AU2009201251B2 - Washer assembly for an inflatable friction bolt - Google Patents

Abstract

WASHER ASSEMBLY FOR AN INFLATABLE FRICTION BOLT A washer assembly for an inflatable friction bolt (1) which has an enlarged head (3) comprising a first washer element (10) which has a semi-spherical leading face (11), an 87 opposing trailing face (12) and a first aperture (13) extending between the leading face (11) and the trailing face (12). The first aperture (13) has an enlarged trailing section (15) opening onto the trailing face (12) defining a recessed annular shoulder for engaging the enlarged head (3) of the friction bolt (1). The washer assembly further comprises a second washer element (20) that has a plate portion (21) and a boss (22) projecting from /O the plate portion (21). The boss (22) has a circular rim (23) for engagement with the leading face (11) defining a second aperture (24) extending through the second washer element (20).

Description

S&F Ref: 901259 AUSTRALIA PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT Name and Address DYWIDAG-Systems International Pty Limited, of Applicant: an Australian company, ACN 093 424 349, of 25 Pacific Highway, Bennett's Green, New South Wales, 2290, Australia Actual Inventor(s): Rhys James Hunter, David William Evans Address for Service: Spruson & Ferguson St Martins Tower Level 35 31 Market Street Sydney NSW 2000 (CCN 3710000177) Invention Title: Washer assembly for an inflatable friction bolt Associated Provisional Application Details: [33] Country: [31] Appl'n No(s): [32] Application Date: AU 2008901563 01 Apr 2008 The following statement is a full description of this invention, including the best method of performing it known to me/us: 5845c(2041096_1) I WASHER ASSEMBLY FOR AN INFLATABLE FRICTION BOLT Technical Field The present invention relates to strata control in civil engineering and mining 5 operations and in particular relates to a washer assembly for an inflatable friction bolt. Background of the Invention A current method of stabilising the roof or wall of an underground mine or other underground excavation involves the use of a class of rock bolts known as friction bolts 1o or friction rock stabilisers. These types of rock bolts rely on friction between the body of the friction bolt and the wall of a bore hole drilled into the rock face to retain the friction bolt within the hole. One form of friction bolt, commercial examples of which are known as the "Swellex@" bolt or "Omega@" bolt, is an inflatable friction bolt. is Referring to Figures 1 and 2 of the accompanying drawings, a typical inflatable friction bolt 1, in the form of an Omega® bolt comprises an inflatable elongate body 2 and an enlarged head 3 (often referred as a ferrule) mounted on the trailing end 2a of the body and a leading ferrule 4 mounted on the leading end 2b of the body 2. Referring particularly to Figure 2, the body 2 has a hollow generally horse-shoe or "1" cross 20 section between the trailing and leading ferrules 3, 4. The trailing and leading ferrules 3, 4 are welded to the body 2 at the extreme ends of the body 2 and act to constrain the cross-section of the body 2 toward the trailing and leading ends 2a, 2b. In use, the inflatable friction bolt 1 is inserted into a bore hole drilled into the rock face of the strata to be supported, with the diameter of the bore hole being slightly greater than the 25 diameter of the leading ferrule 4 and central portion of the body 2. A washer plate (not depicted) is mounted on the body 2 adjacent the flared leading end 3a of the trailing ferrule 3. The inflatable friction bolt 1 is driven into the bore hole such that the washer plate engages the rock face and the flared leading end 3a of the trailing ferrule 3 engages the mine plate. Water is then charged in to the hollow body 2 via a charging port 5 30 formed in the side wall of the trailing ferrule 3 that extends through the outer wall of the body 2 so as to communicate with the hollow interior 6 of the body 2. Charging of the hollow interior of the body 2 results in the central portion of the body 2 bulging, plastically deforming so as to provide an interference fit of the central portion of the body 2 within the bore hole. This interference fit retains the friction bolt within the bore hole, 35 enabling load transfer between the rock strata and the inflatable friction bolt 1.

2 Tension loads generated in the inflatable friction bolt 1, as a result of strata movement, are transferred to the rock face via the flared leading end 3a of the trailing ferrule 3 and the washer plate. When significant loads are generated, however, the flared leading end 3a tends to yield and peel back, allowing the inflatable friction bolt 1 to pull through the plate washer. This problem is exacerbated when the washer plate is not oriented at 900 to the longitudinal axis of the inflatable friction bolt 1, either as a result of inaccurate drilling of the bore hole or inconsistencies in the surface of the rock face. Object of the Invention It is the object of the present invention to substantially overcome or at least ameliorate one or more of the above disadvantages. Summary of the Invention In a first aspect, the present invention provides a washer assembly for an inflatable friction bolt having an enlarged head, said washer assembly comprising: a first washer element having a semi-spherical leading face, an opposing trailing face and a first aperture extending between said leading face and said trailing face, said first aperture having an enlarged trailing section opening onto said trailing face and defining an annular recess for receiving the enlarged head of the friction bolt; and a second washer element having a plate portion and a boss projecting from said plate portion, said boss having a circular rim for engagement with said leading face and defining a second aperture extending through said second washer element. Preferably, said trailing section of said first aperture is tapered adjacent said trailing face. Preferably, said first aperture comprises a cylindrical leading section and said trailing section. Preferably, said trailing section of said first aperture has a cylindrical peripheral wall adjacent said annular shoulder. In a second aspect, the present invention provides a friction bolt assembly comprising: a washer assembly as defined above; and an inflatable friction bolt having an inflatable elongate body and an enlarged head mounted on said body at a trailing end of said body, wherein said body extends through said 2a aperture of said second element and said aperture of said first element, said enlarged head being received in said annular recess. Brief Description of the Drawings A preferred embodiment of the present invention will now be described, by way of an example only, with reference to the accompanying drawings wherein: 3 Figure 1 is a front elevation view of an inflatable friction bolt; Figure 2 is a cross-sectional view of the inflatable friction bolt of Figure 1 taken at section 2-2; Figure 3 is a perspective view from above of a first washer element of a washer 5 assembly; Figure 4 is a perspective view from below of the first washer element of Figure 3; Figure 5 is a cross-sectional perspective view from above of the first washer element of Figure 3; Figure 6 is a cross-sectional front elevation view of the first washer element of io Figure 3; Figure 7 is a perspective view of the first washer element of Figure 3 assembled onto an inflatable friction bolt; Figure 8 is a perspective view of an inflatable friction bolt assembly; Figure 9 is a partially cross-sectional view of an inflatable friction bolt installation; is and Figure 10 is a partially cross-sectional view of another inflatable friction bolt installation. Detailed Description of the Preferred Embodiments 20 Referring to Figures 3 to 6 of the accompanying drawings, a first washer element 10 of a washer assembly has a semi-spherical leading face 11 and an opposing trailing face 12 that is here generally planar. A first aperture 13 extends between the leading face 11 and the trailing face 12. The longitudinal axis LI of the first aperture 13 is perpendicular to the trailing face 12. The first aperture 13 has a leading section 14 opening onto the 25 leading face 11. The leading section 14 is generally cylindrical. The first aperture 13 also has a trailing section 15 that is enlarged relative to the leading section 14. The trailing section 15 opens onto the trailing face 12. The trailing section 15 of the first aperture 13 defines an annular recess 16 having an annular end wall 16a forming a shoulder adjoining the leading section 14 of the first aperture 13 and a cylindrical 30 peripheral wall 16b. The trailing section 15 of the first aperture 13 has a tapered portion 17 between the peripheral wall 16b of the recess 16 and the trailing face 12. The annular interface between the tapered portion 17 and the peripheral wall 16b and the annular interface between the tapered portion 17 and the trailing face 12 are each rounded, typically each having a radius of approximately 3mm. Rounding of these interfaces 35 assists location of the flared leading end 3a of the trailing ferrule 3 within the recess 16, 4 as will be described further below. The leading face 11 is rounded at its leading rim 18 adjacent the first aperture 13. In the arrangement depicted the leading section 14 of the first aperture 13 has a diameter of approximately 40mm, whilst the trailing section 15 of the first aperture 13 has a diameter of approximately 49mm at the peripheral wall 16b of 5 the recess 16. This configuration is to suit a 24 tonne capacity Omega@ bolt available from the present applicant. The first washer element 10 is typically formed of steel. Referring to Figure 7, an inflatable friction bolt 1 of the type described above in relation to Figures 1 and 2 may be assembled with the first washer element 10. The body 2 of the inflatable friction bolt I passes through the first aperture 13 with the leading 10 ferrule 4 (not depicted) passing through the first aperture 13 from the trailing face 12. The flared leading end 3a of the trailing ferrule 3 (enlarged head) is received in the recess 16 defined by the trailing section 15 of the first aperture 13. The flared leading end 3a engages the end wall 16a of the recess 16, and the peripheral wall 16b when loaded. Referring to Figure 8, an inflatable friction bolt assembly is depicted in the form of is the inflatable friction bolt I and a washer assembly comprising the first washer element 10 and a second washer element 20. The second washer element 20 has a square plate portion 21 and a boss 22 projecting from the plate portion 21. Rather than square, the plate portion may be rectangular, circular or any other desired shape. The boss 22 has a circular rim 23 that defines a second aperture 24 extending through the second washer 20 element 20. The rim 23 is arranged perpendicular to the plate portion 21, such that the longitudinal axis L2 of the second aperture 24 is perpendicular to the plate portion 21. The second aperture is tapered and has a minor diameter of approximately 52mm toward the square plate portion 21, and a major diameter of approximately 60mm at the trailing face of the second washer element 20. The second washer element 20 is typically formed 25 of steel and the plate portion 21 typically has a thickness of about 8mm. The semi spherical leading face 11 of the first washer element 10 engages the rim 24 of the second washer element in a ball and socket relationship. Accordingly, the first washer element 10 may be inclined in relation to the second washer element 20, offsetting their longitudinal axes L1, L2, whilst still maintaining full engagement between the leading 30 face 11 of the first washer element 10 and the rim 24 of the second washer element 20. Referring to Figure 9, an inflatable friction bolt installation is depicted. The inflatable friction bolt I is installed in the usual manner, with the washer assembly comprising the first washer element 10 and second washer element 20 replacing the usual washer plate. A bore hole 30 is drilled in the rock face 31 and the inflatable friction bolt 35 1 inserted into the bore hole 30 with the leading ferrule 4 leading. The washer assembly 5 is located on the body 2 of the inflatable friction bolt 1 and adjacent the trailing ferrule 3 with the flared leading end 3a of the trailing ferrule 3 received in the recess 16 of the first washer element 10, engaging the end and peripheral walls 16a, 16b of the recess 16. The inflatable body 2 of the inflatable friction bolt 1 is then charged in the usual manner by 5 application of fluid pressure via the charging port 5. As can be seen from the alternative installation depicted in Figure 10, the inflatable friction bolt I may be installed at an acute angle to the rock face 31 utilising the two element washer assembly whilst still maintaining full and even contact between the first and second washer elements 10, 20 with the specific configuration of the washer 1o assembly depicted the inflatable friction bolt may be inclined at up to at least 15* degrees offset. When the inflatable friction bolt I is subjected to tensile loads resulting from movement of the strata, the flared leading end 3a of the trailing ferrule 3 is restrained within the annular recess 16, inhibiting peeling back of the trailing ferrule 3 even when is the inflatable friction bolt 1 is not arranged perpendicular to the rock face. Utilising the specific configuration described, the present applicant has been able to load the inflatable friction bolt 1 to its ultimate tensile strength without failure of the trailing ferrule 3. A person skilled in the art will appreciate various possible modifications or alterations to the washer assembly and inflatable friction bolt described.

Claims (7)

1. A washer assembly for an inflatable friction bolt having an enlarged head, said washer assembly comprising: a first washer element having a semi-spherical leading face, an opposing trailing face and a first aperture extending between said leading face and said trailing face, said first aperture having an enlarged trailing section opening onto said trailing face and defining a recessed annular shoulder for engaging the enlarged head of the friction bolt; and a second washer element having a plate portion and a boss projecting from said plate portion, said boss having a circular rim for engagement with said leading face and defining a second aperture extending through said second washer element.

2. The washer assembly of claim 1, wherein said trailing section of said first aperture is tapered adjacent said trailing face.

3. The washer assembly of claim 2, wherein said first aperture comprises a cylindrical leading section and said trailing section.

4. The washer assembly of claim 3, wherein said trailing section of said first aperture has a cylindrical peripheral wall adjacent said annular shoulder.

5. A friction bolt assembly comprising: a washer assembly as defined in any one of claims 1 to 4; and an inflatable friction bolt having an inflatable elongate body and an enlarged head mounted on said body at a trailing end of said body, wherein said body extends through said aperture of said second element and said aperture of said first element, said enlarged head being received in said annular recess.

6. A washer assembly substantially as hereinbefore described with reference to the accompanying drawings.

7. A friction bolt assembly substantially as hereinbefore described with reference to the accompanying drawings. DYWIDAG-Systems International Pty Limited Patent Attorneys for the Applicant/Nominated Person SPRUSON & FERGUSON