Expanded – threaded – driven – headed – tool-deformed – or locked-thr – Externally threaded fastener element – e.g. – bolt – screw – etc. – Pilot end having means enhancing fastening or installation
Reexamination Certificate
2000-10-30
2001-10-30
Wilson, Nelli (Department: 3627)
Expanded, threaded, driven, headed, tool-deformed, or locked-thr
Externally threaded fastener element, e.g., bolt, screw, etc.
Pilot end having means enhancing fastening or installation
C411S387100, C411S395000, C405S259100
Reexamination Certificate
active
06309159
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a bolt of the type which is commonly known as rock bolt or a roof bolt and in particular, the invention relates to a self-drilling roof bolt.
Roof bolts are commonly employed in the underground mining industry to support the walls of rock excavations against fragmentation or collapse. The normal procedure for installing a roof bolt involves drilling a pilot hole into the rock wall and inserting the bolt therein. The bolt is fixed within the bole normally by a settable glue, such as a resin or mortar cement, or the bolt may include means to directly interlock with the surface of the pilot hole, such as a thread or an expanding sleeve. A wide variety of roof bolts exist and one particular form is tubular, having a central bore formed lengthwise through the bolt. Advantageously, the central bore provides a conduit for the introduction of water during insertion of the bolt into the pilot hole. Water is employed to flush away rock segments, finings and dust, and to reduce frictional resistance between the bolt and the rock, and excessive temperature generation. The central bore also provides a conduit for the injection of cement mortar or resin into the pilot opening to secure the bolt therein.
The above described methods of installing a roof bolt thus employ a two stage process, in which the pilot hole is first drilled, after which the roof bolt is inserted into the pilot hole and secured therein by the appropriate means. This type of roof bolt therefore has no drilling capability. Roof bolts having a drilling capability, and thereby referred to as “self-drilling roof bolts”, are known, but such bolts are not in common use in the mining industry. This is despite such roof bolts requiring fewer installation steps when compared to roof bolts of the earlier described kind, because a separate drill to form the pilot hole is not required. Thus, the self-drilling type of roof bolt can be installed more quickly, thereby reducing the period in which the excavated rock face may be unstable and likely to fragment or collapse.
Self-drilling roof bolts have not become popular, and one reason for this is because the bolt must be modified to include a reaming or drilling bit at the leading end thereof in order to enable the bolt to drill the pilot hole and that increases considerably the cost of the bolt. Such bits are expensive because they are normally subject to very high wear, given the abrasive material they are required to penetrate and thus, it is normal for the drift bit of the bolt to be hardened, and that is normally facilitated by the provision of a tungsten carbide tip. In one particular form of tubular roof bolt, described in Australian Patent No. 672,428, the roof bolt is formed by rolling or die drawing a pair of elongate members into half cylindrical sections, and connecting them along their longitudinal edges by welding to form a bolt rod. In this form of roof bolt, the central bore adjacent the leading end thereof is threaded, to accept the threaded shark of a tungsten carbide rotary drill bit. Rotary drill bits are well known and the assignee of the current invention makes a range of such bits which include a steel body supporting the tungsten carbide tip, which is brazed thereto. These bits however, are relatively expensive when compared to the rod they are connected to. In each of the above described roof bolts, the addition of the tungsten carbide bit to the leading end of the rock bolt, involves sufficient expense to make general use of a roof bolt formed in this manner, prohibitive. However, it nevertheless remains the case, that the installation advantages of a self-drilling roof bolt outweigh those of the non-self-drilling type.
It is an object of the present invention to provide a self-drilling roof bolt which is less costly to manufacture than roof bolts of that kind described above and so to make their use in the mining industry more attractive.
SUMMARY OF THE INVENTION
According to the invention there is provided an elongate roof bolt having an axially extending central bore and defining a leading end at one end thereof, said leading end including a pair of axially extending abutment elements formed by machining. Each abutment element includes an abutment face for engagement with a drill tip on opposite sides thereof, to support the drill tip during drilling. The drill tip extends across said leading end and is secured to the abutment elements by welding, soldering or brazing. The bore opens through said bolt at or adjacent said leading end.
In a first aspect of the invention, the arrangement is such that the central bore remains open at or adjacent the leading end of the rod when the drill tip is connected thereto. The roof bolt of the invention thus maintains the advantages of a centrally bored bolt, but additionally provides for self-drilling with associated advantages, without requiring attachment of a complete drill bit. The invention thus eliminates the need for separate roof bits and drill rods.
The drill tip is preferably of planar form and extends diametrically across the leading end of the rod across the open end of the central bore. The abutment elements are spaced apart on opposite sides of the central bore, and the thickness of the drill tip is less than the diameter of the central bore, so that the bore is open on either side of the drill tip. This permits an increase in the pumping speed of the glue used to secure the bolt in the hole drilled by the rod, as well as the rate of flushing during drilling, compared to an arrangement having the hole covered (but not closed) by the drill tip,
In a second aspect of the invention, the drill tip extends across and covers the opening of the central bore at the leading end of the rod. In this arrangement, branching conduits extend from the central bore and open through the side wall surface of the rod, adjacent the leading end. A single branching conduit may be provided, although it is preferable to have at least two such conduits opening into opposite sides of the rod.
The branching conduits may extend laterally to the central bore, or at an angle to the central bore. Moreover, the branching conduits may have any suitable cross-section but preferably will be circular and have a diameter which is either the same as, or greater or larger than that of the central bore.
The above arrangement of branching conduits may equally be applied to the first aspect of the invention described above. That is, the roof bolt may have the central bore open at the leading edge thereof, but may also employ branching conduits extending to sidewall surfaces. Such an arrangement may promote greater pumping and flushing speeds, compared to an arrangement that does not include the branching conduits.
In a roof bolt according to the invention, the drill tip extends across the central bore and preferably extends beyond the outer periphery of the rod, Alternatively, the opposite ends of the drill tip may terminate within the outer periphery of the rod, or extend to or adjacent the outer periphery.
In the above arrangements the drill tip is also supported axially against the leading end of the bolt and preferably that support is provided against a base surface of the drill tip located adjacent to the leading end of the bolt and preferably the axial support is provided on either side of the central bore. The axial support of a base surface of the drill tip may extend between an edge of the central bore and an outer edge of the bolt and a planar surface may be machined for that purpose. The machined surface may be a platform distinct from other surface sections of the leading end.
Fixed connection of the drill tip to the bolt can be achieved by bonding in any suitable manner and for example, a tungsten carbide tip may be fixed by brazing. Welding may be possible with other types of tip material. The drill tip can be fixed to any suitable part of the leading and of the bolt and preferably is fixed to both the abutment elements and the axial supporting surface.
The rod of the roof b
Johnson Eric Ivan
McLean Michael Andrew
Weaver Steven Lee
Burns Doane Swecker & Mathis L.L.P.
Sandvik AB
Wilson Nelli
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