EP0397579A1 - Process and device to control the temperature of a tunnel furnace open at both ends - Google Patents

Abstract

The invention relates to the control of the temperature in a tunnel furnace comprising heating or cooling means disposed along its two lateral walls between which the conveyed articles pass. According to the invention, the temperature prevailing in a particular zone of the tunnel furnace, where a predetermined temperature is desired, is sensed, and the transverse displacement of the heating or cooling means (104) perpendicular to the conveying direction of the articles (103) is organised with the aid of a control mechanism acting so that these means are moved automatically, in terms of moving together or moving apart, when the sensed temperature deviates from the said predetermined temperature; this has the effect of permanently providing, for the article or articles concerned, a constant temperature environment in this zone of the tunnel furnace. …<??>Application especially to the shrinking of a heat-shrinkable sleeve for the decoration and/or the protection of flasks and to the cooling of glass containers. …<IMAGE>…

Description

The present invention relates to the field of heat treatments of objects passing through a tunnel oven open at its two ends, and more precisely the temperature control in such tunnel ovens.

The tunnel ovens concerned usually comprise means for conveying the objects, heating or cooling means arranged along their side walls and means for blowing a gaseous fluid at a predetermined temperature in a direction substantially perpendicular to the direction of conveyance. items.

The blowing of gaseous fluid, for example air, can be used in such tunnel ovens as well for cooling as for heating of the conveyed objects, and it is in this broad acceptance that the term "tunnel oven "should be understood in the context of the present invention.

Many fields of application may in fact be concerned, and there may be mentioned, for cooling, the case of glass bottles which should be cooled in a controlled manner after baking mainly for their lightening, and for the heating in the case of the application of a section of heat-shrinkable sheath or sleeve on an object, case in which the sleeve, loosely threaded on the object to be decorated and / or protected, is heated to a temperature higher than that of softening of the constituent film for its retraction on said object.

The invention relates more specifically to the latter case, but it will be understood that this is only a particular application of the temperature control method which is the subject of the said invention, and that the latter is in no way limited to such application.

It is now well known to use certain plastic films, to print them or not, and to form them in a tube by sealing the two folded edges one over the other of the strip, in order to be able to decorate and / or protect an object, or more particularly the packaging of a product.

This is how we are increasingly providing containers such as bottles, bombs, aerosols, flasks, cans and other packaging objects, with a protective sleeve or sheath, or even with a protective ring. tamper-evident, made of heat-shrinkable plastic. This sleeve is arranged around the container and, after external heating to a temperature higher than that of softening, it must conform with the minimum of deformation to the contour of the container (see for example French Patent N ° 2,346,129 and German Patent N ° 26 10 051). To produce such retractable sleeves, plastic films (generally made of polyvinyl chloride) are used to which a memory is imparted during their manufacture, and in general qualified as retractable. These films are generally stretched essentially in the direction of the perimeter of the objects to be coated, so that they acquire a memory in the stretching direction (or percentage of shrinkage) of up to 70% (in fact the commonly used films have a percentage between 50 and 60%); the memory in the longitudinal direction, that is to say that corresponding to the height of the sheath section is only of the order of 3 to 7%.

We know that to give a memory to a plastic film (polyvinyl chloride, polystyrene or polyester for example), it must be heated to a very precise temperature, generally chosen lower than the glass transition point of the plastic material delimiting the amorphous zone and the elastic zone, while it is subjected to transverse and / or longitudinal traction. By heating the film, it causes its softening, allowing the creep of the molecules and thus making it possible to increase the initial dimensions of the film, but in return with a reduction in the initial thickness of said film.

Such films, which generally are printed and / or decorated to serve as labels on the object to be coated, are called "mono-oriented" or "predominantly mono-oriented". If crystal polyvinyl chloride films are used, printing can be done backwards, resulting in an external gloss combined with protection of the printing against the risk of erasure. Besides the decoration aspect, it can be a question of protection, not only for the inviolability of a container, but also as a barrier, for example to reduce perfume losses with a polypropylene packaging, or carbon dioxide losses for carbonated drinks in polypropylene terephthalate packaging.

Such an application has found a large outlet in the sale of products offered to the general public, since it allows in particular a great wealth of decoration, with possible reproduction of photographic photographs, and a use for objects of very varied contours.

If the techniques for manufacturing shrink films, their printing and putting them into tubes, as well as the fitting of sleeves around objects or packaging are now practically mastered, the same cannot be said for the operation of shrinking said films. sleeves, all the more so since the object or the packaging has an irregular section of triangular, square or rectangular shape, with faces having convex and / or concave zones.

It is indeed imperative that the retraction is carried out uniformly around the object or the packaging, that is to say without crease, crimp or crater of the sheath, and without deformation of the impressions produced. on the film, which, in addition to the purely aesthetic aspect, also has an effect on direct use (reading bar codes, legal notices, or instructions for use for example).

The difficulties encountered in mastering the shrinking operation are largely due to problems of an essentially thermal order, since the temperature to which the film is heated must then be both precise, constant, and homogeneous over the entire surface of said film, and furthermore as low as possible.

The temperature must first be precise.

Indeed, you should know that only a few degrees separate the elastic zone from the amorphous zone, and that each plastic film has, depending on its nature and formulation, its own softening point and its separation temperature between the elastic zone and the zone amorphous. Knowledge of the temperature corresponding to the start of the amorphous zone is of paramount importance in order to shrink a film, because the film restores its memory as long as its temperature remains below that of the start of the amorphous zone, the memory acquired in the elastic zone being at least partially lost if this temperature is exceeded.

For example, a film whose start of the amorphous zone is at 110 ° C and having a memory giving it a retraction capacity of 50%, will not be able to restore this percentage if the temperature of 110 ° C is exceeded . It would therefore not be possible in such a case, for an object whose shape requires because of its section to have 50% shrinkage rate, to conform the film to the object in a satisfactory manner. Many types of objects would therefore be excluded from the possibility of being able to be coated with a heat-shrunk sleeve.

The temperature must then be constant, because it is easy, for the specialist who knows the shrinkage curves of a film as a function of the temperature (see FIG. 5, the curves RL of longitudinal shrinkage and RT of corresponding transverse shrinkage). understand that at a given time, if the film is subjected to a temperature of 80 ° C., it is possible to obtain a shrinkage percentage which is around 32% in the transverse direction, but only if at another time the temperature is no more than 75 ° C., the part of the film which has been subjected to this temperature can only undergo a percentage of shrinking of 20%, in the transverse direction: such a difference in terms of the percentage of shrinking (or shrinkage rate) for such a small temperature difference shows the need for a constant temperature.

This temperature must also be uniform over the entire surface of the film.

Indeed, in accordance with the abovementioned retraction curve, and in the case of an object with a simple and straight section, if the conditions of the aforementioned points are produced simultaneously at two points on the film (on the curve RT of FIG. 5, the point At 80 ° C; 32% on the one hand, and point B 75 ° C; 20% on the other hand), the shrinkage will not be the same percentage at the two points of the film, and we will then see a distortion or deformation of printing.

It should also be noted that despite an equally constant temperature uniformity, it is possible to record a loss of calories at the level of the film, consecutive to the fact that the film, in the case of an object with a concave shape, may be partially applied to the surface of said object and partially be in a vacuum. By its contact with the surface of the object, the calories received by the film will be transferred to the object itself, causing the consequences which have been reported for the points A and B mentioned above.

This temperature should finally be as low as possible.

Indeed, the strong mono-orientation of the film makes it possible, for example, to release 50% of transverse retraction for only 7 to 8% of longitudinal retraction. On the other hand, if the temperature to which the film is heated were to notably exceed that which makes it possible to release 50% of transverse retraction, in addition to the fact that one could not obtain these 50%, one would increase the percentage of longitudinal retraction. The transverse retraction on longitudinal retraction ratio would then decrease, to reach a value resulting in an uncontrolled deformation of the impression, since a point of the decoration would move at the same time on a vertical axis and a horizontal axis, its position then becoming completely random. Under these conditions, the decoration cannot be amplified in both directions when it is printed to take account of the shrinkage of the film.

The above considerations show that it is actually essential to be able to control the temperature with great precision in the tunnel oven used.

In an attempt to resolve some of the difficulties mentioned above, various means have been recommended, such as: the use of tunnel-ovens with multiple preheating-shrinking zones with flexible air-blowing tubes (European Patent N ° 0 058 602), or the production of re-entrant folds in contact with the surface of the objects on the perimeter of the sleeve to be constricted. We can also cite the French Patent N ° 2 328 614.

More recently, the applicant has proposed to inject a gaseous fluid between the object and the loose sleeve to be shrunk in order to inflate the sleeve and keep it out of contact with the object to be coated, the temperature of the gaseous fluid being chosen to be significantly lower than that of the softening of the film constituting the sleeve, which allows the temperatures of the inner and outer faces of the sleeve to be progressively balanced, and the thermal gradient in the film to be controlled in order to achieve film-object contact at the desired instant (see this effect the French Patent N ° 2 588 828).

This solution is interesting, but does not solve the problem of controlling the temperature in the tunnel oven, in the zone concerned by the means for blowing the gaseous fluid.

However, this temperature control is crucial in order to achieve effective shrinkage of the sleeve by simultaneously bringing the inner and outer faces of said sleeve to the same predetermined temperature, which is precisely that corresponding to the separation between the elastic zone and the amorphous zone. of the film.

Such control in tunnel ovens is very difficult to carry out because of the numerous external disturbances constantly upsetting the thermal level of the environment in the zone concerned by the blowing means.

It is indeed easy to inject a gaseous fluid at a predetermined constant temperature, but it is however practically impossible to freeze the temperature in a given zone of the tunnel oven, in particular by setting itself to a temperature corresponding to that chosen for the retraction of a sleeve.

However, specialists must inevitably face external disturbances which are of various origins. The interior of the tunnel oven is in fact subjected along its length to convection currents which permanently shift the temperature zones (currents due in particular to the temperature and to the number of objects passing through the tunnel oven and / or to a air intake in said tunnel oven). The thermal inertia of the retraction system and that of the system for conveying objects must also be mentioned.

Finally, specialists in this field note a real need for a technique making it possible to control the temperature satisfactorily.

The state of the art is also illustrated by American Patent N ° 4,198,560 describing a tunnel oven with heated reflectors whose inclination is manually adjustable, French Patent N ° 2,565,553 (heating means mounted on a bracket articulated); we can also cite the German Patents N ° 28 52 967 and N ° 20 24 239, and the European Patent N ° 0 128 056, in which various mechanical means are described making it possible to adjust the spacing of the heating walls as a function of the geometry exterior of the objects concerned.

The object of the invention is to propose a method and an implementation device for precisely controlling the temperature in a tunnel oven open at its two ends, in order to resolve the aforementioned difficulties.

Another object of the invention is to propose a method and a device which are both simple and reliable, and which in particular make it possible to ensure a perfectly homogeneous retraction for a heat-shrinkable sleeve, without deformation of the impressions, or formation of folds, crimps or craters, regardless of the shape and size of the object to be decorated and / or protected.

Alternatively, in the context of the aforementioned particular application, another object of the invention is to be able to operate this controlled shrinkage at average temperatures at the surface of the film, for example 100 ° C., which avoids the many aforementioned drawbacks of random retractions under temperatures conventionally reaching 180 to 250 ° C., and furthermore reduces the energy consumption as well as the length of the retraction tunnel oven used.

It is more particularly a process for controlling the temperature in a tunnel oven open at its two ends and in which objects move by the action of conveying means, said tunnel oven comprising heating means or cooling devices arranged along its two side walls between which pass the conveyed objects, characterized in that it consists in capturing the temperature prevailing in a particular zone of the tunnel oven where a predetermined temperature is sought, and to organize a transverse movement of the heating or cooling means in a direction essentially perpendicular to the direction of conveying of the objects using a servo causing said heating or cooling means to move automatically, according to a mutual approach or distance, when the sensed temperature deviates from said predetermined temperature, which has the effect of permanently ensuring for the object or objects concerned a constant temperature environment in this area of the tunnel furnace.

Preferably, the transverse movement of the heating or cooling means is organized symmetrically with respect to the median plane of the tunnel oven on either side of which the side walls of said tunnel oven are arranged; in particular, the transverse displacement of the heating or cooling means is obtained by moving two lateral boxes on the inner face of which said means are arranged. More specifically, it will be interesting to organize these transverse displacements so that its value varies linearly as a function of the difference detected between the sensed temperature and the predetermined temperature.

Advantageously also, the temperature is sensed in said particular zone of the tunnel oven in the vicinity of the passage of the objects, as far as possible from the heating or cooling means; in particular, the temperature is sensed using a fixed thermo-probe which is protected against the direct action of the heating or cooling means.

In the context of a particular application of the method, aimed at applying a section of heat-shrinkable sheath or sleeve to an object, and in which the sleeve, loosely threaded on the object, is heated for its retraction on said object, said predetermined temperature will be chosen to produce a homogeneous retraction of the sleeve when the object coated with its sleeve enters said particular zone of the tunnel oven where a constant temperature environment is ensured by the controlled transverse displacement of the heating means.

Preferably then, during their passage through the tunnel oven, the objects are also subjected to a blowing of gaseous fluid in a direction essentially perpendicular to the direction of conveying of said objects to achieve a prior swelling of each sleeve when the corresponding object enters the particular zone of the tunnel oven, the blowing taking place at said predetermined temperature in said particular zone; in particular, the blowing of gaseous fluid is carried out by directing a flow of gaseous fluid from above the objects, according to a flow of generally vertical direction.

Advantageously also, before reaching the zone of the tunnel oven concerned by the blowing of the gaseous fluid, the object coated with its sleeve undergoes preheating by the action of the sole means of heating said tunnel oven, in order to reach a temperature very close to the sleeve retraction point.

Preferably also, after the zone of the tunnel oven concerned by the blowing of the gaseous fluid, the object on which the sleeve is retracted undergoes heating by the action of the heating means of said tunnel oven and of a means of additional blowing, to be brought for a short time to a high temperature, significantly higher than the predetermined temperature of the gaseous fluid, which corresponds to a finishing or smoothing phase.

The invention also relates to a device for implementing the above method, and intended to equip a tunnel oven comprising means for conveying objects, heating or cooling means arranged along its two side walls, between which pass the conveyed objects, characterized in that it comprises a temperature sensing member arranged in a particular zone of the tunnel oven where a predetermined temperature is sought, at least one carriage supporting the heating or cooling means, said carriage being movable transversely in a direction essentially perpendicular to the conveying direction of the objects, and motorized drive means for automatically moving said carriage when the temperature sensed by said member deviates from said predetermined temperature, with a view to bringing it closer or mutual distance from said heating or cooling means stiffening.

Preferably, the mobile carriage carries a lateral box on the inner face of which are arranged heating or cooling means, so that the controlled transverse movement relates to said side box of the tunnel oven.

According to a particularly advantageous embodiment, the device comprises two carriages supporting the heating or cooling means associated with each of the side walls of the tunnel oven, the transverse movement of said carriages being organized symmetrically with respect to the median plane of the tunnel oven. on either side of which the side walls of said tunnel oven are arranged. Advantageously then, the two movable carriages move on associated transverse rails provided in the lower part of the tunnel oven, below the means for conveying objects, said mobile carriages being further connected to the motorized drive means by a coupling means. common.

Preferably then, the motorized drive means consist essentially of a motor-reduction unit, the coupling means preferably being in the form of a continuous transverse chain driven by said motor-reduction unit and each strand of which carries a mobile cart.

In this case, it is advantageous for the geared motor assembly to include an electric motor, the control of which is connected to the temperature sensing member by means of an associated temperature regulator, and a reducer at the outlet of which there is provided a pinion meshing with a continuous transverse chain integral with the carriages; in particular, the connection of the geared motor assembly with the drive pinion and with the temperature regulator of the temperature sensing member is such that the displacement of each of the carriages varies linearly as a function of the deviation of temperature detected by said temperature sensing member, for example one mm per degree Celsius.

Advantageously also, the temperature sensing member is a fixed thermo-probe connected to a temperature regulator, said thermo-probe having a means of protection against the direct action of the heating or cooling means.

Preferably, the thermo-probe is housed in an open protective tube in which there is a vacuum, and the open lower end of the protective tube is beveled, being turned towards the side of the conveyed objects; in particular, the protective tube is a quartz tube connected to a suction venturi.

In the context of a particular application aimed at applying a section of sheath or heat-shrinkable sleeve to an object, by heating the sleeve loosely threaded on the object for the retraction of said sleeve on said object, it is advantageous that the device comprises heating means arranged along the two side walls of the tunnel oven essentially constituted by heating elements, for example emitters with infrared radiation.

Preferably then, the device also comprises means for blowing towards the conveyed objects a gaseous fluid in a direction essentially perpendicular to the conveying direction, the blowing taking place in said particular zone of the tunnel oven, at said predetermined temperature associated with controlled transverse movement of the heating elements.

Advantageously in this case, the blowing means comprise a blowing box having an elongated slot below to produce a continuous air gap, said blowing box being disposed above the tunnel oven in order to direct a flow of gaseous fluid from above the objects, in a generally vertical directional flow. More precisely, the blowing box comprises a succession of registers making it possible to vary the air flow rate according to different longitudinal zones of the tunnel oven, and it is supported by a bracket, with the possibility of a height and / or longitudinal adjustment. of the position of said blowing box.

Finally, it is interesting that the device also comprises, downstream of the blowing box, an additional blowing member, for example of the fan-extractor type, allowing possible final overheating of the objects.

• - la figure 1 est une vue latérale d'un dispositif conforme à l'invention, équipant un four-tunnel dans lequel passent des objets convoyés, le dispositif étant ici également muni de moyens de chauffage, et de moyens d'insuflage en partie supérieure, ces derniers moyens n'étant en réalité nullement obligatoires ;
• - la figure 2 est une coupe longitudinale du four-tunnel de la figure 1, permettant de mieux distinguer les éléments chauffants disposés sur la face intérieure de chaque caisson latéral dudit four-tunnel ;
• - la figure 3 est une vue en plan partielle illustrant un détail du four-tunnel des figures 1 et 2, relatif aux moyens d'entraînement associés au déplacement latéral asservi de chacun des caissons ;
• - la figure 4 est une vue en coupe illustrant un autre détail relatif à la thermo-sonde servant à capter la température, cette thermo-sonde étant protégée contre l'action directe des éléments chauffants, et étant relié à un venturi d'aspiration ;
• - la figure 5 est un diagramme illustrant pour mémoire deux courbes typiques RT et RL représentatives des variations du pourcentage de rétreint (% R) en fonction de la température T (en °C) : ce diagramme déjà commenté plus haut illustre l'importance d'avoir une température à la fois précise, constante et homogène pour que la rétraction puisse s'effectuer dans des conditions optimales (le diagramme de la figure 5 ne sera donc pas commenté dans la description qui va suivre).

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, it being understood that this is only an example, because the implementation of the method of the invention can naturally be done according to various variants, with reference to the figures where:

• - Figure 1 is a side view of a device according to the invention, fitted to a tunnel oven through which conveyed objects pass, the device here also being provided with heating means, and blowing means in the upper part , these latter means are in fact in no way mandatory;
• - Figure 2 is a longitudinal section of the tunnel oven of Figure 1, to better distinguish the heating elements arranged on the inner face of each side box of said tunnel oven;
• - Figure 3 is a partial plan view illustrating a detail of the tunnel oven of Figures 1 and 2, relating to the drive means associated with the controlled lateral movement of each of the boxes;
• - Figure 4 is a sectional view illustrating another detail relating to the thermo-probe used to sense the temperature, this thermo-probe being protected against the direct action of the heating elements, and being connected to a suction venturi;
• - Figure 5 is a diagram illustrating for the record two typical curves RT and RL representative of the variations in the percentage of shrinkage (% R) as a function of the temperature T (in ° C): this diagram already commented on above illustrates the importance of 'have a temperature that is both precise, constant and homogeneous so that the retraction can be carried out under optimal conditions (the diagram in Figure 5 will therefore not be commented on in the description which follows).

As can be seen in FIGS. 1 and 2, the temperature control device according to the invention is fitted here with a tunnel oven 101 comprising means for conveying 102 objects 103, and heating means 104 arranged along its side walls 106.

In the case of cooling, the means 104 will be replaced by any means, such as forced air, making it possible to cool the atmosphere.

However, the control device will be described here in the context of its particular application to the shrinking of a heat-shrinkable sleeve on an object to be decorated or protected, application in which the sleeve loosely threaded on the object is heated to a temperature higher than that of the softening of the film constituting said sleeve on said object.

The tunnel oven 101 has two side walls 106 made in the form of a box, the length and height of which depend on the object on which a heat-shrinkable sleeve 107 can be retracted, and on the required rate. On the inner faces of each box 106, a series of heating elements 104, which may be emitters with infrared radiation, have been arranged. These transmitters are distributed over the height of the objects concerned, according to one or more series of superimposed elements. In known manner, these elements are connected to a temperature control device (not shown) either individually or in groups, with a thermo-probe incorporated 190 into the element or group of elements concerned (these thermo-probes do not are visible only in FIG. 2): this is a simple conventional regulation of the heating means of such tunnel ovens. It goes without saying that these infrared radiation emitters could be replaced by any equivalent means, and possibly be supplemented by flaps for distributing the flow of hot air.

The conveying means 102 are illustrated here in the form of an endless conveyor, but it is naturally possible to use as a variant a chain provided with devices allowing the gripping of objects and animated by a continuous movement or step by step, all by keeping the objects in a fixed position or by rotating the said objects on themselves. Thus, the objects to be coated 103 circulate on the endless conveyor 102 after removal of a loose sleeve 107 around each object by a machine known per se, this removal being carried out before the object enters the tunnel oven 101.

According to a fundamental aspect of the process of the invention, the temperature prevailing in a particular zone of the tunnel oven 101 is detected where a predetermined temperature is sought, and a transverse movement of the heating means 104 is organized in a direction essentially perpendicular to the conveying direction of the objects 103, using a servo control such that said heating means move automatically, according to a reconciliation or mutual reciprocation, when the sensed temperature deviates from said predetermined temperature, which has the effect of permanently ensuring for the object or objects concerned a constant temperature environment in this zone of the tunnel oven.

For the implementation of such a method, the device comprises, in accordance with an essential aspect of the invention, a temperature sensing member 108 arranged in a particular zone of the tunnel oven where a predetermined temperature is sought, at least a carriage 109 supporting the heating means 104, said carriage being movable transversely in a direction substantially perpendicular to the direction of conveying objects 103, and motorized drive means 110 for automatically moving the carriage 109 when the temperature sensed by the member 108 deviates from said predetermined temperature, for the purpose of bringing the heating means together or away from each other.

Thus, in accordance with this fundamental aspect of the invention, it is possible to obtain excellent control of the temperature in the tunnel oven by means of a controlled transverse movement of the heating means, it being understood that this control could just as well concern means of cooling for another application.

It is advantageous to provide that the transverse movement of the heating elements 104 is organized symmetrically with respect to the median plane P of the tunnel oven 101 on either side of which the side walls 106 of said tunnel oven are arranged. Indeed, the approximation or the distance of the heating elements 104 is thus always carried out by the same quantity, which preserves the homogeneity of the temperature in the tunnel oven. As a result, during operation, there is a permanent transverse floating, with small corrective oscillating movements, for the heating elements 104.

The heating elements 104, here produced in the form of infrared elements, are usually supported by candles in the lateral boxes 106. As a result, it is simpler to organize the transverse movement of the heating elements 104 by moving the two lateral boxes 106 on the inner face of which said elements are arranged. The transverse movement of the heating elements 104, or more precisely in this case of the side boxes 106 carrying said heating elements, will preferably be organized so that its value varies linearly as a function of the difference detected between the sensed temperature and the temperature predetermined.

As can be seen in FIG. 1, the temperature is preferably sensed by the fixed thermo-probe 108 in the aforementioned particular zone of the tunnel oven 101 in the vicinity of the passage of the objects 103, as far as possible from the heating elements 104. As will be described below with reference to FIG. 4, it will be advantageous to provide a thermoprobe 108 protected against the direct action of the heating means.

As has been said above, at least one movable carriage 109 is provided carrying a lateral box 106 on the inner face of which the heating elements 104 are arranged, so that the controlled transverse movement concerns said lateral box of the tunnel oven 101. It is however advantageous to provide two carriages 109 supporting the heating means 104 associated with each of the side walls of the tunnel oven 101, the transverse movement of said carriages being organized symmetrically with respect to the median plane P of the side tunnel oven and other of which are arranged the side walls of said tunnel oven.

Such an embodiment is illustrated in FIGS. 1 and 2, and the drive means associated with the controlled lateral displacement of each of the boxes will be described in more detail with reference to the partial view of FIG. 3.

Each lateral box 106 is supported by a small column 122 whose base is fixed to a support plate 120. Each of the support plates slides on transverse rails 111 provided on an associated plate 112, by means of associated jumpers 117. We could have naturally provide a single rail serving as a sliding support for the two side boxes 106, however the embodiment illustrated here, comprising pairs of jumpers 119 and 117, provides excellent stability of the system, even in the case of side boxes of great lengths .

The two movable carriages 109 thus move on associated transverse rails 111, which are here provided in the lower part of the tunnel oven, below the means 102 for conveying objects. The movable carriages 109 are also connected to the motorized drive means 110 by a common coupling means 113. In the present case, the coupling means 113 is produced in the form of a continuous transverse chain of which each strand carries a carriage mobile 109: more precisely, one 117 of the two jumpers associated with each mobile carriage is secured by a tab 118 to the continuous transverse chain 113, while the other 119 of these jumpers simply serves as a sliding support. It is thus ensured that the two mobile carriages 109, and therefore the side boxes 106 that they support, are movable transversely by the same amount relative to the median plane P, as shown by the double arrow 127.

In this case, the motorized drive means 110 here essentially consist of a geared motor assembly 114, 115: this geared motor assembly comprises an electric motor 114, the control of which is connected to the thermo-probe 108 by the through an associated temperature regulator (not shown here), and a reduction gear 115 at the outlet of which a pinion 116 is provided meshing with the continuous transverse chain 113. Thus, the continuous transverse chain 113 passes over the pinion 116, and at its other end on a pinion 121 which will preferably be connected to a chain tensioning member.

It will be interesting to ensure that the connections of the geared motor assembly 114, 115 with the drive pinion 116 and with the temperature regulator of the thermo-probe 108 are such that the displacement of each of the carriages 109, and therefore of the lateral boxes 106 that they support, varies linearly as a function of the temperature difference detected by said thermo-probe, for example of one mm per degree Celsius.

It will be advantageous to provide for this purpose an electric gear motor comprising a large reduction, in order to have very slow movements, perfectly controlled: in particular, a reduction of 1: 5000, providing linear displacements of the order of 2 cm / min, can give excellent results in such an application. It goes without saying that the motor-reducer assembly could be replaced by any equivalent mechanical means, such as a screw with two reverse threads, the axis of which would then be perpendicular to the axis of the output shaft of the reducer previously described. . The advantage of such a variant is that the screw with reverse threads performs the reduction itself, but such a screw remains difficult to produce.

In the case where the infrared type 104 heating elements would be replaced by forced air blowing nozzles, the principle of transverse displacement would remain exactly the same, by organizing a displacement of the side boxes in said nozzles (such side boxes would be comparable in volume to those used here for the support of the heating elements 104).

We will now describe more precisely the structure of the thermoprobe 108 with reference to FIG. 4.

As has been said above, the temperature is sensed using a thermo-probe 108 which is fixed, and protected against the direct action of the heating elements 104. It is in fact interesting that the thermo-probe fixed 108, connected to a temperature regulator, has a means of protection against the direct action of the heating elements 104, preferably being housed in an open protective tube such as the tube 180, in which there is a vacuum. The thermoprobe 108 thus comprises a body 191 extended below by a capillary 181 whose free end 182 constitutes the temperature sensing tip. The body 191 is fixed in a T-fitting 184, which supports the protective tube 180, and also serves as connection, by its lateral branch 186, to a hose 187 leading to a suction venturi 188. The suction venturi 188 , being part of a circuit 189, of conventional use to create a vacuum in a circuit, thanks to a connection at the level of the neck of the venturi. The protective tube 180 is preferably made of quartz, to correctly resist the action of the heating elements 104, and it is interesting to observe that its open lower end 183 at a bevel, being turned towards the side of the conveyed objects 103: thus , the bevel provided below the opening of the tube 180 makes it possible both to achieve excellent protection of the probe against the direct action of the heating elements 104, and to admit an air flow (arrows 131) which corresponds with excellent precision with the air which was in the vicinity of the object, that is to say precisely with the air whose temperature is to be measured. Thanks to such protection of the probe against thermal disturbances, it is possible to perform extremely precise measurements, which naturally induces very fine control of the control of the transverse movement of the heating elements. The connection of the thermo-probe 108 is shown here only by the outlet hose 185 from the body 191 of said thermo-probe.

Thus, it will be easy to provide for a displacement of the heating elements 104 organized so that its value varies linearly as a function of the difference detected between the temperature sensed by the thermo-probe 108 and the predetermined temperature that is sought in a particular area of the tunnel oven corresponding to the shrinking area: the predetermined temperature itself in fact varies according to the temperature of the workshop where the shrinking operations are carried out, so it will be advantageous to organize the control so that the sum of the workshop temperature and said predetermined temperature is permanently essentially constant.

Returning to FIG. 1, it can be seen that the thermoprobe 108 is carried by a support 192 here connected to the support for means for blowing a gaseous fluid. The thermo-probe 108 will naturally be mounted on its support 192 with multiple possibilities of positional adjustment, in order to have the bevelled opening 183 of the protective tube 180 in the best possible place.

The controlled transverse movement of the heating elements 104 constitutes an essential characteristic of the method of the device of the invention, this transverse movement being shown diagrammatically by the arrows 126 in FIG. 1. Indeed, it is essentially thanks to this controlled transverse movement of the elements heaters 104 that it is possible to provide an environment at constant temperature in the particular area of the tunnel oven 101 into which the object 103 coated with its sleeve 107 penetrates, which makes it possible to produce a homogeneous retraction of said sleeve on said object.

It is, however, advantageous to provide that, during their passage through the tunnel oven 101, the objects 103 are also subjected to a blowing of gaseous fluid in a direction essentially perpendicular to the conveying direction of said objects to achieve prior swelling of each sleeve. 107 when the corresponding object 103 enters the particular zone of the tunnel oven 101: the blowing takes place in particular at said predetermined temperature in this particular zone. Preferably, the blowing of gaseous fluid will be carried out by directing a flow or gaseous fluid over objects 103 conveyed essentially horizontally, in a flow of generally vertical direction.

As illustrated in FIGS. 1 and 2, the device of the invention also includes means 105 for blowing a gaseous fluid towards the conveyed objects 103, as indicated above. The blowing means 105 essentially comprise a blowing box 150 having an elongated slot 151 below to produce a continuous air gap, said blowing box being disposed above the tunnel oven 101 in order to direct a flow or gaseous fluid over the top objects 103, in a generally vertical directional flow. In FIG. 1, it can be seen that the blowing box is equipped with an internal grid 149, arranged essentially in a horizontal plane, and whose function is twofold: this grid makes it possible to standardize the flow of the gaseous fluid, which allows to obtain a regular flow, and also allows to break the high speed of the fluid when using a blower, as it is the case here.

The blowing box 150 is provided with connection sleeves 155 on top of which are connected associated pipes 156. The blowing means illustrated here naturally only constitute an example, a motor 157 mounted on a base 158 is thus distinguished, and actuating a fan 159, at the outlet of which is provided a box of heating resistors 160, the outlet tips 161 of which are connected to the above-mentioned pipes 156. It will naturally be expected to be able to adjust the heating means of the box 160, so that the temperature of the air thus blown effectively corresponds to the predetermined temperature which is sought.

In addition to the temperature, it is advantageous to also be able to regulate the output flow rate of each of the pipes 156. It may for example be produced by drawers 162 associated with each of the connection end pieces 155, the drawers 162 each being equipped with a register 163 produced in the form of a movable plate which is pulled more or less in the manner of a completely conventional diaphragm. It is thus possible to dose the blown air flow according to successive longitudinal zones, the adjustment being able to prove to be advantageous in certain applications (the adjustment of the registers 163 is shown diagrammatically by the arrow 128 in FIG. 1).

Preferably, the blowing box 150 is supported by a bracket 173, 174, with the possibility of a height and / or longitudinal adjustment of the position of said blowing box.

In this case, the blowing box 150 is fixed on a support 152 having a longitudinal connecting bar 153 which slides in a C-shaped slide 154 secured to a support head 174 making part of the gallows. The support 152 can also also support the thermo-probe 108, as illustrated in FIG. 1. Such an assembly allows a longitudinal assembly of the blowing box 150, shown diagrammatically in FIG. 2 by the arrow 130. As has been said above, it is advantageous to be able to adjust the height of the blowing box 150, in order to have an adjustment of the position thereof in an essentially vertical direction, which makes it possible to perfectly wrap the objects provided with their sleeve passing through the tunnel oven. The views of Figures 1 and 2 illustrate a simple embodiment allowing such height adjustment. The blowing box 150 is indeed here supported by a bracket in a head 174 already mentioned, which is slidably mounted on two vertical branches 173, with interposition of guide rollers 175. The adjustment will be obtained by any conventional mechanical means, for example with the worm screw system illustrated here: this system comprises an adjustment flywheel 177 and a bevel gear 178, mounted on a horizontal plate 176, with an output worm screw 179 leading to a nut 171 carried by a plate upper 172 secured to the support head 174.

The blowing box 150 can thus be perfectly positioned above the objects passing through the tunnel oven, to inject a gas medium brought to the top of these objects brought to the desired predetermined temperature.

It will be noted that the blowing box 150 is here connected to a common fan 159 by associated connection pipes 156, but it is obvious that it will be possible to provide several independent fans associated with independent air supply circuits. As a variant, provision may also be made for placing the fan 159, and the associated resistance box 160 with the support head 174, which provides several advantages. Indeed, with such an arrangement, the fan is completely protected in a closed enclosure, which allows filtering of the blown air, isolating it from any dust passing at ground level; in addition, the connection pipes 156 can be produced with much shorter dimensions.

Although by no means compulsory, the blowing means which have just been described nevertheless make it possible, in the particular application for the shrinkage of a heat-shrinkable sleeve on an object, to obtain an extremely favorable bloating effect of said sleeve before that -It is not retracted on the object. This bloating effect is very advantageous, because it makes it possible to solve a difficulty which specialists in the field knew well. They know indeed that it is not possible to obtain a homogeneous retraction between the surfaces in contact with the object and those which are not: indeed, with such contact, the temperature varies on the periphery of the film according to the zones concerned, causing different percentages of retraction when this is desired to be homogeneous (certain parts of the film then see their retraction stopped as soon as they come into contact with the object, while the zones of the fold or folds, originating from the fact that the sleeve is in the form of a flat sheath section, shrink too much compared to what was initially planned).

We also distinguish, in Figure 2, an additional blowing member 123 mounted downstream of the blowing box 150, for example made in the form of a fan-extractor, to allow possible final overheating of objects 103. Such a member of additional blowing has the function of bringing the object on which the sleeve is retracted, for a short time, to a high temperature (markedly higher than the predetermined temperature mentioned above in the retraction zone), which corresponds to a finishing phase or smoothing. In this case, the blowing member 123 has been produced in the form of a downstream compartment 125 of the blowing box 150, supplied by a clean connection pipe 124. It goes without saying, however, that provision may be made a separate box, with its own power supply and heating means with electrical resistances. The temperature of the air blown in by this additional blowing means 123 will moreover preferably be controlled using a thermo-probe placed inside the outlet nozzle (not shown here).

It is thus possible to organize in optimal conditions the inlet and outlet areas of the tunnel oven 101: in particular, before reaching the area of the tunnel oven concerned by the blowing of the gaseous fluid, provision may be made that the object 103 coated with its sleeve 107 undergoes preheating by the action of the only heating elements 104 of said tunnel oven, to reach a temperature very close to the point of retraction of the sleeve. Furthermore, after the zone of the tunnel oven concerned by the blowing of the gaseous fluid, the object on which the sleeve 107 is retracted may be subjected to heating by the aforementioned additional blowing means 123, while being brought for a short time to a high temperature, significantly higher than the predetermined temperature of the gaseous fluid, which corresponds to a finishing or smoothing phase.

The method of the invention, and the associated implementation device, thus make it possible to operate the perfectly homogeneous retraction of a heat-shrinkable sleeve, thanks to a constant and precise control of the temperature in the tunnel oven.

The control of the thermal field thus avoids any blowing in of air at an excessive temperature, in the case where such a blowing is planned, which would have the consequence of rendering inhomogeneous the shrinking due to the temperature differences between the inner and outer faces of the heat-shrinkable sleeve, and further retract the top of the sleeve before the bottom thereof, which would block the passage of air and hinder the retraction of the lower part of the sleeve. It also avoids blowing air at an insufficient temperature, which would have the consequence of making the shrinkage of the sleeve inhomogeneous, and of sealing the lower part of the sleeve due to premature shrinkage of this lower zone.

The invention thus makes it possible to solve in a particularly simple and effective manner the thermal problem which it is necessary to solve in order to control the shrinking operation, by managing to perform in a critical zone of the tunnel oven, concerned by the shrinking of the sleeve. heat shrinkable, a temperature that is both precise, constant, and homogeneous. Such a control makes it possible to overcome as much as possible the inevitable external disturbances.

The invention is not limited to the embodiment which has just been described, but on the contrary encompasses any variant incorporating, with equivalent means, the essential characteristics appearing in the claims.

Claims (28)

1. A method for controlling the temperature in a tunnel oven open at its two ends and in which objects move by the action of conveying means, said tunnel oven comprising heating or cooling means arranged along its two side walls between which pass the conveyed objects, characterized in that it consists in capturing the temperature prevailing in a particular zone where a predetermined temperature is sought, and in organizing a transverse movement of the heating or cooling means (104) in a direction essentially perpendicular to the conveying direction of the objects (103) by means of a servo control such that said heating or cooling means move automatically, according to a reconciliation or a mutual distance, when the temperature sensed deviates from said predetermined temperature, which has the effect of ensuring perm anence for the object or objects concerned a constant temperature environment in this area of the tunnel oven. 2. Method according to claim 1, characterized in that the transverse movement of the heating or cooling means (104) is organized symmetrically with respect to the median plane (P) of the tunnel oven on either side of which are arranged the side walls of said tunnel oven. 3. Method according to claim 1 or 2, characterized in that the transverse displacement of the heating or cooling means (104) is obtained by moving two lateral boxes (106) on the inner face of which are arranged said means. 4. Method according to one of claims 1 to 3, characterized in that the transverse movement of the heating or cooling means (104) is organized so that its value varies linearly depending on the difference detected between the temperature sensed and the predetermined temperature. 5. Method according to one of claims 1 to 4, characterized in that the temperature is sensed in said particular zone of the tunnel oven in the vicinity of the passage of objects (103), as far as possible from the heating or cooling (104). 6. Method according to claim 5, characterized in that the temperature is sensed using a fixed thermo-probe (108) which is protected against the direct action of the heating or cooling means (104). 7. Method according to one of claims 1 to 6, intended to apply a section of heat-shrinkable sheath or sleeve (107) on an object (103), and in which the sleeve (107), loosely threaded on the object (103), is heated for its retraction on said object, characterized in that said predetermined temperature is chosen to produce a homogeneous retraction of the sleeve (107) when the object coated with its sleeve enters said particular zone of the tunnel oven where a constant temperature environment is ensured by the controlled transverse displacement of the heating means (104). 8. Method according to claim 7, characterized in that, during their passage through the tunnel oven, the objects (103) are also subjected to a blowing of gaseous fluid in a direction essentially perpendicular to the conveying direction of said objects to achieve a prior swelling of each sleeve (107) when the corresponding object (103) enters the particular zone of the tunnel oven, the blowing taking place at said predetermined temperature in said particular zone. 9. Method according to claim 8, characterized in that the blowing of gaseous fluid is carried out by directing a flow of gaseous fluid through the top of the objects (103), in a generally general direction flow. 10. Method according to one of claims 8 and 9, characterized in that before reaching the area of the tunnel furnace concerned by the blowing of the gaseous fluid, the object (103) coated with its sleeve (107 ) undergoes preheating by the action of the only heating means (104) of said tunnel oven, to reach a temperature very close to the point of retraction of the sleeve. 11. Method according to one of claims 8 to 10, characterized in that after the zone of the tunnel oven concerned by the blowing of the gaseous fluid, the object on which the sleeve (107) is retracted undergoes heating by the action of the heating means (104) of said tunnel oven and of an additional blowing means (123), to be brought for a short time to a high temperature, markedly higher than the predetermined temperature of the gaseous fluid, this which corresponds to a finishing or smoothing phase. 12. Device for implementing the method according to one of claims 1 to 11, intended to equip a tunnel oven comprising means (102) for conveying objects, means (104) for heating or cooling arranged on along its two side walls (106), between which the conveyed objects pass, characterized in that it comprises a temperature sensing member (108) disposed in a particular zone of the tunnel oven where a predetermined temperature is sought, at least one carriage (109) supporting the heating or cooling means (104), said carriage being transversely movable in a direction substantially perpendicular to the direction of conveying objects, and motorized drive means (110) for automatically moving said carriage when the temperature sensed by said member (108) deviates from said predetermined temperature, with a view to bringing the muzzle in or out tuel of said heating or cooling means. 13. Device according to claim 12, characterized in that the mobile carriage (109) carries a lateral box (106) on the inner face of which are arranged heating or cooling means (104), so that the transverse movement enslaved relates to said side box of the tunnel furnace. 14. Device according to claim 12 or 13, characterized in that it comprises two carriages (109) supporting the heating or cooling means (104) associated with each of the side walls of the tunnel oven, the transverse movement of said carriages being organized symmetrically with respect to the median plane (P) of the tunnel oven on either side of which the side walls of said tunnel oven are arranged. 15. Device according to claim 14, characterized in that the two movable carriages (109) move on associated transverse rails (111) provided in the lower part of the tunnel oven, below the means (102) for conveying objects , said movable carriages being further connected to the motorized drive means (110) by a common coupling means (113). 16. Device according to claim 15, characterized in that the motorized drive means (110) essentially consist of a geared motor assembly (114, 115), the coupling means preferably being in the form of a continuous transverse chain (113) driven by said motor-reduction unit and each strand of which carries a movable carriage (109). 17. Device according to claim 16, characterized in that the gear motor assembly comprises an electric motor (114), the control of which is connected to the temperature sensing member (108) via a regulator associated temperature, and a reducer (115) at the outlet of which is provided a pinion (116) meshing with a continuous transverse chain (113) integral with the carriages (109). 18. Device according to claim 17, characterized in that the connection of the geared motor assembly (114, 115) with the drive pinion (116) and with the temperature regulator of the temperature sensing member (108) is such that the displacement of each of the carriages (109) varies linearly as a function of the temperature difference detected by said temperature sensing member, for example of one mm per degree Celsius. 19. Device according to one of claims 12 to 18, characterized in that the temperature sensing member is a fixed thermo-probe (108) connected to a temperature regulator, said thermo-probe having a means of protection (180) against the direct action of the heating or cooling means (104). 20. Device according to claim 19, characterized in that the thermo-probe (108) is housed in an open protection tube (180) in which there is a vacuum. 21. Device according to claim 20, characterized in that the open lower end (183) of the protective tube (180) is beveled, being turned towards the side of the conveyed objects (103). 22. Device according to claims 20 and 21, characterized in that the protective tube (180) is a quartz tube connected to a suction venturi (188). 23. Device according to one of claims 12 to 22, intended to apply a section of heat-shrinkable sheath or sleeve (107) on an object (103), by heating the sleeve (107) loosely threaded on the object (103 ) for the retraction of said sleeve on said object, characterized in that it comprises heating means arranged along the two side walls (106) of the tunnel oven essentially constituted by heating elements (104), for example transmitters with infrared radiation. 24. Device according to claim 23, characterized in that it also comprises means (105) for blowing towards the conveyed objects (103) a gaseous fluid in a direction essentially perpendicular to the conveying direction, the blowing being done in said particular zone of the tunnel oven, at said predetermined temperature associated with the controlled transverse movement of the heating elements (104). 25. Device according to claim 24, characterized in that the blowing means (105) comprise a blowing box (150) having an elongated slot below (151) for producing a continuous air gap, said blowing box being arranged above the tunnel oven in order to direct a flow of gaseous fluid through the top of the objects (103), in a flow of generally vertical direction. 26. Device according to claim 25, characterized in that the blowing box (150) comprises a succession of registers (163) making it possible to vary the air flow rate according to different longitudinal zones of the tunnel oven. 27. Device according to claim 25 or 26, characterized in that the blowing box (150) is supported by a bracket (173, 174), with the possibility of a height and / or longitudinal adjustment of the position of said blowing box. 28. Device according to one of claims 25 to 27, characterized in that it also comprises, downstream of the blowing box (150), an additional blowing member (123), for example of the fan-extractor type , allowing possible final overheating of the objects (103).

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