GB2071250A

GB2071250A - Rock bolt assembly

Info

Publication number: GB2071250A
Application number: GB8107704A
Authority: GB
Original assignee: Titan Manufacturing Co Pty Ltd
Current assignee: Titan Manufacturing Co Pty Ltd
Priority date: 1980-03-11
Filing date: 1981-03-11
Publication date: 1981-09-16
Also published as: AU6804381A

Abstract

A three component rock bolt assembly for use in locations where the bolt cannot be inserted perpendicularly to the rock face includes a conventional rock bolt 1 threaded at one end 2, a domed nut 4 threaded on end 2, and a plate washer 3 having a central portion 7 deformed away from the washer plane 6 so that the washer hole has a tapered periphery. The hole periphery is tapered to accommodate the domed nut 4 which is threaded onto the bolt, the nut being provided with tensioning flats 10 to allow the assembly to be secured with the plate rigidly held against the rock face. <IMAGE>

Description

SPECIFICATION Rock bolt assembly This invention relates to a rock bolt assembly and has been devised particularly though not solely for use in applications where the axis of the bolt is not perpendicular to the rock face when inserted therein.

In the past where rock bolts have been used in locations where it is not possible to align the axis of the bolt perpendicularly to the rock face, it has been known to provide a domed plate washer used in conjunction with a ball washer which has a domed face engaging the domed plate washer and a flat face which engages a nut on the threaded end of the rock bolt. Such assemblies have the disadvantages that the assembly is expensive due to the number of components involved and that the ball washer is unevenly stressed and can fracture under load.

It is therefore an object of the present invention to provide a rock bolt assembly which will ameliorate the foregoing disadvantages in a simple yet effective manner.

Accordingly the invention in one broad form provides a rock bolt assembly comprising an eiongate bolt having one threaded end and its other end adapted to be anchored into a bolt hole, a nut adapted to threadedly engage said threaded bolt end and a plate washer having a hole therein adapted for engagement by said bolt and for forcing against a rock face in use by tensioning of said nut, said assembly being characterized by a domed surface on said nut arranged to bear against the periphery of the hole in said plate washer and in that plate washer is deformed out of the plane of the plate in the area surrounding said hole to form a tapering periphery to said hole.

By way of example only, a preferred form of this invention will now be described with reference to the accompanying drawings in which: Fig. 1 is a cross-sectional view of the threaded end of a rock bolt assembly according to the invention; Fig. 2 is a side view of an alternative form of nut for use in the assembly shown in Fig. 1; Fig. 3 is a perspective view of the plate washer used in the rock bolt assembly according to the invention; and Fig. 4 is a cross-sectional view of the plate washer shown in Fig. 3.

The assembly comprises a rock bolt 1 of conventional nature of which a portion has been shown in Fig. 1 and which has a threaded end 2, its other end being adapted to be anchored into a bolt hole drilled in a rock face. The assembly is provided with a plate washer 3 and a nut 4 threadedly engaged with the threaded end 2 of the rock bolt.

The plate washer has a central hole 5 larger in diameter than the bolt 1 and smaller in diameter than the periphery of the nut 4. The plate washer is deformed out of the plane 6 of the plate in the portion 7 surrounding the hole forming a tapered periphery 8 to the hole.

The nut 4 is provided with a domed surface 9 and flats 10 adapted for engagement by a tightening spanner or socket in the normal manner. The domed surface 9 is arranged to bear against the tapered periphery 8 of the hole 5.

In use the assembly is assembled as shown in Fig. 1 and the bolt is engaged in a hole in the rock face according to normal practice. The nut 4 is then tightened causing the domed surface 9 to bear against the tapered periphery 8 of the hole 5 evenly and to force the plate washer against the rock face. Because of the even engagement between the domed surface of the nut and the tapered periphery of the hole in the washer the tension applied to the plate from tightening the nut is evenly applied causing the transfer of torque applied to the nut to induce tension in the bolt without massive friction losses.

The compressive stresses induced into the nut tend to compress the nut thread onto the bolt thread under load and this largely counteracts the normal tendency to nut thread dilation under load.

Because one less component is used when compared with prior art systems, assembly time is reduced aiding increases in mining productivity.

Furthermore tha hole punched and formed in the prior art washer is substantially larger than the punched and formed hole in the washer of this invention and thus the bearing area under load is significantly increased if the washer tends to flatten.

Although the nut has been shown in one configuration in Fig. 1 it will be appreciated that an alternative form of nut having a domed surface may be provided. One such alternative is shown in Fig. 2 in which the nut is provided with conventional flats 11 and an enlarged domed portion 12 forming a mushroom-like configuration.

In addition, prior art rock bolt assemblies with flat washers are prone, when loaded, to distort the centre portion of the washer away from the tightening nut, i.e. "reverse dishing" of the washer. In cases where the hole in the rock is sufficiently large at the rock face, this distortion in the washer may even be sufficient to allow the nut to pull through the washer. The rock bolt assembly of the present invention has been found not to exhibit such "reverse dishing" under similar load conditions.

1. A rock bolt assembly comprising: an elongate bolt having one threaded end and its other end adapted to be anchored into a bolt hole; a nut adapted to threadedly engage said threaded bolt end; and a plate washer having a hole therein adapted for engagement by said bolt and for forcing against a rock face in use by tensioning of said nut, said assembly being characterized by a domed surface on said nut arranged to bear against the periphery of said plate washer hole and in that said plate washer is deformed out of

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Rock bolt assembly This invention relates to a rock bolt assembly and has been devised particularly though not solely for use in applications where the axis of the bolt is not perpendicular to the rock face when inserted therein. In the past where rock bolts have been used in locations where it is not possible to align the axis of the bolt perpendicularly to the rock face, it has been known to provide a domed plate washer used in conjunction with a ball washer which has a domed face engaging the domed plate washer and a flat face which engages a nut on the threaded end of the rock bolt. Such assemblies have the disadvantages that the assembly is expensive due to the number of components involved and that the ball washer is unevenly stressed and can fracture under load. It is therefore an object of the present invention to provide a rock bolt assembly which will ameliorate the foregoing disadvantages in a simple yet effective manner. Accordingly the invention in one broad form provides a rock bolt assembly comprising an eiongate bolt having one threaded end and its other end adapted to be anchored into a bolt hole, a nut adapted to threadedly engage said threaded bolt end and a plate washer having a hole therein adapted for engagement by said bolt and for forcing against a rock face in use by tensioning of said nut, said assembly being characterized by a domed surface on said nut arranged to bear against the periphery of the hole in said plate washer and in that plate washer is deformed out of the plane of the plate in the area surrounding said hole to form a tapering periphery to said hole. By way of example only, a preferred form of this invention will now be described with reference to the accompanying drawings in which: Fig. 1 is a cross-sectional view of the threaded end of a rock bolt assembly according to the invention; Fig. 2 is a side view of an alternative form of nut for use in the assembly shown in Fig. 1; Fig. 3 is a perspective view of the plate washer used in the rock bolt assembly according to the invention; and Fig. 4 is a cross-sectional view of the plate washer shown in Fig. 3. The assembly comprises a rock bolt 1 of conventional nature of which a portion has been shown in Fig. 1 and which has a threaded end 2, its other end being adapted to be anchored into a bolt hole drilled in a rock face. The assembly is provided with a plate washer 3 and a nut 4 threadedly engaged with the threaded end 2 of the rock bolt. The plate washer has a central hole 5 larger in diameter than the bolt 1 and smaller in diameter than the periphery of the nut 4. The plate washer is deformed out of the plane 6 of the plate in the portion 7 surrounding the hole forming a tapered periphery 8 to the hole. The nut 4 is provided with a domed surface 9 and flats 10 adapted for engagement by a tightening spanner or socket in the normal manner. The domed surface 9 is arranged to bear against the tapered periphery 8 of the hole 5. In use the assembly is assembled as shown in Fig. 1 and the bolt is engaged in a hole in the rock face according to normal practice. The nut 4 is then tightened causing the domed surface 9 to bear against the tapered periphery 8 of the hole 5 evenly and to force the plate washer against the rock face. Because of the even engagement between the domed surface of the nut and the tapered periphery of the hole in the washer the tension applied to the plate from tightening the nut is evenly applied causing the transfer of torque applied to the nut to induce tension in the bolt without massive friction losses. The compressive stresses induced into the nut tend to compress the nut thread onto the bolt thread under load and this largely counteracts the normal tendency to nut thread dilation under load. Because one less component is used when compared with prior art systems, assembly time is reduced aiding increases in mining productivity. Furthermore tha hole punched and formed in the prior art washer is substantially larger than the punched and formed hole in the washer of this invention and thus the bearing area under load is significantly increased if the washer tends to flatten. Although the nut has been shown in one configuration in Fig. 1 it will be appreciated that an alternative form of nut having a domed surface may be provided. One such alternative is shown in Fig. 2 in which the nut is provided with conventional flats 11 and an enlarged domed portion 12 forming a mushroom-like configuration. In addition, prior art rock bolt assemblies with flat washers are prone, when loaded, to distort the centre portion of the washer away from the tightening nut, i.e. "reverse dishing" of the washer. In cases where the hole in the rock is sufficiently large at the rock face, this distortion in the washer may even be sufficient to allow the nut to pull through the washer. The rock bolt assembly of the present invention has been found not to exhibit such "reverse dishing" under similar load conditions. CLAIMS

1. A rock bolt assembly comprising: an elongate bolt having one threaded end and its other end adapted to be anchored into a bolt hole; a nut adapted to threadedly engage said threaded bolt end; and a plate washer having a hole therein adapted for engagement by said bolt and for forcing against a rock face in use by tensioning of said nut, said assembly being characterized by a domed surface on said nut arranged to bear against the periphery of said plate washer hole and in that said plate washer is deformed out of the plane of the plate in the area surrounding said hole to form a tapering periphery to said hole.

2. A rock bolt assembly as defined in claim 1, wherein said deformed portion of said plate washer is located substantially centrally of said washer and wherein the periphery of said hole is substantially frusto-conical towards the plane of said plate.

3. A rock bolt assembly as defined in claim 1 or claim 2, wherein the outer surface of said nut is continuous and comprises a domed upper portion and a plurality of adjacent peripheral flats each being planar parallel to the nut axis and each merging with a respective portion of said domed upper nut portion.

4. A rock bolt assembly as defined in claim 1 or claim 2, wherein the outer surface of said nut is stepped between an upper domed portion and a lower portion consisting of a plurality of adjacent flats, the nut being thus of overall mushroomshaped appearance.

5. A rock bolt assembly substantially as described herein with reference to and as illustrated by Figs. 1, 3 and 4 or Fig. 1 as modified by Fig. 2 and Figs. 3 and 4 of the accompanying drawings.