Abstract:
A process for making plastic-lined metallic pipes for conveying liquid or gas includes the steps of heating a metallic pipe evenly to a first temperature; cooling a plastic pipe evenly to a second temperature; inserting the plastic pipe into the metallic pipe to constitute an inner sleeve; drawing the metallic pipe from its two ends; and cooling the sleeved pipe to a storage temperature. The pipe includes a continuous inner plastic sleeve and an outer seamless metallic pipe. The outer diameter of the plastic sleeve is circumferentially melt-bonded to the inner diameter of the outer pipe. The plastic sleeve constitutes an uninterrupted lining for the metallic pipe.

Description:
REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a divisional application of, and claims the benefit of priority to, U.S. patent application Ser. No. 11/479,696, entitled “A PLASTIC-LINED METALLIC PIPE FOR CONVEYING DRINKING-WATER AND THE CONNECTORS FOR THE SAME,” filed on Jun. 30, 2006, the content of which is incorporated in its entirety by reference herein. The applicant certifies that there is no new matter included in this divisional application. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Technical Field of the Invention 
         [0003]    The present invention generally relates to the field of designing and manufacturing of metallic pipe for conveying drinking-water. More particularly the invention relates to a pipe with an outer metallic pipe and an inner plastic pipe suitable for conveying drinking-water and the connectors for the pipe. 
         [0004]    2. Description of the Related Art 
         [0005]    Zecchin, et al, in PCT/EP98/08182, disclosed a composite pipe made of metal-plastic for hydro-thermo-sanitary plants and process for the production thereof. The composite pipe consist of an internal metal pipe, an outer pipe made of a plastic suitable for conveying drinking-water, and an intermediate layer having a bi-adhesive function. The outer pipe and the intermediate layer are both extruded onto the inner metal pipe. The material for the outer pipe and the intermediate layer preferably contains an anti-oxidizer additive for the pipe metal. The primary purpose of Zecchin&#39;s invention is to prevent corrosions due to the action of local leakage currents and/or chemical corrosion caused by acid substances released from building materials like concrete of the floors in which the pipes are embedded. 
         [0006]    David A. Shotts, et al, in U.S. Pat. No. 5,152,323, disclosed a plastic-lined metal pipe which includes an outer metallic pipe having a longitudinal weld and an inner plastic sleeve melt-bonded to the metallic pipe. The metallic pipe is of a size to be in mechanical engagement with the sleeve around the entire circumference of the sleeve. The pipe is manufactured using an extruder, for providing a plastic sleeve, in conjunction with a continuous roll-forming tubing mill production line, for forming and treating the metallic outer tube, so that the lined pipe is made using a continuous process. The plastic sleeve is caused to not collapse during the manufacturing process and the sleeve and pipe are firmly locked together. The pipe may be made by apparatus for continuously manufacturing plastic-lined metal pipe including an extruder for providing a plastic sleeve and a continuous roll-forming tubing mill production line. The production line operates to sequentially deform a substantially flat steel strip to a generally tubular configuration and includes an electric resistance welder or high frequency welder for continuously welding the lateral edges of the moving strip to complete the pipe. A plastic sleeve is fed into the about-to-be-formed metallic pipe upstream of the welder. This plastic sleeve has an outside diameter slightly smaller than the inside diameter of the metallic pipe in the as-formed condition of the sleeve and the sleeve maintains its generally tubular configuration from the time it is inserted into the metal pipe until the manufacture is completed. The production line also includes a station for reducing the inside diameter of the metallic pipe to substantially the outside diameter of the plastic sleeve thereby locking the two components together. 
         [0007]    Alexander Esser in U.S. Pat. No. 6,575,197 disclosed a double-layer pipe for fluidic transport of abrasive solids. The pipe includes a hardened inner pipe portion of steel; an outer pipe portion of weldable steel; terminal coupling collars made of weldable steel; and a heat-insulating layer disposed between the inner pipe portion and the outer pipe portion. The pipe includes a heat-insulating layer between the inner pipe portion and the outer pipe portion to form a barrier during heating of the inner pipe portion to thereby prevent heat from dissipating to a significant degree from the inner pipe portion to the outer pipe portion. The applied heat remains in the inner pipe portion so that the inner pipe portion, especially when thin pipe walls are involved, can be heated evenly within a very narrow temperature window. When the inner pipe portion is then quenched, a markedly even hardness is realized over the entire circumference as well as length of the inner pipe portion. The heat-insulating layer disposed between the inner pipe portion and the outer pipe portion may be formed by a coating made of a combustible non-metallic material and applied upon the outer surface of the inner pipe portion and/or the inner surface of the outer pipe portion. 
         [0008]    John Werner in U.S. Pat. No. 4,507,842 disclosed an improved method for sealing and protecting a plastic lined pipe joint. The improved plastic collar seal is placed in the interior of a pipe joint formed between first and second externally threaded plastic lined pipe sections which are to be held together by an internally threaded pipe collar. The improved plastic collar seal is a hollow, open ended, cylindrical plastic collar seal presized to concentrically fit within the plastic liner of the sections of plastic lined pipe with minimum concentric tolerance. The open ends of the plastic collar seal are internally beveled and the plastic collar seal is equipped with external O-ring grooves and O-rings at each of the ends. The collar seal is further provided with an external ledge or ridge molded concentrically to the collar seal between the O-rings wherein the ledge is adapted to fit within the internally threaded collar and rest on the end of the lined pipe. This ledge is positioned such that the distance from at least one end of the collar seal to the ledge exceeds the length of the internally threaded collar. In operation, the collar is threaded on the first plastic lined pipe section and the improved plastic collar seal is inserted within the pipe section and collar with the ledge coming to rest on the end of the pipe section leaving the other end of the plastic collar seal extending beyond the collar. The second section of plastic lined pipe can then be easily threaded into the internally threaded collar, over the collar seal, thus forming a tight pipe joint with the collar seal within the joint. 
         [0009]    John J. Hunter in U.S. Pat. No. 4,709,946 disclosed a pipe joint which secures two lined pipe sections together and seals the juncture of the pipe sections against the migration of fluids through the joint and methods for forming the pipe joint. The method includes the steps of axially aligning first and second pipe sections; securing the first pipe section to the second pipe section; overlapping the liners of the first and second pipe sections; and compressing the liners of the first and second pipe sections where overlapped to seal the joint against migration of pressurized fluids through the joint. The pipe joint provided by this method includes, in one embodiment, first pipe means having a fluid impervious first liner mounted on the interior thereof; second pipe means having a fluid impervious second liner mounted on the interior thereof; means for securing said first pipe means in axial alignment with said second pipe means wherein said first liner and said second liner are partially overlapped; and means for compressing said first and second liners were overlapped to seal the pipe joint formed at the juncture of said first and second pipe means for the transmission of fluids there through. 
         [0010]    What is desired is a plastic-lined metallic pipe with a food-grade non-poisonous inner plastic lining pipe and an outer metallic pipe made of high strength, light-weight and corrosion resistant aluminum alloy. 
       SUMMARY OF THE INVENTION 
       [0011]    The plastic-lined metallic pipe for conveying liquid or gas includes a continuous inner plastic sleeve or pipe and an outer seamless metallic pipe. The outer diameter of the inner plastic sleeve is circumferentially melt-bonded to the inner diameter of the outer metallic pipe. The inner plastic sleeve constitutes an uninterrupted lining for the outer metallic pipe. The inner plastic sleeve is formed of a non-poisonous plastic, such as polypropylene, suitable for conveying drinking-water. The outer metallic pipe is formed of aluminum alloy. 
         [0012]    The process for a plastic-lined metallic pipe for conveying liquid or gas includes at least the steps of: (1) heating a metallic pipe evenly to a first temperature at which the metallic pipe has a higher tensility; (2) cooling a plastic pipe evenly to a second temperature which is lower than the regular storage temperature; (3) inserting the plastic pipe into the metallic pipe to constitute an inner sleeve; (4) drawing the metallic pipe from its two ends for a specific length; and (5) cooling the sleeved pipe to a storage temperature. 
         [0013]    Also disclosed is a connector used for connecting plastic-lined metallic pipes. The connector includes the following components: 
         [0000]    1. at least one metallic member as the body having a first stepped cylindrical inner space and a section of thread in its outer wall, the first stepped cylindrical inner space including a first cylindrical space as a conveying channel, a second cylindrical space for holding a pipe to be connected to the body, a tapered cylindrical space, and a third cylindrical space, the first cylindrical space&#39;s diameter being identical with the pipe&#39;s inner diameter and the second cylindrical space&#39;s diameter being slightly larger than the pipe&#39;s outer diameter, the tapered cylindrical space merging the second cylindrical space with the third cylindrical space;
 
2. a cap or nut having a second stepped cylindrical inner space and having a section of thread in its inner wall for coupling with the body, the second stepped cylindrical inner space including a fourth cylindrical space for coupling with the body and a fifth cylindrical space in the cap&#39;s end wall for holding the pipe, the fifth cylindrical space&#39;s diameter being slightly larger than the pipe&#39;s outer diameter;
 
3. a tapered rubber washer for filling the gap between the pipe and the wall of the second cylindrical space and filling the tapered cylindrical space of the body;
 
4. a metallic washer for pressing the rubber washer; and
 
5. a “c” type spring washer for locking the pipe when the cap is being coupled with the body, the spring washer having a rough inner surface or a section of male thread for enforcing the locking.
 
         [0014]    In the operation to connect the pipe to the body, the following assembling order is required: inserting one end of the pipe through the cap from the cap&#39;s end wall, then through the “c” type spring washer, the metallic washer and the tapered rubber washer with its wider end facing the metallic washer, then inserting the one end of the pipe into the second cylindrical space of the body, then sliding the tapered rubber washer and the metallic washer into the third cylindrical space of the body, then slightly squeezing the spring washer and inserting it into the third cylindrical space of the body, and then screwing the cap in. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0015]      FIG. 1  is a schematic diagram showing the cross-sectional views of the plastic-lined metallic pipe according to the preferred embodiment of the present invention; 
           [0016]      FIG. 2  is a schematic diagram showing the process of inserting the inner plastic pipe into the outer metallic pipe; 
           [0017]      FIG. 3  and  FIG. 4  are schematic diagrams showing the process of drawing the outer metallic pipe to make the outer metallic pipe being bond to the inner plastic pipe; 
           [0018]      FIG. 5  is a schematic diagram showing the process of cooling the outer metallic pipe to make the outer metallic pipe being firmly bond to the inner plastic pipe; 
           [0019]      FIG. 6  is a block flow diagram showing the process of making the plastic-lined metallic pipe; 
           [0020]      FIG. 7  is a schematic front-view diagram illustrating the components of the connector according to the present invention; 
           [0021]      FIG. 8  is a schematic cross sectional view diagram illustrating the components of the connector and the assembling order; 
           [0022]      FIG. 9  is a schematic diagram illustrating the connector&#39;s inner structure when the cap is screwed in; 
           [0023]      FIG. 10  is a schematic diagram illustrating the side view and the cross sectional views of the connector&#39;s body according to a typical embodiment of the present invention; 
           [0024]      FIG. 11  is a schematic diagram illustrating the side view and the cross sectional views of the tapered rubber washer according to a typical embodiment of the present invention; 
           [0025]      FIG. 12A  is a schematic diagram illustrating the side view and the cross sectional views of the stainless metal washer according to a typical embodiment of the present invention; 
           [0026]      FIG. 12B  is a schematic diagram illustrating the side view and the cross sectional views of the stainless metal washer according to another embodiment of the present invention; 
           [0027]      FIG. 12C  is a schematic diagram illustrating the side view and the cross sectional views of the stainless metal washer according to another embodiment of the present invention; 
           [0028]      FIG. 13A  is a schematic diagram illustrating the side view and the cross sectional views of the “c” type spring washer according to a typical embodiment of the present invention; 
           [0029]      FIG. 13B  is a schematic diagram illustrating the side view and the cross sectional views of the “c” type spring washer according to another embodiment of the present invention; 
           [0030]      FIG. 14A  is a schematic diagram illustrating the side view and the cross sectional views of the cap according to a typical embodiment of the present invention; 
           [0031]      FIG. 14B  is a schematic diagram illustrating the side view and the cross sectional view of the cap according to another embodiment of the present invention; 
           [0032]      FIG. 15A  is a schematic diagram illustrating the inner structure of the connector before the cap is entirely screwed in; 
           [0033]      FIG. 15B  is a schematic diagram illustrating the inner structure of the connector after the cap is entirely screwed in; 
           [0034]      FIG. 16A  is a schematic diagram illustrating a stainless steel washer with an extruding edge facing the end wall of the cap; 
           [0035]      FIG. 16B  is a schematic diagram illustrating a spring washer with a tapered edge facing the connector&#39;s body; and 
           [0036]      FIG. 16C  is a schematic diagram illustrating the inner structure of the connector when the cap is being screwed in. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0037]    The plastic-lined metallic pipe according to the typical embodiment of the present invention, as shown in  FIG. 1 , consists of an outer metallic pipe  11  and an inner plastic pipe  12  suitable for conveying drinking-water. There is no intermediate layer between the inner plastic pipe and the outer metallic pipe. In other words, the inner plastic pipe and the outer metal pipe are firmly bond or melt-bond. 
         [0038]    The outer seamless pipe is made of alloy material with the features of high mechanical strength, non-aging, corrosion resistance and shock resistance. 
         [0039]    The inner pipe is made of food-grade non-poisonous Polypropylene (PP), which is pollution free, corrosion resistant and low resistance in liquid. 
         [0040]      FIG. 3 ,  FIG. 4  and  FIG. 5  are cross sectional view diagrams illustrating the process for making the plastic-lined metallic pipe and  FIG. 6  is a block flow diagram illustrating the primary steps of the process: 
         [0000]    Step  21 : Place the alloy outer pipe  11  in a mould with a diameter slightly larger than the outer pipe&#39;s outer diameter and warm the outer pipe to a temperature (t 1 ) at which the alloy has a higher tensility.
 
Step  22 : Cool the inner plastic pipe  12  to a temperature (t 2 ) which is usually lower than the normal storage temperature. The outer diameter of the inner pipe  12  is slightly smaller than the inner diameter of the outer pipe  11  so that the inner pipe  11  can be inserted into the outer pipe during the process. At the temperature t 2 , the inner pipe&#39;s diameter is at its shortest point. At a temperature higher than t 2 , the inner pipe&#39;s diameter may increase due to the mechanism of heat expansion.
 
Step  23 : As shown in  FIG. 2 , insert the inner plastic pipe  12  into the outer alloy pipe  11 .
 
Step  24 : Draw from both ends of the outer pipe along the axial direction to extend it for a specific length. As shown in  FIG. 3 , L 1  represents the initial length prior to the drawing, and as shown in  FIG. 4 , L 2  represents the length subsequent to the drawing. The tensile ratio may be 0.1˜1% (L 2 −L 1 =0.1˜1% L 1 ) depending upon the materials used. As shown in  FIG. 5  ( a ), the outer pipe  11  contracts during the drawing. Because the initial temperature of the inner plastic pipe  12  is lower than the outer pipe&#39;s temperature, the inner plastic pipe  12  is being warmed up during the process and, as shown in  FIG. 5  ( b ), it expands with the warming. Thus, after the drawing and the accompany heat-transfer, the inner pipe  12  and the outer pipe  11  are tightly merged together as shown in  FIG. 5  ( c ).
 
Step  25 : Cool the outer pipe  11  to a normal temperature (t 3 ). During this cooling phase, as shown in  FIG. 5  ( a ), the outer pipe  11  further contracts such that the pipes are integrated to a melt-bond condition or a substantially melt-bond condition. Note that because the temperature t 2  is lower than t 3 , the cooling process for the outer pipe  11  is actually a warming-up process for the inner pipe  12 , and thus, as shown in  FIG. 5  ( b ), it further expands during this phase.
 
         [0041]    The plastic-lined pipe according to this invention is mechanically superior to stainless steel pipe and copper pipe, while its price is 20% lower than the price of copper pipe. 
         [0042]    The outer surface of the plastic-lined pipe is finished by dull polish and antioxidant process to create a sense of metal quality, giving a feeling as bright, elegant and fashionable. 
         [0043]    The present invention also includes a connector for connecting the plastic-lined pipes. The connector adopts chrome-plating Al pipe, silica rubber washer and a stainless steel lock-loop design. When installing, just use a regular steel-saw to cut the pipe in proper length, then insert it into the connector&#39;s body and tighten the sealing cap. The operation is simple, convenient and fast. 
         [0044]      FIG. 7  is a schematic front-view diagram illustrating the components of the connector according to the present invention and  FIG. 8  is a schematic cross sectional view diagram illustrating the components of the connector and the assembling order thereof. The connector may have a two-way base or a multiple way base. But the connecting mechanism is same. As illustrated in  FIG. 7 , the connector has a three-way base  30 , which has three identical holding bodies such as  31 . The holding body  31  has a section of thread  41  around its outer surface and a stepped cylindrical inner space for holding the pipe  29 , the rubber washer  32 , the stainless metal washer  33 , and the “c” type spring washer  34 . The spring washer  34  may have a rough inner surface or a section of male thread for enforcing the locking. Another member of the connector is the cap  35  which has a section of inner thread  42  for coupling with the holding body  31  and has an end wall  43  with a cylindrical hole for holding the pipe  29 . 
         [0045]    To connect the pipe  29  to the base  30 , first insert the pipe  29  into the cap  35 , then the “c” type spring washer  34 , then the stainless metal washer  33 , then the rubber washer  32 , and then insert the pipe  29  into the holding body  31  to reach the supporting end  44  as shown in  FIG. 8  and  FIG. 9 . Then, slide the rubber washer  32  and the stainless metal washer  33  into the body  31 , and insert the spring washer  34  into the body  31  so that the spring washer  34  has an elastic contact with the inner wall of the body  31 . Then, screw the cap  35  toward the body  31 . By coupling the cap  35  with the body  31 , the washers  32 - 34  are squeezed toward the body  31  by the end wall  43  of the cap  35 . The deeper the cap  35  is screwed in, the tighter the “c” type spring washer  34  is contacted with the pipe  29 . In this way, the pipe  29  is firmly connected with the body  31  as shown in  FIG. 9 . 
         [0046]      FIG. 10  is a diagram illustrating the side view and the cross sectional views of the body  31 . The first inner cylindrical space  45  is for conveying water or other liquid or gas. The diameter of the first cylinder  45  is identical with the inner diameter of the pipe  29  such that when the liquid or gas is conveyed smoothly from the cylinder  45  to the pipe  29  or vice versa. The second cylindrical space  46  is for holding the pipe  29 . The diameter of the cylinder  46  is slightly larger than the diameter of the pipe  29  such that the pipe  29  can be inserted into the cylinder  46 . The bottom of the second cylinder  47  adjacent to the first cylinder  45  constitutes the supporting end  44 , which is a plain ring surface to be contacted by the cross-cut plain ring surface of the pipe  29 . In its front opening, the body  31  has a third cylindrical space  48  for holding the stainless metal washer  33  and the “c” type spring washer  34 . The diameter of the third cylindrical space  48  is larger than the diameter of second cylindrical space  46 . Further, between the second cylinder  46  and the third cylindrical space is a tapered cylindrical space  47  which merges the third cylindrical space  48  with the second cylindrical space  46 . 
         [0047]      FIG. 11  is a diagram illustrating the side view and the cross sectional views of the rubber washer  32 . The rubber washer  32  has a tapered cylindrical structure with a thinner front and a thick back. Because it is made of an elastic material, its inner diameter  49  is slightly smaller than the outer diameter of the pipe  29  such that the rubber washer  32  is tightly covered around the pipe  29  when it is slipped on. The tip  50 , i.e. the thinner front edge, of the rubber washer  32  is toward the body  31 . The tip  50  is inserted into the gap between the pipe  29  and the wall of the cylinder space  46 . When the cap  35  is crewed in, the rubber washer  32  is pressed and the gap between the pipe  29  and the wall of the cylinder space  46  is sealed, such that the liquid or gas conveying through the connector and the pipe does not leak out. 
         [0048]      FIG. 12A  is a diagram illustrating the side view and the cross sectional views of the stainless metal washer  33  according to a typical embodiment of the present invention. Referring back to  FIG. 9 , when the cap  35  is crewed in, the stainless metal washer  33  presses the rubber washer  32  against the body  31  to avoid leak, and at the same time, the stainless metal washer  33  presses the spring washer  34  against the end wall  43  of the cap  35  to force the “c” type spring washer  34  to lock around the pipe  29 . 
         [0049]      FIG. 12B  is a diagram illustrating the side view and the cross sectional views of the stainless metal washer  33  according to another embodiment of the present invention. 
         [0050]    Yet  FIG. 12C  is a diagram illustrating the side view and the cross sectional views of the stainless metal washer  33  according to another embodiment of the present invention. 
         [0051]      FIG. 13A  is a diagram illustrating the side view and the cross sectional views of the “c” type spring washer  34  according to a typical embodiment of the present invention. Referring back to  FIG. 9 , when the cap  35  is crewed in, the end wall  43  of the cap  35  presses the spring washer  34  against the stainless metal washer  33  which further presses the rubber washer  32  against the body  31  to avoid leak, and at the same time, the stainless metal washer  33  presses the spring washer  34  against the end wall  43  of the cap  35  to force the spring washer  34  to lock around the pipe  29 . When the pressure is released by screwing out the cap  35 , the “c” type spring washer  34  unlocks from the pipe  29  and returns to its original shape. 
         [0052]      FIG. 13B  is a diagram illustrating the side view and the cross sectional views of the “c” type spring washer  34  according to another embodiment of the present invention. The “c” type spring washer  34  responds both to the force from the axial direction. It also responds to the pressure from the surrounding. Before the force is applied on it, it can slide along the pipe  29 . However, when the force is applied on it, the gap  51  is getting smaller and smaller such that the spring washer  34  locks on the pipe  29  tightly. When the force is released, the spring washer  34  unlocks from the pipe  29  and returns to its original shape with the gap  51 . 
         [0053]      FIG. 14A  is a diagram illustrating the side view and the cross sectional views of the cap  35  according to a typical embodiment of the present invention. The cap  35  includes a larger cylindrical space  52  and a smaller cylindrical space  53 . The larger cylindrical space  52  is enclosed with a section of thread  42  for coupling with the holding body  31 . The smaller cylindrical space  53  is for the pipe  29  to be inserted there through. The diameter of the smaller cylindrical space  53  should be slightly larger than the diameter of the pipe  29 . The depth  54  of the larger cylindrical space  52  should be smaller than the total thickness of the spring washer  34 , the stainless metal washer  33 , and the rubber washer  32 , such that when the cap  35  is screwed in, the end wall  43  of the cap  35  may provides sufficient pressure on these three washers required to avoid leak and have the spring washer  34  locked around the paper  29 . 
         [0054]      FIG. 14B  is a schematic diagram illustrating the side view and the cross sectional view of the cap  35  according to another embodiment of the present invention. In this embodiment, the end wall  43  of the cap  35  has a cylinder  55  extruding toward the body  31 . The cylinder  55  is used to strengthen the end wall&#39;s support to the “c” spring washer  34 . The depth  56  from the front of the cylinder  55  to the front of the cap  35  should be smaller than the total thickness of the spring washer  34 , the stainless metal washer  33 , and the rubber washer  32 , such that when the cap  35  is screwed in, the front of the cylinder  55  of the cap  35  may provides sufficient pressure on these three washers required to avoid leak and have the spring washer  34  locked around the paper  29 . 
         [0055]      FIG. 15A  is a schematic diagram illustrating the inner structure of the connector before the cap  35  is entirely screwed in.  FIG. 15B  is a schematic diagram illustrating the inner structure of the connector after the cap  35  is entirely screwed in. When the cap  35  is screwed in, the force from the cylinder  55  makes the washers tightly stacked together. Because the rubber washer  32  is elastic, when it is pressed, the surrounding gap between the pipe  29  and the body  31  is sealed, and thus leak is avoided. In addition, because of the pressure from the stainless steel washer  33  and the pressure from the cylinder  55 , the spring washer  34  is squeezed, and thus it tightly locks around the pipe  29 . 
         [0056]      FIG. 16A  is a schematic diagram illustrating a stainless steel washer  71  with an extruding edge  72  facing the end wall of the cap  35 .  FIG. 16B  is a schematic diagram illustrating a spring washer  73  with a tapered edge  74  facing the connector body  31 .  FIG. 16C  is a schematic diagram illustrating the inner structure of the connector when the cap  35  is being screwed in. The extruding edge  72  of the stainless steel washer  71  and the tapered edge  74  of the spring washer  73  are designed in such a manner that when they are squeezed together, the extruding edge  72  of the steel washer  71  applies a force along the axial direction to the tapered edge  74 , and the tapered edge  74  changes the force into a force concentrating toward the center of the spring washer  34 . The concentrating force makes the spring washer  34  locked around the pipe  29 . 
         [0057]    Although the invention has been described with reference to at least one specific embodiment, this description is not meant to be construed in a limiting sense. Various modifications of the disclosed embodiment, alternative embodiments or other equivalent solutions of implementing the disclosed pipe and connector will become apparent to those skilled in the art upon reference to the description of the invention. It is therefore contemplated that such modifications, equivalents, and alternatives can be made without departing from the spirit and scope of the present invention as defined in the appended claims.