Patent Publication Number: US-9415493-B2

Title: Tension device for straining a threaded bolt

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a tension device for straining a threaded bolt by a pull on its threaded end portion, with a one-part or multi-part housing having at least one piston movable therein in the longitudinal direction and connectable to a hydraulic supply, with a supporting tube which is arranged as a prolongation of the housing and discharges the tension forces acting in the housing to a base surrounding the threaded bolt, and with a pull nut which can be fastened by means of thread engagement on a threaded end portion of the threaded bolt and which is supported in the longitudinal direction, by means of a pressure face, against a pressure-transmission face formed on the piston. 
     In as bolt tension device, such as is known, for example, from DE 43 41 707 A1, the hydraulic piston and the tension cylinder has to be pressed back into its lower initial position again after the conclusion of the tensioning process and therefore after pressure relief has occurred. This is troublesome, above all in the case of frequent or recurring tensioning processes, and results in loss of time until the tension device is prepared for the next tensioning process. 
     The object of the invention, therefore, is, by means of measures which can be implemented on the tension device at a low outlay in assembly terms, to arrive at an automatic piston return, so that, after the end of the respective tensioning process, the piston does not first have to be moved back into its initial position again by the application of force. 
     SUMMARY OF THE INVENTION 
     To achieve this object, a tension device for straining a threaded bolt having the following features is proposed: at least one return spring is acting upon the piston in the direction towards the supporting tube and bears, with one end, against a housing-side spring support and, with the other end, against a piston-side spring support. 
     By means of the return springs and its bearing, with one end, against the housing-side spring support, and, with the other end, against a piston-side spring support, an automatic piston return is obtained, so that the piston of the tension cylinder does not always have to be pressed back again by the application of force. This type of piston return can be implemented in or on the tension device at a low outlay in assembly terms. The return spring can be exchanged for another, for example stronger or weaker return spring likewise at low outlay in assembly terms. 
     The return springs are preferably four in number, in which case the springs should be arranged so as to be distributed symmetrically over the circumference of the tension device. There may, however, also be a smaller number of springs, for example there may be overall two parallel-connected return springs lying opposite one another with respect to the mid-axis of the tension device. The advantage of using overall four parallel-connected springs is that an especially tilt-free piston return is thus achieved. 
     In one refinement, it is proposed that the return spring be arranged level with the piston and, in particular, at a level below thread engagement between the pull nut and the threaded end portion. 
     According to a further refinement, the two spring supports are oriented such that the housing-side spring support faces the supporting tube and the piston-side spring support faces away from the supporting tube. 
     According to a further refinement, the return spring, consisting, for example, of layered cup springs or of a helix, surrounds a spar, of which the upper spar end facing away from the supporting tube is secured with respect to the piston, whereas the spar has, at its lower end facing the supporting tube, a widened section, against which the return spring bears. 
     Furthermore, it is proposed that, to secure the upper spar end, the latter is suspended in an orifice in a flange-like widened section of the piston, the upper spar end being supported on the flange-like widened section preferably from above. 
     Furthermore, it is proposed that the spar be led longitudinally movably through an orifice, oriented parallel to the piston, in the housing, that region of the housing which surrounds the orifice forming the housing-side spring support. 
     Furthermore, it is proposed that, as seen in the longitudinal direction, both the flange-like widened section of the piston and the housing have rectangular cross sections level with the orifice, and that in each case a return spring be arranged in the region of each of the four corners of the rectangular cross section. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further details and advantages may be gathered from the following description of an exemplary embodiment illustrated in the drawing. 
         FIG. 1  shows a perspective illustration of a hydraulically operating threaded-bolt tension device which is placed onto a threaded bolt secured by a nut and is supported on the base. 
         FIG. 2  shows a side view of the threaded-bolt tension device, larger regions being reproduced sectionally along the mid-axis. 
         FIG. 3  shows a top view of the threaded-bolt tension device. 
         FIG. 4  shows a section through the threaded-bolt tension device corresponding to the sectional plane IV-IV marked in  FIG. 3  and arranged so as to be offset to the mid-axis. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     The hydraulically driven tension device serves for tightening and, if appropriate, also releasing highly loaded screw connections. The tension device has the task of applying a stipulated pretensioning force to the threaded bolt  3  of a screw connection for a certain time in the bolt longitudinal direction, in order to afford the possibility of tightening or retightening, free of torque, or else releasing the nut  4  screwed onto the threaded bolt  3  and securing the latter. 
     The tension device described here is designed especially for tensioning or straining those bolt connections in which the thread, projecting beyond the nut  4 , of the bolt  3  has a considerable length, and in which this threaded portion has, in particular, a length which amounts to four to eight times the thread diameter D. 
     As an element temporarily exerting a pull on the bolt, a pull nut  10  of the bolt tension device is screwed onto the end portion A of the threaded portion projecting beyond the nut  4 . The pull nut  10  is subsequently subjected hydraulically to a pulling force, with the result that the threaded bolt  3  is strained in the longitudinal direction. 
     The bolt tension device has a rigid housing  1 . In the exemplary embodiment, it consists of two housing parts  1   a ,  1   b . The housing  1  is continued rigidly downwards in the longitudinal direction in a supporting tube  2  which is open on its underside and which is supported on that base B, mostly a machine part, on which the nut  4  is also supported. The supporting tube  2  and a tension device therefore diverts the tension reaction forces acting on the housing  1  to the fixed base B. The supporting tube  2  surrounds the nut  4  and leaves room for the latter, without obstructing the turning of the nut  4  arranged inside the supporting tube  2 . 
     Located laterally on the housing  1  is a hydraulic connection  7 , via which piston spaces arranged in the tension device can be connected to a switchable high-pressure hydraulic supply. 
     Moreover, a gear may be provided, which operates through an orifice  2 A in the supporting tube  2  and with the aid of which the nut  4  seated on the threaded bolt  3  can be turned. This turning is possible only when the tension device is operating and therefore the nut  4  is not loaded by considerable friction, particularly with respect to the base B. 
     The housing  1  comprises at least one hydraulic cylinder which is connected to the external hydraulic supply via the hydraulic connection  7  and a flexible pressure-resistant hydraulic line. 
     In the exemplary embodiment described here, two hydraulic cylinders are connected in series. For this purpose, as can be seen in  FIG. 4 , the housing  1  is composed of two pressure-resistant housing parts  1   a ,  1   b  which in each case surround a piston space and consequently a hydraulic working space. A piston  5   a ,  5   b  is arranged movably in the longitudinal direction in each piston space, at the same time being sealed off with respect to the inner wall of the respective housing part  1   a ,  1   b . The pistons  5   a ,  5   b  bear one against the other in the longitudinal direction and are thus arranged in a series connection. 
     When the hydraulic supply is switched on, by hydraulic pressure being fed into the piston spaces, the pistons  5   a ,  5   b  arranged therein are jointly raised. This takes place counter to the action of spring elements described in more detail below. 
     The piston  5  or, in the case of a multi-part piston, its uppermost piston  5   a  bears in the longitudinal direction with a pressure transmission face  6  against the underside, serving as a pressure face  9 , of the pull nut  10 . Raising the piston  5  therefore results in an identical movement and take-up of the pull nut  10  and consequently in a torsion-free stretching of the threaded bolt. 
     The pull nut  10  which can be screwed together with the end portion A of the external thread of the threaded bolt  3  is configured so as to be exchangeable, that is to say it can, if required, be exchanged for a pull nut  10  of another size or geometry, whereas the one-part or multi-part piston  5  does not have to be exchanged for another piston. 
     For tensioning the threaded bolt  3 , first the pull nut  10  is screwed with its internal thread  11  onto the threaded end portion A of the threaded bolt. The internal thread  11  preferably does not extend over the entire length of the pull nut  10 . Instead, the pull nut  10  has, following the internal thread  11 , a longitudinal stop  12  which bears axially against the end face  3 A of the threaded bolt only when the pull nut  10  is screwed on completely and therefore correctly. The longitudinal stop  12  is located on a threadless longitudinal portion of the pull nut  10 , the longitudinal portion projecting radially inwards with respect to the thread  11 . 
     By hydraulic pressure subsequently being fed in, the piston  5  guided in the cylinder of the housing  1  and supported from below against the pull nut  10  is raised, at the same time taking up the pull nut  10 , thus resulting in the longitudinal straining of the threaded bolt  3 . This entails a loss of friction on the underside of the nut  4 , so that the latter can then be turned, for example retightened, on the thread of the bolt. 
     So as not to have to press the piston  5  back into its initial position again by the application of force after the conclusion of each individual tensioning process, above all in the case of frequent tensioning processes, return springs  20  acting upon the piston  5  in the direction towards the supporting tube  2  are provided. In the exemplary embodiment, there are overall four such springs  20  connected in parallel, although a smaller or larger number of springs  20  may also be suitable. 
     According to  FIG. 4 , the individual return spring  20  is supported, with one end, against a housing-side spring support  21 , that is to say a bearing face designed to be rigid with respect to the housing  1  or  1   a , and, with the other end, against a piston-side spring support  22 , that is to say a bearing face designed to be rigid with respect to the piston  5 . 
       FIG. 4  reveals, in conjunction with  FIG. 3 , the configuration both of the housing  1  and of the two-part piston  5  guided longitudinally therein, and also the especially assembly-friendly accommodation of the return springs  20 , the return springs  20  being arranged in a space-saving way below the thread engagement between the pull nut  10  and a threaded end portion A. 
     For this purpose, indeed, the piston  5  is cylindrical or of circular cross section where it is guided, sealed off, in the housing  1  and thus delimits the working space of the hydraulic cylinder. However, the piston  5  has a longitudinal portion, on which, as seen in the longitudinal direction, it is provided with radial widened sections  31  in the manner of flanges. The widened sections  31  make available the space for accommodating the return springs  20 . 
     In the exemplary embodiment, this longitudinal portion of the piston is provided with overall four widened sections  31  enlarged radially with respect to the remaining cylindrical piston shape, with the result that the longitudinal portion has a rectangular cross section which can be seen clearly in  FIG. 3 . The four widened sections  31 , configured as flanges, form the corner regions of the rectangle. One of the four return springs  20  is arranged in each of the corner regions. 
     Each of the flange-like widened sections  31  of the piston  5  is provided with an orifice  32  which extends parallel to the longitudinal axis of the piston. 
     Correspondingly to the configuration of the piston, the housing  1 , too, has a rectangular cross section over part of its length. The housing  1  has this rectangular cross section essentially on that housing longitudinal portion L 1  on which the one-part or two-part piston  5  is located in the housing interior. 
     In alignment with the orifices  32  in the flange-like widened sections  31  of the piston  5 , the housing  1  is also provided in each case with an orifice  42 . The orifice  42  is followed downwards, that is to say towards the supporting tube  2 , by a preferably cylindrical spring chamber which affords sufficient space for receiving the respectively turned spring  20 . 
     A rigid spar  25  extends longitudinally through the spring chamber. It is secured with its upper spar end  26  to the piston  5  or to the upper piston  5   a , whereas the lower spar end is configured as a widened section  27 , comparable to the shape of a screw head. The top side of the widened section  27  is the piston-side spring support  22 . 
     That region of the housing  1  which surrounds the orifice  42 , that is to say the wall upwardly delimiting the spring chamber, serves as the housing-side spring support  21 . 
     To connect the spar  25  to the piston  5 , a nut  28  is screwed onto a thread at the upper spar end  26 , the diameter of the nut being larger than the diameter of the orifice  32  arranged beneath it. By means of the nut  28 , therefore, the spar  25  can be supported from above on the flange-like widened section  31  of the piston  5 . 
     The spring chamber is open downwards. To assemble or to exchange the return spring  20 , therefore, first the nut  28  is released at the upper spar end  26 . The return spring  20  can then be removed, together with the spar  25 , from the housing  1  downwards. Assembly takes place in reverse order. 
     In the exemplary embodiment reproduced here, each return spring  20  consists of a plurality of cup springs  20 A layered one upon the other. Instead of the cup springs  20 A, a helical spring rated for the corresponding pressure can also be used. 
     The piston  5  is provided with a marking  50  to identify its maximum permissible piston stroke. 
     In order to balance any slight tilting between the pull nut  10  and threaded end portion A, the piston  5  or, here, the upper piston  5 A is configured so as to be divided in two. It is composed of a base body  55 , which, facing away from the supporting tube  2 , is configured as a bowl or spherical cap, and of a correspondingly configured ring  56  which is formed spherically on its underside and is thus located between the piston  5  and the pull nut  10 . Along the common spherical line  57  forming a ball socket, the ring  56  can assume a certain angular pitch relative to the base body  55  of the piston, in order thereby to balance inaccuracies of the thread on the threaded bolt  3 . 
     The specification incorporates by reference the entire disclosure of German priority document 10 2012 109 681.3 having a filing date of Oct. 11, 2012. 
     While specific embodiments of the invention have been shown and described in detail to illustrate the inventive principles, it will be understood that the invention may be embodied otherwise without departing from such principles. 
     LIST OF REFERENCE CHARACTERS 
     
         
           1  Housing 
           1   a  Housing part 
           1   b  Housing part 
           2  Supporting tube 
           2 A orifice 
           3  Threaded bolt 
           3 A end face of threaded bolt 
           4  Nut 
           5  Piston 
           5   a  Piston 
           5   b  Piston 
           6  Pressure transmission face 
           7  Hydraulic connection 
           9  Pressure face 
           10  Pull nut 
           11  Internal thread 
           12  Longitudinal stop 
           20  Return spring 
           20 A Cup spring 
           21  Spring support, housing side 
           22  Spring support, piston side 
           25  Spar 
           26  Upper spar end 
           27  Widened section, lower end of the spar 
           28  Nut 
           31  Flange-shaped widened section 
           32  Orifice 
           42  Orifice 
           50  Marking 
           55  Base body 
           56  Ring 
           57  Spherical line 
         A Threaded end portion 
         B Base 
         D Thread diameter 
         L 1  Part-length