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Rockmore develops retrac-type reaming bit for tunnelling drill and blast

November 17, 2020  By Ground Water Canada

Rockmore International Inc. has developed a retrac-type reaming bit to improve bit retrieval in face drilling and blasting.

Reaming type bits in underground drilling and blasting operations are used to enlarge selected existing blast holes to bigger diameters for effective blasting and rock fragmentation. This is typically performed in tunnelling, mining and underground construction drilling operations.

The larger reamed holes are not loaded with blasting agents and therefore allow the rock formation to implode during the explosion phase. The empty voids in these reamed holes promote better rock fragmentation and more efficient blasting patterns.


After blast holes are drilled in the tunnel face with hole diameters ranging from 43-51 mm, certain holes in the pattern are enlarged with a typical reaming bit to 76-102 mm, depending on the blast and rock formation requirements. Standard reaming bits feature face designs with dome or narrow nose fronts and are intended to effectively enlarge a predrilled hole. When they are retrieved out of the hole, however, at the end of the target hole depth, they often seize up due to the loose rock debris inside the hole formation.

“Our field support engineers recognized the need for better bit retrieval in face drilling operations,” said Pejman Eghdami, executive vice-president. “After close collaboration with various drilling teams, our designers introduced the innovative retrac features in this new reaming bit.”

Rockmore engineers addressed the challenge of retrieving these style of bits by developing this new model that features retrac-style cutting fins in the rear section to promote better retraction out of the hole. The fins effectively push out any rock chips trapped behind the bit when the drill string is pulled from the blast hole resulting in more efficient reaming operations in underground drilling operations.

The particular model shown is designed to ream from 41 mm to 102 mm holes and configured with a R32 thread connection to the tunnelling rod.

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