Corrugator unit, particulary for sheets or webs of paper, or similar

Abstract: A corrugator unit, particularly for sheets or webs of paper, or similar, of the type comprising at least two rolls (1, 2), having a toothed or corrugated surface (101, 202), and being mutually engaged and pushed against each other by a predetermined pressure or force. The invention provides that the mutual compression between rolls (1, 2) is exerted (4, 5, 106, 21, 22, 25, 26) over the whole axial length of the rolls (1, 2). This may be obtained through mechanical (6) or magnetic (21, 22, 23, 25, 26) means.

Description: The invention relates to a corrugator unit, particularly for sheets of webs of paper or similar, comprising at least two rolls having a toothed or corrugated surface and being mutually engaged, which rolls are rotatably supported about their axis at their ends and are pushed radially against each other by a predetermined pressure or force exerted over the whole axial length of the rolls, at least one roll being movable towards the other roll and being held by a cradle which adheres against the side of the movable roll diametrically opposite to the other roll in a plurality of contact locations or areas distributed all over its axial length. A corrugator unit of this kind is known from the document DE-A-39 03 683 and US-A-3 383 133. Said corrugator units are particularly used in corrugated board manufacturing equipment, in which an intermediate corrugated layer is to be interposed between two smooth paper layers. In prior art corrugator units, the two peripherally corrugated or toothed rolls are supported by end hubs, rotatably about their axis. At least one of the two rolls is compressed against the other by means of pushers, acting on the end supports. Since rolls are considerably long (up to about 2.8 mt.), a uniform compressive force between the corrugator rolls is ensured all over their length by making use of roll deflection. Rolls, usually only one thereof, have a peripheral corrugated surface which is crowned in the axial direction to a predetermined extent, so as to obtain a uniform compression between the two corrugator rolls all along their axial length. The need for an accurate crowned profile of the corrugator rolls forces, especially in case of maximum lengths thereof, to provide very low crowning values, of about 0.2 to 0.6 mm, and therefore to use long-diameter rolls. Besides the drawbacks related to the considerable mass of the roll, and so to a higher inconvenience in construction, and to higher costs thereof, the above arrangements also provide that flutes are formed on paper, by forcing the latter through the labyrinth formed by the teeth of the rolls, where it is subject to an undesired braking effect, due to friction, which, in some cases, causes paper resistance to be reduced or even paper to be torn. The necessary crowning values are generally very small, of the order of a few tenths of a millimeter (0.2 to 0.6 mm) and therefore specific pressure values are critically affected by any inaccuracy in construction and by the progressive wear of roll corrugations. Hence, the construction of crowned rolls requires a considerable accuracy, and therefore involves higher manufacturing costs. Moreover, the profile of corrugator rolls is not homokinetic, being designed according to the intended corrugation, and having variations as regards both the velocity ratio and the distance between centers at each tooth pitch. Owing to this particular construction, combined with the considerable roll masses, vibrations may be generated in the operating condition, which may be subject to important autoamplification phenomena, such as resonance, especially at critical speeds. In the document DE-A-39 03 683 a corrugator unit is disclosed, in which the mutual radial compression between the rolls is uniformly exerted over the whole axial length of the rolls by magnetic means. In the corrugator unit known from the document US-A-3 383 133 the cradle which holds one of the rolls is formed by a plurality of ring-shaped pneumatic members rotatably mounted about a common axis parallel to the axis of the roll held by the cradle and having a peripheral surface in rolling contact with a relatively small portion of said roll. The invention has the object to provide a corrugator unit of the above described kind according to the pre-characterizing part of the independent claim, in such a way that by means of simple and relatively cheap arrangements the drawbacks of prior art equipments may be obtained without jeopardizing and even improving the productive efficiency of the corrugator unit. The invention solves the above problem by providing a corrugator unit of the type described hereinbefore and characterized in that the cradle is composed of a set of endless rotatable supporting belts arranged along the length of the movable roll, there being provided means for pushing the belts with a predetermined force towards the associated moving roll. The solution according to the invention allows to obtain considerable advantages. Particularly, the value of specific pressure, uniformly distributed over the whole length of the roll, may be adapted to real needs, imposed by the type of paper, or similar, being produced. The diameter of the roll may be chosen as the most appropriate for manufacturing needs, and without accounting for any stiffness requirement thereof. A roll construction without crowning requires a lower manufacturing accuracy and therefore lower costs. The corrugator unit according to the invention also allows to avoid any variations in specific pressure, required by roll wear. By reducing the mass of one roll, resonance frequencies are brought to higher values with respect to manufacturing speeds. Moreover, the number of paper-gripping teeth or corrugations may be reduced, allowing for the use of a less resistant paper. The invention also allows to adapt and adjust the distribution of the compressive force in the individual attachment locations, or over the length of the roll, so as to compensate for any variation of the compressive force or as to eliminate any vibration auto-amplification or resonance phenomena, thereby enormously reducing the noise of the corrugator unit, with respect to currently attainable values. The invention also addresses further improvements, which form the subject of the dependent claims. The invention is now described in detail, with reference to the embodiment illustrated in the accompanying drawings, in which: Fig. 1 is a side view of a embodiment of the corrugator unit according to the invention. Fig. 2 is a view of the corrugator unit, as shown in fig. 1, taken in the paper sheet feed direction. Fig. 3 is a magnified side view of the belts for compressing the lower roll. Figs. 4 and 5 are two partially sectional views of the unit as shown in the previous figures, with respect to two different transverse planes. Fig. 6 shows a magnified detail of the means for supporting the lower roll and of the means for moving the belt to the rest position, in order to displace the lower roll from the upper roll. Fig. 7 shows a magnified detail of the corrugating labyrinth formed by the mutually engaged teeth, of two corrugator rolls having a substantially identical diameter. Fig. 8 is a view as shown in fig. 7, in which the two rolls have very different diameters. With reference to figures 1 to 6, a corrugator unit comprises at least two corrugator rolls 1 and 2, which are supported at their ends, rotatably about their axis, inside a framework 3. The rolls are rotatably driven, so as to be counterrotating. The roll 1, having a considerably greater diameter than the roll 2, according to a predetermined ratio of 1/2 to 1/10, is supported so as to be stationary with respect to transverse translations of its axis of rotation, particularly in the direction of the line passing through the axes of rotation of the two rolls 1 and 2. The second roll 2 is rotatably supported by end hubs 102, at the end of swinging arms 4, swingably pivoted on axes 5, projecting parallel to the axes of the rolls 1, 2, out of the framework 3. Figures 7 and 8 show the differences between a corrugator unit whose rolls have substantially identical diameters and a corrugator unit according to the present invention. When corrugator rolls have identical diameters the peripheral teeth or corrugations 101, 202 form a much longer labyrinth than the one formed by two corrugator rolls 1, 2, as usable according to the principle of the present invention. Due to the shorter radius of the roll 2, a smaller number of teeth or corrugations 101, 202 are in partial engagement. Therefore, the labyrinth in which the paper C is gripped is much shorter, thereby greatly reducing the risk of its being broken during the corrugation process, and involving less critical operational settings of the corrugator unit. The roll 2 with the smaller diameter rests on a cradle 106, which is formed by a set of adjacent endless belts 6 driven around pulleys 7, 8, 9, 10. All the belts 6 are driven in such a way as to follow coincident paths in the axial direction of the roll, the driving pulleys 7, 8, 9, 10 being identical for each belt and axially coincident. The pulleys 7, 8, 9, 10 are arranged so that the lines joining their axes of rotation form a trapezoid, whereas the driving pulleys 7, 8, which are level with the roll 2 have their axes aligned on a plane substantially parallel to the tangent passing trough the contact line between the two corrugator rolls 1, 2, which plane containing said axes is slightly staggered with respect to the axis of rotation of the roll 2, on the side opposite to the roll 1. The two pulleys 7, 8 which are level with the corrugator roll 2 have a diameter of the same order as the diameter of the latter, whereas their distance from the latter substantially corresponds to the thickness of the belt 6. All the pulleys 7 to 10 associated to each belt 6 are supported at the ends of arms 11, 12, 13, overhangingly projecting out of a central beam 14, extending parallel to the axes of the rolls 1, 2. The beam 14 is particularly swingably supported by a shaft 15, which is also the axis of rotation of the lower pulley 9, placed under the roll 1, whereas, on the opposite, outer side, the beam 14 is supported by the base 103, by means of linear actuators 16, such as hydraulic cylinders or similar, which allow to swing the whole beam 14 between two extreme operating and rest positions. In the operating position, shown in the figures, the belts 6 bring the roll 2 into contact with the roll 1, with the peripheral teeth and corrugations of the two rolls 1, 2 being in mutual engagement. In the rest position, the belts 6, i.e. the cradle 106 displaces the roll 2 from the roll 1, to allow for the introduction of the sheet of paper, or other similar material to be corrugated therebetween. The actuators 16 are disposed in a predetermined arrangement over the length of the roll 2 and of the beam 14, and are articulated on one side to the base 103, and on the other side to a corresponding arm 17 of the beam 14. At least one pulley 10 of each belt 6 is supported at the end of an arm 13, which is supported by the beam 14 so as to swing 110 about an axis parallel to that of the associated pulley 10, a linear actuator 18 being interposed between the arm 13 and a stationary matching member of the beam 14. Thanks to this construction, the tension of each belt 6, and thus the pressure exerted by each belt on the roll 2 in the direction of the roll 1, may be adjusted. The belts 6 are arranged in a predetermined order over the axial length of the roll 2 and particularly, in order to reduce the number of actuators, the belts 6 are supported in groups each formed by a pair of belts, said groups of belts, indicated as 20, being uniformly arranged, i.e. equally spaced all along the roll 2. Particularly, the axial distance between the belts of one group is shorter than the axial distance between the individual groups. When the corrugator unit is in the operating condition, the belts, rotating on themselves, follow the rotation of the roll 2, while exerting a pushing action on said roll 2 against the roll 1; this pushing action is separately adjustable at each group, by a higher or lower tension of the belts 6, by means of the actuators 18. Suitable means, well known per se, for controlling the actuators 18 allow to apply such a tension on the belts, as to obtain a uniform pushing force over the whole axial length of the roll 2 against the roll 1. It should be noted that, since each group, or alternatively each belt 6 is provided with a separate actuator 18, the tension of the belts 6, associated to different segments of the roll 2 may be varied locally, thus allowing for a compensation of any local unevenness, and always ensuring a uniform pressure of the roll 2 against the roll 1, over their whole length. The provision of a swinging beam 14, allows to displace the roll 2 from the roll 1, so as to be able to introduce the paper, and to clean the machine. The actuators 16 are also arranged all along the roll 2 and the beam 14, preferably being associated to the intermediate areas between the individual groups 20 of belts 6. One of the rolls 1, 2 or both are rotatably driven, whereas the belts 6 may be idle or also rotatably driven about the pulleys 7 to 10, so as to be synchronized with the speed of rotation of the roll 2.

Claims: A corrugator unit, particularly for sheets of webs of paper or similar, comprising at least two rolls (1, 2) having a toothed or corrugated surface (101, 202) and being mutually engaged, which rolls (1, 2) are rotatably supported about their axis at their ends and are pushed radially against each other by a predetermined pressure or force exerted over the whole axial length of the rolls, at least one roll (2) being movable towards the other roll (1) and being held by a cradle (106) which adheres against the side of the movable roll (2) diametrically opposite to the other roll (1) in a plurality of contact locations or areas distributed all over its axial length, characterized in that the cradle (106) is composed of a set of end less rotatable supporting belts (6) (7, 8, 9, 10) arranged along the length of the movable roll (2), there being provided means for pushing the belts (6) with a predetermined force towards the associated moving roll (2). A corrugator unit as claimed in claim 1, characterized in that the cradle (106) and the movable roll (2) held by the cradle are supported so as to be movable (4, 5, 15, 16, 17) from an operating position, in which the roll (2) held by the cradle is tangent to the other roll (1) and is pushed against it, to a rest position, in which the roll (2) held by the cradle is displaced to a predetermined extent from the other roll (1). A corrugator unit as claimed in claim 1 or 2, characterized in that at least one and/or both rolls (1, 2) and/or the belts (6) forming the cradle (106) are rotatably driven. A corrugator unit as claimed in the preceding claims, characterized in that the belts (6) are driven around pulleys (7, 8, 9, 10) being all supported by a common frame (14), which frame (14) is movable from and to the other roll (1) between the rest position and the operating position. A corrugator unit as claimed in one or more of the preceding claims, characterized in that for each individual belt or for groups thereof there are provided belt-tightening means (10, 13, 18, 19). A corrugator unit as claimed in one or more of the preceding claims, characterized in that each belt (6) is driven around four pulleys (7, 8, 9, 10) which form the vertices of a quadrilateral and are supported by arms (11, 12, 13) which branch off from a common central beam (14) extending all over the length of the roll (2) held by the cradle, whereas the cradle (106) is formed by the belt branch being in the area of this roll (2), the pulleys (7, 8) which subtend said belt branch being aligned with their axes parallel to the axis of said roll (2) on the side diametrically opposite to the other roll (1). A corrugator unit as claimed in claim 6, characterized in that the plane containing the axes of the pulleys (7, 8) which subtend the belt branches forming the cradle (106) is parallel to the plane tangent to the rolls (1, 2) and passes through the tangent line therebetween. A corrugator unit as claimed in one or more of the preceding claims, characterized in that one roll (1) has a greater diameter and is supported in such a way as to be stationary with respect to a movement transverse to its axis of rotation, whereas the other roll (2) has a smaller diameter and is rotatably held by the cradle (106), being movable within limits transversely to its axis.

Inventors: LUCCA FLAVIO POMPEO, ROSSI RENATO, LUCCA, FLAVIO POMPEO, ROSSI, RENATO
Applicants: AGNATI SPA, AGNATI S.P.A.
Application year: 1998
Main classification: B31F1
IPC codes: B31F1