EP1888442A2

EP1888442A2 - Rewinding machine, method for producing logs of web material

Info

Publication number: EP1888442A2
Application number: EP06745355A
Authority: EP
Inventors: Roberto Morelli; Mauro Gelli
Original assignee: Fabio Perini SpA
Current assignee: Fabio Perini SpA
Priority date: 2005-05-23
Filing date: 2006-05-19
Publication date: 2008-02-20
Also published as: KR20080033170A; CA2608969A1; WO2006126228A3; ITFI20050108A1; BRPI0611168A2; JP2008542151A; US20090302146A1; WO2006126228A2

Abstract

The rewinding machine comprises: a winding system (1, 2, 3) and a feed path for a web material (N) towards said winding system. Positioned along the feed path is at least one air jet severing member (23) to cause severing of the web material after winding of each log (R) has terminated.

Description

Rewinding machine, method for producing logs of web material

DESCRIPTION Technical field

The present invention relates to a rewinding machine for winding a web material to form logs for producing, for example but not exclusively, small rolls of toilet paper, kitchen towels and the like. More specifically, but not exclusively, the invention relates to a "peripheral" rewinding machine, i.e. in which logs are formed by winding the web material in a winding cradle composed of winding members in contact with the outer surface of the log. The invention also relates to a winding method and more specifically, although not exclusively, a "peripheral" winding method. State of the art

To produce logs of paper, tissue paper or other web materials, rewinding machines are used to which the material to be wound is fed, and which produce logs with a pre-established quantity of wound material. The web material is typically fed from unwinders, i.e. machines that unwind one or more reels of large diameter coming, for example, from a papermill.

The logs can be sold "as is", or can undergo further conversion operations; typically they are cut into rolls of smaller axial length, equivalent to the final dimension of the small rolls to be sold.

In some cases, rewinding is performed by central rewinding machines, i.e. in which the logs are formed around motorized spindles, on which winding cores made of cardboard or similar materials, can be inserted, which cores remain inside the logs. The latest rewinding machines are based on the peripheral or surface winding concept. In this case the log is formed in a winding cradle, defined by rotating winding rollers or other winding members, such as belts, or a combination of rollers and belts.

Also known are combined systems, in which winding is obtained by peripheral members, combined with a system to control the axis of the log during formation. In both central winding systems and in peripheral winding systems, machines are sometimes utilized in which the spindle or winding core is removed from the finished log, so that the final product takes the form of a log provided with a central hole, devoid of axial core. Examples of peripheral winding machines of this type are described in WO-A-0172620.

Rewinding machines, both of the peripheral and central type, are machines that operate in automatic and continuous mode, meaning that the_^ web material is fed continuously therein without stopping and substantially at a tendentially constant speed. The web material is provided with transverse perforation lines that divide the material into individual portions, which can be separated from the roll for final use. Typically, an effort is made to produce rolls with a specific and precise number of said portions or sheets.

When a roll or log has been completed, the exchange phase must be performed, during which the log is unloaded and the web material is severed, forming a final end of the completed log and an initial end of the subsequent log. The initial end starts to wind to form a new log. Severing preferably takes place at the level of a perforation line, so that the finished product contains a full and predetermined number of portions of web material. These operations take place without substantial variations in the feed speed of the web material and represent the most critical moment of the winding cycle. The feed speed of the web material reaches and exceeds, in the latest rewinding machines to produce tissue paper, speeds in the order of 1000 m/min, with winding cycles which are at times less than 1 second. It is therefore important to provide efficient, reliable and flexible systems to perform severing of the web material after winding each roll or log has terminated.

GB-A-1435525 describes a rewinding machine in which severing of the web material takes place by means of a blade or jet of compressed air that tears the web material or produces a loop that wedges between the new winding core inserted in the winding cradle and one of the winding rollers. The nozzles that produce the jet of air are positioned downstream of the nip for insertion of the cores, defined by two opposed winding rollers, belonging to a peripheral winding cradle. US-A-4327877 describes a rewinding machine in which severing of the web material takes place through the combined action of suction through the surface of one of the winding rollers and of pinching of the web material between the new core inserted in the winding cradle and the suction winding roller. Suction forms a loop of material which is pinched and pulled in the opposite direction to the direction of feed of the web material being wound around the log reaching completion.

GB-A-2150536 and US-A-5368252 describe methods and rewinding machines in which the web material is torn after winding has terminated solely by controlled acceleration of one of the winding rollers. The same system based on the principal of tearing the web material along a perforation line by acceleration of one of the winding rollers is described in EP-A-1.219.555.

GB-A-2105687 describes a method and a rewinding machine, in which severing of the web material takes place by cutting carried out by a blade in a channel of one of the winding rollers.

US-A-5137225 and EP-A-0199286 describe methods and rewinding machines in which tearing takes place by cooperation between a winding core and a fixed surface against which the core pinches the web material causing it to stop or temporarily slow down. IT-B-1.275.313 describes a device in which tearing of the web material is obtained by a core inserter, which cooperates with the main winding roller.

US-A-6056229 describes a rewinding machine, in which the web material is severed by pinching it between a fixed surface and a moving member, which also inserts the winding cores in the machine. Particularly reliable and flexible machine and method are described in

US-A-5979818. In this case, tearing is carried out by a moving member cooperating with one of the winding rollers around which the web material is driven, or with a belt driven around said roller and which supports the web material during feed towards the winding cradle. The difference in speed between the winding roller and the web material on the one hand and the moving member on the other causes tearing of the web material along a perforation line. With respect to previous tearing systems, this known rewinding machine allows extremely high winding precision to be reached, even at high speed, with a relatively simple and economical configuration, which also allows high production flexibility to be obtained.

WO-A-2004/096684 describes a rewinding machine which uses the same tearing system of the web material already described in the British patent 1435525, i.e. a jet of compressed air which, by acting on the web material, causes tearing thereof along the perforation line. In this case the system with - A - jets of pressurized air is positioned inside the cylindrical surface of the principal winding roller, around which the web material is driven. This configuration is particular complex and difficult to produce, and not devoid of defects. In the first place, if the system of compressed air nozzles is positioned inside the cylindrical casing of the roller, the latter must have a wide perforated area to obtain an adequate tearing effect on the web material. Moreover, very high air pressures are required, as the jet of air delivered from the nozzles must pass through the perforated wall of the winding roller rotating at high speed. Passing through this wall the jet of air loses a great part of its kinetic energy. In a modified embodiment the winding roller has annular grooves, positioned inside which are curved tubes terminating in blowing nozzles. This construction is complex and not very efficient. Moreover, in both embodiments the winding roller cannot have a smooth and regular surface, but must be provided with holes or annular grooves, which damage the web material during winding, decreasing the quality of the finished product.

From the evolution represented by the machines and by the methods described in the aforesaid patents, it is evident that there is a need to produce systems to tear and start winding which are increasingly efficient and reliable even at high speeds, and with which a high level of flexibility can be obtained, i.e. to allow easy variation of the winding parameters, in particular the length of web material wound on each log or the distance between subsequent perforation lines on the web material. Objects and summary of the invention

The object of the invention is to produce a winding method and a rewinding machine which are particularly efficient, economical and reliable and which guarantee a high level of production flexibility.

These and other objects and advantages, which will be apparent to those skilled in the art from reading the text hereunder, are in substance obtained starting from a rewinding machine for producing logs of web material, of the type illustrated in GB-A-1435525, comprising: a winding system with at least a first winding roller and a second winding roller defining therebetween a nip through which the web material is fed; a feed path of the web material towards said winding system; and a severing member which produces a jet of air to sever the web material after winding of each log has terminated. Characteristically, to obtain increased constructional simplicity with respect to other machines based on the same tearing principle by means of jets of air, and to obtain greater efficiency even at high speeds, according to the invention, the severing member is positioned along the feed path of the web material, upstream of said nip. The jet of air applied in a manner synchronized with the remaining machine functions and for a short period of time to the web material along the feed path causes a force orthogonal to the web material, which is under tension due to winding and which consequently tears. The nozzles producing the jets of air can be associated with an opposing surface on which the belts of the flexible member rest and run.

Typically, and preferably, tearing takes place along a perforation line produced on the web material normally provided along the path of said web material. The severing member can have one or more openings, in the form of holes, windows, slots or of any other suitable configuration, a series of aligned nozzles, a single nozzle per slot or a plurality of nozzles per slot, to apply one or more jets of compressed air to the web material.

The jet of air is phased with the position of the perforation line along which the web material is to be severed after winding of each log has terminated. In this way a number of perforation lines are obtained, and therefore a number of individual sheets of web material on each log is determined precisely. Moreover, the perforation line represents a stress riser point, with decreased tensile strength, which facilitates tearing.

The rewinding machine thus produced has considerable advantages with respect to known devices. In fact, it is characterized by the same operating flexibility and by the same reliability as the machines described in US-A- 5979818, but does not require the rotating mechanical member, which performs tearing of the web material. A smaller number of mechanical parts make the machine more economical, easier to run and also more reliable. Furthermore, elimination of the mechanical action of the device to tear the web material reduces wear, vibrations and noise. With respect to known systems in which tearing of the web material is performed by acceleration of one of the winding rollers, the machine according to the invention has advantages of cost, reliability and production speed, besides increased winding precision, with the possibility of more accurate and reliable adjustment of the position of the severing or tearing point of the web material, even at very high speeds.

With respect to known machines, which perform tearing through jets of pressurized air, greater precision in identifying the severing point of the web material is obtained, without having to utilize very complex constructional solutions. The principal winding roller around which the web material is driven can have a smooth surface devoid of holes, or can have annular grooves. In this case, however, belts, with a smooth exterior defining, with the roller, a continuous cylindrical contact surface with the web material, can be driven inside the annular grooves. The wall of the winding roller is no longer interposed between the compressed air nozzles and the web material, obstructing the effect of the air.

As will be apparent from the description of some embodiments, moreover, with the tearing system according to the invention it is possible - if required - to eliminate the glue used to start winding the web material on each core or winding spindle, with a series of advantages which will be apparent to those skilled in the art. Unlike other known devices which start winding without glue, with the system of the present invention it is possible to reach very high speeds and noteworthy reliability, as well as obtain a finished product of high quality, in which there are no inner turns characterized by creases, as is the case in known systems.

The inventive concept defined above can be applied both in rewinding machines producing rolls or logs with a winding core that is left inside the finished product, such as a cardboard or plastic core, and in machines producing rolls or logs without a winding core, in which the log is formed around a spindle or core that is subsequently removed from the wound product before it is cut into small rolls. The finished product is in this case devoid of central core but has an axial hole.

Advantageously, the rewinding machine has a winding core feeder, to feed winding cores to a feed path towards the winding cradle. When the rewinding machine is designed to produce logs around winding cores, a feed member for said cores can advantageously be provided along the feed path of the winding cores. The feed member can, for example, be composed of a flexible member comprising one or more belts defining a closed path. The nozzles of the severing member are advantageously positioned in the spaces between parallel belts. These belts can also be positioned at a considerable distance from each other, so that the severing system of the web material is composed of a very extensive line of compressed air nozzles with only a few interruptions and therefore very efficient. According to an advantageous embodiment of the invention, a rolling surface for the cores can be provided along the feed path thereof, forming with the feed member a channel for insertion of the winding cores. In this way, the cores fed to the feed path roll between the feed member and the fixed rolling surface. In an advantageous embodiment of the invention, the rolling surface and the feed member of the cores forming the channel for insertion of the winding cores are positioned so that the web material is fed between the core and the feed member when the core is in the feed path. In this way the core starts to roil along the feed path and, once the web material has been severed, the initial free end produced is wound around the core already in rotation. The compressed air severing device can be positioned along this channel and can be synchronized to sever the web material in front of the core, i.e. downstream thereto with respect to the direction of feed. Contrary to conventional systems that use jets of compressed air to sever the web material, in which the jets of air are placed closely adjacent to the winding rollers and in some cases even act in the nip therebetween, with a configuration according to the invention, the nozzles, or other equivalent blowing members, can be placed at a distance from the winding rollers. As will be apparent hereunder with reference to some examples of embodiment, this makes it possible to utilize alternative systems rather than glue, for example jets of air or electrostatic charges, to wind the initial free end of web material around the winding cores. This makes it possible to obtain a higher quality product, in which the innermost turns are also wound with increased regularity and less or even no creases. Moreover, the cost of expendable materials is reduced.

In a possible and preferred embodiment, the rewinding machine comprises an opposing surface, along which the web material and the feed member of the cores slide, and along which the severing member can be positioned.

The winding cradle can be produced in various ways preferably providing at least a first winding roller and a second winding roller. In this case, at least one flexible member, on which the web material fed to said winding cradle is in contact, can be driven around the first winding roller.

According to a further aspect, the invention relates to a method for producing logs of wound web material, comprising the steps of: - feeding the web material to a winding cradle, comprising at least a first winding roller (1) and a second winding roller (2), the web material passing through a nip (5) between said winding rollers (1 , 2);

- winding a first log (R) of web material;

- severing the web material with a jet of air after winding of said first log has terminated, forming a final free end (Lf) of said first log and an initial free end (Li) for winding a second log (R); characterized in that said jet of air is produced upstream of said nip between the first and the second winding roller and preferably in a channel for insertion of the winding cores, defined between a fixed surface on which the cores roll and a feed member of the cores, the web material being positioned between the core and the feed member.

Further advantageous features and embodiments of the rewinding machine and of the winding method according to the invention are indicated in the appended claims and will be described in greater detail hereunder with reference to some advantageous examples of embodiment. Brief description of the drawings

The invention will be better understood by following the description of non-limiting practical and advantageous examples of embodiment of the invention, represented in the accompanying drawings. In the drawings: Figures 1A to 1C show an operating sequence of a machine according to the invention in a first embodiment;

Figures 2A to 2D show an operating sequence of a machine according to the invention in a second embodiment;

Figure 3 shows a side view of a machine according to the invention in a further embodiment;

Figures 4A-4E schematically show the sequence of the phase to tear or sever the web material and to start forming the first turn of the new log around the new core, with the aid of jets of air and without glue;

Figures 5A-5D schematically show the operating phases of a variant of the embodiment in Figures 2A-2D;

Figure 6 shows a variant of the embodiment in Figure 3;

Figures 7 and 8 show two variants of the embodiment in Figure 6; and

Figures 9 and 10 show two variants of embodiment of the severing member in a configuration in which it is provided with a movement to "follow" the perforation on which severing of the web material is to take place. Detailed description of preferred embodiments of the invention

In the embodiment illustrated in Figures 1A, 1B and 1C, the winding machine comprises a winding cradle formed of three winding rollers and more specifically: a first winding roller 1 , a second winding roller 2 and a third winding roller 3. The three rollers 1 , 2, 3 rotate about axes parallel to one another and with peripheral speeds which - during the winding cycle - are substantially the same as one another, while they can vary, in a way known per se, at the end of winding to unload the completed log and/or to insert the new core, around which winding of the subsequent log has started, through a nip defined between the winding rollers 1 and 2.

The winding roller 3 is supported on a pair of oscillating arms 7, hinged about an oscillation axis 7A. The oscillating movement allows increase in the roll R being formed inside the winding cradle 1, 2, 3 and unloading of the completed roll along a chute 9.

The web material to be wound to form the logs R is indicated with N. It is fed along a feed path that passes through a perforator unit (not shown) which, in a known way, perforates the material N along perforation lines substantially orthogonal to the direction fN of feed of the material N. Downstream of the perforator unit the web material N is driven around a guide roller 11 , revolving about an axis parallel to the axis of the winding rollers 1, 2 and 3. The feed path of the web material then continues along a portion tangent to the rollers 1 and 11 , defined by a flexible feed member 13, composed of a plurality of belts, preferably flat and parallel with one another, driven around the rollers 1 and 11. The purpose of the feed member is above all to insert and feed the winding cores A around which the logs R are wound, as will be explained hereunder. As the belts forming the feed member 13 are driven around the rollers 1 and 11 , they are fed at the same speed as the web material N and therefore there is no relative movement between said material and the belts. One opposing shoe for each belt is positioned above the lower portion of the belts, to prevent deformation of the belts, which would nullify the driving effect of the core in the channel during transfer thereof.

Extending under the portion of the feed member which is in parallel with the web material N is a curved rolling surface 15, defined by a sheet or a folded section, by a plurality of sheets or folded sections parallel with one another, or by a comb structure. Defined between the rolling surface 15 and the feed member 13 is a channel for insertion and feed of the winding cores, indicated with 17, which has an inlet on the left side in the figures and an outlet substantially at the level of the nip 5 between the winding rollers 1 and 2. The terminal part of the channel is thus defined between the rolling surface 15 and the outer surface of the winding roller 1 around which the feed member 13 is driven, the rolling surface being curved to be approximately coaxial with the surface of the roller 1. The terminal part of the surface 15 penetrates annular grooves produced in the winding roller 2, to facilitate feed of the cores rolling on the surface 15 towards the nip 5 and from this to the winding cradle 1 , 2, 3.

A core inserter is provided in the vicinity of the inlet of the channel 17, composed of a rotating element 19 which, at the right moment, inserts a winding core A into the channel 17. The cores are conveyed to the inserter 19 by a chain conveyor 21. Operation of the core insertion mechanism is known to those skilled in the art, for example from one or more of the patents cited in the introduction of this specification and will not be described in more detail. The core insertion mechanism, indicated schematically in Figures 1A-1C, can be of the type shown and described with reference to Figure 6. The height of the channel 17 is the same as or slightly less than the outer diameter of the winding cores A, which therefore, when inserted in said channel by the inserter 19 are angularly accelerated and roll on the surface 15 fed by the movement of the feed member 13. The web material N remains pinched between the belts forming the feed member 13 and the core inserted in the channel.

Above the lower branch of the inserter member 13 a severing member of the web material is provided, indicated as a whole with 23 and including for example a series of blowing nozzles aligned according to a direction orthogonal to the plane of the drawing, i.e. orthogonal to the direction of feed of the web material and parallel to said material. The individual nozzles can be arranged in the free space between adjacent belts forming the feed member 13 of the winding cores A. These belts can also be spaced at a relative distance from one another, as a limited number of relatively narrow belts are sufficient to feed the cores by rolling along the fixed surface 15. Alternatively, or in combination, the nozzles can define a continuous row also at the level of the belts. The nozzles can be nozzles with a circular or elliptical hole or, in any case, suitable to produce a flow of compressed air of modest dimension, or can be laminar in shape and produce a narrow and elongated jet. In this latter case, one or more elongated nozzles can be provided.

The nozzles of the member 23 that produce jets of air can be associated with an opposing surface 24 on which the belts of the flexible member rest and run. The opposing surface 24 will preferably extend for the entire free lower portion of the belts 13A and can be composed of individual portions at the level of the belts, or of an element of the same width as the overall width of the belts 13 adjacent with one another, and optionally provided with guide grooves of the belts. In general, and preferably, however, the opposing surface 24 is produced so that it does not come into contact with the web material running parallel to and along it, to avoid obstructing the movement thereof. The severing member 23 produces jets of pressurized air against the web material N in the exchange step, i.e. when the log R is almost completed and the web material N must be severed to produce a final free end to be wound on the finished log R and an initial free end to be wound on a new core A inserted in the channel 17 to start winding a new log. Production of the jets of air is preferably synchronized with the passage of a perforation line, so that the jets of air strike the web material with force in the weakest point. The web material is normally already tensioned in the longitudinal direction solely through rotation of the rollers 1, 2 and 3, so that the high speed jets of air produced by the nozzle or nozzles of the severing member 23 cause tearing of the web material. Operation of the machine described hereinbefore is as follows. Figure 1A shows the instant immediately prior to tearing or severing of the web material. The log R wound around the winding core indicated with A1 is ready to be ejected from the winding cradle, while a new core A2 has just been inserted in the channel 17 by the inserter 19. As soon as it is inserted, the core is rapidly angularly accelerated to take the point of contact thereof with the web material to the same feed speed as the web material.

The rolling surface 15 has a comb structure or at least a series of notches which allows the inserter 19 to complete rotation about the axis of rotation thereof and to position itself for insertion of a subsequent core.

The letter P indicates the position of a transverse perforation line, produced on the web material N by the perforator (not shown), along which severing by tearing of the web material will take place. The perforation P is at the level of the severing member 23. The jets of air are controlled and phased to act when the perforation line P is in the position indicated in Figure 1A, or slightly downstream or slightly upstream in the direction of feed of the web material N. In this way, when the jets of air are activated, the web material is torn.

The core A2 is already in contact with the web material N upstream of the tearing area and has already been made to rotate. It constrains the web material N against the belts forming the feed member 13 and thus prevents the initial free end Li of the material N which was formed by tearing from being lost. The final free end Lf of the log R is finished being wound on said log, which is ejected by varying the peripheral speed of the roller 2 and/or the roller 3, in a way known per se. To facilitate tearing or severing of the web material by the jets of air, it is also possible to temporarily accelerate the winding roller 3 before activating the nozzles of the severing member 23. This acceleration, even of modest value, pre-tensions the web material to guarantee tearing as soon as the nozzles are activated. In the example shown, a line of glue has been applied to the surface of the core A2 parallel to the axis of said core. In the arrangement in Figure 1A this line of glue is slightly upstream of the pinching point of the web material N, and so after the core rolls for a short distance the material is glued thereto. It would also be possible for the core to be provided with two lines of glue staggered angularly from each other, one for the tail end of the finished log and one for attaching the leading end of the new log to the winding core.

As the rollers 1 and 11 continue to rotate, after tearing of the web material, the feed member 13 continues to roll and feed the core A2 along the channel 17. The point of contact between core and feed member 13 moves beyond the area of the nozzles of the member 23 which in the meantime are deactivated (Figure 1B) and the initial free end Li of the web material N continues to adhere to the core thanks to the line of glue applied thereon, to start winding of a new log. The finished log R is still in the winding cradle, although its unloading movement may have started. In this phase the jets of compressed air have already been shut off.

In Figure 1C the winding core A2 has completed another rotation through approximately 90° with respect to the position in Figure 1B and the area of the initial free end Li glued to the core starts to revolve therearound, being positioned in the area of pressure between the core and the rolling surface 15. Rolling of the core A2 continues until it reaches the winding cradle 1, 2, 3 passing through the nip 5. In the winding cradle forming of the subsequent log around the core A2 is completed, as the log R has been unloaded from the winding cradle. After winding of the new log around the core A2 has terminated, the exchange cycle described above is repeated.

Instead of using a glue to obtain adhesion of the initial free end Li around the core and forming of the first turn around the core, one or more series of blowing nozzles can be used, suitably positioned around the area in which the core receives the free end. This solution is facilitated particularly by the fact that there are no mechanical members under the rolling surface 15 to tear the web material, as is instead the case in other known machines. Moreover, the severing device or member 23 with its blowing nozzles is positioned at a distance from the winding rollers 1 and 2, so that there is ample space available to provide means other than glue to make the first turn of web material wind around the core. For example, nozzles can be provided positioned over and/or under the channel 17, suitably oriented to force the free end to wind around the core forming the first turn, as will be described hereunder with reference to a further embodiment. Figures 2A-2D show a second embodiment of the machine according to the invention, with a respective operating sequence. The same numbers indicate parts the same as or corresponding to those in the previous Figures 1A-1C. The main difference with respect to the previous example of embodiment consists in the increased distance between the rollers 1 and 11, the increased length of the surface 15 and the increased extension of the opposing surface 24 and of the portions of the belts 13A parallel to the rolling surface 15. The rest of the arrangement and operating sequence is substantially the same. Nonetheless, in the example shown in Figures 2A-2D, the core performs a complete rotation in the channel 17 before severing of the web material, as can be observed by comparing Figures 2A and 2C. The line of glue is indicated with C. Advantageously, the core is inserted with a device of the type shown in Figure 6, which prevents the core A2 from rotating around itself due to the inserting movement, and guarantees the angular position of the line of glue with respect to the web material. When the core is about to be inserted in the channel 17 (Figure 2A) it is in a position to come into contact with the web material after a slight rotation of the core and thus after limited feed thereof in the channel 17. Figure 2B shows the instant in which the line of glue C comes into contact with the web material. The letter P again indicates the position of the perforation line along which tearing of the web material will take place. In Figures 2A and 2B this perforation line is upstream of the core A2.

When the winding core A2 is in the position in Figure 2B, it yields a part of the glue C to a portion of the web material N downstream of the perforation line P along which the web material will subsequently be severed and in proximity to said line. Consequently, a part of the glue (indicated in the subsequent figures with C1) is transferred to the final free end of the log R.

Figure 2C shows the jets of air which tear the web material N along the perforation line P, which at this point has moved beyond the position of the winding core A2, and is downstream thereof with respect to the direction of feed of the web material. This is due to the fact that the axis of the core A2 moves along the channel 17 at half the feed speed of the web material, so that the point of contact between core A2 and web material N is also fed along the channel at a speed substantially equal to half the feed speed of the perforation line P. In the layout in Figure 2C the line of glue C is in the lower part of the core. To prevent the glue from soiling the rolling surface 15 during this movement, this surface can be made of sections positioned at a distance from one another, and the line of glue C can have breaks at the level of the sections.

In Figure 2C an auxiliary glue dispenser, composed of an oscillating element 20 which can be immersed in a glue reservoir 22, is indicated with a broken line. The oscillating element is shaped so that it can be inserted between the plates forming the surface 15 to touch the core A2 to apply in the desired position thereon a line of glue C, which can superimpose the line applied previously (or can be angularly staggered with respect thereto) and partly transferred in C1 to the final free end of the roll in the completion phase. In this way two results are obtained: the quantity of glue is re-established and a glue is applied that can have different qualities with respect to the glue previously applied and at least partly transferred to the final free end. The reason for this is that the final free end of the log must be glued lightly to be easy for the final user to open, while the initial free end of the log must adhere firmly and immediately, with as tacky a glue possible, to the new core to guarantee better grip. Alternatively, two lines of glue, of different quality and quantity, can be applied upstream of the inserter 19, so that the core is inserted in the channel 17 and comes into contact with the web material N phased with the perforation line P on which tearing will take place, i.e. with the two lines of glue each on a respective side of said line.

Downstream of the tearing system 23 a suction system can be provided acting between the belts 13A and respective opposing members 24, to keep the web material adhering to the belts 13 during the tearing phase performed by the jet of air and, subsequently to tearing, to constrain the final end in contact with the belts 13A also after tearing has been performed, to prevent creases from forming or loss of control of said final end. This suction system can advantageously be provided for all the examples of embodiment of the machine of the present invention, also illustrated in the continuation of this description. In Figure 2C the suction system is indicated with a broken line and marked with the number 26, while in the other figures it is omitted for simplicity. The system 26 can, for example, act through the free space between adjacent belts 13. In Figure 2D the final free end Lf formed by tearing and provided with a line of glue C1 transferred from the core A2 finishes being wound on the log R during the unloading phase from the winding cradle, while the core A2 is fed further along the channel 17, to bring the line of glue C into contact with the web material for the second time. Since at this time the web material N has already been severed, the initial free end Li adheres to the core and winding of the new log starts. The core A2 will continue to roll and be fed along the channel 17 to reach the nip 5 and then move beyond it to enter the winding cradle 1 , 2, 3. Figure 3 shows an embodiment similar to the embodiment in Figures 2A-

2D. The same numbers indicate the same or equivalent parts in the two configurations. In this case, however, the channel 17 and the rolling surface 15 extend rectilinearly and the winding rollers 1 and 2 have the same diameter. This forces the winding cores to take a rectilinear path. This is particularly advantageous when movement of the cores is controlled by spindles inserted inside said cores, as described, for example, in WO-A-02055420.

Figures 4A -4E show - limited to the tearing area of the web material N, an example of embodiment in which winding around the new core A2 of the initial free end Li produced by tearing of the web material takes place without the use of glue. The severing member 23 is produced as already described. The jet or jets of air produced thereby per se form an element that facilitates starting to wind the initial free end Li around the new winding core.

Moreover, in this case a further series of nozzles, indicated with 85, is positioned under the rolling surface 15. While the nozzles of the severing member 23 are fixed, the series of nozzles 85 oscillates about a horizontal axis, transverse with respect to the direction of feed of the web material N. The oscillating movement is represented in the sequence in Figures 4A-4E.

Operation of the machine in this example of embodiment is as follows. When the core A2 is upstream of the nozzles forming the severing member 23, these are activated and the web material is torn or severed at the level of the perforation line P, which is approximately at the level of said nozzles. The jets produced by the severing member 23 push the free end 23 downwards, i.e. towards the rolling surface 15. In this way the free end Li tends to wind around the core A2. The jets of air produced by the nozzles 85 urge the free end to wedge between the core A2 and the surface 15. When, during the rolling motion thereof, the core A2 moves beyond the vertical plane containing the axis of oscillation of the oscillating lower nozzles 85, these start to oscillate in a clockwise direction, thereby rotating the jet of air produced, so that it is oriented correctly to push the initial free end Li to complete forming the first turn around the core A2. Further inclined nozzles 81 and 83 (shown in Figure 4B and omitted in the remaining figures for simplicity and clarity of the drawing), facilitate winding of the initial portion of web material around the new core. When the first turn has been completed, the web material N is correctly engaged with the new core and winding of the new roll starts. .

From the description of the embodiment shown in Figures 4A-4E, it is apparent that the first turn, i.e. the innermost turn, of the log formed is devoid of fold, i.e., is not folded back in the opposite direction with respect to the direction of winding of the remaining part of the web material, as is the case in the embodiments described in the previous examples. This is true both in the case of log devoid of central core, i.e. with a hole left by removing a removable and recyclable core, and in the case of log formed around a core which remains inside the log. Moreover, this advantageous conformation of the log is also obtained in the case of combined use of glue and air nozzles, obtaining an advantageous result which was previously impossible when gluing was performed with a longitudinal line of glue.

Besides the advantages mentioned above, with the severing system with jets of air, the machine can also be adapted more easily to different diameters of winding core. In fact, the winding cores are inserted in a channel 17 delimited by a rolling surface 15 which is for the most part rectilinear and optionally has a curve only in a terminal portion. It is therefore possible to adapt the machine to cores of variable diameter simply by translating the sections forming the rolling surface 15, together with the lower roller in the example shown, in particular in the configuration in Figures 6, 7 and 8.

In some embodiments, and in particular the one in Figures 1A-1C, the rolling surface 15 could be composed of a simple sheet, optionally interrupted to allow passage of the inserter 19, while it does not require to have a comb structure for the entire extension thereof. This also prevents damage to the first turn of the web material, caused by the mark left by the plates of the comb structure.

The use of a pneumatic severing system of the web material makes operation more regular and less subject to wear, noise and vibrations, with respect to those in which the web material is severed by pinching the material against a winding roller or a belt by means of a mechanical member moving at a different speed to the feed speed of the web material. Moreover, all the advantages of reliability and flexibility of previous systems are maintained. The ample space available for the nozzles of the member 23 allows a decrease in the flow rate and pressure of the air, resulting in energy saving and further reduction in noise and vibrations with respect to systems which house the severing nozzles of the web material inside the cylindrical surface of the winding roller. The surface of the web material is not damaged by the presence of holes or grooves in the winding roller. The severing member can be regulated in a position along the extension of the channel 17. This facilitates regulation and calibration of the machine, as it makes it simpler to phase the action of the blowing system with respect to the position of the perforation line. The position of the severing member 23 forms an added regulation parameter with respect to control of opening and closing of the blowing nozzles. This is easy to obtain as the distance between the rollers 1 and 11 is considerable with respect to the portion traveled by the web material N during the very short activation time of the blowing nozzles of the severing device 23. Consequent advantages are obtained with respect to conventional solutions in which the jets of air are inside the winding roller. The slots or holes through which the jets of pressurized air pass can also act progressively on the web material N in the direction of feed thereof. This is obtained by making the jets of air produced by the severing member move in the direction of feed of the web material, so that the jets of air act along a thin line moving in the same direction of feed of the belts 13A and of the web material N, allowing said jets of air to act in a concentrated area and for a longer time.

Figures 9 and 10 show two possible configurations of the severing member provided with this function.

Figure 9 shows a diagram in which the severing member 23 is produced in a block provided with a first chamber 51 in which pressurized air is contained, delimited inferiorly by a wall 61 provided with slots or holes 62, which can be opened and closed by a sliding valve 67, provided with slots or holes 68, which can be moved alternatively to the level of the holes or slots 62 or staggered with respect thereto. Under the sliding valve 67 is an opening 53 (continuous or discontinuous, which extends transverse to the direction of feed of the web material N and which is closed inferiorly by a plate 54 provided with an alternating movement according to the double arrow f54. The plate 54 has a slot 55 transverse to the direction of feed of the web material N, which moves forward in concurrence with the web material N when the severing member 23 must perform severing.

Operation of the severing member 23 in this configuration is as follows. When a perforation line P at the level of which the web material must be severed is almost under the opening 53, the slot 55 is approximately at the level of the left end (in the drawing) of said opening, optionally in a position to close communication of the opening 53 with the outside. The valve 67 is open (position shown in the drawing), and therefore the air in the chambers 51 and

53 is pressurized. While the perforation P continues to move forward, the plate

54 moves forward in concurrence with the web material, so that for a certain amount of time a blade of air (closely adjacent to or at the level of the perforation line P) acts on the web material, advancing with said material and therefore characterized by a longer action time on the web material and in particular on the perforation P than the time obtained when using a fixed jet of air. Severing of the web material can therefore be obtained with lower air pressures and flow rates.

It must be understood that the slot 55 can also be discontinuous or replaced by a series of aligned holes.

After severing, the valve 67 closes the slots 62, allowing the plate 54 to return to the initial position without pressurized air acting on the web material N. Figure 10 shows a severing member 23 comprising a plurality of nozzles

23A aligned transverse to the direction of feed of the web material N and oscillating about a transverse axis A. Figure 10 shows three distinct positions taken by the oscillating nozzles 23A in the operating phase are indicated with a broken line and with a continuous line. The direction of oscillation is indicated with f23. In this way too a jet or blade of air acting for a longer time on the perforation line or in proximity thereto is obtained, to further ensure correct tearing.

As the web material N is normally fed at a higher speed than the speed that can be reached by the jet or jets of compressed air, they do not always act precisely on the perforation P but will start to act downstream thereof and stop acting upstream thereof, passing through a position of maximum efficiency in which they are aligned with the perforation. In this way, improvement of the tearing effect is obtained. In substance, in both the solutions in Figures 9 and 10, jets of pressurized air which follow the perforation moving forward with the web material N are obtained.

This principle can also be adopted advantageously in rewinding machines of other types, in which compressed air is used to sever the web material. For example, when the jets of air are produced inside the winding roller around which the web material is driven, it is possible for oscillating nozzles or other means to be provided inside the winding roller (which has a perforated surface) to produce a jet which follows, for a certain curve, the rotational movement of the roller. Alternatively, coaxially to the roller, housed inside the annular grooves produced in said roller, nozzles can be provided which have a rotational or oscillatory movement synchronized with the position of the perforation line, again to follow the perforation line on which they must act. Also in this case, this offers the advantage of improving severing of the web material also at high speeds and optionally decreasing air consumption. This has an advantage also in terms of economizing and reducing machine noise.

Therefore, in general the invention also relates to a rewinding machine comprising a peripheral winding unit with a system to sever the web material after winding has terminated with a severing member which produces at least one jet of air to sever the web material after winding has terminated, wherein said severing member produces a jet moving in the direction of feed of the web material during the web material-severing phase, to track the perforation line on which the web material is to be severed.

The embodiment in Figures 5A to 5D show a variant of execution of the machine in Figures 2A-2D. The same numbers indicate the same or corresponding parts. The parts of the machine which remain the same are not described again. The substantial difference consists in the presence of electrostatic bars to make the initial free end Li of the web material torn by the blowing nozzles adhere to the new winding core, with consequent elimination of the glue. Preferably, as in Figure 4, in the configuration in Figure 5 it is also possible to obtain wound logs in which the first turn, i.e. the innermost turn against the core, is devoid of fold.

More specifically, an electrostatic charging bar, indicated with 501 , is positioned in the space inside the closed path formed by the feed member 13. A second bar, indicated with 503, is positioned under the rolling surface 15. These bars and the high voltage generators connected thereto are known per se in the art and are used, for example, to electrostatically charge plastic films, or - in contrast - as ionizers to eliminate electrostatic charges from plastic films or other products. Electrostatic charging devices which can be used in this application can, for example, be the devices marketed by Haug GmbH & Co KG (Germany) or by Haug Biel AG (Switzerland) with the codes ALS-A and ALS-R. The bars 501 and 503 apply charges of the opposite sign, so that the web material N is charged with charges of one sign and the cores are charged with the opposite sign. The sign of the charges can depend on the material of which the web material N and the cores A are made.

It would be possible to use a single bar or also several bars of the same sign and positioned to charge only the cores or, although this is less preferable, only the web material. In any case, reciprocal adhesion between cores and web material always occurs as a result of the electrostatic charges of opposite sign. Operation of the machine described above is as follows. Figure 5A shows the initial instant of insertion of the new core A2 in the channel 17, on which winding of a new log will start after completion of the log R wound around the core A1. Figure 5B shows the subsequent instant in which the core A2 is in contact with the rolling surface 15 and with the web material N which is pinched between said core and the member 13. The core is rolling on the surface 15 and is angularly accelerated to take the point of contact thereof with the web material N to the same feed speed of said material.

Figure 5C shows the instant immediately prior to tearing or severing of the web material. The log R wound around the winding core A1 is ready to be ejected from the winding cradle, while the new core A2 is traveling between the two bars 501 , 503 and is electrostatically charged by the bar 503, while the bar 501 charges, with the opposite sign, a portion of the web material adjacent to the area in which it will be severed and in which the initial free end that must adhere to the new core A2 will be formed. As can be seen in Figures 5C and 5D, the rolling surface 15 has a comb structure formed of non-metal elements (or in any case in which the rolling surface of the winding cores is made of or covered with insulating material), or at least a series of notches which allows the inserter 19 to complete rotation about the axis of rotation thereof and position itself to insert a subsequent core.

The letter P indicates the position of a transverse perforation line, produced on the web material N by the perforator (not shown), along which the web material will be severed by tearing. The perforation P is substantially at the level of the severing member 23. The nozzles of the severing member 23 are controlled and phased to act when the perforation line P is in the position indicated in Figure 5C, or slightly downstream or slightly upstream in the direction of feed of the web material N. In this way, when the jets are activated, the web material is torn or severed.

As can be seen in Figure 5C, the core A2 is already in contact with the web material N upstream of the tearing area and has already been made to rotate and been electrostatically charged by the bars 501, 503. When the tension induced as described above causes the web material to tear along the perforation line P, the core A2 constrains the web material N against the belts forming the feed member 13 and consequently prevents the initial free end Li of web material N formed by severing from being lost.

The final free end Lf of the log R terminates winding thereon, and is ejected as described previously.

The electrostatic charge applied to the core A2 immediately prior to tearing or during tearing of the web material N (optionally in combination with the charge of opposite sign applied to the web material N) makes the initial portion of web material electrostatically attract to the core and adhere thereto, as if a glue had been applied to the core (Figure 5D). The immediate spatial and temporal vicinity between electrostatic charge of the core and tearing of the web material N prevent dispersion of the electrostatic charges and make electrostatic attraction very efficient.

As the rollers 1 and 11 continue to rotate, after severing of the web material the feed member 13 continues to roll and feed the core A2 along the channel 17. The point of contact between core and feed member 13 moves beyond the area of the severing member 23 and the initial free end Li of the web material N adheres to the core as a result of the electrostatic charges thereon, to start winding a new log.

After winding of the new log around the core A2 has terminated, the exchange cycle described above is repeated. Figure 6 shows a modified embodiment, in which the electrostatic charges are used in combination with glue. The same numbers indicate parts the same as or corresponding to those of the embodiment illustrated in the previous figures. In the example in Figure 6, the terminal part of a chute 601 for the winding cores A is positioned upstream of the mouth of the channel 17. The first core of the row is engaged by an inserter composed of a member 603 rotating about an axis 603A, which supports a fixed jaw 605 and a moving jaw 607 operated by an actuator 609 supported by the rotating member 603, the operation of which will be described hereunder.

Positioned under the chute 601 is a glue applicator 611 comprising a glue reservoir 613, dipped into which is an element 615, provided (in the example shown) with an alternate movement to be dipped into the glue and removed from the glue to apply a line of glue to the core which is in the position Ax.

Operation of the machine in the configuration in Figure 6 is as follows. When a log R is reaching completion, a (continuous or discontinuous) line of glue is applied to the core in the position Ax by means of element 615, which collects it from the reservoir 613. The core is engaged by the fixed jaw 605 and by the moving jaw 607 supported by the rotating member 603. At the moment in which the new core must be inserted in the channel 17, the rotating member 603 rotates clockwise to take the jaws from the position to pick up the core in the position Ax to the position to insert said core into the channel 17, pushing the core between the rolling surface 15 and the web material N driven on the flexible member 13. The core thus inserted tends to start to rotate rolling on the surface 15, and feed thereof is permitted by opening of the moving jaw 607 controlled by the actuator 609. Thanks to use of the jaws 605, 607, the angular position in which the core

A is inserted in the channel 17, and therefore also the position of the line of glue applied to the core, are controlled in a reliable way and are therefore precise. The position of the line of glue is phased with respect to the perforation line P along which the web material N is to be severed, so that when the core starts to roll on the surface 15, the line of glue touches the web material immediately downstream of the perforation line P, at the level of the area of material which, after severing, will form the final free end Lf of the completed log R. In this way, a line of glue is applied to the final free end Lf to close the final free end without the need for a gluing unit downstream of the rewinding machine. To allow the jaw for gripping the core to return to the initial position, the subsequent core can be temporarily constrained by a constraining system, such as a moving stop.

Adhesion of the initial free end Li, obtained by severing the web material N to the core, instead takes place prevalently as a result of electrostatic attraction between initial free end Li and core, according to the methods already defined with reference to the previous examples of embodiment.

Severing of the web material can take place as described above by means of blowing nozzles forming the severing device or member 23. The glue can also be applied to the web material at the level of the final free end Lf using different methods, such as direct application, with a spray system or the like.

Figure 7 shows an embodiment similar to with one in Figure 6, with a modification in the arrangement of the machine members. The same numbers indicate parts the same or equivalent to those in Figure 6. Different consecutive positions taken by the new winding core in the insertion phase are visible. The substantial difference with respect to the configuration in Figure 6 consists in the fact that the positions of the members 23 and 501 are reversed so that the winding core can be charged before or during tearing, while the web material can be charged during or after tearing.

As a further variant of embodiment, two electrostatic bars 501 can be positioned respectively upstream and downstream of the blowing device 23 and over the channel for feed of the cores and two electrostatic bars 503 can be positioned thereunder. This solution is shown in Figure 8. In all the examples of embodiment shown in Figures 5, 6, 7 and 8, an electrostatic bar is mentioned, but it is understood that the term electrostatic bar can mean a single bar or a series of electrostatic bars placed adjacent to one another.

The drawing only shows practical embodiments of the invention, which can vary in forms and arrangements without however departing from the scope of the concept in which the invention is based. Any reference numerals in the appended claims are provided purely to facilitate reading thereof in the light of the description and accompanying drawings, without limiting the scope of protection in any way.

Claims

1. A rewinding machine for producing logs of web material comprising: a winding system (1 , 2, 3); a feed path of the web material (N) towards said winding system; said winding system including at least a first winding roller (1) and a second winding roller (2), defining therebetween a nip (5) through which the web material (N) is fed; and a severing member (23) which produces at least one jet of air to sever the web material after winding of each log (R) has terminated, characterized in that said severing member is positioned along the feed path upstream of said nip.

2. Rewinding machine as claimed in claim 1 , characterized in that said severing member is in a substantially fixed position.

3. Rewinding machine as claimed in claim 1, characterized in that said severing member moves at a substantially different speed with respect to the feed speed of the web material.

4. Rewinding machine as claimed in one or more of the previous claims, characterized by a feeder (19, 21 ; 603) of winding cores (A1 , A2), to feed winding cores in a feed path (17) towards said winding cradle (1, 2, 3).

5. Rewinding machine as claimed in claim 4, characterized in that at least a feed member (13, 13A) for said winding cores, which advances at a speed substantially the same as the speed of the web material, is positioned along said feed path (17).

6. Rewinding machine as claimed in claim 5, characterized in that a rolling surface (15) for said cores is positioned along said feed path (17), forming with said feed member (13) a feed channel (17) for the winding cores.

7. Rewinding machine as claimed in claim 6, characterized in that said severing member (23) is positioned along said feed channel (17) on the opposite side with respect to the rolling surface (15).

8. Rewinding machine as claimed in claim 7, characterized in that said severing member is positioned outside the feed channel (17) on the side of said feed member (13).

9. Rewinding machine as claimed in claim 6, 7 or 8, characterized in that said rolling surface and said feed member of the cores are positioned so that the web material is fed between the core and the feed member (13) when the core (A1 , A2) is in said feed path (17).

10. Rewinding machine as claimed in one or more of the previous claims, characterized by an opposing surface (24) positioned upstream of said nip and along which the severing member (23) is positioned.

11. Rewinding machine as claimed in claims 5 and 10, characterized in that said at least one feed member causes feed of the cores along said opposing surface (24).

12. Rewinding machine as claimed in claims 6 and 11 , characterized in that said opposing surface (24) is positioned opposite said rolling surface (15), the cores (A1 , A2) being inserted between said opposing surface and said rolling surface, with the web material (N) positioned between the cores and the opposing surface.

13. Rewinding machine as claimed in claim 9, 10, 11 or 12, characterized in that said opposing surface (24) is a fixed surface.

14. Rewinding machine as claimed in one or more of claims 5 to 13, characterized in that said feed member comprises at least one flexible member

(13A), the severing member being positioned along the channel defined by said rolling surface and said flexible member, on the outside of the channel on the side of the flexible member.

15. Rewinding machine as claimed in claim 14, characterized in that said flexible member (13A), on which the web material fed towards said nip is in contact, is driven around the first winding roller (1) and around at least a second guide roller (11).

16. Rewinding machine as claimed in claim 5, characterized in that said feed path of the cores is substantially rectilinear.

17. Rewinding machine as claimed in claims 15 and 16, characterized in that said feed path, said nip and said first and second winding roller are arranged and designed so that the winding core is fed along a substantially rectilinear trajectory along said path and during the winding phase in contact with said first and second winding roller.

18. Rewinding machine as claimed in one or more of the previous claims, characterized in that said at least one severing member comprises at least one blowing nozzle to produce a jet of air at high speed transverse to the direction of feed of the web material.

19. Rewinding machine as claimed in one or more of the previous claims, characterized in that said severing member comprises at least one slotted nozzle, oriented in a transverse direction with respect to the direction of feed of the web material.

20. Rewinding machine as claimed in one or more of the previous claims, characterized in that said severing member comprises a plurality of nozzles aligned transverse to the direction of feed of the web material.

21. Rewinding machine as claimed in one or more of the previous claims, characterized by glue applicator means to apply at least one glue to said cores.

22. Rewinding machine as claimed in one or more of the previous claims, characterized by blowing nozzles (85) to facilitate winding of the free end around the winding core.

23. Rewinding machine as claimed in claim 22, characterized in that it comprises at least one series of blowing nozzles (85) positioned substantially at the level of the severing member (23) of the web material.

24. Rewinding machine as claimed in claim 23, characterized in that said series of blowing nozzles oscillates or rotates about an axis transverse with respect to the direction of feed of the web material.

25. Rewinding machine as claimed in one or more of claims 22 to 24, characterized in that said series of blowing nozzles (85) is positioned on the opposite side of the feed path of the cores with respect to said first and to said second series of blowing nozzles (83, 85).

26. Rewinding machine as claimed in one or more of claims 22 to 25, characterized in that it is devoid of means to apply glue to the winding cores, winding of each log commencing by means of said blowing nozzles.

27. Rewinding machine as claimed in one or more of the previous claims, characterized in that the feed path of the cores is arranged and designed so that each core rolls along said path by an extent sufficient to transfer a part of glue previously applied to said core to a portion of web material that will form the final free end of the log (R).

28. Rewinding machine as claimed in one or more of the previous claims, characterized in that it comprises at least one electrostatic device (501 , 503) to apply electrostatic charges to the web material and/or to the winding cores to start winding of each log.

29. Rewinding machine as claimed in one or more of the previous claims, characterized in that said jet of air is provided with a movement to follow the web material.

30. Rewinding machine as claimed in one or more of the previous claims, characterized in that it comprises a suction member (26) positioned downstream of the severing member.

31. Method for producing logs of wound web material, comprising the steps of:

-feeding the web material to a winding cradle, comprising at least a first winding roller (1) and a second winding roller (2), the web material passing through a nip (5) between said winding rollers (1 , 2); -winding a first log (R) of web material;

-severing the web material with a jet of air when winding of said first log has terminated, forming a final free end (Lf) of said first log and an initial free end (Li) for winding a second log (R); characterized in that said jet of air is produced upstream of said nip between the first and the second winding roller.

32. Method as claimed in claim 31, characterized in that the web material is fed parallel to an opposing surface (24), at the level of which said jet of air is applied.

33. Method as claimed in claim 32, characterized in that said opposing surface is fixed.

34. Method as claimed in claim 32, characterized in that said opposing surface moves at a different speed with respect to the feed speed of the web material.

35. Method as claimed in one or more of claims 32 to 34, characterized in that said logs of web material are wound on winding cores (A1 , A2), said cores being fed along an insertion path (17) towards said winding cradle (1, 2, 3).

36. Method as claimed in claims 32 and 35, characterized in that said opposing surface extends along said feed path.

37. Method as claimed in claim 35 or 36, characterized in that a winding core (A1 , A2) is fed along said opposing surface, with the web material (N) fed between the opposing surface and the winding core, the core being fed in contact with the web material at the same feed speed as the web material.

38. Method as claimed in claim 37, characterized in that said jet of air is applied downstream of the position of said core along the feed path causing severing of the web material downstream of said core.

39. Method as claimed in one or more of claims 35 to 38, characterized in that a feed member of the cores is provided along said feed path.

40. Method as claimed in claim 39, characterized in that said feed member of the cores is fed at a speed substantially the same as the feed speed of the web material (N).

41. Method as claimed in claim 39 or 40, characterized in that the web material (N) is made to pass between said feed member and the core which presses the web material against the feed member.

42. Method as claimed in one or more of claims 35 to 41, characterized in that a glue (C) is applied to said winding cores (A1 , A2).

43. Method as claimed in claim 42, characterized in that said glue is applied according to at least one longitudinal line, i.e. extending along the axial extension of said core.

44. Method as claimed in claim 42 or 43, characterized in that at least a part (C1) of said glue (C) is transferred to a portion of web material belonging to the final free end (Lf) to close the final free end of said log.

45. Method as claimed in one or more of claims 35 to 44, characterized in that winding of the initial free end (Li) around said winding core is started or facilitated by one or more jets of air.

46. Method as claimed in one or more of claims 31 to 45, characterized in that the web material is made to adhere to the winding core by means of electrostatic charges.

47. Method as claimed in one or more of claims 31 to 46, characterized in that the final free end (Lf) of the web material is retained by means of suction.

48. A rewinding machine comprising a peripheral winding unit with a severing member which produces at least one jet of air to sever the web material after winding has terminated, wherein said severing member produces a jet moving in the direction of feed of the web material during the phase to sever the web material.

49. Method for severing a web material provided with transverse perforation lines and moving along a feed path, wherein a jet of pressurized air is directed against said web material, characterized in that said jet of air is moved in the direction of feed of the web material.

50. Method for producing logs of web material, wherein after winding of a first log has terminated, the web material is severed by means of a jet of pressurized air directed against the web material at the level of a transverse perforation line, and wherein after the web material has been severed, winding of a subsequent log starts, wherein said jet of pressurized air moves in the direction of feed of the perforation line to increase the time of action of the jet of air on the web material in proximity to the perforation line.