Patent Application
20090041550
1. Field of the Invention
The present invention relates to expansion bail-type mine anchors and methods of their use.
2. Description of the Prior Art
In underground mining operations generally, unsupported rock formations may be reinforced by bolts inserted into bore holes that have been drilled into the rock formations. These bolts may then be secured within the bore hole to the rock formations by utilizing an expansion anchor positioned on the distal end of the bolt. The free end of the bolt extending into the mine passageway receives a bearing plate. Rotation of the bolt within the bore hole expands the expansion anchor to engage the rock surrounding the bore hole. The expansion of the expansion anchor brings the bolt under tension and further compresses the rock strata between the bearing plate and expansion anchor to form a beam of rock strata that resists forces that could stress the rock formations. Accordingly, expansion anchors are widely used for supporting and reinforcing rock formations in underground mining operations.
One type of expansion anchor includes a bail-type anchor having a bail connecting two leaves of a hollow shell surrounding a tapered wedge or plug. The tapered plug is generally internally threaded and is threaded onto the distal end of a bolt. Upon application of a rotation of the bolt, the plug threads downwardly on the bolt, thereby forcing the shell to expand into gripping contact with the bore hole wall.
Other expansion anchors include an expansion shell anchor having three or four upwardly extending expansion leaves of a hollow shell commonly joined at one end opposite a tapered plug that is threaded onto a bolt. Upon rotation of the bolt, the leaves of the shell expand into gripping contact with the bore hole formed in the rock formation through the axial movement of the tapered plug engaging the shell.
Typically, there are several methods employed for securing a mine roof bolt within a bore hole. The bolt may be dry anchored in the rock formation by engagement of an expansion anchor, either the bail-type or the expansion-shell type, positioned on the end of the bolt within the rock formation. Other methods include chemically anchoring the bolt by bonding the bolt with resin to the rock formation surrounding the bore hole, or using both an expansion anchor and resin together to retain the bolt within the bore hole. Resin is generally provided in a two-compartment cartridge, one compartment for each of a curable resin composition and a catalyst or curing agent. The resin cartridge is inserted into the blind end of the bore hole in advance of the mine roof bolt. Upon insertion of the mine roof bolt and rotation thereof, the cartridge is shredded and its contents are mixed. Proper mixing of the curable resin composition and curing agent without interference from the cartridge housing are important to achieve good chemical anchoring.
Bail-type anchors are traditionally difficult to use with chemical anchoring. As the resin mixes and cures, the bail of traditional bail-type expansion anchors has a tendency to bias and become cocked, compromising the ability of the anchor assembly to properly expand and engage the rock formation.
The present invention includes an expansion shell assembly for a mine roof bolt comprising: (i) an expansion shell comprising a pair of leaves, the leaves each having an outer surface for engaging a wall of a mine roof bore hole and an inner surface; (ii) an internally threaded plug received between the inner surfaces of the leaves for threading onto a mine roof bolt, an outer surface of the plug defining a resin groove; and (iii) a bail comprising a pair of legs and a medial member therebetween, each leg being attached to one leaf, the medial member defining an aperture through which a mine roof bolt extends. The present invention also includes a mine roof bolt comprising an elongated member having a threaded portion and the afore-described expansion shell assembly threaded thereon.
The present invention further includes a method of supporting a mine roof comprising: (i) inserting a mine roof bolt into a bore hole containing a frangible curable resin cartridge, the mine roof bolt comprising an elongated member having a threaded portion and an expansion shell assembly received on the threaded portion of the expansion shell comprising: (a) an expansion shell comprising a pair of leaves, the leaves having an outer surface and an inner surface; (b) an internally threaded plug received between the leaves inner surface and threaded on the threaded portion, an outer surface of the plug defining a resin groove; and (c) a bail comprising a pair of legs extending from a medial member defining an aperture, each leg attached to one of the leaves, wherein the elongated member extends through the aperture; (ii) rupturing the resin cartridge; and (iii) rotating the mine roof bolt such that resin is mixed and flows through the resin groove and the expansion shell expands and engages the bore hole wall.
For purposes of the disclosure, the terms “upper”, “lower”, “right”, “left”, “vertical”, “horizontal”, “top”, “bottom” and derivatives thereof shall relate to the invention as it is oriented in the drawing figures generally. However, it is to be understood that the invention may assume various alternative variations and step sequences, except where expressly specified to the contrary. It is also to be understood that the specific devices and methods illustrated in the attached drawings and described in the written description are simply exemplary embodiments of the invention. Hence, specific dimensions and other physical and spatial characteristics related to the embodiments disclosed herein are not to be considered as unduly limiting the present invention.
Referring to the drawings, and particularly to
As shown in
A pair of legs 52 extend from main portion 54 of plug 32, thereby forming tapered surfaces 55. Main portion 54 further defines a plurality of longitudinal plug grooves 56. The longitudinal plug grooves 56 may be provided to encourage passage of resin as described below.
Expansion leaves 34 may have a serrated outer surface 58 that generally extends circumferentially about the longitudinal axis and tapering edge surfaces 60 along the serrated outer surfaces 58. In an assembled position, as shown in
When assembled (
Additionally, the reduced dimension portion 66, 266 may encourage the even flow of resin on either side of expansion anchor 12 and help prevent cocking of the expansion anchor assembly 12. Accordingly, the reduced dimension portion 66, 266 may be formed symmetrically in any given embodiment. Further, the reduced dimensional portion 66, 266 may encourage resin to flow through the plug grooves 56 to further encourage the proper alignment of the expansion anchor assembly 12 into the bore hole 14. In addition, reduced dimensional portion 66, 266 may further encourage shredding and mixing of a resin capsule and/or resin.
In use, a two-component (catalyst and curable resin) capsule 80 is inserted into the blind end of a bore hole 14. The mine roof bolt 10 bearing expansion anchor assembly 12 is inserted into bore hole 14 with bearing plate 24 positioned thereon.
Retaining ring 36, which may be formed of a breakable and/or flexible thermoplastic material, is positioned around the expansion leaves 34 and holds the expansion anchor assembly 12 together, while the bolt 10 is being inserted into the bore hole 14. As the bolt 10 is inserted into bore hole 14, the retaining ring 36 remains outside the bore hole 14 (
It should be appreciated that the improved expansion anchor assembly 12 of the present invention may be implemented in chemical anchoring or mechanical anchoring applications, although the invention has been illustrated showing resin bonding to provide chemical anchorage of the expansion anchor assembly 12.
As can be seen in
The cable bolt 310 may include “birdcages” 313 positioned where the strands of the cable 311 are separated and partially unwound from each other. A nut or washer 318 may optionally be positioned on the medial strand of the cable 311 in the birdcage 313 to assist in maintaining spacing between the medial strand and the surrounding strands. The provision of spaced birdcages may also enhance the mixing and/or shredding of resin capsule 80 during installation, as well as increase the bond strength of the resulting chemical anchorage.
Cable bolt 310 includes a conventional drive head 322 (for rotating the bolt 310) and barrel and wedge assembly 324 (for tensioning the bolt). A sleeve or shaft 326 having a central bore for receiving the cable 311 is fixed to the cable 311, such as by crimping or swaging. The shaft 326 defines exterior threads 328 onto which expansion assembly 12 is threaded.
In use, cable bolt 310 is inserted into a bore hole following insertion of a resin cartridge as with bolt 10 and ruptures the cartridge. The cable bolt 310 is rotated using drive head 322 to mix the contents of the resin cartridge and cause expansion assembly 12 to grip the bore hole wall as described above in reference to bolt 10.
When used with a cable bolt, expansion assembly 12 may be positioned proximal to the drive end (as in
The invention has been described with reference to the preferred embodiments. Obvious modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.
