Tobacco leaf is required to be cut into strands of tobacco which are suitable for tobacco products such as cigarettes. It is known to use rotary cutting machines to cut or shred the tobacco leaf into thin strands. Such tobacco cutting machines commonly comprise upper and lower converging conveyors forming a rectangular throat and being convergent in the direction of tobacco feed. A mouthpiece is provided at the convergent end of the throat. The leaf is fed into the throat at the divergent end and the conveyors drive the leaf continuously towards the mouthpiece.

At the mouthpiece the tobacco leaf is cut by knives mounted on rotating knife holder.

The holder is cylindrical shaped and mounted such that its axis of rotation is substantially parallel to the axis of the throat. The knives are mounted and evenly distributed around the holder such that the cutting edge of each knife is caused to pass across the mouthpiece and hence cut the tobacco leaf.

The convergence of the throat compresses the leaf such that it is cut and not pulled from the mouthpiece. At least one of the conveyors is arranged to be capable of moving in the vertical direction such that a regulated pressure can be applied to compress the tobacco leaf material.

The width of the cut strands can be adjusted by altering the conveyor speeds or the rotational speed of the knife holder. The cutting edges of each knife are continuously sharpened by a grinding unit mounted adjacent the rotating knife holder, on the cutting machine.

The thin shreds of tobacco leaf produced by the cutting machine are then often mixed with larger pieces of tobacco leaf or tobacco stem and used in the manufacture of

cigarettes. The larger pieces of tobacco stem or leaf are used to provide strength to the finished cigarette. The origin of these larger pieces is either a by product of the leaf threshing process which separates the lamina from the stem of the leaf or from a sieving process of the tobacco blend just prior to cutting. One problem associated with this process is the difficulty in mixing the larger pieces of tobacco with the main flow of smaller shredded pieces at a consistent rate such that the mixture and hence a cigarette contains the correct proportions of constant width strands and larger pieces.

It is an aim of the present invention to provide apparatus which alleviates the aforementioned problem and/or other associated problems generally.

According to the present invention there is provided tobacco cutting apparatus for cutting a body of tobacco moveable towards said cutting apparatus, comprising a rotatable member having at least two knives mounted thereon, these first and second knives each having a cutting edge extending substantially parallel to the axis of the rotatable member wherein the width of the cutting edge or the width of a discrete portion of said cutting edge of said first knife is shorter than the cutting edge width of said second knife.

Advantageously the cutting apparatus is able to cut shreds of tobacco material which individually have portions of differing depths.

Preferably the apparatus further includes conveyor means for moving said body of tobacco towards said cutting apparatus.

Preferably the conveyor means includes compression means to compress said body of tobacco material before the cutting operation is performed.

Preferably the conveyor means further includes a mouthpiece through which the body of tobacco is directed towards the rotatable member.

Preferably the cutting edge of at least one of said knives is an equal width to the width of the moveable body of compressed tobacco exited from said mouthpiece.

Preferably the width of at least one knife is equal to the width of the mouthpiece through which the body of tobacco is exited towards the rotatable member.

Preferably the cutting edge of at least one knife comprises a series of discrete cutting edge portions separated from one another by a series of slots formed in said cutting edge.

Preferably the slots comprise a divergent shape, the narrowest width of the slot being at its mouth, such that during a cutting operation the inner surface of each slot does not contact the material to be cut.

Preferably the angle of divergence of each of said slots is within a range of 90° to 95°.

Preferably at least two knives comprise a cutting edge having a width equal to the width of the mouthpiece.

Preferably two of the knives having cutting edge portion substantially equal to the width of the body of tobacco to be cut are located diametrically opposite one another, on the rotatable member.

Also according to the present invention there is provided a method of cutting tobacco material comprising the steps of, substantially continuously feeding the tobacco material towards a rotatable cutting member, said cutting member having at least two knives mounted thereon, rotating said rotatable member such that the knives mounted thereon contact the tobacco material, cutting the material with a first knife, said first knife comprising a cutting edge having its width, or a discrete portion of its cutting edge having a width, shorter than the width of another knife, subsequently

cutting the material with a second knife said second knife having a cutting edge with a greater width than said first knife cutting edge or a discrete portion of said first knife cutting edge such than a shred of tobacco is completely removed from the body of tobacco material.

Preferably said tobacco material is compressed before the cutting operation.

An embodiment of the invention will now be described with reference to the accompanying drawings in which: Figure 1 is a schematic illustration of a cutting machine and associated conveyor means.

Figure 2 is a section view of a rotatable member of a cutting machine according to the present invention.

Figure 3 is a view in the direction of arrow X on figure 2.

Figure 4 is a view in the direction of arrow Y of figure 2.

Figure 5 is an illustration indicating the divergent gap in one of the knives according to the present invention.

Figure 6 is a cross section view of a knife mounted on a retaining plate.

Figure 7 is a plan view of a piece of tobacco leaf cut by the apparatus of figure 1.

Figure 8 is a plan view of a piece of tobacco according to another embodiment of the present invention.

Referring to figure 1, a tobacco cutting machine 1 comprises conveyors 2 and 4 driven by a motor (not shown). Tobacco leaf 6 is inserted into the entrance 7 of the

conveyors, 2,4 and driven towards a mouth 8 through which leaf tobacco 6 is compressed. The conveyor 4 is mounted so as be rotatable about axis A and be capable of movement towards and away from conveyor 2 forming a converging channel into which the tobacco leaf 6 is directed. This allows the tobacco leaf to be held between the conveyors whilst being driven towards the mouth 8. A compression unit 10 is mounted adjacent the mouth 8 to provide compression via the conveyors 2, 4 to the tobacco leaf and form a plug of tobacco at the mouth 8 suitable for cutting.

A rotatable cylinder 12 is situated adjacent the conveyors and is provided with a plurality of knives 14. In this embodiment ten knives 14 are provided although any suitable number can be employed. The knives 14 are each located in a mounting station and located firmly in place by locating plates 16, at circumferential equidistant positions form each other such that the cylinder forms a rotatable cutting apparatus.

Some of the knives 14 have a complete cutting edge 18, as shown in figure 3, whilst the remainder have a cutting edge 20 comprising cut away portions or slots 21 formed therein. These slots 21 divide the cutting edge into discrete portions 22 of the cutting edge. The form of these knives 14 can be seen with reference to figure 4. In the present embodiment two of the ten knives 14 have a complete cutting edge whilst the remaining 8 knives 14 have cut away portions or slots 21 formed within their cutting edges. The cutting edges of the knives 14 are of approximately 3mm depth and are bevelled in the manner of a conventional knife. The two knives 14 with the complete cutting edges are positioned diametrically opposite one another. The mounting plates 16 are formed with grooves 17 in line with the slots 21 of their corresponding knives 14 such that the mounting plates 16 themselves do not interfere with the cutting process. It is also envisaged that these knives 14 need not have a plurality of slots 21. Instead the knife or knives 14 may simply comprise a cutting edge of shorter width than another knife mounted on the cutting apparatus. In effect only one slot at either or both width ends would be formed in the body of tobacco by such a knife.

The cut away portions or slots 21 of the knives 14 are shown more clearly with reference to figure 5 each gap or slot 21 formed in the cutting edge is divergent away from the cutting edge by an angle'x'. In the preferred embodiment of the invention the angle is between 90° and 95° although an angle range between 90° and 120° is employable. This divergent or angled slot is shaped so as to ensure that the inner surface 24 of the slot does not contact the tobacco leaf during the cutting operation.

A grinding or sharpening apparatus 28 is positioned adjacent the cutting apparatus.

The knives 14 are sharpened in the conventional way by grinding the bevel. The grinding apparatus 28 comprises a grindstone 26 and a drive mechanism for traversing the grindstone over the bevelled edges of the knives 14 as they rotate.

A collection chute 30 is provided to collect the cut or shredded tobacco material.

During operation the leaf tobacco 6 is continuously fed into the space between the conveyors which move the tobacco towards the mouthpiece 8. The tobacco leaf is compressed at the mouth, into an extruded plug. This plug is driven towards the rotating cutting apparatus. The cylinder rotates such that the cutting edge of the knives 14 mounted on the cylinder cut through the leaf tobacco 6 forming thin shreds of tobacco.

The knives 14 which comprise a blade having a complete cutting edge 19 cut shreds of tobacco in the conventional manner. In this cutting operation the body of tobacco is cut across its whole width so a shred 32 of tobacco is completely detached from the body of tobacco and falls into the collection chute 30. The knives 14 comprising a blade having a cutting edge 20 incorporating grooves 21 or a castellated portion as shown in fig 4 cut similarly shaped grooves in the tobacco leaf material. After these grooves 34 have been cut in the tobacco material the next knife or a subsequent knife mounted on the rotating knife holder cuts the body of tobacco material across its whole width and hence cuts a discrete shred 32 of tobacco having a cross section shown in fig 7.

It is to be noted that the tobacco material may be cut by a number adjacent knives 14 having shorter or slotted cutting edges 20, providing progressively deeper slots or cut our portions to be formed in the tobacco material, before it is cut across its full width by a knife having a full cutting edge which extends across the whole width of the tobacco material. An example of a shred 33 cut in this way is shown in fig 8.

It is also envisaged that it is not essential that a knife having a cutting edge extending the full width of the tobacco plug needs to be employed. It is essential that a shred is eventually cut in its entirety from the plug of tobacco, however this cutting operation could comprise a series of circumferentially mounted knives having their cutting edges shorter than the width of tobacco to be cut or slotted across their widths.

These cutting edges could be arranged such that upon rotation of the knife holder the series of knives cuts portions of differing depths within the approaching body of tobacco until eventually one of the knives makes the final cutting operation thus removing the shred of tobacco.

Since the tobacco material is being continuously fed towards the rotatable knife holder and hence the knives 14, it is only when a knife with a complete cutting edge performs its cutting operation that the body of tobacco is cut across its whole width that a shred of tobacco material of a width substantially similar to that of the body of tobacco will be formed. In this case the slots 21 cut in the tobacco would become increasingly deeper after each cutting operation by these slotted knives 14. It is envisaged that as a minimum only one knife having a full cutting edge could be employed, the remainder of the knives 14 having a shorter cutting edge width or having a slotted cutting edge forming discrete cutting edge portions These shreds of tobacco are shown in figure 7 and figure 8. Figure 7 shows the cross section of a shred of tobacco cut initially by one or more slotted knives 14 then finally cut by a knife having a full cutting edge which removes the shred from the body of tobacco. This shred comprises tobacco leaf portions of comparatively greater and lesser depths.

Figure 8 shows the cross section of a shred of tobacco having been cut by one or more knives 14 having a shorter cutting edge than the knife having a cutting edge substantially similar to the width of the body of tobacco. This shred of tobacco has only one portion of greater depth.

Advantageously, these shreds of tobacco are combined with conventional shreds of tobacco in the manufacture of tobacco products such as cigarettes to provide strength to the finished product without the need to incorporate tobacco by-products from the tobacco threshing process. The strength and bulk previously provided by these by- products may now, according to this invention, be provided by the cut tobacco leaf itself and also from the same batch of tobacco leaf as the conventionally sized shreds are produced.

The knives 14 are continuously sharpened by the grinding apparatus traversing the bevelled edges of the knives 14.

It is envisaged that the manufacturer of the tobacco products such as cigarettes, can select the amount of conventionally cut tobacco and the amount of tobacco cut by the castellated or slotted blades. The manufacturer would also be able to specify the number, depth, size and position of the cut out portions of the blades according to his specific requirements.