GB2289432A

GB2289432A - A film blowing head with independent cooling rings

Info

Publication number: GB2289432A
Application number: GB9509458A
Authority: GB
Inventors: Klaus-Peter Vos
Original assignee: Windmoeller and Hoelscher KG
Current assignee: Windmoeller and Hoelscher KG
Priority date: 1994-05-18
Filing date: 1995-05-10
Publication date: 1995-11-22
Anticipated expiration: 2015-05-10
Also published as: FR2720027B1; ITBZ950033A0; GB9509458D0; ITBZ950033A1; IT1281282B1; GB2289432B; FR2720027A1

Abstract

A film blowing head for producing tubular film webs of a thermoplastic synthetic material, consists of at least one feeder duct for the synthetic melt and leading into an annular outlet nozzle 3. An outer cooling ring 7, surrounding the extruded synthetic tubular web, is provided with nozzles directed towards the synthetic tubular web 11. An additional cooling ring 6 comprises a plurality of outlet nozzles 18 which discharge additional air flows that can be heated or cooled to different levels. To make it possible to retrofit existing film blowing heads with such an additional cooling ring 6, the additional cooling ring is an independent component. <IMAGE>

Description

a 2289432 A FILM BLOWING BMW FOR PRODUCING TUBULAR FILM WEBS OF A

THERMOPLASTIC SYNTHETIC NATERIAL The invention concerns a film blowing head for producing tubular film webs of a thermoplastic synthetic material.

Such a head has lines for the feeding and evacuation of internal cooling air, and leads into an annular outlet nozzle having an outer cooling ring surrounding the extruded synthetic tubular web. The cooling ring is conventionally provided with nozzles directed onto the synthetic tubular web or with a nozzle slot directed onto the web. There may be an additional cooling ring provided with a plurality of outlet nozzles from which additional discharged air flows that can be heated or cooled to different levels.

In such a film blowing head disclosed in DE-A-4207439 the outer ring delimiting the nozzle gap of the outlet nozzle is provided with bores that extend over a certain distance approximately parallel to the emerging tubular web of the synthetic melt and then lead into a bore passing radially outwardly. A plurality of bores is arranged at approximately the same interspacing on a circular line concentric with the annular nozzle gap of the outer ring of the outlet nozzle. Air, heated or cooled to different levels, is then fed through the connecting bores in a controlled manner to meet the cooling air flow that emerges from the outer cooling ring.

By means of this known film blowing head, the synthetic melt extruded in a tubular form can be heated and/or cooled in sections over its circumference, in order to act on the thickness profile and to adjust it to the same mean thickness. in this connection, during the inflation of the synthetic tubular web into a tubular bubble, the warmer zones are stretched to a greater extent and the cooler zones to a lesser extent.

In the known film blowing head the temperature profile of the outer nozzle lip can be affected directly by the bores or ducts passing through the outer nozzle ring, according to the admission into these individual ducts of air heated or cooled to different levels, whereby it is possible to act more intensively on the emerging synthetic melt. Moreover, the air heated or cooled to different levels, emerging from the bores or ducts also influences the temperature profile of the emerging synthetic tubular web.

In the known film blowing head, the additional cooling ring is combined with the outer ring delimiting the annular nozzle gap, so that this outer ring has a relatively complicated structure; in particular, there is no possibility of retrofitting an additional cooling ring to film blowing heads 15 already in existence.

It is, therefore, the object of the invention to create a film blowing head which not only has a simpler structure, but can also be subsequently fitted with an additional cooling ring.

In accordance with the invention there is provided a film blowing head, for producing tubular film webs of a thermoplastic synthetic material, including at least one feeder duct for the synthetic melt and which leads into an annular outlet nozzle; an outer cooling ring surrounding the extruded synthetic tubular web and provided with nozzles directed towards the position of the synthetic tubular web or with a nozzle slot directed towards that position; and an additional cooling ring provided with a plurality of outlet nozzles from which additional air flows can be discharged, wherein said additional cooling ring is independent of said outer cooling ring.

The additional cooling ring can be installed in a simple m 9 manner into existing film extrusion installations without any need for the existing film blowing head to be changed as part of the retro-fit. Already existing film extrusion installations operating without an adjustment of the temperature profile of the extruded tubular film web can thus be subsequently fitted in a simple way with the additional cooling ring which then produces an improved quality of the film, since it is possible to adjust undesirable differences in the thickness of the tubular film web.

The additional cooling ring also leads to a faster and more flexible action on the temperature profile of the extruded tubular film web since the cooling air, heated or cooled to different levels, acts directly on the individual sections of the extruded tubular film web and not indirectly via the differential heating or cooling of sections of the outer ring of the outlet nozzle delimiting the nozzle gap.

Expediently, leading into the outlet nozzles, the additional cooling ring has tubes, ducts or bores wherein heating or cooling elements are arranged. The heating elements may consist of heating cartridges.

In a further development of the invention, provision is made for the additional cooling ring to be provided with an outer annular line from which the tubes, ducts or bores branch off and into which the cooling air supply line leads. Thus basically the same quantity of air emerges from all the outlet nozzles of the additional cooling ring, giving rise to an arrangement in which the action on the temperature profile of the extruded tubular film web is effected solely by means of the different temperatures of the cooling air emerging from the outlet nozzles.

The axes of the outlet nozzles can extend parallel, radially, or oblique to the axis of the extruded synthetic tubular web.

4 - The outer cooling means of the film blowing head may expediently have a disk-shaped structure, so that the additional cooling ring can be selectively inserted into the annular disk-shaped structure.

in a particularly advantageous embodiment, the additional cooling ring may be inserted between the outer cooling ring and the outer ring of the outlet nozzle. At this point, the cooling air flows emerging from the outlet nozzles of the additional cooling ring, heated or cooled to different levels, act in a particularly favourable manner directly on the synthetic tubular film web that has just been extruded, so that the desired temperature profile can be quickly set.

An embodiment of the invention will be described in greater detail below by way of example, with reference to the drawings, in which:- Fig. 1 Fig. 2 is a vertical section through the upper zone of a film blowing head with an outer cooling ring and an additional cooling ring and is a radial section through the film blowing head of Figure 1 at the level of the additional cooling ring.

Figure 1 shows a longitudinal section through the upper zone of an outlet nozzle which consists of an inner ring 1 and an outer ring 2, which both delimit the outlet nozzle gap 3.

The inner ring 1 concentrically surrounds a central pipe 5 with an interspacing forming an annular space 4. The bubblesupporting and cooling air blown in through the annular feeder duct 4 is drawn off again through the pipe 5.

The disk-shaped cooling rings, that is to say the additional 30 cooling ring 6 and the outer cooling ring 7 arranged on top 9 of one another, are held on the outer ring 2 of the outlet nozzle 10. This outer ring 2 is provided with an annular stepped recess into which the additional cooling ring 6 is inserted in the manner shown. The additional cooling ring 6 has a surface form that is adapted to receiving and holding the outer cooling ring 7.

The outer cooling ring 7 is of a conventional design and consists of an annular inner compartment 8 which leads into the annular outlet gap 9. The edge 10 of the bottom wall is drawn upwards in the manner of a rocker, so that the cooling air emerging from the annular gap 9 flows against the extruded tubular film web 11 at an acute angle. The edge 12 of the upper wall is also drawn upwards in the form of a tubular section, so that the desired outflow conditions are obtained.

The radial outer zone of the annular compartment 8 is provided with a connector 13 for a hose 15 feeding cooling air from a fan 14.

The structure of the additional cooling ring 6 is shown in Figure 2.

The additional cooling ring 6 consists of an outer annular line 16, from which inwardly directed tubes 17 branch off at equal angular interspacings. At their ends, these tubes 17 are bent upwards, so that the additional cooling air emerging from the outlet nozzles 18 flows against the extruded tubular film web 11 approximately at an acute angle. Heating cartridges 18 are mounted in the individual radial tubes 17, by means of which the additional cooling air flowing through the tubes 17 can be heated to different levels.

The outer annular pipe is provided with a connector 19 to which a fan 21 is connected via a hose 20.

C L A 1 M S 1. A film blowing head, for producing tubular film webs of a thermoplastic synthetic material, including at least one feeder duct for the synthetic melt and which leads into an annular outlet nozzle; an outer cooling ring surrounding the extruded synthetic tubular web and provided with nozzles directed towards the position of the synthetic tubular web or with a nozzle slot directed towards that position; and an additional cooling ring provided with a plurality of outlet nozzles from which additional air flows can be discharged, wherein said an additional cooling ring is forming independent of said outer cooling ring.

2. A film blowing head according to claim 1, wherein said additional cooling ring has, leading into said outlet nozzles thereof, tubes, ducts or bores wherein heating or cooling elements are arranged.

3. A film blowing head according to claim 2, wherein the heating elements are heating cartridges.

A film blowing head according to either of claims 2 and 3, wherein said additional cooling ring is provided with an outer annular line from which said tubes, ducts or bores branch off, and into which the cooling air supply line leads.

5. A film blowing head according to any one of claims 1 to 4, wherein said outlet nozzles have axes which extend parallel, radially or obliquely to the axis of the extruded synthetic tubular web.

6. A film blowing head according to any one of claims 1 to 5, wherein said outer cooling ring has an annular disk shaped 1 structure, and said additional cooling ring is selectively insertable into said annular disk-shaped structure 7. A film blowing head according to any one of claims 1 to 6, wherein said additional cooling ring is inserted between said outer cooling ring and an outer ring of said outlet nozzle.

8. A film blowing head constructed and arranged substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.