Strand, cable bolt and its installation

Abstract

A strand (20) for a cable bolt (14) comprises a plurality of metallic elongated members (22, 24) twisted together. At least one of the elongated members has a corrosion resistant coating (54) and surface deformation, so as to improve the bodig efficiency and the anchorage of the strand.

Claims

1. A method of fabricating a strand with improved corrosion resistance and a reliable anchorage, comprising the steps of: (a) preparing a plurality of outer metallic elongated members; (b) coating a surface of the outer metallic elongated members with a corrosion resistant layer having a thickness in a range of 10 g/m.sup.2 to 200 g/m.sup.2; (c) cold working the coated outer metallic elongated members to their final dimensions; (d) deforming the surface of the coated outer metallic elongated members to form indentations having a depth in a range of 80 m to 130 m; and (e) arranging the coated outer metallic elongated members and twisting them together with a central metallic elongated member, wherein step (b) and step (c) are performed prior to step (d) such that a profile of the corrosion resistant layer is conformal to a profile of the indentations, and the central metallic elongated member is a smooth round wire, and wherein the strand forms a cable bolt configured to be inserted in a borehole of a mine roof.

2. The method of fabricating a strand according to claim 1, wherein in step (d) the surface of the coated outer metallic elongated members are deformed by rolling indentation.

3. The method of fabricating a strand according to claim 1, wherein in step (b) the thickness of the corrosion resistant layer is in a range of 30 g/m.sup.2 to 150 g/m.sup.2.

4. The method of fabricating a strand according to claim 1, wherein in step (b) the thickness of the corrosion resistant layer is in a range of 50 g/m.sup.2 to 80 g/m.sup.2.

5. The method of fabricating a strand according to claim 1, wherein the cable bolt is formed by fixing a bolt head at a proximal end of the strand.

6. The method of fabricating a strand according to claim 1, wherein the strand comprises six coated outer metallic elongated members and one central metallic elongated member.

7. The method of fabricating a strand according to claim 1, wherein the strand comprises five coated outer metallic elongated members and one central metallic elongated member.

8. The method of fabricating a strand according to claim 1, wherein at least one outer metallic elongated member is made of steel comprising carbon, manganese, silicon, sulphur, phosphorous and iron.

9. The method of fabricating a strand according to claim 1, wherein at least one outer metallic elongated member is made of steel comprising a carbon content in a range of 0.2 wt % to 0.8 wt %, a manganese content in a range of 0.3 wt % to 0.8 wt %, a silicon content in a range of 0.1 wt % to 0.5 wt %, a maximum sulphur content of 0.05 wt %, a maximum phosphorous content of 0.05 wt %, and iron.

10. The method of fabricating a strand according to claim 8, wherein the steel comprising the at least one outer metallic elongated member further comprises traces of copper, chromium, nickel, vanadium, molybdenum or boron.

11. The method of fabricating a strand according to claim 1, wherein at least one outer metallic elongated member is made of steel comprising carbon, manganese, silicon, chromium, vanadium and iron.

12. The method of fabricating a strand according to claim 1, wherein at least one outer metallic elongated member is made of steel comprising a carbon content in a range of 0.8 wt % to 1.0 wt %, a manganese content in a range of 0.5 wt % to 0.8 wt %, a silicon content in a range of 0.1 wt % to 5.0 wt %, a chromium content in a range of 0.1 wt % to 0.5 wt %, a vanadium content in a range of 0.02 wt % to 0.2 wt %, and iron.

13. The method of fabricating a strand according to claim 1, wherein at least one outer metallic elongated member is made of steel comprising 0.84 wt % carbon, 0.67 wt % manganese, 0.23 wt % silicon, 0.24 wt % chromium, 0.075 wt % vanadium, and iron.

14. The method of fabricating a strand according to claim 1, wherein the corrosion resistant layer comprises zinc or a zinc alloy.

15. The method of fabricating a strand according to claim 1, wherein the corrosion resistant layer comprises a zinc aluminum coating.

16. The method of fabricating a strand according to claim 15, wherein an aluminum content of the zinc aluminum coating is in a range of 2 wt % to 12 wt %.

17. The method of fabricating a strand according to claim 1, wherein the corrosion resistant layer comprises aluminum, magnesium and zinc.

18. The method of fabricating a strand according to claim 17, wherein the corrosion resistant layer comprises 2% to 10% aluminum, 0.2% to 3% magnesium and a remainder of zinc.

Description

BRIEF DESCRIPTION OF FIGURES IN THE DRAWINGS

(1) The invention will be better understood with reference to the detailed description when considered in conjunction with the non-limiting examples and the accompanying drawings, in which:

(2) FIG. 1 is a cross-section of part of a roof illustrating one roof support bolt.

(3) FIG. 2 is a cross-section of a strand according to the invention.

(4) FIG. 3 is a side view of an outer wire of the strand according to the invention.

(5) FIG. 4 is a transverse section of an outer wire for the strand according to the first embodiment of the invention.

(6) FIG. 5 is a transverse section of an outer wire for the strand according to the second embodiment of the invention.

(7) FIGS. 6a, 6b, 6c, 6d, 6e, 6f, 6g, 6h, 6i, 6j are side views of an outer wire of the strand with some possible types of indents thereon.

MODE(S) FOR CARRYING OUT THE INVENTION

(8) FIG. 2 is a cross section of a strand 20 according to the present application. The strand 20 includes a core wire 22 and six outer wires 24 twisted around the core wire 22. The core wire 22 may be a wire with shallow indentations. Preferably, the core wire 22 is a smooth round wire. The outer wires 24 are subjected to a surface deformation. The surface deformation are preferably indentations by rolling. The indents 26 formed on the surface of each outer wire.

(9) As an example, as shown in FIG. 2, the strand has a 1+6 configuration, where the core wire 22 has a diameter larger than the diameter of the outer wires 24. The diameter of the core and outer wires is in the range of 1 to 20 mm. For instance, the diameter of the core wire is 5.3 mm and the diameter of the outer wire is 5.1 mm. The strand may be formed with a right or left hand helix. As an example, the lay length of the helix of the outer wire round the core wire is 200 mm giving a lay length of about 14 diameters.

(10) FIG. 3 is a side view 30 of the outer wire 24 in FIG. 2. As shown in FIGS. 2 and 3, the indentations are in three lines spaced uniformly around the wire and one line of indentation may be inclined in the opposite direction to the other two. Alternatively, the indentations may be in two lines. The indentation is placed in respect to the axis of the wire so that the inclined angle may be ranging from 0 to 180, preferably not less than 30, more preferably not less than 45 as shown in FIG. 3. The shape of the indentation could be parallelogram as shown in FIG. 3, and may also be ellipse. The shape and spacing of the indents are consistent.

(11) As an example, for the outer wire 24 having a diameter of 5 mm, the spacing R of the indents is 5.501.10 and the length L of the indents is 3.500.70 as shown in FIG. 3. The depth of the indentations is in the range of 40 to 150 m, preferably in the range of 80 to 100 m.

(12) In the first embodiment, the wire rod is first drawn to wires with the desirable diameter. This is followed by an indentation on the surface of the wires. Afterwards, the wires pass through a zinc and/or zinc alloy bath to form a galvanized layer on the surface of the wires.

(13) FIG. 4 schematically shows a partial transverse section of an indented wire 40 according to the first embodiment of the invention under microscopic investigation. The steel wire rod 42 is indented having a depth ranging from 50 to 130 m. As shown in FIG. 4, the inclined angle is defined as the angle between the indent surface parallel to the surface of the wire and the inclined indent side which connects the parallel indent surface and wire surface. The inclined angle is in the range of 90<<150.

(14) After indentation, the indented wire is coated with a zinc and/or zinc alloy coating 44. The thickness of the coating is between 10 to 200 g/m.sup.2, preferably 30 to 150 g/m.sup.2, most preferably 50 to 80 g/m.sup.2. It is found that after the formation of coatings, the profile of the indents may be changed, the angle become wider or difficult to be defined. The coating filled in the indentation and the surface of the wire became smooth. While the thicker the coating, the smoother the surface of the wire.

(15) FIG. 5 schematically shows a partial transverse section of an indented wire 50 according to the second embodiment of the invention under microscopic investigation. In the second embodiment, the wire rod 52 is first coated with zinc and/or zinc alloy 54. The galvanized wire rod is then redrawn to the wires with a final desirable diameter. Alternatively, the wire rod is first redrawn to the a desirable diameter and followed by a galvanizing process to form corrosion resistant coating. Thereafter, the wires 52 are indented by rolling.

(16) Under the microscopic investigation as shown in FIG. 5, the galvanized coating 54 is perfectly conformal to the profile of the indent. This is characterized by the inclined angle of the indents has a similar degree to the inclined angle of the coating. As shown in FIG. 5, the inclined angle of the coating is defined as the angle between the coating part parallel to the surface of the indents and the coating part parallel to the inclined side of the indents. As measured by microscopy, when the angle is in the range of 90<<150, the angle is well defined and in a similar range of the angle. The deviation of the angle to the angle is within 20, preferably within 10 and more preferably within 5. For example, when the angle is 135, the angle is in the range of 130<<140.

(17) In this embodiment, the depth of the indents is ranging from 50 to 130 m. The galvanized coating 54 have a similar thickness as in the first embodiment.

(18) Cable bolt is based on a length of strand typically having a length of about 2 to 10 meters. The proximal end portion of the bolt carries a roof support plate which is held against the roof by a head. Upon sufficient insertion of the cable bolt, the distal end of said cable bolt contacts the bonding agent, such as an uncured resin enclosed in a bag and separated from a catalyst which is provided in the inner part of the borehole. This causes the bonding agent to flow around and along the length of the strand to secure the strand within the borehole.

(19) The invention illustratively described herein may suitably be practiced in the absence of any element or elements, limitation or limitations, not specifically disclosed herein. Thus, for example, the type or pattern of indents may be varied or modified as schematically shown in FIG. 6. The indents may have an oriented elongated shape with two attached crescent parts at two sides (FIG. 6a) and may have an oriented parallelogram shape (FIG. 6b). The indents may have an oriented elongated shape and the indented shapes are connected together (FIG. 6c). The indents may have a star shape (FIG. 6d) or a linked-up star shape (FIG. 6e). The indents may have a zigzag shape (FIG. 6f, FIG. 6h), a square shape (FIG. 6g). The indents may have an elongated shape with two attached crescent parts at two sides and the elongated shapes have different orientation (FIG. 6i). The indents may also have narrow elongated shapes having equal orientation (FIG. 6j).

(20) Therefore, it should be understood that although the present invention has been specifically disclosed by preferred embodiments and optional features, modification and variation of the inventions embodied herein disclosed may be resorted to by those skilled in the art, and that such modifications and variations are considered to be within the scope of this invention.

LIST OF REFERENCES

(21) 10 roof 12 bore 14 roof bolt 16 support plate 18 steel rebar or strand 20 strand 22 core wire 24 outer wire 26 indent 30 side view of an outer wire 40 indented wire 42 steel wire rode 44 zinc and/or zinc alloy coating 50 indented wire 52 steel wire rode 54 zinc and/or zinc alloy coating