IMPROVEMENTS IN OR RELATING TO KNIFE BLADES FOR CUTTING MACHINES

Abstract: The present invention provides a knife blade for a cutting machine comprising a plate (10) having a cutting edge (12) and a plurality of generally ''V''-shaped cross-section grooves (11) formed in one surface of the plate transverse to the nominal line of the cutting edge, the cutting edge being formed by a bevel surface extending from the other surface of the plate back to the grooved one surface thereby providing a saw-tooth-like cutting edge (12a, 12b).

Description: IMPROVEMENTS IN OR RELATING TO KNIFE BLADES FOR CUTTING MACHINES This invention relates to a knife blade for a cutting machine, particularly but not solely for machines used to cut tobacco leaf. A machine to which the invention may be applied, used for cutting tobacco leaf, is of a well known type in which the leaf is fed into a convergent throat of rectangular cross section formed by two parallel plates and two converging conveyor bands or by two parallel plates and two converging roller conveyors. At the convergent end of the throat is a mouthpiece. The leaf is fed into the throat at the divergent end and is driven by the conveyor bands or rollers towards the mouthpiece. The leaf is cut as it issues as a plug from the mouthpiece either by a single knife blade caused to reciprocate across the mouthpiece or by one or more knife blades arranged on a drum which rotates on an axis either at right-angles or parallel to the width of the throat, so that the cutting edge of each blade is caused to pass across the mouthpiece cutting off that portion of the plug that has emerged. The convergence of the throat compresses the leaf sufficiently so that it may be cut and not pulled from the mouthpiece. One of the two band or roller conveyors is free to move and pressure is applied so that the compression of the leaf can be regulated. The width of cut of the shreds can be adjusted by altering the conveyor speed and hence the distance the compressed leaf is fed through the mouthpiece between cuts by the knife or knives. STATEMENT OF PRIOR ART One such machine is described in United Kingdom Patent Specification No. 751093. An improved machine is described in United Kingdom Patent Specification No. 1074682 in which the bottom member of the mouthpiece is formed with a V-shaped top surface which provides a progressive cutting action between the cutting edges of the knife blades of the rotating cutter drum and the bottom member of the mouthpiece. Such an arrangement leads to more efficient cutting of the tobacco. A further advantage is achieved in that the cutter can be made considerably more economically since the knife blades may be set with their cutting edges parallel to the axis, than if the cutting edges are arranged helically with respect to the axis of the cutter drum as in other machines. A knife blade for such a machine is disclosed in United Kingdom Patent Specification No. 1195163, and comprises a steel plate having one surface bevelled to produce a cutting edge and a plurality of grooves formed at right angles to the cutting edge in the surface of the knife which is not bevelled thereby providing a crenellated cutting edge. In European Patent Application No. 85901509.1-2302 there is described a knife blade which can simultaneously produce a first cut and a cross-breakage with a single passage of the knife through the leaf. With this knife blade, the leaf only passes once through a cutting machine thus avoiding a second compression and produces a very much more uniform cut. An object of the present invention is to provide a knife blade for a cutting machine providing a progressive cutting action to further improve the cutting efficiency. SUMMARY OF THE INVENTION According to the invention there is provided a knife blade for a cutting machine comprising a plate having a cutting edge, and a plurality of generally V-shaped grooves formed in one surface of the plate transverse to the cutting edge, the cutting edge being formed by a bevel surface extending from the other surface of the plate back to the grooved one surface thereby providing a saw-tooth-1ike cutting edge. BRIEF DESCRIPTION OF DRAWINGS In order to promote a fuller understanding of the above and other aspects of the present invention, an embodiment vπll now. be described, by way of example only, with reference to the accompanying drawings in which: FIGURE 1 shows in end elevation part of a knife blade having grooves of V-shaped cross-section; FIGURE 2 shows the knife blade of Figure 1 in plan; " FIGURE 3 is a section on the line A-A of Figure 2; FIGURE 4 is a side elevation of a rotary cutting machine; FIGURE 5 is an axial elevation of the drum carrying a number of knife blades according to Figures 1, 2, and 3; and FIGURE 6 is a schematic cross-section of a knife blade passing through a tobacco plug in a rotary cutting machine of Figure 4. DESCRIPTION OF PREFERRED EMBODIMENTS The knife blade 10 as shown in Figures 1 to 3 is a steel plate having an overall thickness of about 3 mm and is bevelled at one edge in the manner of a conventional knife blade to form a cutting edge 12. "V"-shaped cross section transverse grooves 11 are cut, in the embodiment at right angles to the cutting edge 12, in one surfaced of the plate having a pitch of from 7.5-40 mm, while the other surface is plane. The effect of the grooves and bevel is to produce a saw toothed cutting edge 12 with sharp, leading tips 12a having diverging trailing cutting edges 12t> on either side thereof. The angle α of the cutting edge 12fc) from the nominal line of the cutting edge through the tips 12a . is from 4-8 , preferably 5 . The knife blade is sharpened by grinding the bevel in the same way as a conventional knife blade. A particular knife blade suitable for cutting tobacco is ground with the bevel at an angle of about 18 degrees to the grooved face of the knife. The knife may be used in a reciprocating single knife cutting machine of the kind described in Patent No. 1195163 or in a rotary knife cutting machine as shown in Figures 4 and 5. In the rotary machine as shown in Figures 4 and 5, tobacco is fed onto the space 32 between two converging conveyor belts 34 and 36 which carry the tobacco to a mouthpiece 38 and at the same time compress it so that it is driven through the mouthpiece as a plug. As the plug emerges it is shredded by knife blade 10 is carried in holders 42 on drum 44 which rotates about an axis 46 parallel to the width of the mouthpiece, in bearings carried by arms 47. The cutting edges of the knife blade all lie on an imaginary cylindrical surface. The knife blades are arranged in this example with the grooves 11 away from the mouthpiece. A continuous sharpening of the blades by grinding can be effected by a grinding wheel 49 which has a drive mechanism for traversing it along the knife blades at a point remote from the mouthpiece, as they rotate on the drum 44 in use. The bevelled surface will be part cylindrical in this case. Al ernatively the knife blade may be brought in turn to a fixed grinding position and ground one at a time by a traversing grinding wheel of which the normal to the grinding face at the point of contact with the blade does not pass through the drum axis. Here the bevelled surface is flat and raked in relation to its cylindrical path. When the bevelled surface is part cylindrical whereby as discussed above and as shown in Figure 6, the saw tooth cutting edges 12 which will be slightly convex along the length, a l travel along the cylindrical path and cut and displace a piece of compressed laminated tobacco leaves having a thickness E. The saw toothed arrangement produces a series of isolated regions where progressive shearing of the tobacco takes place. The saw teeth cutting edges 12t) may be of more pronounced concave or convex shape, i.e. substantially triangular with concave or convex sides, if the V-shaped grooves are formed with concave or convex sides respectively.

Claims: CLAIMS: 1. A knife blade for a cutting machine comprising a plate having a cutting edge and a plurality of generally "V"-shaped cross-section grooves formed in one surface of the plate transverse to the nominal line of the cutting edge, the cutting edge being formed by a bevel surface extending from the other surface of the plate back to the grooved one surface thereby providing a saw-tooth-like cutting edge. 2. A blade as claimed in Claim 1, in which said other surface is plane. 3. A blade as claimed in Claim 1 or 2, in which said grooves are at right angles to the line of the cutting edge. 4. A blade as claimed in Claim 1, 2 or 3, in which said grooves have a pitch across the one surface of between 7.5 mm and 40 mm. 5. A blade as claimed in any preceding Claim, in which the cutting edges of the teeth of said saw-tooth extend back at an angle of between 4 and 8 from the nominal line of the cutting edge extending through the tips of the teeth. 6. A blade as claimed in Claim 5, in which the cutting edges so extend back at an angle of 5 . 7. A blade as claimed in any preceding Claim, in which said grooves have concave side faces. 8. A blade as claimed in any one of Claims 1 to 6, in which said grooves have convex side faces. 9. A blade as claimed in any preceding Claim, in which said bevel surface is part cylindrical. 10. A blade as claimed in any preceding Claim, in which said plate is approximatel 3 mm thick. 11. A knife blade substantially as herein described with reference to Figures 1, 2, 3 and 6 of the accompanying drawings. 12. A cutting machine including a knife blade as claimed in any preceding Claim.

Inventors: RAY ERIC THOMAS, RAY, ERIC, THOMAS
Applicants: GBE INTERNATIONAL PLC
Application year: 1989
Main classification: A24B7
IPC codes: A24B7, B26D1, B26D3