Abstract:
A wire rope having improved durability and that can be used in a medical device to be inserted into a patient&#39;s body. The wire rope includes a core wire and side wires. The core wire is a special metal element wire that has a hardness at an outer periphery in a cross-section thereof that is higher than that at a center in the cross-section thereof. The wire rope does not include grease.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a continuation of PCT/JP2016/063945 filed on May 11, 2016, the contents of which are incorporated by reference herein in their entirety. 
     
    
     BACKGROUND 
       [0002]    The disclosed embodiments relate to a wire rope comprising multiple metal element wires. 
         [0003]    In a conventional wire rope, multiple metal element wires are twisted together to form the wire rope. In general, wire ropes have advantages such as excellent impact resistance and good flexibility as compared with a single metal element wire. Further, wire ropes are often subjected to repeated bending, and thus desirably have good durability under such usage conditions. 
         [0004]    For example, Japanese Patent Application Laid-Open No. 2004-327254 describes an aluminum twisted wire (a wire rope) in which spaces between twisted wires inside an outermost aluminum twisted wire layer are filled with grease to improve the life time of the wire rope (see  FIG. 1  and the like). 
         [0005]    Further, Japanese Patent Application Laid-Open No. H08-144182 describes a twisted wire rope having an improved life time, which can be prepared by (1) forming an uneven surface on each surface of multiple metal element wires, (2) forming element twisted wires by twisting the multiple metal element wires each having the uneven surface, (3) twisting the element twisted wires and then applying a resin coating around the twisted element twisted wires, and (4) filling spaces between the resin coating and the element twisted wires with grease (see  FIG. 2  and others). 
         [0006]    Further, Japanese Patent Application Laid-Open No. 2004-124342 describes an inner wire rope having an improved abrasion resistance and the like, which can be prepared by subjecting side strands to deforestation processing to make surface contacts between a core strand and the side strands, and sealing lubricating oil between the core strand and the side strands (see  FIG. 1  and the like). 
         [0007]    However, a step of grease filling is inevitably required when manufacturing the wire ropes described in Japanese Patent Applications Laid-Open Nos. 2004-327254, H08-144182, and 2004-124342, although containing grease in the wire ropes can improve their durability. 
         [0008]    Further, the wire ropes described in Japanese Patent Applications Laid-Open Nos. 2004-327254, H08-144182, and 2004-124342 cannot be used in medical devices to be inserted into a patient&#39;s body because these wire ropes are filled with grease within the wire ropes. Therefore, there is a need to develop a wire rope having an improved durability without containing grease for use in medical devices. 
       SUMMARY 
       [0009]    The disclosed embodiments have been developed to address the above problem. An object of the disclosed embodiments is to provide a wire rope having improved durability without containing grease, and in particular a wire rope with improved durability which can be used in a medical device to be inserted into a patient&#39;s body. 
         [0010]    In order to achieve the above object, the disclosed embodiments include a wire rope comprising multiple metal element wires wound together, and in which the multiple metal element wires include at least one special metal element wire that has a first hardness at an outer periphery in a cross-section thereof that is higher than a second hardness at the center in the cross-section thereof. The special metal element wire can impart improved durability to the wire rope without requiring the use of grease, enabling the wire rope to be used in a medical device. 
         [0011]    As defined herein, a “special metal element wire” is a metal element wire in which the hardness at the outer periphery of the metal element wire is higher than at the center of the metal element wire. 
         [0012]    The at least one special metal element wire may be arranged at the center of the wire rope. This can further improve the durability of the wire rope. 
         [0013]    Moreover, the wire rope may consist only of the at least one special metal element wire and multiple side metal element wires in contact with the at least one special metal element wire. This can further improve the durability of the wire rope. 
         [0014]    The at least one special metal element wire may have a circular cross-section, and the multiple side metal element wires may each have an approximately trapezoidal cross-section. The cross-section is “approximately trapezoidal” if it resembles a trapezoid having 4 defined sides, even if the sides and/or corners are partially or even completely curved. This can even further improve the durability of the wire rope. 
         [0015]    Furthermore, a bundled wire rope may be formed by twisting together a plurality of any one of the wire ropes discussed above. This can further improve durability. 
         [0016]    Moreover, the wire rope may comprise, at its center, a twisted wire in which multiple special metal element wires are twisted together. This can improve the flexibility of the wire rope. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  shows a cross-sectional view of a wire rope according to the disclosed embodiments. 
           [0018]      FIG. 2  shows a first hardness distribution in a cross-section of a special metal element wire. 
           [0019]      FIG. 3  shows a second hardness distribution in a cross-section of a special metal element wire. 
           [0020]      FIG. 4  shows a side view of a wire rope according to the disclosed embodiments. 
           [0021]      FIG. 5  shows a cross-sectional view taken along line A-A in  FIG. 4 . 
           [0022]      FIG. 6  shows a side view of a wire rope according to the disclosed embodiments. 
           [0023]      FIG. 7  shows a cross-sectional view taken along line B-B in  FIG. 6 . 
           [0024]      FIG. 8  shows a cross-sectional view of a wire rope according to the disclosed embodiments. 
           [0025]      FIG. 9  shows a cross-sectional view of a wire rope according to the disclosed embodiments. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0026]    Below, embodiments of the present invention will be described with reference to the drawings. 
         [0027]      FIG. 1  shows a cross-sectional view of a wire rope according to the disclosed embodiments.  FIG. 2  shows a first hardness distribution of a cross-section of a special metal element wire used for the wire rope.  FIG. 3  shows a second hardness distribution of a cross-section of a special metal element wire used for the wire rope. 
         [0028]    With reference to  FIG. 1 , a wire rope  1  comprises a core wire  3  (which corresponds to the “special metal element wire”) located at the center, and 6 side wires  5  ( 5   a ,  5   b ,  5   c ,  5   d ,  5   e , and  5   f ) wound around the core wire  3 . 
         [0029]    The core wire  3  is a metal element wire having a circular cross-section. There is no particular limitation for the material of the core wire  3 , but stainless steel is used for purposes of this discussion. 
         [0030]    A peripheral part (outer periphery, or outer edge) of the core wire  3  in a cross-section has a higher hardness than a center of the core wire  3  in the cross-section. That is, the core wire  3  is configured to have a structure where only the surface region (surface) of the core wire  3  is hardened, but the inside of the core wire  3  is not hardened. This structure allows the core wire  3  to have both flexibility and improved resistance to abrasion due to contact between the core wire  3  and the side wires  5 . 
         [0031]    Note that conventionally known methods such as swaging and wire drawing can be used in order to obtain a metal element wire (e.g., the core wire  3 ) in which a hardness of the peripheral part in a cross-section of the metal element wire is higher than that of the center in the cross-section. 
         [0032]    Further, the hardness of the core wire  3  may increase in a second-order fashion toward the outer periphery from the center in a cross-section of the core wire  3  as shown in  FIG. 2 , or may increase in a linear fashion. Alternatively, the core wire  3  may include a constant-hardness region in the vicinity of the center of the core wire  3  that spans from the center to an intermediate position of the core wire  3  in a cross-section, and the hardness may increase from the intermediate position toward the outer periphery as shown in  FIG. 3 . 
         [0033]    Note that the hardness described in  FIGS. 2 and 3  is expressed in the Vickers hardness as measured with a Vickers hardness meter, and has a unit of “HV.” 
         [0034]    The hardness of the center of the core wire  3  in  FIG. 2  is about 650 HV, while the hardness at the outer periphery is about 700 HV, showing a difference of 50 HV. The hardness of the core wire  3  in  FIG. 3  is constant at about 650 HV in the vicinity of the center of the core wire  3 , while it is about 700 HV at the outer periphery, showing a difference of 50 HV. 
         [0035]    Note that the experiments performed by the present applicant demonstrated that the flexibility and abrasion resistance were improved even when the hardness at the center in a cross-section was only 550 HV, and the hardness at the outer periphery in the cross-section was only 580 HV. 
         [0036]    In contrast, the flexibility of the wire rope  1  was impaired and the durability decreased when the hardness of the entire region in a cross-section of the core wire  3  was, for example, 700 HV. 
         [0037]    The side wires  5  ( 5   a ,  5   b ,  5   c ,  5   d ,  5   e , and  5   f ), which are metal element wires each having a circular cross-section, are spirally wound around the core wire  3  in the longitudinal direction. There is no particular limitation for the material of the side wires  5  ( 5   a ,  5   b ,  5   c ,  5   d ,  5   e , and  5   f ) as well, but stainless steel is used for purposes of this discussion. Tungsten may also be used. 
         [0038]    In the wire rope  1 , the core wire  3  having a hardness of the peripheral part in a cross-section higher than that of the center is arranged at the center of the wire rope  1  such that the multiple side wires  5  ( 5   a ,  5   b ,  5   c ,  5   d ,  5   e , and  5   f ) all make contact with the core wire  3 . This can improve the durability of the wire rope  1 . 
         [0039]    Below, another wire rope of the disclosed embodiments will be described with reference to  FIGS. 4 and 5 . Throughout this disclosure, descriptions will be omitted for parts that have already been described, to which the same reference numbers will be assigned in the figures.  FIG. 4  shows a side view of the wire rope, and  FIG. 5  shows a cross-sectional view taken along line A-A in  FIG. 4 . 
         [0040]    With reference to  FIGS. 4 and 5 , a wire rope  11  comprises a core wire  3  located at the center of the wire rope  11 , and 6 side wires  15  ( 15   a ,  15   b ,  15   c ,  15   d ,  15   e , and  15   f ) wound around the core wire  3 . 
         [0041]    The side wires  15  ( 15   a ,  15   b ,  15   c ,  15   d ,  15   e , and  15   f ), which are metal element wires each deforestation-processed into an approximately trapezoidal shape, are spirally wound around the core wire  3  in the longitudinal direction. There is no particular limitation for the material of the side wires  15  ( 15   a ,  15   b ,  15   c ,  15   d ,  15   e , and  15   f ), but stainless steel is used for purposes of this discussion. Tungsten may also be used. 
         [0042]    In the wire rope  11 , the core wire  3  having a hardness of the peripheral part in a cross-section higher than that of the center is arranged at the center of the wire rope  11  such that the 6 side wires  15  ( 15   a ,  15   b ,  15   c ,  15   d ,  15   e , and  15   f ) each having an approximately trapezoidal cross-section all make surface contact with the core wire  3 . The wire rope  11  has an approximately circular cross-sectional outer periphery. This can improve not only the torque transmissibility of the wire rope  11  (the torque transmissibility to one end of a wire rope when the other end of the wire rope is rotated), but also the durability of the wire rope. 
         [0043]      FIG. 6  shows a side view of a wire rope according to the disclosed embodiments, and  FIG. 7  shows a cross-sectional view taken along line B-B in  FIG. 6 . 
         [0044]    With reference to  FIGS. 6 and 7 , a wire rope  101  comprises the core wire rope  11  shown in  FIGS. 4 and 5  located at the center, and 6 side wire ropes  21 ,  31 ,  41 ,  51 ,  61 , and  71  wound around the core wire rope  11 . That is, the wire rope  101  is a bundled wire rope. 
         [0045]    The side wire ropes  21 ,  31 ,  41 ,  51 ,  61 , and  71  each have a similar structure to that of the core wire rope  11 , and are spirally wound around the core wire rope  11  in the longitudinal direction. 
         [0046]    That is, the side wire rope  21  comprises a core wire  3   a  located at the center (which corresponds to the “special metal element wire”) and 6 side wires  25  ( 25   a ,  25   b ,  25   c ,  25   d ,  25   e , and  25   f ) wound around the core wire  3   a ; the side wire rope  31  comprises a core wire  3   b  (which corresponds to the “special metal element wire”) located at the center and 6 side wires  35  ( 35   a ,  35   b ,  35   c ,  35   d ,  35   e , and  35   f ) wound around the core wire  3   b ; the side wire rope  41  comprises a core wire  3   c  (which corresponds to the “special metal element wire”) located at the center and 6 side wires  45  ( 45   a ,  45   b ,  45   c ,  45   d ,  45   e , and  45   f ) wound around the core wire  3   c ; the side wire rope  51  comprises a core wire  3   d  (which corresponds to the “special metal element wire”) located at the center and 6 side wires  55  ( 55   a ,  55   b ,  55   c ,  55   d ,  55   e , and  55   f ) wound around the core wire  3   d ; the side wire rope  61  comprises a core wire  3   e  (which corresponds to the “special metal element wire”) located at the center and 6 side wires  65  ( 65   a ,  65   b ,  65   c ,  65   d ,  65   e , and  65   f ) wound around the core wire  3   e ; and the side wire rope  71  comprises a core wire of  3   f  (which corresponds to the “special metal element wire”) located at the center and 6 side wires  75  ( 75   a ,  75   b ,  75   c ,  75   d ,  75   e , and  75   f ) wound around the core wire  3   f.    
         [0047]    The wire rope  101  is formed by twisting a plurality of wire ropes, each of which has arranged at its center a core wire having a hardness of the peripheral part in a cross-section higher than that of the center such that 6 side wires each having an approximately trapezoidal cross-section all make contact with the core wire, each wire rope being configured to have an approximately circular cross-sectional outer periphery. This can further improve not only the torque transmissibility of the wire rope  101  (the torque transmissibility to one end of a wire rope when the other end of the wire rope is rotated), but also the durability of the wire rope  101 . 
         [0048]      FIG. 8  shows a cross-sectional view of a wire rope  81  according to the disclosed embodiments. The wire rope  81  comprises a core twisted wire  13  located at the center, 4 inner side wires  82  arranged at the outside of the core twisted wire  13 , and 8 outer side wires  85  wound around the core twisted wire  13  and the inner side wires  82 . 
         [0049]    The core twisted wire  13  comprises 4 metal element wires ( 13   a ,  13   b ,  13   c , and  13   d  (each corresponds to the “special metal element wire”), and each metal element wire has a circular cross-section. There is no particular limitation for the material of the metal element wires ( 13   a ,  13   b ,  13   c , and  13   d ), but stainless steel is used for purposes of this discussion. 
         [0050]    Here, the metal element wires ( 13   a ,  13   b ,  13   c , and  13   d ), which constitute the core twisted wire  13 , each have a hardness of the peripheral part in a cross-section higher than that of the center in the cross-section. That is, each metal element wire ( 13   a ,  13   b ,  13   c , and  13   d ) has a structure in which only the surface of the metal element wire is hardened, but the inside of the metal element wire is not hardened. Further, the core twisted wire  13  is formed by twisting four of these metal element wires. This can improve the flexibility and durability of the core twisted wire  13 . 
         [0051]    Moreover, 4 inner side wires  82  ( 82   a ,  82   b ,  82   c , and  82   d ) are arranged at the outside of the core twisted wire  13 . Each of the inner side wires  82  ( 82   a ,  82   b ,  82   c , and  82   d ) has a circular cross-section and a diameter smaller than that of each metal element wire ( 13   a ,  13   b ,  13   c , and  13   d ) of the core twisted wire  13 . Note that there is no particular limitation for the material of the inner side wires  82  ( 82   a ,  82   b ,  82   c , and  82   d ), but stainless steel is used for purposes of this discussion. 
         [0052]    Further, 8 outer side wires  85  ( 85   a ,  85   b ,  85   c ,  85   d ,  85   e ,  85   f ,  85   g , and  85   h ), which are metal element wires each having a circular cross-section, are arranged at the outside of the core twisted wire  13  and the inner side wires  82  ( 82   a ,  82   b ,  82   c , and  82   d ). Note that there is no particular limitation for the material of the outer side wires  85  ( 85   a ,  85   b ,  85   c ,  85   d ,  85   e ,  85   f ,  85   g , and  85   h ), but stainless steel is used for purposes of this discussion. 
         [0053]    In the wire rope  81 , the core twisted wire  13  (formed by twisting 4 metal element wires each having a hardness of the peripheral part in a cross-section higher than that of the central part) is arranged at the center. This can further improve the flexibility and durability of the wire rope  81 . 
         [0054]      FIG. 9  shows a cross-sectional view of a wire rope  91 . The wire rope  91  comprises a core twisted wire  23  located at the center, 4 inner side wires  92  arranged at the outside of the core twisted wire  23 , and 8 outer side wires  95  wound around the core twisted wire  23  and the inner side wires  92 . 
         [0055]    The core twisted wire  23  comprises 4 metal element wires ( 23   a ,  23   b ,  23   c , and  23   d , and each of the metal element wire has a circular cross-section. There is no particular limitation for the material of the metal element wires ( 23   a ,  23   b ,  23   c , and  23   d ), but stainless steel is used for purposes of the discussion. 
         [0056]    Here, among the metal element wires ( 23   a ,  23   b ,  23   c , and  23   d ) of the core twisted wire  23 , the metal element wire  23   d  has a hardness of the peripheral part in a cross-section higher than that of the center in the cross-section. That is, the metal element wire  23   d  is configured to have a structure in which only the surface of the metal element wire is hardened, but the inside of the metal element wire is not hardened (the metal element wire  23   d  corresponds to the “special metal element wire”). On the other hand, the metal element wires  23   a ,  23   b , and  23   c  each have an approximately constant hardness profile throughout a cross-section. 
         [0057]    Further, the core twisted wire  23  is formed by twisting the 4 metal element wires. This can further improve the flexibility of the core twisted wire  23 . 
         [0058]    Moreover, 4 inner side wires  92  ( 92   a ,  92   b ,  92   c , and  92   d ) are arranged at the outside of the core twisted wire  23 . Each of the inner side wires  92  ( 92   a ,  92   b ,  92   c , and  92   d ) has a circular cross-section and a diameter smaller than that of each metal element wire ( 23   a ,  23   b ,  23   c , and  23   d ) of the core twisted wire  23 . Note that there is no particular limitation for the material of the inner side wires  92  ( 92   a ,  92   b ,  92   c , and  92   d ), but stainless steel is used for purposes of this discussion. 
         [0059]    Furthermore, 8 outer side wires  95  ( 95   a ,  95   b ,  95   c ,  95   d ,  95   e ,  95   f ,  95   g , and  95   h ), which are metal element wires each having a circular cross-section, are arranged at the outside of the core twisted wire  23  and the inner side wires  92  ( 92   a ,  92   b ,  92   c , and  92   d ). Note that there is no particular limitation for the material of the outer side wires  95  ( 95   a ,  95   b ,  95   c ,  95   d ,  95   e ,  95   f ,  95   g , and  95   h ), but stainless steel is used for purposes of this discussion. 
         [0060]    In the wire rope  91 , the core twisted wire  23  formed with the metal element wires each having a hardness of the peripheral part in a cross-section higher than that of the central part is arranged at the center of the wire rope  91 . This can improve the flexibility and durability of the wire rope  91 . 
         [0061]    Although disclosed embodiments of wire ropes are described above, the present invention shall not be limited to these embodiments. The present invention can be practiced with various modifications made without departing from the scope of the present invention. 
         [0062]    For example, as described above, the side wires  5 ,  15 ,  25 ,  35 ,  45 ,  55 ,  65 , and  75  in the wire ropes  1 ,  11 , and  101  are each formed with 6 metal element wires. The number of metal element wires is, however, not limited to 6, and 3 or more may be sufficient. 
         [0063]    Moreover, the core twisted wires  13  and  23  are described as being formed by twisting 4 metal element wires. The number of metal element wires is, however, not limited to 4, and two or more may be sufficient. 
         [0064]    Moreover, the outer side wires  85  and  95  in the wire ropes  81  and  91  each comprise 8 metal element wires. The number of metal element wires is, however, not limited to 8, and any number may be used as long as the core twisted wire  13  or  23  is covered. 
         [0065]    Moreover, the inner side wires  82  and  92  are provided in the wire ropes  81  and  91 , but the inner side wires  82  and  92  may not be present.