ROOF BOLTS FOR USE IN MINES, A METHOD FOR THEIR PRODUCTION AND METHOD FOR THEIR INSTALLATION

摘要

A roof bolt comprises a shaft for insertion in a hole drilled in a mine roof and a head whereby the bolt may be rotated, the head being offset with respe ct to the longitudinal axis of the shaft so that when the bolt is rotated by means of its head the shaft is caused to describe a circle of greater diamet er than its own diameter, and where the offset is at least 2mm and not more tha n 6,30mm. Preferably the offset is from 2,50 to 4mm. The invention includes a method for the production of roof bolts which comprise a shaft for insertion in a hole drilled in a mine roof and a head whereby the bolt may be rotated, the method being characterised by being controlled so that at least 90 % of the bolts produced have their head central axis offset with respect to the longitudinal axis of the shaft by an amount of at least about 1,5mm and not more than about 0,63mm.