Patent ID: 8857537

Claim:
A method for down-the-hole drilling, the drilling being carried out by an apparatus comprising a drilling device comprising a casing and a drilling unit essentially inside the casing part at least during drilling, the drilling unit comprising a drilling head comprising a first drill configured to drill a center hole, a second drill configured to ream the center hole for the casing and a flushing flow arrangement configured to feed a flushing medium and return the flushing medium together with drilling waste at least partly internally inside the casing, the flushing flow arrangement comprising at least one feed flow channel and at least one return flow channel, the method comprising: removably and power-transmittingly coupling the first drill with the second drill to carry out cooperation thereof at least during drilling with the second drill for at least one of a rotational motion, a feeding motion or a hammering motion and to enable removal thereof from the hole, whereby the casing is arranged to be drawn into a hole to be drilled by the drilling unit; bringing the flushing medium with the at least one feed flow channel onto a drilling surface; and returning the flushing medium from the drilling surface together with the drilling waste with the at least one return flow channel, wherein the at least one feed flow channel and at least one return flow channel are axially directed with respect to each other, the flushing flow arrangement being placed at least partly between the first drill and the second drill, wherein when viewed in a cross section the feed flow of the flushing medium is fed to the drilling surface through the at least one feed flow channel between the first drill and the second drill on an outer periphery of the first drill and/or on an inner periphery of the second drill, and wherein the flushing medium with the drilling waste is fed from the drilling surface through the at least one return flow channel between the first drill and the second drill on an outer periphery of the first drill and an inner periphery of the second drill.