Patent Publication Number: US-2005136255-A1

Title: High-strength abrasion-resistant monofilament yarn and sleeves formed therefrom

Description:
FIELD OF THE INVENTION  
      This invention concerns monofilament yarns formed from different materials combined to provide high strength and abrasion resistance.  
     BACKGROUND OF THE INVENTION  
      It is often desirable to have yarns with combinations of properties that are not normally present in a single yarn formed of a single material. For example, a sleeve for protecting elongated items such as wiring harnesses or optical fibers should have both adequate tensile strength as well as abrasion resistance. These characteristics are desirable due to the nature of the use of the sleeve, which, when deployed for use, is drawn over considerable distances through narrow, crowded ducts and over and around obstacles and the like. The drawing process places high tensile loads on the sleeve and induces in it significant stress, hence the need for relatively high tensile strength. Contact with the duct sidewalls (especially at 90° bends in the duct), as well as other sleeves and objects within the duct induce frictional forces on the sleeve which causes heating and abrasion, hence the desire for abrasion resistance.  
      Other protective sleeves may require abrasion resistant yarns that have relatively high resilience in order to provide radially oriented biasing forces that keep the sleeve in an open configuration. The abrasion resistance protects the sleeve from vibration induced wear, as might occur with sleeves used to protect wiring harnesses in an automobile or an aircraft.  
      In the past, it was the practice to form such sleeves from different types of yarns made from different materials having the desired characteristics. For example, a sleeve would be woven from aramid or polyester yarns to provide high tensile strength, and lower strength nylon yarns would be interwoven with the high strength yarns to provide abrasion resistance. The nylon yarns would have a greater diameter than the aramid or polyester yarns so as to form an outwardly extending contact surface of nylon that would protect the higher strength yarns from abrasion. However, such sleeves are relatively expensive to manufacture due to the need for different yarns.  
     SUMMARY OF THE INVENTION  
      The invention concerns a filamentary member comprising an elongated inner core formed of a first material and an elongated outer sheath surrounding the inner core. The outer sheath is formed of a second material. The first material has a higher tensile strength than the second material, said second material has a greater abrasion resistance than the first material.  
      Preferably, the first material is polyester and comprises about 70 wt % of the filamentary member, and the second material is nylon and comprises about 30 wt % of the filamentary member. The filamentary members have a minimum diameter of 0.006 inches and may range in diameter between 0.006 inches and 0.015 inches.  
      The invention also includes tubular sleeves made from the aforementioned filamentary members. The sleeves may be woven, knitted or braided. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a cross-sectional view of a filamentary member according to the invention;  
       FIG. 2  is a longitudinal sectional view of a spinnerette used in manufacturing the filamentary member shown in  FIG. 1 ;  
       FIG. 3  is a perspective view of an exemplary sleeve structure made of filamentary members according to the invention;  
       FIG. 4  is a perspective view of a plurality of sleeves within a duct;  
       FIG. 5  is a perspective view of a sleeve assembly comprising sleeves according to the invention;  
       FIG. 6  is a cross-sectional view taken at line  6 - 6  of  FIG. 5 ; and  
       FIGS. 7 and 8  are perspective views of further examples of sleeves manufactured using filamentary members according to the invention. 
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS  
       FIG. 1  shows a cross-sectional view of a filamentary member  10  according to the invention. Filamentary member  10  is a monofilament having a core  12  surrounded by a sheath  14 . Preferably, core  12  is a polyester such as PET and sheath  14  is a nylon or amide polymer such as nylon 6, nylon 66 and nylon 610. The polyester core  12  provides the desired tensile strength and resilience to the monofilament  10 , and the nylon sheath  14 , surrounding core  12 , provides the abrasion resistance.  
      Other high-strength polymer materials, such as PPS and PEEK, are also feasible for forming core  12 . Alternative materials for sheath  14  include PFA and PTFE.  
      Monofilament  10  is preferably manufactured using a sheath/core extrusion process illustrated in  FIG. 2 . A spinnerette  16  is used having an inner nozzle  18  positioned within an outer nozzle  20 . A material  22  comprising the core  12 , in this example polyester, is extruded under pressure from the inner nozzle  18 . Simultaneously, another material  24 , the abrasion resistant nylon, for example, is extruded under pressure from the outer nozzle  20 . The nozzles  18  and  20  are aligned so that the core  12  exits the spinnerette  16  surrounded by the sheath  14  to form the filamentary member  10 .  
      The materials  24  and  22  forming the sheath  14  and core  12  are preferably compatible with one another such that, upon extrusion, the sheath and core fuse together at the interface  26  between them to provide transverse shear continuity to the filamentary member  10 . Fusing of the sheath  14  to the core  12  is facilitated by the particular details of the extrusion process, which may, for example, be a melt extrusion wherein materials  22  and  24  are extruded in a molten state and fuse together in this state upon contact within the spinnerette  16 .  
      Filamentary members  10  may be interlaced by weaving, braiding or knitting techniques to produce various types of sleeves for protecting elongated items from various harsh environments, particularly abrasion. Three examples of practical protective sleeves are presented below.  
      Flat Woven Sleeve  
       FIG. 3  shows an elongated sleeve  30  comprising opposed layers  32  and  34  of woven filamentary members  10  according to the invention. Filamentary members  10  include warp yarns  36  and fill yarns  38 , the fill yarns being common to both layers  32  and  34 . Preferably, the core  12  of filamentary member  10  is a polyester and the sheath  14  is nylon. Other candidate materials for the core include PPS and PEEK, and the sheath could also be made of PFA and PTFE.  
      Because the yarns have a high-strength inner core  12  and an abrasion-resistant outer sheath  14 , the sleeve  30  is able to withstand both the tensile stresses imposed, as well as the friction between the sleeve and objects which it contacts while being drawn through a duct. The single filamentary member  10  combines both properties of tensile strength and abrasion resistance, thus the sleeve  30  may be woven simply and inexpensively using a single type of yarn for both warp and fill yarns  36  and  38 . This contrasts with sleeves made from a combination of different yarns to provide multiple, and sometimes mutually exclusive characteristics such as high strength and abrasion resistance. The weaving of such sleeves is more complex and expensive than a sleeve  30  made from filamentary members  10  having a high-strength core  12  and an abrasion resistant outer sheath  14  according to the invention.  
      The opposed layers  32  and  34  may have a common seamless edge  40  and are joined to one another along a second edge  42  formed by various means. Preferably, as shown in  FIG. 4 , the opposed layers  32  and  34  are of equal width and surround and define a central space  44 . The opposed layers  32  and  34  are nominally in a substantially flat, closely spaced relationship. This allows them to be easily drawn through a duct  46  as depicted in  FIG. 4 . As further shown in that Figure, opposed layers  32  and  34  are resiliently separable into a spaced apart relationship, in which relationship a plurality of elongated items  48 , such as optical fiber cables or wire bundles may be accommodated within the central space  44 . Preferably, the opposed layers  32  and  16  are resiliently biased to return to the substantially flat configuration in the absence of the elongated items  48 .  
      In one preferred embodiment, both the warp and fill yarns  36  and  38  consist essentially of sheath and core filamentary members  10  and are interwoven using a weave pattern characterized by “floats” of either warp or fill yarns on the surface of the woven layers. A yarn is said to “float” when it is not interwoven alternately with each cross yarn but skips two or more cross yarns before being interwoven. Weaves using floats include twill, satin and sateen weaves. In twill and satin weaves, the warp yarns float over the fill yarns, whereas in the sateen weave, the fill yarns float over the warp yarns. Satin weaves are characterized by having longer floats than twills. In general twill, satin and sateen weaves are favored because they provide a durable fabric which resists wear and abrasion and provides a smooth surface with low friction. However, plain weaves are perfectly satisfactory for many applications. The floats are preferably positioned on the inner surface of the sleeves. This allows elongated items  48  to be drawn more easily through the central space  44  when such items are being installed within the sleeve  30 . The flat configuration of the sleeve also provides advantage when it is drawn through a duct, as it maintains a low profile, allowing the sleeve to more readily traverse crowded ducts and sharp curves in comparison with a sleeve that is normally biased into an open configuration.  
      In a particular embodiment using sheath and core warp and fill yarns, the warp yarns have a diameter from about 0.006 to about 0.015 inches, the fill yarns have a diameter from about 0.006 to about 0.015 inches, and the sleeve  30  has a weave density of 25 to 75 ends per inch by 20 to 60 picks per inch. The weave density depends upon the sizes of the warp and fill yarns comprising the sleeve. Preferably, the core comprises about 70 wt % of the filamentary member and the sheath comprises about 30 wt %.  
      As shown in  FIG. 3 , sleeve  30  also includes a pull tape  50  arranged within the central space  44  between the opposed layers  32  and  34 . The pull tape  50  extends the length of the sleeve  30  and facilitates the installation of elongated items. Once the sleeve is positioned within a duct, the elongated item is attached to one end of the pull tape  50  and the other end is drawn through the sleeve, the elongated item replacing the pull tape within the sleeve. Note that the use of yarns  36  and  38  having an abrasion resistant outer surface facilitates drawing of the elongated item through the sleeve  30 , as well as drawing of the sleeve through the duct. Preferably, pull tape  50  has a flat cross-sectional profile to reduce the bulk of the sleeve. The pull tape  50  may be woven, braided or otherwise interlaced from high strength fibers such as aramids which will withstand significant tensile loads during the pulling operation. Pull tapes having a tensile capability between 300 lbs and 2,600 lbs tension force are considered feasible with the invention.  
      As shown in  FIG. 3 , the sleeve  30  includes an attachment piece  52 . Attachment piece  52  may take one of several embodiments and serves to attach multiple sleeves  30  to one another in overlying relation to form an assembly as illustrated in  FIG. 5 . As further shown in the figure, the attachment piece  52  may also provide a location where a line  54  may be attached to draw one or more sleeves  30  through a duct.  
      As shown in  FIGS. 3, 5  and  6 , in a preferred embodiment of the sleeve  30 , the attachment piece  52  comprises a grommet  56  located at one end of the sleeve  30 . As shown in cross-section in  FIG. 6 , grommet  56  comprises a tube  58  that extends through one or more sleeves  30 . A flange  60  is attached to one end of the tube  58 . The flange  60  provides a surface  62  engageable with an opposed layer  32  of one of the sleeves  30  to retain the grommet to the sleeve. The grommet also comprises a ring  64  which receives tube  58  and is positionable in overlying relation with flange  60 . Ring  64  provides a surface  66  engageable with another opposed layer  34 , either on the same sleeve  30  or on another sleeve, in overlying relation with the first named sleeve to retain the grommet to the sleeve or assembly of sleeves. The ring  64  is retained by a lip  68  formed by outwardly reverse folding the tube in a cold-working process. Grommet  56  may be used on a single sleeve  30  as shown in  FIG. 3 , or as shown in  FIG. 5 , on a sleeve assembly to attach a plurality of sleeve structures to one another in overlying relationship. The grommet  56  enables single or multiple sleeves  30  to be drawn through a duct. After the sleeves are positioned within the duct, the grommet  56  is removed, preferably by severing the sleeves at or near the grommet.  
      Braided Sleeve  
       FIG. 7  shows a sleeve  70  formed by braiding filamentary members  10  having a high-strength, resilient core  12  and an abrasion resistant sheath  14  as shown in  FIG. 1 . Due to its combination of high tensile strength and abrasion resistance afforded by filamentary members  10 , braided sleeves such as  70  may be advantageous for use as protective/reinforcing coverings for flexible hoses carrying pressurized fluids. The high strength of the filamentary members provide the hose with a high burst pressure while the abrasion resistance provides for a robust design capable of withstanding rough handling.  
      Braided sleeves made from filamentary members having a resilient core within an abrasion resistant sheath are also useful, for example, in automotive applications where a protective sleeve may be used to protect a wiring harness from abrasion caused by contact with the automobile structure due to engine or road vibration. The resilient qualities of the core provide a radially directed biasing force that keeps the braided sleeve in an open configuration.  
      Woven Biased Slit Sleeves  
      The combination of resilience and abrasion resistance is also useful in the manufacture of protective sleeves  72 , shown in  FIG. 8 , that are biased into an open configuration by the resilience of the fill filaments  74 . Sleeve  72  may have a lengthwise slit  76  providing an opening  78  that allows the sleeve  72  to be positioned around a wiring harness or other elongated item  48  for which the ends are inaccessible. The slit  76  also allows splices or breakouts to be conveniently formed at any point along the length of the sleeve.  
      Slit  76  may be closed by the resilience of the fill filaments  74  biasing the edges  80  into contact or overlying engagement, or closing means  82 , such as hook and loop fasteners may be used to secure the slit closed but allow it to be conveniently opened as necessary for access to the elongated items therein. While the resilience of the core provides the biasing force to maintain the sleeve  72  in an open configuration with the edges  80  engaged so as to close the opening  78 , the abrasion resistant sheath of the filamentary members protects the sleeve and its contents from damage due to vibration or motion induced friction.  
      Filamentary members having a high-strength resilient core surrounded by an abrasion resistant sheath combine desirable and mutually exclusive characteristics in a single filamentary member and thus allow protective sleeves also having these characteristics to be made simply and inexpensively.