Abstract:
A closing element, which has an open position and a closed position and is actuated by an actuating element, is arranged in the nozzle channel of a nozzle body. In the closing position, the closing element separates a region that is at least temporarily in open communication with the injection mold, the region being able to be influenced by a second actuating element associated with the nozzle body. Due to the fact that the pressure element is arranged in the nozzle body and can be actuated independently from the nozzle body and the plastifying cylinder, a nozzle body is created and a method is provided that enable the dosing process and dwell pressure process to be separated with a compact structure.

Description:
REFERENCE TO RELATED APPLICATIONS  
         [0001]    The present application claims the priority of the German patent application 101 13 352.9, lodged on 20.03.2002, the disclosure content of which is herewith also made expressly the subject of the present application.  
         BACKGROUND SECTION  
         [0002]    A nozzle body for an injection molding machine for processing plastic materials and other plastifiable materials, such as pulverulent or ceramic materials, is known from DE 15 54 934 A, wherein a piston shaft is moved hydraulically, which from a starting position first drives into the bore of a mouth ring and hence closes the nozzle opening and then serves for generating the holding pressure. Insofar this piston shaft is at the same time closure element and pressure element. Therein a change in volume already occurs when the piston shaft is transferred into closure position.  
           [0003]    From PATENT ABSTRACTS OF JAPAN, vol. 014, no. 428 (M-1025),  14 . Sep. 1990 &amp; JP 02 169219 A a nozzle body is known comprising a cyclically usable closure and pressure element that is axially movable in the nozzle body to influence the holding pressure which significantly influences the quality of the moldings. In actuating the pressure element, however, a change in volume occurs, what is influencing the process control and hence at least also the cycle by cycle reproducible quality of the moldings.  
           [0004]    A nozzle body having a closure element which can be used cyclically, is also known from GB 976,369 PS. The plastified material is injected alternately into two mould cavities, the closure element releasing the runner to the one mould cavity when it closes the other. One pressure cylinder unit respectively is associated with the runners so that, as soon as the closure element closes the one runner, the pressure cylinder unit on the associated mould cavity can influence the holding pressure, whilst material is already injected again into the other mould cavity. The time advantage obtained therewith is based however on the fact that two mould cavities are operated alternately so that this device cannot be applied to a compact nozzle unit which possibly operates only one mould cavity.  
           [0005]    It is known furthermore to use a shut-off nozzle on a plastic material injection molding machine depending on the material, said shut-off nozzle opening and closing the nozzle opening cyclically. Closure nozzles of this type are known for example from EP 0 322 497 A2. Closure is effected only at the end of the holding pressure phase which is required for obtaining a qualitatively high-grade molded article without sinks or shrinkholes. However, precisely in the case of thick-walled molded articles a long holding pressure time is required, which in this respect contributes directly to increasing the cycle time.  
         SUMMARY OF THE INVENTION  
         [0006]    Starting from this state of the art, the object underlying the present invention is to produce a nozzle body and to make available a method which, with a compact construction, permits a separation between the dosing process and the holding pressure process.  
           [0007]    For this purpose, a holding pressure chamber is provided in the nozzle body in addition to the closure element, said holding pressure chamber being able to be influenced by a pressure element actuated in the nozzle body by a further actuation member. It is consequently possible on the one hand to have an influence with the actuation member on this chamber and on the mould cavity which is connected thereto, in order for example to build up the holding pressure. On the other hand, dosing can already take place again at the same time however in front of the closure element, independently of the application of the holding pressure. As a result, precisely with PET preforms, which generally have a large wall thickness and hence require a long holding pressure time, this long holding pressure time can be used already once again for dosing, so that the cycle time is significantly reduced. However, only the separation in the nozzle body is essential for the invention so that, by external actuation, the holding pressure in the nozzle can be influenced, preferably can be influenced in a controlled manner, even if no use is made of this option. A separation of holding pressure and material pressure is therefore possible. The separation of dosing chamber and holding pressure chamber in the nozzle body leads however also to the fact that the material to be dosed can be dosed over a fairly long period of time and hence, if required, more slowly. Hence a smaller torque acts upon the screw, so that the material is subjected to fewer shear forces. This also ensures gentler handling with sensitive materials.  
           [0008]    Due to the actuation of the pressure element independently of the nozzle body and plastifying cylinder, the holding pressure force is no longer dependent upon the nozzle touch force. At the same time, the impermeability of the nozzle unit is increased.  
           [0009]    Therein the actuation member engages on a pressure element which is mounted so as to float in the nozzle channel. As a result, a compact construction is produced since the pressure element is controllable on the one hand for influencing the holding pressure chamber but can be subjected to a flow of the newly dosed material already, without the thereby resultant pressure preventing the movement of the pressure element.  
       
    
    
     BRIEF DESCRIPTION OF THE FIGURES  
       [0010]    The invention is explained subsequently in more detail with reference to the enclosed figures, which show:  
         [0011]    [0011]FIG. 1 a side view of an injection molding unit with a nozzle body according to the invention, disposed on a machine base,  
         [0012]    [0012]FIG. 2 an enlarged section through the nozzle body according to FIG. 1 at the beginning of the mould filling phase,  
         [0013]    [0013]FIG. 3 an illustration according to FIG. 2 near the end of the mould filling phase,  
         [0014]    [0014]FIG. 4 an illustration according to FIG. 2 at the beginning of the holding pressure phase,  
         [0015]    [0015]FIG. 5 an illustration according to FIG. 2 at the end of the holding pressure phase,  
         [0016]    [0016]FIG. 6,7 sections through FIG. 1 along the lines  6 - 6  or  7 - 7 , 
     
    
     DETAILED DESCRIPTION  
       [0017]    The invention is now explained in more detail by way of example with reference to the enclosed drawings. However, the embodiments only concern examples which are not intended to restrict the inventive concept to a specific arrangement.  
         [0018]    [0018]FIG. 1 shows an injection molding unit S of an injection molding machine for processing plastic materials and other plastifiable materials, such as pulverulent or ceramic materials which machine is disposed on a machine base  36 . The injection molding unit has a plastifying cylinder  30 , on the front end of which a nozzle body  10  is disposed. Rings  20 ,  21  are disposed on the nozzle body as actuation elements for parts disposed in the interior of the nozzle body, said rings being actuated by actuation members  40 ,  41 . Other elements can also be provided instead of the rings as long as only one reliable power introduction is possible into the parts disposed within the nozzle body  10 . The injection molding unit S plastifies the material and injects it via the nozzle body  10  into a mould cavity of an injection mould  25 . At least one part of the generally multi-part injection mould  25  is mounted on the stationary mould carrier  35 , which according to FIG. 1 is penetrated by the nozzle body  10  in a passage opening.  
         [0019]    According to FIGS.  2  to  5 , the nozzle body  10  has a nozzle opening  11  for injecting the plastified material into the injection mould  25 . In the nozzle opening  11 , there discharges a nozzle channel  12  which is connected at the other end to a plastifying cylinder  30  in which a feeding means  31 , here a feed screw, feeds the plastified material in the direction towards the nozzle opening  11 .  
         [0020]    Furthermore, a closure element  13  is provided for closure if required of the nozzle channel  12 , and is actuated by an actuation member  40 . The closure element  13  separates, in the closure position, a chamber which is in open communication at least at times with the injection mould  25 . This chamber can be influenced by a further actuation member  41  which is associated with the nozzle body  10 .  
         [0021]    The closure element  13  hence separates, in the closure position, a chamber configured as holding pressure chamber  14  in the nozzle body  10  from a dosing chamber  15  which is connected to the feeding means  31  of the plastifying cylinder  30 . As a result, the internal pressure and/or the volume of the holding pressure chamber  14  can be influenced independently of the dosing taking place on the other side of the closure element and can be controlled or regulated in the embodiment by means of a pressure element  16 . The pressure element is disposed preferably coaxially to an injection axis s-s in the nozzle body  10 , which axis goes through the nozzle opening  11 .  
         [0022]    The pressure element  16  is disposed in the nozzle channel  12  in the embodiment of FIGS.  2  to  7  and is moveable there in a limited manner. FIGS. 2 and 7 show that the ring  21  actuated by the actuation member  41  is in operational connection by means of an actuation element  51  with the pressure element  16  disposed in the nozzle channel  12 . The maximum movement possibility is limited by a slot. On its front end, the pressure element  16  has a piston  17  which acts upon the holding pressure chamber  14  and is guided in this embodiment in the closure element  13 . The pressure element  16  is mounted so as to float in the nozzle channel  12 , so that it can itself be reliably actuated when material is again already feeded and dosed behind the closure element  13 . As a result, a compact construction is produced since the pressure element is controllable on the one hand for influencing the holding pressure chamber, but at the same time can be subjected to a flow already from the newly dosed material, without the thereby resultant pressure preventing the movement of the pressure element.  
         [0023]    The movement of the pressure element  16  and of the piston  17 , which is securely connected thereto, leads not to a change in volume when the closure element  13  is open but only to a volume displacement since the shape of the pressure element  16  and piston  17  is configured such that, when the holding pressure chamber  14  and dosing chamber  15  are in open communication, the pressure around the pressure element is cancelled out. The open communication is ensured by the passage channels  13   a  and the through-flow channels  16 . Because of the floating mounting in the nozzle channel, the forces in front of and behind the pressure element are hence cancelled out. The pressure ratios around the pressure element remain unchanged so that the pressure element has no influence or at least no substantial influence upon the process control. The same applies fundamentally also during actuation of the closure element  13 .  
         [0024]    According to FIG. 7, the pressure element  16  has through-flow channels  16   a  for the passage of plasticised material, which channels are delimited in the embodiment by the wall of the nozzle channel  12 . The through-flow channels can however also be disposed such that they come to lie entirely in the pressure element and no contact with the wall of the nozzle channel  12  occurs. As FIGS.  2  to  5  show, the closure element  13  is disposed in the flow direction of the plastified material after the pressure element  16 , however its piston  17  lies parallel to the pressure element  16 . The closure element  13  is likewise disposed in the nozzle channel and has passage channels  13   a  for the passage of plastified material into the holding pressure chamber  14 . These passage channels  13   a , which are present in the open position according to FIG. 6, are closed by an axial movement of the closure element  13  on the wall of the nozzle channel  12 , preferably at the end-side on the nozzle head  18 . Other closure possibilities are possible but this embodiment has the advantage that a relatively large sealing face is produced with a small closure path.  
         [0025]    In this embodiment, the device operates in the following manner:  
         [0026]    The state at the beginning of the filling phase is illustrated in FIG. 2. The feeding means  31  is still located in the withdrawn state on the right in FIG. 2. In the chamber in front of the feeding means  31 , plastified and dosed material is situated. The pressure element  16  is moved further forwards at the end of the last cycle, whilst the closure element is transferred to the right into its open position. If the feeding means  31  is now moved to the left in FIG. 2, then firstly material is conveyed via the through-flow channels  16   a  and also the passage channels  13   a  into the injection mould  25 .  
         [0027]    An illustration according to FIG. 3 is produced towards the end of the filling phase. On the one hand, the pressure element  16  was thereby withdrawn or pushed to the right so that a holding pressure chamber  14  is formed in front of the piston  17  of the pressure element  16 . The closure element  13  is still located in the open position. The movement of the pressure element  16  and of the piston  17 , which is securely connected thereto, leads not to a change in volume when the closure element  13  is open but only to a volume displacement. Because of the floating mounting in the nozzle channel, the forces in front of and behind the pressure element are hence cancelled out. The pressure ratios around the pressure element remain unchanged so that the pressure element has no influence upon the process control.  
         [0028]    However, the closure element  13  is also configured such that the same forces are applied in front of and behind the closure element in the open position. The movement of pressure element  16  with piston  17  and also the movement of the closure element therefore have above all no influence upon the injection molded part.  
         [0029]    This pressure equalization only changes when the closure element according to FIG. 4 is transferred to the left into the closure position by the actuation element  50  in conjunction with the ring  20  and the associated actuation member  40 . The channel between the closure element  13  and the nozzle head  18  which is still present there in FIG. 3 is hence closed. What is thereby advantageous is the relatively long sealing face relative to a simple closure of the passage channel  13   a.    
         [0030]    The holding pressure now applies on the one side of the closure element in the direction of the injection mould and, on the other side, the dosing pressure. However, the pressure ratios at the pressure element  16  have also changed since the piston  17  of the pressure element  16  is now subjected to holding pressure. Hence a separation is effected between the holding pressure chamber  14  and the dosing chamber  15  which is present behind the closure element. If new material is now dosed, a uniform pressure is set in front of the pressure element in the region of the nozzle channel  12  and between closure element and pressure element  16 , however since the piston  17  is subjected to a different pressure, the forces around the pressure element  16  are no longer cancelled out. Since the holding pressure and hence the actuation of the pressure element  16  with piston  17  is effected from the outside via the actuation element  50  and the ring  20  due to the actual values of an internal pressure sensor preferably in the injection mould, this is however without consequence for the injection molded part since this is not influenced by the pressure ratios around the pressure element.  
         [0031]    As a result, the pressure element  16 , although it is located in the nozzle channel  12 , can move freely as an element which is mounted so as to float. Whilst material is therefore dosed for the next cycle already in the dosing chamber  15 , the holding pressure can still be applied from the holding pressure chamber  14  by actuation of the pressure element by means of ring  21  and actuation element  51 . The movement of the pressure element leads not to a change in volume but only to a volume displacement so that dosing can take place nevertheless in a uniform manner behind the closure element. Hence, simultaneous dosing and application of holding pressure is therefore possible so that the holding pressure time, the length of which normally definitively determines the cycle e.g. in the case of PET preforms, can be used already for dosing the next cycle. The separation thus offered between dosing and holding pressure is possible in the nozzle body  10  by means of the externally actuated elements.  
         [0032]    According to the method, a cyclical separation of a chamber in the nozzle body  10  and influencing of this chamber by means of a further actuation member  41  is effected. The holding pressure chamber  14  and dosing chamber  15  are thereby configured such that the holding pressure chamber  14  can be influenced in a controlled or regulated manner during the holding pressure phase, whilst the dosing of the next cycle can begin at the same time already behind the closure element.  
         [0033]    It goes without saying that this description can be subjected to the most varied of modifications, changes and adaptations which act as equivalents with respect to the dependent claims.