CA1060428A - Feed leg for a percussive drilling machine - Google Patents
Feed leg for a percussive drilling machineInfo
- Publication number
- CA1060428A CA1060428A CA281,586A CA281586A CA1060428A CA 1060428 A CA1060428 A CA 1060428A CA 281586 A CA281586 A CA 281586A CA 1060428 A CA1060428 A CA 1060428A
- Authority
- CA
- Canada
- Prior art keywords
- feed leg
- piston
- cylinder
- piston rod
- variable
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
- 238000005553 drilling Methods 0.000 title claims abstract description 38
- 239000012530 fluid Substances 0.000 claims abstract description 24
- 239000007789 gas Substances 0.000 claims description 6
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 4
- 229910052757 nitrogen Inorganic materials 0.000 claims description 2
- 230000035939 shock Effects 0.000 abstract description 3
- 229910000831 Steel Inorganic materials 0.000 description 7
- 239000010959 steel Substances 0.000 description 7
- 238000007789 sealing Methods 0.000 description 5
- 239000011435 rock Substances 0.000 description 4
- 238000010276 construction Methods 0.000 description 3
- 238000004873 anchoring Methods 0.000 description 1
- 239000002775 capsule Substances 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 238000009877 rendering Methods 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
Classifications
-
- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B19/00—Handling rods, casings, tubes or the like outside the borehole, e.g. in the derrick; Apparatus for feeding the rods or cables
- E21B19/08—Apparatus for feeding the rods or cables; Apparatus for increasing or decreasing the pressure on the drilling tool; Apparatus for counterbalancing the weight of the rods
- E21B19/087—Apparatus for feeding the rods or cables; Apparatus for increasing or decreasing the pressure on the drilling tool; Apparatus for counterbalancing the weight of the rods by means of a swinging arm
Landscapes
- Engineering & Computer Science (AREA)
- Life Sciences & Earth Sciences (AREA)
- Geology (AREA)
- Mining & Mineral Resources (AREA)
- Mechanical Engineering (AREA)
- Physics & Mathematics (AREA)
- Environmental & Geological Engineering (AREA)
- Fluid Mechanics (AREA)
- General Life Sciences & Earth Sciences (AREA)
- Geochemistry & Mineralogy (AREA)
- Earth Drilling (AREA)
- Drilling And Exploitation, And Mining Machines And Methods (AREA)
Abstract
A FEED LEG FOR A PERCUSSIVE DRILLING
MACHINE
ABSTRACT OF THE DISCLOSURE
A hydraulically-extendable feed leg for a percussive drilling machine, which includes a variable--volume closed chamber for containing a pressurised compressible fluid which acts, in use of the feed leg, to cushion shocks applied to the feed leg from the drilling machine.
MACHINE
ABSTRACT OF THE DISCLOSURE
A hydraulically-extendable feed leg for a percussive drilling machine, which includes a variable--volume closed chamber for containing a pressurised compressible fluid which acts, in use of the feed leg, to cushion shocks applied to the feed leg from the drilling machine.
Description
" i06~428 This invention relates to a feed leg for a percussive drilling machine.
Feed legs which are extended using hydraulic fluid suffer from the disadvantage that, in use, the feed leg is effectively a solid column due to the presence of the fluid.
This causes considerable vibration which may dislodge the foot of the feed leg, rendering it ineffective in supporting the drill and holding it against the rock face.
According to the present invention there is provided a feed leg for a percussive drilling machine, the feed leg comprising a cylinder in which is slidably disposed a piston to which is connected a piston rod, the cylinder being provided with an inlet port for admitting hydraulic fluid under pressure into the working chamber of the cylinder to cause the piston rod to be extended from the cylinder, there being provided a variable-volume closed chamber which is adapted to contain a compressible fluid under pressure and is separated from the working chamber of the cylinder by a movable wall, an end of the feed leg being provided with means for connecting the feed leg to the drilling machine.
The movable wall may comprise a flexible member, for example a bellows or a rubber bag, so that the variable-volume closed chamber comprises a flexible-walled capsule which contains the gas under pressure. In a first preferred construction the variable-volume chamber is constituted by a portion of the interior of the cylinder, which portion may be in the region of that end of the cylinder remote f~om the piston rod The auxiliary piston then separates the variable-volume chamber from the rest of the interior of the cylinder and is slidable within the cylinder. In a second --~ preferred construction, the piston rod is hollow, and the auxiliary piston is slidable within it. The variable-volume chamber is C 0f~ 5tl t 1~ +e.~
B then æ~rd by the interior of the piston rod . ' '' ~ ~ , , . . , . ,- ' . ': ' : . ' ,' ' .. -: -. .- . .. .: . .. . . . . . . .
., , ,., . . :i~ . .. - .. , . . . . : . . .. .
,: .. , . , - .... .. : . . : .
~ 1060428 on one side of the auxiliary piston. The interior of the piston rod on the other side of the auxiliary piston communicates with the cylinder chamber.
A suitable valve may be provided by means of which the variable-volume chamber can be charged with the compressible fluid, which is preferably gas. The gas may be air, nitrogen, or any other suitable gas.
The inlet port for admitting hydraulic fluid into the cylinder may be disposed in a collar which is coaxial with the cylinder and affords a stop to limit the movement of the piston and thereby to define the fully retracted position of the piston rod. In the first pre-ferred construction, the collar may also afford a stop for the auxiliary piston to define the maximum volume of the variable-volume chamber.
Conveniently, a second inlet port is provided for admitting hydraulic fluid to the cylinder to cause retract-ion of the piston rod.
The means for connecting the feed leg to the drilling machine preferably comprises a yoke having a through bore, whereby ~he feed leg is adapted for pivotal connection to the drilling machine. The other end of the feed leg is preferably adapted to afford, or for connection of, an end piece suitable for digging into the ground to give a secure anchorage for the feed leg.
The present invention also provides drilling apparatus comprising a percussive drilling machine to which is pivotally connected a feed leg as defined above.
The present invention may be carried into practice in a number of ways, but one specific embodiment will now be described, by way of example only, with re-ference to the accompanying drawings, in which:
Figure 1 shows diagrammatically a percussive drill having a feed leg;
Figure 2 is a sectional view through one embodi-ment of a feed leg; and Figure 3 is a sectional view through another embodiment of a feed leg.
In Figure 1 a hydraulic percussive drilling ~:'........ .... ,: ' - , .. . ... ,., .. : . "
. ~ . ~: , : . . . :
~060428 machine 2 is supported on an extensible feed leg 4. In use of the drilling machine to drill into roc~, a drill steel 6 is rotated and repeatedly struck by a piston in the drilling machine to drive it into the rock. One end of the feed leg 4 rests on the ground (not shown) while the other end is pivotally connected to the drilling machine.
The thrust T exerted by the feed leg, when under pressure tending to extend it, on tne drilling machine can be resolved into two components, a vertical thrust TV and a feed thrust TF. The vertical thrust TV supports the weight of the drilling machine while the feed thrust TF
presses the drill steel 6 into the rock. As the drill steel bites further into the rock, the feed leg 4 leans lS further over, and must be extended in order to keep the drilling machine at the required level so as to prevent the weight of the drilling machine from being supported by the drill steel in the drilled hole. As the feed leg leans further over, the thrust T must be progressively increased-so as to maintain constant the vertical thrust Tv.
Figure 2 shows an extensible feed leg which in-cludes a cylinder in the form of an outer tube 12 in which is ~lidable a piston 10 which is mounted on a piston rod in the form of an inner tube 8. The free end of the inner tube 8 carries a yoke 14 having a through bore 16 for pivotally supporting a drilling machine. The connection between the feed leg and the-drilling machine may be read-ily releasable or relatively permanent. The base of the outer tube 12 carries a connecting piece 18 for attaching an end piece (not shown) adapted to give a secure anchorage for the foot of the feed leg, for example by digging into the grou~d. An extension member (not shown) may be fitted between the connecting piece 18 and the end piece to in-crease the length OL the feed leg.
The piston 10 is welded to the inner end of the inner tube 8 and is composed of two sections 20 and 22 which are held together by a nut 24 and bolt 26 and located against rotation relatively to each other by a pin 28.
Between the two sections is clamped a sealing ring 30 for " : -- . ;-. . . . . . . .
. :. . ., . . ~.. . . . , . ~ ..
: , ,. :: . : , . . .
. .'- ~, . ' .. , - - .: ' . . .
.. . . . . . .
~. . .. .. .
.
_ 5 _ lO 60 428 sealing between the piston and the inner surface of the outer tube 12. Another sealing ring 32 provides a seal between the inner and outer tubes 8 and 12.
A collar 34 is provided in the wall of the outer tube 12, near the lower end, which acts as a stop for the piston to define the fully retracted position of the feed leg. This collar 34 includes an inlet port 36 for the admission of hydraulic fluid under pressure to extend the feed leg. At the upper end of the outer tube is welded another inlet port 38 for the admission of hydraulic fluid pressure to retract the feed leg.
In the lower end region of the outer tube below the collar 34 is situated an auxiliary piston 40 having an extended skirt 42 and sealing rings 44 for providing a seal between the inner surface of the outer tube and the auxiliary piston. A variable-volume closed chamber 46 is defined in the interior of the outer tube 12 between the auxiliary piston 40 and the lower end of the outer tube 12.
This variable-volume chamber 46 is filled with air, although other suitable compressible fluids may be used, under a pressure which will depend upon the magnitude of the recoil force which will occur in use of the drilling machine, and must be greater than the supply pressure of the hydraulic fluid to the feed leg, for example the air pressure may be between 1500 and 2000 p.s.i. A port 48 including a valve (not shown) is provided in the connecting piece 18 for charging the chamber 46 with air.
In use of the feed leg, a drilling machine is mounted on the yoke 14 and an end piece is attached to the connecting piece 18 and planted firmly on the ground in such a position that, when the drill steel engages the surface to be drilled, the feed leg leans towards that surface (see Figure l). The feed leg should not be fully extended, but need not be fully retracted. The drilling machine is hand held by the operator but the weight of the machine is taken by the feed leg.
As drilling proceeds, hydraulic fluid is admitted to the feed leg through the inlet port 36, at a pressure of 1500 to 2000 p.s.i. by means of a throttle valve which is .. . .. . .
: . , ~ . -.: : . : , - . , , ~ : - ~ .. . -. ~. . . .
. :. : . - . , , . . :
, . : .,, .: : : - . .:
- -- 6 - ~ ~06~428 under the manual control of an operator, to cause the feed leg to extend as required to keep the drilling machine at the correct level so as to prevent the weight of the drill-ing machine from being supported by the steel.
Most of the time, the pressure of the hydraulic fluid in the working space between the piston 10 and the auxiliary piston 40 is below the pressure of the air in the chamber 46, and so tlle piston 40 usually abuts the collar 34, and the chamber 46 has its maximum volume. However, each time the drill steel is struck by the piston in the drilling machine, the recoil is transmitted by the inner tube 8 and the piston 10 to sharply increase the pressure of the hydraulic fluid in the working space 48 to above the pressure in the chamber 46. The piston 40 is thus moved away from the collar 34 to compress further the air in the chamber 46 and so to absorb the recoil. The chamber 46 thus acts as a cushion for the shocks applied by the drill-ing machine to the feed leg and allows smoother operation than would be obtained if the chamber 46 were not present, in which case the feed leg would be considered to be a rigid body.
When drilling has proceeded to such a depth that the feed leg is fully extended, the end piece is lifted out of the ground and hydraulic fluid is supplied through the inlet port 38 to retract the feed leg until the end piece can be planted at another position at which drilling can continue as before.
In the embodiment shown in Figure 3, the same re-ference numerals are used as in Figure 2 to designate the same or similar parts.
The difference between the feed leg of Figure 3 and that of Figure 2 is that, in the feed leg of Figure 3, the chamber 46 is afforded in the hollow inner tube. The auxiliary piston 40 is, therefore, slidably mounted in the inner tube 8. Sealing rings 44 again provide a seal between the auxiliary piston 40 and the inner tube 8.
The piston 10 has a hole 50 through it to allow hydraulic fluid to pass from the interior of the outer tube 12 into the interior of the inner tube 8 to act on the . .
: : -' ' ~ "; ., ., , , .', . ', ' '. I' ~ ', ~ ' ' ' ' _ 7 _ 10~428 auxiliary piston 40 ayainst the pressure of the air in thechamber 46.
Hydraulic fluid can be supplied to the interior of the outer tube 12 to extend the feed leg through an in-let port 36 provided in an end piece 52, which carries ayoke 14 for connection to the drilling machine. Again, there is a further inlet port 38 at tne lower end of the feed leg through which hydraulic fluid can be supplied to retract the feed leg, by acting on the annular face 54 of the piston 10.
The lower end of the feed leg affords a port 48 with a non-return valve (not shown) through which the chamber 46 can be charged with air. The lower end of the feed leg carries an end piece 56 having a pair of anchor-ing spikes 58, only one of which is visible in Figure 3,for digging into the ground to support the feed leg.
The feed leg of Figure 3 is used in the same manner as that of Figure 2. Normally, when the pressure in the working chamber of the outer tube 12 above the piston 10 is below the pressure of the air in the chamber 46, the auxiliary piston 40 abuts an annular face 50 of the piston 10. However, the pressure above the piston 10 may increase during,operation of the drilling machine, to above the pressure in the chamber 46. When this happens, the increased pressure, transmitted to the auxiliary piston through the hole 50, causes the auxiliary piston to move downwards away from the face 60. This decreases the volume of the chamber 46, increasing the pressure of the air in it, to cushion the shocks applied by the drilling machine.
' ~ . : . .
Feed legs which are extended using hydraulic fluid suffer from the disadvantage that, in use, the feed leg is effectively a solid column due to the presence of the fluid.
This causes considerable vibration which may dislodge the foot of the feed leg, rendering it ineffective in supporting the drill and holding it against the rock face.
According to the present invention there is provided a feed leg for a percussive drilling machine, the feed leg comprising a cylinder in which is slidably disposed a piston to which is connected a piston rod, the cylinder being provided with an inlet port for admitting hydraulic fluid under pressure into the working chamber of the cylinder to cause the piston rod to be extended from the cylinder, there being provided a variable-volume closed chamber which is adapted to contain a compressible fluid under pressure and is separated from the working chamber of the cylinder by a movable wall, an end of the feed leg being provided with means for connecting the feed leg to the drilling machine.
The movable wall may comprise a flexible member, for example a bellows or a rubber bag, so that the variable-volume closed chamber comprises a flexible-walled capsule which contains the gas under pressure. In a first preferred construction the variable-volume chamber is constituted by a portion of the interior of the cylinder, which portion may be in the region of that end of the cylinder remote f~om the piston rod The auxiliary piston then separates the variable-volume chamber from the rest of the interior of the cylinder and is slidable within the cylinder. In a second --~ preferred construction, the piston rod is hollow, and the auxiliary piston is slidable within it. The variable-volume chamber is C 0f~ 5tl t 1~ +e.~
B then æ~rd by the interior of the piston rod . ' '' ~ ~ , , . . , . ,- ' . ': ' : . ' ,' ' .. -: -. .- . .. .: . .. . . . . . . .
., , ,., . . :i~ . .. - .. , . . . . : . . .. .
,: .. , . , - .... .. : . . : .
~ 1060428 on one side of the auxiliary piston. The interior of the piston rod on the other side of the auxiliary piston communicates with the cylinder chamber.
A suitable valve may be provided by means of which the variable-volume chamber can be charged with the compressible fluid, which is preferably gas. The gas may be air, nitrogen, or any other suitable gas.
The inlet port for admitting hydraulic fluid into the cylinder may be disposed in a collar which is coaxial with the cylinder and affords a stop to limit the movement of the piston and thereby to define the fully retracted position of the piston rod. In the first pre-ferred construction, the collar may also afford a stop for the auxiliary piston to define the maximum volume of the variable-volume chamber.
Conveniently, a second inlet port is provided for admitting hydraulic fluid to the cylinder to cause retract-ion of the piston rod.
The means for connecting the feed leg to the drilling machine preferably comprises a yoke having a through bore, whereby ~he feed leg is adapted for pivotal connection to the drilling machine. The other end of the feed leg is preferably adapted to afford, or for connection of, an end piece suitable for digging into the ground to give a secure anchorage for the feed leg.
The present invention also provides drilling apparatus comprising a percussive drilling machine to which is pivotally connected a feed leg as defined above.
The present invention may be carried into practice in a number of ways, but one specific embodiment will now be described, by way of example only, with re-ference to the accompanying drawings, in which:
Figure 1 shows diagrammatically a percussive drill having a feed leg;
Figure 2 is a sectional view through one embodi-ment of a feed leg; and Figure 3 is a sectional view through another embodiment of a feed leg.
In Figure 1 a hydraulic percussive drilling ~:'........ .... ,: ' - , .. . ... ,., .. : . "
. ~ . ~: , : . . . :
~060428 machine 2 is supported on an extensible feed leg 4. In use of the drilling machine to drill into roc~, a drill steel 6 is rotated and repeatedly struck by a piston in the drilling machine to drive it into the rock. One end of the feed leg 4 rests on the ground (not shown) while the other end is pivotally connected to the drilling machine.
The thrust T exerted by the feed leg, when under pressure tending to extend it, on tne drilling machine can be resolved into two components, a vertical thrust TV and a feed thrust TF. The vertical thrust TV supports the weight of the drilling machine while the feed thrust TF
presses the drill steel 6 into the rock. As the drill steel bites further into the rock, the feed leg 4 leans lS further over, and must be extended in order to keep the drilling machine at the required level so as to prevent the weight of the drilling machine from being supported by the drill steel in the drilled hole. As the feed leg leans further over, the thrust T must be progressively increased-so as to maintain constant the vertical thrust Tv.
Figure 2 shows an extensible feed leg which in-cludes a cylinder in the form of an outer tube 12 in which is ~lidable a piston 10 which is mounted on a piston rod in the form of an inner tube 8. The free end of the inner tube 8 carries a yoke 14 having a through bore 16 for pivotally supporting a drilling machine. The connection between the feed leg and the-drilling machine may be read-ily releasable or relatively permanent. The base of the outer tube 12 carries a connecting piece 18 for attaching an end piece (not shown) adapted to give a secure anchorage for the foot of the feed leg, for example by digging into the grou~d. An extension member (not shown) may be fitted between the connecting piece 18 and the end piece to in-crease the length OL the feed leg.
The piston 10 is welded to the inner end of the inner tube 8 and is composed of two sections 20 and 22 which are held together by a nut 24 and bolt 26 and located against rotation relatively to each other by a pin 28.
Between the two sections is clamped a sealing ring 30 for " : -- . ;-. . . . . . . .
. :. . ., . . ~.. . . . , . ~ ..
: , ,. :: . : , . . .
. .'- ~, . ' .. , - - .: ' . . .
.. . . . . . .
~. . .. .. .
.
_ 5 _ lO 60 428 sealing between the piston and the inner surface of the outer tube 12. Another sealing ring 32 provides a seal between the inner and outer tubes 8 and 12.
A collar 34 is provided in the wall of the outer tube 12, near the lower end, which acts as a stop for the piston to define the fully retracted position of the feed leg. This collar 34 includes an inlet port 36 for the admission of hydraulic fluid under pressure to extend the feed leg. At the upper end of the outer tube is welded another inlet port 38 for the admission of hydraulic fluid pressure to retract the feed leg.
In the lower end region of the outer tube below the collar 34 is situated an auxiliary piston 40 having an extended skirt 42 and sealing rings 44 for providing a seal between the inner surface of the outer tube and the auxiliary piston. A variable-volume closed chamber 46 is defined in the interior of the outer tube 12 between the auxiliary piston 40 and the lower end of the outer tube 12.
This variable-volume chamber 46 is filled with air, although other suitable compressible fluids may be used, under a pressure which will depend upon the magnitude of the recoil force which will occur in use of the drilling machine, and must be greater than the supply pressure of the hydraulic fluid to the feed leg, for example the air pressure may be between 1500 and 2000 p.s.i. A port 48 including a valve (not shown) is provided in the connecting piece 18 for charging the chamber 46 with air.
In use of the feed leg, a drilling machine is mounted on the yoke 14 and an end piece is attached to the connecting piece 18 and planted firmly on the ground in such a position that, when the drill steel engages the surface to be drilled, the feed leg leans towards that surface (see Figure l). The feed leg should not be fully extended, but need not be fully retracted. The drilling machine is hand held by the operator but the weight of the machine is taken by the feed leg.
As drilling proceeds, hydraulic fluid is admitted to the feed leg through the inlet port 36, at a pressure of 1500 to 2000 p.s.i. by means of a throttle valve which is .. . .. . .
: . , ~ . -.: : . : , - . , , ~ : - ~ .. . -. ~. . . .
. :. : . - . , , . . :
, . : .,, .: : : - . .:
- -- 6 - ~ ~06~428 under the manual control of an operator, to cause the feed leg to extend as required to keep the drilling machine at the correct level so as to prevent the weight of the drill-ing machine from being supported by the steel.
Most of the time, the pressure of the hydraulic fluid in the working space between the piston 10 and the auxiliary piston 40 is below the pressure of the air in the chamber 46, and so tlle piston 40 usually abuts the collar 34, and the chamber 46 has its maximum volume. However, each time the drill steel is struck by the piston in the drilling machine, the recoil is transmitted by the inner tube 8 and the piston 10 to sharply increase the pressure of the hydraulic fluid in the working space 48 to above the pressure in the chamber 46. The piston 40 is thus moved away from the collar 34 to compress further the air in the chamber 46 and so to absorb the recoil. The chamber 46 thus acts as a cushion for the shocks applied by the drill-ing machine to the feed leg and allows smoother operation than would be obtained if the chamber 46 were not present, in which case the feed leg would be considered to be a rigid body.
When drilling has proceeded to such a depth that the feed leg is fully extended, the end piece is lifted out of the ground and hydraulic fluid is supplied through the inlet port 38 to retract the feed leg until the end piece can be planted at another position at which drilling can continue as before.
In the embodiment shown in Figure 3, the same re-ference numerals are used as in Figure 2 to designate the same or similar parts.
The difference between the feed leg of Figure 3 and that of Figure 2 is that, in the feed leg of Figure 3, the chamber 46 is afforded in the hollow inner tube. The auxiliary piston 40 is, therefore, slidably mounted in the inner tube 8. Sealing rings 44 again provide a seal between the auxiliary piston 40 and the inner tube 8.
The piston 10 has a hole 50 through it to allow hydraulic fluid to pass from the interior of the outer tube 12 into the interior of the inner tube 8 to act on the . .
: : -' ' ~ "; ., ., , , .', . ', ' '. I' ~ ', ~ ' ' ' ' _ 7 _ 10~428 auxiliary piston 40 ayainst the pressure of the air in thechamber 46.
Hydraulic fluid can be supplied to the interior of the outer tube 12 to extend the feed leg through an in-let port 36 provided in an end piece 52, which carries ayoke 14 for connection to the drilling machine. Again, there is a further inlet port 38 at tne lower end of the feed leg through which hydraulic fluid can be supplied to retract the feed leg, by acting on the annular face 54 of the piston 10.
The lower end of the feed leg affords a port 48 with a non-return valve (not shown) through which the chamber 46 can be charged with air. The lower end of the feed leg carries an end piece 56 having a pair of anchor-ing spikes 58, only one of which is visible in Figure 3,for digging into the ground to support the feed leg.
The feed leg of Figure 3 is used in the same manner as that of Figure 2. Normally, when the pressure in the working chamber of the outer tube 12 above the piston 10 is below the pressure of the air in the chamber 46, the auxiliary piston 40 abuts an annular face 50 of the piston 10. However, the pressure above the piston 10 may increase during,operation of the drilling machine, to above the pressure in the chamber 46. When this happens, the increased pressure, transmitted to the auxiliary piston through the hole 50, causes the auxiliary piston to move downwards away from the face 60. This decreases the volume of the chamber 46, increasing the pressure of the air in it, to cushion the shocks applied by the drilling machine.
' ~ . : . .
Claims (15)
1. A feed leg for a percussive drilling machine, the feed leg comprising a cylinder in which is slidably disposed a piston to which is connected a piston rod, the cylinder being provided with an inlet port for admitting hydraulic fluid under pressure into a working chamber of the cylinder to cause the piston rod to be extended from the cylinder, there being provided a variable--volume closed chamber which is adapted to contain a compressible fluid under pressure and is separated from the working chamber of the cylinder by a movable wall, an end of the feed leg being provided with means for connecting the feed leg to the drilling machine,
2. A feed leg as claimed in claim 1, in which the movable wall comprises a flexible member.
3. A feed leg as claimed in claim 1, in which the movable wall comprises an auxiliary piston.
4. A feed leg as claimed in any one of claims 2 or 3, in which the variable-volume chamber is disposed within the cylinder on the other side of the piston from that which the piston rod extends.
5. A feed leg as claimed in claim 2, in which the auxiliary piston is slidable within the cylinder.
6. A feed leg as claimed in claim 1, in which the inlet port is disposed in a collar which is coaxial with the cylinder and constitutes a stop to limit the movement of the piston, thereby to define the fully retracted position of the piston rod.
7. A feed leg as claimed in claim 6, in which the collar constitutes a stop for the movable wall, thereby to define the maximum volume of the variable-volume chamber.
8. A feed leg as claimed in claim 1, in which the piston rod is hollow and in which the variable-volume chamber is dis-posed within the piston rod.
9. A feed leg as claimed in claim 8, in which the movable wall comprises an auxiliary piston which is slidable within the piston rod whereby the variable-volume chamber is constituted by the interior of the piston rod on one side of the auxiliary piston.
10. A feed leg as claimed in claim 9, in which the communication between the interior of the piston on the other side of the auxiliary piston and the interior of the cylinder is constituted by a hole in the crown of the piston.
11. A feed leg as claimed in claim 1, in which a second inlet port is provided for admitting hydraulic fluid to the cylinder to cause retraction of the piston rod.
12. A feed leg as claimed in claim 1, in which a valve is provided through which the variable-volume chamber may be charged with compressible fluid.
13. A feed leg as claimed in claim 1, in which the variable-volume chamber contains a compressible fluid in the form of a gas.
14. A feed leg as claimed in claim 13, in which the gas is air or nitrogen.
15. Drilling apparatus comprising a percussive drilling machine to which is pivotally connected a feed leg in accordance with claim 1.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB31992/76A GB1531337A (en) | 1976-07-30 | 1976-07-30 | Feed leg for a percussive drilling machine |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1060428A true CA1060428A (en) | 1979-08-14 |
Family
ID=10331410
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA281,586A Expired CA1060428A (en) | 1976-07-30 | 1977-06-28 | Feed leg for a percussive drilling machine |
Country Status (3)
| Country | Link |
|---|---|
| CA (1) | CA1060428A (en) |
| GB (1) | GB1531337A (en) |
| ZA (1) | ZA773786B (en) |
-
1976
- 1976-07-30 GB GB31992/76A patent/GB1531337A/en not_active Expired
-
1977
- 1977-06-23 ZA ZA00773786A patent/ZA773786B/en unknown
- 1977-06-28 CA CA281,586A patent/CA1060428A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| ZA773786B (en) | 1978-05-30 |
| GB1531337A (en) | 1978-11-08 |
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