A METHOD AND APPARATUS FOR UNIFORMLY CUTTING TOBACCO SHEETS

Abstract: A method and apparatus are disclosed for shredding recon­ stituted and blended leaf sheets, wherein the sheet (14) is first slit longitudinally (at 18), and then cut off transversely by bringing the points (62) of a serrated blade (60) into contact with the slit sheet at an angle to penetrate the sheet, and then moving the blade to tear off the portion of the sheet between the point of penetration and the end of the sheet. This produces much more uniform shreds, with less dust and shattering, than has hitherto been possible.

Description: A METIlOD AND APPARATtJS FOR UNIFORMLY CUTTING TOBACCO SHEETS The present invention pertains generally to apparatus and methods for cutting reconstituted tobacco sheets and pertains more particularly to such apparatus and methods requiring less frequent and less costly maintenance than is conventionally possible. Small particles of tobacco ("fines") produced as an undesired by-product of cigarette making are commonly recaptured and made into a sheet (reconstituted leaf or blended leaf, depending on the process used to manufacture the sheet) by conventional paper making or other methods. Such sheets are then cut into pieces of a convenient size (e.g., about 1Ccm square), after which the pieces are shredded to produce cigarette filler. Conventionally, the process of cutting the sheets into pieces is effected by moving the web continuously past a set of parallel rotating disc knives located which slit the web into sections of the desired width. The slit web is then moved to a cutter mechanism, which cuts off lengths of the web. The two cutting processes together result in generally square or rectangular (preferably square) pieces; In its usual arrangement, such apparatus includes a planar table along which the slit web is moved, with a ledger blade located at the downstreani end of the table. A rotor located adjacent the ledger blade carries several additional blades, which it moves in sequence past the ledger blade. The rotor blades each cooperate with the ledger blade to cut off the portion of the web projecting past the end of the table at the instant the rotor blade in question passes. Most commonly, the ledger blade and rotor blades are complementarily serrated. The described conventional arrangement works satisfactorily, producing pieces of the desired size and an acceptable percentage of smaller pieces and fines. Nonetheless, there are several respects in which the performance of such conventional apparatus could be improved. First, it would be highly desirable to reduce the frequency with which.it is necessary to replace worn blades. Second, to reduce maintenance time, it would also be desirable to reduce the precision with which the the replacement blades must be positioned to provide the correct degree of interference between the ledger and the rotor blades. Third, it would be desirable to reduce still further the percentage of pieces produced smaller than the desired- size and to reduce, particularly, the number of very small pieces produced by shattering of the web (i.e., local powdering of the web due to the impact of the rotor blades on it). Fourth, the above-described arrangement requires a degree of interference between the ledger blade and the rotor blades. This prevents the use of such a machine to cut a web of greater than a certain length, since sagging of the rotor shaft makes it very difficult and time-consuming if not impossible, to achieve the correct interference all along the length of the blades. Due to the necessary interference of the blades1 operation of the conventional device is also fairly noisy. It would be desirable to overcome these problems. One aspect of the present invention provides a process for uniformly cutting a tobacco sheet of reconstituted or blended leaf, in which the tobacco sheet is fed continously past an edge, and portions of said sheet projecting beyond said edge are cut from the sheet, characterised in that at least part of projecting portions of said sheet not supported by said edge are transversely cut against the inertia of said projecting portions. With the invention, less frequent maintenance is required than is the case with conventional technology. Moreover, the precision with which blades must be positioned in such apparatus is reduced. Another advantage of the invention is that it permits the use of ordinary saw blades in such an apparatus. Still another advantage of the invention is that it is adapted to produce cut pieces of sheet tobacco having tidier edges than is conventionally achievable, so as to produce fewer fines and improve the quality of cigarettes made therefrom. Still another advantage of the invention is that the lenath of sheet or web taken into the apparatus in the form of a blanket when the web breaks is less than is conventionally the case. Yet another advantage of the invention is that it is feasible to cut a wider web than is conventionally possible. The invention is preferably put into practice by feeding a preferably pre-slit web of reconstituted or blended leaf off the end of a support table or the like having a preferably serrated stationary ledger blade if the latter is serrated, is moved past the ledger blade in such a manner that the points of the moving blade strike the projecting portion of the web at an acute angle to the latter. The points of the moving blade initially penetrate the web, and the motion of the blade then completes the separation of the projecting portion of the web by tearing it off. (Depending on the web speed relative to the speed of the moving blade, the web may advance significantly during the cutting, in which case less than the entire projecting portion of the web is severed). The angle of incidence between the moving blade and the web is preferably no greater than approximately 25 degrees and is most preferably between approximately 10 and 15 degrees, inclusive. The method of the invention therefore makes it possible to eliminate interference between the moving blade and the ledger blade. In fact, the best results have been are obtained with a clearance of between 0.38 and 3.2 mm (0.15 inch and .125 inch, the clearance beina measured as the minimum distance between the moying and the stationary blades). This greatly reduces wear on the blades, as well as noise. This clearance also solves the problem of blade adjustment due to sagging of the rotor shaft, if a rotor is used. In addition, because the clearance is not very critical, less precision is required in positioning a replacement blade. This further reduces required maintenance time. It has also been found that, by using the method of the invention, the percentage of the web which is shattered or otherwise reduced to fines is greatly decreased, and the uniformity in size and shape of the pieces cut off from the web is greatly increased. The neatness of uniformity of the edges of the pieces cut from the web is also improved, further reducing the production of fines. All this improves the uniformity of cigarettes made from the tobacco in question, and decreases the number of loose ends. In another aspect, the invention comprises the method of cutting of a piece of a web of reconstituted or blended leaf projecting past the edge of a support table or the like, by striking the projecting portion of the web obliquely with a moving blade in such a manner that the moving blade contacts the web while moving with a velocity component normal to the web approximately equal to the web speed, and progressively increasing the ratio of the normal component of the blade's velocity to the web speed from about one to a value sufficient to separate the projecting portion from the web. (A value of three has been found satisfactory, although the invention is not limited to this value.) In another aspect, the invention is the method of cutting off an end portion of a web of reconstituted or blended leaf against its own inertia while the portion to be cut off is suspended in a fluid medium. The apparatus of the invention comprises a stationary support for the moving, preferably pre-slit web and a stationary ledger blade at the end of the support. The ledger blade is preferably serrated. Adjacent the ledger blade is a device supporting one or more additional serrated blades. The latter blades are movable, and positioned so as to strike a portion of a web projecting from the end of the support table at an acute angle to the web. As described above, the points of the moving blade first penetrate and cut, and then tear off, the end of the web and the moving blades are spaced to clear the stationary blade. Another aspect of the invention is apparatus for cutting off an end portion of a web suspended in a fluid medium, including blade means for striking the end portion to cut the end portion off against its own inertia. Another aspect of the invention is apparatus comprising a moving blade and means for causing it to strike an unsupported portion of a web in such a direction and at such a speed that the ratio of the component of the blade's velocity normal to the web at the point of impact to the web speed is approximately one at the time of initial impact, and such that this ratio progressively increases to a value sufficient to cause the end portion to separate from the web. The value of this ratio at the time of separation may typically be about three, although the invention is not limited to this value. Still another aspect of the invention is an apparatus as summarized above, including a housing into which the web or sheet is moved to be. cut and from which dust and other fine debris produced by the cutting operation is evacuated. The moving blades are preferably borne by a rotor, and the removal of the debris is preferably effected by means of placing the entrance of an evacuation passage adjacent the rotor with such an orientation that the rotor motion blows substantially all the fine particulate debris into the passage. A suction system may be used to aid in removing the debris from the outlet of the passage. At some web feed-in speed in the general vicinity of 2.00 rs 1 (400 ft min ), the fanning action of the rotor may sufficiently retard the web to prevent proper functioning of the apparatus. According to one aspect of the invention, this problem can be prevented by using the apparatus in a region of reduced atmospheric pressure. According to another aspect of the invention, an air cushion may be provided between the web and the support table or plane. The pressure of the moving blade against the web can, in the absence of an air cushion, tend to fold the web part-way over the edge of the support plane. Even if this does not significantly impede cutting, it will cause the web to bunch up on the support plane by interfering with the movement of the web. An air cushion prevents this. Still another aspect of the invention comprises apparatus with a housing and with an apron dividing an opening of the housing into a portion through which the web is fed to be cut and an adjacent portion through which fines are taken off. The proper placement of the apron, together with use of a proper rotor speed, causes substantially all the fines to be thrown by the rotor motion into the passage, from which they are taken by an' exhaust manifold exerting relatively mild suction, while the heavies are allowed to fall to a conveyor or similar device for transport to the next work station. These and other objects and features of the invention will be more completely understood from a consideration of the following detailed description of several preferred embodiments of the invention, taken in conjunction with the figures, in which like reference characters refer to like elements throughout. Figure 1 is a cross-sectional view of one preferred embodiment of the apparatus of the invention. Figure 2 is a plan view of the apparatus of Figure 1. Figure 3 is a view taken from section line 3-3 of Figure 2. Figure 4 is a perspective view of a part of the apparatus of Figure 1. Figures 5-7 are details showing the angle of the rotor blade and the web. Figure 8 is a detail of Figure 2, showing the clearance between the rotor and ledger blades. Figure 9 is a cross-sectional view similar to Figure 1, showing a second preferred embodiment of the apparatus of the invention. As shown in Figure 1, the apparatus 10 of the invention includes a support plane 12, which is preferably inclined at an angle to the horizontal to permit a sheet or web 14 to be fed by means of gravity to a cutter 16 located adjacent the lower end of the support plane 12. Conventional slitter discs 18 (only one of which is visible in Figure 1) are used as shown to slit the web 14 longitudinally before feeding it to the apparatus of the invention. A ledger blade 20 is disposed at the lower end of the support plane 12. The cutting edge 22 of the ledger blade faces downstream and preferably is serrated. A sheet or web 14 of reconstituted or blended leaf is moved downward along the support plane 12 past the slitter discs 18- and toward the ledger blade 20 by means of gravity. As is weil known, the weight of the web is sufficient to cause it to be slit by the discs 18. The cutter assembly 16 comprises a rotor 24 mounted in a housing 26 for rotation about a horizontal axis 28 transverse to the direction of movement of the web 14. The housing 26 preferably comprises two vertical end plates 30 having apertures 32 in which the ends of the rotor shaft 34 are journaled in a known fashion, one end of the shaft being driven by a suitable motor (not shown). The top 36 of the housing 26 is open, and the lower end of the support plane 12 is supported by a plate 38 secured to, or integral with, the upstream side of the top of the housing 26. The upper part of the back, or downstream, side of the housing 26 preferably comprises a removable weldment cap 40 which permits easy access to the rotor 24 for maintenance. The end and back faces of the cap 40 are defined by respective metal plates. Flanqes 42 are provided to enable the weldment cap 40 to be bolted to the remainder of the housing 26. The interior surface of the back wall of the cap 40 is further reinforced by means of a plurality of brackets 44 of generally U-shaped cross-section (see Figure 2) In this embodiment, the apertures 32 are preferably defined by adjacent recesses 46, 48 in the end walls of the housing 26 and in those of the cap 40. The lower portion of the contour of the brackets is recessed at 50 (see Figure 1) to accommodate the rotor 24. Tobacco pieces 52 cut from the web 14 by the rotor 24 fall onto a conveyor belt 54 at the bottom of the housing 26 (see Figures 1 and 3). The conveyor belt 54 is preferably shaped like a trough, its lower and side portions being propelled by suitable drive rollers 56, which are driven in a known manner. The rotor 24 itself comprises one or more, and preferably six, blade bearers 58 equally spaced around the shaft 34. Each blade bearer 58 has at its outer end a removable blade 60 generally parallel to the shaft 34. The rotor blades 60 are serrated, ans are preferably approximately complementary in shape to the ledger blade 20 if the latter is serrated. A cage or basket comprising a set of parallel semi-annular breaker rings is disposed in the lower part of the housing 26 and serves to ensure that if a "blanket" (a reladvely large piece of web) falls into the housing 26 without being properly cut up, as due to the web breaking, for example, the blanket will not pass through the apparatus of the invention without being broken up by the action of the rotor assembly 16. The cage functions in very much the same way as the cage or basket of a standard thrasher. In the preferred embodiment illustrated, the cage comprises rings spaced apart about eight inches, although this dimension can be vaired as desired without departing from the scope of the invention. As can be seen most clearly from Figures 4-8, the rotor 24 is arranged so that each blade 60, in passing the ledger blade 20, strikes the portion of the web 14 overhanging the ledger blade 20, the overhanging web portion being supported in the ambient air (or in whatever other fluid medium the process is conducted in). The points 62 of the rotor blades 60 strike the web 14 first at an acute angle thereto and penetrate the web 14 to perforate it. Continued rotation of the rotor 24 causes the blade 60 engaging the web 14 to tear off the perforated projecting portion of the web 14. Despite the tearing action by means of which the separation is completed, it has been found that the combined cutting-and-tearing action produces a cut with little shattering or production of fines. The conveyor 54 located beneath the rotor 24 collects both the cut-off pieces and any fines produced and removes them for conventional further processing. The angle of impingement should be greater than zero (i.e., the attack should not be flat), and should preferably be no greater than approximately 25 degrees. (Greater angles of attack are included within the scope of the invention, but have been found to be less effective than angles less than 25 degrees). It has been found that this cutting and tearing action can be effected quite satisfactorily with absolutely no interference of the rotor and ledger blades. In fact, a minimum clearance of approximately O.38 mm is desirable for optimum results, and spacings as great as 3.2 irm (1.25 in) have produced excellent results. The exact clearance which will be hest in a given case will depend on the angle of attack. When the latter angle is between 10 degrees and 15 degrees, the exact clearance is particularly uncritical. Accordingly, this range of angles is especially preferred. It is preferred to use an air cushion between the web 14 and the support plane 12. Such an air cuschion can be provided using apparatus 10' like that illustrated in Figure 9. In the embodiment of Figure 9, the support plane 121, rather than being simply a flat element, has an apron 80 as its upper part. The apron 80, which is not flush with but is slightly raised from the part of the support plane 12' to which it is attached, comprises several gas manifolds 82, 84, 86. The first (lowest) manifold 82, which is rectangular in cross section and is transverse to the direction of feed of the web 14, provides a transverse row of air jets flowing downward, through a narrow opening 88 at the lower end of apron 80 and along the upper surface of the support plane- 12. This results in an air cushion which supports and steadies the web (not shown in Figure 9), and prevents bunching and backing up of the web due to fanning action of the rotor 16 or to pressure exerted on the web by the rotor 16. Farther up the support plane 12', two additional transverse air manifolds 84, 86 are provided. The uppermost manifold 86 is circular in cross section and provides a row of downward longitudinal air jets, which blow along the support plane 12' through apertures 90 defined between the apron 80 and a bolted-on plate 92. The intermediate manifold 84, which is approximately rectangular in cross section, is immediately below manifold 86, and expels air through the same orifices as the jets provided by mani fold 86. The air jets provided by the second and third manifolds 84, 86 are activated only during the initial threading of the web 14 through the machine prior to beginning the cutting operation. ,It has been found that such use of these air jets ensures proper threading of the machine, because the air pulls the web downward and keeps it in position. The fanning action of the rotor 16 blows a certain amount of air out the top of the machine, while air is drawn in through both the top and bottom of the housing. The blown-out air tends to carry with it large amounts of dust and other fine particulate debris, impeding visibility and affecting the comfort of people working near the machine. In order to prevent this, it is desirable to remove such debris from the machine in a controlled manner so that none is released into the atmosphere. If the upper opening of the housing is sufficiently narrow, as in Figure 1, this can be achieved simply by positioning a suction device (not shown) at that opening. If the suction device is sufficient powerful, virtually all of the dust thrown out by the rotor movement will be taken away by suction. Another, preferred, approach is shown in Figure 9, where the upper opening 94 of the housing 26' is considerably larger than in the embodiment of Figure 1. As in the embodiment of Figure 1, air is taken into the housing 26' through both the top opening 94 and the bottom opening 96. The downstream side 98 of the top opening 94 of the housing 26' is separated from the remainder of the opening 94 by a vertical apron 100 supported at each end by the housing 26. The apron 100 is spaced a distance from the back or downstream wall 102 of the opening 94 such a distance that, at the intended operating speed of the rotor 24, virtually all of the dust produced by the cutting operation is thrown by the rotor 24 up into the escape duct 98. An exhaust manifold (not shown) can then1 with only moderate suction, remove substantially all the debris from the duct 98. To ensure that virtually no debris is thrown out through the forward portion 104 of the top opening 94, an air manifold 106 of circular cross section is placed at the top of the apron 102. The air which it provides is formed into jets by openings in a nozzle plate 108 bolted onto the upper portion of the apron 100. The jets so produced flow downward along the upstream side of the apron 100. Since this apron surface is not completely smooth, a certain amount of turbulence results This diffuses the air expelled by the rotor. A flexible wiper 110 is located at the lower edge of the apron 100 and is serrated in a form generally comp-lementary to that of the rotor blades 60. The wiper 110 remaves from the blades 60 whatever debris may have remained on them. This, together with the air jets and the proper placement of the apron 100, has been found sufficient to ensure that virtually all of the particulate debris produced by the cutting operation is removed from the housing 26' by the desired route. This arrangement, in effect, acts as a classifier, expelling the fines from the cutter 10' and allowing the heavies to fall to the conveyor (not shown in Figure 9). The apron 100 could be placed at an angle to the rear wall 102 of the dust-removal duct, if desired, to control the velocity of the air therethrough. The illustrated version, however, has been found to produce excellent results and is therefore preferred. The apparatus of the invention can be used at web speeds up to perhaps 1.0 - 2.0 ms-Ú (200- ft min-Ú) difficulty. At some point, however, the rotor speeds necessary to cut off pieces of the desired size are such that the fanning action of the rotor may tend to blow the web backwards or to fold it downward around the ledger blade. This can be avoided by floating the web on an air cushion, as shown, by using a conventional pneumatic take-away device, by providing air jets across the top surface of the web to smooth it, or by carrying out the method of the invention in a vacuum or in a chamber with reduced pressure. It is believed that suitable choice of one or more of these expedients will permit speeds of 6.1 - 7.6 ms-Ú (1200-1500 ft min-Ú to be achieved successfully. It has also been found that problems of flutter can be controlled, at least in some cases, by proper selection of the rotor speed dnd of tie angle of inclination of the support plane. Especially when blended leaf is used, such an arrangement produces highly satisfactory results, using rotor speeds in the nelgborhood of, for example, from 0 to 1.27 ms-Ú (0-250 ft min ) and a support plane inclination of approximately 23 fiom the vertical. It will be understood, of course, that some departure from these values would still produce highly acceptable results and is within the scope of the inveention. The gr-lp of the rotor blades on the web, pulling the web downward, also aids in controlling flutter. If the straight blades shown dre replaced wltJu curved blades, noise is seduced, and, It has beeb found, flutter is controlled still mole effectively. The invention can be practiced with ordinary steel saw blades for both the ledger and the rotor blades, further reducing costs. Alternatively, steel blades having carbide points cemented in place (wet carbide inserts) can be used, as can flame-sprayed tips. Carbide inserts are preferred for cutting reconstituted leaf (i.e., a web made by the foudrinier process), and flame-sprayed tips for blended leaf (i.e., a web made by the pectin process). It is very important that the web 14 have the proper moisture content in carrying out the process of the invention. If the web moisture content exceeds approximately 17-19 percent (as a percentage of total weight), a degree of gumminess occurs, and the tobacco will stick to the apparatus in a rapid build-up that must be periodically cleaned off. If the moisture exceeds 20 percent, the gumminess problem becomes acute. On the other hand, if the moisture content is below approximately 12 percent, the web 14 has a tendency to powder, increasing the production of fines. The moisture level is preferably to be selected within the range 12-16 percent to produce pieces with a moisture of about 14-14.5 percent.

Claims: CI1A IMS A A process for uniformly cutting a tobacco sheet of reconstituted or blended leaf, in which the tobacco sheet is fed continously past an edge, and portions of said sheet projecting beyond said edge are cut from the sheet, characterised in that at least part of projecting portions of said sheet not supported by said edge are transversely cut against the inertia of said projecting portions. 2. A process according to claim 1, wherein said projecting portion of said sheet is cut transversely to its direction of feeding by bringing a blade into contact with said sheet at an acute angle relative to said sheet to penetrate said sheet and subsequently to tear off at least part of said projecting portion. 3. A process according to claim 2, wherein the blade is serrated, and the points of the blade initially penetrate the sheet and the motion of the blade completes the separation of the projecting portion or part thereof by tearing. 4. A process according to claim 3, wherein said edge is defined by a serrated ledger blade having a shape approximately complementary to that of the firstmentioned serrated blade. 5. A process according to claim 2, 3 or 4, wherein the clearance between said edge and the first-mentioned blade is from 0.38 to 3.2mm (0.015 inch to 1/8 inch). 6. A process according to any of claims 2 to 5, wherein said acute angle is greater than zero and less than 25 degrees, preferably between 10 and 15 degrees. 7. A process according to any of claims 1 to 6, wherein said tobacco sheet is fed at a rate between 1.0 and 7.6 ms-l (200 and 1,500 feet per minute). 8. A process according to claim 7, wherein said sheet is fed on an air cushion. 9. A process according to claim 7, wherein the cutting is performed at less than atmospheric pressure, preferably in a vacuum. 10. An apparatus for cutting reconstituted or blended tobacco leaf sheets, comprising a support (12) for supporting a moving tobacco sheet, and a movable blade (60) having a serrated edge (62) for cutting off a portion of the sheet projecting from said support, characterised in that said movable blade is mounted for movement past but spaced from said support at a predetermined angle to the surface of the sheet, for cutting off tile projecting portion of such sheet by a combined cutting and tearing action. 11. Apparatus according to claim 10, wherein said predetermined angle is greater than zero and not greater than approximately 25 degrees, preferably between 10 and 15 degrees. 12. Apparatus according to claim 11 or 12, characterised by a ledger blade (20) located adjacent said support (12), said movable blade (60) having a predetermined clearance relative to said ledger blade of between 0.38 and 3.2mm (0.015 inch and 0.125 inch).

Inventors: THATCHER, RICHARD E., TOMANOVITS, JOHN
Applicants: PHILIP MORRIS INCORPORATED
Application year: 1984
Main classification: A24B7
IPC codes: A24B7, A24B3