Cooling ring for an apparatus for the production of plastic blown films
Patent Information
- Application Number
- EP2023728429
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2022-05-03
- Filing Date
- 2023-05-02
- Publication Date
- 2025-03-12
AI Technical Summary
Conventional cooling rings for plastic blown film production exhibit poor uniformity in airflow, leading to significant thickness variations along the bubble's circumference, which complicates the stability and cooling capacity of the bubble formation process.
A turbulator device with flow-perturbating elements is positioned within the cooling ring's hollow body to create turbulence, ensuring a more uniform airflow distribution without increasing pressure drops or affecting system efficiency.
The solution achieves uniform airflow distribution, enhancing process controllability and cooling capacity with reduced thickness variations, thereby increasing hourly film output within tight thickness tolerances.
Smart Images
Figure 1.1
Abstract
Description
[0001] COOLING RING FOR AN APPARATUS FOR THE PRODUCTION OF PLASTIC BLOWN FILMS
[0002] Technical field of the invention
[0003] The present invention relates generally to the field of apparatuses for producing plastic blown films, i.e., extruded plastic films in bubble form. More particularly, the present invention relates to a cooling ring for an apparatus for the production of plastic blown films, wherein the cooling ring is provided with a system, which may be static, translating and / or rotating about its own axis, to make the flow of the cooling air leaving the ring more uniform.
[0004] State of the art
[0005] Referring to Figure 1 of the accompanying drawings, a conventional apparatus for the production of plastic blown film basically comprises an extrusion head 1 from which a tubular film FT exits, a cooling ring 2 placed at the outlet of the extrusion head 1 for blowing cooling air onto the tubular film FT, a calibration cage 3 for guiding the tubular film FT, a thickness measuring device 4 for measuring the thickness of the tubular film FT, a take-up unit 5 for flattening the tubular film FT to form a flattened film FA and finally a winding unit 6 where the flattened film FA is trimmed and possibly divided into several parts before being wound onto reels B. The example of Figure 1 illustrates an apparatus in which the plastic material is extruded vertically, in a bottom-up direction. Other apparatus configurations are known, however, in which cooling rings can be used, e.g. extrusion lines with a still vertical direction, but with top-down direction, and horizontal extrusion lines.
[0006] A known example of a cooling ring 2 is shown in detail in Figures 2 and 3.
[0007] With reference to those figures, the cooling ring 2 comprises a hollow body 7 of annular shape extending around a circular central bore 8 through which the tubular film FT exiting the extrusion head 1 flows. The hollow body 7 has at least one inlet opening 9 for allowing the entry of air, which entry in this case is directed in a tangential direction. The hollow body 7 defines within it a path, generally of spiral shape in the case of a single inlet, along which the air, that is blown into the hollow body through the inlet opening 9, flows. In the present case, the hollow body 7 comprises an inclined inner wall 10, which acts as a deflector element to help divert the direction of the airflow from horizontal to vertical. The air then passes through a plurality of windows 11 each defined by a pair of separating walls 12, oriented for example vertically and radially, to finally exit the cooling ring 2 through a plurality of outlet openings (not shown) directed radially or, more generally, towards the axis of the central bore 8 or, alternatively, through a single circular outlet opening. Such windows and separating walls may however, depending on the design of the cooling ring, have different shapes and configurations than those shown in Figures 2 and 3. A possible alternative configuration of windows and separating walls is known, for example, from CA1115471.
[0008] Appropriate fluidic and / or thermal adjusting means are normally provided to adjust the airflow leaving the cooling ring 2 through the aforementioned outlet openings. For example, flow adjusting members 13 that are translatable radially inwards or outwards, under control of suitable actuators, may be provided as adjusting means to decrease or increase, respectively, the cross-sectional area of the windows 11. Further solutions are known for example from US2021 / 291426 and W090 / 15707.
[0009] One problem of the known cooling rings is the poor uniformity of the airflow flowing through the windows 11 to finally reach the outlet opening(s) or, more generally, in the case where no windows are provided upstream of the outlet opening(s), the poor uniformity of the airflow flowing through the outlet opening(s). In this regard, Figure 4 shows the distribution of air flow velocities in two of the windows 11 of the cooling ring 2, obtained by computer simulation. As can be seen from this figure, the distribution of the air flow velocities measured immediately upstream of each window 11 is highly inhomogeneous and, more importantly, there may be areas where the air flow velocity is even negative, i.e. where the air is sucked backwards instead of flowing towards the outlet openings. In addition, as shown by the dotted curve in Figure 5 (also obtained by computer simulation), which shows for all windows 11 of the cooling ring 2 the trend of the average air flow velocity immediately upstream of each window, there are quite significant deviations in the average air flow velocities from window to window.
[0010] This causes significant thickness variations along the bubble's circumference, which makes the control of the stability of the bubble formation process more difficult. Achieving a uniform flow is crucial to maximise the cooling capacity. Only if the bubble is highly uniform and stable it will be possible to enhance the cooling capacity, thereby achieving a higher hourly film output within tight thickness tolerances.
[0011] It is known from US 2019 / 358884, on which the preamble of independent claim 1 is based, a cooling ring comprising a hollow body, extending around a central bore, and at least one supply channel connected to the hollow body to supply a flow of cooling air, wherein, in order to obtain a uniform airflow exiting the hollow body there is provided, in each supply channel, a turbulator device having a plurality of flow-perturbating elements configured to interact with the airflow so as to cause at least part of the airflow to rotate around a flow axis before the airflow enters the hollow body. Such flow-perturbating elements are arranged and configured to make the airflow turbulent at the periphery of the supply channel.
[0012] Summary of the invention
[0013] It is an object of the present invention to provide an improved solution with respect to the prior art, in particular a solution that allows to make the airflow leaving the hollow body through the outlet opening(s) more uniform.
[0014] This and other objects are achieved according to the invention by virtue of a cooling ring as defined in the appended independent claim 1.
[0015] Further advantageous aspects of the cooling ring according to the invention are defined in the dependent claims, the subject-matter of which is to be understood as forming part of the following description.
[0016] The present invention also relates to an apparatus for the production of plastic blown films comprising a cooling ring as specified above.
[0017] In summary, the present invention is based on the idea of positioning within the hollow body of the cooling ring a turbulator device having a plurality of flow-perturbating elements which are arranged in a distributed manner along at least one circumferential ring around the central bore of the hollow body and are configured to make the airflow with which said elements interact turbulent.
[0018] Thanks to such a configuration of the turbulator device within the hollow body of the cooling ring, a more uniform airflow is achieved compared to the prior art, thereby achieving an advantage in terms of process controllability without increasing the pressure drops, i.e., without adversely affecting the efficiency of the system. Furthermore, the proposed solution avoids, in the case of a cooling ring with several inlet channels, having to position the elements of the turbulator device in each inlet channel, as is necessary in the prior art discussed above.
[0019] Brief description of the drawings
[0020] Further features and advantages of the present invention will become more apparent from the following description, which is made purely by way of non-limiting example with reference to the accompanying drawings, where:
[0021] - Figure 1 is a perspective view of a known example of an apparatus for the production of plastic blown film to which a cooling ring according to the present invention is applicable;
[0022] - Figure 2 is a perspective view of a known example of a cooling ring;
[0023] - Figure 3 is an axial sectional view of part of the cooling ring of Figure 2;
[0024] - Figure 4 is a graph showing the distribution of air flow velocities immediately upstream of two adjacent windows of the cooling ring of Figure 2;
[0025] - Figure 5 is a graph showing the distribution of the average air flow velocities immediately upstream of the windows of the cooling ring of Figure 2, as well as of a cooling ring according to the present invention;
[0026] - Figure 6 is a perspective view showing part of a cooling ring according to an embodiment of the present invention, sectioned through an axial section plane;
[0027] - Figure 7 is an axial sectional view of the turbulator device of the cooling ring of Figure 6;
[0028] - Figure 8 is a perspective view of the turbulator device of the cooling ring of Figure 6;
[0029] - Figure 9 is a graph similar to that of Figure 4, but relating to the cooling ring of Figure 6;
[0030] - Figure 10 is a perspective view of a further example of a turbulator device for a cooling ring according to the present invention;
[0031] - Figures 11 and 12 are a perspective view from above and a perspective view from below, respectively, showing in detail part of the turbulator device of Figure 10; and
[0032] - Figures 13 and 14 are perspective views showing two further examples of a turbulator device for a cooling ring according to the present invention.
[0033] Detailed description
[0034] Referring first to Figure 6, where parts and elements identical or corresponding to those of Figure 3 (prior art) are indicated with the same reference numerals, a cooling ring 2 according to the present invention comprises, in addition to the components already described above with reference to Figure 3, a turbulator device 14 positioned inside the hollow body 7, immediately upstream of the windows 11, so as to intercept the airflow which flows from the inlet opening (not visible in Figure 6) towards the outlet openings (also not visible in Figure 6) passing through the windows 11. The turbulator device 14 is configured to interact with the air flowing from the inlet opening towards the outlet openings to generate turbulence and thus make the velocity distribution in the airflow upstream of the outlet openings more uniform. As can best be observed in Figure 8, the turbulator device 14 basically comprises a support structure 15 of annular shape and a plurality of flow-perturbating elements 16 protruding from the support structure 15 to interact with the airflow to make it turbulent.
[0035] With regard to the support structure 15, although in the drawings it is illustrated as a circular structure, it may also have a different shape, for example a polygonal one. The expression "annular shape" above is therefore not to be understood as being limited to a circular shape. Furthermore, even if in the embodiment proposed herein the support structure 15 is formed of a single piece of annular shape, it might alternatively be formed of several separate pieces, angularly spaced apart from each other, along an annular path.
[0036] The flow-perturbating elements 16 extend radially inwards or, more generally, towards the axis of the central bore of the hollow body, thus not necessarily in a radial direction. The flow-perturbating elements 16 are arranged along the entire inner perimeter of the support structure 15, preferably equally spaced from each other. More generally, the flow-perturbating elements 16 are arranged in a distributed manner along a circumferential ring around the central bore of the hollow body.
[0037] The number of flow-perturbating elements 16 can be appropriately chosen depending on the specific application. For example, according to one embodiment, the number of flow- perturbating elements 16 is twice the number of windows 11 , as shown in Figure 9. In this case, the turbulator device 14 may be positioned so that, for each window 11 , there is a flow-perturbating element 16 arranged at the centreline of said window and that the two adjacent flow-perturbating elements 16 are each aligned with a respective separating wall 12 of said window, as shown in Figure 9. Alternatively, the turbulator device 14 may be arranged rotated by a certain angle with respect to the position of Figure 9, for example so that none of the flow-perturbating elements 16 is aligned with one of the separating walls 12.
[0038] In the embodiment of Figures 6 to 9, the flow-perturbating elements 16 have a transverse cross-section (i.e. , in the present case, a cross-section in a plane perpendicular to the radial direction) that is substantially isosceles trapezoid in profile, with a pair of bases extending horizontally and a pair of inclined sides joining the bases at their opposite ends and having the same length. The shape of the transverse cross-section of the flow- perturbating elements 16 may, however, differ from that shown in Figures 8 and 9. For example, the flow-perturbating elements 16 may always have a trapezoidal shape, but with oblique sides of different lengths from each other, and therefore with an inclination with respect to the horizontal which differs from each other.
[0039] The function of the turbulator device 14 is, as mentioned above, to generate turbulence in the airflow flowing towards the outlet openings of the ring, not to channel the airflow along a certain direction. In this respect, the turbulator device 14 is arranged within the hollow body 7 so that the flow-perturbating elements 16 are at a certain distance from the walls of the hollow body 7 and the separating walls 12 of the windows 11 (if any). In this way, the airflow flowing into the turbulator device 14 is not divided by it into individual airflows that are no longer communicating, but the various airflows flowing through the passages identified by each pair of adjacent flow-perturbating elements 16 have the possibility of interacting with each other downstream of the turbulator device 14 (but of course upstream of the outlet openings).
[0040] Furthermore, since in the embodiment proposed herein (as can be observed in particular in Figure 7) there is a certain free space between the turbulator device 14 and the inner wall 10 of the hollow body 7, a part of the airflow upstream of the turbulator device 14 can flow through said free space, without therefore flowing through the passages defined by each pair of adjacent flow-perturbating elements 16.
[0041] Furthermore, in order to allow the turbulator device 14 to perform the function of generating turbulence in the airflow passing through it, the flow-perturbating elements 16 are configured, as shown in Figure 7, in such a way that, considering the cross-section of said elements in a section plane extending longitudinally with respect to the airflow flowing through the turbulator device 14 (i.e., in the present case, a plane passing through the axis of the central bore of the cooling ring) the longitudinal dimension L of each element (i.e., the dimension of the element along the main direction of the airflow, which in the present case is the vertical direction or, more generally, the direction parallel to the axis of the central bore of the cooling ring) and the transverse dimension H of each element (i.e., the dimension of the element in a direction perpendicular to the main direction of the airflow) are linked by the following relation: L < 1.5 H. Preferably, the longitudinal dimension L is smaller than the transverse dimension H, i.e. L < H.
[0042] In the embodiment of Figures 6 to 8, the turbulator device 14 further comprises a plurality of flow-deviating elements 17, which in the present case extend upwards from an upper annular edge of the support structure 15, preferably equally spaced from each other. More generally, the flow-deviating elements 17 are arranged distributed along a circumferential ring around the central bore of the hollow body 7. In the proposed embodiment, the flow-deviating elements 17 are all inclined by the same angle with respect to the radial direction, but might also be directed radially. Furthermore, in the proposed embodiment the number of flow-deviating elements 17 is equal to the number of flow-perturbating elements 16, but the two types of elements might also be different in number from each other.
[0043] The solution illustrated herein has windows 11 in a substantially perpendicular plane with respect to the axis of the hollow body 7 (i.e. the axis of the central bore of the hollow body), which in the typical case of a system in which the plastic material is extruded in a vertical direction is a horizontal plane, with the windows 11 being separated by substantially radial separating walls 12. Obviously, the flow-passage surfaces of the windows 11 might be arranged according to a different geometry, for example arranged on conical or cylindrical surfaces (the latter configuration corresponding to the case in which the windows open on radial channels).
[0044] Furthermore, the general configuration of the hollow body 7 may be different from the one proposed herein. For example, a plurality of inlet openings may be provided and / or the inlet opening(s) may lie in a different plane than a plane parallel to the axis of the central bore of the hollow body. Furthermore, the outlet opening(s) may be directed not radially, but in any other direction oriented towards the axis of the central bore of the hollow body.
[0045] According to a variant embodiment, instead of several outlet openings, a single outlet opening may be provided, which extends over 360° around the central bore of the hollow body.
[0046] Thanks to the presence of such a turbulator device within the hollow body of the cooling ring, a more uniform airflow is achieved already in the common chamber, upstream of the windows (if they are present in the ring) or more generally upstream of the outlet opening(s), therefore with flow velocities uniformly distributed over the cross-sectional area of each individual window (if any) and with negligible variations in the average flow velocities in the various windows (if any), thereby leading to an advantage in terms of process controllability without increasing the pressure drops, and hence without adversely affecting the system efficiency, compared to the prior art.
[0047] In this regard, Figure 9 shows the distribution of flow velocities in two adjacent windows, which distribution is evidently more uniform than that in Figure 4 (prior art). Likewise, Figure 4 shows in a continuous line the course of the average velocities in the various windows of the cooling ring of Figure 6, which course, compared to that depicted in a dotted line and relating to a cooling ring according to the prior art, evidently shows greater uniformity, i.e., fewer deviations from one window to the other.
[0048] Figures 10 to 12 illustrate another possible embodiment of the turbulator device 14, which differs from that of Figures 6 to 8 substantially only in that it does not comprise the flow-deviating elements 17. What has already been set out above with reference to Figures 6 to 8 applies in all other respects.
[0049] Figure 13 illustrates a further embodiment of the turbulator device 14, which differs from that of Figures 6 to 8 substantially only in that it comprises a further group of flow- perturbating elements, indicated with 18, which are arranged in a horizontal plane placed at a higher elevation than that at which the plane of the flow-perturbating elements 16 is placed. The flow-perturbating elements 18 preferably have a geometry similar to that of the flow-perturbating elements 16. Furthermore, the flow-perturbating elements 18 are preferably arranged equally spaced from each other and / or alternating circumferentially with respect to the flow-perturbating elements16. Of course, one or more further groups of flow-perturbating elements might be provided.
[0050] Finally, Figure 14 shows a further example of a turbulator device 14, in which the support structure 15 is formed by a simple flat ring and in which only one group of flow- perturbating elements 16 of a different shape than the flow-perturbating elements of the turbulator devices described above is provided. In this case, each flow-perturbating element 16 comprises a central flat portion 16a, extending radially inwards from the support structure 15, substantially coplanar with the latter, and a pair of lateral flat portions 16b, extending inclined by a certain angle downwards from opposite edges of the central portion 16a. Anyway, the aforementioned relations between the longitudinal dimension and the transverse dimension of each flow-perturbating element in a section plane extending longitudinally with respect to the airflow apply also to this case.
[0051] The present invention has so far been described with reference to certain possible embodiments thereof. As noted above, it is to be understood that other embodiments may be envisaged which share the same inventive core with those described herein, as defined by the appended claims.
[0052] In particular, although the invention has been described herein with reference to a type of cooling ring having the general configuration shown in Figure 2, the invention is clearly not limited to such configuration, but is equally applicable to any other cooling ring configuration.
[0053] For example, the cooling ring may not have separating walls within the hollow body, which two by two define windows for the airflow, in which case the turbulator device would preferably be arranged immediately upstream of the outlet opening(s). Alternatively, there might be two sets of separating walls, and thus two sets of windows, placed at a distance from each other along the airflow path, in which case the turbulator device would preferably be arranged upstream of the first set of windows or, alternatively, between the first and second sets of windows. However, it is also possible to place the turbulator device downstream of the set of windows.
Claims
CLAIMS1. A cooling ring (2) for an apparatus for the production of plastic blown films, the cooling ring (2) comprising- a hollow body (7) extending around a central bore and having at least one inlet opening for a flow of cooling air and at least one outlet opening facing said central bore, so that the airflow entering the hollow body (7) through said at least one inlet opening leaves the hollow body (7) through said at least one outlet opening to be blown onto a tubular film (FT) which, after leaving an extrusion head (1) of the apparatus, is moved forward through said central bore, and- a turbulator device (14) which is positioned within the hollow body (7) and comprises a plurality of flow-perturbating elements (16, 18) configured to interact with the airflow flowing through the hollow body (7) so as to generate turbulence in said airflow, characterized in that said flow-perturbating elements (16, 18) are arranged distributed along at least one circumferential ring around said central bore so as to make the airflow, that flows in the hollow body (7) and leaves the latter through said at least one outlet opening, uniform.
2. Cooling ring according to claim 1 , wherein said flow-perturbating elements (16, 18) are configured in such a manner that, in a section plane extending longitudinally with respect to the airflow flowing in use through the turbulator element (14), the longitudinal dimension (L) of each flow-perturbating element (16, 18), i.e., the dimension of said element (16, 18) along the main direction of the airflow, and the transverse dimension (H) of each flow-perturbating element (16, 18), i.e., the dimension of said element (16, 18) in a direction perpendicular to the main direction of the airflow, are linked by the relation L < 1.5 H, preferably by the relation L < H.
3. Cooling ring according to claim 1 or claim 2, wherein the turbulator device (14) is arranged within the hollow body (7) so that said flow-perturbating elements (16, 18) are at a certain distance from the walls of the hollow body (7) to allow the various airflows flowing through the passages defined by each pair of adjacent flow-perturbating elements (16, 18) to interact with each other downstream of the turbulator device (14), but upstream of said at least one outlet opening.
4. Cooling ring according to any one of the preceding claims, further comprising a plurality of pairs of separating walls (12) defining a corresponding plurality of windows (11) through which the air flows in its path from said at least one inlet opening to said at least one outlet opening, wherein the turbulator device (14) is arranged upstream of saidwindows (11), so as to make the airflow uniform from window (11) to window (11), as well as within each of said windows (11), or downstream of said windows (11), and wherein said flow-perturbating elements (16, 18) are at least partially not circumferentially aligned with said separating walls (12).
5. Cooling ring according to any one of the preceding claims, wherein the turbulator device (14) comprises a support structure (15) arranged around said central bore and wherein said flow-perturbating elements (16, 18) are carried by the support structure (15) so as to protrude therefrom.
6. Cooling ring according to any one of the preceding claims, wherein said plurality of flow-perturbating elements (16, 18) comprises a set of first flow-perturbating elements (16) extending towards the axis of said central bore, in particular in a radial direction.
7. Cooling ring according to claim 4 and claim 6, wherein the number of said first flow- perturbating elements (16) is equal to the number of windows (11) or a multiple of the number of windows (11).
8. Cooling ring according to claim 6 or claim 7, wherein said plurality of flow-perturbating elements (16, 18) further comprises a set of second flow-perturbating elements (18) extending towards the axis of the central bore of the hollow body (7), in particular in a radial direction, in a plane placed at a different height from that in which said first flow- perturbating elements (16) are placed.
9. Cooling ring according to claim 4 and claim 8, wherein the number of said second flow-perturbating elements (18) is equal to the number of windows (11) or a multiple of the number of windows (11).
10. Cooling ring according to any one of claims 6 to 9, wherein said first flow-perturbating elements (16) and / or said second flow-perturbating elements (18) are arranged equally spaced from each other in a circumferential direction.
11. Cooling ring according to any one of claims 6 to 10, wherein said first flow- perturbating elements (16) and / or said second flow-perturbating elements (18) have in cross-section a substantially trapezoidal shape, in particular a substantially isosceles trapezoid shape.
12. Cooling ring according to any one of claims 6 to 11 , wherein said first flow- perturbating elements (16) are alternating in a circumferential direction with respect to said second flow-perturbating elements (18).
13. An apparatus for the production of plastic blown films, comprising a cooling ring (2) according to any one of the preceding claims.