Patent Application
20230405962
The present invention relates to machines for producing corrugated board. Particularly, the invention relates to improvements to the so-called single facers.
Corrugated board is produced from sheets of flat paper unwound from master rolls. In its simplest form, corrugated board is formed by a web of flat paper and a web of corrugated paper, glued together at the crests of the flutes of the corrugated paper web. The resulting board web is called “single face corrugated board”. Usually, a second web of flat paper is attached to this base structure, i.e., glued to the corrugated paper web so that this latter is interposed between the two flat paper webs, which are also called liners. In some cases, other webs are added to this structure formed by three paper webs, resulting in a sequence of corrugated paper webs interposed between flat paper webs.
Single face corrugated board is produced by a single facer, that comprises a pair of meshing corrugating rollers, between which a first flat paper web is fed. The first flat paper web is hot-deformed in the nip between the two corrugating rollers and becomes a corrugated paper web. Glue is applied to the crests of the flutes of the corrugated paper web adhering to one of the corrugating roller, and a flat paper web is pressure- and hot-applied to the corrugated paper web provided with glue.
A pressure unit is provided for gluing the corrugated paper web and the flat paper web together, this unit comprising at least a pressure member that is pressed against one of the corrugating rollers. The flat paper web and the corrugated paper web are fed between the corrugating roller and the pressure member.
U.S. Pat. Nos. 10,618,242 and 8,714,223 disclose examples of single facers.
Both the paper sheets are preheated before entering the single facer, in order better to be glued together. To this end, heating rollers are usually used, inside which steam flows and around which the paper web is driven. Examples of single facers with heating rollers are disclosed in U.S. Pat. Nos. 5,512,020, 6,745,807, EP1757548, EP1270472. In order to vary the amount of heat transferred to the paper web from the heating roller, guide rollers are provided, which can take different angular positions around the rotation axis of the heating roller and thereby modify the arc of contact between heating roller and paper web.
These preheating systems have some drawbacks and limits. In particular, condensate is formed inside the heating roller by the transfer of latent vaporization heat from the steam to the paper web through the cylindrical wall of the heating roller. Because of centrifugal force, condensate forms a layer on the inner surface of the cylindrical wall of the heating roller. The condensate layer may significantly hinder the transfer of heat from steam to corrugated board, thus making the heating system inefficient.
Moreover, the systems for varying the arc of contact between heating roller and paper web have high inertia and do not allow to vary the arc of contact quickly. Due to the above, the single facer is not able to modify its operating conditions fast. For example, it is not able to react promptly to the variation of the web feed speed that would require a corresponding prompt variation of the arc of contact between paper web and heating rollers. Due to the delay in adjusting the arc of contact between paper web and heating roller, sometimes long paper portions could be heated too much or too little, and this results in defects in the finished product and, consequently, in wastes.
The use of heating rollers requires a high number of guide rollers for the paper webs. The guide rollers take heat away from the paper web, thus increasing the energy consumption of the single facer. In fact, to achieve the temperature required for correct gluing, it is necessary to provide more heat, part of which is taken by the drive rollers.
Moreover, the guide rollers, as well as the heating rollers, have high moment of inertia, thus generating significant tension fluctuations in the paper web, especially during speed changes. These tension fluctuations result in an incorrect operation of the single facer and in production defects.
In some less recent single facers, curved heating plates have been used instead of the heating rollers. A schematic example of this kind of single facer is disclosed in EP0260526. This single facer has neither systems for controlling the arc of contact between paper web and heating plate, nor systems for adjusting and controlling the tension of the paper webs. The temperature adjustment shall be performed by means of heating rollers and corresponding adjustment members, not shown, for adjusting the arc of contact between roller and paper, arranged upstream of the heating plates.
EP0260525 discloses a single facer where the paper web forming the liner (flat web) of the corrugated board is preheated by a heating plate, whilst the web to corrugate is preheated by a heating roller. Systems are not provided for adjusting the arc of contact between paper webs and preheating members, and it is therefore necessary to provide a further heating roller arranged upstream of the heating plate and provided with adjustment members, not shown, for adjusting the arc of contact between paper and heating roller.
U.S. Pat. No. 5,156,714 discloses a single facer where the paper web (flat web) forming the liner is preheated by heating rollers, whilst the paper web to corrugate is preheated by one heating plate. The arc of contact between paper web and heating plate is adjusted through a guide roller that translates with respect to the heating plate. Adjusting the heating conditions is a slow process, resulting in an unsatisfactory system.
EP3,375,601 discloses a single facer where the paper web to corrugate is preheated by a heating roller, whilst the flat web forming the liner is heated by a heating plate having two opposite convex surfaces, along which the paper web is fed. In order to change the arc of contact between the paper web and the two active surfaces of the heating plate, two guide rollers are provided with respective actuators, which modify the position of each guide roller with respect to the heating plate. In this case again, the operations of paper heating and adjusting temperature are inefficient.
Therefore, the prior art preheating systems with heating plates are, in general, poorly efficient, difficult to be controlled, and slow, and can cause undesired tension fluctuations in paper webs.
A need therefore exists, for a single facer with a heating system, i.e., a system for preheating paper webs, that completely or partially overcomes the drawbacks of the prior art single facers.
In order to solve or alleviate one or more drawbacks of the single facers of the prior art, a single facer is provided comprising a first feed path for feeding a first paper web towards a corrugating nip defined between a first corrugating roller and a second corrugating roller. The single facer also comprises a second feed path for feeding a second paper web towards a pressure nip defined between the first corrugating roller and a pressure member co-acting with the first corrugating roller. A respective heating system is provided along each feed path. Each heating system comprises at least a pair of heating plates, on which the respective paper web is fed.
In advantageous embodiments, systems are provided for adjusting the angular position of each heating plate with respect to a bearing structure, so as to adjust the arc of contact between the respective paper web and the heating plate.
Particularly, in some embodiments a single facer is provided comprising a first feed path for feeding a first paper web towards a corrugating nip defined between a first corrugating roller and a second corrugating roller. The single facer also comprises a first heating system arranged along the first feed path and adapted to heat the first paper web upstream of the corrugating nip.
A second feed path is also provided for feeding a second paper web towards a pressure nip defined between the first corrugating roller and a pressure member co-acting with the first corrugating roller. A second heating system is provided along the second feed path and adapted to heat the second paper web upstream of the pressure nip.
A glue dispenser co-acts with the first corrugating roller to apply glue to crests that are formed on the first paper web by the first corrugating roller and the second corrugating roller.
The first heating system advantageously can comprise at least a first heating plate and a second heating plate. The second heating system advantageously can comprise at least a third heating plate and a fourth heating plate. Each heating plate has an active surface adapted to contact the respective paper web; its angular position may be advantageously adjusted to modify promptly the arc of contact between the heating plate and the respective paper web, so that the paper web is heated properly.
The invention will be better understood by following the description below and the attached drawing, showing a non-limiting embodiment of the invention. More specifically, in the drawing:
The single facer 1 comprises a bearing structure 3 connected to a bridge 5, along which a single face corrugated board, produced by the single facer 1, is fed.
The single facer 1 comprises a first feed path P1 to feed a first paper web N1 coming from a first unwinder, not shown. The single facer 1 also comprises a second feed path P2 to feed a second paper web N2 coming from a second unwinder, not shown. The first paper web N1 forms the fluting of the single face corrugated board NS exiting from the single facer 1, whilst the second paper sheet N2 forms the liner of the single face corrugated board NS. Through a lifting device 7, the single face corrugated board NS, produced by the single facer 1, is fed to the bridge 5, and from here it is fed to a double facer, in order to be glued to other webs of single face corrugated board coming from other single facers, and/or to a second liner, to form a corrugated board with one or more flutes. In other embodiments, the web of single face corrugated board is directly cut into sheets or wound in rolls.
The single facer 1 comprises a first corrugating roller 9 and a second corrugating roller 11, co-acting together to form a corrugating nip, through which the first paper web N1 is fed so as to be permanently deformed, i.e., fluted. The feed path P1 extends through the corrugating nip between the corrugating rollers 9 and 11 and between the corrugating roller 9 and a glue dispenser 13, which is adapted to apply glue to the crests of the flutes formed on the first paper web N1. The glue dispenser 13 is arranged adjacent to the first corrugating roller 9, downstream of the corrugating nip in the feed direction of the paper web N1, and co-acts with the first corrugating roller 9. More precisely, the glue dispenser 13 is arranged between the corrugating nip, defined by the corrugating rollers 9 and 11, and a pressure member 15, co-acting with the first corrugating roller 9 and defining, with this latter, a pressure nip to glue the two paper webs N1, N2 together.
In the embodiment of
The second feed path P2 extends through the pressure nip, between the pressure member 15 and the first corrugating roller 9, so that the first paper web N1 and the second paper web N2 are bonded together while moving through the first corrugating roller 9 and the pressure member 15, thanks to the glue applied by the glue dispenser 13. Gluing is performed through pressure and heat applied to the paper webs N1, N2. To this end, the paper webs N1, N2 are preheated before being fed to the corrugating rollers 9, 11. Moreover, also the corrugating rollers 9 and 11 may be heated, so as to transfer heat to the paper webs N1, N2. The corrugating rollers may be heated, for example, through saturated or superheated steam flowing inside the corrugating rollers 9, 11.
A first heating system 21 is arranged along the first feed path P1 to preheat the first paper web Ni before it arrives to the corrugating rollers 9 and 11. Analogously, a second heating system 23 is arranged along the second feed path P2 to preheat the second paper web N2 before it arrives to the first corrugating roller 9 and the pressure member 15.
As it will be better described below, each heating systems 21, 23 comprises at least one stationary heating plate, and preferably two stationary heating plates, on which the respective paper web N1 or N2 moves. “Stationary plate” means a plate that is substantially stationary during operation (in contrast to a preheating roller, that rotates at the same feed speed of the paper web). As better explained below, each heating plate is provided with an adjustment movement to modify the arc of contact with the respective paper web N1, N2.
More in particular, the first heating system 21 comprises a first heating plate and a second heating plate 29. The second heating system 23 comprises a third heating plate 27 and a fourth heating plate 33.
In the illustrated embodiment, the first heating system 21 also comprises a fifth heating plate 31, and the second heating system 23 also comprises a sixth heating plate 35.
In the present description and the attached claims, if not otherwise indicated the adjective “first”, “second”, “third” etc. have the sole function of uniquely identifying the single heating plates and are not limiting, for example they do not limit the overall number of heating plates provided in each feed path nor the reciprocal position of the heating plates. For example, the heating plate 31 of the first heating system 21 is indicated as “fifth” heating plate, to distinguish it from the remaining heating plates 25, 27, 29, 33, 35; but this does not necessarily imply that the single facer comprises five (or more) heating plates.
In some embodiments, the second heating system 23 arranged along the second feed path P2 also comprises a heating roller 37.
In general, even if in
Currently, the preferred configuration of the first heating system 21 is that illustrated, with the three heating plates 25, 29, 31, and the preferred configuration of the second heating system 23 is that illustrated, with the three heating plates 27, 33, 35.
The minimal configuration provides for two heating plates in each feed path P1, P2. In this case, the plates may be arranged so as to touch respectively a first face and a second face of the respective paper web N1, N2. However, this is not strictly necessary.
In the example of
In some embodiments, two heating plates are provided along each feed path, which touch the face of the respective paper web N1, N2 that is in contact with the glue applied by the glue dispenser 13. Therefore, in the first feed path P1 of the first paper web N1 only the two heating plates 25 and 29 are provided, heating the face of the paper web N1 that, in the corrugating nip between the first corrugating roller 9 and the second corrugating roller 11, faces the second corrugating roller 11.
Along the second feed path P2 of the second paper web N2 only the two heating plates 27 and 33 are provided, heating the face of the paper web N2 that faces the first corrugating roller 9. If provided (as in
In some embodiments, the heating roller 37 is replaced by a heating plate and/or the heating plate 35 is omitted.
In advantageous embodiments, each heating element 25, 27, 29, 31, 33, 35, 37 comprises adjusting members for adjusting the arc of contact between the respective paper web N1 or N2 and the heating element.
In the embodiment of
Each heating plate 25, 27, 29, 31, 33, 35 comprises a respective preferably cylindrical curved active surface (in advantageous embodiments a round cylindrical surface), on which the respective paper web N1 or N2 moves (when the plate is in active position).
Advantageously, each heating plate 25, 27, 29, 31, 33, 35 is mounted on the bearing structure 3 so as to rotate around an adjustment axis, in order to adjust the angular position of the heating plate. The adjustment axis is substantially horizontal and orthogonal to the feed direction of the first paper web N1 and of the second paper web N2. The adjustment axis of each heating plate is substantially parallel to the generating lines of the cylindrical active surface of the respective heating plate. In the drawing, the adjustment axes of the heating plates 25, 27, 29, 31, 33, 35 are indicated with the reference number of the respective heating plate followed by the letter “A”. For example, the adjustment axis of the heating plate 25 is indicated with 25A. In the illustrated embodiment, the rotation axes 27A, 33A of the heating plates 27 and 33 coincide.
The rotation of each heating plate is controlled by a respective actuating device, comprising for example a linear actuator, or preferably a pair of linear actuators, one on each side of the single facer 1, for example a pair of pneumatic or preferably hydraulic cylinder-piston actuators. The actuating device may alternatively comprise mechanical jacks or even linear or rotary electric motors.
Rotation can be controlled continuously within a given angle, between two end positions, for example a position where the arc of contact between the active surface of the heating plate and the paper web is substantially null, and a position where the arc of contact between the active surface of the heating plate and the paper web is to maximum.
In case hydraulic actuators are used, these may be provided with proportioning valves on the pressure fluid supply line, for greater precision in adjusting the angular position of each heating plate.
The angular position of one, some or all heating plates may be detected by a sensor or an encoder. In some embodiments, temperature sensors are provided at one or more points of the feed path of the first and/or the second paper web N1, N2. The angular position of one or more heating plates is adjusted based on the temperature detected by the one or more temperature sensors. For example, a temperature sensor may be provided between the furthest downstream heating plate and the first corrugating roller 9, to detect the temperature of the respective paper web immediately before the web directly or indirectly contacts the first corrugating roller 9, and to compare the detected value with a preset value. In further embodiments, for adjusting each heating plate in an independent and more accurate manner, a temperature sensor is provided downstream of each heating plate, that detects the temperature and gives a value to be compared with a temperature value required downstream of the respective heating plate.
In simpler embodiments, the temperature sensors may be omitted and the position of the heating plate(s) is detected through preset curves that have been experimentally calculated based on the feed speed of the paper webs.
Just by way of non-limiting example, in
Just by way of example, in
The heating plates 25, 31, 35 are configured similarly to the heating plate 29, each with a respective actuating device, for example a pair of linear actuators (an actuator on each side of the single facer) in order to change and to register the angular position of the respective heating plate.
Each heating plate comprises an inner chamber, in which a heat-transferring fluid flows and which is delimited by a wall defining the curved active surface, and by an opposite closing wall that can be flat. In
As can be understood from
As mentioned above, the heating plates 27 and 33 are mounted pivoting around a common adjustment axis indicated with 27A, 33A. The rotation of the heating plates 27, 33 is controlled by a common actuating device. This common actuating device can comprise a pair of cylinder-piston actuators, as in the case of the remaining heating plates.
The structure bearing and moving the two heating plates 27, 33 is illustrated in greater detail in
Referring again to
Each arm 43 is connected to the corresponding arm 45 by means of an actuator, for example a linear cylinder-piston actuator 47, which is arranged outside the respective arms, i.e. on the side of the arms opposite the heating plates 27, 33. The set of the two actuators 47 forms the actuating device for adjusting the angular position of the two heating plates 27, 33. Lengthening and shortening of the actuators 47 cause the scissor opening and closing of the arms 43, 45 and therefore the change of the angular position of the two heating plates 27, 33.
In practical embodiments, the arrangement is such that, starting from a closing position of the arms 43, 45, as shown in
Once the arms 43 and the plate 27 have achieved the maximum opening position, the further lengthening of the actuators 47 causes the lifting, i.e., the clockwise rotation in the drawing (i.e., opposite to the initial rotation of the heating plate 27), of the heating plate 33, up to the maximal extension of the actuators 47, corresponding to the position where the arms 43, 45 and the heating plates 27, 33 are moved away from each other as much as possible. In the maximum opening position, the arc of contact between the paper web N2 and the heating plates 27, 33 is maximal.
During the closing step, the movement of the heating plates 27 and 33 is reverse to what described: firstly the heating plate 33 rotates counterclockwise, then the heating plate 27 rotates clockwise, with a consequent gradual decrease of the overall contact surface between paper web N2 and heating plates 33, 27.
In advantageous embodiments, a tension regulator is provided in one or both paths P1, P2. The tension regulator is preferably arranged between two adjacent heating plates.
In the embodiment of
In the embodiment of
Whilst in the illustrated embodiment the take-up rollers are supported by pivoting arms, in other embodiments they can be provided with a translation movement, instead of a pivoting movement around an axis. In that case, the take-up roller can be carried by slides movable on low-friction guides.
The tension regulator, combined with a heating system with heating plates, is particularly advantageous as it allows to balance friction variations resulting either from changes in the arc of contact between paper web N1 or N2 and heating plates, or from other factors. In fact, by changing the angular position of a heating plate, the friction exerted onto the paper web by the heating plate changes quickly and also the tension of the paper web consequently changes. The tension regulator allows to limit these changes also while the heating plates move. Tension variations in the paper web, which can be balanced by the tension regulator, can be also caused by other factors, such as change in the feed speed of the paper web, or by the effect of liquid dispensers, described below.
Practically, an encoder may be associated with each take-up roller of the tension regulators, which identifies the position of the respective support arms 57 e 65 and, therefore, of each take-up roller 55, 63. The signal from the encoder is transmitted to a central control unit (schematically indicated with reference number 100 in
In this way, if for example a change in the arc of contact between paper web and heating plate tends to increase the paper web tension, the take-up roller moves in such a direction to reduce this tension increase. The change in the position of the take-up roller, detected by the respective encoder, causes such a change in the feed speed of the paper web (if necessary, by modifying the tension) to eliminate the displacement of the take-up roller. The tension change can be caused by a change in the arc or contact between paper web and heating plate upstream of the take-up roller. Typically, if the arc of contact between paper web and heating plate increases, the tension detected by the roller also increases. The opposite condition occurs in case of reduction in the arc of contact between paper web and heating plate.
In some embodiments, liquid dispensers are provided along one or both the first feed path P1 and the second feed path P2, that are adapted to apply a liquid to one of the two opposite faces of the respective paper web N1, N2. In particular, the liquid may be water.
In the embodiment of
In advantageous embodiments, the first liquid applying device 71 is so arranged as to apply liquid to the face of the first paper web N1 that goes into contact with the first heating plate met by the paper web N1 after having received the liquid applied by the liquid applying device 71, i.e. the heating plate 31 in the example of
In some embodiments, the liquid applying device 71 is a so-called bar coater or rod coater, comprising a fountain roller 73 rotating around a horizontal axis, i.e., an axis orthogonal to the feed direction of the paper web N1, coated with a helical wire forming a surface for receiving the liquid and transferring it to the face of the paper web N1 touching the fountain roller 73. The fountain roller 73 takes the liquid from a fountain 75 below. The fountain roller 73 may be motorized and rotate at adjustable peripheral speed greater than, lower than, or equal to the feed speed of the first paper web N1. The peripheral speed of the fountain roller 73 is so modulated as to dose adequately the quantity of water, or other liquid, applied to the face of the paper web N1.
By changing the peripheral speed of the fountain roller 73 and setting it to a value different than the feed speed of the respective paper web N1, variations in the tension of the paper web N1 can occur. The use of the tension regulator 53 allows to balance these tension variations, tending to keep the tension of the paper web N1 around a preset value.
In some embodiments, the liquid applying device 71 may comprise a guide member 75 adapted to guide the paper web N1 so that it is selectively in contact with the fountain roller 73 or spaced from it, to receive or not liquid, based on the operating needs. In the illustrated embodiment, the guide member comprises a guide roller 77 carried by movable arms 76 and controlled by an actuator 79. In this way, the liquid application may be omitted, if required.
In the embodiment of
In advantageous embodiments, the second liquid applying device 81 is so arranged as to apply the liquid to the face of the second paper web N2 that goes into contact with the first heating plate met by the paper web N2 after having received the liquid, i.e., the heating plate 35 in the example of
In some embodiments, also the liquid applying device 81, similarly to the applying device 71, is a bar coater comprising a fountain roller 83 rotating around a horizontal axis, i.e. an axis orthogonal to the feed direction of the paper web N2, that takes the liquid from a fountain 85 below. The fountain roller 83 may be motorized and the rotation speed may be controlled in the same manner as described for the fountain roller 73.
In some embodiments, the liquid applying device 81 may comprise a guide member adapted to guide the paper web N2 so that it is selectively in contact with the fountain roller 83 or spaced from it, to receive or not the liquid. In the illustrated embodiment, the guide member comprises a guide roller 87 carried by movable arms 86 and controlled by an actuator 89.
In some embodiments, any one or both the liquid applying devices 71, 81 are omitted, in order to simplify the structure of the single facer 1. In case only one liquid applying device is provided, this is preferably the applying device 81 that applies liquid to the paper web N2 intended to form the liner (flat sheet) of the single face corrugated board NS.
The use of the liquid applying device 71 allows some advantages as regards preparation of the paper web N1 to be glued. As mentioned above, when the paper web N1, that has received the layer of liquid (typically water) on its surface, goes into contact with the heating plate 31 downstream of the liquid applying device 71, the applied water evaporates, thus forming a steam film between the heating plate 31 and the paper web N1. This steam film protects the paper from too quick or too high heating and opens the paper pores, thus facilitating the following absorption of glue. In this way, the amount of glue applied by the glue dispenser 13 may be reduced, with consequent savings in term of material and thermal energy.
In fact, the glued used in these application is typically a starch- and water-based glue, wherein water constitutes the transferring fluid to make the penetration of starch into the cellulose fibers of the paper web easier. If steam has been applied to the paper web N1 in the feed path P1 upstream of the corrugating rollers 9, 11, the amount of glue can be reduced. To a lower amount of applied glue corresponds a lower amount of energy required for the reciprocal adhesion of the paper webs N1, N2, as well as a lower glue consumption.
In the illustrated embodiment, water is applied to the face of the paper web N1 opposite the face on which glue is applied. The reason thereof is that the feed path of the paper web N1 is such to make the application of water to that surface easier. Usually, the paper web N1 is thin; therefore, steam penetrates through it causing dilation of paper pores also on the face opposite to that where water is applied. However, it is also possible to apply water (only or also) to the opposite face, i.e. the face to which glue is then applied.
The application of water to the paper web N2 forming the liner of the single face corrugated board NS has analogous advantages in terms of facilitating gluing and reducing the amount of glue and, consequently, energy consumption. Water is preferably applied to the face intended to contact the crests of the paper web N1, because the feed path P2 allows it smoothly and also because the paper web N2 usually has a thickness greater than the thickness of the paper web N1.
Applying water to the paper web N2 has also further advantages. In particular, applying water to the paper web N2 increases dimensional stability of the paper web during the subsequent steps of gluing, cutting into sheets and stacking, thus reducing the risk for the sheets formed by the corrugated board to warp.
In addition to the advantages in terms of material and energy consumption, reducing the amount of applied glue also allows to reduce the drawbacks connected with the dispersion of glue caused by centrifugal force once the glue has been applied to the crests of the corrugated paper web N1. This is advantageous because reduces the accumulation of glue residues on the mechanical members of the single facer.
With any one or both the liquid applying devices 71, 81, humidity sensors may be associated, adapted to measure the water percentage in the respective paper web N1, N2. Some known humidity sensors are able to determine the water percentage in, or on, the paper web, whether humidity is absorbed in the cellulose structure or is partially or completely distributed on the outer surface in the form of a liquid film. In this way, it is possible to adjust the amount of liquid supplied by the respective liquid applying device so as to keep the humidity content of the paper web approximately at a preset value.
In some embodiments, along the first feed path P1 a humidifier can be provided, comprising for example a box, from which steam is supplied to the first paper web N1. In
The humidifier 91 can comprise for example a box, to which steam is supplied and which has a sliding surface for the paper web N2, which is defined by a wall having openings for supplying steam towards the paper web N1 moving along the sliding surface.
The use of movable heating plates to change the arc of contact between paper web and heating surface allows to solve many technical problems typical of the roller heating systems. In particular, those problems are reduced, resulting from condensate accumulation on the inner surface of the heat exchange wall, that in the rollers is caused by the centrifugal force.
Moreover, by using the movement of the heating plates to change the arc of contact between paper web and heating surface, it is possible to have changes of the arc of contact quicker than those obtained with roller preheating systems or with preheating systems utilizing heating plates that use movable deviating rollers to change the arc or contact between heating plate and paper web.
To this end, as shown in
As shown in the embodiment of
For example, the shape of the feed path P1 in the area of the heating plate 31 is defined by a guide roller 31X coaxial with the adjustment axis 31A and by a guide roller 32 upstream (with respect to the feed direction of the paper web N1) of the heating plate 31. For the heating plate 29, the path of the paper web N1 is defined by a guide roller 29X adjacent to the adjustment axis 29A and by the take-up roller 55. The guide roller 29X, together with a guide roller 25X coaxial with the axis 25A, defines the segment of feed path adjacent to the heating plate 25.
For the pair of heating plates 27, 33, a common guide roller 27X is provided, coaxial with the adjustment axis 27A coinciding with the adjustment axis 33A. The segment of feed path associated with the heating plate 27 is defined between the guide roller 27X and the roller 15.3 of the pressure member 15 (
In addition to allowing a quicker adjustment of the surface of contact between the paper web and the heating members, the use of heating plates instead of heating rollers also reduces the overall number of guide rollers along the paper web feed paths. This is advantageous from many viewpoints. Firstly, the overall structure of the single facer is simplified. Moreover, as part of the heat supplied to the paper web is subsequently removed by the guide rollers, by reducing the number thereof the heat loss decreases and the overall thermal efficiency of the single facer increases.
Moreover, the guide rollers are not motorized and have high inertia (high moment of inertia). Therefore, they cause significant tension variations in the paper web when changes in the paper web feed speed occur. This problem is mitigated by reducing the number of guide rollers.
The use of heating plates limits the formation of wrinkles in the paper webs N1, N2 thanks to the effect of friction between webs and plates. Wrinkle reduction may be also improved by machining the cylindrical surfaces of contact between paper web and heating plate, for example by providing small reliefs or grooves arranged symmetrically with respect to the centerline of the plate and inclined towards the side ends of the plate, that tend to stretch transversally the paper web sliding moving on the heat exchange surface of the heating plate. In this way the heating plate has also the function of stretcher of the paper web.
At least some of the advantages of the embodiments described above may be also obtained through simpler and currently less preferred embodiments, for example by providing a lower number of heating plates and/or by omitting one or more of the other components.
For example, the liquid applying device 71 and/or the tension regulator 53 and/or a heating plate, for example the heating plate 31 or the heating plate 29, or in some cases the plate 25, may be omitted along the feed path P1 of the first paper web N1. By removing any one of the two heating plates 25, 29 and leaving the other one in combination with the heating plate 31, the two opposite faces of the paper web N1 are heated.
Along the feed path P2 of the second paper web N2 the liquid applying device 81 and/or the tension regulator 61 and or a heating plate, for example the heating plate may be omitted. In other embodiments, the heating roller 37 is omitted and/or is replaced by a further heating plate.
In some embodiments, the lifting device 7 lifting the single face corrugated board NS up to the bridge 5 can co-act with the system of heating plates described above. This configuration is illustrated in
The invention has been described above in various embodiments. It is however clearly apparent to those skilled in the art many modifications, changes and omissions can be done to the invention without however departing from the protective scope as defined in the attached claims. The reference numbers in the attached claims have the only purpose of facilitating reading thereof and do not limit the protective scope of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102020000028172 | Nov 2020 | IT | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2021/082300 | 11/19/2021 | WO |
