WO2020039393A1

WO2020039393A1 - A percussion mechanism

Info

Publication number: WO2020039393A1
Application number: PCT/IB2019/057098
Authority: WO
Inventors: Rudolph BÜHRMANN
Original assignee: Individual
Current assignee: Individual
Priority date: 2018-08-23
Filing date: 2019-08-23
Publication date: 2020-02-27
Anticipated expiration: 2021-02-23
Also published as: ZA202101930B

Abstract

An impact mechanism (100) has a cylindrical poppet valve (112) provided in a valve chamber (114) located in a sidewall of a drive chamber (110). A switching seal (116) is located in a return chamber (108). A fluid inlet is connected to the return chamber (108) in front of the switching seal (116) and to the valve chamber (114). A drive chamber (110) supply passage extends from behind the switching seal (116) in the return chamber (108). Valve chamber (114) pressure biases the poppet valve (112) to close a drive chamber (110) inlet. Towards an end of a return stroke, the piston (102) moves the poppet valve (112) off a drive chamber (108) inlet seat (131) and onto an exhaust passage seat (133). A piston switching shoulder (118) piston enters the switching seal (116) towards an end of the drive stroke to interrupt supply to the drive chamber (110), which allows valve chamber (114) pressure to switch the poppet valve (112) back onto the drive chamber (110) supply seat.

Description

A PERCUSSION MECHANISM

FIELD OF THE INVENTION

The invention relates to a hydraulic impact mechanism and more particularly to such a mechanism for a rock drill or a down/in-the-hole hammer. The hydraulic fluid is preferably pressurised water (which may be used with a small amount of lubricating oil).

BACKGROUND TO THE INVENTION

The use of water as a pressurised working fluid is a desirable feature for a rock drill and an in-the-hole drill hammer. These water powered rock drills and hammers play an essential part in some underground mines, which are dedicated to the use of pressurised water to power equipment.

The components of such a water powered hydraulic rock drill or in-the-hole hammer suffer from a high degree of wear. They are subjected to significant forces and water, as a working fluid, offers little lubrication.

The profitability of mining and the viability of recovering ore from a particular reef depend on mining costs. One such cost is related to the operation and maintenance of the rock drills/hammers and this is assessed in proportion to metres drilled between break down or services and also the rate of rock penetration.

Where a drill/hammer fails or does not perform properly, for whatever reason, it will be sent for repair. It is in the mining industry’s best interests for this drilling equipment to operate as efficiently and cost effectively as possible.

OBJECT OF THE INVENTION An impact mechanism that is more cost effective and/or provides for a better rate of rock penetration (particularly for drifter-type rock drills and in-the-hole drill hammers) would be beneficial to the mining industry and in other drilling applications. It is an object of the invention to provide an impact mechanism, which at least partially provides such benefits.

SUMMARY OF THE INVENTION

In accordance with the invention there is provided an impact mechanism, comprising:

a reciprocating piston having a front, striking end and a rear end;

the piston located inside a housing and having a return stroke working area inside a return chamber and a drive stroke working area inside a drive chamber;

a cylindrical, end seating poppet valve provided in a valve chamber located in a sidewall of the drive chamber;

a switching seal located in the return chamber and a switching shoulder provided on the piston to co-operate with the switching seal;

a working fluid inlet connected to:

(a) the return chamber at a position forward of the switching seal; and

(b) the valve chamber to provide a bias on a valve shoulder towards a forward position wherein the poppet valve is

- seated against a drive chamber inlet seat to close a drive chamber inlet; and

- unseated from an exhaust passage seat to open, at a rear end of the poppet valve, an exhaust passage from the drive chamber;

wherein

a drive chamber supply passage extends from the return chamber, at a position rearward of the switching seal to the drive chamber inlet;

the piston interacts with the poppet valve as it approaches an end of a return stroke to [impart a rearward bias on and\ move the poppet valve off the drive chamber inlet seat and onto the exhaust passage seat, pressurise the drive chamber, and generate a drive stroke; and

the switching shoulder of the piston enters the switching seal as the piston approaches an end of the drive stroke to interrupt working fluid supply to the drive chamber through the drive chamber supply passage, which [causes pressure in the drive chamber to drop and] allows pressure in the valve chamber to switch the poppet valve onto the drive chamber supply seat and off the exhaust passage seat, whereupon pressure in the return chamber forward of the switching seal acts on the return stroke working area to generate a return stroke.

In accordance with one embodiment the invention further provides for an impact mechanism as defined, in which:

the fluid inlet is provided through the housing adjacent a front end of the return chamber and connected to the return chamber through a first inlet port;

the fluid inlet is connected to the valve chamber via a valve chamber passage through a second inlet port;

the valve chamber passage extends from the fluid inlet through an accumulator and around the drive chamber to the second inlet port;

the drive stroke working area of the piston is provided on the rear end of the piston; and

the valve chamber is located at a back end of the drive chamber.

The invention further provides for an impact mechanism as defined in which: the fluid inlet is provided through the housing adjacent a front end of the return chamber and connected to the return chamber through a first inlet port;

the valve chamber passage extends from the fluid inlet through an accumulator and around the drive chamber to the second inlet port; the drive stroke working area of the piston is provided on the rear end of the piston; and

the valve chamber is located at a back end of the drive chamber.

In accordance with a first embodiment of the invention, the impact mechanism is for a drifter-type rock drill.

In accordance with a second embodiment of the invention there is provided an impact mechanism as defined, in which:

the exhaust passage from the drive chamber extends into a cavity behind the piston and around a rear end of the piston to exhaust via an axial bore of the piston; and

an annular drive stroke working area is provided on the piston between middle bearing seals at the front of the drive chamber (with a larger diameter) and rear bearing seals at the back of a drive chamber (with a smaller diameter), which support a reduced diameter portion of the piston throughout its reciprocation cycle.

The invention further provides an in-the-hole drill hammer comprising the impact mechanism (of the second embodiment) as defined above located in a wear sleeve supporting a chuck and a drill bit with an exhaust bore.

The invention further provides for the fluid inlet to extend from a back-head along the wear sleeve to a first inlet port of the return chamber; and for a second inlet port to be provided between the exhaust passage and the valve chamber.

In accordance with both embodiments there is provided an impact mechanism as defined, in which:

a drive stroke snubber formation is provided in an insert at a front end of the return chamber that slidably engages on a piston stem; and

a return stroke snubber formation is provided at a rear end of the of the drive chamber. BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of the invention will be described, by way of example only, with reference to the accompanying drawings in which:

Figure 1 shows a side cross-sectional view of a percussion mechanism for a rock drill; and

Figures 2 to 4 show side cross-sectional views of top, middle and bottom portions taken along a length of a drill hammer.

DETAILED DESCRIPTION OF THE INVENTION

Referring to Figure 1 , a hydraulic impact or percussion mechanism (100) is shown for use in a “drifter” type rock drill. These drifters are generally mounted on a feed supported by a drill rig used in tunnel construction and in mining development.

A reciprocating piston (102) has a front, striking end (104) and a rear end (106). The front end (104) extends through a return chamber (108). The rear end (106) extends into a drive chamber (1 10). In this embodiment, the rear end (106) is exposed to working fluid in the drive chamber (1 10).

A cylindrical, end seating poppet valve (1 12) is provided in an annular valve chamber (1 14) located within (or formed into) a sidewall of the drive chamber (1 10).

A switching seal (1 16) is located in the return chamber (108), between a front region (108.1 ) and a rear region (108.2). A switching shoulder (1 18) is provided on the front of a piston head (102.1 ) around a piston stem (102.2).

A fluid inlet (120) is connected into the return chamber (108) through a first inlet port (122) for supply of working fluid. The first inlet port (122) is provided at a position forward of the switching seal (116). The hydraulic working fluid is pressurised water, which may have a small amount of oil added. The fluid inlet (120) is also connected to the valve chamber (1 14) via a valve chamber passage (124) and through a second inlet port (126). The valve chamber passage (124) extends from the fluid inlet (120) through an accumulator (128) and around the drive chamber (1 10) to the second inlet port (126).

The components of the impact mechanism (100) are stacked with the required passages and ports provided between parts and inserts or by boring of the necessary openings.

The pressure supplied to the valve chamber (1 14) acts on a rearwardly facing valve shoulder (130) that biases the poppet valve (1 12) to a forward position wherein it is seated against a drive chamber inlet seat (131 ). In this position, a drive chamber inlet (132) is closed and the poppet valve (1 12) is unseated from an exhaust passage seat (133) to open, at a rear end of the poppet valve (1 12), an exhaust passage (134) from the drive chamber.

The valve shoulder (130) is provided between smaller (rearward) and larger (forward) diameter portions of the poppet valve (1 12), which are slidably supported between small and large diameter lands in the valve chamber (1 14) that are fitted with suitable poppet valve bearing seals. Supply of pressurised fluid to the valve chamber (1 14) is constant during operation of the percussion mechanism (100) and present as soon as pressure is communicated to the fluid inlet (120), on start-up of the mechanism (100).

In Figure 1 , the piston (102) is in a forward position with an enlarged region, the piston head (102.1 ), behind a stem (102.2) of the piston (102) located inside the switching seal (1 16). The front region (108.1 ) of the return chamber (108) is isolated from the rear region (108.2) of the return chamber (108) by the switching seal (1 16). Pressure in the front region (108.1 ) biases the piston (102) to commence a return stroke. The drive chamber inlet (132) is closed by the poppet valve (1 12) under biasing force produced by pressurised working fluid in the valve chamber (1 14) and the drive chamber exhaust passage seat (133) is open. This allows for displacement of water from the drive chamber (1 10) as the piston (102) is moved rearwardly.

The piston (102) accelerates on the rearward, return stroke. The switching shoulder (1 18) pulls out of the switching seal (1 16). The front region (108.1 ) of the return chamber (108) is placed in communication with the rear region (108.2) of the return chamber (108). A drive chamber supply passage (136) that extends from a position in the rear region (108.2) at the back of the return chamber (108), behind the switching seal (1 16), is supplied with pressurised water. The drive chamber supply passage (136) extends to the drive chamber inlet (132), which is controlled by the poppet valve (1 12) and still closed at this stage.

As the piston (102) continues on its rearward travel and approaches an end of the return stroke, the rear end (106) comes sufficiently close to the poppet valve (1 12). The rear end (106) of the piston (102) and poppet valve (1 12) are configured to, through this interaction, move the poppet valve (1 12) off the drive chamber inlet seat (131 ) and onto the exhaust passage seat (133) against the fluid bias in the valve chamber (1 14).

During normal running of the rock drill there is (preferably) no metal-to-metal contact between these components as the valve is then switched through generation of forces in the fluid medium between the suitably configured interacting parts, as in normal water drill practice. In some embodiments or modes of operation or when there is over-travel of the piston (102), there may be contact with the poppet valve (112).

The exhaust passage seat (133) is closed and the drive chamber inlet (132) opened. Pressure builds up in the drive chamber (1 10) as a result of the still moving piston (102) and supply of working fluid from the drive chamber inlet (132). This generates a force that decelerates the piston (102) and changes its direction of travel to commence a drive stroke.

The configuration of the rear end (106) of the piston and the inside, front facing formation of the poppet valve (1 12) are also provided to halt rearward movement of the piston (102) through hydraulic resistance forces as the exhaust passage (134) is closed. The internal form of the poppet (1 12) provides a snubber to interact with a snubbing shoulder at the rear of the piston (102). The operation of these formations in the hydraulic environment will be understood by persons skilled in the art.

Both front (108.1) and rear (108.2) regions of the return chamber (108) remain charged with pressure from the fluid inlet (120). This pressure acts on the switching shoulder (1 18) but represents a suitably smaller force than that generated by pressure in the drive chamber (1 10) which acts on the rear end (106) of the piston (102). The piston (102) is accelerated on the drive stroke as a result of the differential.

The drive stroke working area of the piston is represented by the diameter of middle bearing seals (138) at the front of the drive chamber (1 10). In this embodiment, the drive stroke working area is provided on the rear end (106) of the piston (102). The return stroke working area is only that represented by the difference between the diameter of the aforesaid middle bearing seals (138) and front bearing seals (140) at the front of the return chamber (108).

The arrangement provides for a reset cycle for reciprocation of the piston (102) with the smaller constant force acting in the return stroke direction and the larger impact force being intermittently generated from the drive chamber.

As the piston (102) approaches an end of the drive stroke, the switching shoulder (1 18) moves through the switching seal (1 16), which cuts off supply of pressurised water to the drive chamber supply passage (136). The isolation of the rear region (108.2) of the return chamber (108) from working fluid supply and thus also the drive chamber (1 10) allows pressure in the valve chamber (1 14) which remains under constant supply to switch the poppet valve (1 12) from the exhaust passage seat (133) onto the drive chamber supply seat (131 ). The drive chamber (1 10) is vented.

The exhaust passage (134) from the back of the drive chamber (1 10) will be directed as required. In the current embodiment, the exhaust water feeds into a return line in a closed-circuit arrangement. The water is pressurised and then reused as supply water.

The drill will be designed for the piston (102) to deliver its impact or blow against an anvil (or the anvil end of a drill steel) before a decelerating force from pressure in the front region of the return chamber (108) acts significantly on the switching shoulder (1 18). Once the piston (102) has delivered its blow energy and is brought to a halt, it commences another return stroke to repeat the cycle.

A snubber formation (142) is provided to stop the piston (102) when it crosses into a state of over-travel. This is usually the case when an anvil is not presented in an impact zone to receive the blow energy delivered by the piston (102). The snubber formation (142) is provided inside an insert (144) that is guided on the piston stem through a pair of insert bearing seals (145). The first inlet port (122) extends through the insert (144) from the fluid inlet (120) which is provided in a front housing component (147) of the impact mechanism (100).

The return chamber (108) does not have a separate exhaust and is not directly vented during the drive stroke as the piston (102) moves forward into the return chamber (108). Instead, it is located along the supply path to the drive chamber (1 10) via the drive chamber supply passage (136), which is intermittently isolated from the supply pressure by the switching shoulder (1 18). Water displaced by the forwardly moving piston (102) becomes supply water to the drive chamber (1 10). The piston (102) displaces a (relatively) large volume of water very rapidly on the drive stoke so that the working fluid at pressure can impart energy to the piston (102).

The gas charged accumulator (128) allows sufficient water to pass through the passages (124) and ports (122) over and above the water that is constantly supplied through the inlet (120) to the drive chamber (1 10). The gas charged accumulator (128) functions in the usual manner, as is common practice in pressurised fluid storage.

During a slower return stroke the accumulator (128) is re-filled by the drive fluid that is constantly supplied through the inlet port (120). In this way the accumulator (128) serves to maximise the transfer of hydraulic energy to the piston (102) and to smooth the inflow through port (120) which also reduces hydraulic vibration in the supply lines (not shown).

Referring to Figures 2 to 4, another percussion mechanism in accordance with the invention is illustrated in a down- or in-the-hole hammer (200). Pressurised supply fluid/water enters at a back-head (202), through an accumulator (204), and flows forwardly through a fluid inlet (206) that extends as an annular passage along a wear sleeve (208) to a first inlet port (210).

The accumulator (204) provided at the back-head (202) evens the flow of the working fluid to a reciprocating piston (212) and takes vibrations out of the working fluid.

A second inlet port (214) extends from the fluid inlet (206) to supply a poppet valve chamber (216). Working fluid pressure in the valve chamber (216) acts on a valve shoulder to bias a cylindrical poppet valve (218) in the direction of a drive chamber inlet seat (220) and away from an exhaust seat (222).

The first inlet port (210) feeds a return chamber (224.1 ; 224.2) and acts on a return stroke working area of the piston (212). The return stroke working area in this embodiment is defined by the difference in diameter between front bearing seals (226) at the front of the return chamber (224.1 ; 224.2) [with a smaller diameter] and middle bearing seals (228) at the front of a drive chamber (230) [with a larger diameter]

A switching shoulder (232) is provided to interact with a switching seal (234). These two formations (232) and (234) serve to either isolate a rear region (224.2) of the return chamber (224.1 ; 224.2) from a front region (224.1 ) which is under constant supply pressure or to have these two regions (224.1 ) and (224.2) in communication. The first inlet port (210) is once again in the front region (224.1 ) of the return chamber (224.1 ; 224.2) and a drive chamber supply passage (236) leads from the rear region (224.2) to a drive chamber inlet (238) controlled by the poppet valve (218).

The cycle of the impact mechanism in the drill hammer (200) is the same as for the embodiment in Figure 1 . However, when an exhaust passage (240) is opened from the drive chamber (230) by the poppet valve (218), exhaust water flows into a cavity (242) behind the piston (212) and around a rear end (244) of the piston (212) to exhaust from the percussion mechanism via an axial bore (246) in the piston (212). The exhaust along this path exits through a second bore (248) in a bit (250) at the front of the hammer (200) to provide flushing water as required for drilling.

The exhaust/flushing arrangement is provided by having an annular drive stroke working area on the piston (212) between the middle bearing seals (228) at the front of the drive chamber (with a larger diameter) and rear bearing seals (252) at the back of the drive chamber (with a smaller diameter), which support a reduced diameter portion (254) of the piston throughout its reciprocation cycle.

The drive stroke working area will once again be sufficiently greater than the return stroke working area.

The piston (212) is shown in an impact position. A snubbing shoulder (256) is provided around a piston stem (258) at the front end of the piston (212). A snubber formation (260) is located provided in an insert (262) at the front of the return chamber (224.1 ; 224.2). The snubber formation (260) is guided on the piston stem (258) through a set of bearing seals. The arrangement is similar to that of the first embodiment and serves to arrest the piston (212) when operating in an over-travel condition.

The rear end of the drive chamber at (264) also provides a snubber formation to stop the piston (212) and switch travel from a return stroke to a drive stroke by imparting force on the valve (218) near the end of the return stroke.

The invention provides for a novel arrangement of components and drill cycle which the applicant has designed to provide improved manufacturing, wear performance and blow delivery. The working fluid passages and paths have also been selected for convenience in part manufacture and assembly as well as desirable performance of the impact mechanism.

A trapanning hammer would not have an exhaust bore in the piston and may include any other suitable modifications for that application.

The impact mechanism of the invention may also be used in a churn drill, where a bit is provided on the front end of the piston. Such a hammer may be used as part of a trepanning arrangement for making larger holes.

A person skilled in the art will appreciate that a number of variations may be made to the features of the described embodiment without departing from the scope of the current invention.

Claims

1. An impact mechanism, comprising:

a reciprocating piston having a front, striking end and a rear end; the piston located inside a housing and having a return stroke working area inside a return chamber and a drive stroke working area inside a drive chamber;

a switching seal located in the return chamber and a switching shoulder provided on the piston to co-operate with the switching seal; a working fluid inlet connected to:

(a) the return chamber at a position forward of the switching seal; and

(b) the valve chamber to provide a bias on a valve shoulder of the poppet valve towards a forward position wherein the poppet valve is

- seated against a drive chamber inlet seat to close a drive chamber inlet; and

wherein

the piston interacts with the poppet valve as it approaches an end of a return stroke to move the poppet valve off the drive chamber inlet seat and onto the exhaust passage seat, pressurise the drive chamber, and generate a drive stroke; and

the switching shoulder of the piston enters the switching seal as the piston approaches an end of the drive stroke to interrupt working fluid supply to the drive chamber through the drive chamber supply passage, which allows pressure in the valve chamber to switch the poppet valve onto the drive chamber supply seat and off the exhaust passage seat, whereupon pressure in the return chamber forward of the switching seal acts on the return stroke working area to generate a return stroke.

2. An impact mechanism as claimed in claim 1 in which the fluid inlet is provided through the housing adjacent a front end of the return chamber and connected to the return chamber through a first inlet port.

3. An impact mechanism as claimed in claim 2 in which the fluid inlet is connected to the valve chamber via a valve chamber passage through a second inlet port.

4. An impact mechanism as claimed in claim 3 in which the valve chamber passage extends from the fluid inlet through an accumulator and around the drive chamber to the second inlet port.

5. An impact mechanism as claimed in claim 4 in which the drive stroke working area of the piston is provided on the rear end of the piston.

6. An impact mechanism as claimed in claim 5 in which the valve chamber is located at a back end of the drive chamber.

7. An impact mechanism as claimed in claim 6 which is for a drifter-type rock drill.

8. An impact mechanism as claimed in claim 1 in which:

an annular drive stroke working area is provided on the piston between middle bearing seals at a front end of the drive chamber and rear bearing seals at a back end of a drive chamber, which support a reduced diameter portion of the piston throughout its reciprocation cycle.

9. An in-the-hole drill hammer comprising an impact mechanism as claimed in claim 8 located in a wear sleeve supporting a chuck and a drill bit with an exhaust bore.

10. An in-the-hole drill hammer as claimed in claim 8 in which the fluid inlet extends from a back-head along the wear sleeve to a first inlet port of the return chamber.

1 1. An in-the-hole drill hammer as claimed in claim 8 in which a second inlet port is provided between the valve chamber passage and the valve chamber.

12. An impact mechanism as claimed in claim 1 or claim 8, in which:

a return stroke snubber formation is provided at a back end of the of the drive chamber.