The specialist behind the Diarot program is Åke Eklöf at Atlas Copco Rock Drills in Örebro. He comments: "We have been building a database with specifications and performances of all rock drills for some 20 years, and the amount of data we have now is huge. The more information that is added, the more the usefulness and accuracy of the Diarot simulation program becomes."

Optimal drilling with Diarot

Practical testing and evaluation are a necessary part of achieving optimal performance from a drill rig. But this process need not be as time-consuming as before. Atlas Copco's Diarot rock drilling simulation program makes it easier and faster to "test drill" with various rock drills and even adjusts settings, including feed force and impact pressure, to obtain an optimum drilling performance.

Willy Ingemansson was using an Atlas Copco ROC 642 rig with a COP 1238 LP rock drill to drill 12 m long, horizontal and vertical holes with a diameter of only 45 mm.
The holes were drilled with a spacing of 300 mm and were required to meet at a depth of 12 m at a dimension stone production site in Lönsboda, southern Sweden.

However, Willy's problem was the low penetration rate of the COP 1238 LP rock drill he was using - and the Diarot system was used to simulate alternative rock drills. The recommended replacement rock drill was the Atlas Copco COP 1432 ED - which confirmed the simulated results of the Diarot tests when it started work at the site in April, 1999.

Penetration doubled

Drilling in hard diabase, penetration rate more than doubled to 0.8 m/min, compared to the less than 0.4 m/min achieved by the COP 1238 LP rock drill.

The temperature and life of the drill string was also considerably improved, and all was well until summer approached. Then the temperature in the drill string soared and was as high as 120°C on the couplings. A visit to the site revealed that oil temperature in the hydraulic system was too high - a major factor being the high air temperature of 52°C in the pit.

To solve the problem, an oil cooler for tropical conditions was mounted on the rig and the hydraulic oil was changed from 46 cSt to 68 cSt viscosity - and the drilling performance was quickly back to expectations.

Tommy Karlsson: Production went up from 1,400 metres to 1,700 metres per week.

Last October, Willy was at another worksite in Bårarp, close to Halmstad on Sweden's west coast, on a similar project - drilling 10 m-long, 45 mm diameter holes for dimension stone production.

He wanted to further increase penetration rate and asked for a new simulation. With the revised settings, penetration rate increased from 1.05 m/min to 1.20. Temperature on the coupling was on the high side at 80-85°C, but acceptable. Then a 48 mm diameter button bit was tested and, mainly due to the improved flushing rate, penetration increased to 1.5 m/min.

Better performance

At a worksite close to Stockholm's international airport, Arlanda, Tommy Karlsson is using an Atlas Copco ROC 642 HP drill rig for bench drilling 76 mm holes. The temperature on the coupling was 80°C and a Diarot simulation was carried out to evaluate different drill bits and the optimal settings of the COP 1838 HE rock drill. Ballistic bits were tested and proved to be the best resulting in increased performance.

The COP 1838 HE rock drill being used has different stroke positions, as opposed to a conventional drill with a single fixed stroke length. Changing stroke length gives an extra dimension in tuning the impact energy end frequency and Tommy has been using position 3 with an impact pressure of 180 bar.

The Diarot recommendation was to change to a shorter stroke, using position 2 with an impact pressure of 205 bar. Different rotation speed and feed force settings were adjusted to the higher frequency produced by the rock drill and the Diarot simulation also provided a full recommendation for all settings.

Big savings

Tommy was pleased with the recommendations and says: "The rock drill is now running much more smoothly and the couplings temperature has halved from around 80°C to 40°C." He is using 3.6 m-long T45 rods for drilling holes ranging between 6 m and 15 m deep and the regrinding interval is some 50 m. After some 10 regrindings, it is difficult to maintain the ballistic profile of the buttons and Tommy resharpens them to a conventional spherical profile. With the new Diarot settings, wear on the threads is low, uncoupling the rods is easy and the life of the Atlas Copco bits exceeds 1,200 m.

Tommy concludes: "I have increased my weekly production from 1,400 m to an average of 1,700 m and my best week was 1,820 m. Fuel consumption is low at 15 litres an hour - less than half that of many rigs this size - and, despite the fact that I'm drilling much faster than other rigs on the site, I'm consuming only 0.32 litres of diesel per drilled metre. And this means I'm saving more than half a litre per metre - and as I'm drilling some 40,000 metres per year, that amounts to a lot of money!"

How Diarot works

Drilling data are collected at the site and sent to the Diarot specialist for analysis. The results are delivered to the Atlas Copco representative who presents them to the customer. When the recommendations are implemented, the results are fed back to the Diarot specialist. All communications can be carried out via the Internet.