Abstract:
In a method for extending a threaded bolt by tensioning a threaded end section thereof with a tensioning device, an exchange socket of the tensioning device is screwed onto the threaded end section and a first pin end of a pin slidable in the exchange socket is supported against an end of the threaded end section so that the pin moves in longitudinal direction as the exchange socket is screwed on. A sensor senses a longitudinal position of the pin relative to the exchange socket. An evaluation and control unit compares whether the detected longitudinal position of the pin relative to the exchange socket corresponds to a predefined minimum position value indicating sufficient thread engagement length. When the detected longitudinal position corresponds to the predefined minimum position value, the evaluation and control unit acts on the hydraulic supply to tension the threaded end section of the threaded bolt.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation application of U.S. patent application Ser. No. 13/941,581 having a filing date of 15 Jul. 2013, the United States patent application claiming a priority date of 18 Jul. 2012, based on prior filed German patent application No. 10 2012 106 503.9, the entire contents of the aforesaid United States patent application and the aforesaid German patent application being incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The invention relates to a tensioning device for extending a threaded bolt by way of tension on the threaded end section thereof, having a supporting tube surrounding the threaded end section, a cylinder which is arranged in continuation of the supporting tube and has at least one piston that is movable in the longitudinal direction therein and is connectable to a hydraulic supply, an exchange socket which is screwable to the threaded end section and is configured such that it can be carried along axially by the piston, and a pin which is arranged so as to be movable in the longitudinal direction and the pin end of which is supportable in the longitudinal direction against that end of the threaded bolt that has the threaded end section. 
         [0003]    A hydraulically operating bolt tensioning device having these features is known from US 2011/0271798 A1. The tensioning device has measures for monitoring the thread projection, i.e. the length of the threaded end section, gripped by the exchange socket, of the threaded bolt. To this end, the exchange socket is provided with a longitudinal channel in which a measuring rod is fitted in a longitudinally movable manner. The lower end of said measuring rod is supported in the longitudinal direction against the end face of the threaded bolt to be tensioned. At its other end, the measuring rod is provided with coloured markings, by way of which it is possible to read, with respect to the exchange socket, whether the thread projection, i.e. the length of the threaded section gripped by the exchange socket, is large enough for the tensioning process. With the measuring rod according to US 2011/0271798 A1, given appropriate attention on the part of the machine operator, it is possible for the thread projection actually present to be assessed. However, if the necessary attention is absent, operating errors cannot be ruled out. 
         [0004]    The invention is based on the object, in the case of a generic tensioning device for extending a threaded bolt, of providing increased security against a thread engagement length that is insufficient for the extension process. 
       SUMMARY OF THE INVENTION 
       [0005]    In order to achieve this object, a generic tensioning device for extending a threaded bolt by way of tension on the threaded section thereof is characterized by
       a means for sensing the position of the pin in the longitudinal direction,   an evaluation and control unit which is connected to the sensing means and by way of which the hydraulic supply can be enabled.       
 
         [0008]    With such a tensioning device, a prerequisite prior to starting each bolt tensioning process is that a sufficient actual length of the thread engagement is objectively present between the exchange socket and the end of the threaded bolt. To this end, according to the invention, a means is present which is able to sense the position of the pin in the longitudinal direction. An evaluation and control unit arranged downstream in the signal flow compares whether the detected longitudinal position of the pin corresponds to an internally predefined minimum position value, and therefore it is possible objectively to proceed from a sufficient thread engagement length. Only if this is the case does the evaluation and control unit in principle enable the hydraulic supply such that only then is the latter activatable for building up the hydraulic pressure in the piston chamber. As a result, increased security is achieved in that the possibility is ruled out that, on account for example of a lack of attention, the tensioning device is set into operation in the event of an insufficient thread engagement length. Rather, setting into operation is only possible after the evaluation and control unit has in principle enabled the hydraulic supply. 
         [0009]    According to one configuration of the tensioning device, a wireless signal path may be a constituent part of the evaluation and control unit, having a transmitting module arranged on the cylinder and a receiving module arranged in the region of the hydraulic supply. This configuration takes account of the circumstance that, in the case of generic tensioning devices, the hydraulic supply, including the valves controlling the build-up of pressure, is connected to the actual tensioning cylinder by a flexible pressure line, and thus there is a certain distance between the tensioning cylinder and the hydraulic supply. In order to bridge this distance and to avoid additional lines, signal transmission by means of a transmitting and receiving module is advantageous. 
         [0010]    According to a further configuration of the tensioning device, inductively operating means for sensing the position of the pin are provided. 
         [0011]    In a further configuration, it is proposed that the sensing means are arranged in the region of the other pin end, i.e. that end of the pin that is remote from the threaded bolt. 
         [0012]    Preferably, the sensing means are configured to sense the longitudinal position of the pin with respect to the exchange socket. 
         [0013]    A further configuration is characterized by a display unit, arranged on the cylinder, for displaying the position of the pin in the longitudinal direction. Preferably, the display unit is configured to display the longitudinal position of the pin with respect to the exchange socket, preferably in the form of an optical display. 
         [0014]    A further configuration provides that the pin has a signal-emitting or signal-triggering section on which the pin changes its diameter. For example, the pin can be configured in a conically tapering manner at this end, this being able to be felt by a measuring pin mounted transversely thereto. 
         [0015]    For a compact structure, it is proposed that the pin is arranged in a longitudinal guide in the exchange socket. This has the additional advantage that when the exchange socket is replaced, the pin is also exchanged at the same time. This is because the two are matched to one another in terms of their geometric dimensions and to the threaded bolt to be tensioned. 
         [0016]    According to a further configuration, the pin is formed in a radially widened manner at its lower pin end compared with the pin cross section. As a result of this radial widened section, the contact between the pin and the bolt to be tensioned always takes place in a single plane, specifically in the plane of the end face of the bolt and thus in that plane as far as which the external thread, available for the tensioning process, of the bolt usually extends. This measure makes it possible to assess the actual length of the thread engagement even in cases in which imprecise evaluation results would otherwise arise in the evaluation and control unit, for instance because the bolt has a central thread depression and the narrow end of the pin is supported in the latter and not on the actual end face of the threaded bolt. 
         [0017]    In a further configuration, it is proposed that the widened section is provided, opposite the end face of the threaded bolt, with an identification element which operates as a sensor and senses at least one feature formed on the end face. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    Further details and advantages will become apparent from the following description of an exemplary embodiment illustrated in the drawing, in which: 
           [0019]      FIG. 1  shows, largely in a section illustration, a hydraulically operating threaded bolt tensioning device, placed on a threaded bolt secured by a nut and supported on a base; 
           [0020]      FIG. 2  shows the threaded bolt tensioning device according to  FIG. 1 , but not supported on the base, with the thread engagement with the threaded bolt being too short; 
           [0021]      FIG. 3  shows the detail designated III in  FIG. 1  on an enlarged scale; 
           [0022]      FIG. 4  shows a partial plan view of the threaded bolt tensioning device. 
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0023]    The hydraulically operated tensioning device serves to tighten and optionally also to release highly stressed screw connections. The tensioning device has the task of applying a predetermined pre-tensioning force onto the threaded bolt  3  for a certain amount of time in the longitudinal direction of the bolt, in order to create the possibility of tightening or retightening in a torque-free manner the nut  4 , screwed onto the threaded bolt  3 , of the screw connection. For this purpose, an exchange socket of the tensioning device which is described in more detail in the following text is screwed onto the thread, protruding beyond the nut  4 , of the threaded bolt  3  and subsequently put under hydraulic tension, as a result of which the threaded bolt  3  is extended in the longitudinal direction. 
         [0024]    The screw-in depth of the threaded bolt is limited by the length, which is available as a bolt projection above the nut  4 , of the threaded section A. The screw-in depth available should be at least the same as, and preferably 1.5 times, the thread diameter of the bolt. It is only the minimum screw-in depth that ensures that the threaded bolt  3  is not damaged by the tensioning process. If a minimum value for the length A1 of the thread engagement is not maintained, the threaded bolt end can break off. 
         [0025]    The bolt tensioning device has a housing which consists of one or more cylinders  1 . The downward continuation of the housing or the cylinders  1  in the longitudinal direction L is formed by a supporting tube  2  which is open on its underside and is supported on that base  8 , usually a machine part, on which the nut  4  is also supported. A hydraulic connection, via which the tensioning device is connected to a hydraulic supply  6 , is located laterally on the housing composed of the cylinders  1 . 
         [0026]    Furthermore, a gear mechanism  15  which operates through orifices in the supporting tube  2  and by way of which the nut  4  screwed onto the threaded bolt  3  can be rotated may be provided. This rotation is of course only possible when the tensioning device is in operation and therefore the nut  4  is not subjected to considerable frictional loading. 
         [0027]    In the exemplary embodiment, the housing contains a plurality of, in this case two, hydraulic cylinders which are connected in parallel and are each connected to an external hydraulic supply  6  via a flexible, pressure-tight hydraulic line  6 A connected to a hydraulic connection  7 . A piston  5  is arranged in each of the cylinders  1  so as to be movable in the longitudinal direction L, said piston being sealed off in the direction of the cylinder  1 . In the exemplary embodiment, these are thus a lower piston  5  and an upper piston  5 , which are moreover only movable jointly. When the hydraulic supply  6  is activated, the feeding of hydraulic pressure into the working spaces of the cylinders causes the pistons  5  arranged therein to be raised. This may take place counter to the action of a compression spring  16  supported on the uppermost piston  5 . 
         [0028]    The pistons  5  are connected rigidly to an exchange socket  10  arranged centrally therein, and so the movement of the pistons  5  results in an identical movement of the exchange socket  10 . The latter is designed to be exchangeable by means of suitable measures, and can thus be exchanged for an exchange socket  10  of different geometry, whereas the piston  5  or the pistons  5  are not exchanged for other pistons. 
         [0029]    The exchange socket  10  is composed integrally of a lower coupling section and an upper shank section. The coupling section is located inside the supporting tube  2  and has an internal thread which is screwable together with the external thread of the threaded bolt  3 . The shank section of the exchange socket  10  is surrounded by the pistons  5 , to which it is rigidly connected, preferably by way of a screw connection. 
         [0030]    In order to tension the threaded bolt, the exchange socket  10  is screwed onto the threaded end section A of the threaded bolt. By feeding hydraulic pressure, the pistons  5  are raised, carrying along the exchange socket  10 , as a result of which longitudinal extension of the threaded bolt  3  occurs. Associated with this is a loss of friction on the underside of the nut  4 , such that the latter can be rotated on the thread of the bolt, i.e. can be retightened. 
         [0031]    It is important for the tensioning operation that the screw-in depth, made available by the length of the threaded end section A, of the threaded bolt  3  is utilized fully by the corresponding internal thread of the exchange socket  10 , and a sufficient length A1 of the thread engagement is reliably achieved. 
         [0032]    In order to monitor the thread engagement length, a pin  20  is located centrally in a longitudinal bore in the exchange socket  10 . Said pin  20  is provided with a collar or a widened section  21 , against which a spring  21 A, which is supported on the other side opposite the exchange socket  10 , is supported. In this way, the pin  20 , which is longitudinally movable in a longitudinal guide  17  in the exchange socket, is always acted on by a force, which pushes it slightly downward, i.e. in the direction of the threaded bolt  3 . 
         [0033]    At its lower end  22 , the pin  20  is supported axially against the end face  3 A of the threaded bolt  3 . The other end  23  of the pin  20  is located in the region of the upper part of the tensioning device. There, technical measures, which are described in more detail in the following text, are taken in order to sense the longitudinal position of the pin end  23  and thus the position of the pin  20  in the longitudinal direction L. From this longitudinal position, it is possible to deduce the height at which the lower pin end  22  is located, thereby in turn allowing a direct conclusion to be drawn about the length of the thread engagement A1 at the threaded end section A. Specifically, if, in the situation according to  FIG. 1 , the length A1 of the thread engagement were less than illustrated, the pin  20  would be lowered further, and this is detectable from the position of the upper pin end  23  in relation to the exchange socket  10  or in relation to the cylinder. 
         [0034]    In order to detect the height position of the pin  20 , sensing means  30  for sensing the longitudinal position of the pin with respect to the exchange socket  10  are arranged in the region of the pin end  23 . These means  30  are configured to sense the position of the pin  20 , e.g. in an inductive manner. The electric position signals pass to an evaluation and control unit  35 A,  35 B via a signal line  31 . 
         [0035]    The evaluation and control unit  35 A can be arranged at the top on the housing of the tensioning device. However, an arrangement at some other location is also possible, e.g. the evaluation and control unit  35 B can, as likewise illustrated in  FIG. 1 , be arranged in the region or as a constituent part of the hydraulic supply  6 . 
         [0036]    The sensing means  30  reproduced on an enlarged scale in  FIG. 3  operates in an electric-inductive manner. It is fitted firmly into a corresponding recess in the top of the exchange socket  10 . The longitudinal position of the pin  20  with respect to the exchange socket  10  is sensed by the sensing means  30 . 
         [0037]    The inductively sensed position signals pass via the signal line  31  to the evaluation and control unit  35 A or  35 B. A comparison of the sensed longitudinal position of the pin  20  with an internally predefined value and in particular a minimum value takes place therein. If this value is dropped below, as is illustrated by way of example with the value A1′ in  FIG. 2 , a too short length A1′ of the thread engagement is internally assumed. In this case ( FIG. 2 ), the evaluation and control unit  35 A or  35 B does not enable the hydraulic supply  6  and so it is not possible for a hydraulic pressure to build up with respect to the piston  5 . An operating error on account of a lack of concentration in reading off displayed values or dimensions is ruled out. 
         [0038]    It is not necessary to arrange the evaluation and control unit directly on the cylinder  1 . According to  FIG. 1 , the evaluation and control unit  35 B can also be located in the region of the valve-controlled hydraulic supply  6  from which the flexible pressure line  6 A leads to the hydraulic connection  7  on the device. If the evaluation and control unit  35 B is located at or in the region of the hydraulic supply  6 , a wireless signal path  38  from the sensing means  30  is expedient. To this end, a transmitting module  36  is arranged on the cylinder  1  and the corresponding receiving module  37  is arranged in the region of the hydraulic supply. 
         [0039]    The lower pin end  22  can be radially widened compared with the rest of the pin cross section. For this purpose, the lower pin end is in the form of a disc  25 , the radial width of which is greater than the remaining cross section of the pin  20 . The widened section  25  formed in this way should not be larger than the size of the end face  3 A of the threaded bolt. As a result of the radial widened section  25 , the contact between the pin and the bolt  3  to be tensioned always takes place in a single plane, specifically in the plane of the end face  3 A of the bolt. This makes it possible to assess the length Al of the actually engaged thread projection even in cases in which imprecise evaluation results would otherwise arise, for instance because the threaded bolt  3  has a central thread depression. Specifically, if the pin  20  were to end in a slender manner at the bottom, it would be supported in this thread depression and not on that end face  3 A of the threaded bolt  3 , up to the height of which the thread of the threaded bolt  3  frequently extends. Therefore, the radial width of the widened section  25  should be at least the same size as the depression. 
         [0040]    An identification element may be located in the disc  25 , opposite the end face  3 A of the threaded bolt  3 . In order to accommodate said identification element, the disc  25  may be provided with a correspondingly dimensioned recess. The identification element is configured to sense at least one feature formed or arranged on the end face  3 A of the threaded bolt. This feature may be a marking on the bolt or the screw connection, e.g. a barcode, or the grade of the material of which the threaded bolt consists. However, other markings which are located in the region of the end face  3 A may also be detectable by the identification element. The sensor signal of the identification element passes via a signal cable to an evaluation unit. This may be the same evaluation and control unit  35 A or  35 B to which the signals from the means  30  for sensing the longitudinal position of the pin  20  also pass. In order to accommodate the signal cable, the pin  20 , which is itself axially guided in the longitudinal guide  17  of the exchange socket  10 , is provided with a longitudinal channel preferably arranged on the pin axis. The signal cable coming from the identification element is in this way guided along the pin  20 . In the evaluation and control unit  35 A, the signals coming from the identification element in the disc  25  are also evaluated in a suitable manner, and if appropriate processed further. Electronic documentation of the data collected by the identification element can also take place in the evaluation and control unit  35 A,  35 B as part of the documentation of the tensioning process. 
         [0041]    The other pin end, that is to say the upper pin end  23 , is in the form of a signal-emitting or signal-triggering pin section. The pin end  23  does not have a constant thickness here, but rather its thickness, or its diameter, changes with length, for instance by way of a narrowing, reproduced in  FIG. 3 , of the pin  20  towards its end. If the pin  20  changes its position in the longitudinal direction L, a measuring pin  55  which is mounted transversely to the pin axis and is supported with its one end  55 A against the pin end  23 , moves in a corresponding manner transversely to the pin  20 . 
         [0042]    In this variant, the position of the pin  20  is not mechanically sensed directly, but rather the position of the additional measuring pin  55 . The latter is connected at its other end, within a sensor housing  56  fastened to the cylinder  1 , to a displacement measuring device having a display unit  50  ( FIG. 4 ). The display unit  50  reproduces the mechanically sensed height position of the pin  20  optically or by way of numerical values, this allowing the machine operator an additional means for monitoring of the thread engagement length. 
         [0043]    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 
       [0044]      1  cylinder 
         [0045]      2  supporting tube 
         [0046]      3  threaded bolt 
         [0047]      3 A end face of the threaded bolt 
         [0048]      3 B depression 
         [0049]      4  nut 
         [0050]      5  piston 
         [0051]      6  hydraulic supply 
         [0052]      6 A pressure line 
         [0053]      7  hydraulic connection 
         [0054]      8  base 
         [0055]      10  exchange socket 
         [0056]      15  gear mechanism 
         [0057]      16  compression spring 
         [0058]      17  longitudinal guide 
         [0059]      20  pin 
         [0060]      21  widened section 
         [0061]      21 A spring 
         [0062]      22  pin end 
         [0063]      23  pin end 
         [0064]      25  widened section, disc 
         [0065]      30  means for sensing the longitudinal position 
         [0066]      31  signal line
         35 A evaluation and control unit     35 B evaluation and control unit       
 
         [0069]      36  transmitting module 
         [0070]      37  receiving module 
         [0071]      38  signal path 
         [0072]      50  display unit 
         [0073]      55  measuring pin 
         [0074]      55 A pin end 
         [0075]      56  sensor housing 
         [0076]    A threaded end section 
         [0077]    A1 length of thread engagement 
         [0078]    A1′ length of thread engagement 
         [0079]    L longitudinal direction