FIELD OF THE INVENTION

Embodiments described here concern a log saw blade preferably suitable to cut oblong rolls of paper material to obtain rolls of smaller sizes. In particular, the log saw blade of the present invention is particularly suitable for cutting rolls of tissue paper, that is, toilet paper, kitchen paper, paper tissues or similar and comparable materials. However, the use of the log saw blade is not excluded also for cutting rolls of fabric, for example for clothes, upholstery or other.

BACKGROUND OF THE INVENTION

Cutting tools are known, suitable for use in industrial processes for the production of rolls of tissue paper.

In particular, the tools in question are used in one of the last production steps of the rolls of tissue paper. In detail, in this step, an oblong roll of tissue paper, with a longitudinal development that can reach up to a few meters, is cut transversely with respect to its longitudinal development to obtain shorter rolls of tissue paper, for example suitable to be packaged to be used by a final consumer.

Typically these tools have a disc-shaped body with a thin section and are called log saw blades.

The log saw blade has a central portion, or “hub”, closer to the central axis and able to cooperate with a possible motion transmission mean connected to a motor in order to rotate the blade, and a peripheral portion, or “chamfer”, farther from the axis of rotation and provided with a sharp end edge. In this particular field, this sharp end edge is called “wire”.

In known log saw blades, the chamfer has a rectilinear profile that develops radially, in continuity with the hub, linearly reducing its thickness toward the end edge.

During the cutting operation of the rolls, the area of the blade most subject to friction is the peripheral portion. In fact, the progressive transverse entry of the blade into the roll to be cut entails a sliding of the peripheral portion on the sections of roll which involve the cut.

This problem causes an excessive overheating of the blade which sets a limit to the operating speed of rotation that can be reached and therefore on the productivity of the production process of these rolls.

Another disadvantage is that, in some situations of use that entail this overheating, the blade tends to be subject to oscillations. The oscillations can lead to a faster wear of the blade, decreasing the quality of the cuts and therefore increasing the number of non-compliant products. Furthermore, the rapid wear of the blade requires frequent machine downtimes in order to replace the blade itself, considerably reducing the overall productivity of the machine in which it is installed.

DE 10 2018 107495 and WO 00/21722 show solutions for disk-shaped blades that partly address the problems and disadvantages mentioned above.

There is therefore a need to perfect a log saw blade which can limit the disadvantages of the state of the art.

In particular, one purpose of the present invention is to provide a log saw blade which, during use, is subjected to limited heating.

Another purpose of the present invention is to provide a log saw blade which, during use, is not subject to oscillations.

Another purpose of the present invention is to provide a log saw blade which allows to increase the hourly productivity of the machine for cutting oblong rolls in which it is installed.

The Applicant has devised, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages.

SUMMARY OF THE INVENTION

The present invention is set forth and characterized in the independent claims. The dependent claims describe other characteristics of the present invention or variants to the main inventive idea.

In accordance with the above purposes, the present invention concerns a log saw blade which overcomes the limits of the state of the art and eliminates the defects present therein.

According to some embodiments, the log saw blade comprises a central portion which develops radially from a central axis, and a peripheral portion which develops radially in continuity with the central portion.

According to some embodiments, the peripheral portion can be provided with a first and a second lateral surface both disposed symmetrically with respect to a center plane orthogonal to the central axis. Furthermore, the peripheral portion can comprises a cutting edge.

According to one characteristic aspect of the invention, the first lateral surface and the second lateral surface of the peripheral portion are concave.

In preferred embodiments, the log saw blade is symmetrical with respect to the center plane.

Advantageously, this conformation limits the lateral friction between the log saw blade and the roll of tissue paper to be cut. This reduction entails less overheating, making the log saw blade less subject to oscillations. Furthermore, this limits the wear of the log saw blade, reducing the frequency of sharpening operations and machine stops to replace the exhausted blade.

In possible variants, the first lateral surface and the second lateral surface are defined by a generating curve which can be chosen in a group comprising a parabola segment, an arc of a circumference, an ellipse branch and/or combinations thereof.

According to some embodiments, the ratio between the distance between the cutting edge and the point at which the first lateral surface and/or the second lateral surface has/have the maximum concavity, and the length of the peripheral portion is comprised between about 0.4 and about 0.7. The maximum concavity is understood to be measured in a direction parallel to the central axis. The distance between the cutting edge and the point at which the first lateral surface and/or the second lateral surface has/have the maximum concavity is understood to be measured in the radial direction. The length of the peripheral portion is understood to be measured from the cutting edge in the radial direction.

In some embodiments, the ratio between the maximum concavity of the first lateral surface and/or of the second lateral surface, and the half-difference between the maximum thickness and the minimum thickness of the peripheral portion is comprised between about 0.01 and about 0.12, preferably between about 0.05 and about 0.11.

In possible embodiments, the cutting edge has an angle of sharpening comprised between about 5° and about 20°, preferably between about 12° and about 17°, even more preferably the angle of sharpening is about 15°. In some embodiments, the log saw blade comprises connection means made in the central portion and configured to cooperate with motion transmission means.

The present invention also concerns a method to produce a log saw blade which according to some embodiments comprises:

- providing a metal disc;

- grinding the metal disk so as to define a ground peripheral portion;

- sharpening the radial end of the peripheral portion so as to define a cutting edge;

According to one characteristic aspect of the invention, the grinding defines a pair of concave lateral surfaces on the peripheral portion.

According to other possible embodiments, the method provides to sharpen the cutting edge with an angle of sharpening comprised between about 5° and about 20°, preferably between about 12° and about 17°, even more preferably the angle of sharpening is about 15°.

The present invention also concerns a machine for cutting oblong rolls of tissue paper.

In particular, according to one characteristic aspect of the present invention, the machine as above comprises at least one log saw blade as described in the present invention rotating around a central axis.

Furthermore, according to other embodiments, the machine as above comprises at least one log saw blade produced according to the method described in the present invention and rotating around a central axis.

BRIEF DESCRIPTION OF THE DRAWINGS These and other aspects, characteristics and advantages of the present invention will become apparent from the following description of some embodiments, given as a non-restrictive example with reference to the attached drawings wherein:

- fig. 1 is a schematic three-dimensional representation of a log saw blade according to the present invention;

- fig. 2 is a schematic representation of a section, with respect to any section plane II-II whatsoever containing the axis X, of a log saw blade according to the present invention.

To facilitate comprehension, the same reference numbers have been used, where possible, to identify identical common elements in the drawings. It is understood that elements and characteristics of one embodiment can conveniently be combined or incorporated into other embodiments without further clarifications.

DETAILED DESCRIPTION OF SOME EMBODIMENTS

We will now refer in detail to the possible embodiments of the invention, of which one or more examples are shown in the attached drawings by way of a non-limiting illustration. The phraseology and terminology used here is also for the purposes of providing non-limiting examples.

Referring to fig. 1, the present invention concerns a log saw blade 10 particularly suitable to be used in processes for producing rolls of tissue paper.

Here and hereafter in the description, by tissue paper we mean toilet paper, kitchen paper, paper tissues or similar and comparable materials. In particular, the log saw blade 10 is suitable to transversely cut oblong rolls of tissue paper, in order to divide them into multiple smaller rolls.

Although the log saw blade 10 is particularly suitable to cut rolls of tissue paper, we do not exclude its use to cut rolls of other materials, for example fabric for clothes, upholstery, or rolls of paper or cardboard or other.

According to some embodiments, the log saw blade 10 is configured as a solid of rotation with a discoidal shape and with a cross-section A that is constant with respect to a central axis X.

According to some embodiments, the log saw blade 10 comprises a central portion 12 which develops radially from the central axis X and is configured to cooperate with motion transmission means. The people of skill in the art refer to the central portion 12 as “hub” or “flange”.

The log saw blade 10 also comprises a peripheral portion 13 which develops radially in continuity with the central portion 12. The peripheral portion 13 is provided with a cutting edge 14, a first lateral surface 15a and a second lateral surface 15b both disposed symmetrically with respect to a center plane Y orthogonal to the central axis X. The people of skill in the art refer to the peripheral portion 13 as “chamfer” and to the cutting edge 14 as “wire”.

According to one characteristic aspect of the present invention, the first lateral surface 15a and the second lateral surface 15b are concave. In particular, the thickness S of the peripheral portion 13 decreases as a function of the radial development thereof, that is, as the radial distance from the central axis X increases, defining at least one curve, or recess, facing toward the inside of the log saw blade 10.

According to possible embodiments, the first surface 15a and the second surface 15b are defined by a generating curve which can be chosen in a group comprising a parabola segment, an arc of a circumference, an ellipse branch or combinations thereof.

According to possible embodiments, the first lateral surface 15a and the second lateral surface 15b have different concavities.

According to preferred embodiments, the first lateral surface 15a and the second lateral surface 15b have the same concavities. In this case, the log saw blade 10 is symmetrical with respect to the center plane Y.

Advantageously, this conformation limits the lateral friction between the log saw blade 10 and the roll of tissue paper. The reduction of the lateral friction entails a lower overheating of the log saw blade 10, thus making it less subject to oscillations. By virtue of this, a log saw blade 10 as described in the present invention allows to increase its rotation speed during use, with a consequent increase in the hourly productivity of the entire process.

Another advantage consists in the fact that the log saw blade 10, since it is less subject to oscillations, can be made with a smaller thickness than known log saw blades, thus reducing the use of material, the mass and the inertia with respect to the central axis. X. This also entails obvious advantages from an energy point of view, since the log saw blade 10 requires less energy to be set in rotation.

Furthermore, another advantage deriving from the reduction of the friction between the log saw blade and the roll of tissue paper consists in the fact that the wear of the log saw blade 10 is limited. In this way, the times and costs of re sharpening the log saw blade 10 are reduced, and machine downtime for replacement is limited and less impacting on the economy of the process for producing rolls of tissue paper.

According to some embodiments, the ratio R1 between the distance D, defined as the distance between the cutting edge 14 and the point at which the first lateral surface 15a and/or the second lateral surface 15b has/have the maximum concavity H, and the length B of the peripheral portion 13 is comprised between about 0.4 and about 0.7 (fig. 2). The maximum concavity H is understood to be measured in a direction parallel to the central axis X. The distance D is understood to be measured in the radial direction. The length B of the peripheral portion 13 is understood to be measured from the cutting edge 14 in the radial direction.

According to some embodiments described here, the peripheral portion 13 has a thickness S which gradually reduces from the point of attachment with the central portion 12 toward the cutting edge 14. In particular, in correspondence with the point of attachment with the central portion 12, the thickness S has a maximum value S _max , maximum thickness, while in correspondence with the cutting edge 14 the thickness S has a minimum value S _min , minimum thickness, fig. 2.

According to some embodiments, the ratio R2 between the minimum thickness S _min and the maximum thickness S _max is smaller than the ratio R1 as above.

According to some embodiments, the ratio R2 is comprised between about 0.12 and about 0.38.

According to other embodiments, it is possible to define a ratio R3 between the measurement of the maximum concavity H, of the first lateral surface 15a and/or of the second lateral surface 15b, and the half-difference between the maximum thickness S _max of the central portion 12 and the minimum thickness S _min of the peripheral portion 13.

In some embodiments, the ratio R3 can be comprised between about 0.01 and about 0.12, preferably between about 0.05 and about 0.11. The maximum concavity H of the first lateral surface 15a and/or of the second lateral surface 15b is understood to be measured in a direction parallel to the central axis X.

According to some embodiments, during use, the cutting edge 14 is the first part of the log saw blade 10 that contacts the roll of tissue paper to be cut.

The cutting edge 14 can be sharpened with an angle of sharpening a comprised between about 5° and about 20°, preferably between about 12° and about 17°, even more preferably the angle of sharpening a is about 15°.

According to some embodiments, the central portion 12 comprises connection means 11 configured to cooperate with motion transmission means able to set the circular blade 10 in rotation.

According to some embodiments, the connection means 11 can comprise a central aperture 11a, suitably shaped, for attaching the log saw blade 10 to a rotation shaft and possibly one or more holes 1 lb for one or more bolts, or other coupling/attachment means of a known type.

In some preferred embodiments, the log saw blade 10 according to the present invention is made of metal material. For example, the metal material can be steel with high resistance to wear and high thermal stability. In the present case, for example, the log saw blade 10 is made of 1.2379 type steel.

The present invention also concerns a method to produce a log saw blade 10 which, according to one embodiment, can comprise:

- providing a metal disc;

- grinding the metal disc so as to define a ground peripheral portion 13;

- sharpening the radial end of the peripheral portion 13 in order to define a cutting edge 14.

According to one aspect of the present invention, grinding the metal disc defines on the peripheral portion 13 a pair of lateral surfaces 15a, 15b of which at least one is at least partly concave.

According to other embodiments, the method provides to sharpen the cutting edge 14 with an angle of sharpening a comprised between about 5° and about 20°, preferably between about 12° and about 17°, even more preferably the angle of sharpening a is about 15°.

According to other embodiments, the method can provide to make connection means 11 in the central portion 12. In some embodiments, the connection means 11 can comprise a suitably shaped central hole 1 la and/or one or more holes 1 lb for one or more bolts, or other coupling/attachment means of a known type.

In accordance with some embodiments, a log saw blade 10 as described in the present invention is suitable to be incorporated in a specific type of machines for cutting oblong rolls of tissue paper.

According to possible embodiments, the log saw blade 10 can be integrally connected, or keyed, to a rotation shaft of said machine, for example by means of a pin and/or one or more bolts cooperating with the connection means 11.

In some embodiments, a machine for transversely cutting oblong rolls of tissue paper can comprise one or more log saw blades 10 as described in the present invention.

In some embodiments, a machine for transversely cutting oblong rolls of tissue paper can comprise one or more log saw blades 10 made according to the method described in the present invention.

According to some embodiments, during use, each log saw blade 10 comprised in the machine can be made to rotate on itself, that is, around the central axis X. At the same time, each log saw blade 10 can be moved according to an orbital rotation that defines the engagement and detachment times of the log saw blade 10 with the roll of tissue paper.

It is clear that modifications and/or additions of parts or steps may be made to the log saw blade 10 and to the method as described heretofore, without departing from the field and scope of the present invention as defined by the claims. In the following claims, the sole purpose of the references in brackets is to facilitate reading: they must not be considered as restrictive factors with regard to the field of protection claimed in the specific claims.