EP0545886B1 - Method and device for draining a fibre suspension with a drainage element - Google Patents

Description

The invention relates to methods for dewatering, in particular pre-dewatering, of sieve belt-supported fiber-water suspensions, in particular for paper production, which are guided by at least one vibrating dewatering element, preferably foil, and devices for carrying out these methods.

Known methods and devices for the dewatering of sieve belt-supported fiber-water suspensions guided over dewatering elements, preferably foils, use, in particular, several individual dewatering elements or foils, foil boxes, cascade foils, register rollers and egoutteurs connected in series.

1 and 2 of the drawing, a (such) individual drainage element or foil is illustrated, etc. 1 shows the cross section through such a drainage element or such a foil 1 and a partial longitudinal section through the sieve belt 2 guided over it, through the fleece 3 already formed above it, and through the fiber-water suspension 4 still present. As a rule, there are several such drainage elements or foils 1 - seen in the direction of movement of the belt (arrow 5!) - connected in series at a distance from one another, as can be seen, for example, from EP-A-0 241 439.

A natural vacuum builds up on the diverging sides between the drainage screen and the surface of the drainage element or foil due to the screen speed. In this way and as a result of gravity, water is withdrawn from the suspension and passed through the screen to the underside of the screen.

This water is wiped off at the front edge of the next drainage element or foil. The downward movement of the sieve over the drainage element or foil, caused by the vacuum that builds up in the gap between the drainage element or foil surface and the sieve, or by a vertical acceleration of the sieve after breaking off the vacuum zone at the rear edge Turbulence on the fabric surface is generated. The corresponding pressure profile 6 or the pressure and turbulence development on the drainage element or foil can be seen in FIG. 2.

The well-known foil box mentioned above works on the same principle as a single foil. It consists of a close series of narrow individual foils. Due to the small foil spacing, it leads to microturbulence.

The also known cascade foil 7 according to FIGS. 3 and 4 has a similar function as a single foil. The drainage performance can be increased by a sequence of active 8 and passive surfaces 9. The active surfaces are inclined, the passive surfaces parallel to the screen belt. The reduced tubulence formation has a disadvantageous effect.

5 shows part of a known register roller 10 with the part of a screen belt 11 guided over it. The maximum suction takes place in area 12. The end of suction takes place at 13. Such a device is only used in slow-running paper machines. 6 shows the pressure profiles occurring along the register roller 10 between the roller surface and the screen 11 at different speeds (500, 1000, 1500, 2000, 2500 fpm [1 fpm = 0.3048 m / min]). The use of such rollers is limited by the high pressure and vacuum pulses at higher paper machine speeds. It leads to leaching of fine substances.

All these previously known drainage devices or drainage elements have the disadvantage that the fiber distribution is unsatisfactory; this also applies to the design according to EP-A-0 241 439 even if the distance between the foil surface and the sieve belt can be adjusted.

The aim of the invention is above all to improve the sheet formation of papers produced. Basically, formation in the paper sheet means the areal fiber distribution. According to the invention, it is primarily a matter of constantly distributing the mass over the surface. Irregularities in the raw material result in differences in network formation. Since the sheet formation represents the fiber distribution in the suspension, dosed turbulence must be introduced into the suspension by means of suitable dewatering elements in such a way that an optimal fiber distribution is achieved and maintained up to fiber immobility (= certain solids content). This is to achieve the best possible paper quality.

This goal is achieved according to the invention, starting from the method specified at the outset, in that for the purpose of influencing, in particular making the fiber distribution or turbulence energy more efficient, the sieve belt-supported suspension or fiber material web is first passed over the fixed leading or front edge directed against the sieve belt movement of the at least one vibrating dewatering element, preferably foils, and then guided over a surface of this dewatering element that faces the material web and is movable relative to this edge, while this surface of this dewatering element is at least partially set in vibrations, in particular pivoting movements. The vibration of the drainage element or foil thus achieved changes the vacuum and thus influences the pressure pulses at the next edge of the drainage element or foil in accordance with the oscillation frequency, which results in the fiber flakes being released.

A foil, which as a whole can be pivoted about an axis, has already become known through the SU-PS 874 820. The fixed leading edge according to the invention is therefore missing. In the known design, the leading edge flutters when vibrating and, in contrast to the invention, is therefore not fully fed by the sieve belt. Fiber distribution or turbulence are therefore less favorable than according to the invention, which has a very disadvantageous effect on the sheet formation of the papers produced. According to the invention, the advantageous effects can be intensified if the suspension or material web is guided over at least two drainage elements arranged at a distance from one another, each with a fixed leading edge and a surface facing the material web that is movable relative to this edge. A cheap, space-saving solution is obtained if, according to the invention, the sieve belt-supported suspension or fiber material web is passed over immediately adjacent movable surfaces of the at least one drainage element after passing through the fixed edges or their supports.

Particularly favorable results can be achieved if the frequency and / or the amplitude and / or the quantity or strength of the vibrations of the movable surfaces of the dewatering elements are dependent on the intermediate or final quality of the dewatered, in particular pre-dewatered, fiber material web a regulation of the vibration exciters acting on these movable surfaces can be changed. The frequency of the vibrations can advantageously be set between approximately 50 and 1000 Hz, in particular between approximately 50 and 500 Hz. In practice, it is advantageous if the setting of a desired angle between the screen belt and the surface of the drainage element or foil facing it, or zeroing of the vibrations generated by an electrical vibration generator, is carried out by means of a DC voltage superimposition. In this case, in particular at the same time, the speed of movement of the filter belt-supported fiber-water suspension or the filter belt can be regulated between 100 and 2000 m / min. The effects according to the invention can be amplified if, after the Screen-supported suspension over at least one dewatering element with a fixed leading edge and a surface that can be moved with respect to this edge, which is then guided over at least one fixedly mounted, ie not vibratable, dewatering element arranged at a distance from that dewatering element.

According to the embodiment of the invention, in devices or systems for carrying out one of the methods according to the invention with at least one vibrating dewatering element, preferably foil, and a sieve belt guided over the at least one dewatering element, in particular for paper production, the at least one vibrating dewatering element , preferably foil, is formed with a fixed run-up or front edge directed against the movement of the sieve belt and stands with a - seen in the direction of movement of the sieve belt - set back from this, in particular gradually receding, surface in each case - seen in the direction of movement of the sieve belt - opposite to the Run-up or leading edge movable drain part under the action of at least one vibration exciter or generator. For practical implementation, the at least one drainage element, preferably foil, is expediently connected to an electrical vibration exciter or generator, which advantageously has an electromagnet with a voice coil. There are also conceivable designs within the scope of the invention in which the dewatering elements, preferably foils, are connected to a mechanical vibration exciter or generator, advantageously a camshaft or a hydraulic or pneumatic pressure cylinder.

By controlling several drive elements of a vibrating foil over its entire length there is hardly any risk of natural vibration in the carrier.

The operation of the device or system according to the invention can be designed or automated particularly advantageously if the purpose of adjusting the turbulence energy is the surface of the sieve of the vibration exciter or generator and, if applicable, the sieve belt drive and, if appropriate, the suspension feeder are connected to a control system or a control circuit for changing the amplitude and frequency of the movement of the discharge part, in or in the a setpoint is entered in the form of a voltage control of the vibration exciter and is connected to an online formation measurement, in particular the final and / or the intermediate quality of the fiber material web.

For practical operation, it is particularly advantageous if, according to the further embodiment of the invention, the frequency and / or the amplitude and / or the quantity or strength of the vibrations of the vibration generator or exciter depending on the measured intermediate or Final quality of the dewatered, especially pre-dewatered. Fiber material web can be controlled by means of voltage regulation of the vibration generator. According to the invention, devices and systems with several drainage elements or foils can be electrically connected to both for the purpose of generating a superposition frequency of the movements of the drainage parts and connected to the control or the control circuit.

Another advantageous practical solution according to the invention is characterized in that the fixed leading edge of the at least one drainage element, preferably the foil, is fixedly mounted or mounted on a compact ramp part, which on its discharge side can be moved elastically with a bridge, independently of the carrier of the drainage element, via a bridge or pivotable drain part is connected.

According to the invention, the surface of the at least one drainage element facing the sieve belt can run continuously from the run-up edge to the drain part or to its drain edge, which results in particularly good guidance.

For the purpose of changing the paper quality or the operating conditions, it can be advantageous according to the invention if the at least one drainage element or the foil can be displaced in the direction of the screen belt when the leading or leading edge is fixed or if the horizontally guided run of the screen belt operates the at least one drainage element or the foil is vertically adjustable or the entire at least one dewatering element or the foil can be pivoted for the purpose of adjusting the angle between the screen belt and the surface of the dewatering element or foil facing it when the leading or leading edge is fixed. A wear strip, in particular ceramic strip, can be inserted in the leading edge of the foil.

The advantageous effects of the device according to the invention are particularly striking if - as seen in the direction of movement of the sieve belt - at least one fixed bearing, i.e. a fixed bearing edge, i.e. at a distance behind the at least one dewatering element with a fixed leading edge and with a surface movable relative to this edge. non-vibratable, drainage element is arranged.

In relation to the known state of the art, egoutteurs should also be mentioned in the present context: an egoutteur is a cylinder covered with a fine metal fabric, which is immersed in the nonwoven fabric from above. The fleece, which has already been partially fixed, is resuspended. Its use is with higher basis weights of e.g. planned from 115 g / m. It is not an actual drainage element.

Toothed rollers are also known, which are driven and immerse into the screen from below. The speed and number of teeth results in a certain frequency with which pressure pulses can be introduced into the suspension. It is not a drainage element; however, such a roller represents a possibility for introducing energy into the suspension or the fleece. Above all, it does not succeed in providing the necessary turbulence energy with undisturbed To regulate drainage as according to the invention, mainly because the vacuum can not be designed in a corresponding manner.

7 to 9, the invention is explained below, for example.

7 shows a schematic illustration of a device or system according to the invention in a side view, FIG. 8 shows a drainage element or a foil according to the invention in a front view, FIG. 9 shows a side view, the latter with a screen belt part in the area in question.

According to FIG. 7, the dewatering, in particular pre-dewatering section has a driven (see arrow 5) driven belt 2, which is mounted on a machine frame by means of rollers or rollers. In addition to the headbox 15, a sieve table 16, foils 1, a register roller 10, a cascade foil 7, foil boxes 17, wet vacuum cleaners 18, an egoutteur 19 and flat vacuum cleaners 20 can be seen.

8 and 9 now show, for example, one of the foils 1 designed according to the invention. The part 21 of the foil facing the sieve belt 2 has a compact ramp part 22, the ramp edge 23 of which is directed against the movement of the sieve belt (arrow 5!). The part 24 of the foil is connected to the compact part 22 via a thin bridge 25, so that an (elastic) movement of the part 24 relative to the part 22 is possible. For high abrasion resistance, a ceramic strip 23 'can be incorporated in the front edge of the foil. The elastic foil surface is preserved. The part 24 is connected to an electrical vibration generator, which is constructed from an electromagnet and voice coils. The coils are designated 26 and the drive for part 24 with 27; the connection consists of the sleeve 28, the washer 29 and the shaft joint 30. In order to set the zero position, an adjusting screw 30a is provided between the shaft joint 30 and an adjusting plate 31 in this connection. The overall arrangement of the foil with its drive is arranged on a slide-in box 33. The compact part 22 is mounted on the slide-in box 33 by means of the holding strip 34 Countersunk screw 35 and the stable support or rails 36, 37. The adjustment plate 31 is provided between the drain part 24 and the vibration drive.

The function of the wire section takes place in the following way: The fiber suspension flows out of the headbox 15 approximately at the wire speed onto the machine. The material jet (with about 0.5-1% solids content, in this machine) strikes the screen table 16 evenly across the entire machine width and is transported through the dewatering screen 2 over the screen section. The built-in drainage elements increase the solids content to around 13 - 15% by the end of the wire section; then it is accepted into the press section. The main area of application of the oscillating foil 1 according to the invention is advantageously in the first third of the wire section (depending on the weight per unit area driven). The formation can only be influenced by turbulence up to about 1.5% solids content.

In summary, it should be emphasized: the basic idea when using the oscillating foil 1 according to the invention is the simple controllability of the necessary turbulence energy with undisturbed drainage. The foil, which is fixedly mounted on its front edge 23, is made to vibrate on the outlet side 24 via the exciter. By swinging the trailing edge of the foil, a fluctuating vacuum is created (changed foil angle). The vacuum fluctuations generated with this oscillation frequency draw a different amount of water to the underside of the sieve. This results in pressure impulses at exactly the same frequency at the following foil edge. At the same time, the sieve is deflected over the foil due to the vacuum that is formed, thus causing turbulence on the surface of the sieve. Due to a relatively low energy, which is introduced perpendicular to the main direction of movement of the screen belt or the material web, flow energy of the stock suspension can be converted into turbulence. Preliminary tests with a loudspeaker resulted in an optimal frequency range of about 50-500 Hz for flock resolution. In the present case - because of the simple control stimulated by an electromagnet and a voice coil - the amplitude and so that the movement of the trailing edge (part 24) can be influenced. The frequency of the individual foil 1 can also be controlled, as can an overlapping frequency by interconnecting several oscillating foils. In the expansion phase, a control loop can be set up via an online formation measurement, by means of which all the basis weight ranges traveled can be optimized by means of setpoint specifications. In this way, long foil setting times when changing the basis weight can be saved. The known static drainage elements work optimally only in a small area (basis weight, speed) and can only be adjusted with relatively great effort. The advantage over the previously known dewatering elements is the infinitely adjustable turbulence energy in every area of the wire section with the same dewatering performance, since practically the entire wire section can be equipped with oscillating foils. An oscillation frequency applied to a single foil according to the invention is physically comparable to an embodiment with several static foils, if one wants to maintain the quality of the product immediately. A high frequency on a single foil according to the invention would correspond to many foil edges according to the prior art at short intervals and, according to the invention, a low frequency on a single foil would correspond to a few foils according to the prior art at large distances from one another. This gives the possibility of apparently varying a sieve section with the aid of a variable frequency according to the invention in its geometry such that the quality of the product is improved while the drainage effect remains approximately the same. The vibration can also be generated mechanically, for example by a camshaft, or hydraulically or pneumatically by pressure cylinders.

Claims (20)

1. A process for draining fiber-water suspensions (3) supported by a screen or filter belt (2) and passed via at least one drainage element (1) capable of being vibrated, particularly for paper making, characterized in that, for the purpose of influencing the distribution of fibers and/or the energy of turbulence, the screen belt-supported suspension is first passed across the stationary leading or supply edge (23) of the at least one drainage element (1) capable of being vibrated, which edge is directed against the screen belt movement (5), and which suspension is then passed across a surface of said drainage element (1) directed towards the material web and movable relative to said edge (23), while said surface of said drainage element (1) is at least partly vibrated, particularly pivoted.
2. A process according to claim 1, wherein the suspension is passed via at least two drainage elements (1) spaced apart from each other, each of them having one stationary leading or supply edge (23) and one surface directed towards the material web and movable relative to said edge.
3. A process according to claim 1, wherein the screen belt-supported suspension having passed the stationary edge (23) or its supports is passed across a contiguous movable surface of the at least one drainage element (1).
4. A process according to any of the claims 1 to 3, comprising a plurality of drainage elements, wherein the frequency and/or amplitude and/or quantity or intensity, respectively, of the vibrations of the movable surfaces of the drainage elements (1) are modified in accordance with the intermediate and/or final quality of the drained fiber material web by means of controlling the vibrators (26, 27) acting on said movable surfaces.
5. A process according to any one of claims 1 to 4, wherein the frequency of vibrations is set between 50 and 1000 Hz, particularly between 50 and 500 Hz.
6. A process according to any one of claims 1 to 5, wherein adjusting a desired respective angle between the screen belt (2) and the surface of the drainage element (1) directed towards said screen belt or adjusting a zero position of the vibrations generated by an electrical vibrator is effected by means of DC voltage superimposition.
7. A process according to any one of claims 1 to 6, wherein the velocity of the screen belt-supported fiber-water suspension and/or of the screen belt is set between 100 and 2000 m/min.
8. A process according to any one of claims 1 to 7, wherein, after passing the screen belt-supported fiber-water suspension via the at least one drainage element (1) having a stationary leading or supply edge (23) and a surface movable relative to said edge, the suspension is then passed via a drainage element (17, 7, 10) which is spaced apart from said drainage element and is stationary, i.e. not capable of being vibrated.
9. A device for carrying out one of the processes according to any one of claims 1 to 8, comprising at least one drainage element (1) capable of being vibrated and a screen belt being passed across the at least one drainage element, particularly for paper making, characterized in that the at least one drainage element (1) capable of being vibrated has a stationary leading or supply edge (23) directed against the screen belt movement (5) and, with a surface which - as seen in the moving direction of the screen belt (2) - is positioned behind the screen belt (2), particularly gradually receding therefrom, is acted on by at least one vibrator (26, 27) in the - as seen in the moving direction of the screen belt (2) - rear discharge element (24) movable relative to the leading or supply edge (23).
10. A device according to claim 9, wherein the at least one drainage element (1) is connected to an electrical vibrator (26, 27) which particularly is provided with an electromagnet comprising an oscillation coil (26).
11. A device according to claim 9, wherein the at least one drainage element (1) is connected to a mechanical vibrator, particularly a camshaft, or to a hydraulic or pneumatic pressure cylinder.
12. A device according to claim 10, wherein, for the purpose of adjusting the energy of turbulence on the surface of the screen (2), the vibrator (26, 27) and optionally the screen belt drive as well as optionally the suspension supply (15) are connected to a controlling means for modifying the amplitude and frequency of the movement of the discharge element (24), said controlling means being fed with a reference input in the form of a desired voltage input of the vibrator and being connected to an online lookthrough measuring device, particularly of the final and/or intermediate quality of the fiber material web.
13. A device according to claim 10, wherein the frequency and/or amplitude and/or quantity or intensity, respectively, of the vibrations generated by the vibrator (26, 27) are controllable depending on the measured intermediate and/or final quality of the drained fiber material web by controlling the voltage input of the vibrator.
14. A device according to claim 12 or 13, comprising a plurality of drainage elements, wherein said drainage elements (1) are electrically connected and are connected to the controlling means, in order to generate a heterodyne frequency of the movements of the discharge elements (24).
15. A device according to any one of claims 9 to 14, wherein the stationary leading or supply edge (23) of the at least one drainage element (1) is firmly mounted onto a compact supply element (22) which, on its discharge side, is elastically connected via a bridge (25) to a discharge element (24) movable or pivotable independently from the support (36, 37) of the drainage element (1).
16. A device according to any one of claims 9 to 14, wherein the surface of the at least one drainage element (1) directed towards the screen belt (2) runs steadily from the leading or supply edge (23) to the discharge element (24) or its discharge edge, respectively.
17. A device according to any one of claims 9 to 15, wherein the at least one drainage element (1) is displaceable in the direction of the screen belt (2), with the leading or supply edge (23) being stationary.
18. A device according to claim 17, wherein, in the area of the horizontally guided trum or portion, respectively, of the screen belt (2), the at least one drainage element (1) is vertically adjustable.
19. A device according to claim 17, wherein, for the purpose of adjusting the angle between the screen belt (2) and the surface of the drainage element (1) directed towards said screen belt, the entire at least one drainage element (1) is pivotable, with the leading or supply edge (23) being stationary.
20. A device according to any one of claims 9 to 19, wherein - as seen in the moving direction of the screen belt (2) - at least one drainage element (17, 7, 10) which is stationary, i.e. not capable of being vibrated, is disposed in spaced relationship behind the at least one drainage element (1) having a stationary leading or supply edge (23) and a surface movable relative to said edge.

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