. “They’ll look at things like the breaker housing, looking for scuff marks or damaged ports or flat spots on the casing,” he says. “The dealer has to use his knowledge of whether the casing needs replacement or can be buffed out.”
Maintenance and operation
The surest way to keep your hammer rebuild and consumable costs as low as possible is to read and follow the instructions in the owner’s manual.
In operation, the key is to keep the tool as perpendicular to the work surface as possible to reduce side loading. “When you have side loading you’re squeezing the grease out from between the tool and the bushing and getting metal-to-metal contact,” Atchley says. “As the tool moves with a side load you get galling and metal transfer. A poor operator can destroy a tool and bushing in four hours.”
And while on some demolition applications it is necessary to use the hammer in the horizontal position, this should be minimized. The reason, explains Kitson, is that when the hammer is horizontal the force acting on the piston and tool is uneven, which will result in accelerated bushing and seal wear. For this same reason, he says, if storing a hammer for extended periods you should remove the breaker tool or store the hammer upright, preferably in a hammer stand.
One of the most important jobs an operator needs to do in the field to keep the hammer up and running is to grease it with high temperature moly grease at the start of every shift per instructions provided with the hammer, regardless of the lubrication system used, Paranic says. Not only do the operators need to pay close attention to the proper lubrication intervals, but they should watch for excessive movement of hammer components in the box housing. Water can be another hazard, he adds. Operators should never let the hammer body touch water surfaces during operation unless a proper underwater kit has been installed and is in use on the hammer.
Unlike most machine greasing schedules, hammers sometimes need grease every hour to two hours. On bigger units this makes auto-lube systems an attractive option. Operators also have to be careful to do the greasing correctly. “If you don’t have down pressure on the tool and eliminate the gap between the piston and the top of the tool the grease will find the path of least resistance and go between the piston and the tool,” Atchley says. “Then when you set it against a rock and jam the tool against the piston, there’s no place for that grease to go and it will break the lips on the seals, causing leakage.” Atchley also cautions against using powered grease guns as these can put grease in too fast and too hard. Manual grease guns, even though they may require 15 to 30 shots of grease, are less likely to cause problems.
Proper sizing of the hammer according to the hardness and density of the material to be broken and to the carrier is also important for safety and to prevent premature wear, says Kubish. Don’t use the tool to pry, pull or push large objects, and avoid extreme slant hammering or slant hammering with excessive boom down force, he says.
And keeping fresh, clean hydraulic oil in the carrier machine’s reservoirs is also critical. “If you spend $20,000 on a breaker you should be able to spend $200 or $300 to change the hydraulic oil regularly,” Kitson says. “If you keep the oil clean the breaker will last longer.”
Safety quick tip
If you have a new hammer or a new hammer operator, or your crews could use a fresh look at hammer safety and best practices, be sure to order the Association of Equipment Manufacturers Hydraulic Mounted Breakers Safety Manual for Operating and Maintenance Personnel. This glove-box-size handbook costs $6 for single copies plus shipping and handling and can be ordered from AEM at this site. For additional information, call 866-236-0442.