Abstract:
A method and an apparatus for the manufacture of pipes of thermoplastics with transverse profile features comprises mold segment halves which are circulated by twos on a molding path. A conveying device of the type of a gantry crane is provided for recirculation of the mold segment halves. On a conveying bridge that bridges the molding path, provision is made for two conveying carriages, which are movable in opposite directions and cross-wise of the direction of production and which have mounted on them a downward conveying arm with a holding device for a respective mold segment half. Provided downstream of the downstream end of the molding path are parking positions for additional mold segment halves, those of which that are closest to the molding path being carriages which are movable out of the path of displacement of the conveying arms.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention relates to a method for the manufacture of pipes of thermo-plastics with transverse profile features, comprising mold segment halves which are circulated and, subsequent to an injection head, disposed in two lines opposite to each other, with the mold segment halves of a line not being interconnected, and which complement one another by twos along a straight molding path, forming a closed hollow mold; wherein each of the mold segment halves of a line is guided out of the molding path at the downstream end thereof and substantially at right angles to a direction of production by means of a conveying device and is re-circulated to the up-stream end of the molding path, where it is again inserted in the molding path and attached to the respective mold segment half that leads in the direction of production; wherein downstream of the downstream end of the molding path and on both sides thereof, an additional first mold segment half is kept in a first parking position for insertion in the molding path; the invention further relates to an apparatus for putting the method into practice. 
   2. Background Art 
   A method of the generic type and an apparatus of the generic type are known for example from U.S. Pat. No. 5,693,347. 
   In order to obtain a reliable connection of pipes that are provided with a socket at one end and with a spigot at the other end, a minimum length of the connecting socket is required. Practice and literature proceed from a so-called plug-in length i.e., a length by which the spigot is inserted into the socket. As a rule, the plug-in length must exceed the outside pipe diameter by 30 percent. If pipes of very great diameters are to be manufactured, this means that, given a single-piece design of the mold segment halves that serve for molding the socket, these mold segment halves and consequently all the mold segment halves will be very long, which is accompanied with some problems in terms of manufacturing. In particular, the mold segment halves will become very heavy, demanding for an enormous increase in the power required in the process, in particular the accelerating power. This applies especially to cases when the socket and spigot are molded directly one after the other during the continuous manufacture of the pipe, with an intermediate section being in between which has to be cut out subsequently. 
   When the apparatus is embodied in the way of a gantry crane, having a conveying carriage and conveying arms, as known from U.S. Pat. No. 5,693,347, the entire system is largely free from torque i.e., there are no tilting forces that have to be compensated by corresponding constructional measures. This known apparatus is applicable in particular where pipes of great diameters are to be produced, requiring very big and heavy mold segment halves. 
   EP 0 636 462 B1, U.S. DES. Pat. No. 199 46 571 C2 and U.S. DES. Pat. No. 200 11 668 U1 teach further apparatuses in which mold segment halves that serve for molding sockets can be added to, and removed from, the circulating mold segment halves. In all these cases—as with the apparatus of the generic type—it is only possible to mold a pipe section that deviates from a standard pipe, for instance a socket that can be molded by means of a pair of mold segment halves. 
   SUMMARY OF THE INVENTION 
   It is the object of the invention to embody a method of the species in such a way that optionally, greater pipe sections may be molded that deviate from a standard pipe and cannot be molded in a pair of mold segment halves; and to specify an apparatus for putting the method into practice. 
   According to the invention, this object is attained in a method of the species by the features wherein at least one additional mold segment half is kept in at least one additional parking position between the first parking positions for the first mold segment halves and the downstream end of the molding path, these additional mold segment halves also being insertable in the molding path. 
   The gist of the invention resides in that at least two pairs of mold segment halves can be inserted in the molding path directly one after the other and may again be removed and parked. They are used without hindering each other in the displacement. 
   An apparatus for putting the method into practice is characterized in that downstream of the downstream end of the molding path and on both sides thereof, provision is made for a first parking position for an additional first mold segment half that is approachable by the conveying device; and in that between the first parking positions for the first mold segment halves and the downstream end of the molding path, provision is made for at least one additional parking position for at least one further additional mold segment half that is also approachable by the conveying device. In this case too it is important for the conveying device to be able to approach any parking position without mold segment halves being in the way that are closer to the molding path. 
   When the conveying device is designed in the way of a gantry crane, then there is no need for the mold segment halves to be lifted one above the other; they may be led past one another. 

   
     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 
       FIG. 1  is a plan view of an apparatus for the manufacture of pipes; 
       FIG. 2  is an elevation, partially broken open, of the apparatus in accordance with the arrow II of  FIG. 1 ; 
       FIG. 3  is a plan view of the apparatus in a position of operation that deviates from  FIG. 1 ; and 
       FIG. 4  is a partial cross-sectional view through the apparatus on the line IV—IV of FIG.  3 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIGS. 1 and 2  illustrate an apparatus for the manufacture of pipes of thermoplastics having transverse profile features. This apparatus has a base  1  with a molding path  2  situated on it. On this molding path  2 , mold segments  3  are lined up, each consisting of two mold segment halves  4 ,  5 . As long as the mold segment halves  4 ,  5  are joined together by twos, forming a mold segment  3 , and as long as adjacent mold segments  3  are joined together, forming a mold, they move in a straight line corresponding to a direction of production  6  on the base  1 . For the continuous drive of the mold formed by the mold segments  3 , a lower driving pinion  8  is provided right behind an extrusion head  7  of an extruder, the pinion  8  reaching through a recess  9  in the base  1  and engaging with an indentation  10  formed on the respective lower side of the mold segment halves  4 ,  5 . The lower driving pinion  8  is non-rotatably mounted on a drive shaft  11  which is located underneath the base  1  and driven by a gear motor (not shown). The mold segment halves  4 ,  5  are guided and kept together on the molding path  2  by guide rails  12 ,  13  which engage with such portion of the mold segment halves  4 ,  5  that is adjacent to the base  1 . 
   A counterpart bearing  14  is provided above the base  1  and above the mold. It has a base plate  15  on which is supported an upper driving pinion  16 . This upper driving pinion  16  is likewise non-rotatably mounted on a drive shaft  17 , both ends of which are run in bearings  18 ,  19  which are fastened to the base plate  15 . The drive shaft  17  is driven by a gear motor  20  which is attached to the adjacent bearing  19 . Supporting rollers  21  are located on the lower side of the base plate  15 , having a horizontal axis of rotation  22  and supporting themselves on supporting surfaces  23  formed on the upper side of each mold segment half  4 ,  5 , which defines the position of the counterpart bearing  14  relative to the mold segment halves  4 . Guide rollers  24  are positioned on the lower side of the base plate  15 , having a vertical axis of rotation  25  and engaging laterally with guide surfaces  26  that are also formed on the upper side of the mold segment halves  4 ,  5 . By means of these guide rollers  24 , two mold segment halves  4 ,  5  that constitute a mold segment  3  are guided and held together by their upper portion. Between the supporting surfaces  23  and the guide surfaces  26 , respectively, the upper driving pinion  16  engages with an indentation  27 , which is formed on the upper sides of the mold segment halves  4 ,  5 . Only one third to one quarter of the amount of advance exercised on the mold segments  3  by the lower driving pinion  8  is transmitted to the mold segments  3  by the upper driving pinion  16 . The counterpart bearing  14  is supported in torque converter bearings  28 , which are mounted on the base  1  and stand vertically upright thereon and which absorb the torque exercised by the gear motor  20  on the counterpart bearing  14 . The counterpart bearing  14  itself rests on the supporting surfaces  23  substantially by its own weight. This weight is sufficient to compensate the forces that occur where the upper driving pinion  16  engages with the indentation  27  and act vertically upwards on the counterpart bearing  14 . 
   A conveying device  29  for the mold segment halves  4 ,  5  is provided above the base plate  1 . This conveying device  29  is designed in the way of a gantry crane. It has two guide rails  31 ,  32  extending parallel to each other and parallel to the direction of conveyance  6 , to the central longitudinal axis  30  of the mold segments  3  and to the base  1 . These guide rails  31 ,  32  are disposed above the counterpart bearing  14  and supported relative to the base  1  by props  33 . A conveying bridge  34  is supported on the guide rails  31 ,  32  by bogie wagons  35 . Displacement of the conveying bridge  34  on the guide rails  31 ,  32  takes place by means of linear drives  36 , which are spindle drives in the concrete embodiment. Consequently, these linear drives  36  have threaded spindles  37 , which are disposed on the guide rails  31 ,  32  and on which are disposed threaded nuts  38  which are again fixed to the bogie wagons  35 . The threaded spindles  37  are driven each by a gear motor  39 ,  40 , these two gear motors  39 ,  40  being forcibly synchronized by way of a horizontal coupling shaft  41  that extends at right angles to the guide rails  31 ,  32 . These two threaded spindles  37  are driven precisely at the same speed so that the conveying bridge  34  is displaced free from tilting on the guide rails  31 ,  32 . The conveying bridge  34  has two bridge sections  42 ,  43 , which, seen from the guide rails  31 ,  32 , run toward each other, inclining toward the base  1 . Consequently, the lowest distance of the bridge  34  from the base  1  is in the middle of the bridge  34  vertically above the central longitudinal axis  30 . A conveying carriage  44 ,  45  is displaceably disposed on each of the two bridge sections  42 ,  43  and is movable in the respective direction of displacement  46  or  47  by means of a linear drive  48  or  49 . These linear drives  48 ,  49  substantially consist of a threaded spindle  50  that is housed in the respective bridge section  42  or  43  and engages with a threaded nut  51  on the respective conveying carriage  44  or  45 . The two threaded spindles  50  are driven by a common gear motor  52 . The gear motors  39 ,  40  and the gear motor  52  are reversible motors, i.e. they are suitable for advance and reverse motion. 
   A conveying arm  53 , which extends vertically downwards, is attached to each conveying carriage  44 ,  45 . Each conveying arm  53  is provided with a holding device  54  for a mold segment half  4  and  5 , respectively. Allocated to the holding device  54 , a holding abutment  55  is formed on each mold segment half  4  and  5 , respectively. Each holding device  54  has an upper stop  56  which a holding abutment  55  is pressed against from below. Further, a clamping device  57 , which substantially consists of a pneumatic or hydraulic piston-cylinder drive  58 , belongs to the holding device  54 . A locking pin  60  is formed on the piston rod  59  of this drive  58 , which, upon corresponding actuation of the drive  58 , engages with a locking recess  61  on the lower side of the holding abutment  55 , simultaneously pressing the abutment  55  against the stop  56 . In the position shown on the left of  FIG. 2 , the holding device  54  and the holding abutment  55  of the adjacent mold segment half  4  or  5  are tightly interlocked; consequently, the latter is tightly united with the conveying arm  53 . 
   Proximity switches—only some,  62   63 , of which are shown—are disposed on the guide rails  31 ,  32  and, upon approach of the conveying bridge  34 , transmit signals reflecting the position thereof to a central control unit (not shown). Proximity switches  65 ,  66  are also provided on the conveying bridge  34 , transmitting signals to the central control unit that reflect an inner or outer position of the respective conveying carriage  44 ,  45 . 
   Two tubes of thermally plastic material are extruded from the extrusion head  7  of the extruder, entering the mold at the upstream end  67  of the molding path  2  where they are molded, by means of overpressure or vacuum and, if necessary, support air, into a twin-wall pipe  68  which has a smooth inside wall and an outer corrugation  69 , as known in detail from U.S. Pat. No. 5,320,797 which reference is made to. By alternative, it is also possible to mold single-piece corrugated pipes or ribbed pipes. 
   The mold consisting of the mold segments  3  advances in the direction of production  6 . The pipe  68  produced therein migrates at the same rate. When a mold segment  3  has reached the downstream end  70  of the molding path  2 , the two mold segment halves  4 ,  5  that constitute this mold segment  3  must be removed from the molding path  2  crosswise of the direction of production  6 . As shown by dot-dashed lines in FIGS.  1  and  2 —this is done by the transverse conveying means formed by the conveying carriages  44 ,  45  with conveying arms  53 . During the last short distance covered by the—in the direction of production  6 —last mold segment  3 , the conveying bridge  34  is run along therewith at the same rate, the two conveying carriages  44 ,  45  being moved into a position in which they adjoin each other. In this position, the holding devices  54  and the holding abutments  55  of the two mold segment halves  4 ,  5  have been interlocked. When reaching the downstream end  70 , the two conveying carriages  44 ,  45  are moved apart upon a corresponding signal of the proximity switches  63 , to which end the gear motor  52  is correspondingly triggered. Owing to the inclination of the two bridge sections  42 ,  43 , the mold segment halves  4 ,  5  held by the conveying arms  53  are lifted off the base  1  and moved out-wards without friction. When the conveying carriages  44  reach the outer proximity switches  66 , they are stopped. The gear motors  39 ,  40  are triggered so that the conveying bridge  34  is moved counter to the direction of production  6  as far as to the upstream end  67  of the molding path  2 . Also during their transport counter to the direction of production  6 , the mold segment halves  4 ,  5  do not contact the base  1 , but are frictionless there-above. They are always moved parallel to themselves. 
   When the upstream proximity switches  62  are reached, the gear motors  39 ,  40  are stopped so that the conveying bridge  34  is at a standstill. The gear motor  52  is switched on, moving the conveying carriages  44 ,  45  inwards toward the molding path and, at the upstream end  67 , leading the two mold segment halves  4 ,  5  crosswise of the direction of production  6  into the molding path  2 , as shown by solid lines in  FIGS. 1 and 2 . Upon displacement of the conveying carriages  44 ,  45  toward the molding path  2 , owing to the inclination of the bridge sections  42 ,  43 , the mold segment halves  4 ,  5  are again lowered toward the base  1 , on which they rest when the two mold segment halves  4 ,  5  of a mold segment  3  contact, as seen in FIG.  2 . Then the conveying bridge  34  is moved in the direction of production  6  until the two mold segment halves  4 ,  5  that already form a mold segment  3  bear against the mold segment halves  4 ,  5  that lead in the direction of production  6  and are seized and moved on by the driving pinions  8  and  16 . Then the clamping devices  57  are released and the conveying arms  53  are again moved outwards away from the molding path. The conveying bridge  34  is then again displaced as far as to the downstream end  70 , as described above. As far as described hereinbefore, the apparatus is known from U.S. Pat. No. 5,693,347 A. 
   The apparatus for the manufacture of pipes  68  as described hereinbefore may also employ additional mold segment halves  4   a ,  5   a ,  4   b ,  5   b ,  4   c ,  5   c  that constitute additional mold segments for instance when sockets  71  of great length are to be produced at given intervals in the continuous pipe  68 , these sockets  71  comprising a socket bottom  72 , an intermediate area  73  and an inlet area  74 . The inlet area  74  is followed by a transition area  75  that must be cut out and that is followed by a spigot  76 . This portion that extends from the socket bottom  72  to the spigot  76  is to be molded in-line. As mentioned at the outset, the invention primarily relates to the production of pipes of major diameter; the diameters seen in the drawing are too small relative to the respective length. The in-line molding of sockets as such within a pair of mold segment halves is known for instance from U.S. Pat. No. 5,320,797 which reference is made to as far a molding technology is involved. 
   Related to the direction of production  6 , the additional mold segment halves  4   a ,  5   a ,  4   b ,  5   b ,  4   c ,  5   c  are downstream of the downstream end  70  of the molding path  2  in parking positions  77 ,  78 ,  79  on the base plate  1 . The conveying bridge  34  may be moved into these parking positions  77 ,  78 ,  79 . The parking position  77  is formed by a setting  80  on the base  1 , the height of which above the base  1  results from the inclination of the bridge sections  42 ,  43 . The setting  80  is sufficiently high for the respective mold segment half  4   a  or  5   a  to rest thereon in the associated position of the conveying arms  53  that carry it. 
   The two other parking positions  78 ,  79  that are further upstream are formed by carriages  81 ,  82  which are displaceable on rails  83  crosswise of the direction of production  6  on the base  1 . Linear drives  84  serve for displacement; they may be pneumatically or hydraulically actuated piston-cylinder drives. The carriages  81 ,  82  are movable between a position of rest seen in  FIG. 2 and a  position of access seen in FIG.  1 . In the position of rest, the carriages  81  that carry the mold segment halves  4   b ,  5   b  and the carriages  82  that carry the mold segment halves  4   c ,  5   c  are moved sufficiently far out of the path of displacement  85  of the conveying arms  53  for the mold segment halves  4   a ,  5   a  not to collide with them, as illustrated in FIG.  3 . The same applies to the displacement of the mold segment halves  4   b ,  5   b  when they have to be conveyed past the mold segment halves  4   c  and  5   c . As regards the height of the carriages  81 ,  82 , the same applies as for the settings  80 . While the mold segment halves  4   a ,  5   a  that are in the parking position  77  on the settings  80  may stay in the path of displacement of the conveying arms  53  because they are the mold segment halves farthest downstream, the mold segment halves  4   b ,  5   b  and  4   c ,  5   c  must be moved into the position of rest after being placed on the carriage  81  and  82 ; they are again moved into the position of access according to  FIG. 1  right before being lifted by the conveying arms  53 . 
   Allocated to the parking positions  77 ,  78 ,  79  are proximity switches on the guide rails  31 ,  32 , with only the proximity switches  64  being shown. When the additional mold segment halves  4   a ,  5   a  are to be employed that serve for molding the socket bottom  72 , then the conveying bridge  34  is moved until it reaches the parking position  77  and interlocking of the additional mold segment halves  4   a ,  5   a  and the conveying arms  53  of the conveying carriages  44 ,  45  takes place, as shown by dot-dashed lines in FIG.  3 . Then the conveying operation takes place counter to the direction of production  6  in the manner described, until the two additional mold segment halves  4   a ,  5   a  can be inserted in the molding path  2  at the upstream end  67 . Afterwards the mold segment halves  4   b ,  5   b  and then the mold segment halves  4   c ,  5   c  are lifted by twos in the same way and transported to the upstream end  67  and inserted in the molding path  2 . All of them are removed from the molding path in the manner described at the downstream end  70  and moved into their respective parking position  77  and  78  and  79 . The mold segment halves  4   b ,  5   b  kept in the parking position  78  substantially serve to mold part of the socket bottom  72  and of the intermediate area  73  of the socket  71 , whereas the mold segment halves  4   c ,  5   c  substantially serve to mold the inlet area  74  and the transition area  75 . 
   As known from U.S. Pat. No. 5,693,347, pipes  68  of varying diameters may be produced on the apparatus. In the case of minor pipe diameters, the continuous pipe  68  section that is composed of the socket  71 , transition area  75  and spigot  76  may be so short that only two additional mold segment halves are necessary for molding.