CENTER TUBE RETENTION

Abstract

A center tube retention system of a down-the-hole tool includes a casing having an inner wall, a feed tube centrally disposed within the casing, the feed tube having an upper end and a tapered outer surface at the upper end, and a tube holder arranged to receive the top end of the feed tube, the tube holder having a tapered inner surface, the tapered surface of the feed tube matching the taper of the tube holder to form a tapered seat. The tube holder is formed as a collet having a plurality of machined slits aligned radially to a central axis of the casing. The slits are arranged to allow the tube holder to expand outward and press against the inner wall of casing ensuring alignment and retention of the feed tube within the casing.

Description

TECHNICAL FIELD

The present disclosure relates to a center tube retention system for retaining the feed tube of a DTH or rotary percussive hammer for drilling rock.

BACKGROUND

For the type of DTH (down-the-hole) tool, such as a hammer, which utilizes a central feed tube, there are several methods for retaining the tube in the hammer. As shown in FIG. 1, a pin, which while effective, is quite difficult to manufacture to ensure good tube alignment with the other components in the hammer. Referring to FIG. 1, such a retention for a DTH tool uses a very close tolerance press-fit through pin 16 inserted into a hole in the top sub 12′ and through the feed tube 14′. The pin is closely ground and must be installed with a hammer. The high tolerances needed for the pin and hole increase cost and yield failure site locations unnecessarily.

Another option is the use of a single machined component that is held in place with a machined shoulder in the piston case and a squeezable ring that pushes down with the screwed in top-sub. Although such an arrangement keeps the tube centralized, it requires a large piece of raw material, plus it tends to loosen up while the hammer is running due to only the linear force holding it in place.

Still another prior solution is a tube with a small flange that has a rubber ring on each side of this flange and this is turn is installed in a larger flange, which is held in place with a shoulder in the case and squeezable ring much like version the above.

Accordingly, there is a need to change and improve current central tube retention method in DTH and percussion product lines.

SUMMARY

Drilling in rock can be performed by percussive drilling, which is a combination of percussion and rotation. Percussive drilling and DTH tools use a piston assembly that slidably oscillates against, or relative to, non-moving components.

In order to reduce failure risk and create multiple product line uniformity while keeping complexity and, therefore, costs low, the present disclosure eliminates the press fit pin.

There is a matching taper on the central tube and the tube holder that fit together. By using a taper fitment on these designated parts there is no need for tight tolerances or interference fits. This is because as the tube is pushed into the holder, the holder expands and creates concentricity with the casing, which is critical for alignment with the vertical oscillating piston also concentric to the casing. The collet feature of the tube holder grips the central tube and casing inner diameter to prevent axial movement. Retaining pressure is achieved by assembling the top sub which compresses a makeup ring onto the tube and holder and centering in the case.

The present disclosure provides a tube retention system of a down-the-hole tool, the system including a casing having an inner wall, a feed tube centrally disposed within the casing, the feed tube having an upper end and a tapered outer surface at the upper end, and a tube holder arranged to receive the top end of the feed tube, the tube holder having a tapered inner surface, the tapered surface of the feed tube matching the taper of the tube holder to form a tapered seat.

A top sub is disposed within an upper end of the casing.

A make-up ring is positioned between an end of the top sub and a guide member.

An upper end of the feed tube communicates with the guide member, wherein pressure from the top sub forces the make-up ring, which in turn forces the guide member to push the feed tube into the tube holder at the tapered seat.

The tube holder is formed as a collet having a plurality of machined slits aligned radially to a central axis of the casing, the slits being arranged to allow the tube holder to expand outward and press against the inner wall of casing ensuring alignment and retention of the feed tube within the casing.

The guide member can be a check valve guide or a choke tube guide.

A method of retaining a center tube in a down-the-hole tool is provided. The method includes the steps of providing a center tube retention system, and moving the top sub to compress the makeup ring, which in turn forces the guide member to push the feed tube into the tapered seat formed in the tube holder to expand the tube holder into the casing wall.

The foregoing summary, as well as the following detailed description of the embodiments, will be better understood when read in conjunction with the appended drawings. It should be understood that the embodiments depicted are not limited to the precise arrangements and instrumentalities shown.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a prior art feed tube retention mechanism.

FIG. 2 is a longitudinal cross-section of an embodiment of a DTH tool.

FIG. 3 is a perspective view of a tube holder according to the present disclosure.

FIG. 4 is a longitudinal cross-section of an embodiment of a rotary percussion tool.

DETAILED DESCRIPTION

FIG. 2 illustrates a DTH tool 10, which utilizes a central feed tube 14 extending along a central axis 8. Tool 10 can be a DTH hammer, as well as a rotary percussive tool (RPS) that is a combination of percussion and rotation. The tool 10 of FIG. 2 is a piston actuated DTH drilling tool, such as a hammer, which includes a casing or housing 18 having opposed top and bottom ends. A top sub 12 is threadedly coupled to a top end 17 of the casing 18. A piston 20 is movably disposed within casing 18. Piston 20 includes a choke 22. As is well known, the movement of piston 20 is regulated by the timing of pressure between fluid chambers formed in the casing. A drive sub (not shown) and mandrel (not shown) are located at a bottom end of casing 18 and the mandrel is arranged as a substantially solid component to which a drill bit (not shown) can be attached to. The top sub 12 is threadedly connected to a drill string (not shown), which is connected to a rotation motor on a drilling rig at the surface. Rotational torque is then applied through the rotating assembly including casing 18, the drive sub and the mandrel.

Central feed tube 14 is horizontally and vertically located within casing 18. The vertical location is critical as the tube controls timing functions within the percussion device interaction of the tube and piston. The horizontal location of the tube is important for function and long life as off-center alignment increases wear potentially leading to failure. Feed tube 14 is replaceable due to wear or breakage during use.

Feed tube 14 can be a ferrous, nonferrous, or polymer material. The material may be combined with lubrication/corrosion/wear protection.

As will be explained further herein, feed tube 14 is horizontally and vertically located by a tapered seat 28 located in an outer surface of the upper end 15 of the feed tube. The taper 28 provides very high accuracy alignment and interchangeability between components during service. In addition, the central and axial location due to taper seat 28 provides low cost and ease of assemble without error.

Tool 10 includes a check valve 24 and a check valve guide member 26. A make-up ring 30 is located between top-sub 12 and guide 26. Makeup ring 30 contributes to secure the tube within the holder. Ring 30 may be a ferrous or a non-ferrous material. It should be appreciated that ring 30 is designed with a fit, form and function of the specific percussion hammer/tool as needed. The makeup ring has an uncompressed state and a compressed state.

Tool 10 includes a tube holder 32 that is positioned within an inner wall 19 of casing 18. Tube holder 32 receives and aligns central feed tube 14. The tube holder 32 has a taper 34 that matches taper 28 of the feed tube and accepts the tube with an expanding collet design, which will be described further herein. The tapered surface of the feed tube matches the taper of the tube holder to form a tapered seat.

Tube holder 32 grips an upper end 15 of the feed tube 14 to prevent movement during operation. Holder 32 can be a ferrous, nonferrous metal, or polymer material and may be coated or treated with secondary heat treatment processing to increase hardness, lubricity, corrosion resistance.

As discussed above, tube holder 32 has a taper design to receive the feed tube 14 with an expanding collet design. The taper seat may be machined into both components, is uniform, low cost, and has a very high accuracy, concentric alignment and interchangeability between components.

As set forth above, centrally locating the tube is important for function and long life as off-center alignment will increase wear and will fatigue the tube leading to failure. Axial alignment is necessary as the tube controls timing functions relative to piston travel.

Referring to FIG. 3, tube holder 32 is formed as a collet having a plurality of machined slits 36 aligned radially to central axis 8. Slits 36 allow the tube holder 32 to expand outward and press against the inner wall 19 of casing 18, applying pressure as the central tube is inserted and makeup ring 30 is compressed. The pressure acts both against the tube and casing wall by expansion ensuring alignment of central tube axis to piston axis, which is longitudinally traversing inside the casing.

Tube holder or collet 32 provides a linear and radial lock. During assembly, top sub 12 crushes makeup ring 30, which puts force on the check valve guide member 26, which in turn forces the feed tube 14/taper 28 into mating taper with collet 32/taper 34. As such, outer taper 28 of feed tube 14 matingly engages the inner taper 34 of collet 32. Thus, the tapered surface of the feed tube matching the taper of the tube holder to form a tapered seat.

As top sub 12 mates against the top portion of makeup ring 30 it compresses it against the central feed tube 14, which applies axial pressure and eliminates any axial movement of the central tube 14 and collet 32.

The central tube 14 subsequently seats on its taper 28 to the mating taper 34 of the collet 32. This results in a very firm fitment because it is located on the shoulder of casing 12 and expanded radially against casing 12. Such slip fit is relatively tight, but is not dependent on tool operation, thus reducing the need for expensive tight machining tolerances.

Referring to FIG. 4, a RPS version of tool 10 is shown. It should be appreciated that like terms refer to like elements between the DTH and RPS tool versions. Tool 10 includes a choke tube guide member 38. A make-up ring 30 is located between top-sub 12 and choke tube guide member 38.

Tool 10 includes tube holder 32 that is positioned within inner wall 19 of casing 18. Tube holder/collet 32 receives and aligns central feed tube 14. The tube holder 32 has a matching taper 34 to accept the tube with an expanding collet design in the same manner as described supra. Thus, collet 32 and feed tube 14 have mating tapers function as described above to hold feed tube in place in a similar manner.

In operation, top sub 12 forces the makeup ring 30 to put force on the check valve guide member 36 or choke tube guide member 38, which in turn pushes the feed tube 14 into the tapered seat in the tube holder/collet 32 to expand it into the casing wall 19. This provides a very firm fitment because it is located on the shoulder in the casing and expanded radially against the casing 18.

Slits 36 allow the tube holder 32 to expand outward and press against the case wall applying pressure as the central tube is inserted and makeup ring 30 is compressed. The pressure acts both against the tube and casing wall by expansion ensuring alignment of central tube axis to the piston axis, which is longitudinally traversing inside the casing.

Although the present embodiment(s) has been described in relation to particular aspects thereof, many other variations and modifications and other uses will become apparent to those skilled in the art. It is preferred therefore, that the present embodiment(s) be limited not by the specific disclosure herein, but only by the appended claims.

Claims

1. A center tube retention system of a down-the-hole tool, the system comprising: a casing having an inner wall;a feed tube centrally disposed within the casing, the feed tube having an upper end and a tapered outer surface at the upper end;a tube holder arranged to receive the top end of the feed tube, the tube holder having a tapered inner surface, the tapered surface of the feed tube matching the taper of the tube holder to form a tapered seat.

2. The center tube retention system of claim 1, wherein a top sub is disposed within an upper end of the casing.

3. The center tube retention system of claim 2, wherein a make-up ring is positioned between and end of the top sub and a guide member.

4. The center tube retention system of claim 3, wherein the upper end of the feed tube communicates with the guide member, wherein pressure from the top sub forces the make-up ring, which in turn forces the guide member to push the feed tube into the tube holder at the tapered seat.

5. The center tube retention system of claim 1, wherein the tube holder is formed as a collet having a plurality of machined slits aligned radially to a central axis of the casing, the slits being arranged to allow the tube holder to expand outward and press against the inner wall of casing ensuring alignment and retention of the feed tube within the casing.

6. The center tube retention system of claim 4, wherein the guide member is a check valve guide.

7. The center tube retention system of claim 4, wherein the guide member is a choke tube guide.

8. A method of retaining a center tube in a down-the-hole tool, the method comprising the steps of: providing a center tube retention system of claim 1;moving the top sub to compress the makeup ring, which in turn forces the guide member to push the feed tube into the tapered seat formed in the tube holder to expand the tube holder into the casing wall.