Abstract:
A duct having lubricious interior qualities includes a cylindrical continuous polymeric layer and a plurality of longitudinally extending stripes of material coupled to the inside the cylindrical layer. The striping material comprises as a component at least silicone in order to provide a lubricious quality to the interior of the duct. A composition for a striping material for application to the interior of a duct comprises a mixture of a polyethylene component and a silicone component. A coloring component may also be used to color the striping.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to U.S. Provisional Application No. 60/868,449, filed Dec. 4, 2006, the disclosure of which is incorporated herein by reference in its entirety. 
     
    
     FIELD 
       [0002]    This technology relates to a duct having inner striping and a composition for a lubricious inner striping of a duct for lowering the amount of friction inside the duct. 
       BACKGROUND 
       [0003]    Ducts are currently utilized for storing cables, such as fiber optic cables, electric cables, and coaxial cables for cable television. These ducts are utilized in construction projects, buried under the ground, or used in other known installations. Ducts are utilized to easily thread various cables throughout an installation, or to replace or upgrade cables within an installation. It is beneficial to provide the interior of ducts with prelubrication in order to allow easy insertion and threading of cables within the duct. Currently known techniques for lubricating pipes include coating the interior of pipes with a silicone material. U.S. Pat. No. 4,892,442 to Shoffner discusses coextruding an inner lubricious layer with an outer layer. The inner lubricious layer may be ribbed and coats the entire inner surface area of the duct. Other techniques for coating the interior of a duct include spray coating the interior with a lubricious material, such as silicone. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
         [0004]      FIG. 1  is a perspective view of an example duct having part of the wall of the duct enlarged; 
           [0005]      FIG. 2  is an end view of the example duct of  FIG. 1 , also showing the enlarged portion from an end view; 
           [0006]      FIG. 3  is another top plan cross-sectional view of an example duct having part of the wall of the duct cut away; 
           [0007]      FIG. 4  is an end view of an example duct with the striping having a spacing such that the spacing between stripes is narrower than that depicted in  FIG. 2 ; 
           [0008]      FIG. 5  is a cross-sectional view of parts of an extruder utilized for manufacturing a duct having striping; 
           [0009]      FIG. 6  is a perspective view of parts of the pin assembly shown in part in  FIG. 5 , including the nut and the pin; and 
           [0010]      FIG. 7  is a perspective view of parts of the pin assembly shown in  FIG. 5  including the pin tip and the land. 
       
    
    
     DETAILED DESCRIPTION 
       [0011]    The examples discussed herein involve known extruding techniques. Therefore, the extruding techniques themselves will not be covered in great detail. The terms duct and tube may be used interchangeably herein to refer to the example duct  10 . 
         [0012]      FIGS. 1-4  depict example ducts  10  that incorporate an example lubricious material  12  coupled to the interior of a duct wall  14 . The lubricious material is in the form of a plurality of longitudinally extending markings  12  that form a pattern on the interior of the duct wall  14 . As shown, the markings or patterns  12  may be formed as multiple stripes  12  that extend continuously and longitudinally inside the duct  10 . The stripes  12  have a width W and a spacing S such that portions of the underlying duct wall  14  are visible between the stripes. The stripes are made of a lubricious material that reduces friction inside the duct wall  14 . The striping material  12  is utilized to lower the coefficient of friction inside the duct wall  14  such that less friction is encountered by cables that are passed through the interior of the duct wall  14 . 
         [0013]    The striping material  12  includes as a component a lubricious material, such as silicone, although other materials may also be utilized. The striping material  12  is applied to the interior  16  of the duct and is useful in allowing tubing, cables, and conduits (not shown) to pass easily through the tubing. The duct wall  14  may be made of a polymeric material, such as polyethylene. The striping material  12 , depicted in  FIGS. 1-4 , is exaggerated somewhat in that the striping material  12  will generally not be as thick as that depicted. 
         [0014]    One formulation for the striping material  12  is a three part mixture that includes high density polyethylene, color concentrate, and silicone. The polyethylene may be in amounts ranging from about 88% to about 96.5%, with one example amount being about 94%. The polyethylene may alternatively be in the range of about 90% to about 97% of the mixture. The color concentrate may range from about 0.5% to 2% of the mixture, with an example amount being about 1%. The silicone may range from about 3% to 10% of the mixture, with an example amount being about 5%. The color concentrate may be excluded if desired. 
         [0015]    One type of polyethylene that may be utilized in the composition is TC46-25 polyethylene copolymer by INEOS Olefins &amp; Polymers USA, of League City, Tex. TC46-25 is a natural, high density polyethylene copolymer designed specifically for telecommunications ducting to meet or exceed the material requirements in conduit specifications ASTM F2160, UL651B, and NEMATC-7. TC45-25 balances stiffness, ESCR and molecular weight to provide required toughness and crush strength for use in the telecommunications industry. Other types of polyethylenes may also be utilized. Other materials having similar properties may also be utilized. 
         [0016]    The silicone and color concentrate may be purchased from a company called CLM Industrial Polymers of Oakville, Ontario, Canada. One color concentrate that may be utilized is white CLM product 11003. Other colors may also be utilized including red, orange, yellow, green, blue, grey, brown, and variations thereof without limitation. One silicone material that may be utilized is CLM product 10560. Other materials from other manufacturers may alternatively be utilized, the example ducts not being limited to a particular brand of materials. The materials making up the composition may be provided in pelletized or other form. 
         [0017]    The ducting  10  may have any range of thicknesses. For example, one example duct  10  may have a wall thickness  18  of 0.138 inches. Any size tubing may benefit from the example striping. For example, one example duct  14  has an outside diameter of about 1.526 inches and a wall thickness  18  of about 0.138 inches. Another example duct  14  has an outside diameter of 1.488 inches and a wall thickness  18  of 0.109 inches. Tubes can range in diameter from about 8 mm to about 7 inches. Thickness  18  of the ducting may also vary. 
         [0018]    The size and number of stripes  12  can vary depending upon the size of the tube and the particular application. For example, the stripes  12  may range in width W from about 0.04 inches to about 0.08 inches, although any size of stripes  12  is contemplated with the example duct  10  and is dependent in part on the size of the duct wall  14 . All the stripes  12  within a single duct  10  may have the same width W. Alternatively, it is possible that varying width stripes within a single duct may be utilized. For the example 1.526 inch OD duct, discussed above and shown in  FIGS. 1-3 , the stripes  12  shown have a width W of about 0.080 inches. For the 1.488 inch OD duct, shown in  FIG. 4 , the stripes  12  shown have a width W of about 0.040 inches. The stripes  12  may be evenly spaced around the interior surface  16  of the duct wall  14  or may be unevenly spaced. 
         [0019]    The stripes  12  are raised slightly relative to the interior surface  16  of the tubing  14  so that they serve as the first contact point for any cables entering the tubing. The stripes  12  may be raised by about 0.01 inches, or greater or lesser than this amount. The raised stripes  12  present a smaller surface area for any cables that enter the duct  10 , which also results in a reduction in the coefficient of friction inside the duct  10 . The tubing may be made of any type of material, such as high density polyethylene. The tubing preferably has a composition that allows either chemical interaction with the striping  12 , or that firmly adheres to the striping so that the striping does not release from the duct wall  14  during prolonged usage. 
         [0020]    The tooling for manufacturing the example duct  10  is shown in  FIGS. 5-7 . The tooling consists of a die pin assembly  20 . The die pin assembly  20  includes a pin  22 , a nut  24 , a pin tip  26 , and a land  28 . The nut  24  couples to the top end of the pin  22  via screw threads  36  and includes a cavity  38  for mating with an extruder. A seal (not shown) seats in the mating cavity  38  between the pin  22  and the extruder. Duct material enters the pin assembly  20  through an inlet  42  in the side of the nut  24 . Molten duct material flows into the pin assembly  20  through the nut inlet  42  into a cylindrical counter bore (not shown) in the nut  24 . The cylindrical counter bore distributes the molten duct material around the pin  22 . Molten duct material travels around the pin between the wall  30  of the die and the exterior surface  32  of the pin  22 . The molten duct material then flows around the pin tip  26  where it enters a reservoir  44  formed between the pin tip  26  and the die  30  of the extruder. Molten duct material then travels around the land  28  to form the duct  10 . 
         [0021]    Molten striping material enters the pin tip assembly  20  at the top end of the pin  22  and travels through the pin  22 . The molten striping material enters internal passageways defined inside the pin tip  26  and into a reservoir  46  defined at the top end of the land  28 . A series of holes  48  are drilled at an approximately  45  degree angle from the exterior wall of the land  28  to the interior of the land. The holes  48  are for introducing the striping material from the pin assembly  20  to the interior surface  16  of the duct wall  14 . Molten striping material is delivered from the reservoir  46  inside the land  28  through the holes  48  in the exterior of the land  28  to the duct wall  14 . 
         [0022]    The pin tip  26  is coupled to the pin  22  via screw threads  50 . A seal  52  is positioned between the pin tip  26  and the pin  22  inside the mating cavity  38  of both parts. The mating cavity  28  is an air hole is positioned inside the pin assembly  20  that extends along the entire length of the pin assembly  20 . The air hole  38  may be used for delivering a feed or pull tape (not shown) into the interior of the duct  10 . The pull tape is used to feed cables through the tubing during installation and may be a woven polyester material or cord that is placed inside the air hole. The land  28  and pin tip  26  each include longitudinally extending mounting holes  54  used to couple the land  28  to the pin tip  26 . Bolts  56  may be inserted through the base of the land  28  into the base of the pin tip  26  to couple the parts together. 
         [0023]    The pin assembly  20  is positioned in a die  30  that is mounted in a normal fashion to a primary extruder (not shown). An auxiliary extruder (not shown), capable of delivering enough striping material  12  as needed to the inside  16  of the duct  14 , is coupled to the pin assembly  20 . The speed of the auxiliary extruder is matched to the speed of the primary extruder to deliver the proper amount of striping material  12  to the inner surface  16  of the duct  14 . An automatic additive auger may be used to mix the pelletized components prior to extrusion. Other mixing techniques used to make a uniform mixture may alternatively be used, including hand mixing. Thus, the striping  12  is coextruded with the duct  14 . 
         [0024]    It was previously known to coat the interior of a duct with silicone. Silicone inner striping is advantageous over previously known techniques because it provides a lubricious surface that lowers the coefficient of friction inside the duct, but uses less material than conventionally known coating techniques. Because of the coextrusion process, the stripes  12  are raised slightly relative to the interior wall of the duct. This presents a smaller surface area inside the duct  14  for contacting cables within the duct, which further lowers the coefficient of friction. 
         [0025]    While the lubricious material utilized in the composition has been discussed as silicone. It is anticipated that other alternative lubricious materials may be utilized with equal success and little experimentation. Thus, the disclosure is not limited to the use of silicone as the lubricious material. The term “silicone” as used in the claims is defined to refer to any type of lubricious material that may be extruded with the composition. Moreover, the disclosure is also not limited to the use of high density polyethylene as the base polymer for the composition. Other types of polyethylene materials may alternatively be used, as well as other polymers. 
         [0026]    While stripes  12  are shown and described for the pattern inside the duct  14 , other patterns or markings may alternatively be utilized. In addition, while the striping  12  is shown to be continuous along the length, the striping  12  may alternatively be non-continuous or intermittent. 
         [0027]    Any type of color additive may be utilized. Different colors may be used in different ducts to distinguish, for example, the duct size, the duct type, the striping size or spacing, or to identify other features of the duct. Color may be used as a means to identify the manufacturer or user of the duct, if desired. 
         [0028]    The term “substantially” as used herein is a term of estimation. 
         [0029]    While various features are presented above, it should be understood that the features may be used singly or in any combination thereof. Further, it should be understood that variations and modifications may occur to those skilled in the art to which the claimed examples pertain. The examples described herein are exemplary. The disclosure may enable those skilled in the art to make and use alternative designs having alternative elements that likewise correspond to the elements recited in the claims. The intended scope may thus include other examples that do not differ or that insubstantially differ from the literal language of the claims. The scope of the disclosure is accordingly defined as set forth in the appended claims.