Rock bolt

摘要

A method of making a rock bolt (1) with a thread on a section thereof comprising the steps of; providing a metal bar of circular or near circular cross-section having a diameter which is substantially equal to the pitch diameter of the thread to be provided thereon; passing the bar in a single pass between a pair of rolls (8, 9) to pinch the bar at intervals to cold form protrusions (2) spaced from one another in staggered formation on opposite sides of the bar along a selected section thereof; displacing one or more of said rolls (8, 9) away from the other at a selected time to ensure that said protrusions are formed only on said selected section of bar; straightening the bar in its cold condition; and cold rolling in a thread (4) with said pitch diameter on a further selected section of the bar which is free of the said protrusions.