Threshing device

Abstract: The device (1) has a first threshing rotor (3) bearing a first number of radial blades (5), and a second counter-­ rotating loading rotor (4) having a different number of radial blades (6). The rotors (3,4) are arranged side by side and adapted to be driven in phase at different speeds. A fan (9) generates a flow of air at a region of alignment of the radial blades (5,6) of the first and second rotors (3,4), and the first rotor (3) has a rear outlet (18) for threshed leaves.

Description: The present invention relates to a threshing device particularly for tobacco leaves. In the processing of tobacco it is currently known to use devices which have the function of breaking tobacco leaves, thereby separating the laminar part of the leaves from the ribs or stems; said laminar part assumes the form of particles of lamina termed "strips". This operation is indispensable since it is the lamina which is subsequently used in the manufacture of tobacco products and must therefore have the greatest and most uniform possible size. Some known devices use a rotor which is provided with a series of radial blades arranged on diametrical planes, which will be referred to hereafter as dynamic blades. Such known devices furthermore have a series of fixed blades associated with a static blade holder fixed to the framework. Advantageously, the fixed blades are arranged on an axis which is diametrical to the rotor so that each series of dynamic blades passes cyclically between two flanking fixed blades. A grid or a series of grids is provided below said rotor. The rotor usually rotates at a speed of approximately 400-450 rpm and may have six blades on each diametrical plane, whereas the leaves are introduced, by gravity or by pneumatic conveyance, at the region overlying the fixed blades. The operation of said known devices is aimed at causing the leaves to become arranged transversely between two fixed blades, and then threshed by a dynamic blade in order to mechanically separate the lamina from the rib. The threshing action is completed by rubbing the leaves against a grid, also known as "basket", which is arranged below the rotor. These known devices, however, are not devoid of disadvantages, not least of which is the fact that perfect placement of the leaves between the fixed blades is very rarely achieved in practice. This results in some leaves not being threshed, while other leaves are subjected, due to the rotation rate of the rotor, to multiple threshings which break up the lamina excessively, thereby reducing the size of the strips obtained. This is a serious disadvantage because, in order to obtain a high quality product, it is preferable to have the largest and most uniform possible size of strips. In fact, at the threshing region between rotating blades and fixed blades, the condition occurs in which strips already separated from the ribs are undesirably forced to undergo the continuous threshing action of the subsequent rotating blades, because the fixed blades tend to oppose the downward outflow of the strips and ribs, thus causing the very harmful reduction of strip size and loss of uniformity. Once it has left the threshing region, the product should be completely expelled through the grid. However, a part does not escape and continues the rotation induced by the rotor. This product, retained by the grid, undergoes a further threshing action at the rear static blades, if these are adopted, or continues to rotate until it is threshed again at the static blades. This causes even further undesirable breakage of the strips, which deteriorate and lose uniformity. In known devices, the use of ducted air flows at the region where the leaves are fed to the rotor has the mere function of conveying the leaves, and said ducted air flow does not prevent the leaves from undergoing numerous threshings. An other known device is described in US-A-3 126 014. The known device includes a two-stage threshing device, with two rotors, which respectively interact in a conventional manner with corresponding cages (grid member 36 and grid rods 30) and with each other, to attain efficient removal of lamina from the stems of tobacco in one pass. The rotors are respectively provided with a plurality of knives or blades, which are arranged in groups with axial spacing to one another along a shaft and which, within a group, protrude radially from said shaft with equi-angular spacing to one another. The two rotor shafts are arranged with their axes parallel to one another and spaced apart from one another in such a way, that the respective groups of radially protruding blades of the respective rotor inter-leaf without collision. While such a device is comparable in size to conventional single stage threshing machines, it still mainly relies on the interaction of the rotors with the corresponding cages, apart from the interaction with one another, for threshing the tobacco leaves. Therefore, such a device will also have the foregoing mentioned disadvantages that go hand in hand with threshing machines using rotors and herewith co-acting grids. The aim of the present invention is therefore to eliminate the disadvantages described above in known types of threshing devices by providing a threshing device which allows to break tobacco leaves, separating the laminar part from the ribs. Within the scope of the above described aim, one important object of the invention is to provide a device which allows to thresh tobacco leaves so as to obtain a good size of the laminar part or strips to be sent for subsequent processing and the greatest possible length of the rib sections. A further object of the invention is to provide a device which associates with the preceding characteristics that of being structurally simple as well as being reliable and safe in use. This aim, these objects and others which will become apparent hereinafter are achieved by a threshing device, particularly for tobacco leaves, as defined in the accompanying claims. Further characteristics and advantages of the invention will become apparent from the detailed description of a particular but not exclusive embodiment, illustrated only by way of non-limitative example in the accompanying drawing, wherein: figure 1 is a schematic view of the various components of the device. With reference to the above-cited figure, the device 1 for threshing tobacco leaves 2 for separating the rib and the lamina, is constituted by a first threshing rotor 3 and by a second loading rotor 4 rotatably mounted on the casing or framework 11 of the device. The rotors 3,4 are arranged side by side and driven in phase with respect to one another. Any convenient power-assisted means may be used for driving the rotors such as, e.g., an electric motor, and any means may be used for transmitting motion generated by the power-assisted means to the rotors such as, e.g., gear wheels, belts, etc. The first rotor 3 advantageously but not necessarily has a smaller diameter than that of the second rotor 4 and in any case a rotation speed which is considerably greater than the rotation speed of said second rotor. Indicatively but not necessarily, the first rotor 3 may rotate at a rate above 400 rpm, whereas the second rotor 4 may rotate at a rate which varies between 40 rpm and 80 rpm. For the sake of clarity, it will be assumed that the first rotor 3 of figure 1 rotates in a clockwise direction indicated by the arrow 30, and that the second rotor 4 rotates in an anticlockwise direction indicated by the arrow 40, though said directions may vary in other embodiments. The first rotor 3 is provided with a plurality of first radial blades or dynamic blades 5 which protrude along a plurality of diametrical planes, and comprise a number of blades which may be varied. The second rotor 4 also has a plurality of second radial blades 6 which are also arranged along such diametrical planes as to occupy the interspace between two consecutive parallel planes of arrangement of the first blades 5. A number of eight blades at each plane has also been indicated merely by way of example for the second rotor 4. The diameter of the first and second rotors as well as the respective speeds and the number of blades are in any case such as to allow a single threshing passage of each of said first blades for each pair of second blades, which occurs at the diametrical plane which is common to both the first and second rotors. Thus, tobacco leaves 2 can be fed into the device 1 at the feed region 7, which lies above the threshing region and in which said first and second blades are aligned, for example by means of a suitable conveyor 8 arranged above said first and second rotors. The leaves 2, fed into the device, become arranged at the feed region 7, and are forced thereat toward said underlying first and second blades by means of a flow of forced air obtained by means of a fan 9 and an appropriate first duct 10 which lies above the casing or framework 11 of the device. The fan 9 generates a flow of air which conveys the leaves 2 to the threshing region at a speed which is higher than the peripheral speed of the second rotor 4, so as to force the deposition of the leaves on the backs of the second blades 6. This avoids effects of rejection and ejection of the leaves on the part of the second rotor and achieves a certain pre-orientation of the leaves on the second blade in a transverse direction. The use of the fan 9 to generate an air flow having a greater velocity than the peripheral speed of the second rotor 4 does not have the function of mere conveyance of the leaves, but, together with the use of the second rotor, that of forcing the leaves between the rear surfaces 41 of blades of said second rotor, thereby achieving a partial pre-orientation of the leaves themselves. The fact that the first and second rotors are set in phase, for example by means of an appropriate transmission with a reduction ratio, ensures that the leaves undergo just one single threshing operation, thereby causing the resulting lamina and rib to be expelled due to the rotation action of the second rotor and the overlying flow of air. In this manner, useless and harmful further threshing of the leaves is avoided. The device may have, below the first rotor 3, a grid or "basket" 12, and a first hopper 13 connected to a second duct 14 which extends laterally to said first rotor. Similarly, a second hopper 15 provided with a valve 16 for interconnection with the second duct 14 is provided below the second rotor 4. The first hopper 13 furthermore has a first tab 17 which protrudes within the second duct 14 to create a Venturi effect. A rear outlet 18 is provided behind the first rotor 3 on the framework 11 on the opposite side with respect to the first duct 10 and may also be under negative pressure by virtue of the presence of a second tab 19 which protrudes into the second duct 14 or may exploit the kinetic energy induced in the product by the rotation of the threshing rotor. Said outlet 18 allows to extract the strips which, having failed to pass through the basket 12, would tend to keep rotating, undergoing further useless and harmful threshings at the first and second blades or at other static blades possibly provided. It has thus been observed that the invention has achieved the intended aim and objects, since the use of the two separate rotors with different speeds and with a different number of blades allows to subject each individual leaf to a single threshing operation which leads to the obtainment of a lamina of considerable size. The device furthermore allows to remove, at the outlet 18 of the first rotor 3, the lamina already separated from the rib (also termed "free lamina") without said lamina being subjected to further threshings if it is kept rotating due to failure to pass through the basket 12. This, also contributes to the obtainment of laminae with the largest and most uniform possible size for subsequent manufacturing steps. The device is furthermore structurally very simple and requires only minimal maintenance, since there are no fixed blades on which laminae may accumulate during threshing. Furthermore, the device is less subject to damage than known devices in the event of accidental introduction of foreign matter. Any number of blades may constitute the first and second pluralities of blades, and any suitable arrangement of the blades at the peripheral surface of the rotors may be adopted, such as, e.g., a possible arrangement in a spiral or helical configuration may be employed, providing that said blades be arranged periodically mutually in phase at the threshing region defined between the first and second rotors. The device may furthermore comprise a plurality of said first and second rotors arranged mutually in sequence, in order to achieve successive further threshings if desired. The device may also employ a single threshing rotor with a rear outlet. The materials and the dimensions of the individual components of the device may naturally be the most appropriate according to specific requirements.

Claims: Threshing device, particularly for tobacco leaves, comprising: at least one first threshing rotor (3) having a plurality of radially protruding first blades (5) positioned with axial and circumferential distance to one another thereon; at least one second loading rotor (4) having a plurality of radially protruding second blades (6) positioned with axial and circumferential distance to one another thereon; said first and said second rotor (3;4) being arranged with their axes parallel to each other and at a distance, as well as said first and said second blades (5;6) being spaced at an axial distance on said first and said second rotor (3;4) so that said first and said second blades (5;6) lap in inter-leafing position with one another; and at least one outlet (18) for removing threshed leaves; characterized in that said first and said second rotor (3;4) are driven at such rotational rates, that first blades of said first rotor (3) protruding in the same radial direction and second blades of said second rotor (4) protruding in the same radial direction come into parallel alignment in a diametrical plane common to both first and second rotors (3;4) defining there between a region of alignment; in that the device further comprises means (9,10) for generating a flow of forced air to convey leaves to the region of alignment with a speed and orientation sufficient for forcibly placing and pre-orientating said leaves on said second blades (6) for said first blades (5) passing the region of alignment to thresh said leaves; and in that one rear outlet (18) is arranged on a side of said first rotor (3) substantially opposite with respect to said alignment region. Threshing device according to claim 1, characterized in that said means (9,10) for generating a flow of forced air comprise: an air flow generator (9) and an appropriate first duct (10) for delivering said flow of forced air at said region of alignment. Threshing device according to claims 1 or 2, characterized in that said forced air flow has a speed which is higher than the peripheral speed of said second rotor (4). Threshing device according to claims 1, 2 or 3, characterized in that said forced air flow is delivered by said means (9,10) for generating a flow of forced air in a pre-orientating direction with respect to rear surfaces (41) of said second blades (6), whereby leaves fed into the threshing device are pre-orientated. Threshing device according to any preceding claim, characterized in that said first and said second rotor (3;4) are driven at different rotational rates; and in that said plurality of first and second blades (5;6) have a different number of blades. Threshing device according to claim 5, characterized in that said first rotor (3) has a higher rotational rate than said second rotor (4). Threshing device according to claims 1, 5 and 6, characterized in that said first and said second rotors (3;4) have a rotational speed rate and a respective number of said first and said second blades (5;6) which are adapted to obtain a single threshing for said leaves at said alignment region. Threshing device according to any preceding claim, characterized in that said rear outlet (18) is provided to permit extraction of threshed strips obtained by a single threshing of leaves and is arranged in a rearward position at the framework (11) of the threshing device on the opposite side with respect to said first duct (10). Threshing device according to claim 8, characterized in that means (19) are provided for generating negative pressure at said rear outlet (18) to enhance extraction of said threshed strips of leaves. Threshing device according to claims 8 or 9, characterized in that said rear outlet (18) is defined by a seat of said first rotor (3) interconnecting with a second duct (14), by means of a second tab (19) which protrudes into said second duct (14) and is adapted to create a Venturi effect. Threshing device according to claim 10, characterized in that a second hopper (15), provided with a valve (16) for interconnection with said second duct (14), is arranged below said second rotor (4).

Inventors: TOGNANA ALDO, TOGNANA, ALDO
Applicants: GARBUIO SPA, GARBUIO S.P.A.
Application year: 1990
Main classification: A24B5
IPC codes: A24B5