FIELD OF THE INVENTION

The invention relates to a water powered hydraulic rock drill and to an improvement in the flow of exhaust water through the rock drill mechanism and along a drill steel to provide flushing water. BACKGROUND TO THE INVENTION

Water powered rock drills are well known and commonly used in underground mining. The exhaust water from an impact mechanism is directed through a front head with a rotation mechanism along an axial bore of a drill steel. This provides flushing water which returns broken rock from a bottom of a drill hole.

OBJECT OF THE INVENTION It is an object of the invention to provide an improvement in such a rock drill that relates to the flow passages that provide the flushing water.

SUMMARY OF THE INVENTION In accordance with a first aspect of the invention there is provided a water powered rock drill comprising

an impact mechanism having a piston and a housing that define a drive chamber and a return chamber,

the impact mechanism operating for reciprocation of the piston to strike a slidably supported anvil in an impact chamber,

a front head casing including a rotation mechanism for a chuck to slidably support a drill steel,

an anvil chamber located to a front side of the impact chamber and connected to a conduit for flushing water, an air inlet suction passage fitted with a check valve that is connected to the impact chamber, and

the anvil providing a transmission valve from the impact chamber to the anvil chamber.

The invention further provides for a rock drill as defined with:

a recoil absorber for the anvil located in a recoil absorber chamber provided in a sidewall of the impact chamber, and

the anvil and recoil absorber providing the transmission valve from the impact chamber to the anvil chamber.

The anvil provides a moveable transmission valve closure and the recoil absorber provides a seat for the transmission valve closure. The check valve controlled air inlet suction passage is connected into the impact chamber so that when the piston retracts it draws or sucks air into the impact chamber and when the piston moves forward it compresses the air. After impact the anvil moves forward and opens the transmission valve from the impact chamber to the anvil chamber. The invention further provides for the impact mechanism to operate on a reset cycle for reciprocation of the piston; for the impact mechanism to include an annular [end seating poppet] distribution valve arranged between a supply seat and an exhaust seat, with an exhaust passage from the exhaust seat connected to the anvil chamber through a conduit provided with an orifice.

The invention still further provides for the anvil to include an axial flushing bore which is open at a drill steel engaging face and radially arranged flush feed ports for communication between the bore and the anvil chamber. Further features of the invention provide for a stop collar around the chuck to provide a stop for forward travel of the anvil; for an annular shoulder on the anvil to be engageable against the recoil absorber; and for a stem of the anvil to be guided in the stop collar and a back end, extending behind the annular shoulder, guided in the recoil absorber. In accordance with a second aspect of the invention there is provided a hydraulic rock drill comprising

an impact mechanism having a piston and a housing that define a drive chamber and a return chamber for reciprocation of the piston to strike a slidably supported anvil in an impact chamber,

a front head casing including a rotation mechanism for a chuck to slidably support a drill steel,

an anvil chamber located to a front side of the impact chamber connected to a conduit for flush medium, and

an air inlet passage provided for supply of air to the to the anvil chamber.

The invention further provides for the air inlet passage to be connected to a source of compressed air.

Further features of the invention provide for the air inlet passage to extend through the housing directly into the anvil chamber; or for the air inlet passage to extend through the housing directly into the impact chamber and for the impact chamber to be in communication with the anvil chamber.

A further feature of the invention provides for the rock drill to be an oil hydraulic rock drill; and for the flush medium to be pressurized water.

BRIEF DESCRIPTION OF THE DRAWING

These and other features of the invention will become more apparent from the following description of one embodiment made by example only with reference to the accompanying drawing in which

Figure 1 shows a side, cross sectional view of a relevant portion from a rock drill of the invention with a piston in a rearward position.

DETAILED DESCRIPTION OF THE INVENTION Referring to Figure 1 , a water powered hydraulic rock drill (200) is provided in accordance with the invention.

The drill (200) includes an impact mechanism (202) connected to a front head casing (204) with a rotation mechanism for a chuck (206) that receives a drill steel (not shown) in the known manner. The impact mechanism (202) includes a reciprocating piston (208) that together with a housing (210) of the impact mechanism (202), defines a drive chamber (212) and a return chamber (214).

The impact mechanism (202) operates on what is sometimes referred to as a reset cycle. Water under (substantially) constant pressure is supplied to a drive chamber (212). The drive chamber (212) is intermittently placed in communication with a return chamber (214). The reciprocating piston (208) is arranged between these two chambers (212) and (214) and has a larger working area exposed in the return chamber (214).

An annular distribution valve (216) is provided as a valve of the end seating poppet kind located in a valve chamber (218). The valve chamber (218) is provided in a sidewall of the return chamber (214). The poppet valve (216) switches between opposite supply (220) and exhaust (222) seats to either:

(a) place the return chamber (214) in communication with the drive chamber (212) to supply working fluid to the return chamber (214); or

(b) isolate the two chambers (212) and (214) from each other and vent the return chamber (214).

When the poppet valve (216) is in the latter position, exhaust water flows past the exhaust seat (222) from the return chamber (214) into an exhaust chamber (224). The operation of the poppet valve (216) directs the pressurized working fluid to drive the reciprocating piston (208). Figure 1 shows the piston (208) in a rearward position, at the end of a return stroke and the beginning of an impact or drive stroke. Further description of the drill cycle is not required but will be understood by a person skilled in the art.

A series of spaced apart exhaust passages (226) extend forwardly from an exhaust plenum (228) adjacent the exhaust seat (222) to the exhaust chamber (224). The exhaust passages (226) are formed into a front collar component (230) of the rock drill housing (210) that is secured at the front end of the impact mechanism (202) and against the front head casing (204).

The exhaust chamber (224) includes an exhaust accumulator (232). The accumulator (232) has a diaphragm (234). An enclosed space in the accumulator (232) behind the diaphragm (234) is charged with a suitable gas to the required pressure. The pressure biases the diaphragm (234) against a perforated support (236).

The exhaust chamber (224) is provided with a fluid recirculation passage (240, which includes 240.1 ; 240.2; and 240.3 referred to below) that feeds a recirculation line (242) through which flow is controlled by a pressure sensitive outlet valve (244). In the illustrated embodiment, the fluid recirculation passage (240) extends through the perforations (240.1 ) of the support (236). The water in the exhaust chamber (224) interacts with the diaphragm (234) through perforations (240.1 ) in the support (236). Outlet openings (240.2) are provided at the periphery of the support (236).

The diaphragm (234) operates as a closure of the pressure sensitive valve (244) at its outer regions which seat over or around the openings (240.2). The arrangement and configuration of these components serves to provide for a desired discharge pressure from the exhaust chamber (224) to the recirculation line (242). The openings (240.2) feed collection cavities (240.3) at a predetermined pressure which are in turn connected to the recirculation line (242). The exhaust chamber (224) also includes a second outlet provided as a conduit (246) for drill steel flushing water. The conduit (246) is provided with an orifice (248) selected to provide flow from the exhaust chamber (224) to maintain an adequate supply of flushing water at a desired substantially constant pressure.

The conduit (246) leads from the orifice (248) to an anvil chamber (250) in the front head casing (204), which provides:

(a) a cushion around and to a front side of an anvil (252); and

(b) a feed for flushing water to a drill steel (not shown).

The anvil (252) is slidably supported, extending across the anvil chamber (250) with a front face (270) presented for contact with a rear end of a drill steel and a back end located in an impact chamber (260).

In accordance with a first aspect of the invention, at least one air inlet suction passage (254) is provided in the front collar component (230). The suction passage (254) connects an air inlet (256) fitted with a check valve (258) to the impact chamber (260) located to a front side of the return chamber (214). The impact chamber (260) includes an impact zone where a front end (262) of the piston (208) strikes a back end of the anvil (252). Any suitable number of suction passages (254) may extend from the check valve (258) to introduce air into the impact chamber (260).

A thrust sleeve (264) provides a recoil absorber (264) for the anvil (252). The thrust sleeve (264) is suitably configured with differential working areas and located in a recoil absorber chamber (265) provided in a sidewall of the impact chamber (260). A supply port (263) to the recoil absorber chamber (265) is provided and will include a suitable orifice or similar arrangement. The supply port (263) serves to introduce pressurized working fluid that biases the recoil absorber (264), through the differential working areas, against a step at the front of the recoil absorber chamber (265). The supply port (263) can extend from somewhere else in the rock drill where the working fluid is available at substantially constant pressure, such as in part of the rotation mechanism, for example. The recoil absorber (264) transmits recoil energy to the water in the recoil absorber chamber (265). The arrangement serves to absorb the recoil energy from the drill steel and prevents the transfer of associated shock loads to the rock drill housing. Transfer for recoil energy to the drill housing is a common cause of tie rod failure and other shock load associated damage to the mechanism parts.

The slidably supported anvil (252) is located between the recoil absorber (264) and the chuck (206) to provide the striking interface between the piston (208) and a drill steel. The anvil (252) is also located between the impact chamber (260) and anvil chamber (250). The position of the anvil (252) seated on the recoil absorber (264) defines a substantially fixed impact point for the piston (208) and its front end provides a positive stop for a rear end of the drill steel. The arrangement also allows for use of a drill steel that is absent a collar.

A forward stop ring or stop collar (274) around the chuck (206), at a front of the anvil chamber (250) provides a stop for forward travel of the anvil (252).

The stop collar (274) defines an annular bore (276) with a curved edge (adjacent the anvil) that receives a stem (278) on the anvil (252). The curved edge (substantially) matches a curve on a front side of a shoulder (280) of the anvil (252).

A back side of the shoulder (280) abuts the recoil absorber (264) in use and these two components are shaped to provide a seal between the impact chamber (260) and the anvil chamber (250). The stem (278) of the anvil (252) is guided in the annular bore (276) and a back end, extending behind the shoulder (280), is guided in the recoil absorber (264). The check valve controlled air inlet (256) is connected into the impact chamber (260), so that when the piston (208) retracts, to the position shown in Figure 1 , it draws or sucks air into the impact chamber (260). When the piston (208) moves forward it compresses the air.

In the current embodiment, the anvil (252) and recoil absorber (264) provide a transmission valve (282) from the impact chamber (260). More specifically, the anvil (252) provides a moveable transmission valve closure and the recoil absorber (264) provides a seat for the closure.

During use, the rock drill (200) is thrust or pressed against rock. The drill steel is pushed back into the impact chamber (260) against the anvil face (270) and the anvil (252) is pressed against the recoil absorber (264). The piston (208) impacts the anvil (252) which then moves forward with the blow energy delivered to the drill steel. The forward movement of the anvil (252) opens an air/water by-pass through the transmission valve (282) from the impact chamber (260) to the anvil chamber (250).

Operation of the rock drill (200) results in an amount of water from the return chamber (214) that leaks past front bearing seals (266) on the piston (208) into the impact chamber (260). The air (and water) from the impact chamber (260) are conveyed to the anvil chamber (250) that receives the water feed via the conduit (246) and orifice (248). In this manner, the anvil chamber (250) receives an air/water mixture that will be a function of the specific design of the rock drill components and operating cycle.

The anvil (252) includes an axial flushing bore (268) which is open at the drill steel engaging face (270) and is movable into the chuck (206). Radially arranged, inclined flush feed holes or ports (272) from the bore (268) extend to the anvil chamber (250) for communication of the pressurized flushing air/water mixture to the rear end of a drill steel and down the usual axial passage to a drill bit. The arrangement of the suction passage (254) and check valve (258) provides an air feed to the impact chamber (260) that mixes into the flushing water that is conveyed down the drill steel. Relatively high pressure exhaust water is channeled via orifice (248) to the flush feed ports (272) of the anvil (252). The flush feed ports (272) direct the water and air mixture to and along an axial bore (268) of the drill steel which opens through holes in a drill bit at the front end of the steel.

An almost“closed-circuit” water powered rock drill is provided with some flushing water that is directed via the orifice (248) and the rest of the water going to tank via recirculation passage (242) from the accumulator (232). It is only the flushing water which is essential for the drilling that is discharged onto the footwall.

In use, the pressure in the exhaust chamber (224) is maintained by the accumulator (232) which operates as a pressure sensitive outlet valve (244). This component also absorbs impulses in the closed recirculation circuit. Pressure in the recirculation line (240) will be adequate for reintroduction of the water into a low pressure water reticulation system of the mine. This reintroduction of the water is achieved without the cost of secondary tanks and re-pressurisation pumps, for example. The return pressure can also be varied without affecting the drill performance (subject to the charge in the accumulator).

The arrangement provides for the compression of air to feed a desirable air/water mixture as the flushing medium into the drill steel. The water that leaks past the front bearing seals (266) into the impact chamber (260) is also flushed with the compressed air.

The introduction of air into the impact chamber and the mixture of air into the exhaust or flushing water have a dynamic effect. - Introduction of air reduces the component of water and increases the component of air to provide a desirable water/air mixture in the flushing water of the anvil chamber which also provides a cushion for the anvil.

- The presence of the air/water mixture reduces energy losses in the transmission of the piston blow energy through the anvil to the drill steel. The bulk modulus of water in the anvil chamber is reduced. The air that is introduced into the water thus improves efficiencies.

- The air that is introduced also reduces loads and pressure pulses that would otherwise be transmitted to the components around the anvil chamber (and particularly those in the front head casing) through transmission via the water as the anvil is struck.

- Air in the water enters into the drill steel preferentially as a component of the flushing water. The presence of air reduces the amount of water that is discharged onto the footwall.

In accordance with a second aspect of the invention, an alternative embodiment will be provided as a hydraulic rock drill that has a similar flushing water anvil chamber located to a front side of the impact chamber. An air inlet passage is also provided in the rock drill for supply of air to mix with the water in the anvil chamber. The air inlet passage is however connected to an external source of compressed air. A flushing water feed to the anvil chamber may be provided through alternative means (compared to the first embodiment described above) or from an external source, as would be the case with an oil hydraulic rock drill.

The air inlet passage may extend through the housing directly into the anvil chamber or it may be arranged to direct air into the impact chamber which will be in suitable communication with the anvil chamber (as with the first embodiment). The alternative embodiment provides for the benefit of air/water mixture for flushing and to reduce the bulk modulus of the water in the anvil chamber and this is achieved through an arrangement that will find application in rock drills that operate on pressurized oil.

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