Abstract:
An impact tool has a vibration damper which vibration damper comprises an envelope which surrounds a working part of the tool and thereby encloses a liquid-like material having damping properties. The liquid-like material is enclosed in a bag for easier handling.

Description:
The present invention relates to impact tools comprising a vibration damper for damping lateral vibrations of a working part of the tool. Examples of such tools are breakers for breaking up concrete pavements and the like, spades and chisels of different kinds and drill rods for rock drilling. 
     A tool of the above mentioned kind is designed to transfer considerable impact energies in its longitudinal direction from an impact machine, to which the tool is connected, to the material being worked. In order to damp the emission of sound from the tool, caused by lateral vibrations of the tool, one has earlier used either sleeves of rubber or plastic surrounding the tool or channels in the tool filled with damping material e.g. certain metal alloys or sand. 
     SUMMARY OF THE INVENTION 
     According to the present invention the vibration damper comprises an envelope which surrounds the working part of the tool, preferably along a shorter part of its length, and encloses a liquid-like material. The envelope encloses a bag containing the liquid-like material. Liquid-like material hereby refers to a liquid with or without admixtures. A liquid is hereby defined as a body having an indefninite form but a definite volume. As examples of suitable liquid-like materials one could mention unvulcanized silicon rubber, silicon grease, oils and other liquids containing dispersed or dissolved polymeric material or dispersed solid material e.g. iron powder. 
     By means of the present invention a more even distribution of heat is obtained in the damper than in rubber or plastic dampers, which results in a lower temperature and thereby a longer service life. The rubber material in rubber dampers often reaches such a high local temperature that it is broken down. A tool according to the present invention is considerably cheaper in manufacture than those tools which are provided with internal channels filled with damping material. 
     According to a preferred embodiment of the invention the liquid-like material in the vibration damper comprises a liquid which hardens when in contact with oxygen or humid air. The vibration damper is in this way made self-sealing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows an embodiment of the invention. 
     FIG. 2 shows a part of the tool according to FIG. 1 comprising a detachable collar; 
     FIG. 3 shows another part of the tool of FIG. 1 comprising the vibration damper; 
     FIG. 4 shows a section along the line 4--4 in FIG. 2. 
     FIG. 5 shows a section along the line 5--5 in FIG. 3. 
     FIG. 6 shows a bag containing a liquid-like material; and 
     FIG. 7 shows a section according to 7--7 in FIG. 6. 
    
    
     DETAILED DESCRIPTION 
     The tool according to FIG. 1 comprises a working part 10 which is surrounded by a vibration damper 13 shown in greater detail in FIG. 3. The working part comprises a shank 11 meant to be put into a (not shown) impact machine and a working end 12 in form of a spade. The tool is furthermore provided with a collar 14, shown in greater detail in FIG. 2, for restricting the movement of the tool into the machine. The detachable collar according to FIGS. 2 and 4 comprises an elastic body 40 provided with an annular round 42 and a metal ring 41 or spring. By means of the round 42 the collar 14 is locked to cut-outs 20 in the tool by means of snap action when the collar is pushed onto the tool. The ring 41 guarantees that the collar is kept steadily in place. The vibration damper according to FIGS. 3 and 5 comprises an envelope 30 of elastic material which at its ends is provided with annular rounds 37. By means of these rounds and rings or springs 31 the envelope 30 is locked to cut-outs 21 in the tool as described above in connection with the collar 14. A bag 32, shown more in detail in FIGS. 6 and 7, containing a liquid-like material 33 is situated between the envelope 30 and the working part 10 of the tool. As is shown in FIG. 1 the damper 13 surrounds the working part 10 only along a part of its length. 
     The bag 32 shown in FIGS. 6 and 7 is made from a plastic hole-like structure which by means of weldings 34 has been closed at the ends. The bag 32 has furthermore been divided into three sections 36 by means of weldings 35, through which an even distribution of the liquid-like material 33 around the working part 10 of the tool is guaranteed. The manufacture of the bags can easily be automated if two foils are used as initial material. These are then welded together along the sides so that a hose-like structure is formed immediately below the filling place. The filled hose is then provided with transverse weldings as shown in FIGS. 6 and 7. The hose is then cut into suitable lengths. The bag is shown in the drawing as divided into three sections but can of course have another number of sections. 
     In case the damper 13 is to be used for damping the sound of drill rods or other tools which penetrate into the material being worked the ends of the enevelope 30 can be made bevelled in order to decrease the wear. The vibration damper could also be made such that it surrounds the main part of the working part of the tool. 
     The sleeve 30 shown in FIG. 3 is made of plastic but can of course be made of another material since its purpose is to enclose and protect the bag 32 in which the vibrations are damped because of the internal work. 
     The above described and in the drawings shown embodiments of the invention are only to be regarded as examples which can be modified within the scope of the subsequent claims.