Expand the limit

In early 2021, Sandvik Mining and Rock Solutions launched a new top hammer drill rig – Pantera DP1600i. It is the newest member of the Pantera DPi family of large hydraulic crawler-based drill rigs, characterized by high penetration rates and advanced automation options for data-based fleet management and drilling performance optimization. However, their hole size range has until now maxed out at 152 millimetres (6 inches).

The design engineers’ starting point for Pantera DP1600i was to craft a careful balance between all three dominant components of the drill rig: the carrier, the rock drill and the rock tools, to be able to drill large hole sizes between 140 and 178 millimetres (5.5–7 inches).

The carrier solution is essentially based on the reliable and proven Pantera DPi series platform, upgraded with critical parts in the hydraulic system and a redesigned boom structure to carry a more powerful rock drill. This results in a higher capacity and eventually a larger hole size, without increasing the physical drill rig footprint.

“We have a long track record with proven performance in top hammer drilling with the Pantera DPi series rigs, starting as far back as 2008, so therefore it was a natural choice to upgrade the existing platform to the next level for this new solution,” explains Jarno Vii-taniemi, product manager surface drilling at Sandvik Mining and Rock Solutions.

product line manager rock drills at Sandvik Mining and Rock Solutions. “It truly works very well as a whole.”

As an option, RD1840C comes with the Sandvik RockPulse tool stress monitoring system, which offers the drill operator real-time measurement data on three key drilling parameters: drill bit response, tool load and feed level. The system measures in real time the stress waves induced by each piston impact, and this helps the operator to avoid poor rock contact and excessive tensile stresses as well as over- or underfeed.

The tooling system optimized for the Top Hammer XL drill rig concept is the new Sandvik LT90 family. The challenge in developing these rock tools was the longer, more powerful shockwave generated by the new RD1840C rock drill. More specifically, how to transfer it in a controlled manner to the bottom of the hole with minimal energy losses to maximize penetration rate.

“We have more energy in the whole system,” says Fredrik Björk, product manager rock tools surface drilling at Sandvik Mining and Rock Solutions. “If you don’t crush rock with that energy, it will destroy the drill string and threads instead. It will transform to heat.”

The challenge was mainly solved by improving the drilling dynamics, which in turn requires careful balancing of several potentially conflicting parameters. One of these is the stiffness of the drill string to achieve straight holes, while at the same time avoiding excessive stiffness to prevent breaking of the tools under bending. Limiting the stiffness practically also means avoiding overly large rod diameters because that will result in higher stresses in the thread joints under bending.

In the rod threads, the balancing is about making the threads as slim as possible but still strong enough to optimize the coupling char-acteristics of the drill string. The practical benefit of this is easy threading and unthreading of the rods and the bits.

Yet another key balance is between wear resistance and hardness, because excessively hard tool steel will also be too brittle. A major asset for Sandvik in this respect is the steel grade and heat treatment know-how available in house at Sandviken, Sweden.

The RD1840C rock drill went through thousands of hours of bench testing, and the entire rig has clocked more than 100,000 metres of real-life drilling in difficult rock conditions. The field tests have been taking place in northern Europe since January 2019, which means that the Top Hammer XL solution needed to endure the wide spectrum of conditions typical to subarctic areas, including two winter seasons, with temperature minimums close to –40 ˚C, and also hot summer weather, up to 30 ˚C. The rig and the tools have taken the beating in stride.

The results show a 50 percent reduction in fuel consumption, 25 percent reduction in total drilling costs and 15 percent increase in productivity compared with the down-the-hole (DTH) drilling method*. Additionally, the new rock tools deliver excellent bit service lives compared with competing products and technologies. To illustrate the scale of the fuel savings in typical mining conditions, they are comparable to the annual consumption of 107 average family cars. The benefits are also available in high-altitude mining applications. The 50 percent reduction in fuel consumption naturally has a significant impact on CO2 emissions as well.

Sandvik is the first OEM to introduce this kind of innovative top hammer drilling technology that can achieve cost-effective drilling results in large mining hole sizes. Top Hammer XL expands the hole size range of top hammer drilling technology up to 178 millimetres (7 inches), making the inherently more fuel-efficient top hammer drills a viable alternative to DTH technology on a significantly larger scale than before. ■