ROTARY DRIVEN ROCK CUTTING EQUIPMENT
United States Patent 3743033
The invention relates to mobile rock cutting equipment which includes a rotor carrying a series of swing hammers which are adapted to strike cutting tools positioned against a rock face and mounted in the equipment for limited axial movement. The invention further uses this axial movement to determine pressure applied to the cutting tool tip and to use the pressure to operate control mechanisms acting on the rotor and motive power unit for the equipment.
US Patent References:
Mining machine
Brown - September 1925 - 1552909
Rotating hammer
Rasch - April 1926 - 1579840
Demolition device
Bourdon - April 1958 - 2829633
/1283618.html
App - November 1918 - 1283618
Rock crushing apparatus
Maruta - August 1968 - 3397916
Mining machine
Brown - September 1925 - 1552909
Rotating hammer
Rasch - April 1926 - 1579840
Demolition device
Bourdon - April 1958 - 2829633
/1283618.html
App - November 1918 - 1283618
Rock crushing apparatus
Maruta - August 1968 - 3397916
Application Number:
05/149154
Publication Date:
07/03/1973
Filing Date:
06/02/1971
View Patent Images:
Export Citation:
Assignee:
Anglo-Transvaal Consolidated Investment Company Limited (Johannesburg, ZA)
Primary Class:
Other Classes:
173/210, 173/99, 299/1.500, 173/11, 37/904, 299/37.500
International Classes:
B25D15/02; B25D15/02
Field of Search:
299/1,37,69,70,94 173/10,11,51,99,4
Primary Examiner:
Purser, Ernest R.
Claims:
What I claim as new and desire to secure by Letters Patent is
1. Rock cutting equipment comprising:
2. Rock cutting equipment as claimed in claim 1 in which the striking face of the hammer is made as a replaceable insert.
3. Rock cutting equipment comprising:
4. Rock cutting equipment as claimed in claim 3 in which the hammer is held inoperative unless a predetermined minimum pressure is applied to the tool.
5. Rock cutting equipment as claimed in claim 3 in which the speed of the means for traversing the frame is controlled and dependent on the maximum pressure applied to the tool and the position of the tool relative to the frame.
6. Rock cutting equipment as claimed in claim 3 including a catch which holds said hammer inoperative and wherein said control mechanism includes means, responsive to the position of said tool relative to said frame, for controlling said catch, said hammer being held inoperative in a position in which the hammer is swung back relative to its pivot and the direction of rotation of said rotor.
7. Rock cutting equipment comprising:
1. Rock cutting equipment comprising:
2. Rock cutting equipment as claimed in claim 1 in which the striking face of the hammer is made as a replaceable insert.
3. Rock cutting equipment comprising:
4. Rock cutting equipment as claimed in claim 3 in which the hammer is held inoperative unless a predetermined minimum pressure is applied to the tool.
5. Rock cutting equipment as claimed in claim 3 in which the speed of the means for traversing the frame is controlled and dependent on the maximum pressure applied to the tool and the position of the tool relative to the frame.
6. Rock cutting equipment as claimed in claim 3 including a catch which holds said hammer inoperative and wherein said control mechanism includes means, responsive to the position of said tool relative to said frame, for controlling said catch, said hammer being held inoperative in a position in which the hammer is swung back relative to its pivot and the direction of rotation of said rotor.
7. Rock cutting equipment comprising:
Description:
This invention relates to rock cutting equipment used in mining or other excavationary work and more particularly to equipment using rotary power elements.
Rotary driven rock cutting machines carrying swinging hammers tipped with cutting tips are simple and practical. However, cutting tips such as those used on the hammers are likely to shatter if the energy which they are required to transmit to the rock per blow exceeds a certain maximum for the design of tip used.
Under certain circumstances, for instance when cutting highly siliceous rocks, it is apparent that the tips wear excessively if the striking velocity is too high.
For a given energy per blow it is possible to use light hammers rotating at high speed or heavier hammers rotating more slowly. A disadvantage of the light hammers rotating at a fast speed is that, due to the high striking velocity, the tip wear might be excessive. However, heavier hammers, which for the same blow energy could rotate more slowly and therefore have less tip wear, have the disadvantages that they are bulky and that less energy can be put into the rock in a confined space due to the lower frequency of blows.
With the existing rock cutting machines carrying swinging hammers tipped with cutting tips it is difficult to control the angle at which the tip strikes the rock.
It is the object of the present invention to provide an alternative construction wherein rotating hammers can be used to provide power for cutting of rock without directly striking the rock by the interposition of tools capable only of axial movement.
According to the invention there is provided rock cutting equipment comprising a frame, at least a pair of rock cutting tools supported for limited axial movement in either direction against resilient buffers in the frame and spaced apart, one or more rotors carrying at least two swinging hammers adapted to strike each cutting tool and means for traversing the frame across a rock face with the tools in contact therewith.
The equipment would be adapted to hold the tools against the rock to be cut in such a manner that the tools would tend to cut or chip parallel grooves in the rock so spaced that the rock between the grooves would break out easily.
An advantage to be obtained from cutting spaced grooves is that cutting tip wear would be less per ton of rock excavated than if the tools cut grooves with no free spaced between.
The invention also provides for the speed of movement of the equipment along the rock face to be controlled so as to allow for an optimum rate of excavation (within the capacity of the machine) and for means for preventing the hammers from striking the tools when the tools are not pressing against the rock, and thus possibly damaging the tools or other parts of the equipment.
A preferred embodiment of this invention will be described with reference to the accompanying drawings in which:
FIG. 1 shows a diagrammatic layout of one rotor carrying one series of hammers for one cutting tool;
FIG. 2 and FIG. 3 are part sectional elevations showing the arrangement of one hammer with stopblocks on the rotor.
As shown the equipment comprises a power driven rotor 1 carrying a series of three swinging hammers 2a, 2b and 2c mounted on pivots 3 adjacent the periphery thereof.
The hammers carry striking faces 4 which are made of any suitably hard material and these striking faces 4 are preferably made as replaceable inserts so that the hammers may be used for longer periods than would be possible if these faces were integral with the hammers.
The hammers are adapted to strike a rigid cutting tool 5 which is adjustably supported in a suitable frame (see below) provided for the equipment.
The cutting tool carries a suitably shaped tip 6 of tungsten carbide and is held between stops 7 on the frame and a pair of resilient buffers 8 and 9 are provided on either side of a locating collar 10. These buffers must be carefully designed to give the desired restraining effect on the cutting tool and may be either metal springs or sleeves of resilient material. Hydraulic cushioning devices may also be used if this is desired.
The cutting tool 5 will be mounted in the desired relationship to the hammers and the rotor tool assembly will be mounted in the desired relationship to the rock to be cut. This latter position will preferably be angularly adjustable so that the direction of the blow applied by the cutting tools to the rock may be varied. It will be realized that it is desirable to angle the tool 5 to the rock face so that shear and bending forces in the tool are minimized.
The complete mechanism comprising at least two tools with the requisite hammers driven by one or more rotors and together with the necessary backstops and controls would be mounted in the frame and would be made to traverse approximately parallel to the surface of the rock 11 to be cut (in the direction shown by the arrow in FIG. 1) and at a distance from the rock such that the cutting tools could chip the rock at the desired rate of excavation.
The device producing the traversing motion which could be similar to that used currently on coal cutters or coal ploughs or tunnelling machines would be controlled by a mechanism sensitive to the loads on the cutting tools. The preferred form of such mechanism is illustrated in the diagram FIG. 1 where the main frame 12 (shown dotted) presses by means of a spring 13 a pressure arm 14.
The pressure arm is free to slide within limits in suitable guides 15 attached to the main frame 12 in a direction parallel to the direction of movement of the tool 5 and terminates in a collar 16 into which the tool 5 is placed. The collar 16 would be positioned between the collar 10 and the buffer 9.
As the machine traverses along the rock face the tip 6 of the cutting tool will engage against the rock and, provided that the machine continues to traverse and the rock does not break, the pressing force of the tip against the rock will continue to increase. This increased pressure will be transmitted by the collar 10 to the collar 16 and thence down the arm 14 to the spring 13 which will allow movement of the pressure arm to take place and in particular will allow lug 17 to press against the control button 18 which will ensure that the traversing mechanism will slow down and, if the pressure continues to increase, will stop.
On the other hand should there be a gap in the rock and little or no resistance is offered to the tip 6 of the cutting tool, the spring 13 will extend and the lug 17 will release its pressure on the control button 18 thus allowing the traversing mechanism to speed up.
A further feature of the invention intended to prevent the hammers hitting the tools when little or no resistance is offered by the rock comprises an on-off control button 19 operated by the lug 17. This control button operates retractable catches 20 which, when button 19 is pressed, protrude and engage with notches 21 in the hammers restraining them in their swing back positions.
When the tip 6 again engages with the solid rock and a reaction again builds up in the arm 14, the lug 17 releases the control button 19 which in turn causes the catches 20 to retract allowing the hammers 2 to swing out and strike the end of the cutting tool 5.
The restraint of the hammers in the swing back position need not be accomplished by catches mechanically engaging in notches in the hammers but friction pads may be used. Should friction pads be used it would be preferable in order to ensure that they grip the hammer only when it is stationary or moving slowly in the swing back position to trigger the application of these pads to coincide with the moment when the hammers are stationary or nearly stationary against the back stop. Such triggering action would only take place while the button 19 was depressed and could be initiated by the hammer striking either a suitably placed trigger or striking the back stop block 22. Such additional triggering action might be preferred for the catches 20 as well as for the friction pads.
As a safety precaution the complete mechanism housed in 12 should pivot about a point 23 situated ahead of the line 24 drawn at 90° to the rock face and originating in that zone of the rock face where chipping takes place. This point 23 is thus forward of the cutting tip 6 of tool 5.
The pivot 23 would be mounted in some form of chassis which would be able to traverse parallel to the rock face and which would be capable of containing any reaction forces transmitted from the rock face. The mechanism housed in 12 would be held in position on this framework by the pivot 23 and some other device such as a shearpin which, should the control button 18 fail to stop the traverse, would shear and allow the mechanism to swing out of engagement with the rock.
Under such circumstances the button 19 should operate and the hammers should be held back from striking the tool. However, it is preferable to incorporate a separate series of controls which, when the shear pin shears, will latch the hammers back and switch off the power drive.
The arrangement with the pivot 23 and the shearpin could conveniently be used to set the angle of the tools relative to the chassis.
The preferred design of the rotor 1 and swing hammers 2 is such that when the hammer strikes the cutting tool no shock load is thrown back onto the hammer pivot. It is also desirable that all the energy given up by the hammer in striking the tool is restored to the hammer by the centrifugal force applied thereto during the remaining portion of the revolution of the rotor in order to bring the hammer back into the striking position just at the correct time to strike the tool 5.
Both design features are difficult to achieve together in practice with a free swinging hammer mounted eccentrically to the axis of rotation of the rotor which is rotating at a high speed, although the simple way of achieving the first design feature is described later in this specification.
Because of difficulties in obtaining the second design feature practical considerations may make it desirable to have resilient stops positioned to prevent overswinging of each hammer in either direction about its pivot.
A hammer with its two resilient stop blocks and part of the rotor is shown in FIGS. 2 and 3.
The hammer 2 and the stop blocks 22 and 25 are mounted between backing discs 26. Each hammer will normally require two stop blocks, thus if there are three hammers in a row, as shown in the drawings, then six stop blocks will be required.
The stop block 22 is required to prevent excessive swing back and the stop block 25 is required to stop the hammer in the swing out position so that it will strike the cutting tool 5.
The stop blocks have to absorb and dissipate considerable quantities of energy and it has been found practical to construct them with fluid passages 27 leading to them from the rotor shaft 28 and other fluid passages 29 leading away through nozzles. The passages would be equipped with ball valves 30 or similar one way valves to ensure a one way flow of fluid.
A practical form of stop block consists of a cylindrical metal reinforced hollow rubber bulb similar to the commercially available "Oscillith" bush construction. The stop block would normally be filled with fluid but when struck by the hammer, would force the fluid out through one or more nozzles at high speed. In mining the fluid would preferably be water and the jets of water would play on the zone in which the rock was breaking in order that the tool 5 and tip 6 were kept cool and also to allay dust.
In essence, the hammer acts as a compound pendulum balanced in such a way as to limit the operational impact loading applied to the hammer pivot 3 to a minor proportion of that applied to the hammer striking tip. The eccentricity of the center of gravity of the hammer relative to its pivot, the spacing of the striking tip from the hammer pivot, and the polar radius of gyration of the hammer all co-operate to result in very little shock load being transmitted to the hammer pivot. The method of balancing has been proposed in an earlier patent but is redescribed hereunder.
The hammer 2 has its pivotal axis B spaced from the axis of rotation A of the rotor. The distance from the point C to B is equal to the polar radius of gyration of the hammer about the pivot B. The center of gravity of the hammer is indicated at D. The point relative to the rotor at which the hammer strikes the tool 5 is indicated at E.
Ideally the dimensions should accord with the following formula:
(B C) 2 = BD × BE
It is preferable that the distance between the hammer axis 3 and the stops 22 and 25 should also be the same as the distance between the hammer axis and the point of impact of the hammer on the cutting tool 5. The resilience of the stops, however, ensures that this requirement is not critical.
The rotor 1 is then driven either electrically or by means of an air motor or the like to rotate the hammers 2 at high speed. These hammers strike the end of the tool repetitively to apply cutting power to the tip.
From the lay-out indicated in FIG. 1, it will be appreciated that the hammer arrangements can be varied in number and consequently position on the rotor. Furthermore, sufficient sets of hammers would be incorporated on the rotor so that the tools struck by them would cut a swathe of the desired width. Furthermore, more than one rotor assembly might be required in order to cut sufficient space for the machine to operate in.
FIG. 1 shows diagrammatically the rotor (which in this case is rotating in a clockwise direction) with a set of three hammers. Hammer 2c is in the act of striking the tool 5. Hammer 2a has swung back to the stop block 22 just after striking the tool and hammer 2b has swung forward again and rests against stop block 25 ready to hit the tool 5.
The equipment can be made compact and powerful for use in confined areas such as underground mining or tunnelling operations.
It will be appreciated that the design of the particular components of the control mechanisms may be varied from those described in the specification. The particular embodiments are to be considered as being examples only. It will be further appreciated by those skilled in the art that where springs have been referred to hydraulic or pneumatic means can usually be interchanged therewith.
Alternatively, where desired, the control mechanisms can be operated electrically with the initiating pressures arranged to act on strain gauges or the like.
Other constructional details can also be varied while remaining within the scope of this invention.
Rotary driven rock cutting machines carrying swinging hammers tipped with cutting tips are simple and practical. However, cutting tips such as those used on the hammers are likely to shatter if the energy which they are required to transmit to the rock per blow exceeds a certain maximum for the design of tip used.
Under certain circumstances, for instance when cutting highly siliceous rocks, it is apparent that the tips wear excessively if the striking velocity is too high.
For a given energy per blow it is possible to use light hammers rotating at high speed or heavier hammers rotating more slowly. A disadvantage of the light hammers rotating at a fast speed is that, due to the high striking velocity, the tip wear might be excessive. However, heavier hammers, which for the same blow energy could rotate more slowly and therefore have less tip wear, have the disadvantages that they are bulky and that less energy can be put into the rock in a confined space due to the lower frequency of blows.
With the existing rock cutting machines carrying swinging hammers tipped with cutting tips it is difficult to control the angle at which the tip strikes the rock.
It is the object of the present invention to provide an alternative construction wherein rotating hammers can be used to provide power for cutting of rock without directly striking the rock by the interposition of tools capable only of axial movement.
According to the invention there is provided rock cutting equipment comprising a frame, at least a pair of rock cutting tools supported for limited axial movement in either direction against resilient buffers in the frame and spaced apart, one or more rotors carrying at least two swinging hammers adapted to strike each cutting tool and means for traversing the frame across a rock face with the tools in contact therewith.
The equipment would be adapted to hold the tools against the rock to be cut in such a manner that the tools would tend to cut or chip parallel grooves in the rock so spaced that the rock between the grooves would break out easily.
An advantage to be obtained from cutting spaced grooves is that cutting tip wear would be less per ton of rock excavated than if the tools cut grooves with no free spaced between.
The invention also provides for the speed of movement of the equipment along the rock face to be controlled so as to allow for an optimum rate of excavation (within the capacity of the machine) and for means for preventing the hammers from striking the tools when the tools are not pressing against the rock, and thus possibly damaging the tools or other parts of the equipment.
A preferred embodiment of this invention will be described with reference to the accompanying drawings in which:
FIG. 1 shows a diagrammatic layout of one rotor carrying one series of hammers for one cutting tool;
FIG. 2 and FIG. 3 are part sectional elevations showing the arrangement of one hammer with stopblocks on the rotor.
As shown the equipment comprises a power driven rotor 1 carrying a series of three swinging hammers 2a, 2b and 2c mounted on pivots 3 adjacent the periphery thereof.
The hammers carry striking faces 4 which are made of any suitably hard material and these striking faces 4 are preferably made as replaceable inserts so that the hammers may be used for longer periods than would be possible if these faces were integral with the hammers.
The hammers are adapted to strike a rigid cutting tool 5 which is adjustably supported in a suitable frame (see below) provided for the equipment.
The cutting tool carries a suitably shaped tip 6 of tungsten carbide and is held between stops 7 on the frame and a pair of resilient buffers 8 and 9 are provided on either side of a locating collar 10. These buffers must be carefully designed to give the desired restraining effect on the cutting tool and may be either metal springs or sleeves of resilient material. Hydraulic cushioning devices may also be used if this is desired.
The cutting tool 5 will be mounted in the desired relationship to the hammers and the rotor tool assembly will be mounted in the desired relationship to the rock to be cut. This latter position will preferably be angularly adjustable so that the direction of the blow applied by the cutting tools to the rock may be varied. It will be realized that it is desirable to angle the tool 5 to the rock face so that shear and bending forces in the tool are minimized.
The complete mechanism comprising at least two tools with the requisite hammers driven by one or more rotors and together with the necessary backstops and controls would be mounted in the frame and would be made to traverse approximately parallel to the surface of the rock 11 to be cut (in the direction shown by the arrow in FIG. 1) and at a distance from the rock such that the cutting tools could chip the rock at the desired rate of excavation.
The device producing the traversing motion which could be similar to that used currently on coal cutters or coal ploughs or tunnelling machines would be controlled by a mechanism sensitive to the loads on the cutting tools. The preferred form of such mechanism is illustrated in the diagram FIG. 1 where the main frame 12 (shown dotted) presses by means of a spring 13 a pressure arm 14.
The pressure arm is free to slide within limits in suitable guides 15 attached to the main frame 12 in a direction parallel to the direction of movement of the tool 5 and terminates in a collar 16 into which the tool 5 is placed. The collar 16 would be positioned between the collar 10 and the buffer 9.
As the machine traverses along the rock face the tip 6 of the cutting tool will engage against the rock and, provided that the machine continues to traverse and the rock does not break, the pressing force of the tip against the rock will continue to increase. This increased pressure will be transmitted by the collar 10 to the collar 16 and thence down the arm 14 to the spring 13 which will allow movement of the pressure arm to take place and in particular will allow lug 17 to press against the control button 18 which will ensure that the traversing mechanism will slow down and, if the pressure continues to increase, will stop.
On the other hand should there be a gap in the rock and little or no resistance is offered to the tip 6 of the cutting tool, the spring 13 will extend and the lug 17 will release its pressure on the control button 18 thus allowing the traversing mechanism to speed up.
A further feature of the invention intended to prevent the hammers hitting the tools when little or no resistance is offered by the rock comprises an on-off control button 19 operated by the lug 17. This control button operates retractable catches 20 which, when button 19 is pressed, protrude and engage with notches 21 in the hammers restraining them in their swing back positions.
When the tip 6 again engages with the solid rock and a reaction again builds up in the arm 14, the lug 17 releases the control button 19 which in turn causes the catches 20 to retract allowing the hammers 2 to swing out and strike the end of the cutting tool 5.
The restraint of the hammers in the swing back position need not be accomplished by catches mechanically engaging in notches in the hammers but friction pads may be used. Should friction pads be used it would be preferable in order to ensure that they grip the hammer only when it is stationary or moving slowly in the swing back position to trigger the application of these pads to coincide with the moment when the hammers are stationary or nearly stationary against the back stop. Such triggering action would only take place while the button 19 was depressed and could be initiated by the hammer striking either a suitably placed trigger or striking the back stop block 22. Such additional triggering action might be preferred for the catches 20 as well as for the friction pads.
As a safety precaution the complete mechanism housed in 12 should pivot about a point 23 situated ahead of the line 24 drawn at 90° to the rock face and originating in that zone of the rock face where chipping takes place. This point 23 is thus forward of the cutting tip 6 of tool 5.
The pivot 23 would be mounted in some form of chassis which would be able to traverse parallel to the rock face and which would be capable of containing any reaction forces transmitted from the rock face. The mechanism housed in 12 would be held in position on this framework by the pivot 23 and some other device such as a shearpin which, should the control button 18 fail to stop the traverse, would shear and allow the mechanism to swing out of engagement with the rock.
Under such circumstances the button 19 should operate and the hammers should be held back from striking the tool. However, it is preferable to incorporate a separate series of controls which, when the shear pin shears, will latch the hammers back and switch off the power drive.
The arrangement with the pivot 23 and the shearpin could conveniently be used to set the angle of the tools relative to the chassis.
The preferred design of the rotor 1 and swing hammers 2 is such that when the hammer strikes the cutting tool no shock load is thrown back onto the hammer pivot. It is also desirable that all the energy given up by the hammer in striking the tool is restored to the hammer by the centrifugal force applied thereto during the remaining portion of the revolution of the rotor in order to bring the hammer back into the striking position just at the correct time to strike the tool 5.
Both design features are difficult to achieve together in practice with a free swinging hammer mounted eccentrically to the axis of rotation of the rotor which is rotating at a high speed, although the simple way of achieving the first design feature is described later in this specification.
Because of difficulties in obtaining the second design feature practical considerations may make it desirable to have resilient stops positioned to prevent overswinging of each hammer in either direction about its pivot.
A hammer with its two resilient stop blocks and part of the rotor is shown in FIGS. 2 and 3.
The hammer 2 and the stop blocks 22 and 25 are mounted between backing discs 26. Each hammer will normally require two stop blocks, thus if there are three hammers in a row, as shown in the drawings, then six stop blocks will be required.
The stop block 22 is required to prevent excessive swing back and the stop block 25 is required to stop the hammer in the swing out position so that it will strike the cutting tool 5.
The stop blocks have to absorb and dissipate considerable quantities of energy and it has been found practical to construct them with fluid passages 27 leading to them from the rotor shaft 28 and other fluid passages 29 leading away through nozzles. The passages would be equipped with ball valves 30 or similar one way valves to ensure a one way flow of fluid.
A practical form of stop block consists of a cylindrical metal reinforced hollow rubber bulb similar to the commercially available "Oscillith" bush construction. The stop block would normally be filled with fluid but when struck by the hammer, would force the fluid out through one or more nozzles at high speed. In mining the fluid would preferably be water and the jets of water would play on the zone in which the rock was breaking in order that the tool 5 and tip 6 were kept cool and also to allay dust.
In essence, the hammer acts as a compound pendulum balanced in such a way as to limit the operational impact loading applied to the hammer pivot 3 to a minor proportion of that applied to the hammer striking tip. The eccentricity of the center of gravity of the hammer relative to its pivot, the spacing of the striking tip from the hammer pivot, and the polar radius of gyration of the hammer all co-operate to result in very little shock load being transmitted to the hammer pivot. The method of balancing has been proposed in an earlier patent but is redescribed hereunder.
The hammer 2 has its pivotal axis B spaced from the axis of rotation A of the rotor. The distance from the point C to B is equal to the polar radius of gyration of the hammer about the pivot B. The center of gravity of the hammer is indicated at D. The point relative to the rotor at which the hammer strikes the tool 5 is indicated at E.
Ideally the dimensions should accord with the following formula:
(B C) 2 = BD × BE
It is preferable that the distance between the hammer axis 3 and the stops 22 and 25 should also be the same as the distance between the hammer axis and the point of impact of the hammer on the cutting tool 5. The resilience of the stops, however, ensures that this requirement is not critical.
The rotor 1 is then driven either electrically or by means of an air motor or the like to rotate the hammers 2 at high speed. These hammers strike the end of the tool repetitively to apply cutting power to the tip.
From the lay-out indicated in FIG. 1, it will be appreciated that the hammer arrangements can be varied in number and consequently position on the rotor. Furthermore, sufficient sets of hammers would be incorporated on the rotor so that the tools struck by them would cut a swathe of the desired width. Furthermore, more than one rotor assembly might be required in order to cut sufficient space for the machine to operate in.
FIG. 1 shows diagrammatically the rotor (which in this case is rotating in a clockwise direction) with a set of three hammers. Hammer 2c is in the act of striking the tool 5. Hammer 2a has swung back to the stop block 22 just after striking the tool and hammer 2b has swung forward again and rests against stop block 25 ready to hit the tool 5.
The equipment can be made compact and powerful for use in confined areas such as underground mining or tunnelling operations.
It will be appreciated that the design of the particular components of the control mechanisms may be varied from those described in the specification. The particular embodiments are to be considered as being examples only. It will be further appreciated by those skilled in the art that where springs have been referred to hydraulic or pneumatic means can usually be interchanged therewith.
Alternatively, where desired, the control mechanisms can be operated electrically with the initiating pressures arranged to act on strain gauges or the like.
Other constructional details can also be varied while remaining within the scope of this invention.