THE POWER OF REPOWERING

by Thord Wikström,
Product Manager, Rock Drills

There are times when drill rigs fail to live up to their owner's expectations. The reasons can be many and varied, resulting in slow progress, frequent breakdowns and higher costs in terms of increased drill steel consumption and overall downtime.

In situations like these, which naturally impact total project economics, it is understandable when drillmasters wish they had better equipment at their disposal.

But if an investment in new and better equipment is not an option, all is not lost. The performance of an old drill rig can sometimes be significantly enhanced simply by upgrading its rock drills.

This is called "repowering", and it is becoming an increasingly popular way to solve short-term rock drilling problems.

Among the best

Atlas Copco rock drills, which are widely considered to be among the best in the world, are developed and manufactured for optimum performance together with the drill string and the rigs.

And today, there are many instances where customers have chosen to fit our rock drills to their rigs - irrespective of their make - with vastly improved results.

Thord Wikström, Technical Product Manager, Rock Drills

In all cases, they report improved penetration rate, lower drill steel costs, fewer re-grinding operations, fewer servicing intervals and drastic reductions in downtime.

Different drill rigs require different solutions before they can be equipped with new rock drills. First, all data must be collected regarding the capacity of the power pack, the hydraulic system and so on.

Diarot simulation

We use the software program Diarot to simulate the sort of performances that customers can expect, including a recommendation for the most suitable drill string and settings of the drilling system.

The most common way of repowering a drill rig is, of course, to use a rock drill of the same brand as the rig. To change from a COP 1238 rock drill to a double-dampened rock drill like COP 1432 or COP 1838 might require modifications of the cradle and drill steel support, hoses and valves. We have experience in how to do this, and in many cases a significant improvement in productivity and drill steel life has been achieved by repowering old Atlas Copco rigs.

It must be clear, however, that to mount an advanced rock drill onto a rig of another make is not an easy task and that it is not accomplished in just a few hours. Rig modifications are often required, especially to the rig's hydraulic system, including settings and controls.

After refitting, the "new" rig must also be thoroughly tested before being put into full-scale operation and, even then, the end result will not be the same as a new Atlas Copco rig.

Getting ahead in Germany

Here are two examples of where this method of rejuvenating rigs has paid off for their owners - one in Germany, the other in Finland.

DSK Anthracit Ibbenbüren GmbH produces 1.7 million tonnes of anthracite per year from an old German mining area that was opened up in the 17th century.

All drifting and development at the mine is by drill and blast and some 500,000 drill metres per year is accomplished with a fleet of crawler-mounted, single and twin-boom, coal mining rigs.

The company wanted an increase in drilling capacity, heard that there was a new COP 1432 on the market and contacted us at last year's Bauma exhibition.

New double dampener

The COP 1432 is a short machine particularly suited for combined drifting and bolting in coal mines. One option was to re-power the fleet with the new Atlas Copco COP 1432 rockdrill and, using the Diarot program, simulations showed that it would provide an increase in drilling capacity of at least 20%.

Tests totalling 41,000 drillmetres confirmed that a minimum increase of 20% was possible and, thanks to the new rock drill's efficient double-dampening system, it would also prolong drill steel life.

We promised that the COP 1432 would increase penetration rates by 20 per cent. Not only has this been achieved, but drill steel costs have been cut by 20 per cent.

In Finland: Site Manager Jukka Rasanen (left) and Foreman Reijo Mara of YIT Corporation.

Using a 51 mm diameter spherical button bit with a life-length of 500 metres, drilling time for a 3.2 m-deep hole in the hard (150 Mpa) sandstone took only 100 seconds. Not only that, its high torque proved to be excellent for rotating resin bolts at 400 rpm to mix the resin.

Modifications required to fit the rock drills included changes in the cradle and drill steel support and in some of the connections between the hydraulic hoses and the rock drill.

Fine form in Finland

In Finland, YIT Corporation, the largest contractor in the country, has been using rigs and rock drills from different manufacturers for many years. Lately, the company has not been entirely satisfied with some of the results it had been achieving and asked us if it was possible to repower its rigs.

YIT conducted a test in the summer of 1998 by comparing an Atlas Copco COP 1838 rock drill on a 3-boom rig with rock drills of another make.

The Atlas Copco COP 1838 rock drills achieved 30 per cent better rock penetration, drilling 2.2 to 2.7 metres per minute - a significant improvement on the previous performance.

The company was satisfied. By choosing to repower its existing rigs with Atlas Copco rock drills, it found that it could save a great deal of time without having to make any major new investments.

This rig, with its new rock drills, is now helping YIT to drive a multi-purpose tunnel under the Lauttasaari sound in Helsinki. It is also being used for drilling 22 metre-long holes for pre-grouting, 64 mm in diametre, and YIT reports that the life-length of the drill steel has increased substantially.

Work on the tunnel, which will be 1,341 metres long, 5.4 metres wide and 4 metres high, started in October, 1998, and is to be finished this summer.

Pathway to productivity

These examples show that repowering can be the ideal way to increase productivity, particularly for short-term projects where time is limited and where an investment in a brand new rig is not economically justifiable.

In this way, contractors can gain access to Atlas Copco's advanced rock drill technology precisely when they need it and at a modest price. The first step to repowering is to ask Atlas Copco for a free Diarot simulation.

Cool result with double dampening The Atlas Copco concept of repowering was born in the mid-1980s when it was realised that some drilling operators wanted better performances from their existing rigs. Measuring the temperature on the coupling is a simple way to determine the efficiency of your rock drill and your rig. Ideal temperatures with double dampened rock drills and cylinder feeds should be down to 60° C for flushing and 45° C for water flushing. In 1992, Atlas Copco began to produce a new generation of rock drills equipped with double dampeners and last year these machines, in the COP 1838 and COP 4050 ranges, were joined by the COP 1432. These machines have double dampeners which not only dampen the recoil in the drill string, they absorb the excess energy from the returning shockwave, giving lower temperature and longer life of the drill string. In addition, the drill string joints are kept at an optimal tightness, enabling the bit to maintain full and constant contact with the rock throughout the drilling process and resulting in higher penetration rate.

For more information please contact thord.wikstrom@atlascopco.com