CUTTING MACHINE

Field of the invention The present invention belongs to the technical field of rotary die cutting machines, and more specifically to the counter-die cylinder, which is the cylinder which acts as a base on which the cutting elements of the die-holder cylinder contact one another to provide a suitable cutting of the material without deteriorating. The invention relates, in particular, to a protective cylindrical cover for the counter-die cylinder freely rotatable around said counter-die cylinder formed by a set of bands connectable to one another.

Background of the invention

As is known, rotary die cutting machines are used for cutting flat cardboard sheets and similar materials, among others. These rotary die cutting machines are formed mainly by two cylinders made of steel, where the cardboard sheet passes between them. One of the cylinders, that is, the die- holder cylinder, incorporates the die cutter, which are the cutting elements, and acts as the cutter, while the other cylinder, that is, the counter-die cylinder, acts as the base to allow the cutting elements of the die-holder cylinder to cut the sheets without deteriorating. The dies of the die cutting cylinder pass through the workpiece in different orientations to make different cuts and form products from flat sheet material, such as corrugated sheets for example.

The second cylinder, that is, the counter-die cylinder, which acts like the base, is provided with a protective cover, or a blanket, made of a relatively soft material, which is typically made of polyurethane, to allow the cutting elements of the die-holder cylinder to cut the sheets of material without deteriorating it. More specifically, these covers are thick bands designed for surrounding the counter-die cylinder, i.e. , for forming a type of cylindrical sleeve. Sometimes, the cover is fixed to the cylinder by dimensional interference between a complementary projection of the cover or key and a slot of the cylinder or key slot, by screwing them together or by other different means. The cover is thereby secured on the cylinder but has the drawback that since the position does not change with respect to the counter-die cylinder, in certain areas, and due to the impact of the cutting elements of the die-holder cylinder, the cover becomes warn and its thickness reduced, which diminishes its efficacy in certain areas. Document WO2017000991 A1 , belonging to the same applicant as the present application, shows a cover fixed to the counter-die cylinder by means of a key of the cover housed in a key slot made in the cylinder.

An alternative embodiment for solving the aforementioned problem consists of a cover which covers the counter-die cylinder but is not fixed to same, such that when the cutting elements of the die-holder cylinder impact against the cover, said cover rotates freely around the counter-die cylinder, a more uniform wear of the cover across the entire surface thereby being achieved, prolonging the service life of same and its efficacy not being diminished in any area. This alternative is known as freely rotatable cover or bands.

At present, there are different versions of this freely rotatable cover, all of which are mainly formed by a set of bands or bushings arranged around the counter-die cylinder, with the contiguous bands being connected to one another by “tongues” causing the entire set of bands or bushings to rotate in a joint and integral manner, as a single part. At the ends of the set of bands, there are rings preventing them from being moved longitudinally along the cylinder. Conventional tongues are arranged in an inner layer of high hardness and rigidity, there furthermore being an outer layer of lower hardness and rigidity on which the cutting elements impact. Conventional tongues are metallic cylindrical connectors for having sufficient resistance against the tangential forces received. Therefore, due to metallic character, the connectors or tongues must be positioned at least in the central part of the inner layer of the bushings or bands, separated from the counter-die cylinder, in order to prevent them from rubbing against said counter-die cylinder during the rotation of the bands. This causes an inner layer of high thickness to be necessary, increasing the weight of said bushings or bands, and furthermore causes the thickness of the outer layer (the one that actually receives the impact of the cutting elements) to be lower, which will lead to rapid wear over time, in addition to a less efficient basic function for the impact of the cutting elements. Figures 1 and 2 show two different embodiments of current freely rotatable covers with conventional tongues which are metallic cylindrical connectors. As can be observed in said figures, these connectors or tongues are located in the intermediate area of the thickness of the bushing, as shown in Figures 1 and 2, to prevent the connector or tongue from damaging the counter-die cylinder, which causes an inner layer of high thickness to be necessary, increasing the weight of the bushings or bands, and furthermore causes the thickness of the outer layer (the one that actually receives the impact of the cutting elements) to be lower.

Document EP2210718A2, belonging to the same applicant as the present application, shows a protective cover for a counter-die cylinder of a die cutting machine formed by bands arranged around the counter-die cylinder, being freely rotatable around said counter-die cylinder, connectable to one another by means of rods or metallic cylindrical connectors such as those previously described, with the aforementioned problems.

In some embodiments existing in the state of the art, the bands forming the protective cover are formed by two half-shells. In these embodiments, the bands for the closing and in turn the fixing to the counter-die cylinder are by means of metallic elements such as fixed flats, pins or various types of hardware, which complicates and slows down the assembly and disassembly of the protective cover on the cylinder. Document US2007028741A1 shows a protective cover for a counter-die cylinder configured by bands formed by two half-shells which are closed and in turn fixed to the counter-die cylinder by means of rectangular flats with pins.

An alternative embodiment solving the aforementioned problem consists of a closure of the bands on the counter-die cylinder by means of a jigsaw or plurality of fingers with a geometry configured for ensuring the clamping of the ends of the band to one another, and thereby securing the closing of the band on the counter-die cylinder. With a closure of this type, the band is assembled and disassembled on the cylinder in a quick and easy manner without needing any type of metallic element or hardware for the closing thereof on the counter die cylinder.

Sometimes, the bands making up the protective cover are formed by a reinforcement layer which is formed by at least one web layer, with the web layer being arranged in the innermost part, in contact with the counter-die cylinder. The reinforcement layer can be formed by several overlapping web layers. Whether the reinforcement layer is formed by one or more web layers, since said web layer is arranged in the innermost part, in contact with the counter-die cylinder, if it is applied in a system of freely rotatable bands, when the bands freely rotate on the counter-die cylinder, they could damage the latter. Document WO2015175626A1 shows a protective cover for a counter-die cylinder formed by an inner reinforcement layer, in turn formed by several web layers overlapping one another and wherein the innermost web layer is in contact with the counter-die cylinder.

A protective cover for a counter-die cylinder which provides efficient protection for counter-die cylinders, preventing the drawbacks of earlier covers existing in the state of the art, is therefore desirable. Description of the invention

The present invention solves the problems existing in the state of the art by means of a protective cover for a counter-die cylinder of a die cutting machine, formed by a set of bands adaptable around the counter-die cylinder, such that they form a cylindrical cover freely rotatable around said counter-die cylinder. The contiguous bands are connectable to one another by means of connector means arranged on the sides of the bands. The cover also has stop rings arranged on both sides of the set of bands for preventing the movement of the bands in the longitudinal direction of the counter-die cylinder. The bands have an outer layer, also called the filler layer, an inner layer which, when in use, contacts the counter-die cylinder, and an intermediate web arranged between the outer layer and the inner layer. The outer layer, or filler layer, is what receives the impact of the cutting elements, and it must have a hardness and thickness assuring correct operation and an acceptable useful service life. The inner layer and the intermediate web form an inner reinforcement. The inner layer consists of a composition of a material of high hardness, abrasion resistance and with a low coefficient of friction, to enable freely sliding once the band is assembled on the counter-die cylinder. Furthermore, the inner layer must have a hardness and thickness sufficient for providing the band with an impact resistance that prevents torsion, preventing it from curling or twisting with the die cutting force. As for the intermediate web, it provides dimensional stability to the bands, and it was not previously used in freely rotatable covers but rather in covers fixed to the counter-die cylinder, where they were arranged in the inner part of the cover to provide stability. In the case of the present invention, said web is not arranged in the inner part of the bands, but rather between the inner layer and the outer layer so as to prevent it from rubbing against the counter-die cylinder during the rotation of the cover.

The connector means in charge of attaching the contiguous bands together are formed by tongues having a width sized along the circumference of the bands in which they are arranged, a thickness sized in the direction perpendicular to the lateral surface of the bands, and a depth sized in the longitudinal direction of the bands and the counter-die cylinder. The tongues are arranged in the inner layer, on one side of the bands, and are insertable in corresponding housings arranged in the inner layer, on the opposite side of the contiguous band, the width of the tongues being greater than their thickness. There can be three tongues attaching two contiguous bands to one another, although they may vary in number.

Therefore, by means of the present invention, since the width of the tongue is greater than its thickness, this provides sufficient rigidity and resistance for withstanding tangential stresses without having to be metallic, and they can thus be adhered to the counter-die cylinder.

A band with an inner layer of high thickness for housing the cylindrical tongues separated from the counter-die cylinder as occurs in all the freely rotatable systems today is therefore not required.

The tongue has the characteristics of its innermost part having a low coefficient of friction to enable freely sliding on the counter-die cylinder without damaging it once the band is assembled on the cylinder and having a hardness and resistance sufficient for enabling the connection and integral movement of the plurality of bands so that the wear is even. This characteristic achieves a reinforcement layer of low thickness, and therefore a freely rotatable band of low thickness, unlike all the freely rotatable systems existing today, which require a large thickness.

Therefore, the present invention provides a freely rotatable cover of low thickness, with a lower weight facilitating the handling and the rotation of the bands forming it on the cylinder by operators. By means of the present cover, the wear of the bands is reduced and the twisting or curling thereof when it withstands the die cutting force is prevented.

According to a particular embodiment of the invention, the tongues are of a polygonal section, and preferably they are of a rectangular section, the larger side being the width and the smaller side being the thickness. According to an embodiment that is an alternative to the previous one, the tongues are of a section of double the arc of circumference with a centre in the axis of the counter-die cylinder, of a width the width of the tongue, and with a distance between the two arcs of circumference being the thickness.

Preferably, the depth of the tongues is such that they are completely insertable in the corresponding gaps of the contiguous band.

According to particular embodiments of the invention, the inner layer of the band and the tongues are made from polyurethane. Particularly, the outer layer of the band is made from polyurethane.

Preferably, the inner layer of the band is harder than the outer layer. Particularly, the intermediate web is made from materials selected from fibre, plastic materials, metallic materials, and a combination of the foregoing.

According to a particular embodiment of the invention, the cover can have closing elements in order to, when in use, close off a key slot of the counter-die cylinder, which allows for the use of these covers in already existing counter-die cylinders initially designed for fixing the bands by means of a key in the key slot of the cylinder.

According to different particular embodiments of the invention, the ends of the bands comprise a plurality of fingers that can be fitted together with a geometry configured for ensuring the clamping of the ends of the bands to one another and so as to enable forming the cylindrical cover freely rotatable around the counter-die cylinder.

Brief description of the drawings

To help understand the invention, an embodiment of the invention will be described below by way of non-limiting illustration in reference to a series of Figures.

Figure 1 shows an embodiment of a freely rotatable cover of the state of the art with conventional tongues.

Figure 2 shows a different embodiment of a freely rotatable cover of the state of the art with conventional tongues.

Figure 3a is a perspective view of an embodiment of the tongues of the present invention of a rectangular section. Figure 3b is a perspective view of an alternative embodiment of the tongues with a section of double the arc of circumference. Figure 3c schematically shows the section of the tongue of Figure 3b. Figure 4 shows the attachment of two contiguous bands of a cover by means of tongues.

Figure 5 is a schematic view of a die cutting machine showing the die- holder cylinder and the counter-die cylinder on which an embodiment of a cover of the present invention is arranged.

Figure 6 is a side perspective view of the counter-die cylinder with the cover of the present invention showing the stop rings.

Figure 7 is a view of a counter-die cylinder in which closing elements of the cover of the present invention are arranged for closing off an existing key slot.

Figure 8 is a schematic section view showing the different layers of a cover object of the present invention arranged on a counter-die cylinder.

Figure 9a shows a tongue arranged in a band and Figure 9b shows the complementary housing arranged on the opposite side of the contiguous band. Figure 10 shows a perspective view of a tongue of a band partially introduced in the complementary housing of the contiguous band, for showing both bands before the attachment thereof.

Figure 11a shows a counter-die cylinder and a single band of a cover arranged on said cylinder for showing the tongue. Figure 11b is a figure of an enlarged detail of the tongue of Figure 11 a.

Figure 12 shows an embodiment of a plurality of fingers arranged at the ends of the bands that can be fitted together for closing the bands and forming the cylindrical cover freely rotatable around the counter-die cylinder.

These figures refer to a set of elements, said elements being: 1. die cutting machine

2. die-holder cylinder

3. counter-die cylinder

4. band

5. stop rings 6. outer layer of the band

7. intermediate fibre web of the band

8. inner layer of the band

9. tongues of the connector means of the bands

10. housings of the connector means of the bands 11. closing elements for closing off the key slot of the counter-die cylinder 12. fingers of the ends of the bands that can be fitted together a. width of the tongues e. thickness of the tongues p. depth of the tongues

Detailed description of the invention

The object of the present invention is a protective cover for counter-die cylinder (3) of die cutting machine (1 ).

As shown in the figures, the protective cover is formed by a set of adaptable bands (4) around the counter-die cylinder (3), such that they form a cylindrical cover freely rotatable around said counter-die cylinder (3).

Although the figures schematically show the connection of two bands (4) on the counter-die cylinder (3), there are commonly between about nine and fifteen bands (4) on each counter-die cylinder, depending on the length thereof, although the number of bands (4) may vary.

The contiguous bands (4) are connectable to one another by means of connector means arranged on the sides of the bands (4). The cover has also stop rings (5) arranged on both sides of the set of bands (4) used for preventing the movement of the bands (4) along the longitudinal direction of the counter- die cylinder (3). As can be observed in Figure 8, the bands (4) have an outer layer (6), an inner layer (8) which, when in use, is what contacts the counter-die cylinder (3), and an intermediate web (7) arranged between the outer layer (6) and the inner layer (8). The connector means attaching the contiguous bands (4) together are formed by tongues (9) having a width (a) sized along the circumference of the bands (4) in which they are arranged, a thickness (e) sized in the direction perpendicular to the lateral surface of the bands (4), and a depth (p) sized in the longitudinal direction of the bands (4) and the counter-die cylinder (3). As can be observed in the figures, namely in Figures 3a, 3b, 9a, 9b and 10, the tongues (9) are arranged in the inner layer (8), on one side of the bands (4) and are insertable in corresponding housings (10) arranged in the inner layer (8), on the opposite side of the contiguous band (4), the width (a) of the tongues (9) being greater than their thickness (e).

According to a particular embodiment of the invention, the tongues (9) are of a polygonal section, and preferably, as observed in Figure 3a, they are of a rectangular section, the larger side being the width (a) and the smaller side being the thickness (e).

According to an embodiment that is an alternative to the previous one shown in Figure 3b, the tongues (9) are of a section of double the arc of circumference with a centre in the axis of the counter-die cylinder (3), of a width the width (a) of the tongue (9), and with a distance between the two arcs of circumference being the thickness (e). As can be observed in the figures, with this type of section the innermost part of the tongues (9) is adapted on the counter-die cylinder (3) once the band (4) is assembled on said counter-die cylinder (3), and the outermost part of the tongues (9) is located below the outer layer (6) of the band (4), with precise contact being obtained.

Preferably, the depth (p) of the tongues (9) is such that they are completely insertable into the corresponding gaps (10) of the contiguous band, such that continuity in the bands (4) for forming the cover without leaving spaces between them, as well as a higher resistance to tangential stresses in the tongues (9) are achieved.

According to particular embodiments of the invention, the inner layer (8) of the band (4) and the tongues (9) are made from polyurethane. Particularly, the outer layer (6) of the band (4) is made from polyurethane.

Preferably the outer layer (6) of the band (4) has a hardness between 85 ShA and 95 ShA.

Furthermore, preferably, the inner layer (8) of the band (4) is harder than the outer layer (6).

Particularly, the intermediate web (7) is made from materials selected from fibre, plastic materials, metallic materials, and a combination of the foregoing.

According to a particular embodiment of the invention, the cover can have closing elements (11) in order to, when in use, close off a key slot of the counter-die cylinder (3), as can be observed in Figure 7, which allows for the use of these covers in already existing counter-die cylinders (3) initially designed for fixing the bands by means of a key in the key slot of the cylinder. Preferably these closing elements (11) can be made from rigid polyurethane or steel.

According to different particular embodiments of the invention, the ends of the bands (4) comprise a plurality of fingers (12) that can be fitted together with a geometry configured for ensuring the clamping of the ends of the bands (4) to one another and so as to enable forming the cylindrical cover freely rotatable around the counter-die cylinder (3). Figure 12 shows a particular embodiment of fingers (12) that can be fitted together for closing the bands (4) of the protective cover. The fingers (12) can have any other geometry, provided that they ensure the clamping of the ends of the bands (4) and therefore the correct fixing thereof on the counter-die cylinder (3).