AU6115696A - An improved up-hole hammer drill bit - Google Patents

Description

AN IMPROVED UP HOLE HAMMER DRILL BIT

This invention relates to an improved up hole hammer drill bit, and in particular to air delivery passages within the drill bit.

The use of pneumatically driven hammers in combination with percussion drill bits is common. A drill string is used to convey a compressed air source to a pneumatic hammer at the end of the drill string, which in turn is coupled to a percussion drill bit. The hammer makes use of a reciprocating piston to impact against the drill bit to provide the percussive drill force.

In conventional drilling systems, the exhaust from the hammer is vented through the centre of the drill bit and back through the hole around the hammer and drill string. In reverse circulation hammers, the exhaust air is vented outside of the hammer with the exhaust air travelling around the bit and back through the centre of the drill string.

Reverse circulation hammers are used where it is important to recover drilling chips for sample purposes .

In the main however, the conventional hammer used, particularly for drilling blast holes, is of the aforementioned type where the exhaust air together with drill debris and chips travels back to the entrance of the hole via the space between the hole and the outside surface of the drill string hammer.

This type of drill bit is provided with air flow conduits which normally have apertures on the cutting face of the bit. Air flow from and across the cutting face flushes away drilling debris and chips . One problem with this type of drilling bit, particularly in respect of up hole hammers, is the tendency for drilling debris to fall through the apertures and air conduits when the drilling operation ceases. Drilling operations are paused for many reasons, including the addition of lengths of drilling tube. When a hammer ceases operation, the air flow obviously also ceases, and it is at this stage that drilling debris is able to fall into the apertures and air conduits of the drill bit. The debris in turn finds its way into the drilling hammer and the connection between the drill bit and the hammer. This is extremely undesirable, as drilling debris is abrasive and will cause excessive wear and failure of the various moving components.

Therefore, it is an object of this invention to provide a means whereby the drilling debris is prevented from entering the hammer or the connection between the drill bit and hammer.

In its broadest form, the invention is an up-hole drill bit comprising, a head having a cutting face thereon, a shank extending from said head, terminating in a strike end, a main air exit tube extending from said strike end toward, but not opening onto, said cutting face, at least one intermediate passage extending from the end of said exit tube to a side of said drill bit, and at least one secondary delivery tube extending from said intermediate passage to said cutting face, the connection of said secondary delivery tube to said intermediate passage spaced from said main air exit tube so that debris that may fall through said secondary delivery tube is prevented from falling directly into said main air exit tube.

The non-alignment of the secondary delivery tube with respect to the main air exit tube prevents debris falling directly though the secondary tube into the main tube. Preferably, the intermediate passage slopes away from the cutting face so that any debris falling through the secondary delivery tube is encouraged to move outwardly away from the main air exit tube. Preferably, the secondary exit tube connects to the intermediate passage at a position roughly midway between the centre of the drill bit and its outer edge.

Preferably, the main air exit tube extends through the centre of the drill bit, and there is provided a pair of intermediate passages, both of which extend away from the centre of the drill bit so that a pair of openings are provided on either side of the drill bit. A corresponding pair of secondary delivery tubes are used to connect to respective intermediate passages.

In addition to the intermediate passages preferably sloping, the secondary air delivery tubes may also be angled with respect to the longitudinal axis of the drill bit. In this arrangement, the entrance of the secondary delivery tube at the cutting face is closer to the centre of the drilling bit than its opposite end. This ensures that the momentum of the drilling debris as it enters the intermediate passage is already carrying it away from the centre of the drill bit.

Preferably, under operating conditions, the back pressure or resistance to flow along the intermediate passage is such that air flow occurs more freely through the main air exit tube into the secondary delivery tube, across the face of the cutting bit and along the sides of the drill bit and hammer. In this way, air flow is prevented from short circuiting through the intermediate passage to the side of the drill bit. This ensures sufficient air flow to clear debris from the cutting face.

In order for the invention to be fully understood, a preferred embodiment will now be described, but is should be realised that the invention is not to be confined or restricted to the precise details of this embodiment.

This embodiment is illustrated in the accompanying representations in which:

Fig 1 shows a part cross-sectional view of a drill bit, and Fig 2 shows a plan view of a cutting face of a drill bit.

In this embodiment, the drill bit 10 has a cutting face 11 and side walls 12 forming a drill bit head. The drill bit 10 has a splined shank (not illustrated) for attachment to a pneumatic hammer.

A main air exit tube 13 extends through the centre of the drill bit 10, but does not extend through to the cutting face 11. In this embodiment, a pair of intermediate passages 14 extend from the end of the main air exit tube 13 to the side wall 12 of the drill bit 10.

A pair of secondary delivery tubes 15 extend from the intermediate passages 14 to the cutting face 11.

As seen in the illustration, the intermediate passages 14 are angled so that they slope away from the cutting face 11 as they extend from the exit tube 13 to the side walls 12. The secondary delivery tubes 15 also slope so that their openings on the cutting face 11 are closer to the centre of the drill bit 10 by comparison to the opposite ends which open into the intermediate passages 14. The degree of slope of the intermediate passages 14 may be varied, depending on how far from off the vertical the drill bit is intended to work. The greater the degree of inclination, then the greater the angle of the intermediate passages.

With this arrangement, when operation of the pneumatic hammer ceases, any drilling debris which may enter the secondary delivery tubes 15 and intermediate passages 14 is directed away from the opening of the main air exit tube 13 and is able to exit the intermediate passages 14 at their openings on the side wall 12 of the drill bit 10.

With this arrangement, for an up hole hammer drill bit, debris is effectively prevented from entering the connection between the drill bit and the pneumatic hammer and the hammer itself. Clearly, such an arrangement provides a significant advantage over conventional drill bits which simply allow debris to fall into the hammer through the main air delivery tube which opens directly to the cutting face.

Claims (7)

The claims defining the invention are as follows:

1. An up-hole drill bit comprising, a head having a cutting face thereon, a shank extending from said head, terminating in a strike end, a main air exit tube extending from said strike end toward, but not opening onto, said cutting face, at least one intermediate passage extending from the end of said exit tube to a side of said drill bit, and at least one secondary delivery tube extending from said intermediate passage to said cutting face, the connection of said secondary delivery tube to said intermediate passage spaced from said main air exit tube so that debris that may fall through said secondary delivery tube is prevented from falling directly into said main air exit tube.

2. An up-hole drill bit according to claim 1 further comprising at least two intermediate passages and at least two secondary delivery tubes .

3. An up-hole drill bit according to either claim 1 or 2 wherein said secondary delivery tube connects to said intermediate passage substantially midway between said main air delivery tube and the opening on the side of said drill bit.

4. An up-hole drill bit according to either claim 1, 2 or 3 wherein said intermediate passages are angled with respect to the longitudinal axis of said drill bit so that the end connected to said main air exit tube is closer to said cutting face than the opening on the side of said drill bit.

5. An up-hole drill bit according to any one of the preceding claims wherein said secondary delivery tubes are angled so that they diverge away from the longitudinal axis of said drill bit as it extends away from said cutting face.

6. An up-hole drill bit according to any one of the preceding claims wherein the positioning of the opening of said intermediate passage of the side of said drill bit is such that air flowing past said opening causes a resistance to flow directly from said main air exit tube through said intermediate passage and instead air is caused to flow from said main air exit tube through said secondary delivery tube,

7. An up-hole drill bit substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings .