Abstract:
A pipe joint for plastic pipe includes a bell member and a spigot member. The bell member includes a tubular plastic body wall having a metal reinforcement ring. The spigot member, which is insertable into the bell member, includes a tubular plastic body wall having an internal surface and an external surface and a longitudinal axis and metal reinforcement encased within the tubular plastic body wall. A plurality of plastic ribs extend from the external surface of the tubular plastic body wall and form a gasket channel.

Description:
CROSS-REFERENCES 
     This application is a continuation of U.S. application Ser. No. 12/474,902, filed May 29, 2009, now issued as U.S. Pat. No. 8,109,540, and claims the benefit of U.S. Provisional Application Ser. No. 61/057,567, filed May 30, 2008, each of which is hereby incorporated by reference. 
    
    
     TECHNICAL FIELD 
     This application relates generally to a pipe systems utilized to convey liquids under gravity induced flows and more particularly to a pipe joint useful in connecting together pipes in such systems. 
     SUMMARY 
     In an aspect, a bell member for a pipe joint includes a tubular plastic body wall having a radially outer side including a pair of spaced apart circumferentially extending ribs and a metal reinforcement ring located between the ribs. The tubular plastic body wall includes a circumferential plastic ring portion extending between the ribs and radially exterior of the metal reinforcement ring to encase the metal reinforcement ring within the tubular plastic body wall. A radial gap may be provided between the plastic ring portion and the metal reinforcement ring to accommodate differing thermal shrinkage rates as between the two different materials. 
     In another aspect, a spigot member for a pipe joint includes a tubular plastic body wall having an internal surface and an external surface and a longitudinal axis and metal reinforcement encased within the tubular plastic body wall. A plurality of plastic ribs extend from the outer surface of the tubular plastic body wall and forming a gasket channel, including a first circumferentially extending solid plastic rib, a second circumferentially extending solid plastic rib spaced apart from the first circumferentially extending solid plastic rib, and a third circumferentially extending solid plastic rib positioned between the first circumferentially extending solid plastic rib and the second circumferentially extending solid plastic rib. The third circumferentially extending solid plastic rib defines a rib diameter that is smaller than respective rib diameters defined by each of the first circumferentially extending solid plastic rib and the second circumferentially extending solid plastic rib. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A and 1B  are partial cross-sections of bell and spigot portions of a pipe joint prior to joinder; 
         FIG. 2  is a partial cross-section of a pipe joint produced by joining the bell and spigot portions of  FIGS. 1A and 1B ; 
         FIG. 3  depicts roll bending equipment; 
         FIGS. 4A and 4B  depict a partially formed bell portion in side (metal reinforcement inserted) and cross-sectional (metal reinforcement not yet inserted) views; 
         FIG. 5  shows an overmolding fixture; 
         FIG. 6  shows a co-extrusion fixture; 
         FIGS. 7A and 7B  are partial cross-sections of bell and spigot portions respectively with representative dimension indicators; 
         FIG. 8  is a partial cross-section of an alternative bell end structure; 
         FIG. 9  is a partial cross-section of the bell end structure of  FIG. 8  with dimension indicators; and 
         FIGS. 10 and 11  depict partial cross-sections of alternative bell-end structures. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIGS. 1 and 2 , one embodiment of a pipe joint is illustrated as being formed by mating bell and spigot portions. A bell portion  10  is connected to an end  12  of a polyethylene pipe  14  with reinforced, helically extending ribs  16  having a steel reinforcement strip  18  encased within rib sidewalls  20 ,  22  and a rib cap  24 . The bell portion  10  is also formed of polyethylene material and includes an attachment part  30  with an outer surface  32  engaging the inner surface  34  of the pipe end  12  and a weld seal  35 , again of polyethylene, formed between the two. The bell part of the bell portion is formed by a radially outward extending wall  36 , a generally L-shaped transition  38 , a cylindrical part  40  and a frusto-conical part  42 . The cylindrical part  40  includes an encapsulated steel reinforcement band  44  and a number of annular strengthening ribs  46 A- 46 D located between the reinforcement and the frusto-conical part  42 . 
     The spigot portion  50  is connected to an end  52  of a pipe  54  that is similar in configuration to pipe  14 . The spigot portion is also formed of polyethylene material and includes a connection part  56  with an outer surface  58  engaged with an inner surface  60  of pipe end  52  and a weld seal  62 , again of polyethylene, formed between the two. The outer surface of the spigot portion  50  includes spaced apart, solid PE ribs  64 ,  66  of similar size with a smaller rib  68  positioned therebetween. A gasket  70  is located between the ribs and includes a lower slotted portion  72  that receives the smaller rib  68 . The spigot portion further includes an encapsulated steel reinforcement band  74  with an axial width that extends roughly from side  76  of rib  66  to side  78  of smaller rib  68 . 
     In one embodiment, the bell portion  10  and spigot portion  50  may be formed together (e.g., via extrusion or molding) with end portion  90  of the bell portion connected to end portion  92  of the spigot portion. In the case of extrusion, the two pieces can be separated either before or after being curved into a cylinder form. In the case of molding, the two pieces can be separated prior to attachment to respective pipe end portions. In another embodiment, the bell portion  10  and spigot portion  50  can be formed separately (e.g., each being extruded separately or molded separately). In the latter case, the leg of the attachment part  30  of the bell portion may be formed as part of the profile extrusion, or the initial bell profile extrusion may lack the leg portion, which would be attached later as described below. 
     Considering an embodiment which the pieces are extruded separately. The bell portion is initially extruded as an elongate strip having the cross-section of the bell part (i.e., not including the pipe  14 ) of  FIG. 1A , but with the steel reinforcement  44  not present. In this case, the layer of PE material  94  may be formed as a flap with one end  96  attached and another end  98  unattached enabling the flap to be opened. The open end of the flap faces away from the bell end. The elongate strip is then cut to length suitable for forming a bell portion of desired diameter. The cut strip is then rolled to appropriate diameter with suitable roll bending equipment such as that represented in  FIG. 3 . A preformed metal reinforcement ring of desired diameter is then placed within the space under the flap  94  (e.g., per the directional arrows  99  of  FIGS. 4A and 4B ), with the elongate strip  44  having been sized to result in a slight gap  100  at adjacent ends of the rolled strip (e.g., between ¼″ and 1″ or so), to form a gapped bell structure  102 . As shown, the metal reinforcement strip  44  is a full cylinder and traverses the gap  100  of this structure. Typically the metal reinforcement (e.g., steel) may be a preformed, sized continuous cylinder (e.g., created by bending an elongate steel plate into a cylinder shape and joining the adjacent ends of the steel plate by butt welding, fasteners, crimping or other suitable means). 
     The gapped bell structure  102  is then placed in an overmold fixture and the plastic cylinder of the bell is completed via an overmold process (e.g., using the same material as the strip, preferably PE) that fills the gap  102  with plastic in the same profile as the rest of the unit. At this point the flap  94  remains largely unsealed, though in the gap region  102  the reinforcement may be completely encased. Referring to  FIGS. 5A ,  5 B and  5 C an overmold assembly  120  is shown in isometric, side and front views, with the bell structure in place for overmolding, but with the exterior  122  and interior  124  overmold components in open position. The interior overmold component  124  is moved downward to close the assembly over the bell and then the plastic is injected for molding. 
     Once overmolding of the gap  100  is completed, the structure is placed in an extruder fixture that utilizes one or more nozzles to form a weld seal at end  98  of the flap while the bell structure is rotated past the nozzle of the fixture. Full sealing of the flap results in a completed bell unit in which the steel reinforcement  44  is completely encased within the plastic of the bell wall. Where the bell profile is initially formed lacking the leg of the attachment part  30 , the leg can be attached using a weld seal in the same fixture and step while the flap is being sealed. Referring to  FIGS. 6A ,  6 B and  6 C an extruder assembly  130  is shown in isometric to and side views, and includes a table/fixture  132  that supports and rotates the bell through a rotation assembly  134  mounted thereon. As shown, the table can be utilized to support and rotate multiple different diameters of bells or spigots for flap sealing. An extrusion system  136  is mounted alongside the fixture with nozzles positioned and oriented to seal the flap. A control unit  138  is provided for automatically controlling the operation of the extruder. 
     It is recognized that the flap could also be sealed by a heat welding process. For example, heat welding could be achieved by initially forming the free end of the flap (or a corresponding segment of the main bell body) with a bead (or other formation) of sufficient plastic that could be melted (e.g., by a heater) to bond the flap to the free end of the flap to rest of the bell. 
     The completed bell unit can then be attached to a pipe. In this regard, referring back to  FIG. 1A , the smaller diameter attachment part  30  of the bell unit is inserted within a pipe end and a suitable attachment fixture with nozzles may be used to form the weld seal  35 . In another embodiment ultrasonic or friction welding could be used to form the weld seal  35 . 
     In the case of a bell profile that is molded rather than extruded, the initial molding may take the form of a complete cylinder (i.e., no gap) of desired diameter with the flap  94  again having a free end. The reinforcement is inserted beneath the flap and the process proceeds in much the same manner described above using the co-extruder fixture and then attaching to a pipe end. 
     The spigot portion may be formed in much the same way as the bell portion, using either extrusion or molding to form the profile with the rib  66  defining the end of an unsealed flap for receiving the reinforcement  74 . Attachment of the spigot to the pipe end can also be completed in the same manner as with the bell portion. 
     As a general rule, each length of pipe for a pipe system will be formed with one end having a bell portion  10  attached and the opposite end having a spigot portion  50  attached. Multiple pipe lengths can then be connected end to end during a given installation, with spigot portions inserted into bell portions to provide a sealed connection. Positioning sized cylindrical metal reinforcements within the wall of both the spigot portion and the bell portion in the region of the gasket aids in maintaining a desirable seal. 
     The exact thickness and size of the various parts of any bell portion or spigot portion can be varied depending upon the structural requirements and intended diameter usage. A distinct profile could be provided for each pipe diameter. A single profile could be used for multiple diameters or diameters within a certain specified range. 
     As noted above, the exact profile and dimensions of bell and spigot portions could vary. However, applicant has found the following exemplary dimensions (provided in ranges in Tables I and II below) to be both practical and advantageous. 
     
       
         
               
             
               
               
               
               
               
               
               
               
             
           
               
                 TABLE I 
               
             
             
               
                   
               
               
                 Bell Dimensions (inches) - Polyethylene Material With Steel Reinforcement 
               
             
          
           
               
                 Pipe 
                   
                   
                   
                   
                   
                   
                   
               
               
                 Diameter 
                 A B   
                 B B   
                 C B   
                 D B   
                 E B   
                 F B   
                 G B   
               
               
                   
               
               
                 24″ 
                 7″-9″ 
                   1″-1.5″ 
                 3.1″-3.4″ 
                 0.250″-0.350″ 
                 0.100″-0.150″ 
                 0.500″-1.00″  
                 0.50″-1.50″ 
               
               
                 30″ to 42″ 
                 7.75″-9.75″ 
                 1.7″-2.2″ 
                 3.35″-3.65″ 
                 0.425″-0.525″ 
                 0.215″-0.265″ 
                 0.75″-1.25″ 
                 0.50″-1.50″ 
               
               
                 48″ to 60″ 
                  8.3″-10.3″ 
                 2.1″-2.6″ 
                 3.6″-3.9″ 
                 0.44″-0.54″ 
                  0.3″-0.35″ 
                 1.05″-1.55″ 
                 0.50″-1.50″ 
               
               
                 66″ to 96″ 
                   10″-12.5″ 
                 2.35″-2.85″ 
                 5.3″-5.7″ 
                 0.67″-0.77″ 
                 0.49″-0.55″ 
                 1.20″-1.70″ 
                 0.50″-1.50″ 
               
               
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
               
               
               
               
             
           
               
                 TABLE II 
               
             
             
               
                   
               
               
                 Spigot Dimensions (inches)- Polyethylene Material With Steel Reinforcement 
               
             
          
           
               
                 Pipe Diameter 
                 A S   
                 B S   
                 C S   
                 D S   
                 E S   
               
               
                   
               
               
                 24″ 
                 2.5″-3.1″ 
                 0.6″-0.9″ 
                 0.50″-0.55″ 
                 0.95″-1.1″  
                 0.85″-0.95″ 
               
               
                 30″ to 42″ 
                   3″-3.6″ 
                 0.8″-1.2″ 
                 0.61″-0.67″ 
                 1.2″-1.4″ 
                 1.05″-1.15″ 
               
               
                 48″ to 60″ 
                 3.25″-3.85″ 
                 1.1″-1.5″ 
                 0.90″-0.98″ 
                 1.45″-1.65″ 
                 1.24″-1.34″ 
               
               
                 66″ to 96″ 
                 3.85″-4.6″  
                 1.15″-1.55″ 
                 0.86″-0.94″ 
                 1.75″-1.95″ 
                 1.67″-1.77″ 
               
               
                   
               
             
          
         
       
     
     Referring now to  FIG. 8 , an alternative embodiment of a pipe joint bell  200  is illustrated in partial cross-section. The bell  200  could be utilized in conjunction with the spigot structure of  FIG. 1B , or another suitable spigot structure. 
     Bell  200  includes a frusto-conical end part  202 , a main cylindrical part  204  and a reduced diameter pipe connecting part  206 . Cylindrical part  204  includes raised solid ribs  208  and  210  between which a steel, or other material, reinforcement ring  212  is placed, and an annular plastic strip  214  encases the steel ring  212  within the bell wall. To produce the bell of this embodiment, a primary bell portion, consisting of end part  202  at one end, main part  204  with external ribs  208 ,  210  and downwardly projecting flange or leg  216 , is extruded together as an elongated strip. The extruded strip is then cut to length suitable for forming a bell portion of desired diameter. The cut strip is then rolled to the proper diameter. The rolled strip is then either overmolded or butt fused to form a completed ring. A metal reinforcement ring is then placed over the outer portion of the bell between the ribs  208  and  210 . In this regard, the metal reinforcement ring may be placed by initially wrapping a steel band and then butt welding the ends of the steel band to complete the reinforcement ring. The plastic ring  214  is then placed over the reinforcement, with side edges of the plastic ring sitting atop land areas of the ribs  208 ,  210 . The plastic ring  214  may be preformed into a cylinder of desired diameter before placing it on the bell ring. A co-extrusion process is then used to seal the plastic ring to the ribs  208 ,  210 , with a weld bead applied at locations  218  and  220 , completing the encasement of the reinforcement ring  214 . 
     In order to connect the primary bell portion to a pipe, a secondary bell portion (e.g., the connecting part  206 ) is initially formed separately from the primary bell portion. In one implementation, the secondary part  206  is formed from the same extruded strip as that used for the spigot. The strip is cut to length and rolled to diameter and then either overmolded or butt-welded to form a complete cylinder. The unsealed end of the flap that would normally receive the spigot reinforcement is welded closed using an extrusion weld or heat weld, which could occur before or after the cylinder formation, eliminating the flap. The connecting part  206 , now formed as a separate ring structure, is then inserted within the end  230  of a pipe  232 . The connecting part  206  is tack welded in place to the pipe end (e.g., at the location  234  where rib  66  abuts the pipe end). 
     The formed primary bell portion is then placed over the connecting part  206  to position the leg  216  in the space between ribs  64  and  68 . In this regard, the primary bell portion may be angled to move the primary bell portion onto the end of the connecting part  206 , the upper part of the leg  216  placed between the ribs  64  and  68  and the lower part of the primary bell portion then allowed to drop downward and onto the end of the connecting part. Centering spacers are then inserted into the annular space  236  between the radially exterior end of rib  64  and the radially inner surface of cylindrical part  204 . Once the proper uniform spacing is achieved, the primary bell portion is tacked in place to the connecting part  206  (e.g., at the location  238  where rib  68  abuts against leg  216 ). The connecting part  206  is then permanently welded to the pipe end (e.g., by placing a continuous internal plastic weld bead or seal at the location  240  where the inside end of the connecting part  206  meets the inner surface of the pipe end  230 ). The centering spacers are removed and then the primary bell portion is permanently welded to the connecting part  206  (e.g., by placing a continuous internal plastic weld bead or seal within the annular space  236 . 
     As shown in  FIG. 8 , the inside surface of the plastic ring  214  is spaced away from the external surface of the reinforcement ring. The purpose of providing this spacing is to account for the differing rates of thermal shrinkage as between the plastic (e.g., polyethylene) and the metal reinforcement (e.g., steel). In this regard, at colder temperatures the shrinkage rate of the plastic can be 10 times that of the steel and providing the spacing prevents the plastic ring  214  from shrinking so much that it wraps too tightly upon the steal reinforcement and ruptures or breaks. In one embodiment, the radial height H1 of the ribs  208  and  210  may be at least three times the radial thickness T1 of the reinforcement  214 . For example, reinforcement having a thickness of 40-75 thousands of an inch may be used in conjunction with ribs having a height of 150 to 250 thousands of an inch. In such case the radial thickness of the gap between the reinforcement and the plastic ring would generally be at least 1oo thousandths of an inch. 
     Referring now to  FIG. 9  and Table III below, the following exemplary dimensions have been found to be both practical and advantageous for the bell structure of  FIG. 8 . 
     
       
         
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE III 
               
             
             
               
                   
               
               
                 Bell Dimensions (inches) - Polyethylene Material With Steel Reinforcement 
               
             
          
           
               
                 Pipe Diameter 
                 A B′   
                 B B′   
                 C B′   
                 D B′   
                 E B′   
                 F B′   
               
               
                   
               
               
                 24″ 
                 7.0-8.5″ 
                 8.00-9.50″ 
                 2.9-3.6″ 
                 1.3-1.9″ 
                 0.5-1.1″ 
                 0.90-0.17″ 
               
               
                 30″ to 42″ 
                 7.5-9.0″ 
                 8.75-9.25″ 
                 3.1-3.9  
                 1.5-2.3″ 
                 0.7-1.5″ 
                 0.18-0.28″ 
               
               
                 48″ to 60″ 
                 8.0-9.5″ 
                  9.50-11.00″ 
                 3.6-4.4″ 
                 1.8-2.6″ 
                 1.0-1.8″ 
                 0.27-0.37″ 
               
               
                 66-96″ 
                 10.5-12.0″ 
                 12.25-13.75″ 
                 5.5-6.5″ 
                 2.2-3.0″ 
                 1.4-2.2″ 
                 0.27-0.37″ 
               
               
                   
               
             
          
         
       
     
     It is to be clearly understood that the above description is intended by way of illustration and example only and is not intended to be taken by way of limitation, and that changes and modifications are possible. For example, while  FIG. 8  illustrates one embodiment of a multi-piece bell structure, it is recognized that alternatives are possible, such as those shown in  FIGS. 10 and 11  that do not rely upon the use of the spigot extrusion to form the connecting parts  206 ′ and  206 ″ of the bell. Accordingly, other embodiments are contemplated and modifications and changes could be made without departing from the scope of this application.