Abstract:
An sealing gasket is shown for use in forming joints of plastic pipe. The gasket has a bulbous region which is bisected by a planar region which forms a pair of oppositely extending wing-like flaps. These features of the gasket allow it to be more reliably seated on the working mandrel used to bell a female, thermoplastic pipe end. The wing-like flap portions of the gasket form wiper surfaces for a subsequently installed male, spigot pipe end as the joint is formed.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The present application claims priority from earlier filed provisional application Ser. No. 60/933,542, filed Jun. 6, 2007, entitled “Plastic Pipe Gasket and Process for Belling Plastic Pipe,” by inventors Gerardo Darce and Randall Chinchilla. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates generally to sealing systems for thermoplastic pipes and, more specifically, to an improved pipe gasket and to an improved belling process for installing a gasket in a socket end of a thermoplastic pipe. 
         [0004]    2. Description of the Prior Art 
         [0005]    Pipes formed from thermoplastic materials including polyethylene and PVC are used in a variety of industries. In forming a joint between sections of pipe, the spigot or male pipe end is inserted within the female or socket pipe end. An annular, elastomeric ring or gasket is typically seated within a groove formed in the socket end of the thermoplastic pipe. As the spigot is inserted within the socket, the gasket provides the major seal capacity for the joint. It is critical, during the installation process, that the gasket not be able to twist or flip since a displaced or dislocated gasket will adversely affect the ultimate sealing capacity of the joint. 
         [0006]    In the early 1970&#39;s, a new technology was developed by Rieber &amp; Son of Bergen, Norway, referred to in the industry as the “Rieber Joint.” The Rieber system employed a combined mould element and sealing ring for sealing a joint between the socket end and spigot end of two cooperating pipes formed from thermoplastic materials. In the Rieber process, the elastomeric gasket was inserted within an internal groove in the socket end of the female pipe as the female or belling end was simultaneously being formed. The provision of a prestressed and anchored elastomeric gasket during the belling process at the pipe factory provided an improved socket end for a pipe joint with a sealing gasket which would not twist or flip or otherwise allow impurities to enter the sealing zones of the joint. These features increased the reliability of the joint and decreased the risk of leaks or possible failure due to abrasion or other factors. The Rieber process is described in the following issued U.S. Pat. Nos. 4,120,521; 4,061,459; 4,030,872; 3,965,715; 3,929,958; 3,887,992; 3,884,612; and 3,776,682. 
         [0007]    In the Rieber process, the gasket is installed in a circumferential groove provided upon the working surface of a mandrel and abuts a backup collar which helps to position and retain the gasket during the subsequent belling operation. It is critical that the gasket be properly positioned on the forming mandrel and that the gasket not ride over the backup collar during the belling process. 
         [0008]    With prior art gaskets used with the Rieber belling process, it was sometimes possible to reverse or otherwise mis-install the gasket in the circumferential groove provided on the outer working surface of the mandrel. When the heated thermoplastic pipe end was forced over the mandrel, the gasket would fail to be seated properly in the subsequently formed pipe groove within the female, belled pipe end. It was then generally necessary to discard the defective pipe section. 
         [0009]    A need exists for an improved sealing gasket for use in a Rieber type manufacturing process, which sealing gasket would be easier and more reliable to seat on the working surface of the forming mandrel. 
         [0010]    A need also exists for such a sealing gasket which would be simple in design and simple to manufacture and which could also be used with existing belling technologies. 
         [0011]    A need also exists for such a sealing gasket which would simplify handling, which would help to insure correct position on the exterior surface of the working mandrel and which would thereby improve quality control in the pipe belling process. 
         [0012]    A need also exists for such a sealing gasket which would effect a more stable bell shape in the subsequently formed female, belled pipe end. 
         [0013]    A need also exists for such a gasket which would incorporate a wiping lip feature to wipe the male, spigot pipe end of dirt or other contamination upon subsequent assembly of a pipe joint. 
       SUMMARY OF THE INVENTION 
       [0014]    The present invention has as its object to provide an improved sealing gasket, an improved pipe belling process, and an improved pipe assembly method, all of which meet the needs described in the prior art and which meet the previous objectives. 
         [0015]    The improved pipe sealing gasket of the invention is designed for receipt within a groove provided within a socket end of a thermoplastic pipe. The gasket has a ring shaped elastomeric body which, when viewed in cross section, has a central bulbous region formed of a suitable elastomer such as a natural or synthetic rubber. The central bulbous region has located therein a planar angled region which bisects the bulbous region at a selected radial location and which extends outwardly from the central region to form a pair of oppositely arranged wing-like flaps. The planar angled region is formed of a dissimilar, resilient material, preferably a suitable plastic material. 
         [0016]    The central bulbous region of the gasket forms an oval profile when viewed in cross section. The oval profile has an outer surface region which is adapted to seat within the groove provided in the socket end of a thermoplastic pipe. The oval profile also having an inner surface region which forms a compression seal region for a mating spigot end of a mating thermoplastic pipe during insertion of the spigot end within the mating socket end of the thermoplastic pipe. 
         [0017]    The oppositely arranged wing-like flaps which extend outwardly from the central bulbous region form a V-shaped cavity bounded by a leading and a trailing flap, which cavity receives the inner surface region of the central bulbous region of the gasket. The leading flap has an outer edge which makes contact with the spigot pipe end during insertion and wipes any dirt present from the spigot end, keeping the dirt from reaching the cavity and the inner surface region which forms a compression seal region for sealing against the spigot end. The socket end of the female, thermoplastic pipe terminates in a mouth region with the groove being located adjacent the mouth region. The tip of the leading flap is separated from the mouth region of the socket end by a gap, whereby any dirt wiped from the spigot end by the leading flap accumulates in the gap between the flap and the socket. 
         [0018]    In the method of forming a pipe joint of the invention, a sealing gasket of the type previously described is prelocated within a groove provided within a female socket end of a first section of pipe in a Rieber style manufacturing process. The spigot end of one section of thermoplastic pipe is then inserted within the socket end of a second pipe section to form a pipe joint. As has been described, the socket end of the thermoplastic pipe terminates in a mouth region with the groove being located adjacent the mouth region, and wherein the tip of the leading flap is separated from the mouth region of the socket end by a gap, and wherein any dirt wiped from the spigot end by the leading flap accumulates in the gap between the flap and the socket. Upon assembly of the joint, the central bulbous region of the gasket forms a compression seal with the mating spigot pipe end and the oppositely extending flaps forming lip seal regions with the spigot pipe end. 
         [0019]    In the improved pipe belling method of the invention, a forming mandrel is provided with an inner end and an outer end, the mandrel also having an outer working surface. An improved gasket of the type previously described is installed at a first circumferential position on the outer working surface in a circumferential groove. The socket end of a thermoplastic pipe is then heated and forced over the working surface of the mandrel and over the gasket, whereby the heated socket end of the thermoplastic pipe flows over the gasket to form a retention groove for retaining the gasket. The heated socket end of the thermoplastic pipe is then cooled and the socket end is retracted from the mandrel, whereby the gasket is retained within an internal groove which is formed in the interior of the female, belled pipe end. The unique shape of the improved gasket helps to insure proper positioning of the gasket on the outer working surface of the forming mandrel. 
         [0020]    In one form of the invention, the working mandrel is provided with a backup collar at a second circumferential location on the mandrel, the backup collar having an exposed lip portion which initially abuts the gasket. The backup collar is retracted once the heated thermoplastic pipe end is forced over the forming mandrel and the gasket. 
         [0021]    In another form of the invention, the belling process is carried out as previously described without the presence of a backup collar on the working mandrel. In this case, the contact between the edges of the opposing flaps of the gasket with the sidewalls of the circumferential groove provided on the forming mandrel facilitates proper positioning of the gasket within the mandrel groove, thereby assuring improved quality control of the pipe belling process. 
         [0022]    Additional objects, features and advantages will be apparent in the written description which follows. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]      FIG. 1  is a perspective view of a sealing gasket of the invention. 
           [0024]      FIG. 2  is a cross sectional view of the sealing gasket of  FIG. 1 . 
           [0025]      FIG. 3  is a partial sectional view of the gasket of the invention in place on a working mandrel, showing the female thermoplastic pipe end being forced over the mandrel and over the sealing gasket. 
           [0026]      FIG. 4  is a view similar to  FIG. 3 , but showing the optional use of a backup collar on the working mandrel. 
           [0027]      FIG. 5  is a partial cross sectional view of the make-up of a pipe joint, showing the male, spigot pipe end being installed within the belled, female pipe end. 
           [0028]      FIGS. 6-9  illustrate the prior art Rieber pipe forming process. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0029]    The embodiments herein and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. Descriptions of well-known components and processes and manufacturing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the invention herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the claimed invention. 
         [0030]    The primary advantages of the present invention can perhaps be best understood with reference to a simplified discussion of the prior art Rieber pipe belling process and with reference to  FIGS. 6-9  of the drawings.  FIG. 6  shows a section of a conventional elastomeric sealing gasket  11  having a steel reinforcing ring  13  in place on the generally cylindrical outer working surface  15  of the mandrel  17  used in the belling process. The elastomeric gasket  11  can be formed of, for example, rubber and is a ring shaped, circumferential member having an inner compression surface  19  and an exposed nose portion  21  which, as shown in  FIG. 6 , abuts a backup or forming collar  23 . The nose portion  21  forms a sloped contact area for contacting the lip portion  22  of the backup collar  23 . The backup collar  23  has a first generally cylindrical extent  25  which is joined to a second cylindrical extent  27  by a step region  29 , whereby the second extent  27  is of greater external diameter than the first cylindrical extent  25 . The lip portion  22  of the backup collar  23  forms a right angle with respect to the working surface  15  of the mandrel  17 . 
         [0031]    In the first step of the prior art process, the steel reinforced elastomeric ring  11  is placed onto the working surface of the mandrel  17  and pushed to a position against the back-up or forming collar  23 . In this position, the gasket is anchored to the mandrel surface with the rubber between the mandrel and the steel ring of the gasket being compressed by approximately 20% 
         [0032]    In the second step of the prior art process, the socket end  33  of the thermoplastic pipe  31  ( FIG. 7 ) is heated and pushed over the steel mandrel  17 , gasket  11  and back-up collar  23 . The socket end  33  is expanded due to the thermoplastic nature of the pipe. A number of thermoplastic materials, such as polyethylene, polypropylene and polyvinylchloride (PVC) are known in the prior art having the required expansion characteristics, depending upon the end application of the pipe joint. The preferred material for the pipe is PVC. The socket end  33  of the PVC pipe flows over the first cylindrical extent  25  of the back-up collar  23  and abuts the step region  29  in the second step of the process. 
         [0033]    In the next step of the prior art process ( FIG. 8 ) the mandrel and pipe move away from the back-up collar  23  and the pipe socket end  33  retracts around the mandrel and gasket  11  due to the elastic forces of the thermoplastic material. Typically, vacuum was also applied through ports  35 ,  37  which connected the mandrel working surface with a vacuum source (not shown). 
         [0034]    In the final step of the prior art process ( FIG. 9 ), the pipe socket end  33  is cooled by means of a water spray bar  39  and spray nozzles  41 . As the cooling takes place, the pipe socket end  33  shrinks around the gasket  11 , thus compressing the rubber body of the gasket between the steel reinforcing ring  13  and the socket-groove to establish a firm seal. 
         [0035]    The above described Rieber process has been in commercial use since the early 1970&#39;s and is described in the above referenced issued United States patents, among other sources. It will thus be well familiar to those skilled in the thermoplastic pipe sealing arts. Turning now to  FIG. 1 , there is shown a pipe sealing gasket of the invention, designated generally as  45 . The gasket  45  is designed to be received within a groove ( 47  in  FIG. 5 ) provided within a socket end  49  of a thermoplastic pipe. As will be appreciated from  FIG. 1 , the sealing gasket  45  of the invention has a ring shaped elastomeric body which is formed of, for example, a natural or synthetic rubber. As shown in  FIG. 2 , when the body is viewed in cross-section, it has a central bulbous region  51  formed of a suitable elastomer such as a natural or synthetic rubber. The central bulbous region  51  has located therein a planar angled region  53  which bisects the bulbous region  51  at a selected radial location and which extends outwardly from the central region to form a pair of oppositely arranged wing-like flaps  55 ,  57 . The planar angled region is formed of a dissimilar resilient material, such as a suitable plastic material, for example a suitable polyolefin such as polypropylene. 
         [0036]    The central bulbous region  51  forms an oval profile when viewed in cross-section (see  FIG. 2 ). The oval profile has an outer surface region  59  which is adapted to seat within the groove ( 47  in  FIG. 5 ) provided in the socket end  49  of the belled, female pipe end. The oval profile also has an inner surface region  61  which forms a compression seal region for a mating spigot end of a mating thermoplastic pipe during insertion of the spigot end within the mating socket end of the thermoplastic pipe. 
         [0037]    As can be seen in  FIG. 2 , the oppositely arranged wing-like flaps  55 ,  57  which extend outwardly from the central bulbous region  51  of the gasket form a V-shaped cavity, indicated generally as  63  in  FIG. 2 , which is bounded by the leading flap  57  and the trailing flap  55 . The cavity  63  receives the inner surface region  61  of the central bulbous region  51  of the gasket. The leading flap  57  has an outer edge  65  which makes contact with the spigot pipe end ( 67  in  FIG. 5 ) during insertion and wipes any dirt present from the spigot end, keeping the dirt from reaching the cavity  63  and inner surface region  61  which forms a compression seal region for sealing against the spigot pipe end  67 . 
         [0038]    The socket end of the thermoplastic pipe  49 , as shown in  FIG. 5 , terminates in a mouth region, shown generally as  69 . The mouth region includes the inner circumferential groove  47  which is located adjacent to the mouth region. The tip of the leading flap  65  is separated from the mouth region of the socket pipe end by a gap  71 . As a result, any dirt which is wiped from the spigot end  67  by the leading flap end  65  accumulates in the gap  71  between the flap and the socket. 
         [0039]    As shown in  FIG. 2 , the central bulbous region  51  of the gasket has a radial diameter, indicated by the phantom line  73 , and a mid-point  75 . The planar angled region  53  bisects the central bulbous region at a pre-defined point on the radial diameter  73  which is less than that of the mid-point  75 . The wing-like flaps  55 ,  57  form downwardly extending projections from the planar angled region  53  and form acute angles with respect to the axis of the radial diameter  73 , as viewed in  FIG. 2 . 
         [0040]    The previously described sealing gasket can be used in a method of forming the belled end of a section of thermoplastic pipe which is used to form a pipe coupling. As shown in  FIG. 3 , a steel forming mandrel  75  is provided with an inner end  77 , an outer end  79  and an outer working surface  81 . The outer working surface includes a circumferential groove  83  having oppositely arranged sidewall extents  85 ,  87 . As can be seen in  FIG. 3 , the gasket of the invention is installed on the outer working surface of the mandrel with the central bulbous region  51  contacting the groove  83  and with the winged-like flaps  55 ,  57  contacting the grooved sidewalls  85 ,  87  so that the seal locks against the edges of the groove. This insures a more precise seal positioning and ultimately better bell quality. It also simplifies handling since it is not possible to load the seal facing the wrong side of the working mandrel. 
         [0041]    In the next step the method of manufacturing a thermoplastic pipe, the thermoplastic pipe is heated and forced over the working surface of the mandrel and over the gasket, whereby the retention groove ( 47  in  FIG. 5 ) is formed in the female belled pipe end. The heated socket end  49  of the thermoplastic pipe is then cooled and retracted whereby the gasket is retained within the groove  47  formed in the pipe mouth region. While the improved manufacturing method of the invention has been described with respect to a working mandrel having only a retention groove, it will be appreciated with respect to  FIG. 4 , that the mandrel may also include a traditional backup collar  89  having an exposed lip portion  91  which initially abuts the gasket of the invention. While the improved sealing gasket of the invention is perfectly capable of use with existing belling machines which feature such a back-up collar  89 , it is not necessary to utilize the back-up collar due to the features of the improved design. As a result, once the back-up collar  89  is removed from the process, other seal designs become incompatible with the belling process. 
         [0042]      FIG. 5  illustrates in simplified fashion the advantages of the improved pipe joint which is formed using the sealing gasket of the invention. The improved sealing gasket is designed for receipt within a grove provided within a female socket end of a first section of pipe for forming a seal between an internal surface of the female pipe socket ( 47  in  FIG. 5 ) and a male spigot end  67  of a mating second pipe section. The previously described sealing gasket is first installed within the groove  47 . The spigot end  67  is then installed within the belled, female pipe end, as shown in  FIG. 5 . As the spigot end  67  enters the mouth opening of the female pipe section, the tip of the leading flap  65  of the gasket contacts the spigot pipe end  67  and wipes any dirt or debris from the spigot end before the spigot end contacts the central bulbous region  51  of the gasket. Any debris wiped from the spigot end  67  is generally collected in the gap region illustrated as  71  in  FIG. 5 . Upon assembly of the joint the central bulbous region  51  forms a compression seal with the mating spigot pipe end  67 . 
         [0043]    An invention has been provided with several advantages. The improved sealing gasket is simple in design and economical to manufacture. The gasket features a “dual durometer” aspect in that the polypropylene seal core is more rigid than the remainder of the central bulbous region of the gasket. The polypropylene planar, angled region of the gasket replaces rubber at neutral locations for sealing purposes. The new shape enforces a more stable bell shape during subsequent belling operations and improves quality control. The new gasket is compatible with existing belling machines. The tip of the wing-like flaps of the gasket lock against the opposing edges of the retention groove provided on the external working surface of the forming mandrel. This assures precise seal positioning and better bell quality. The particular shape of the new gasket design thereby simplifies handling since it is not possible to load the sealing gasket improperly on the outer surface of the working mandrel. 
         [0044]    While the invention has been shown in only one of its forms, it is not thus limited but is susceptible to various changes and modifications without departing from the spirit thereof.