Abstract:
A pipe construction kit comprises two pipe sections in the form of twin-wall pipes. A spigot is formed on one end of a pipe section, while a socket is formed on the associated end of the other pipe section. The socket and the spigot are twin-wall pipes, having predominantly smooth-walled internal pipe sections and corrugated external pipe sections with elevations and troughs. The outside diameter of the pipe sections and the outside diameter of the socket are approximately equal.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The invention relates to a pipe construction kit comprising a first and a second pipe section of plastic material, each of which having a smooth-walled cylindrical internal pipe and a corrugated external pipe with annular cylindrical elevations and troughs, and an outside diameter D 4 ; a socket, which is in-line molded on one end of the first pipe section, having an outside diameter D 18  and an inside diameter D 17 ; and a spigot, which is in-line molded on an end of the second pipe section, comprising the internal pipe and a second external pipe section, and having an outside diameter D 22 , to which the following applies in relation to the inside diameter D 17  of the socket: D 22 ≈D 17 .  
           [0003]    2. Background Art  
           [0004]    A pipe construction kit of the generic type is known from U.S. Pat. No. 5,071,173. This known design includes a smooth-walled pipe socket, the outside diameter of which does not project over the outside diameter of the elevations of the pipe sections. In this way, this known design enables the pipe construction kits of the species to be used for sewer pipe reconstruction, because the consecutively joined-on pipe sections have a uniform maximum outside diameter. Likewise, this design of a pipe socket has the advantage that transporting the pipe sections which have a socket at one end and a spigot at the other is possible without the risk of socket damaging. If the spigot also has an outside diameter that corresponds to the outside diameter of the pipe sections—which is prior art—and if, consequently, the socket has an internal diameter that corresponds at least to the outside diameter of the pipe sections, then there is the risk of the socket being damaged during transportation. Moreover, the socket does not impede the insertion of interconnected pipes in conduits and the like. The internal pipes of these twin-wall pipes are smooth-walled, having, however, some minor manufacturing irregularity. The term “smooth-walled” as employed in this application also includes this minor irregularity.  
           [0005]    In the case of great nominal widths, for instance in the case of nominal widths≧DN 400, there is the problem of sockets that have smooth walls internally and externally no longer being sufficiently stable.  
           [0006]    U.S. Pat. No. 5,992,469 teaches to provide sockets that are in-line molded on corrugated twin-wall pipes also in the form of twin-wall pipes over part of their axial length, having a smooth-walled internal pipe section and a corrugated external pipe section with elevations and troughs. This known design has the drawback that the outside diameter of the socket distinctly exceeds the outside diameter of the pipe sections, because the respective regular pipe section is also employed as a spigot.  
         SUMMARY OF THE INVENTION  
         [0007]    It is an object of the invention to embody a pipe construction kit of the generic type in such a way that high stability of the pipe socket is reached and the advantages of the species are maintained.  
           [0008]    According to the invention, this object is attained in that the socket is a twin-wall pipe having a smooth-walled internal pipe section and a corrugated first external pipe section with elevations and troughs. The gist of the invention resides in that the spigot as well as the socket are twin-wall-pipe sections with the available overall height of the elevations of the pipe sections, inclusive of the thickness of the internal pipes of the pipe sections, being split up among the height of the elevations, inclusive of the internal pipe section of the socket, and the height of the elevations and of the internal pipe of the spigot. A favorable splitting ratio is reflected by 0.3 (H 18 +H 22 )≦H 18 ≦0.7(H 18 +H 22 ) applying to the radial height H 18  of the socket as compared to the radial height H 22  of the spigot.  
           [0009]    The elevations of the socket on the one hand and of the spigot on the other have a clearly smaller spacing than the elevations of the pipe sections. Favorable relations of this are reflected by 0.3 T 5 ≦T 19 ≦0.7 T 5  applying to the spacing T 5  of the elevations of the pipe sections as compared to the spacing T 19  of the socket, and by 0.3 T 5 ≦T 23 ≦0.7 T 5  applying to the spacing T 5  of the elevations of the pipe sections as compared to the spacing T 23  of the elevations of the spigot.  
           [0010]    Further features, advantages and details of the invention will become apparent from the ensuing description of an exemplary embodiment, taken in conjunction with the drawing. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0011]    [0011]FIG. 1 is a partial lengthwise sectional view of a twin-wall pipe that is continuously produced from a pipe section, a socket and another pipe section; and  
         [0012]    [0012]FIG. 2 is an illustration of a pipe joint between two pipe sections after the twin-wall pipe has been cut through. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0013]    As seen in FIG. 1, a twin-wall pipe is continuously produced, forming an extruded run of piping which substantially consists of the virtual pipe sections  1 ,  2 . They generally include a smooth-wall, cylindrical internal pipe  3  and a corrugated external pipe  4 . This external pipe  4  has approximately trapezoidal elevations  5 , a trough  8  being formed between the flanks  6 ,  7  of two adjacent elevations  5 . At the bottom  9  of the trough  8 , the external pipe  4  and the internal pipe  3  are welded together. Twin-wall pipes of this type and structure are generally known and widely spread in practice.  
         [0014]    Adjoining the pipe section  1 , a socket  10  is formed between the two pipe sections  1 ,  2 . In the vicinity of the socket bottom  11  i.e., subsequent to an expanded section  12  of the pipe section  1 , the socket  10  has a short, smooth-walled and cylindrical section  13 . This smooth-walled section  13 , same as the expanded section  12 , has a predominantly single-wall configuration instead of a twin-wall design. The smooth-walled section  13  is again followed by a twin-wall pipe section  14 . Subsequent thereto, the socket  10  is again of single-wall design, including an insertion section  16  that expands conically outwards toward an inlet  15 . Fundamentally, the twin-wall pipe section  14  is structured in the same way as the pipe sections  1  and  2 , i.e., it has a substantially cylindrical, smooth-wall internal pipe section  17  and a corrugated first external pipe section  18  with elevations  19 , with the first external pipe section  18  and the internal pipe section  17  being welded together in the vicinity of the troughs  20 . The elevations  19  are disposed substantially over the full length of the socket  10  with the exception of the insertion section  16  and the short section  13 .  
         [0015]    Formed between the socket  10  and the pipe section  2 , and directly subsequent thereto, is a spigot  21 , the inside of which is formed and defined by the internal pipe  3 . It is provided with a corrugated second external pipe section  22  with elevations  23 , the second external pipe section  22  and the internal pipe  3  also being welded together in the vicinity of the troughs  24 . The outer contours of all the elevations  5 ,  19 ,  23  are substantially annular cylindrical.  
         [0016]    Located between the socket  10  and the spigot  21  is a transition section  25  which is cut out as waste by two saw cuts  26 ,  27  as seen in FIG. 1. Since this cutting job takes place continuously, a pipe section  1  or  2  is obtained, having a socket  10  at one end and a spigot  21  at the other. As seen in FIG. 2, the illustrated spigot  21  of the pipe section  2  serves for insertion into the socket  10  of the neighboring pipe section  1 , as a result of which two pipe sections  1 ,  2  are interconnected. Upon complete insertion of the spigot  21  into the socket  10 , the foremost elevation  23  bears against the expanded section  12  in the vicinity of the socket bottom  11 , in which case the elevation  5  that adjoins the spigot  21  lies in direct vicinity to the inlet  15  of the insertion section  16  of the socket  10 . Consequently, the length of the spigot  21  and the length of the socket  10  are approximately equal.  
         [0017]    The pipe sections  1 ,  2  have an outside diameter D 4  that corresponds to the outside diameter of the external pipe  4 . The socket  10  has an outside diameter D 18  that corresponds to the outside diameter of the first external pipe section  18 , with the outside diameter of the insertion section  16  not exceeding D 18 . The outside diameter D 22  of the spigot  21  corresponds to the outside diameter of the second external pipe section  22 . The inside diameter D 17  of the socket  10  corresponds to the inside diameter of the internal pipe section  17 . The outside diameter D 22  of the spigot  21  and the inside diameter D 17  of the socket  10  are approximately equal—allowing for some minor clearance and work tolerances. In this regard, 1.01 D 22 ≦D 17 ≦1.02 D 22  applies. As for the outside diameter D 18  of the socket  10  in relation to the outside diameter D 4  of the pipe sections  1  and  2 , respectively, D 4 ≈D 18  applies.  
         [0018]    The overall height H 22  of the elevations  23  of the second external pipe section  22 , inclusive of the wall thickness of the internal pipe  3 , exceeds the overall height H 18  of the elevations  19 , inclusive of the thickness of the internal pipe section  17  of the first external pipe section  18  of the socket  10 . 0.3 (H 18 +H 22 )≦H 18 ≦0.7 (H 18 +H 22 ) applies. As further seen in the drawing, the following applies to the spacing T 19  of the elevations  19  of the socket  10  in relation to the spacing T 5  of the elevations  5  of the pipe sections  1 ,  2  in the direction of the central longitudinal axis  28 : 0.3 T 5 ≦T 19 ≦0.7 T 5 . As for the spacing T 23  of the elevations  23  of the spigot  21 , 0.3 T 5 ≦T 23 ≦0.7 T 5  applies by analogy.  
         [0019]    As results from the above explanations, the axial extension and the radial extension of the troughs  24  of the spigot  21  are considerably smaller than those of troughs  8  of the pipe sections  1  and  2 . Therefore, an O-ring  29  disposed in the trough  24  may have a substantially smaller volume than an O-ring that is to be disposed in a trough  8 .  
         [0020]    Manufacturing the continuous twin-wall pipe, in which a socket  10  and a spigot  21  are in-line molded between two pipe sections  1  and  2 , takes place by the aid of familiar technology, for instance as specified and described in EP 0 563 575 B1 or EP 0 890 770 A2, which may be referred to.