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Rheinische Provinzial-Basalt- und Lavawerke (RPBL) is one of Germany’s medium sized producers of aggregates.
Based Sinzig in Königswinter, some 25 kilometres southwest of Bonn, the company owns and operates a series of quarries in the Middle Rhine Highlands, which are volcanic in origin. The quarries are located in the so-called 'Seven Hills' district, a cluster of about forty hills to the east of the river, and in the Eifel plateau region west of the river. The principal products supplied by RPBL are aggregates of basalt and a more porous, abrasive rock known locally as ‘Eifel lava’, for which there is great demand in road construction.
One of RPBL’s divisions is the Hühnerberg Works, with Hans-Gerd Schlangen as technical manager. He operates three basalt quarries: Hühnerberg and Naak, both close to Königswinter, and Birresborn, situated some 90 km to the south-west in the Eifel plateau region, whose aggregate is much prized as ballast for high-speed railways.
RPBL’s products are consumed mainly in the region, although they are also shipped to the Ruhr, Luxembourg, Belgium and the Netherlands. Hühnerberg Works produces also special products like fine sand, which has a wide-spread use in Germany. Some of it is even shipped overseas.
“Being so close to the Rhine is a tremendous advantage,” he says, “since the river offers a cheap means of transportation.”
Indeed, RPBL makes full use of the world’s most famous waterway, and even has its own port facilities at several localities along its course. The confluence of the densely populated Ruhr valley, which has more infrastructure than anywhere else in Germany, is a mere 100 km downstream. Further downstream, the Netherlands is another ready market for the company’s products.
The 100 year-old Hühnerberg quarry currently produces five to six thousand tonnes of rock a day, amounting to between 1.2 and 1.7 million tonnes a year.
“This requires about 38,000 metres of blast-holes to be drilled and blasted each year,” says Schlangen. The boundary of the quarry is only 200 metres from the nearest house in Hühnerberg village. The demands on hole straightness are therefore very high and there are strict blasting-restrictions. “To minimize the amount of fly-rock and ground vibrations, I started to look for drilling tools that would drill more precise and in order to get better blasting result,” he says.
One Tamrock Pantera 900 crawler drill-rig equipped with an HL 1000 hydraulic tophammer is used to produce the blast holes at both Hühnerberg and Naak. One of the first two units of its kind to be delivered in Germany, the rig was commissioned in April 1998 and originally equipped with a T45 tool system. This was changed to the Sandvik S51 system almost immediately, with Ø89-mm drill bits. The holes in the 12 – 16 metre benches are drilled at an inclination of 80 degrees from the horizontal, with a burden of 4 metres and spacing of 4.5 metres. Conventional sub-drilling is substituted with toe holes every 2 to 3 metres, in order to keep down vibration. The charge weight per hole is limited to 85 kg of Nobelite 100 (an emulsion explosive) at Hühnerberg, and even less at Naak, where the rock is more jointed and the products are more directed to hydro-construction work.
While hole deviation with the S-51 tool system was never considered serious in either Hühnerberg or Naak, Ralf Ogroske, the local Sandvik representative, had a hunch that a thicker tool system would give better drilling economy.
“At the beginning of 2000,” recalls RPBL main manager of the area Hans-Gerd Schlangen, “Ralf suggested we should test a new tool system called Sandvik 60, saying he was convinced we would obtain much longer drill-steel life, as well as straighter holes.”
Since Ogroske had by that time introduced Tamrock Pantera rigs and the Sandvik 60 tool system successfully in a number of other quarries in the region, he was no stranger to its performance capabilities. His argument was that the 65 per cent greater rigidity of Sandvik 60, compared with Ø 51-mm rods, would give not only straighter holes but also longer tool life, and that the latter would turn out to be the main advantage for RPBL. “ After some demonstration drilling I started to believe in the Sandvik 60 system and decided to change over from what we had before” says Mr Schlangen. Since changing to Sandvik 60, the company has had no problems whatsoever with hole deviation, and the driller Klaus Reimer confirms that the biggest advantage of the system is indeed longer tool life. Additionally, Reimer is pleased with the much higher penetration rate achieved with Sandvik 60.
“There is a big difference between drilling in Hühnerberg and drilling in Naak,” he continues. “In the homogenous Hühnerberg basalt, which has a hardness of 6-7 according to Mohs’ scale, the penetration rate with a Ø92-mm drill-bit is 0.8 metres per minute, using a percussion pressure of 120 to 125 bar. In Naak, where the rock is softer and more jointed, the percussion pressure has to be reduced to about 100 bar, and the penetration rate is only about 0.8 metres per minute. Owing to the jointing in Naak, moreover, we have to limit the charge density to about 5 kg/m, compared with 9 kg/m in Hühnerberg. Since the 3 x 3,25m burden-and-spacing was originally set on the basis of the Ø89-mm drill bits we used with S51, there is an argument for increasing it a little now that we are using Ø92-mm bits, which are the smallest available for Sandvik 60. However, since the blasting results remain satisfactory, I am sticking to the original pattern for the time being.”
Dramatic increase in tool life due to optimal energy transmission
Since tool life is followed up rigorously in the Hühnerberg division, the differences between S51 and Sandvik 60 can be seen in black and white. Shank-adapter life has increased from 3500 to 6000 drillmetres. Rod life is up from between 2500 and 4000 metres to an average of 6500 metres. Even the Sandvik 60 version of the Sandvik CAPP drill-bits, which are of the Retrac design and fitted with cemented-carbide grade MP 45 ballistic buttons, last considerably longer. Indeed, Reimer reports an average life of 1050 drillmetres for the Sandvik 60 version of the bits, compared with 800 drillmetres for the S51 version. The bits at Hühnerberg are reground every 150-200 drillmetres, or 5 to 6 times before being discarded.
The explanation behind the longer tool life is that the diameter of the Sandvik 60 tool system approximates very closely the diameter of the piston in the HL 1000 rock drill. This means that, provided the machine settings are made correctly, the amplitude of the shock wave that travels through the drill string after each blow from the rock-drill piston is small, while the transmission of impact-energy is optimal. The result is less stress to the rock tools and higher efficiency in the in the drilling system as a whole, since the impact energy is used precisely for what it is intended, i.e. to break up the rock, rather than to heat up and wear out the joints in the drill string, which is what happens when the rock-drill piston and drill string are not properly harmonized.
Klaus Reimer is most satisfied with the performance and service life of the Sandvik 60 tool system. “The only drawback,” he says, “is that Sandvik 60 rods are proportionately heavier, which makes it more difficult to load them into the carrousel on the rig. However, since we have had to put in only six new rods in over ten months, the increase in rod weight doesn’t make that much difference to us.”
For more information, www.sandvik.com