There are four different drilling methods to select from:
− Rotary wearing
− Rotary cutting
− Rotary crushing
− Top hammer percussive
− Down the hole percussive
− Rotary wearing method’s application is normally for sampling for geotechnical exploration.
− Drill bit is made of a couple of 3-edges, 3-edges consist outer edge, middle edge and internal edge. Every edge only take one third working load during drilling.
− It is easy to get cuttings out of drill bit by its special bit shape.
− It has been widely used in for underground tunneling like for mining and metro construction
− The Rotary Tricon bit is driven by drill rod and drill collar. It makes rotary tricon bit rotating at center of drill rod and cone rotate at cone center. The rotation from tricon bit and cone make the whole rotary bit have up-down movement as well and compressive force on rock. This up – down movement and compressive foce can break the the rock via the way of crusing, impacting and shearing.
− The up-down movement of rotary tricon bit also has the each cone contact the rock in turn to break rock continuously.
− In addition the drilling fluid helps on corrosion and enlarger the breaking volume.
Top Hammer Percussive
− This drilling method has been worked with compressor which is integrated into drilling rig, the air pressure is normally 7-10 bar and air flow is 6-11 L/min, the drilling work is done by rock drill on the top of drill mast and compressor together.
Down the Hole Percussive
− The DTH drilling method belongs to air drilling as well. Its difference from top hammer drilling is that it needs much powerful compressor to provide power for drilling. The main drilling work is executed by DTH hammer and DTH bit in the bottom of drill string and take compressor as power source.
− Therefore, the hole depth and hole diameter, are mainly decided by compressor capacity.
Different Drilling methods has their own application accordingly, it classified by drilling hole depth and hole diameter shown as below.