BRIEF DESCRIPTION OF THE DRAWINGS
Preferred embodiments of the inventive devices are illustrated in the drawings and will be described below.
FIG. 1 illustrates a film blowing system according to the invention with two cooling rings which each comprise a controllable partial cooling ring with control elements for independently influencing the cooling gas flows in sectors, and an uncontrolled partial cooling ring.
FIG. 2 illustrates a film blowing system according to FIG. 1 with additional temperature setting means of the film extrusion die, which are controllable in sectors.
FIG. 3 illustrates a film blowing system with two cooling rings which each comprise a uniformly shaped cooling ring with control elements for independently influencing the cooling gas flows in sectors.
FIG. 4 illustrates a film blowing system according to FIG. 3 with additional temperature setting means of the film extrusion die, which are controllable in sectors.
FIG. 5 illustrates a film blowing system with two cooling rings which each comprise a standard cooling ring with control elements for independently setting the temperature of the cooling gas flows in sectors.
FIG. 6 illustrates a film blowing system according to FIG. 5 with additional temperature setting means of the film extrusion die, which are controllable in sectors.
FIG. 7 illustrates a film blowing system with two cooling rings of which the first one comprises a controllable partial cooling ring with control elements for independently influencing the cooling gas flows in sectors and an uncontrolled partial cooling ring, and of which the second one comprises a uniformly shaped cooling ring with control elements for independently influencing the cooling gas flows in sectors.
FIG. 8 illustrates a film blowing system with two cooling rings which each comprise a controllable partial cooling ring with control elements for independently influencing the cooling gas flows in sectors, and an uncontrolled partial cooling ring for independently influencing the cooling gas flows in sectors
FIG. 9 illustrates a film extrusion die, the lower controllable partial cooling ring with corresponding cooling gas supply means according to FIGS. 1, 2 and 7 in an enlarged partial section.
FIG. 10 illustrates nozzle exits at the lower controllable cooling ring according to FIG. 9 as an enlarged detail.
FIG. 11 illustrates a disc element of the lower controllable cooling ring according to FIG. 9 in a plan view.
FIG. 12 illustrates an extrusion die with the lower controllable partial cooling ring, the lower uncontrolled partial cooling ring and the inner cooling ring according to FIG. 8 in an enlarged partial section.
FIG. 13 illustrates exit nozzles of the lower controllable cooling ring and the inner cooling ring according to FIG. 12 as enlarged details.
FIG. 14 illustrates a disc element of the inner cooling ring according to FIG. 12 in a plan view.
DETAILED DESCRIPTION
A device according to the invention shown in FIG. 1 comprises a film blowing extruder 10 with an extrusion die 11, a first cooling ring 12 with an annular channel 13 for a constantly uniformly emerging partial cooling gas flow and a segment disc 14 arranged underneath the latter, for a partial cooling gas flow controllable in sectors, as well as a second cooling ring 12′ arranged thereabove. A annular channel 13′ is provided for a constantly uniformly emerging partial cooling gas flow and a segment disc 14′ arranged underneath the latter, for a partial cooling gas flow controllable in sectors. Both cooling rings 12, 12′ serve to cool a film tube 17 emerging from an annular nozzle 16 at the extrusion die 11.
A circumferentially arranged measuring device 31 is provided for controlling the thickness profile of the film tube 17, which measuring device 31 scans the film thickness at the film tube 17 above a freezing limit. A control device 34 is provided which varies in sectors the cooling gas flows as a function of the film thickness measured around the circumference.
The segment discs 14, 14′ are each arranged underneath the annular channels 13, 13′ in order to exert the greatest possible influence on reducing the film thickness tolerances in that the respective hotter material regions of the film tube at the entry into a cooling ring are controlled in sectors. The segment disc 14, 14′ are each connected to a blower 18, 18′ for the partial cooling gas flows controllable in sectors. A control device 19, 19′ is provided for dividing the cooling gas flows generated by the blower 18, 18′ into individual separate partial cooling gas flows which comprises a plurality of individually controllable flaps and/or valves. The cooling rings 12, 12′ can be axially adjusted relative to one another by adjusting means 15, with the lower cooling ring 12 preferably being secured directly to the extrusion die 11.
The control devices 19, 19′ which are controlled by the regulating device 34 permit a very accurate regulation of the thickness profile during the production of blown film due to the cooling gas supply which is controllable in sectors over a long axial range.
The controllable partial cooling gas flows are supplied in the direction of production of the film tube 17 in front of the uniform partial cooling gas flows and directed against the film tube 17 emerging from the extrusion die 11. The controllable partial cooling gas flows, before entering the segment discs 14, 14′, can be varied individually in their volume flow by the control devices 19, 19′.
The extrusion die 11 comprises an annular nozzle 16 which, with the vertical central axis A, emerges from the top end of the extrusion die. From the annular nozzle 16 there emerges the film tube 17 which is expanded and stabilised by an internal pressure generating device 20 and is pulled off upwardly by an extraction device 30. It is supported by a calibration basket 22 positioned above the cooling rings 12, 12′ and substantially defined in respect of its end diameter. The film tube 17 is enclosed annularly by the two cooling rings 12, 12′ with the annular channels 13, 13′ from which there escapes a substantially annularly uniform partial cooling gas flow, and by segment discs 14, 14′ which are positioned directly underneath and from which there escape partial cooling gas flows which are controllable in sectors. On the one hand, the cooling gas flows have a stabilising effect on the expanding film tube 17 and, on the other hand, they cool the plastic film material emerging from the annular nozzle 16 until, in a continuous freezing zone, the plastic expansion of the tube material is ended due to the cooling effect. The cooling rings 12, 12′ each substantially consist of a torus-shaped annular channel 13, 13′ which comprises some circumferentially distributed supply muffs 23, 23′ and at least one annular nozzle 24, 24′ from which the annularly uniform partial gas flow emerges as uniformly as possible.
The segment discs 14, 14′ each consist of an annular segment member produced in one piece which comprises a plurality of supply muffs 25, 25′ and which, at its inside close to the film tube 17, comprises individual exit nozzles 26, 26′ from which there emerge individual partial cooling gas flows which are controllable in sectors. Whereas the supply lines to the muffs 23, 23′ of the annular channels 13, 13′ are not illustrated, there are shown, by way of example, individual lines 27, 27′ leading to the supply muffs 25, 25′ of the segment discs 14, 14′. The lines are each connected to one of the control devices 19, 19′ which comprise a number of control valves 29, 29′ which corresponds to the actual number of circumferentially distributed lines 27, 27′ and of which four are shown by way of example and which are all air-pressure-loaded by a blower 18, 18′ via a supply line 28, 28′.
Above the calibration basket 22, a contact-free thickness measuring unit 31 is provided and which is arranged on a turntable 32 arranged coaxially relative to the tube and which, by periodically moving around the film tube 17, is able to measure the thickness distribution around the circumference. Between the individual measurements of the circumferential distribution of thickness, the measuring device 31 can be fixed in position and measure the longitudinal thickness values of the film tube along a longitudinal line, with the longitudinal thickness values being representative of the change in longitudinal thickness of the entire film tube. As is symbolised by a signal line 33, the results of the thickness measurements are processed in a control unit 34 of which one control line 35, 35′ leads to the blowers 18, 18′ and one control line 36, 36′ to the control devices 19, 19′. The control lines 35, 35′ allow the blower performance as a whole to be varied. It is possible to individually control the opening cross-section of the normally pulse-width-modulated control valves 29, 29′ via the control lines 36, 36′ which are representative of a plurality of control lines leading to the individual control valves 29, 29′.
The measurements of the circumferential thickness distribution can be converted into a control of the partial cooling air flows individually controllable in sectors, as a result of which the thickness profile is controlled to achieve the least possible deviations. The measurement of the longitudinal thicknesses serves to determine the period of change in longitudinal thickness which, by changing the cooling gas flows as a whole, can also be controlled to achieve as few deviations as possible.
FIG. 2, in addition to the details of FIG. 1, shows in the extrusion head 11 a plurality of circumferentially distributed heating cartridges 65 or cooling elements (e.g. Peltier elements) which, via control lines 66, can be independently controlled by the regulating unit 34 in sectors. This permits an additional variable temperature setting for the film tube 17 prior to it leaving the annular nozzle 16.
In FIG. 3, the cooling rings 12, 12′ can be provided in an alternative embodiment to deviate from FIG. 1 in that they do not comprise any segment discs, but only uniform annular channels 13, 13′ in which there are arranged circumferentially distributed control elements 67, 67′ (e.g. flaps) with setting members 68, 68′ which, in individual circumferential regions, are able to vary the volume flow individually. The setting units 68, 68′ are also connected to the central regulating unit 34 via control lines 69, 69′.
FIG. 4, in addition to the details of FIG. 1, shows in the extrusion head 11 a plurality of circumferentially distributed heating cartridges 65 or cooling elements (e.g. Peltier elements) which, via control lines 66, can be independently controlled by the regulating unit 34 in sectors. This permits an additional variable temperature setting for the film tube 17 prior to it leaving the annular nozzle 16.
In FIG. 5, the cooling rings 12, 12′ can be provided in an alternative embodiment to deviate from FIG. 1 in that they do not comprise any segment discs, but only uniform annular channels 13, 13′ in which there are arranged circumferentially distributed heating cartridges 71, 71′ or cooling elements (e.g. Peltier elements) which, in individual circumferential regions, are able to independently set the temperature for the volume flow. The heating cartridges 71, 71′ are also connected to the central regulating unit 34 via control lines 72, 72′.
FIG. 6, in addition to the details of FIG. 5, shows in the extrusion head 11 a plurality of circumferentially distributed heating cartridges 65 or cooling elements (e.g. Peltier elements) which, via control lines 66, can also be independently controlled by the regulating unit 34 in sectors. This permits an additional variable temperature setting for the film tube 17 prior to it leaving the annular nozzle 16.
In FIG. 7, the lower cooling ring 12 and the control of same can be provided in an alternative embodiment as shown in FIG. 1, whereas the upper cooling ring 12′ and its control are designed like the cooling ring 12 shown in FIG. 3.
The inside of the extrusion die 11 can be provided with circumferentially distributed heating cartridges 65 or cooling elements (e.g. Peltier elements) which, via additional control lines 66, are circumferentially controllable in sectors.
FIG. 8 shows an alternative embodiment of the invention shown in FIG. 1. Inside the film tube 17 there is additionally provided an inner cooling device 47 which is threaded on to the extrusion head 11 and comprises a plurality of elements which will be described in greater detail below. At the circumference of the device 47 there are provided annular nozzles 49, 50 which are arranged in different planes and which exit radially outwardly. The nozzles are supplied with cooling gas via an inner hollow chamber 51, which gas is subsequently extracted via a coaxial central extractor pipe 52 with an open upper end. Between the inner cooling device 47 and the extrusion head 11 there is inserted a further supplementary cooling ring 48 which generates a plurality of inner supplementary cooling gas flows 53 via individual nozzles 54 which, via individual supply lines 55, are supplied with cooling gas which is controllable in sectors. The lines 55 can be branch lines of the individual lines 27, so that certain circumferential regions of the film tube 17 can be charged with uniformly controlled additional cooling gas from the inside and outside in a way which is controllable in sectors.
In FIG. 9, the annular nozzle 16 and the lower cooling ring 12 are shown in an enlarged partial section. One of the supply muffs 23 is followed by a supply line 37. It can be seen that the lower cooling ring 12 is provided in the form of an annular channel 13 which, in addition to a first nozzle exit ring 24, comprises a further nozzle exit ring 38. The annular channel 13 comprises a lower planar face 39 at least in its inner region against which there is threaded a segment disc 14 which comprises an upper substantially planar face 41.
A segment disc 14 can provided with individual radial grooves 42 which, on their radial outside portions, can be connected via through-holes 43 to the individual connecting pieces 25 whereas, on their radial inside portions, they can end in the supplementary nozzles 26. The radial grooves 42, together with the planar face 39, form the individual cooling gas channels. The segment disc 14 can be centred relative to the extrusion head 11 by centring clamps 44. The annular channel 13 threaded to the segment disc 14 can also be centred by said centring clamps 44 relative to the extrusion die 11. An insulating disc 40 can be positioned between the extrusion die 11 and the segment disc 14 in the region of the individual nozzles 26. The design of the upper cooling ring (not shown) can be identical with the exception of its diameter.
FIG. 10 shows the extrusion die 11 in the form of a detail in an enlarged drawing as in FIG. 9, having an annular nozzle 16 from which there emerges the film tube 17 which, for the sake of simplicity, is shown with a uniform wall thickness. On the extrusion die 11, the insulating disc 40 can be provided, above which the annular channel 13 can be positioned with the annular nozzles 24, 38 and the segment disc 14 can be threaded on underneath and have individual nozzles 26.
FIG. 11 shows the segment disc 14 according to FIG. 9 in the form of a detail in a plan view. In a substantially planar flange face 41, the radial grooves 42 are provided and which end on the outside at a distance from the circumferential disc. The radial grooves 42 can be connected to the through-holes 43 and which end towards the inside in nozzle apertures 26 separated from one another by intermediate webs 45. In the centre, a central through-hole 46 can be provided for the film tube.
In FIG. 12 the extrusion die 11, the lower cooling ring 12 with the annular channel 13 and the segment disc 14 are illustrated in an alternative embodiment, and such as shown in FIG. 9. Identical details have been given the same reference numbers and to that extent, reference is therefore made to the description of same. Inside the film tube 17, the inner cooling device 47 is provided which has been placed on to the extrusion die 11 whose lowermost element is the inner supplementary cooling ring 48 which is threaded onto the cylindrical pipe 56 inside the extrusion die 11.
Inside the pipe 56, supply lines 55 are provided in the form of bores. The supplementary cooling ring 54 comprises through-bores 57 for providing a connection with the supply lines 55 as well as with radial grooves 59 which are provided in a planar face 58 and whose ends form the individual nozzles 54. Furthermore, the inner cooling device 47 can comprise a plurality of disc elements which are placed one above the other and of which the lower one comprises a planar underside 60 which upwardly closes off the radial grooves 59, so that there are formed individual cooling gas channels. The individual disc elements, together, form annular nozzles 49, 50 and are connected to one another by grid sleeves. A further insulating ring 62 is provided between the segment disc and the extrusion die 11.
In FIG. 13, an alternative embodiment of the invention is shown for the device as shown in FIG. 12. In such an embodiment, the formation of the supplementary cooling gas exits 54 through the supplementary cooling ring 48 and the lower one of the annular elements of the inner cooling device 47 as well as the connection of the through-bores 57 with the supply channels 55 being particularly clearly visible.
FIG. 14 shows the inner supplementary cooling ring 48 with the above-mentioned details, i.e. the through-bores 57 and the radial grooves 59 milled into a planar surface 58. Close up to the outer circumference, said radial grooves 59 are separated from one another by separating webs 63. The annular disc 48 comprises a central aperture 64 for the general supply of cooling gas.
Thus, a process of controlling the thickness profile of a blown tubular film is described. The process produces blown film by means of blown film extruders, having a film extrusion die, wherein the blown tubular film can comprise thermoplastic plastic. The process includes measuring the film thickness of the tubular film around the circumference by a measuring device, variably controlling the cooling gas flow as a function of the measured film thickness around the circumference in sectors by a control device, and supplying cooling gas flows from the outside in the direction of production in two planes arranged at a distance from one another, and variably controlling the cooling gas flows in sectors around the circumference in the two planes in respect of their physical parameters.
Patent Application
20080061460
