Patent Publication Number: US-8979083-B2

Title: Welding unit for welding rails

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention relates to a welding unit for welding two rails of a track, including two unit parts which are movable towards one another in the longitudinal direction of the rails along guides of the unit by means of displacement cylinders and are each equipped with clamping jaws having contact surfaces intended for application to a rail web. 
     Welding units of this kind are known, for example, from EP 0 132 227 A2 or US 2003/0141283 A1. The clamping jaws have to be pressed onto the rail web with great force in order to be able to move the rails with precision towards one another in their longitudinal direction for the upset stroke finalizing the welding operation. 
     BRIEF SUMMARY OF THE INVENTION 
     It is the object of the present invention to provide a welding unit of the type mentioned at the beginning which enables an improved transmission of great forces to the rail web. 
     According to the invention, this object is achieved with a welding unit of the specified kind by means of the features cited in the characterising clause of the main claim. 
     With the aid of the cylindrical sliding surface, the clamping jaws acquire a small degree of freedom of movement in order to be able to optimally adjust to the position of the rail web in spite of irregularities which may exist due to rail head tolerances, for example. This enables a problem-free transmission of also particularly great forces, such as are required especially for closure welding within the range of a temperature which deviates from the neutral temperature. 
     Additional advantages of the invention become apparent from the dependent claims and the description of the drawing. 
     The invention will be described in more detail below with reference to an embodiment represented in the drawing in which 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         FIG. 1  shows a view of the welding unit with two unit parts movable towards one another, 
         FIG. 2  shows a simplified cross-section of a unit part, 
         FIG. 3  shows a cross-section of clamping jaws abutting on a rail web, and 
         FIG. 4  shows a view of a clamping jaw. 
     
    
    
     DESCRIPTION OF THE INVENTION 
     A welding unit  1 , represented in  FIGS. 1 to 3 , is composed of two unit parts  4  which are displaceable towards one another along guides  3  of the unit with the aid of displacement cylinders  2 . These unit parts  4  are connected in each case to two clamping drives  5  by means of which clamping jaws  6  can be pressed onto rails  7  to be welded to one another. 
     Pull rods  8 , extending parallel to the guides  3  of the unit, are fastened to the first unit part  4  and pass through the second unit part  4 . The two pull rods  8  are connected to a crossbeam  9  to which the two displacement cylinders  2  are articulatedly connected. The clamping drives  5 —extending perpendicularly to a longitudinal direction  10  of the rails—are each equipped, in the region of piston rods  11 , with an opening  12  for passage of the pull rod  8 . 
     As visible particularly in  FIGS. 2 and 3 , each of the clamping jaws  6 —lying opposite one another in a transverse direction  13  of the rails—is supported in a jaw mount  14 . One of these is fixedly connected in each case to the unit part  4 , and the opposite jaw mount  14  is connected to the piston rod  11 . 
     As shown in  FIG. 3 , each clamping jaw  6  has a sliding surface  16 , spaced from a contact surface  15 , which is curved—with respect to a cross-section extending perpendicularly to a neutral axis  17  of the rail  7 —in the shape of a circular arc having a radius R. The jaw mounts  14  provided for fixation of the clamping jaw  6  also have a sliding surface  18  which is curved with the radius R in accordance with the sliding surface  16  of the clamping jaw  6 . Thus, the two sliding surfaces  16 ,  18  form part of a cylindrical surface so that the clamping jaw  6  is movable in each case relative to the jaw mount  14  about the neutral axis  17 . 
     The connection of each clamping jaw  6  to the associated jaw mount  14  is accomplished by means of a screw  23  which, having a correspondingly shaped head, enables the said rotatability of the clamping jaw  6  over a range of approximately 1 to 2 degrees. 
     As can be seen in  FIGS. 2 and 3 , the jaw mount  14  lying opposite the clamping drive  5  is connected to a stop bar  19  extending parallel to the longitudinal direction  10  of the rails. With this, the rails  7  to be welded can be lined up in a joint alignment. Of the two clamping jaws  6  lying opposite one another in pairs, only one is movable relative to the unit part  4  by the clamping drive  5  in a direction extending perpendicularly to a plane of symmetry  20  of the rail. 
     As visible particularly in  FIG. 4 , the clamping jaw  6  has two contact bars  21 , extending parallel to one another and in the longitudinal direction of the rail and forming the contact surface  15 , which are separated from one another by a recess  22 . Bores  24  are provided in each case for receiving the afore-mentioned head of the screws  23 . The contact surface  15  on each clamping jaw  6  or contact bar  21  is tempered by plasma transfer arc welding for improving the force-locked connection to a rail web  25 . 
     To initiate the welding procedure, the rails  7  are lifted by means of a lifting device (not shown) from the sleepers of the track and pressed against the stop bars  19 . Subsequently, the clamping drives  5  are actuated in order to press the clamping jaws  6 , connected thereto, against the rail web  25  of the rail  7  as well as to the oppositely positioned clamping jaws  6  with a clamping force of approximately 350 tons. 
     Now, if the two rails  7  abutting the stop bars  19  do not lie precisely in a common plane of symmetry  20  of the rail—for example, due to cross-sectional deviations within the tolerance range—there is a corresponding automatic rotation and adjustment of the clamping jaws  6 . In further sequence, this enables a problem-free transmission of the great clamping forces to the rail web  25  in order to finally press the rails  7  to one another by means of the displacement cylinders  2  for the welding of said rails.