As it is known, in nearly all cultivars of tobacco and other herbs the leaves once harvested should be subjected to a drying process, which in the field of tobacco is called curing, to be then forwarded to the subsequent processing steps.

The drying takes place in suitable ovens with specific conditions of temperature, moisture and hot-air ventilation. Actually, the leaves are contained in metal baskets or containers of the most varied shapes and dimensions, depending on the equipment manufacturer and on the type of leaves or herb to be treated, but in any case the packaging and the handling of these containers requires specific equipments, substantial spaces for the processing and the storing thereof, as well as a remarkable cost for the manpower required for the preparation thereof.

The shape of the at present used ovens is referable to a parallelepiped having 1. 5 to 3 m width, 2.5 to 3 m height and 6 to 11 m length. Usually, the product is inserted from the front, where there are one or more hinged doors, whereas at the rear it is placed the heater, for air heating, the fan for conveying hot air and the operation cycle control and command devices.

The leaves are charged on said containers and inserted into the oven, by sliding the containers themselves either on suitable guides that may be anchored to the sidewalls or resting on the ground.

The fan-propelled hot air rises from the bottom of the oven or vice versa, crossing the floor commonly made of metal grids, and rises, crossing the leaves to be dried, up to the top of the oven where it can be sucked again or mixed with outside air by the fan and recycled, after having flown through the heatheater.

At these stages, controlling the air moisture rate and temperature is crucial in order to obtain a product exhibiting a satisfactory grade. Therefore, the oven has control units with various probes located at different sites of the oven. The air, along its bottom-to-top path, should come into contact with all leaves, as only thus a homogeneous-grade product will be obtained.

For this purpose, the operators should try to distribute the leaves in the suitable containers as uniformly and correctly as possible. Moreover, it is often required that at strategic spots of the oven walls there be arranged foam-rubber contours serving as seals, so as to leave to the air, flowing through the spaces among the leaves, no alternative paths. Otherwise, most of the hot air would flow through the latter, thereby not carrying out its function.

In any case, with the known ovens and charging systems, often between the leaves at the oven bottom and those at the oven top a certain difference in the features of the dried leaves subsists. This is so since the leaves at the bottom are impinged upon by a hotter air flow with respect to the leaves at the top. Increasing the temperature at the top entails the risk of damaging the leaves at the bottom.

Therefore, the oven running modes imposed by the art often cause production rejects, product downgrading and lengthening of the drying steps, with the entailed increase of the costs.

The technical problem underlying the present invention is to provide a drying oven overcoming the drawbacks mentioned with reference to the known art.

Such a problem is solved by an oven for the drying as above specified, comprising: a plurality of conveyor beds internal to the oven, horizontally arranged, such as to take up the entire useful length of the space of the oven and movable in a loop along two directions, for the charging and the discharging of a corresponding layer of leaves taking up the space between adjacent conveyor beds, each bed comprising a plurality of cleats, arranged on rows substantially parallel, evenly spaced and orthogonal to the sliding direction of each bed, which remain substantially projecting from the respective conveyor bed in a preset position at a respective charging end of the conveyor bed.

The main advantage of the oven according to the present invention lies in the option of inletting air not merely from the bottom but also among the interspaces corresponding to the beds, thereby ensuring a more homogeneous distribution of the heating flows. Moreover, there are allowed the easy and quick charging and discharging of the produce to be dried and the drying thereof, eliminating the use of containers.

The present invention will hereinafter be described according to a preferred embodiment thereof, given by way of a non-limiting example with reference to the annexed drawings, wherein: * Figure 1 shows a partially sectional perspective view of an oven for the drying according to the invention; * Figure 2 shows an elevation longitudinal section of the oven of Figure 1, illustrating the internal air flows;

* Figure 3 shows an elevation cross-section of the oven of Figure 1, illustrating the internal air flows; * Figures 4A, 4B and 4C show elevation longitudinal sections of the oven of Figure 1, illustrating different steps of charging; * Figures 5,6 and 7 are a perspective view, a side view and a top plan view, respectively, of an ancillary charging device that can be used together with the oven of Figure 1, ; * Figure 8 shows a section of the charging end of the oven of Figure 1 and of the device of the three preceding figures; and * Figures 9A, 9B, 9C and 9D illustrate in detail some steps of charging the leaves into the oven, with or without the aid of said charging device.

With reference to the figures, an oven for the drying of leaves is generally indicated by F. It comprises insulated perimeter walls 1 delimiting a drying space 2, centrally and frontally arranged, an ancillary space 3, which may receive a heater C, and a ventilation system 12 driven by a motor drive 13.

The drying space 2 contains a plurality of conveyor beds 5, sideways defined and delimited by respective chains 4.

These conveyor beds 5 internal to the oven F, here three in number, are horizontally positioned, so as to take up the entire useful width of the space 2 of the oven F.

By virtue of the chains 4 that are mounted on suitable drive wheels 6, the beds 5 are movable in a loop along two directions, forward (charging) and rear (discharging), for the charging and the discharging of a

corresponding layer of leaves taking up the space between adjacent conveyor beds 5.

The toothed drive wheels 6 are connected by transverse shafts 20 and operated by respective electric motors 17, driven in the two directions by a suitable control unit.

However, it is understood that the electric motors are merely one of the viable solutions. They may be replaced by equivalent means like hydraulic motors, jacks, cranks, etc.

Moreover, especially when adapting extant ovens, the beds may be mounted on idle wheels, so that the beds themselves could be handled by pulling and/or pushing with hooks or other alike means.

Each bed has evenly spaced crosspieces 19, extending from one chain 4 to the other one and being connected thereto by suitable sliders 8. On said crosspieces, a net, preferably metallic and flexible, is spread, substantially defining said conveyor beds for supporting the leaves. The net has a mesh such as not to hinder the air flow.

The net may be functionally replaced by other means, like e. g. a thick arrangement of crosspieces.

On each conveyor bed a plurality of cleats 7 are comprised, arranged on substantially parallel rows, evenly spaced and orthogonal to the sliding direction of each bed 5, remaining substantially projecting from the respective conveyor bed 5 in a preset position at a respective charging end of the conveyor bed 5. The cleats 7 are made of slightly cambered lightweight rods, mounted on respective crosspieces 19. The former face upwards onto the top face of the respective bed 5, whereas they face downwards onto the bottom face thereof.

The motion of the conveyor bed 5 leads said cleats to pivot at the charging end of the oven F, in which they assume a so-called charging position, substantially horizontal (Figures 9A and 9D).

At the center of each cleat 7 a respective needle 27 <BR> <BR> projects, , helping to support the leaves as it will be apparent hereinafter.

Also in order to allow the transition of the cleats 7, below the bottom conveyor bed 5, the oven F comprises an interspace 9 at the bottom thereof.

At the interspace 9 and at the space partitioning each bed 5, wide enough to allow the passage of the cleats 7, an air supplying valve 10 is provided. The valve consists of a movable bulkhead extending along the entire width of the oven.

Moreover, there are an outside air supplying valve 11 and a valve 15 for sucking air from the oven F. In Figures 2 and 3, the arrows indicate the air flow inside of the oven F.

Of course, the flow spreads in the free spaces among the leaves, i. e. just below the conveyor beds in the space left free by the loop formed thereby. This space, for each bed, forms a sort of interspace and of collector for the hot air, which thus spreads under uniform pressure under each bed of leaves supported by the respective bed.

The operation of the abovedescribed oven can be described as follows: The charging cycle (Figure 4A) starts from the topmost conveyor bed 5, arranging the first row of cleats 7 horizontally and externally to the oven F, whereas all the other cleats 7 will have remained at the bottom of the respective conveyor beds, by rotating the motor 17 so

as to shift the bed clockwise with respect to the figures. The leaves may be brought to the height of the charging bed by means of dedicated conveyor belts, or of suitable elevators, optionally equipped with drives that may be interfaced to the rotation of the motors 17 so as to have a timing between the feeding belt and the rotation of the charging bed.

The quantity of leaves by volume chargeable between the space from the horizontal cleats 7 and the cleats 7 already into the oven F in a vertical position is remarkably greater than the space between two rows of vertical rods. Therefore, by continuing the rotation of the chains, the horizontal cleats 7 will come to a vertical position, compacting towards the preceding row the mass of leaves and reducing the volume thereof.

Moreover, the leaves falling from the feeding belt deposit basically horizontally into the horizontal plane formed by the cleats 7, post-compaction being found for the most part vertically. This kind of compaction with a vertical positioning of the leaves is an important condition for a good outcome of the drying cycle.

Upon filling the top conveyor bed 5, the intermediate one (Figure 4B) is filled, and so on down to the bottom conveyor bed (Figure 4C).

Upon completing the charging of the entire drying space 2, the drying and curing cycle is activated: all the spaces among the beds 5 are concerned by the air inletting, whereas below and above the beds 5 interspaces are formed where the air is collected and then crosses the layer of leaves.

The uniform arrangement of the leaves generates a likewise uniform air circulation, improving the product features and reducing the treatment times.

The step of discharging is it also remarkably simplified and accelerated, starting from the bottommost bed and reverting the motion of the motor 17 driving the chains 4 of the various beds 5. The extraction will be facilitated by conveyor belts that will take the dried leaves from the moving rods and bring them directly to the sorting stations. In the step of extracting the dried leaves from the oven, it is desirable for a better subsequent workability of the product to keep the same at a balanced moisture rate. In our case, such a condition is viable since, by starting from the bottom with the step of discharging, onto the front of the oven a roller shutter or any other suitable means may be applied, so as to leave uncovered only the space necessary to let the layer of leaves pass from the charging bed which is being discharged, and leaving the fan running in the humidifier position.

The abovedescribed devices and the modes of employ are applicable, besides to novel construction ovens in the various shapes and sizes, also to extant ovens, made of concrete, insulated sheet panels, etc. , effecting the modifications required for the housing of the charging beds and of the ancillary devices required to optimize the drying process.

Moreover, by applying to the oven walls optical sensors detecting the color of the leaves as the drying progresses, with suitable electronics it is possible to act on the revolutions of the fan motor, on the temperature of the hot air generator and on the mixer valves, so as to adjust the air flow according to the requirements of the produce to be treated.

The charging may be facilitated by the use of a charging device 30 having a pivotable bulkhead 31, provided with slits 37 for the passage of the cleats 7, that may be

neared to the charging end at the conveyor bed 5. The bulkhead 31 could be slidably mounted on a suitable movable frame 32 and connected to suitable moving members 33.

The bulkhead 31 is neared to the horizontal bed 5, with the cleats 7 positioned at the slits 37 (Figure 9A).

Thus, instead of the cleats 7 the bulkhead 31 supports the weight of the charged leaves. When an adequate quantity of leaves has been charged, the bulkhead 31 is pivoted to carry out the compaction (Figure 9B). Then, also the cleats 7 are pivoted by advancing the conveyor bed 5. Thus, the cleats need not endure compaction stresses. Then, the bulkhead 31 is reversibly pivoted, to receive the subsequent row of cleats 7 between the slits 37 thereof, so as to start over with another compaction.

Optionally, this compaction system may be replaced by a device pushing the cleats and assisting their pivoting.

It has to be pointed out that in lieu of the crosspieces there may be used drilled rubber mats, metal nets, and any other means suitable for supporting the leaves and the cleats.

The shape of the cleats may be straight, semicircular or any other suitable one, and they may be made of metal or other material. At the conveyor bed 5 there may be used cleats assuming a reclined position at the bottom face thereof.

Optionally, the motor 13 setting in rotation the fan 12 has a variable rotation rate so as to adjust the quantity of air to be inletted in the oven according to the parameters dictated by the control unit, controlled by the various probes present in different parts of the oven itself.

To the abovedescribed oven a person skilled in the art, in order to satisfy further and contingent needs, may effect several further modifications and variants, all however encompassed by the protective scope of the present invention, as defined by the annexed claims.