Mining roof bolt basics
Roof bolting is a method of inserting metal rods into a mine roof to prevent roof collapse. The introduction of mining roof bolts in the 1940s has resulted in the standardisation of roof support systems that could not be destroyed by blasting. As a result, mining roof bolts have contributed to a significant decrease in roof fall fatality rates for underground coal mines.
What is a mining roof bolt?
A mining roof bolt is a long anchor bolt used to stabilise rock excavations in tunnels or rock cuts. It transfers load from the unstable exterior to the confined and much stronger interior of the rock mass.
A mining roof bolt is the most fundamental component of roadway support in coal mines. It plays a crucial role to strengthen the surrounding rock, ensuring the surrounding rock support itself. Mining roof bolts are used in mines and used in engineering technology to strengthen the main body of slopes, tunnels, and dams.
Installation of mining roof bolts
Mining roof bolts are almost always installed in a pattern. The design of this pattern depends on the rock quality and type of excavation. Mining roof bolts are an essential component in tunnelling methods.
Mining roof bolts work by ‘knitting’ the rock mass together before it can move enough to loosen and fail by separating piece by piece. Mining roof bolts may also be used to support wire mesh.
Mining roof bolt bodies can be divided into a free section and an anchoring section. In the free section, tension force at the bolt head is transmitted to the anchoring section. The anchoring section refers to the area where cement paste bonds a prestressing tendon to the soil layer. Its function is to increase bonding friction between the mining roof bolt and soil layer and increase the anchoring pressure of a mining roof bolt.
Rolled vs cut thread bolts
Threads of a mechanical fastener, regardless of whether it is a headed bolt, rod, or bent bolt, can be produced by either cutting or rolling.
Rolled Threads
Reunko Steel provides mining roof bolts that are thread rolled. Roll threading is a process where steel is extruded to form the threaded portion of a fastener. In this process, a bolt is manufactured from a reduced diameter round bar. For example, a 2.5 cm diameter bolt is manufactured from a 2.3 cm diameter round bar. The bolt is “rolled” through a set of threading dies that displaces the steel and forms the threads. The end result is a fastener with a full 2.5 cm diameter threaded portion but a reduced body diameter (2.3 cm). Roll threading is a highly efficient process and often results in significant cost savings.
The weakest area of any mechanical fastener, such as a mining roof bolt, is the minor diameter of the threads. However, since the thread dimensions of a cut thread and rolled thread fastener are identical, there is absolutely no difference in strength. In fact, the work hardening that occurs during the roll threading process may even make a mining roof bolt with rolled threads stronger.
Because a roll threaded mining roof bolt has a smaller body diameter, it weighs less than its full-bodied counterpart. This reduces the cost of the steel, galvanising, heat-treating, plating, freight, and any other costs associated with the mining roof bolt based on weight.
Cold working makes threads more resistant to damage during handling, and rolled threads are often smoother due to the burnishing effect of the rolling operation.
Cut Threads
Cut threading is a process where steel is cut away from a round bar of steel to form the threads. A 2.5 cm diameter bolt, for example, is produced by cutting threads into a whole 2.5 cm diameter body of the bolt.
While cut threading offers fewer limitations concerning diameter and thread length, significantly longer labour times mean higher costs.
Reunko Steel roof bolts
Our steel mining roof bolts are high-quality thread rolled anchor bolts that ensure the stabilisation of rock excavations.
Our standard lengths mining roof bolts range from 0.6 metres to 3.0 metres and are tested in-house in accordance with an ISO 9001:2015 compliant integrated quality management system.
To find out more about our mining roof bolts, get in touch with one of our representatives today.