GB2465653A

GB2465653A - Drill bit with air hammer and bleed passageway

Info

Publication number: GB2465653A
Application number: GB0915405A
Authority: GB
Inventors: John Arthur Hurt; Michael Fareham
Original assignee: BULROC
Current assignee: BULROC
Priority date: 2008-11-26
Filing date: 2009-09-04
Publication date: 2010-06-02
Anticipated expiration: 2029-09-04
Also published as: GB2465653B; HK1140244A1; GB0821564D0; GB0915405D0

Abstract

A drill means comprises a compressed air hammer and a drill head 1 within a lining casing 23. The drill head has at least one segment 12 located in a recess towards the end of the drill head and mounted for rotation from an inoperative position where the extremity of the segment lies within the confines of the outer diameter of the drill head, to an operative position where it extends beyond the outer diameter of the lining casing. The drill head also has a primary air passageway 32 communicating with both the air exhaust outlet from the hammer and the interior of the lining casing. A bleed air passageway 33 extends from the primary air passageway through the drill head and emerges towards the face 4 of the drill head, at one side, and a return air bleed passageway 36 extends through the drill head at the opposite side, leading to the primary passageway.

Description

DRILL MEANS

This invention relates to drill means and is particularly concerned with a drill means adapted to drill and ream a hole in the ground in advance of a trailing casing tube.

Well known in the art is the provision of a compressed-air driven hammer lying with a casing tube, acting on a drill head extending beyond the lower end of the casing tube.

To enable the drilling of a hole to take a casing tube, it is necessary that the periphery of the drill means on the drill head is at a radius greater than the radius of the casing. At the end of the drilling operation, there is the need for the drill means and the hammer to be withdrawn through the casing, for otherwise it would be lost at the bottom of the hole. Thus the drill means must be capable of a radial displacement in a transverse plane from a first position where a hole of the outer diameter of the casing can be drilled, to a position where the drill means is within the inner diameter of the casing.

During the drilling of a hole, debris inevitably collects in the bottom of the hole, which if not removed, would impair drilling efficiency, reduce drill head life, and reduce hole drilling 1 5 speeds. It is therefore already known to direct exhaust air from the hammer through the drill head to blow directly into the ground at the centre of the bottom of the bore. This drives debris away from the bottom of the bore passed the drill head and through passageways leading to the interior of the casing, the debris being carried up through the casing to be gathered at the top of the casing above ground.

Such a drill means is disclosed in British Patent 2316964, where a drill head is provided with drill segments and pivotally mounted at the end of a drill head, and such that during drilling, the segments are pivoted to a position where their extremities lie outside the confines of the drill head. At the end of the drilling operation, and on reversal of the direction of rotation of the drill head, the segments rotate inwardly until they lie within the confines of the drill head diameter, thereby to allow the drill head to be withdrawn through the casing. On the drill head is a pilot bit fitted to a bore in the end of the drill head, to overlie the pivotal segments, and hence defend their pivotal connection to the drill head, and maintain the segments in position without the need for a locking means between the segments and the drill head. By having a pilot bit much of the loading on the segments is eliminated during drilling, and the segments allowed to pivot from an inner to outer position during drilling to enable the drilling of a hole of the diameter of a trailing casing tube, and to pivot from an outer to an inner position when the drill head is rotated in the opposite direction.

With the construction of British 2316964 the pilot bit is secured to the main driver by drive/locking pins that pass through bushes in transverse holes in the drill bit and engage with a co-operating recess in the stem of the pilot bit, the pins allowing a drive force to be applied to the pilot bit. Such a construction works well but, prolonged use of it, and use in hard ground conditions can lead to wear and damage to the drive pins. Once the pins wear, which in turn causes wear on bushes in the drill bit, the connection between the pilot bit and drill bit loosens and a considerable strain can be put on the drill bit and cause cracking that can be sufficiently extensive to cause the loss of the head end of the drill.

Drill heads in accordance with British Patent 2316964 have a central bore to co-operate with an air exhaust outlet from the hammer, and channels through the drill head to allow exhaust air from the hammer to pass through the drill head and be directed at the bottom of the bore being drilled. The force of such air flow can be considerable, and which can apply an unacceptably high loading on the wall of the bore beyond the casing, with a resultant below ground disturbance around the bore.

The object of the present invention is to avoid those difficulties of known drill means of the type defined.

According to the present invention, a drill means comprises a compressed air hammer and an associated drill head within a lining casing, the drill head having at least one segment located in a co-operating recess towards the end of the drill head, the at least one segment being mounted on the drill head for rotation from an inoperative position where the extremity of the segment lies within the confines of the outer diameter of the drill head, to an operative position where it extends beyond the outer diameter of the lining casing, the drill head having a primary air passageway communicating with the air exhaust outlet from the hammer, said primary air passageway being in communication with the interior of the lining casing, and there being a bleed air passageway extending from the primary air passageway through the drill head and emerging towards the operative end of the drill head, at one side, and a return air bleed passageway extending through the drill head at the opposite side, leading to the said primary passageway.

Thus, during the drilling of a hole, a high proportion of the exhaust air from the hammer is prevented from reaching the bottom of the drilled hole, by being directed through the primary air passageway in the drill head and into the interior of the lining casing.

Preferably, more than 90% of the exhaust air is so directed. Given the pressure of the exhaust air, it is inevitable that a minority, within the capacity of the diameter of the bleed air passageway, will emerge through the bleed air passageway and into the bottom of the hole.

The velocity of the exhaust air entering the casing generates a vacuum effect in the return air bleed passageway to draw bleed air across the face of the drill head and into the return air bleed passageway carrying with it debris collecting in the bottom of the hole, the debris being picked up by the return air entering the casing to carry it to the surface.

To ensure that the drill head is effectively in sealing engagement with the bottom of the casing, the casing may be provided with a casing shoe, so shaped as to prevent air from escaping from around the drill head, and entering the drilled hole externally of the casing.

Still further improvements over the known art can be provided. Thus, and in accordance with a second aspect of the present invention, a drill means as is defined above, further comprises a drill head having at least one segment located in a co-operating recess towards the end of the drill head, the at least one segment being mounted on the drill head for rotation from an inoperative position where the extremity of the or each segment lies within the confines of the outer diameter of the drill head, to an operative position where it extends beyond the outer diameter of the drill head, the front end of the drill head having a centrally located boss on which is mounted a ring bit to overlie the at least one segment, the boss and the ring bit having engaging formations to hold the ring bit to the drill head during drilling rotation of the drill head, and a securing means to hold the ring bit to the drill head during reverse rotation of the drill head.

The drill head may have a number of rotatable segments determined by the size of the drill head, equally spaced around its periphery, and co-operating lands are provided on the drill head and on which the segments are located, the segments each having a peg to locate in a hole in its land, and the drill head having inwardly directed slots extending below the boss from each land, to receive the segments when rotation of the drill head is reversed.

Thus, and for example, there may be three, four or five segments and co-operating lands.

To enable the segments to be fitted to the drill head, the side wall of the boss has a longitudinal recess for each segment, extending from each land to the end face of the boss, to enable each segment to be located on its respective land, and the ring bit has locking projections on its inner face to engage in lateral slots in the side wall of the boss, which are closed at one end and which emerge in a respective longitudinal recess. Thus, once the segments are fitted to the drill head, the locking ring can be positioned on the boss, with its locking formations aligned with the longitudinal recesses, and the ring rotated to engage the locking formations in the lateral slots. To ensure that the ring bit remains in place as the drill head is reversed to cause the segments to swing into their recesses in the boss, a locking pin may be provided, passing through the wall of the ring bit and into contact with the boss.

During drilling, rotation of the drill head causes a force to be applied to the ring bit to urge its locking formations against the closed end of the lateral recesses on the boss, thereby ensuring that the ring bit remains in place.

By having a ring bit closely fitting the boss on the drill head, with its exposed annular face co-planar with the end face of the boss, the possibility of there being damage caused to the ring bit and hence the drill head during drilling is much reduced in comparison with the prior art displaying a pilot bit, and the means of locking the ring-bit to the drill head is defended against damage to a considerable degree, whilst at the same time, there is the considerable reduction of the possibility of damage to the segments and their connection to the drill head in comparison with the prior art construction where the segments are fully exposed.

At the end of a particular drilling operation, and with the drill head withdrawn through the trailing casing, it is inspected for wear and damage. The considerable advantage of the invention over the prior art is that the locking pin is substantially defended against damaging loads and can easily be removed from the hole through the ring bit, and the ring bit simply rotated to remove it and expose the segments that can then be inspected and replaced if necessary.

A still further improvement over the prior art can be attained by forming the boss to hold the ring bit, integral with the body of the drill head, and to have the unitary body of less length than has previously been the custom and practice with drill means of the type to which the invention relates. The result is that a greater impact energy is transferred through the shorter single piece body than has previously been achieved with resultant faster ground penetration rates, and additionally a shorter length of drill head makes easier the keeping of the drill means in line and hence produce a straighter hole.

One embodiment of the invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a drill head in accordance with the invention; Figure 2 corresponds to Figure 1 but shows the drill head in exploded form; Figure 3 is a part schematic cross-sectional view of a drill head of the prior art; and Figure 4 is a part schematic cross-sectional view of the drill head of Figure 1.

In the drawings, a drill head 1 has a splined shaft 2 for connection to a compressed air hammer (not shown). At the opposite end of the drill head, there is an integral boss 3, the exposed surface 4 of which is provided with an array of cutting elements 5, and as is shown in Figure 2, the side wall of the boss 3 is provided with three recesses 6 extending from co-operating lands 7 to the exposed surface 4. The lands 7 are each formed with a pivot hole 8 to receive a liner sleeve 9, in which is fitted a respective peg 10 extending from the under surface 11 of a respective segment 12, to allow each segment to pivot from an operative to an inoperative position. The upper surface 13 of each segment 12 is provided with cutting elements 14. Fitted on the boss 3 is a ring bit 15, the ring bit having at least one, and preferably three locking projections 16 on its inner surface 17, to engage in co-operating locking recesses 18 in the surface of the boss 3. A locking pin 19 may also be provided extending through the locking ring and into contact with the boss.

The exposed surface 20 of the ring bit 15 is provided with cutting elements 21, and with the assembled drill head fitted to a compressed air hammer and the exposed surfaces 4 and 20 of the boss and ring bit respectively brought into ground contact, the drill head 1 is rotated and driven downwards to commence the drilling of a hole, the segments 12 being caused to rotate and extend out of the recesses 6.

As is indicated in Figure 4, the drill head is attached to the end 22 of a casing 23 such as by way of the internal face 24 at the end of the casing being welded to an external section 25 on an annular shoe 26 that is itself secured to the drill head by co-operating threaded sections at 27 on the shoe and the drill head. By swinging outwardly, the segments 12 provide a diameter of a hole drilled by the drill head that is greater than the outside diameter of the drill string 23. This not only facilitates the pulling of the casing down the hole with the drill head as the hole is drilled, it also allows the removal of the drill head with the hammer, as once the hole has been drilled to its require depth, rotation of the drill head is reversed, to disconnect the shoe from the drill head, and swing the segments 12 to lie within the recesses 6 in the boss 3, and when the drill head 1 can be withdrawn through the casing 23 to leave the casing 23 in place as a liner to the drilled hole.

As is mentioned earlier, the drill head is attached to a compressed air hammer, and after live air has caused the hammer to move, it creates return air that must be disposed of.

It is also the case that during drilling, debris and cuttings gather in the bottom of the drilled hole that would impair the drilling action if not removed. Thus, in the prior art, and as is illustrated in Figure 3, return air from the hammer is directed down a primary air passageway 28 in the drill head and through secondary air passageways 29 to the bottom of the hole, where the return air picks up cuttings and other debris in the bottom of the hole, and from where it passes through passageways 30 in the outer surface of the drill head and into the annular gap 31 between the drill head and the drill string to be carried to the surface. With certain ground conditions, or where numerous holes have been drilled in relatively close spaced relationship, allowing compressed air at the pressure at which it leaves the compressed air hammer to reach the bottom of the hole can cause considerable damage.

Therefore, and in accordance with the invention as is illustrated particularly in Figure 4, exhaust air from the compressed air hammer is passed through a primary air passageway 32 and then through secondary air passageways 33 leading directly to the annular gap 34 between the drill head and the casing 23, to prevent it from reaching the bottom of the hole.

A proportion of the return air passes through a bleed hole 35 in the boss that emerges in one of the recesses 6 in the boss, from where it can pass across the face 4 of the boss and the face 20 of the ring bit 15, to a return air passageway 36, the force of air passing through the secondary passageways 33 causing a reduced pressure in the return air passageway 36 to draw bleed air and entrained cuttings and debris into the stream of return air passing through the secondary passageways 33. By having the casing 23 engage the shoe 26, return air is prevented from passing down the outside of the casing.

Thus, not only is full return air at its pressure prevented from reaching the bottom of the hole, but also is there the effective removal of cuttings and debris from the bottom of the hole as it is being drilled.

It is usual in the prior art, and as is illustrated in Figure 3, for button bit 37 to be provided, with a shaft 38 to engage a bore 39 in the drill head.

However, with the invention, advantageously and as is illustrated in Figure 4, the boss 3 is formed integral with the drill head 1 and faced with cutting elements, to serve the purpose of a button bit, and the ring bit, also faced with cutting elements is readily removable from the boss to facilitate replacement of the segments when repair is required.

Claims

CLAIMS1. A drill means comprising a compressed air hammer and an associated drill head within a lining casing, the drill head having at least one segment located in a co-operating recess towards the end of the drill head, the at least one segment being mounted on the drill head for rotation from an inoperative position where the extremity of the segment lies within the confines of the outer diameter of the drill head, to an operative position where it extends beyond the outer diameter of the lining casing, the drill head having a primary air passageway communicating with the air exhaust outlet from the hammer, said primary air passageway being in communication with the interior of the lining casing, and there being a bleed air passageway extending from the primary air passageway through the drill head and emerging towards the operative end of the drill head, at one side, and a return air bleed passageway extending through the drill head at the opposite side, leading to the said primary passageway.
2. A drill means as in Claim 1, wherein the velocity of the exhaust air entering the casing generates a vacuum effect in the return air bleed passageway to draw bleed air across the face of the drill head and into the return air bleed passageway carrying with it debris collecting in the bottom of the hole, the debris being picked up by the return air entering the casing to carry it to the surface.
3. A drill means as in Claim 1 or Claim 2, wherein the casing is provided with a casing shoe, so shaped as to prevent air from escaping from around the drill head, and entering the drilled hole externally of the casing.
4. A drill means as in any of Claims 1 to 3, wherein the drill head has at least one segment located in a co-operating recess towards the end of the drill head, the at least one segment being mounted on the drill head for rotation from an inoperative position where the extremity of the or each segment lies within the confines of the outer diameter of the drill head, to an operative position where it extends beyond the outer diameter of the drill head, the front end of the drill head having a centrally located boss on which is mounted a ring bit I0 to overlie the at least one segment, the boss and the ring bit having engaging formations to hold the ring bit to the drill head during drilling rotation of the drill head, and a securing means to hold the ring bit to the drill head during reverse rotation of the drill head.
5. A drill head as in Claim 4, wherein the drill head has three rotatable segments equally spaced around its periphery, and co-operating lands are provided on the drill head and on which the segments are located, the segments each having a peg to locate in a hole in its land, and the drill head having inwardly directed slots extending below the boss from each land, to receive the segments when rotation of the drill head is reversed.
6. A drill head as in Claim 4 or Claim 5, wherein to enable the segments to be fitted to the drill head, the side wall of the boss has a longitudinal recess for each segment, extending from each land to the end face of the boss, to enable each segment to be located on its respective land, and the ring bit has locking projections on its inner face to engage in lateral slots in the side wall of the boss, which are closed at one end and which emerge in a respective longitudinal recess.
7. A drill head as in Claim 6, wherein to ensure that the ring bit remains in place as the drill head is reversed to cause the segments to swing into their recesses in the boss, a locking pin is provided, passing through the wall of the ring bit and into engagement with the co-operating wall of the boss.
8. A drill head as in any of Claims 4 to 7, wherein the boss to hold the ring bit is integral with the drill head.
9. A drill head substantially as hereinbefore described with reference to Figure 1, Figure 2 and Figure 4 of the accompanying drawings.