Abstract:
A piston for a setting tool and including a piston head ( 10 ) having a hollow-chamber ( 12 ) adjoining opening ( 11 ) formed in the end surface of the piston head, and a stopper ( 20 ) securable in the hollow chamber ( 12 ) of the piston head ( 10 ) with a solder seam for closing the opening ( 11 ), a centering element ( 23 ) provided on an outer circumference of the outer surface ( 22 ) of the stopper ( 20 ).

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a piston for a setting tool and including a piston head having, in its combustion chamber-side end, an opening, and a hollow chamber adjoining the opening, and a stopper securable in the hollow chamber of the piston head with a solder seam for closing the opening. 
     2. Description of the Prior Art 
     In setting tools, a piston is displaceably supported in a hollow chamber. The piston is driven as a result of an explosive combustion of an appropriate fuel in the combustion chamber of a setting tool. With its setting direction side end, the piston engages a fastening element, which is located in a pin guide of the setting tool, and drives the fastening element into a, e.g., constructional component. 
     In combustion-engined setting tools, because of weight consideration, the piston is formed hollow and is closed with a stopper. The stopper is secured at the end of the piston hollow chamber by a soldering connection. In a conventional piston, it often happens that the stopper is not adequately centered. As a result, upon the soldering of the stopper in the hollow chamber, the solder seam is not uniform. The soldering connection is subjected to high loads as a result of action of high dynamic and thermal loads on the piston during the operation of the setting tool. The non-uniformity of the solder seam can lead to a premature breaking of the soldering connection and to the loss of the stopper. 
     Accordingly, an object of the present invention is to provide a setting tool piston in which the non-uniformity of the solder seam, which connects the stopper with the piston head, is prevented. 
     SUMMARY OF THE INVENTION 
     This and other objects of the present invention, which will become apparent hereinafter, are achieved by providing centering means on the outer surface of the stopper. 
     The provision of the centering means on the circumference of the outer surface of the stopper, e.g., in form of knurling or a plurality of projections insures a concentric arrangement of the stopper in the hollow chamber of the piston head and, thereby, a formation of a soldering gap around the outer circumference of the stopper and which provides, at all of the points of the stopper circumference, similar geometrical conditions for a capillar effect between the piston head and the outer circumference of the stopper. The present invention noticeably reduces amount of rejects during manufacturing of hollow pistons. Further, the present invention increases the service life of the piston as in each case, a stable soldering connection can be achieved. 
     According to an advantageous embodiment of the present invention, the outer diameter of the centering means, which is formed e.g., as a knurling, is somewhat greater than the inner diameter of the hollow chamber of the piston in the stopper insertion region. This insures that the stopper cannot move during the assembly and the soldering process. The present invention ensures precise and quality manufacturing of the piston resulting in a quality end product. 
     According to the present invention, the stopper is provided with a solder repository, which can also be formed at the opening in the piston head or in the hollow chamber of the piston head. The solder repository prevents deposition of the excess solder, during the soldering process, on the finished, continuous end surface of the stopper which, otherwise, would have to be subjected to additional treatment. The elimination of the additional treatment of the end surface of the stopper after soldering reduces manufacturing costs. 
     The novel features of the present invention, which are considered as characteristic for the invention, are set forth in the appended claims. The invention itself, however, both as to its construction and its mode of operation, together with additional advantages and objects thereof, will be best understood from the following detailed description of preferred embodiment, when read with reference to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the Drawings: 
     FIG. 1 shows a side, partially cross-sectional view of a piston according to the present invention with a stopper; and 
     FIG. 2 a longitudinal, cross-sectional view of the piston shown in FIG. 1 with the inserted stopper. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A piston according to the present invention for a setting tool, which is shown in FIGS. 1-2, has a hollow piston head  10  and a piston skirt  13  (shown only partially). In the end side of the piston head  10 , an opening  11  is formed. A hollow chamber  12  is located behind the opening  11 . The hollow chamber  12  has a front region  18  and a rear region  17 . The rear region  17  of the hollow chamber  12  has a smaller inner diameter than the diameter of the front region  18 . In the transition region between the front region  18  and the rear region  17 , the wall  15  of the piston has a conical annular surface  16 . 
     According to the present invention, the piston has a stopper  20  having, in the embodiment shown in the drawing, a continuous end surface  21 . The stopper  20  further has, in the embodiment shown in the drawings, a cylindrical outer surface  22 . Outside of the outer surface  22 , in the region adjacent to the outer end surface of the stopper  20 , a circumferential knurling is provided. In the embodiment shown in the drawings, the outer diameter  24  of the stopper  20  in the region of the knurling  23  is greater than the inner diameter  14  of the hollow chamber  12  in the region of the opening  11  in the front region  18 . During the assembly of the piston, the stopper  20  is inserted in the front region  18  of the piston by being displaced in the direction shown with arrow  28 . The stopper  20  is insertable into the hollow chamber  12  until a conical annular surface  26 , that adjoins the outer surface  22  of the stopper, engages the conical annular surface  16  provided in the wall  15  of the piston. The knurling  23  insures a precise uniform distribution of a solder gap  29  between the outer surface  22  of the stopper  20  and the piston wall  15 . In the embodiment shown in the drawings, the solder gap  29  has, e.g., a width of 0.1 mm with a tolerance of +/−0.02 to 0.05 mm. The knurling  23  has a height of 0.15 mm above of the outer surface  22 . The difference of 0.05 mm between the height of the knurling  23  and the solder gap  29  provides for a press fitting of the stopper  20  in the hollow chamber  12  of the piston. Thereby, an inadvertent displacement of the stopper  20  in the hollow chamber  12  of the piston head  10  during a soldering process is prevented. The soldering seam, which insures securing of the stopper  20  in the hollow chamber  12  of the piston head  10 , is not shown in the drawings. 
     Conveniently, a solder repository  24  is provided on the stopper  20 . The repository  25  is formed by an inter space between a conical annular surface  27  in the region of the end surface  21  of the stopper  20  and the piston wall  15  in the region of the opening  11  in the end surface of the piston. In the repository  25 , an excess solder can accumulate during the soldering process, so that it would not flow along the end surface  21  of the stopper  20 . This simplifies the assembly of the piston, as a solder on the outer end surface of a stopper should be remove by a subsequent manufacturing process. 
     Though the present invention was shown and described with references to the preferred embodiment, such is merely illustrative of the present invention and are not to be construed as a limitation thereof and various modifications of the present invention will be apparent to those skilled in the art. It is therefore not intended that the present invention be limited to the disclosed embodiment or details thereof, and the present invention includes all variations and/or alternative embodiments within the spirit and scope of the present invention as defined by the appended claims.