Selecting the right hammer
The optimum range of hole size for DTH drilling is 90 mm (3.5”) to 254 mm (10”). Smaller holes are generally drilled using tophammer drill rigs, and larger holes generally use rotary drill rigs.
As a rule of thumb, the smallest hole diameter a DTH hammer can drill is its nominal size. i.e. standard 102 mm (4”) hammer will drill a hole down to a minimum diameter of 102 mm (4”). The limiting factor is the outside diameter of the hammer, because as the hole diameter reduces due to diameter wear of the bit, airflow is restricted. Maximum hole size for production drilling is the nominal hammer size plus 25 mm (1”), so for a 102 mm (4”) hammer the maximum hole size is 127-130 mm (5”).
Choosing the right hammer is largely determined by type of application, hole size and type of rock formation. Ideally, the size of the hammer should match the required hole dimension as closely as possible, leaving just enough space for cuttings to evacuate the hole efficiently.
Epiroc hammers are purpose-matched for all rock types and applications where high performance and low total cost per drill meter are the main criteria. The standard design is a suitable choice for production drilling in quarries, shallow waterwell drilling, and underground blasthole drilling. For demanding conditions in abrasive formations, the QM (quarry master) version is the optimum selection. It has the same internal components as the standard, but with larger OD of the chuck and wear sleeve, and a top sub-fitted with tungsten carbide buttons for wear protection in harsh and abrasive conditions. These also protect the top sub from excessive wear when rotating out of the hole through broken rock.
The COP M-series, Gold and QLX hammers are designed for the most demanding drilling conditions and for applications that require premium performance. These hammers feature state-of-the-art technology and deliver both maximum productivity and profit.
As a rule of thumb, a DTH hammer used in production drilling should be replaced when it has lost 10% in net penetration rate. The total drilling cost per meter increases drastically when productivity drops. All Epiroc hammers have the rebuild option with an E-kit, a kit consisting of external and internal wear parts. This is a valuable option particularly in abrasive to medium abrasive formations. With unique combination of highest quality in design, production and material, the hammers can be rebuilt with sustained performance.