EP1267649A1

EP1267649A1 - Apparatus and process for threshing tobacco

Info

Publication number: EP1267649A1
Application number: EP01902502A
Authority: EP
Inventors: William Cunningham
Original assignee: Imperial Tobacco Ltd Great Britain
Current assignee: Imperial Tobacco Group Ltd
Priority date: 2000-01-28
Filing date: 2001-01-26
Publication date: 2003-01-02
Also published as: AR027300A1; AP2002002608A0; WO2001054520A1; CN1419423A; AU2001230360A1

Abstract

An apparatus for threshing tobacco comprises a housing (1) having an upper entrance (2) for charging tobacco leaves or parts thereof to the housing and a lower exit (3) for discharging threshed tobacco from the housing. Located within the housing is a rotatable stripping means (4) having a plurality of radially extending elements (5) each presenting a leaf puncturing tip (6) for puncturing the lamina of a tobacco leaf and means for rotating the rotatable stripping means. The housing and the stripping means are arranged such that, in use, the leaf puncturing tip (6) of a radially extending element (5) on the stripping means (4) as it rotates punctures the lamina of a tobacco leaf, or part thereof, entering into the housing through the upper entrance thereof and effects a slashing action on the lamina during the downward movement of the leaf, or part thereof, through the housing so as to separate at least partially the lamina from the stem of the leaf. The apparatus produces larger pieces of lamina, useful in the production of handrolling tobacco, than conventional threshing machines.

Description

APPARATUS AND PROCESS FOR THRESHING TOBACCO

The present invention relates to an apparatus for threshing tobacco leaf material and to a process of threshing tobacco leaf material using the apparatus.

In the tobacco industry, it is well known, that in order to process the tobacco into a suitable form for use in the manufacturing of products, the tobacco leaf has to have the midrib stem removed from the rest of the tobacco leaf.

For some tobacco products it is desirable to have large pieces of tobacco leaf.

To obtain large pieces of tobacco leaf the separation is commonly done by hand.

Some machines have been described for obtaining large pieces of leaf such as those disclosed by Jenkins et al., in US 4,237,909, or by Da Silva in GB 2, 290.694A. These, however, rely on the correct alignment of the leaves into the stripping process and are not, therefore, suited to handling large bulk flows of tobacco leaves.

The most common form of stripping machine for handling bulk flows of tobacco are threshing mills as described by Allen in US 2,760,492 and by Bonner et al., in US 3,141 ,485. In these threshing mills the action of the rotating elements on the tobacco is a hammering action. The impact of a flat area of a rotor arm onto the lamina portion of the leaf, where this impact occurs on an area near the stem, causes a piece of the lamina to shear from the stem thus removing a large particle of lamina. Where the impact of the hammer is on an area away from the stem, a small piece of lamina will be broken off. Where the piece of lamina broken off is too large to pass through the basket it will be carried round the mill to be struck again as it is held back by a stator element. This will be repeated until the piece of lamina is small enough to pass through the basket. This process results in the production of smaller pieces of lamina and dust is created by attrition of the lamina against the walls of the thresher as it travels round. These machines produce leaf pieces which are considerably smaller than those obtained by hand stripping.

Various patents exist which include two or more rotating threshing elements inside a single machine with various claims for improvements over existing single rotor threshers. For instance, Bonner et al., in US 3,126,014 and US 3,696,817 describe a thresher containing two or more rotating elements with radial teeth meshing with rotating elements consisting of discs. These are variations on a convention style threshing mill, and none are in common use.

WO 98/26677 describes a machine for tobacco threshing in which the tobacco is not all forced through a fixed screen but instead the threshing rotor and two feeding rotors are mounted inside a rotating drum and the tobacco can pass down the drum through the rotors without being forced through a screen. Whilst this has the advantage over current processes in that it will generate less small-sized lamina pieces as waste, it does not produce a significantly greater lamina size.

In US 5,026,322, Tognana describes a threshing mill in which some of the tobacco is not forced through a screen with the intention that this will produce pieces of tobacco with a larger particle size. The type and speed of the beaters described in this patent are similar to those found in a conventional thresher.

The aim of the present invention is to provide a means for threshing tobacco leaf material to obtain pieces of tobacco lamina, the majority of which are of a large particle size.

Accordingly, the present invention provides an apparatus for threshing tobacco comprising a housing having an upper entrance for charging tobacco leaves or parts thereof to the housing and a lower exit for discharging threshed tobacco from the housing and, located within the housing, a first rotatable stripping means having a plurality of radially extending elements each presenting a leaf puncturing tip for puncturing the lamina of a tobacco leaf and means for rotating the rotatable stripping means, the housing and the stripping means being arranged such that, in use, the leaf puncturing tip of a radially extending element on the stripping means as it rotates punctures the lamina of a tobacco leaf, or part thereof, entering into the housing through the upper entrance thereof and effects a slashing action on the lamina during the downward movement of the leaf, or part thereof, through the housing so as to separate at least partially the lamina from the stem of the leaf.

Several criteria are used to assess the performance of tobacco threshing apparatus. These include the threshing efficiency which is defined as the amount of free tobacco lamina that is removed from the tobacco leaf relative to the total amount of lamina available. Another criterion is the particle size (or particle size distribution) of the pieces of lamina obtained from the threshing process and a further criterion is the number of impacts to which the tobacco is subjected in order to achieve a particular threshing efficiency and/or particle size.

In conventional threshing apparatus, such as that described in US 3,126,014 and US 3,696,817, operated at conventional speeds, a basket is provided which collects larger pieces of tobacco leaf. These larger pieces are subjected to further impacts by the rotating elements in the thresher and it is only through these further impacts that a useful threshing efficiency is achieved. Unfortunately, by subjecting the basket-retained tobacco pieces to further impact by the rotating elements the size of the lamina product is reduced and the particle size distribution achieved is such that a high proportion of lamina pieces is of relatively small size. Contrary to this, the threshing apparatus of the invention, which does not require a basket, is able to achieve a relatively high threshing efficiency by a single impact or a controlled number of impacts by the radially extending elements to produce lamina pieces of large size and a particle size distribution which has a high proportion of lamina pieces of relatively large size and a small proportion of pieces of relatively small size. In the apparatus described in WO 98/26677, unless the desired throughput of tobacco is assured some tobacco will, unfortunately, be subjected to a greater number of impacts by the rotating elements than is necessary with the inevitable result that more smaller pieces of lamina than is desired are produced. We have found that the action of the leaf puncturing tips of the radially extending elements on the rotating stripping means to puncture the laminas of the tobacco leaves and to slash the laminas during the downward movement of the leaves gives rise to an advantage over prior art threshing machines in that larger pieces of the lamina can be produced. Larger pieces of tobacco lamina are useful in the production of tobacco for hand rolling of cigarettes. There is according to the invention no need to reduce the size of the lamina pieces to enable them to pass through a thresher basket. Further benefits that can be achieved, compared to prior art threshing machines, include a reduction in the amount of stem waste being produced and a reduction in the amount of dust produced during processing. Processing can be carried out using tobacco leaf material having a higher moisture content than is usually the case with conventional threshing processes and apparatus.

The apparatus comprises rotatable stripping means located within a housing. The axis of rotation of the rotatable stripping means may be tilted at from 0° to 10° to the horizontal but preferably, will be substantially horizontal.

The stripping means has a plurality of radially extending elements each presenting a leaf puncturing tip. The radially extending elements may be radially extending plates, teeth, blades or flexible arms, for example continuous plates, single or multiple spaced teeth which may be straight, bent or curved, knives and spines, which may be flexible. Preferably, however, the radially extending elements are blades which according to a particularly preferred embodiment are L-shaped with the bend in the intended direction of rotation of the stripping means.

The radially extending elements each present a leaf puncturing tip for puncturing the lamina of tobacco leaf material. The leaf puncturing tip may comprise a single sharpened projection at the tip of the radially extending element or, alternatively, may comprise a saw-tooth projection at the tip of the radially extending element. When saw-tooth projections are used each individual tooth will typically have a depth to pitch ratio in the range of from 1:1 to 2:1, for instance, having a depth to pitch ratio of 2:1 , such as one having a depth of 1 inch and a pitch of about 0.5 inch or, alternatively, the depth may be foreshortened in such a way as to eliminate the pinch point at the base of the teeth and thus reduce the propensity of the blade to clogging.

According to a preferred embodiment of the invention, where teeth or blades are used as the radially extending elements on the stripping means, there is also provided at least one stator element which typically is fixed to or mounted on the internal wall of the housing in which the stripping means is located. The stator element extends into the housing such that it co-operates with the radially extending elements provided on the rotatable stripping means. Preferably, the position of any stator element in relation to the position of the radially extending elements on the rotatable stripping means is such that as the rotatable stripping means rotates in the housing the leaf puncturing tips intermesh with the stator element to improve the puncturing performance of the tips and to create shearing forces that apply to the tobacco leaf material caught between the stator element and the leaf puncturing tips. When the leaf puncturing tips are so intermeshed the distance between the stator element and the leaf puncturing tip is typically less than 100mm.

The housing is preferably in the form of a substantially vertical tower providing a substantially vertical chute for introducing the tobacco leaves to the stripping means. The stripping means is typically in the form of a rotatable cylindrical element having an axis of rotation coincidental with the horizontal axis of a drum-like chamber provided in the housing from which rotatable cylindrical element the radially extended elements radiate outwardly towards the internal surfaces of the drum-like chamber along the length of the rotatable cylindrical element. The drum-like chamber will have an internal diameter which is slightly greater than the total diameter of the stripping means, typically in the range of from 12 to 30 inches (30 to 77cm), preferably in the range of from 18 to 24 inches (45 to 61cm) and will have a length of several feet, typically about 6 to 7 feet (1.8 to 2.2m) in length. Where the radially extending elements have the form of separate teeth or sharpened blades radiating outwardly from the rotatable cylindrical element of the stripping means they will be disposed separately along the length of the cylindrical element typically at a distance of from 2 to 8 inches (5 to 21cm) from each other. Preferably, however, the spacing along the cylindrical element between one such separate tooth or sharpened blade and the next one to it along the length of the cylindrical element will typically be from 3 to 6 inches (7.6 to 15.2cm).

The radially extending elements provided on the stripping means may, alternatively, radiate outwardly from the rotatable cylindrical element continuously along the length of the cylindrical element.

The total diameter of the stripping means (i.e., from tip to tip of the radially extending elements) will typically be in the range of from 12 to 30 inches (30 to 77cm) preferably in the range of from 18 to 24 inches (45 to 61cm). The rotatable stripping means will, in use, be rotated at a speed of rotation typically in the range of from 400 to 1200 rpm (based on a stripping means having a total diameter of about 24 inches (61cm)). Where the radially extending elements are sharpened teeth or blades then a rotation speed in the range of 400 to 600 rpm is sufficient to achieve good separation of large lamina pieces of tobacco leaf. However, where the radially extending elements comprise conventional less sharp blades then it is preferred to use a higher rotation speed of the order of 800 to 1200 rpm. This increased speed of rotation improves the puncture performance of the puncturing tip on the radially extending element to puncture the leaf and to slash the lamina thereof in order to effect separation thereof from the leaf stem.

Since a basket, as is used in conventional threshing machines, is absent from the apparatus of the present invention losses from attrition on internal surfaces of the housing in the region of the stripping means are reduced and, thus, the rotation speed of the stripping means used in the present invention can be higher than that used in conventional apparatus. This use of a higher speed improves the puncturing and slashing performance of the stripping means. In addition, the use of tobacco leaves having a higher moisture content than are used in conventional threshing machines is possible since the absence of a basket means that tobacco will not clog and be ground to a paste in the machine. This, in turn, significantly reduces the amount of dust generated.

According to one preferred embodiment the housing contains a first rotatable stripping means, a second rotatable stripping means and means for rotating the second rotatable stripping means. The second rotatable stripping means will have a plurality of radially extending elements each presenting a leaf puncturing tip for puncturing the lamina of tobacco leaf material and will be arranged in the housing such that, in use, it acts in series with the first stripping means. The leaf puncturing tip of a radially extending element on the second rotatable stripping means, as it rotates, punctures the lamina of a tobacco leaf, or part thereof, received from the first stripping means and effects a slashing action on the lamina during the downward movement of the leaf, or part thereof, through the housing so as to separate at least partially the lamina from the stem of the leaf. The use of a second stripping means in series with a first stripping means improves the yield of pieces of lamina free of leaf stem material.

Preferably, the tobacco leaf material passing from the first stripping means to the second stripping means is re-oriented, i.e., it's alignment is changed so as to present the lamina in a position more amenable to being removed from the stem in the second stripping means. When a tobacco leaf approaches the first stripping means with an alignment with the butt end downwards a large piece of lamina will be removed since the stripping action will tend to act inwards towards the stem. However, if the stripping action is effected on a tobacco leaf presented tip downwards the leaf will tend to tear outwards way from the stem leaving a tear in the leaf but without removing the lamina. The leaf, thus, remains largely intact until it is presented to a subsequent stripping means butt end downwards. By subjecting the tobacco leaf material received from the first stripping means to re-orienting before it is processed by the second stripping means the amount of lamina removed from leaf stems can be increased. Re-orienting of the leaf material may, typically, be achieved by transporting the tobacco leaf material from one stripping means towards a subsequent stripping means using a vibrating screen. The apparatus may advantageously also contain a third and subsequent separate rotatable stripping means, in series, in a cascade. Preferably, however, not more than three separate stripping means are arranged in series since the particle size of the lamina pieces obtained will be reduced and the proportion of very small pieces and/or dust obtained will be correspondingly increased.

According to a further embodiment, therefore, the apparatus additionally comprises in the housing a third rotatable stripping means located in the housing downstream of a second rotatable stripping means as described above and means for rotating the third stripping means. The third stripping means has a plurality of radially extending elements each presenting a leaf puncturing tip for puncturing the lamina of tobacco leaf material. The housing and the third stripping means being arranged such that, when the apparatus is in use, the third stripping means acts in series with the second stripping means and wherein the leaf puncturing tip of a radially extending element on the third stripping means as it rotates, punctures the lamina of the tobacco leaf, or part thereof, received from the second stripping means and effects a slashing action on the lamina during the downward movement of the leaf, or part thereof, through the housing so as to separate the lamina from the stem of the leaf. A second and/or a third stripping means may act in co-operation with a suitably positioned stator element as described above.

Between the second and third stripping means the tobacco leaf material can be subjected to re-orienting as described above. Following the exiting from the third stripping means the processed leaf material can be sieved, for instance using a vibrating sieve screen, to separate dust and small particles of leaf and stem from the larger pieces of lamina.

The invention will now be described, by way of examples only, with reference to the accompanying drawings, wherein:

Figure 1 shows a cross-section through an apparatus according to one embodiment of the invention using a single rotatable stripping means; Figure 2 shows a cross-section through an apparatus according to another embodiment of the invention using a single rotatable stripping means and a stator element;

Figure 3 shows a cross-section through an apparatus according to yet another embodiment of the invention using a cascade of three rotatable stripping means;

Figure 4 shows a cross-section through an apparatus according to a yet further embodiment using a cascade of three rotatable stripping means;

Figure 5 shows a cross-section through an apparatus according to a still further embodiment using three rotatable stripping means in series;

Figure 6 shows perspective view of rotatable stripping means suitable for use in the apparatus of the invention;

Figure 7 shows perspective views of three types of radially extending elements (or teeth) for use in the apparatus of the invention; and

Figure 8 shows a plan view of another type of radially extending element for use in the apparatus of the invention.

Figure 9 shows a plan view of another type of radially extending element, which shows a modified saw tooth intended to reduce clogging.

Figure 10 illustrates types of radially extending elements used in the Tests and the Tables of Results.

Referring to Figure 1 , a housing 1 , having an entrance 2 and an exit 3, houses a rotatable stripping means 4 which is driven by a motor (not shown). The stripping means 4 has a plurality of radially extending elements 5. Each of the elements 5 comprises an L-shaped blade presenting a leaf puncturing tip 6 which, in use, points in the direction of rotation of the stripping means 4. In use, tobacco leaves are fed into the entrance 2 of housing 1 and drop under the influence of gravity into the path of the radially extending elements

5 mounted on the rotating stripper means 4. The action of the puncturing tips

6 on the leaves causes puncturing of the leaves. As the elements 5 rotate during the downwards movement of the leaves the lamina of the leaves are slashed and parts of the lamina are removed from the leaf stems. The processed tobacco leaf material falls out of the exit 3 of the housing. Figure 2 shows an apparatus similar to that shown in Figure 1 with the exception that the stripping means 4 has a plurality of blades 7 each having a puncturing tip 8 and in that there is provided a stator element 9 mounted on the internal wall of the housing 1 and extending therein to co-operate with the rotating blades 7. The blades 7 run along the length of the stripping means 4 as shown in Figure 6. The blades 7 may have a flat edge or may have an edge tapered to a point and may also taper from one end to a narrower other end as shown in Figure 7 in order to assist in the shearing of the leaves. The puncturing tips of the blades 7 and the stator element 8 intermesh. In use, a tobacco leaf entering the housing entrance 2 falls vertically into the path of the advancing blade 7, on the rotating stripping means 4, and the lamina of the leaf is punctured by the tip 8 and is slashed or partially slashed. The leaf is then carried through the housing by the rotation until it meets with the stator element 9, where the stator element and the rotating blade 7 co-operate in completing the slashing action where the slashing action was previously partial. Or where the leaf has not been slashed on entry, due to masking by other leaves, the stator element 9 and rotating blade 7 will co-operate to effect a slashing action on this. In view of the high speed of rotation of the stripping means a leaf may be punctured and slashed by the tips on successive blades on the stripping means.

In Figure 3, three stripping means are located in series in a substantially vertical housing 10 having an entrance 11 and an exit 12. A first stripping means 13 which is driven by a motor (not shown) has a plurality of radially extending elements 14 in the form of L-shaped blades each presenting a leaf puncturing tip 16. A second stripping means 16 is located beneath the first stripping means in the housing 10. The second stripping means which has a direction of rotation opposite to that of the first stripping means is driven by a motor (not shown) and is provided with a plurality of radially extending elements 17 in the form of L-shaped blades pointing in the intended direction of rotation. Each element 17 presents a leaf puncturing tip 18.

A third stripping means 19 is located in the housing 10 beneath the second stripping means. The third stripping means 19 is driven by a motor (not shown) and has an intended direction of rotation opposite to that of the second stripping means. The third stripping means is provided with a plurality of elements 20 in the form of L-shaped blades pointed in the intended direction of rotation. Each of the L-shaped blades is provided with a leaf puncturing tip 21.

In use, tobacco leaves are fed into the entrance 11 of housing 10 and drop under the influence of gravity into the path of the radially extending elements 14 and are subjected to stripping action as described above with reference to Figure 1. Tobacco leaf material processed by the stripping means then falls into the path of the radially extending elements 17 mounted on second stripping means 16 which is rotating in the direction shown and is further processed after which it falls into the path of the radially extending elements 20 mounted on the third stripping means 19 which is rotating in the direction shown. After final processing by the third stripping means the pieces of lamina and leaf stem material leave the housing at exit 12.

Figure 4 shows a variation of the vertical cascade of three stripping means illustrated in Figure 3. According to Figure 4 the lower wall 22 of housing 10 between the first and second stripping means and the lower wall 23 of the housing 10 between the second and third stripping means are each in the form of a sieve, e.g., wire mesh or a screen punched with a plurality of holes, to enable dust and small particles of lamina to leave the housing for collection.

Figure 5 shows a different embodiment of a threshing apparatus according to the invention which involves the use of three different stripping means. In this embodiment, there is provided, between the exit from the first stripping means and the entrance to the second stripping means and between the exit from the second stripping means and the entrance to the third stripping means vibrating screens 24, 25. The vibrating screens are associated with a means (not shown) for vibrating the screens. In use, the vibration of the vibrating screens 24, 25 changes the alignment of the tobacco leaf material for further processing at a subsequent stripping means. Beneath the third stripping means there is a vibrating bed sieve 26 and an associated vibrating means for the sieve (not shown) which, in use, allows the separation of dust and small particle leaf material from the larger pieces of lamina such that this can be collected separately.

EXPERIMENTAL

Tests 1 to 19

Tobacco leaves, of various moisture contents, were used in threshing tests using an apparatus according to the invention. In the tests, various types of radially extending element (as provided on the rotatable stripping means) were used and the tests were carried out for different total numbers of passes, i.e., the total number of times the tobacco was recycled through the apparatus.

The radially extending elements used in the tests were as follows:

1) L-shaped plates (generally as shown at 5 in Figure 1) with various different leaf puncturing tips, A to E as shown in Figure 10. No stator element was used.

2) L-shaped multiple, spaced teeth (generally as shown at 5 in Figure 1) with pitch of 30mm (F) or pitch of 60mm (G) as shown in Figure 10. Each of these teeth arrangements was used in association with an intermeshing stator element provided on the internal wall of the housing (as shown generally in Figure 2).

Of all of the radially extending elements tested, the tooth arrangement of type G was most similar to a conventional thresher blade.

For each test, the threshing efficiency was calculated and the pieces of lamina obtained after threshing were sieved into different sizes. The pieces of lamina obtained after threshing were separated, in this way, into those which do not pass through a 1 inch diameter round hole sieve, those which pass through a 1 inch diameter round hole sieve but not through a 0.5 inch diameter round hole sieve, those which pass through a 0.5 inch diameter round hole sieve but not through a 0.25 inch diameter round hole sieve and those which pass through a 0.25 inch diameter round hole sieve. No classification took place until after the total number of passes was complete. The percentages of amounts of lamina of different sizes were determined. The results are shown in Table 1. The results obtained in Test 14 (compared with those obtained in Tests 10 and 11) show that by using the blade D, with fewer passes, a high threshing efficiency was obtained and that sieving results were superior for the same amount of threshing.

TABLE 1

Element type is the type of radially extending element. The part of the element which acts against the tobacco is identified by reference to Figure 10

The number of times the tobacco was recycled through the thresher before the obtained lamina pieces were sieved into different size ranges. The thresher apparatus did not have a basket or screen and the total diameter of the stripping means was 18 inches. The stripping means was, in all cases, rotated at a speed of 355 rpm.

Threshing efficiency is the amount of free lamina removed relative to the total lamina available. Tests 20 to 41

These tests were carried out using, as the radially extending elements in the threshing apparatus of the invention, multiple, spaced, tapered, pointed teeth. The size and shape of the teeth used were constant but their pitch, i.e., the distance between one tooth and the next was varied throughout the tests. In all cases intermeshing stators, mounted on the internal wall of the apparatus, were used. The results are shown below in Table 2.

TABLE 2

The thresher apparatus used did not have a screen or basket and the total diameter of the stripping means was 18 inches. The stripping means had a rotation speed of 355 rpm. Tests 42 to 50

Further tests were carried out using a threshing apparatus having one of three different types of radially extending elements on the rotatable stripping means. In Tests 42 to 44, the radially extending elements were conventionally used flat-bladed hammers (Figure 7A and as used in US 3,696,817 Figure 3) wherein the pitch was set at 80mm. These were used in association with flat-bladed stators mounted on the internal wall of the apparatus housing (as shown in US 3,696,817 Figure 3); the flat-bladed hammers meshing (in use) flat side to flat side with the associated stators. In Tests 45 to 47, the radially extending elements used were tapered blades (Figure 7B), wherein the pitch was set at 80mm, which were used in association with similar-bladed stators mounted on the internal wall of the apparatus housing. In Tests 48 to 50, the radially extending elements used were L-shaped blades having saw-toothed edge having 20mm pitch between the teeth (Figure 10).

In these tests, the tip speed is the tangential speed of the tip of the radially extending element. In a conventional thresher rotor, in a first stage thresher, having a typical diameter of 24 inches and a rotation speed of 450 rpm the tip speed will be about 4.6ms^"1.

The tests were carried out using tobacco having a moisture content of about 19% which is similar to conventional threshing moisture levels. The results are shown below in Table 3.

The results show that the radially extending elements presenting a leaf puncturing tip give greater threshing efficiencies and larger size product compared to flat-bladed hammers conventionally used in threshing machines.

Claims

1. An apparatus for threshing tobacco comprising a housing having an upper entrance for charging tobacco leaves or parts thereof to the housing and a lower exit for discharging threshed tobacco from the housing and, located within the housing, a first rotatable stripping means having a plurality of radially extending elements each presenting a leaf puncturing tip for puncturing the lamina of a tobacco leaf and means for rotating the rotatable stripping means, the housing and the stripping means being arranged such that, in use, the leaf puncturing tip of a radially extending element on the stripping means as it rotates punctures the lamina of a tobacco leaf, or part thereof, entering into the housing through the upper entrance thereof and effects a slashing action on the lamina during the downward movement of the leaf, or part thereof, through the housing so as to separate at least partially the lamina from the stem of the leaf.

2. An apparatus according to claim 1 , wherein the radially extending elements on the rotatable stripping means are selected from radially extending plates, teeth, blades and flexible arms.

3. An apparatus according to claim 2, wherein the radially extending elements comprise blades or teeth.

4. An apparatus according to claim 3, wherein the radially extending elements comprise L-shaped blades each of which presents at least one leaf puncturing tip which, in use, points substantially in the direction of rotation of the rotatable stripping means.

5. An apparatus according to claim 3, wherein there is additionally provided a stator element mounted on the wall of the housing which element extends into the housing such that, in use, the stator element co-operates with the radially extending elements on the rotatable stripping means as it rotates.

6. An apparatus according to any one of claims 1 to 5, wherein the leaf puncturing tip comprises a single sharpened projection at the tip of the radially extending element.

7. An apparatus according to any one of claims 1 to 5, wherein the leaf puncturing tip comprises a saw-tooth projection at the tip of the radially extending element.

8. An apparatus according to any one of claims 1 to 7, which additionally comprises in the housing a second rotatable stripping means located in the housing downstream of the first rotatable stripping means and means for rotating said second stripping means, said second stripping means having a plurality of radially extending elements each presenting a leaf puncturing tip for puncturing the lamina of a tobacco leaf, the housing and second stripping means being arranged such that, in use, said second stripping means acts in series with said first stripping means and wherein the leaf puncturing tip of a radially extending element on the second stripping means as it rotates punctures the lamina of a tobacco leaf, or part thereof, received from the first stripping means and effects a slashing action on the lamina during the downward movement of the leaf, or part thereof, through the housing so as to separate at least partially the lamina from the stem of the leaf.

9. An apparatus according to claim 8, wherein the radially extending elements on the second rotatable stripping means are selected from radially extending plates, teeth, blades and flexible arms.

10. An apparatus according to claim 9, wherein the radially extending elements on the second rotatable stripping means comprise blades or teeth.

11. An apparatus according to claim 10, wherein the radially extending elements on the second rotatable stripping means comprise L-shaped blades each of which presents at least one puncturing tip which, in use, points substantially in the direction of rotation of the rotatable stripping means.

12. An apparatus according to claim 10, wherein there is additionally provided a stator element mounted on the wall of the housing which element extends into the housing such that, in use, the stator element co-operates which the radially extending elements on the second rotatable stripping means as it rotates.

13. An apparatus according to any one of claims 8 to 12, wherein the leaf puncturing tip comprises a single sharpened projection at the tip of each radially extending element on the second rotatable stripping means.

14. An apparatus according to any one of claims 8 to 12, wherein the leaf puncturing tip comprises a saw-tooth projection at the tip of each radially extending element on the second rotatable stripping means.

15. An apparatus according to any one of claims 8 to 14, wherein there is additionally provided, between the first stripping means and the second stripping means, means for re-orienting the tobacco.

16. An apparatus according to any one of claims 8 to 15, which additionally comprises in the housing a third rotatable stripping means located in the housing downstream of the second rotatable stripping means and means for rotating said third stripping means having a plurality of radially extending elements each presenting a leaf puncturing tip for puncturing the lamina of a tobacco leaf, the housing and third stripping means being arranged such that, in use, said third stripping means acts in series with said second stripping means and wherein the leaf puncturing tip of a radially extending element on the third stripping means as it rotates punctures the lamina of a tobacco leaf, or part thereof, received from the second stripping means and effects a slashing action on the lamina during the downward movement of the leaf, or part thereof, through the housing so as to separate the lamina from the stem of the leaf.

17. An apparatus according to claim 16, wherein the radially extending elements on the third rotatable stripping means are selected from radially extending plates, teeth, blades and flexible arms.

18. An apparatus according to claim 17, wherein the radially extending elements on the third rotatable stripping means comprise blades or teeth.

19. An apparatus according to claim 18, wherein the radially extending elements on the third rotatable stripping means comprise L-shaped blades each of which presents at least one leaf puncturing tip which, in use, points substantially in the direction of rotation of the rotatable stripping means.

20. An apparatus according to claim 18, wherein there is additionally provided at least one stator element mounted on the wall of the housing and which extends into the housing such that, in use, the stator element co-operates with the radially extending elements on the third rotatable stripping means as it rotates.

21. An apparatus according to any one of claims 16 to 20, wherein the leaf puncturing tip comprises a single sharpened projection at the tip of each radially extending element on the third rotatable stripping means.

22. An apparatus according to any one of claims 16 to 20, wherein the leaf puncturing tip comprises a saw-tooth projection at the tip of each radially extending element on the third rotatable stripping means.

23. An apparatus according to any one of claims 16 to 22, wherein there is additionally provided, between the second stripping means and the third stripping means, means for re-orienting the tobacco.

24. An apparatus according to either claim 15 or claim 23, wherein the means for re-orienting the tobacco is selected from a vibrating screen.

25. A process for threshing tobacco comprising treating tobacco in an apparatus as claimed in any one of claims 1 to 24.