US3365022A - Silencing means for percussive pneumatic tools - Google Patents

Silencing means for percussive pneumatic tools Download PDF

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Publication number
US3365022A
US3365022A US602967A US60296766A US3365022A US 3365022 A US3365022 A US 3365022A US 602967 A US602967 A US 602967A US 60296766 A US60296766 A US 60296766A US 3365022 A US3365022 A US 3365022A
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United States
Prior art keywords
piston
cylinder
expansion chamber
expansion
chamber
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Expired - Lifetime
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US602967A
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English (en)
Inventor
Antony D Barber
Adamson Michael George
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Holman Brothers Ltd
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Holman Brothers Ltd
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B25—HAND TOOLS; PORTABLE POWER-DRIVEN TOOLS; MANIPULATORS
    • B25D—PERCUSSIVE TOOLS
    • B25D17/00—Details of, or accessories for, portable power-driven percussive tools
    • B25D17/11—Arrangements of noise-damping means
    • B25D17/12—Arrangements of noise-damping means of exhaust silencers

Definitions

  • This invention relates to percussive pneumatic tools of the reciprocating piston and cylinder type, for example rock drills and roadbreakers, and is concerned with the provision of means for silencing such tools, that is, reducing substantially the noise of their operation.
  • the predominant noise produced by a pneumatic impact tool such as a roadbreaker or rock drill is that caused by the sudden expansion of compressed air exhausted from the working cylinder into the atmosphere, and to achieve a worthwhile reduction in noise it is necessary to find some means for reducing the impact of the emerging exhaust air stream.
  • a percussive pneumatic tool of the type specified includes exhaust silencing means comprising first and second expansion chambers located outside the cylinder, the cylinder having a discharge port controlled by the piston and leading into the first expansion chamber and arranged to be uncovered at a late stage in the working stroke of the piston to allow the discharge of compressed air from the cylinder into the first expansion chamber, and transfer means controlled by the piston for placing the interior of the second chamber in communication with that of the first chamber at the same or a later stage in the working stroke of the piston to allow the discharge of the partly-expanded compressed air from the first expansion chamber into the second expansion chamber, the second expansion chamber having an open exhaust discharging into the atmosphere.
  • the transfer means comprises an elongated passage of restricted cross-section formed in and passing around or through the piston and arranged to inter-connect the two expansion chambers at the said late stage in the working stroke of the piston.
  • This interconnecting passage may conveniently be afforded by a surface groove formed in the cylindrical flank of the piston and extending around it, the groove being arranged to overlap simultaneously a first transfer port in the cylinder wall leading into the first expansion chamber and a second transfer port in the cylinder wall leading into the second expansion chamber at the said late stage in the working stroke of the piston.
  • the first expansion chamber preferably has only a single port communicating with its interior, the single port constituting both the discharge port and the first transfer port, the single port being wide enough to overlap the ate r t ice groove in the piston at the same time as it is partly uncovered and open beyond the piston into the cylinder.
  • the re-entry of the partly-expanded exhaust air stream from the first expansion chamber is effected through the same discharge port through which it orig inally left the cylinder the discharge port being made wide enough for this purpose.
  • the discharge port might be duplicated to provide the desired wide overlap.
  • the invention has the effect of reducing the liability of ice formation in the exhaust passages, by avoiding a substantial temperature drop in the exhausted air when discharged into the atmosphere.
  • the compressed air discharged from the cylinder into the first expansion chamber is not free to pass directly therefrom into the atmosphere and tends to be brought to rest in that chamber. Even if not brought completely to rest it will not develop the very high velocity which it would otherwise have reached if discharged directly into the atmosphere. Since the air will have expanded in the first expansion chamber without doing significant physical work and without developing kinetic energy, its temperature will remain nearly constant, in accordance with Joules Law.
  • the combined volume afforded by the working chamber of the cylinder and the first expansion chamber will contain, at any stage in the exhaust phase, a quantity of partly-expanded air at a reduced pressure but at a temperature only slightly below its original temperature before expansion.
  • the exhaust air does not attain a very high velocity and therefore its temperature drop is correspondingly small. Thus the danger of icing at the final exhaust is reduced.
  • the single wide exhaust port may be arranged to allow initial discharge of the exhaust and re-entry of the exhaust air stream from the first expansion chamber into the circumferential groove on the return stroke as well as on the working stroke of the piston.
  • the transfer means comprises simply a transfer port in the wall of the cylinder leading into the second expansion chamber and arranged to be uncovered by the piston at a late stage in its working stroke (i.e., after the discharge port has been uncovered) to interconnect the two expansion chambers via the already uncovered discharge port and the interior of the working chamber of the cylinder above the crown of the piston.
  • a tool having a long stroke such as a roadbreaker, which allows the discharge port to be so positioned as to be uncovered by the piston and the first expansion chamber to be filled well before the transfer port is uncovered by the piston.
  • FIGURE 1 is a diagrammatic side view partly sectioned, of a pneumatic rock drill provided with one form of exhaust silencing means embodying the invention, the drill piston being shown at a late stage in its working stroke;
  • FIGURE 2 shows the silencing means of FIGURE 1 with the drill piston at a late stage in its return stroke
  • FIGURE 3 shows a modified form of the embodiment 1% of FIGURES l and 2 with the drill piston at a late stage in its return stroke;
  • FIGURE 4 is a view in longitudinal section of part of a pneumatic roadbreaker incorporating another form of silencing means embodying the invention, and shown in its initial exhaust stage;
  • FIGURE 5 is a cross-section on the line V-V of FIG- URE 4.
  • FIGURE 6 is a fragmentary view similar to FIGURE 4 of the silencing means but shown in the final exhaust stage.
  • the invention is incorporated in a pneumatic impact rock drill 10 comprising a double-acting piston 11 which reciprocates in a cylinder 12 under the influence of compressed air supplied alternately to opposite ends oft-he cylinder under the control of a distributing valve mounted in the head13 of the drill.
  • the spent air is exhausted from the cylinder 12 through a discharge port 15 in the side of the cylinder at a late stage in the working and return strokes of the piston 11 when the latter uncovers the exhaust port 15 to the operative end of the cylinder, thereby enabling an adequate pressure differential to be maintained across the piston during both of its strokes.
  • the piston 11 is mounted on a piston rod 16 which extends through one end of the cylinder to the rotary holder for the drill steel 17 in the usual way.
  • the cylinder 12 Mounted externally on opposite sides of the cylinder 12 are two part-cylindrical, arcuate expansion chambers 20 and 21 each of which extends axially over substantially the whole length of the cylinder and ciroumferentially subtends about 150 at the axis of the cylinder.
  • Access to the first expansion chamber 20 is provided by the discharge port 15 which is formed in the wall of the cylinder mid-way along its axial length.
  • the piston 11 is formed with a circumferential groove 23 in its cylindrical surface mid-way between its ends, and the width of the discharge port 15 is such that when it is initially uncovered by the trailing edge of the piston 11 on either stroke, its other edge will still overlap the circumferential groove 23 in the piston.
  • the exhaust air stream will be initially discharged from the operative end of the cylinder 12 into the first expansion chamber 20 through the uncovered edge portion of the exhaust port 15, and after initial expansion therein the air stream will then return from the expansion chamber 20 into the groove 23 in the piston, re-entering the cylinder 12 through the opposite edge portion of the exhaust port 15 which then still overlaps the groove 23.
  • the exhaust air stream will travel around the piston 11 in the groove 23 to a transfer port 25 formed in the other side of the cylinder wall, for example in this case diametrically opposite to the discharge port 15, this transfer port 25 giving access to the interior of the second eX- pansion chamber 21.
  • the exhaust air stream will enter the second expansion chamber 21 via the transfer port 25, and after further expansion therein will escape to atmos phere through a discharge stub pipe 26 extending through one axial end wall of the second expansion chamber 21.
  • the discharge port 15, is necessarily wider than the transfer port 25, and the two ports 15 and 25 are so positioned relatively to one another in the axial direction of the cylinder 12 that exhaust air from the operative end of the cylinder is constrained to pass through the uncovered edge of the discharge port 15 into the first expansion chamber 20, rather than into the transfer port 25 direct, which would bypass the first expansion chamber 20 and the connecting passage constituted by the groove 23.
  • the exhaust air may pass along the groove 23 on both sides of the piston between the discharge port 15 and the transfer port 25, with an effective attenuation of noise due to the appreciable length of each path along the groove.
  • the silencer construction described above enables effective silencing to be obtained without undue increase in the external diameter of the pneumatic tool 11], and operates on both the working and the return strokes.
  • the expansion chambers 20 and 21 may be cast integrally with the wall of the main cylinder, or may be made of sheet metal welded onto the exterior of the main cylinder.
  • the silencer assembly might be fabricated separately as a one-piece or two-piece shell and detachably secured to the cylinder, with a suitable seal interposed.
  • the two expansion chambers maybe made of a suitable plastics material instead of metal, for example of polyurethane synthetic resin which has good s0und-deadening qualities as well as being readily moulded and capable of resisting impact and pressure fluctuations.
  • the two expansion chambers 20 and 21 need not necessarily be located on diametrically-opposite sides of the cylinder 12 as described and illustrated but they would be formed and arranged in a variety of different ways, for example even disposed coaxially one within or above the other and completely surrounding the cylinder, the discharge port and transfer port being correspondingly located.
  • the energy of the percussive action derives from the pressure and volume of the compressed air in the operative end of the cylinder during the working stroke of the piston.
  • the compressed air admitted to the other end of the cylinder serves to return the piston for a subsequent power stroke and also, in the case of a rock drill, to provide the power for rotating the drill steel holder to turn the drill steel and its bit.
  • the air pressure required for these duties during the return stroke is less than that required for the working stroke, and its volume may also be less.
  • the noise generated by the discharge of the return stroke exhaust will thus normally be less than that generated by the working stroke exhaust, and accordingly an alternative path for the return stroke exhaust air may be provided in some circumstances.
  • the cylinder 12 is formed with the forward edge 15 of its discharge port 15 (i.e., the edge of the port 15 which will be uncovered first during the return stroke of the piston 11) substantially level with the corresponding edge 25 of the transfer port 25, so that both will be uncovered simultaneously by the piston 11 and some of the return stroke exhaust air will be discharged directly into the second expansion chamber 21, bypassing the first expansion chamber 20 and the groove 23, whilst the remainder will pass into the first expansion chamber 20 and thence via the circumferential groove 23 to the second expansion chamber 21 as before.
  • This modified arrangement may be less effective in reducing noise in certain circumstances, but because of the lesser quantity of energy involved in the return stroke exhaust, it may nevertheless be satisfactory for use in some applications.
  • FIGURES 1 and 2 relate to a rock drill which is a relatively short-stroke implement, but the use of a silencing arrangement whose two expansion chambers are inter-connected by a restricted passage such as the circumferential groove in the piston may not prove so effective in a tool such as a roadbreaker which has a longer working stroke and fewer reciprocations per minute of the piston.
  • a different silencing arrangement in which the moving piston is employed to isolate the two expansion chambers for a portion of the working stroke but to allow them to communicate via the working chamber of the cylinder at a late stage of the working stroke to exhaust the spent compressed air.
  • a roadbreaker tool 50 comprises a cylinder 51 in which a free piston 52 can slide, and compressed air is admitted alternately to opposite ends of the cylinder 51 by means of a distributing valve 53. At the end of its working stroke the piston .52, moving in the direction of the arrow 54,
  • the cylinder 51 which is of flattened form as shown in FIGURE 5, is surrounded by an external cylindrical shroud 60 divided by a partition 61 into two compartments constituting the expansion chambers 62 and 63.
  • the first expansion chamber 62 is closed apart from the discharge port 64, but the second expansion chamber is provided with one or more exhaust vents 66 discharging to the atmosphere.
  • the partly-expanded compressed air in the first expansion chamber 62 leaves through the discharge port 64, crosses the interior of the cylinder above the crown of the piston 52 and, together with air at the same pressure from the cylinder, leaves the cylinder through the transfer port 65 and expands still further in the second expansion chamber 63, from which it escapes to the atmosphere through the exhaust vent or vents 66.
  • the compressed air from the cylinder will once again be discharged first into the expansion chamber 62 and subsequently, after the piston has travelled further up the cylinder, will be transferred into the second chamber 63 from which it will be exhausted to the atmosphere.
  • the distance which the piston has to travel between the instance at which it starts to uncover the discharge port 64 and the instant at which it starts to uncover the transfer port 65 is slightly less than on the downward working stroke, the transfer port being slightly nearer to the lower end of the discharge port than to its upper end as measured along the longitudinal axis of the cylinder.
  • a percussive pneumatic tool of the reciprocating piston and cylinder type provided with an exhaust silencing means comprising first and second expansion chambers located outside the cylinder, the cylinder having a discharge port controlled by the piston and leading into the first expansion chamber and arranged to be uncovered at a late stage in the working stroke of the piston to allow the discharge of compressed air from the cylinder into the first expansion chamber, and transfer means controlled by the piston for placing the interior of the second chamber in communication with that of the first chamber at the same or a later stage in the working stroke of the piston to allow the discharge of the partly-expanded compressed air from the first expansion chamber into the second expansion chamber, the second expansion chamher having an open exhaust discharging into the atmosphere.
  • a percussive pneumatic tool as claimed in claim 2 in which the interconnecting passage comprises a surface groove formed in the cylindrical flank of the piston and extending around it, the groove being arranged to overlap simultaneously a first transfer port in the cylinder wall leading into the first expansion chamber and a second transfer port in the cylinder wall leading into the second expansion chamber at the said late stage in the working stroke of the piston.
  • a percussive pneumatic tool as claimed in claim 3 in which the first expansion chamber has only a single port communicating with its interior, the single port constituting both the discharge port and the first transfer port, the single port being wide enough to overlap the groove in the piston at the same time as it is partly uncovered and open beyond the piston into the cylinder.
  • a percussive pneumatic tool as claimed in claim 1 in which the said transfer means comprises a transfer port in the wall of the cylinder leading into the second expansion chamber and arranged to be uncovered by the piston at a late stage in its working stroke to inter-connect the two expansion chambers via the already uncovered discharge port and the interior of the cylinder.
  • a percussive pneumatic tool as claimed in claim 1 which is double-acting, and in which the same discharge port and transfer means are arranged to operate to silence the cylinder exhaust during the return stroke of the piston in the same manner as during the working stroke.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Percussive Tools And Related Accessories (AREA)
  • Earth Drilling (AREA)
US602967A 1965-12-20 1966-12-19 Silencing means for percussive pneumatic tools Expired - Lifetime US3365022A (en)

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GB53996/65A GB1164999A (en) 1965-12-20 1965-12-20 Improvements relating to Silencing Means for Percussive Pneumatic Tools.

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DE (1) DE1299578B (es)
ES (1) ES334699A1 (es)
GB (1) GB1164999A (es)

Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3635299A (en) * 1970-04-20 1972-01-18 Gardner Denver Co Muffler for pneumatic tool
US3891049A (en) * 1972-09-28 1975-06-24 Bosch Gmbh Robert Pneumatic tool construction
US4244442A (en) * 1978-10-13 1981-01-13 Rensselaer Polytechnic Institute Method and apparatus for treating exhaust gases particularly for air-operated tools
US4294330A (en) * 1979-02-13 1981-10-13 Inco Limited Mufflers for percussive pneumatic machines
US4327817A (en) * 1978-10-13 1982-05-04 Rensselaer Polytechnic Institute Method and apparatus for treating exhaust gases particularly for air-operated tools
US5366353A (en) * 1994-04-13 1994-11-22 Hand Kent P Air valve with bleed feature to inhibit icing
US5376762A (en) * 1992-09-28 1994-12-27 Ingersoll-Rand Company Muffler for a fluid-activated, percussive apparatus
US20050191148A1 (en) * 2002-09-10 2005-09-01 Helmut Schlessmann Attachment pin for an exhaust-gas muffler
US20090090530A1 (en) * 2007-07-13 2009-04-09 Longyear Tm, Inc. Noise abatement device for a pneumatic tool
US20090294211A1 (en) * 2008-05-28 2009-12-03 Longyear Tm, Inc. Noise reducing device for a pneumatic tool
US20110126541A1 (en) * 2009-12-02 2011-06-02 Longyear Tm, Inc. Muffler system for noise abatement and ice control

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2138728B (en) * 1983-04-22 1986-07-23 Inst Gornogo Dela Sibirskogo O Pneumatic impact tool

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2896580A (en) * 1957-05-21 1959-07-28 Atlas Copco Ab Pneumatic percussion tools
US3332504A (en) * 1964-05-18 1967-07-25 James V Lowery Impact tool

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2896580A (en) * 1957-05-21 1959-07-28 Atlas Copco Ab Pneumatic percussion tools
US3332504A (en) * 1964-05-18 1967-07-25 James V Lowery Impact tool

Cited By (17)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3635299A (en) * 1970-04-20 1972-01-18 Gardner Denver Co Muffler for pneumatic tool
US3891049A (en) * 1972-09-28 1975-06-24 Bosch Gmbh Robert Pneumatic tool construction
US4244442A (en) * 1978-10-13 1981-01-13 Rensselaer Polytechnic Institute Method and apparatus for treating exhaust gases particularly for air-operated tools
US4327817A (en) * 1978-10-13 1982-05-04 Rensselaer Polytechnic Institute Method and apparatus for treating exhaust gases particularly for air-operated tools
US4294330A (en) * 1979-02-13 1981-10-13 Inco Limited Mufflers for percussive pneumatic machines
US5376762A (en) * 1992-09-28 1994-12-27 Ingersoll-Rand Company Muffler for a fluid-activated, percussive apparatus
US5366353A (en) * 1994-04-13 1994-11-22 Hand Kent P Air valve with bleed feature to inhibit icing
US7228935B2 (en) * 2002-09-10 2007-06-12 Andreas Stihl Ag & Co. Kg Attachment pin for an exhaust-gas muffler
US20050191148A1 (en) * 2002-09-10 2005-09-01 Helmut Schlessmann Attachment pin for an exhaust-gas muffler
US20090090530A1 (en) * 2007-07-13 2009-04-09 Longyear Tm, Inc. Noise abatement device for a pneumatic tool
US7681690B2 (en) 2007-07-13 2010-03-23 Longyear Tm, Inc. Noise abatement device for a pneumatic tool
US20100155174A1 (en) * 2007-07-13 2010-06-24 Longyear Tm, Inc. Noise abatement device for a pneumatic tool
US7845464B2 (en) 2007-07-13 2010-12-07 Longyear Tm, Inc. Noise abatement device for a pneumatic tool
US20090294211A1 (en) * 2008-05-28 2009-12-03 Longyear Tm, Inc. Noise reducing device for a pneumatic tool
US7735603B2 (en) 2008-05-28 2010-06-15 Longyear Tm, Inc. Noise reducing device for a pneumatic tool
US20110126541A1 (en) * 2009-12-02 2011-06-02 Longyear Tm, Inc. Muffler system for noise abatement and ice control
US8215449B2 (en) 2009-12-02 2012-07-10 Longyear Tm, Inc. Muffler system for noise abatement and ice control

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ES334699A1 (es) 1967-10-16
GB1164999A (en) 1969-09-24
DE1299578B (de) 1969-07-17

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