US3202239A

US3202239A - Acoustic shield for a tool powered by a gas-operated motor

Info

Publication number: US3202239A
Application number: US372470A
Authority: US
Inventors: Clarke Ronald Albert William
Original assignee: Individual
Current assignee: Individual
Priority date: 1963-06-10
Filing date: 1964-06-04
Publication date: 1965-08-24
Anticipated expiration: 1982-08-24
Also published as: CH413756A; BE649108A; DE1300477B; NL6406499A

Description

1965 R. A- w. CLARKE 3,202,239

ACOUSTIC SHIELD FOR A TOOL POWERED BY A GAS-OPERATED MOTOR Filed June 4, 1964 2 Sheets-Sheet 1 I H l Aug. 1965 R. A. w. CLARKE 3,202,239

ACOUSTIC SHIELD FOR A TOOL POWERED BY A GAS-OPERATED MOTOR Filed June 4, 1964 2 Sheets-Sheet 2 29 l l f 3 QJJ 28 32 -26 Q 35 2 fj 38 36 l L/ 24 T 37 25 l 25 5] 57 48 I I 50 49 I I -27 22-t I I 44 ML United States Patent 3,202,239 ACOUSTEC SHIELD FUR A TOOL POWERED BY A GAS-@PERATED MOTOR Ronald Albert William larke, 21 Raymond Road,

London SW. 19, England Filed June 4, 1964, Ser. No. 372,470

Claims priority, application Great Britain, June 10, 1963,

23,032/63; July 12, 1963, 27,759/ 63 9 Claims. (Cl. 181--36) This invention relates to an acoustic shield for a tool powered by a gas-operated motor and of the type having an axially elongated body containing the motor, exhaust outlet means arranged to discharge exhaust gas laterally from the body, and a working member which extends from one end of the body and is axially movable relative to the body, the member being actuated by the motor.

The present invention includes an acoustic shield for a tool powered by a gas-operated motor and of the type set forth, comprisingan elongated casing lined with a sound-absorbing material and shaped so as at least partly to surround the body of the tool when fitted thereto and to provide between the body of the tool and an inner surface of the lining of the casing a passage which is open to atmosphere and is of cross-sectional area at least as great as that of the exhaust outlet means, the casing being adapt-ed to be fitted to the tool relatively to the exhaust outlet means so that the exhaust gas flows through the passage.

The invention will now be described, by way of example, with reference to the accompanying somewhat diagrammatic drawings, in which:

FIGURE 1 is a longitudinal cross-section through a pneumatic drill fitted with an acoustic shield according to the invention, parts of the drill of no relevance to the invention being omitted in the interests of clarity; and

FIGURE 2 is a fragmentary longitudinal cross-section taken at right angles to FIGURE 1.

Referring first to FIGURE 1, the drill has an elongated body 10 at the top of which is a handle 11, operating trigger 12, and a coupling 13 by which a compressed air line can be connected to the drill. Within body 10 is formed a cylinder 14, at the upper end of which is an advance inlet port 15, at the lower end of which is a return inlet port 16, and which has between the advance port and the return port an exhaust outlet port 17. Exhaust port 17 opens into an exhaust outlet 18 which projects laterally from body 10 and is angled so as to direct air exhausting from chamber 14 outwardly from the body and downwardly away from handle 11.

A piston 19 is provided within chamber 14 which reciprocates therein on the admission of compressed air alternately to opposite ends of chamber -14 through advance port 15 and return port 16 respectively, passage of air through

ports

15 and 16 being controlled by a valve mechanism actuated by movement of the piston 19, which mechanism is conventional and is therefore not illustrated. Cylinder 14, piston 19 and the ports and valve mechanism constitute an air-operated motor of the drill.

An anvil 20 is provided within body 10 so as to be struck by piston 19 at the end of each advance of the piston and transmit the blow to a chisel 21 which projects from the lower part or front head 22 of body 10 and can be moved axially thereof. At the bottom of the body is a spring loaded latch 23 which limits axial movement of chisel 21 and can be operated to permit chisel 21 to be withdrawn for replacement.

Front head 22 is connected to the upper part of the body by bolts 24 on which are engaged respective nuts 25. Each bolt 24 passes through a helical compression spring which biases the front head into engagement with the lower part of the body. The maximum cross-sectional dimension of body 19 is about 5 inches.

When the drill is in use so that reciprocation of the piston causes the chisel to strike a succession of rapid blows on the hard surface being drilled, the familiar noise of a pneumatic drill arises. A large part of the noise is due to the rapid expansion and frequency of pulses of exhaust air. Another important cause of noise is vibration of the chisel, which is a member made of high-tensile steel and so emits a high-pitched ringing note. Noise results also from the impact of moving parts of the drill and from the chisel striking the surface being drilled.

An acoustic shield for this drill consists of two parts, a noise converter 26 and a vibration reducer 27. Noise converter 26 comprises a metal tube 28 of about 9 inches diameter and 12 inches length which has an internal lining about 1 inch thick of sound absorbing material. Lining 29 is suitably made of a pressure felted hair felt having a density of about 30 lbs. per cubic foot, but other materials could be used as will be described.

At its upper end tube 28 is outwardly rolled to provide rim 30 and is provided with an inwardly extending annular flange 31 which constitutes a retaining stop for lining 29 when this is inserted in tube 28. Lining 29 is held in position by internal bands 32 which are a press fit Within the lining. At the lower end of the tube 28 is provided a stepped tube having an outer cylindrical portion 33 which is welded to tube 2 8 and an inner cylindrical portion 34 which serves to hold lining 29 in position,

portions

33 and 34 being joined by an annular portion 33a of width little more than the thickness of lining 29.

At diametrically opposed locations of annular portion 33a respective lugs 35 are secured to flange 33 each by three bolts such as bolt 36, shown in FIGURE 2. Between each bolt 36 and portion 33a is a rubber vibration mounting 37. Lugs 35 extend inwardly from portion 33a and are formed each with a slot 38' which fits about one of the front head bolts 24 and is secured thereto by one of the nuts 25. Noise converter 26 is thus fitted to the drill so as to surround body 10 and extend therealong to a location above exhaust outlet 18 and below coupling 13 so that air exhausted through outlet 18 is discharged into casing 26.

A passage 38 is formed between body 10 and lining 29, the lower end 39 of passage 38, towards which end exhaust air is directed being open. The upper end of passage 38 is closed by a rubber annular plate 40 the outer periphery of which is provided with a skirt 41 which embraces tube 28, skirt 41 being pressed over rolled rim 30. Plate 40 has a central thickened portion 42 which presses against the interior of lining 29 to keep the lining in place. The interior periphery of annular plate 40 is shaped complementarily to the exterior of body 10 at the location between exhaust outlet 18 and coupling 13 where plate 40 embraces body 10, and forms an air seal with the body at that location.

A slit 43 extends from the outer periphery of the plate to the inner periphery thereof, to permit the parts of the plate on opposite sides of the slit to be twisted apart so the plate can be fitted around the body of the drill. When plate 40 is fitted to the drill the inner edge of flange 31 presses into mutual contact the parts of plate 40 which lie on opposite sides of slit 43.

When the drill is in use, exhaust air discharged from outlet 18 is directed through passage 38 to the'open end 39 and, passage 38 having a cross-sectional area much greater than that of exhaust outlet 18, the air can expand freely Within passage 38 so that the efliciency of the airoperated motor is not significantly, if at all, impaired. Some of the energy of the expanding air is absorbed by so lining 29, thus partly silencing the drill, while a large part of the high frequency noise produced around the body of the drill is converted to lower-frequency noise.

It will be appreciated that specific dimensions and shapes of casing 28 and specific lining materials can be selected according to the characteristics of the drill to be fitted with the acoustic shield of the invention. For example, the casing may only partly surround the drill if the drill has a single exhaust outlet, and the size of the passage between the body of the drill and the lining of the casing may be varied provided the flow of air through the passage or through the passage and the lining is not so retrictedas to produce any significant back-pressure in the cylinder. For use with a tool powered by an internal combustion engine, the lining may be a steel mesh resistant to attack by exhaust gases, the manufacturers of such mesh commonly stating the sound-absorptioncoefiicient of their material for a given angle ofincidence. The casing described or a similar casing one inch longer can be fitted to most makes of pneumatic drill, road breaker, hammer and like tools with good results, the arrangements of the majority of these tools being similar.

Vibration reducer 27 is a resilient tubular gaiter' which comprises a flexible cylindrical rubber tube 44 one end of which is formed with an inwardly extending convoluted wall 45 provided with a centrally mounted boss 46. An aperture 47 extends axially through boss 46. Rubber tube 44 surrounds the bottom of body It and the upper part of chisel21 which projects from the end of the body, and boss 46 embraces and grips chisel 21. A rib 48 extends inwardly from the inner surface of tube 44 near the other end thereof, and engages a complementary chamber for reception of exhaust gas from the outlet means, the improvement in said shield in which the shield comprises a rigid outer casing and a lining of sound-absorbent material on the inside wall of the casing, the lining co-operating with the body of the tool to form an axially extending passageway which is open to the atmosphere at one end thereof so that exhaust gas can pass freely through and out of said passageway;

2. A shield as claimed in claim 1, wherein the shield surrounds the body of the tool, and the passageway formed between the lining of sound-absorbent material and th body is anannular passageway. t

3. A shield as claimed in claim 1, wherein the outer casing is a tubular metal casing Within which is contained the lining, and having at the end of'the casing remote from the working member of the tool a sealing member which fits about the body of the tool so as to close said passageway at the end thereof remote from the working member. I

4. An acoustic shield as claimed in claim 3, in which 'the sealing member is a flexible annular plate having an outer periphery provided with skirt means whereby the groove 49 formed in the outer edge of a rubber sealing 7 ring 50 which surrounds the body of the drill. Ring 50 has two holes 51 formed in its upper surface to receive the heads of front head bolts 24, and has a slit 52 whichextends from the inner to the outer edge of ring d, so that parts of the ring on opposite sides of slit 52 can be bent apart to permit ring 49 to be fitted about body 10.

When the drill is in use, vibration reducer 27 permits chisel 21 to moveaxiallyof body without hindrance, but reduces the natural vibration of chisel 21. Consequently the unpleasant ringing normally emitted by a pneumatic drill is lessened.

Comparative instrumental analyses of the noise made by a pneumatic drill when fitted with an acoustic shield according to the invention and when unshielded have shownthat when the drill is shielded there is substantially less sound in the relatively high frequency bands of above 300 cycles per second, the reduction being about 5 decibels in the 300600 cycles/sec. band and in the bands above 4,800 cycles/secs, and approximately 10 decibels in the bands from 600 to 4,800 cycles per second. The loudness of the drill in the low frequency bands, below 300 cycles per second, is not appreciably lessened, and

may even be slightly increased according to the construction of drill. However, because of the reduction of sound in the higher frequencies, the noise of the drill is made less disagreeable to the human ear, and the level of in terference with speech is lowered by as much as decibels.

In a practical test, it has been found that when a pneumatic drill is fitted with an acoustic shield according to the invention, the noise of the drill does not seriously impede a telephone conversation within a room near the drill, whereas the same drill without the shield makes a telephone conversation impossible under the same conditions.

I claim:

1. In the known combination of a drill, hammer or like 7 tool having an, axially elongated body, a working member which extends from one end of the body and can be reciprocated axially of the body, and a gas-driven motor within the body operable to impart repeated impact blows to the working member, the body being formed to provide shaped complementarily with the exterior cross-section of the body of the tool, and formed with a slit which extends from the outer periphery to the inner periphery so as to permit the flexible plate to be fitted about the body.

5. In the known combination of (A) a drill, hammer or like tool having a longitudinally extending body, a gasoperated motor within the body, and a working member which extends from one'end'of the body and can be reciprocated longitudinally of the body by the motor so as to deliver blows to a Work surface, the body being formed to provide outlet means through which exhaust gas from the motor is discharged laterally of the body, together with (B) a rigid acoustic shield for the tool which extends longitudinally of the body and fits thereabout so as to provide between the shield and the body of the tool an is open at the end thereof adjacent the working mem ber, whereby exhaust gases flowing from the outlet means longitudinally through the passage can escape to atmosphere longitudinally through the open end,

'of the passage, and

(2) A lining of sound-absorbent material .within the.

shield, the lining being spaced from the body of the tool so as to leave clear the annular passage between the body and the lining.

6. A shield as claimed in claim 5, wherein the soundabsorbent material comprises strands interlaced to provide air-filled interstices.

7. A shield as claimed in claim 5, in which the soundabsorbent material is a pressure-felted hair felt.

8. A drill, hammer or like tool having an axially elongated body, a working member which extends from one end of the body and can be reciprocated axially of the body, a gas-driven motor within the body operable to impart repeated impact blows to the working member, the body being formed to provide outlet means through which exhaust gas is discharged laterally of the body, an acoustic shield comprising an outer casing mounted on the body and a lining of sound absorbent material on the inside Wall of the'casing, the lining co-operating with the body of the tool to form an axially extending passageway which is open to the atmosphere at one end thereof so that exhaust gas can pass freely through and out of said passageway, and a resilient tubular gaiter fitted to the body of the tool adjacent the Working member thereof so as to extend from the body of the tool about the Working member, said gaiter being secured to the working member so as to permit axial movement of the working member but dampen the natural vibration thereof.

9. A drill, hammer or like tool as claimed in claim 8, in which the gaiter comprises a resilient tube having an inwardly extending convoluted wall at one end thereof, said wall having an apertured boss which engages firmly around the Working member, and an annular, less-resilient plate having an outer periphery connected to the other end of the tube and an inner periphery engaging around 15 the body of the tool, the plate being formed with a slit which extends from the outer to the inner periphery as to permit the plate to be fitted to the body.

References Cited by the Examiner UNITED STATES PATENTS 11/14 Manes 181-36 4/29 Warhus 18156 8/38 Fuehrer 18l36 11/38 Pettit 181-36 8/58 Wieczorek 18l-33 10/ 5 9 Kiekhaefer 181--3 3 8/60 Plummer 18136 4/ 62 Leavell 181-36 FOREIGN PATENTS 2/ 62 Austria.

11/3 8 Great Britain.

3 50 Great Britain. 7/63 Great Britain. 5/3 3 Sweden.

LEO SMILOW, Primary Examiner.

Claims

1. IN THE KNOWN COMBINATION OF A DRILL, HAMMER OR LIKE TOOL HAVING AN AXIALLY ELONGATED BODY, A WORKING MEMBER WHICH EXTENDS FROM ONE END OF THE BODY AND CAN BE RECIPROCATED AXIALLY OF THE BODY, AND A GAS-DRIVEN MOTOR WITHIN THE BODY OPERABLE TO IMPART REPEATED IMPACT BLOWS TO THE WORKING MEMBER, THE BODY BEING FORMED TO PROVIDE OUTLET MEANS THROUGH WHICH EXHAUST GAS IS DISCHARGED LATERALLY OF THE BODY, TOGETHER WITH AN ACOUSTIC SHIELD FOR THE TOOL WHICH IS FITTED TO THE BODY TO SURROUND AND BE SPACED FROM A PORTION OF THE BODY INCLUDING THE PART OF