Hammer Time

Aug. 1, 2000
Specifying the right hydraulic hammer depends on a number of factors, starting with the characteristics of the material to be broken. The hammer also

Specifying the right hydraulic hammer depends on a number of factors, starting with the characteristics of the material to be broken. The hammer also must be matched to a carrier on hand. Too small a hammer means poor productivity and excessive wear. Too large a hammer also results in excessive wear as well as inefficient operations because a larger hammer means a larger, more expensive carrier.

If the job is primary or secondary breaking in a quarry application for construction-grade materials, chances are the material will be relatively hard, tough and compact. If large boulders are encountered, the carrier has to be big enough to turn them. If the material is weak or fractured rock, it is easily broken with a hammer, and a much smaller carrier/hammer package should be used.

Concrete, for instance, is similar to conglomerate rock material because it is brittle and abrasive. Concrete mechanical properties can vary widely, however, because of mix and age.

Heavy breaking requires high-impact power or energy per blow; whereas, lighter work such as breaking concrete slabs requires higher frequency or more blows per minute.

The carrier Choosing the right hammer size on a carrier depends on the weight the carrier can handle. For example, users should not put a small hammer on a big excavator. It costs more to run a big excavator than a small one, and the small hammer can do only a certain job regardless of the carrier's size. It is also not ideal to hang a hammer that might weigh 7 tons on a backhoe. Stability is important, as is basic carrier capacity.

The carrier must be in good condition. An old excavator with tired hydraulics and excessive wear won't allow users to position the breaker easily, and when they do position it, oil pressure/flow might be insufficient to achieve optimum efficiency.

While it might seem that more velocity means more productivity, there is an upper limit. Speeds above a certain limit will exceed the yield strength of steel and cause excessive deformation and fatigue when the hammer piston contacts the tool's steel. The time duration for the stress wave produced, impulse and frequency are important in hammer design to achieve maximum productivity.

The tool Sometimes tool selection is relegated to what is in the hammer at the time. This is one of the biggest factors contributing to poor productivity, inefficiency and excessive tool wear. Users should know how to operate the hammer and understand its breaking methods. These factors are just as important, perhaps even more so, than selecting the right carrier/hammer package.

In most cases, the harder the material, the less penetration by the tool and the blunter the tool design. Breaking is caused by stress waves induced in the hard material, not by penetration.

Generally, the shortest tool possible should be used in penetrative applications, and the tool should be repositioned as the penetration rate slows. Hammering in the same position after penetration has slowed is wasting energy. A good operator won't work in the same spot more than 15 seconds before repositioning the tool. Using a shorter tool can force a less experienced operator to reposition the tool after a certain amount of penetration.

The tool should be positioned as near as possible to 90 degrees to the material. Angles where the tool is tilted to the surface cause more tool bending and fatigue. Mushrooming on tools is a sign of high temperature on the working end, as might be found in foundries or other hot conditions or when the tool works on hard materials without pause for an extended period. The use of pirate tools not designed to the proper hardness also can cause premature failure. Proper greasing of the lower tool bushing should be practiced to lengthen tool life.

Special considerations Certain applications require special considerations. Tunnel work, for instance, is one of the toughest applications for a hammer. It usually calls for an extremely high utilization factor, i.e., the unit is working twice as much as a typical unit in other applications in a given time period.

Also, the contact force applied by the excavator to the tool is much higher in a horizontal position than in a vertical position. Tunneling work usually calls for long chisel tools because the excavating frequently is done near walls. Bending stresses can be extreme, and an experienced operator can make a big difference on tool life.

Demolition work might require a hammer, cutter-crusher and/or a pulverizer. When using a hammer, it is important to note the boom being used on the carrier. Long booms and sticks might dictate that a smaller hammer with a lighter weight be used. It is also important to consider the awkward working positions that are the norm in demolition projects and the ability to position the hammer easily.

The hammer/carrier match The user doesn't have to do all the calculations, but a basic knowledge of impact energy, the proper hammer-to-carrier match, hammer design and how the hammer handles different oil flow and pressure, proper tool choice, proper maintenance and the experience level of the operator all affect productivity, efficiency and equipment life. Even the best-designed hammers won't be satisfactory if they are improperly sized or used.

A good operator with good equipment is a joy to watch. There is maximum efficiency and no wasted motion. Select the right equipment and give it to a good operator. You'll be happy with the results.