The rock hammering method of boulder breaking is a process of hammering the boulder by either a hydraulic or pneumatic hammer until the boulder breaks. The hammer is usually mounted on a boom. The motor, hydraulic pump, and oil reservoir are usually located near the boom. Figure 14 shows a typical hammer installation.
The advantages of this method are continuous operation (minimal downtime for boulders), no need for explosives, safer environment for the operator, and the hammer can be used to clean grizzlies.
The major disadvantage of the rock hammering method is the initial capital cost of the hammer.
The breakers have developed into a third generation model which requires less maintenance than earlier models. A variety of breaker points are available in order to achieve optimum performance for different rock characteristics.
Rock breaker designs are of two basic types. One type utilizes high impact blows at low frequency while the other type produces a much lower impact blow delivered at a much higher frequency. Frequencies can range from 25 to 450 blows per minute with blow energies developing between 1,000 and 20,000 ft-lbs per blow.
A variety of breaker points are available as shown in Figure 15. They can easily be replaced by simply driving out the locking pin. Various shape points are necessary because different rock characteristics require a specialized point. In other words, one point design will not give optimum efficiency for all types of rock, rock hardness being the primary consideration.
A number of operations visited were using hydraulic or pneumatic rock breakers. With rock having compressive strength of 20,000 psi, breaking a boulder can take about 5 minutes. Oftentimes the breaker is used to clean a grizzly as a preventative measure to boulder blockage. Breakers can be mounted on mobile units so secondary breakage could be accomplished at the quarry pit before the boulder is loaded and sent to the crusher, as shown in Figure 16.
Owners of rock breakers generally overhaul the units every seven years depending on use. The newer heavy duty models may require less maintenance, particularly for the boom, where new design efforts have been concentrated.
