GB2079214A - Improvements in or Relating to Impact Tools and Like Percussive Apparatus - Google Patents

Abstract

An impact tool has a tool bit 16, and a reciprocable mass 10 movable in one direction by a pressure pulse in a chamber 34 against the action of liquid pressure in a chamber 60 and in the opposite direction by the pressure of the liquid in chamber 60 to apply impact to the tool bit 16. The mass 10 acts on the liquid through an intermediate plunger 54 of smaller dimensions and the mass is able to perform limited movement before striking the plunger 54. High pressure liquid from duct 71 moves piston 82 leftwards against gas spring 90 and then moves spring 90 rightwardly to apply high pressure to chamber 60 via duct 38. The movement of piston 92 rightwardly causes the gas spring to move piston 82 rightwardly thereby removing the high pressure on piston 120. Piston 116 is thus moved leftwards to connect duct 38 to exhaust via duct 144 and thus end the high pressure part of the cycle. <IMAGE>

Description

SPECIFICATION Improvements in or Relating to Impact Tools and Like Percussive Apparatus The invention relates to impact tools and like percussive apparatus, hereinafter referred to as impact tools, and is applicable especially to impact tools for use in mining, quarrying or excavating.

In a known such impact tool, impact force for driving a chisel or other tool into the material to be broken, or otherwise worked, is obtained from a spring, which is compressed prior to the impact or working stroke.

Usually the tool bit is struck by a reciprocating piston in a cylinder and the spring comprises a gas which is compressed in a sealed chamber by retraction of the piston. The piston is retracted against the action of the spring by application of a pressure fluid, until a desired pre-loading of the spring is achieved. The pressure fluid is then released allowing the spring to recoil and drive the piston against the tool causing it to impact against the material being worked.

Such impact tools tend to be cumbersome because, having a large volume, the gas spring usually has low stiffness i.e. is easily compressible. Hence a long retraction stroke is necessary in order to store in the spring sufficient energy to achieve a desired impact force. Also the sealed chamber or reservoir for the gas is quite large.

An object of the present invention is to provide an impact tool which can be made more compact and effective.

Thus, according to the present invention, there is provided an impact tool comprising a tool bit or holder therefor, a reciprocable mass movable in one direction against the action of spring means and in the opposite direction by the spring to apply impact to the tool bit or holder wherein the mass is movable a limited distance in the one direction before meeting spring resistance. The spring may be a liquid sealed in a chamber.

The mass may act against the spring means by way of an intermediate plunger member, preferably much smaller than the mass itself.

Preferably the cross-section of the plunger member will be small compared with that of the mass giving a correspondingly longer stroke for a required volumatic compression of the spring.

This is of particular advantage with a liquid spring.

The plunger member may be slidingly supported, coaxial with the mass, in the rear end wall of a cylinder containing the mass. The end of the plunger remote from the mass may then project into a sealed chamber for the liquid. Then retraction of the mass will, on contact with the plunger, force the plunger into the chamber, compressing the liquid.

In embodiments having damping effective at the end of the forward travel of the mass, the degree of limited movement is sufficient to ensure that any such damping of the mass has ceased to have effect before the spring is encountered.

An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 illustrates, schematically, an impact tool having a liquid spring: Figure 2 illustrates a fluid control system, for controlling application of pressure fluid to the impact tool of Figure 1, and which is the subject of our copending application number.

The impact tool shown in Figure 1 comprises a mass in the form of a piston 10 slidably housed in a cylinder 12 in a casing 14. A chisel or other tool bit 16, projects from the cylinder 1 2 through a cylindrical aperture 18 in the frontal part 20 of the casing 1 4 and is retained in a conventional manner (not shown).

The piston 10 has a front portion 22 of lesser diameter than its rear portion 24. Front and rear portions 26 and 28, respectively, of the cylinder 1 2 correspond in diameter to the associated portions of the piston and fluid tight seals 30 and 32 are provided between the piston and cylinder.

The central cylinder part is recessed forming an annular chamber 34 surrounding the stepped part 36 of the piston 10. The axial extent of the annular chamber 34 is sufficient to accommodate movement of the stepped part 36 throughout the working stroke. A port 38 for supply and return of pressure fluid from the fluid control system (Figure 2), is provided in one wall of the chamber 34.

The shoulder between the front wall ot the annular chamber 34 and the front aperture 18 is inclined rearwardly and outwardly to form a conical seating 40 which is connected to the chamber 34 by a short cylindrical portion 42. The annular front face 36' of the stepped piston 36 is of complementary conical shape, and its maximum diameter a close fit in the cylindrical portion 42. Thus, during forward travel of the piston 10, entry of the stepped piston into the closely-fitting cylindrical portion 42 traps pressure fluid between part 36 and the conical seating 40. Further forward movement of the piston will be damped as the entrapped pressure fluid exits by way of the relatively small annular space surrounding the piston part 36. Some damping will, of course, also be effective during the first part of the return stroke.

The front face of the piston 1 0 has a forwardlydirected peripheral flange 43, its inner surface diverging outwardly and forwardly. The casing 14 has a correspondingly shaped recess 44 to receive the flange during the impact stroke.

The rear face 50 of the piston 10 is centrally recessed and, as shown, spaced from the end wall 52 of the cylinder 12, which is of complementary form.

A plunger 54 is slidably mounted in a cylindrical hole 56 in the end wall 52 of the cylinder 12, coaxially with the piston 10.

An enlarged rear end 58 of the plunger 54 extends into a chamber 60 which is connected to a further chamber 62 by a passage 64. The plunger 54 is a fluid-tight working fit in the hole 56. The chambers 60, 62 and passage 64 are filled with a liquid such as hydraulic oil or a fire resistant fluid. Forward movement of the plunger 54 is limited by the enlarged part 58 acting against the casing around the hole 56. The space between the flange 43 and recess 44 at the front of the piston 10 may be connected to the space 57 at the rear of the piston to provide oil mist lubrication for the chisel bearing 1 8.

To operate the tool, pressure fluid is applied to the annular chamber 34 via the port 38.

Differential pressures act on the stepped portion 36 due to the different diameters of the front and rear piston parts 26, 28, respectively, so that the piston 10 is driven rearwardly gaining momentum until it strikes the plunger 54 and compresses the liquid in the chamber 60. The pressure fluid is then released to exhaust and the liquid spring recoils, forcing the piston 10 forwards and hence impacting the chisel or other tool bit 1 6 against the material being worked.

The damping will not usually be utilised in normal working, since the impact energy will be expended in breaking the material, but is necessary for preventing the piston from striking the casing interior when the impact tool is operated with the chisel or tool bit acting against little or no resistance, for example during tests, demonstrations or when the material breaks prematurely.

If damping becomes effective, in normal operation the crowd force assists initial retraction of the piston from the damped region.

The reiative dimensions of the piston 10, damping portions 36, 40, 42 and the extent to which the plunger 54, in its foremost position, projects into the cylinder, are such that a small amount of free travel is provided after damping ceases and before the spring resistance is encountered. Figure 1 shows the piston during such free travel.

This arrangement provides significant advantages in operation of the tool.

In view of the low compressibility of the liquid, compared with a gas, the stiffness of the liquid spring is high, so that, even at the start of compression, quite high forces will be encountered. Thus, were the spring resistance to be encountered at the same time as the damping, much greater force would be required to move the chisel and piston into the working position shown in Figure 1.

As can be seen from Figure 1, the piston dimensions are such that, even in normal operation, when the damping effects are not encountered, there will be free travel of the piston after completion of the impact stroke and before it encounters the spring resistance.

A system for controlling supply and return of the pressure fluid to and from the port 38 of the impact tool is disclosed in our copending application No.

The system comprises a cylinder having a central portion 70 of less diameter than one end portion 72. The central cylinder portion 70 has an entry port 71 for the supply of pressure fluid from an external supply (not shown). A hollow piston 76 is slidingly located in the other end portion 74 of the cylinder and has fluid-tight circumferential seals 78 and 80, one at each end of the piston body. Between the seals, the piston 76 diameter is reduced, providing an annular space 77 around the piston 76. When the piston 76 is in one extreme position (shown in Figure 2) with its end 82 abutting the shoulder 84 between the central cylinder portion 70 and end cylinder portion 74, the annular space 77 interconnects two ports, 86 and 88, in the cylinder wall. Port 86, nearest the end of the cylinder 74, is connected to a pressure fluid return.Port 88 is located immediately adjacent the crown end of the piston 76 so as to be opened to the central cylinder portion 70 seen after the piston 76 starts to move out of its endmost position.

The cylinder portion 74 connects to a gas-filled reservoir 90, and a shoulder 93 between the cylinder part 74 and the reservoir 90 limits travel of the piston 76.

An inlet valve piston 92 is slidingly located in the first-mentioned end part 72 of the cylinder 70 and has fluid-tight circumferential seals 94 and 96 spaced apart along its length. The circumferential surface of the piston 92, between the seals, is stepped, providing an annular space 102 having a port 103 connected to the pressure fluid return.

Crown end 104 of piston 92 seats against the valve seating 106 between the central cylinder portion 70 and an adjacent annular recess 108 in that end of the cylinder portion 72. A passage 110 connects the gas reservoir 90 to the sealed space 112 behind the piston 92.

The annular recess 108 communicates with the pressure feed port 38 (Figure 1) of the impact tool, and with a similar annular recess 114 around a hollow exhaust valve piston 1 16 which is slidably located in a further cylinder 118 and has circumferential seals 119. Within the piston 116 a spool piston 120 in a cylinder 122, is slidable to act against the internal wall of the crown of piston 11 6 on application of pressure fluid to the cylinder 122, which is connected to port 88 by a duct 124. The valve piston cylinder 1 18 is vented to atmosphere by a non-return valve 1 26.

The exhaust valve piston 1 16 is shown in its position corresponding to application of pressure to the internal biassing piston 1 20 and, in that position, projects through the annular recess 114 to seat against a circumferential valve seating 130 between the recess 114 and a cylinder part 132 of less diameter. This lesser diameter cylinder part extends between annular recess 1 14 and a further annular recess 134 in the adjacent end of another cylinder 136. A piston 138 is housed in cylinder 136 and has axially spaced circumferential seals 137 and 139. The crown 1 40 of the piston 138 seats against a shoulder 142 between the recess 134 and the lesser diameter intermediate cylinder part 1 32. The sealed space behind the valve piston 140 is gas filled.

The annular recess 134 is connected to a pressure fluid return port 144, which also connects to the chamber 62 (Figure 1) of the impact tool, by way of a one way valve 146 and passage 147. This enables the chamber 62 to be replenished, as required, from the pressure fluid return 1 44. A bleed groove 148 between the recess 1 34 and intermediate cylinder part 1 32 facilitates closure of pistons 11 6 and 1 38 to their seatings 1 30 and 142, respectively.

In operation of the system, pressure fluid is admitted to the cylinder part 70 via feed port 71, with the various pistons in the positions shown in Figure 2.

The fluid pressure causes the piston 76 to retract, compressing the gas in reservoir 90 and uncovering the port 88. Fluid pressure is thus admitted to cylinder 122, biassing the piston 120 against the interior of piston 11 6 to force it firmly against its seating 1 30.

The increased gas pressure in reservoir 90, which is substantially equal to the applied fluid pressure, is transmitted via the passage 110 to the rear of valve piston 92, maintaining it in the closed position, as shown, due to the cylinder part 72 being of greater diameter than cylinder part 70.

When the piston 76 has reached the limit of its travel, abutting the shoulder 93, the gas pressure remains constant. The fluid pressure in chamber 70 continues to increase until the pressuredifferential keeping valve piston 92 closed is overcome. The valve piston 92 than lifts from its seating 106. The fluid pressure is thus applied directly to the impact tool feed port 38 by way of the annulus 108. In view of the step between the seals 94 and 96, the area now presented to the pressure fluid is greater than that acted upon by the gas in the sealed space 112 behind the piston 92. Thus a differential force is produced to accelerate the valve to the fully open position.

At the same time piston 76 starts to return under the action of the compressed gas, exhausting the pressure fluid in the cylinder parts 70 and 74, also via the impact tool feed port 38.

This causes the retraction of the impact tool piston 10 towards the liquid spring.

When the piston 76 has reached again its initial position abutting shoulder 84 the compressed gas in sealed chamber 11 2 recloses inlet valve piston 92 to its seating 106.

As the valve piston 76 arrives again at its initial position, port 88 is connected to return port 86, venting the cylinder 122, and removing the closure bias from piston 11 6.

In view of the difference in diameter and step between seating 130 and cylinder 118, differential pressure is applied to the piston 11 6 by the pressure fluid in port 38, causing it to lift from its seating 1 30.

The pressure fluid from the tool cylinder 1 2 (Figure 1), acted upon by the recoiling hammer piston 10, acts against the crown of piston 1 38 causing it to retract, compressing the gas in cylinder 136 and allowing the fluid to exhaust via the fluid return port 1 44. When the pressure of the fluid leaving the tool has diminished sufficiently, the gas pressure in cylinder 136 restores the piston 138 to its initially shown position. The cycle then repeats.

In view of the extremely high pressure at the start of the impact stroke of the tool the piston 138 will retract initially beyond the annulus 134, allowing temporary accommodation of pressure fluid in that part of valve cylinder 136. Absorption of the initial surge in this way allows rapid exhausting of the pressure fluid from the impact tool cylinder 12. Thus the impact stroke can take place quickly and with improved efficiency due to the reduction in energy otherwise wasted in expelling the pressure fluid.

For this reason the system described above is considered more efficient, at least for high speed switching of high pressure fluids, than known spool-type valves, used hitherto, particularly since such spool valves, when open, provide a more restricted exit for fluid.

It is envisaged that the exhaust valve piston 11 6 and its associated cylinder might be stepped to provide an annular space similar to that (102) around the inlet valve piston 104. Then the biassing piston 120 could be dispensed with and pressure fluid applied to the annulus by way of passage 1 24 to provide the required closure bias.

An advantage of embodiments employing a liquid rather than a gas spring is that their performance is less susceptible to variation due to temperature changes.

An advantage of replenishing the liquid spring from the pressure fluid return is that the liquid spring can thus be maintained at a low initial pressure, without intermediate regulation, which would be required if replenishment were to be from the pressure fluid supply.

It should be noted that impact repetition frequency will be determined primarily by the pressure fluid supply rate, for a given valve.

Whilst described with particular reference to impact tools for use in mining, the invention comprehends other piston/cylinder apparatus in which an impact stroke is produced by releasing a spring compressed during a previous return stroke.

In view of the provision for limited movement of the impactor mass before encountering spring resistance, impact tools embodying the invention may have a shorter stroke, using a stiffer spring, than would otherwise be practicable due to the high crowd force which would be required to retract the tool bit. Hence the impact tool may be more compact yet still produce a high energy blow.

Claims (Filed on 22/5/81) 1. An impact tool comprising a tool bit or holder therefor, and a reciprocable mass movable in one direction against the action of fluid spring means and in the opposite direction by the spring

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (12)

1. **WARNING** start of CLMS field may overlap end of DESC **.

   sealed space behind the valve piston 140 is gas filled.

   The annular recess 134 is connected to a pressure fluid return port 144, which also connects to the chamber 62 (Figure 1) of the impact tool, by way of a one way valve 146 and passage 147. This enables the chamber 62 to be replenished, as required, from the pressure fluid return 1 44. A bleed groove 148 between the recess 1 34 and intermediate cylinder part 1 32 facilitates closure of pistons 11 6 and 1 38 to their seatings 1 30 and 142, respectively.

   In operation of the system, pressure fluid is admitted to the cylinder part 70 via feed port 71, with the various pistons in the positions shown in Figure 2.

   The fluid pressure causes the piston 76 to retract, compressing the gas in reservoir 90 and uncovering the port 88. Fluid pressure is thus admitted to cylinder 122, biassing the piston 120 against the interior of piston 11 6 to force it firmly against its seating 1 30.

   The increased gas pressure in reservoir 90, which is substantially equal to the applied fluid pressure, is transmitted via the passage 110 to the rear of valve piston 92, maintaining it in the closed position, as shown, due to the cylinder part 72 being of greater diameter than cylinder part 70.

   When the piston 76 has reached the limit of its travel, abutting the shoulder 93, the gas pressure remains constant. The fluid pressure in chamber 70 continues to increase until the pressuredifferential keeping valve piston 92 closed is overcome. The valve piston 92 than lifts from its seating 106. The fluid pressure is thus applied directly to the impact tool feed port 38 by way of the annulus 108. In view of the step between the seals 94 and 96, the area now presented to the pressure fluid is greater than that acted upon by the gas in the sealed space 112 behind the piston 92. Thus a differential force is produced to accelerate the valve to the fully open position.

   At the same time piston 76 starts to return under the action of the compressed gas, exhausting the pressure fluid in the cylinder parts 70 and 74, also via the impact tool feed port 38.

   This causes the retraction of the impact tool piston 10 towards the liquid spring.

   When the piston 76 has reached again its initial position abutting shoulder 84 the compressed gas in sealed chamber 11 2 recloses inlet valve piston 92 to its seating 106.

   As the valve piston 76 arrives again at its initial position, port 88 is connected to return port 86, venting the cylinder 122, and removing the closure bias from piston 11 6.

   In view of the difference in diameter and step between seating 130 and cylinder 118, differential pressure is applied to the piston 11 6 by the pressure fluid in port 38, causing it to lift from its seating 1 30.

   The pressure fluid from the tool cylinder 1 2 (Figure 1), acted upon by the recoiling hammer piston 10, acts against the crown of piston 1 38 causing it to retract, compressing the gas in cylinder 136 and allowing the fluid to exhaust via the fluid return port 1 44. When the pressure of the fluid leaving the tool has diminished sufficiently, the gas pressure in cylinder 136 restores the piston 138 to its initially shown position. The cycle then repeats.

   In view of the extremely high pressure at the start of the impact stroke of the tool the piston

   138 will retract initially beyond the annulus 134, allowing temporary accommodation of pressure fluid in that part of valve cylinder 136. Absorption of the initial surge in this way allows rapid exhausting of the pressure fluid from the impact tool cylinder 12. Thus the impact stroke can take place quickly and with improved efficiency due to the reduction in energy otherwise wasted in expelling the pressure fluid.

   For this reason the system described above is considered more efficient, at least for high speed switching of high pressure fluids, than known spool-type valves, used hitherto, particularly since such spool valves, when open, provide a more restricted exit for fluid.

   It is envisaged that the exhaust valve piston 11 6 and its associated cylinder might be stepped to provide an annular space similar to that (102) around the inlet valve piston 104. Then the biassing piston 120 could be dispensed with and pressure fluid applied to the annulus by way of passage 1 24 to provide the required closure bias.

   An advantage of embodiments employing a liquid rather than a gas spring is that their performance is less susceptible to variation due to temperature changes.

   An advantage of replenishing the liquid spring from the pressure fluid return is that the liquid spring can thus be maintained at a low initial pressure, without intermediate regulation, which would be required if replenishment were to be from the pressure fluid supply.

   It should be noted that impact repetition frequency will be determined primarily by the pressure fluid supply rate, for a given valve.

   Whilst described with particular reference to impact tools for use in mining, the invention comprehends other piston/cylinder apparatus in which an impact stroke is produced by releasing a spring compressed during a previous return stroke.

   In view of the provision for limited movement of the impactor mass before encountering spring resistance, impact tools embodying the invention may have a shorter stroke, using a stiffer spring, than would otherwise be practicable due to the high crowd force which would be required to retract the tool bit. Hence the impact tool may be more compact yet still produce a high energy blow.

   Claims (Filed on 22/5/81) 1. An impact tool comprising a tool bit or holder therefor, and a reciprocable mass movable in one direction against the action of fluid spring means and in the opposite direction by the spring

   means to apply impact to the tool bit or holder, the fluid spring means comprising a liquid stored in a chamber.
2. 2. An impact tool as claimed in Claim 1, wherein the mass is movable a limited distance in the one direction before meeting spring resistance.
3. 3. An impact tool as claimed in Claim 1 or Claim 2, in which the mass acts against the spring means by way of an intermediate plunger member.
4. 4. An impact tool as claimed in Claim 4, in which the plunger member is much smaller than the mass itself.
5. 5. An impact tool as claimed in Claim 4, in which the cross-section of the plunger member is small compared with that of the mass giving a correspondingly larger working stroke for a required volumatic compression of the spring means.
6. 6. An impact tool as claimed in any one of Claims 3 to 5, in which the plunger member is slidingly supported, co-axial with the mass, in the rear end wall of a cylinder containing the mass.
7. 7. An impact tool as claimed in Claim 6, in which the end of the plunger remote from the mass projects into a scaled chamber for the fluid spring means.
8. 8. An impact tool as claimed in Claim 2, or any one of Claims 3 to 7 when dependent on Claim 2, having damping effective at the end of the forward travel of the mass, in which the degree of limited movement is sufficient to ensure that any such damping of the mass has ceased to have effect before the spring means is encountered.
9. 9. An impact tool constructed and arranged substantially as herein described with reference to the accompanying drawings.
10. 1 0. A fluid control valve comprising a chamber having an inlet portion communicating with an inlet port for receiving fluid under pressure from a source thereof, an intermediate portion communicating with a service port for dispensing fluid therefrom, a movable valve closure element housed in and sealed to the intermediate portion and cooperable with a valve seating between the first and intermediate chamber portions to close communication between those portions biassing means responsive to fluid pressure in the inlet portion to bias the closure element to its seating and means for limiting such response such that increase of said fluid pressure beyond a predetermined level initiates opening of the closure element from its seating.
11. 11. A fluid control valve comprising a chamber having a first portion communicating with a port for exhaustion of pressure fluid, a second portion communicating with a service port for admitting fluid under pressure, two valve seatings spaced apart, between the two ports, two valve closure elements for example pistons, each cooperable with a different one of the seatings to close communication between the two ports, and means for biassing each valve closure element to its seating.
12. 12. A fluid control system for controlling supply and return of pressure fluid to and from pressure fluid operated apparatus comprising a service port for conducting pressure fluid alternately to and from the apparatus, inlet valve means operable alternately to open and close communication between the service port and an inlet port for pressure fluid from a supply, and exhaust valve means operable alternately to open and close communication between the service port and an exhaust for pressure fluid returned from the apparatus, further comprising means operative to inhibit opening of the inlet valve means for a predetermined interval after closure of the exhaust valve means and to permit opening of the exhaust valve means on reclosure of the inlet valve means.