GB2106256A - Indicating tension in bolts - Google Patents

Abstract

An anchor such as a rock bolt includes a washer (22) which is coloured to contrast with the domed washer (14) and which, when compressed during tensioning of the bolt, is extruded radially to display a visually striking tell-tale fringe around the tensioning nut (20). The washer (22) may be of a plastics material. <IMAGE>

Description

SPECIFICATION Rock anchors such as rock bolts Field of the invention This invention lies within the field of those anchoring means which consist of a shank that is inserted into a cavity and is anchored in it by means such as grouting or the expansion of a split sleeve or other mechanical device, and is then tensioned by an axial force imposed on it from outside the cavity. Examples of such anchoring means are rock bolts, in which the axial force is applied to the shank by means of a nut engaging the end of the shaft protruding from the rock bore in which the bolt is anchored.

Background of the invention It is important that the shank should be tensioned to a prescribed extent during installation, and, in the case of a rock bolt in a mine, this requirement is more than important-it could be vital. In current practice in mines, reliance is placed upon the conscientiousness of the installer. Proposals have been made for the use of washers which are deformed during tensioning to provide a visual indication; but, as far as the applicant is aware, there has been no widespread use of such devices, possible because illumination underground is not good enough to make the deformation easily visible.

The object of the present invention is to provide a means that tells at a glance whether the bolt (or other anchoring device) has been properly tensioned.

The invention According to the invention, a method of indicating the attainment of a prescribed tension in the anchor (which, for convenience' sake, will be broadly referred to herein as a rock bolt without limiting the wider applications) consists in locating around the shank of the bolt and between the rock face and a compression element, a washer that is deformable under pressure and which is coloured in contrast to its surroundings; applying pressure to the compression element by tensioning the bolt for the compression element to bear on the washer and cause it to be extruded beyond the compression element to display a tell-tale fringe around the element; and ending the tensioning of the bolt when the fringe has reached a prescribed radial dimension.

Further according to the invention, the washer is of a material the colour of which is in high contrast to the colour of the surroundings.

The drawings An embodiment of the invention is seen in the accompanying drawings, in which: Figure 1 is a side view, partly sectioned, of the bolt, and Figure 2 is an "exploded" view of the components of the bolt.

The illustrated anchor consists of a shank or bolt 10 which is anchored within a bore 12 in a rock body by means which are not shown and which are irrelevant to the invention. The bolt projects from the bore and, outside the bore, has threaded on to it in succession a domed washer 14, a "tell-tale" washer 16, a normal washer 1 8 and a nut 20.

As seen in the "exploded" view, Figure 2, the "tell-tale" washer 1 6 is initially of substantially the same diameter as the washer 1 8. It is made of a ductile material, and preferably a suitable plastic, which, on being squeezed between the washers 1 4 and 1 8 during tensioning of the bolt, is extruded to provide a visible fringe or ring 22 beyond the contour of the washer 18. The "telltale" washer is coloured in high contrast to the colour of the domed washer 14, for instance bright red or yellow. It is, of course, so dimensioned and of such nature than the fringe or ring 22 is not fully formed until the prescribed tension has been imposed on the bolt. It follows that the conditions under which the bolt is to be used will determine the characteristics of the material of which the washer is made and its dimensions.Thus, for a loading of say 20 tons the material and dimensions will be different from those needed for a loading of say 5 tons. What material is used and the dimensions of the washer can readily be determined by design or empirically once the conditions are given.

Claims

1. A method of indicating the attainment of a prescribed tension in a rock bolt or the like, which consists in locating, around the shank of the bolt and between the rock face and a compression element, a washer that is deformable under pressure and which is coloured in contrast to its surroundings; applying pressure to the compression element by tensioning the bolt for the compression element to bear on the washer and cause it to be extruded beyond the compression element to display a tell-tale fringe around the element; and ending the tensioning of the bolt when the fringe has reached a prescribed radial dimension.

2. A method of claim 1 in which the washer is of a material colour of which is in high contrast to its surroundings.

3. A rock bolt or the like comprising a screwthreaded shank, a first washer on the shank which is deformable under compression and which is coloured in contrast to its surroundings when the bolt is in use; and a second, rigid washer of substantially the same diameter as the first washer, adapted to bear on it to compress it; and a nut on the shank to tension the bolt and simultaneously to cause the first washer to be extruded radially beyond the contour of the second washer.

4. The bolt of claim 3 in which the first washer is of a colour that is in strikingly visible contrast to the surroundings in which the bolt is to be used.

5. The bolt of either of claims 3 or 4 in which the first washer is resiliently deformable.

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

Claims (8)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Rock anchors such as rock bolts Field of the invention This invention lies within the field of those anchoring means which consist of a shank that is inserted into a cavity and is anchored in it by means such as grouting or the expansion of a split sleeve or other mechanical device, and is then tensioned by an axial force imposed on it from outside the cavity. Examples of such anchoring means are rock bolts, in which the axial force is applied to the shank by means of a nut engaging the end of the shaft protruding from the rock bore in which the bolt is anchored. Background of the invention It is important that the shank should be tensioned to a prescribed extent during installation, and, in the case of a rock bolt in a mine, this requirement is more than important-it could be vital. In current practice in mines, reliance is placed upon the conscientiousness of the installer. Proposals have been made for the use of washers which are deformed during tensioning to provide a visual indication; but, as far as the applicant is aware, there has been no widespread use of such devices, possible because illumination underground is not good enough to make the deformation easily visible. The object of the present invention is to provide a means that tells at a glance whether the bolt (or other anchoring device) has been properly tensioned. The invention According to the invention, a method of indicating the attainment of a prescribed tension in the anchor (which, for convenience' sake, will be broadly referred to herein as a rock bolt without limiting the wider applications) consists in locating around the shank of the bolt and between the rock face and a compression element, a washer that is deformable under pressure and which is coloured in contrast to its surroundings; applying pressure to the compression element by tensioning the bolt for the compression element to bear on the washer and cause it to be extruded beyond the compression element to display a tell-tale fringe around the element; and ending the tensioning of the bolt when the fringe has reached a prescribed radial dimension. Further according to the invention, the washer is of a material the colour of which is in high contrast to the colour of the surroundings. The drawings An embodiment of the invention is seen in the accompanying drawings, in which: Figure 1 is a side view, partly sectioned, of the bolt, and Figure 2 is an "exploded" view of the components of the bolt. The illustrated anchor consists of a shank or bolt 10 which is anchored within a bore 12 in a rock body by means which are not shown and which are irrelevant to the invention. The bolt projects from the bore and, outside the bore, has threaded on to it in succession a domed washer 14, a "tell-tale" washer 16, a normal washer 1 8 and a nut 20. As seen in the "exploded" view, Figure 2, the "tell-tale" washer 1 6 is initially of substantially the same diameter as the washer 1 8. It is made of a ductile material, and preferably a suitable plastic, which, on being squeezed between the washers 1 4 and 1 8 during tensioning of the bolt, is extruded to provide a visible fringe or ring 22 beyond the contour of the washer 18. The "telltale" washer is coloured in high contrast to the colour of the domed washer 14, for instance bright red or yellow. It is, of course, so dimensioned and of such nature than the fringe or ring 22 is not fully formed until the prescribed tension has been imposed on the bolt. It follows that the conditions under which the bolt is to be used will determine the characteristics of the material of which the washer is made and its dimensions.Thus, for a loading of say 20 tons the material and dimensions will be different from those needed for a loading of say 5 tons. What material is used and the dimensions of the washer can readily be determined by design or empirically once the conditions are given. Claims

1. A method of indicating the attainment of a prescribed tension in a rock bolt or the like, which consists in locating, around the shank of the bolt and between the rock face and a compression element, a washer that is deformable under pressure and which is coloured in contrast to its surroundings; applying pressure to the compression element by tensioning the bolt for the compression element to bear on the washer and cause it to be extruded beyond the compression element to display a tell-tale fringe around the element; and ending the tensioning of the bolt when the fringe has reached a prescribed radial dimension.

2. A method of claim 1 in which the washer is of a material colour of which is in high contrast to its surroundings.

3. A rock bolt or the like comprising a screwthreaded shank, a first washer on the shank which is deformable under compression and which is coloured in contrast to its surroundings when the bolt is in use; and a second, rigid washer of substantially the same diameter as the first washer, adapted to bear on it to compress it; and a nut on the shank to tension the bolt and simultaneously to cause the first washer to be extruded radially beyond the contour of the second washer.

4. The bolt of claim 3 in which the first washer is of a colour that is in strikingly visible contrast to the surroundings in which the bolt is to be used.

5. The bolt of either of claims 3 or 4 in which the first washer is resiliently deformable.

6. The bolt of any of claims 3 to 5, including a domed washer between which and the second washer the first washer is sandwiched.

7. A method of rock bolting substantially as herein described with reference to the accompanying drawings.

8. A rock bolt or the like, substantially as herein described with reference to the accompanying drawings.