ZA200603858B - Rotary boring bit with gauge reaming formation - Google Patents

Description

BACKGROUND TO THE INVENTION

THIS invention relates to a rotary boring bit with a gauge reaming formation.

The invention is particularly concerned with boring bits used to bore holes in coal or other soft rock formations. The bits used in such applications can have any one of a number of different forms. A typical example is a muiti- wing boring bit in which the bit body includes two or more forwardly extending wings or prongs. Each wing is formed with a recess that accommodates a hardmetal cutting insert the leading or forward edge of which performs a cutting action as boring proceeds. In another example, the bit has a single, usually gable-shaped cutting insert set in a slot at the forward or leading end of the body of the bit.

In coal mining in particular it is common practice to consolidate the hanging ‘wall or roof with roof bolts which are anchored and tensioned in holes bored for the purpose. Anchorage of a roof bolt in its hole is commonly achieved by fast-setting resins or cements located in the hole about the shank of the bolt.

A problem which has been encountered is that the bored hole frequently has a smooth side wall which limits the bond that can be achieved between the resin or cement and the surrounding rock mass.

SUMMARY OF THE INVENTION

According to one aspect of the invention there is provided a rotary rock boring bit for boring a hole in a rock formation, the boring bit comprising a bit body, one or more forward-mounted cutting inserts arranged on the bit body to form a hole in the rock formation when the bit is rotated and driven into the rock formation, the cutting insert(s) furthermore being arranged to form a gauge surface of the hole, characterised in that bit also comprises at least one gauge reaming formation arranged to ream a groove in the gauge surface when the bit is so rotated and driven. There may be a plurality of gauge reaming formations which are axially and/or circumferentially off-set from one another.

The or each gauge reaming formation may be provided by a further cutting insert carried by the bit body and extending laterally beyond a gauge- forming edge of the or each forward-mounted cutting insert. Typically, the or each further, laterally extending cutting insert is carried by the bit body at a position trailing the forward-mounted cutting insert(s).

Alternatively or in addition, the or each gauge reaming formation may be provided as an integral part of the or each forward-mounted cutting insert, such part extending laterally beyond a gauge-forming edge of the insert.

According to another aspect of the invention there is provided a method of boring a hole in a rock formation, the method comprising the steps of: - providing a rotary boring bit comprising a bit body, one or more forward- mounted cutting inserts arranged on the bit body, and at least one gauge reaming formation, and - rotating the boring bit while driving it into the rock formation such that the bit bores a hole in the rock formation, the hole having a gauge surface formed by the forward-mounted cutting inserts, and furthermore such that the gauge reaming formation forms a spiral groove in the gauge surface.

According to yet another aspect of the invention there is provided a method of installing a roof bolt in a rock formation, the roof bolt having an elongate tendon and the method comprising the steps of using the hole boring method summarized above to bore a hole in the rock formation and anchoring the tendon in the hole by means of a resin or cement which surrounds the tendon in the hole and occupies the spiral groove.

It will be understood that the spiral groove which is reamed by the formation provides the wall of the hole with an unsmooth profile to promote the formation of a strong bond between material used to anchor a roof bolt in the hole and the wall of the hole.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in more detail, by way of example only, with reference to the accompanying drawings in which:

Figure 1 shows a perspective view of a muiti-wing, rotary boring bit according to a first embodiment of the invention;

Figure 2 shows a roof bolt anchored in a hole bored in a rock formation using the boring bit of Figure 1; and

Figure 3 partially illustrates a multi-wing, rotary boring bit according to a second embodiment of the invention.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Figure 1 shows a first embodiment of boring bit 10 according to the invention. The bit 10 is of a multi-wing design and includes a steel bit body 12 with a pair of forwardly projecting, diametrically opposed wings 14.

Each wing 14 is formed with a recess 16 in which a forward-mounted cutting insert 18 is secured by brazing. The cutting inserts, which are made of tungsten carbide or other suitable hardmetal, present forward or leading cutting edges 20 which perform a cutting action during the boring of a hole in a coal or other soft rock formation. The cutting inserts also present side or gauge-forming edges 21.

The bit body 12 has a generally cylindrical side surface 22 trailing the wings 14. In accordance with one embodiment of the invention, the side surface 22 is formed with a blind socket 24 in which a further, laterally directed cutting insert 26 is secured by brazing. The cutting insert 26, which is also made of tungsten carbide or other suitable hardmetal, presents a laterally directed cutting edge 28 that extends laterally beyond the edges 21 of the cutting inserts 18.

In order to bore a hole in a coal, limestone or other soft rock formation, the boring bit is rotated about its axis while being driven into the rock formation.

With reference to Figure 2, during the boring of the hole 29 in the rock formation 30, the gauge-forming edges 21 of the cutting inserts 18 form the gauge surface or side wall 31 of the hole. At the same time, the cutting insert 26 reams a spiral groove 32 in this surface as the depth of the hole itself is extended by the forward boring action of the cutting inserts 18.

It will be understood that the number of turns of the spiral groove per unit depth of the hole 29 will be dependent on the relationship between the rotational speed of the bit and the speed at which the depth of the hole is increased, i.e. the speed at which the boring bit is driven into the rock formation. The groove 32 provides the wall of the hole 28 with an unsmooth profile.

Figure 2 also shows a roof bolt 34 anchored in the hole 29 by a resin or cement 36 which surrounds the shank or tendon 38 of the bolt and fills the space between the shank and the wall of the hole. While still relatively fluid prior to setting the resin or cement finds its way into the groove 32.

After setting, the resin or cement occupying the groove ensures that there is strong axial anchorage of the tendon in the hole and allows the roof bolt to be tensioned to an appropriate level for proper consolidation of the rock formation.

The invention is equally applicable to other designs of boring bit, for example those which have a single leading or forward-mounted cutting insert only, such as a gable-shaped spade bit. Also, while the illustrated embodiment only has a single laterally directed cutting insert 26, other embodiments of the invention may employ multiple cutting inserts extending laterally beyond the gauge surface. In such embodiments, the gauge cutting inserts may be axially and/or circumferentially off-set from one another.

Figure 3 shows a side view of a multi-wing boring bit according to a second embodiment of the invention. In this Figure, components corresponding to those seen in Figure 1 are indicated with the same reference numerals.

The Figure 3 embodiment differs from the Figure 1 embodiment in that instead of a separate cutting insert mounted in the side surface of the bit body, one of the cutting inserts 18 is itself formed with an integral, laterally projecting gauge reaming formation 50. It will be understood that this formation, like the gauge-mounted insert 26 of the first embodiment, will ream a spiral groove in the side wall of the drilled hole in order to improve the bonding of a roof bolt.

Although not visible in Figure 3, it would be possible for both inserts 18 to have integral, laterally extending gauge reaming formations 50, possibly axially off-set with respect to one another. It is also within the scope of the invention for one or more integral gauge reaming formations to be provided in situations where there is only a single cutting insert.

In this specification, terms such as “forward”, “leading” and the like are used with reference to the boring direction, designated the forward direction, as indicated by the arrow 40 in Figure 1.

Also, although specific mention has been made of hardmetal cutting inserts, it should be understood that the inserts could be made of other hard materials, such as PCD (polycrystalline diamond) or ceramic material.

The term “roof bolt” is used in this specification for convenience and should be interpreted to include any rock anchor that has an elongate tendon which is anchored in a predrilled hole in a wall of a rock formation by means of resin or cement, irrespective of whether rock formation is a roof, side wall or floor formation.

Claims (9)

1. CLAIMS A rotary rock boring bit for boring a hole in a rock formation, the boring bit comprising a bit body, one or more forward-mounted cutting inserts arranged on the bit body to form a hole in the rock formation when the bit is rotated and driven into the rock formation, the cutting insert(s) furthermore being arranged to form a gauge surface of the hole, characterised in that bit also comprises at least one gauge reaming formation arranged to ream a groove in the gauge surface when the bit is so rotated and driven.
2. 2. A boring bit according to claim 1 wherein the or each gauge reaming formation is provided by a further cutting insert carried by the bit body and extending laterally beyond a gauge-forming edge of the or each forward- mounted cutting insert.
3. 3. A boring bit according to claim 2 wherein the or each further, laterally extending cutting insert is carried by the bit body at a position trailing the forward-mounted cutting insert(s).
4. 4, A boring bit according to claim 1 wherein the or each gauge reaming formation is provided as an integral part of the or each forward-mounted cutting insert, such part extending laterally beyond a gauge-forming edge of the insert.
5. 5. A boring bit according to any one of the preceding claims and comprising a plurality of gauge reaming formations which are axially and/or circumferentially off-set from one another.
6. A method of boring a hole in a rock formation, the method comprising the steps of: - providing a rotary boring bit comprising a bit body, one or more forward- mounted cutting inserts arranged on the bit body, and at least one gauge reaming formation, and - rotating the boring bit while driving it into the rock formation such that the bit bores a hole in the rock formation, the hole having a gauge surface formed by the forward-mounted cutting inserts, and furthermore such that the gauge reaming formation forms a spiral groove in the gauge surface.
7. 7. A method of installing a roof bolt in a rock formation, the roof bolt having an elongate tendon and the method comprising the steps of using the method of claim 6 to bore a hole in the rock formation and anchoring the tendon in the hole by means of a resin or cement which surrounds the tendon in the hole and occupies the spiral groove.
8. 8. A rotary rock boring bit substantially as herein described with reference to Figure 1 or Figure 3 of the accompanying drawings.
9. 9. A method of boring a hole in a rock formation substantially as herein described with reference to the accompanying drawings.

   A method of installing a roof bolt in a rock formation substantially as herein described with reference to Figure 2 of the accompanying drawings.

   A" day of May 2006 ar WV A > k Fisher pplicant’s Patent Attorneys