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(11) | EP 0 112 040 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Tobacco threshing apparatus |
| (57) A tobacco thresher is provided having a plurality of rotors (11) provided with cutting
teeth (12) and mounted on a common shaft (10), a housing (14) having an arcuate surface
(16) surrounding part of the rotors, an entry opening (13) for tobacco leaves, a screen
(20) surrounding another part of the rotor having openings for discharge of portions
of laminae cut from the tobacco stems, only one set of fixed cutters (18) disposed
parallel to the shaft and arranged to coact with the cutting teeth (12) of the rotors
(11), and a discharge means (15) provided between the fixed cutters (18) and the adjacent
end (19) of the arcuate surface (16) of the housing (14), whereby the tobacco leaves
are first threshed between the cutting teeth (12) and the openings in the screen (20)
followed by cutting between the cutting teeth (12) and the fixed cutters (18). Such a combination enables lamina produced by the thresher to be increased, in order to increase in turn the strand length when the lamina is cut and hence the filling power in the cigarette. |
[0002] A known form of tobacco thresher is described in our U.S. Patent No. 4077573 and comprises a plurality of rotors provided with cutting teeth and mounted on a common shaft, a housing having an arcuate surface surrounding part of the rotors and an entry opening for tobacco leaves, openings (e.g., a screen) surrounding another part of the rotor for discharge of portions of laminae cut from the tobacco stems, and two sets of fixed cutters parallel with the shaft and offset 180° to each other and co-operating with the rotor cutting teeth for threshing the tobacco.
[0003] The rotating teeth have a small clearance from the .inside of the housing and are arranged to interleave the two rows of fixed teeth.
[0004] The moving teeth, the fixed teeth and the screens all contribute to the cutting or removal of the lamina from the mid-rib of the tobacco leaf. The diameter of the drum over the rotating teeth is typically 26"_(66 cms) and the rotational speed 500 to 600 giving a tooth tip speed of 3,400 to 4,000 fpm., (1036 to 1219 metres per minute).
[0005] The action is as follows:
1. Entering leaf is hit by the fast moving teeth and the first cut takes place.
2. The leaf rotates with the drum and passes through the first row of fixed teeth receiving a second cut.
3. The leaf continues to rotate with the drum and wipes past the screen receiving a third cut from the edges of the apertures of the screen. Pieces of leaf, lamina or stem which are small enough, pass through the screen and are discharged.
4. The remaining leaf continues to rotate with the drum and passes through a second row of fixed teeth receiving a fourth cut.
[0006] By observation of the time it takes to clear the thresher and by high speed photography, we-have found that leaf rotates with the drum for several rotations and receives several cycles of cutting, but with diminishingly effective removal of leaf and reduction in the thresher's capacity.
[0007] We also observed by high speed photography that the third cut against the screen is the most effective at removing lamina and that approximately 65% is removed in the first time past the screen.
[0008] We further found that the second and fourth cut against the fixed cutters are the most destructive in reducing the leaf to small size. However, by arranging that the moving teeth pass close to the fixed cutters, the latter have the desirable effect of removing a small percentage of leaf which otherwise wraps around the moving teeth making them ineffective.
[0009] An object of this invention to increase the size of lamina produced by the thresher, in order to increase the strand length when the lamina is cut and hence the filling power in the cigarette.
[0010] Another object of the invention to increase the throughput capacity of a given size of thresher.
[0011] According to the invention we provide a tobacco thresher having a plurality of rotors provided with cutting teeth and mounted on a common shaft, a housing having an arcuate surface surrounding part of the rotors, an entry opening for tobacco leaves, a screen surrounding another part of the rotor having openings for discharge of portions of laminae cut from the tobacco stems, only one set of fixed cutters disposed parallel to the shaft and arranged to coact with the cutting teeth of the rotors, and a discharge means provided between the fixed cutters and the adjacent end of the arcuate surface of the housing, whereby the tobacco leaves are first threshed between the cutting teeth and the screen openings followed by cutting between the cutting teeth and the fixed cutters.
[0012] Said entry opening and said discharge means may each extend over approximately 90° of said rotor, said fixed cutters being offset approximately 90° from the adjacent end of said arcuate surface.
[0013] The entry opening may be near the top of the rotor and the fixed cutters may be at the bottom of the rotor.
[0014] A curved or inclined discharge surface may be provided adjacent said adjacent end of the arcuate surface, said inclined surface being arranged to direct tobacco from the tangential direction as it leaves the fixed cutters to a downwards direction with a curved discharge surface. The length of the screen may extend over an angle of up to 1800.
[0015] An apparatus for.threshing may comprise a plurality of threshers and pneumatic means for separating fine tobacco from the stems between each adjacent pair of threshers, the stems being passed through the next thresher and so on, the aperture size in the screens being less in each succeeding thresher.
[0016] The invention will be further illustrated by way of example with reference to the accompanying diagrammatic drawings wherein:
FIGURE 1 is an axial view of a thresher made in accordance with the invention, and
FIGURES 2 and 3 are similar views showing modifications.
[0017] In Figure 1 a shaft 10 carries a series of rotors 11 which are provided with cutting teeth 12. The rotors may be spaced every 5 cm. over the width of the thresher which is preferably 1 m. wide. In all about 18 rotors may be provided. A housing 14 has an entry opening 13 near the top of the rotor and has an arcuate surface 16 concentric with the rotor surrounding approximately 90° of the rotor from the opening 13 in the direction counter to the rotation of the rotor. Mounted in the housing at the bottom of the rotor is the single row of fixed cutters 18 offset approximately 90° to the adjacent end 19 of the arcuate surface 16. A single screen 20 concentric with the rotor extends from the fixed cutters 18 through approximately 90° towards the opening 13. The fine portions of the laminae discharge through the screen as shown by the arrows 21 and the stems continue as shown by the arrows 22.
[0018] The leaf is first subjected to the action of the rotary teeth 12 and the screen 20 and leaf is removed and discharged with minimum reduction of size, before passing the fixed teeth 18 where greater breakage of leaf occurs. After passing the fixed teeth 18 the smaller portions of the tobacco leaf are discharged through the discharge opening 15.
[0019] In the modification shown in Figure 2 the arcuate surface 16 is continued to within an angular space of about 40° from the cutters 18 and an inclined deflecting surface 25 extends from the end 26 of the arcuate surface downwards so as to direct the tobacco leaving the cutters downwardly and discharging completely.
[0020] The discharge of all the tobacco as it leaves the fixed cutters prevents the leaf from continuing to rotate ineffectively in the thresher and accordingly an increased throughput capacity can be obtained.
[0021] The arrangement shown in Figure 3 is similar but the deflecting surface 27 is arcuate and the lower end 28 of the arcuate surface 16 is angularly offset by about 60° from the cutters 18. The screen 20 may alternatively extend up to an angle of about 180° by shaping the adjoining surfaces of the lower end 28 of the arcuate surface 16 and the upper end of the deflecting surface 27 to a more acute angle.
[0022] A complete threshing process may consist of several successive stages of threshing, typically five, each followed by one or more stages of pneumatic separation. The separation removes the "clean" lamina (without stem) and passes the "unclean" stem (with lamina still attached) on to the next stage of threshing. By reducing the aperture size in successive screens, the severity of the threshing action is increased in succeeding stages.
1. A tobacco thresher having a plurality of rotors provided with cutting teeth and
mounted on a common shaft, a housing having an arcuate surface surrounding part of
the rotors and an entry opening for tobacco leaves, and a screen surrounding another
part of the rotor having openings for discharge of portions of laminae cut from the
tobacco stems, characterized in ¦ that only one set of fixed cutters (18) is disposed
parallel to the shaft (10) and arranged to coact with the cutting teeth (12) of the
rotors (11), and in that a discharge means (15) is provided between the fixed cutters
and the adjacent end (19) of the arcuate surface (16) of the housing (14), whereby
the tobacco leaves are first threshed between the cutting teeth (12) and the openings
of the screen (20) followed by cutting between the cutting teeth (12) and the fixed
cutters (18).
2. A tobacco thresher according to Claim 1, characterized in that each said entry
opening (13) and said discharge means (15), extends over approximately 90° of said
rotor, said fixed cutters (18) being offset approximately 90° from the adjacent end
(19) of said arcuate surface (16).
3. A tobacco thresher according to Claim 1 or 2, characterized in that the entry opening
(13) is near the top of the housing and the fixed cutters (18) are at the bottom of
the housing.
4. A tobacco thresher according to Claim 1, characterized in that an inclined discharge
surface (25) is provided adjacent said adjacent end (26) of the arcuate surface (16),
said inclined surface being arranged to direct tobacco laminae, leaving the rotors
tangentially therefrom as they leave the fixed cutters, to a downward direction.
5. A tobacco thresher according to Claim 4, characterized in that the juncture of
the arcuate surface (16) and the inclined surface (25) is spaced from said cutters
(18) by an angle of about 40d.
6. A tobacco thresher according to Claim 1, characterized in that a curved discharge
surface (27) is provided adjacent said adjacent end (28) of the arcuate surface (16),
said curved surface (27) being arranged. to direct tobacco laminae, leaving the rotors
tangentially therefrom as they leave the fixed cutters, to a downward direction.
7. A tobacco thresher according to Claim 6, characterized in that the juncture of
the arcuate surface (16) and the curved discharge surface (27) is spaced from said
cutters (18) by an angle of about 60°.
8. Apparatus for threshing tobacco characterized in that a plurality of threshers
according to Claim 1 are arranged in sequence and pneumatic means are provided between
each adjacent pair of threshers for separating fine tobacco from the stems, the aperture
size in the screens being less in each succeeding thresher.