Abstract:
A rope structure adapted to engage an intermediate structure while loads are applied to ends of the rope structure comprises a primary strength component and a coating. The primary strength component comprises a plurality of fibers adapted to bear the loads applied to the ends of the rope structure. The coating comprises a mixture of a lubricant portion and a binder portion. The lubricant portion comprises particles having an average size of within approximately 0.01 microns to 2.00 microns. The binder portion is applied to the primary strength portion as a liquid and dries to support the lubricant portion relative to at least some of the fibers. The matrix supports the lubricant portion such that the lubricant portion reduces friction between at least some of the plurality of fibers and between at least some of the plurality of fibers and the intermediate structure.

Description:
RELATED APPLICATIONS 
       [0001]    This application (Attorney&#39;s Ref. No. Docket No. 217258) is a continuation of U.S. patent application Ser. No. 12/776,958 filed May 10, 2010. 
         [0002]    U.S. patent application Ser. No. 12/776,958 is a continuation-in-part of U.S. patent application Ser. No. 11/522,236 filed Sep. 14, 2006, now U.S. Pat. No. 7,739,863, which issued on Jun. 22, 2010. 
         [0003]    U.S. patent application Ser. No. 11/522,236 claims benefit of U.S. Provisional Patent Application Ser. No. 60/717,627 filed Sep. 15, 2005. 
         [0004]    The subject matter of the foregoing related applications are incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0005]    The present invention relates to rope systems and methods and, in particular, to ropes that are coated to improve the resistance of the rope to bending fatigue. 
       BACKGROUND 
       [0006]    The characteristics of a given type of rope determine whether that type of rope is suitable for a specific intended use. Rope characteristics include breaking strength, elongation, flexibility, weight, bending fatigue resistance and surface characteristics such as abrasion resistance and coefficient of friction. The intended use of a rope will determine the acceptable range for each characteristic of the rope. The term “failure” as applied to rope will be used herein to refer to a rope being subjected to conditions beyond the acceptable range associated with at least one rope characteristic. 
         [0007]    The present invention relates to ropes that are commonly referred to in the industry as “lift lines”. Lift lines are used to deploy (lower) or lift (raise) submersible equipment used for deep water exploration. Bending fatigue and abrasion resistance characteristics are highly important in the context of lift lines. 
         [0008]    In particular, a length of lift line is connected at a first end to an on-board winch or capstan and at a second end to the submersible equipment. Between the winch and the submersible equipment, the lift line passes over or is wrapped around one or more intermediate structural members such as a closed chock, roller chock, bollard or bit, staple, bullnose, cleat, a heave compensating device, or a constant tensioning device. 
         [0009]    When loads are applied to the lifting line, the lifting line wraps around such intermediate structural members and is thus subjected to bending fatigue and abrasion at the intermediate structural members. Abrasion and heat generated by friction at the point of contact between the lifting line and the intermediate structural members can create wear on the lifting line that can affect the performance of the lifting line and possibly lead to failure thereof. 
         [0010]    The need thus exists for improved ropes for use as lifting lines that have improved bending fatigue and abrasion resistance characteristics. 
       SUMMARY 
       [0011]    The present invention may be embodied as a rope structure adapted to engage an intermediate structure while loads are applied to ends of the rope structure comprising a primary strength component and a coating. The primary strength component comprises a plurality of fibers adapted to bear the loads applied to the ends of the rope structure. The coating comprises a mixture of a lubricant portion and a binder portion. The lubricant portion comprises particles having an average size of within approximately 0.01 microns to 2.00 microns. The binder portion is applied to the primary strength portion as a liquid and dries to support the lubricant portion relative to at least some of the fibers. The matrix supports the lubricant portion such that the lubricant portion reduces friction between at least some of the plurality of fibers and between at least some of the plurality of fibers and the intermediate structure. 
         [0012]    The present invention may also be embodied as a method of forming a rope structure adapted to engage an intermediate structure while loads are applied to ends of the rope structure, comprising the following steps. A plurality of fibers is combined to form a primary strength component adapted to bear the loads applied to the ends of the rope structure. A coating material is provided in liquid form and comprises a lubricant portion and a binder portion. The coating material comprises substantially between 5% and 40% by weight of the lubricant portion. The coating material is applied in liquid form to the primary strength component. The coating material applied to the primary strength component is allowed to dry on the primary strength component such that the binder portion at least partly surrounds at least some of the fibers to support the lubricant portion relative to at least some of the fibers such that the lubricant portion reduces friction between adjacent fibers and between at least some of the plurality of fibers and the intermediate structure. 
         [0013]    The present invention may also be embodied as a rope structure adapted to engage an intermediate structure while loads are applied to ends of the rope structure comprising a primary strength component and a coating. The primary strength component comprises a plurality of fibers adapted to bear the loads applied to the ends of the rope structure, where the plurality of fibers are combined to form a plurality of yarns, the plurality of yarns are combined to form a plurality of strands, and the plurality of strands are combined to form the primary strength component. The coating comprises particles suspended within a matrix formed of binder material such that the binder fixes the particles relative to at least some of the fibers such that the particles reduce friction between at least some of the plurality of fibers and between at least some of the plurality of fibers and the intermediate structure. An average size of the particles is within approximately 0.01 microns to 2.00 microns. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIGS. 1A and 1B  are schematic cut-away views of example ropes constructed in accordance with, and embodying, the principles of the present invention; 
           [0015]      FIG. 2  is a side elevation view of a first example of a rope of the present invention; 
           [0016]      FIG. 3  is a radial cross-section of the rope depicted in  FIG. 2 ; 
           [0017]      FIG. 4  is a close-up view of a portion of  FIG. 3 ; 
           [0018]      FIG. 5  is a side elevation view of a second example of a rope of the present invention; 
           [0019]      FIG. 6  is a radial cross-section of the rope depicted in  FIG. 5 ; 
           [0020]      FIG. 7  is a close-up view of a portion of  FIG. 6 ; 
           [0021]      FIG. 8  is a side elevation view of a third example of a rope of the present invention; 
           [0022]      FIG. 9  is a radial cross-section of the rope depicted in  FIG. 8 ; 
           [0023]      FIG. 10  is a close-up view of a portion of  FIG. 9 ; 
           [0024]      FIG. 11  is a side elevation view of a fourth example of a rope of the present invention; 
           [0025]      FIG. 12  is a radial cross-section of the rope depicted in  FIG. 8 ; and 
           [0026]      FIG. 13  is a close-up view of a portion of  FIG. 12 . 
       
    
    
     DETAILED DESCRIPTION 
       [0027]    Referring initially to  FIGS. 1A and 1B  of the drawing, depicted in cross-section therein are rope structures  20   a  and  20   b  constructed in accordance with, and embodying, the principles of the present invention. The rope structures  20   a  and  20   b  are each formed by one or more plys or strands  22 . The plys or strands  22  are formed by one or more yarns  24 . The yarns  24  are formed by a plurality of fibers  26 . By way of example, the fibers  26  may be twisted together to form the yarns  24 , the yarns  24  twisted to form the plys or strands  22 , and the strands  22  braided or twisted to form the rope structure  20   a  or  20   b.    
         [0028]    In addition, the example rope structures  20   a  and  20   b  each comprises a coating  30  that is applied either to the entire rope structure ( FIG. 1A ) or to the individual strands ( FIG. 1B ). In the example rope structures  20   a  and  20   b , coating material is applied in liquid form and then allowed to dry to form the coating  30 . The coating  30  comprises a binder portion  32  (solid matrix) and a lubricant portion  34  (e.g., suspended particles). The binder portion  32  adheres to or suspends the fibers  26  to hold the lubricant portion  34  in place adjacent to the fibers  26 . More specifically, the coating  30  forms a layer around at least some of the fibers  26  that arranges the lubricant portion  34  between at least some of the adjacent fibers  26  and between the fibers  26  and any external structural members in contact with the rope structure  20   a  or  20   b.    
         [0029]    The fibers  26  are combined to form the primary strength component of the rope structures  20   a  and  20   b . The lubricant portion  34  of the coating  30  is supported by the binder portion  32  to reduce friction between adjacent fibers  26  as well as between the fibers  26  and any external structural members in contact with the rope structure  20   a  or  20   b . The lubricant portion  34  of the coating  30  thus reduces fatigue on the fibers  26  when the rope structures  20   a  or  20   b  are bent around external structures. Without the lubricant portion  34  of the coating  30 , the fibers  26  would abrade each other, increasing bending fatigue on the entire rope structure  20   a  or  20   b . The lubricant portion  34  of the coating  30  further reduces friction between the fibers  26  and any external structural members, thereby increasing abrasion resistance of the rope structures  20   a  and  20   b.    
         [0030]    With the foregoing understanding of the basic construction and characteristics of the rope structures  20   a  and  20   b  of the present invention in mind, the details of construction and composition of the rope structures  20  will now be described. 
         [0031]    In the liquid form, the coating material comprises at least a carrier portion, the binder portion, and the lubricant portion. The carrier portion maintains the liquid form of the coating material in a flowable state. However, the carrier portion evaporates when the wet coating material is exposed to the air, leaving the binder portion  32  and the lubricant portion  34  to form the coating  30 . When the coating material has dried to form the coating  30 , the binder portion  32  adheres to the surfaces of at least some of the fibers  26 , and the lubricant portion  34  is held in place by the binder portion  32 . The coating material is solid but not rigid when dried as the coating  30 . 
         [0032]    In the example rope structures  20   a  and  20   b,  the coating material is formed by a mixture comprising a base forming the carrier portion and binder portion and PolyTetraFluoroEthylene (PTFE) forming the lubricant portion. The base of the coating material is available from s.a. GOVI n.v. of Belgium under the tradename LAGO 45 and is commonly used as a coating material for rope structures. Alternative products that may be used as the base material include polyurethane dispersions; in any event, the base material should have the following properties: good adhesion to fiber, stickiness, soft, flexible. The base of the coating material is or may be conventional and will not be described herein in further detail. 
         [0033]    The example lubricant portion  34  of the coating material is a solid material generically known as PTFE but is commonly referred to by the tradename Teflon. The PTFE used in the coating material of the example rope structures  20   a  and  20   b  is in powder form, although other forms may be used if available. The particle size of the PTFE should be within a first preferred range of approximately 0.10 to 0.50 microns on average but in any event should be within a second preferred range of 0.01 to 2.00 microns on average. The example rope structures  20   a  and  20   b  are formed by a PTFE available in the marketplace under the tradename PFTE30, which has an average particle size of approximately 0.22 microns. 
         [0034]    The coating material used by the example rope structures  20   a  and  20   b  comprises PTFE within a first preferred range of approximately 32 to 37% by weight but in any event should be within a second preferred range of 5 to 40% by weight, with the balance being formed by the base. The example rope structures are formed by a coating material formed by approximately 35% by weight of the PTFE. 
         [0035]    As an alternative to PTFE, the lubricant portion  34  may be formed by solids of other materials and/or by a liquid such as silicon oil. Other example materials that may form the lubricant portion  34  include graphite, silicon, molybdenum disulfide, tungsten disulfide, and other natural or synthetic oils. In any case, enough of the lubricant portion  34  should be used to yield an effect generally similar to that of the PTFE as described above. 
         [0036]    The coating  30  is applied by dipping the entire rope structure  2   a  and/or individual strands  22  into or spraying the structure  20   a  and/or strands  22  with the liquid form of the coating material. The coating material is then allowed to dry on the strands  22  and/or rope structure  20   a . If the coating  30  is applied to the entire rope structure  20   a , the strands are braided or twisted before the coating material is applied. If the coating  30  is applied to the individual strands  22 , the strands are braided or twisted to form the rope structure  20   b  after the coating material has dried. 
         [0037]    In either case, one or more voids  36  in the coating  30  may be formed by absences of coating material. Both dipping and spraying are typically done in a relatively high speed, continuous process that does not allow complete penetration of the coating material into the rope structures  20   a  and  20   b . In the example rope structure  20   a , a single void  36  is shown in  FIG. 1A , although this void  36  may not be continuous along the entire length of the rope structure  20   a . In the example rope structure  20   b , a void  36  is formed in each of the strands  22  forming the rope structure  20   b . Again, the voids  36  formed in the strands  22  of the rope structure  20   b  need not be continuous along the entire length of the rope structure  20   a.    
         [0038]    In the example rope structures  20   a  and  20   b , the matrix formed by the coating  30  does not extend through the entire volume defined by the rope structures  20   a  or  20   b . In the example structures  20   a  and  20   b , the coating  30  extends a first preferred range of approximately ¼ to ½ of the diameter of the rope structure  20   a  or the strands of the rope structure  20   b  but in any event should be within a second preferred range of approximately ⅛ to ¾ of the diameter of the rope structure  20   a  or the strands  22  of the rope structure  20   b . In the example rope structures  20   a  and  20   b , the coating matrix extends through approximately ⅓ of the diameter of the rope structure  20   a  or the strands  22  of the rope structure  20   b.    
         [0039]    In other embodiments, the matrix formed by the coating  30  may extend entirely through the entire diameter of rope structure  20   a  or through the entire diameter of the strands  22  of the rope structure  20   b . In these cases, the rope structure  20   a  or strands  22  of the rope structure  20   b  may be soaked for a longer period of time in the liquid coating material. Alternatively, the liquid coating material may be forced into the rope structure  20   a  or strands  22  of the rope structure  20   b  by applying a mechanical or fluid pressure. 
         [0040]    The following discussion will describe several particular example ropes constructed in accordance with the principles of the present invention as generally discussed above. 
       FIRST SPECIFIC ROPE EXAMPLE  
       [0041]    Referring now to  FIGS. 2 ,  3 , and  4 , those figures depict a first specific example of a rope  40  constructed in accordance with the principles of the present invention. As shown in  FIG. 2 , the rope  40  comprises a rope core  42  and a rope jacket  44 .  FIG. 2  also shows that the rope core  42  and rope jacket  44  comprise a plurality of strands  46  and  48 , respectively.  FIG. 4  shows that the strands  46  and  48  comprise a plurality of yarns  50  and  52  and that the yarns  50  and  52  in turn each comprise a plurality of fibers  54  and  56 , respectively.  FIGS. 3 and 4  also show that the rope  40  further comprises a coating material  58  that forms a matrix that at least partially surrounds at least some of the fibers  54  and  56 . 
         [0042]    The exemplary rope core  42  and rope jacket  44  are formed from the strands  46  and  48  using a braiding process. The example rope  40  is thus the type of rope referred to in the industry as a double-braided rope. The strands  46  and  48  may be substantially identical in size and composition. Similarly, the yarns  50  and  52  may also be substantially identical in size and composition. However, strands and yarns of different sizes and compositions may be combined to form the rope core  42  and rope jacket  44 . Additionally, the fibers  54  and  56  forming at least one of the yarns  50  and  52  may be of different types. 
       SECOND ROPE EXAMPLE  
       [0043]    Referring now to  FIGS. 5 ,  6 , and  7 , those figures depict a second example of a rope  60  constructed in accordance with the principles of the present invention. As perhaps best shown in  FIG. 6 , the rope  60  comprises a plurality of strands  62 .  FIG. 7  further illustrates that each of the strands  62  comprises a plurality of yarns  64  and that the yarns  64  in turn comprise a plurality of fibers  66 .  FIGS. 6 and 7  also show that the rope  60  further comprises a coating material  68  that forms a matrix that at least partially surrounds at least some of the fibers  66 . 
         [0044]    The strands  62  are formed by combining the yarns  64  using any one of a number of processes. The exemplary rope  60  is formed from the strands  62  using a braiding process. The example rope  60  is thus the type of rope referred to in the industry as a braided rope. 
         [0045]    The strands  62  and yarns  64  forming the rope  60  may be substantially identical in size and composition. However, strands and yarns of different sizes and compositions may be combined to form the rope  60 . In the example rope  60 , the strands  62  (and thus the rope  60 ) may be 100% HMPE or a blend of 40-60% by weight of HMPE with the balance being Vectran. 
       THIRD ROPE EXAMPLE  
       [0046]    Referring now to  FIGS. 8 ,  9 , and  10 , those figures depict a third example of a rope  70  constructed in accordance with the principles of the present invention. As perhaps best shown in  FIG. 9 , the rope  70  comprises a plurality of strands  72 .  FIG. 10  further illustrates that each of the strands  72  comprises a plurality of yarns  74 , respectively. The yarns  74  are in turn comprised of a plurality of fibers  76 .  FIGS. 9 and 10  also show that the rope  70  further comprises a coating material  78  that forms a matrix that at least partially surrounds at least some of the fibers  76 . 
         [0047]    The strands  72  are formed by combining the yarns  74  using any one of a number of processes. The exemplary rope  70  is formed from the strands  72  using a twisting process. The example rope  70  is thus the type of rope referred to in the industry as a twisted rope. 
         [0048]    The strands  72  and yarns  74  forming the rope  70  may be substantially identical in size and composition. However, strands and yarns of different sizes and compositions may be combined to form the rope  70 . 
       FOURTH ROPE EXAMPLE  
       [0049]    Referring now to  FIGS. 11 ,  12 , and  13 , those figures depict a fourth example of a rope  80  constructed in accordance with the principles of the present invention. As perhaps best shown in  FIG. 12 , the rope  80  comprises a plurality of strands  82 .  FIG. 13  further illustrates that each of the strands  82  comprise a plurality of yarns  84  and that the yarns  84  in turn comprise a plurality of fibers  86 , respectively.  FIGS. 12 and 13  also show that the rope  80  further comprises a coating material  88  that forms a matrix that at least partially surrounds at least some of the fibers  86 . 
         [0050]    The strands  82  are formed by combining the yarns  84  using any one of a number of processes. The exemplary rope  80  is formed from the strands  82  using a braiding process. The example rope  80  is thus the type of rope commonly referred to in the industry as a braided rope. 
         [0051]    The strands  82  and yarns  84  forming the rope  80  may be substantially identical in size and composition. However, strands and yarns of different sizes and compositions may be combined to form the rope  80 . The first and second types of fibers are combined to form at least some of the yarns  84  are different as described above with reference to the fibers  24  and  28 . In the example rope  80 , the strands  82  (and thus the rope  80 ) may be 100% HMPE or a blend of 40-60% by weight of HMPE with the balance being Vectran. 
         [0052]    Given the foregoing, it should be clear to one of ordinary skill in the art that the present invention may be embodied in other forms that fall within the scope of the present invention.