EP4793005A1

EP4793005A1 - Perforating or cutting device, machine comprising the device, and method

Info

Publication number: EP4793005A1
Application number: EP26158609.3A
Authority: EP
Inventors: Graziano Mazzaccherini
Original assignee: Valmet Tissue Converting SpA
Current assignee: Valmet Tissue Converting SpA
Priority date: 2025-02-17
Filing date: 2026-02-13
Publication date: 2026-08-19

Abstract

The perforating or cutting device comprises: a support rotating around a rotation axis and at least one rotary blade, carried by the rotary support; and a stationary support, on which there is mounted at least one stationary counter-blade arranged to cooperate with the rotary blade. During the rotation of the rotary support, the rotary blade cooperates with the stationary blade to perforate or cut a web material supplied in a machine direction between the rotary support and the stationary support. The stationary counter-blade comprises a cutting edge having a variable inclination with respect to the machine direction, to generate, cooperating with the cutting edge of the rotary blade, a perforation or cutting line with a non-straight shape on the web material.

Description

TECHNICAL FIELD

The present invention relates to devices for processing web materials. Embodiments disclosed herein in particular relate to devices for perforating or cutting a web material according to non-straight lines. The devices described herein are in particular configured to cut or perforate for example a cellulosic material, typically for example tissue paper.

BACKGROUND ART

In the field of converting continuous web materials, for example made of tissue paper, it is well known to perforate or cut lines on continuous web material for separating the web into individual sheets, or for generating along the extension of the of the web material several perforation lines, which form preferential breaking lines. The web material is therefore divided into several portions of web material, each of which can be detached by tearing along a perforation line.
Web materials, comprising one or more cellulosic plies bonded to each other, are perforated for example to form toilet paper rolls, paper towel, or similar articles.
In the paper, in particular tissue paper, converting industry it is well known to generate undulated, i.e., non-straight, perforation lines. A perforating device for generating perforation lines with non-linear development in a web material is disclosed in EP3007871 . This prior art perforating device comprises a rotary roller, on which there is arranged at least one undulated, i.e., non-linear perforating blade which cooperates with a fixed straight blade.
This perforating device has some drawbacks, in particular a high cost. A perforating blade for producing non-linear perforation lines as disclosed in EP3007871 , has a higher cost than a blade of the prior art, that is a blade for providing straight perforations. A perforating device or a cutting assembly of the paper-converting machines usually has, for production purposes, from four to eight blades. This results in a high cost of blades, which are also subject to wear and need to be replaced.

SUMMARY

According to a first aspect, the invention relates to a perforating or cutting device comprising a rotary support, adapted to rotate around a rotation axis and comprising a lateral surface extending along the rotation axis. On the lateral surface of the rotary support, at least one rotary blade is fixed, carried by the rotary support and comprising a cutting edge. The device further comprises a stationary support, on which at least one stationary counter-blade is fitted, provided to cooperate in a contact relationship with the rotary blade carried by the rotary support. The arrangement is such that, during the rotation of the rotary support, the rotary blade cooperates with the stationary blade to perforate or cut a web material supplied in a machine direction between the rotary support and the stationary support. The stationary counter-blade comprises a cutting edge having a variable inclination with respect to the machine direction, to generate, in cooperation with the cutting edge of the rotary blade, a perforation or cutting line with a non-straight shape on the web material.
With this arrangement, a number of rotary blades greater than one may be provided, limiting the cost of the device, given that the blade shaped to form the undulated cutting or perforation line, i.e., the line with a variable inclination, consists of the single stationary blade.
The expression machine direction is used to indicate the direction along which the web material to be perforated or to be cut advances. Therefore, the machine direction corresponds to the direction of the tangential velocity of the rotary blade in the point of contact with the stationary counter-blade. Hereinafter, reference will also be made to the transversal direction, which is intended as the direction orthogonal to the machine direction and parallel to the web material.
If the device is a cutting device, blade and counter-blade, all have a continuous cutting edge. If the device is a perforating device, the rotary blade or the stationary counter-blade comprise a serrated cutting edge, i.e., an edge having a plurality of teeth, wherein adjacent teeth are separated from each other by a recess or cavity.
In embodiments described herein, the device comprises a supply system, for supplying the web material at a controlled velocity between the rotary support and the stationary support; and a rotation actuator, for rotating the rotary support. The supply system and the rotation actuator are controlled to supply the web material between the rotary support and the stationary support at a velocity different from the peripheral velocity of the cutting edge of the rotary blade.
For example, the supply system and the rotation actuator may be controlled to supply the web material with a difference between the linear velocity of the web material and the peripheral velocity of the cutting edge of the rotary blade or rotary blades comprised between -40% and +40%, preferably between -25% and +25, more preferably between -10% and +10% of the peripheral velocity of the cutting edge of the rotary blade.
The supply system may consist of any set of members that control the linear advancement velocity of the web material, for example one or more motor-driven rollers arranged along the supply path of the web material.
The rotation actuator may generally be any system which drives in rotation the rotary support, for example an electric motor.
In advantageous embodiments, the stationary counter-blade comprises a cutting edge lying on a concave surface, in particular on a cylindrical surface with a diameter approximately equal to a diameter of a cylindrical surface enveloping the cutting edge of the rotary blade during the rotary movement thereof. The enveloping surface is the surface defined by the positions of the cutting edge of the rotary blade during the movement thereof around the rotation axis of the rotary support.
According to a further aspect, the invention relates to a machine for converting a web material, for example paper and in particular tissue paper, comprising a station for converting web material, and a perforating or cutting device as defined above, arranged upstream of the converting station.
According to still a further aspect, the invention relates to a method for perforating or cutting a continuous web material, comprising the following steps: supplying a web material according to a machine direction between a rotary support, on which at least one rotary blade is supported, and a stationary counter-blade; wherein the stationary counter-blade comprises a cutting edge having a variable inclination with respect to the machine direction;

rotating the rotary support and the rotary blade around a rotation axis;
perforating or cutting the web material by cooperation of the rotary blade with the stationary counter-blade generating on the web material perforation or cutting lines, each of which has a non-straight shape and a variable inclination with respect to the machine direction.

Further advantageous features and embodiments of the perforating or cutting device, of the machine which comprises it and of the perforating or cutting method are described below with reference to the drawings and defined in the attached claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be clearer from the description and the attached drawings, which illustrate embodiments of the invention provided by way of non-limiting example. More particularly, in the drawings:

Fig.1 is a schematic view of a rewinder with a perforating device according to the present invention;
Fig.1A is a plan view of a portion of a rotary blade of the perforating device of Fig.1;
Fig.2 is a front view of a block or segment of the counter-blade;
Fig.3 is a plan view according to III-III of Fig.2;
Fig.4 is a cross-section according to IV-IV of Fig.2;
Fig.5 is an enlargement of the detail indicated with V of Fig.4;
Fig.6 is an axonometric view of the block or segment of Figs. 2 to 5;
Fig.7 is an enlargement of the detail of Fig.5 in another embodiment; and
Fig.8 is a diagram of possible forms of perforation lines which can be obtained with a perforating device according to the present invention.

DETAILED DESCRIPTION

In the following description, reference is made to the application of the invention to a perforating device, in particular for a rewinder. However, it is clear that novel features disclosed herein may also apply to cutting devices, i.e., to devices carry out full cutting operations, instead of perforating operations, along the web material, for example to divide it into single sheets with shaped cutting edges.
Furthermore, the embodiment described below provides for a perforating device used for perforating a web material made of tissue paper, consisting of one or more plies. However, it should be noted that the novel features disclosed herein may also be used for providing perforating or cutting devices for other types of web material, for example uncreped paper, cardboard, polymeric films and the like.
The perforating or cutting device illustrated herein is fitted into a rewinding machine. However, those skilled in the art will understand that a perforating or cutting device according to the present invention may also be fitted into another type of machine for processing a continuous web material, whenever the need arises to provide non-linear, specifically non-straight, for example undulated or zig-zag, perforating or cutting lines.
With reference to the attached drawings. Fig.1 schematically shows a rewinder 1 provided with a perforating device 3. The rewinder 1 is shown by way of example of a generic machine for processing or converting a continuous web material N. The structure of the rewinder 1 is shown purely by way of example and may vary in a manner per se known to those skilled in the art. Generally, the rewinder 1 may be a peripheral rewinder, preferably an automatic and continuous peripheral rewinder, i.e., a rewinder capable of producing automatically and without stopping, in rapid sequence rolls R of wound web material N.
The rewinder 1 may comprise a winding head 5 provided with a plurality of motor-driven rewinding rollers 7, 9, 11, 13 and other members per se known to those skilled in the art. Embodiments of rewinding machines are disclosed for example in EP2621844 , EP0694020 , EP2655227 . In other embodiments, not shown, the rewinder may be a central rewinder, i.e., a rewinder wherein the winding motion is imparted to the rolls from the centre of a spindle or winding core. In yet further embodiments, the rewinder machine may be a combined peripheral and central rewinding machine, in which the winding motion is transmitted partly by friction through contact between the outer surface of the roll being formed and peripheral rewinding members (such as rollers or belts), and partly through a pair of tailstocks or other members that engage the roll axially.
In yet other embodiments, the rewinder may be a slitter-rewinder, which comprises members for slitting the web material into single strips, which are simultaneously wound on rolls that are smaller in axial size than the width of the initial web material.
While in Fig.1 the rewinder is continuous, and produces rolls without stoppage, except for the replacement of a parent reel from which the initial web material is dispensed, in other embodiments the rewinder may be a start-stop rewinder, in which at the end of the winding cycle, the supply of the web material is temporarily stopped to discharge the rolls produced and introduce new winding cores into the rewinding machine, before resuming the supply of the web material.
Although in the present context the perforating device 3 is described in combination with a rewinder 1 which produces rolls R of wound material, in other embodiments the perforating device 3 may be combined with one or more machines for converting a web material to produce different articles. For example, the perforating device 3 may be associated with a machine for producing packages formed from a continuous web material that is perforated and zig-zag folded.
The perforating device 3 comprises a rotary support 15 for one or more rotary blades. In the illustrated embodiment, six rotary blades 19 are provided. The rotary support 15 is rotatably supported on a load-bearing structure 17, for example comprising two opposite sides, between which a rotary support 15 is arranged. The rotary support 15 rotates around a rotation axis A-A.
The perforating device 3 further comprises a stationary counter-blade 21, carried by the load-bearing structure 17 and extending, similarly to the rotary support 15, between the two sides 17 and supported thereby. As understood herein, the expression "fixed" or "stationary" referring to the counter-blade 21 or to the support thereof (described below) is used to indicate that the stationary counter-blade 21 does not contribute to the rotation motion which generates the perforation of the web material N. This does not rule out that the stationary counter-blade 21 be provided with some movement. For example, the stationary counter-blade 21 may be provided with a translation and/or rotation movement so as to carry out an adjustment, and/or to select one or the other of multiple counter-blades present in the perforating device 3, as better detailed below.
In order to obtain perforating lines, instead of a full cut of the web material, the stationary counter-blade 21 may have a serrated, i.e., interrupted, cutting edge with a plurality of consecutive teeth, separated from each other by respective cavities or recesses at which the web material N remains intact, i.e., is not cut, thus forming continuity points of the web material. A tooth may be long, for example from 1 to 4 mm. The recesses may long, for example from 0.1 mm a 2 mm.
The length of teeth and recesses which are alternating with respect to each other along the cutting edge may be constant or variable. In other words, there may be provided recesses and/or teeth all with the same or different lengths along the cutting edge. For example, there may be provided perforation lines that are more resistant to tear at the edges of a sheet with respect to the central part, which is equal to having recesses with greater length and/or teeth with smaller length. Alternatively, perforation lines may be provided that are more resistant to tear at the centre of a sheet which is equal to having recesses with smaller length and/or teeth with greater length. Still, there may be provided a hardness or resistance to tear of the perforation, that changes progressively, i.e., wherein the recesses and/or the teeth change length progressively along the cutting edge.
Alternatively, the cutting edge of the stationary counter-blade 21 may be continuous, and each rotary blade 19 may have a serrated cutting edge, i.e., comprising teeth which are separated from each other by recesses or cavities, so as to form an interrupted cutting edge. In Fig.1A a portion of one of the rotary blades 19 is shown, with an interrupted cutting edge consisting of the succession of teeth 19.1 and cavities or recesses 19.2.
Although in Fig. 1A teeth 19.1 and cavities or recesses 19.2 with a respective constant length are shown, a configuration with teeth 19.1 and/or recesses or cavities 19.2 with variable length and distribution along the cutting edge may be provided, as described above.
In the illustrated embodiment, the stationary counter-blade 21 is carried by a stationary, i.e., non-rotating support, indicated with 22. The stationary support 22 extends in a direction approximately parallel to the rotation axis A-A of the blade-holder 15.
In the illustrated embodiment, in addition to the stationary counter-blade 21, the stationary support 22 carries a further supplementary stationary counter-blade 23, which may have a shape different from the stationary counter-blade 21, so as to obtain perforation lines with different shapes. The rotation of the stationary support 22 around its axis allows to plce the stationary counter-blade 21 or the supplementary stationary counter-blade 23 in the operative position. In the position of Fig.1, the stationary counter-blade 21 is in the operative position, while the supplementary stationary counter-blade 23 is in the standby position, i.e. the non-operative position.
In other embodiments, the stationary support 22 may comprise more than two stationary counter-blades 21, 23, shaped differently, for generating variously-shaped perforation lines. In other cases, at least two of the stationary counter-blades fitted on the stationary support 22 may be identical to each other, in which case they are swapped (from the standby position to the operative position and vice versa) in the event of wear or breakage of the stationary counter-blade in the operative position, for example.
In some embodiments, a supplementary stationary counter-blade 23 may have a linear shape, so as to cooperate with the rotary blades 19 to form linear perforating lines orthogonal to the advancement direction of the web material N.
The stationary support 22 may be supported on the sides 17 of the load-bearing structure through eccentric supports, so that a small rotation of the stationary support 22 approaches or moves away the stationary counter-blade 21 with respect to the rotation axis A-A of the rotary blades 19, therefore adjusting the interference between the rotary blades 19 and the stationary counter-blade 21, 23.
The web material N is supplied along a path which extends between the rotary support 15 and the stationary counter-blade 21, so as to be subjected to the action of the rotary blades 19 and of the stationary counter-blade 21.
To obtain a gradual perforating action through the width of the web material N, the rotary blades 19 may be helical, in the sense that their cutting edge extends according to a helical line, arranged on an ideal cylindrical surface coaxial to the rotation axis A-A of the rotary support 15. The stationary counter-blade 21 may generally extend in a direction parallel to the axis A-A. However, as described below in greater detail, it has an undulated cutting edge or however with a development, i.e. an extension, which has a variable inclination with respect to the machine direction, so as to generate, in cooperation with the cutting edge of the rotary blades 19, a perforating line with a non-straight shape on the web material N. The machine direction is indicated with the arrow MD and it is the direction along which the web material N advances in the supply motion thereof through the perforating device 3.
In some embodiments, the stationary counter-blade 21 is formed by a single block having a length equal to the total length of the stationary counter-blade 21. In other embodiments, the stationary counter-blade 21 comprises a plurality of counter-blade segments aligned with each other along the stationary support 22. Figs. 2 to 6 show a single segment in a plurality of views and sections. The segment is indicated with 21.1. Each segment 21.1 comprises one or more through holes 21.2 for fixing screws, which serve to fix the segment 21.1 in a seat 24 (Fig.1) of the stationary counter-blade 21, formed in the stationary support 22. The use of segments shorter than the total length of the stationary counter-blade 21 may be advantageous with respect to the embodiment of a stationary counter-blade 21 consisting of a single block. For example, the division into a plurality of blocks or segments allows to replace single portions of the stationary counter-blade 21 in the event of local breakage or damage.
Each segment comprises faces 21.3, 21.4 adapted to rest on surfaces of the seat 24, and an outer surface 21.5, on which a portion of the cutting edge 26 of the stationary counter-blade 21 is formed. The outer surface 21.5 is approximately cylindrical and concave. The diameter of the outer cylindrical surface 21.5 and the protrusion of the cutting edge 26 from such cylindrical surface are such that the cutting edge 26 lies approximately on a concave cylindrical surface, whose radius R1 (Fig.4) is approximately equal to or slightly smaller than the radius of the cylinder enveloping the cutting edges of the rotary blades 19.
As shown in particular in Figs. 2 and 6, the cutting edge 26 of the stationary counter-blade 21, which is obtained by aligning the segments 21.1 to one another, has a non-straight development with an inclination with respect to the machine direction MD which varies along the longitudinal extension of the stationary counter-blade 21.
In the embodiment shown in Figs. 2 to 6 the cutting edge 26 of the stationary counter-blade 21 has a sinusoidal development, the symmetry line whereof being indicated with L-L. It should be noted that the illustrated shape is provided by way of example. In other embodiments, the shape of the cutting edge 26 of the stationary counter-blade 21 may be different. For example, the cutting edge 26 may consist of straight portions arranged to form a zig-zag line, or it may comprise straight portions and curvilinear portions.
Generally, the shape of the cutting edge 26 is such that, when the cutting edge 26 of the stationary counter-blade 21 cooperates with the cutting edge of a rotary blade 19, a non-straight perforation line is formed on the web material N, and in particular a perforation line which has a variable inclination with respect to the longitudinal direction of the web material, i.e., parallel to the direction to the longitudinal edges of the web material N.
The shape of the perforation line depends on the on the non-linear shape of the stationary counter-blade 21. For example, if the stationary counter-blade 21 has a sinusoidal shape, as shown in Fig.2, the cooperation between each rotary blade 19 and the stationary counter-blade 21 generates an undulated, in particular sinusoidal, perforation line as shown in P1 in Fig.8.
Fig.8 shows different shapes of the perforation line which may be generated on the web material N. P0 is a conventional linear perforation line, having a straight extgension orthogonal to the machine direction, that is to the longitudinal direction shown by arrow MD, along which the web material N develops. Other possible non-linear shapes of the perforation line are indicated with P2, P3, P4 and P5 .
The web material N is wound on rolls R, whose axial length is usually much longer than the axial length of the rolls intended for end consumption. Therefore, each roll R produced by the rewinder 1 is usually divided into several smaller rolls, each formed by a strip of web material with a width equal to a fraction of the width of the web material N. In Fig.8 there are shown three strips S1, S2, S3 obtained by cutting the web material N along the cutting lines T1, after winding into rolls. The development of the perforation lines shown by way of example in Fig.8, is preferably such that in a single strip S1, S2, S3 there is a development of the perforation line according to a variable orientation, that is with an inclination that does not remain constant along the width of the single strip S1, S2, S3. As described above, the perforation lines may have variable resistance, for example more resistant or less resistant in portions of strips S1, S2, S3 surrounding the cutting lines T1, T2, depending on whether one wants to facilitate the tearing of the perforation lines during normal use or if it is preferable to have a more resistant tearing on the edges so as to avoid inadvertent tearing of the perforation lines.
The position of each rotary blade 19 and the position of the stationary counter-blade 21 with respect to the rotation axis A-A may be such to generate a scissor cutting so as to obtain gradual perforation, thus reducing mechanical vibrations which are generated due to the cooperation between the rotary blade 19 and the stationary counter-blade 21.
To this end, it may be provided for that the cutting edge of each rotary blade 19 extends along a helical line lying on a cylindrical surface. Furthermore, the rotation axis A-A may form with the transversal direction CD, i.e., with the direction oriented at 90° with respect to the machine direction MD, an angle equal to the inclination angle of the helix with respect to the rotation axis A-A or different, for example as a function of supply rate of the web material.
For example, the inclination of the helix formed by the cutting edge of each rotary blade 19 with the rotation axis A-A may be comprised between 1° and 45°, preferably between 1° and 20°, even more preferably between 1° and 10°, for example between 2° and 5°.
The stationary counter-blade 21 is in turn arranged so as to develop along a median line which is inclined by the same angle as the inclination of the axis of the rotary support 15. In the case of the stationary counter-blade 21 with a sinusoidal cutting edge 26, the median line and the zero line of the sinusoid, indicated with L-L in Fig.2, i.e., the line which divides the cutting edge 26 into two symmetrical portions and around which there oscillates the line consisting of the development of the cutting edge 26. The line L-L is on the perforated web material N and it is orthogonal to the direction MD, i.e., to the edges of the web material N and therefore to the longitudinal extension direction of such web material.
There cannot be ruled out the possibility that the rotary blades 19 be arranged with the respective cutting edges along generatrixes of a cylinder, consisting of the on the enveloping of the cutting edges during the rotation around the axis A-A. In such case, the axis A-A will be arranged at 90° with respect to the machine direction MD, i.e., parallel to the transversal direction. Similarly, the line L-L, or generally the line around which the cutting edge 26 of the stationary counter-blade 21 oscillates, will in this case be arranged orthogonally to the machine direction MD, and therefore parallel to the transversal direction.
In order to obtain a perforating line which extends through the width of the web material N with a non-straight development, each cooperation point, that is the point of mutual contact, between the cutting edge of each rotary blade 19 and the cutting edge 26 of the stationary counter-blade 21 suitably has a relative velocity with respect to the web material N, the relative velocity having a component orthogonal to the direction MD.
To this end, the advancement velocity V_MD of the web material N in the direction MD is different from the tangential velocity of the cutting edge of the rotary blade 19. The latter is given by ω*r, where r is the distance of the cutting edge of the rotary blade 21 from the rotation axis A-A of the rotary blade 19, while ω is the angular velocity of the rotary support 15.
Typically, the velocity V_MD may be comprised between -40% and +40%, preferably between -25% and +25, more preferably between -10% and +10% of the peripheral velocity ω*r of the cutting edge of the rotary blade 19.
In the case of a sinusoidal-shaped cutting edge 26 of the stationary counter-blade 21, changing the difference between the two velocities V_MD and ω*R allows to change the width of the sinusoid which forms the perforating line P1 or P2 on the web material N.
In order to obtain this difference between the feed rate of the web material N and the peripheral velocity of the cutting edge of the rotary blade 19, a supply system is provided, which controls the supply of the web material N, and an actuator which controls the rotation of the rotary support 15, which are controlled to obtain the desired velocity difference. In Fig.1, the supply system, which is functionally connected to members which interact with the web material N controlling the feed rate thereof, is generally indicated with 51. This function is schematically shown by a functional connection between the block 51 and motor-driven rollers arranged along the path of the web material N, which may comprise, in addition to the guide rollers 53, 55, also the guide rollers 7, 9, 11, 13, as well as the unwinding members of the unwinders which supply one or more plies forming the web material N and possible further guide rollers similar to the guide rollers 53, 55.
In Fig.1, the actuator, for example an electric motor, which controls the rotation of the rotary support 15, is indicated with 57. The functional blocks 51, 57 may be integrated in a common control system, or they may be part of separate control devices and hierarchically subjected to a supervisor system of a higher level or provided in another manner. For example, a common control unit may be provided, which is interfaced with a plurality of motors for driving the rollers which control the advancement velocity of the web material N (and which therefore define the velocity V_MD in the perforating area), and which is further interfaced with the actuator which controls the rotation velocity of the rotary support 15 and therefore the peripheral velocity of the cutting edge of the rotary blades 19.
In some embodiments, it is advantageous to provide that the rotary blades 19 are less hard than the stationary counter-blade 21. In this manner, the wear due to the contact and the friction between the rotary blades 19 and stationary counter-blade 21 concentrates on the rotary blades 19. Having a simpler structure, with linear cutting edge, the latter have a lower cost.
For example, the stationary counter-blade 21 may have a hardness equal to 62 HRC or higher, for example 64 HRC or higher. The rotary blades 19 preferably have a lower hardness, for example lower than the hardness of the stationary counter-blade 21.
In order to reduce the impacts and the vibrations, and therefore the mechanical stresses due to the contact between the rotary blades 19 and stationary counter-blade 21, the cutting edge 26 of the latter may have a cross-section shaped so as to generate a contact that is more gradual and with lesser stresses. In Fig.5 the cross-section of the cutting edge 26 in an embodiment of this type is shown. The cutting edge 26 has a trapezoidal cross-section, with an outer side 26.1 inclined to form a guide surface.
Exemplifying embodiments have been described above and illustrated in the attached drawings. Those skilled in the skilled in the art will understand that various changes, omissions and additions to what is specifically described herein may be made without departing from the scope of protection of the invention as described in the claims below.
For example, in other embodiments, the cutting edge 26 of the stationary counter-blade 21 may have a different shape, for example as shown in Fig. 7.
Furthermore, in the description outlined above there has been described a perforating device for generating non-straight perforation lines on a web material. With a similar approach, there may be provided a cutting device which generates non-straight cutting lines. In this case, the cutting edges of the rotary blades 19 will be continuous instead of being interrupted by cavities or recesses.
Furthermore, in the illustrated embodiments the cutting edge 26 of the stationary counter-blade 21 is continuous, while the cutting edge of each rotary blade 19 is interrupted, i.e., it is provided with a plurality of teeth 19.1, interspaced by cavities or recesses 19.2. A different embodiment is not excluded, in which the cutting edges of the rotary blades 19 are continuous, while the cutting edge 26 of the stationary counter-blade 21 is serrated, i.e., it comprises a plurality of teeth separated by cavities or recesses.

Claims

A perforating or cutting device comprising:
a rotary support, adapted to rotate around a rotation axis and comprising a lateral surface extending along the rotation axis;

on the lateral surface of the rotary support, at least one rotary blade, carried by the rotary support and comprising a cutting edge;

a stationary support, on which at least one stationary counter-blade is fitted, arranged to cooperate in a contact relationship with the at least one rotary blade carried by the rotary support; and wherein during rotation of the rotary support the at least one rotary blade cooperates with the stationary blade to perforate or cut a web material supplied in a machine direction between the rotary support and the stationary support;
characterized in that: the stationary counter-blade comprises a cutting edge having a variable inclination with respect to the machine direction, to generate, when cooperating with the cutting edge of the at least one rotary blade, a perforation or cutting line with a non-straight shape on the web material.
The perforating or cutting device of claim 1, wherein at least one of said stationary counter-blade and said at least one rotary blade comprises a plurality of teeth, wherein adjacent teeth are separated from each other by a recess.
The perforating or cutting device of claim 1 or 2, wherein: the cutting edge of the at least one rotary blade has a straight shape and is arranged parallel to the rotation axis; the rotation axis of the rotary support is directed orthogonally to the machine direction; and the stationary counter-blade extends generally in a direction orthogonal to the machine direction.
The perforating or cutting device of claim 1 or 2, wherein: the cutting edge of the at least one rotary blade has a helical shape extending around the rotation axis; the rotation axis of the rotary support is inclined by an angle other than 90° with respect to the machine direction; and the stationary counter-blade extends generally in a direction inclined by an angle other than 90° with respect to the machine direction.
The perforating or cutting device of claim 4, wherein the at least one rotary blade has a linear cutting edge which extends in a helical fashion around the rotation axis of the rotary support, in particular with an angle greater than 0° and smaller than 45° with respect to the rotation axis of the rotary blade, preferably between 0° and 20°, more preferably between 0° and 10°, preferably comprised between 1° and 10°, or between 2° and 5°.
The perforating or cutting device of one or more of the preceding claims, comprising:
a supply system, for supplying the web material at a controlled velocity between the rotary support and the stationary support; and

a rotation actuator, for rotating the rotary support;
wherein the supply system and the rotation actuator are controlled to supply the web material between the rotary support and the stationary support at a velocity different from the peripheral velocity of the cutting edge of the at least one rotary blade.
The perforating or cutting device of claim 6, wherein the supply system and the rotation actuator are controlled to supply the web material with a difference between the linear velocity of the web material and the peripheral velocity of the cutting edge of the at least one rotary blade comprised between -40% and +40%, preferably between -25% and +25, more preferably between -10% and +10% of the peripheral velocity of the cutting edge of the at least one rotary blade.
The perforating or cutting device of one or more of the preceding claims, wherein the stationary counter-blade is fitted in a straight seat formed in the stationary support.
The perforating or cutting device of one or more of the preceding claims, wherein the rotary support comprises a plurality of rotary blades.
The perforating and cutting device of claim 9, wherein the rotary blades are equal to each other.
The perforating and cutting device of one or more of the preceding claims, wherein the stationary counter-blade is formed by a plurality of segments arranged aligned to each other along the stationary support.
The perforating and cutting device of claim 11, wherein said segments are replaceable independently from each other.
The perforating and cutting device of one or more of the preceding claims, wherein the stationary counter-blade has a cutting edge with a wedge-shaped or trapezoidal cross-section, forming a guide element for the cutting edge of the at least one rotary blade.
The perforating and cutting device of one or more of the preceding claims, wherein the stationary counter-blade comprises a cutting edge lying on a concave surface, in particular on a cylindrical surface with a diameter approximately equal to a diameter of a surface enveloping the cutting edge of the at least one rotary blade during the rotary movement thereof.
The perforating and cutting device of one or more of the preceding claims, wherein the stationary counter-blade has a hardness equal to or greater than 62 HRC, preferably equal to or greater than 64 HRC.
The perforating and cutting device of one or more of the preceding claims, wherein the at least one rotary blade has a hardness lower than the hardness of the stationary counter-blade.
The perforating and cutting device of one or more of the preceding claims, wherein the stationary counter-blade comprises a plurality of segments aligned with each other along a longitudinal extension of the stationary support, each segment being interchangeable independently from the adjacent segments, and each segment comprising a portion of the stationary counter-blade, so that the counter-blade portions of the segments arranged sequentially along the stationary support as a whole form the stationary counter-blade.
A machine for converting a web material, in particular paper or tissue paper, comprising a station for converting web material, and a perforating or cutting device according to one or more of the preceding claims, arranged upstream of the converting station.
A method for perforating or cutting a continuous web material, in particular paper or tissue paper, comprising the following steps:
supplying a web material according to a machine direction between a rotary support, on which at least one rotary blade is supported, and a stationary counter-blade; wherein the stationary counter-blade comprises a cutting edge having a variable inclination with respect to the machine direction;

rotating the rotary support and the at least one rotary blade around a rotation axis;

perforating or cutting the web material by cooperation of the at least one rotary blade with the stationary counter-blade generating on the web material perforation or cutting lines, each of which has a non-straight shape and a variable inclination with respect to the machine direction.
The method of claim 19, comprising the step of supplying the web material with a velocity different from a peripheral velocity of the at least one rotary blade.