Published in September 2006 Australian Longwall Magazine

Sydney-based manufacturing company Roadway Reinforcement Services says the

main bolt/dowel gloving issues in coal mines are operational, such as poor installation and handling, and design factors of the bolt/dowel such as surface profile and tip-end designs.

In response to this problem, the company conducted an in-house test and trial on its cuttable fiberglass dowels to improve resin mixing and reduce the bolt gloving problem.

“Although improving operational factors would reduce resin gloving and improve resin mixing, bolt tip shape has a more far-reaching effect on reducing bolt gloving,” the company said.

After conducting several tests and trials on different dowel tips and surface profile design, it was determined that the design of the dowel should incorporate the following modifications:

• V-shaped tip end design to improve shredding of the resin capsule;
• abrasive rough surface to improve bonding to the resin; and
• raised rib profile to 24mm of the dowel.

“The shape of the tip will cut the capsule casing, eliminating over-pressurisation and expansion of resin cartridge rather than gloving into it, while dowel surface abrasiveness will increase shredding of the cartridge and the raised profile will improve resin mixing,” the company said.

The previous Bevelled Cropped Dowel tip design allowed the dowel to puncture through the resin anchor cartridge encapsulating the dowel and minimised resin bonding to host material.

The new Thrust Fibreglass Dowel was put on the market in July 2005 and has been used at Moranbah, Oaky North Oaky No1, Newland, Tahmoor, Chain Valley and Central Colliery.

The dowel has a tensile strength of 285kN, shear strength of up to 82.5kN and a head load bearing capacity of 60kN, with the dowel installation method simplified to spin, thrust and hold.

So far, the feedback received from collieries using the new dowel reported a higher consistency in resin setting time, indicating the modifications made by Roadway Reinforcement Services had been successful.