The high rotation speeds of diamond drilling add dynamic loads to the joints of thin-wall drill rods, which are already highly stressed supporting drilling loads. Drill rod joints need to maintain their strength by resisting wear against the hole, and the wear of make-ups and break-outs due to bit changes. With the pending release of Boart Longyear’s third generation XQ drill rod, this article reviews how each generation delivered breakthroughs in load capacity and wear life, substantially boosting reliability and productivity.
The original Q drill rod joint is renowned for introducing coarse, tapered threads with a self-locking “interference fit,” but it had room for improvement. As the thread’s load flank (loaded face of each thread) wore, the joint load capacity dropped, leading to failure: threads jumped, box ends expanded and climbed, or pin ends snapped from fatigue. To address these types of issues, Boart Longyear added hardening to the top half of the pin thread to maximum hardness (60 HRC), creating a significant hardness difference between pin and box. This hardness difference minimized wear compared to the rapid adhesive wear on threads of similar hardness. Case hardening is unmatched in protecting the thread from wear, while keeping the toughness required to carry drilling loads.