Abstract:
A blow molding machine for producing hollow bodies from heated preforms has at least one blow mold and at least one blow nozzle which can be moved vertically relative with respect to each other via a drive. To design the drive more flexibly, an electromagnetic drive is employed.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The present application claims the benefit of priority of German Application No. 102009024408.5, filed Jun. 9, 2009. The entire text of the priority application is incorporated herein by reference in its entirety. 
       FIELD OF THE DISCLOSURE 
       [0002]    The disclosure relates to a blow molding machine for producing hollow bodies from heated preforms, such as used in forming containers for beverage bottling operations. 
       BACKGROUND 
       [0003]    Such a blow molding machine is known from EP 1 328 396. In the known blow molding machine, the relative movement between the blow nozzle and the blow mold which is required for introducing the preform into the blow mold and for blowing is achieved by a merely mechanical drive of the vertical movement. The mechanical drive contains a cam roller which, in connection with a radial cam, defines the vertical movement and the position of the blow nozzle. The cam roller is associated to the blow nozzle and the radial cam to the blow mold, so that by the usual relative rotation about a vertical axis of the blow mold and the blow nozzle, the vertical movement is derived from the drive of the rotary motion. A disadvantage of this embodiment is the lack of flexibility of the drive as the radial cam is fixed locally and with respect to the dimension of the movement. 
       SUMMARY OF THE DISCLOSURE 
       [0004]    The object underlying the disclosure is to provide a blow molding machine offering greater flexibility with respect to the vertical movement. 
         [0005]    The electromagnetic drive according to the disclosure can be employed and designed essentially more universally than the fixed mechanical drive. For example, the stroke, i.e. the amount of the vertical movement, or the response time or the like can be modified in a simple manner. 
         [0006]    Magnet coils in blow molding machines have been only used up to now for applying the contact force between the blow nozzle and the blow mold, i.e. merely statically, to act against the pressure of the high-pressure gas. Such an application is known from EP 1 572 435. 
         [0007]    Preferably, at least one magnet coil is provided for a predetermined stroke, the return force being applied by gravity. However, it is also possible to employ one magnet coil each for each direction of movement. 
         [0008]    With an electromagnetic drive, it is furthermore easily possible to realize various lengths of stroke, at least one magnet coil being provided for each length of stroke. 
         [0009]    Finally, in the electromagnetic drive, the predetermined force of pressure of the blow nozzle against the blow mold can also be realized. 
         [0010]    By means of a spring, a linear relation between the electric current and the stroke can be adjusted. 
         [0011]    In an advantageous embodiment, the blow nozzle consists, at least in sections, of a ferromagnetic material. It is particularly preferred to mount permanent magnets to the blow nozzle. The ferromagnetic material or the permanent magnets cause a reduction of a force required for the drive. Thus, the magnet coils require less energy. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    In the following, one embodiment of the disclosure is illustrated more in detail with reference to the single FIGURE. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0013]    The FIGURE shows in a partial section a blow molding machine  1  of which here only the blow nozzle  2  and the blow mold  3  are represented. The blow mold  3  is split in a conventional way, with a mold cavity  4  and an opening  5  facing upwards which is opposite to the blow nozzle  2 . A non-depicted preform is inserted into the cavity  4  and the opening  5  and blown via the blow nozzle  2  to the shape defined by the mold cavity  4 . 
         [0014]    The blow nozzle  2  has a tubular design and contains at its lower end a blow opening  6  opposite to the opening  5 . The openings  5  and  6  are brought to a predetermined distance for introducing the preform and to a pressing contact for blowing. This movement is accomplished via a vertical movement H in the direction of the double arrow of the blow nozzle  2 . This vertical movement H is realized via a drive  7 . 
         [0015]    Except for the drive  7 , the blow nozzle  2  is of a conventional type, i.e. it contains a common stretch mandrel  8  movable relative with respect to the blow nozzle  2 , a bearing and guide  9  for the movement of the blow nozzle  2  in the direction of the double arrow H, the necessary supplies  10  of blowing gas, and the actual nozzle arranged at the lower end, and the like. 
         [0016]    The electromagnetic drive  7  contains at least one magnet coil  11  which extends annularly around the blow nozzle  2  and a magnet body  12  fixed to the blow nozzle  2  which is preferably simultaneously used as a guide for the blow nozzle  2  in a sliding guide bore  13  of the mounting  9 . The magnet body can be embodied as separate part from a ferromagnetic material or consist of the blow nozzle consisting at least in sections of a ferromagnetic material, or designed as permanent magnet. 
         [0017]    In the represented embodiment, two magnet coils  11   a,    11   b  superimposed in the direction H are provided, the magnet coil  11   a  being used for lifting and the magnet coil  11   b  located thereunder being used for lowering the blow nozzle  2  in a movement over a single stroke H 1 . 
         [0018]    Further magnet coils can be provided to realize deviating lengths of stroke. For example, a third magnet coil can be provided above the first magnet coil  11   a  which realizes a second, longer stroke H 2 , the lower magnet coil  11   b  causing the return into the lowered position drawn in  FIG. 1  for both strokes. 
         [0019]    All magnet coils  11  are supplied via a power source  14  and provided with a non-depicted control means which controls the stroke and the application of the magnet coil required in each case. 
         [0020]    Furthermore, the force of pressure between the two openings  5 ,  6  can also be caused electromagnetically, which can be realized, for example, by an additional coil in the region of the openings  5 ,  6  or by the lower coil  11   b.    
         [0021]    Furthermore, a non-depicted spring can be provided which acts against the magnetic force to cause a linear behavior between the electric current and the stroke. 
         [0022]    In variation to the described and drawn embodiment, the electromagnetic drive according to the invention can also be employed in differently constructed blow nozzles and/or blow molds. 
         [0023]    It would be conceivable to employ such a system not only for the blow nozzle. Such magnetic drives can also be employed for all elements which transfer the mold cavity of the blow mold into a closed state. One of these elements represents a non-depicted bottom which can be added separately. The bottom closes a spatial area located opposite to the blow nozzle. A further one of these elements is the stretch mandrel. A stretching force adaptable by the control and that can be adjusted via the current flow in the magnet coils would be advantageous for the stretch mandrel. Theoretically, such an electromagnetic drive would also be conceivable for parts for mold halves of the blow mold. 
         [0024]    In an advantageous embodiment, at least two of these elements are controlled by means of such an electromagnetic drive.