WO2020188530A2

WO2020188530A2 - A drill hammer

Info

Publication number: WO2020188530A2
Application number: PCT/IB2020/052578
Authority: WO
Inventors: Bernard Lionel Gien
Original assignee: Gien Bernard L
Priority date: 2019-03-20
Filing date: 2020-03-20
Publication date: 2020-09-24
Also published as: WO2020188530A3; ZA202107670B

Abstract

A drill hammer includes an air distribution chamber in a rear end of a piston and a bore that extends to a front end. A chamber divider extends from a back-head to slidably engage inside the distribution chamber and a control tube slidably engages inside the bore. An air supply passage is provided between the control tube and the chamber divider. An exhaust port from the drive chamber extends through the chamber divider to an inside of the control tube. A distribution port to alternately supply a drive chamber and return chamber extends through the piston from the distribution chamber.

Description

A DRILL HAMMER

FIELD OF THE INVENTION

The invention relates to a pneumatic down- or in-the-hole drill hammer with a unique percussion mechanism that applies to both embodiments that have a foot valve tube on the drill bit (referred to as a tube design) and also to tubeless designs (which have a piston stem that interacts with a piston stem bush).

BACKGROUND TO THE INVENTION

Down- or in-the-hole drill hammers are well known and extensively used to drill or bore holes in rock. Various constructions for these hammer mechanisms have been proposed to achieve supply and exhaust of pressurised air to and from drive and return chambers to cause a piston to reciprocate and impact a drill bit.

In one popular construction of hammer, a control tube extends from a back-head and moves into and out of a piston bore as a finger valve to respectively seal and vent (or exhaust) the drive chamber.

In addition, when the hammer is withdrawn from a position against the hole bottom, a flushing mode is required wherein the piston ceases its reciprocation. It is generally desirable and advantageous for a drill hammer to be of relatively simple and/or lightweight construction and to have relatively few parts and, especially in recent times, be capable of achieving a low carbon footprint.

OBJECT OF THE INVENTION

It is an object of the invention to provide a drill hammer with a novel configuration of air supply and drive chamber exhaust passages, which may enable any of the aforementioned or other advantages. The hammer should also be capable of cost effective manufacture and/or efficiency in use. SUMMARY OF THE INVENTION

In accordance with the invention there is provided a drill hammer comprising

- a reciprocating piston with a drive chamber at a first end and a return chamber at a second end;

- an air distribution chamber provided as an axial, elongate cavity formed into the first end of the piston with an axial bore of reduced diameter extending along the piston from the air distribution chamber to the second end;

- a cylindrical chamber divider extending from a back-head through the drive chamber to slidably engage inside the air distribution chamber;

- a control tube that extends from the back-head co-axially with the chamber divider to slidably engage inside the piston bore;

- an air supply passage for the distribution chamber provided along the chamber divider; and

- an exhaust port from the drive chamber provided spaced apart from a free end of the chamber divider and extending to an inside of the control tube.

The invention further provides for the air distribution chamber to have a distribution port that extends to an exterior of the piston and is locatable [at respective drive and return phases of a drill cycle] in communication with a drive chamber supply cut-out in a wear sleeve or a return chamber supply cut-out in the wear sleeve.

The invention still further provides for the control tube to be supported inside the chamber divider and for the air supply passage to the distribution chamber to be provided between the control tube and the chamber divider; for the exhaust port to be provided by a laterally arranged conduit; and for the conduit to extend across the air supply passage.

Further features of the invention provide for a spring biased check valve to be supported by the control tube; and for the check valve to have a stem that slides within the control tube and a head spring biased against a seat provided by the back- head. Further features of the invention provide for the chamber divider to be clamped against a rearwardly disposed shoulder by the back-head [the shoulder may be provided in the wear sleeve or by an inner component of a two-part back-head]; and for the control tube to be secured by a radial support with openings to the air supply passage that engages into an open back end of the chamber divider.

A further feature of the invention provides for the drive chamber supply cut-out to extend to adjacent the back-head [to provide increased drive chamber volume]

A further feature of the invention provides for a working area on the piston inside the air distribution chamber around the axial bore to provide a biasing force that serves to move the piston into a flushing mode.

A further feature of the invention provides for a spring biased check valve to be supported by the control tube; and for the check valve to include a by-pass extending from a downstream side of a valve closure and along a valve spindle to exit inside the control tube. [The by-pass of the check valve is preferably fitted with an orifice.]

A further feature of the invention provides for the distribution port to open into an annular, circumferential recess.

[The return chamber may exhaust through a foot valve tube on a drill bit or past a piston stem bush.]

Further features of the invention provide for an inward step on an anvil head of a drill bit or on the piston stem to provide a vent from the return chamber past a bit guide bush or the piston stem bush when the piston in moved into a flushing mode.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of the invention will become more apparent from the following description, made by way of example only, with reference to the accompanying drawings, in which: Figures 1-2 show a cross-sectional side view of an embodiment of a hammer with a foot valve tube;

Figures 3-4 shows a cross-sectional side view of an embodiment of a hammer with a piston stem and piston stem bush;

Figure 5 shows an enlarged cross-sectional side view of a dual tube provided by chamber divider and control tube with check valve, from Figures 1-4; and

Figure 6 shows a modification to the check valve of Figure 5.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the drawings, two embodiments of the drill hammer (1) of the invention are shown in Figures 1-2 and Figures 3-4, respectively. The drill hammer (1) is provided with a dual tube arrangement that includes a control tube (2) located concentrically inside a cylindrical chamber divider (3). A preferred construction of these dual tube components for implementing the invention is shown separately in Figure 5. The chamber divider (3) includes an annular flange (4) that is clamped against a shoulder (5) in a wear sleeve (6) by a back-head (7). The flange could alternatively be clamped between components of a two-part back-head that are screwed together. The control tube (2) includes a radial support (8) with openings that lead from a plenum (9) around a check valve and inside the back-head (7) to an air supply passage (11) that extends between the chamber divider (3) and control tube (2). The support (8) engages with a press-fit into an enlarged portion of an opening at a rear end of the chamber divider (3), which provides an inlet to the air supply passage (11).

The chamber divider (3) and control tube (2) of the dual tube extend from the back- head (7) that secures these components in the assembly and into a distribution chamber (12) provided in a recess or axial cavity formed into a first end (13) of a reciprocating piston (14). The distribution chamber (12) is stepped outwardly from a reduced diameter axial bore (15) that extends to a second end (16) of the piston (14).

The dual tube includes two passages:

- the [outer] annular air supply passage (11) between the components (2) and (3) is provided to carry compressed air to the distribution chamber (12); and

- an [inner] central passage (17) inside the control tube (2) that serves to carry exhaust air away from a drive chamber (18).

The purpose of the dual tube is accordingly twofold: firstly, to deliver compressed air to distribution chamber (12); and secondly, to convey exhaust air from drive chamber

(18) via an exhaust port (19) to the axial bore (15) and an exhaust passage (20) in a drill bit (21) that opens to atmosphere.

The control tube (2) has a further purpose of acting as a finger valve in the axial bore (15) of the piston (14) that extends from the distribution chamber (12) to the second end (16). When disengaged from bore (15), distribution chamber (12) will vent through axial bore (15) and exhaust passage (20) and vents (22) in the drill bit (21) and to the atmosphere, as required for the hammer (1) to assume a flushing mode.

The compressed air supply flow path extends from the check valve (10), into supply passage (11) past an exhaust port (19) and continues into distribution chamber (12).

The exhaust passage for the drive chamber (18) extends through the exhaust port

(19) and leads to through central passage (17), bore (15), exhaust passage (20) and vents (22) to atmosphere. From exhaust port (19), it becomes a dual tube since the compressed air is in one passage, crossing over exhaust port (19), and continues into distribution chamber (12). The exhaust air is in the other passage and therefore the dual tube carries both, exhaust as well as compressed air in two separate passages, so the exhaust air passage crosses over the compressed air passage at one stage. Distribution chamber (12) is filled with compressed air and alternatively feeds the top, drive chamber (18) and a bottom, return chamber (23) above and below the piston (14). A working surface area (24) in distribution chamber (12) has pressure acting on it throughout the working cycle of the hammer (1) and serves to add to a drive chamber surface area at (13) on the piston (14) when the drive chamber (18) is compressed. A further function of surface area (24) is that when the hammer (1) is required to drill at horizontal or at an angle above the horizontal and the piston (14) tends to fall away from the drill bit (21) due to gravity or in the horizontal it sits somewhere between the points (25), (26) and (27) (see Figures 1-4) adjacent undercuts or recesses in the wear sleeve (6), the pressure on surface area (24) will cause the piston (14) to move towards the drill bit (21) and into starting or flushing position.

The embodiments of Figures 1-2 and Figures 3-4 are respectively of a piston for a tube (or foot valve tube) and another for a tubeless hammer design.

A drill bit may be supplied complete with a foot valve tube. To use the bit in a tubeless hammer the foot valve tube may be removed. The bore in a piston stem for the tubeless design, as shown in Figures 3-4, could optionally be made large enough to fit over the foot valve tube. In that case, it will not be necessary to remove the foot valve tube. The arrangement selected may depend on the thickness and strength of the wall required for the piston stem.

In Figures 1-4, as indicated, the points (25), (26) and (27) in cut-outs in the bore of the wear sleeve (6) determine the cut off of the air flow to the drive (18) and return (23) chambers as the corresponding or cooperating points on the piston (14) pass them. As indicated in the drawing of Figures 1-4 and as a result of point (25), there is also a cut-out (31), adjacent the back-head thread, which adds volume to the drive chamber (18) above the piston (14).

In one embodiment, there may be provided a by-pass passage (10.1) that extends through the check valve (10) with an optional metering plug (10.2) providing an orifice to allow for extra flushing when necessary (see Figure 6). The opening to the by-pass passage (10.1) which is fitted with the plug (10.2) is located on the head (33) at a position that is downstream from the valve seat (34). The by-pass passage (10.1) exits through the surface (B) on the end of the check valve stem.

When the compressed air enters the hammer via inlet bore (32) of the back-head (7), the air flows past surface (A) on a head (33) of the check valve (10) and urges the check valve (10) forwards away from a valve seat (34) provided at an inner end of the back-head bore (32) and into an open condition allowing the flow to reach the respective drive (18) and return (23) chambers. The surface area (B) on the check valve (10) is always exposed to exhaust air pressure in passage (17) which is considerably lower than the "live compressed air" on surface (A) on the other end of the check valve (10). This lower pressure on the side of surface (B) will allow the check valve (10) to remain in a forward position even when the air flow stops (but pressure remains) intermittently as the piston (14) opens and shuts ports during its reciprocation.

When flow stops past the check valve head (33) for a short while due to all ports being shut at certain times in the piston cycle the check valve (10) tends to bounce but since surface area (B) is exposed to exhaust pressure via exhaust passage (17), the check valve (10) will stay down in the forward open position and does not reciprocate (in sync with the pistons reciprocation) even though it is biased to return under force of a check valve spring (35).

The higher pressure on surface (A) and lower pressure on surface (B) provides unbalanced forces acting on the two ends of the check valve (10) and prevents the check valve (10) from returning to its upward position by counteracting the force of the spring (35), when there is no flow due to the piston (14) shutting the relevant ports.

The following is a description of the working of the hammer (1) with the aid of the Figures 1-4. Compressed air enters bore (32) in the back-head (7) and opens the check valve (10) off the valve seat (34). A flow of air continues past the check valve (10) down the inlet or supply passage (11) of the dual tube and into distribution chamber (12). The piston (14) is brought into starting position with the drill bit (21) abutting an annular face of a chuck (37). In this position compressed air from distribution chamber (12) flows via distribution ports (36) which extend through the wall of the piston (14), into a return chamber cut out (38). The cut-out (38) is defined by precise points (26) and (27). The flow continues into return chamber (23) and the pressure build up acts on a surface at the second end (16) to urge the piston (14) in an upward direction.

The point (29) on the piston passes point (26) in the bore of the wear sleeve (6) and cuts off or stops the flow into return chamber (23).

As the piston (14) continues moving upwards, point (39) where the axial bore (15) opens at the second end (16) of the piston (14) will pass point (40) on a free end of: i. a foot valve tube (41) in the embodiment of Figure 1; or

ii. a piston stem bush in the embodiment of Figures 3-4 to allow return chamber (23) to exhaust through (15) and (22) to atmosphere.

The piston (14) gains upward speed and point (28) on the piston (14) will pass point (25) in the bore of the wear sleeve (6) to allow compressed air from distribution chamber (12), via distribution ports (36) to enter drive chamber (18). In the meantime, exhaust port (19) has been shut off by the walls of air distribution chamber (12) to provide a sealed environment for drive chamber (18).

The pressure build up in drive chamber (18) acts on a surface at the first end (13) of the piston (14) and causes it to slow down and commence a reverse direction of travel. Pressure on surface area at the first end (13) combined with existing pressure on surface area (24) accelerate the piston (14) towards the bit (21) to deliver an impact blow. During its drive stroke towards the bit (21), the walls of the air distribution chamber (12) uncover exhaust port (19) allowing drive chamber (18) to exhaust down (17), (15), (20) and (22) to atmosphere. Point (28) passes point (25) shutting off distribution ports (36) from drive chamber (18). The distribution ports (36) will now be exposed by point (29) on the piston (14) passing point (26) in the wear sleeve (6) and compressed air again flows into return chamber (23) to lift the piston (14) and repeat the process. When lifting the hammer (1) from the bottom of the bore hole in order for the piston (14) to stop reciprocating and only flush the full complement of compressed air through the hammer (1), the bit (21) drops forward, away from the annular face of a chuck (37). A shoulder (43) on a neck of the bit (21) stops against the bit retaining rings (44). The piston (14) follows and point (45) on the piston (14) passes point (27) in the bore of the wear sleeve to shut off the compressed air coming into return chamber (23). Point (46) in the axial bore 30 of the piston (14) pulls past point (47) on the end of the control tube (2)and the compressed air from distribution chamber (12) flushes down (17), (15), (20) and (22) to the atmosphere.

To get the hammer (1) into flushing mode the bit (21) has to drop forward with the piston (14) following but in the case of horizontal or upward drilling, the bit (21) cannot fall forward due to gravity so when the hammer (1) is pulled backwards from the hole bottom, the piston (14), powered by surface area (24) in the distribution chamber (12), will push the bit (21) forward to eventually stop against the bit retaining rings (44).

Ideally, return chamber (23) should be vented to the atmosphere since if there is no escape for the air trapped in return chamber (23), the piston (14) will hit this body of air, compress it and bounce back into starting position thus preventing the piston (14) from stopping and the hammer (1) from going into flushing mode.

In order to vent return chamber (23) point (30): i. on an anvil head of the bit in the embodiment of Figures 1-2; and ii. on piston stem in the embodiment of Figures 3-4 passes point (48): i. on bit guide bush (51) (Figures 1-2); and

ii. on piston stem bush (52) (Figures 3-4) to allow return chamber (23) to vent via the reduced diameters: on the anvil head (Figures 1-2); and ii. piston stem (Figures 3-4).

These are preferred methods of venting return chamber (23). Alternative methods and exhaust flow paths may be used.

The piston is guided and in sliding engagement with the control tube throughout normal reciprocation during the drill cycle. The airflow path is very direct to the chambers which increases the energy output and optimises the frequency of the piston.

A person skilled in the art will appreciate that a number of changes can be made to the features of the embodiments described above without departing from the scope of the invention when considered for its novelty and inventiveness.

Claims

1. A drill hammer comprising:

a reciprocating piston with a drive chamber at a first end and a return chamber at a second end;

an air distribution chamber provided as an elongate cavity formed into the first end of the piston with a bore of reduced diameter extending along the piston from the air distribution chamber to the second end;

a cylindrical chamber divider extending from a back-head through the drive chamber to slidably engage inside the air distribution chamber;

a control tube that extends from the back-head co-axially with the chamber divider to slidably engage inside the piston bore;

an air supply passage for the distribution chamber provided along the chamber divider; and

an exhaust port from the drive chamber provided spaced apart from a free end of the chamber divider and extending to an inside of the control tube.

2. A drill hammer as claimed in claim 1 in which the air distribution chamber has a distribution port that extends to an exterior of the piston, a wear sleeve includes a drive chamber supply cut-out and a return chamber supply cut-out in the wear sleeve and the distribution port is alternately locatable in communication with the drive chamber supply cut-out and the return chamber supply cut-out on reciprocation of the piston.

3. A drill hammer as claimed in claim 1 in which the control tube is supported inside the chamber divider and the air supply passage to the distribution chamber is provided between the control tube and the chamber divider.

4. A drill hammer as claimed in claim 3 in which the exhaust port is provided by a laterally arranged conduit that extends across the air supply passage and is open through the chamber divider and through the control tube.

5. A drill hammer as claimed in claim 1 in which a check valve is supported by the control tube and wherein the check valve has a stem that slides within the control tube and a head that is spring biased against a seat provided by the back-head.

6. A drill hammer as claimed in claim 1 in which the chamber divider is clamped against a rearwardly disposed shoulder by the back-head and the control tube is secured by a radial support with openings to the air supply passage that engages into an open back end of the chamber divider.

7. A drill hammer as claimed in claim 1 in which a working area on the piston inside the air distribution chamber around the bore provides a biasing force that serves to move the piston into a flushing mode.

8. A drill hammer as claimed in claim 2 in which the distribution port opens into an annular, circumferential recess on the exterior of the piston.

9. A drill hammer as claimed in claim 1 in which an inward step on an anvil head of a drill bit provides a vent from the return chamber past a bit guide bush when the piston is moved into a flushing mode.

10. A drill hammer as claimed in claim 1 in which an inward step on a piston stem provides a vent from the return chamber past a piston stem bush when the piston is moved into a flushing mode.