Outstanding drill steel life has been achieved at a quarry site on the west coast of Sweden where drilling conditions would normally stretch most rods and bits to the limit.
At the Angered Quarry near Gothenburg, drilling contractor Skanska decided to use Atlas Copco Secoroc?s shank adapters,
T45 drill rods and 76 and 89 mm retrac bits in combination with an Atlas Copco
ROC D7C drill rig (renamed SmartROC T35).
The shank adapter, rod and retrac bit setup was a good choice for the prevailing conditions due to its solid reputation for durability and reliability. But it was this in combination with the ROC D7C and the skill of the operator that produced results that are rarely achieved in surface drilling.
Long holes were drilled on 25???30 m high benches in hard, often fissured granite, quartz and mica. The drilling pattern was 2.5 by 3.0 m and the penetration rate was 1.1???1.6 m/min. Nothing unusual in that, but deviation was only 10???50 cm per 20 m and drill steel consumption was extremely low.
The rig, which is equipped with the latest GPS Rock Manager Control system, controls the process by drilling in the right place, and feeding the rods from the seven-rod cassette. These rods are subjected to dampening pressure of 60??70 bar, which steers the feeding pressure to 40 bar.
This results in good penetration rate and a rod service life of up to 26?000 m. With shank adapters lasting an average of 8?000 m, the operator has been able to drill 1?100???1?200 m of blast holes every week.
Atlas Copco Secoroc?s Product Specialist Per-Olof Einarsson says: ?These results are fantastic ? one of the best examples I have ever seen. It goes to show that by synchronizing Atlas Copco Secoroc rock drilling tools with the right drill rig and an experienced operator you keep costs to a minimum and productivity at its best.?
Einarsson also emphasizes that the skill of the operator is still of great importance in order to achieve exceptional lifelength of the drill steel and adds: ?Contrary to what many peopl-e think, it is not just the penetration rate that affects productivity.?
Atlas Copco?s rock drilling tools are subjected to a special heat treat-ment proces-s to provide optimum durability.
Why straightness is important
A deviation of 10?50 cm over a 20 m hole depth is considered very satisfactory. Large hole deviation results in poor blasting as the bottom of some holes will be too close to each other and some too far apart. Consequently this leads to a variation of rock fragments. The larger fragments may not fit the crusher which creates the need for secondary blast-ing which in turn reduces productivity. Another disadvantage of large hole deviation is that shank adapters and rods bend more easily and break, also reducing productivity and increasing costs.
Epiroc operated under the trademark “Atlas Copco” prior to January 1, 2018.