CALIBRATION CAGE FOR THE PRODUCTION OF BLOWN FILMS

Abstract

A calibration cage for the production of a blown film is provided. It has a supporting structure and a plurality of frames rotatable in the horizontal plane which are pivoted along the perimeter of the supporting structure at the vertices of a regular polygon, each frame carrying a vertical rod rotatable with respect thereto which in turn carries at least one element for guiding a blown film, each vertical rod being connected to the vertical rods adjacent thereto through connection elements that are rigid in the horizontal plane yet have a length variable in the plane, each connection element being pivoted between two horizontal pivots each of which forms with a vertical radial plane having the axis of rotation of the respective vertical rod an angle that is equal to half of the internal angle () of the regular polygon.

Claims

1.-18. (canceled)

13. A calibration cage for the production of a blown film, said calibration cage comprising: a) a supporting structure; b) a plurality of frames rotatable in the horizontal plane which are pivoted along the perimeter of said supporting structure at the vertices of a regular polygon; c) a vertical rod on each of said frames, each rod being carried by one of said frames and being rotatable with respect thereto; and d) at least one element on each of said vertical rods, each element being configured to guide a blown film, wherein each of said vertical rods is connected to at least one of the vertical rods adjacent thereto through at least one connection element that is rigid in the horizontal plane yet has a length variable in said plane through the relative motion of at least two parts thereof, said at least one connection element being pivoted between said adjacent vertical rods through two horizontal pivots, the axis of rotation of each of said horizontal pivots forming with a vertical radial plane comprising the axis of rotation of the respective vertical rod an angle that is equal to half of the internal angle of said regular polygon.

14. Calibration cage according to claim 13, wherein each vertical rod is provided with a top bracket and a bottom bracket for the mounting on the respective frame, and in that at least one of said mounting brackets carries at least one of the horizontal pivots on which the at least one connection element is pivoted.

15. Calibration cage according to claim 13, wherein the at least one connection element consists of an articulated rod made up of a first part and a second part connected through a horizontal pivot, said parts optionally being identical.

16. Calibration cage according to claim 15, wherein the two parts of the articulated rod overlap in the radial direction at the horizontal pivot connecting them, and in that the pivot used for the fixing to the respective vertical rod of the radially external part is longer by a length equal to the thickness of the radially internal part with respect to the pivot used for the fixing to the respective vertical rod of the radially internal part, the same difference in length being present in respective spacers arranged between said parts and the respective vertical rods.

17. Calibration cage according to claim 15, wherein each vertical rod is connected to both of the vertical rods adjacent thereto through connection elements pivoted at both ends in the proximity of the top of the respective frames, optionally at the same height.

18. Calibration cage according to claim 13, wherein the at least one connection element consists of a telescopic rod made up of at least two parts introduced one inside the other.

19. Calibration cage according to claim 18, wherein each vertical rod is connected to both of the vertical rods adjacent thereto through connection elements pivoted diagonally in the proximity of the top and bottom of the respective frames, optionally at the same height.

20. Calibration cage according to claim 13, wherein it further includes at least one axial movement unit comprising a supporting structure provided with brackets for the mounting on the supporting structure of the cage at the top and bottom thereof, said unit comprising a carriage provided with a horizontal mounting plate projecting on the outside, said carriage being vertically mobile due to a relative rotary motion between a female screw secured on the carriage and a vertical screw engaging said female screw.

21. Calibration cage according to claim 20, wherein the axial movement unit comprises at least one guide parallel to the vertical screw and the carriage is provided with at least one slider suitable to slidably engage said guide.

22. Calibration cage according to claim 20, wherein the female screw is driven into rotation by a jack mounted on the carriage.

23. Calibration cage according to claim 20, wherein it includes a plurality of axial movement units, said units being optionally arranged at regular intervals along the perimeter of the supporting structure of the cage.

24. Calibration cage according to claim 23, wherein it further includes an auxiliary frame suitable to connect the mounting plates of the multiple axial movement units so as to guarantee that said mounting plates are correctly aligned and levelled.

25. Calibration cage according to claim 14, wherein the at least one connection element consists of an articulated rod made up of a first part and a second part connected through a horizontal pivot, said parts being optionally identical.

26. Calibration cage according to claim 16, wherein each vertical rod is connected to both of the vertical rods adjacent thereto through connection elements pivoted at both ends in the proximity of the top of the respective frames, optionally at the same height.

27. Calibration cage according to claim 14, wherein the at least one connection element consists of a telescopic rod made up of at least two parts introduced one inside the other.

28. Calibration cage according to claim 21, wherein the female screw is driven into rotation by a jack mounted on the carriage.

29. Calibration cage according to claim 21, wherein it includes a plurality of axial movement units, said units being optionally arranged at regular intervals along the perimeter of the supporting structure of the cage.

30. Calibration cage according to claim 22, wherein it includes a plurality of axial movement units, said units being optionally arranged at regular intervals along the perimeter of the supporting structure of the cage.

Description

[0025] Further advantages and characteristics of the calibrator according to the present invention will become apparent to those skilled in the art from the following detailed and non-limiting description of some embodiments thereof with reference to the accompanying drawings in which:

[0026] FIG. 1 is a top perspective view, with an enlarged detail, of a first embodiment of the cage, which is adjusted to the maximum diameter of the tubular film;

[0027] FIG. 2 is a view similar to the preceding one of a second embodiment which is different in the type of connection element;

[0028] FIG. 3 is a view similar to the preceding one of a cage according to the first embodiment of FIG. 1 but in a configuration with a greater number of roller-carrying rods;

[0029] FIG. 4 is a side view of the cage of FIG. 3;

[0030] FIG. 5 is a top plan view of the cage of FIG. 3;

[0031] FIG. 6 is a view similar to the preceding one with the cage adjusted to an intermediate diameter of the tubular film;

[0032] FIG. 7 is a view similar to the preceding one with the cage adjusted to the minimum diameter of the tubular film;

[0033] FIG. 8 is a top perspective view of a movement unit of the axial adjustment mechanism;

[0034] FIG. 9 is a view similar to FIG. 3, further comprising an axial adjustment mechanism formed by two opposed movement units; and

[0035] FIG. 10 is a view similar to the preceding one, further comprising an additional external frame that connects the two movement units.

[0036] Referring to FIG. 1, there is seen that a calibration cage according to the present invention conventionally comprises a supporting structure 1 and a plurality of rotatable rectangular frames 2 which are cantilever pivoted along the perimeter of structure 1 at regular intervals, i.e. in correspondence with the vertices of a regular polygon (an hexagon in this case). At the free end of each of frames 2 there is pivoted a vertical rod 3 which carries a plurality of horizontal rollers 4 (five in the example shown) mounted vertically aligned and equally spaced, the rollers 4 of adjacent rods 3 being alternately staggered in the axial direction as mentioned earlier.

[0037] More specifically, structure 1 essentially consists of an upper ring 1a and a lower ring 1b, of circular shape in the example shown in FIG. 1, connected by a plurality of uprights 1c. Similarly, each frame 2 essentially consists of an upper arm 2a and a lower arm 2b connected close to the outer end by a first upright 2c pivoted between rings 1a, 1b while a second upright 2d is pivoted between the inner ends of arms 2a, 2b and carries rod 3.

[0038] In particular, rod 3 is provided with a pair of substantially rectangular mounting brackets to make it integral with the second upright 2d, namely an upper bracket 3a and a lower bracket 3b respectively close to arms 2a and 2b. Note that the axis of rotation of upright 2d is included in the common vertical midplane of rollers 4 which also includes the points of contact with the tubular film.

[0039] The cage also includes a mechanical mechanism for synchronizing the rotation of frames 2, and therefore the radial movement of rollers 4, which is quite similar to the mechanism described in U.S. Pat. No. 3,980,418. In brief, a horizontal crank 5 is integral with each frame 2 and is connected to the adjacent cranks 5 through connecting rods 6 pivoted between them. Therefore a single actuator 7 is sufficient to rotate one of cranks 5, which transmits the motion to the other cranks 5 via the connecting rods 6.

[0040] A first novel aspect of the calibration cage according to the present invention lies in the presence of connection elements 8 pivoted between two adjacent rods 3 by means of horizontal pivots, each connection element 8 being rigid in the horizontal plane yet of variable length in said plane through the relative motion of at least two parts thereof. In this context, the expression rigid in the horizontal plane means that a connection element 8 has a resistance to bending with respect to a torque with a vertical axis.

[0041] More specifically, the connection elements 8 are pivoted in correspondence of the upper mounting brackets 3a, each of which is provided in the outer corners of horizontal pivots 9a, 9b arranged symmetrically with respect to the axis of rotation of the second upright 2d. The axes of rotation of pivots 9a, 9b converge towards the center of the cage forming an angle equal to the internal angle of a regular polygon having a number n of sides equal to the number of frames 2 (i.e. =60 in the illustrated example with six frames 2). In other words, the axis of each pivot 9a, 9b forms an angle /2 with the radial vertical plane comprising the axis of rotation of the respective upright 2d on which rod 3 is fixed.

[0042] In this way, when rods 3 are oriented correctly so that rollers 4 are in tangential contact with the film, the bisector of said angle formed by the axes of pivots 9a, 9b is comprised in said radial vertical plane. Consequently, in this condition the pivot 9a of each bracket 3a is parallel to the pivot 9b of the adjacent bracket 3a to which it is connected through the connection element 8.

[0043] Therefore, when frames 2 are rotated to adjust the calibration diameter of the cage the connection elements 8, which are rigid in the horizontal plane, maintain pivots 9a, 9b connected by them parallel and therefore maintain rollers 4 correctly oriented. The change of distance between pivots 9a, 9b caused by the rotation of frames 2 is compensated by the connection elements 8 through a relative motion between at least two parts that make up each element 8.

[0044] In the first embodiment of the cage illustrated in FIG. 1 a connection element 8 consists of an articulated rod formed by a first part 8a and a second part 8b connected via a horizontal pivot 8c, so that element 8 has a V-shape in the vertical plane that can become narrower or wider. For simplicity of construction, the two parts 8a, 8b are preferably identical and preferably have a square cross-section, but they may have any other suitable shape and even be of different length.

[0045] Since the first part 8a is at a radially more internal position with respect to the second part 8b, due to the overlapping of the two parts in correspondence with pivot 8c, pivot 9b used for fixing the external part 8b to bracket 3a is preferably longer than pivot 9a used for fixing the internal part 8a by a length equal to the thickness s of the internal part 8a, and the same applies to the relevant spacer 10b located between the external part 8b and bracket 3a which is longer than the corresponding spacer 10a. In this way you get a smoother operation without bending stresses on pivots 8c, 9a, 9b and without having to give an S-shape to one of the ends of the two parts 8a, 8b to compensate for the different radial distance, thus obtaining always interchangeable parts but more complex.

[0046] Note that if the thickness of the parts 8a, 8b is sufficient to obtain a mutual fork connection that is robust enough, there is no difference in radial distance and therefore there is no need to have pivots 9a, 9b and spacers 10a, 10b of different lengths but the two parts 8a, 8b in this case are different and not interchangeable.

[0047] In the second embodiment illustrated in FIG. 2, where the same reference numerals indicate the same components, the only difference lies in the connection elements 8 between rods 3. In this case each element 8 consists of a telescopic rod with two parts 8a, 8b inserted one inside the other, instead of the two hinged parts 8a, 8b of the articulated rod 8. More specifically, the inner part 8a is pivoted on the upper bracket 3a of a rod 3 and the outer part 8b is pivoted on the lower bracket 3b of an adjacent rod 3, so that the connection element 8 is arranged diagonally.

[0048] Note that the arrangement of the connection elements 8, 8 in FIGS. 1 and 2 is to be understood as merely illustrative since these elements could be arranged in various other configurations obvious for a person skilled in the art. In other non-illustrated embodiments, for example, the elements 8 could be pivoted along the other diagonal, i.e. with part 8a on bracket 3b and part 8b on bracket 3a, or arranged horizontally between brackets 3a or 3b and in this case elements 8 could be formed by three or more parts to cover the whole of the cage adjustment stroke.

[0049] Similarly, elements 8 could be diagonally arranged as elements 8 or pivoted between brackets 3b, and the same brackets 3a and/or 3b could be positioned at different heights on frames 2, for example for reasons of access at selected points of the cage. In practice, an embodiment may include any combination of connection elements 8, 8 and/or of their configurations and/or of their positions, and a pair of rods 3 could be connected even by two or more connection elements 8, 8.

[0050] Furthermore, the above described compensation mechanism could also operate by connecting rods 3 only in pairs rather than all in sequence, thus dispensing with half of the connection elements 8, 8 and of the horizontal pivots 9a, 9b. In fact, a rod 3 remains correctly orientated even if it is connected via a single pivot 9a or 9b to only one of the two rods 3 adjacent thereto. The fact of connecting a rod 3 to both the adjacent rods serves only to provide a greater operating precision and symmetry to account for any vertical play in pivots 8c, 9a, 9b or for small deformations of the components.

[0051] The simple and effective operation of the calibration cage according to the present invention is now illustrated with reference also to FIGS. 3 to 7 which show a cage similar to that of FIG. 1 but with eight frames 2. In this case rings 1a, 1b do not have a circular shape but an octagonal shape with alternating sides of two different lengths, with frames 2 all pivoted on the long sides but always arranged at the vertices of a regular octagon. Furthermore each frame 2, being larger, is also strengthened by a diagonal strut attached between arms 2a and 2b, but for the rest the structure and the configuration of the cage are those described above.

[0052] In FIGS. 3 to 5 the cage is illustrated in the position of maximum opening corresponding to the maximum diameter F of the tubular film, with frames 2 substantially parallel to the sides of the octagonal structure 1 and with the connection elements 8 in the V-shaped configuration of the maximum amplitude (wide V). In the plan view of FIG. 5 there is also depicted the minimum diameter F of the tubular film, to provide an indication of the adjustment stroke of the cage, as well as the angle which in this case is 45.

[0053] In the plan view of FIG. 6 the cage is represented in an intermediate position reached by means of a synchronized rotation of about 15 of frames 2 in a clockwise direction, which has led uprights 2d to be arranged substantially along the maximum diameter F. This synchronized rotation is obtained, as explained above, by means of actuator 7 and the synchronization mechanism formed by cranks 5 connected through rods 6. This view clearly shows how rollers 4 are still correctly oriented due to the compensation function provided by the connection elements 8 that by maintaining pivots 9a, 9b parallel have caused a corresponding counterclockwise rotation of rods 3 with respect to frames 2, so as to compensate for the clockwise rotation of the frames.

[0054] Finally, the plan view of FIG. 7 shows the cage in the minimum opening position reached by means of a synchronized rotation of about 50 of frames 2 in a clockwise direction, which led rollers 4 to be arranged along the minimum diameter F. In this position pivots 9a, 9b are at the minimum distance therefore the connection elements 8 are in the V-shaped configuration of the minimum amplitude (narrow V). This view clearly shows how the axially staggered rollers 4 are arranged on parallel planes to form squares alternately rotated by 45, so that the contact with the film always takes place at the vertices of a regular octagon.

[0055] Obviously the radial adjustment movement of the cage in the opposite direction to switch from the minimum diameter F to the maximum diameter F is obtained simply by reversing the direction of movement of actuator 7 and consequently of the other components.

[0056] Turning now to FIG. 8 there is illustrated an axial movement unit of the cage according to the present invention. This unit essentially consists of a supporting structure 11 formed by an upper plate 11a and a lower plate 11b connected by two lateral uprights 11c, each upright 11c carrying on the inside a flat guide 12. A stationary screw 13 is fixed centrally between plates 11a, 11b and is engaged by a rotating female screw 14 set in rotation by a jack 15 mounted on a carriage that slides on guides 12 by means of four C-shaped sliders 16.

[0057] Note that only the upper sliders are visible in the figure and in fact two sliders 16 might suffice, but the use of four sliders arranged in pairs above and below the carriage makes the movement smoother and more precise. Similarly, the use of two guides 12 is preferable but the unit could comprise a single guide 12 or even no guide 12 if the guiding function is performed by screw 13. It is also (clear that the relative motion between screw 13 and the female screw 14 could also be achieved by rotating screw 13, in which case the jack 15 (or other equivalent actuator) would be fixed to structure 11 rather than to the carriage.

[0058] The axial adjustment stroke of the cage is defined by a pair of end stops 17a, 17b located respectively in the vicinity of plates 11a, 11b and adapted to actuate the corresponding switches 18a, 18b mounted respectively above and below the carriage and suitable to interrupt the operation of jack 15. Additionally, the carriage is provided with a horizontal plate 19 that protrudes outward and is provided with mounting holes 19a.

[0059] Referring also to FIG. 9, there is seen that structure 11 of the axial movement unit is mounted on the supporting structure 1 of the cage by means of two pairs of upper 20a and lower 20b brackets which project laterally from uprights 11c and are integral therewith. More specifically, brackets 20a, 20b are vertically spaced apart as much as rings 1a, 1b so that they can be respectively fixed to rings 1a, 1b so as to exploit the rigidity of the supporting structure 1 of the cage.

[0060] The illustrated example shows a cage provided with two axial movement units mounted on structure 1 at opposite positions but this configuration should not be understood as limitative since the two units may also be in non-opposite positions and in certain cases a single unit might be sufficient, or vice versa there might be three or more movement units that are preferably but not necessarily equally spaced along the perimeter of structure 1.

[0061] The entire cage is mounted on the extrusion plant structure through plates 19 so that the rotation of the female screws 14 which are axially locked on said structure causes by reaction the axial displacement of screws 13, and therefore of the cage through brackets 20a and 20b, when jacks 15 are activated (in the case of two or more jacks 15 it is preferable that these are electronically synchronized to obtain a smooth and precise motion). Therefore the position illustrated in FIG. 9 with the upper switch 18a in abutment on the upper end stop 17a corresponds to the lowest position for the cage, and the upward axial adjustment stroke is equal to the distance between the lower end stop 17b and the lower switch 18b.

[0062] Finally, FIG. 10 shows a variant of FIG. 9 in which the mounting of the cage on the extrusion plant structure is not direct in that plates 19 are fixed to an auxiliary frame 21 which in turn is fixed to said structure. The presence of the optional frame 21 can be useful in case the cage has two or more axial movement units, since the cage can be pre-assembled at the factory with frame 21 as a guarantee that the cage arrives to be mounted on the plant with plates 19 properly aligned and levelled.

[0063] It is clear that the embodiments of the calibrator according to the invention described and illustrated above represent only examples susceptible of numerous other variations besides those already mentioned above. In particular, other solutions mechanically equivalent to those illustrated above are within the reach of a person skilled in the art such as, for example, the use of guides 12 and relevant sliders 16 of different shapes, a different number and/or shape of frames 2 and of the film guide elements, another mechanism of synchronization of the rotation of frames 2 and so on.

[0064] Moreover it is clear that the actuator means used for the radial and/or axial adjustment of the calibrator may be of any suitable type (pneumatic, hydraulic, etc.) or made otherwise (belts, racks, etc.).