Patent Publication Number: US-2009218809-A1

Title: Pressurized-fluid pipe made of thermoplastic material, in particular polyolefin material, with a bell end

Description:
TECHNICAL FIELD 
     The present invention relates to a pipe made of thermoplastic material, with a bell end. 
     The present invention may be used to particular advantage in relatively thick pipes made of polyolefin material such as polyethylene or polypropylene, and therefore capable of conducting pressurized fluid, to which the following description refers purely by way of example. 
     BACKGROUND ART 
     A pressurized-fluid pipe of polyolefin material is known comprising a given longitudinal axis, and a bell end for connecting the pipe to a second pipe inserted into the bell end. 
     The bell end is fitted to the second pipe in fluidtight manner with the interposition of an annular lip seal, and in axially fixed manner by means of a toothed annular retaining member. 
     The annular lip seal and toothed annular retaining member are housed inside respective seats formed in an inner surface of the bell end. 
     The bell end and relative seats are normally formed using two known methods. 
     In a first method, the end of the pipe is defined by a tubular fitting, which is first injection-molded into a bell shape, is then machined to form the seats, and is finally butt welded to the normally extruded pipe. 
     In the second known method, the end of the pipe is first heated, is then engaged by a forming die shaped to form the bell end and the annular lip seal seat simultaneously, and is finally machined to form the toothed annular retaining member seat. 
     Given the presence of two separate seats for the annular lip seal and the toothed annular retaining member, forming the bell end of known pipes of the type described above therefore involves relatively complex, high-cost, time-consuming production processes. 
     DISCLOSURE OF INVENTION 
     It is an object of the present invention to provide a pipe made of thermoplastic material, with a bell end, designed to eliminate the aforementioned drawbacks. 
     According to the present invention, there is provided a pipe made of thermoplastic material, with a bell end, as claimed in the accompanying Claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A non-limiting embodiment of the present invention will be described by way of example with reference to the accompanying drawings, in which: 
         FIG. 1  shows a schematic longitudinal section of a preferred embodiment of the pipe according to the present invention; 
         FIG. 2  shows a larger-scale, schematic longitudinal section of a detail of the  FIG. 1  pipe. 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     Number  1  in  FIGS. 1 and 2  indicates as a whole a pipe made of thermoplastic material, and which comprises a given longitudinal axis  2 , is made of polyolefin material such as polyethylene or polypropylene, and is relatively thick for conducting pressurized fluid. 
     In the example shown, pipe  1  has a substantially circular cross section, and comprises a substantially cylindrical portion  3  coaxial with axis  2 ; and a bell end  4 , which is bounded axially by a substantially flat surface  5  perpendicular to axis  2 , has a wall thickness normally greater than that of portion  3 , and comprises an end portion  6  bounded internally by a substantially cylindrical surface  7  and coaxial with axis  2 , and a substantially truncated-cone-shaped intermediate portion  8  connecting portion  6  and portion  3 . 
     End  4  provides for connecting pipe  1  to a pipe  9 , which is fitted inside end  4 , coaxially with axis  2 , and comprises a substantially truncated-cone-shaped end portion  10  inserted inside portion  8 ; and a substantially cylindrical portion  11  inserted inside portion  6 . 
     End  4  is fitted in fluidtight manner to pipe  9  with the interposition of an annular lip seal  12 —in the example shown, a fluidtight lip seal known by the trade name F-576 Anger-Lock™—and is fitted in axially fixed manner to pipe  9  with the interposition of a toothed annular retaining member  13 . 
     Seal  12  and member  13  are housed inside one seat  14  formed in surface  7 , at an intermediate point along portion  6 , and comprising, as of surface  5 , two portions  15 ,  16  arranged successively along axis  2  and housing member  13  and seal  12  respectively. 
     Portion  15  is bounded by a substantially truncated-cone-shaped surface  17 , which converges towards surface  5 , slopes with respect to axis  2  by an angle a ( FIG. 2 ) of less than 30° and preferably ranging between 6° and 10°, and is connected to surface  7  with a given radius of curvature. 
     In a variation not shown, surface  17  is connected to surface  7  by a substantially truncated-cone-shaped surface sloping with respect to axis  2  by an angle greater than angle a, or by a flat surface substantially perpendicular to axis  2 . 
     Portion  16  is bounded by two substantially truncated-cone-shaped surfaces  18 ,  19  with opposite concavities; surface  18  slopes by a substantially 30° angle b ( FIG. 2 ) with respect to axis  2 ; and surface  19  slopes by a substantially 60° angle c ( FIG. 2 ) with respect to axis  2 , and is connected to surface  7  with a given radius of curvature. 
     Surface  18  and, therefore, portion  16  are connected to surface  17 , and therefore to portion  15 , by an annular shoulder  20 , which projects towards axis  2 , coaxially with axis  2 , to separate portions  15  and  16  and prevent any interference between seal  12  and member  13 , has a minimum diameter larger than the diameter of surface  7 , and is connected to surfaces  17  and  18  with respective given radii of curvature. 
     Seal  12  comprises a sealing portion  21  made of elastomeric material and substantially facing surface  19 ; and a stiffening portion  22 , which is made of plastic material, substantially faces surface  18 , and provides for ensuring a high degree of rigidity of seal  12 , and for stabilizing seal  12  firmly inside seat  14 . 
     Member  13  is bounded externally by a substantially truncated-cone-shaped surface  23  facing and contacting surface  17 , and has a number of gripping teeth  24  formed on its substantially cylindrical inner surface  25  coaxial with axis  2 . In a variation not shown, surface  23  also has gripping teeth. 
     It should be pointed out that, with seat  14  so designed, end  4  can be formed using various production methods, such as the one described in European Patent Application n. 05425862.9, which is included integrally herein by way of reference.