US3820427A

US3820427A - Method and device for cutting split film

Info

Publication number: US3820427A
Application number: US00285752A
Authority: US
Inventors: J Stomph
Original assignee: Nederlandse Organisatie voor Toegepast Natuurwetenschappelijk Onderzoek TNO
Current assignee: Nederlandse Organisatie voor Toegepast Natuurwetenschappelijk Onderzoek TNO
Priority date: 1972-09-01
Filing date: 1972-09-01
Publication date: 1974-06-28
Anticipated expiration: 1991-06-28

Abstract

To cut split film into narrow strips, the film while being kept under considerable longitudinal stress is fed over a sharp edge and a number of parallel rotating circular knives which have a small fold angle and the cutting edges of which intersect the plane of the film under an acute angle closely behind the said sharp edge.

Description

United States Patent 1191 Stomph June 28, 1974 METHOD AND DEVICE FOR CUTTING SPLIT FILM [56] References Cited [75] Inventor: Joannes Gerardus Stomph, UNITED STATES PATENTS Maasland, Netherlands 324,155 8/1885 Parsons 242/564 1,238,086 8/1917 Bauer 242/562 X [73] Ass'gneef gsgggggfi gi ggr sg 2,310,153 2/1943 Ro senfarb 242/562 Onderzoek Ten Bebe-eve Van 2,569,589 10/1951 Trissell 242/562 X Nijverheid Handel En Verkeer The Primary Examiner.1. M. Meister Hague Netherlands Attorney, Agent, or Firm-Brumbaugh, Graves, Dono- [22] Filed: Sept. 1, 1972 hue & Raymond 21 A l. N 285752 1 pp 0 57 ABSTRACT To cut split film into narrow strips, the film while [30] Forelgn Application Pnomy Data being kept under considerable longitudinal stress is Sept. 14, 1971 Netherlands 7112613 fed over a Sharp edge and a number of paraugl rotat ing circular knives which have a small fold angle and [52] US. Cl 83/18, 83/175, 83/483, the cutting edges of which intersect the plane of the 51' 1111.01 B263 gig gf j awe angle closely behind the said [58] Field of Search 83/175, 18,508, 483;

5 Claims, 1 Drawing Figure METHOD AND DEVICE FOR CUTTING SPLIT FILM BACKGROUND OF THE INVENTION The invention relates to a method for cutting split film into narrow strips, the film that moves continually in its plane being made to pass a number of knives placed in its path, which are mounted side by side and parallel to the direction of movement of the film. Such methods are applied to both fibrillated and unfibrillated films and the strips obtained therefrom, which for instance are 1 mm wide, are as yarn applied for several objectives, either direct or after having been subjected to further treatments.

When the small strips are being cut, the problem arises, however, that their width is not always the same. The cause of this is that the knives tend to divide the split film according to its direction of orientation and in the process also follow the deviations of the direction of orientation that can never be avoided completely. As a result the yarns have an uneven thickness and it may even occur that two lines of cut coincide, so that two strips change into one single strip that then because of its too great thickness may jam between the knives and at any rate implies a derangement of the process.

SUMMARY OF THE INVENTION tions in the direction of orientation of the film is suppressed in order to obtain yarns of an even and mutually equal thickness.

For this purpose the method according to the invention is characterized in that, very close before the place where the knives are in the path of the film, the latter is carried over a sharp edge under a tensile stress that is considerably greater than is needed to surmount the cutting forces, and in that knives with a very small fold angle are applied and the film is carried past these knives according to a plane that is intersected by the cutting edges of the knives under an acute angle with the direction of movement of the film.

It has been found that upon application of this method deviations in the orientation of the split film do not cause changes in width of the cut strips. For this purpose it is of importance that the tensile stress at which the film is drawn over the sharp edge is chosen so great that the frictional forces the film is subjected to are considerably greater than the forces exerted on the film by the knives. The sharp edge over which the film is carried should also be as close to the cutting edges of the knives, without touching them, as is possible under the given conditions of flexibility of the arrangement, manufacturing tolerances and the like. Moreover, the fold angle of the knives, which is the angle between two cutting planes that together form the cutting edge of a knife, should be so small as the technique of manufacturing and the requirements of strength the knife has to meet allow; in practice this means a fold angle of approximately 2.

In the process, the inclined position of the cutting edge in respect of the plane of the film has the effect that the apparent fold angle seen in the plane of the film, is smaller than the real fold angle seen in a plane perpendicular to the cutting edge of the knife.

The invention also relates to a device for carrying out the method according to the invention. This device comprises, like devices for carrying out the methods known in the art, a feeding device for the film, a num ber of parallel knives, placed side by side and a discharge device for the cut strips and is further characterized in that the feeding and discharge devices are arranged so as to subject to a tensile stress the film moving between them, and in that between the feeding device and the knives a sharp deflecting edge is mounted very close to the cutting edges of the knives, and in that the fold angle of the knives is very small, and in that the knives take up such a position in respect of the moving plane of the film leading from the deflecting edge to the discharge device that their cutting edges intersect this plane under an acute angle.

There are several possibilities of exerting a tensile stress on the film with the aid of the feeding device. The simplest way is the application of a brake on the supply coil of the film or on one or more rollers over which the film is fed. A more constant tensile stress is obtained when the feeding device is driven at a lower speed than the discharge device; then the tensile stress is determined by the stretch-properties of the film.

According to a further characteristic of the device according to the invention at least the surface of the deflecting edge consists of material that yields a high coefficient of friction when in contact with the split film. Several plastics are known in the art that yield a high coefiicient of friction and besides are hard and wear resistant, so that they are very suitable as materials for the deflecting edge.

Preferably the deflecting edge is formed by two planes intersecting each other under an angle that is smaller than approximately If the angle is small, the deflecting edge might be too sharp and damage the film; the edge is then preferably somewhat rounded. At an angle that is greater than approximately 90 it has been found, however, that the effect aimed at by the invention is inadequately obtained.

The device according to the invention is further characterized in that the edge under which the cutting edges of the knives intersect the path of the film amounts to approximately 30. At a greater angle, the most important object of the inclined position, viz. the reduction of the effective fold angle of the knives, is realized at too small an extent, while at an inclined position under a smaller angle the film might be pushed aside somewhat by the knives, so that the cutting proper would take place at too great a distance of the deflecting edge and the effectaimed at by the invention would be lost.

The device according to the invention is, also in connection with the above, further characterized in that the knives are rotating circular knives whose direction of rotation is preferably opposite to the direction of movement of the film.

DESCRIPTION OF THE DRAWING The invention is further elucidated below with reference to the drawing that schematically shows a device according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Split film 1 that is to be cut is situated on supply coil 2, which is rotatable around shaft 3. Film 1 is fed from coil 2 over a number of rollers 4, which, in the direction indicated by arrors 5, are driven at constant speed by a motor and gear that are not drawn and transport film 1 in accordance with this speed.

After rollers 4 film l is guided around fixed

pins

6 and 7; these serve to keep film 1 stretched transversely so as to prevent the formation of wrinkles. Next the path of film 1 leads over sharp upper edge 8 of wedgeshaped body 9, which consists of or is coated with a material that yields a high coefficient of friction when in contact with the material of film l.

A number of knives 10, which rotate around shaft 11 in the direction indicated by arrow 12 and correspond to the number of strips to be cut from film 1, is mounted immediately behind edge 8, such that they just do not touch edge 8. The path of the film that in the meantime has been cut into strips 13 leads past knives to guiding edge 14 and in a direction that encloses an angle of approximately 30 with the cutting edge of knives 10 where these intersect film 1 near edge 8. Knives 10 have been ground to a very sharp shape, the angle between the planes on either side of a cutting edge, the fold angle, amounting to approximately 2. A smaller fold angle is more favourable for the operation of the knives but is difficult to realize, while at the same time the lateral strength and stiffness of the knives may then become inadequate.

Next strips 13 pass rollers 15, which are driven at constant speed in the direction of arrows 16. The speed of rollers 15 is higher than that of rollers 4, so that film 1 and small strips 13 between these two pairs of roller groups are under a tensile stress determined by their elasticity and the difference in speed.

After passing rollers 15, strips 13 are wound up on bobbins 17, which are rotated in the direction of arrow 18, or they are immediately carried further in order to be subjected to a next treatment.

I claim:

1. The method of cutting split film into strips which comprises the steps of subjecting the film to a high tensile stress; advancing the stressed film over a deflection edge formed by two planes that intersect each other at an angle that is smaller than 90; and passing the film after the deflection edge into a cutting plane under high stress and past the leading edge of at least one knife means in said cutting plane, the leading edge having a small fold angle and the knife means being positioned so that the leading edge intersects the cutting plane at an acute angle and wherein said leading edge is close to the deflection edge, and cuts the film into at least two strips by means of said leading edge of said knife means immediately after it passes over said deflection edge.

2. A split film cutting device comprising, in combination:

means for supplying the film to be cut;

means for advancing the film from the supply means;

means defining a cutting plane along which the film,

advanced from said supply means, passes for cutting, said cutting plane defining means including a sharp deflection edge formed by two planes that intersect each other at an angle that is smaller than at least one knife means having a leading edge with a small fold angle, said knife means intersecting said cutting plane and said leading edge positioned in close proximity to said deflection edge and forming an acute angle with said cutting plane; means for high tensile stressing of the film before the film, advanced from said supply means, reaches said knife means leading edge; and

means for receiving the cut film from said cutting plane defining means.

3. A device according to claim 1, wherein the angle under which the cutting edges of the knives intersect the path of the film amounts to approximately 30.

4. A device according to claim 2, wherein said high tensile stressing means includes:

means for supplying the film from below said cutting plane; and

means for deflecting the film from below said cutting plane across said deflection edge onto said plane, said deflection edge being formed of a material having a high coefficient of friction with the film.

5. A device according to claim 2, wherein said at least one knife means includes a circular knife rotating in a direction opposite the direction of advancement of

Claims

1. The method of cutting split film into strips which comprises the steps of subjecting the film to a high tensile stress; advancing the stressed film over a deflection edge formed by two planes that intersect each other at an angle that is smaller than 90*; and passing the film after the deflection edge into a cutting plane under high stress and past the leading edge of at least one knife means in said cutting plane, the leading edge having a small fold angle and the knife means being positioned so that the leading edge intersects the cutting plane at an acute angle and wherein said leading edge is close to the deflection edge, and cuts the film into at least two strips by means of said leading edge of said knife means immediately after it passes over said deflection edge.

2. A split film cutting device comprising, in combination: means for supplying the film to be cut; means for advancing the film from the supply means; means defining a cutting plane along which the film, advanced from said supply means, passes for cutting, said cutting plane defining means including a sharp deflection edge formed by two planes that intersect each other at an angle that is smaller than 90*; at least one knife means having a leading edge with a small fold angle, said knife means intersecting said cutting plane and said leading edge positioned in close proximity to said deflection edge and forming an acute angle with said cutting plane; means for high tensile stressing of the film before the film, advanced from said supply means, reaches said knife means leading edge; and means for receiving the cut film from said cutting plane defining means.

3. A device according to claim 1, wherein the angle under which the cutting edges of the knives intersect the path of the film amounts to approximately 30*.

4. A device according to claim 2, wherein said high tensile stressing means includes: means for supplying the film from below said cutting plane; and means for deflecting the film from below said cutting plane across said deflection edge onto said plane, said deflection edge being formed of a material having a high coefficient of friction with the film.

5. A device according to claim 2, wherein said at least one knife means includes a circular knife rotating in a direction opposite the direction of advancement of the film.