Show captionHide caption

Sandvik rock tools specialists Robert Grandin and Fredrik Björk with the Top Hammer CT thread.

One system to rule them all

Top hammer rock tools – same old, nothing new? Sandvik’s rock tool specialists decided there was still progress to be made. The new CT55 and CT67 tool families for surface bench drilling help leverage the full potential of powerful Sandvik Ranger DXi and Pantera DPi drill rigs. The innovative CT threads give remarkable  benefits in underground drilling as well.

Text: Turkka KulmalaPhoto: Stefan EstassyPublished: 9 December 2024

The heart of the new rock tools is a patented, first-of-its-kind curved thread design, referred to as the CT  (or Curved Thread) system. “We realized that we could not really push the industry standard of rock tools any further,” says Fredrik Björk, Product Manager Top Hammer Surface Tools, describing the starting point. “You can always change the material and tweak a little bit with heat treatments and the radii here and there, but a real raise in the performance was not possible.”

The conventional, bottom-driven thread geometry was an obstacle for more aggressive drilling parameters; achieving those required a stiffer tool system and better performance from the thread than what was possible with conventional rock tools. The Sandvik rock tool experts started to look for a completely new solution. The result is  a new shoulder-driven thread which transfers energy more effectively from the rock drill to the drill bit and also gives a stiffer and stronger connection between drill rods.

The new tool coupling transfers impact energy from the shoulder of the male end of the coupling to the face of the female coupling, as opposed to from the end of the male thread to the bottom of the female thread. This provides a larger area for the energy transfer and therefore better efficiency with minimal losses. It also prevents excessive heating and gives a stiffer and stronger connection. The shape  of the new thread is curved; in other words, the diameter of the male thread consecutively decreases towards the thread end along a curve of a specific radius. The cross-section is larger where it needs to be and reduces stress levels by distributing loads over a larger area in the tool. This enables the drill string to endure significantly higher power levels and makes it possible to fully use the increased drilling power capacity of modern top hammer drill rigs.

Tech specs – Sandvik Curved Thread rock tools

CT55 (55 millimeter thread, diameters 89–127 millimeter) and CT67 (67 millimeter thread, diameter 102–152 millimeter) underground drilling tools dedicated to more stable and cost efficient longhole drilling
CT55 (55 millimeter thread, diameters 89–127 millimeter) and CT67 (67 millimeter thread, diameter 102–152 millimeter) surface drilling tools dedicated to maximizing productive bench drilling

The performance of CT tools relies on a painstakingly engineered thread geometry. It enables larger rod diameters while keeping the cross section of the rod roughly the same,  to match the rock drill, resulting in a stiffness increase of up to 45 percent. The results are impressive: “We can reach higher values of productivity,  15 percent more drilled meters per hour or even more. This is a huge improvement and the main value of these tools,” Björk says.

In surface drilling, by far the most important value is the potential to increase productivity simply in terms of meters drilled, thanks to the more aggressive rock drill settings: the stiffer CT tools allow a higher feed and percussion pressure. Faster drilling also cuts back specific fuel consumption by 15 percent because the same number of drilled meters can be accomplished in a shorter time. Easier coupling and uncoupling also improves productivity by shortening rattling times and reducing downtime caused by drill rods that have gotten stuck inside the hole. Furthermore, the CT tools last roughly 30 percent longer, thanks to shorter rattling times, lower stress levels and lower temperatures.

In underground drilling, the most important key words are stability and cost. The underground applications typically involve up to 10 times higher tool costs compared with surface drilling, and more than a year of field testing in Australia has proven that  the CT technology can substantially increase drill tube service lives and cut back cost per drilled meter (see box). “Another important point in underground is automation,” says Robert Grandin, Product Manager  Top Hammer Underground Tools. “Automation can’t really handle broken drill tubes, so just delaying that is worth it because the automated drilling can stay on longer. The predictable discards of the CT threads support this as the operator can see when a tube should be replaced, before something happens.”

Rusting carrots in Australia

BHP Olympic Dam not only operates the world’s largest deposit of copper, gold, and uranium – the company is also a pioneer when it comes to implementing Sandvik’s CT system. R&D tests began in longhole drilling back in 2020 and the immediate results showed a more than 50 percent increase in drill tube service life.

“It was like clockwork. We decided to start rollout of CT67 on all six longhole rigs and now the results are even better,” says Robert Grandin, Product Manager Top Hammer Underground Tools.

After a year, tube service life has increased by more than 60 percent, while rock tools cost per meter has decreased by more than 20 percent.

One way of measuring how effective and reliable the operating process is with CT67 is by counting how many fishing pikes – called “carrots” in Australia – have been used to retrieve the drill string after a thread breakage. Jeremy Rigden, Production Coordinator BHP Olympic Dam, says: “Today the carrots are sitting and rusting on the drill rig.”

If one is used today, it’s considered an extraordinary event. Robert Grandin says, “We are very grateful that BHP Olympic Dam have the courage to try this new technology at the very heart of their operation. It is critical this process runs smoothly, and the numbers prove it works.”