FR2697545A1 - Papermaking machine web dryer - has applicator of HF at the drying cylinder section - Google Patents

Abstract

The drying section, for the continuous web in a papermaking machine, has a HF applicator (16) with a vertical movement under the machine. The rollers (17) are at fixed mountings, accessible from below the machine. The four rollers (17) are in a U-shape array, near a lower drying cylinder, without diverting the paper (10) path. The HF applicator (16) is supplied from a HF generator (46) through a coaxial connection column (28) of a critical dia., with an external and internal conductor as metal bellows. The outer conductor can be a bellows of a metal fabric, with a hinged inner conductor to match the inner dia. of the outer bellows to give a connection of variable length as the HF applicator (16) is raised and lowered. An impedance adaptor (26) is linked to the HF generator (46) through a coaxial cable (27). Its output is connected to the coaxial connection column (28) to modify the transmitted energy according to the impedance of the HF applicator (16). The adaptor (26) has a coaxial symmetry to match the coaxial cable (27) and the coaxial connection column (28). The HF applicator (16) has a metal structure (15) to guide the vertical movements. A lifter (22) gives the vertical up and down movement to the HF applicator (16), which has an electro-magnetic lock to hold it at the required level. USE/ADVANTAGE - The station is for drying continuous paper webs through HF energy, at a papermaking machine. The system can be fitted easily to existing papermaking machines, between two groups of drying cylinders.

Description

HIGH FREQUENCY DRYING DEVICE
FOR CONTINUOUS PAPERMAKING MACHINE
DESCRIPTION
FIELD OF THE INVENTION
The invention relates to the continuous production of paper, and in particular of paper-cardboard. It relates more precisely to a drying device involved in the continuous production lines.

PRIOR ART AND PROBLEM POSED
Figure 1 shows schematically the main sections of a continuous paper making machine. Such a machine measures several tens of meters long and a few meters wide.

 The paper pulp 2 contained in a headbox 1 is first deposited in a thin layer on a drip table 3. On this occasion, it is cut laterally to the required width, called "width". The dough is then wrung out by cylindrical presses 4 before starting a drying route on steam heated cylinders. The paper 10 undergoes on this occasion a pre-drying 5 around steam drying cylinders, then a post-drying 7 around steam drying cylinders. The paper 10 thus dried undergoes a humidity control 8 before being rolled up by means of a winder 9.

 If the regularity of humidity in the direction of travel is well controlled by regulating the speed of the machine, it is not the same in the transverse direction. The major causes of disparity in the humidity of the paper webs are of two kinds.

 The first concerns the variation in the thickness of the paper at the level of the deposition of the pulp 2 on the table 3 and at the level of the quality of the pressing 4.

 The second is due to direct irregular drying or fouling of the felts and where the variation in thickness plays a key role.

 High frequency drying overcomes this drawback. Such high-frequency drying, called "HF", can be carried out, as shown in FIG. 1, after pre-drying 5 and before post-drying 7. Indeed, high-frequency electrical exchange makes it possible to heat the paper from a distance, like infrared radiation, but in all its thickness. This is explained by the fact that paper and a dielectric whose losses increase with humidity. When it is crossed by a high frequency and constant intensity electric field, the wettest areas of the paper heat up first and the power of the energy source is focused there. In particular, electromagnetic fields are used whose frequency is between 3 and 30 MHz (3 and 30 MHz), for example 13.56 MHz.

 The high frequency drying device or oven 6 of FIG. 1 uses a large number of horizontal and parallel bars supplied with high frequency electricity. The paper 10 flows just above these bars so that a very intense electric field passes through it. However, this type of high-frequency drying device using a large number of bars takes up a relatively large amount of floor space.

The use of such a drying device 6 was nevertheless able to be implemented in a production line where a place left vacant during a prior modification of the end of the machine. Such an opportunity vis-à-vis the congestion occurs only very rarely. Consequently, the existing production lines do not allow the installation of such a high frequency drying device, as it is currently used.

 The object of the invention is to remedy this drawback by proposing a high-frequency drying device of a different design allowing it to be installed on existing production lines and not having a large place between two series of cylinders steam dryers.

SUMMARY OF THE INVENTION
In the context of paper production lines installed above a basement of several meters, the main object of the invention is a high-frequency drying device for a continuous paper production machine, comprising
- a high frequency generator
- a high frequency applicator powered by the high frequency generator .. and consisting of several series of parallel bars serving as electrodes; and
- rollers for diverting the paper along these series of bars, so that the paper undergoes the high frequency electric field created between the bars.

 According to the invention, the high frequency applicator is movable vertically below the machine, the rollers being mounted at fixed locations accessible from below the machine.

 The main embodiment of such a device, in the case where the machine has several lower steam drying cylinders, provides that the rollers are four in number and are arranged in a U instead of one of the lower drying cylinders of the machine , so as not to impose any additional diversion on the paper.

 A preferred characteristic of the invention, when the high frequency applicator is supplied by the high frequency generator by means of a coaxial column (or line) of very large diameter connection comprising an external conductor and an internal conductor, provides that this external conductor is produced in the form of an external bellows of wire mesh and the internal conductor is produced in the form of a hinge articulation system to form a column of variable length and allow the high frequency applicator d '' be mounted and lowered below the machine.

 The external and internal conductors can also be each produced in the form of a metal fabric bellows.

 In the case where the high frequency generator supplies energy with a determined output impedance, an impedance adapter connected to the high frequency generator is used and the output of which is connected to the column or coaxial connection line with bellows.

 Such an impedance adapter preferably comprises at least two capacitors and at least one inductor mounted in a T-diagram, while having a coaxial structure respecting the coaxial structure of a coaxial cable coming from the high frequency generator and the coaxial structure of the coaxial connection column leading to the high frequency applicator.

To operate the device according to the invention, a device for lifting the high frequency applicator is used comprising
- a metal structure equipped with guide means for 11 applicators, in order to guide this applicator
- cylinders mounted vertically to raise and lower the high frequency applicator; and
- electromechanical locking means of the high frequency applicator in a high position and a low position.

LIST OF FIGURES
The invention and its various technical characteristics will be better understood on reading the following description which is accompanied by eight figures representing respectively
- Figure 1, already described, a continuous paper making machine equipped with a device according to the prior art
- Figure 2, in front section, the device according to the invention installed on a continuous paper making machine
- Figure 3, a global view of the device according to the invention in the high position
- Figure 4, an overall view of the device according to the invention in the low position, the rollers being detached
- Figure 5, a detailed view of the upper part of the device according to the invention
- Figure 6, the central part of a first embodiment of the coaxial connection column used in the device according to the invention
- Figure 7, the electrical diagram of the impedance adapter used in the device according to the invention; and
- Figure 8, in section, the impedance adapter of Figure 7 and a second embodiment of the coaxial column.

DETAILED DESCRIPTION OF AN IMPLEMENTATION OF
THE INVENTION
In general, continuous paper making machines are built on metal structures in beams overhanging pits which constitute the basement of production buildings.

 Referring to FIG. 2, the continuous manufacturing machine is symbolized by steam dryer cylinders 11 placed above the machine level symbolized by an artificial soil 12 overhanging a basement 13.

 The only constraint for the installation of the machine according to the invention is the ablation of a lower drying cylinder, in this case that which would be placed in the center of this figure 2. Taking into account that the space in below the machine is easy to access and often unoccupied, it constitutes a privileged place for installing there an additional device to the machine, such as the device according to the invention and its ancillary devices.

 The main elements of the high frequency drying device according to the invention are, among others, a high frequency generator 46, a high frequency applicator generally identified 16 and placed at the top of the device under the machine and rollers 17 intended to guide the paper. It can be seen in this regard that the location left free by the ablation of a lower steam dryer cylinder roller makes it possible to install four rollers 17 forming for example a quadrilateral, such as a trapezoid or a square, making it possible to divert the paper 10 of a path equivalent to that taken by the paper 10 around the steam dryer cylinder which has been removed. The rollers 17 can therefore be arranged in an overall shape resembling a V or a U. They are fixed in translation, but free in rotation.

 In correspondence of the rollers 17, series of bars 18 are placed opposite the sides formed by these four rollers 17. As a result, these bars 18 are very close to the path taken by the paper 10 placed around the detour rollers 17. They are mounted in the applicator relative to each other by two side panels 19 and two longitudinal panels not shown constituting the structure of the high frequency applicator 16. The bars 18 are preferably made of copper and are mounted in series on adjustable supports 23 making it possible to adjust the orientation of the bars 18 relative to the paper 10. The connection of each bar 18 to the high frequency potential or to ground can be carried out by means of copper foils connected to conductive buses high frequency integral with the structure of the applicator and connected to an impedance adapter 26 by means of a coaxial column 28. The high frequency applicator 16 can also be equipped with hot and dry air blowing nozzles guaranteeing a homogeneous distribution of the air flow over the width of the sheet of paper. These nozzles are symbolized by arrows in broken lines 24. The fact that the space left free is used below the machine, that is to say below the machine level 12, makes it possible to mount the high frequency applicator 16, that is to say the set of bars 18, which is movable, in particular in vertical translation. As a result, it is possible to remove the high frequency applicator 16 from the rollers 17 and from the paper 10.

 We can then proceed in the basement to maintenance operations of the applicator and these accessories or to an operation of placing paper at the start of a manufacture.

 In this embodiment, a lifting device is used to raise and lower the high frequency applicator 16. Such a lifting device can consist of a metal structure 15 resting on the ground 14 of the basement 13. This structure 15 has rails 20 vertical bearings. In correspondence, the high frequency applicator 16 has rollers 21 mounted rotating around horizontal axes and placed opposite the rolling rails 20. Cylinders are used to actuate the assembly. Use is preferably made of screw jacks 22 fixed to the metal structure 15 driven by a motor 25. It is also possible to use four shock absorbers at the end of the travel. The whole can be supplemented by electromechanical locking means of the high frequency applicator 16 in the high position and in the low position. This can avoid any false manipulation. In addition, a system of optical beams can prohibit maneuvering operations in the presence of personnel.

 We can see in this figure 2 the high frequency transmission elements to 1 the high frequency applicator 16. They consist of an impedance adapter 26 fixed in the structure 15 below the high frequency applicator 16. I1 receives via a coaxial line 27 the high frequency energy from the high frequency generator 46 and transmits it to the high frequency applicator with a corresponding ohmic value.

 A coaxial connection column (or line) 28 is used, connected to the impedance adapter 26 and to the high frequency applicator 16. This coaxial connection column 28 has a very large diameter and is produced in the form of elements. bellows, so that it can be folded down to allow the descent of the high frequency applicator 16.

 Referring to Figure 3, we understand that it is thus easy to mount the high frequency adapter 16 in place of a lower steam dryer cylinder that was removed to come surrounded by a set of four detour rollers 17 put in place of this lower dryer cylinder.

 Figure 4 shows the device according to the invention with the high frequency applicator 16 descending towards the impedance adapter 26, so as to clear the space where the rollers and their panels are located. This assembly can also be dismantled on this occasion, as shown by the horizontal arrow, for reasons of maintenance and cleaning of this assembly and the surrounding steam dryer cylinders 11.

 FIG. 5 shows in detail all of the rollers 17. These are assembled by means of two lateral flanks 29 joined by a central tube 32. The assembly is mounted in the original bearing 33, fixed on the structure 34 of the machine and previously receiving the steam dryer cylinder which has been dismantled. Preferably, the rollers 17 are mounted on the lateral flanks 29 by means of self-aligning bearings. The rollers 17 may even have a groove 35 making it possible to ensure the passage of the loading rope for the sheet of paper at the start of the positioning of the latter in the machine. Blowing and suction nozzles for hot and dry air can be installed on the tube 32. This can make it possible to evacuate internal fogging in the drying device.

 In this FIG. 5, the interior of the high frequency applicator 16 can also be seen with greater precision. It can thus be seen that the bars 18 are mounted in series on their support 23 inside a box made up of the side panels 19 and longitudinal panels 36. One or more systems 31 for adjusting the orientation of these supports 23 can be installed on the longitudinal panels 36, to allow adjustment of the positioning of the bars 18 relative to the paper to be dried. The box can be completed with doors or windows which can be formed in the longitudinal sides 36 and the side panels 19 to allow cleaning and maintenance of the bars 18.

Hot and dry air blowing nozzles 30 mounted through the side panels 19 can allow a homogeneous distribution of the air flow over the entire width of the sheet of paper, thus contributing to the stability of the latter. Finally, a slot 37 is provided in the upper part of the side panels 19 to allow the high-frequency applicator 16 to come around the detour rollers 17, the end pieces 38 of the tube 32 each entering a slot 37.

 FIG. 6 represents the coaxial column, referenced 28 in FIG. 2, making it possible to supply the high frequency applicator, by the high frequency generator, via the impedance adapter. This column 28 is telescopic to allow movement of the high frequency applicator. It therefore ensures continuity of high frequency and ground potentials and prohibits the radiation of electromagnetic energy at this level.

 It mainly consists of two elements: a conductor with an external bellows 40 and an internal conductor equipped with an articulation system of the hinge type 41.

 The external bellows 40 is made up of strips of stainless steel or welded and encircled brass fabrics. A guide system with an external rod can complete this external bellows 40.

 This FIG. 6 mainly represents the internal conductor and its internal hinge articulation system 41. This hinge articulation system consists of several stainless steel panels 42 hinged together by a hinge system. It supports two copper foils 43, ensuring the connection between the high frequency potentials of the impedance adapter and the high frequency applicator. Once folded, these two elements take positions, shown in phantom. Insulating pads 44 are thus placed at the top of the clicks folds 43 to avoid contact with the external bellows 40.

 A second version of the internal conductor using the structure of the external bellows can be provided using a silver brass fabric for the external conductor. This embodiment makes it possible to significantly reduce the disturbance introduced by this link and brings certain advantages compared to electromagnetic considerations (transfer of powers, limitation of the level of harmonics).

 With reference to FIG. 7, the impedance adapter, marked 26 in the first figures, preferably uses capacitors 45 mounted in a T-type diagram, of which FIG. 7 is an equivalent diagram.

The coaxial connection column 28 is shown there, as is the coaxial cable 27 connecting the high frequency generator to the impedance adapter. The diagram is completed by two inductors 47 each connected on the one hand to ground and on the other hand to a central point through which the two capacitors 45 are also connected.

 This symmetrical structure makes it possible to respect the coaxial structure of the connection line of electrical energy in the form of high frequency, from the generator to the high frequency applicator.

 Figure 8 shows the realization of such an impedance adapter 26. It and consists of a housing 49 of aluminum inside which are the adaptation elements. These finally consist of three capacitors 45 distributed over two stages and separated by a carcass of hardened copper sheet 50, which constitutes the inductors 47 of the diagram of FIG. 7 which therefore have a double electrical and mechanical function. The lower capacitor is connected to the high frequency conductor of the upstream coaxial cable 27, while the two capacitors of the upper stage are connected to the high frequency conductor 48 of the coaxial connecting column 28 with the high frequency applicator. The adjustment of the capacitors 45 is obtained by means of motorization boxes 51 placed on the same axis as the capacitors 45.

 In this FIG. 8, the second version of this coaxial connection column 28 is shown, that is to say that the internal connector is also produced in the form of a bellows 48.

 The upper part of this figure 8, in phantom, symbolizes the deployment of the connection column 28.

 The copper parts of this impedance adapter are silver-plated to minimize ohmic losses and maintain good connections over time.

 Regarding the impedance adapter, the capacitors used 45 are of the water-cooled type. In correspondence, the two copper inductors 47, which constitutes the carcass 50, are preferably covered with a water cooling coil.

ADVANTAGES OF THE INVENTION
Reduction of the space occupied in the machine
The gathered shape of the high-frequency applicator allows the device according to the invention to be installed on an existing manufacturing machine by only taking the place of a lower steam cylinder.

It should be noted that the heating surface offered by the electrodes made up of the bars is close to the contact surface obtained with a drying cylinder.

The impedance adapter is located in the basement, i.e. outside the machine. It can thus be easily ventilated by a deducted ambient air flow. This isolation of the adapter is favorable to its thermal operating conditions since it is placed at room temperature.

 The fact that the device according to the invention can be placed in place of a lower drying cylinder makes it possible to best choose its location because it is essential in this technique.

Improvements in machine operating conditions
Since the high frequency applicator is mobile, that is to say retractable downwards, the positioning of the paper strip is without risk of snagging and easy; visual control of the device is also facilitated. On the other hand, maintenance of this high frequency applicator can be carried out while the paper machine continues to operate, since the paper is not affected by this movement. It is thus possible to obtain paper production during maintenance of the applicator by slightly lowering the operating speed of the whole machine to obtain equivalent drying with only the drying cylinders.

Adaptation to the evolution of continuous paper making machines
These machines regularly undergo transformations aimed at increasing their capacities, such as production, flexibility or reliability. Users are therefore led to envisage possible displacements of the elements of this machine, therefore of the high-frequency dryer along the series of drying cylinders. By design, the dryer device according to the invention allows this adaptation at lower cost, since the mechanical structure of the whole machine is not modified. It then suffices to extract the drying cylinder concerned and to reinstall the old drying cylinder which had been removed. The coaxial electrical link connecting the high frequency generator and the impedance adapter can be shortened or lengthened without problem.

Production gain
Because one is able to have a useful drying surface comparable to the contact surface of the paper on a steam dryer cylinder and the fact that the evaporative efficiency of the high frequency drying is significantly higher than that of 'a steam dryer cylinder in the targeted areas, very significant production gains are obtained. This is particularly obvious for medium and heavy grammage papers, since these papers are relatively thick.

 For example, for an average grammage, the high frequency drying device according to the invention can evacuate twice as much water as a steam drying cylinder while allowing a local reduction of the difference in peaks of very sensitive paper moisture.

 The drying device according to the invention is also advantageous for diaper support papers or fluted papers.

Claims (7)

 1. High frequency drying device for continuous paper making machine, comprising  - a high frequency generator (46)  - a high frequency applicator (16) supplied by the high frequency generator (46) and consisting of several series of bars (18) parallel to each other, serving as electrodes; and  - rollers (17) for diverting the paper (10) along the series of bars (18), so that the paper (10) undergoes the high frequency electric field created between the bars (18), characterized in that l 'high frequency applicator (16) is movable vertically below the machine, the rollers (17) being mounted at fixed locations, accessible from below the machine.  2. Drying device according to claim 1, the machine having several lower drying cylinders, characterized in that the rollers (17) are four in number, and are arranged in a U shape instead of one of the cylinders. lower drying, so as not to impose on the paper (10) any additional diversion.  3. Drying device according to claim 1, the high frequency applicator (16) being supplied by the high frequency generator (46) by means of a coaxial connection column (28) of very large diameter comprising an external conductor (40 ) and an internal conductor (41), characterized in that the internal (41) and external (40) conductors are each produced in the form of a metal bellows (40, 48).  4. Drying device according to claim 1, the high frequency applicator (16) being supplied by the high frequency generator (46) by means of a coaxial connection column (28) of very large diameter comprising an external conductor (40 ) and an internal conductor (41), characterized in that the external conductor (40) is produced in the form of a metal fabric bellows and that the internal conductor (41) is produced in the form of a system of hinge joint, so as to fold back inside the diameter of the external conductor (40), to form a connection of variable length and allow the high frequency applicator (16) to be raised and lowered below the machine.  5. Drying device according to claim 1, the high frequency generator supplying energy with a determined output impedance, characterized in that it comprises an impedance adapter (26) connected to the high frequency generator (46) by a cable coaxial (27) and whose output is connected to the coaxial connection column (28), to adapt the energy transmitted to the impedance of the high frequency applicator (16).  6. A drying device according to claim 5, the impedance adapter (26) comprising at least two capacitors (45) and at least one inductor (47) mounted in a T-type diagram, characterized in that the impedance adapter (26) is mounted so as to see a symmetrical coaxial structure thus respecting the coaxial structure of the coaxial cable (27) coming from the high frequency generator (46) and the coaxial structure of the coaxial connection column (28) terminating to the high frequency applicator (16).  7. Drying device according to claim 1, characterized in that it comprises a device for lifting the high frequency applicator (16), comprising  - a metal structure (15) equipped with guide means for the applicator (16) in order to guide the latter in these upward and downward movements;  - cylinders (22) mounted vertically to raise and lower the applicator (16); and  - Electromagnetic locking means of the high frequency applicator (16) in a high position and a low position.