IMPORTANCE OF STRAIGHT HOLE DRILLING

摘要

This case history details the issues surrounding the rock drilling industry's growing demand for straight holes, the importance of straight holes and the introduction of a new production drilling systems that can effectively and economically drill a true bore hole. Since the introduction of the hydraulic rock drill, the rock drilling industry has asked for a drilling system that would provide the fast penetration and low operating costs of Top Hammer drilling systems combined, with the directional control of Tube or DTH drilling techniques.With this request Svedala Reedrill and Boart Longyear evaluated the opportunities available to meet this request. Together they developed the LASEROD Straight Hole Drilling System. Employing finite element analysis and computer aided modelling, it was determined that a drill string with a minimum cross section of 70mm (2 3/4") was required to maintain hole straightness to depths of 20m (60ft). The demands of the larger 70mm(2 3/4") cross section necessitated a rewrite of the old rule book about how to hold a drill string together and as a result the EL68 thread profile was invented.