DE2658518C2 - Plant for the production of blown films made of thermoplastic material - Google Patents

Description

the measuring device in the area of the winding device or between the lay-flat device and the take-up device over the width of the blown film distributed or having a measuring head scanning the blown film width and the device for the Circumferential temperature influence of the film tube controlled by the measured values obtained in this way is, furthermore the device for influencing the peripheral temperature of the film tube in accordance with the deviation of an actual value of the blown film thickness from this circumferential area predetermined setpoint is controllable, characterized in that the device for the Influencing the temperature of the film tube (6) a plurality of above the outside air blow ring (3) on one of the film tube (6) Surrounding circle arranged correction air nozzles (16), wherein the individual correction air nozzles (16) appropriately controlled adjusting valves (17) are assigned.

2. Installation according to claim 1, characterized in that the correction air nozzles (16) for supply of warm air are set up.

3. Plant according to claim 1, characterized in that the correction air nozzles (16) for cold air supply are set up.

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The invention relates to a plant for the production of blown films made of thermoplastic material, consisting of plastic screw press, blow head with external air blow ring, flattening device for the film tube, Winding device, measuring device for the film thickness and device for influencing the peripheral temperature of the film tube, the measuring device in the area of the winding device or between the lay-flat device and the take-up device over the blown film width or one of the Has blown film width scanning measuring head and the device for influencing the peripheral temperature of the film tube is controlled by the measured values obtained in this way, and the device for the Circumferential temperature influence of the film tube according to the deviation of an actual value of the Blown film thickness can be controlled from a setpoint value predetermined for this circumferential range.

In such systems, the formation of unwanted barrel hoops is on the one hand by thickness measurement and on the other hand, can be avoided by influencing the peripheral temperature of the film tube. There is also in a known system of the type described above (DE-OS 22 52 084) the device for Circumferential temperature influence from heating elements that are controlled or regulated accordingly. Leading however, at very considerable dead times with the result that the formation of barrel hoops cannot be avoided

Otherwise is known (GB-PS 714194) the To form outside air blowing ring from nozzles, which are combined to form a nozzle ring. These nozzles are controllable, but only with regard to the outside air to be supplied

The invention is based on the object of specifying as in the production of blown films from thermoplastic with a system of The type described above reliably prevents the formation of barrel hoops on the film roll can be.

This object is achieved in that the device for influencing the peripheral temperature of the film tube a large number of above the outside air blow ring onto the film tube Has surrounding circle arranged correction air nozzles, the individual correction air nozzles appropriately controlled adjustment valves are assigned. The correction air nozzles can either be used for Be set up for warm air supply or for cold air supply.

In addition to the external air blow ring, the system according to the invention also has a correction nozzle ring, The circumferential temperature of the film tube via its individually controllable nozzles according to the Thickness measurement can be influenced. That allows for surprisingly precise control or Regulation of the blown film thickness in such a way that barrel tires are definitely avoided. The scheme works not only precisely, but also very quickly, because the adjustment valves can be adjusted with practically no inertia can. In this way, however, the correction air also acts practically without inertia on the film tube, its The peripheral temperature adapts accordingly quickly to the new conditions.

In the following the invention is illustrated by means of a drawing which shows only one exemplary embodiment explained in more detail; it shows in a schematic representation

F i g. 1 shows an axial section through a plant for the production of blown thermoplastic films Plastic,

2 shows a section in the direction AA through the object according to FIG. 1,

F i g. 3 shows an enlarged section of the object according to FIG. 1,

F i g. 4 shows a section in the direction BB through the object according to FIG. 3,

FIG. 5 on a further enlarged scale and corresponding to the section of FIG. 3 in another Embodiment of the nozzle ring,

F i g. 6 shows a section in the direction CC through the object according to FIG. 5.

In the system shown in the figures, a plastic screw press 1 can initially be seen Blow head 2. In the exemplary embodiment and according to a preferred embodiment of the invention, the blow head has 2 an outside air blow ring 3, an inside air blow ring 4 and a pipe socket 5 which is inserted into the film tube 6 protrudes and represents a central internal air outlet. A plastic tube first emerges from the blow head 2 7, which is then inflated and thereby widens to form the film tube 6. In sufficient At a distance from the blow head 2 is the flattening device 8 for the film tube 6, a

Winder 9 is connected downstream. Furthermore The device always includes a measuring device 10 for the film thickness. The measuring device 10 is always in constructed in a special way and in the embodiment according to FIG. 1 characterized by certain Measuring heads 11 assigned to peripheral areas of the film tube 6, which are arranged in a row and in a housing 12 can be accommodated. In any case, the system also includes a nozzle ring 15 from a large number of arranged in a circle, assigned to the circumferential areas of the measuring heads U. Correction air nozzles 16 in the area of the blow head 2. With the individual correction air nozzles 16 are adjusting valves 17 connected. In addition, a control device 18 is provided and the control arrangement is such that that the control device 18 specifies the deviation of an actual value of the measured blown film thickness from one for this circumferential area NEN setpoint the assigned adjusting valve 17 or actuated several. In the embodiment and after In a preferred embodiment of the invention, the correction air nozzles 16 are located outside and above the outside air blow ring 3. They can be adjustable and set up for cold or warm air supply, correction air is preferably used, but warm air can also be used. Will namely a certain scope of art

fabric tube 7 in the zone of transition to the film tube 6 or before it is cooled, so the The resulting blown film is thicker at this point; if this area is heated, the blown film becomes thinner. The measurement and control measures required to carry out this mode of operation are known per se and therefore do not need to be described in detail.

For this purpose 3 sheets of drawings

Claims (1)

Patent claims: 1. Plant for the production of blown films made of thermoplastic material, - consisting of Plastic screw press, Blow head with outside air blow ring, Flattening device for the film tube, Take-up device, Measuring device for the film thickness, and ι ο Device for influencing the peripheral temperature of the film tube,