Abstract:
Threaded mechanical fastening systems and methods are provided that allow the simple deflection of a washer to indicate that a desired minimum torque has been reached or that a desired maximum torque has been exceeded. The method includes providing a threaded connection having a washer, installing the threaded connection so that the washer is supported as a simple beam over a gap, and using an amount of deflection of the washer as a result of torque applied by the threaded connection as an indicator. The torque indicating threaded mechanical fastening system includes a threaded connection and a washer supported as a simple beam over a gap so that the threaded connection, when tightened to a predetermined torque, deflects, in bending, the washer into the gap.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application Ser. No. 62/018,229 filed Jun. 27, 2014, the contents of which are incorporated by reference herein. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present disclosure is related to threaded mechanical fastening systems and methods. More particularly, the present disclosure is related to threaded mechanical fastening systems and methods that provide an indication of torque during assembly of the system. In some embodiments, the threaded mechanical fastening systems and methods are calibrated so that the indication is a sign of over torque, while in other embodiments the indication is a sign of a desired torque level. 
         [0004]    2. Description of Related Art 
         [0005]    Threaded mechanical fastening systems have been used to connect various components to one another for many years. The over tightening of the threaded mechanical fastening system can potentially damage one or more portions of the fastening system and/or one or more of the components that the fastening system is being used to connect. 
         [0006]    In some instances and in order to prevent damage, a special device that measures and/or limits the torque applied during the assembly of the components and threaded mechanical fastening system. For example, some prior art assembly operations require the use of a torque measuring device—such as but not limited to a torque wrench. Other prior art assembly operations require the use of a torque limiting device—such as, but not limited to, a torque clutch. 
         [0007]    Unfortunately, it has been determined by the present disclosure that the use of such special tools often adds complexity and/or cost to the assembly. 
         [0008]    Accordingly, there is a need for threaded mechanical fastening systems and methods that overcome, alleviate, and/or mitigate one or more of the aforementioned and other deleterious effects of prior art systems. 
       SUMMARY 
       [0009]    Threaded mechanical fastening systems and methods are provided that allow the simple deflection of a washer to indicate that a desired minimum torque has been reached or that a desired maximum torque has been exceeded. 
         [0010]    Threaded mechanical fastening systems are provided that, in most basic form, include a threaded connection and a washer supported as a simple beam. In this position, the washer forms a structural member that is deflected by tightening the threaded connection to or above a predetermined torque. 
         [0011]    The above-described and other features and advantages of the present disclosure will be appreciated and understood by those skilled in the art from the following detailed description and drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    This application contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee. 
           [0013]      FIG. 1  is a bottom perspective view of an exemplary embodiment of a threaded mechanical fastening system according to the present disclosure; 
           [0014]      FIG. 2  is a side view of the threaded mechanical fastening system of  FIG. 1 ; 
           [0015]      FIG. 3  is a bottom view of the threaded mechanical fastening system of  FIG. 1 ; 
           [0016]      FIG. 4  is a top view of the threaded mechanical fastening system of  FIG. 1 ; 
           [0017]      FIG. 5  is a first end view of the threaded mechanical fastening system of  FIG. 1 ; 
           [0018]      FIG. 6  is a second end view of the threaded mechanical fastening system of  FIG. 1 ; 
           [0019]      FIG. 7  is a first end view of an upper pad of the threaded mechanical fastening system of  FIG. 1 ; 
           [0020]      FIG. 8  is a second end view of the threaded mechanical fastening system of  FIG. 1  in use at a first torque; 
           [0021]      FIG. 9  is a second end view of the threaded mechanical fastening system of  FIG. 1  in use at a second torque; 
           [0022]      FIG. 10  is a second end view of the threaded mechanical fastening system of  FIG. 1  in use at a third torque; 
           [0023]      FIG. 11  is a first end view of the threaded mechanical fastening system of  FIG. 1  in use at a fourth torque; 
           [0024]      FIG. 12  illustrates an exemplary embodiment of boundary conditions on the washer of  FIG. 1  during loading for use in a finite element analysis (FEA); 
           [0025]      FIG. 13  illustrates an FEA resultant displacement plot of the washer at the second torque as shown in  FIG. 9 ; 
           [0026]      FIG. 14  illustrates an FEA stress plot of the washer at the second torque as shown in  FIG. 9 ; 
           [0027]      FIG. 15  illustrates an FEA resultant displacement plot of the washer at the third torque as shown in  FIG. 10 ; 
           [0028]      FIG. 16  illustrates an FEA stress plot of the washer at the third torque as shown in  FIG. 10 ; 
           [0029]      FIG. 17  illustrates an FEA resultant displacement plot of the washer at the fourth torque as shown in  FIG. 11 ; 
           [0030]      FIG. 18  illustrates an FEA stress plot of the washer at the fourth torque as shown in  FIG. 11 ; 
           [0031]      FIG. 19  illustrates an exemplary embodiment of boundary conditions on the upper pad of  FIG. 1  during loading for use in FEA; 
           [0032]      FIG. 20  illustrates an FEA section view stress plot of the upper pad at the third torque as shown in  FIG. 10 ; 
           [0033]      FIG. 21  illustrates an FEA stress plot of the upper pad at the third torque as shown in  FIG. 10 ; 
           [0034]      FIG. 22  illustrates an FEA section view stress plot of the upper pad at 535 inch-pounds of torque; 
           [0035]      FIG. 23  illustrates an FEA stress plot of the upper pad at 535 inch-pounds of torque; 
           [0036]      FIG. 24  is a first end view of an alternate exemplary embodiment of a threaded mechanical fastening system according to the present disclosure; 
           [0037]      FIG. 25  is a top view of the threaded mechanical fastening system of  FIG. 24 ; and 
           [0038]      FIG. 26  is a first end view of an upper pad of the threaded mechanical fastening system of  FIG. 24 . 
       
    
    
     DETAILED DESCRIPTION 
       [0039]    Referring to the drawings and in particular to  FIGS. 1 through 7 , an exemplary embodiment of a threaded mechanical fastening system according to the present disclosure is shown and is generally referred to by reference numeral  10 . 
         [0040]    System  10  is shown by way of example incorporated into a spring loaded parallel pad clamp such as that shown and described in U.S. Pat. No. 7,666,024, the entire contents of which are incorporated by reference herein. For reasons of brevity, only the portions of the spring loaded parallel pad clamp that are necessary for understanding of system  10  will be described herein, while the remaining portions will be omitted for reasons of brevity. Specifically, system  10  includes an upper pad  12 , a threaded connection consisting of a bolt  14  and a nut  16 , and a washer  18 . Advantageously, system  10  includes is configured so deflection of washer  18  can be an indication over torque of the system or an indication of a desired torque level. 
         [0041]    For example, system  10  can be calibrated so that washer  18  does not deflect at the desired system torque. Here, system  10  can be used to verify that excess torque was not applied. Stated another way, any deflection of washer  18  in this embodiment would be an indication that more than a desired amount of torque had been applied. 
         [0042]    Alternately, system  10  can be calibrated so that washer  18  begins deflecting at a desired torque. Here, system  10  can be used as an indication that the correct torque has been applied. Stated another way, the operator can apply torque to system  10  in this embodiment until washer  18  begins to deflect, which would be an indication that a desired amount of torque had been applied. 
         [0043]    It should be recognized that washer  18  is illustrated herein by way of example only as a flat washer. Of course, it is contemplated by the present disclosure for washer  18  to have any configuration such, as but not limited, to a Bellville washer, split washers, fender washers, internal tooth lock washers, external tooth lock washers, finishing washers, and others. 
         [0044]    Referring now to  FIG. 7 , an end view of upper pad  12  is shown. The deflection of washer  18  is made possible by providing a gap  20  in upper pad  12 . In this manner, the edges of gap  20  act as landings  22  that support washer  18  as a “simple beam”, namely where the washer is supported at two outer extents. 
         [0045]    Accordingly, system  10 , in its most basic form, a threaded connection and a washer supported as a simple beam. In this position, washer  18  forms a structural member of the connection. 
         [0046]    Referring now to  FIGS. 8 through 11 , system  10  is shown in use at different levels of torque. As is shown, the torque applied to the threaded connection (i.e., bolt and nut  14 ,  16 ) causes the threaded member to apply a linear force  24  onto washer  18 . The liner force  24  in combination with the simple beam support of washer  18  result in deflection of the washer when the linear force reaches a predetermined level. 
         [0047]    System  10  can be calibrated by adjusting one or more parameters so that the same level of torque results in different levels of deflection of washer  18 . 
         [0048]    Various properties of washer  18  that can be used to calibrate system  10  include, but are not limited to, a material, a thickness, internal washer diameter (ID), outer washer diameter (OD), heat treatment, and others. 
         [0049]    Gap  20  can also be adjusted to calibrate system  10 , where a larger gap can result in increased deflection at a certain torque, while a smaller gap can result in decreased deflection at that same torque. It should be noted that there is a lower limit below which gap  20  cannot be reduced. Specifically, linear force  24  is applied to washer  18  in a contact region  26 . Thus, gap  20  must be larger than contact region  26  to ensure that washer  18  remains supported as a simple beam. 
         [0050]    Similar to gap  20  discussed above, contact region  26  can be adjusted to calibrate system  10 , where a smaller contact region can result in increased deflection at a certain torque, while a larger contact region can result in decreased deflection at that same torque. In the illustrated embodiment, contact region  26  is shown being applied by a second washer  28  that is disposed between nut  16  and washer  18 . Here, second washer  28  is shown as a lock washer that has a smaller contact region than that of nut  16 . Of course, it is contemplated by the present disclosure for second washer  28  to have a contact region that is the same as nut  16  or is larger contact region than that of nut  16 —again provided that gap  20  is be larger than contact region  26  to ensure that washer  18  remains supported as a simple beam. 
         [0051]    Without wishing to be bound by any particular theory, it is believed that, given the common deflection characteristics of washer  18  when configured as a simple supported beam disclosed herein that it is desired for the washer to extend far enough from the bolt to allow deflection at the designed torque/clamping force. Thus in some embodiments, gap  20  has a width that is approximately 60% larger than a diameter of the shaft of bolt  14  and the outer diameter (OD) of the washer  18  is approximately 60% larger than the width of gap  20 . Of course, it is contemplated by the present disclosure for washer  18  to have any desired width and or diameter necessary to calibrate the system to the desired torque and use. 
         [0052]    System  10  is shown in  FIGS. 8 through 11  having different torque levels applied to illustrate the resulting deflection of washer  18 . 
         [0053]    In  FIG. 8 , system  10  is shown after application of a torque of  180  inch-pounds, which is sufficient to deflect washer  18 . The deflection results in a distance  30  between a point on upper pad  12  and a bottom of washer  18  being decreased by about 0.012 inches. 
         [0054]    In  FIG. 9 , system  10  is shown after application of a torque of 200 inch-pounds, which is sufficient to result in distance  30  being decreased by about 0.015 inches. In  FIG. 10 , system  10  is shown after application of a torque of 250 inch-pounds, which is sufficient to result in distance  30  being decreased by about 0.019 inches. In  FIG. 11 , system  10  is shown after application of a torque of 300 inch-pounds, which is sufficient to result in distance  30  being decreased by about 0.021 inches. 
         [0055]    Accordingly, system  10  can be calibrated during design to provide a desired deflection at a given torque. In some embodiments, system  10  can be calibrated so that washer  18  does not deflect at the desired system torque so that the system can be used to verify whether excess torque was applied. Alternately, system  10  can be calibrated so that washer  18  begins deflecting at a desired torque so that the system  10  can be used to determine when to stop tightening the threaded connection. 
         [0056]    In some embodiments, system  10  can include one or more indicators, which allow the user to be able to visually verify the amount of deflection. For example, system  10  can include minimum and maximum deflection marks  32 ,  34  on pad  12  as shown in  FIG. 9 . Here, the user can ensure that washer  18  is deflected between the desired marks  32 ,  34 . In another example, system  10  can include only a maximum deflection mark  32  or only a minimum deflection mark  34 . 
         [0057]    In yet another example shown in  FIG. 10 , system  10  can include a protrusion  36  on pad  12  extending towards washer  18 . In use, system  10  can be tightened and as long as washer  18  does not contact the protrusion  36 , the user can be assured that the system has not exceeded the maximum torque. 
         [0058]    It should be recognized that the threaded connection is shown in the example provided above as bolt  14  and nut  16 . However, it should be recognized that the present disclosure finds equal use with any threaded connection such as, but not limited to, screws including wood screws, machine screws, thread cutting screws, sheet metal screws, self-drilling screws, socket screws, and others, bolts including hex bolts, lag bolts, carriage bolts, eye bolts, U bolts, shoulder bolts, and others. 
         [0059]    Moreover, system  10  is shown in the example provided above incorporated into a spring loaded parallel pad clamp such that the simple beam support of the washer is formed by gap  20 . It should be recognized that the present disclosure finds equal use anywhere that a threaded connection is used. 
         [0060]    In the example where system  10  is incorporated into a spring loaded parallel pad clamp many of such pads are made from a cast process (e.g., sand cast, die cast, shell mold casting, investment cast, and others). The castings can crack when system  10  is tightened beyond the recommended torque. Accordingly, system  10  can be used to ensure that excess torque is not applied—by giving a visual indication through the aforementioned deflection of washer  18 . Again, the deflection of washer  18  can indicate that too much torque was applied such that a new spring loaded parallel pad clamp should be applied. Alternately, the beginning of deflection of washer  18  can indicate that the correct torque has been applied such that further torque is not necessary. 
         [0061]    Referring now to  FIGS. 12 through 23 , an exemplary embodiment of a Finite Element Analysis (FEA) of system  10  is shown.  FIG. 12  illustrates an exemplary embodiment of boundary conditions on washer  18  during loading, while  FIG. 19  illustrates an exemplary embodiment of boundary conditions on upper pad  12  of  FIG. 1  during loading. 
         [0062]    The resultant deflection and stress on washer  18  at the boundary conditions of  FIG. 12  are illustrated in  FIGS. 13 and 14  at 200 inch-pounds of torque, in  FIGS. 15 and 16  at 250 inch-pounds of torque, and in  FIGS. 17 and 18  at 300 inch-pounds of torque. 
         [0063]    Additionally, the resultant stress and pressure on upper pad  12  at the boundary conditions of  FIG. 19  are illustrated in  FIGS. 20 and 21  at 250 inch-pounds of torque and in  FIGS. 22 and 23  at 535 inch-pounds of torque. 
         [0064]    Referring now to  FIGS. 24 through 26 , an alternate exemplary embodiment of a threaded mechanical fastening system according to the present disclosure is shown and is generally referred to by reference numeral  10 ′. Description of components parts performing similar or analogous functions to those described with respect to the embodiment of  FIG. 1  are omitted for reasons of brevity. 
         [0065]    In this embodiment, upper pad  12 ′ is configured so that landings  22  further include a washer guide edge  22 ′. It has been determined that centering of washer  18  with respect to gap  20  can be desired in some embodiments. Accordingly, edge  22 ′ is positioned on both sides of gap  20  and assists in ensuring that washer  18  remains centered over the gap. In some embodiments, edge  22 ′ can include a chamfer to ensure that washer  18  seats on landings  22  in a centered manner. 
         [0066]    Of course, it should be recognized that the centering of washer  18  over gap  20  is described above by way of example only as edge  22 ′ acting on the washer. However, it is also contemplated by the present disclosure for system  10 ′ to include one or more features (e.g., edge  22 ′) that act on one or more of washer  18 , bolt  14 , nut  16 , and any combinations thereof so as to ensure that washer remains centered with respect to gap  20 . The centering feature can be incorporated into upper pad  12 ′ and/or into the lower pad  12 ″ and/or can be a separate centering component. 
         [0067]    It should also be noted that the terms “first”, “second”, “third”, “upper”, “lower”, and the like may be used herein to modify various elements. These modifiers do not imply a spatial, sequential, or hierarchical order to the modified elements unless specifically stated. 
         [0068]    While the present disclosure has been described with reference to one or more exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the present disclosure. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the disclosure without departing from the scope thereof. Therefore, it is intended that the present disclosure not be limited to the particular embodiment(s) disclosed as the best mode contemplated, but that the disclosure will include all embodiments falling within the scope of the appended claims.