ZA200108803B

ZA200108803B - Hammer Drill Assembly.

Info

Publication number: ZA200108803B
Application number: ZA200108803A
Authority: ZA
Inventors: Reginald Frederick Taylor
Original assignee: Reginald Frederick Taylor
Priority date: 1999-03-26
Filing date: 2001-10-25
Publication date: 2002-06-10

Description

, ~~ WO00/58058 PCT/1B00/00344

HAMMER DRILL ASSEMBLY

BACKGROUND OF THE INVENTION

This invention relates to a drill assembly, typically forming part of a down-the- hole hammer drill, and to a liner for a drill assembly.

Down-the-hole hammer drills typically comprise a drill bit having a splined : shank which is located in a complementally splined drive chuck or drive sub which permits axial motion of the drill bit under the urging of a hammer powered by compressed air.

Particularly with large diameter bits (typically above 250 mm diameter) the axial movement of the bit is difficult to control, and tends to result in excessive wear and seizing taking place on the drive faces of mating splines of the bit and drive chuck. This leads to the development of fatigue cracks in the bit, eventually resulting in failure of the bit.

It is an object of the invention to address this problem.

CONFIRMATION COPY

SUMMARY OF THE INVENTION

According to a first aspect of the invention there is provided a drill assembly comprising a drill bit having a shank formed with a plurality of splines, a chuck formed with a plurality of complemental splines for engaging the shank of the bit and for permitting axial movement thereof relative to the chuck, and a generally cylindrical liner between the splines of the bit and the chuck, the liner being formed of a material selected for suitable wear-resistance and frictional properties.

The liner may be formed, for example, from a tough plastics material or from a suitable non-ferrous metal.

The liner is preferably formed with an outer surface shaped complementally to the inner surface of the chuck and with an inner surface shaped complementally to the outer surface of the bit shank, so that it fits snugly between the mating splines of the bit and the chuck.

The liner may further have concentrically curved inner and outer wall portions and radially extending leading and trailing wall portions joining adjacent inner and outer wall portions.

The leading wall portions of the liner are preferably thicker than the trailing wall portions of the liner.

More preferably, the leading wall portions of the liner are at least double the thickness of the trailing wall portions of the liner.

The liner may be a tight fit in the chuck.

) «© WO 00/58058 PCT/1B00/00344

The invention extends to a liner for use with a drill assembly, the liner having an outer surface shaped complementally to the inner surface of a chuck of the drill assembly, and an inner surface shaped complementally to the outer surface of a bit shank of the drill assembly, so that that the liner is able to fit snugly between the mating splines of the bit and the chuck.

According to a second aspect of the invention there is provided a drill assembly comprising: a chuck formed with a plurality of drive cavities on an inner surface thereof; a generally cylindrical liner sized to be inserted into the chuck, the liner being formed with a plurality of drive cavities on an outer surface thereof and having at least one formation on an inner surface thereof ’ for engaging a drill bit, the liner being formed of a material selected for suitable wear-resistance and frictional properties; and a plurality of drive members each sized to be received in one of a plurality of composite drive cavities formed when the liner is inserted into the chuck and the respective drive cavities on the chuck and liner are aligned with one another.

The drive members are preferably pins which are made of steel! or another kind of metal .

The liner preferably defines radially extending wall portions which are shaped complementally to drive formations on the drill bit.

The plurality of drive cavities in the chuck and in the liner may have a semi-

circular cross section so that the composite drive cavities have a circular cross section, and the drive members will then be circular in cross section.

The invention extends to a liner for use with a drill assembly, the liner having a plurality of drive cavities formed in an outer surface thereof, the drive cavities being shaped complementally to drive cavities of a chuck of the drill assembly so that composite drive cavities are formed when the liner is inserted into the chuck, the liner having at least one formation on an inner surface thereof for engaging a drill bit.

The inner surface of the liner may have a plurality of radially extending leading and trailing wall portions.

The leading wall portions of the finer are preferably thicker than the trailing wall portions of the liner, and more preferably are at least double the thickness of the trailing wall portions of the liner.

The liner may be formed from a tough plastics material or from a suitable non-ferrous metal.

The invention also extends to a chuck for a drill assembly, the chuck having an outer surface adapted to engage with the drill assembly, and an inner surface having a plurality of drive cavities formed therein, the drive cavities being shaped complementally to drive cavities of a liner of the drill assembly so that composite drive cavities are formed when the liner is inserted into the chuck.

«© WO 00/58058 PCT/IB00/00344

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a sectional side view of a hammer drill to which the invention is applied;

Figure 2 is a partial sectional side view of a chuck or chuck nut of the drill assembly, incorporating a wear resistant liner according to a first embodiment of the invention:

Figure 3 is a sectional view of the liner in the chuck of Figure 2;

Figure 4 is a partial sectional side view of a chuck or chuck nut of the drill assembly, incorporating a wear resistant liner according to a second embodiment of the invention:

Figure 5 is a sectional side view of the chuck of Figure 4 without the liner inserted;

Figure 6 is a sectional end view on the line 6-6 in Figure 5;

Figure 7 is a sectional end view of the liner in the chuck of Figure 4;

Figure 8 is a sectional view on the line 8-8 of the liner in the chuck of

Figure 7; and

Figure 9 is a sectional view showing two liners which are placed ) between two aligning indexes of the chuck and the drill bit,

DESCRIPTION OF EMBODIMENTS

Figure 1 shows a hammer drill assembly which is used in down-the-hole drilling and which comprises a cylindrical casing 10 with a drive chuck or chuck nut 12 (also referred to as a drive sub) at one end, and a backhead or top sub 14 at the other end for connection to a drill string. The cylindrical chuck 12 is formed with a number of axial splines on its inner surface (see below), which mate with complemental splines formed on the shank 16 of a drill bit 18, permitting axial movement of the drill bit relative to the chuck. The free end 20 of the bit abuts the end of a piston 22 which is driven reciprocally by compressed air fed through the pipes of the drill string and the backhead 14 via a series of ports, in a conventional manner.

The oscillation of the piston 22 causes it to strike the upper end 20 of the drill bit, driving the drill bit into the rock being drilled with an axial percussive force. In use, the entire drill string comprising the drill pipes and the drill assembly are rotated slowly and are fed downwards as the rock is broken by ’ the bit, with the broken rock being flushed upwardly around the drill assembly by compressed air passing through ports in the bit.

With relatively large diameter drill bits, typically above 250 mm in diameter, the axial movement of the drill bit shank in the chuck tends to cause adhesive wear between the drive faces of the mating splines on the bit shank and the chuck, leading to the development of fatigue cracks and premature wear and failure of the drill bit. Also, in certain drilling applications such as post-hole drilling, in which shallow holes, typically less than 2 m deep, are made in overburden, the bit tends to oscillate in the drive chuck, causing the mating splines of the chuck and bit to scuff and seize.

+ WO 00/58058 PCT/1B00/00344

In order to address this problem, the present invention provides a wear resistant liner having suitable frictional properties which is fitted to the inner surface of the drive chuck 12. The liner has an outer surface shaped complementally to the inner surface of the chuck, and an inner surface shaped complementally to the outer surface of the bit shank, so that it fits snugly between the mating splines of the bit and the chuck, but permits relative axial movement between them, with low friction.

Figure 2 is a partial sectional view of the drive chuck 12, showing a hollow cylindrical liner 24 fitted thereto, in accordance with a first embodiment of the invention. As can best be seen in the sectional view of Figure 3, the liner 24 has a shape which follows the profile of the splines 26 of the drive chuck, and which also defines internal grooves 28 which are complemental in shape to the splines 32 formed on the shank of the drill bit 16. Thus, the liner wall 38 has a generally zig-zag shape in section, with concentrically curved inner and outer wall portions 38.1 and 38.2, and radially extending leading and trailing wall portions 38.3 and 38.4 joining adjacent inner and outer wall portions. As : is best shown in Figure 2, the upper end of the liner 24 has a circumferential outwardly extending lip 30 which serves to locate the liner in the drive chuck, and the length of the liner corresponds to the length of the splines 26 of the chuck.

The splines 26 of the drive chuck and the splines 32 of the drill bit have adjacent parallel drive faces 34 and 36, respectively, which transfer rotational force from the drive chuck to the bit in use. The thickness of the leading liner wall portions 38.3 where they fit between the drive faces is thicker than at the trailing edges 38.4 of the liner profile, where less wear is experienced. In a prototype liner, used in a hammer drill with a bit having a shank diameter of approximately 200 mm, the thickness of the leading wall section 38.3 was approximately 7 mm, while that of the trailing wall section 38.4 was approximately 3 mm. Obviously, these dimensions will vary according to the dimensions and design of different drill components, but in general, the thickness of the leading wall section 38.3 will be approximately double that of the trailing wall section 38.4.

The material used for the liner needs to have suitable wear resistant properties as well as suitable frictional properties, so that it does not hamper the axial movement of the drill bit in the chuck. Possible materials include

Vesconite and Vesconite Hilube (trade marks) or non ferrous metals such as phosphor bronze. Other engineering plastics which are believed to be potentially suitable include Ertalon 66SA, Ertalon 6XAU+ and Ertalyte (trade marks).

A second embodiment of the invention is illustrated in Figures 4 to 8 wherein parts common to the first embodiment have common reference numerals.

Referring first to Figure 4, the cylindrical liner 24 is fitted to the drive chuck 12 with a plurality of drive members in the form of elongate drive pins 42 (only one of which is shown in Figure 4). The pins 42 are inserted into respective drive cavities 44.1 and 44.2 machined in the liner 24 and the drive chuck 12.

As can be more clearly in Figures 6 and 8, each of the liner 24 and the drive chuck 12 contains eight elongate cavities 44.1 and 44.2 respectively, having a semi-circular cross section.

When the liner 24 is inserted axially into the drive chuck 12 and aligned with it, the cavities 44.1 in the liner and the corresponding cavities 44.2 in the drive chuck will align with one another to form complete or composite cavities 46 of circular cross section, into which the pins 42 are inserted.

In the prototype, the total diameter of each cavity 46 was 16mm. The cavities 44.1 in the liner 24 were formed by milling the insert longitudinally

© WO 00/58058 PCT/IB00/00344 with a round-nosed cutter to form eight equi-spaced grooves or cavities disposed about the periphery of the liner and extending parallel to the longitudinal axis of the liner. The corresponding cavities 44.2 in the drive chuck 12 were formed by first drilling 16mm diameter holes in the wall of the chuck, parallel to the longitudinal axis of the chuck, before the inside of the chuck blank was machined out. This had the effect of “leaving half the hole” in the chuck 12, thereby effectively forming the cavities 44.2. It can be noted that the ends of the cavities 44.1 are closed, due to the use of a round-nosed cutter, which ensures retention of the drive pins 42 in the cavities 46.

The chuck, liner and pins are assembled by inserting the inner end of the liner a short distance into the chuck. The pins 42 are then greased and placed in position in the drive cavities 44.1 spaced about the periphery of the liner, the pins being held in position by the grease. The liner is then inserted fully into the chuck, so that the pins are then held captive in the composite : cavities 46 formed between the aligned cavities 44.1 and 44.2. : in the prototype, the pins 42 were formed from 16mm diameter round bar.

However, carbon steel bright bar or any other suitable material may be used.

It will also be obvious to one skilled in the art that the cavities 46 need not necessarily be circular, but could be polygonal, for example, and in that case the pins 42 need not be made using round bar. The length of the pins in the prototype was 125mm, slightly less than the length of the cavities in which they are received.

It will be understood that the second embodiment of the liner engages the splined shank of the drill bit in the same way as in the case of the first liner. }

The difference between the two liner arrangements is largely that in the case of the second embodiment the inner surface of the chuck is not splined, and that the above described drive member/drive cavity arrangement is used instead.

Referring now to Figure 9, two anti-friction liners 48 and 50 respectively, are placed on either side of the liner 24. These two ant-friction liners 48 and 50 are situated between the two indexing (aligning) journals of the drive chuck 12 and the drill bit, so that all of the indexing and drive surfaces of the chuck 12 are protected.

The anti-friction liners 48 and 50 can be made from the same material as the liner 24, as described above, or alternatively from bronze, for example.

The above described liner helps to prevent excessive wear of the drill bit and chuck, and can have a substantial service life, possibly exceeding the life of the bit. When worn, the liner is relatively easy to remove and replace, particularly compared with earlier attempts to insert rods or plates of a low friction material between the mating splines of the bit and chuck.

Claims

+ WO 00/58058 PCT/1B00/00344 CLAIMS:

1. A drill assembly comprising a drill bit having a shank formed with a plurality of splines, a chuck formed with a plurality of compiemental splines for engaging the shank of the bit and for permitting axial movement thereof relative to the chuck, and a generally cylindrical liner between the splines of the bit and the chuck, the liner being formed of a material selected for suitable wear-resistance and frictional properties.

2. A drill assembly according to claim 1 wherein the liner is formed from a tough plastics material or from a suitable non-ferrous metal.

3. A drill assembly according to claim 1 or claim 2 wherein the liner is formed with an outer surface shaped complementally to the inner surface of the chuck and with an inner surface shaped complementally to the outer surface of the bit shank, so that it fits snugly between the mating splines of the bit and the chuck.

4. A drill assembly according to any preceding claim wherein the liner has concentrically curved inner and outer wall portions and radially extending leading and trailing wall portions joining adjacent inner and outer wall portions.

5. A drill assembly according to claim 4 wherein the leading wall portions of the liner are thicker than the trailing wall portions of the liner.

6. A drill assembly according to claim 5 wherein the leading wall portions of } the liner are at least double the thickness of the trailing wall portions of the liner.

7. A drill assembly according to any preceding claim wherein the liner is a tight fit in the chuck.

8. A drill assembly according to any preceding claim further including at least one anti-friction lining adapted to be situated between at least one of the indexing journals of the chuck and the drili bit.

9. A drill assembly according to claim 8 further including two anti-friction linings adapted to be situated between two of the indexing journals of the chuck and the drill bit.

10. A liner for use with a drill assembly, the liner having an outer surface shaped complementally to the inner surface of a chuck of the drill assembly, and an inner surface shaped complementally to the outer surface of a bit shank of the drill assembly, so that that the liner is able to fit snugly between the mating splines of the bit and the chuck.

11. A liner according to claim 10 wherein the liner has concentrically curved inner and outer wall portions and radially extending leading and trailing wall portions joining adjacent inner and outer wall portions.

12. A liner according to claim 11 wherein the leading wall portions of the liner are thicker than the trailing wall portions of the liner.

13. A liner according to claim 12 wherein the leading wall portions of the liner are at least double the thickness of the trailing wall portions of the liner.

14. A liner according to any one of claims 10 to 13 wherein the liner is formed from a tough plastics material or from a suitable non-ferrous metal.

) + WO 00/58058 PCT/1B00/00344

15. A drill assembly comprising: a chuck formed with a plurality of drive cavities on an inner surface thereof: a generally cylindrical liner sized to be inserted into the chuck, the liner being formed with a plurality of drive cavities on an outer surface thereof and having at least one formation on an inner surface thereof for engaging a drill bit, the liner being formed of a material selected for suitable wear-resistance and frictional properties; and a plurality of drive members each sized to be received in one of a plurality of composite drive cavities formed when the liner is inserted into the chuck and the respective drive cavities on the chuck and liner : are aligned with one another. :

16. A drill assembly according to claim 15 wherein the drive members are pins which are made of metal.

17. A drill assembly according to claim 16 wherein the drive members are made from steel.

18. A drill assembly according to any one of claims 15 to 17 wherein the liner defines radially extending wall portions which are shaped complementally to drive formations on the drill bit.

19. A drill assembly according to any one of claims 15 to 18 wherein the plurality of drive cavities in the chuck and in the liner have a semi- circular cross section so that the composite drive cavities have a circular cross section.

20. A drill assembly according to claim 19 wherein the drive members are circular in cross section.

21. A drill assembly according to any of claims 15 to 20 further including at least one anti-friction lining adapted to be situated between at least one of the indexing journals of the chuck and the drill bit.

22. A drill assembly according to claim 21 further including two anti-friction linings adapted to be situated between two of the indexing journals of the chuck and the drill bit.

23. A liner for use with a drill assembly, the liner having a plurality of drive cavities formed in an outer surface thereof, the drive cavities being shaped complementally to drive cavities of a chuck of the drill assembly so that composite drive cavities are formed when the liner is inserted into the chuck, the liner having at least one formation on an inner surface ’ thereof for engaging a drill bit.

24. A liner according to claim 23 wherein the inner surface of the liner has a plurality of radially extending leading and trailing wall portions.

25. A liner according to claim 24 wherein the leading wall portions of the liner are thicker than the trailing wall portions of the liner.

26. A liner according to claim 25 wherein the leading wall portions of the liner are at least double the thickness of the trailing wall portions of the liner.

27. A liner according to any one of claims 23 to 26 wherein the liner is formed

, = WO 00/58058 PCT/IB00/00344 \ from a tough plastics material or from a suitable non-ferrous metal.

28. A chuck for a drill assembly, the chuck having an outer surface adapted to engage with the drill assembly, and an inner surface having a plurality of drive cavites formed therein, the drive cavities being shaped complementally to drive cavities of a liner of the drill assembly so that composite drive cavities are formed when the liner is inserted into the chuck.

29. A drill assembly substantially as herein described with reference to the illustrated embodiments.

30. A liner substantially as herein described with reference to the illustrated embodiments.

31. A chuck substantially as herein described and illustrated with reference to Figures 4 to 6 of the accompanying drawings.