JPH07251449A - Method and device for cooling sylindrical web of melt thermoplastic synthetic material extruded from film blow head - Google Patents

Abstract

PURPOSE: To increase the heat output of an inflation device by exposing a tubular web of a thermoplastic synthetic melt to primary cooling air with below specific temp. and surrounding this primary cooling air by a secondary air stream comprising dry air with a specific temp. or more. CONSTITUTION: In a method for cooling a tubular web 3 of a thermoplastic synthetic melt extruded from a film blowing head 1, cooling air is blown to the tubular web 3 in the direction going toward the tubular web 3 or in the direction parallel thereto from the annular nozzle gap 2 of the film blowing head 1 or a cooling ring 6 equipped with the annular outlet cap 8 surrounding the tubular web 3. The tubular web 3 is exposed to primary cooling air with a temp. of below 0 deg.C supplied to the annular outlet cap 8 from a vertical connection pipe 10 through an annular chamber 9. The primary cooling air is surrounded by the secondary air stream of dry air with a temp. higher than 0 deg.C supplied to an outlet gap 14 from a horizontal intake pipe 17 through an annular chamber 16.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to a method of cooling a tubular web of thermoplastic compound melt extruded from a film blowing head, which encloses an annular nozzle gap or tubular web of the blowing head. It relates to a method of blowing cooling air in a direction towards or parallel to a tubular web from at least one cooling ring with an annular outlet gap.

[0002]

2. Description of the Related Art An inflator system (film blowing inst
the heat output of allations), and
This can also be increased by lowering the temperature of the cooling air.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to carry out a method of the type described above which makes it possible to increase the heat output of an inflator device by using cooler cooling air. .

[0004]

Accordingly, one aspect of the present invention is a method of cooling a tubular web of thermoplastic compound melt extruded from a film blowing head, the annular nozzle of the blowing head. A method of blowing cooling air towards or parallel to a tubular web from at least one cooling ring having an annular exit gap surrounding the gap or tubular web, the tubular web being below 0 ° C. Of primary cooling air at a temperature of 0 ° C. and surrounding this cooling air with a secondary air stream of dry air at a temperature above 0 ° C. If the temperature of the cooling air is lowered in order to increase the output performance of the inflator system, drops, snow or ice crystals will precipitate in the area where the cooling air comes into contact with or swirls with the ambient air. These deposits may cause damage to extruded tubular webs or inflated film bubbles. The risk of water condensation from ambient air is 1
When the sub-cooling air stream is very cold, therefore its temperature is −
Particularly high at 10 ° C or lower. According to the invention, in order to avoid undesired condensation of water from the ambient air when very cold cooling air is used, cold 1
The secondary cooling air stream is surrounded by a secondary air stream of dry air above 0 ° C. This secondary air flow surrounding the cooling air prevents it from making premature contact with the ambient air when the cold cooling air flow is still cold enough to condense water from the ambient air. This secondary air flow first isolates the cooling air flow from the ambient air and the cooling air flow is
Moisture cannot condense from the secondary air stream, because the secondary air stream consists of dry air and no moisture condenses in the boundary region between the secondary air stream and the ambient air.
This is because the dry secondary air stream can absorb a certain amount of moisture from the ambient air, and the mixing of the cooling air stream with the surrounding secondary air stream cannot cause dew condensation from the ambient air to a detrimental extent. To the extent that it only occurs when the cooling air stream is warmed. In the present invention, due to the dry secondary air flow surrounding the cooling air flow, the temperature of the cooling air flow can be lowered to a very low temperature, increasing the heat output.
The temperature of the primary cooling air is preferably in the range of -10 ° C to -25 ° C.

The temperature of the dry secondary cooling air stream is, on the one hand,
To effectively protect the cooling airflow from the ambient air,
Also, on the other hand, it should be chosen to avoid condensation between the secondary air stream and the ambient air. The temperature of the secondary air stream should be in the range 5 ° C to 15 ° C, preferably about 10 ° C. In another embodiment of the invention, the secondary air stream is separated from the primary air stream and warmed to the higher temperature of the secondary air stream. In fact, a certain amount of cooling air is lost due to the separation of air from the primary air stream. On the other hand, warming the air separated from the cooling air stream results in a dry secondary air stream, which meets the requirements of the secondary air stream. A second aspect of the present invention is a bubble extrusion process.
providing an inflation extrusion head for use in a ble extrusion process, the head being located at the top of the cooling ring with a low cooling ring with an annular outlet gap for the cold primary cooling air flow. It includes a cooling ring with another annular outlet gap for the warmer secondary air stream and means for ensuring that the temperature of the secondary air stream is higher than the temperature of the primary cooling air stream.

In this structure, the warmer secondary air flow is
Both outlet gaps are arranged relative to each other so as to concentrically surround the inner cooling air flow. A line is provided for separating a proportion of the cold primary cooling air stream and for supplying the separated cooling air stream to the annular outlet gap for the warmer air stream, at least one wall being heated. It is advisable to delimit the exit gap for the warmer air flow. The heated walls heat the separated cooling air stream to the desired temperature of the secondary air stream. The conduit for separating a proportion of the cooling air stream preferably comprises a bore through a ring separating the air streams from each other. The wall delimiting the exit gap for the warmer air stream may be formed by a ring with heating elements.
In another embodiment of the present invention, a film blowing head comprises a cylindrical tubular portion surrounding an extruded tubular web, the portion being perforated with a heating element for heating the tubular portion. Have walls. This cylindrical wall, which is heated and provided with passages, forms, as it were, a heating grill through which ambient air is drawn in by a cooling air stream, during which heating ambient air no longer condenses any moisture. It is dried so that it does not happen.

The cylindrical, perforated cylindrical portion is preferably made of a material having good thermal conductivity, such as copper. The annular element for warming the secondary air stream is subdivided into ring-shaped sectors, the temperature of which can be adjusted independently. In this case, the temperature distribution surrounding the extruded tubular film web can be influenced. The annular outlet gap for the cold primary cooling air flow may be subdivided into individual outlet segments so that the cross-section of the outlet segments can be adjusted independently. By suitable adjustment of the cross-section of the outlet, a desired temperature distribution can be created over the circumference of the extruded tubular film web.

[0008]

Embodiments of the present invention will now be described in detail with reference to the accompanying drawings. Shown is a film blowing head 1 of conventional design and having an annular nozzle gap 2 from which a tubular web 3 of compound melt emerges and is inflated to blow a film or film bubble. Then, a flat tubular web flattened by conventional nip rollers is drawn from the blown film. A first cooling ring 6, which is preferably made of a material with poor thermal conductivity, is mounted on the outer ring 4 of the film blowing head 1 above the insulating gap 5. This ring 6 together with the second cooling ring 7 delimits an annular outlet gap 8 for a sufficiently cooled primary cooling air flow, which gap extends in the direction along the extruded tubular film web 3. Practically suitable for. An annular chamber 9 is arranged in front of the outlet gap 8 and supplies dry cooling air to the outlet gap via a longitudinal connecting pipe 10. The cooling ring 7, which is screwed to the intermediate holding / separating plate 11 of the outer cooling unit 12, faces along the direction of the extruded tubular film web 3 together with the upper cooling ring 13, and the warm second dry air is used. Form an exit gap 14 through which The annular outlet gap 14 has a larger diameter than the annular outlet gap 8 for the primary cooling air, so that the annular outlet gap 14 concentrically surrounds the annular inner outlet gap 8 when viewed in plan. The warmer secondary air is supplied to the outlet gap 14 via an annular chamber 16 arranged in front of the outlet gap 14. The annular chamber has a horizontal intake pipe 17 for the warmer dry secondary air.

In the embodiment shown in FIG. 2, the film blowing head 1 corresponds to the design shown in FIG. First outer cooling ring 20 made of material with poor thermal conductivity
Attached to the outer ring 4 of the film blowing head 1 with an insulating gap 21. Cooling ring 20
Together with the second cooling ring 22 arranged thereon,
An annular outlet gap 23 for the sufficiently cooled cooling air is delimited, which gap 23 points along the direction of the extruded tubular film web 3. Cooling ring 2
2 is provided with a heating element 25, and the intermediate cooling ring 2
Along with 2, a third ring 24 is attached which bounds an exit gap 26 oriented along the direction of the extruded tubular film web 3. An annular chamber located in front of the outlet gap 26 is connected to a bore 27, which runs longitudinally through the cooling ring 22 and reaches an annular chamber 28, which is sufficiently cooled by the annular chamber. Primary cooling air is supplied to the inner outlet gap 23. The outlet gaps 23, 26 are arranged concentrically with each other, like the outlet gaps 8, 14 of FIG.
The air mass separated from the cold primary cooling air stream by the bore 27 is warmed by the heated ring 24, and the warmer air stream surrounding the cooling air stream emerging from the annular gap 23 is cooled by the annular gap 26. Come out through.

In the embodiment shown in FIG. 3, the upper ring 24, which warms the separated cooling air stream, supports a cylindrical wall 30 made of a material having good thermal conductivity, which wall 30 has a sieve on its side. 2 is different from the embodiment of FIG. 2 in that the bore 31 is provided. Further, a ring 32 having a heating element that heats both the cylindrical portion 30 and the ring 24.
Is provided. The ambient air has an annular gap 23,2.
The concentric airflow emerging from 6 is sucked through the bore 31 by the fluidentrainment pump principal by the fluidentrainment pump principal, warming and drying the ambient air, resulting in an airflow. Singles together in one area above the cylindrical section, at a temperature that prevents condensation.

[Brief description of drawings]

FIG. 1 is a longitudinal partial cross-sectional view of a first embodiment of a film blowing head.

FIG. 2 is a longitudinal partial cross-sectional view of a second embodiment of the film blowing head.

FIG. 3 is a longitudinal sectional view of a third embodiment of the film blowing head.

[Explanation of symbols]

 1 Film Blowing Head 2 Annular Nozzle Gap 3 Cylindrical Web 4 Outer Ring 5 Adiabatic Gap 6 Cooling Ring 7 Second Cooling Ring 8 Annular Exit Gap 9 Annular Chamber 14 Exit Gap 16 Annular Chamber

Claims (12)

[Claims] 1. A method of cooling a tubular web of thermoplastic composite melt extruded from a film blowing head, comprising an annular nozzle gap of the blowing head or an annular exit gap surrounding the tubular web. Exposing the tubular web to primary cooling air at a temperature of less than 0 ° C., wherein the cooling air is blown from at least one cooling ring towards or parallel to the tubular web;
Surrounding the cooling air with a secondary air stream of dry air at a temperature above 0 ° C. 2. The method of claim 1 wherein the temperature of the primary cooling air stream is in the range of -10 ° C to -25 ° C. 3. Process according to claim 1 or 2, characterized in that the temperature of the secondary air stream is in the range 5 ° C to 15 ° C, preferably about 10 ° C. 4. The secondary air stream is separated from the primary cooling air stream, which is warmed to a higher temperature of the secondary air stream, according to any one of claims 1 to 3. the method of. 5. A device for carrying out the method according to claim 1, comprising a film blowing head with a cooling ring, comprising an annular outlet gap for the cold primary cooling air flow. An apparatus, characterized in that it has a low cooling ring and a cooling ring arranged on top of the cooling ring with an annular outlet gap for the warmer secondary air flow. 6. A conduit is provided for separating a proportion of the cold primary cooling air stream and supplying the separated cooling air stream to an annular outlet gap for the warmer air stream, the warming air stream At least one demarcating the exit gap
Device according to claim 5, characterized in that one wall is heated. 7. The apparatus of claim 6, wherein the conduit comprises a bore that passes through the ring and separates the air streams from each other. 8. The upper wall defining the exit gap for the warmer air is formed by a ring with heating elements.
The device according to any one of 1. 9. The film blowing head comprises a cylindrical portion surrounding an extruded tubular web, the portion comprising a heating element for warming it and a perforated wall. The device according to any one of claims 5 to 8. 10. Device according to claim 9, characterized in that the cylindrical part is made of a material with good thermal conductivity, for example copper. 11. The method according to claim 5, wherein the annular element for heating the secondary air flow is subdivided into ring-shaped sectors, and the temperature of these ring-shaped sectors is independently adjustable. The device according to any one of claims 1. 12. An annular outlet gap for a cold primary air flow is subdivided into individual outlet segments, the cross-section of these outlet segments being independently adjustable. The device according to.