Patent Document

BACKGROUND OF THE INVENTION 
     The present invention relates generally to the attachment of pipes and thermoplastic fitting components by means of fusion welding. More particularly, the invention relates to improved fittings for joining thermoplastic components. 
     A number of companies have developed plastic welding equipment which utilizes specialized fitting components to join thermoplastic piping. Plastic welding can be categorized into three types: fusion welding, IR Butt Fusion, and Bead and Crevice Free welding. Fusion welding is used for high purity installations of thermoplastic piping. Thermoplastic piping has grown in industrial usage because of its compatibility with chemicals, its non-corrosive nature, ease of installation, long life, and its smooth internal surfaces. These features of thermoplastic piping make it ideal for high purity applications. 
     Standard fusion welding involves the heat fusion of a pipe into a female socket fitting. Bonding is achieved by heating the mating surfaces of the pipe end and of the fitting to a temperature above the melt point of the material. The heated parts are then engaged and held together until fused. Fusion occurs when the parts are cooled to below the melt point of the material. 
     Heating is typically achieved through conductive means via an electric heater that reaches temperatures in the regions of 500° F.±10° (or 260° C.). With the appropriate time, the pipe and fitting surfaces which come in direct contact with the heating tool will melt. The parts are then carefully removed from the heating tool and quickly pushed together thereby fusing the two parts together. Fusion welding is also used for welding a pipe or fitting to a plate in the same manner described above except the plate replaces the female socket. 
     The relationship between the outside diameter of the pipe and the bore of the fitting or plate is critical for successful fusion welding. Interference is essential when the hot surfaces are mated together. A carefully designed interference fit of the heated mating parts provides consistency of joining. It also results in the appearance of a weld bead as excess melted material is “scraped” off one of the surfaces. This weld bead is undesirable to some users because of its fabricated, unfinished look; and because of the potential for the weld to entrap airborne particles that can be embedded in the material while in a melted state. 
     The weld bead provides insight to whether the heat fusion joint was properly made. Ideally a double weld should be present and it should not be large in size. As stated above, one disadvantage to the weld bead is that it gives the joint a fabricated appearance. Another disadvantage is that dark spots may appear on the areas of the weld bead due to normal heating or particles which may have been captured when the material was in a melted state. Some manufacturers that use heat fusion to produce products machine the weld bead in order to create a more professional molded look. This adds an additional step to the manufacturing process. 
     Accordingly, there is a need for an improved fitting that integrates the weld bead into the fitting resulting in the final product having a more finished look. Additionally, an improved fitting that will prevent the common mistake of over inserting a mated component by providing an additional stop to the fitting is needed. Moreover, there is a need for reducing the manufacturing steps involved in heat fusion by eliminating removal of the weld bead through machining. The present invention fulfills these needs and provides other related advantages. 
     SUMMARY OF THE INVENTION 
     The present invention relates to a fitting for use in fusion welding of mating thermoplastic components. The fitting comprises a body defining a passageway therethrough and having a weld bead chamber disposed about a portion of the body. The weld bead chamber is configured to receive excess thermoplastic material resulting from a fusion weld joining the body to a mating thermoplastic component. The mating thermoplastic component may be a pipe or a hole in a plate, a wall, a vessel, a pressurized chamber, etc. The fitting is preferably cylindrical in shape, but may also be triangular, square, rectangular, etc. 
     In one preferred embodiment, the fitting includes a threaded connector on an end opposite the weld bead chamber. The body of the fitting adjacent to the weld bead chamber is configured for interference fit reception within the mating thermoplastic component. The weld bead chamber includes a stop ledge to prevent over insertion of the fitting into the mating thermoplastic component. 
     In another preferred embodiment, the fitting has a second weld bead chamber adjacent to an end of the body opposite the first weld bead chamber. As in the first embodiment, the body adjacent to either weld bead chamber is configured for interference fit reception with a mating thermoplastic component. Again, the weld bead chamber includes a stop ledge to prevent over insertion of the pipe into the fitting. 
     The body of the fitting is made from a heat fusible thermoplastic material, such as, polypropylene, polyethylene, polybutylene, polyvinylidene fluoride, or Teflon. 
     The weld bead chamber includes a window to view the excess thermoplastic material that results from the interference fit between the fitting and the mating thermoplastic component. 
     The body of the fitting may include a bend between a first end and a second end of the body. In addition, the body of the fitting may include a T-junction between a first end and a second end of the body, where a third opening of the T-junction includes a third weld bead chamber. 
     A method for fusion welding a fitting to a mating thermoplastic component comprises the step of heating mating surfaces of the fitting and the mating thermoplastic component to a temperature above the melt point of each, typically at least 500° F. Next, surfaces of the fitting and the mating thermoplastic component configured for an interference fit are engaged until a stop ledge in the weld bead chamber until the mating thermoplastic component engages a stop ledge. Excess thermoplastic material removed from either the fitting or the mating thermoplastic component as a result of the interference fit is captured in the weld bead chamber. The engaged parts are then cooled. The excess thermoplastic material may be inspected through the window in the weld bead chamber. 
     Other features and advantages of the present invention will become apparent from the following more detailed description, taken in connection with the accompanying drawings which illustrate, by way of example, the principles of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings illustrate the invention. In such drawings: 
         FIG. 1  is an elevational view of a fitting of the present invention showing an internal passageway in dashed lines; 
         FIG. 2  is a sectional view taken generally along line  2 - 2  in  FIG. 1 ; 
         FIG. 3  is a sectional view similar to  FIG. 2 , additionally depicting the fitting mated to a pipe; 
         FIG. 4  is a sectional view taken generally along line  4 - 4  in  FIG. 1 ; 
         FIG. 5  is a perspective view of the fitting of  FIG. 1 , fusion welded to a plate; 
         FIG. 6  is an elevational view of the assembly of  FIG. 5 ; 
         FIG. 7  is a cross-sectional view generally taken along line  7 - 7  in  FIG. 6 ; 
         FIG. 8  is a side view of an alternate embodiment of the fitting of the present invention welded to two pipes; 
         FIG. 9  is a sectional view generally taken along line  9 - 9  in  FIG. 8 ; 
         FIG. 10  is a sectional view of the fitting of  FIGS. 8 and 9 ; 
         FIG. 11  is a sectional view of a T-shaped fitting embodying the present invention; and 
         FIG. 12  is a sectional view of an elbow fitting embodying the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention is directed to improved fittings to be used in fusion welding of mating thermoplastic components. Standard fusion welding results in a weld bead which is undesirable to some users because of its fabricated, unfinished look, and because of the potential for the weld to entrap air borne particles that can be embedded in the material while in a melted state. The improved fittings of the present invention allow manufacturers to continue using fusion welding in their manufacturing steps while giving their products a more finished and injection-molded look by integrating the weld bead, and helping prevent the common mistake of over insertion by providing an additional stop in the fitting. It also reduces manufacturing steps by eliminating removal of the weld bead through machining which some companies current perform on their products. 
     As illustrated in  FIGS. 1 through 7 , an improved fitting  20  embodying the present invention comprises a body  22  having a weld bead chamber  24 . A passageway  26  runs through the body  22  and provides physical communication between adjoining thermoplastic components, i.e., pipes, vessels, etc., mated to the fitting  20 . The body  22  and passageway  26  are preferably cylindrical but may take the form of any shape that is compatible with the shape of a mated thermoplastic component, i.e., triangular, square, rectangular, etc. The fitting  20  also includes a threaded coupling  28  which can receive a cap, flare tube and nut, compression connection with a split ring, ferrule, and nut, or other type of connector (not shown). 
     The weld bead chamber  24  is preferably a continuous annular ring provided on the outer perimeter of the body  22  and oriented toward an end of the body. However, it may be a discontinuous annular ring, but such construction will not completely integrate and conceal the weld bead. A stop ledge  30  is included in the weld bead chamber  24  to prevent over insertion of the fitting  20  and mated thermoplastic component, i.e., a pipe  32  or a wall/plate  34 . The function of the stop ledge  30  will be discussed more fully below. 
     The fitting  20  of is typically joined by fusion welding to either a pipe  32  or a plate or wall of a vessel  34 . When joined to a pipe  32 , the end of the fitting  20  adjacent to the weld bead chamber  24  is inserted into the pipe  32 . The pipe  32  with which the fitting  20  is mated may be a regular straight pipe or may comprise a multi-junction pipe, i.e., a T-shaped junction, which can be joined to multiple fittings  20 . 
     The diameters of the fitting  20  and the mating pipe  32  are chosen so as to create and interference fit. This means that the outer diameter of the fitting  20  is so close to the inner diameter of the pipe  32  that there is substantial surface contact around the perimeter of the fitting  20 . This carefully designed interference fit of the heated mating parts provides consistency of jointing. 
     Prior to insertion of the fitting  20  into the mating pipe  32 , the outer surface of the fitting  20  and the inner surface of the pipe  32  are heated to a temperature above the respective melting points of each. The heated surfaces of the fitting  20  and pipe  32  are then engaged and held together until cool and fused. 
     The interference fit results in a portion of the surface of the fitting  20  being “scraped” off and accumulating as a bead  36  around the end of the pipe  32 . In prior fusion welding processes, this bead  36  would be machined off for a more finished appearance. However, in the present invention, the weld bead chamber  24  on the fitting  20  conceals the bead  36  so that it does not need to be machined off. 
     In addition, the weld bead chamber  24  includes a stop ledge  30  ( FIG. 2 ) within the weld bead chamber  24  to prevent over insertion of the fitting  20  into the pipe  32 . The stop ledge  30  presents a surface against which the end of the mating pipe  32  abuts to prevent insertion of the fitting  20  beyond that point of abutment. This stop ledge  30  is positioned from the end of the fitting  20  so that there is a minimum amount of surface contact between the fitting  20  and the pipe  32  to ensure a strong fusion weld. In cases where the outside diameter of pipe  32  is too large for the end to fit within the weld bead chamber  24 , or when it is more practical to simplify the fitting, then a stop ledge edge  31  will prevent over insertion. 
     The fitting  20  also includes one or more view windows  38  to inspect the quality of the bead  36  after the parts are mated. The appearance of the bead  36  correlates to the quality of the fusion weld between the mated parts. It is important that one be able to inspect the bead  36  to determine the quality of the fusion weld before using the mated pieces. 
     When the fitting  20  is fusion welded to a plate or wall of a vessel  34 , the end of the fitting  20  is inserted into a hole in the plate or wall  34 . The manner in which these pieces are mated is nearly as described above: the respective diameters are close enough to create an interference fit; the mating surfaces are heated to above the melt point; the heated surfaces are mated; excess surface material is “scraped” off the surface of the fitting  20  and accumulated as a bead  36  around the surface of the plate or wall  34 ; the parts cool and fusion weld together; the bead  36  is covered by the weld bead chamber  24 . One difference involves that part of the fitting  20  that acts as the stop ledge  30 . When welding the fitting  20  to a plate or wall  34 , the stop ledge is an edge  31  ( FIG. 7 ) of the weld bead chamber  24  rather than a surface inside the weld bead chamber  24  as described above. 
       FIGS. 8 through 12  depict another preferred embodiment of the present invention for coupling together opposed ends of two pipes by fusion welding (or more then two as in a tee). In this embodiment, the fitting  40  comprises a body  42  including a passageway  44  therethrough. This fitting  40  includes a first weld bead chamber  46  at a first end and a second weld bead chamber  48  at a second end. These weld bead chambers  46 ,  48  comprise continuous annular grooves around the inside diameter of the passageway  44 . The weld bead chambers  46 ,  48  may be discontinuous annular grooves, but such construction will not completely integrate and conceal the weld bead. The fitting  40  includes a stop ledge  50  adjacent to each weld bead chamber  46 ,  48  to perform a similar function as described above. In this embodiment, the stop ledge  50  is included in the passageway  44 . 
     The diameters at each extreme end  52  of the fitting  40  are larger than the diameter of the passageway  44  but smaller then the diameter of the weld bead chambers  46 ,  48 . Because the diameters at each extreme end  52  of the fitting  40  are larger, they will not contact the heater and the extreme end material will not melt. The extreme end  52  diameter is smaller then the diameter of the weld bead chambers  46 ,  48  to provide a means to keep the bead  52  (discussed below) within the chambers  46 ,  48 . 
     The fitting  40  is designed to receive a pipe  54  within each end of the fitting  40 . For the joining of one pipe  54  to a first end of the fitting  40 , the inner diameter of the passageway  44  is closely matched to the outer diameter of the pipe  54  so as to create an interference fit between the two parts. The mating surfaces are then heated and the pipe  54  is inserted into the fitting  40 . The interference fit results in excess material being scraped off of the heated surfaces and forming a bead  56  which accumulates in the weld bead chamber  46 . The stop ledge  50  prevents over insertion of the pipe  54  into the fitting  40  by abutting against the end of the pipe  54 . Again, a view window  58  permits inspection of the bead  56 . 
     This configuration may be formed integral with a member such as a valve body, a tee ( FIG. 11 ), an elbow ( FIG. 12 ), or a pipe connector ( FIGS. 8-10 ). The pipe connector style fitting  40  has been described above. As shown in  FIG. 11 , the fitting  40  may include more than two openings and hence, more than two weld bead chambers  46 ,  48 ,  60 . When more than two pipes  54  are mated to this fitting  40 , a corresponding number of weld bead chambers  46 ,  48 ,  60  are provided. Similarly, as shown in  FIG. 12 , a fitting  40  may include a bend or elbow to allow for an angled mating of pipes  50 . 
     The fittings  20 ,  40  and their mated components,  32 ,  34 ,  54  are preferably manufactured from heat fusible thermoplastic materials. Such heat fusible thermoplastic preferably includes Polypropylene (PP), Polyethylene, Polybutylene, Polyvinylidene Fluoride (PVDF), Teflons such as PFA and FEP, and other materials. Fusion welding has become established in industry as a primary joining system for small and medium sizes of Polyvinylidene Fluoride (PVDF) and polypropylene pipe (PP). Fusion welding is typically used for sizes from ½″ up to 100 mm or 4″ piping diameter. Heating of the components is typically achieved through conductive means via an electric heater that reaches temperatures in the regions of 500° F.±10° (or 260° C.). With the appropriate time, the surfaces of the fittings  20 ,  40  and mating components  32 ,  34 ,  54  which come in direct contact with the heating tool will melt. The parts are then carefully removed from the heating tool and quickly pushed together thereby fusing the two parts together. 
     Although various embodiments have been described in detail for purposes of illustration, various modifications may be made without departing from the scope and spirit of the invention.

Technology Category: 7