WO2023148676A1 - Cooling ring for extrusion plants - Google Patents

Abstract

This is a cooling ring for plastic film extrusion blow-moulding equipment. More specifically, it is a cooling ring that efficiently achieves a flow of air acting on the film in an adjustable manner depending on the areas of interest.

Description

COOLING RING FOR EXTRUSION PLANTS

Specification

The present invention relates generally to a cooling ring for extrusion blowmoulding equipment for a polymeric film. More particularly, it relates to a cooling ring which efficiently provides an air flow acting on the film in an adjustable manner depending on the areas of interest.

As is well known, cooling rings for extrusion blow-moulding systems comprise an outer chamber, circular in shape, from which air is tapped and exits radially through one or more cooling lips towards the blown film.

These spillages may be continuous, conforming as a single uninterrupted annular opening, or they may be discrete ducts, i.e. covering a limited circular portion and in a variable number depending on the need for localised cooling of the blown film.

Usually, this external annular chamber is supplied with air through several inlets, evenly spaced at equal angular distances.

In this way, an attempt is made to decrease the inhomogeneity in pressure and air velocity within the outer chamber. In fact, the greater the inhomogeneity of the air flow inside the annular chamber, the more difficult it is to obtain a homogeneous air flow at the outlet towards the polymer film.

Therefore, systems must be implemented to eliminate or at least mitigate the inhomogeneity of the airflow from the outer annular chamber towards the cooling lips or discrete cooling ducts.

Such systems, in addition to making the cooling loop more complex, have little flexibility and are not always fully effective.

In fact, in the event that one wants to change the number of air pushes from the discretely distributed outer annular chamber, one usually has to modify the geometry of the outer annular chamber itself.

Possible solutions to the inhomogeneity of the air flow from the outer annular chamber include the construction of an intermediate chamber between the outer annular chamber itself and the cooling lips.

But the realisation of such an intermediate chamber results in a significant pressure drop due to the decrease in volume from the outer annular chamber to the intermediate chamber itself.

Another problem related to the entry of air into the outer annular chamber relates to the component of the rotational motion of the air around the axis of said tubular film. This component disturbs the stability of the tubular film and the uniformity of its thickness.

In order to solve this problem, channels or rectifiers with multiple ducts are realised to eliminate the rotational motion component of the cooling fluid of said tubular film.

Such channels or rectifiers also involve a significant pressure drop.

It is an object of the present invention to realise a cooling loop for extrusion blow-moulding systems of a polymeric film, which solves these and other problems of the known systems.

A further scope of the invention is to provide a cooling ring which eliminates as much as possible the component of the rotational motion of the air from the outer annular chamber towards the innermost portion wherein the air is tapped and exits radially through one or more cooling lips towards the blown film.

A further scope of the invention is to obtain a cooling ring which avoids as much as possible pressure losses of the air flow from the outer annular chamber to the cooling apertures of the extruded polymer film.

A further purpose of the invention is to provide a cooling ring which allows the number of air tappings from the outer annular chamber to be varied without changing the geometry of the outer annular chamber itself.

These and other purposes are all achieved, according to the invention, by a cooling ring for extrusion equipment for blow moulding a polymeric film F extruded from an extruder in accordance with the appended claim 1 .

The cooling ring according to the invention comprises an annular structure in which an outer annular chamber is formed connected to at least one inlet duct for bringing an air flow into the outer annular chamber.

The outer annular chamber is connected to an inner annular chamber from which departs at least one slit with at least one end open towards the inside of the cooling ring, so as to bring out on the polymeric film F the air to be used for adjusting the thickness of the same film.

In particular, the cooling ring according to the invention is characterised in that a perforated grid is arranged between the outer annular chamber and the inner annular chamber.

The holes in the perforated grille can have a radial development and can have a diameter equal to or less than the thickness of the perforated grille. In this way, the perforated grille determines that the air flow inside the inner annular chamber has a radial direction.

In this way, in addition to creating a radially directed air flow, the air streams emerging inside the grille are uniform in flow rate, minimising pressure losses.

Furthermore, the perforated grille can have a circular cross-section with an axis coincident with the axis of the cooling ring, so that the air inside the inner annular chamber has uniform velocity.

In addition, the perforated grille allows for appropriate mixing of the air inside the outer annular chamber, in particular the air which continues to move in rotation in the outer annular chamber itself, and the air which enters the same annular chamber through the inlet duct.

At least one duct may be connected to the inner annular chamber which develops radially, and which has an open end suitable for blowing air onto the polymer film F.

The one or more ducts are connected directly to the same inner annular chamber, without the need for any systems or devices to regulate the pressure and speed within the one or more ducts.

By tapping air for the one or more pipes directly from the inner annular chamber, which is in turn connected to the outer annular chamber, pressure losses, i.e. fluid energy, are reduced.

Advantageously, in order to regulate the air flow rate of each duct independently, the ducts themselves can be connected to the inner annular chamber by means of a respective shutter.

Furthermore, the one or more ducts may be arranged inferiorly to the one or more open ends blowing air onto the polymer film F. In this way, the one or more ducts blow air onto the polymer film F before the one or more open ends.

Advantageously, the outer annular chamber may have a spiral development with a non-constant angular cross-section and having a geometric axis coincident with the axis of the extruded polymer film F, wherein the angular cross-section of the outer annular chamber is greater in proximity to the inlet duct, decreasing as the angle varies. This spiral conformation generates an air flow with a velocity and pressure field having characteristics of axial symmetry. In particular, the pressure distribution inside the outer annular chamber has an axial symmetry that is not dependent on angle such as to allow a regularised flow of air towards the cooling apertures.

In essence, the shape of the outer annular chamber allows for homogenous pressure along the entire inner lateral portion of the outer annular chamber itself.

Advantageously, the outer annular chamber may have an outer lateral face of spiral development and an inner lateral face of circular development, so as to facilitate the design and realisation of the discrete pins and/or the one or more slots for continuous pins towards the polymeric film F.

Furthermore, the height of the outer side face is greater than the height of the inner side face, so as to optimally convey the air flow from the outside to the inside of the ring.

Advantageously, at least two radial development baffles can be included in the inner annular chamber to provide structural support for the annular structure.

In addition, heating means for heating the air in the outer annular chamber itself may be included in the outer annular chamber.

Further features and details can be better understood from the following description, which is given as a non-limiting example, as well as from the accompanying drawing tables in which

Figs. 1 and 2 are axonometric and bottom views, respectively, of a cooling ring, made according to the invention;

Fig. 3 is a cross-sectional side view of the cooling ring of Fig. 1 in a transverse plane; Fig. 4 is an enlarged view of a detail of figure 3;

Fig. 5 is a bottom view and sectional view of an annular structure forming part of the cooling ring of figure 1 , sectioned in a longitudinal plane;

Fig. 6 is a three-dimensional sectional view of the cooling ring of figure 1 in a transverse plane.

With reference to the attached figures, a cooling ring for extrusion blowmoulding equipment for a polymer film F is indicated by 10.

The cooling ring 10 comprises an annular structure 12 having a side face 14 with a spiral profile and to which a duct 16 is connected.

As illustrated in section in Figure 5, an inlet chamber 15, connected to the duct 16, and an outer annular chamber 18 are formed within the annular structure 12.

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

In particular, the angular cross-section is greater in the vicinity of the duct 16, decreasing as the angle varies.

In other words, the outer annular chamber 18 has an outer side face of spiral development, while the inner side face defined by a perforated grid 17, has a perfectly circular development.

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

The duct 16 supplies air to the outer annular chamber 18 inside which, thanks to the previously defined spiral conformation, an air flow having a velocity component with radial direction is generated.

In particular, the pressure distribution of the air inside the outer annular chamber 18 has an axial symmetry independent of the angle. In this way, a homogeneous radial air displacement towards the inside of the ring 10 can be achieved.

The perforated grid 17 separates the outer annular chamber 18 from the inner annular chamber 20 and has a circular cross-section with an axis coincident with the axis of the cooling ring 10.

In the perforated grille 17 there are holes of radial development whose diameter is equal to or less than the thickness of the same perforated grille 17. Thus, the air which passes through the perforated grille 17 through the holes and enters the inner annular chamber 20, has a purely radial direction

Thus, the perforated grille 17 creates an air flow radially directed towards the inside of the cooling ring 10.

Furthermore, the air flows emerging from the perforated grille 17 inwards and around its circumference are uniform in flow rate, minimising pressure losses.

In fact, the perforated grille 17 acts as an equaliser of the air pressure inside the inner annular chamber 20. In other words, the holes in the perforated grille 17 only allow the passage of air flows in the outer annular chamber 18 that have a radial velocity between desired values.

The number of holes present in the perforated grille 17 is chosen, in fact, according to the range of radial velocity values of the air desired to pass through the perforated grille 17.

The perforated grille 17, in addition to realising what has just been illustrated in the inner annular chamber 20, also allows for an appropriate mixing of the air inside the outer annular chamber 18, in particular of the air that continues to move in rotation in the outer annular chamber 18 and of the air that enters the same annular chamber 18 through the inlet chamber 15.

The inner annular chamber 20 is formed in the innermost portion of the annular structure 12, inferiorly to an adjusting ring 24, on which an upper ring 25 is screwed.

In the inner annular chamber 20, radially arranged septa 22 are positioned, which serve as structural support to the annular structure 12.

The septa 22, arranged radially and at equal angular distances, also maintain the direction of the air inside the inner annular chamber 20 purely radial.

Attached to the annular structure 12 is a lower disc 26, to which is, in turn, attached a formation cone 28. Thanks to this structure, a first interstice 30 is created between the formation cone 28 and the adjustment ring 24 which is opened upwards by an upper opening 32.

In the formation cone 28, passage holes 34 are obtained so as to put the first interstice 30 in communication with a second interstice 36 communicating towards the film F by means of a lower opening 38.

From the upper opening 32 and the lower opening 38, air is blown over the polymer film so as to cool it.

The dimensions of the first interstice 30, in particular the dimensions of a restriction 40 formed in the same first interstice 30, can be adjusted by screwing or unscrewing the adjusting ring 24.

In this way, by means of the adjustment ring nut it is possible to adjust the air flow rate at the outlet from both the upper opening 32 and the lower opening To the inner annular chamber 20 are inferiorly connected ducts 42 arranged radially, so as to generate an air flow with a velocity orthogonal to the surface of the bubble film.

Each duct 42 is connected to the inner annular chamber 20 via a shutter 44 and an associated shutter holder 46.

The position of closure means 48 present in the shutter 44 can vary the size of the air passage section from the outer annular chamber 18 to the respective duct 42.

The air exiting such ducting 42 allows adjustment of the thickness of the plastic film in the area facing the film exit from the extrusion head.

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

A removable profile 50 with a truncated cone head 52 suitable for generating an axial component in the velocity of the air flow incident on the surface of the film is attached to the open end 49 of each duct 42.

There may also be variations to be considered within the scope of the invention as defined by the following claims. For example, an element may be included in the outer annular chamber which yields thermal power to the air stream flowing past it, through forced convection, and increases the temperature of the air itself.

In this way, the change in air temperature can be exploited to reduce convective heat transfer and mitigate the cooling of the polymer film.

Furthermore, the shape of the angular section of the annular chamber can be different from the trapezoidal one, while still meeting the requirements of having a narrower portion facing the conveying slots leading to the cooling lips.

Claims

1. Cooling ring (10) for extrusion systems for blowing a polymeric film F extruded by an extruder, comprising an annular structure (12) in which an outer annular chamber (18) is formed, connected to a duct (16) for bringing an air flow inside the outer annular chamber (18), said outer annular chamber being connected to an inner annular chamber (20) from which there is at least one slot (30, 36) with at least one open end (32, 38) towards the inside of the cooling ring (10) so as to bring air out on the polymeric film F, characterized in that the outer annular chamber (18) and the inner annular chamber (20) are separated by a perforated grid (17) having a determined thickness.

2. Cooling ring (10) according to the preceding claim, wherein the perforated grid (17) has a circular cross-section with an axis that is coincident with the axis of the cooling ring (10).

3. Cooling ring (10) according to one of the preceding claims, wherein the holes obtained in the perforated grid (17) have a radial development.

4. Cooling ring (10) according to one of the preceding claims, wherein the holes obtained in the perforated grid (17) have a diameter equal to or smaller than the thickness of the perforated grid (17).

5. Cooling ring (10) according to one of the preceding claims, wherein the at least one pipeline (42) having a radially developed open end (49) suitable for blowing air onto the polymeric film F is connected to the inner annular chamber (20).

6. Cooling ring (10) according to the preceding claim, wherein the at least one conduit (42) is connected to the inner annular chamber (20) by means of a shutter (44).

7. Cooling ring (10) according to any of the preceding claims, wherein the at least one conduit (42) is disposed inferiorly to the at least one open end (32, 38) so as to blow air onto the polymer film F before the at least one open end (32, 38).

8. Cooling ring (10) according to one of the preceding claims, wherein 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 extruded polymeric film F, the angular section of the outer annular chamber (18) being greater in proximity to the duct (16), decreasing as the angle varies.

9. Cooling ring (10) according to the preceding claim, wherein the outer annular chamber (18) has an outer lateral face of spiral development, and an inner lateral face of circular development, and/or wherein the height of the outer lateral face is greater than the height of the inner lateral face.

10. Cooling ring (10) according to any of the preceding claims, wherein the inner annular chamber (20) comprises at least two radially developed septa (22).

11. Cooling ring (10) according to any of the preceding claims, wherein the angular distance between the at least two septa (22) is equal.