Abstract:
A device for the production of film tubes includes a die head having an annular nozzle, from which a plastic melt for producing the film tube can be extruded in a transport direction (y), a fluid-application device, which is annular in shape at least in certain regions and which follows the die head in the transport direction (y) and which surrounds the film tube annularly, and via which a fluid can be guided toward the film tube, and a ring, the diameter of which is larger than the annular nozzle of the fluid-application device. The device has an adjusting device, via which the ring can be adjusted in height relative to the fluid-application device.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a national stage of PCT/EP10/066248 filed Oct. 27, 2010 and published in German, which claims the priority of German number 10 2009 046 539.1 filed Nov. 9, 2009, hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The invention relates to a device for the production of film tubes as defined in the generic clause of claim  1  and a method as defined in the generic clause of claim  8 . 
     2. Description of the Prior Art 
     Film tubes are usually produced by means of blow-extrusion devices and methods. For this purpose, a die head is used, to which one or more melt streams made of plasticized plastics are supplied. Each melt stream is distributed in the form of a ring as uniformly as possible in the die head. If several melt streams are supplied, the individual melt layers are combined together. The thus molded single-layer or multilayered tube leaves the die head through an annular nozzle in a transport direction. 
     In order to cool down the film tube as rapidly as possible and bring it to a stable form, at least one fluid-application device, which surrounds the film tube annularly at least in certain regions, follows the die head in the transport direction. Air is frequently provided as the fluid, but other fluids, more particularly gaseous ones, are also possible. The fluid can be cooled or heated in sectors in order to be able to locally influence the thickness of the film tube. Its flow rate can also be modified. 
     The fluid is likewise conveyed by the fluid-application device and also by the film tube in the transport direction. After the fluid leaves the fluid-application device, a pressure equalization with the ambient air takes place, so that the cooling effect reduces rapidly. 
     The fluid-application device usually has a very limited overall height since the film tube is expanded in the radial direction by means of an internal pressure that is slightly higher than the ambient pressure. This determines the size of the film tube. 
     In order to increase the cooling effect of the fluid, the document CA 2 155 135 C suggests the provision of a ring that concentrically surrounds the annular region of the fluid-application device and projects above the same in the transport direction. Specifically, this means that the ring, which can be made of Plexiglas, is attached to the top end of the annular region. The ring can be followed by an additional ring in each case. Each additional ring has a larger diameter as compared to the preceding ring and is kept at a distance from the latter in the radial direction by means of spacers and is attached to the top edge of the preceding ring by means of screws. As a result of these rings, the cooling air remains longer on the film tube and the cooling effect is thus improved. Open regions are provided between the annular region and the ring or between two rings, and a pressure equalization can further take place through these open regions. Usually, additional air is drawn in through these open regions (known as the chimney effect) that can unfold an additional cooling effect. Since more heat per unit of time can now be released from the film tube, the production rate of the film tube is increased. 
     However, the solution suggested in CA 2 155 135 suffers from the shortcoming that the rings can be adjusted only by dismounting and mounting other rings when the tube size is changed. Furthermore, the annular nozzle of the die head is poorly accessible, which is a disadvantage particularly at the start of production when the melt oozing out of the annular nozzle must be pulled off manually. 
     SUMMARY OF THE INVENTION 
     It is therefore the object of the present invention to suggest a device described below and a method for the production of film tubes that overcome these disadvantages. 
     This object is achieved by a device and by a method as described herein. 
     Thus an adjusting device is provided, by means of which the ring can be adjusted in height relative to the fluid-application device. In this way, the ring surrounding the annular portion of the fluid-application device can first be held in a position in which said ring does not or does not substantially project above the annular portion of the fluid-application device. Thus the annular nozzle is easily accessible, which is important for the start of production. As soon as production has started successfully and the film tube has achieved a sufficiently stable shape, the ring can be shifted in the transport direction of the film tube by means of the adjusting device. Since the transport direction is usually vertical and is bound upward, mention is made of the term “height adjustment” in the context of the adjustment process for the sake of convenience. The amount of adjustment can be selected in dependence of the diameter of the blown film. If the film tube is made of the same film material, the diameter is larger at a higher internal pressure than at a lower internal pressure. In the first case, the ring is then not shifted as far as in the second case. Thus the optimum cooling effect can be achieved for blown film of any diameter by means of the device of the invention. It is now no longer necessary to replace the ring for enabling an adjustment of the ring to the diameter of the blown film. 
     In a further advantageous embodiment of the invention, provision is made for the ring to be surrounded concentrically by an additional ring in each case. Each ring can be adjusted in height relative to the fluid-application device and relative to the ring surrounded by this ring by means of the adjusting device. A separate adjusting device can be assigned to each ring that adjusts the ring relative to the surrounded ring. In this case, the heights of the individual rings are selected such that they can adapt effectively to the shape of the blown film, which results in a good cooling effect. However, provision can also be made for a common adjusting device that shifts all the rings at the same time. Such an adjusting device can be easier to construct mechanically. 
     In an advantageous embodiment of the invention, provision is made for the adjusting device to comprise support members which extend in the transport direction of the film tube and which rest on the fluid-application device and/or the rings. The support members have inclined guide grooves that extend approximately in the form of a helix. Each ring comprises inwardly extending pins, and each pin engages in a guide groove. A height adjustment is carried out by means of a simple rotation of the ring. Since the rings are easily accessible from the outside, this type of adjustment can be carried out manually. Said adjustment can be carried out by a single individual. 
     It is further advantageous if each ring can be locked in place on the ring that it surrounds or on the fluid-application device. While there is no requirement of a locking mechanism for the rings in a simple embodiment as there is sufficient static friction, it is advisable to provide locking means. These locking means can include a clamping screw, a clamping element, a normal screw or a pin that can engage in a bore. 
     It is also advantageous if the guide grooves comprise groove extensions extending in the direction of the gravitational force. Thus the rings can be hooked into these groove extensions or snapped into place in the same. Locking means are not required in this case. 
     In a further, advantageous embodiment of the invention, there is at least one electromotor drive provided for the height adjustment, by means of which the ring or the rings can be adjusted in height. The electric motor can act upon, for example, the spindle or the spindle nut of a spindle/spindle nut combination. Many other mechanical, adjustable connections are also possible. 
     More particularly, it is possible that at least one electromotor drive is assigned to each ring. Thus the relative positions of the individual rings can be adjusted without manual intervention. It is advantageous to provide a plurality of electromotor drives when the device involves automated production of blown film. For example, the internal pressure of the blown film can be adjusted by a control device. The individual electric motors for positioning the rings can also be controlled according to these control instructions. 
     Additional exemplary embodiments of the invention are revealed in the figures and the following description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the individual figures: 
         FIG. 1  is a schematic diagram of a device of the invention in a side view 
         FIG. 2  is a perspective view of the device of the invention 
         FIG. 3  is a further perspective view of the device of the invention 
         FIG. 4  is a perspective view of a further embodiment of the device of the invention 
         FIG. 5  is a perspective view of another embodiment of the device of the invention. 
         FIG. 6  is a perspective view of one more embodiment of the device of the invention. 
         FIG. 7  is a view taken along the line VII-VII marked in  FIG. 6 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
       FIG. 1  is a side view of a schematic diagram of a device  1  of the invention for the production of film tubes, the schematic diagram being bisected by the dashed line  2  denoted by the arrow. The left half shows the device during operation, whereas the right half shows the device of the invention in a non-operating state. The arrow at the top of the dashed line also shows the transport direction y of the film tube  3 . 
     The left half of the figure shows the film tube  3  as it leaves the annular nozzle  4  of the die head  5 . The film tube increases in width when viewed in the transport direction y. The film tube  3  can be stretched readily, that is, expanded in the radial direction in its unsolidified state as it leaves the nozzle  4 . This is achieved by building up a slight positive pressure in the interior of the film tube  3 . For this purpose, a so-called internal cooling device  6  is provided that starts from the die head and extends into the interior of the film tube  3 . The air required is supplied by means of corresponding bores and/or lines in the die head  5 . Cooling air is discharged from orifices made in the external periphery of the internal cooling device  6 . The cooling air is directed at the internal wall of the film tube in order to achieve a cooling effect. The positive pressure causes the film tube to expand increasingly, as indicated by way of example by the shape of the film tube in the figure, until the tube reaches the so-called frost line. Air that has heated up as a result of this process is removed from the interior of the blown film by means of the air exhaust  7 . The arrows  8 ,  9 ,  10 , and  11  show the air flow. 
     An external cooling device  12  is disposed above the die head  5 . Said external cooling device  12  extends completely around the film tube  3  and can be lifted relative to the die head  5  by lifting devices  13 . The direction of movement in or against the transport direction y is denoted by the arrow  14 . The left half of  FIG. 1  shows the external cooling device in a lifted position. A coolant is supplied to the external cooling device  12  by means of supply pipes  15 . The temperature of this coolant, preferably air, can be controlled in sectors in the manner known per se. The coolant stream can now be divided into smaller streams by various separators. A resulting first portion of the coolant stream can be guided at the wall of the film tube  3  at right angles thereto, while a second portion is deflected and guided in a direction extending parallel to the film tube  3 . 
     The external cooling device  12  comprises an annular region  17  at the top end of which an annular border  18  is provided. This annular border is connected to the annular region of the external cooling device  12  by means of a thread (not shown in the figure). The annular border comprises orifices (not shown in detail), by means of which a pressure equalization can take place with the ambient air, as shown by the arrow  19 . 
     The annular border  18  is surrounded by a first ring  20  that can be adjusted by means of an adjusting device  21  relative to the external cooling device  12  in and against the transport direction of the film tube  3  (see arrow  22 ). The adjusting device  21  is merely indicated by a dotted line in  FIG. 1 . Specific embodiments of the adjusting device are explained with reference to  FIGS. 3 to 5 . The adjusting device  21  is supported on the external cooling device  12 . The ring  20  is followed by the rings  23  and  24 , each of which has a larger diameter so that the rings encircle each other. The right half of  FIG. 1  shows the rings  20 ,  23 ,  24  in their lowered position, in which they barely project above the annular border and thus do not restrict or do not considerably restrict access to the annular nozzle  4  of the die head  5 . The left half of  FIG. 1  shows that the rings  20 ,  23 ,  24  can be moved along the arrow  22 . In the case illustrated, the ring  23  is supported on the ring  20 , and the ring  24  on the ring  23 . The supports  27  are in the form of open constructions and are therefore shown in the form of dotted lines. This means that wide regions between the ring  20  and the ring  23 , and between the ring  23  and the ring  24 , respectively, are open so that a pressure equalization can take place through these open regions. Depending on pressure conditions, the air can flow in one of two flow directions indicated by the double arrow  25 . The air flow along the external periphery of the film tube  3  is shown by the arrow  26 . The flow within the rings  20 ,  23 ,  24  usually results in a negative pressure at the open regions between the rings so that additional air is supplied through the open regions and this additional air ensures a further cooling effect. 
     Advantageously, the rings are made of Plexiglas so that the film tube  3  can be observed. The rings, however, can also be made of other plastics and also of metals such as aluminum, which is light by itself. Additional materials such as glass are also feasible, in principle. However, light materials are preferred. 
       FIG. 2  is a perspective view of the device of the invention as shown in the right half of  FIG. 1 , that is, all the rings  20 ,  23  and  24  are located in their lowered position. The annular nozzle  4  that can be accessed easily for starting the extrusion process and also for cleaning purposes can be seen in this illustration. 
       FIG. 3  shows a first embodiment of the adjusting device  21 . A support plate  28  rests on the surface of the external cooling device. For this purpose, the plate  28  can comprise a beveled portion  29 . Only one plate  28  is shown in the figure, but it is advisable to provide at least three, more particularly four, such plates  28 . The plate  28  comprises a groove  30  extending upwardly at an angle. A pin  31  that is inserted into the wall of the ring  20  and that extends inwardly in the radial direction engages in this groove. By a rotation of the ring  20  counterclockwise, it is lifted so as to correspond to the course of the groove  30  at the same time. In order to prevent the ring  20  from slipping back into its initial position, the groove can be provided with a plurality of extensions, one  32  of which is shown in the figure. The groove extensions represent various snap-in stops and thus various heights that can be selected only discretely. The ring  20  carries a plate  33  that comprises a groove  34  which likewise extends upwardly at an angle and in which the pin  35  of the ring  23  engages. A plurality of plates  33  can be distributed on the periphery of the ring  20 . The ring  23  can be locked in place on the ring  20  simply in that the internal periphery of the ring  23  presses against the plate  33  so that there results a static friction that is sufficient for securing the ring  23 . 
     The ring  23  can also be provided with plates  33  that comprise grooves  34 . The pins  35  of the ring  24  engage in these grooves  34 . A further possibility of locking the ring is illustrated by means of the ring  24 . In this case, a knob  36  is provided, by means of which a screw, which passes through a threaded hole, can be rotated against the ring  23  or against the plate  33  of the ring  23 . 
     Various possibilities of locking the rings are illustrated in  FIG. 3 , and these possibilities are naturally applicable to all the rings. 
     The height of all the rings is adjusted by means of rotation. Since each ring is supported only by the nearest inner ring, the height of every ring can be adjusted independently. The heights of the rings can therefore be adjusted easily and optimally to suit the shape of the film tube  3  (not shown in this figure). 
       FIG. 4  shows an embodiment of the adjusting device. In this case, an outwardly protruding support piece  37  that is attached to the ring  23  supports a rod  38  that extends into a bore inserted in the ring  24 , for example. For the purpose of height adjustment, the ring  24  can now be moved relative to the ring  23  in the y direction and locked in the desired position by means of the fixing screw  40 . In an embodiment provided with an electric motor (not shown in the figure), the rod could be in the form of a threaded rod that is then set into rotation by the electric motor. The bore  39  would then be in the form of a threaded hole, into which the rod  38  is screwed. The rotation of the rod  38  results in an adjustment of the height of the ring  24 . The electric motor could rest on the support piece  37 . A plurality of such arrangements (not shown in the figure) would have to be provided on the rings  20  and  21  and on the external cooling device  12 . 
     A further exemplary embodiment of the invention is shown in  FIG. 5 . The basic construction of the device corresponds to  FIG. 3 . In this case, the ring  24  comprises a toothed-ring segment  41  on its external surface that meshes with a shaft  42  that is in the form of a toothed wheel over its entire length. The shaft  42  is driven by a worm gear  43  that is set into rotation by the electric motor  44 . A common drive system for all rings  20 ,  23  and  24  is made possible by means of this embodiment. Starting from the lowered position, the ring  24  is rotated first and thus lifted. Then the ring  24  entrains the ring  23  and then the ring  23  entrains the ring  20  until all the rings are lifted. In order to enable the individual adjustment of each ring, the drive system shown can be provided for every ring. 
     The embodiment shown in  FIG. 6  is a slight modification of the one shown in  FIG. 3 . In  FIG. 6 , the groove extensions  32  are replaced with flat portions  43 . These flat portions  43  have horizontal or sloping edges, the term “sloping” referring to the counterclockwise direction of rotation. In contrast to the use of the groove extensions  32 , it is not necessary to lift the nearest ring  20  in the case of these flat portions in order to reach the nearest snap-in stop. Rather, it is sufficient to apply slightly increased effort in the direction of rotation. 
     Instead of the support plate  28  being made to rest on the surface of the external cooling device, the support plate  28  can also be attached to the annular border  18 , as shown in  FIG. 6 , which results in slightly reduced assembly effort. 
     An alternative to the pin  31  or  35  is explained by means of the exemplary embodiment shown in  FIG. 6 . The pins  31 ,  35  are replaced with guide elements  50  that are explained in more detail with reference to  FIG. 7 . 
       FIG. 7  shows a preferred embodiment of the ring  23 . The ring  23  is composed of two rings  51  and  52  that are located on top of each other and can be made of metal, for example, aluminum. Grooves, into which circular arc-shaped spacers  53  are inserted, can be made in the surfaces of these rings facing each other. Provision can be made for one circumferentially extending spacer  53 ; however, a plurality of spacers is also feasible that, taken together, extend around the circumference of the rings. The rings  51 ,  52  can be connected to each other by the plates  33  and/or further fixing elements (not shown in the figure). The spacers  53  are made of Plexiglas, for example, that is light and enables the blown film to be observed. Aluminum, being an even lighter metal, can be used for the spacers. The use of other metals such as steel is also possible for this purpose. The rings  20  and  24  can be constructed exactly like the ring  23 . 
     The guide element  50  comprises a basic element  54  that is inserted through a bore in the ring  51  of the ring  24  and is fixed suitably. The basic element  54  can support a head  55 . The basic element and the head can also be formed integrally, for example, in the form of a screw that is screwed into the ring  51 . A spacer  56  is slid or screwed onto the basic element  54 . Furthermore, the basic element  54  supports a guide roll  57  that can be rotated on the basic element  54 , but that cannot be moved in the axial direction. This guide roll runs along the groove  34  of the plate  33  and it thus enables a movement of the ring  24  relative to the ring  23  which takes place without excessive effort. The guide roll can be made of brass, for example, or similar suitable materials so that the friction between the roller  57  and the basic element  54  is as low as possible. Ball and roller bearings can also be provided between the guide roll  57  and the basic element for this purpose. Apart from the portion that rolls in the groove  34 , the guide roll also comprises a bridge  58  that has an enlarged diameter and that prevents the guide element  50  from moving in a direction relative to the groove. Since there are at least three such guide elements provided over the circumference of the ring  24 , a radial movement of the ring  24  relative to the ring  23  is prevented in this way. 
     The embodiments shown are only examples. Features of the examples shown can be combined with each other. Other exemplary embodiments will also be readily apparent to a person skilled in the art and these could be used without going beyond the idea of the invention. 
     The invention being thus described, it will be apparent that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be recognized by one skilled in the art are intended to be included within the scope of the following claims. 
     
       
         
               
             
               
               
             
           
               
                   
               
               
                 List of reference numerals 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 1 
                 Device for the production of film tubes 
               
               
                 2 
                 Dashed line 
               
               
                 3 
                 Film tube 
               
               
                 4 
                 Annular nozzle 
               
               
                 5 
                 Die head 
               
               
                 6 
                 Internal cooling device 
               
               
                 7 
                 Air exhaust 
               
               
                 8 
                 Air flow inside the film tube 
               
               
                 9 
                 Air flow inside the film tube 
               
               
                 10 
                 Air flow inside the film tube 
               
               
                 11 
                 Air flow inside the film tube 
               
               
                 12 
                 External cooling device 
               
               
                 13 
                 Lifting device 
               
               
                 14 
                 Arrow 
               
               
                 15 
                 Supply pipe 
               
               
                 16 
                 Separator 
               
               
                 17 
                 Annular region 
               
               
                 18 
                 Annular border 
               
               
                 19 
                 Arrow 
               
               
                 20 
                 First ring 
               
               
                 21 
                 Adjusting device 
               
               
                 22 
                 Arrow 
               
               
                 23 
                 Ring 
               
               
                 24 
                 Ring 
               
               
                 25 
                 Double arrow 
               
               
                 26 
                 Arrow 
               
               
                 27 
                 Support 
               
               
                 28 
                 Support plate 
               
               
                 29 
                 Beveled portion 
               
               
                 30 
                 Groove 
               
               
                 31 
                 Pin 
               
               
                 32 
                 Groove extension 
               
               
                 33 
                 Plate 
               
               
                 34 
                 Groove 
               
               
                 35 
                 Pin 
               
               
                 36 
                 Knob 
               
               
                 37 
                 Support piece 
               
               
                 38 
                 Rod 
               
               
                 39 
                 Bore 
               
               
                 40 
                 Fixing screw 
               
               
                 41 
                 Toothed-ring segment 
               
               
                 42 
                 Shaft 
               
               
                 43 
                 Flat portion 
               
               
                 44 
               
               
                 45 
                 Worm gear 
               
               
                 46 
                 Electric motor 
               
               
                 47 
               
               
                 48 
               
               
                 49 
               
               
                 50 
                 Guide element 
               
               
                 51 
                 Ring 
               
               
                 52 
                 Ring 
               
               
                 53 
                 Spacer 
               
               
                 54 
                 Basic element 
               
               
                 55 
                 Head 
               
               
                 56 
                 Spacer 
               
               
                 57 
                 Guide roll 
               
               
                 58 
                 Enlarged bridge 
               
               
                 y 
                 Transport direction of the film tube 3