The present Application claims priority from Italian Patent Application No. TO2010A001023 filed on Dec. 20, 2010, the contents of which are incorporated in this disclosure by reference in their entirety.
1. Field of the Invention
The present invention refers in general to percussion tooling that can be used in perforation, demolition or excavation operations.
2. Background Art
Known percussion tools of the type mentioned above comprise a first portion, that, when operating, is housed at least partly inside the hammer, and a second portion that includes a working bit. Normally, such tools are manufactured in a single piece of a material, typically steel, chosen in order to satisfy a compromise between two opposite needs. In fact, the first portion of these tools, whose upper end is cyclically subjected to impacts of a high amount due to the percussion action performed by a beating mass moving inside the hammer, requires a mean hardness and a high flexural strength and a high resistance to impacts, and therefore a good elastic resistance. The second portion of such tools, that is subjected to impacts against the material to be demolished, requires a high hardness and toughness and a high resistance to hot wear. Since such known tools are made in a single piece, steel used for making them is chosen in order to be able to simultaneously satisfy the required requirements for both above portions, and therefore has not wholly optimum characteristics either for the first or for the second portion. In particular, for the whole tool, steels are used that are alloyed with elements such as nickel, molybdenum, chromium, vanadium and similar metals, many of which, being rather costly, affect the global tool cost.
It would instead be desirable to be able to have tools available of the above-defined type whose material has different characteristics for each portion, so that the two portions are suitable for supporting the types of specific stresses to which each one of them is subjected during use.
In principle, it can be deemed that the first portion of the tool provides a contribution approximately for 85% of the weight, while the second portion, equipped with the working end, gives a contribution approximately for 15% of the weight. The two tool portions could be made separately with different materials, each one chosen to optimally bear its related stresses. In this way, the first portion could be made of a chromium-molybdenum or chromium-manganese alloyed steel, relatively inexpensive, while the second portion could be made of a highly specialized steel, with high resistance to hot wear, for example alloyed with tungsten and cobalt, and therefore relatively more expensive but only in relation to a small part of the tool.
In this way, much better tool performances could be obtained with greater reliability and use length, at a lower cost than the one required for making the tool wholly with a high-performance steel alloy.
There is anyway the problem, having a difficult solution, of managing to guarantee a connection of these two portions that is rigid, stable in time and reliable. In particular, the most common types of connection, for example of the screw and nut screw type, are absolutely unsuitable to resist in time to the high pulse stresses to which a tool of the type herein described is subjected.
Document BE-A-440648 discloses a percussion tool according to the prior art.
In particular, object of the invention is proposing a tool of the above-defined type, whose two portions are each one made of an optimum material for bearing the stresses applied thereto during use, and that are mutually connected in a high reliable and lengthy way.
This object is obtained due to a tool having the characteristics mentioned in the enclosed claims.
In particular, according to the invention, the two tool portions are made of mutually different materials, and are mutually rigidly connected by means of a connection member that can be applied outside the two portions, both portions having formations adapted to be engaged by corresponding formations of the connection member.
Due to this arrangement, each one of the two tool portions is made of a material that allows optimally bearing the stresses applied during use, and therefore the tool length is strongly increased. Moreover, the connection member allows rigidly connecting its two portions in a wholly reliable way. Since the two portions are mutually connected, it is also possible, according to needs, to replace only one of the two portions, after having removed the connection member.
According to a preferred feature of the invention, the connection member is a metallic ring.
In this way, the connection member is composed of an element that is simple and inexpensive to make.
According to another preferred feature of the invention, the two tool portions have respective circumferential grooves next to the related ends aimed to be mutually connected, whose grooves are aimed to be engaged by corresponding radial ribs of the metallic ring.
Further characteristics and advantages of the invention will more clearly result from the following detailed description, provided as a non-limiting example and referred to the enclosed drawings, in which:
With reference firstly to
The tool 10 has a first portion 12 aimed to be housed at least partially inside the body of the demolishing hammer (not shown in the figures), whose upper end (with reference to
The tool 10 further comprises a second portion 16 aimed to be connected to the first portion 12, which has a working end 18, on the opposite part of the portion 12. The end 18 can be shaped differently depending on the type of working to be made and the type of material to be treated, and can therefore be shaped as a chisel, cone, pyramid, or plate.
While the first portion 12 is made of a metallic material, typically steel, with high elasticity characteristics, the second portion 16 is made of a metallic material, also typically steel, with high hardness characteristics and high resistance to hot wear. The portion 12 can be made with a chromium-molybdenum or chromium-manganese alloyed steel, while the portion 16 can be made of tungsten or cobalt alloyed steel.
In order to mutually connect the two portions 12 and 16 in a rigid and reliable way, a connection member 24 is used, preferably shaped as a metallic ring. The ring 24 is applied from outside onto the two portions 12 and 16 after having placed them in contact next to respective ends 12a and 16a.
In particular, next to the two ends 12a and 16a of the two portions 12 and 16, engagement formations are obtained, typically circumferential grooves 20 and 22, that can be engaged by corresponding formations, typically annular ribs composed of radial collars 26 and 28 of the ring 24.
Preferably, the grooves 20 and 22 have a slightly tapered cross section in order to be converging towards the general axis of the tool 10, and/or tapered edges, in order to decrease the stress concentration next to the related edges and to enable the engagement of collars 26 and 28 therein. The collars 26 and 28 of the ring 24 conveniently have a cross section corresponding to the related grooves 20 and 22.
In order to allow applying the ring 24 next to the ends 12a and 16a of the portions 12 and 16, it has at least one opening aimed to be closed after assembling onto the tool 10.
According to a first variation of the ring 24 and with reference to
The openings 30 can have different shapes, for example extending axially or diagonally, in this latter case in order to increase the length of the contact surfaces between the ends of the various sectors of the ring 24 and to distribute the load also along a tangential component.
According to a variation shown in
In any case, the connection member 24, 24a, 24b or 24c can be removed to allow, if needed, replacing one of the portions 12 or 16, in the most common case the second portion 16 following the wear of the working bit 18. After having replaced the affected portion, the removed connection member can be re-used, or a new connection member can be used as replacement of the previous one.
In order to guarantee a correct and accurate mutual positioning of the two ends 12a and 16a, they preferably have respective radial centering formations. For such purpose, at the axial end 12a of the portion 12, a recess 32 can be formed, for example with a cylindrical shape, while from the axial end 16a of the portion 16 a corresponding projection 34 can extend, or vice versa. In the most common case, both recess 32 and projection 34 will have a circular shape and their edges will have fitting areas 36 to avoid the stress concentration. Alternatively, the recess 32 and the projection 34 can be shaped in such a way as to prevent the relative rotation of the two portions 12 and 16, in which case they can have a triangular, squared, hexagonal, cross-like or star-like shape, or any other shape useful to obtain such result.
In this way, the mutual centering of the two ends 12a and 16a is guaranteed by the engagement of the projection 34 into the recess 32.
Although the present invention has been discussed in considerable detail with reference to certain preferred embodiments, other embodiments are possible. Therefore, the scope of the appended claims should not be limited to the description of preferred embodiments contained in this disclosure.
Number | Date | Country | Kind |
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TO2010A1023 | Dec 2010 | IT | national |
Number | Name | Date | Kind |
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398308 | Barth | Feb 1889 | A |
431239 | Walter | Jul 1890 | A |
480979 | Turner | Aug 1892 | A |
752180 | Rauscher | Feb 1904 | A |
1355793 | Bernay | Oct 1920 | A |
3807804 | Kniff | Apr 1974 | A |
4804231 | Buljan et al. | Feb 1989 | A |
Number | Date | Country | |
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20120153706 A1 | Jun 2012 | US |