Patent ID: 7740060

Claim:
Slacking off device ( 24 ) for use at a drilling device ( 2 ) for rock drilling, which drilling device ( 2 ) comprises a rock drill ( 4 ) to which a drill string ( 10 ) is adapted to be jointed by means of a thread joint, said drill string ( 10 ) comprising an arbitrary number of drill rods ( 12 , 14 , 16 ) adapted to be jointed together by means of thread joints, said drilling device ( 2 ) comprising a driving device for forward and back rotation of the drill string ( 10 ), characterized in that the slacking off device ( 24 ) comprises: a clamping device ( 25 ) arranged to clamp up the drill string ( 10 ), and a separate striking device ( 33 ) adapted to strike, using an angle towards the longitudinal direction of the drill string ( 10 ) of principally 75°-105°, on a first ( 32 ) of any of said thread joints during back rotation, such that an impressed torque on the drill string ( 10 ) is obtained in a thread slacking rotation direction, to provide slacking of the first thread joint ( 32 ).