EP0124255B1

EP0124255B1 - A method and apparatus for uniformly cutting tobacco sheets

Info

Publication number: EP0124255B1
Application number: EP84302095A
Authority: EP
Inventors: Richard E. Thatcher; John Tomanovits
Original assignee: Philip Morris Products Inc; Philip Morris USA Inc
Current assignee: Philip Morris Products Inc
Priority date: 1983-03-31
Filing date: 1984-03-28
Publication date: 1988-07-20
Also published as: BR8401492A; EP0124255A2; ES8600895A1; AR242487A1; ES531140A0; EP0124255A3; PT78344A; PT78344B; DE3472751D1

Description

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 10 cm square), after which the pieces are shredded to produce cigarette filler.
GB-A-1 426 785 describes a process of cutting the sheets into pieces 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 includes a plate over which the slit web is moved, with a fixed cutting element located at the downstream end of the table. A rotor located adjacent the fixed element carries a rotating blade, which moves past and cooperates with the fixed element to cut off the portion of the web projecting past the end of the plate at the instant the rotor blade in question passes. The two cutting process together result in generally square or rectangular (preferably square) pieces.
The described 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 replacement blades must be positioned to provide the correct degree of interference between the fixed element 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 fixed 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 blades, 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 characterised in that the blade strikes the sheet with a clearance between the blade and the edge of a support and at an acute angle greater than zero and less than 25 degrees relative to the surface of the support.
The apparatus of this invention is characterised in that the movable blade is spaced by clearance from the support to strike the sheet at a predetermined angle greater than zero and not greater than 25 degrees relative to the surface of the support.
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 serrated stationary ledger blade, and at least one serrated moving blade 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 between 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 obtained with a clearance of between 0.38 and 3.2 mm (0.15 inch and .125 inch, the clearance being measured as the minimum distance between the moving 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 feature of the method of the invention the piece of a web of reconstituted or blended leaf projecting past the edge of a support table is struck 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).
According to another feature of this 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.
Another feature of the apparatus of this invention is a housing into which a 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 output of the passage.
At some web feed-in speed in the general vicinity of 2.00 ms-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, preferably in a substantial vacuum.
Still another feature of the apparatus of the invention comprises 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 well 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. Flanges 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, and 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 relatively 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 varied 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 0.38 mm is desirable for optimum results, and spacings as great as 3.2 mm (1.25 inch) have produced excellent results. The exact clearance which will be best 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 cushion can be provided using apparatus 10' like that illustrated in Figure 9. In the embodiment of Figure 9, the support plane 12', 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 assembly 16 or to pressure exerted on the web by the rotor assembly 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 manifold 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 assembly 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 then, with only moderate suction, remove substantially all the debris from the duct 98.
To ensure that virtually no debris is thrown out through theforward portion 104ofthetop 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 ofturbulence 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 complementary to that of the rotor blades 60. The wiper 110 removes 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-¹ (200-400 ft min-¹) 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 surfaces of the web to smooth it, or by carrying outthe 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-¹ (1200-1500 ft min-¹) 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 and of the 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 neighborhood of, for example, from 0 to 1.27 ms-¹ (0-250 ft min-¹) and a support plane inclination of approximately 23° from 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 invention.
The grip of the rotor blades on the web, pulling the web downward, also aids in controlling flutter. If the straight blades shown are replaced with curved blades, noise is reduced, and, it has been found, flutter is controlled still more 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

1. A process for uniformly cutting a tobacco sheet of reconstituted or blended leaf, in which the tobacco sheet is fed continuously over the surface and past an edge of a support, and portions of said sheet projecting beyond the edge are cut transversely to the direction of feeding of the sheet by bringing a blade into contact with the sheet, characterised in that the blade strikes the sheet with a clearance between the blade and the said edge and at an acute angle greater than zero and less than 25 degrees relative to the surface of the support.

2. A process according to claim 1, wherein said acute angle is between 10 and 15 degrees.

3. A process according to claim 1 or 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 of 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 first-mentioned serrated blade.

5. A process according to any of claims 1 to 4, wherein the clearance between said edge and the first-mentioned blade is from 0.38 to 3.2 mm (0.015 inch to 1/8 inch).

6. A process according to any of claims 1 to 5, wherein said tobacco sheet is fed at a rate between 1.0 and 7.6 ms-¹ (200 and 1,500 feet per minute).

7. A process according to claim 6, wherein said sheet is fed on an air cushion.

8. A process according to claim 6, wherein the cutting is performed at a pressure less than atmospheric pressure or in a vacuum.

9. 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) and mounted for movement past the support for cutting off a portion of the sheet projecting from an edge of the support (12); characterised in that the movable blade (60) is spaced by a clearance from the support (12) to strike the sheet at an acute angle greater than zero and not greater than 25 degrees relative to the surface of the support (12).

10. Apparatus according to claim 9, wherein said acute angle is between 10 and 15 degrees.

11. Apparatus according to claim 9 or 10, wherein the support (12) includes a ledger blade (20), said movable blade (60) having a predetermined clearance relative to said ledger blade (20) of between 0.38 and 3.2 mm (0.015 inch and 0.125 inch).

12. Apparatus according to claim 9, wherein the support (12) includes a ledger blade (20), and wherein said movable blade (60) and said ledger blade (20) are both serrated and are disposed in such a manner that the serrations of each are approximately complementary to and spaced from each other.

13. Apparatus according to any of claims 9 to 12, further comprising a rotor (24) bearing said movable blade (60), and a housing (26) containing said rotor and having an inlet for feeding a sheet in and an outlet for evacuating debris; said outlet being so oriented and so located relative to said rotor that said rotor is capable, while rotating, of moving fines produced by operation of said apparatus into said outlet while allowing heavies to drop toward the bottom portion of said housing.

14. Apparatus according to any of claims 9 to 13, further comprising at least one air jet (88) to direct air parallel to the direction of motion of a sheet along the said support, for providing an air cushion between a sheet being cut and the support.

15. Apparatus according to any of claims 9 to 12, further comprising a housing (26) containing said movable blade (60) and having an inlet for feeding a sheet into said housing to be cut, and at least one air jet (108) for diffusing air blown out through said inlet by motion of said movable blade.

16. Apparatus according to claim 13, wherein said blades are saw blades.