HIGH PROFILE
towards our new grades like GC81 ( Gradient Carbide ) and SH70 ( Self-Hardening ), which are based on improved knowledge about the wear of the drill bit in different types of rock .”
GC81 is developed for abrasive ground conditions with high silica levels in the rock . A new , unique method makes it possible to produce buttons that are wear-resistant on the outside , while the centre provides a toughness that pushes the service life and grinding intervals even further . SH70 is a grade with homogeneous properties throughout the material . Sandvik calls it ‘ selfhardening ’ because it has the ability to get more wear resistant as you drill with it , due to enhanced deformation hardening . The surface hardness is continuously ‘ refilled ’, which means that the hard top never wears off . The hardening effect is greatest in hard and competent ground .
So what proportion of Sandvik bits are using these new grades today ? Bengtsson : “ Item by item , we are phasing out the standard XT48 grade across all of our surface and underground bits . This involves SH70 on Autobit and GC81 on other bit ranges . And it isn ’ t limited to top hammer either – our DTH and rotary bits are also benefitting from new PowerCarbide ® grades . The time taken just relates to ramping up production of the new carbide grades , getting through existing bit stocks on the customer side , switching over on our side in terms of the button production and incorporation of those into the bits , but also the sheer amount of bit products that need to be switched over such as the Retrac ranges . As well as the three to four months lead time that we give to ship to customers in many mining areas .”
A new thread following
Moving to other developments for surface tools , at CONEXPO 2023 , Sandvik had a soft launch of the CT55 and CT67 , whose development first began with a Sandvik engineer saying they wanted to set out to make the ‘ perfect thread .’ These curved thread systems are designed for surface mining and quarrying , as well as longhole drilling underground . These systems accommodate higher drilling power than the standard ones and feature a curved profile that reduces stress levels strategically while optimising the product for fatigue strength .
Fredrik Björk , Product Manager for Top Hammer Surface Tools , told IM : “ Both the new threads are built on the same technical platforms . The main reasoning behind their development was that on the typical surface crawler top hammer rigs , there was a lot of power that could not be used realistically with our standard T51 and GT60 rod systems due to too much heat limiting service life . Or put another way as our rigs got more powerful , we had to step up the drill string as well to match their performance . With CT55 and CT67 we have achieved a higher penetration rate , and good flushing performance . They allow more efficient energy transfer and have a stiff and strong connection .”
The curved thread has a bigger cross-section where it is needed , reducing stress levels , plus a more robust coupling system , allowing for easier coupling and uncoupling with double thread entrances and minimal rattling . Rattling refers to a process used to uncouple drill rods using high pressure percussion for some seconds to get them to come loose . With CT you can reduce this rattling time to 0.5 to 1 second and even saving a few seconds of rattling is critical for service life of the rods .
Björk adds : “ The design of the CT ( Curved Threads ) means the energy is transferred from the shoulder to the female end . This means we can handle higher percussion forces . The curved thread has also allowed us to further strengthen the male and female where needed . Traditionally on top hammer threads all the wear is at the beginning and the end with the middle untouched – with the new threads the wear is much more evened out . All the new design features were run through hundreds of simulations as well as on our test rig here at Sandviken , using different pitches and combinations . Everything is also now protected by a set of new patents as well .”
Thanks to the stiff coupling Sandvik Rock Tools has also dared to also increase the dimensions – with the T51 thread , it is 52 mm with a 21.5 mm hole – its replacement the CT55 has gone up to 56 mm and opened up the hole also to 28.5 mm . “ So with just a small increase in area , which is crucial as there needs to be a balance with the hammer , we have 27 % higher stiffness ie it doesn ’ t bend meaning higher percussion and feed force . Its the same story with the GT60 and CT67 , its replacement where you have a 45 % increase in stiffness . Better contact with rock means better penetration .”
The formal global launch of the CT55 and CT67 took place in November 2023 , for surface bench drilling but also for underground longhole drilling as well , for example underground instead of replacing the GT60 , the CT67 replaces the ST68 . Björk : “ Our new CT system radically increases the fatigue strength and we ’ ve also seen 30 % longer tool life together with better hole precision in our product evaluation tests with early-adopting customers . This is a fully optimised system that includes the drill rig , the rock drill and the rock tool . The CT system also brings out the full potential of Ranger™ DXi and Pantera™ DPi rigs , especially the powerful Ranger DX900i and Pantera DP1500i .”
As with the Sandvik Alpha™ 330 , the GT60 in particular , launched over 20 years ago , is used very widely in mining today , so the phase in process of the new CT threads will take some time . “ The results again are impressive – a productivity
increase of 15 % conservatively as we have also seen much higher numbers in tests . Extensive use on our own rigs , from which we get very good data collection from the onboard SanRemo Mobile system , has shown we drill faster per metre and per hour . That means we are also reducing fuel consumption per drilled metre by about 15 %. Plus it means a much better service life on rods and shanks of at least 30 %.”
What is the value for a typical small mine or quarry or for their contractor ? “ With the same rig for the same time and with the same operator a contractor can invoice a significant number of additional metres drilled . Plus they are saving on fuel too . And this is based on one shift . The upside and savings in mining for 24 / 7 operations for presplit and contour drilling will be higher again . And for an owner operated drill fleet it means a better bottom line . Drilling metres faster and using less fuel to drill them also makes for a compelling sustainability argument as well .” In an example given to IM , using similar rigs for 89 mm holes , using T51 took 16.7 h to drill 1,000 m but CT55 took only 13.6 h . As the fuel use was similar per hour , the fuel saving really adds up .
The CT rods similar to Sandvik Alpha™ also have a bigger flushing hole . Looking at the CT shank , the shoulder is transferring a lot of the energy to the other end , so a bigger flushing hole compensates for that . The team at Sandvik agreed that the CT is such a game changer that it has the potential to boost Sandvik crawler rig sales with customers wanting to go with a Sandvik drill to get the full benefits of the tools . This also reflects the fact that you need to use the Sandvik rig to use CT on surface . As underground production drills have a more universal design it is possible to use CT technology on competitor drill rigs as well , as long as you are using the whole Sandvik drill string . Going forward , Sandvik is looking at smaller CT dimensions as well .
Finally , also worth a mention is the complete top hammer drilling system that is directly aimed as a alternative to DTH in certain applications which Sandvik refers to as Top Hammer XL – it expands the hole size range of top hammer drilling up to 178 mm ( 7 in ). It provides a faster and more fuelefficient drilling method that can considerably reduce CO 2 emissions . The fully optimised drilling system consists of the Pantera™ DP1600i drill rig , RD1840C rock drill and LT90 rock tools . LT90 MF tube rods are developed to convey high energy shock waves with minimal energy loss in the threads .
This solution has proved very effective in hard and competent ground . For softer or fractured material , DTH still has the edge – and Sandvik offers both anyway . One option is also to use Top Hammer XL on the lower , more homogenous lower benches and DTH on the more fractured upper benches in an open pit . IM
42 International Mining | MARCH 2024