Improved rock bolt

Abstract

 A rock bolt (10) for example for use in supporting a mine roof has a leading portion (12) provided with at least one groove (15) extending longitudinally and angularly of the bolt, said groove extending angularly about the bolt in the direction opposite to that in which the bolt is spun.

Description

[0001] The present invention relates to rock bolts and more particularly but not exclusively to rock bolts as employed to support a mine roof.

[0002] In the mining industry, bolts are required to support the mine roof. These bolts are held in position by chemical bonding of the bolt into drilled holes in the roof's draft.

[0003] Current methods involve the drilling of a 27 mm nominal diameter hole in the mine roof. Thereafter, a plastic tube containing a two-part solution is inserted in the hole. The roof bolt, usually a 25 mm diameter standard round steel with a threaded rearward portion, is inserted and spun as it is driven into the hole. This driving and spinning action breaks the plastic tube and mixes the two-part bonding agent which is required to flow back down between the hole side and the bolt to effect a chemical bond therebetween. The bolt, typically having a ridge extending longitudinally and angularly of the bolt (i.e. in a thread-like form), is then rotated after 15 to 20 seconds to effect a retention force between the bolt and the bonding agent.

[0004] The above-discussed known methods have the disadvantage that the plastic tube containing the chemicals frequently jams at the head of the roof bolt, thereby restricting the proper distribution and mixing of the two-part chemical bonding agent. This jamming effect increases substantially the torque and driving force required to properly insert the roof bolt in the hole. Still further, an inferior bonding of the bolt can result greatly detracting from the safety and efficiency of the bolt when tightened with respect to the bonding agent.

[0005] It is the object of the present invention to overcome or substantially ameliorate the above disadvantages.

[0006] This invention provides a rock bolt having a leading portion provided with at least one groove extending longitudinally and angularly of the bolt, said groove extending angularly about the bolt in the direction opposite to that in which the bolt is spun.

[0007] Preferably the rock bolt has a leading edge which is chamfered so as to provide the leading portion with a frusto-conical configuration.

[0008] A preferred form of the present invention will now be described by way of example with reference to the accompanying drawings wherein:

Fig. 1 is a schematic side elevation of a roof rock bolt;

Fig. 2 is a schematic top plan view of the bolt of Fig. 1; and

Fig. 3 is a schematic longitudinal sectional view of the rock bolt of Fig. 1 being inserted into a drilled hole.

[0009] In the accompanying drawings there is schematically depicted a roof bolt 10 having an elongated shank 11 with a leading portion (head) 12. The other end of the shank 11 is threaded so as to have a threaded portion 13 which receives a tightened nut 14.

[0010] The leading portion 12 is provided with two slots 15 which extend angularly about and longitudinally of the shank 11, preferably extending approximately 20 to 50 mm (Dimension 'A') from the leading edge 17 of the rock bolt 10. Still further, the leading portion 12 is chamfered so as to provide the leading portion 12 with a "frusto-conical" configuration. Accordingly, the leading portion 12 has sloping surfaces 16 extending angularly about the longitudinal axis of the shank 11.

[0011] The slots 15 intersect with the sloping surfaces 16 so as to provide cutting edges 18 which aid in the breaking open of the plastic tube 19, and hence allowing the two-part bonding agent to be efficiently discharged from the plastic tube 19.

[0012] The slots 15 extend angularly about the shank 11 in the direction opposite to that in which the rock bolt 10 is spun upon entry into the hole. The slots 15 provide a convenient passage for the bonding agent to move away from the end of the hole and ensures that the two-part chemi cal bonding agent is distributed longitudinally of the shank 11 in order to provide a good bond with the drilled hole.

[0013] It is envisaged that the slots 15 and sloping surfaces 16 (i.e. the chamfer) can be provided in conjunction with the standard features of previously known rock bolts wherein at least one positive (or raised) ridge 19 extending longitudinally and angularly (in an opposite sense to the slot(s) 15) is/are provided along the length of the bolt up to the threaded rearward portion 13. When the rock bolt 10 is spun whilst being driven into the hole, the ridge(s) 19 provide a screw feed means for the bonding agent to be distributed along the length of the shank 11.

[0014] In operation of the above-described roof bolt 10, a hole 1 is drilled in the mine roof 2. Thereafter, a two-part plastic tube 3 is inserted containing the two-part bonding agent 4. The roof bolt 10 is simultaneously inserted in the hole and spun. As the roof bolt 10 is spun whilst being driven longitudinally into the hole, the leading edge of the rock bolt 10 breaks the plastic tube 3 thus releasing the contents thereof when are then mixed by the leading portion 12 of the rock bolt 10. As the roof bolt 10 is spun, the combination of gravity force, a pumping action due to compressive forces on the bonding agent 4 by the bolt 10, the ridges 19, and the slots 15 causes the two parts of the chemical bonding agent 4 to be sufficiently mixed and distributed longitudinally of the shank 11 to ensure a good bond with the drilled hole 1.

[0015] Upon curing of the bonding agent 4, the slots 15 the ridges 19, and the bonding agent 4 adhered thereto provide the necessary resistance to longitudinal movement of the bolt 10, thus negating the need to "tighten" the bolt 10 after the bonding agent 4 is cured. It is preferably that the bonding agent 4 adheres to the surfaces of the hole 1 and the rock bolt 10.

[0016] A ceiling retainer strip 20 may then be mounted onto the threaded rearward portion 13 of the rock bolt 10 using the retention nut 14.

Claims

1. A rock bolt having a leading portion provided with at least one groove extending longitudinally and angularly of the bolt, said groove extending angularly about the bolt in the direction opposite to that in which the bolt is spun.

2. The rock bolt of Claim 1 wherein a leading edge of said leading portion is chamfered so as to provide said leading portion with a frusto-conical configuration.

3. The rock bolt of Claim 2 wherein said chamfer and said groove combine to provide at least one cutting edge on said leading edge.

4. The rock bolt of any one of Claims 1, 2 or 3 wherein said leading portion has a predetermined longitudinal dimension, and wherein said dimension is smaller than the longitudinal length of said rock bolt.

5. The rock bolt of Claim 4 wherein said longitudinal dimension of said leading portion is approximately 30 mm to 50 mm.

Drawing