Patent Publication Number: US-2004047936-A1

Title: Injection unit for a plastic injection molding machine

Description:
[0001] The invention relates to an injection unit for an injection-molding machine, in particular for plastics, with a screw which is connected to a first actuator for rotating movement and to a second actuator for axial movement.  
       [0002] EP 0 280 743 B1 discloses an injection-molding machine in which the screw can be rotated by a first actuator and can be moved linearly in relation to the rotary drive by a second actuator. Both actuators are electrically driven, a gaseous medium is not used.  
       [0003] WO 94/09982 discloses a pressure controlling and/or regulating device in which a fluidic medium is fed to the polymer melt in an injection mold, these medium inflow control valves being actuable by the valve control in dependence on the pressure difference respectively present at a pressure sensor.  
       [0004] This pressure generator/accumulator is intended only for an injection system, not for axial displacement of the screw of an injection-molding machine.  
       [0005] The object of the invention is to provide an injection unit of a simple construction which permits reliable axial adjustment of the screw with low energy consumption.  
       [0006] The invention achieves this object by the features of claim 1. The remaining claims are advantageous developments of the invention. According to the invention, the injection unit of the injection-molding machine concerned here, in particular for plastics, has a first actuator, which is designed as an electric motor, and a second actuator, which is designed as a pressure bellows and the volume of which can be altered by adjusting elements.  
       [0007] The housing of the pressure bellows may in this case be constructed from rubber or from metal. The pressure bellows can be compressed by a fixed plate and a movable plate by means of adjusting elements. In one embodiment, the adjusting elements are formed as springs, which counteract the internal pressure of the pressure bellows. The springs may in this case be provided independently of the housing of the pressure bellows, but they may also be configured as a metallic compensator which at the same time forms the housing of the pressure bellows.  
       [0008] In one particular embodiment, the adjusting elements are spindle nut units, in which at least one component is driven. It is particularly advantageous for the spindle to be designed as a ballscrew which is driven and moves in a fixed nut.  
       [0009] To prescribe the exact rotational movement, the rotational speed is sensed and brakes, preferably disk brakes, are provided on the spindles, permitting low-maintenance braking.  
       [0010] In a further embodiment of the injection unit, the pressure bellows is provided with a counter-bellows, the two bellows being connected to each other by means of an adjusting valve connected in the conveying direction.  
       [0011] It is additionally proposed to design the electric motor as a hollow-shaft motor, in particular as a reluctance motor.  
       [0012] In a further advantageous embodiment, the pressure bellows is of an annular design, and if appropriate the counter-bellows is likewise of an annular design, the connecting shaft being such that it can pass centrally through the pressure bellows, so that the rotating motor can be arranged on the side of the pressure bellows remote from the screw.  
       [0013] For the exact guidance of the linear movement, it is further proposed to provide a pressure gage, which is connected to a measuring and regulating device by which the axial expansion of the pressure bellows can be controlled. 
     
    
    
     [0014] An example of the invention is represented in the accompanying drawing, in which:  
     [0015]FIG. 1 shows an injection unit with the arrangement of the rotating motor between the pressure bellows and the screw  
     [0016]FIG. 2 shows a ballscrew with disk brake  
     [0017]FIG. 3 shows a hollow-shaft motor as a rotating motor and springs for the adjustment of the bellows  
     [0018]FIG. 4 shows an injection unit with a connecting shaft passed through the annular bellows. 
    
    
     [0019] In this case, FIG. 1, FIG. 3 and FIG. 4 show an injection-molding machine  11  with a screw  12  arranged in a cylinder  13 . The screw is connected to a connecting shaft  14 . Provided on the cylinder  13  is a filling hopper  15 .  
     [0020] Furthermore, a pressure bellows  31  is arranged between a fixed pressure plate  71  and a movable pressure plate  72 . The pressure bellows  31  is connected via a pressure line  54  to a pressure accumulator  53 , which is in connection with a pump  52  via a guiding device  51 . Arranged on the pressure line  54  is an adjusting valve  38 .  
     [0021] In FIG. 1, the first actuator is an electric motor  21 , which is in connection with the connecting shaft  14  via a gear mechanism  24 . In the present example, the electric motor  21  is supported on the movable pressure plate  72 .  
     [0022] A nut/spindle unit  34 ,  35 , which is connected—in the upper part of the figure via a gear mechanism  74 —to a motor  75 , is provided as adjusting elements for the pressure plate  73 ,  72 .  
     [0023] The connecting shaft  14  is rotationally mounted in a connecting bearing  16  connected to the movable pressure plate.  
     [0024] In FIG. 2, the nut  34  is arranged in the movable pressure plate  72 . The nut  34  is in operative connection with a ballscrew  35 , which is mounted in the fixed platen and, arranged on the ballscrew  35 , on the side of the fixed pressure plate  71  facing away from the bellows  31 , is a disk brake  36 . The disk brake  36  is in metrological connection with a speed sensing means  41 , which is connected to a measuring and regulating device  42 .  
     [0025] The pressure bellows  61 , constructed here as rubber, is connected to the pressure accumulator  53  via the pressure line  54 .  
     [0026] In FIG. 3, the connecting shaft  14  is driven by a hollow-shaft motor  22 , which is designed as a reluctance motor  23 .  
     [0027] The connecting shaft  14  is mounted in a connecting bearing  16  connected to the movable pressure plate  72 .  
     [0028] Provided as the adjusting element of the pressure bellows  31 , in the upper part of the figure, is a spring  33 , which is in operative connection with the pressure plates  71  and  72 .  
     [0029] In the lower part of the figure, the pressure bellows is designed as a metallic compensator  62 , the compensator being operatively connected as a spring to the pressure plates  71  and  72 .  
     [0030] In FIG. 4, the connecting shaft  14  is guided up to the side of the fixed pressure bellows  71  remote from the screw  12 . The connecting shaft  14  is rotated by an electric motor  21 , which is axially movable on a rail.  
     [0031] A counter-bellows  37 , which at one end leans against the movable pressure plate, on which the pressure bellows  31  is also supported, and at the other end connected to a second fixed pressure plate  73  is provided as an adjusting element.  
     [0032] The pressure bellows  31  and the counter-bellows  37  are connected to the pressure actuator  53  via pressure line  54  or  55 , via an adjusting valve  38 .  
     [0033] Also arranged on the screw/cylinder unit  12 ,  13  is a pressure gage, which is connected to a measuring and regulating device  44 , which is connected in control terms to the adjusting valve  38 .  
                               List of items                                            Injection                             11   Injection-molding machine           12   Screw           13   Cylinder           14   Connecting shaft           15   Filling hopper           16   Connecting bearing                         Rotation                             21   First actuator, electric motor           32   Hollow-shaft motor           23   Reluctance motor           34   Gear mechanism           35   Rail                         Axial movement                             31   Second actuator, pressure bellows           32   Adjusting element           33   Spring           34   Nut           35   Spindle           36   Brake           37   Counter-bellows           38   Adjusting valve                         Measuring                             41   Speed sensing means           42   Measuring and regulating device, brake           43   Pressure gage           44   Measuring and regulating device, bellows                         Filling                             51   Filling device           52   Pump           53   Pressure accumulator           54   Pressure line (31)           55   Pressure line (37)                         Material                             61   Rubber           62   Metal compensator                         Plates                             71   Fixed pressure plate           72   Movable pressure plate           73   Second fixed pressure plate           74   Gear mechanism           75   Drive