WO2020049459A1

WO2020049459A1 - Cooling ring for film extrusion plants

Info

Publication number: WO2020049459A1
Application number: PCT/IB2019/057415
Authority: WO
Inventors: Daniele CAZZOLA; Matteo ANSALONI
Original assignee: Doteco S.P.A.
Priority date: 2018-09-03
Filing date: 2019-09-03
Publication date: 2020-03-12
Also published as: EP3847000A1

Abstract

The present invention refers to a cooling ring (10) for extrusion plants for extrusion by blowing of a plastic film (F). More particularly, the present invention refers to a cooling ring (10) that allows to efficiently obtaining a flow of air acting on the film (F) in an adjustable way.

Description

COOLING RING FOR FILM EXTRUSION PLANTS

Specification

The present invention refers in general to a cooling ring for extrusion plants for extrusion by blowing of a polymeric film. More particularly, the present invention refers to a cooling ring that allows to efficiently obtaining an air flow acting on the film in an adjustable way according to the areas of interest.

As it is known, the cooling rings for blow molding extrusion plants include an outer chamber with a circular annular shape, from which air is bled and exits radially through one or more cooling lips towards the blown film.

Said air bleeding can be continuous so that a single circular lip is formed without interruptions. Otherwise, the air bleeding can be discontinuous so that discrete ducts are formed which cover a limited circular portion and are in a variable number depending on the localized cooling requirements of the blown film.

Usually, said outer annular chamber is supplied with air through several bleeds that are arranged homogeneously at the same angular distance.

In this way, it is possible to try to reduce the lack of homogeneity in air pressure and air speed inside the outer chamber. In fact, the greater the lack of homogeneity of the air flow inside the annular chamber, the more difficult it is to obtain a homogeneous air flow towards the polymeric film.

Therefore, it is necessary to realize systems that cancel or at least mitigate the lack of homogeneity of the air flow coming from the outer annular chamber towards the cooling lips or towards the discrete cooling ducts.

These systems, in addition to making the cooling ring more complex, have little flexibility and are not always full effective. In fact, in the case it is necessary to change the number of air bleeds of the outer annular chamber, arranged in a discrete way, the geometry of the outer annular chamber must be usually changed.

Among the possible solutions to lack of homogeneity of the air flow coming from the outer annular chamber, there is also the realization of an intermediate chamber between the same outer annular chamber and the cooling lips.

However, the realization of this intermediate chamber involves a significant load loss due to the decrease in volume from the outer annular chamber to the same intermediate chamber.

An object of the present invention is to provide a cooling ring for extrusion plants for the extrusion by blowing of a polymeric film in order to solve the aforesaid problems and other problems of the known systems.

Another object of the invention is to provide a cooling ring that avoids load losses of the air flow as much as possible from the outer annular chamber to the cooling openings for the extruded polymeric film.

A further object of the invention is to provide a cooling ring that allows to vary the number of air bleeds in the outer annular chamber without having to modify the geometry of the same outer annular chamber.

All the aforesaid objects and other objects are reached according to the invention through a cooling ring for extrusion plants for extrusion by blowing of a polymeric film F extruded from an extruder.

The cooling ring according to the invention comprises an annular structure in which an outer annular chamber is formed and is connected to an inlet duct to bring a flow of air into the outer annular chamber.

The outer annular chamber is connected to an intermediate chamber from which at least one slot starts which has at least one open end, open towards the inside of the cooling ring so as to let the air out on the polymeric film F, this air being used to adjust the thickness of the film itself.

In particular, the cooling ring according to the invention is characterized by the fact that at least one pipeline is connected to the outer annular chamber and develops radially, the at least one pipeline having an open end, adapted to blow air on the polymeric film F.

The one or more pipelines are directly connected to the same outer annular chamber, without the need to have systems or devices adjusting pressure and speed inside said one or more pipelines.

Hence, the one or more pipelines may be connected to the outer annular chamber without passing through the intermediate chamber.

With air bleeding for the one or more pipelines directly from the outer annular chamber, it is possible to avoid deriving air from a suitable chamber of lower volume than the outer chamber, realized according to prior art specifically to make air pressures and air speeds homogeneous. Indeed, this volume reduction would lead to high load losses, namely losses of fluid energy.

Advantageously, in order to independently regulate the air flow rate of each pipeline, the same pipelines may be connected to the outer annular chamber by means of a respective shutter.

Moreover, the one or more pipelines may be placed below the one or more open ends blowing on the polymeric film F. In this way, the one or more pipelines blow air on the polymeric film F before the one or more open ends.

Advantageously, a removable profile may be received in the open end of the one or more pipelines, a frusto-conical head being fixed to said removable profile so as to generate an axial component on the air flow incident on the surface of the polymeric film.

To strengthen the aforesaid purpose, the frusto-conical head may be arranged externally at the open end of the one or more pipelines.

Advantageously, the outer annular chamber may have a spiral development with a non-constant angular section and having a geometric axis coinciding with the axis of the extruded polymeric film F, the angular section of the outer annular chamber being greater near the inlet duct and decreasing as the angle changes.

Said spiral development generates an air flow with speed and pressure range having characteristics of axial symmetry. In particular, the pressure distribution inside the outer annular chamber has an axial symmetry that does not depend on the angle so as to allow a regularized air bleeding of air flow rates towards the cooling openings.

In essence, the shape of the outer annular chamber allows having a homogeneous pressure along the entire lateral portion of the same outer annular chamber.

Besides, in the case of discrete bleeds, said characteristic allows varying the number of bleeds without having to change the geometry of the same outer annular chamber as it happens instead in many solutions according to prior art.

Advantageously, the outer annular chamber may have an outer side face of spiral development, and an inner side face of circular development so as to facilitate planning and implementation of the discrete bleeds and/or the one or more slots for continuous bleeding towards the polymeric film F.

Besides, the height of the outer side face is greater than the height of the inner side face so as to convey in an optimal way the air flow from the outside to the inside of the ring.

Advantageously, at least two septa with radial development may be included between the outer annular chamber and the intermediate chamber so as to make the air flow direction radial from the outer annular chamber to the intermediate chamber.

Moreover, heating means are included in the outer annular chamber and are adapted to heat the air present in the same outer annular chamber.

Further features and details can be better understood from the following specification that is supplied by way of a non-restricting embodiment as well as from the annexed drawing, wherein:

Figures 1 and 2 are an axonometric view and a view from below of a cooling ring, made according to the invention, respectively;

Figure 3 is a side view in section of the cooling ring in Figure 1 , according to a transverse plane;

Figure 4 is an enlarged view of a detail in Figure 3;

Figure 5 is a view from below and in section of an annular structure forming part of the cooling ring in Figure 1 , sectioned according to a longitudinal plane.

With reference to the annexed drawing, reference number 10 denotes a cooling ring for extrusion plants for extrusion by blowing of a polymeric film F.

The cooling ring 10 includes an annular structure 12 which has a side face

14 with spiral profile to which a duct 16 is connected.

As represented in section in Figure 5, an inlet chamber 17, connected to the duct 16, and an outer annular chamber 18 are formed inside the annular structure

12.

The outer annular chamber 18 has a spiral development with angular section with non-constant area and having a geometric axis coinciding with the axis of the extruded polymeric film F.

In particular, the angular section is greater near the duct 16, then decreasing as the angle changes.

In other words, the outer annular chamber 18 has an outer side face of spiral development while the inner side face has a perfectly circular development.

Besides, the height of the outer side face is greater than the height of the inner side face so as to convey in an optimal way the air flow; in particular, the shape of the angular section of the outer annular chamber 18 is substantially trapezoidal, as also evident from Figures 3 and 4.

The duct 16 supplies air to the outer annular chamber 18 in the inside of which owing to the aforesaid spiral conformation, an air flow is generated which has a speed component with radial direction.

In particular, the air pressure distribution inside the outer annular chamber 18 has an axial symmetry which is independent of the angle. In this way, it is possible to obtain a homogeneous radial air bleeding towards the inside of the ring 10.

The outer annular chamber 18 communicates with an intermediate chamber 20 formed between the innermost portion of the annular structure 12 and an adjustment ring nut 24 on which an upper ring nut 25 is screwed.

Septa 22 of radial development are arranged between the outer annular chamber 18 and the intermediate chamber 20.

Said septa 22 are arranged in a circular manner at equal angular distances and serve to eliminate the tangential component of the air flow speed. In this way, the direction of the air inside the intermediate chamber 20 is purely radial. A lower disk 26 is fastened inferiorly to the annular structure 12 and in turn, a cone of formation 28 is fixed to the lower disk 26. This structure allows the formation of a first slot 30 between the cone of formation 28 and the adjustment ring nut 24, this first slot 30 being open upwards by means of an upper lip 32.

Passage holes 34 are formed in the cone of formation 28 to connect the first slot 30 with a second slot 36 communicating towards the film F by means of a lower lip 38.

Air is blown from the upper lip 32 to the lower lip 38 on the polymeric film so as to cool it.

The size of the first slot 30, in particular the size of a narrowing 40 obtained in the same first slot 30, may be adjusted by screwing or unscrewing the adjustment ring nut 24.

In this way, by means of the adjustment ring nut it is possible to adjust the air flow rate of the air exiting both the upper lip 32 and the lower lip 38.

Pipelines 42 are arranged radially and are connected inferiorly to the outer annular chamber 18 so as to generate an air flow with a speed orthogonal to the surface of the blown film.

Each pipeline 42 is connected through a shutter 44 and its relative shutter- holder 46 to the outer annular chamber 18.

The position of a piston 48 in the shutter 44 may vary the size of the air passage section from the outer annular chamber 18 to the relative pipeline 42.

The air coming out of said pipelines 42 allows the plastic film thickness to be adjusted in the area facing the film exit from the extrusion head.

Consequently, by controlling the shutter 44 of each pipeline 42, independently of each other, it is possible to adjust the film thickness along its circumference adjacent to the outlet of the pipelines 42.

A removable profile 50 is fixed to the open end 49 of each pipeline 42 and has a frustoconical head 52 generating an axial component in the speed of the air flow incident on the surface of the film.

Besides, variants may be provided which are to be considered as included in the scope of protection of the present invention as defined by the following claims. For example, the outer annular chamber may include an element that transfers thermal power to the current of air that touches it, through forced convection, and increases the temperature of the air itself.

In this way, it is possible to exploit the variation of air temperature to reduce the convective heat exchange and mitigate the cooling of the polymeric film.

Besides, the shape of the angular section of the annular chamber may be different from the trapezoidal shape, satisfying in any case the requirements of having a narrower portion facing the conveying slots leading to the cooling lips.

Claims

1. Cooling ring (10) for extrusion plants for extrusion by blowing a polymeric film F extruded from an extruder, comprising an annular structure (12) in which an outer annular chamber (18) is formed and is connected to a duct (16) to bring a flow of air into the outer annular chamber (18), said outer annular chamber being connected to an intermediate chamber (20) from which at least one slot (30, 36) starts which has at least one open end (32, 38) open to the inside of the cooling ring (10) so as to let the air out on the polymeric film F,

characterized by the fact that at least one pipeline (42) is connected to the outer annular chamber (18) and develops radially, the at least one pipeline having an open end (49) adapted to blow air on the polymeric film F.

2. Cooling ring (10) according to the preceding claim, wherein the at least one pipeline (42) is connected to the outer annular chamber (18) without passing through the intermediate chamber (20).

3. Cooling ring (10) according to one of the preceding claims, wherein the at least one pipeline (42) is connected to the outer annular chamber (18) by means of a shutter (44).

4. Cooling ring (10) according to one of the preceding claims, wherein the at least one pipeline (42) is placed below the at least one open end (32, 38) so as to blow air on the polymeric film F before the at least one open end (32, 38).

5. Cooling ring (10) according to one of the preceding claims, wherein a removable profile (50) is received in the open end (49) of the at least one pipeline (42), a frustoconical head (52) being fixed to said removable profile.

6. Cooling ring (10) according to the preceding claim, wherein the frustoconical head (52) is arranged externally at the open end (49) of the at least one pipeline(42).

7. Cooling ring (10) according to one of the preceding claims, wherein the the outer annular chamber (18) has a spiral development with a non-constant angular section and having a geometric axis coinciding with the axis of the polymeric film F extruded, the angular section of the outer annular chamber (18) being greater near the duct (16) and decreasing as the angle changes.

8. Cooling ring (10) according to the preceding claim, wherein the outer annular chamber (18) has an outer side face of spiral development, and an inner side face of circular development.

9. Cooling ring (10) according to the preceding claim, wherein the height of the outer side face is greater than the height of the inner side face.

10. Cooling ring (10) according to one of the preceding claims, wherein at least two septa (22) with radial development are comprised between the outer annular chamber (18) and the intermediate chamber (20).

11. Cooling ring (10) according to the preceding claim, wherein the angular distance between the at least two septa (22) is the same.

12. Cooling ring (10) according to one of the preceding claims, wherein heating means are included in the outer annular chamber (18) and are adapted to heat the air present in the outer annular chamber (18).