METHOD AND APPARATUS FOR DRYING A STRIP OF PASTY MATERIAL INTENDED FOR THE PRODUCTION OF SMOKING ARTICLES

Description

TECHNICAL FIELD

This invention relates to a method and an apparatus for drying a strip of pasty material intended for the production of smoking articles.

This description explicitly refers, without thereby losing in generality, to a pasty material containing tobacco or a product derived therefrom, or more generally speaking, a substance capable of generating an aerosol in the context of smoking products such as cigarettes or the like.

BACKGROUND ART

Patent document WO 2020/058814 describes obtaining a continuous strip of reconstituted tobacco, which is then rolled up or cut into thread-like shreds of predetermined size, which are suitably mixed with each other before being fed to traditional cigarette making machines.

More generally speaking, the continuous strip from which the shreds are obtained, is made using tobacco by-products and processing waste (midribs, small pieces of leaves, dust, etc) which, when suitably comminuted until they are practically reduced to powder and mixed with water, glycerine binders and other liquid additives, allow obtaining a mixture having a moisture content of about 30%-50%, preferably 35%-40%, which is then processed to obtain a strip of substantially constant thickness of, for example, 90-280 μm, preferably approximately 100-140 μm. This strip is then dried until the required moisture content is reached, generally around 7%-15%, and is used to obtain a product which can be processed immediately, in particular by shredding, or it can be stored in rolls to be used at a later stage.

Drying the strip is a critical part of the process in that the product is still soft on account of its high moisture content and, in order to be dried quickly, could be placed in a drying chamber on a mesh conveyor which, on the one hand, enables it dry quickly because it allows the hot air to flow over both of its surfaces, but on the other hand, leaves the marks of the mesh on the product because the product is still soft and malleable.

This drawback could be avoided by using a steel belt conveyor instead of a mesh conveyor since the steel belt is smooth and would not leave any marks on the strip of product, even if the product is very wet; however, not only does this involve high installation and running costs but, because it would not allow the air to blow on the underside surface of the strip, it would also mean prolonged drying times, a larger plant occupying more factory floorspace and higher energy consumption.

To find a compromise between these two contrasting needs, two-stage dryers have been proposed. The first stage (main dryer) comprises a steel belt which does not leave any marks on the strip of product and brings its moisture content to a value greater than the required final value but such as to considerably reduce the plasticity and deformability of the product. It can then be transferred to the second stage (mesh dryer) and placed on a mesh conveyor which can reduce its moisture content to the required final level without marking it.

This solution too, however, involves considerable constructional complexity and high costs, owing to the need to use a steel belt conveyor, and also involves high energy consumption because, in practice, it consists of two distinct dryers.

AIM OF THE INVENTION

The aim of this invention is to propose a method and an apparatus capable of drying strips of pasty material of the type described above but without incurring the disadvantages of the prior art methods and plants.

In particular, this invention has for an aim to propose a method and an apparatus which allow further reducing the size of the dryer, making it substantially comparable to that of a traditional mesh dryer.

Another aim of the invention is to propose a method and an apparatus which, compared to traditional dryers offering the same performance, involve appreciably lower energy consumption.

Another aim of the invention is to propose a method and an apparatus which involve lower installation and running costs than a traditional drying oven offering the same performance.

All the above aims and others that may be inferred from the description which follows are achieved, according to size, by a method and an apparatus for drying a strip of pasty material intended for the production of smoking articles according to the appended claims.

In particular, according to an aspect of it, this invention provides a method for drying a strip of pasty material intended for the production of smoking articles, comprising the steps of:

• • feeding the strip of pasty material into a drying chamber;
  • conveying the strip of pasty material inside the drying chamber between an infeed station and an outfeed station of the drying chamber. In particular, the step of conveying comprises rolling the strip on a plurality of conveying surfaces arranged in succession along a first conveying path extending between the infeed and outfeed stations.

Advantageously, this step of conveying prevents the strip of material from having marks impressed on it as could happen, for example, with a mesh surface.

According to a further aspect of this invention, the step of conveying comprises a preliminary step whereby an initial portion, or end, of the strip is picked up in the infeed station and is taken to the outfeed station along a second conveying path which is different from the first conveying path. This preliminary step may be fully automated, as described in more detail below or it may be carried out manually or semi-manually.

According to a further aspect of this invention, during the aforementioned preliminary step, the initial portion of the strip is placed on at least one supporting and entraining surface by means of which it is brought from the infeed station to the outfeed station along said second conveying path.

According to a further aspect of this invention, the first conveying path runs linearly between the infeed and outfeed stations of the drying chamber. This embodiment ensures a high level of constructional and operational simplicity.

According to a further aspect of this invention, the first conveying path runs in zigzag fashion between the infeed and outfeed stations of the drying chamber. This embodiment, with the same footprint, allows drying to be performed on a longer strip compared to the case where the first conveying path is linear.

According to a further aspect of this invention, the second conveying path runs above and over the first conveying path. This embodiment ensures a high level of constructional and operational simplicity.

According to a further aspect of this invention, the first and second conveying paths are parallel.

According to a further aspect of this invention, the steps of feeding the strip of pasty material into the drying chamber and conveying the strip inside the chamber are mutually coordinated so that both impart the same longitudinal feed speed to the strip. Advantageously, this embodiment is such that the strip of material being fed is not damaged and/or subjected to undesirable stresses which might cause it to lose its shape and/or tear.

According to another aspect of it, this invention provides an apparatus for drying a strip of pasty material intended for the production of smoking articles, comprising:

• • a drying chamber;
  • feeding means to feed the strip of pasty material into said drying chamber;
  • conveying means for conveying the strip of pasty material inside the drying chamber between an infeed station and an outfeed station of the drying chamber.

In particular, the conveying means comprise a plurality of conveying surfaces which are arranged in succession along a first conveying path extending between the infeed station and the outfeed station to roll on the strip of pasty material while it is being conveyed.

Advantageously, the presence of the conveying surfaces rolling on the strip prevents the strip of material from having marks impressed on it as could happen, for example, with a mesh surface.

According to a further aspect of this invention, the first conveying path runs linearly between the infeed and outfeed stations of the drying chamber. This aspect ensures a high level of constructional and operational simplicity.

According to a further aspect of this invention, the first conveying path runs in zigzag fashion between the infeed and outfeed stations of the drying chamber. This aspect, in apparatuses with the same footprint, allows drying to be performed on a longer strip compared to the case where the first conveying path is linear.

According to a further aspect of this invention, the conveying means comprise a roller conveyor, with rollers which are at least partially motorized and define said plurality of conveying surfaces arranged in succession along the first conveyor path.

Advantageously, providing a conveyor with motorized rollers allows the strip to roll without rubbing, thus preventing it from being damaged.

According to a further aspect of this invention, the feeding means which feed the strip of pasty material into the drying chamber and the conveying means which convey the strip inside the chamber are mutually coordinated so that both impart the same longitudinal feed speed to the strip. Advantageously, this aspect is such that the strip of material being fed is not damaged and/or subjected to stresses which might damage it, cause it to lose its shape and/or tear.

According to a further aspect of this invention, the conveying means comprise at least one supporting and entraining surface, which is movable from the infeed station to the outfeed station along a second conveying path which is different (distinct and independent) from the first conveying path, and which is disposed and configured to pick up an initial portion, or end, of the strip of pasty material in the infeed station and to take it to the outfeed station along the second conveying path. The supporting and entraining surface allows performing a first step of starting, during which the strip of material moves through the drying chamber without the risk of suffering damage which might occur as a result of contact between the strip, which has an initial portion, or free end, and the conveying surfaces.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is clarified in further detail below with regard to some embodiments of it, described by way of non-limiting example only, with reference to the accompanying drawings, in which:

FIG. 1 shows a schematic side view of an apparatus according to the invention in a first embodiment of it and during an intermediate stage of its operation,

FIG. 2 is a view like that of FIG. 1, showing the aforementioned apparatus in a subsequent stage of its operation,

FIG. 3 is a schematic, cross-section through the line III-III of FIG. 1,

FIG. 4 is a view like that of FIG. 1, showing an apparatus according to the invention in a second embodiment of it,

FIG. 5 is a view like that of FIG. 1, showing an apparatus according to the invention in a third embodiment of it,

FIG. 6 is a view like that of FIG. 1, showing an apparatus according to the invention in a third embodiment of it and in an initial stage of its operation, and

FIG. 7 shows the apparatus of FIG. 6 in a subsequent stage of its operation.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

As shown in the drawings, the apparatus or dryer according to the invention comprises a drying chamber 2, defined or delimited by walls 2A (illustrated only partly for greater clarity) and provided with an inlet 4 to which a strip of pasty material 6, to be dried and intended for the production of smoking articles, is fed.

The drying chamber 2 delimits a space in which the drying of the strip of pasty material 6 occurs at least partly.

The strip of pasty material 6 is fed in at the inlet 4 from where it enters the drying chamber 2.

It should be noted that the expression “smoking articles” is used to mean articles of various kinds such as, for example, articles of the “heat not burn” type (where the article is only heated and not burnt), or articles which burn at least partly, such as, traditional cigarettes, for example.

For example, the moisture content of the strip of pasty material 6 is greater than 20%.

In particular, the moisture content may be between 30% and 50%.

In particular, the moisture content may be between 35% and 40%.

The strip of pasty material 6 may be obtained, for example, using the method according to WO 2020/058814. In that solution, the strip of pasty material 6 is obtained by a process known as lamination, where the mixture, with a moisture content of less than 50%, is squeezed between two rollers to form a layer.

In an alternative not illustrated, the strip is obtained using a process known as casting, where the liquid or semi-liquid material (with a moisture content generally greater than 50%) is poured onto a conveyor belt, made of a metallic material, for example, which conveys it into a first drying chamber where a first drying step is carried out, and then into a second drying chamber, where drying is completed.

In the description which follows, reference is generally made to the drying chamber 2 of a strip of pasty material 6, which may be a drying chamber of a strip 6 obtained for example with the method according to WO 2020/058814, that is, by lamination, or to a second drying chamber of a strip obtained with a casting process.

The pasty material of the strip 6 may contain tobacco (for example, reconstituted tobacco) or a substance derived therefrom, or more generally speaking, a material capable of generating an aerosol in the context of smoking articles, such as, for example, one or more between cellulose, rapeseed and hemp, as well as water and/or flavourings and/or binders and/or other additives. The drying chamber 2 is also provided with an outlet 8, downstream of the inlet 4 along the conveying direction, for feeding out a dried strip 10.

Preferably, the dried strip 10 generally has a moisture content of approximately 7%-15% and is ready for immediate use, for further processing (for example, shredding) or to be wound into a roll 12 for use at a later stage (as in the case illustrated in the accompanying drawings).

The drying chamber 2 at least partly houses conveying means 20, 14, used for conveying the strip of pasty material 6.

Both of these elements can be made in different ways, depending on the embodiment of the apparatus according to the invention, as will become clearer as this descriptions continues.

Inside the drying chamber 2, the apparatus comprises a heating system which may comprise, for example, one or more apparatuses for generating and circulating a hot air flow, infrared plates or microwave generators.

In the embodiment illustrated for example in FIGS. 1 and 2, the heating system inside the drying chamber 2 comprises an apparatus 28, 28′, 30, 30′ for generating and circulating a flow of hot drying air.

The drying chamber 2 and the heating system define an oven in which drying of the strip of pasty material 6 occurs.

In a first embodiment, illustrated in FIGS. 1-3 , the conveying means 20, 14 which convey the strip of pasty material 6 comprise a pickup unit 14, consisting, for example, of a first conveyor 14 comprising, for example, a pair of endless chains 16 or other flexible drive elements such as cables, belts or the like. In the case of chains, these are trained around transmission sprockets 18, at least one of which is motorized and synchronized with the corresponding sprocket of the other chain. Preferably, the two sprockets 18 of the two chains 16 are solidly connected to the same shaft, with which an electric motor driving it (not illustrated) is associated.

The electric motor is controlled by a control unit, which controls the operation of the apparatus as a whole and which is not described further.

Two upper transmission sprockets 18 of each chain 16 are located at the same level, on the outside of the side walls 2A of the drying chamber 2 in the example illustrated.

The upper transmission sprockets 18 define a horizontal stretch of the chains 16, running substantially at the same level as a roller conveyor 20, also forming part of the apparatus and described in more detail below.

More specifically, the straight stretch of the first conveyor 14 runs from an infeed or inlet station 22 for the strip of pasty material 6 to be dried to an outfeed station, where the dried strip 10 leaves the apparatus, defining a second conveying path of the strip 6.

The straight stretch of the first conveyor 14 extends substantially entirely inside the drying chamber 2.

The remaining stretch of each chain 16 between the two upper sprockets 18 runs below the straight stretch, as may be seen clearly in the drawings.

Between the two chains 16 there is a bridge structure 24 for supporting the strip of pasty material 6 to be dried. It may be made in different ways but preferably comprises a plurality of openings through which the hot dry air can flow. For example, the bridge structure 24 may comprise or be composed of a plurality of laminas, made of metal, for example, which have openings made all over their surfaces and which are fixed with their ends slightly spaced from the two chains 16. Alternatively, the bridge structure 24 may comprise or be composed of a metallic mesh portion, also fixed with its two longitudinal sides to the chains 16.

The bridge structure 24 constitutes means for receiving the strip 6 and, in particular, a supporting and entraining surface 24 for the strip 6.

The bridge structure 24 does not extend along the full length of the two chains 16 but only along a part of them, which must be such as to supportably receive the initial portion of the strip of pasty material 6 and to entrain it by friction, as explained in more detail below. In particular, the length of the bridge structure 24 may be approximately the same as the length of the straight, upper stretch of the two chains 16.

The bridge structure 24 thus allows performing a first step of starting, during which the strip of material 6 moves through the drying chamber 2 without the risk of suffering damage which might occur as a result of contact between the strip 6, which has an initial portion, or free end, and the conveying surfaces of the roller conveyor 20.

In the accompanying drawings, a winding station is located downstream of the outfeed station to wind the dried strip 10 onto a roll 12. The winding station contributes to the advancing motion of the strip being conveyed in that winding the strip onto the roll may also have the function of entraining it.

As mentioned above, the roller conveyor 20 runs at substantially the same level as the straight, upper stretch of the chains 16 from the infeed station 22, and may extend as far as the outlet 8 of the drying chamber 2 (as in the accompanying drawings) or it may reach the downstream end of the straight, upper stretch of the chains 16 (outfeed station). Whatever the case, the roller conveyor 20 defines a first conveying path for the strip 6.

Preferably, the roller conveyor 20 extends inside the drying chamber 2, between the inlet 4 and the outlet 8 thereof.

The inlet 4 of the drying chamber 2 may coincide with the infeed station 22.

The outlet 8 of the drying chamber 2 may coincide with the outfeed station.

The axes of the individual rollers 26 of the roller conveyor 20 are perpendicular to the conveying direction of the strip of pasty material 6.

At least some of the rollers 26, in particular the rollers 26 closest to the infeed station 22, are motorized, although preferably all the rollers 26 are motorized. Advantageously, the presence of the (at least partly) motorized rollers 26 allows the strip 6 to be conveyed without rubbing against the rollers 26, thus avoiding possible damage to the strip 6 as it moves along the drying chamber 2. In the first embodiment, illustrated in FIGS. 1-3 , the heating system, in the part above the two conveyors 14, 20 inside the drying chamber 2, comprises at least one hot, dry air generator 28 which, through suitable ducts 30, channels flows of hot, dry air onto the conveyors 20 and 14 and blows them onto the upper surface of the strip of pasty material 6 moving through the drying chamber 2 from the inlet 4 to the outlet 8.

In the first embodiment, illustrated in FIGS. 1-3 , the heating system, in the part below the two conveyors 14, 20 inside the drying chamber 2, comprises at least one hot, dry air generator 28′ which, through suitable ducts 30′, channels flows of hot, dry air onto the conveyors 20 and 14 and blows them onto the underside surface of the strip of pasty material 6 moving through the drying chamber 2 from the inlet 4 to the outlet 8. In other words, more generally speaking, the heating system is outside of, and distinct from, the conveyors 20, 14. More in detail, the heating system does not coincide with the conveyors 20, 14 (that is, it is a distinct entity, separate from the two conveyors 20, 14).

The hot, dry air generators 28, 28′ may be of any known kind and the ducts associated therewith may be advantageously composed of a sheet metal box with conduits 32, 32′ extending across the full width of the bridge conveyor 14 and the roller conveyor 20 and provided, on the walls facing them, with holes through which jets of hot, dry air are blown onto the upper and underside surfaces of the strip of pasty material 6.

The operation of the apparatus now described can be better understood if reference is made to an initial instant, where the front end of the strip of pasty material 6 to be dried is located in the infeed station 22. In this condition, the control unit of the apparatus commands the first conveyor 14 to move the front edge of its bridge structure 24 in proximity to the infeed station 22 and then to advance at substantially the same speed as the strip of pasty material 6, which leaves the infeed station 22.

As the first conveyor 14 advances, the strip of pasty material 6, which, for example, has a moisture content of around 35%-50%, advances at the same speed and is placed on the bridge structure 24 of the first conveyor 14 itself.

The length of the bridge structure 24 is preferably defined as a function of the consistency of the strip of pasty material 6, its weight, and the characteristics of the surface of the bridge structure 24, so as to ensure that the initial portion of the strip of pasty material 6 adheres to it so that, as the first conveyor 14 advances, the strip of pasty material 6, simply resting with its initial portion on the bridge structure 24, is entrained along with it inside the drying chamber 2.

Owing to the consistency of the strip of pasty material 6, it is practically inevitable that its initial portion, resting on the bridge structure 24, will be “marked” by the bridge structure, but this is not a problem because the initial portion is a very small, minimal part of production as a whole and can be scrapped.

When the rear edge of the bridge structure 24 has passed the infeed station 22, the portion of web of pasty material 6 following the initial portion is placed directly onto the roller conveyor 20 which, in the meantime, is no longer covered by the bridge structure 24 of the first conveyor 14. Thanks to its continuity, the strip of pasty material 6 continues to advance, supported partly by the first conveyor 14 and partly by the roller conveyor 20.

When the bridge structure 24 of the first conveyor 14 has completely uncovered the roller conveyor 20 and, in fact, continuing in its movement, is positioned under it, as shown in FIG. 2, the first conveyor 14 is stopped and the drying apparatus works with the roller conveyor 20 alone.

The heating system inside the drying chamber, thanks to its air jets, for example, completes the drying process by bringing the moisture content of the strip of pasty material 6 down to a desired value, thus obtaining the dried strip 10.

Preferably, when the bridge structure 24 of the first conveyor 14 has completely uncovered the roller conveyor 20, the latter (that is, the rollers thereof) is the only means which guides the strip towards the outlet 8. Advantageously, this aspect distinguishes the invention from prior art solutions in which a strip of material is guided along a roller feed path with the aid of a support belt whose function is to keep the strip of material in contact with the rollers but which, at the same time, considerably complicates the constructional and functional aspect of the process of drying the material.

The surface of the rollers 26 may be perfectly smooth.

Alternatively, the surface of the rollers 26 may be slightly knurled or embossed.

In the first case, both surfaces of the dried strip 10 are smooth, whereas in the second case, the underside surface of the dried strip 10 is also slightly knurled or embossed.

In both cases, the surface finish of the dried strip 10 is determined by the surface finish of the rollers 26 and does not have unwanted markings on it, imparted to it by the underlying conveyor as in the prior art. In all cases, the surface finish of the rollers 26 is selected to ensure that the friction coefficient is high enough to enable the rollers 26 to convey the strip 6 by rolling but without it rubbing against them.

Preferably, the rollers 26 are not heated because in the apparatus of this invention, the heat needed to dry the strip of pasty material 6 is provided by the heating system. This aspect makes the structure of the apparatus simpler: if the rollers were heated, the overall complexity would increase and the strip would be more likely to dry non-uniformly, impacting negatively on the quality of the end product. In effect, direct contact between the strip and the heated rollers would cause some parts of the strip to be subjected to higher temperatures than others, leading to considerable thermal shocks during the drying process.

It will be appreciated that the apparatus according to the preferred embodiment illustrated is much improved over traditional dryers, and in particular:

• • it requires a drying chamber 2 that is much shorter than the drying chambers currently in use and offering the same performance; it has been calculated that a drying chamber 2 of the dryer according to the invention equal in performance to a traditional dryer with main dryer and mesh dryer occupies approximately 30% less floorspace in length and consumes 40% less energy.
  • it allows a significant reduction in energy consumption because of the reduced size not only of the drying chamber 2 but also of the first conveyor 14.

In particular, the fact that the strip 6 rolls on the second conveyor 20 means that the second conveyor 20 allows rolling to occur, that is to say, it does not comprise flat surfaces. That way, the strip 6 advances without rubbing against the second conveyor 20.

It should also be noted, with reference to the drawings, that irrespective of the size of the rollers 26, there is preferably, between one roller and the next, a connecting surface which acts as a bridge between the conveying surfaces of two successive rollers 26. This connecting surface is preferably provided with a plurality of through holes to allow hot, dry air to be blown through the holes towards the underside surface of the strip to be dried.

The connecting surface may be made of steel, for example, to facilitate the strip feed motion.

In an embodiment, illustrated in FIG. 4, where the principle of alternating operation of the first conveyor 14 and the roller conveyor 20 continues to apply, the heating system comprises a plurality of infrared plates 34, interposed between the individual rollers 26 of the roller conveyor 20. These infrared plates 34 may be provided as an alternative to, or in combination with, the connecting surface.

In an embodiment, illustrated in FIG. 5, downstream of the drying chamber 2, there is a cooling chamber 36, whose function is to cool the dried strip 10 down to ambient temperature after its passage through the drying chamber 2 has taken it to a high temperature which, in some cases, is so high as to make it unsuitable for subsequent processes.

The cooling chamber 36 is traversed by both the bridge conveyor 14 and the roller conveyor 20 but, unlike prior art drying systems provided with a cooling chamber, the apparatus according to this invention allows considerable energy saving since it does not use a single conveyor which passes from a hot environment to a cool environment undergoing continual changes from low to high temperatures but which, although it does use a single bridge conveyor moving through the two environments at different temperatures, does not involve high energy consumption thanks to its reduced size and, consequently, its reduced thermal inertia.

In an embodiment, illustrated in FIGS. 6 and 7, the apparatus comprises, inside the drying chamber 2, a first conveyor 14 which is substantially the same as the first conveyors 14 of the embodiments described above, except for the slightly different form of the two chains 16 which move the bridge structure 24, nevertheless in the same way as described above for the previous embodiments.

The roller conveyor 20 comprises a sequence of lower rollers 26, 26′ corresponding, in practice, to the rollers of the preceding embodiment.

The roller conveyor 20 comprises fixed rollers 26 alternated with rollers 26′ mounted on a single liftable structure such as to subject the rollers 26′ to a substantially vertical translational motion.

The fixed rollers 26 are motorized, whilst the rollers 26′ may be mounted idly on their liftable structure or they may themselves also be motorized.

The roller conveyor 20 also comprises a second sequence of rollers 38, mounted idly on the respective fixed shafts, at a level higher than the fixed rollers 26 and facing the latter.

In this embodiment, the heating system may, for example, comprise a single hot air generator 28, whose duct 30 is provided with a plurality of hollow projections 40 having a trapezoidal transverse profile, extending vertically as far as the rollers 38 and transversely along the full axial length of the rollers themselves. In a variant not illustrated, there may be more than one hot air generator or a hot air generator located above the rollers and different drying means, infrared plates, for example, located under and/or to one side of the rollers.

The inclined walls of the projections 40 are provided with a plurality of holes, through which hot air jets are blown.

The operation of this embodiment of the apparatus is as follows: the process is the same as in the previous embodiments until the initial portion of the strip of pasty material 6 to be dried is placed on the bridge structure 24 of the first bridge conveyor 14. After the entire bridge structure 24 has passed the underlying roller conveyor 20 and the next portion of the strip of pasty material 6 has been placed on the rollers 26, 26′, a command issued to the supporting structure of the rollers 26′ causes the structure to be lifted until the rollers 26′ practically reach the top of the transverse cavities delimited by projections 40 adjacent to the hot air duct 30.

This causes the strip of pasty material 6 to be arranged in zigzag fashion (thus following a first zigzag path), deflected sequentially upwards by the rollers 38 and downwards by the rollers 26′, the individual stretches facing the inclined walls of the projections 40 and being struck by the jets of hot, dry air blowing out of the holes made in the walls of the projections.

This embodiment allows the drying chamber 2 to be considerably reduced in length, without reducing the performance of the apparatus.

Generally speaking, the rollers 26, 26′ of the roller conveyor 20 may be between 50 and 100 mm in diameter.

The rollers 26, 26′ arranged linearly may have a centre-to-centre distance of between 200 and 300 millimetres. That way, the hot. dry air generators 28, 28′ and/or the infrared heating plates 34 can be positioned between them.

In the embodiment of FIGS. 6 and 7, the height of the rollers 26′ (relative to a plane through the fixed rollers 26) may be between 250 and 750 millimetres and depends, for example, on the type of strip to be dried.

It was calculated that compared to a traditional dryer offering the same performance with a main dryer and a mesh dryer, the apparatus according to this fourth embodiment of the invention allows its longitudinal dimension to be reduced by approximately 70%-80% and its energy consumption by approximately 40%.

This invention has been described in terms of some preferred embodiments of it but it is understood that it may be modified in several ways without thereby departing from the scope of the protection afforded by this industrial invention patent.