Published in March 2006 Australian Longwall Magazine

The bolts were becoming entangled in the armoured face conveyor (AFC) and conveyor transfer points, particularly at the start of a block where the shearer comes into contact with the bolts across the longwall install face. This resulted in equipment damage, hazardous maintenance activities and production downtime.

Other underground mines had addressed this problem by using fibreglass or plastic, glass reinforced polymer (GRP) rib bolts.

The difficulty with implementing this solution at Beltana lay in the recovery of the bolts from the coal product before they were transferred to the Bulga Complex Washery, where they caused maintenance problems.

Ordinarily, steel bolts would be recovered from the run of mine (ROM) coal via a series of magnets installed along the conveyor belts. However, Beltana had no system that screened and recovered GRP bolts before they arrived at the washery.

As GRP bolts normally have a specific gravity of around 1.6, very much the same as coal, they would fall within the recovery range of the washery’s dense medium bath circuit.

This meant the GRP bolts might attempt to follow the clean coal through the washery circuit and finish up in the clean product pile – that is if they did not get stuck in something along the way and cause damage.

In order to avoid these possibilities in using GRP bolts, modifications to the plant would involve considerable cost.

Beltana therefore sought to find a solution to the problem and asked Cutabolt, a specialist supplier of GRP rib bolts, to help.

Representatives of Beltana, the Bulga Washery and Cutabolt identified the issues associated with steel bolts and their effect on mining, transporting and marketing.

Armed with this knowledge, Simon Knight from Cutabolt approached his rod supplier, Pultron, to see what they could do.

Their efforts led to the production of a high-density (HD) fibreglass rib bolt with a specific gravity of 2.0.

The newly designed GRP rib bolt has a tensile strength of no less than 250kN and shear strength of no less than 70kN, which makes it suitable for rib support within Beltana’s geological conditions.

Thanks to the collaborative efforts of Beltana and Cutabolt, the new HD fibreglass rib bolts are now in use on the longwall install face.

The GRP bolts are easily cut out by the shearer without the risk of jamming any equipment or splitting belts.

Further, the bolts are reported directly to ash at the Bulga Washery, resulting in no problems at the plant and no bolts in the washed coal. Most importantly, hazards at longwall start-ups have been eliminated through this engineering improvement, Beltana said