Abstract:
A method of cooling blown film consisting of thermoplastic plastics during the production of blown film by means of a blown film extruder with a film blowing head which comprises an annular nozzle from which the blown film emerges and is guided away in an extraction direction, wherein at least two cooling gas flows are made to approach the blown film from the outside in at least two blowing-out planes located at a distance from the annular nozzle, wherein at least one cooling gas flow K G  is blown out in the direction opposed to the extraction direction of the blown film and wherein at least one cooling gas flow K A  is blown out in the extraction direction of the blown film, and wherein, at least one of the cooling gas flows K G , K A  can be controlled around their circumference in sectors, at least in respect of its volume flow or temperature.

Description:
BACKGROUND AND SUMMARY OF THE INVENTION 
     The invention relates to a method of cooling blown film comprising thermoplastic plastics during the production of blown film by means of a blown film extruder with a film blowing head which comprises an annular nozzle from which the blown film emerges and is guided away in an extraction direction. At least two cooling gas flows are made to approach the blown film from the outside in at least two blowing-out planes located at a distance from the annular nozzle. The invention also relates to a device for cooling blown film comprising of thermoplastic plastics during the production of blown film arranged at a blown film extruder with a film blowing head comprising an annular nozzle from which the blown film emerges and is guided away in an extraction direction. At least two annular cooling gas nozzles are arranged at a distance from the annular nozzle from at least two blowing-out planes for cooling gas. 
     The blown film can be produced and extracted along a vertical longitudinal axis A, and, an extraction direction can extend from the bottom to the top. The annular nozzle can be aligned in a corresponding direction. Alternatively, if the annular nozzle is suitably aligned, the extraction direction can be orientated from the top to the bottom. 
     As described herein, the extraction direction is generally provided from the bottom to the top. However, alternative embodiments and methods according to the invention can be provided wherein the extraction direction is from the top to the bottom. 
     For the output performance and thus for the economic efficiency of the above-mentioned method of producing blown film and of the devices involved, the process of cooling the blown film at the time of its exit from the annular nozzle up to the point in time of reaching a freezing limit comprises an important factor, wherein output rate can be increased by improving the cooling effect. 
     For cooling purposes, dual cooling rings can be provided and which can be arranged directly above the annular nozzle and can comprise a uniform cooling ring housing. Cooling gas nozzles can be provided, which form two blowing-out planes for cooling gas. An example of cooling gas is described in U.S. Pat. No. 5,804,221 A. 
     For improving the cooling effect further, double cooling rings can be provided wherein two independent cooling ring housings can be arranged one behind the other and can be spaced from one another in the direction of production, with the lower cooling ring being mounted directly on the film blowing head and with the upper cooling ring being arranged in such a way that its height is adjustable relative to the lower cooling ring. When the blown film enters the upper cooling ring, it can have been pre-cooled by the lower cooling ring. In this case, the effect of the upper cooling ring can be adversely affected in that the cooling gas emerging from the lower cooling ring has already been heated along the blown film and enters the upper cooling ring from below. Furthermore, access to the annular nozzle, which is important when starting the system, can be complicated by the lower cooling ring positioned on the film blowing head. A similar such device is described in EP 1 719 602 A1 for example. 
     In DE 32 43 884 A1, a method is described for delivering cooling air during the production of a film tube in the extraction direction. These cooling rings are provided with an annular channel being supplied via a single air supply neck. Cooling rings of similar design are shown and described in JP 59-007 019 A, in JP 58-191 126 A and in JP 58-094 434 A. 
     OBJECTS OF THE INVENTION 
     One object of the present invention is to provide a method and a device of the initially mentioned types wherein the cooling effect can be improved, and thereby extraction speed of the blown film can be increased and consequently the output rate of the device can be increased. A further object is avoidance of loss in quality of the blown film produced. 
     One of the objectives can be achieved by using a method of the above-mentioned type wherein at least a first cooling gas flow K G  is blown out in a direction opposed to the extraction direction of the blown film. In addition, at least one further cooling gas flow K A  is blown out in the extraction direction of the blown film. At least one of the cooling gas flows K G , K A  can be controlled around their circumference in sectors at least in respect to its volume flow and/or its temperature. Preferably the cooling gas flow K A  blown out most near to the annular nozzle is blown out in the direction opposed to the extraction direction of the blown film, and the cooling gas flow K A  blown out most distant from the annular nozzle is blown out in the extraction direction of the blown film. A mutual disturbance or interference of the cooling gas flows can thereby be avoided. The first blowing-out plane can be arranged at some distance from the annular nozzle. An important aspect which leads to an increase in the cooling effect is that cooling gas already heated from the first blowing-out plane can be prevented from entering the region of the further blowing-out plane or planes in the extraction direction. Furthermore, cooling by the first cooling gas flow K G —directed in the direction opposed to the extraction direction—can be provided in accordance with the above described counter flow cooling principle. Namely, the freshly introduced cooling gas can be provided to be relatively coldest in that region where a reduced blown film temperature has already been achieved, whereas in the region where the blown film is still hot upon leaving the annular nozzle, the cooling gas has already been slightly heated. In this way it is possible to maintain a relatively uniform, adapted temperature difference along the entire cooling path, and thereby produce the most advantageous cooling effect. The increased thickness deviations that can result when increasing output rate can thus be compensated by providing the controllable cooling in sectors around the circumference of the blown film in accordance with the invention. 
     A method and device according to the invention are provided wherein at least one of the cooling gas flows K G , K A  can be controlled in respect to its volume flow around the circumference in sectors. In addition or in the alternative, the temperature of the cooling gas flows can be influenced around the circumference in sectors. In this way it is possible to minimize any deviations in the thickness profile of the blown film around the circumference during the production process, with use being made of the effect that during the process of blowing the film, i.e. when widening the tube diameter, hotter regions are widened to a greater extent than cooler regions. In the case of a greater cooling effect in one circumferential sector, the blown film cools more quickly and can be expanded to a lesser extent and thus can retain its relatively greater film thickness. If the cooling effect is less pronounced in one circumferential sector, the blown film can be made to retain a higher temperature and can thus be expanded to a greater extent, and as a consequence, the film thickness can be reduced to a greater extent. The differences in film thickness around the circumference can be determined by a measuring device and transmitted to a control device for the purpose of varying the cooling or heating output. In one embodiment, a measuring device can be arranged in the direction of production at a point behind a freezing limit of the film material, behind which freezing limit, the film material may not be plastically expanded. A device which permits variable cooling of the blown film in sectors is described in EP 1 736 297 A1. 
     As the first cooling gas flow K G  can be provided to be blown out against the extraction direction and is effective according to the counter flow cooling principle; a second cooling gas flow K A  can also be provided to be blown out in the extraction direction, and which flows off along the blown film so as to be relatively undisturbed by the first cooling gas flow. The first cooling gas flow K G  can be substantially removed from the region, or sucked off substantially annularly in the region of the annular nozzle, so that any gas emissions from the blown film, which are most pronounced in the region directly adjoining the annular nozzle, can be removed together with the first cooling gas flow. The system parts following in the extraction direction are thus prevented from being polluted. The second cooling gas flow K A  which is blown out in the extraction direction no longer has any major effects after the blown film has reached the so-called freezing limit. However, in the interest of preventing an adjoining calibrating device and/or flattening device from being polluted, it can also be advantageous to suck off or substantially remove the second cooling gas flow K A , which can be annularly distributed around the circumference. A device providing gas removal is described in EP 1 491 319 A1. 
     According to an advantageous embodiment of a process according to the invention, at least one of the cooling gas flows K G , K A , can be formed by at least two partial flows K G   1 , K G   2 , K A   1 , K A   2  emerging in different blowing-out planes. It is thus possible to increase the cooling gas quantity without adversely affecting the shape of the blown film. 
     In one embodiment, the distance of the blowing out plane of the at least one cooling gas flow K G  blown out against the extraction direction of the blown film from the annular nozzle can be provided to be constant. However, for setting the cooling effect, it can be advantageous to adjust this distance and thereby permit the length of the cooling path to be influenced directly. In addition, for a starting phase of a system according to the invention, it can be advantageous if the distance can be increased, and free access provided to the annular nozzle. 
     In a further embodiment of the invention, the distance of the blowing-out plane of the at least one further cooling gas flow K A  blown out in the extraction direction of the blown film from the annular nozzle and, respectively, from the blowing-out plane of the first cooling gas flow K G  can be adjustable for changing the cooling effect. 
     In accordance with the above-mentioned processes, an embodiment of a device according to the invention can be provided wherein at least a first annular cooling gas nozzle is directed against the extraction direction of the blown film and wherein at least a further annular cooling gas nozzle is directed in the extraction direction of the blown film. In addition, circumferentially variably controllers can be provided in sectors for controlling the volume flow. In addition, or in the alternative, the circumferentially variably controllers can be provided in sectors for controlling the temperature of the cooling gas flow of at least one of the annular cooling gas nozzles. In addition, or in the alternative, at least two annular cooling gas nozzles can be provided and directed in the extraction direction of the blown film. In addition, or in the alternative, at least two annular cooling gas nozzles can be provided and directed opposed to the extraction direction of the blown film. In addition, or in the alternative, at least two annular cooling gas nozzles can be provided and directed opposed to the extraction direction of the blown film. In order to avoid disadvantageous effects of the emissions emitted by the blown film after having left the annular nozzle, it is proposed that, between the annular nozzle of the film blowing head and the first annular cooling gas nozzle directed against the extraction direction of the blown film, a gas removal or a sucking-off device can be provided for cooling gas, which gas removal device can be provided to extend and/or be distributed around the circumference. The gas removal device can be comprised of individual gas-removal elements attached to hoses, as a result of which mounting and dismantling procedures can be simplified. To protect the film blowing head from cooling down, which is preferably kept at a constant temperature, an annular thermal insulator or an annular deflection plate can be provided above the film blowing head. 
     In an embodiment of the invention, at least one annular cooling gas nozzle can be provided and directed against the extraction direction of the blown film and the at least one annular cooling gas nozzle can be directed in the extraction direction of the blown film. These nozzles can comprise a common cooling ring or cooling ring module. In an embodiment of the invention, one common annular chamber can be provided to be supplied with cooling gas via circumferentially distributed connecting sleeves, and prior to the cooling gas finally leaving the cooling ring module, the cooling gas can be divided into individual cooling gas flows. 
     According to an alternative embodiment, at least one annular cooling gas nozzle can be directed against the extraction direction of the blown film and can constitute an element of a first cooling ring or cooling ring module. The at least one annular cooling gas nozzle can be directed in the extraction direction of the blown film and can constitute an element of a second cooling ring or cooling ring module. These two modules, too, can be supplied by one single cooling gas blower, with the cooling gas flow being divided in front of the cooling ring modules. However, it is also possible to provide a dedicated blower for each cooling ring module for ensuring a separate cooling gas supply. Providing two cooling ring modules is advantageous in that the distance between them can be varied, so that in addition to controlling the cooling gas quantity, the length of the cooling path can be varied too, if desired. The two cooling ring modules can be supplied with respective adjusting devices. Between the first cooling ring module and the second cooling ring module a further cooling ring in form of a disc-shaped housing can be arranged. 
     Further design details will be explained below with reference to the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of devices according to the invention are illustrated in the drawings and will be described below. 
         FIG. 1 , in a vertical longitudinal section, illustrates a film blowing system with a cooling ring which forms an annular cooling gas nozzle pointing against the extraction direction, and two annular cooling gas nozzles pointing in the extraction direction. 
         FIG. 2  illustrates a cooling ring according to  FIG. 1  with a cooling gas flow which can be controlled in sectors in the volume flow. 
         FIG. 3  illustrates details of a cooling ring according to  FIG. 2  in a cross-section through the cooling ring. 
         FIG. 4  illustrates the cooling ring which is similar to that shown in  FIG. 2 , with the temperature of the cooling gas flow being controllable in sectors. 
         FIG. 5  illustrates the cooling ring according to  FIG. 4 , as well as a gas removal device or sucking ring for cooling gas arranged above the film blowing head. 
         FIG. 6  illustrates a cooling device with two separate cooling rings connected to one another. 
         FIG. 7  illustrates details of the upper cooling ring according to  FIG. 6  in a cross-sectional view through the cooling ring. 
         FIG. 8  illustrates a cooling device with two cooling rings similar to those shown in  FIG. 6 , with a further cooling ring in form of a disc-shaped housing arranged therebetween. 
         FIG. 9  illustrates the disc-shaped housing according to  FIG. 8  in an axial view with volume flow control means. 
         FIG. 10  illustrates the disc-shaped housing according to  FIG. 8  in an axial view with temperature control means. 
         FIG. 11  illustrates the cooling device with two separate cooling rings connected to one another in a modified embodiment. 
         FIG. 12  illustrates a cooling device with two separate cooling rings, with the distance therebetween being adjustable. 
     
    
    
     DETAILED DESCRIPTION 
     The device shown in  FIG. 1  comprises a blown film extruder  10  with a film blowing head  11  which forms an annular nozzle  12  for producing a blown film  14 . The joint axis A of the film blowing head  11 , of the annular nozzle  12  and of the blown film  14  can be provided to extend vertically. The extraction direction of the blown film can extend from the bottom to the top. 
     Above, and at a distance from the film blowing head  11 , a co-axially arranged cooling ring  13  can be provided which can emit cooling gas for cooling the blown film  14  and whose details of the embodiment shown here will be explained in connection with  FIG. 2 . Inside the blown film  14  an inner cooling device  15  is provided with a gas removal device, i.e., an inner suction device  16  for further cooling gas. The cooling ring  13  can comprise one or more annular cooling gas nozzles which can generate via a venturi effect a widening effect on the blown film  14  so that the diameter of the latter can be increased in a thermo-plastically deformable phase until it has reached a freezing limit  17 . Above the freezing limit  17 , a mechanical calibrating device  18  can be provided in which the film diameter and film cross-section can be stabilised. As can be seen, the calibrating device  18  can be comprised of a plurality of rollers  19  and can be arranged substantially annularly around the blown film  14 . A calibrating device of the type shown here is described in greater detail in DE 20 2005 006 532 U1. 
     Above the calibrating device  18 , a flattening device  20  can be provided which also comprises a plurality of rollers  21 . The flattening device  20  can deviate from the calibrating device in that it is approximately wedge-shaped and can cause the round blown film to form into a flat film connected at the edges. Above the flattening device  20 , a pulling-off device  22  can be provided with two pulling-off rollers  23  which can convey and compress the blown film. The blown film can be further guided in the form of a double-layer flat film  24 , and optionally in a cut and coiled form. 
     In  FIG. 2 , any details identical to those shown in  FIG. 1  have been given the same reference numbers.  FIG. 2 , in a longitudinal section through the longitudinal axis A, the film blowing head  11  can be provided with the annular nozzle  12  for forming the blown film  14 . A thermal insulation disc  25  can be placed onto the film blowing head  11 . At a distance from the film blowing head  11 , a multi-part cooling ring  13  can be provided which can be connected to the film blowing head  11  via a height-adjustable holding device  26 . The cooling ring  13  can comprise an annular housing  27  forming an annular chamber  40 , and individual tangentially extending running-in sleeves  28  which can change into the annular chamber  40  via a rectangular cross-section and which, in a cross-sectional view, can form round attaching sleeves  29 . On the inside of the annular housing  27 , an annular exit gap  30  can be provided in which radial conducting webs  31  can calm the cooling gas flow. The annular exit gap  30  can be divided into a lower first annular channel  35  and two annular channels  36 ,  37  positioned there above and, via said channels, can supply an annular cooling ring nozzle  32  whose exit aperture can be directed against the extraction direction, as well as two annular cooling gas nozzles  33 ,  34  whose exit apertures can point in the extraction direction. At the cooling ring module  13 , a volume flow control device  43  can be arranged which can comprise an annular, radially slotted flat spring  44  positioned inside the annular chamber  40 , as well as circumferentially distributed individual setting elements  45  which can be controlled independently of one another and which can be enclosed by an annular housing  46 . 
     The inner contour of the cooling ring  13  can be provided to widen in the extraction and production direction and, together with the blown film, to generate a venturi effect, i.e., a pressure reduction on the cooling air and thereby a suction effect on the blown film. The effect of this forming method is that the diameter of the blown film  14  can be widened in the region of the cooling ring  13  because a vacuum can be provided at the exit of the cooling ring  13 , whereas at the same time an excess pressure can be generated inside the blown film by the above-mentioned inner cooling device. The widening of the blown film can be continued until the thermoplastic plastic material solidifies as a result of the cooling effects of the cooling gas, such as when the freezing limit has been reached. 
     An annular threaded insert  61  can be threaded in at the bottom end of the cooling ring  13 , and a threaded insert  62  can be threaded in at the top end of the cooling ring  13 . Thereby the threaded inserts  61 ,  62 , the gap width of the annular cooling gas nozzles  32  and  34  can be adjusted. Adjustment levers  38  can be connected to the threaded insert  61  and adjustment levers  39  are connected to the threaded insert  62 . 
     In the left-hand half of  FIG. 2 , the directions of the cooling gas flows are indicated by arrows. The two annular cooling gas nozzles  33 ,  34 , can allow the exit of cooling gas flows K A   1 , K A   2  in the extraction direction, and can be combined to form a cooling gas flow K A , whereas the annular cooling gas nozzle  32  can be provided to guide a cooling gas flow K G  along the direction of production of the blown film  14  until it hits the thermal insulation disc  25  on the film blowing head  11  from which, it can be deflected radially outward. 
       FIG. 3  shows a cooling ring  13  according to  FIG. 2  in a horizontal section. The cooling ring  13  is provided with the annular housing  27 , individual running-in sleeves  28  and round attaching sleeves  29 . In the annular chamber  40 , shown in section, the entire annular, inwardly radially slotted flat spring  44  can be fixed via circumferentially distributed screws  47  on the inside by a clamping ring  51 , and which can comprise individual inwardly directed tongues  48  which can be loaded by one of the adjusting elements  45 , and can be bent upwardly. The tongues  48  can each comprise a plurality of tongue ends  49  which engage radial channels  50  which can be formed by circumferentially guiding webs  31  in the exit gap  30 . In this way, it is possible to vary the free passage cross-sections of the radial channels  50 , with several channels being jointly controlled by one single adjusting element  45 . In additional, the volume flow can be controlled in sectors around the circumference of the annular exit gap  30 , so that the cooling effect on the blown film  14  can be controlled in such a way that a uniform film thickness can be achieved around the circumference, which film thickness can be measured during production from behind the freezing limit either continuously or at intervals. 
     In  FIG. 4 , any details identical to those shown in  FIG. 2  have been given the same reference numbers. To that extent, reference is made to the description of same. In the cooling ring module  13 , a temperature controlling device  73  can be provided which comprises circumferentially distributed, individual heating elements  74  which can be positioned in the annular exit gap  30  at the annular chamber  40  and which can be controlled independently of one another. Control and energy supply can be effected via an annular housing  75 . The remaining details have been described in connection with  FIG. 2 . 
     In  FIG. 5 , any details identical to those shown in  FIG. 4  have been given the same reference numbers. To that extent, reference is made to the description of same. An annular, inwardly opening suction device  41  can be placed onto the film blowing head, from which suction device  41 , the heated cooling gas can be extracted via individual circumferentially distributed sleeves  42 , and a filter element can be optionally added. The remaining details have been described in connection with  FIG. 2  and  FIG. 4 . 
     In  FIG. 6 , any details identical to those shown in  FIG. 2  have been given the same reference numbers. To that extent, reference is made to the description of same. A cooling ring  13  can be provided which can form two annular cooling gas nozzles  32 ,  52  directed against the extraction direction, and a second cooling ring  53  can be arranged above the cooling ring  13 , which second cooling ring  53  in this embodiment can form the two annular cooling gas nozzles  33  and  34  which can be directed in the extraction direction. The two cooling rings  13 ,  53  can be provided to rest on one another in a planar way and can be threaded to one another. The adjusting holding element  26  can engage directly at the lower cooling ring  13  and, as shown in  FIG. 2 , can be secured to the film blowing head  11 . 
     The cooling ring  13  can comprise an annular housing  27  and individual tangentially extending running-in sleeves  28  which, via a rectangular cross-section, can change into the annular chamber  40  and, in a cross-sectional view, form the round attaching sleeves  29 . On the inside of the annular housing  27 , an annular exit gap  30  can be provided in which radial conducting webs  31  can be provided to calm the cooling gas flow. The annular exit gap  30  is divided into a lower first annular channel  35  and a second annular chamber  55  positioned there above, and, via the channels, can supply two annular cooling gas nozzles  32 ,  52  whose exit apertures are directed against the extraction direction. 
     The cooling ring  53  can comprise an annular housing  57  forming an annular chamber  60 , and individual tangentially extending running-in sleeves  58  which, via a rectangular cross-section, can change into an annular chamber  60  and, in a cross-sectional view, form the round attaching sleeves  59 . On the inside of the annular housing  57 , an exit gap  70  can be provided in which radial guiding webs  71  can be provided to calm the cooling gas flow. The exit gap  70  is divided into two annular channels  36 ,  37  and, via the channels, can supply the two annular cooling gas nozzles  33 ,  34  whose exit apertures are directed in the extraction direction. 
     The entire inner contour of the cooling rings  13 ,  53  widens in the extraction and production direction and, together with the blown film, can generate a venturi effect, i.e., a pressure reduction acting on the cooling air and thereby a suction and widening effect on the blown film. The effect of said type of forming process is that the diameter of the blown film  14  can widen in the region of the cooling rings  13 ,  53 , because a vacuum is generated at the exit of the cooling ring  53 , whereas, at the same time, excess pressure can prevail inside the blown film as a result of the above-mentioned inner cooling device. The widening of the blown film can continue until the thermoplastic plastic material solidifies as a result of the cooling effects of the cooling gas, i.e. the freezing limit has been reached. 
     An annular threaded insert  61  is threaded in at the bottom end of the cooling ring  13 , whereas a threaded insert  62  is threaded in at the top end of the cooling ring  13 , by means of which threaded inserts  61 ,  62  the gap width of the annular cooling gas nozzles  32  and  34  can be adjusted. Adjustment levers  38 ,  39  are connected to the threaded inserts  61 ,  62 . 
     The cooling gas supply for the two cooling rings  13 ,  53  can be effected by a blower for each of the cooling rings, and the blowers or the supply channels can be controllable. Alternatively, it is possible to provide one single cooling blower for supplying both cooling rings  13 ,  53 . In the supply channels a controllable junction can be provided. In addition, or in the alternative, the blower can also be controllable. 
     At the lower cooling ring  13 , a temperature controlling device  73  can be provided which comprises an attached annular housing  75  and individually controllable, circumferentially distributed heating elements  74  in the exit gap  30 . This temperature controlling device can be used for the differentiated, circumferential control of the temperature of the cooling gas emerging against the extraction direction. At the upper cooling ring  53 , a volume flow controlling device  43  can be provided which comprises individually controllable, circumferentially distributed setting elements  45  which, via a journal, can act on a slide which can vary the cross-section of a circumferential region of the annular exit gap  70 . 
     The directions of the cooling gas flows are indicated by arrows in the left-hand half of the Figure. The annular cooling gas nozzles  33 ,  34  conduct the cooling gas along the blown film in the production and extraction direction, whereas the annular cooling gas nozzles  32 ,  52  allow cooling gas to flow along the blown film against the production direction until it hits the thermal insulation disc  25  at the film blowing head  11 . 
       FIG. 7  shows the cooling ring  53  according to  FIG. 6  in a horizontal section. As shown, the annular housing  57 , individual running-in sleeves  58  and round attaching sleeves  59  are provided. In the annular chamber  60 , shown in section, an exit gap  70  can comprise circumferentially distributed slide elements  72  which can be loaded by one of the adjusting elements  45  and set as a result. In this way, the respective free passage cross-sections of the radial channels  80  can be varied, with a plurality of channels being jointly controllable by one single adjusting element  45 . In this way, the volume flow can be controlled in sectors around the circumference of the annular exit gap  70 , so that the cooling effect on the blown film  14  can be varied in such a way that, around the circumference, it is possible to achieve a uniform blown film thickness, which, during production, is measured continuously or at intervals behind the freeze limit. 
     In  FIG. 8 , any details identical to those shown in  FIG. 6  have been given the same reference numbers. To that extent, reference is made to the description of  FIG. 2  and the additional description of  FIG. 6 . Two cooling rings  13 ,  53  can be provided which do not adjoin one another directly in a planar way, but can be connected via an intermediate disc-shaped housing  63  which can substantially comprise planar attaching faces and individual deepened radial channels  64  and a radially inwardly opening annular cooling gas nozzle  65 . Additional cooling gas can be supplied to the individual radial channels  64  via the individual supply lines  66 . 
     In  FIG. 9 , the disc-shaped housing  63  is shown in a plan view. Deepened milled radial channels  64  can be provided having supply lines  66  which can be combined at the inner circumference to form one single annular cooling gas nozzle  65 . A cooling gas blower  67  can be provided which, via a branch line  68  and individual control elements  69 , can variably control the individual supply lines  66  for the cooling gas. In this way, it is possible to achieve an effect which is similar to that of the volume flow control according to  FIGS. 2 and 3 . Only some of the lines  66  in the Figures have been shown in continuous lines and others in dashed lines in order to illustrate that all of the radial channels  64  can be controllably supplied with cooling gas by the supply lines  66 . 
     In  FIG. 10 , the disc-shaped housing  63  is shown in a plan view. Deepened milled radial channels  64  can be provided having supply lines  66  which, can be combined at the inner circumference to form one single annular cooling gas nozzle  65 . A cooling gas blower  67  can be provided which can variably control the temperature of the cooling gas in the individual supply lines via a branch line  68  and individual heating elements  79 . Thus, it is possible to achieve an effect which is similar to that of the temperature control according to  FIGS. 4 and 5 . Only some of the lines  66  in the Figures have been shown in continuous lines and others in dashed lines in order to illustrate that all the radial channels  64  can be supplied with cooling gas with a differentiated controllable temperature via supply lines. 
     In  FIG. 11 , any details identical to those shown in  FIG. 6  have been given the same reference numbers as in  FIG. 6 . To that extent, reference is made to the description of  FIG. 2  and to the additional description of  FIG. 6 . In  FIG. 11 , however, spacing elements  77  are provided between the two cooling rings  13 ,  53 . Said cooling device can substantially function in the same way as that shown in  FIG. 6 . 
     In  FIG. 12 , identical details have been given the same reference numbers as in the preceding Figures, with particular reference being made to the description of  FIG. 6 . Instead of the spacing elements according to  FIG. 11 ,  FIG. 12  shows a further height-adjustable holding element  76  which can be arranged between the cooling rings  13 ,  53 , and which can be firmly arranged at the lower cooling ring  13  and which can be adjustable with respect to height of the upper cooling ring  53  relative to the lower cooling ring  13 . This adjusting device is able to adjust the length of the so-called neck of the blown film prior to the widening of its diameter, and thus the length of the effective cooling path. 
     It can be appreciated that the cooling rings  13 ,  53  can include the cooling gas ring in form of a segment disc  63  which can optionally be provided with volume flow control means and/or temperature control means in order to achieve a variable volume flow control or temperature control of the cooling gas in sectors around the circumference.