US 3809179 A
A muffler for the air exhaust of pneumatic tools to reduce the noise level thereof. Composition of the muffler comprises an abrasive grit distributed on a thin flexible base to which it is secured. An example of the composition is represented by commercially available grades of common emery cloth. Positioning the muffler in a manner affording retention of its flexibility enables sound muffling within an otherwise restrictive exhaust passage with only minimal, if any, adverse effect on operational characteristics of the tool. With this construction it is possible to muffle the exhaust of tools previously regarded as impossible or impractical to muffle satisfactorily because of space limitations ordinarily insufficient to accommodate a muffler device.
Description (OCR text may contain errors)
United States Patent 191 Delaney, Jr. et al.
[451 May 7,1974
[ EXHAUST MUFFLER FOR PNEUMATIC TOOLS  Assignee: Dresser Industries, Inc., Dallas, Tex.
 Filed: Apr. 18, 1973 21 Appl. No.: 352,169
 US. Cl. 181/36 A, l8l/36 R  Int. Cl. F0ln 3/06  Field of Search..... 181/336, 33 M, 35 R, 35 G, 181/36 R, 36 A, 47 R, 47 A, 44, 57,64,
 I References Cited UNITED STATES PATENTS 3,129,642 4/1969 Sorensen et a1. 173/163 3,270,834 9/1966 Bratt 187/36 A 2,830,560 4/1958 Poeden 181/36 A 2,073,480 3/1937 Jimerson 181/36 A FOREIGN PATENTS OR APPLICATIONS 932,373 7/1963 Great Britain 181/36 A Primary Examiner-Richard B. Wilkinson Assistant Examiner-Vit N. Miska Attorney, Agent, or Firm--Daniel Rubin [5 7 ABSTRACT A mufiler for the air exhaust of pneumatic toolsto reduce the noise level thereof. Composition of the muffler comprises an abrasive grit distributed on a thin flexible base to which it is secured. An example of the composition is represented by commercially available grades of common emery cloth. Positioning the muffler in a manner affording retention of its flexibility enables sound muffling within an otherwise restrictive exhaust passage with only minimal, if any, adverse effect on operational characteristics of the too]. With this construction it is possible to muffle the exhaust of tools previously regarded as impossible or impractical to muffle satisfactorily because of space limitations ordinarily insufficient to accommodate a muffler device.
9 Claims, 4 Drawing Figures EXHAUST MUFFLER FOR PNEUMATIC TOOLS BACKGROUND OF THE INVENTION The field of art to which the invention pertains includes the art of acoustics and particularly to mufi'lers for noise level reduction of rotary-type pneumatic hand tools.-
By and large, the majority of commercially available pneumatic hand tools include a muffler of sorts for maintaining the noise level of the air exhaust within to]- erable limits that are somewhat arbitrarily determined by industry. Common muffler compositions comprise sintered metal, metal wool, felt, screenwire, etc., as for example disclosed in US. Pat. Nos. 2,688,798; 2,950,775; and 2,966,138. Typically, these mufflers are used in tools having sufficiently large housing volumes affording an expansion chamber, exhaust extension or the like in which such a muffler can be readily accommodated.
Federal regulations recently enacted by the Occuptional Safety and Health Administration (OSHA) have now imposed legal limits for the operational noise levels of pneumatic tools. These limits are generally lower than previous standards of the industry dictating the need for better and more effective solutions to the problem. At the same time, some pneumatic tools of relatively small mass such as small hand-held grinders known as die grinders have previously relied totally on internally staged diffusion by means of a tortuous baffling. Inadequate space to accommodate a separate muffler without adversely affecting tool size and/or performance has precluded satisfactory muffling of those tools. It should be appreciated that such die grinders are of relatively small physical size for utilization in close operating quarters and characteristically lack the internals such as gear trains, clutch mechanisms, expansion chambers or the like contributing to increased bulk of other type pneumatic tools. A common model die grinder weighs less than a pound and is under 6 inches in total length yet operates to on the order of 27,000 to 30,000 rpm. Despite the relatively high noise level exhaust produced at that operating speed, it has not heretofore been known how to further muffle sound of a die grinder without .deleteriously affecting performance, size, etc., yet because of the more stringent standards recently imposed by OSHA, further muffling of die grinder exhaust has become not only an engineering challenge but a hurdle to continuing commercial success.
SUMMARY OF THE INVENTION The invention relates to an improved muffler device for pneumatic hand tools. More specifically, the invention relates to an inexpensive muffler construction utilizing minimal consumption of space yet capable of being used alone or in combination with other muffler units for effecting noise reduction from the exhaust of pneumatic tools. By virtue of the minimal space requirements, the muffler construction hereof can be effectively used in compact tools such as die grinders which because of space limitations were previously unable to readily accommodate a muffler of any sort. With the muffler hereof such tools can nowoperate at a noise level below current OSHA standards to thereby exceed minimum compliance. This is accomplished in accordance with the invention by a muffler comprised of an abrasive grit on a flexible base commercially available in the form of inexpensive grades of common emery cloth. By doubling the cloth into a U-shaped cross sectional foldover, it can be readily installed into even the narrowest of exhaust passages without adversely affecting tool operation as might normally be expected.
It is therefore an object of the invention to provide a novel mufiler device .for use with pneumatic hand tools.
It is a further object of the invention to provide a novel muffler device of composition able to effectively reduce sound levels from the exhaust of pneumatic tools without materially increasing the size or weight of the tool with which it is to be utilized.
It is a further object of the invention to effect the foregoing objects with a muffler device of relatively inexpensive composition that may be easily added to ex- BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an overscale side view of a partially sectioned die grinder utilizing the muffler device hereof;
FIG. 2 is a sectional view taken substantially along the lines 22 of FIG. 1;
FIG. 3 is an isometric view of the muffler device as utilized in the die grinder of FIG. 1; and
FIG. 4 is an enlarged fragmentary sectional elevation through an exemplary muffler composition in accordance herewith.
Referring now to the drawings, there is illustrated a die grinder l0 exemplifying a pneumatic-type hand tool in which a muffler device 11, in accordance herewith, can be advantageously utilized. Comprising the die grinder is a tubular housing 14 enclosing an air motor (not shown) to which compressed air is supplied from inlet 15 under control of a throttle lever 16.Connected to the housing at its opposite end is a bearing retainer 19 threaded thereon via threads 20. Extending forward from the retainer to the terminal end of the tool is a chuck guard 21 mounted on retainer threads 18.
Rotatable output of the tool is provided by a rotor 22 supported in bearing 23 that in turn supports a collet body 24 containing a collet 25. Opening and closing of the collet jaws for receiving the .shank of deburring grinding element 28 is governed by the position of a cylindrical sleeve 29 under control of adjusting nut 31. For these purposes sleeve 29 at its inward end terminates in a radial flange 30 received in the counterbore of adjusting nut 31 threadedly supported on body thread 32. Removal of the chuck guard provides access to the adjusting nut which is threadedly advanced leftward for release of the collet jaws and rightward for closing them.
Without use of muffler device 11 to be described below, limited sound reduction has been achieved by a baffled stage difiusion of the exhaust air in a tortuous discharge path from the motor within housing 14. The flow path comprising the latter is generally indicated by arrows leading from a series of axial passages 40 opening into an annular chamber 41 which via a series of offset passages 42 communicates with annular chamber 43. From the latter, the exhaust air flows axially through a series of slotted apertures 46 opening into an annular chamber 47. At that point the air turns radially and axially in quick succession into tubular bore 48 of the chuck guard before discharging to atmosphere through annular bore 49. With this diffusion arrangement, bafiling within the tool has been effective in reducing sound level to on the order of about 93 dBA while the OSHA minimum depending on other factors as well is about 90 dBA.
Muffling in accordance herewith is effected by muffler device 1] formed as a foldover annular ring installed in exhaust bore 48. The outside surface 50 of ring 11 is of a diameter affording a relatively snug fit against the inside annular surface of the chuck guard thereat while the inside ring surface 51 is loosely spaced about adjusting nut 3!. Composition of the muffler comprises a commercial grade of a flexible abrasive paper or cloth which when folded over forms a U-cross section with a narrow intervening gap 52. By placing the closed loop end of the fold facing the air discharge,
grit is contained on all surfaces exposed to the exhausting flow. In this arrangement, gap 52 affords flexibility to the'laterally passing flow enabling the cloth to act resiliently as a springboard to the sound waves in achieving noise reduction. For the embodiment being described, the muffler composition comprised a commercial grade of common 150 grit emery cloth situated in the exhaust passage in the manner illustrated. In this relation it was able to reduce the exhaust noise level from about 93 dBA to 82 dBA with only an insignificant reduction in too] speed being encountered on the orderof. less than about 2 percent.
' A sectional enlargement through a fragment of abrasive muffler composition in accordance herewith is shown in FIG. 4. Typically, the composition comprises a base or substrate 55 of flexible material such as paper, cloth, plastic, etc. able to withstand the velocity forces of the air without tearing. Secured to the base by glue or other suitable binder 56 is a generally uniform distribution of abrasive grit 57. For emery cloth the abrasive generally comprises a mixture of corundum and magnetite or other iron oxide. Where the grit bond is insufficient to withstand the velocity forces of the air without being blown from its base, it may be necessary to apply a protective coating of lacquer, paint or the.
like. Under those circumstances, the coating should be of sufficient thickness to enhance bonding of the grit or otherwise render it less susceptible to other constituents. The coating should not be so thick as to reduce tendency of the grit to diffuse the sound waves. A thickness of about 0.0002 to 0.001 inches has been found suitable. Likewise, the degree of coarseness is in itself not critical although it has been found that superior results were obtained with about 100 to 200 grit, preferably about 150 grit. Below minimum coarseness the beneficial effectswere found to fall off sharply. It is to be understood, however, that these given values will vary depending on the. particular application and tool with which the muffler device is utilized. In that regard, a balanced trade off can be anticipated between the size of exhaust cavity and extent of emery surface to which the exhaust air is subjected. Generally speaking, the abrasive surface must be coarse enough to de- By the above description there is disclosed a novel muffler device capable of functioning alone or in combination with other muffler devices for substantially re ducing the level of exhaust noise from a pneumatic tool. Composition of the muffler can comprise a variety of suitable abrasives on a flexible base capable of being formed and situated in even a narrowly restrictive exhaust passage of the tool. The base need only be characterized by sufficient durability to withstand the velocity forces without tearing and for which common emery cloth has been found adequte. At the same time, emery cloth is readily available and relatively inexpensive in enabling an uncostly solution to an otherwise difficult problem. It is, of course, anticipated that other materials'such as felt metal, sandpaper, etc., could also be used depending on the air velocity and volume of air passage with which it is to be utilized. By a relatively simple and inexpensive, yet highly efi'ective composition, the invention hereof has effected a substantial improvement in reducing noise levels of such tools enabling these tools to perform at lower than current OSHA standards. While a die grinder has been prominently mentioned for the preferred embodiment, it is not intended as a limitation since the muffler device hereof canobviously be adapted for use in most common forms of pneumatic tools.
Since many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the drawings and specification shall be interpreted as illustrative and not in a limiting sense.
The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:
1. In a pneumatic tool including an air motor, an output drive operably connected to said motor, a compressed air inlet to receive input air for operating said motor, and means defining an exhaust passage for discharging exhaust air from said motor to atmosphere, a muffler situated in said exhaust passage in the flow path of the exhaust air and comprising a predetermined width of a thin flexible base material and a distribution of an abrasive composition fixedly adhering to said base material.
2. In a pneumatic tool according to claim 1 in which said muffler also includes an adhesive overcoating said abrasive composition.
3. In a pneumatic tool according to claim 2 in which said adhesive overcoating is of a thickness of about 0.001 inches or less.
fleet the sound waves about the exhaust cavity in which the muffler device is situated.
4. In a pneumatic tool according to claim 1 in which said abrasive composition has a coarseness range of about 100 grit to 200 grit.
5. In a pneumatic tool according to claim 4 in which the coarseness of said abrasive composition is about 150 grit.
6. In a pneumatic tool according to claim 5 in which said muffler comprises an annular ring, at least a portion or which is U-shaped in cross section.
7. In a pneumatic tool according to claim 4 in which said mufiler comprises emery cloth.
8. In a pneumatic tool according to claim 4 in which said muffler comprises sandpaper.
9. In a pneumatic tool according to claim 7 in which said emery cloth is folded over and loosely fitting within said exhaust passage.