Dynamic rockbolt
A friction bolt includes a first tube having an internal diameter and defining a longitudinal split, the tube being radially expandable. The bolt has a first leading or distal end for insertion into a bore and a second or proximal end defining a head and further includes a second tube defining a longitudinal split and having an external diameter which is substantially the same as or larger than the internal diameter of the first tube. The second tube is located inside the first tube with its exterior in contact with the interior of the first tube. The bolt includes a slip and lock mechanism that allows the first or exterior and second or interior tubes to move relative to each other along the longitudinal axis of the friction bolt when a tensile force is applied to the bolt, but to lock together after the force is removed.
1 . A friction bolt comprising a first elongate tube having an internal diameter and defining a longitudinal split, the tube being radially expandable, the bolt having a first leading or distal end for insertion into a bore and a second or proximal end defining a head and further comprising a second elongate tube defining a longitudinal split and having an external diameter which is substantially the same as or larger than the internal diameter of the first tube located inside the first tube with its exterior in contact with the interior of the first tube and wherein the bolt comprises a slip and lock mechanism that allows the first or exterior and second or interior tubes to move relative to each other along the longitudinal axis of the friction bolt when a tensile force is applied to the bolt, but to lock together after the force is removed,
wherein the slip and lock mechanism comprises formations or deformations on one or both of the first and second tubes which interlock the tubes together but which can disengage and allow the tubes to slide relative to one another under longitudinal tension.
2 . The friction bolt as claimed in claim 1 , wherein the first and second tubes are generally part-circular in cross section.
3 . The friction bolt as claimed in claim 1 , wherein the first elongate tube has a length and wherein the second elongate tube has a length which is at least half the length of the first elongate tube.
4 . The friction bolt as claimed in claim 1 , wherein the length of the second elongate tube is substantially the same as the length of the first elongate tube.
5 . The friction bolt as claimed in claim 1 , wherein the formations or deformations on one or both of the first and second tubes comprise overlapping radial crimps or corrugations on the first and second tubes, the corrugations defining a series of ribs and grooves with the ribs of the corrugations of the first tube nesting in the grooves of the corrugations of the second tube.
6 . The friction bolt as claimed in claim 5 , wherein the corrugations of the second tube extend further along the tube than the corrugations of the first tube so that they are overlapped by both a corrugated section of the first tube and an un-corrugated part cylindrical section defining a smooth outer surface.
7 . The friction bolt as claimed in claim 5 , wherein the first and second tubes define at least two overlapping corrugated sections, one near or towards the proximal end of the friction bolt and one near or towards the distal end of the friction bolt.
8 . The friction bolt as claimed in claim 1 , wherein the proximal end which engages with a bearing plate or the like is defined on one tube and the distal tapered end of the friction bolt is defined on the other tube.
9 . The friction bolt as claimed in claim 1 , wherein the proximal end of the second tube defines a ring for engagement with a bearing plate or the like and the distal end of the first tube is tapered for insertion into a bore.
10 . The friction bolt as claimed in claim 1 , wherein the formations on one or both of the first and second tubes comprise overlapping spaced ribs formed on the first and second tubes, the ribs of the first tube nesting in spaces between the ribs of the second tube.
11 . The friction bolt as claimed in claim 10 , wherein the ribs are formed on the exterior of the second tube by welding or other additive manufacturing process and the ribs are formed on the interior of the first tube by welding or other additive manufacturing process.
12 . The friction bolt as claimed in claim 10 , wherein the ribs are separated by spaces which are from 1 to 5 times the diameter of the ribs.
13 . The friction bolt as claimed in claim 10 , wherein there is at least one set of ribs on each tube.
14 . The friction bolt as claimed in claim 13 , wherein each set of ribs comprises from 2 to 10 ribs.
15 . The friction bolt as claimed in claim 1 , wherein the slip and lock mechanism comprises a layer of adhesive.