US3768712A - Process for cutting sheet material - Google Patents

Abstract

A process of cutting sheet material into strips, including the steps of applying a drawing force to a sheet of said material to cause said sheet to be drawn along and simultaneously causing restraining forces to be applied to said sheet on either side thereof to restrain it against the drawing action of said drawing forces.

Description

[ 1 Oct. 30, 1973 [56] References Cited UNITED STATES PATENTS PROCESS FOR CUTTING SHEET MATERIAL w w. n" "0L n u a m I. if; U mnm nSS a .l enn m rmnwcoo mmninn RMTPPBVAA 994397793 68465 623 988999999 111111111 260 75802 11 11 452870276 548497564 7431473 9 20 92333 ,3 ,3 1 3 3213 m e s Ha m 9P. r .l b s u mm M m e ri 1.. nh W .mA U 1 h. we F mD 9 1 n WE 7 9 ES 9 b u C l m Da I b 7 4 6 86 l 4 cc .wT 3 r. D V n r 9 8 P 8 8 5 .Ir. e r 2 PF SDF M 1 n a o o e N t n n g d l e a e D. m S "H p l. A F A l. l. 11 l. 5 3 2 11 7 7 2 2 .l 1 [r1 Primary ExaminerJ. M. Meister AttorneyJacob & Jacob [57] ABSTRACT A process of cutting sheet material into strip [30] Foreign Application Priority Data s, includ- July 19, 1967 France 67114728 July 24, 1967 67115317 sheet of France ing the steps of applying a drawing force to a said material to cause said sheet to be drawn along and simultaneously causing restraining forces to be ap- [52] US. Cl. 225/3 [51] Int. 326d 7/14 li d to said sheet on either side thereof to restrain it Fleld of Search against the drawing action of said drawing forces.

12 Claims, 12 Drawing Figures PATENTEDUBI 30 1975 SHEET 2 BF 4 FIGS FIG.5

PATENTED BET 30 I975 I SHEET 3 BF 4 FIG] PROCESS FOR CUTTING SHEET MATERIAL This is a division of application Ser. No. 744,876, filed July 15, 1968, now US. Pat. No. 3,628,409.

The present invention relates to the conversion of sheet material into strips or pieces thereof.

It is applicable to any material in the form of separate sheets or continuous bands designed to be cut longitudinally into thin strips as the result of the movement thereof in relation to a cutting member, it being possible for strips to be cut transversely to provide pieces of strip, or strands. The invention is notably applicable to the conversion of a continuous layer of material having a structure similar to that of paper (such as reconstituted tobacco) into thin strips or fragments thereof.

Certain known longitudinal cutting devices have the disadvantage of causing rapid wear of the cutting members, which operate against one another as they cut the material.

Also known are devices the cutting members of which work without a backing element by tearing the sheet. This is the case with devices utilizing two rotary cylinders mounted on parallel axes, which are rotated in opposite directions at the same speed and which are formed on their peripheries with preferably opposite screw-threads or with meshing circular grooves, the cylinders being made of a material having a high coefficient of friction in relation to paper.

Such devices, which operate uniquely by a transverse pull designed to cause longitudinal tearing, require a material capable of withstanding such forces. They produce a ragged out without clean-cut edges and are unsuitable for industrial uses in which the strips must be relatively narrow (about i millimetre).

With a view to improving the parting process by tearing, it has already been proposed to produce an initial small tear with the sharp edges of upstanding ribs on one of the rotating cylinders, the other cylinder being formed with blunt ribs. But here again the process involves a transverse elongation or stretching of the material.

It is the object of the present invention to provide an apparatus a method which overcomes the foregoing disadvantages, in accordance with which the sheet material is entrained by a rotary cutting member and is stretched thereagainst at the same time as a restraining action is exerted thereon on either side of said cutting member. Thus the sheet material is subjected to longitudinal stresses which cooperate with the shearing effect produced by the cutting member.

By cyclically varying the restraining forces applied on either side of the sheet, the longitudinal stresses to which the sheet is subjected are spread more widely. The concerted effects of the entrainment by the cutting member and the restraint imposed on either side thereof produce a curvature in the cut strip. As the restraining effect changes, this curvature varies and results in a wavy effect. The parallel longitudinal stresses have different intensities, being greater in the cutting zone and lower in the restraining zone. By varying the restraining force, the distortions to which the texture of the sheet is subjected during the operation are modified.

By adjusting the stresses applied to the sheet in these zones, each strip is subjected to a longitudinal pulling force which snaps it when its length reaches a certain limit dependent on the cutting conditions.

The apparatus subject method of this invention enables wavy strip fragments or strands to be obtained.

This advantage is enhanced by the roof tiling" effect obtained as a result of the configuration of the restraining means on either side of the cutting member. This new product, which has notable utility by reason of the improved bulk volume of the strands it ensures, likewise falls within the scope of the present invention.

It is a further object of the present invention to provide a device for performing the method hereinbefore disclosed, comprising two members of which at least one rotates, and which exhibit, on a plane passing through the rotation axis, a wavy profile formed by sharp ridges on one member and by blunt ridges on the other, the ridges of the one engaging between the ridges of the other (from which they are preferably spaced by an amount greater than the thickness of the sheet in order to avoid cutting thereof between the two members). Said members have different linear speeds. Although such a device operates without backing means, it will thus enable cutting to be obtained instead of tearing the longitudinal stresses of different magnitude to which the sheet is subjected in its parts in contact with either the sharp ridges or the blunt ridges cooperate with the cutting edges of said sharp ridges.

Preferably, the member bearing the blunt ridges is mobile whereby to renew the restraining surface in contact with the sheet material. Further, this mobile member is of the rotary variety, being consequently circular or with screw-threads thereon whereby to provide more progressive operation by virtue of the arcs resulting from the sequence of circles described by said members.

Preferably also, the speed of the sharp-ridged member is greater in absolute terms than that of the other member in order to take advantage of the braking effect produced by the blunt ridges, which effect is necessarily greater than that which the sharp ridges would be able to produce.

The speed differential can be obtained by using different diameters. Preferably, the diameter of the sharpridged member is greater than that of the other member in order to obtain entrainment of the sheet by the ridges of the latter member before it is drawn into the zone of mesh.

A further advantage can be obtained by devising the blunt ridges so that they are rough only over part of their peripheries, thus making it possible to vary the friction of the sheet against the ridges and thereby create conditions favourable for waving the strips or strands.

In order to permit the cutting of non-straight strands, the invention further provides for equipping the rotary cutting member with peripheral ribs such that when it is rotated said ribs revolve at different peripheral linear velocities in order to cause the sheet to advance faster at the points where it is gripped by the faster-revolving ribs than at the points where it is gripped by the more slowly revolving ribs. The fast-revolving ribs draw in a greater length of the band in a given space of time, thereby imparting an apparent arcing motion to the band.

In a possible embodiment of means for carrying into practice the above-disclosed alternative mode of performing the subject method of this invention, at least one of the two rotating members of the device described precedingly can be frusto-conical in shape,

whereby the tangential velocities of the ribs thereon go increasing from the small end to the large end of the cone frustum.

Preferably, the member with sharp ridges is chosen as the rotating member so as to obtain the restraining effect with the ridges of the other member. If both members rotate, the one with sharp ridges preferably has a greater angular velocity than the other member.

The description which follows with reference to the accompanying non-limitative exemplary drawing will give a clear understanding of how the invention can be carried into practice.

7 In the drawing FIG. I shows in front elevation a two-roll device formed with non-meshing screw-threads thereon.

FIG. 2 is a detail sectional view taken on the line II-lI of FIG. 3 of the profile of the screw-threads on the two rolls in FIG. 1.

FIG. 3 is a side elevation view of the device in FIG. 1.

FIGS. 4, 5 and 6 are views corresponding to FIGS. 1, 2 and 3, respectively, but in which the rolls are formed with circular grooves thereon, FIG. 5 being a sectional view on the line VV of FIG. 6.

FIGS. 7 and 8 are views corresponding to FIGS. 4 and 5, respectively, but in which the rolls are formed by stacked discs.

FIGS. 9 and 10 are diagrammatic illustrations of the longitudinal stresses imposed upon the sheet material when performing the cutting method according to this invention.

FIG. 11 is a schematic plan view of a frusto-conical roll used in the device according to this invention, and

FIG. I2 shows a strand obtained with the device of FIG. 11, from a sheet of height h.

The device shown in FIGS. 1 to 3 comprises two rolls 1 and 2 rotating in opposite directions. These rolls have no direct point of contact between them, their angular rotation velocities are equal but opposite, the gearwheels 3 and A being identical. The rolls are here shown as being of different diameter.

Each of rolls 1 and 2 is formed on its periphery with a screw-thread of appropriate profile. Although the pitches of these two screw-threads are strictly identical, one is a left-hand thread and the other a right-hand thread; thus contact can never take place between the two rolls providing they are correctly positioned initially, but only interpenetration of the threads, with the peaks of the one engaging into the middle of the hollows of the other.

The rolls are carried by two parallel shafts 5 and 6 interconnected by rigid supports 7 which are designed to enable the centre distance 5-6 to be adjusted as required and to ensure optimum interpenetration of the two screw-threads. Should the adjustment range prove narrow, the slight backlash between the two gearwheels 3 and 4 will allow the necessary adjustments to be made.

Screw-thread 8 is formed on the roll of greater diameter, and its tapered ridge is designed to perform the function of a knife, as explained precedingly. The screw-thread 9 is formed on the roll of smaller diameter, and its ridge of trapezoidal (or rounded) shape acts as a backing element; it is used to tension the sheet 10 upon the ridges ii, to restrain the sheet by the friction between it and the flat tips of the trapezoidal screwthreads, and to impart a profile to the cut strands such that they disengage better from the rolls.

By reason of the different roll diameters and although the rotation speeds are identical, the linear velocities at the points of contact with the material to be out are different, the linear velocity of the cutting edge of thread 8 being much greater than that of the flat tip of thread 9, whereby, as explained precedingly, the friction effect imparts to sheet 10, upon the latter being drawn in, a linear velocity which is much closer to that of thread 9 than to that of thread 8. This results in a very substantial relative motion between the sheet and the cutting edge of thread 8 at the points of contact 11, thus producing the cutting effect. Conversely, no cutting occurs against the thread 9, firstly because the speed differential is small and secondly because the profile of thread 9 is blunt.

Obviously, the cutting width will be equal to the linear distance between two adjacent points 11.

It is possible to polish all or part of one or the other profile, or on the contrary to make it rough (profile 9); also, the threads can be protected against wear, for instance by depositing a very hard metallic coating on all or part of one or the other thread, an example being by chromium-plating or by spraying tungsten carbide on one of the sides of the thread 8.

In the embodiment shown in FIGS. 4 to 6, the device likewise includes two facing rolls 12 and 13, and the cutting process is similar to that described hereinabove with reference to FIGS. 1 to 3. Instead of being formed with two threads over their peripheries, however, the rolls embody parallel circular grooves lying in crosssectional planes of the rolls. These grooves are uniformly spaced at the same distance on both rolls.

With this particular arrangement it is no longer indispensable for the angular velocities of the two rolls to be equal in absolute terms. This may be an advantage since it enables the relative linear velocities at the peripheries of rolls 12 and 13 to be varied independently of their diameters. In particular, roll 12 can rotate very fast while roll 13 rotates very slowly; it may even be stationary or rotate in the opposite direction (at slow speeds). In the example of FIG. 4, shaft 14 is driven at high speed in the direction shown by the arrow, by any convenient means. Shaft 15 is driven, separately or not, so as to rotate at any preselected speed, either in the same direction as shaft 14 or in the opposite direction. Alternatively, shaft 15 can be left free (with roll 13 rotating freely), or be clamped by any convenient means (thus making roll 13 stationary).

At the same time, the ratio between the diameters of the rolls is no longer subject to the constraints existing in the embodiment of FIGS. 1 to 3. The diameter of roll 13 can be greater than, equal to, or smaller than that of roll 12. At the limit, it may be infinite (impiying a flat surface) in the case where roll 13 does not rotate. In practice, it is preferable for roll 13 to have a smaller diameter than roll 12 since this causes sheet 10 to be more readily absorbed (see FIG. 6).

The profile of grooves 16 shown in Figure is that formed on roll 12 and is such that the edges of the ridges are very sharp and the angle formed by the sides of the ridges is very acute. Profile 17 is formed on roll 13; the ridge edges thereof are blunt, being rounded or trapezoidal, and are rough. The angle between the sides of these ridges is not very acute.

The process of cutting into strands takes place under conditions similar to those described with reference to FIGS. 1 to 3, except that the difference between the linear velocities at the level of grooves 16 and 17 can be much greater than in the previous embodiment described, for the reasons discussed precedingly. This can only lead to improved and easier cutting.

In the embodiment portrayed in FIGS. 7 and 8, the two rolls 18 and 19 positioned face to face (FIG. 7) are no longer made of a single block of material but of a stack of bevelled discs. Though the discs are preferably abutting, they may be separated by spacers if desired. The outward appearance of the roll-forming cylinders is substantially identical to that of the grooved cylinders described hereinbefore.

The discs 20 (FIG. 8) form the roll 18 and their profile is similar to that of grooves 16 (FIG. 5). Discs 21 form the roll 19 and their profile is similar to that of grooves 17 (FIG. 5).

Transverse cutting or prior shredding is no longer essential even if a continuous band of material is to be transformed into strands. This arises from the fact that, because of the comparatively rough nature of the process and the high speeds reached, experience has shown that under certain conditions the cut strips will snap of their own accord into strands of variable length, their average length being dependent upon various factors and notably upon the gap between the rolls, the rotation speeds thereof, the profile of the screw-threads, grooves, or interstices, the surface condition of the roll peripheries, the sharpness of the ridges, and the way the raw material is offered up.

FIGS. 9 and show the effect of the transverse snapping of the longitudinally cut strands or strips.

Consider the sheet 10 on the device shown in FIG. 3. It is gripped (and distended) between the rolls 1 and 2, and in the process is in contact with both rolls at once, the contact pressure being considerable on both sides (since the sheet is distended). Now the linear velocities at the peripheries of rolls 1 and 2 are different along the contact line, even if the rotation speeds are equal the linear velocity at the periphery of roll 1 is distinctly higher than at the periphery of roll 2, the difference being all the greater as the ratio between the radii departs farther from unity (the rotation speeds remaining unchanged). This being so, when cutting takes place, the sheet and hence the strands are subjected to two parallel longitudinal stresses of different magnitude, to wit C and C where C, is greater than C (see FIG. 9). Mechanically speaking, this is equivalent to two forces applied at A and B, parallel to C and C but acting in opposite directions. Thus each strand is subjected at the time of cutting to a longitudinal pulling force in the direction of travel of the material, and it is this pulling force that causes snapping.

However, snapping does not occur before the length of the cut strip has reached a certain limit dependent upon the cutting conditions. For consider two sheets placed back to back (FIG. 10) which penetrate together between two cylinders of radius R and r respectively, rotating at the same speed, the sheets being able to slip over each other. It will readily be appreciated that because of the different linear speeds the two marks a and B will move away from each other and that the gap between them will increase with time.

By analogy, this increasing gap between a and B can be likened to the condition of internal stress in the strand. This stress increases likewise as the strand travels along, until the latter breaks.

As already stated, snapping can occur only under certain conditions. Otherwise the longitudinal stresses described precedingly, which result from the different rotation speeds of the two rolls, will remain and will produce a waviness in the strips resulting from successive curvatures.

The same applies when strands are produced by transverse breakages, for here the edges of the strands are subjected to stresses higher than those imposed on the middle areas of the strands. Hence, prior to rupture, the strands undergo a deformation resulting in curvature. When associated to the roof tiling effect on the strands due to the sheet being bent round the blunt ridges, these curvatures increase the filling capacity of the strands. The extent of the waviness can be advantageously modified by varying the degree of roughness of the blunt ridges and hence the degree of friction between these ridges and the sheet. The edge of each ridge may comprise rough portions and less rough or even smooth portions, the latter being possibly formed as a flat area spread over the periphery of each ridge in order to periodically modify the restraining effect on the strip as well as the transverse tension therein.

Alternatively, without departing from the scope of the present invention, it would be possible to moisten the strip or to heat one of the two rolls in order to create an effect similar to that obtained when ironing with a damp cloth.

It goes without saying that the embodiment of FIGS. 1 to 3 may feature rolls formed with a plurality of screw-threads; likewise, one of the roll shafts can be driven by the other through a gear train.

In the embodiment shown in FIGS. 4 to 6, the roll 13 may be possessed of reciprocating motion (i.e. rotating first in one direction, then in the other). In the limit case of an infinite diameter, the roll is represented by a flat grooved surface possessed of rectilinear vibratory motion, the direction of the motion being longitudinally of the grooves, and such reciprocating motion can be imparted to both rolls. A case in point would be a vibrating conveyor with blunt ridges cooperating with a sharp-ridged roll having its axis fixed to the moving surface of the conveyor.

The profiles of grooves 16 (FIG. 5) and 20 (FIG. 8) may be otherwise than symmetrical; more particularly, one flank of the outer portion may be straight, only the other being bevelled, as exemplified by the discs 20.

Alternatively, a roll consisting of a grooved cylinder may be associated to a roll formed by a stack of discs.

The subject device of this invention can be made to operate in any position whatsoever, notably with the roll-supporting shafts lying vertically or horizontally. Furthermore, such a device can be used in combination with others placed ahead so as to permit initial cutting or shredding into fragments of a continuous sheet wound to form a spool; in particular, such a device can be associated to a transverse cutting system or to a strip-delivering system, the link being of the conventional vertical type, or horizontal as exemplified by a vibrating conveyor.

In the embodiment shown in FIG. 11, the frustoconical roll 31 rotates about an axis 32 and is formed with circular ridges 33 thereon (of which only one is shown) having a sharp-edged profile.

Cylindrical roll 35 rotates about an axis 38 and is formed with circular ribs 36 thereon (of which only one is shown) having a blunt-edged profile. The ribs on rolls 3]; and 35 interpenetrate in the same way as those of rolls 1 and 2 of FIGS. 1 and 2.

Rolls 31 and 35 rotate in opposite directions shown by the arrows in FIG. 11. Roll 31 rotates very fast whereas roll 35 rotates fairly slowly. Roll 35 is cylindrical, and hence the peripheral speed is constant along its length. On the other hand, Roll 31 is frusto-conical, and hence the peripheral speed varies from point-topoint along the length of roll 31, from a minimum at the smaller end to a maximum at the larger end. The band of material is offered up above the device in such manner that its lower edge is parallel to the rotation axis 38 of roll 35 and is entrained and gripped by the ribs 33 and 36, with the former entraining it and the latter restraining it. The band tends to position itself more and more obliquely in relation to rotation axis 35 because the linear velocity at 40 is much higher that at 41, as explained above, thereby causing the precut band to be swallowed up much more quickly on the side of the larger end than on the side of the smaller end of cone frusturn 31.

Clearly, it is thus possible to obtain strands of the type shown in FIG. 12, or even strands of wavy profile, by virtue of the apparent rotational motion of the band about the point 42, in the plane tangential to both rolls 31 and 35.-

Obviously, roll 35 may be otherwise than cylindrical; in particular, a frustoconical shape would enable the restraining force to be adjusted to suit the entrainment speed of the ribs on roll 31.

What I claim is:

l. A process of cutting sheet material into strips, which comprises cutting said sheet along at least one longitudinally extending cutting line while applying a drawing force to said sheet to cause said sheet to be drawn along and simultaneously causing restraining forces to be applied to said sheet on either side thereof to restrain it against the drawing action of said drawing forces, the magnitude of said restraining forces being varied cyclically.

2. A process as in claim 1, further comprising the step of adjusting the sheet drawing force in relation to the restraining forces applied on either side of said sheet, whereby to cause the resistance of said sheet to produce successive transverse snappings of the strip being cut.

3. A process as in claim 1, wherein a plurality of parallel drawing forces are applied to said sheet at different points thereof and at different linear velocities thereat.

4. A process of cutting sheet material into strips along at least one longitudinally extending cutting line, in which the sheet is entrained by at least one rotary cutting member against which it is applied at the same time as it is restrained on either side of each said cutting line, comprising adjusting the sheet entraining forces resulting from the peripheral velocity of said cutting member in relation to the restraining forces applied on either side of each said cutting line and to the strength of said sheet whereby to produce, further to the longitudinal cutting into strips, waving of said strips cut by said cutting member, the magnitude of at least one of the restraining and entraining forces applied to the sheet being varied cyclically.

5. A process as claimed in claim 4 in which the entraining forces and the restraining forces are adjusted in relation to one another further to produce successive transverse snappings of the strips cut by said cutting member.

6. A process as claimed in claim 4 in which the magnitude of the restraining forces applied to the sheet is varied cyclically.

7. A process as claimed in claim 4 in which the magnitude of the entraining forces applied to the sheet is varied cyclically.

8. A process as claimed in claim 5 in which the magnitude of the restraining and entraining forces applied to the sheet are varied cyclically.

9. A process as claimed in claim 4 in which the action of said rotary cutting member is exerted at different points on said sheet and at different linear velocities thereat.

10. A process as claimed in claim 5, in which the action of said rotary cutting member is exerted at different points "on said sheet and at different linear velocities thereat.

11. A process as claimed in claim 4 in which the action of said rotary cutting member is exerted at different points on said sheet and at different linear velocities thereat.

12. A process as claimed in claim 8 in which the action of said rotary cutting member is exerted at different points on said sheet and at different linear velocities thereat.

Claims (12)

1. A process of cutting sheet material into strips, which comprises cutting said sheet along at least one longitudinally extending cutting line while applying a drawing force to said sheet to cause said sheet to be drawn along and simultaneously causing restraining forces to be applied to said sheet on either side thereof to restrain it against the drawing action of said drawing forces, the magnitude of said restraining forces being varied cyclically.

2. A process as in claim 1, further comprising the step of adjusting the sheet drawing force in relation to the restraining forces applied on either side of said sheet, whereby to cause the resistance of said sheet to produce successive transverse snappings of the strip being cut.

3. A process as in claim 1, wherein a plurality of parallel drawing forces are applied to said sheet at different points thereof and at different linear velocities thereat.

4. A process of cutting sheet material into strips along at least one longitudinally extending cutting line, in which the sheet is entrained by at least one rotary cutting member against which it is applied at the same time as it is restrained on either side of each said cutting line, comprising adjusting the sheet entraining forces resulting from the peripheral velocity of said cutting member in relation to the restraining forces applied on either side of each said cutting line and to the strength of said sheet whereby to produce, further to the longitudinal cutting into strips, waving of said strips cut by said cutting member, the magnitude of at least one of the restraining and entraining forces applied to the sheet being varied cyclically.

5. A process as claimed in claim 4 in which the entraining forces and the restraining forces are adjusted in relation to one another further to produce successive transverse snappings of the strips cut by said cutting member.

6. A process as claimed in claim 4 in which the magnitude of the restraining forces applied to the sheet is varied cyclically.

7. A process as claimed in claim 4 in which the magnitude of the entraining forces applied to the sheet is varied cyclically.

8. A process as claimed in claim 5 in which the magnitude of the restraining and entraining forces applied to the sheet are varied cyclically.

9. A process as claimed in claim 4 in which the action of said rotary cutting member is exerted at different points on said sheet and at different linear velocities thereat.

10. A process as claimed in claim 5, in which the action of said rotary cutting member is exerted at different points on said sheet and at different linear velocities thereat.

11. A process as claimed in claim 4 in which the action of said rotary cutting member is exerted at different points on said sheet and at different linear velocities thereat.

12. A process as claimed in claim 8 in which the action of said rotary cutting member is exerted at different points on said sheet and at different linear velocities thereat.

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