Abstract:
A pelletizer comprises a knife head, which is mounted by a denture coupling on a rotatably drivable shaft. The denture coupling comprises at least one serrated ring mounted on the knife head and on the shaft, respectively, the serrated rings having a frontal tooth system and intermeshing. Furthermore, a chucking arrangement of the type of a collect chuck is provided for releasably locking the knife head and the shaft in the direction of their axis.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a pelletizer comprising a housing; a pelletizing hood; a knife head, which is disposed in the pelletizing hood; a rotatably drivable shaft mounted in the housing, which shaft has a central longitudinal axis in common with the knife head, and on the front of which the knife head is mounted non-rotatably and releasably. 
     2. Background Art 
     Prior public use discloses to fasten the knife head of a pelletizer by means of screws, which are screwed frontally into the shaft. Torque transmission takes place by means of a feather key or a splined shaft connection. Large pelletizers will need several feather keys for torque transmission, which reduces the carrying capacity of the shaft and the knife head. Further, mounting bulky and heavy parts is very complicated in large pelletizers. Accurate alignment of the shaft and the knife head relative to each other is necessary prior to the assembly. Automatization of replacement is rendered complicated and expensive by the use of screws. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to embody a pelletizer of the generic type such that mounting and dismounting the knife head is feasible rapidly and easily. 
     According to the invention, this object is attained in that the shaft and the knife head are coupled with each other non-rotatably by a denture coupling, which, on the knife head and on the shaft, respectively, comprises at least one serrated ring with a frontal tooth system, the frontal tooth systems being turned toward each other and inteimeshing; and in that a chucking arrangement of the type of a collet chuck is provided for releasably locking the knife head and the shaft in the direction of the axis. The measures according to the invention ensure simple mounting and dismounting of the knife head on the shaft. The knife head only has to be placed on the associated end of the shaft; the frontal tooth systems of the serrated rings, which are turned toward, and allocated to, each other, engage automatically with each other. Then only the chucking arrangement has to be operated for the knife head and the shaft to be clamped together in the direction of the axes, as a result of which the torque connection is simultaneously fixed between the knife head and the shaft, namely between the intermeshing frontal tooth systems of the serrated rings. Once the chucking arrangement has been released, the knife head can simply be detached. The frontal tooth systems have a surface which exceeds by far any feather key connection, ensuring high carrying capacity and important torque transmission. 
     Special advantages are offered by the use of a serration. An especially compact design is obtained when the chucking arrangement is disposed within the serrated rings. In the case of fluidic actuation of the chucking arrangement by the shaft, the chucking arrangement applies a gripping power which is precisely defined by the pressure of the pressure fluid and acts in the direction of the axis so that defects in assembling as they may be produced by not correctly tightened screws are avoided. This design further ensures automatic mounting and dismounting of the knife head; but it also facilitates the manual replacement of the knife head. 
     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 lateral longitudinal view of a pelletizing plant; 
     FIG. 2 is a lengthwise section through a chucking arrangement for the connection of the knife head and the shaft in the locked condition of the chucking arrangement; 
     FIG. 3 is a lengthwise section through the chucking arrangement in the unlocked condition; 
     FIG. 4 is a plan view of a serrated ring; and 
     FIG. 5 is a partial cross-sectional view through a chucking device of the chucking arrangement. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The pelletizing plant seen in FIG. 1 comprises a pelletizer  1 , which is disposed in the direction of production  3  downstream of an extruder  2 , of which only a pelletizing die head  4  with a stationary pelletizing die  5  are shown. 
     The pelletizer  1  comprises a knife head  6  driven by a drive  7  in the form of an electric motor via a shaft  8 , in which a coupling  9  is inserted. The drive  7  and the pelletizer  1  are disposed on a carriage  10 , which is movable on the foundation  11  for example in the form of rails from the position of operation seen in FIG. 1 in the direction of production  3  into a position in which it is spaced from the pelletizing die head  4 . 
     The pelletizer comprises a pelletizing hood  12 , which encircles the knife head  6  and which is provided with a lower water inlet  13  and an upper water outlet  14 . In the direction toward the drive  7 , the pelletizing hood  12  is followed by a bearing housing  15 , in which the shaft  8  is run as usual. As far as heretofore described, the pelletizing plant is a known and general practice. 
     The knife head  6  comprises a knife carrier  16 , which is called a blade impeller in practice because of its impeller type appearance and which is provided, on the front turned toward the pelletizing die head  4 , with knives  17  which, during pelletization, brush at a high speed over the front, turned toward them, of the pelletizing die  5 , cutting the strands of plastic melt from the pelletizing die  5  into pellets which are conveyed to the water outlet  14  and out of it by the water, which enters the pelletizing hood  12  through the water inlet  13 . This too corresponds to technology that is general practice. 
     The knife carrier  16  has a cup-shaped hub  18  which is open toward the shaft  8  so that the associated end of the shaft  8  can be led into the hub  18 . A denture coupling  19  helps obtain a connection against rotation between the shaft  8  and the hub  18  and thus the knife head  6 . This denture coupling  19  substantially comprises two serrated rings  20 ,  21 , each of which is provided with a frontal tooth system  22  in the form of a so-called Hirth serration. One serrated ring  20  is fixed by screws  23  to the bottom  24  of the hub  18 , whereas the other serrated ring  21  is also fixed by screws  23  to the front  25  of the shaft  8 . The two serrated rings  20 ,  21  have the same diameter and, as seen in FIG. 4, identical front serrations  22  extending radially to the central longitudinal axis  26  of the knife head  6  and the shaft  8 . By its cylindrical coupling end  28  which adjoins the front  25 , the shaft  8 , in the position of operation seen in FIG. 2, is centered radially to the axis  26  in the suited cylindrical recess  29  of the hub  18 , the frontal tooth systems  22  of the two serrated rings  20 ,  21  inteimeshing. In the position of operation seen in FIG. 2, the hub  18  and thus the knife head  6  is tightly, but releasably connected to the coupling end  28  and thus to the shaft  8  in the direction of the axis  26  by means of a chucking arrangement  30 . 
     The chucking arrangement  30  is disposed radially within the serrated rings  20 ,  21  and concentrically of the axis  26  and comprises a locking pin  31  which is tightly mounted on the bottom  24  of the hub  18  and projects beyond the bottom  24  in the direction toward the shaft  8 . For being locked, the pin  31  comprises, on its end turned toward the coupling end  28 , an annular locking projection  32  which stands out radially to the axis  26 . 
     A chucking device  33 , which is in practice called a collet chuck, is disposed in the equally cup-shaped coupling end  28 , which is open toward the hub  18 . This chucking device  33  comprises a cylindrical housing  34 , which is inserted into the coupling end  28 , where it is held in place by means of screws  35  screwed into the front  25 . A cup-shaped locking piston  37 , which is sealed toward the inner wall of the housing  34 , is guided in the direction of the axis  26  in the housing  34  in vicinity to the bottom  36  thereof. The locking piston  37  is closed toward the bottom  36 . A guide element  39  of the chucking device  33  is disposed on the side, open toward the front  25 , of the interior space  38  of the locking piston  37  and is concentric of the axis  26 . In the portion turned toward the front  25 , it has a circumferential groove  40 , in which collet elements  41  are held and guided firmly in the direction of the axis  26 , but for displacement radially thereto. On their free ends which project toward the locking pin  31 , these collet elements  41  have clamping jaws  42 , which can back up the locking projection  32  of the locking pin  31  as seen in FIG.  2 . The collet elements  41  are surrounded by a locking bush  43 , which is disposed non-displaceably radially to the axis  26 , but axially displaceably on the guide element  39 . The locking bush  43  is sealed toward the inner wall of the housing  34  and rests sealingly on the guide element  39  so that the interior space  38  is closed in the direction toward the front  25 . On the end of the locking bush  43  that is turned toward the locking piston  37 , guide jaws  44  are mounted on the locking bush  43 , which are displaceable radially to the axis  26  and relative to the bush  43  and which, by a slope  45 , are guided on, and bear against, a guide surface  46  of the guide element  39  which widens in the shape of a truncated cone toward the locking piston  37 . On their periphery, the guide jaws  44  are provided with pressure surfaces  48 , which are adapted to the inner surface  48  of the locking piston  37 . As seen in FIG. 5, the guide jaws  44  are connected to each other by means of prestressed tension springs  49 , which exercise a resultant force directed radially to the axis  26  on the guide jaws. Disposed between the guide element  39  and the collet elements  41 —for example in the circumferential groove  40 —are prestressed compression springs  50 , which exercise a force that is directed radially away from the axis  26  on the collet elements  41 . 
     Mounted in the bearing housing  15  is a commercial pressure oil supply  51  which encloses the shaft  8  and is disposed tightly thereon for the supply and discharge of pressure fluid. It is connected to two channels which are formed in the shaft  8 , namely a locking channel  52  and an unlocking channel  53 . The locking channel  52  leads into the housing  34  between the bottom  36  thereof and the locking piston  37 . The unlocking channel  53  leads into the interior space  38  in the vicinity of the locking bush  43 . 
     For the release of the non-rotatable connection, seen in FIG. 2, between the shaft  8  and the knife head  6 , pressure oil is forced as a pressure fluid via the unlocking channel  53  into the interior space  38 . Simultaneously, the locking channel  52  is open for pressure oil to escape that is in the housing space  54  between the bottom  36  of the housing  34  and the locking piston  37 . The locking piston  37  is displaced in the direction toward the bottom  36  of the housing  34 , whereas the guide element  39  is displaced in the direction toward the front  25  of the shaft  8 . In this way, the clamping jaws  42  of the collet elements are free from the locking bush  43  so that the collet elements  41  are pushed outwards radially to the axis  26  by the compression springs  50 . As a result, the clamping jaws  42  release the locking projection  32  of the locking pin  31 ; the knife head  6  can be pulled off the coupling end  28  of the shaft  8  in the direction of the axis  26  and counter to the direction of production  3 . The guide jaws  44  have been shifted outwards on the guide surface  46  of the guide element  39  against the force of the tension springs  49 . 
     For the production of a connection between the knife head  6  and the coupling end  28  of the shaft  8 , the knife head  6  is pushed on the coupling end  28  until the locking projection  32  of the locking pin  31  has arrived between the collet elements  41 . The front serrations  22  of the serrated rings  20 ,  21  intennesh in the direction of the axis  26 . Then compressed oil is supplied to the locking channel  52  while the unlocking channel  53  is open. The locking piston  37  is displaced in the direction towards the guide element  39 , it being possible that the compressed oil in the housing space  54  flows off through the unlocking channel  53 . The inner surface  47  of the locking piston  37  encompasses the outer pressure surfaces  48  of the guide jaws  44 , as a result of which the guide jaws  44 —supported by the tension springs  49 —migrate radially toward the axis  26 , by their inclined motion on the guide surface  46  of the guide element  39  displacing same in the direction toward the locking piston  37 , i.e. into the interior space  38  thereof In this way, the collet elements  41  are also moved in the direction toward the bottom  36  and displaced radially inwards by the locking bush  43  so that their clamping jaws  42  back up the respective locking projection  32 , simultaneously clamping it in the direction of the axis  26 .