Abstract:
A composite pipe and method of manufacture comprises an inner core made of a resinous material, a prepreg material helically wound about the inner core and an outer shell covering the wound prepreg materials. The materials are applied at preselected melt temperatures to assure coherence among the materials and preclusion of voids and/or annuli therebetween. A cooling of the inner pipe core during initial application of the tape layer of prepreg materials stabilizes the radial configuration of the pipe core during tape wrapping and thus the appearance of undesirable voids and/or annuli in the composite pipe mass.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of co-pending provisional application Ser. No. 61/654,327, filed Jun. 1, 2012. 
     
    
     BACKGROUND 
       [0002]    This invention relates to a composite pipe and the manufacture thereof 
         [0003]    Flexible and rigid pipes are commonly used to transport various types of fluids or gases. The pipes comprise a plurality of materials joined together in various manners to form a conduit for advance of the fluid and/or gas materials therethrough. 
         [0004]    The use of the extrusion process to form a pipe having multiple material layers is known. Various disadvantages with the extrusion process have arisen including the possibility of variances in the pipe thickness over the length of the pipe and radial/hoop expansion of the pipe during the manufacturing process. Such actions may cause internal deformities leading to leakage and/or burst during fluid and/or gas transport. Also, longitudinal movement between the material layers will cause abrasion therebetween resulting in premature wear and possible pipe failure. Moreover, in past pipes annuli and/or voids may appear between the pipe layers. If not properly vented, undesirable permeation of the gases of the transported fluid and/or gas into these areas may occur, which may lead to pipe failure. 
         [0005]    In response thereto a coherent, multi-layer pipe is desired which avoids the above problems. A method of pipe manufacture is presented, which provides a coherent bond among the material layers so as to present a unitary mass of material with no voids therein as well as longitudinal or radial movement therebetween. The process is enhanced by a cooling of the extruded pipe core during the subsequent wrapping of intermediate reinforcing layers of a resinous prepreg or similar material. This cooling precludes expansion and contraction of the pipe core and thus the appearance of undesirable annuli or voids between the material layers. Accordingly, the bonding presents a cohered multi-layer pipe, which has various desirable properties including chemical, pressure and pressure resistance, the preclusion of annuli and/or voids between material layers and resistance to lateral and radial layer movement. 
         [0006]    It is therefore a general object of the invention to provide a versatile composite pipe and method of manufacture for effectively transporting pressurized fluids or gases therethrough. 
         [0007]    Another object of this invention is to provide a composite pipe and method of manufacture, as aforesaid, having a plurality of layered materials cohered into a unitary mass. 
         [0008]    A further object of this invention is to provide a composite pipe and method of manufacture, as aforesaid, which precludes the appearances of voids and annuli between the material layers. 
         [0009]    Still another object of this invention is to provide a composite pipe having a method of manufacture, as aforesaid, which precludes undesirable radial movement of the inner core during pipe manufacture and subsequent application of the material layers. 
         [0010]    Another particular object of this invention is to provide a composite pipe, as aforesaid, having no free floating fibers within the pipe mass. 
         [0011]    Still a further object of this invention is to provide a composite pipe, as aforesaid, which can be effectively butt fused in the field. 
         [0012]    Other objects and advantages of this invention will become apparent from the following description taken in connection with the accompanying drawings, wherein is set forth by way of illustration and example, a now preferred embodiment of this invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a block diagram showing the manufacturing process; 
           [0014]      FIG. 2  illustrates one form of the cooling apparatus for the pipe core; and 
           [0015]      FIG. 3  illustrates another form of the cooling apparatus for the inner pipe core. 
       
    
    
     DESCRIPTION 
       [0016]    Turning more particularly to the drawings,  FIG. 1  illustrates the basic manufacture of the composite pipe so as to present a composite pipe having the above-described advantages. 
         [0017]    Pipe includes an inner core  110 , which is formed by a conventional extrusion process initiated at extruder  1000 . The utilized material is preferably a high density thermoplastic PE 4710 industrial polythene material. The advantages of such a material are a good chemical resistance, high impact resistance, good abrasion resistance, low weight and ease of coupling. At this time, longitudinal tape having Fiberglas® strands or other materials may be introduced into the thickness of core  110 , via extruder  1000 , to provide longitudinal support therealong. The outer coating  120  of the core  110  presents a thin polyethylene material having a lesser density with a melt temperature of approximately 230° F. This melt temperature approximates the melt temperature of the resin in the prepreg tape material to be subsequently wrapped about the inner core  110  at stations  2000   a - 20000   h.    
         [0018]    Subsequent to the extrusion process at  1000  the pipe core  110  passes through a conventional vacuum/cooling tank  1100 , which sizes the pipe to its desired outside diameter. Sprayers  1200  cool the core  110  towards an ambient temperature. Puller  1300  directs the relatively rigid pipe core  110  downstream so that proper line speed and pipe stabilization can be achieved. 
         [0019]    Subsequently, tape layers of a prepreg or similar material having Fiberglas® strands therein are to be helically wound in opposed directions about the inner core. One form of the tape is as discussed in the Dyksterhouse patent U.S. 6,524,690. My tape currently comprises a 35% polyethylene, 5% moleic anhydride and 60% Fiberglas® mixture. It is understood that other materials may be used in lieu of Fiberglas®, particularly those to provide a strengthening effect and/or enhance conductivity during various forms of heating. Carbon black or other material suitable for induction heating may also be utilized to enhance the heating process, particularly if microwaves are to be used. The melt temperature of the polyethylene resin in the tape approximates 230° F. similar to the melt temperature of the outer coating  120  of the pipe core  110 . 
         [0020]    During the wrapping process cooler air is to be introduced into the interior of the pipe core  110  by apparatus as shown in  FIG. 2  or  3 . The cooler air stabilizes the pipe core  110  so minimal expansion and subsequent contraction, if any, will occur during the subsequent wrapping and heating processes. Heretofore, the disadvantages of such radial movements of the pipe core  110  have not been considered. Undesirable voids may appear between the pipe core  110  and subsequent tape layers during the wrapping process as radial movement of the heated core  110  may cause displacement from the applied wraps. Thus, it is desirable to maintain a temperature within the pipe core below the melt temperatures of the coating  120  and tape layers so as to preclude such radial movement. The cooling air temperature must not only cool the pipe core  110  but avoid crystallization of the pipe core  110  mass. 
         [0021]    To achieve such cooling, an elongated conduit  1400  is inserted through a central aperture in the initial extrusion die  1050  so that it is centrally located within the inner core  110 . The conduit  1400  follows the path taken by the inner core  110  through stations  1100 ,  1200 ,  1300  and at least two subsequent wrapping and heating stations. The conduit  1400  is supported within the core  110  and away from its inner wall  118  by a plurality of supports  1450  attached about the conduit  1400  at the downstream end thereof. The conduit supports  1450  are made of a slick material, e.g., acetal, to provide a maximum slippage between the stationary supports  1450  and interior surface  118  during movement of the pipe core  110 . As such the inner core  110  is not inhibited in its downstream travel. 
         [0022]    Cold air is introduced into the inner core  110  via nozzle  1500   a  or  1500   b  fixed at the end of pipe  1400 . The nozzle terminus is preferably after the core  110  is helically wrapped with the first tape layer at station  2000   a  and prior to entry into the first heat station  2100   a.  Nozzle  1500  may be of various shapes and materials as shown in  FIGS. 2 and 3 . Cold air is introduced into the pipe  1400  at the opposed end by any suitable fan/refrigeration unit combination positioned upstream of die  1050 . 
         [0023]    A screen  1550  is positioned at the open end conduit  1400 . Screen  1550  has a plurality of apertures  1560  therein so as to regulate the discharge of air from conduit pipe  1400 . The number of apertures is selected so that the desired cooling temperature will be achieved as the core is wrapped and heated at stations  2000   a,    2100   a,    2000   b  and  2100   b.  The air discharge precludes a pressure buildup therein which may undesirably expand the inner core  110 . 
         [0024]    After each wrapping station  2000   a - 2000   g,  a heater  2100   a - 2100   g  raises the resin temperatures of the coating  120  and resin in the first and second helically-wrapped tape layers to their melt temperatures to insure a coherent bond therebetween. Such heat may be supplied by conventional film heat apparatus, e.g., microwave, infrared, laser induction heating, etc. The microwave process may be enhanced by impregnating carbon black fibers within the tape being wound about the exterior surface of the core. 
         [0025]    During wrapping of the first two layers at stations  2000   a,    2000   b,  the above-described cooling pipe apparatus  3000 , as shown in  FIGS. 2-3 , introduces cool air into the inner pipe core so that the heat applied by heaters  2100   a,    2100   b  does not expand the pipe core  110 . At station  2000   b,  the tape is helically wound in an opposed direction about the first helical layer of the tape thus covering the exterior coating  120  of the pipe core  110 . As such, temperature migration resulting from the heating of the helically-wrapped tape layers about the pipe core  110  is diminished, if not precluded. Thus, internal cooling of the pipe core  110  may no longer be needed beyond heat station  2100   b.  Subsequent layers of the prepreg or similar materials are helically wound in opposed directions about core  110 . Heaters  2100   a  et seq. insure that the melt temperatures of the resin in the preceding tape layer and preceding contiguous layers are achieved to attain a coherent bond therebetween. As such, no voids appear in the mass surrounding the inner core  110 . The absence of such voids/annuli precludes the confinement of gases within the pipe layers which may permeate from the pipe core. It is understood that future tapes may be developed wherein only one wrapping to cover the exterior coating  120  is needed. 
         [0026]    After the last wrapping station  2000   h,  the pipe with tape layers therearound passes through a cross head overlay dye at  3050 . An outer shell of a polyethylene  100  or similar material is extruded at  3000  to encompass the pipe and tape layers. The extended temperature of the resin in this outer shell is approximately 400° F. Thus, the resin in the preceding tape layers which are adjacent this outer shell will also reach their melt temperature such that a coherent bond is achieved between the exterior shell and preceding tape layers. As such, heat need not be applied after the last tape layer is wrapped about the inner core. 
         [0027]    A composite pipe having a plurality of cohered layers with no voids and/or annuli therebetween are presented for cooling at stations  3100 ,  3200 , cutting  3400  and coiling  3500 . 
         [0028]    It is understood that the above process enables flexible coil pipe to be manufactured up to diameters of six inches with rigid pipe of larger diameters. In either case it is necessary to join the pipe sections in the field at a minimal cost. The above-described pipe construction enables a cost-effective butt fusion therebetween. The end joints of the pipe sections are wound with the same or similar tape of prepreg materials as utilized in the wrapping process. Other types of wraps hereafter developed may be used. The tape and pipe ends are heated on site so as to provide cohesion therebetween. As such there is no need for expensive mechanical couplings or welding of the pipes in the field. Moreover, during this process the exterior surfaces of the pipe remain intact, which enhances the juncture between pipe sections. 
         [0029]    It is understood that the interior surface of pipe core  110  may be fluorinated prior to the core  110  reaching the first wrapping station  2000   a.  Alternatively, an EVOH barrier material may also be applied. Such applications may preclude the need for subsequent wrapping in certain applications. If not, subsequent wrapping of the core  110  may still be required with the wraps being secured either by heating as above described or adhesives in lieu of heating. 
         [0030]    It is to be understood that while certain forms of this invention have been illustrated and described, it is not limited thereto, except in so far as such limitations are included in the following claims.