Abstract:
A device for producing pipes made of thermoplastic with annular transverse profilings with a cross section in the form of undulation peaks and undulation troughs has half-moulds, which complete one another pairwise along a straight mould section to form a closed mould, which can be moved in a movement direction. Projecting into the mould is an extrusion tool, which has a nozzle support body. To produce an adequate seal between the half-moulds and nozzle support body, the latter is covered with exchangeably attached hollow half-shells, which form a cylindrical external face.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
       [0001]    This application claims the priority of German Patent Application, Serial No. 10 2010 043 786.7, filed Nov. 11, 2010, pursuant to 35 U.S.C. 119(a)-(d), the content of which is incorporated herein by reference in its entirety as if fully set forth herein. 
       FIELD OF THE INVENTION 
       [0002]    The invention relates to a device for producing pipes made of thermoplastic with annular transverse profilings with a cross section in the form of undulation peaks and undulation troughs, with half-moulds, which complete one another pairwise along a straight mould section to form a closed mould, which is moveable in a motion direction, with a central longitudinal axis, which is transportable in the circuit counter to the movement direction of the mould to an upstream end of the mould section and which have an annular internal profiling, which is loadable with a partial vacuum, with a smallest internal diameter D 39  to produce the transverse profiling, and with an extrusion tool, which has a nozzle support body with one of an external diameter D 33  and D 33 ′ with at least one channel for plastic melt, which has a nozzle with a diameter D 19 , which is connected by means of a channel end portion widening toward the nozzle to the channel, which has an inner nozzle ring and an outer nozzle ring, which between them limit the channel end portion and which are fastened to the nozzle support body, 
       BACKGROUND OF THE INVENTION 
       [0003]    Devices of this type known, for example, from EP 2 116 352 B1 or U.S. Pat. No. 5,320,797 have been extraordinarily successful in practice. In the configuration of devices of this type for producing pipes with a nominal width ≧400, the problem emerges that the extrusion tool, also designated a pipe head, becomes very heavy, which leads to not inconsiderable additional structural outlay and additional costs resulting from this. 
       SUMMARY OF THE INVENTION 
       [0004]    The invention is based on an object of configuring a device of the generic type in such a way that even in a configuration for large nominal widths, the weight of the extrusion tool is as small as possible, without endangering the sealing of the mould to the outside to maintain the partial vacuum. 
         [0005]    This object is achieved according to the invention by the external diameter D 33  or D 33 ′ being smaller than the internal diameter D 19 , wherein the nozzle support body—in relation to the movement direction—upstream of the outer nozzle ring, is covered with exchangeably attached hollow half-shells, which form a cylindrical external face with a diameter D 37  and wherein a narrow annular gap with a gap width a is formed between the cylindrical external face and the internal profiling with the smallest internal diameter D 39 . Between the cylindrical external face formed by the half-shells and the internal profilings of the smallest diameter generally formed by mould webs, only a narrow annular gap is limited, which acts as a restrictor point and therefore prevents an increase in pressure relevant to the process in the region of the partial vacuum. One or more annular gaps of this type are generally sufficient to maintain the partial vacuum; in addition, however, by the seals projecting outwardly over the external face, which is bringable into sealing abutment with the internal profiling with the smallest internal diameter D 39 , being provided on the half-shells, an additional seal can also be achieved, with a plurality of seals being provided at a spacing c in the direction of the centre longitudinal axis such that at least one seal always rests in a sealing manner on an internal profiling with the smallest diameter D 39  being particularly advantageous. 
         [0006]    Further features, advantages and details emerge from the following descriptions of two embodiments of the invention with the aid of the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  shows a device for producing a composite pipe in a schematic partial view; 
           [0008]      FIG. 2  shows a partial longitudinal section through the device according to  FIG. 1 , 
           [0009]      FIG. 3  shows a partial cross section through the device according to  FIG. 2  in accordance with the section line in  FIG. 2  and 
           [0010]      FIG. 4  shows a partial longitudinal section in accordance with the view in  FIG. 2  with a modified extrusion tool. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0011]    As  FIG. 1  allows it to be seen, a device for producing plastics material composite pipes with transverse grooves has two extruders  1 ,  2 , which are connected to an extrusion tool  3 , which in practice is also called a pipe head. From the extrusion tool  3 , two tubes of plastics material melt are coextruded within one another, from which the composite pipe mentioned is molded. Used for this purpose is a mould machine  4 , in practice also called a corrugator, which is formed from half-moulds  6 ,  6   a , which are provided with an internal profiling  5 , are set against one another pairwise on a mould section  7  and are located tightly against one another in a movement direction  8  of the mould  9  thus formed. The composite pipes mentioned are molded in the mould  9 . This method is generally known in practice and shown and described, for example, in U.S. Pat. No. 5,693,347, to which reference may be made for explanation. 
         [0012]    The extruder  1  is a so-called side extruder, because it opens by means of a lateral melt line  10  into the extrusion tool  3 , while the other extruder  2  opens centrally, i.e. concentrically with respect to the centre longitudinal axis  11  of the mould  9  into the extrusion tool  3 . 
         [0013]    The extrusion tool  3  has an internal nozzle mandrel  12 , which is screwed together from a plurality of parts and is arranged concentrically with respect to the axis  11 . The internal nozzle mandrel  12  is surrounded by an internal nozzle jacket  13 , which is also multi-part and is also in turn surrounded concentrically with respect to the axis  11  by an external nozzle mandrel  14 . The latter is in turn surrounded by an external nozzle jacket  15 . An internal channel  16  configured concentrically with respect to the axis  11  is limited between the internal nozzle mandrel  12  and the internal nozzle jacket  13 , while an external channel  17  is limited between the external nozzle mandrel  14  and the external nozzle jacket  15 . The internal channel  16  opens by means of an internal nozzle  18  out of the extrusion tool  3 , while the external channel  17  opens by means of an external nozzle  19  out of the extrusion tool  3 . Extruded from the two nozzles  18 ,  19  are the internal tube  20  mentioned and the external tube  21  mentioned, which are connected to one another to form a composite pipe in a manner known, for example, from U.S. Pat. No. 5,320,797. The internal nozzle mandrel  12 , the internal nozzle jacket  13 , the external nozzle mandrel  14  and the external nozzle jacket  15  are fastened with the interposition of an internal star distributor  22  and an external star distributor  23  and a sleeve tool  24  to a support part  25 . In the region of this support part  25 , the extrusion tool  3  is supported by means of a support construction, not shown, on a base, also not shown, as is conventional in practice. The melt line  10  from the side extruder  1  opens into the sleeve tool  24 , as can be inferred from  FIG. 1 . The details of the star distributors  22 ,  23  and the sleeve tool  24  are shown and described in detail, for example, in EP 2 116 352 B1, to which reference is made. 
         [0014]    The internal nozzle  18  is limited by an inner internal nozzle ring  26  and an outer internal nozzle ring  27 , which limit an internal channel end portion  28  connecting the internal channel  16  to the actual internal nozzle  18  and widening in a funnel shape to the internal nozzle  18 . The external nozzle  19  is limited by an inner external nozzle ring  29  and an outer external nozzle ring  30 , which also limit an external channel end portion  31  widening outwardly in a funnel shape, specifically toward the external nozzle  19 . The inner internal nozzle ring  26  is attached to the internal nozzle mandrel  12 . The outer internal nozzle ring  27  is attached to the internal nozzle jacket  13 . The inner external nozzle ring  29  is attached to the external nozzle mandrel  14 . The outer external nozzle ring  30  is fastened to the external nozzle jacket  15 . A cooling and calibrating mandrel  32  is attached to the inner internal nozzle ring  26 . 
         [0015]    The internal nozzle  18  has a diameter D 18 , while the external nozzle  19  has a diameter D 19 . The portion of the extrusion tool  3  surrounded by the external nozzle jacket  15  and designated the nozzle support body  33  has an external diameter D 33 , which is significantly smaller than D 18  and D 19 . The external nozzle jacket  15  is surrounded by heating devices  34  configured in the form of heating strips. The outer internal nozzle ring  27  can also be surrounded by a corresponding heating device  35 . 
         [0016]    The nozzle support body  33  is surrounded by thin-walled half-shells  36  made of aluminum, which surround the nozzle support body  33  with a continuous cylindrical external face  37 . The diameter D 37  of this cylindrical external face  37  substantially corresponds to the diameter D 19  of the external nozzle  19 . If tubes with a larger diameter D 18  and D 19  are to be extruded, the nozzle rings  26 ,  27 ,  29 ,  30  are exchanged. Accordingly, the half-shells  36  are replaced by half-shells with a larger diameter. The remaining nozzle support body  33  remains unchanged. The nozzle support body  33  can thus remain unchanged, in each case, even when producing pipes with a different nominal width. It is adapted to the pipe to be produced with the smallest possible nominal width. 
         [0017]    As can be inferred from  FIG. 2 , the internal profiling  5  of the half-moulds  6 ,  6   a  consists of annular mould recesses  38 , between which likewise annular mould webs  39  with the smallest internal diameter D 39  are also configured, in each case. The external tube  21  is formed into undulation peaks  40  in the mould recesses  38 , while the external tube  21  is formed into undulation troughs  41  of the external tube  21  by the mould webs  39 . The internal tube  20  is welded to the external tube  21  on the cooling and calibrating mandrel  32  in the region of the undulation troughs  41 . This method is known in detail, for example, from U.S. Pat. No. 5,320,797, already mentioned. The mould recesses  38  are loaded with a partial vacuum by vacuum channels  42 , which are configured in the half-moulds  6 ,  6   a  and are connected by vacuum slots  43  to the respective mould recesses  38 . Either support air with the required excess pressure relative to the atmospheric pressure is introduced into the space  44  between the tubes  20 ,  21  or else this space  44  is vented to the outside. Both take place by means of a gas channel  45 . If a pipe socket  51  is to be formed at fixed intervals in a composite pipe to be continuously produced, half-moulds  46  having a corresponding socket recess  47  are then used, which is also shown in  FIG. 2 . These half-moulds  46  are also provided with corresponding vacuum channels  42 , from which vacuum slots  43  lead into the socket recess  47 . The forming of the external tube  21  into undulation peaks  40  or pipe sockets  51  takes place as described above. It can thus—as shown above—take place by the so-called vacuum method or else the combined blow molding-vacuum method. 
         [0018]    As can be inferred from  FIG. 2 , only a narrow annular gap  48  with a gap width a of 2 mm to 10 mm exists between the mould webs  39  of the half-moulds  6 ,  6   a  and the cylindrical external face  37  of the half-shells  36 . Configured between the two mould webs  39   a , which—in relation to the movement direction  8 —directly follow the socket recess  47 , and the cylindrical external face  37  is, in each case, an annular gap  48   a  with the gap width b, to which there applies: 2 mm≦b≦5 mm. The reason is that the undulating portion of the pipe directly adjoining the pipe socket  51  is cut out after production. The restriction can therefore be increased, without the composite pipe being weakened in the undulation trough  41 . The internal diameter D 39   a  of these mould webs  39   a  is thus generally slightly smaller than the internal diameter D 39 . In addition, seals  49  projecting radially slightly outwardly and made of a suitable plastics material can be attached to the half-shells  36  and in each case engage with the mould webs  39  upon movement of the mould  9  in the direction  8 , thereby forming a complete seal. If a plurality of lamellar-like seals  49  of this type is provided, it is expedient to select the spacing c thereof in the movement direction  8  in such a way that at least one seal  49  in each case always rests on a mould web  39  or  39   a . Independently of these seals  49 , the annular gaps  48  or  48   a  can be selected to be so narrow that the partial vacuum built up by means of the vacuum channels  42  and the vacuum slots  43  between the mould recesses  38  or the socket recess  47  and the external tube  21  is also maintained. The external tube  21  is thus reliably held on the internal profiling  5  of the mould  9  or placed there in the course of the pipe production. 
         [0019]    As soon as the internal tube  20  is placed against the external tube  21  at least partially preformed in the socket recess  47  for the pipe socket  51 , the pair of half-moulds  6 ,  6   a  following the pair of half-moulds  46  having the socket recess  47  is already placed on the pair of half-moulds  46 . An adequate number of restrictor points is thus produced as soon as the venting between the external tube  21  and the internal tube  20  begins. 
         [0020]    So that the mould  9  is already closed off with an adequate spacing upstream of the external nozzle  19  and therefore also of the internal nozzle  18 , in other words can maintain the partial vacuum in the manner described, it is expedient if the half-moulds  6 ,  6   a  or  46  are transported after removal from the mould section  7  and back to the upstream end  50  of the mould section  7  in the manner indicated in  FIG. 1 . The respective half-moulds  6 ,  6   a  and, accordingly, the half-moulds  46 , after the return transport, are returned transverse to the movement direction  8  of the mould back into the mould section  7 , whereby the corresponding seal relative to the cylindrical external face  37  formed by the half-shells  36  is immediately achieved. The details of this transportation are shown and described in U.S. Pat. No. 5,693,347 A and U.S. Pat. No. 4,212,618 A, to which reference may be made. 
         [0021]    As emerges, in particular from  FIG. 3 , two respective half-shells  36 ,  36   a  are positioned and centered with respect to one another by means of adjusting pins  52  and connected to one another by means of screws  53 , whereby two half-shells  36  and  36   a  in each case extend over the full periphery, in other words form a type of pipe portion. 
         [0022]    The half-shells  36  and  36   a  in each case have flanges  54 ,  54   a ,  54   b  at their ends, two flanges  54 ,  54   a  resting against one another in the direction of the axis  11  in each case being connected to one another by means of screws  55 . The entirety of the half-shells  36 ,  36   a  is supported by means of the individual flanges  54 ,  54   a ,  54   b  relative to the nozzle support body  33  in the radial direction and mounted by means of the screws  53  on the external nozzle ring  30 . 
         [0023]    The seals  49  are in each case arranged in the joint between two flanges  54  or  54   a  resting against one another in the axial direction and clamped by means of the screws  55  and  56 . 
         [0024]    The embodiment according to  FIG. 4  differs from that according to  FIG. 2  only with respect to structural details. Structurally identical parts are therefore provided with the same reference numerals as in  FIG. 2 . If the parts are functionally the same but structurally slightly different, the parts are designated by the same reference numerals as in  FIG. 2  but with an apostrophe. Reference can therefore entirely be made to the above description.