Abstract:
The invention relates to a mold clamping unit on a plastic injection molding machine, the unit having a clamping mechanism for opening and closing an injection mold, the mechanism having a servo motor as the drive motor ( 21 ). The drive motor drives at least one spindle drive ( 10 ) which has a spindle nut ( 12 ) and spindle which work together on a bearing position ( 14 ). A cooling system with cooling channels ( 25 ) is provided for removing heat from the clamping mechanism. A more efficient cooling of the spindle drive is achieved in that the cooling channels ( 25 ) penetrate the bearing position ( 14 ) of the spindle drive ( 10 ) and/or one of the cooling plates ( 23 ) assigned to the bearing position.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application claims the priority of the German patent application 10 2008 051 285.0, filed on Oct. 10, 2008, whose disclosure is hereby expressly incorporated herein. 
     TECHNICAL FIELD 
     The invention relates to a mold clamping unit for injection moldsi on an injection molding machine for processing plastics and other plasticizable compounds such as ceramic or powdery compounds. 
     BACKGROUND 
     A mold clamping unit of this type is known from EP 0 658 136 B1 wherein a liquid-cooled servo motor is used to achieve a higher energy yield as a drive motor for a symmetrical force transmission to a toggle mechanism as well as for an energy-saving operation. Using the water as a cooling medium, heat given off by the electric servo motor can be recovered as energy and then used for tool tempering for example. The servo motor drives a rotationally-fixed spindle such that a favourable mechanical system is obtained. 
     A clamping unit for an injection molding machine in which a lubricant supply is provided to supply lubricant both to the joints of a toggle and to a spindle drive with spindle and spindle nut is known from DE 10 2004 042 744 A1. 
     BRIEF SUMMARY 
     The invention achieves a more efficient cooling of the spindle drive. 
     Since electromechanical drives on plastic injection molding machines are also increasingly being operated with very high dynamics both in regard to speed and acceleration, the heat generated by the interaction of spindle and nut in a mechanical drive of such a type is now dissipated directly from the spindle drive, comprising spindle, nut and bearing. The effect of the direct cooling is to extend the service life of both the spindle system and the bearing. This enhances the precision of the system as a whole owing to the even expansion which cannot be guaranteed when heat is only dissipated from the motor which is some way away from the bearing position that generates most of the heat. In this way, heat can be directly removed from the machine&#39;s bearing elements such as support elements or mold carriers and indirectly dissipated from the motor systems as well. 
     At the same time, by preferentially flange-connecting the motor to the bearing or cooling unit, so much heat can be removed from the motor that there is no need for a basically highly efficient liquid cooling of the motor itself, e.g. by means of water. The pure radiation of heat by cooling fins, or the significantly less efficient air cooling, is usually sufficient to cool the motor. 
     Of particular benefit is an arrangement of the bearing position within the support element for the clamping mechanism, because then the support element can guarantee accurate bearing and the cooling can also be effected through it. Of equal benefit is an arrangement of the cooling channels in an intermediate flange which isolates the bearing position and drive motor ‘climatically’ from one another and which, as a heat sink, can dissipate heat simultaneously in both directions, i.e. both from the motor and from the bearing position. 
     If extremely high precision is demanded, then besides the normal water cooling an exactly regulated temperature control can be beneficial. 
     Further advantages arise out of the dependent claims and out of the following description of a preferred embodiment. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       The invention is explained in more detail herein below by reference to the attached figures. In the figures: 
         FIG. 1  shows a longitudinal section through a mold clamping unit with a toggle mechanism as clamping mechanism, 
         FIG. 2  shows an enlarged portion of the drive unit carried in support element  20  of  FIG. 1  with drive motor and spindle drive 
     
    
    
     DETAILED DESCRIPTION 
     The invention will now be explained in greater detail by reference to the attached drawings by way of example. The embodiments are however just examples which are not intended to restrict the inventive concept to a particular configuration. 
     Before the invention is described in detail it must be pointed out that it is not confined to the particular components of the device or the particular process steps, since said components and processes may vary. The terms used here are intended solely to describe special embodiments and are not employed restrictively. Moreover, if the singular or indefinite articles are used in the description or in the claims, this also refers to the plural of these elements unless the overall context unequivocally indicates to the contrary. 
     The figures depict a mold clamping unit for injection molds as the injection mold M that is suggested by the broken line in  FIG. 1 . The mold clamping unit is used on an injection molding machine for processing plastics and other plasticizable compounds such as ceramic or powdery compounds. A plasticizing unit which is not depicted is usually arranged on the right-hand side of the mold clamping unit in  FIG. 1 . The plasticizing unit plasticizes the plasticizable compound and injects it into a mold cavity of the injection mold M. In order to manufacture the injected parts, the injection mold M is opened and closed cyclically by a clamping mechanism C. For this purpose the injection mold M is accommodated in a mold-clamping space R which is arranged between a first, preferably stationary mold carrier  30  and a movable mold carrier  31 . In  FIG. 1  the injection mold is closed. The clamping mechanism C is supported on a support element  20 , wherein in the embodiment an electromechanical clamping mechanism is provided which is configured here as a toggle mechanism. Other electromechanical drives are conceivable, for example by way of pure spindle drives. The actuation of clamping mechanism C opens and closes injection mold M cyclically while moving movable mold carrier  31  towards and away from the first mold carrier  30 . Support element  20  and first mold carrier  30  are interconnected by force transmission elements such as tie bars  32 . These tie bars may—but need not—serve to guide movable mold carrier  31  at the same time. 
     Clamping mechanism C has a servo motor as drive motor  21 , with an AC synchronous motor or a three-phase synchronous motor acting as the servo motor for example. The servo motor drives a spindle drive  10  with a spindle nut  12  and a spindle  11 . Spindle nut  12  and spindle engage in each other in the region of a bearing position  14  as said bearing position is shown in  FIG. 2 . The known spindle drives, i.e. for example threaded spindles, circular tracks or recirculating ballscrews, are possible for example as spindle drives. In order to move movable mold carrier  30 , spindle  11  is interactively coupled with it. In the embodiment, the spindle is connected in a rotationally fixed manner to crosshead  15  of clamping mechanism C, but it could also be connected in a rotationally fixed manner to another point on the toggle mechanism or to another element of the mold clamping unit or of another clamping mechanism provided a cyclical movement of the movable mold carrier  31  is guaranteed. Instead of the triple-plate mold clamping unit shown in  FIG. 1 , a two-plate mold clamping unit in which the drive unit is disposed on stationary mold carrier  30  for example may also be used. 
       FIG. 2  depicts an enlarged portion of  FIG. 1  in the region of bearing position  14 . It clearly shows that this region is provided with cooling channels  25  which penetrate bearing position  14 , i.e. the region in which spindle nut  12  is interactively coupled with spindle  11 , and/or a cooling plate  23  that is assigned to the bearing plate.  FIG. 2  further shows bearings  13  which in the embodiment carry spindle nut  12  such that it is rotationally turnable but not axially displaceable. Alternatively it is also conceivable to mount the nut in a rotationally fixed manner and to rotate the spindle. What is important is that the heat generated by the relative motion of spindle and spindle nut as they engage in one another is directly dissipated in the region of the bearing position of the two elements. 
     Drive motor  21  drives the rotating element of spindle  11  and spindle nut  12 , i.e. spindle nut  12  in the embodiment, via drive shaft  22 . In the embodiment, drive shaft  22  engages in an intermediate plate in the form of cooling plate  23  which is provided between drive motor  21  and bearing position  14  and which to this extent already creates a ‘climatic’ separation between drive motor  21  and spindle drive  10 . 
     The direct cooling even allows such drives to be operated as high-performance drives with the highest dynamics in regard to both speed and acceleration. It is then in particular, but not only then, that the direct cooling contributes to a longer service life of both the spindle system and the bearing. This is accompanied by greater precision owing to the even expansion of the system. Since bearing position  14  is also usually in direct contact with or supported on other elements of the machine, as in the region of support element  20  in the embodiment, the heat can also be directly dissipated from the machine&#39;s carrying elements from said region, whereby in addition more heat can be dissipated from the motor systems themselves. By flange-connecting drive motor  21  to bearing position  14  and/or cooling plate  23 , so much heat is simultaneously removed from drive motor  21  itself that the need for a highly efficient liquid cooling such as for example using water can be obviated. The pure radiation of heat by cooling fins, or by the significantly less efficient air cooling, is now usually sufficient. Nevertheless the described cooling of the bearing position can also be effected in conjunction with a liquid-cooled servo motor. 
     The drive motor is preferably a hollow-shaft motor because during a transfer of the toggle mechanism as a clamping mechanism C in  FIG. 1  from the extended position to the retracted position, spindle  11  in  FIG. 1  plunges to the left. However the drive of spindle nut  12  is effected outside the motor because a liquid cooling of the bearing position is more favourable than a liquid cooling inside the motor. 
     Spindle  11  also at least partially penetrates cooling plate  23 . Where cooling plate  23  is referred to as a ‘plate’, this refers to its actual embodiment. Other non plate-shaped embodiments are conceivable provided the desired aim of cooling near to the bearing position is guaranteed. 
     If extremely high degrees of precision are required, then as well as normal liquid cooling, an accurately regulated temperature control may also be used so that bearing position  14  and/or cooling plate  23  are temperature-controlled as required. 
     In the embodiment, bearing position  14  carries the rotationally turnable and axially undisplaceable spindle nut  12  in bearing  13 . Cooling is effected through cooling channels  25 , with the coolant being supplied via cooling connections  24 . Bearing position  14  is advantageously arranged mainly in support element  20 . As a result, the metal support element itself forms bearing position  14  which is indicated in  FIG. 1  by the broken line, and in so doing serves the cooling at the same time. It is an advantage if an oil or other temperature-conducting material is used as a slip agent and lubricant because then cooling can be more easily transmitted from bearings  13  and bearing position  14  inward to the nut and spindle. 
     It goes without saying that this description is susceptible to a very wide variety of modifications and adaptations which fall within the scope of equivalents to the appended claims.