WO1999065320A1

WO1999065320A1 - Apparatus and process for reducing the size of leaf material

Info

Publication number: WO1999065320A1
Application number: PCT/GB1999/001834
Authority: WO
Inventors: William Cunningham
Original assignee: Imperial Tobacco Limited
Priority date: 1998-06-15
Filing date: 1999-06-09
Publication date: 1999-12-23
Also published as: AU5047499A

Abstract

Apparatus for reducing the size of leaf material, such as tea or herb leaves, comprises rotatable stripping means (3) and a feeder comprising a pair of cooperating counter-rotatable elements (1, 2) for delivering leaf material to the stripping means. The feeder and the stripping means are arranged such that, in use, the leaf material experiences shearing forces as it passes from between the counter-rotating elements to the rotating stripping means. The apparatus further comprises means for separating out the fraction of leaf material which has been reduced in size to below 10 mm.

Description

APPARATUS AND PROCESS FOR REDUCING THE SIZE OF LEAF MATERIAL

This invention relates to apparatus and a process for reducing the size of leaf material, such as tea or herb leaves.

In the manufacture of tea and dried herbs, it is well known that the leaf particle size has to be reduced in some way. Normally, this is achieved by some form of milling process, such as a hammer mill or roll mill or by using some form of cutting machine to chop the leaves into fine particles.

Conventional types of milling process have a high wastage rate due to the generation of excess dust in the process. The cutting process has the disadvantage of being high maintenance due to the need to keep cutting edges sharp.

The present invention aims to alleviate the problems associated with the conventional processes by avoiding the need for constantly sharp cutting edges and/or by reducing the level of dust generated in the process.

Accordingly, the present invention provides apparatus for reducing the size of leaf material comprising rotatable stripping means and a feeder comprising a pair of co-operating counter-rotatable elements for delivering leaf material to the stripping means, the feeder and the stripping means being arranged such that, in use, the leaf material experiences shearing forces on passing from between the counter- rotating elements to the rotating stripping means which forces reduce the size of the leaf material, the apparatus further comprising means for selectively separating out the fraction of leaf material which has been reduced in size to below 10mm.

The leaf material preferably has a moisture content of at least 50% by weight (more preferably at least 70% by weight, such as 70% to 80% by weight, for example) and is preferably tea leaves or herb leaves.

The term "leaf material", as used herein, is intended to cover both whole leaves, as picked or harvested, and parts of leaves. The leaf material may be used in the invention after it has been freshly picked or harvested from plants or after drying or, in the case of tea leaves for example, after fermentation.

The apparatus of the invention allows the selective separation of the fraction of leaf material which has been reduced in size to below 10mm, preferably to below 5mm. This separation can be achieved, for instance, by the use of a suitable screen or sieve. Those skilled in the art will appreciate that the size of leaf material, particularly where the particles are irregularly shaped, refers to its maximum dimension.

The exact size range for the size reduced leaf material which is required in any given case will, of course, depend on the type of leaf material being processed and the size to which it is conventionally reduced. The apparatus of the invention may be readily modified such that a fraction having the appropriate size range is obtained.

The stripping means preferably comprises radially extending arms. The arms may be in the form of continuous plates or spaced teeth (which can be straight, bent or curved) and may include parts which are capable of cutting the leaf material or are capable of puncturing and tearing through it.

The elements also preferably comprise radially extending arms which also may be in the form of straight, curved or bent continuous plates or spaced teeth, optionally including parts which are capable of cutting the leaf material. Alternatively, the feeder elements may comprise a pair of rollers or may consist of a flexible membrane wrapped around a framework which allows variable quantities of leaf material to be fed.

The arms may be flexible, inflexible or a mixture of fixed and flexible components.

The rotating elements and the stripping means can take the same form and may be the same shape and size, differing only in their function which is dictated by their position in the apparatus.

The stripping means and the feeder are arranged at a relatively close distance from each other in order to subject the leaf material to the shearing forces which are at least partially responsible for the size reduction. Preferably, the distance between the outermost parts of the two elements in the feeder is less than 50mm and the distance between the outermost parts of each of these elements and the outermost parts of the stripping means is less than 50mm. The shearing forces are experienced by the leaf material as it is directed from the feeder to the rotating stripping means. The leaf material is preferably delivered to the rotating stripping means substantially along a radius of the axis of rotation of the stripping means. The size reduction chiefly takes place in the region where the leaf material passes from being moved under the influence of the feeder to being moved by the stripping means and, as the skilled person will appreciate, the exact position of this region will vary depending upon the particular configuration of the apparatus and the rate of rotation of its various rotating components. The shearing force can be considered, at least in certain circumstances, as arising from the action of the stripping means on one part of the leaf material while the feeder is holding another part of the leaf material.

Preferably, where the arms of the stripping means and those of the elements consist of spaced teeth, the teeth are intermeshed. With such an arrangement, the size reduction is effected, to some extent, by the interaction of the stripping means and the feeder. When the teeth are intermeshed, the distance between the teeth as they pass each other is typically less than 25mm, more preferably less than 1 2.5mm.

The apparatus preferably comprises a rotatable drum in which the stripping means and the feeder are arranged. The drum may be generally cylindrical and its walls may be solid. However, the drum preferably comprises a screen (e.g., in its walls) which allows the fraction of leaf material reduced in size to below 10mm to pass out of the drum. The screen can form all or only part of the side walls of the drum.

The drum preferably incorporates internally protruding lugs for directing the leaf material to the feeder elements. As the drum rotates, the lugs collect the leaf material so that it travels around the inside of the drum until it falls (preferably solely under the influence of gravity) into the feeder. The positioning of the feeder within the drum and/or the speed of rotation of the drum are adjusted so as to ensure that a suitable amount of the leaf material is delivered to the feeder as the drum rotates.

To assist transfer through the drum, an additional fixed or rotating element, running down the drum parallel to the stripping means, may be used to slow down the leaf material leaving the stripping means. The leaf material thus slowed will then be able to fall under the influence of gravity onto a lower portion of the surface of the drum. Preferably the tangential speed of the additional rotating element is similar to that of the drum (i.e., ± 50% of the speed of the drum) and it is also preferred that the additional rotating element has a direction of rotation opposite to that of the drum.

The stripping means and the elements preferably rotate about axes which are parallel to the axis of rotation of the drum. Preferably, the axes of rotation are either substantially horizontal or are tilted at from 0° to 10° (more preferably from 2° to 6°) to the horizontal.

The stripping means and elements can converge as they approach the exit end of the drum to take account of reduced loading resulting from the small particles being sieved out of the main flow. This also allows the amount of size reduction that takes place to increase towards the exit end of the drum. This convergence can be achieved by varying the diameter of the stripping means and/or the elements along their length. By adopting this method, an additional effect will be to increase the tangential velocity of the arm tips as the diameter increases and this will affect the size reduction characteristics.

The diameter of the drum will typically be in the range of from 300 to 2500mm, preferably from 900 to 1 800mm. The diameters of the stripping means and the elements (as defined by the end of any radially protruding arms) are typically from 5 to 50% of the diameter of the drum.

The tangential velocity of the drum is preferably in the range of from 0.04 to 0.5 m/s with the tangential velocity of the stripping means and the elements being from 3 to 250 times (preferably 10 to 100 times) greater than that of the drum.

The rotating components of the apparatus (other than the drum) can be run at synchronous speeds to achieve true intermeshing of the stripping means and the rotating elements. Alternatively, the rotating components can be run such that they have different tangential velocities, thus setting up shear actions between the various rotating components. The choice of rotational speed and mode of operation depend upon the design of the rotating component and drum protrusions used and this in turn depends on the nature of the leaf material being threshed and upon the required size reduction.

The conveyer used for feeding the leaf material into the drum can be constructed such that it will move the feed point of the leaf material into the drum. This can be used to control the amount of size reduction that takes place.

The apparatus of the invention can comprise more than one (e.g., two) stripping means and the extra stripping means can be provided by one or more additional rotating elements. These additional elements may carry out a degree of size reduction of the leaf material and they may participate in the delivery of the partially size reduced leaf material to the feeder and/or the stripping means. The apparatus may also comprise additional rotating elements which act solely to direct leaf material into the stripping means.

The invention also provides a process for reducing the size of leaf material which comprises treating the leaf material (in order to reduce its size) in the apparatus of the invention.

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

Figure 1 shows a cross-section through an apparatus according to one embodiment of the invention;

Figure 2 shows a cross-section through an apparatus according to another embodiment of the invention;

Figure 3 shows a cross-section through an apparatus according to yet another embodiment of the invention;

Figures 4 and 5 show perspective views of stripping means suitable for use in the apparatus of the invention;

Figure 6 shows perspective views of three types of arm (or teeth) for use in the apparatus of the invention;

Figure 7 shows a plan view of another arm for use in the stripping means of the invention; and

Figure 8 is a side view of yet another stripping means suitable for use in the apparatus of the invention. Referring to Figure 1 , drum 6 rotates about a substantially horizontal axis in an anti-clockwise direction. A series of lifting pins (or lugs) 7 are attached to the inside surface of drum 6. The function of the pins 7 is to move the leaf material up the side of drum 6. The leaves are then gathered by co-operating counter-rotating elements 1 and 2 which form a feeder for the leaves. Elements 1 , 2 comprise radially extending arms 1 a, 2a which run the full length of the drum. In the embodiment of the invention shown in Figure 1 , the arms 1 a, 2a are as depicted in Figure 5. The leaf material is forced between elements 1 ,2 where some of the shearing or cutting of the leaf material may take place. The leaf material is delivered from between elements 1 ,2 into stripping means 3 which has arms 3a. Stripping means 3 rotates in the same direction as the drum in the Figure, i.e., anti-clockwise, although it may rotate in the opposite direction. It is in the region of delivery of the leaf material from elements 1 ,2 to arms 3a of stripping means 3 that the major part of the size reduction takes place as the leaf material which is still partially held by elements 1 ,2 is torn by the shearing action of stripping means 3. Stripping means 3 may also act to cut the leaf material to some extent. The leaf material reduced in size by stripping means 3, excluding any parts of the leaf material which may have fallen to the bottom of drum 6 and/or left the drum through a sieve in the drum, is gathered between stripping means 3 and element 4 which is located further round the drum 6 (in the direction of its rotation) and are forced towards second stripping means 5 creating a second shearing zone within the drum. The rotational direction of the rotating elements 1 ,2,4, the stripping means 3,5 and the drum 6 are indicated by the broken arrows.

Another embodiment of the invention is illustrated in Figure 2. Here the leaf material is carried up the side of the drum 10 on the lugs 1 1 by the rotational movement of the drum 10 (anti-clockwise in the Figure). The leaf material is then drawn into the gap between the counter-rotating elements 1 2 and 1 3 which run the length of the drum 1 0 and co-operate to act as a feeder which directs the leaf material into stripping means 14. The main function of stripping means 14 is to shear or rip the leaf material into smaller sized pieces. Stripping means 14 and elements 1 2,13 have bent arms 14a, 1 2a, 1 3a and are of the general design shown in Figure 4. An alternative design for the arms 14a, 1 2a, 1 3a is illustrated in Figure 7.

In Figure 3, drum 20 rotates anticlockwise and, in use, lugs 21 transfer leaf material to counter-rotating elements 22 and 23. The differently designed arms 22a and 23a of elements 22 and 23, respectively, feed the leaf material to stripping means 24 which has arms 24a. Arms 24a intermesh with arms 23a. Fixed element 25 catches the leaf material which has been reduced in size as it leaves stripping means 24 and allows it to fall back down to the inside surface of drum 20.

Referring to Figure 6, the arms 1 a, 2a of the feeder and/or the stripping means may have a flat edge. Alternatively, as shown for arms 23a, 24a, the outermost edge of the arms may be tapered to a point and may taper from one end to a narrower other end along the drum direction in order to assist in the size reduction of the leaf material.

The process of the invention may be run continuously or as a batch process. For continuous operation, the leaf material is fed into one end of the drum, the leaf material is reduced in size throughout the length of the drum and the smaller pieces of leaf material which have not already passed out of the drum (e.g., through screens in its walls) exit the drum at the other end. Passage of the leaf material from one end of the drum to the other can be achieved by tilting the drum and, optionally, also the rotating components of the apparatus at an angle to the horizontal or by including a helical screw 1 5 in the apparatus, as shown in Figure 8. The helical screw can constitute the stripping means and/or the rotating elements of the apparatus.

Alternatively, the transfer of the leaf material down the drum can be effected by arranging the lugs helically on the inside of the drum or the transfer can be caused by air currents acting on the leaf material.

As mentioned above, the surface of the drum used in the apparatus of the invention, which is preferably cylindrical, can be either solid or may comprise screens. Where the drum comprises one or more screens, these can be responsible for allowing separation of the leaf material which has been appropriately reduced in size.

Where the drum surface is solid, the whole mass of leaf material travels the full length of the drum passing through the stripping means. The separation of the leaf material which has been appropriately reduced in size can then be achieved by suitable means for separation (e.g., a screen or sieve) at or near to the end of the drum.

Where the drum surface consists of one or more screens, smaller size reduced leaf material passes out of the drum without having to traverse the full length of the drum. This means that the smaller particles of leaf material will avoid further unnecessary impacts and will suffer less damage as a result once they have been threshed. Larger particles of leaf material unable to pass through the screens can be recycled back into the drum to receive further processing. The screens have a mesh size suited to the requirements of the desired final product.

Where the process requires an improved screening efficiency, the length of the elements and the stripping means can be less than the full length of the drum. This allows extra screening to be carried out before, after or before and after the threshing zone by suitable location of the elements and stripping means within the drum. Alternatively, additional separate sieves can be installed in the process after the drum, to allow extra screening.

Claims

1 . Apparatus for reducing the size of leaf material comprising rotatable stripping means and a feeder comprising a pair of cooperating counter-rotatable elements for delivering leaf material to the stripping means, the feeder and the stripping means being arranged such that, in use, the leaf material experiences shearing forces on passing from between the counter-rotating elements to the rotating stripping means which forces reduce the size of the leaf material, the apparatus further comprising means for selectively separating out the fraction of leaf material which has been reduced in size to below 10mm.

2. Apparatus as claimed in claim 1 , wherein the leaf material has a moisture content of at least 50% by weight.

3. Apparatus as claimed in claim 1 or claim 2, wherein the leaf material is tea leaves or herb leaves.

4. Apparatus as claimed in any one of claims 1 to 3, wherein the stripping means comprises radially extending arms.

5. Apparatus as claimed in any one of claims 1 to 4, wherein the elements comprise radially extending arms.

6. Apparatus as claimed in claim 4 or claim 5, wherein the arms are in the form of plates or teeth.

7. Apparatus as claimed in claim 4 or claim 5, wherein the arms are flexible.

8. Apparatus as claimed in claim 6 or claim 7, wherein the arms of the stripping means and the arms of at least one of the elements are intermeshed.

9. Apparatus as claimed in any one of claims 1 to 8, wherein the stripping means and the feeder are arranged within a rotatable drum.

10. Apparatus as claimed in claim 9, wherein the means for separating out the fraction of leaf material which has been reduced in size to below 10mm comprises a screen formed as part of the drum.

1 1 . Apparatus as claimed in claim 9 or claim 10, wherein the drum comprises internally protruding lugs for directing the leaf material to the feeder.

12. Apparatus as claimed in any one of claims 9 to 1 1 , wherein the stripping means and the elements rotate about axes which are parallel to the axis of rotation of the drum.

13. Apparatus as claimed in claim 12, wherein the axes of rotation are substantially horizontal.

14. Apparatus as claimed in any one of claims 1 to 13, which comprises two rotatable stripping means.

15. Apparatus as claimed in any one of claims 1 to 14, which further comprises means for reducing the velocity of the leaf material after it exits from the stripping means.

16. Apparatus as claimed in claim 15, wherein said means for reducing the velocity of the leaf material is either fixed or rotates and has its axis aligned substantially parallel to the axis of rotation of the stripping means.

1 7. Process for reducing the size of leaf material to obtain a fraction which has been reduced in size to below 10 mm which comprises treating the leaf material in the apparatus of any one of claims 1 to 1 6.

18. Process as claimed in claim 17, wherein the fraction of leaf material which has been reduced in size to below 10mm is obtained during size reduction in the apparatus.

19. Process as claimed in claim 1 7, wherein the fraction of leaf material which has been reduced in size to below 1 0mm is obtained after size reduction in the apparatus.