GB1581714A - Apparatus for internal cooling in tubular films made of extruded plastic material - Google Patents

Description

(54) AN APPARATUS FOR INTERNAL COOLING IN TUBULAR FILMS MADE OF EXTRUDED PLASTIC MATERIAL (71) We, ING. L. DOLCI S.p.A., of Via Zucchi, 18-20095 Cusano Milanino (Milan) Italy, a Company organized under the laws of Italy, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to an apparatus for internal cooling in tubular films made of extruded plastic material, according to which such a cooling is provided by air continuously supplied and interchanged by flowing through coaxial conduits within the tubular film and passing through the extruder head.

It is the object of the present invention to propose an apparatus of the above mentioned character, capable of considerably improving the efficiency of internal cooling in a tubular film, thus enabling to increase the extrusion rate and, as a result, the output of the tubular film.

The foregoing is accomplished by an apparatus according to the invention, comprising annular air blowing nozzles, axially spaced apart and connected by means of tubular distributors to the feeding conduit for cooling air, and wherein at least one convergent nozzle is provided within the air outlet conduit, substantially comprising a jet pump which is used for air suction from inside the tubular film at zones between the annular blowing nozzles. Thus, the action of the air flow exiting from the tubular film is taken advantage of for creating a depression or vacuum between the annular blowing nozzles causing the tubular film to move closer to said nozzles, thereby further increasing the c6oling -efficiency.

Hereinafter, the invention will be described in further detail with reference to the accompanying drawing, in which: Fig. 1 is a schematic longitudinal sectional view showing an extruder head provided with a device according to the invention for internal cooling of a tubular film; and Fig. 2 is a cross-sectional view taken along line 2-2 of Fig. 1.

Referring to Fig. 1, there is shown a general type of extruder head substantially comprising a helical distributor 1 supplied at 2 with molten plastic material to feed the same along an annular slit 3 of a die 4, a per se known tubular film 5 being extruded therefrom.

Within said distributor 1 and die 4 of the extruder head, provision is made for a cooling air supply conduit 6 and a conduit 7 coaxial with the former, extending internally of the tubular film 5 for exhausting and interchanging the cooling air from inside said tubular film 5.

As shown in the sectional view of Fig. 1, internally of tubular film 5 at the zone im mediately next to the extruder head, where said tubular film 5 is still in a plastic condition, annular blowing nozzles 8, 9 and 10 are respectively provided, these nozzles being axially spaced apart from one another and individually connected through respective tubular distributors 11, 12 and 13 of their own with the cooling air supply conduit 6.

As it will be also seen in Fig. 1, said tubular distributor 11, 12 and 13 are coaxially arranged about the air outlet conduit 7, extending to their own annular blowing nozzle, so as to individuallly supply an even and regular air flow throughout the circumferential development of the associated blow ing nozzle. Thus, an even air flow can be provided at a higher speed for an improved cooling efficiency. As shown, the passage section for the air flow in each of the distributors will vary, namely increasing from the outermost distributor 13 associated with nozzle 10, which is closest to the extruding die 4, to the innermost distributor 11 associated with the farthest nozzle 8, thus allowing an even exploitation of the pressure stage.

In order to further improve the cooling effect by the apparatus according to the invention, provision is made for building up depressions or vacuum conditions within tubular film 5, located into the spaces comprised between the contiguous blowing nozzles; this depression has the effect of getting near the tube 5 to the blowing nozzles 8, 9 and 10, thus increasing further the cooling efficiency.

According to the characteristic of this apparatus, said depression is created by aspirating air from the inside of the tube, by means of radial channels or tubes 14 of a relatively reduced diameter, on one side opening to the inside of the tubular film 5, while opening on the other side to the air outlet conduit 7 at the narrow section of a convergent nozzle 15 positioned internally of said outlet conduit. Thereby, the side suction effect of the air jet provided by the narrowing or throttling of nozzle 15 is taken advantage of for drawing air from the inside of the tubular film, so as to create the desired depression or vacuum.

In the particular case shown, it is provided to use two nozzles 15, substantially comprising two jet pumps positioned after each other, for air suction between the annular nozzles 8, 9 and 10, respectively. However, other equivalent solutions or solutions comparable with that herein shown could be adopted for creating a vacuum condition within the tubular film, as previously stated.

The proposed solution is advantageous in that it makes possible to use air suction tubes 14 having an extremely reduced diameter in order to disturb at least as possible the evenness of the air flow directed in each of the annular distributors 11 and 12 to said blowing nozzles 8 and 9. Thus, a slight disturbance in the evenness of the cooling air flow outgoing from the blowing nozzles 8 and 9 would cause irregularities in the extruded tubular film.

In a per se known manner, the apparatus can be provided with a system for external cooling of the tubular film, in the exemplary embodiment shown comprising a nozzle 16 located at the extruder head and supplied through an annular distributor 17.

Therefore, from the foregoing and as shown in the accompanying drawings, it will be appreciated that an apparatus has been provided for internal cooling in tubular films of extruded plastic material, which is highly efficient and of extremely simple construction bceause of using the same cooling air flow, which is caused to outflow from the tubular film, to provide an air suction from within the tubular film for building up depressions or vacuum conditions localized between the blowing nozzles, thus increasing the cooling efficiency.

WHAT WE CLAIM IS: - 1. An apparatus' for internal cooling in tubular films of extruded plastic material, comprising coaxial conduits for cooling air supply and outlet or discharge, such conduits being located internally of the tubular film, wherein axially spaced apart, annular air blowing nozzles are connected through single tubular distributors to said air supply conduit, and at least one convergent nozzle is located in the air outlet conduit, at which suction channels are provided, on one side opening in the tubular film between said annular nozzles, and on the other side opening in said outlet conduit, laterally of the air flow established by said convergent nozzle.

2. An apparatus according to Claim 1, wherein said tubular distributors are arranged coaxially and around the air outlet conduit.

3. An apparatus according to the preceding claims, wherein the passage section for the air of the distributors varies by increasing from the outermost distributor to the innermost distributor.

4. An apparatus according to the preceding claims, wherein said air suction channels are arranged radially to and coplanar with the narrow section of the convergent nozzle inside said air outlet conduit.

5. An apparatus according to the preceding claims, wherein a plurality of nozzles are sequentially provided internally of said air outlet conduit, for each of said nozzles radial channels for air suction from the tubular film being provided.

6. An extruder head for tubular films of plastic material, comprising an extruding die supplied with molten plastic material, having coaxial cooling air supply and outlet conduits passing therethrough, wherein an apparatus is provided for internal cooling of the tubular film according to any of the preceding claims.

7. An apparatus for internal cooling in tubular films of extruded plastic material substantially as hereinbefore described with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (7)

**WARNING** start of CLMS field may overlap end of DESC **. depressions or vacuum conditions within tubular film 5, located into the spaces comprised between the contiguous blowing nozzles; this depression has the effect of getting near the tube 5 to the blowing nozzles 8, 9 and 10, thus increasing further the cooling efficiency. According to the characteristic of this apparatus, said depression is created by aspirating air from the inside of the tube, by means of radial channels or tubes 14 of a relatively reduced diameter, on one side opening to the inside of the tubular film 5, while opening on the other side to the air outlet conduit 7 at the narrow section of a convergent nozzle 15 positioned internally of said outlet conduit. Thereby, the side suction effect of the air jet provided by the narrowing or throttling of nozzle 15 is taken advantage of for drawing air from the inside of the tubular film, so as to create the desired depression or vacuum. In the particular case shown, it is provided to use two nozzles 15, substantially comprising two jet pumps positioned after each other, for air suction between the annular nozzles 8, 9 and 10, respectively. However, other equivalent solutions or solutions comparable with that herein shown could be adopted for creating a vacuum condition within the tubular film, as previously stated. The proposed solution is advantageous in that it makes possible to use air suction tubes 14 having an extremely reduced diameter in order to disturb at least as possible the evenness of the air flow directed in each of the annular distributors 11 and 12 to said blowing nozzles 8 and 9. Thus, a slight disturbance in the evenness of the cooling air flow outgoing from the blowing nozzles 8 and 9 would cause irregularities in the extruded tubular film. In a per se known manner, the apparatus can be provided with a system for external cooling of the tubular film, in the exemplary embodiment shown comprising a nozzle 16 located at the extruder head and supplied through an annular distributor 17. Therefore, from the foregoing and as shown in the accompanying drawings, it will be appreciated that an apparatus has been provided for internal cooling in tubular films of extruded plastic material, which is highly efficient and of extremely simple construction bceause of using the same cooling air flow, which is caused to outflow from the tubular film, to provide an air suction from within the tubular film for building up depressions or vacuum conditions localized between the blowing nozzles, thus increasing the cooling efficiency. WHAT WE CLAIM IS: -

1. An apparatus' for internal cooling in tubular films of extruded plastic material, comprising coaxial conduits for cooling air supply and outlet or discharge, such conduits being located internally of the tubular film, wherein axially spaced apart, annular air blowing nozzles are connected through single tubular distributors to said air supply conduit, and at least one convergent nozzle is located in the air outlet conduit, at which suction channels are provided, on one side opening in the tubular film between said annular nozzles, and on the other side opening in said outlet conduit, laterally of the air flow established by said convergent nozzle.

2. An apparatus according to Claim 1, wherein said tubular distributors are arranged coaxially and around the air outlet conduit.

3. An apparatus according to the preceding claims, wherein the passage section for the air of the distributors varies by increasing from the outermost distributor to the innermost distributor.

4. An apparatus according to the preceding claims, wherein said air suction channels are arranged radially to and coplanar with the narrow section of the convergent nozzle inside said air outlet conduit.

5. An apparatus according to the preceding claims, wherein a plurality of nozzles are sequentially provided internally of said air outlet conduit, for each of said nozzles radial channels for air suction from the tubular film being provided.

6. An extruder head for tubular films of plastic material, comprising an extruding die supplied with molten plastic material, having coaxial cooling air supply and outlet conduits passing therethrough, wherein an apparatus is provided for internal cooling of the tubular film according to any of the preceding claims.

7. An apparatus for internal cooling in tubular films of extruded plastic material substantially as hereinbefore described with reference to the accompanying drawings.