Abstract:
A joining method wherein ends of multilayer composite tubing and/or fittings having at least one middle layer of malleable metal are flared radially outwardly so that exposed ends of the middle layer of malleable metal are directed radially outward and away from a fluid flow path within the tubing and/or fittings. The flared-out ends are then fused using infrared butt welding so that the resulting bead protrusion into the fluid flow path is small enough to be acceptable for use in a high purity water system.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to U.S. Provisional Patent Application No. 60/980,583, filed Oct. 17, 2007, which is incorporated herein by reference. This application is related to International Application No. PCT/US2007/007686 (Atty. Docket No. 65978PCT), which claims priority to U.S. Provisional Patent Application No. 60/744,212, filed Apr. 4, 2006, both of which are incorporated herein by reference. 
     
    
     TECHNICAL FIELD OF THE DISCLOSURE 
       [0002]    The present disclosure relates to a joint and joining method for multilayer composite tubing and fittings having at least one middle layer of malleable metal. The joint and joining method prevent the middle layer from being exposed to liquid flow within the joined tubes and fittings and result in an inner surface that has almost no bead protrusion into the waterway so that the joint is acceptable for use in a high purity water system. 
       BACKGROUND OF THE DISCLOSURE 
       [0003]    High purity water (water highly purified through filtering, deionization, reverse osmosis, distillation or some combination thereof) is extensively used in research as well as in the commercial manufacture of pharmaceutical products and electronic components. Once water has been purified, it must be run through pipes that are very stable, clean and smooth, or the water will tend to become contaminated through impurities it gains from the piping materials. Over the last forty years, it has become widely recognized that thermoplastic materials are the cleanest, most stable and smoothest materials that exist to convey high purity water. In the most extreme applications, where water is purified to the greatest extent possible (a condition referred to as 18.2 mega ohm, which is the theoretical maximum resistance achievable in ultrapure water), such as in pharmaceutical or semiconductor chip manufacturing, polypropylene (PP), polyvinylidene fluoride (PVDF), and perfluoroalkoxy (PFA) materials have become the established materials of choice. This is due to the fact that these materials can be produced without pigmentation or other additives, are highly crystalline thermoplastics which can be extruded into very smooth bores, and can be joined with techniques that minimize internal imperfections in the bore of the piping. 
         [0004]    Joining methods which produce the least internal irregularities or intrusions are preferable as any internal formations or crevices that exist can lead to stagnant areas where bacteria or other microorganisms can grow. This is very undesirable in high purity water applications, and particularly in applications where microorganisms can lead to adverse effects on the finished products or affect test results. The best joint forming techniques that have been developed to date for thermoplastic materials include a technique known as bead and crevice free butt-welding, which results in a virtually undetectable joint in the piping material. This method consists of heating the plain ends of pipes against a heating surface, and then butting the materials together while simultaneously inflating a device, a solid plug, or introducing a gas that prevents the formation of an internal bead. The only drawbacks to this method is that it is very labor intensive, is typically performed on pipes with fixed lengths (e.g. 5 meter extruded lengths and separate fittings) which require a large number of welds, and it is not possible to perform this type of welding on 100% of the joints in the system. The joints that cannot be made using bead and crevice free butt-welding (such as where a valve is located) must be accomplished via flanged connections, union connections, or other mechanical attachments. 
         [0005]    Another method which has proven useful in high purity applications, especially when PFA tubing is involved or where the expense of bead and crevice free joining is unacceptable, is a method referred to as infrared (IR) butt fusion that uses IR radiant heat to fuse pipes and fittings together. By using radiant heat, the pipe never touches a heating surface, thus offering a purer, non-contaminated end product. In addition, the equipment which has been developed to perform infrared butt fusion is typically CNC controlled so that very careful pressures are applied for a very tightly controlled period of time, resulting in butt weld internal and external beads of reduced size and a very uniform, well rounded geometry. By comparison with traditional contact butt fusion, this reduced and uniform bead result substantially reduces the possibility that bacteria can collect and thrive at the fusion weld seam. 
         [0006]    In the 1990&#39;s multilayer composite tubing was introduced and comprises an inner layer of thermoplastic material (such as polyethylene (PE) or cross-linked polyethylene (PEX) or PP), a malleable metallic layer such as welded aluminum or copper, and an outer layer of thermoplastic material. The inner and outer layers are typically bonded to the aluminum by means of an adhesive layer to result in a gas tight construction. Such an assembly results in tubing which can be made with thin layers for economy, yet has reasonably high-pressure ratings. In addition, the tubing is flexible due to the malleable nature of the metallic products involved, and since the inner and outer layers are relatively thin, so that the tubing can be deliverable in coiled bundles and rolled out straight. In addition, elbows can be field formed in the flexible multilayer thermoplastic tubing. 
         [0007]    It has been recognized by the author of the present disclosure that multilayer composite tubing could also work well for high purity water piping systems if suitable joining methods can be developed. For example, the inner layer can be extruded using an unpigmented, virgin resin, such as polypropylene, PVDF, a more flexible copolymer form of PVDF (a copolymer created from monomers of vinylidene fluoride and hexafluoropropylene, sometimes referred to as Kynar Flex®, which is a tradename of Arkema, Inc.), or PFA, materials which are already readily accepted into high purity water applications. The outer layer can be offered as a pigmented product with special additives such as UV inhibitors to protect against UV attack of the pipe (a problem inherent in PP materials without additives), since the outer layer is not a wetted component. Dissimilar systems such as PVDF-AL-PP combinations can even be offered where PVDF is needed for the wetted contact layer. Such a system could be delivered into a project in long coils (e.g. 100 meter coils) and rolled out into seamless and jointless straight lengths. Further, a certain number of consecutive bends can be field formed using forming and bending tools, and flexible inserts. 
         [0008]    What is still desired is a new and improved joint and method for joining multilayer composite tubing having at least one middle layer of malleable metal. The joint and joining method will preferably prevent the middle metal layer from being exposed to liquid flow within coupled tubes. In addition the joining method will preferably provide a joint acceptable for use in a high purity water system. 
       SUMMARY OF THE DISCLOSURE 
       [0009]    The present disclosure provides exemplary embodiments of joints and joining methods for connecting multilayer composite tubing and fittings having at least one middle layer of malleable metal. The joint and joining method of the present disclosure prevent the middle layer of malleable metal from being exposed to liquid flow within the joined tubes and fittings and result in an inner surface that has almost no bead protrusion into the fluid flow path so that the joint is acceptable for use in a high purity water system. 
         [0010]    According to one exemplary embodiment, a joining method according to the present disclosure comprises flaring out ends of multilayer composite tubing and/or fittings to be joined so that exposed ends of the middle layer of malleable metal are directed radially outward and away from the fluid flow path within the tubing and/or fittings, and then fusing the flared out ends using infrared butt welding so that the resulting bead protrusion into the fluid flow path is small enough to be acceptable for use in a high purity water system. 
         [0011]    According to one aspect, the ends are flared outwardly such that a small radius at the wetted base of the flare is achieved so that fusion weld beads occupy the space created by the radius, and thereby result in an inner surface that has almost no bead protrusion into the waterway. The flared ends, therefore, make the resulting joint even more acceptable than standard infrared butt fusion welds, which are already widely accepted by the industry. 
         [0012]    The middle layer of malleable metal incorporated into a flared end formed in accordance with the present disclosure would act to reinforce the joint, as well as provide a heat sink to allow the wetted surfaces to be thoroughly and uniformly fused together. The middle layer of malleable metal will also act to prevent problems associated with creep of the thermoplastics, thereby minimizing future potential failures due to creep at the joints. 
         [0013]    Unlike contact butt fusion, and in traditional infrared butt fusion, fusion in accordance with the present disclosure does not occur at the ends of the pipe surface, but rather is being made at flat flange faces that are at a right angle to the flow. Since these small flat faces are produced by flaring material that originates from the inside diameter of the pipe, the material is clean, and will be highly regular in surface shape, and will not need to be subjected to shaving or planning using a rotating cutting or planning tool (a standard step in contact or normal infrared butt fusion). This means that another major potential source of impurity is eliminated whereby metal fragments can be introduced or imbedded into the pipe due to contact with the cutting tools. This feature also serves to make the joints produced from the modified infrared method in this disclosure even cleaner and even more desirable than those produced by traditional infrared butt fusion. 
         [0014]    It is apparent that the joining methods and the resulting joints provided in accordance with the present disclosure have many advantages over previous high purity systems. For example, the presently disclosed joint and joining method makes multilayer composite tubing more practical so that the use of coiled tubes in long lengths that can be rolled out in rigid fashion, together with the field formability of many of the elbows, will eliminate 70 to 90 percent of the joints found in previous high purity systems. Where fusion joints are required, the presently disclosed joint and joining method provides joints having smaller beads joint and less potential for contamination. 
         [0015]    Additional aspects and advantages of the present disclosure will become readily apparent to those skilled in this art from the following detailed description, wherein only exemplary embodiments of the present disclosure are shown and described, simply by way of illustration of the best mode contemplated for carrying out the present disclosure. As will be realized, the present disclosure is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the disclosure. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    Reference is made to the attached drawings, wherein elements having the same reference character designations represent like elements throughout, and wherein: 
           [0017]      FIG. 1  is an end sectional view of a multilayer composite tube; 
           [0018]      FIG. 2  is a side sectional view of a flared end flange face that has been formed on the multilayer composite tube of  FIG. 1  in accordance with the present disclosure; 
           [0019]      FIG. 3  is a side sectional view of the flared end flange face of  FIG. 2  being formed using a single-sided mandrel in accordance with one exemplary embodiment of the present disclosure; 
           [0020]      FIG. 3A  is a side sectional view of two of the flared end flange faces of  FIG. 2  being formed using a double-sided mandrel in accordance with another exemplary embodiment of the present disclosure; 
           [0021]      FIG. 4  is a side sectional view of two of the flared end flange faces of  FIG. 2  shown positioned in an infrared butt welding tool in accordance with an additional exemplary embodiment of the present disclosure; 
           [0022]      FIG. 5A  is a side sectional view of the two flared end flange faces of  FIG. 4  joined together after being melted and clamped in the infrared butt welding tool in accordance with the present disclosure; 
           [0023]      FIG. 5  is a side sectional view of the two flared end flange faces of  FIG. 4  joined together after being removed from the infrared butt welding tool in accordance with the present disclosure; 
           [0024]      FIG. 6  is an illustration showing an exemplary embodiment of an infrared heating element of the infrared butt welding tool of  FIGS. 4 and 5A ; and 
           [0025]      FIG. 7  shows a cross section of a finished joint where a multilayer tube constructed in accordance with the present disclosure is joined to a fitting, such as a tee fitting. 
       
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0026]    The present disclosure overcomes many of the prior art problems with joints and joining of high purity water tubing and piping systems. In general, the joints and joining methods are used to create extensive yet highly sanitary plumbing networks. Among other features and benefits, the disclosed joints and joining methods facilitate high quality and strong joints and can create complex networks of piping. The advantages and other features disclosed herein, will become more readily apparent to those having ordinary skills in the art from the following detailed description of exemplary embodiments taken in conjunction with the drawings which set forth representative embodiments of the present disclosure and wherein like reference numerals identify similar structural elements. 
         [0027]    All relative descriptions herein such as upward, downward, left, right, up, down, length height, width, thickness, and the like with reference to the Figures are not meant in a limiting sense. Additionally, the illustrated embodiments can be understood as providing exemplary features of varying detail of certain embodiments, and therefore, features, components, modules, elements, and/or aspects of the illustrations can be otherwise combined, intersected, sequenced, separated, interchanged, positioned, and/or rearranged without materially departing from the disclosed joints or joining methods. Additionally, the shapes or sizes of certain components are also exemplary and can be altered without materially affecting or limiting the disclosed joint and joining method. Referring first to  FIG. 1 , there is shown a cross sectional view of a multilayer composite tube  100 , which in the exemplary embodiment shown includes five layers. This five layer construction consists of an inner layer  103  of extruded thermoplastic material, consisting of a material like PFA (perfluoroalkoxyalkane polymer), PVDF (polyvinylidene fluoride), VF2-HFP copolymer (a copolymer of vinylidene fluoride and hexafluoroprylene monomers), PP (polypropylene copolymer or homopolymer), HDPE (high density polyethylene), PE100 (bimodal resin consisting of ultra high molecular weight polyethylene and linear low density polyethylene), or PEX (cross linked polyethylene). The inner layer  103  is preferably manufactured from an unpigmented form of one of these resins when the multilayer pipe  100  is being used for the transport of high purity water of other high purity substances. 
         [0028]    Although not viewable in  FIG. 1 , the five layers include an adhesive layer provided on the exterior of the inner layer  103 . A layer  102  of malleable metal, such as aluminum or copper, is formed around the adhesive layer provided on the exterior of the inner layer  103 . The malleable metal layer  102  is formed, for example, by means of welding using laser welding techniques, which results in a very uniform layer. Surrounding the middle malleable layer  102  is a fourth layer, not viewable in  FIG. 1 , which is another application of adhesive. 
         [0029]    The outer fifth layer  101  is also an extruded thermoplastic, which can be from among one of the same resins described above. The outer layer  101  may be a pigmented material which has additives that protect or inhibit against the harmful effects of ultraviolet light, which is particularly important when using a material such as PP, HDPE, PE100 or PEX, each of which are affected to some degree by UV light. The resin used to manufacture the outer layer  101  may also have any number of additional additives such as flame retardants, smoke suppressants, impact modifiers or other additives to achieve fire resistance or other desirable performance characteristics such as impact resistance, etc. In this manner, the inner layer  103  has the best form of the material to maintain purity, while the outer layer  101  has the best protection of the multilayer pipe  100  against external ambient effects. Also, the inner layer  103  can be one material and the outer layer  101  can be a dissimilar material. In this manner, an expensive material such as PFA or PVDF can be used as the inner layer  103  and the outer layer  101  can be a less expensive material such as PP or HDPE, thereby making the entire assembly  100  an economical overall combination while preserving the performance characteristics of the inner most layer  103 . As a result, the entire assembly  100  can be less expensive than a solid pipe of extruded thermoplastic material of typical thicknesses produced to handle the same class of service for a comparable diameter size. 
         [0030]    Referring now to  FIG. 2 , an end of the tube has been flared into a small flange-shaped flare configuration  104 . The size of the flare  104  is preferably limited in size to that which is necessary to result in a butt weld joint of adequate strength. It is not necessary to make the flare  104  any larger than the minimum required, as the larger the flare  104  produced, the greater the risk that the middle malleable layer  102  will be cracked or compromised in the process. Note that as the result of forming the end of the multilayer tube  100  into the flange-shaped flare  104 , a clean section of the inner layer  103  is now exposed and is perpendicular to the direction of fluid flow through the multilayer tube  100 . This is an important characteristic to enable butt weld joints of high quality to be made, without having to plane or shave the surface. 
         [0031]    In  FIG. 3 , an exemplary embodiment of a mandrel  105 , which produces the flare  104 , is shown. The mandrel  105  is preferably made out of a hard material such as steel, stainless steel, or ceramic. If the mandrel material is a metal, it should be coated with a tough, resilient high purity material such as ceramic, or a durable form of a fluoropolymer such as PTFE, FEP, PFA, or PVDF. The mandrel  105  can be mounted into a hand tool, or it can be mounted onto a bench top tool. The bench top tool can also serve as the same tool used to perform the butt-welding procedure. Regardless of whether the tool is hand held, or a bench tool, it is necessary to clamp the multilayer pipe  100  using an external clamp  106  and force it into the mandrel  105  in order to produce the flare. It is not necessary in most circumstances to first heat the end of the multilayer tube  100  since the flare  104  is relatively small in size. However, the mandrel  105  may be required to have several tapered steps or stages in its design, resulting in a longer mandrel that produces the flare  104  one step at a time so as not to cause the middle malleable metal layer  102  to split or crack. The mandrel  105  shown is a simple one step mandrel. However, it is understood that the mandrel could be more complex in shape, with multiple tapers. 
         [0032]      FIG. 3A  shows a variation of  FIG. 3 , where the mandrel  105  is two sided, so as to enable the flaring of multilayer tubes  100  on either side into the flared flange-shape  104 . This could either be done simultaneously, or one at a time. 
         [0033]    Referring now to  FIG. 4 , sections of multilayer tubes  100  having flared ends  104  already formed into the tube ends are shown mounted into a butt fusion tool  107 . The butt fusion tool  107  is manufactured to have a flat surface with one stationary bed  108 . The multilayer tubes  100 , having the already produced small flanged-shaped flared ends  104  are clamped into the stationary and moving beds  108  and  109 , respectively, using a clamp  106 . The clamp  106  may be the same set of clamps used to produce the flare  104  in the flaring step, especially if the butt fusion tool  107  also is used to produce the flares  104  as well as to accomplish the butt fusion. To accomplish the heating of the ends of the pipes, an infrared heating mirror  111  is used, which is positioned in the middle of the two adjacent flared ends  104  of the tubes  100 , and at a short distance of ¼ inch (6 mm) or more from the flat surface of either tube. The heating mirror is powered by infrared heating elements that allow the heating mirror to achieve a temperature of between 1250° F. to 2000° F., and thereby enabling the heating to take place by means of radiation to the flat surfaces of the exposed inner thermoplastic material  103 . While heating by means of radiation via an infrared source is preferred due to eliminating the need to contact the surface, it is also understood that heating can also take place by means of traditional contact-type butt fusion through direct conduction, where contact can be tolerated. 
         [0034]    In  FIG. 4 , an optional external clamp  110  is indicated. The external clamp is in place so as to prevent the outer thermoplastic material  101  from move outward when the two tubes  100  are brought together under pressure after the flared ends  104  have been heated and the heating element  111  is removed. This will allow an external bead to form properly at the outer edge of the joint, which will fully cover the malleable middle layer  102  in the finished joint, which is shown and described in  FIGS. 5A and 5B . 
         [0035]    Referring now to  FIG. 5A , the joined parts as shown after the flared ends  104  of the adjacent tubes  100  are brought together under pressure. The weld seam is indicated by  114  and consists of mostly the inner thermoplastic material  103  of both multilayer tubes  100  uniformly mixed together. These molten inner thermoplastic materials  103  will eventually recrystallize into a unitary homogeneous bond once they reach the temperatures to which the thermoplastic materials turn solid. In the finished joint, there is a small weld seam  112  at the inner waterway or flow path, which protrudes slightly into the waterway and restricts the water flow only to a minor degree. The protrusion is so small because the flare ends  104  are rounded, which creates a natural pocket with which to receive molten material, thereby restricting the development of bead size to a great degree. There is also a small, relatively uniform rounded weld seam  113  that forms at the outer edge of the joint. This weld seam  113  consists of materials from both the outer material  101  and the inner material  103  of the multilayer tubes  100  from each adjacent multilayer tube  100 . Note that the middle malleable metal layer  102  of each tube is both sealed off completely from the inner fluid, and also sealed off to a great degree, or even entirely from the outside atmosphere as well. In  FIG. 5 , the finalized joint is shown after it has been removed from the butt fusion tool. 
         [0036]    Referring now to  FIG. 6 , the illustration shows a side view of the infrared heating element  111 . The heating element  111  can be constructed with flat surfaces of a material type that when heated can glow and emit heat via light in the infrared range from its flat surfaces. The heater element may be constructed of ceramic or may be a quartz heater with electric heating elements  112  embedded in the surface of the heater. The temperature at the surfaces of the heater may vary but it has been found that temperatures produced in the range of 1250° F. to 2000° F. are successful. The heating element  111  has a handle  114 , and is equipped with an LCD or other display  115  that can indicate the temperature at the surface of the heating element. The heating element&#39;s handle  114  also contains various switches and indicator lights  116  to turn the unit on and off, as well as to indicate when it the unit is ready to perform the fusion. Other controls will also be available on the base of the butt fusion tool  107  to perform the other tasks of the tool such as fixing the proper distance of the flared ends  104  from the surface of the tool, the insertion and later removal of the heating element, the time of fusion, and the speed with which contact is made, the pressure of fusion, and the cool down period. The heating element  111  also is equipped with a frame  117  that is positioned within a slide opening  118  on the base of the heating element. This frame is designed so that the tool can either be controlled manually with a handle  119 , or can alternatively be mounted directly onto the butt fusion tool to be automatically controlled by the microprocessor based butt fusion tool. 
         [0037]      FIG. 7  shows a finished joint where a multilayer tube  100  is joined to a fitting  120 , which in this case is shown to be a tee fitting. It is understood that the fitting could also be an elbow, valve, adapter, reducer, or other type of fitting. The fitting is manufactured to also be of similar construction to the multilayer tubes, such that it also has an inner layer  103 , middle malleable layer  102  and an outer layer  101  of matching construction to the tube, and also has integrally formed flared ends  104  of matching shape and size to those of the tubes. The necks of the fitting  121  are such that they are long enough to accommodate insertion into the butt fusion tool. 
         [0038]    Thus, the present disclosure provides a new and improved joint and method of joining multilayer composite tubing. It should be understood, however, that the exemplary embodiments described in this specification have been presented by way of illustration rather than limitation, and various modifications, combinations and substitutions may be effected by those skilled in the art without departure either in spirit or scope from this disclosure in its broader aspects and as set forth in the appended claims. Accordingly, other embodiments are within the scope of the following claims. In addition, the improved joint and method of joining disclosed herein, and all elements thereof, are contained within the scope of at least one of the following claims. No elements of the presently disclosed joint and method of joining are meant to be disclaimed.