HK1088861B - Pneumatic rock drill - Google Patents

Description

Pneumatic rock drill

Technical Field

The invention relates to a pneumatic reciprocating rock drill.

Background

Pneumatic percussive rock drilling machines are well known. Such machines typically include a percussion motor including a piston that reciprocates in a housing and is configured to deliver reciprocating impacts to the end of the drill tool in operation. Pneumatic rock drills are also often equipped with a rotation device to rotate the drill. Such a rotary device may be a pneumatic rotary motor separate from the impact motor or a mechanical coupling, such as a reciprocating lever mechanism, as is well known.

Pneumatic percussion rock drilling machines are also usually equipped with a small diameter rigid tube that passes from the rear of the rock drilling machine and ends just short of the impact face of the drilling tool. Such a tube passes through a hole in the centre of the piston and is more or less concentric with the hole along the centre of the drill. The tube terminates at the rear of the rock drill in an external hose connection. During drilling, a relatively low pressure hose is connected to the nipple and water is sprayed along the rigid pipe and through the hole in the drill. This water is expelled from the drill tool adjacent the rock break-off point during drilling and serves to suppress air-entrained dust and to flush broken rock cuttings from the hole being drilled. Water injection is an essential part of the drilling process for functional and health and safety reasons, and therefore most underground pneumatic rock drilling sites are provided with compressed air and a relatively low pressure water supply.

In order to lubricate such rock drills, oil is usually added to the compressed air supply via a venturi type oiler. A small amount of airborne oil entering the rock drilling machine is deposited on the inner surfaces to ensure proper lubrication. This is a well known technique of oil mist lubrication. In addition to the air channel to and from the impact motor and the swing motor, different auxiliary channels or leak paths are provided to carry dust-laden air and thus oil to other locations in the rock drilling machine where lubrication is required. The oil has the auxiliary function of preventing corrosion of the various rock drill parts.

A large proportion of the oil entering this type of rock drilling machine will exit the rock drilling machine in the form of small droplets suspended in the exhaust gas. This is a serious health hazard for people close to such a machine. Other disadvantages of passing large quantities of oil through rock drilling machines are the cost of the oil and the contamination of the ore in certain mining applications.

Various designs are known which aim to reduce the amount of oil passing through a pneumatic rock drill. Us patent 3,983,788 discloses an impact motor having two separate air lines, one being oil-free and the other being oil-free. The enlarged central head of the impact piston is arranged with a clear annular gap in the central area of the cylinder bore, while the elongated end of the impact piston is guided in a closed fitting bush. Due to the presence of the annular gap, the piston can be swung by an oil-free air supply, while the guide bush and the auxiliary parts are lubricated by a second oil-filled air line. Most of the compressed air consumed by the pneumatic rock drill is used to move the percussion piston back and forth, so by driving this part of the rock drill with oil-free air, the amount of oil mist discharged can be reduced considerably. A disadvantage of this approach is the complexity of the dual air lines.

Us patent 4,333,538 discloses the use of an oil separator in the air line upstream of the impact motor. A larger proportion of the oil feed is separated from the air entering the impact motor, thereby ensuring that the least amount of oil required for lubrication passes through the impact motor. The remaining oil and some air are piped directly to the auxiliary parts of the rock drill, such as the chuck bushing and ratchet mechanism. Although not declared an object of the present invention, a more efficient distribution of oil will result in an overall reduction of oil consumption and thus of oil mist emitted.

Hydraulic percussive rock drilling machines are also well known in the rock drilling industry. These rock drills use high pressure water as the working fluid instead of mineral oil in a conventional hydraulic machine. Some of the water discharged by these rock drills is sprayed along the hole in the centre of the drill, whereby the functions of dust suppression and hole flushing are achieved. Various design techniques and material choices have evolved to allow these rock drills to operate successfully without oil or grease lubrication. The only lubrication required is provided by the working fluid, water, and the use of appropriate materials to ensure corrosion is not a significant problem. Hydraulic rock drilling machines therefore do not have the above-mentioned drawbacks of oil mist lubricated pneumatic rock drilling machines at all.

Hydraulic percussive rock drills have the disadvantage that they require a different infrastructure than pneumatic rock drills.

It is an object of the present invention to provide a pneumatic rock drilling machine which seeks to overcome the above disadvantages, or at least to provide a useful alternative to existing pneumatic rock drilling machines.

Disclosure of Invention

According to a first aspect of the invention there is provided a pneumatic rock drill comprising:

-a housing comprising an air supply inlet for receiving compressed air and a cylinder connected to the air supply inlet by a set of air channels;

-an impact piston, at least a part of which is reciprocable in the cylinder; and

-air flow control means for controlling the supply of compressed air from the air supply inlet to the cylinders;

the rock drill comprises at least one pair of corresponding contact surfaces at which the relatively moving parts contact each other; and is

The rock drill is characterised by comprising at least one water supply inlet and a water circuit connected to the water supply inlet and configured to deliver water to the drilling tool in operation so as to flush the hole being drilled and supply water to wet the above-mentioned contact surfaces.

The contact surface may be located at the interface between the impact piston and the cylinder. One or more bearings may be provided to one of the cylinder and the impact piston, and the contact surface is a surface on the other of the bearing and the cylinder and the impact piston.

The cylinder may include a drive chamber and a return chamber. The impact piston includes a first portion and a second portion, the first portion having a larger diameter than the second portion and reciprocating inside the cylinder. The first portion of the impact piston may divide the cylinder into a drive chamber and a return chamber.

The air flow control device may be configured to control a flow rate of the compressed air from the air supply inlet so as to intermittently supply the compressed air to at least one of the driving chamber and the return chamber. Preferably, the air flow control means is configured to control the alternate supply of compressed air from the air supply inlet into the drive chamber and the return chamber.

The air flow control means may be provided by a valve.

The water circuit may comprise a primary water flow path and at least one secondary water flow path, wherein the primary water flow path is configured to supply water to the drilling tool in operation and the secondary water flow path is configured to supply water to wet the contact surface in operation.

At least one of the auxiliary water flow paths is in fluid communication with the cylinder. Preferably, the auxiliary water flow path is in fluid communication with both the drive chamber and the return chamber.

In operation, water is introduced into the cylinder due to the pressure differential between the water supplied to the water supply inlet and the air in the cylinder. Water may be introduced into the discharge chamber of the drive chamber and the return chamber due to the pressure differential described above.

In one embodiment the rock drill may include a venturi in the air passage adjacent the air supply inlet and the water path includes a passage in fluid communication with the venturi, such that, in operation, water entrained in the compressed air is supplied to the cylinder to wet the contact surfaces.

The first portion of the impact piston may be located in a proximal region of the impact piston; and the cylinder is provided with a piston guide at its longitudinal end, in which the impact piston is supported. The cylinder and the first part of the impact piston are dimensioned to provide a small annular gap between the cylinder and the first part of the impact piston. The piston conduit is preferably provided with sealing means and the water path is configured to wet the contact surface on the impulse piston adjacent the sealing bearing such that water is drawn through the contact surface on the sealing bearing as the impulse piston reciprocates.

The rock drill comprises a rotation device for rotating the drilling tool in operation.

The rotating device may include at least one respective contact surface, and the water path is configured to supply water to wet the respective contact surface of the rotating device.

The rotating means may comprise clutch means. The clutch means may be located in a chamber in fluid communication with the set of water circuits such that in operation the chamber is filled with water.

Alternatively, the clutch is located in a chamber in fluid communication with an air supply having water entrained therein.

The clutch mechanism may comprise a wrap spring clutch mechanism.

Alternatively, the clutch means may comprise a ratchet and pawl mechanism.

The rotation means may comprise conversion means for converting the reciprocating motion of the impulse piston into a rotational motion. The switching means may be provided by a toggle mechanism.

Alternatively, the rotating means may be provided by a pneumatic rotary motor.

The rock drill may include at least one channel configured to convey moist gas exhausted from the cylinder to a further contact surface in operation, thereby wetting the contact surface. The rock drill may include a chuck for imparting rotary motion to the drill tool and include a passage configured to convey water to a contact surface at an interface between the chuck and the housing. One or more bearings may be provided to either of the chuck and the housing, with the contact surface being at the interface between the bearing and the other of the chuck and the housing.

The chuck may of course comprise a single element or an assembly of elements configured to impart rotational motion from the impact piston to the drill tool.

The passages may also be configured to deliver water to a contact surface at the interface between the impact piston and the chuck.

According to a second aspect of the present invention there is provided a method of operating a rock drilling machine including a reciprocating impact piston and at least one pair of contact surfaces between relatively moving parts, the method including the steps of:

-supplying compressed air to the rock drill, thereby reciprocating the percussion piston;

-providing a water supply to the rock drill; and

-draining water from the water supply through the drilling tool into the hole being drilled;

the method is characterized by the step of wetting the above mentioned contact surface with water from a water supply.

Drawings

The invention will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:

fig. 1 is a longitudinal section through a rock drilling machine according to a first embodiment of the invention;

FIG. 2 is a transverse cross-sectional view through A-A shown in FIG. 1;

fig. 3 is an enlarged cross-sectional view of the valve area of the rock drill shown in fig. 1;

fig. 4 is a longitudinal section through a rock drilling machine according to a second embodiment of the invention;

fig. 5 is a longitudinal section through a rock drilling machine according to a third embodiment of the invention;

fig. 6 is an enlarged cross-sectional view of the valve area of the rock drill shown in fig. 5;

FIG. 7 is a transverse cross-sectional view through B-B shown in FIG. 5; and

fig. 8 is a transverse cross-sectional view through C-C shown in fig. 5.

Detailed Description

The rock drill 99 according to the first embodiment of the invention and as shown in fig. 1-3 has a housing comprising an end cover 1, a body 2 and a rotor housing 3 all preferably made of corrosion resistant steel or stainless steel. The body 2 comprises a cylinder 50, and the impact piston 14 reciprocates in the cylinder 50.

The chuck 4 is free to rotate about a longitudinal axis in chuck bearings 5, 6 and 7. The chuck 4 is also axially constrained by chuck bearings 5 and 6. The chuck 4 is preferably made of fully hardened martensitic stainless steel. The cartridge bearings 5, 6, 7 are preferably made of an engineering plastic such as polyester or acetal and are press fitted into the inner diameter of the rotor housing 3. The hexagonal packing 8 is fixedly connected to the chuck 4 as is well known and serves to transfer rotational motion from the chuck 4 to the drill rod 9. The ratchet ring 10 is free to rotate about the longitudinal axis on the chuck bearings 5 and 6. The ratchet ring 10 is also axially constrained by the chuck bearings 5 and 6, as shown in FIG. 1. The ratchet ring 10 is preferably made of fully hardened martensitic stainless steel. The chuck 4 is adapted to support a series of spring-loaded pawls 11 (springs not shown), the pawls 11 being configured to engage with a ratchet ring 10 as is well known. The pawl 11 is preferably made of surface or fully hardened steel. The ratchet ring 10 is driven in alternating directions by two indexing plungers 12 and a reset plunger 13 in a well known manner. The plungers 12, 13 are equipped with sealed bearings 32. The plungers 12, 13 are preferably made of acetal and the sealed bearings 32 are made of ultra high molecular weight polyethylene as are all sealed bearings in the whole rock drilling machine. One such mechanism for use in a hydraulic rock drill is described in south african patent 92/4302.

The piston 14 is supported for linear movement in sealed bearings 15 and 16. The function of the sealing bearings 15 and 16 is preferably achieved by "O" rings (energised). The piston 14 includes an enlarged portion 17, and the enlarged portion 17 may effectively divide the cylinder 50 into a drive chamber 50.1 and a return chamber 50.2. The enlarged portion 17 of the piston 14 has a diameter slightly smaller than the inner diameter of the cylinder 50. A bore 18 extends through the center of the piston 14. The piston 14 is preferably made of fully hardened martensitic stainless steel.

At the rear of the body 2 is a valve assembly comprising a valve 19, a valve front plate 20, a valve body 21 and a valve guide 22 as is well known. In contrast to known rock drills, however, the valve 19 is slightly extended and supported on a pair of sealing bearings 23, the sealing bearings 23 fitting in grooves in the valve guide 22. At least one bore 24 passes through the valve guide 22 which is disposed between two sealed bearings 23. The valve 19 is preferably made of acetal and the other valve parts 20, 21 and 22 are preferably made of fully hardened martensitic stainless steel. Alternatively, the sealing bearing 23 and its groove in the valve guide 22 may be omitted and the valve 19 has a close sliding fit on the valve guide 22.

Various conduits are included within the body 2 and the valve elements 20, 21, 22 so that when compressed air is supplied to the inlet 25, the piston 14 and the valve 19 move in synchronism, causing compressed air to be alternately supplied to the drive chamber 50.1 and the return chamber 50.2, which in turn causes the piston 14 to reciprocate and deliver reciprocating impacts to the end of the drill rod 9, as is well known. The conduit connecting the bore of the plungers 12 and 13 to the inlet for the gas supply is not shown. The location of these conduits will be apparent to those skilled in the art and the manner in which the drill rod is indexed by the plungers 12 and 13 as the piston 14 reciprocates is well known.

The used air is discharged from the rock drilling machine via the discharge port 30 in a well known manner.

No oil or water is added to the compressed air supplied to the rock drilling machine.

In use, the pit water supply hose is connected to an inlet 26 in the rotor housing 3. Water enters the rotor housing 3, passes through holes 27 in the cartridge bearings 5 and 6, enters the region 28 in the cartridge 4, passes through the holes 18 in the piston 14 and enters the region 29 in the end cap 1. Water in region 29 passes through the apertures 24 and wets the interior of the valve 19 between the seal bearings 23. The oscillation of the rotor parts and the reciprocating movement of the piston 14 serve to thoroughly distribute and agitate the water present inside the rotor housing 3 and the zones 28 and 29. The bore 31 through the centre of the drill rod 9 is the substantially only outlet path for water entering the drill bit through the inlet 26. There may be an auxiliary leakage path not shown in the figure. Thus, water entering through the inlet 26 will eventually flow along the drill pipe and into the hole being drilled, thus performing the hole flushing and dust suppression functions. This is similar to the hole flushing technique used in current hydraulic rock drills, whereby the drained water is dumped into the area within the rotor housing of such a drill bit.

A careful study of the figures may show that the sealed bearings 15, 16, 23, 32 serve to separate the "dry" air zone from the wet zone inside the rock drill which is agitated. All bore diameters and journals cooperating with the sealed bearings will be wetted continuously on the "away from air" side and the mechanical parts of the rotor mechanism will be thoroughly wetted through. The applicant believes that a satisfactory wear life can be achieved due to the selection of appropriate materials and the provision of an abundance of water.

Due to the above-mentioned difference in diameter, the enlarged portion 17 of the piston 14 does not come into contact with the inner diameter of the cylinder 50. The radial clearance is small enough that only a small amount of air passes through the enlarged portion 17, and the lack of direct contact means that the interface in the dry zone does not need to be lubricated. Such a technique is taught in us patent 3,983,788.

The sealed bearings 15, 16, 24 do not need to be completely sealed. The small amount of water that bypasses the seals and enters the air stream does not adversely affect the operation of the rock drilling machine.

It should be understood that the various channels shown may be varied to achieve substantially the same effect. For example, the water inlet 23 may be located in the end cap 1 in the inflow region 29.

A rock drilling machine 100 according to an alternative second embodiment of the invention as shown in fig. 4 is similar in many respects to known rock drilling machines. Differences from known rock drills include the replacement of corrosion resistant steel with carbon steel, the replacement of engineering plastics with bronze, and the addition of several plastic parts to a separate mating steel part. The main difference between the rock drilling machine and the known rock drilling machine is that it comprises small channels for connection of water intake and compressed air supply. By employing the well known venturi principle, a small proportion of water is entrained in the compressed air supply and distributed through the drill bit to wet the contact surfaces. The applicant expects that such wetting can be used for lubrication and cooling of the contact surfaces.

The rock drill 100(100 not shown in fig. 4) has a housing comprising an end cap 101, a body 102 and a front end shield 103 all preferably made of corrosion resistant steel or stainless steel. The body 102 includes a cylinder 150, and the impact piston 111 reciprocates within the cylinder 150.

The chuck 104 is free to rotate about a longitudinal axis in chuck bearings 105 and 106. The chuck 104 is also axially constrained by chuck bearings 105 and 106. The chuck 104 is preferably made of fully hardened martensitic stainless steel. The chuck bearings 105, 106 are preferably made of an engineering plastic such as polyester or acetal and are press fit into the inner diameter of the rotor housing 103. Hexagonal spacer 108 is fixedly attached to chuck 104 as is well known and is used to transfer rotational motion from chuck 104 to boring bar 131.

A front piston conduit 109, preferably made of ultra high molecular weight polyethylene or similar engineering plastic, is press fitted into a suitable recess in the front face of the cylinder 150. A series of sealed bearings 110, preferably made of ultra high molecular weight polyethylene, fit within grooves in the cylinder 150. The piston 111 is supported for linear movement in a sealed bearing 110 and a front piston guide 109. The piston has an enlarged diameter piston head 112 and a smaller diameter piston rod 113. The piston head 112 effectively divides the cylinder 150 into a drive chamber 150.1 and a return chamber 150.2. A small-diameter hole 114 penetrates the piston 111. On the front end of the piston rod 113 there is a set of straight external splines 115. The seal bearing 110 continuously engages and disengages the piston head 112 as the piston 111 reciprocates in the cylinder 150. The seal bearing 110, cylinder 150 and piston head 112 are sized such that the piston head 112 is always engaged in at least one seal bearing 110. The sealed bearings 110 tend to be self-energizing due to their inherent flexibility and pressure differential between them. The function and application of such a sealed bearing in a hydro-dynamic rock drill is described in south african patent 97/9994. In this embodiment, the sealed bearing cannot be used to seal the cylinder 150 using the piston rod 113, as the spline 115 is likely to make such a sealed bearing unsuitable.

A chuck nut 116, preferably made of acetal or similar engineering plastic, is fixedly attached to the chuck 104. Within the chuck nut 116 are a set of straight internal splines 117 that mate with the external piston splines 115. Thus, the piston 111 is rotatably coupled to the chuck 104 in a well known manner.

A nut 118, preferably made of acetal or similar engineering plastic, is fixedly attached within a recess in the piston head 112. Within the nut 118 is a set of helical internal splines 119.

The reciprocating rod 120, preferably made of fully hardened martensitic stainless steel, can rotate freely within the press-fitted bearing 122 in the valve guide 129. The reciprocating rod 120 is also axially constrained by bearings 121, 122. The bearings 121, 122 are preferably made of acetal or similar engineering plastic. On the reciprocating rod 120 there is a set of external helical splines 123 that mate with internal reciprocating nut splines 119. A set of spring-loaded detents (not shown in fig. 4) are supported on the enlarged diameter rearward end 124 of the reset lever 120. The pawl is preferably made of surface or fully hardened steel.

A ratchet ring 125, preferably made of surface or fully hardened steel, is fixedly mounted to the rear of the body 102. As is well known, the ratchet ring 125, the reciprocating rod 120, the pawls, the chuck nut 116 and the reciprocating nut 118 all combine to impart a stepped rotational motion to the chuck 104 as the piston 111 reciprocates.

At the rear of the body 102 is a valve assembly which, as is well known, includes a valve 126, a valve cowl 127, a valve body 128 and a valve duct 129. The valve 126 is preferably made of acetal or similar engineering material and the other valve parts are preferably made of fully hardened martensitic stainless steel.

The end cap 101, body 102, valve elements 127,128, 129 and ratchet ring 125 include various conduits and flow paths therein such that when compressed air is supplied to inlet 130, the piston 111 and valve 126 move in unison, causing compressed air to be alternately supplied to drive chamber 150.1 and return chamber 150.2, which in turn causes the piston 111 to reciprocate as is well known and deliver a reciprocating impact to the end of drill rod 131. The used air is exhausted from the rock drill 100 through an exhaust port 132 in a well known manner.

A rigid water pipe 133 extends through the rear of the rock drill 100, the piston 111 and the centre of the reciprocating rod 120 as is well known and ends just short of the drill rod 131. The water pipe 33 through the reciprocating rod 120 is not shown in fig. 4 for clarity. In use, the pit feed hose is connected to a fitting at the end of the water pipe 133.

There is a venturi 134 and a bore 135, with the venturi 134 formed in the inlet 130 and the bore 135 for connecting a slightly enlarged diameter portion 136 of the water tube 33 to the throat of the venturi 134. By noting typical water pressure and compressed air pressure and carefully sizing the venturi throat 134, orifice 135 and water tube portion 136, a small portion of the incoming flush water is entrained within the compressed air in the inlet 130. The applicant believes that the water mist laden air is thus able to lubricate the rock drill parts in the same way as the oil mist laden air in known rock drills.

Flushing of the holes is accomplished by the portion of the incoming water that is not entrained in the incoming compressed air. This water is sprayed from the end of the water pipe 133 in the form of a fairly high velocity spray that enters the bore directly into the center of the drill pipe 131 in a well known manner.

Not shown in fig. 4 is a combination trigger valve that simultaneously closes and opens both the water and compressed air supply.

Additional conduits for ducting humid air to the chuck bearings 105 and 106 are also not shown, but are well known in the art.

Thus a water mist lubricated rock drill is described, which has a venturi in the intake pipe and a channel for connecting the supply of flushing water and the venturi throat. The air pressure in the venturi throat is lower than the flush water supply pressure and therefore a small amount of water is drawn into the air stream. This water then lubricates the contact surfaces of the rock drill.

Typical pit water and gas supply pressures are similar (typically around 500 kpa) and are expected to vary from mine to mine and at different locations in any given mine. Supply and supply pressures in the range of 400 to 600 kpa are not typical.

There is a limit to the extent to which the venturi pressure can be reduced before the pressure is not fully recovered downstream of the venturi throat causing unacceptable losses of drill bit power. Applicants' experience is that if the venturi is sized to have acceptable drilling performance, the pressure drop in the throat will be very small — on the order of 100 kilopascals at a supply pressure of 500 kilopascals. Pressure drops of this magnitude are insufficient compared to possible supply and supply pressure variations, and the amount of water injected can vary between zero (air entering the circulation circuit) and more than necessary.

Therefore, in the case where the supply air pressure and the supply water pressure are varied, the third embodiment described below will be superior to the second embodiment.

A rock drilling machine 200 according to a third preferred embodiment is shown in fig. 5-8.

Most of the structure of the rock drilling machine 200 is also very similar to known rock drilling machines. Differences from known rock drills also include the replacement of corrosion resistant steel with carbon steel, the replacement of engineering plastics with bronze, and the addition of several plastic parts to a separate kit steel part.

The rock drill 200 has a housing comprising an end cap 201, a main body 202 and a front end shield 203 all preferably made of corrosion resistant steel or stainless steel. The body includes a cylinder 290, and the impact piston 211 reciprocates within the cylinder 290.

Chuck 204 is free to rotate about a longitudinal axis in chuck bearings 205 and 206. The chuck 204 is also axially constrained by chuck bearings 205 and 206. Chuck 204 is preferably made of fully hardened martensitic stainless steel. The chuck bearings 205, 206 are preferably made of an engineering plastic such as polyester or acetal and press fit into the inner diameter of the front end shield 203. A hexagonal spacer 208 is fixedly attached to the chuck 204 as is well known and is used to transfer rotational motion from the chuck 204 to the drill rod 207.

A front piston guide 209, preferably made of ultra high molecular weight polyethylene, acetal or similar engineering plastic, is press fitted into a suitable recess in the front of the cylinder 290. A series of sealed bearings 210, preferably made of ultra high molecular weight polyethylene, fit within grooves in the cylinder 290. The piston 211 is supported for linear movement in a sealed bearing 210 and a front piston guide 209. The piston has an enlarged diameter piston head 212 and a smaller diameter piston rod 213. The piston head 212 divides the cylinder into a drive chamber 230 and a return chamber 231. The diameter of the piston rod 213 is slightly smaller than the inner diameter of the front piston guide 209. A small diameter hole 214 extends through the piston 211. On the front end of the piston rod 213 there is a set of straight external splines 215. The seal bearing 210 continuously engages and disengages the piston head 212 as the piston 211 reciprocates in the cylinder 290. The seal bearings 210, the cylinder 290 and the piston head 212 are dimensioned such that the piston head 212 is always engaged in at least one seal bearing 210. The sealed bearings 210 tend to be self-energizing due to their inherent flexibility and pressure differential between them. The function and use of such a sealed bearing in a hydraulic rock drill is described in south african patent No. 97/9994.

A chuck nut 216, preferably made of acetal or similar engineering plastic, is fixedly attached to chuck 204. Within the chuck nut 216 is a set of straight internal splines 217 that mate with the external piston splines 215. Thus, piston 211 is rotatably coupled to chuck 204 in a well known manner.

A rifnut 218, preferably made of acetal or similar engineering plastic, is fixedly attached within a recess in the piston head 212. Within the rifled nut 218 is a set of helical internal splines 219. (note that fig. 5 and 6 are not strictly exact, where splines 219 are shown straight for convenience) pass through nut 218 with a series of radially spaced holes 260 that serve to prevent air from closing and compressing in cavity 261 as piston 211 reciprocates. The addition of these holes 260 solves the problem of overheating that can lead to failure of the reciprocating nut 218.

The reciprocating rod 220, preferably made of fully hardened martensitic stainless steel, rotates freely in bearings 221 and 222, the bearings 221 and 222 being press fitted into the end cap 201 and valve guide tube 229, respectively. The reciprocating rod 220 is also axially constrained by bearings 221, 222. The bearings 221, 222 are preferably made of acetal or similar engineering plastic. On the rifle bar 220 is a set of external helical splines 223 that mate with the internal rifle nut splines 219 (note that fig. 5 and 6 are not strictly accurate, where the splines 223 are shown as straight for convenience). A set of spring-loaded pawls 207 (only one set of springs is shown) are supported in the enlarged diameter rear end 224 of the reset lever 220. The pawl is preferably made of surface or fully hardened steel.

A ratchet ring 225, preferably made of fully hardened martensitic stainless steel, is fixedly mounted to the rear of the body 202. As is well known, the ratchet ring 225, the reciprocating rod 220, the pawls 207, the chuck nut 216 and the reciprocating nut 218 all combine to impart a stepped rotational motion to the chuck 204 as the piston 211 reciprocates.

At the rear of the body 202 is a valve assembly which, as is well known, includes a valve 226, a valve front plate 227, a valve body 228 and a valve conduit 229. The valve 226 is preferably made of ultra high molecular weight polyethylene, acetal, or similar engineering material, and the other valve parts are preferably made of fully hardened martensitic stainless steel.

An on/off valve assembly 233 fits within a transverse bore above the valve body 228 and, when in an open position, allows compressed air to pass through an inlet 234 into an annular cavity 235 formed around the exterior of the valve body 228. There are a series of cutouts 236 spaced radially around the valve body 228 that allow compressed air to pass from the annular cavity 235 to the valve 226. The valve 226 is used to allow compressed air to enter either the drive chamber 230 or the return chamber 231 via the annular region 250 and the delivery port(s) 232, depending on the position of the valve 226, as is well known. The piston 211 and valve 226 move in synchronism, causing the piston 211 to reciprocate and deliver reciprocating impacts to the end of the drill pipe 270 in a well known manner.

The on/off valve assembly 233 includes a rotating drum 237, the rotating drum 237 preferably being made of fully hardened martensitic stainless steel, which is supported on a pair of bearings 238 preferably made of acetal or similar engineering plastic. The drum is rotated between the open and closed positions by a handle 239. In addition to material selection and bearings 238, the open/close valve configuration is well known. Compressed air is supplied to the rock drill by an air tube (not shown) connected to swivel 240 as is well known.

Conveniently, the pipe joint 241 fits into the end cap 201, but not necessarily on the centerline of the drill bit. In use, a hose (not shown) is connected to the coupler 241. Along the center of the reciprocating rod 220 has an inner diameter 242. A rigid or semi-rigid tube 243 is fixedly connected to the end of the inner diameter 242 closest to the drill pipe 270. The tube 243 is preferably made of nylon or similar engineering plastic. Tube 243 passes through hole 214 in the center of piston 211 and ends just short of the strike face of drill pipe 270. Thus, in use, water can pass through the trip bar 220, the pipe 243 and into the bore centrally along the drill pipe 270 to perform dust suppression and bore flushing functions as is well known.

A series of holes 244 (visible only in fig. 8) are radially spaced around the enlarged diameter portion 224 of the reciprocating rod 220. These holes 244 allow water to enter the area occupied by the pawls 207 and ratchet ring 225 from the inner diameter 242. The pawl is thus continuously immersed in water during use.

There is a series of radially spaced holes 245 through the reciprocating rod 220 that connect the inner diameter 242 to an annular cavity 246 formed between the reciprocating rod 220 and the reciprocating rod bearing 222. In the reciprocating rod bearing 222 are a series of radially spaced holes 247 that connect an annular cavity 246 with an annular cavity 248 formed between the reciprocating rod bearing 222 and the valve conduit 229. There is also a series of radially spaced holes 249 which serve to connect the annular cavity 248 with the annular cavity 250 formed between the valve conduit 229 and the valve body 228. The annular cavity 250 is connected to the piston return chamber 231 via the transfer port/ports 232. The piston return cavity 231 is therefore in communication with the inner diameter 242 at all times. The total area of the holes 249 is much less than the total area of the holes 245, the total area of the holes 246 and the area of the annular cavities 246 and 248. The flow rate between the inner diameter 242 and the piston return chamber 231 (which may be water or air depending on their respective pressures) may thus be controlled by the size and number of apertures 249.

Also in the reciprocating rod 220 are a series of radially spaced bores 251 which connect the inner diameter 242 directly to the piston drive chamber 230 at any one time. The total area of the apertures 251 is similar to the total area of the apertures 249. An O-ring (or similar seal) 252 is provided between the trip rod 220 and the trip rod bearing 222 adjacent the annular cavity 246 to prevent fluid flow from the annular cavity 246 to the drive chamber 230.

A series of radially spaced apertures 251 and 249 connect the flush water supply to the piston drive chamber and the return chamber respectively.

As is well known, there is an exhaust port 253 at the approximate center of the cylinder 250. The exhaust port 253 divides into a direct outlet 254 that communicates with the atmosphere and an extension 255 that leads into the front end shield 203. The exhaust port extension 255 communicates with an annular cavity 256 surrounding the chuck 204. There are one or more openings 257 that communicate the annular cavity 256 to the atmosphere. The chuck bearings 205 and 206 have a series of radially spaced grooves 258 that ensure that the wet exhaust gas wets the entire contact area of the chuck bearings 205 and 206 and the contact surface between the chuck nut 216 and the piston 211.

The applicant believes that this third embodiment overcomes the disadvantages of the second embodiment described above by introducing the necessary water for lubrication and cooling into the regions of the drill bit which are at least at times filled with air at a lower and more constant pressure than the water supply pressure.

When the rock drill 200 is in circulation, the piston drive chamber 230 and the return chamber 231 alternate between a "high" pressure associated with the supply air pressure (and similar to the supply water pressure) and a "low" pressure associated with atmospheric pressure (and significantly lower than the supply water pressure), depending on the position of the valve 226 and the piston 211. The "low" pressure is more or less constant regardless of the supply air pressure.

Two appropriately sized ports (or sets of ports), in this description apertures 251 and 249, connect the flush water supply directly or indirectly to the piston drive chamber 230 and piston return chamber 231, respectively, depending on the location of the port (or set of ports). Two ports (or port sets) are conveniently, but not necessarily, placed on either side of the valve 226 and adjacent to the valve 226.

When a particular chamber (drive or return) is at a "high" pressure, there will be a nominal flow of water or air through the associated port (or group of ports) depending on the pressure differential between the supply water pressure and the "high" pressure. If the "high" pressure is higher than the supply pressure, a small amount of air will flow into the flushing water, which is not very important. If the "high" pressure is below the supply pressure, a small amount of water will flow into the particular chamber, thereby aiding lubrication and cooling of the contacting surfaces.

When a particular chamber (drive or return) is at a "low" pressure, a relatively large volume of water can flow through the associated port (or group of ports) into the particular chamber and provide a significant amount of the lubrication and cooling requirements of the contacting surfaces. Sufficient water will be sprayed to ensure that the contact surface remains wetted during the "high" pressure stage when no or only a small amount of water is sprayed. Because the "low" pressure is more or less constant, the resulting water flow is more or less independent of the supply air pressure. Moreover, because the pressure differential between the nominal supply pressure and the "low" pressure varies greatly relative to typical variations in the supply pressure, the water flow rate is not significantly affected by such variations in the supply pressure.

As indicated above, some or all of the humid exhaust gas is ducted through the extension passages 255 and the annular cavity 256 to provide water to wet the chuck bearings 205 and 206 before being vented to atmosphere.

Thus, by introducing water downstream of the valve, as opposed to upstream as in the second embodiment described above, the applicant has utilized a more constant air pressure and a pressure differential between water and air that is much greater than that possible using a venturi.

It will be appreciated that the features of the third embodiment are equally well applicable to rock drills having opposite plunger drive rotors, as described above in the first embodiment, instead of reciprocating rod type rotation as described above.

Thus, each of the embodiments described above provides a water lubricated oil free rock drill.

While all of the embodiments described above use a ratchet and pawl clutch mechanism, a wrap spring clutch mechanism such as that described in south african patent No. 92/2561 may be used as well.

Furthermore, although all the above described implementations comprise valve members other than pistons, the invention may also be used in rock drills using different air switching systems, such as "valveless" drill bits.

Claims (26)

1. A pneumatic rock drill comprising:

-a housing comprising an air supply inlet for receiving compressed air and a cylinder connected to the air supply inlet by a set of air channels;

-an impact piston, at least a portion of which has an interface with the cylinder and is reciprocable in the cylinder; and

-air flow control means for controlling the supply of compressed air from the air supply inlet to the cylinders;

-a water supply inlet adapted to deliver water to the drilling tool in operation so as to flush the hole being drilled;

the rock drill comprises at least one pair of corresponding contact surfaces at which the relatively moving parts contact each other;

the rock drill is characterized by comprising a water path connected to a water supply inlet, so that at least the interface between the impact piston and the cylinder is supplied with lubricating water or air laden with lubricating water;

the water circuit includes a primary water flow path configured to supply water to the drilling tool in operation and at least one secondary water flow path configured to supply water to the contact surface in operation, at least one of the secondary water flow paths being in fluid communication with the cylinder.

2. A rockdrill according to claim 1, wherein a bearing is provided to one of the cylinder and the impact piston, and the contact surface is a surface on the other of the bearing and the cylinder and the impact piston.

3. A rockdrill according to claim 1, wherein the impact piston includes a first portion and a second portion, the first portion having a larger diameter than the second portion and being reciprocable in the cylinder.

4. A rockdrill according to claim 3, wherein the cylinder includes a drive chamber and a return chamber, the air flow control means being configured to control the flow of compressed air from the air supply inlet so as to intermittently supply compressed air to at least one of the drive chamber and the return chamber, wherein the air flow control means is provided by a valve.

5. A rockdrill according to claim 1, wherein the auxiliary water flow path is in fluid communication with both the drive and return chambers.

6. A rockdrill according to claim 1, wherein, in operation, water is introduced into the cylinder as a result of a pressure differential between water supplied to the water supply inlet and air in the cylinder.

7. A rock drill according to claim 6 wherein the cylinder includes a drive chamber and a return chamber, wherein in operation water is introduced into the discharge chamber and the return chamber due to a pressure differential between the water supply and air in the discharge chamber of the drive chamber.

8. A rockdrill according to claim 1, including a venturi in the air passage adjacent the air supply inlet, and wherein the water path includes a passage in fluid communication with the venturi such that, in operation, water is entrained in the compressed air supplied to the cylinder so as to wet the contact surfaces.

9. A rock drill according to claim 4, characterized in that the first part of the impact piston is located in the proximal area of the impact piston; and the cylinder is provided with a piston guide at its longitudinal end, in which the impact piston is supported.

10. A rockdrill according to claim 9, wherein the cylinder and the first portion of the piston are dimensioned to be adjacent one another so as to provide an annular gap between the cylinder and the first portion of the impact piston.

11. A rockdrill according to claim 9, wherein the piston guide incorporates sealing means.

12. A rockdrill according to claim 11, wherein the water paths are configured to wet contact surfaces on the impact piston adjacent the sealed bearings so that as the impact piston reciprocates, water is drawn through the contact surfaces on the sealed bearings.

13. A rockdrill according to claim 1, including rotation means for rotating the drilling tool in operation.

14. A rockdrill according to claim 13, wherein the rotary means includes at least one pair of respective contact surfaces, and the water paths are configured to supply water to wet the respective contact surfaces of the rotary means.

15. A rockdrill according to claim 14, wherein the rotation means includes clutch means.

16. A rockdrill according to claim 15, wherein the clutch means is located in a chamber in fluid communication with the set of water paths such that in operation the chamber is flooded with water.

17. A rockdrill according to claim 15, wherein the clutch means is located in a chamber in fluid communication with an air supply in which water is entrained.

18. A rockdrill according to claim 15, wherein the clutch means includes a wrap spring clutch mechanism.

19. A rockdrill according to claim 15, wherein the clutch means includes a ratchet and pawl mechanism.

20. A rockdrill according to claim 13, wherein the rotary means includes conversion means for converting reciprocating motion of the impact piston into rotary motion.

21. A rockdrill according to claim 20, wherein the conversion means is provided by a jack-rod mechanism.

22. A rockdrill according to claim 13, wherein the rotation means is provided via a pneumatic rotary motor.

23. A rockdrill according to claim 3, including at least one passage configured in operation to convey moist gas exhausted from the cylinder to a further contact surface, thereby wetting said contact surface.

24. A rockdrill according to claim 23, including a chuck for imparting rotary motion to the drill, wherein the passage is configured to convey water to a contact surface at an interface between the chuck and the housing.

25. A rockdrill according to claim 23, including a chuck for imparting rotary motion to the drill, wherein the passage is configured to convey water to a contact surface at an interface between the impact piston and the chuck.

26. A method for operating a pneumatic rock drilling machine including a reciprocating impact piston and at least one pair of contact surfaces between relatively moving parts, the method comprising the steps of:

-supplying compressed air to the rock drill, thereby reciprocating the percussion piston;

-providing a water supply to the rock drill; and

-draining water from the water supply through the drilling tool into the hole being drilled;

the method is characterized by comprising the following steps: wetting at least the contact surface between the impact piston and the cylinder with water from a water supply for lubrication purposes;

water is supplied to the rock drill through a flow path comprising a primary water flow path supplying water to the drill tool and at least one secondary water flow path in fluid communication with the cylinder to supply water to the interface between the impact piston and the cylinder.