ES2788683T3 - Coil Sawing Machine with Grinding Wheels and Grinding Procedure - Google Patents

Abstract

Sawing machine (1) for cutting coils of web material, comprising: a feed path (PA) for the coils (L) to be cut; a cutting head (5) arranged along the feed path (PA); a disk-shaped cutting blade (9), which is mounted on the cutting head (5), rotates around an axis of rotation (B-B) and is provided with a cyclical movement to cut the coils (L); two grinding wheels (32, 34), which are arranged and configured to grind two sides of a cutting edge (9B) of the disc-shaped cutting blade (9), and each of which rotates around its own axis of rotation (CC; DD); wherein the grinding wheels (32, 34) are idly supported and driven in rotation by friction with the disc-shaped cutting blade (9); characterized in that the grinding wheels (32, 34) are arranged with respect to the disc-shaped cutting blade (9) so that, in a contact zone (Z32, Z34) between each grinding wheel (32; 34) and the disc-shaped cutting blade (9), the grinding wheel (32; 34) has a speed directed towards the inside of the cutting edge; The grinding wheels (32, 34) are arranged relative to the disc-shaped cutting blade (9) so that the contact areas (Z32, Z34) between the grinding wheels (32, 34) and the blade disc-shaped cutting wheels (9) are arranged between two planes (P32; P34), each of which contains the axis of rotation (CC, DD) of a respective one of the grinding wheels (32; 34); said planes are approximately parallel to each other and to an additional plane (P) containing the axis of rotation (BB) of the disc-shaped cutting blade (9), said plane containing the axis of rotation (BB) of the cutting blade. disc-shaped cut (9) that is arranged between the two planes (P32, P34) that contain the axes of rotation (CC; DD) of the grinding wheels (32, 34).

Description

DESCRIPTION

Coil sawing machine with grinding wheels and grinding procedure.

Technical field

The present invention relates to the field of machines for processing web material reels, in particular, but not limited to, reels of paper, for example, but not limited to, tissue paper or the like for producing toilet paper, kitchen paper and the like. .

Previous technique

In many industrial fields, reels of significant axial dimensions are produced for the production of wound web material rolls and subsequently cut into smaller rolls, that is, into rolls of smaller axial dimension intended for packaging and marketing. Some typical examples of this type of processing are in the field of converting tissue paper, to produce rolls of toilet paper, kitchen towels and the like. In this field, layers of cellulose material are produced by continuous machines and wound on so-called mother reels. The latter are unwound and rewound in rewinding machines, to form reels, the axial length of which corresponds to the width of the layer produced by the paper mill and is equal to a multiple of the axial length of the products to be marketed.

Sawing machines are then used to cut the coils into rolls of smaller axial dimensions, intended for packaging and marketing. Some examples of sawing machines of this type are disclosed in documents US6786808, US5522292, US20060000312, US20060011015 and WO201603125. Sawing machines for coils of wound web material, especially tissue paper, typically comprise a feed path for the coils to be cut and a cutting head arranged along said feed path. The cutting head comprises one or more disk-shaped cutting blades that rotate around their axis and also have a cyclical movement (a rotary or oscillating movement, for example) to sequentially cut the coils of larger axial dimensions, supplied to along the feed path, on corresponding individual rolls.

Disc-shaped cutting blades are subject to wear and tear and therefore often have to be ground. When ground, the disc-shaped cutting blade gradually erodes, reducing its diameter. When the minimum diameter dimension is reached, the disc-shaped cutting blade must be replaced.

The cutting blade is generally ground by two grinding wheels pressed against opposite sides of a circular cutting bevel of the disc-shaped cutting blade. The grinding wheels can be motorized, that is, they can be driven in rotation by means of respective motors, for example electric or pneumatic motors. In other embodiments, the grinding wheels are idly supported and rotated by friction between the active surface of the grinding wheel and the surface of the blade to be ground.

Grinding is crucial as it affects both the life of the blade and the quality of cut. For example, repeated grinding that is not optimal causes uneven wear of the disk-shaped cutting blade, a consequent poorer quality of cut and deformation of the disk-shaped cutting blade, the cutting edge of which tends to lose its round shape and to become polygonal. The life of a disc shaped cutting blade decreases significantly as its cutting edge becomes polygonal in shape.

Document WO-A-01/36151 discloses a grinding device for a coil saw according to the preamble of claim 1. The grinding device comprises two grinding wheels arranged on opposite sides of a cutting edge of the blade disc-shaped cutting machine. The two grinding wheels are driven in rotation by friction contact with the disc-shaped blade and by air jets generated by air nozzles.

Document US-A-2006/0162522 discloses a coil saw provided with three disc-shaped cutting blades. Each cutting blade is, in turn, provided with a grinding unit composed of two motorized grinding wheels.

GB-A-2171345 discloses a sharpening device for a disc blade for use in a cigarette making machine. Said sharpening device is made up of two grinding elements. The grinding elements are motor driven and have different shapes and dimensions. They are arranged with their axes of rotation located outside the circular cutting edge of the disk blade. A first grinding element has an annular cup shape and is provided with a grinding surface on its rim. Said flange surrounds a gap. The second grinding element is a grinding wheel, the axis of rotation of which is inclined towards the annular cup-shaped grinding element. Grinding wheel diameter it is substantially smaller than the diameter of the grinding rim of said cup-shaped grinding element. Therefore, a part of the grinding wheel enters the recess of the cup-shaped grinding element when the grinding wheel enters the recess of the cup-shaped grinding element when the two grinding elements are in contact with the two opposite sides of the cutting edge of the disc blade.

Grinding is also carried out in other fields, for example in food slicers. WO-A-00/40367 discloses a sharpening assembly for a food slicer. The sharpener comprises two grinding wheels. Said two grinding wheels are made of different materials, so that one wheel is more aggressive and the other is less aggressive and is used for grinding. To properly carry out their operation, the two grinding wheels are arranged relative to the disc blade so that the speed vectors of the two wheels are oriented in opposite directions relative to the cutting edge of the disc blade. Specifically, one of the wheels is arranged so that the relative velocity vector faces outward with respect to the cutting edge.

Therefore, it is useful to provide improvements to sawing machines and especially to their grinding systems as well as to grinding procedures.

Summary of the invention

According to the invention, there is provided a coil sawing machine comprising a feed path for the coils to be cut and a cutting head arranged along the feed path. The cutting head comprises a disk-shaped cutting blade that rotates around an axis of rotation and exhibits a cyclical movement.

it comprises two grinding wheels, which are arranged and configured to grind two sides of a cutting edge of the disk-shaped cutting blade, and each of them rotates around its axis of rotation. Said grinding wheels are arranged in such a way that, with respect to the disk-shaped cutting blade, in a contact area between each grinding wheel and the disk-shaped cutting blade, the grinding wheel has a directed speed toward the inside of the cutting edge. In other words, the area of contact between the grinding wheel and the respective side of the cutting edge has a velocity represented by a vector directed towards the inside of the cutting edge instead of towards the outside of it. If this condition of relative motion occurs on both grinding wheels, a more regular grind is provided, as well as a better quality of cut.

The grinding wheels are arranged so that, with respect to the disk-shaped cutting blade, the contact areas between the grinding wheels and the disk-shaped cutting blade are arranged between two approximately parallel planes, each containing one of them the axis of rotation of one of the grinding wheels. The planes are approximately parallel to a plane containing the axis of rotation of the disk-shaped cutting blade.

The grinding wheels are idly supported and are driven in rotation by friction with the disc-shaped cutting blade thanks to the torque generated in the grinding wheels by friction between the latter and the disc-shaped cutting blade.

In advantageous embodiments, the two contact areas between the grinding wheels and the disk-shaped cutting blade are symmetrical with respect to a plane containing the axis of rotation of the cutting blade and extending between the axes. rotation of the two grinding wheels.

According to some embodiments, the two grinding wheels can be arranged so that, when they are in an operating position in contact with the disk-shaped cutting blade, the axis of rotation of a first of said two grinding wheels grinding wheel is arranged outside the cutting edge of the disc-shaped cutting blade, and the axis of rotation of the other of said two grinding wheels is positioned inside the cutting edge, so that it intersects the cutting blade disk.

According to the invention, there is provided a method for grinding a disc-shaped cutting blade of a sawing machine for cutting coils of web material. Said method is defined in claim 5.

Brief description of the drawings

In the following, the invention will become more clearly apparent by following the description and accompanying drawings showing a practical embodiment of the invention. More in particular, in the drawings:

Figure 1 is a partial schematic side view of the main elements of an embodiment of a sawing machine;

Figure 2 is a sectional view, according to a vertical plane, of the head of the sawing machine Figure 1 with the disc-shaped cutting blade and grinding wheels;

Figure 3 is an enlarged cross section of the grinding wheels near the cutting edge of the blade, according to the plane MI-MI of Figure 4; Y

Figure 4 schematically shows the position of the grinding wheels and the disc-shaped cutting blade according to arrow IV of Figure 3.

Detailed description of some embodiments

The following detailed description of the exemplary embodiments refers to the accompanying drawings. The same reference numbers in different drawings identify the same elements or similar elements. Also, the drawings are not necessarily drawn to scale. Similarly, the following detailed description does not limit the invention. Rather, the scope of the invention is defined by the appended claims.

Reference throughout this specification to "one embodiment" or "the embodiment" or "some embodiments" means that the particular appearance, structure or feature described with respect to an embodiment is include at least one embodiment of the subject matter to be disclosed. Therefore, mention of the phrase "in one embodiment" or "in the embodiment" or "in some embodiments" in various places throughout this document does not necessarily refer to it / themselves. form / s of realization. Furthermore, the particular aspects, structures or characteristics may be combined in any suitable way in one or more embodiments according to the appended claims.

Figure 1 schematically shows the main elements of a sawing machine 1 that may comprise the novel aspects described herein for the grinding system. It should be understood that the structure of the sawing machine may be different from what is briefly described herein. For example, different drive means may be provided to transmit the forward motion of the reels and the disc-shaped cutting blade. The latter can have a reciprocating movement, for example a pivoting movement, instead of a continuous movement. Furthermore, the cutting head of the sawing machine may comprise more disc-shaped cutting blades.

The sawing machine 1 illustrated herein comprises a feed path indicated schematically by the reference P, along which the coils L, to be cut into rolls R of smaller axial dimension, move forward. These rolls are then fed to packaging machines, which are not shown. The sawing machine is arranged downstream of a rewinding machine and other processing stations that are not shown and known to those skilled in the art.

In some embodiments, the sawing machine 1 comprises a cutting station 3 which, in turn, comprises a cutting head indicated schematically with the reference number 5. Said cutting head 5 may comprise an orbital head 7 that rotates about the axis of rotation AA which can generally be oriented approximately in the same direction as the feed path P of the coils L to be cut. Said orbital head 7 of the cutting head 5 carries at least one disk-shaped cutting blade 9, which can rotate about an axis of rotation B-B. The axis of rotation B-B of said disk-shaped cutting blade 9 can generally be oriented approximately in the direction of the axis A-A. As is known to those skilled in the art, there are sawing machines in which the axes AA and BB are not perfectly parallel to each other and / or in the feed direction along the feed path PA of the coils. that are going to be cut. This is due to some aspects of the sawing machine that are not relevant to the present description and is related to the relative movements between the cutting head 5 and the forward movement of the coils L to be cut.

The sawing machine 1 may comprise a motor 11, which provides the rotary movement to the disk-shaped cutting blade 9, and a further motor 13, which provides the rotary movement around the axis AA to the cutter head 5 and the head orbital 7.

The coils L can be moved forward according to the feed path PA along one or more rails parallel to each other, to simultaneously cut more coils and increase the productivity of the sawing machine 1, as known from the subject matter experts.

The forward movement of the coils L can be provided, for example, by means of a continuous flexible element 15, such as for example a chain or a belt, driven by a motor 17. Advantageously, the motors 11, 13 and 17 can be control by means of a central control unit 19, in a way already known to those skilled in the art and not described in greater detail.

The flexible element 15 may comprise pushers 16 preferably arranged at regular intervals along the extension of the flexible element 15, to push each individual coil L along the feed path PA through the cutting station 3.

In some embodiments, the forward motion of the coils can be continuous, constant or variable speed. In other embodiments, the forward movement can be intermittent. During stops, the coil is cut with the disk-shaped cutter blade 9. The orbital head 7 and / or the disk-shaped cutter blade 9 can move back and forth along the path PA to cut coil L as the latter moves along the feed path PA without stopping, as is known to those skilled in the art. In some embodiments, clamps that close during the cutting step can be provided to hold the coil, thus ensuring a better quality of cut, and that open when the coil must advance. Preferably, two clamps are provided: one, upstream of the cutting plane, to clamp the coil, and another, downstream of the cutting plane, to clamp the part of the coil that is cut to form a roll.

During operation, the rotation of the orbital head 7 around the axis A-A transmits a cyclical movement to the disc-shaped cutting blade 9, so that said coils L can move forward between subsequent cuts of the coils L.

Figure 2 illustrates an embodiment of the cutting head 5 and, especially, of the orbital head 7.

In this embodiment, the cutting head 5 comprises a slider 21 mounted on the orbital head 7 so that it moves according to the double arrow 21 for the purpose that will be better described below. In some embodiments, the slide 21 is guided in guides supported on the orbital head 7. A reduction motor 25 moves the slide 21 according to the double arrow f21. The movement can be transmitted by means of a system with a threaded rod 27 and a spindle screw 29, for example a recirculating ball screw. Said spindle screw 29 can be fixed to the slide 21.

In advantageous embodiments, two grinding units can be arranged on the slide 21, indicated by the reference numerals 31 and 33. Each of said grinding units 31, 33 comprises a respective grinding wheel for grinding the cutting blade disk-shaped 9, and a controlled approach system for moving the respective grinding wheel towards the cutting edge of the disk-shaped cutting blade, so as to periodically move the grinding wheel towards the shaped cutting blade disc 9. The grinding wheels of the two grinding units 31 and 33 are designated by 32 and 34, respectively. The grinding wheel 32 rotates about an axis C-C and the grinding wheel 34 rotates about an axis D-D. The two grinding wheels 32 and 34 are arranged so that each of them can approach one of the two sides of the cutting edge or bevel 9B of the disc-shaped cutting blade 9, so that each of they grind one of the two sides of the cutting bevel 9B.

The two grinding wheels 32, 34 of the two grinding units 31, 33 can be equal to each other, for example, when the disk-shaped cutting blade is symmetrical with respect to its median plane, indicated with the reference T in Figure 2. However, this aspect is not necessary, but is only preferred in some embodiments. As is known, according to some embodiments, the disk-shaped cutting blade 9 can have an asymmetric bevel. In this case, the grinding wheels of the two grinding units can be different from each other and / or can be adjusted differently from each other.

The two grinding wheels are supported on the supports 36, 38 by means of the shafts 40, 42. In the embodiment described herein, said shafts 40, 42 and, therefore, the grinding wheels 32, 34, are supported idly on supports 36, 38; therefore, the rotation of the grinding wheels 32, 34 is due to friction between the active surface of each grinding wheel and the respective side of the cutting edge 9B on which the wheel 32, 34 acts.

Reference numerals 32A and 34A indicate the abrasive surfaces of the two grinding wheels 32 and 34, which act on the sides of the cutting bevel or cutting edge 9B. Each grinding wheel 32, 34 can have two opposite abrasive surfaces, and can be mounted in two different positions, in order to obtain a longer wheel life, using the two abrasive surfaces until they are consumed and can no longer be used. grind.

Furthermore, the cutting head 5 comprises a coupling for the disk-shaped cutting blade 9, indicated as a whole with the reference number 35. Said coupling 35 may comprise a rotating mandrel or shaft 37, driven in rotation by a wheel or toothed pulley 39, around which can be driven a toothed belt 41, controlled by a motor 11 or other suitable source of movement, not shown in detail.

For a better understanding of the innovative aspects of the grinding system and procedure described herein, reference will now be made to Figures 3 and 4. The grinding wheel 32 is mounted on the slide 21 such that the axis of CC rotation of the grinding wheel 32 is external with respect to the disc-shaped cutting blade 9, that is, external with respect to the edge or bevel 9B of the disc-shaped cutting blade 9. Furthermore, the cutting wheel Grinding 32 is mounted so that it touches the respective side of the cutting edge 9B of the disc-shaped cutting blade 9 in the area Z32 (Figure 4). Zone Z32 is arranged between a plane P containing the axis of rotation BB of the disc-shaped cutting blade and a plane P32 (figure 4) containing the axis CC of the grinding wheel 32 and approximately parallel to the plane P In practice, the Plane P is orthogonal to the median plane (plane T, figure 3) of the disc-shaped cutting blade 9.

In figure 4, the reference F0 indicates the resultant of the friction force generated by the contact between the grinding wheel 32 and the disk-shaped cutting blade 9 acting on the grinding wheel 32. The vector F0 is tangent to the cutting edge 9B in the area Z32. It can be divided into the elements F1 and F2, orthogonal to each other, in which the element F1 is orthogonal to the radius R of the grinding wheel 32. Therefore, the element F1 generates the motor torque that makes the grinding wheel rotate 32 rotating according to the arrow f32, when it is in contact with the disk-shaped cutting blade 9. The element F1 of the friction force F0 is directed in the same direction as the vector representing the tangential velocity of the grinding wheel 32. Therefore, as can be easily understood from FIG. 4, the direction of rotation of the grinding wheel 32 "enters" the cutting edge 9B. "Enter" means that the surface 32S of the wheel in the zone Z32 moves from the cutting edge or bevel 9B towards the axis BB of the disc-shaped cutting edge 9. Therefore, the vector speed of the wheel Grinding in the area of contact with the disk-shaped cutting blade 9 is directed towards the inside of the cutting edge. The smallest a of the angles between the vectors representing the tangential speeds of the disc-shaped cutting blade 9 and the grinding wheel is less than 90 °.

The "in" direction of movement of the grinding wheel 32 with respect to the disc-shaped cutting blade 9 in the reciprocal contact area between the grinding wheel 32 and the disc-shaped cutting blade 9 is optimal for cleaning the cutting edge of the bevel 9B; that is, any chips or filaments move away from the cutting edge 9B towards the axis of the disk-shaped cutting blade 9; in this way they do not project from the cutting edge 9B, which would negatively affect the quality of the cut.

The grinding wheel 34 is arranged so that it touches the cutting edge 9B in an area Z34. The zone Z34 is arranged in an intermediate position between the plane P defined above and a plane P34, approximately parallel to the plane P and containing the axis of rotation DD of the grinding wheel 34. Also in this case, F0 indicates the resultant of the frictional forces between the grinding wheel 34 and the disk-shaped cutting blade 9 acting on said grinding wheel 34. Vector F0 can be divided into elements F3 and F4, in which vector F3 (so similar to vector F1) transmits the torque to the grinding wheel 34 and is directed in the same direction as the vector representing the peripheral speed of the grinding wheel 34 in the zone Z34, rotating the grinding wheel 34 according to with the arrow f34.

Therefore, in a similar way to what happens for the grinding wheel 32, in the zone Z34 of contact with the disc-shaped cutting blade 9, the grinding wheel 34 also has a peripheral speed directed towards the inside of the edge. cutting 9B; this avoids the formation of chips or filaments that can project out of the cutting edge 9B, and, more precisely, outside the line of union of the two sides that define the cutting edge 9B.

The condition described above is due to the fact that the grinding wheel 34 is arranged with its axis of rotation DD close to the axis of rotation BB of the disc-shaped cutting blade 9. More particularly, the axis of rotation DD of the grinding wheel 34 is arranged so as to intersect the disc-shaped cutting blade 9, at a radial distance DR with respect to the line defining the edge of the cutting chamfer 9B.

The arrangement of the grinding wheels 32, 34 described above allows, for both grinding wheels, a direction of rotation which, in the area of contact between the grinding wheel 32, 34 and the disk-shaped cutting blade 9, the peripheral speed of said grinding wheel 32, 34 is directed towards the inside of the cutting edge, that is, it has a speed element directed radially towards the axis of rotation BB of the disk-shaped cutting blade 9, of so that optimal grinding conditions are obtained, avoiding the formation of filaments or chips that project out of the disc-shaped cutting blade 9.

Furthermore, the grinding wheels 32, 34 are in a position that allows the contact zones Z32 and Z34 between the grinding wheels and the disk-shaped cutting blade 9 to be close to each other. That is to say, the two contact areas are located between the two planes P32 and P34 (figure 4) that contain the axes of rotation CC and DD of the two grinding wheels 32, 34. This condition is particularly advantageous, since it limits the bending of the disk-shaped cutting blade 9 during grinding due to the pressure of the grinding wheels 32, 34 against said disk-shaped cutting blade 9.

Preferably, the contact zones Z32 and Z34 between each of the grinding wheels 32, 34 and the disk-shaped cutting blade 9 are symmetrical with respect to the plane P, that is, with respect to the plane containing the axis of rotation BB of the disc-shaped cutting blade 9 and intermediate between the axes of rotation CC and DD of the grinding wheels 32, 34.

In Figures 1 to 4, the supports 36, 38 of the grinding wheels 32, 34 are arranged on the same side of the plane T where the circular line that defines the edge of the cutting bevel 9b is located, that is, the line formed by the intersection of the two sides of the cutting edge 9B. This aspect is particularly advantageous for access and replace the disk-shaped cutting blade 9. In other embodiments, the two supports 36, 38 may be arranged on opposite sides of the T-plane. In this case, the advantages may result from the possibility of moving the rotational axes CC and DD of the two grinding wheels 32, 34 closest to each other, consequently bringing the zones Z32 and Z34 closer to each other.

Furthermore, in the previously described embodiments, the grinding wheels 32 and 34 are idly mounted and are driven in rotation by friction between each grinding wheel 32, 34 and the disk-shaped cutting blade 9. This aspect results particularly advantageous since its result is a simple and reliable grinding device. The lack of rotating motors prevents the grinding wheels from malfunctioning and stalling due to motor failure.

Claims (8)

1. Sawing machine (1) for cutting coils of web material, comprising: a feed path (PA) for the coils (L) to be cut; a cutting head (5) arranged along the feed path (PA); a disk-shaped cutting blade (9), which is mounted on the cutting head (5), rotates around an axis of rotation (B-B) and is provided with a cyclical movement two grinding wheels (32, 34), which are arranged and configured to grind two sides of a cutting edge (9B) of the disc-shaped cutting blade (9), and each of which rotates around its own axis of rotation (CC; DD); wherein the grinding wheels (32, 34) are idly supported and driven in rotation by friction with the disc-shaped cutting blade (9); characterized in that the grinding wheels (32, 34) are arranged with respect to the disk-shaped cutting blade (9) so that, in a contact zone (Z32, Z34) between each grinding wheel (32; 34) and the disc-shaped cutting blade (9), the grinding wheel (32; 34) has a speed directed towards the inside of the cutting edge; The grinding wheels (32, 34) are arranged relative to the disc-shaped cutting blade (9) so that the contact areas (Z32, Z34) between the grinding wheels (32, 34) and the blade disc-shaped cutting machines (9) are arranged between two planes (P32; P34), each of which contains the axis of rotation (CC, DD) of a respective one of the grinding wheels (32; 34); said planes are approximately parallel to each other and to an additional plane (P) that contains the axis of rotation (BB) of the disc-shaped cutting blade (9), said plane containing the axis of rotation (BB) of the cutting blade. disc-shaped cut (9) that is arranged between the two planes (P32, P34) that contain the axes of rotation (CC; DD) of the grinding wheels (32, 34). Sawing machine according to claim 1, in which the contact zones (Z32, Z34) are symmetrical with respect to a plane (P) substantially orthogonal to the disk-shaped cutting blade (9) and containing the axis rotation (BB) of the disc-shaped cutting blade (9). Sawing machine (1) according to claim 1 or 2, wherein, when the two grinding wheels (32, 34) are in an operating position in contact with the disk-shaped cutting blade (9) , a first (32) of said two grinding wheels (32, 34) is arranged with its axis of rotation (CC) outside the cutting edge (9B) of the disc-shaped cutting blade (9), and the other (34) of said two grinding wheels (32, 34) is arranged with its axis of rotation (DD) within the cutting edge (9B) so as to intersect the disk-shaped cutting blade (9) . Sawing machine (1) according to one or more of the preceding claims, in which said two grinding wheels (32, 34) are supported by two respective supports (36, 38) that are arranged on the same side of a median plane (T) of the circular blade, on which the cutting edge (9B) of the disk-shaped blade (9) is arranged. 5. Procedure for grinding a disk-shaped cutting blade (9) of a sawing machine (1) to cut coils (L) of strip material, said procedure comprising the following steps: - placing a first grinding wheel (32) in contact with a first side of a cutting edge (9B) of the disk-shaped blade (9) in a first contact zone (Z32); - placing a second grinding wheel (34) in contact with a second side of the cutting edge (9B) of the disk-shaped blade (9) in a second contact zone (Z34); - positioning the first contact area (Z32) and the second contact area (Z34) between a first plane (P32), which contains the axis of rotation (CC) of the first grinding wheel (32), and a second plane (P34), which contains the axis of rotation (DD) of the second grinding wheel (34), said first plane (P32) and said second plane (P34) being approximately parallel to each other and approximately parallel to an additional plane (P ) containing the axis of rotation (BB) of the disk-shaped cutting blade (9) and arranged between the first plane (P32) and the second plane (P34); - rotating the first grinding wheel (32) and the second grinding wheel (34) by friction between the disk-shaped cutting blade (9) and said first grinding wheel (32) and said second grinding wheel (34 ), around their respective axes of rotation (CC, DD) in a direction such that, in each of said first contact area (Z32) and second contact area (Z34), the first grinding wheel (32) and the Second grinding wheel (34) have a respective rotational speed directed towards the inside of the cutting edge (9B). 6. Method according to one or more of claims 5, in which the first contact area (Z32) and the second contact area (Z34) are symmetrical with respect to a plane (P) substantially orthogonal to the cutting blade at disc-shaped (9) and containing the axis of rotation (BB) of the disc-shaped cutting blade (9). Method according to one or more of claims 5 or 6, in which the first grinding wheel (32) is arranged with its axis of rotation (CC) outside the cutting edge (9B) of the cutting blade in the form of disc (9) and the second grinding wheel (34) is arranged with its axis of rotation (DD) within the cutting edge (9B) so as to intersect the disc-shaped blade. Method according to one or more of claims 5 to 7, in which the first grinding wheel (32) and the second grinding wheel (34) are supported by two respective supports (36, 38) that are arranged on the same side of a median plane (T) of the circular blade, on which the cutting edge (9B) of the disk-shaped cutting blade (9) is arranged.