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How to choosse the correct top hammer drilling tools

2021-03-20

The wide range of applications and drilling conditions suitable to down-the-hole (DTH) drilling tools pneumatic percussion technique requires consideration of more than one type of tool to drill efficiently and profitably. A variety of factors, from hammer size to determining whether or not an economy hammer represents the best value, all figure into the hammer’s overall cost of operation on a given job.

 

CHOOSING THE CORRECT HAMMER
The selection of hammer size is largely determined by the hole diameter and type of rock formation. The optimum blasthole range for DTH drilling is 3 ½ to 10 in. Smaller holes are typically drilled with a top hammer rather than DTH hammer, and larger holes generally use rotary drilling technique, mainly with the focus on hole straightness.
As a general rule, the smallest hole diameter a DTH hammer can drill is its nominal size. A 4-in. hammer is optimally designed to drill a 4-in. hole. The closer the hole diameter is to the hammer’s diameter, the more restricted the hole’s evacuating airflow is. Drilling holes at the nominal size leaves adequate space for cuttings to evacuate the hole up the annulus between the hammer and drill pipe diameters and the internal diameter of the hole’s wall.
Maximum bit size for production drilling is the nominal hammer diameter plus 1 in. For instance, a 4-in. hammer’s maximum bit size is regarded to be 5 in. in diameter.

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