Eccentric element for silencing tool and method

Abstract

A method and a means for silencing the noise generated by a vibrating impact transmitting tool such as a pneumatic hammer operated chisel, pick, spade or ballast tamper in which an elastomeric damping element in saddle-like manner is clamped fast eccentrically to a shaft portion of the tool by an encasing metallic sleeve. The sleeve is slipped over and past a retaining collar on the tool and bent along lines longitudinal thereto in order to provide a firm radial grip around the damping element and shaft portion.

Description

The invention relates generally to silenced percussion tools and more particularly to silenced percussion tools of the type incorporating a shank and a working section with a shaft portion located therebetween and adapted to transmit impacts from said shank to said working section whereby the tool is caused to vibrate and to produce noise. The noise is combated by a damping element contiguous with the shaft portion and affixed to the tool.

In hitherto presented constructions of the abovementioned character the damping element usually is an elastomeric sleeve which is placed around the shaft portion and kept in place by various means, for example by metallic retaining rings. Normally these solutions when applied to pneumatic hammer operated chisels, picks, spades and similar tools in practical operation lead to rapid destruction of the vibration dampener by reason of excessive penetration of the tool into the working material, especially if such penetration has to be combined with a bending lever movement of the tool. A further disadvantage is that the prior methods for affixing the retaining rings normally have proved to be insufficient to retain the vibration dampener axially on a cylindrical smoothly shaped shaft portion. Therefore, the shaft portion usually has been provided with cost-increasing axial shoulders formed by the opposite ends of a recess on the tool or by a collar therearound against or around which the vibration dampener was squeezed or clamped. In conventional vibration dampeners it furthermore is a time-consuming and cumbersome operation to replace a worn or destroyed vibration dampener after sharpening or reforging of the tool. Finally conventional vibration dampeners in some cases, particularly when the tool is provided with a retaining collar at the shank thereof, incorporates sleeves which for purposes of assembling the dampener have to be passed over the front portion of the tool. This precludes application of such dampeners for silencing integral tools provided with enlarged working sections such as chisels, spades and wedges.

It is the main object of the invention to create a silenced percussion tool in which the vibration dampener is more efficiently protected against harmful contact with and penetration into the working material, particularly when the tool is being operated in the manner of a bending lever. Another object of the invention is to create a silenced percussion tool in which the vibration dampener in a better and more readily exchangeable way can be affixed to a smooth shaft portion of the tool without one having to provide cooperating collars or recesses for the axial retaining of the dampener thereon. A further object is to create a silenced tool in which the vibration damping element is firmly retained and encased by an undivided clamping sleeve applicable from the shank end of the tool past the retaining collar thereon.

SUMMARY OF THE INVENTION

According to one aspect of the invention there is provided a method for silencing a percussion tool by affixing a vibration damping element in contiguous relation thereto, said tool incorporating a shaft portion and a retaining collar adjacent thereto, the method comprising slipping an undivided substantially cylindrical metallic sleeve over said vibration shaft portion past said collar, encasing said damping element between said sleeve and said shaft portion in eccentric mass relation to said shaft portion, and thereupon bending said sleeve locally at at least a portion thereof peripherally spaced from the portion of said sleeve opposite to a large mass portion of said vibration damping element and along lines extending longitudinally thereof for shrinking said sleeve radially to fixedly circumclamp said vibration damping element to shaft portion.

According to another aspect of the invention there is provided a silenced percussion tool comprising a shank, a retaining collar adjacent the shank, a working section, a shaft portion disposed between said collar and said working section for transmitting impacts therebetween whereby the tool is caused to vibrate and to produce noise, a vibration dampener on said shaft portion axially spaced from said collar and incorporating a vibration damping element which in saddle-like manner eccentrically straddles one side of said shaft portion for silencing said noise, and means for affixing said damping element to said tool in simultaneous unilateral surface contact and eccentric mass relation thereto.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other purposes of the invention will become obvious from the following description and from the accompanying drawings in which three embodiments of the invention are illustrated by way of example. It should be understood that these embodiments are only illustrative of the invention and that various modifications thereof may be made within the scope of the claims following hereinafter.

In the drawings, FIG. 1 shows an upper view of a spade tool according to the invention. FIG. 2 shows a side view and FIG. 3 a fragmentary upper view of a silenced ballast tamping tool according to the invention. FIG. 4 is an enlarged fragmentary longitudinal section and side view of the shaft portion of the tool in FIGS. 1-3. FIG. 5 is a cross section of the tool in FIG. 4. FIG. 6 shows the tool according to FIG. 1 in operation. FIG. 7 shows in a fragmentary side view the shaft portion of a tool with a modified vibration dampener thereon shown in longitudinal section. FIG. 8 is a cross section through the tool in FIG. 7. FIG. 9 is a top view of the tool in FIG. 7. FIG. 10, finally, is a cross section corresponding to FIGS. 5, 8 but through a modified tool.

DETAILED DESCRIPTION OF ILLUSTRATED EMBODIMENTS

The tools in FIGS. 1- 3 are provided with a shank 1, a working section 2 which in FIG. 1 is a spade and in FIGS. 2, 3 a ballast tamping blade, and a shaft portion 3 located between the shank 1 and the working section 2. The shank 1 receives impacts from a hammer, preferably a percussive machine such as for instance a pneumatic hammer 4 provided with a conventional impact motor, not illustrated in more detail in the figures. The front end of the percussive machine 4 receives the shank 1 as shown in FIG. 6 and embraces by means of an aside-swingable tool holder 5 a rear part of the shaft portion 3 in front of a circumferential collar 6 arranged between the shank 1 and the rear part of the shaft portion 3.

When the percussive machine 4 is running, its impact motor will deliver impacts against the shank 1. The shaft portion 3 transmits the impacts to the working section 2 and the tool is thereby set in noise-producing vibrations. In order to combat the noise the shaft portion 3 is provided with one or more vibration dampeners 7 of a novel type appearing in more detail in FIGS. 4 and 5 respectively.

The vibration dampener 7 comprises a damping element in the form of a rubber or elastomeric cushion 8 which has a thickness preferably exceeding half the thickness of the shaft portion 3. The rubber cushion 8 straddles the shaft portion 3 in saddle-like manner eccentrically and is clamped unilaterally thereagainst by means of a metallic sleeve 10 preferably of steel. The sleeve 10 encases the rubber cushion 8 and has one or more, preferably two, longitudinal compressing ridges or loops 11, 12 which project in transverse outward direction of the tool for purposes of enabling clamping of the rubber cushion 8 unilaterally to the shaft portion 3 by shrinking together of the partly-cylindrical portions 13, 14 of the sleeve 10 which are located between the ridges 11, 12. The compression of the ridges 11, 12 is carried out by bending the sleeve 10 along longitudinal lines at the base of the ridges with a double pair of tong jaws by means of which the ridges 11 and 12 are simultaneously compressed thereby squeezing the portions 13, 14 towards each other with great power. In order to avoid direct metallic contact between the portion 14 and the shaft portion 3, a thin frictional coating or liner (of plastic or rubber) with a thickness in the order of 0.5 mm, can be applied before clamping on or between the elements 14 and 3 as has been indicated by numeral 15 in FIG. 4.

The ridges 11, 12 project laterally relative to the tool, FIG. 5, and are disposed adjacent the interface between the damping element 8 and the shaft portion 3. During operation, therefore, the compressing loops 11, 12 and the damping element 8 will normally not encounter compact unbroken portions of the working material. Unbroken working material will normally affect the vibration dampener 7, FIG. 7, only at its strongest point, i.e. the one where bending the frictional forces are transmitted via the side portion 14 of the sleeve 10 directly to the shaft portion 3. The coating 15, FIG. 4, assists in such direct transmission and in preventing undesirable axial displacements of the vibration dampener 7.

In case of need, several encasing sleeves 10 can be utilized and clamped adjacent each other to protect one common vibration damping element 8 as has been indicated by the dashed dividing line 16 in FIG. 4.

As evident from FIG. 2, several metallically protected and encased vibration dampeners 7 can be utilized simultaneously on the shaft portion 3. In this connection the number of damping elements 7 is chosen so that one obtains the most efficient silencing with respect to the working conditions of the tool. The operational conditions and the type of tool and hammer to be used are decisive for how big a part of the shaft portion that on the whole can be used for the disposition of vibration dampeners. The silencing effect as such is determined by the fact that the tool like a tuning fork is being silenced by the vibration dampener suppressing the vibrations thereof.

In the embodiment according to FIGS. 7-9 the damping element 7 again comprises of a rubber or elastomeric cushion 8 which in saddle-like manner is kept in place by a modified protecting and encasing sleeve 20. The latter is a metallic sleeve, preferably of steel, with cylindrical initial shape. The sleeve 20 has an internal perimeter somewhat larger than the perimeter of the collar 6. While in cylindrical state, the sleeve 20 is moved over the collar 6, not shown, in FIGS. 7-9 but appearing in FIGS. 1, 2 and 6, and is thereupon squeezed to oval shape. At the desired place on the shaft portion 3 the rubber cushion 8 is then pushed into the sleeve 20 and a friction liner 17 is inserted into the sleeve 20 at the opposite side of the shaft portion 3, FIG. 8. The liner 17 comprises of friction material of brake lining type, for example incorporating asbestos fibres in rubber as a carrying material and may have a thickness of at most 2 mm. It should have a hardness of about 90.degree.IRH and such floatability under compression that the surface irregularities in the shaft portion 3 and the sleeve 20 are filled out during final setting of the sleeve 20.

The rubber cushion 8 preferably is comprised of silicone rubber with a hardness in the order of 75.degree.IRH. Silicone rubber has good vibration damping properties and high resistance to heat. The heat resistance is important in the present application because of the damping element generating heat in the course of damping. Since silicone rubber has a low coefficient of friction, the rubber cushion 8 is preferably glued by a suitable adhesive in place against the shaft portion 3 and the inner surface of the sleeve 20. In case of need the liner 17 may be coated with adhesive, as well, for instance by phenolic resin glue.

With the elements 8, 17 in place in the oval sleeve 20, the latter by means of a suitable tool is provided with a local inward bend or ridge 18 along lines extending longitudinally of the sleeve 20. The ridge 18 is directed towards and into the rubber cushion 8. Alternatively two or more similar bends or ridges may be provided adjacent each other. Due to the resulting deformation, the sleeve 20 is shrunk radially and there is attained a strong attachment of the components 8, 17 and 20 to the shaft portion 30. By applying adhesive prior to bending, the binding together of the involved components is further promoted.

The ridge 18 protruding into rubber cushion 8 eliminates the need of lateral compression ridges 11, 12 for the vibration dampener 7 shown in FIGS. 4 and 5, whereby a more compact and stronger embodiment is attained. The openings 21 between the rubber cushion 8 and the liner 17 promote cooling by ventilation.

Silencing can be attained with fairly good results also in the simplified embodiment illustrated in FIG. 10 in which the cushion 8 of suitable rubber, for example natural or silicone rubber, is vulcanized fast to the shaft portion 3 along the material portion designated by numeral 22. For better fixation the shaft portion 3 may be provided with one or possibly several upwardly forged ribs 23. In this embodiment the clamping sleeve for the rubber cushion 8 is dispensed with, the rubber cushion 8 then, however, receiving less protection during work.

Claims

What I claim is:

1. A method for silencing a percussion tool by affixing a vibration damping element in contiguous relation thereto, said tool incorporating a shaft portion and a retaining collar adjacent thereto, the method comprising:

passing an undivided substantially cylindrical metallic sleeve over said shaft portion past said collar;

encasing a vibration damping element between said sleeve and said shaft portion in eccentric mass relation to said shaft portion over substantially the whole length of said sleeve and over substantially the whole length of said damping element in the axial direction of said shaft portion; and

thereupon bending said sleeve locally at at least one portion thereof peripherally spaced from the portion of said sleeve opposite to an eccentric mass portion of said vibration damping element and along at least one line extending longitudinally thereof for shrinking said sleeve radially to fixedly circumferentially clamp said vibration damping element to said shaft portion with said vibration damping element disposed in said eccentric mass relation to said shaft portion.

2. A method according to claim 1 further comprising clamping a retaining liner between said sleeve and said shaft portion in opposite position to said eccentric mass portion of said vibration damping element.

3. A method according to claim 1 further comprising locally bending said sleeve adjacent an interface between said vibration damping element and said shaft portion.

4. A method according to claim 1 further comprising locally bending said sleeve by forming at least one longitudinal ridge along its full length and depressed into said eccentric mass portion of said vibration damping element.

5. A method according to claim 1 wherein said vibration damping element straddles in a saddle-like manner substantially only one circumferential side of said shaft portion and comprising locating a retaining liner between said shaft portion and the portion of said sleeve opposite to said vibration damping element.

6. A silenced percussion tool comprising:

a shank;

a retaining collar adjacent said shank;

a working section;

a shaft portion disposed between said collar and said working section for transmitting impacts therebetween, whereby the tool is caused to vibrate and to produce noise;

a vibration dampener on said shaft portion and axially spaced from said collar, said vibration dampener including a vibration damping element comprising a large mass portion extending substantially over the whole length thereof which large mass portion straddles in saddle-like manner only a portion of the circumference of said shaft portion for silencing said noise; and

means extending axially of said shaft portion and being substantially coextensive with said vibration damping element in the axial direction of said shaft portion for affixing said vibration damping element to said tool in simultaneous unilateral surface contact and with said large mass portion in eccentric mass relation thereto.

7. A silenced tool according to claim 6 in which said vibration damping element is an elastomeric cushion with a thickness exceeding half the thickness of said shaft portion.

8. A silenced tool according to claim 6 in which said affixing means includes at least one sleeve encasing said vibration damping element and circumferentially clamping said vibration element to said shaft portion;

and in which a retaining liner is disposed between said shaft portion and the portion of said sleeve opposite to said vibration damping element.

9. A silenced tool according to claim 8 in which said sleeve has at least one longitudinal inwardly directed ridge along its full length and depressed into said large mass portion of said vibration damping element for clamping said sleeve therearound and around said shaft portion.

10. A silenced tool according to claim 8 in which said sleeve has at least one outwardly directed ridge thereon adjacent the interface between said vibration damping element and said shaft portion, said at least one ridge being depressable for clamping said sleeve around said vibration damping element and shaft portion.

11. A silenced tool according to claim 8 wherein said friction liner and said vibration dampening element are dimensioned so as to form a space therebetween, said void space also being bounded by said sleeve and a portion of the outer periphery of said shaft portion.

12. A silenced tool according to claim 6 wherein said vibration damping element straddles substantially only one circumferential side of said shaft portion.

13. A silenced percussion tool comprising:

a shank;

a retaining collar adjacent said shank;

a working section;

a shaft portion disposed between said collar and said working section for transmitting impacts from said shank to said working section whereby the tool is caused to vibrate and to produce noise;

a vibration dampener on said shaft portion and axially spaced from said collar, said vibration dampener including a vibration damping element comprising a large mass portion which in saddle-like manner eccentrically straddles a portion of the circumference of said shaft portion for silencing said noise;

at least one undivided metallic sleeve having an internal perimeter larger than the perimeter of said collar and for circumferentially clamping said vibration damping element to said shaft portion for affixing said vibration damping element to said tool in unilateral surface contact therewith, and with said vibration damping element confined to substantially one side of said shaft portion; and

a friction liner clamped between said shaft portion and the portion of said sleeve opposite to said vibration damping element.

14. A silenced tool according to claim 13 in which said sleeve has at least one longitudinal inwardly directed ridge along its full length and depressed into said large mass portion of said vibration damping element for clamping said sleeve therearound and around said shaft portion.

15. A silenced tool according to claim 13 wherein said friction liner and said vibration dampening element are dimensioned so as to form a space therebetween, said void space also being bounded by said sleeve and portion of the outer periphery of said shaft portion.

16. A method for silencing a percussion tool by affixing a vibration damping element in contiguous relation thereto, said tool incorporating a shaft portion and retaining collar adjacent thereto, the method comprising:

passing an undivided substantially cylindrical metallic sleeve over said shaft portion past said collar;

encasing a vibration damping element between said sleeve and said shaft portion in eccentric mass relation to said shaft portion with said vibration damping element straddling in a saddle-like manner substantially only one circumferential side of said shaft portion;

locating a retaining liner between said shaft portion and the portion of said sleeve opposite to said vibration damping element; and

thereupon bending said sleeve locally at at least one portion thereof peripherally spaced from the portion of said sleeve opposite to an eccentric mass portion of said vibration damping element and along at least one line extending longitudinally thereof for shrinking said sleeve radially to fixedly circumferentially clamp said vibration damping element to said shaft portion with said vibration damping element disposed in said eccentric mass relation to said shaft portion.

17. A silenced percussion tool comprising:

a shank;

a retaining collar adjacent said shank;

a working section;

a shaft portion disposed between said collar and said working section for transmitting impacts therebetween, whereby the tool is caused to vibrate and to produce noise;

a vibration dampener on said shaft portion and axially spaced from said collar, said vibration dampener including a vibration damping element comprising a large mass portion which in saddle-like manner straddles substantially only one circumferential side of said shaft portion for silencing said noise; and

means for affixing said vibration damping element to said tool in simultaneous unilateral surface contact and with said large mass portion in eccentric mass relation thereto.