WO2001016543A1

WO2001016543A1 - Tunnel kiln with infrared elements

Info

Publication number: WO2001016543A1
Application number: PCT/FR2000/002348
Authority: WO
Inventors: Eric Fresnel
Original assignee: Sleever International Company
Priority date: 1999-08-27
Filing date: 2000-08-21
Publication date: 2001-03-08
Also published as: EP1218682A1; FR2797944A1; AU7014900A; FR2797944B1

Abstract

The invention concerns a tunnel kiln (10) open at its two ends, comprising means for conveying objects (11) arranged between two side walls (14) of the tunnel kiln, and radiating heating means (20) constituted by infrared elements lining each of the side walls (14). The invention is characterised in that the tunnel kiln (10) further comprises a retractable thermal screen system (25) capable of being arranged in front of all or part of the radiating surface of some of the radiating elements (20), said thermal screen system involving the two side walls (14). Said thermal screen system enables to line with a heat-shrinkable sleeve objects with complex shapes, in particular with downward facing taper.

Description

Infrared oven tunnel

The invention relates to the field of heat treatment of objects passing through a tunnel furnace open at its two ends, each object being coated with a sleeve of heat-shrink plastics material, and the temperature Ge ^¬ Nérée inside the pro- tunnel used to perform the retraction of the sleeve on the object concerned during the passage of said object in the tunnel oven. Traditionally, tunnel ovens of this type comprise means for conveying objects arranged between two side walls of the tunnel oven substantially at the level of a vertical median plane of said tunnel oven, as well as heating means arranged along these two side walls between which the conveyed objects pass.

For the heating means equipping such tunnel ovens, use has been made of hot air blowing means for a long time. We can thus refer to documents US-A-3,897,671, US-A-3,760,154, US-A-3,711,961, US-A- 3,267,585, DE-A-2,852,967, DE-A -20 24 239, as well as more recent documents EP-A-0 128 056 and FR-A-2 588 828.

The document FR-A-2 588 828 cited last emanates from the applicant, and its teaching is fundamental insofar as it shows why it is essential to achieve a homogenization of the temperatures of the internal and external walls of the film so that the retraction heat shrink sleeve occurs satisfactorily on the coated object. Homogeneous heating of the sleeve to be retracted is therefore an essential condition for achieving satisfactory contraction. One generally uses an amorphous film with transverse memory, mono-oriented by stretching, and the heating of the film carried out in accordance with an evolution curve determined as a function of time, makes it possible to carry out the homogeneous and progressive recall of the memory of the film, which produces the shrinkage of the sleeve on the object.

More recently, it has been proposed to use means of heating by radiation produced in the form of infrared elements, and we can in this respect, refer to documents EP-A-0 397 579 and EP-A -0 397 580 of the demand ^¬ resse.

In these latter documents, the tunnel furnace is open at the top, and each side wall of the tunnel furnace is produced in the form of a box, the inner face of which faces the median vertical plane is furnished with infrared elements fixedly mounted on the box. associated.

The techniques described in these two aforementioned documents generally give complete satisfaction. However, for some items, in particular geometry, it is ap- appeared some difficulties to realize preheating homo ^¬ gene over the entire height of the heat shrinkable sleeve ^¬ Tourant the object.

These difficulties are encountered, for example, in the case of objects having complex sections, for example a section with a taper facing downwards, or a section with a central bulge, or a diabolo section, or even a section defining facets on a part of the object. Indeed, for such objects, the section decreases more or less strongly below an area of maximum diameter. However, the sleeve which surrounds the object contacts the external surface of said object at the level of its maximum cross-sectional diameter, so that the lower part risks being incorrectly retracted due to premature closure at the level of the contact ring, i.e. at the maximum diameter of the object. This premature closure naturally thwarts the shrinking process, and has the effect of more or less marked irregularities such as bubbles or crimps on the lower part of the sleeve retracted on the object. this is all the more regrettable since we now know how to make mono-oriented films having an extremely large transverse memory, that is to say capable of shrinking rates reaching 70 to 80%. However, blocking at the largest diameter of the object precisely prohibits taking advantage of these transverse retraction capacities in the case of the aforementioned forms, in particular forms with tapered in ^¬ verse.

The object of the invention is precisely to solve this problem, by designing a tunnel oven arrangement equipped with heating means produced in the form of infrared elements, which is capable of heating the wall of the sleeves surrounding the objects passing through the tunnel furnace which is of optimal homogeneity, and this whatever the shape of the objects concerned, even having a taper turned downwards, in particular to avoid the presence of bubbles or crimps after shrinking the sleeves.

This problem is solved in accordance with the invention, thanks to a tunnel oven open at its two ends, comprising means for conveying objects arranged between two side walls of the tunnel oven substantially at the level of a vertical median plane of said oven. - tunnel, as well as means of heating by radiation produced in the form of infrared elements lining each of the two side walls between which the conveyed objects pass, said tunnel oven further comprising a retractable heat shield system which can be placed in front of any or part of the radiating face of some of the infrared elements, said heat shield system relating to the two side walls.

Thanks to this retractable heat shielding means, it becomes possible to delay the closing of the heat-shrinkable sleeve at the level of the large diameter, that is to say for the part of the sleeve which is weakest shrunk, giving the lower zone which is below this large diameter part time to warm up. This thermal shielding thus constitutes a very precious barrier blocking the radiation, which in particular makes it possible to delay the recovery of the memory of the film in the upper part of the sleeve.

It was certainly known to use heat shielding systems (see documents DE-A-2 629 760, JP-A-01 079 581, US-A-5 444 814, JP-A-09 103 730) or not (see documents US-A-5,766,426, EP-A-0,335,615), but in fields having nothing to do with that of furnaces - tunnels, and for very different purposes from that sought ^¬ invented. Moreover, in certain cases (US-A-5,444,814 and JP-A-09,103,730), the heat shield used serves as a radiant reflector, which goes radically against the object of the present invention.

Preferably, the arrangement of the heat shield system is symmetrical relative to the median vertical plane. This is compatible with the fact that the objects circulating in the tunnel oven and coated with a heat-shrinkable sleeve are most of the time organized with a vertical central axis, each object being at least partly of revolution around this axis. As a variant, the arrangement of the heat shield system is asymmetrical with respect to the median vertical plane: this makes it possible to deal with the particular case of objects of asymmetrical configuration, faceted or not.

Advantageously also, the heat shield system is non-radiating and without reflective power. This guarantees the effectiveness of the thermal barrier formed by the screen system.

In accordance with a particularly advantageous embodiment, the heat shield system is arranged under form of non-heat-deformable insulating panels. In particular, each insulating panel may consist of a rigid frame surrounding a plate of glass fibers. Provision may also be made for the insulating panels to have holes, openings, slots or the like with predetermined geometry and arrangement. This makes it possible, for example, to delay the recovery of memory from an upper and lower part of an object while allowing reinforced reheating of an intermediate zone of the sleeve surrounding said object.

Provision may be made for the tunnel furnace thus to include sets of insulating panels of predetermined dimensions and shapes. It is then enough to select the insulating panels which are appropriate for the type of object concerned.

Advantageously, the location of the insulating panels is adjustable horizontally and / or vertically.

The insulating panels can be hung by the high ^¬ tie of the side walls, or even suspended from a mobile carriage in a horizontal direction which is parallel to the median vertical plane. For height adjustment, one could for example provide that the insulating panels are suspended from an articulated parallelogram.

According to another possibility, the insulating panels can be tilted relative to the vertical. In particular, the insulating panels are articulated in the upper part of the side walls, being able to pivot around a horizontal axis which is parallel to the median vertical plane. If it is expected that the insulating panels are hinged by their upper edge, these panels then form a space of privileged convection between them and the adjacent side wall. This makes it possible to further improve the control of the end of the insulation of the film constituting the sleeve with respect to the heat source. According to another characteristic, the insulating panels may extend vertically away re ^¬ adjustable from the adjacent side wall. In particular, the adjustable distance will preferably be between 0.5 and 2 cm.

Other characteristics and advantages of the invention will appear more clearly in the light of the description which follows and of the appended drawing, relating to a particular embodiment, with reference to the figures in which: - Figure 1 is an elevational view of 'a tunnel furnace equipping a retraction machine, with a tearing off of a side wall to distinguish a heat shield system according to the invention;

- Figure 2 is a section on II - II of Figure ι to better distinguish the insulating panels suspended in front of infrared elements of each of the side walls of the tunnel oven, -

- Figure 3 is a top view of the aforementioned tunnel oven; - Figures 4a, 4b, 4c are schematic sectional views illustrating various embodiments of the heat shield system according to the invention, depending on the geometry of the object concerned;

- Figures 5 and 6 respectively illustrate in elevation and at the end an insulating panel hung in the upper part of a side wall, -

- Figure 7 is a view similar to Figure 5, illustrating a suspension by a parallelogram articulated to a movable carriage; - Figure 8 is an end view illustrating the particular case of an insulating panel adjustable in inclination.

FIGS. 1 to 3 illustrate a tunnel oven 10 integrated in a shrinking machine 1, the lower part 2 of which forms a ventilation box, and the upper part a space in which the tunnel furnace 10 is arranged, this space being closed by articulated panels 3, preferably transparent, in order to be able to examine the constituent elements of the tunnel furnace during operation. An external control cabinet 4 makes it possible to make the appropriate adjustments for each operation concerned, these adjustments naturally concerning the temperatures in the various zones of the tunnel oven and the speed of travel of the objects in said tunnel oven. The four-channel 10 is equipped with conveying means 11, for example made in the form of an endless chain or carpet of elements, of plastic material or metal, connected together in an articulated manner, and passing around two end pulleys 12. These means pass over a horizontal support profile mounted on the frame of the machine. The conveying means 11 are also wedged on a vertical vertical plane denoted P of the tunnel oven. The tunnel furnace 10 is superiorly open and at its two ends, and cha ^¬ CUNE of its two side walls 14 is in the form of a box whose inner side facing the median vertical plane P is provided with heating means by radiation, here in the form of infrared elements denoted 20. The two boxes 14 furnished with infrared heating elements 20 are here suspended from a bracket 15 which is connected to a support column 16 surmounted by a column 17 adjustable in height relative to the frame 13 of the machine. A space 18 is thus defined above the conveyor belt or chain between the panels of infrared elements 20 which each line the side walls 14 of the tunnel oven 10. The objects placed on the conveyor belt 11 can thus be scrolled at inside the tunnel furnace 10, in the space 18, between the two panels of infrared elements 20, the direction of travel being denoted X. When an object 100 coated with a heat-shrink sleeve ^¬ table 101 is conveyed by the conveyor belt 11, it passes inside the tunnel furnace in front of the panels of infrared elements 20, and, during this passage, the man- shrinkable chon 101 gradually warmed to reach the film oriented mono ^¬ the softening point. The object 100 coated with its sleeve 101 goes on ^¬ between hot air nozzles in the form of panels arranged face to face, here two pairs of finishing nozzles 22 and 23 with straight and inclined outlet slots. Downstream of the last pair of nozzles 23, the sleeve 101 is perfectly retracted on the object 100.

It will be noted in FIGS. 1 and 2 the presence, illustrated in dashed lines, of an upper element 19 for blowing hot air. It is indeed possible to have such an element in so far as the tunnel furnace is also open at the top. It will for example be a plenum supplied by a tube 19.1, and making it possible to blow, by a longitudinal outlet slot wedged on the median vertical plane P of the tunnel oven, hot air above the objects coated with their sleeve. This blowing technique allows excellent homogenization of the outside and inside temperatures of the film walls while centering the sleeve around the object as described in detail in document FR-A-2 588 828 by the applicant cited above. .

In accordance with an essential characteristic of the invention, the tunnel oven 10 further comprises a retractable heat shield system which can be placed in front of all or part of the radiating face of some of the infrared elements 20.

This heat shield system relates to the two side walls 14, preferably with an arrangement symmetrical with respect to the median vertical plane P. However, it is possible to alternatively, provide a heat shield with an asymmetrical arrangement. this is interesting in the case of objects of asymmetrical configuration.

Such a heat shield system makes it possible, by blocking the radiation, to delay the closing of the sleeve in the parts with low shrinkage, which makes it possible to control the retraction of said sleeve on the object, even in the very unfavorable case of objects having a taper turned downwards. It thus becomes possible to soften the area of the sleeve surrounding the object at the level of its largest diameter, without shrinking the film at this level. This delays the recovery of memory from a predetermined part of the sleeve, so as to obtain a uniform temperature for the two faces of the sleeve over the entire height of the latter. For the heat shield system ensures full ^¬ its barrier function in general will be provided a nonradiative screen system without reflectivity.

According to the embodiment illustrated here, the heat shield system is arranged in the form of insulating panels 25 which are not heat-deformable. There are thus in Figures 1-3 a set of two pan ^¬ Neaux insulation 25 arranged in front of the radiating face of some infrared elements 20 lining the side walls 14 of the tunnel furnace 10. The insulation board 25 must be non-deformable at the heat, that is to say to withstand temperatures of the order of 450 ° C., so as to exercise their function homogeneously over their entire surface, and so that they can also be reused several times with the same type of 'object. In particular, it will be possible to use insulating panels constituted by a rigid frame surrounding a plate of glass fibers. By way of example, it is possible to use glass fiber plates sold under the brand name PA ITHERM (registered trademark of Dielectric Mills and Modern Insulated Wire).

The arrangement and the geometry of the insulating panels 25 will be chosen as a function of the particular shape of each object and concerned. In Figures 4a, 4b, 4c, there are illustrated three different situa ^¬ tions which will now be described in more detail.

Figure 4a, shows that the object 100 surrounded by a heat shrinkable sleeve 101 is a body of revolu ^¬ lution having a major diameter D at the top, and then a surface which tapers inwardly with a conicity oriented towards the bottom, up to a base diameter d. Such a situation was almost impossible to treat with conventional tunnel furnaces using panels of infrared elements without a thermal shield system: indeed, we would then have obtained a very rapid closure of the sleeve at the diameter D, this which would strongly interfere with the shrinking process, by preventing the proper progressive heating of the lower part of the sleeve 101. In the present case and in accordance with the invention, two insulating panels 25 are provided arranged in front of the radiating face 21 of certain infrared elements 20 lining the side walls 14 of the tunnel oven 10. Thanks to these insulating panels 25, it is possible to delay the closing of the sleeve in the part with low shrinkage, that is to say the zone situated at the level of the diameter D, which allows time for the lower part of the sleeve to gradually warm up, until a uniform temperature of the wall of the sleeve is obtained, both on its fac e outer than its inner face, over the entire height of said sleeve.

The insulating panels 25 have a dimensioning which is adapted to the type of object concerned, in particular a length (in the direction of travel of the objects) which corresponds to the time required linked to the delay of the closure. ture of the sleeve in the weakly shrunk part (large diameter part). In Figures 1 to 3, each panel iso ^¬ lant 25 mask and four of six infrared elements 20 of the top row of the panel and a portion of the four infrared components of the middle row, the other ele ^¬ ments downstream and the elements of the lower row being uncovered. This is of course only an example, tending to show that the dimensioning of the insulating panels 25, both for its height and for its length in the horizontal dimension, will be chosen according to the type of object concerned.

In FIG. 4b, the object 100 has a central bulge at the level of a large diameter D to taper down to a small diameter d. In this case, it is rather the zone at mid-height of the object which should have a delay in closing the sleeve for the part with low shrinkage: an insulating panel 25 will then be used for each side wall 14, which will be essentially wedged on either side of the large diameter horizontal plane of the object.

In FIG. 4c, the object 100 has a diabolo shape, with a large diameter D1, followed by a central tightening of diameter d, then a new lower enlargement of diameter D2. In this case, the zone to be screened is above all the upper zone of diameter D1, like the situation in FIG. 4a. However, it is also possible to screen the lower zone of diameter D2, so as to favor the heating of the central part at mid-height of the sleeve 101. For this, a hole or an opening or a slot 26 of adequate size is provided at the level tightening of the object. The geometry and the arrangement of such holes, openings, slots or the like, will naturally be predetermined according to each type of object. We have seen that the dimensions and profiles of heat shields can vary depending on the type of object concerned. It will thus be possible to have sets of iso ^¬ lant panels of predetermined dimensions and shapes. It is furthermore advantageous to provide that the arrangement of the insulating panels can also be adjusted with respect to the panels of infrared elements concerned.

We will illustrate, by way of example, with reference to FIGS. 5 to 8, different means for supporting the insulating panels 25 allowing a positional adjustment with respect to the vertical plane of the radiating faces 21 of the infrared elements 20 lining each side wall 14 of the tunnel furnace 10.

In FIGS. 5 and 6, the insulating panel 25, the frame 27 and the central plate 28 of which can be distinguished, is hung by means 30 in the upper part of the side wall concerned 14. The hooking elements are used for this purpose 31 to which are suspended flanges 32 arranged so that they can be hung on two of the hooking elements lining the upper part of the side wall 14, and this at different heights thanks to successive rings. Thanks to the various attachment combinations thus made possible, possibilities of horizontal and vertical adjustment of the insulating panel 25 are obtained. In FIG. 7, another variant has been illustrated in which the insulating panel 25 is suspended from a carriage 33 which is movable on a horizontal rail 34, the direction of the rail also being parallel to the median vertical plane P. The panel 25 is thus movable parallel to the vertical plane of the radiating faces 21 of the infrared elements 20 of the panel concerned. This allows horizontal adjustment of the position of the insulating panel 25. For the height adjustment, an ad hoc hanging system connected to the carriage 33 can be provided. Another possibility has been illustrated here by way of example, using an articulated parallelogram suspension 35.

In Figure 8, there is illustrated yet another va ^¬ laughing in which the insulating panel 25 is tiltable relative to the vertical. More specifically, the insulation panel 25 is hinged in the upper part of the wall concerned laté ^¬ rale 14, pivotably about a hori zontal axis ^¬ 37 mounted at the end of a carrier 36, which axis is parallel to the median vertical plane P. The insulating panel 25 is here articulated by its upper edge, so as to form a privileged convection space 38 between said panel and the adjacent side wall 14. The angle of inclination of the insulating panel 25 is noted α vertically. This inclination adjustment makes it possible to very advantageously control the end of the insulation of the film with respect to the heat source. The space 38 thus makes it possible to locally favor convection, which makes it possible to accumulate calories in the lower part of the sleeve 101, while the upper part, that is to say extending above the lower edge of the insulating panel, its retraction is prohibited. Two heating zones are thus obtained for the infrared heating elements which make it possible to better control the progressiveness of the heating of the walls of the sleeve. One is then, even in the case of very complex shapes, completely assured of avoiding the creation of bubbles of air trapped in an area with uncontrolled retraction.

Like the angular adjustment illustrated in FIG. 8, it is possible to adjust the distance between the plane of the insulating panel 25 extending vertically and the adjacent side wall 14. In fact, if we return to FIG. 6, it can be seen that this distance, denoted e, can be adjustable by hooking onto smooth pegs 31. This parameter e is important in practice, and it will preferably be included in the range going from 0.5 to 2 cm. Finally, to finish with the possible adjustments cited by way of example, it may be mentioned that, in the case where the panel 25 has holes or slots 26, as is the case in FIG. 4c, systems may be provided. movable shutters, such as the shutter 29, which make it possible to close off part of the hole or of the slot 26, the movement of said shutter possibly being able to be controlled automatically.

We have thus achieved a tunnel oven providing extremely detailed control of the shrinkage of the sleeves on the objects passing through the tunnel oven, thanks to an extremely flexible system of heat shield placed in front of all or part of the face. radiating infrared elements. This control is very interesting in the case of objects of complex shapes, in particular with downward taper, and thus makes it possible to optimize the control of the deformation (or anamorphosis) of the decorations and / or information which are printed on the sleeve. heat-shrinkable before shrinking it.

Claims

1. Four-tunnel (10) open at its two ends, com ^¬ carrying means for conveying objects (11) arranged between two side walls (14) of the tunnel-oven substantially at the level of a median vertical plane (P ) of said tunnel pro-, as well as radiant heating means (20) sheave ^¬ ized as infrared elements filling each of the two side walls (14) between which pass the conveyed objects, characterized in that it comprises in addition to a retractable heat shield system (25) which can be disposed in front of all or part of the radiating face (21) of some of the infrared elements (20), said heat shield system relating to the two side walls (14).

2. Oven-tunnel according to claim 1, characterized in that the arrangement of the heat shield system (25) is symmetrical relative to the median vertical plane (P).

3. Oven-tunnel according to claim 1, characterized in that the arrangement of the heat shield system (25) is asymmetrical with respect to the median vertical plane (P).

4. Four-tunnel according to one of claims 1 to 3, characterized in that the heat shield system (25) is non-radiating and without reflective power.

5. Four-tunnel according to one of claims 1 to 4, characterized in that the heat shield system (25) is arranged in the form of non-heat-deformable insulating panels.

6. tunnel oven according to claim 5, characterized in that each insulating panel (25) consists of a rigid frame (27) surrounding a glass fiber plate (28).

7. tunnel oven according to claim 5 or claim 6, characterized in that the insulating panels (25) have holes, openings, slots or the like (26) of predetermined geometry and arrangement.

8. Oven-tunnel according to one of claims 5 to 7, characterized in that it comprises sets of iso ^¬ lants panels (25) of predetermined dimensions and shapes.

9. Oven-tunnel according to one of claims 5 to 8, characterized in that the location of the insulating panels (25) is adjustable horizontally and / or vertically.

10. Oven-tunnel according to claim 9, characterized in that the insulating panels (25) are hung in the upper part of the side walls (14).

11. Oven-tunnel according to claim 9, characterized in that the insulating panels (25) are suspended from a carriage (33) movable in a horizontal direction which is parallel to the median vertical plane (P).

12. A tunnel oven according to claim 10 or claim 11, characterized in that the insulating panels (25) are suspended from an articulated parallelogram (35).

13. Tunnel furnace according to one of claims 5 to 8, characterized in that the insulating panels (25) are tiltable relative to the vertical.

14. tunnel oven according to claim 13, characterized in that the insulating panels (25) are articulated in the upper part of the side walls (14), being able to pivot about a horizontal axis (37) which is parallel to the vertical plane median (P).

15. Oven-tunnel according to claim 14, characterized in that the insulating panels (25) are articulated by their upper edge, so as to form a preferred convection space (38) between them and the adjacent side wall (14 ).

16. Tunnel furnace according to one of claims 5 to 8, characterized in that the insulating panels (25) extend vertically at an adjustable distance (e) from the adjacent side wall (14).

17. A tunnel oven according to claim 16, characterized in that the adjustable distance (e) is preferably between 0.5 and 2 cm.