Muffled tool for vibratory or impact machines

[57] ABSTRACT

A tool for vibratory or impact machines, having a collar of vibration dampening material mounted around the tool body for reducing or muffling tool noise occurring during operation of the machines. The collar should be located at least around the point of maximum lateral amplitude of the tool body during operation of the machine, and may be enclosed in a casing or otherwise secured to the tool body.

Claims, 4 Drawing Figures

PATENTED ΜΑΠ 6 1972

3.662,855

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ATTORNEY

3,662,855

MUFFLED TOOL FOR VIBRATORY OR IMPACT MACHINES

BACKGROUND OF THE INVENTION

The present invention relates to tools for use in vibratory or impact machines such as, for example, paving breakers, rock drills, riveters, and rammers and more particularly to the reducing or muffling of the tool noise occurring during operation of such machines.

During the operation of a machine of this type (such as, for example, a paving breaker), impulses or vibrations are communicated to a tool which resultantly vibrates both flexurally and axially. Both of these types of vibrations contribute to cause noise to be generated, the former due to the direct sidewise action on the surrounding air and the latter by the associated changes in lateral dimensions due to Poisson’s ratio. The noise created by the axial vibrations of the ends of the tool are, however, to a great extent muffled in that these ends are enclosed. Hence, the primary source of the tool noise is 20 caused by the lateral vibrations of the tool.

Studies have indicated that the noise level due to vibration is not steady but rather reaches a peak with each impact and then dies away. The greater the dampening or muffling that can be applied, the lower the mean noise level, particularly in 25 the event that the peaks of the noise level can also be reduced in level.

SUMMARY OF THE INVENTION

An object of the present invention is to provide such a tool with new and improved means particularly constructed and arranged to muffle the noise generated by the lateral vibrations of the tool occuring during operation of the machine.

Another object of the invention is to provide such a tool with new and improved means of the type set forth particularly adapted to muffle without adversely affecting either the efficiency of the tool and/or its suitability for its intended purpose.

Another object is to provide such a tool with new and improved means of the type set forth which, although relatively simple and economical in construction, is highly efficient in operation.

These objects, and other objects and advantages of the invention which will become apparent from the following 45 description taken in connection with the accompanying drawings, may be attained by the construction of the tool to comprise a tool body and a collar of vibration dampening material mounted on the tool body to extend around the tool body at least at the point of maximum lateral amplitude of the 50 tool body during operation of the machine.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an elevational view of a paving breaker provided with a tool constructed in accordance with one embodiment ⁵⁵of the present invention;

FIG. 2 is an enlarged fragmentary perspective view, partially broken away and in section, of the tool shown in FIG. 1;

FIG. 3 is an elevational sectional view on a reduced scale of a paving breaker tool constructed in accordance with another embodiment of the invention; and

FIG. 4 is a view generally similar to FIG. 3, but illustrating a paving breaker tool constructed in accordance with a third embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring more particularly to the drawings wherein similar reference characters designate corresponding parts throughout the several views, FIG. 1 illustrates a paving 70 breaker machine designated generally as 10 which is provided with a tool 12 constructed in accordance with one embodiment of the invention. The machine 10, per se, may be of any suitable conventional construction and in the conventional manner during operation causes impact blows to be delivered 75 parts to the tool 12. The tool 12 comprises an elongated hard-steel tool body 14 having a rearward end 16 receiving the impact blows and a sharpened forward working end 18; and the tool body 14 in the conventional manner is provided adjacent its rearward end 16 with an integral annular circumferential collar 20 which connects the tool 12 to the machine 10.

In the embodiment of the invention illustrated in FIGS. 1 and 2, the tool body 14 is surrounded for a major portion of its length forwardly of the collar 20 by a casing or housing 22 which terminates sufficiently rearwardly of the forward end 18 to permit repeated resharpening of such end 18. The rearward end of the casing 22 abuts the forward end of the collar 20; and the casing 22 is preferably constructed of hardened mildsteel, but may alternatively be constructed of material noted for high dampening such as, for example, manganese-copper high dampening alloy. The casing 22 is preferably, as illustrated, shrunk onto the body 14, but alternatively the casing 22 may be welded or brazed along its entire interfacing to the tool body 14 or crimped to the latter. The abutment of the casing rearward end against the collar 20, as will be understood, serves to prevent the forces acting on the casing 22 during the operation of the machine 10 from urging the casing 22 rearwardly along the tool body 14. The casing 22, as illustrated, has a cylindrical outer circumference and includes a plurality of axial portions of different thicknesses or radial dimensions mating or engaging along their inner circumferences with corresponding portions of the tool body 14.

More particularly, the forward end portion 24 of the casing 30 22 is of greater thickness or radial dimension that more rearwardly portions 26, 28 which are separated by a relatively short enlarged portion 30 of radial cross-section substantially that of the casing portion 24. The tool body 14 includes a portion 32 located immediately forwardly of the collar 20 which > corresponds in diameter to the internal diameter of the casing portion 28 and also a portion 34 located opposite the casing portion 24 which corresponds to the internal diameter of such casing portion 24. Intermediate the tool body portions 32,34, a pair of annular circumferential channels or recesses 36, 38 • are machined into the tool body 14, such recesses 36,38 being separated by a radially outwardly projecting enlarged portion or ridge 44 having an outer diameter corresponding to the inner diameter of the enlarged casing portion 30. Thus, with the casing 22 mounted on the tool body 14, the recesses 36,38 cooperate with aligned annular recesses 40, 42, respectively, in the casing 22 to form a pair of annular spaces or chambers around the tool body 14.

The space formed by one of the cooperating pairs of recesses 38,42 or 36,40 is located to extend circumferentially around the point of maximum lateral amplitude of the tool body 14 during the operation of the machine 10. Also, the space provided by the recesses 38, 42 is axially longer than that provided by the recesses 36,40 to avoid the generation of resonant frequencies. Although the engaging enlarged portions 30, 44 in addition to separating the spaces increase the flexural stiffness of the assembly to increase the permissible lengths of the otherwise unsupported casing portions bounding the outside of the spaces, they provide noise transmission paths. The engaging faces of one or both of the portions 30,44 may be coated with a relatively thin layer of vibration insulant polymer to prevent noise transmission through the portions

Although a degree of noise reduction may be attainable merely by the aforedescribed arrangement of the casing 22, vibration absorbing solid material should be located in the spaces formed by the cooperating recesses 36, 40 and 38,42. As illustrated in FIG. 2, bores 46, 48 are formed radially through the casing 22 in communication with such spaces. Granular solid material such as, for example, dry sand or aluminum oxide powder may be poured into such spaces through the bores 46, 48 to provide the spaces with annular collars of vibration dampening material. It is believed that the introduction of such granular solid material into the spaces is facilitated in the event that a second bore (not shown) is

3,662,855 formed through the casing 22 in communication with each space whereby during the introduction of the granular solid material through the bores 46, 48 suction may be applied to the spaces. It will be understood that, after the spaces are filled with granular solid material, the bores 46, 48 (and also the other aforementioned bores in the event such be provided) are suitably plugged to prevent escape of the granular solid material from the spaces.

Although, as aforedescribed, sand or aluminum oxide powder is preferably employed as the granular solid material, it will be understood that other suitable granular solid materials could be substituted. It is believed, however, that metallic granular materials, such as for example lead or steel shot, should not be employed due to their tendency to yield plastically and to coagulate whereby, as the dampening properties of a granular media are caused by interfacial action between the particles, dampening efficiency is undesirably reduced. Also, alternatively, a polymeric material may be employed in the space in place of the granular material. In this event, the bores 46, 48 could be employed for injection molding the polymer into the spaces and, by way of example, the polymeric material could be synthetic resilient material used for the flexible bushes employed to isolate vehicle springs and shockabsorbers from the vehicle chassis or other high hysteresis polymer material. Also, alternatively, strip polymer material may be wrapped around the tool body 14 in the spaces and employed as the dampening material. In this event, the strip polymer material may be wrapped tightly around the tool body 14 and allowed to creep radially outwardly when the casing 22 is in position. As it is desirable that good contact be made between the polymer and the casing 22 and the tool body 14 an anaerobic curing adhesive may be coated at one or both faces of the polymer. By way of example of laboratory testing of the invention, a table follows indicating the results of 35 such testing.

TABLE —-------------------- ₄₀

Noise Level in Decibels (dB)

<td> machine supply pressure</td><td> unmuffled standard tool</td><td> unfilled manganesecopper casing</td><td> sand filled manganesecopper casing**</td><td> unfilled mild steel casing</td><td> sand filled mild steel casing</td>

<td> 40 psi</td><td> 107 dB</td><td> 93</td><td> 100</td><td> 99</td><td> 94.5</td>

<td rowspan="2"> 60 psi</td><td></td><td> (9)*</td><td> (7)*</td><td> (8)*</td><td> (12.5)*</td>

<td> 109.5</td><td> 100</td><td> 101.5</td><td> 101</td><td> 97</td>

<td rowspan="2"> 90 psi</td><td rowspan="2"> 112</td><td> (9.5)*</td><td> (8)»</td><td> (8.5)*</td><td> (12.5)*</td>

<td> 101</td><td> 103.5</td><td> 103</td><td> 97</td>

<td></td><td></td><td> (11)»</td><td> (8.5)»</td><td> (9)*</td><td> (15)*</td>

•Reduction in noise level * ’Increase in noise level due to heating of material casing during working which is a fault generally when high dampening material is used as the casing material.

FIG. 3, wherein parts corresponding to those aforedescribed with reference to the embodiment of the invention illustrated in FIGS. 1 and 2 are designated by the corresponding reference characters followed by the suffix a, illustrates a tool 12α constructed in accordance with an alternative embodiment of the invention. In the FIG. 3 embodiment, the tool body 14α is provided with a single annular circumferential recess 50 cooperating with a reduced diameter portion 52 of the casing 22α to provide an annular space around the tool body 14α. The recess 50 is particularly formed in the tool body 14α to cause the space to extend around such tool body 14α at the point of maximum lateral amplitude of the tool body 14α during operation of the machine. The space is filled to provide an annular collar of suitable vibration dampening material such as, for example, a polymeric material or the aforedescribed solid granular material. The forward end of the casing 22α in this embodiment terminates adjacent the tool forward working end 18α and may be axially shortened during resharpening of the tool forward working end 18α. It is recognized that during resharpening of the forward working end 18α there will be exposed a less hard ring of casing material ⁵ where the inner portion of its radial thickness is exposed. To avoid this difficulty the casing 22α and tool body 14α may be constructed from different materials and the casing 22α formed from a softer material than the tool body 14α. In this event rather than hardening the casing 22α separately from ⁰ the tool body 14α, the whole formed assembly could be heated and quenched to provide surface hardness and, with suitable combinations of materials apparent to those skilled in the art, resultant relative shrinkage of the casing 22α and tool body ., 14α could be provided to tighten the casing 22α onto the tool body 14α.

FIG. 4, wherein parts corresponding to those aforedescribed with reference to the embodiments of the invention illustrated in FIG. 1, 2 are designated by the cor20 responding reference characters followed by the suffix b, illustrates a tool 12b constructed in accordance with α-other alternative embodiment of the invention. In the FIG. 4 embodiment, the tool body 14b is provided with an annular circumferential recess 54 which extends around the point of max25 imum lateral amplitude of the tool body 14b during the operation of the machine. A collar 56 of rubber or rubber-like material or other suitable vibration dampening material encircles the tool body 14b in the recess 54, the collar 56 being clamped in fixed position to the tool body 14b by a pair of 30 spaced annular clamps 58 extending therearound. In this embodiment of the invention, as illustrated, the collar 56 may be longitudinally split and is of relatively short length to terminate in spaced relationship to the collar 20b and the forward working end 18b of the tool body 14b.

The operation of a tool including the invention is believed to be apparent from the aforegoing description.

Although only three embodiments of the invention have been illustrated and hereinbefore specifically described, it will be understood that the invention is not limited merely to these three embodiments but rather contemplates other embodiments and variations within the scope of the following claims. Moreover, although the invention has been illustrated and hereinbefore described primarily with reference to a paving breaker tool, it will be understood that the application of the ⁴³ invention is not so limited, but rather the invention is equally applicable to other similarly driven tools.