WO1989011561A1

WO1989011561A1 - Headbox for paper-making machines

Info

Publication number: WO1989011561A1
Application number: PCT/AT1989/000048
Authority: WO
Inventors: Hans Peter Arledter
Original assignee: J.M. Voith Ag
Priority date: 1988-05-17
Filing date: 1989-05-12
Publication date: 1989-11-30
Also published as: AT392989B; ATA128888A; EP0366768A1

Abstract

A headbox for paper-making machines comprises at least one bundle of throughflow pipes in the flow channel between the distributing pipe which feeds the pulp and the discharge nozzle. The throughflow cross-section of the bundle of pipes or throughflow pipes (16, 27, 38) can be varied across the width of the headbox for the purpose of controlling and/or adjusting the headbox.

Description

Headbox for paper machines

The invention relates to a headbox for paper machines with at least one tube bundle formed from flow tubes in the flow channel between the distributor tube to be fed and the outlet nozzle.

The headbox of a paper machine has the task of distributing the StuffSuspension machine-wide and placing it on the running sieve.

The uniformity with regard to speed, thickness and direction of the material jet across the width of the paper machine is decisive for the quality of the paper web.

The level of numerous quality features of the paper required for further processing depends on the ratio of the material jet speed to the screen speed (outlet ratio) and on the speed profile (transverse direction) in the flow channel between the distribution pipe and the outlet nozzle. These are primarily the fiber orientation, the distribution of the strength potential of the paper between the machine's longitudinal and transverse directions, the formation, the specific volume and the porosity.

With the latter properties, the dependence on the run-out ratio and on the speed profile is far less pronounced than for the strength properties of the formation and the fiber orientation.

A speed difference between jet and sieve of only 2% can, for example, lead to a change in the tear length ratio (RL _^ / RL) from 1.9 to 2.7. In the case of an 8 m wide paper machine, speed differences of the jet across the width of more than 3% (min. To max.) Are not uncommon. - 2 -

As for other strength properties, such as Elongation, bursting resistance and tear propagation resistance, their behavior depending on the leakage ratio is either the same or opposite to that of the tear length.

Increasing demands on the paper on the part of the further processors have led to the realization that the ratio of the strength properties in the machine direction and the transverse direction is sometimes not sufficient to describe properties of the paper which are directly related to the fiber orientation.

The effects of different fiber orientation are: a) Different tendency to curl across the width of the web b) Direction-dependent strength behavior in the plane across the width of the paper machine when gauzing webs c) Dimensional stability d) The formation of crepe folds on the edge of rolls during the weighing process.

The defined curl (based on the machine axis) is an important requirement for papers for high-speed copiers and continuous printers. One requirement of the producers of fluting and kraftliner is the uniform distribution of strength in the connection plane of the layers, ie the preferred fiber orientation of the rubberized surfaces is one of the decisive factors for the strength of the bond between the layers. The fiber orientation influences the strength vector in the plane far more than the strength vector out of the plane. Such relationships between fiber orientation and problems in further processing have long been known. The targeted fight fails so far, however, on the complex measurement of the main fiber direction.

There are several methods for determining the fiber orientation. According to a frequently used laboratory measuring method, the main fiber direction is determined by measuring the tear length. To do this, the tear length must be determined in three directions. In addition to the tear length in the machine running direction, two tear lengths are preferably used, which are directed at an angle of 30 ° to the driver side and the drive side. Using the ellipse equation, the angle of the main axis of the tear length ellipse to the machine running direction is then obtained. This method is very complex. The measurement effort is reduced if one is satisfied with the relative tearing length difference of the strips inclined at 60 ° to one another and thus dispenses with the absolute value of the angular deviation. The measurement outlay is still very large for process engineering use.

The simplest way to determine the fiber orientation is a recently developed optical measuring method, which can also be used in on-line operation. This optical measuring method opens up new possibilities for headbox cross-profile control with respect to basis weight and fiber orientation, since the measuring data of this method can be used directly to control the paper machine.

According to the prior art, deviations in the area-related mass in the cross-machine direction are carried out by finely adjusting the lip opening of the material outlet nozzle.

A diaphragm protruding into the material flow is displaced by a large number of adjusting spindles, as a result of which a good basis weight cross section should be achieved.

The inadequacy of this method is that the parameters required to achieve an optimal basis weight profile suitable aperture position does not necessarily coincide with an optimal fiber orientation profile. To avoid angular deviations of the main fiber direction from the machine running direction, there are substantially higher requirements for the headbox than to avoid sheet weight deviations.

In addition to the above-described influencing of deviations in the main direction of the fiber across the width by different outlet conditions, there are local pressure and

Speed differences (cross flows) in the headbox across the width are decisive for the alignment of the fiber in the suspension. Such pressure differences arise due to the design, construction and production of the headboxes which are up to 10 m wide or even wider.

The distributor contour of the distributor pipe can be calculated using the energy equations and empirically determined variables. As a result, a more or less uniform flow over the web width can be achieved for a small operating area of the paper machine. A variation of the throughput amounts leads to clear differences in the distribution of the fiber orientation over the web width. The fiber orientation is also influenced by pressure and temperature-related deviations in parallelism in the flow and nozzle channels, by cross-sectional differences in the tube bundle and in the turbulence tube bundle (deposits, etc.) and by different wall friction across the width and in the peripheral zones.

The object of the invention is to provide a headbox in which the disadvantages described above are avoided, so that the fiber orientation is formed uniformly over the entire web width and the headbox can easily be adapted to different operating conditions. Furthermore, it should be possible to various paper types and headbox constructions can dispense with an aperture control and / or the arrangement of a mixing chamber between the distribution pipe and the nozzle chamber. The control and regulation of the headbox should be possible during the paper production process, suitable measuring methods providing the required control variables.

The invention is primarily characterized in that the flow cross section of the tube bundle is variable over the width of the headbox in order to control and / or regulate the headbox. In a preferred embodiment of the invention, the tube bundle is divided zone by zone into zone chambers, the flow cross section of each zone chamber being controllable and / or adjustable.

The zone chambers preferably comprise flow tubes made of flexible material, which can be compressed by pressure medium, so as to change the flow cross section.

Further features and advantages of the invention can be found in the patent claims, the following description and the drawings.

The invention is explained in more detail below, for example, with reference to the drawings. 1 shows a schematic overview of the arrangement according to the invention. 2 and 3 schematically show sectional views through various embodiments of the tube bundle. 4 to 10 illustrate embodiments of the arrangement according to the invention in various cuts and cracks.

In Fig. 1 the paper machine for the headbox according to the invention is only hinted at. It comprises a rotating screen 1, which is deflected around a roller 2, such as a breast roller 2 or a suction roller 2a. The fiber suspension is applied to the screen 1 via the stock outlet nozzle 3 and fed from the screen for further processing. The Fiber suspension is fed to the headbox via the distribution pipe 4 and reaches the outlet nozzle 3 via the flow channel 5 serve to feed the substance to the discharge nozzle 3 as evenly as possible. According to an embodiment variant of the present invention, the tube bundle is divided zone by zone into zone chambers 7 and each of these zone chambers can be pressurized by pressure medium. Hydraulic cylinders 8 are shown schematically, each of which is connected to the associated zone chamber 7 with a pressure line on the pressure side. The mode of operation is further explained below. The flow cross-section of each individual zone chamber is controlled by the hydraulic cylinders, so that the material outlet can be controlled or regulated over the entire width of the headbox and the paper web formed on the screen 1. In the course of further paper production, according to the current state of the art in or after the dryer section 1 a, a traversing measuring head 9 is arranged which continuously detects a fiber orientation profile of the paper web. This fiber orientation profile and / or basis weight profile serves as a measurement variable for controlling the headbox. The measurement data of the measuring head 9 reach the schematically indicated computer system 11 via the lines 10, the measurement data representing the basis weight and / or the fiber orientation of the paper web formed. Signals reach the computer system via the line 12 and are a function of the outlet pressure prevailing in the outlet nozzle 3. A pressure transmitter is shown schematically at 13 and a converter at 14. Furthermore, measurement data relating to the prevailing pressure in the regulating device, which will be explained in more detail later, come from the zone chambers 7 via the line 15 to the computer system 11 and the computer system returns the calculated setpoint value for each individual zone chamber, which then gives the associated hydraulic cylinder 8 controls. The individual controls related to the individual values are compared with the setpoint, which is normally a straight line with a fiber orientation angle of 0 °. Depending on the deviation from the desired value, the pressure in the corresponding zone chambers is increased or decreased, which leads to a corresponding change in cross-section of the flow tubes and thus to a decrease or increase in the flow rate of the substance.

The criteria for control operation are continuously monitored by the computer system. As already mentioned, this includes the basis weight (atro) of the paper web formed and the total pressure 13 in the headbox. The type of inclusion of the basis weight in the control depends on whether the headbox is provided with or without a separate basis weight control device. In any case, the aim of the regulation is to achieve uniform fiber orientation across the width of the paper machine with an optimal basis weight profile. With the device according to the invention, optimal flow conditions can be set across the entire machine width.

The arrangement of a tube bundle in the flow channel 5 is known per se and serves to supply the stock suspension 3 with the stock suspension as evenly as possible and with high turbulence.

According to the invention, the flow cross-section of the tube bundle is variable over the width of the headbox in order to control and / or regulate it.

According to FIG. 2, in the simplest example, the tube bundle consists of an arrangement of parallel through-flow tubes 16 (shown schematically in section), the arrangement extending over the entire width of the headbox. In the exemplary embodiment in FIG. 2, each individual flow tube 16 can be controlled and regulated by a corresponding control device 17.

In the embodiment shown in FIG. 3, the flow tubes 16 are located in zone chambers 18, and the flow tubes lying within a zone chamber are controlled by the control devices 17.

The flow cross-section of the flow tubes can be controlled in a variety of ways within the scope of the invention. 4, the zone chamber 7 is made of elastic material and the flow tube 19 is also elastic. By adjusting the screw 20, the zone chamber wall 21 is pressed inwards, so that a pressure medium 22 (gas or liquid) located in the zone chamber in turn compresses the flow tube 19 and thus changes the flow cross section until the pressure prevailing in the flow tube p2 is equal to the pressure pl in the zone chamber. The zone chamber made of elastic material is surrounded by a housing 24 made of rigid material, such as steel. The pipe sockets 25, 26 serve to supply and remove the substance suspension. Fig. 5 shows another embodiment for the control of the flow cross section. The individual tubes 27 of the tube bundle are inserted in an end plate 28. In front of the end plate 28, rubber rings 29 are arranged, against which a pressure plate 30 can be pressed. FIG. 5a shows the arrangement with a full flow cross section, while FIG. 5b shows the arrangement with a reduced cross section. The flow cross-section is reduced by compressing the rubber rings between the end plate 28 and the pressure plate 30. If the pressure plate 30 is zoned in several sections to the end plate 28, for example by a split or elastic design, each of these zones can be controlled separately become. The distance to the end plate is achieved by different support (mechanical .. screws, etc.) across the width. 6, 7 show, in mutually associated sections, another embodiment variant with mechanical control of the flow cross section. The tube bundle here consists of three rows of flow tubes 27 lying one above the other and only the bottom row is changed zone by zone to control the flow rate. The change in the flow cross-section takes place by means of pinch strips 31 arranged in zones, which can be adjusted by means of corresponding mechanical drive devices (spindle, electromagnets, hydraulics, etc.). 6 shows the arrangement with a full flow cross section and FIG. 7 shows the arrangement with a reduced flow cross section of the lowest flow tube in a section along the line VII-VII. The controlled zones along the width of the headbox are defined by the length of the squeeze strips 31. Zone chambers are not required here.

The mechanically acting squeezing device can easily be modified by any person skilled in the art in such a way that not only the bottom row of the flow tubes, but also others

Rows or all flow tubes can be changed in their flow cross-section.

As can be seen in FIG. 7, the flow tubes 27 are arranged between two end plates 32. The lowermost flow tube is interrupted over a section and the interruption is bridged by a flexible hose 33. The squeeze strip 31 presses up, thereby squeezing the hose and reducing the flow cross-section. The counter bearing 34 serves to limit the stroke and supports the hose accordingly.

Fig. 8 shows the cross section through a zone chamber made of rigid material, such as sheet steel. In this zone chamber either one flow tube 27 can be arranged or in a row several flow tubes, such as this would correspond to Fig. 3. The flow tube 27 is interrupted and the interruption is bridged by the hose 33. A stable zone chamber, which contains the pressure medium 36, is formed by the end plates 32 and the housing 35. Liquid or gas can be used as the pressure medium. If the pressure or the volume of the pressure medium 36 is increased by any means, the flexible hose 33 is compressed and thus narrows the flow cross-section, as indicated by the arrow 37. The pressure in the zone chamber can be increased, for example, by pumping in the pressure medium, by pressing a liquid-displacing object into the pressure medium 36, by heating, etc.

Another advantageous embodiment for the zone chambers is shown in FIGS. 9 and 10. As already described for FIG. 4, the zone chamber consists of a flexible plastic insert, which forms both the wall 37 of the zone chamber and the flow tubes 38. The zone chamber space 39 for receiving the pressure medium remains between the wall 37 and the flow tubes 38. The plastic insert is surrounded on the outside by a rigid housing 40. The flow tubes 41 of the tube bundle are tightly connected to the flow tubes 38.

Pressure medium can be pressed into the zone chamber space 39 via the connection 42, the flexible flow tubes 38 being compressed in the manner already described and thus reducing the flow cross-section.

For the measurement of the weight per unit area and the fiber orientation (FIG. 1), it should also be noted that different sensors are currently required which are housed in the measuring head 9 (measuring frame), such as lasers for fiber orientation and beta emitters for Basis weight. The measurement data - left

represent the basis weight and / or the fiber orientation of the paper web formed, because the measured variable (s) are determined by the priority of the control (basis weight, fiber orientation).

Claims

PATENT CLAIMS

1. Headbox for paper machines with at least one tube bundle formed of flow tubes in the flow channel between the feed tube and the outlet nozzle, characterized in that the flow cross section of the tube bundle or the flow tubes (16, 27, 38) is variable over the width of the headbox to control and / or regulate the material outlet.

2. Headbox according to claim 1, characterized in that flow tubes (16) of the tube bundle (6) along the width of the headbox each have individually variable flow cross sections.

3. Headbox according to claim 1, characterized in that the tube bundle (6) is divided zone by zone into zone chambers (7) and that the flow cross-section of each zone chamber is controllable and / or adjustable.

4. Headbox according to claim 3, characterized in that in the zone chamber (7) all flow tubes are control and / or adjustable.

5. Headbox according to claim 3, characterized in that in the zone chamber (7) only a part of the flow tubes can be controlled and / or regulated.

6. Headbox according to claims 1 to 3, characterized in that the zone chambers (7) each have a flow tube

(16, 23) included.

7. Headbox according to one of claims 3 to 6, characterized in that the zone chamber (7) comprises flow tubes (27, 33) made of flexible material by pressure medium are compressible so as to change the flow area.

8. Headbox according to one of the preceding claims, characterized in that the pressure medium is a mechanical squeezing device.

9. Headbox according to one of the preceding claims, characterized in that the pressure medium is a liquid or a gas.

10. Headbox according to claim 9, characterized in that a pressure source is provided for controlling the pressure medium.

1L headbox according to claim 10, characterized in that the pressure source is a pump (stamp).

12. Headbox according to claim 10, characterized in that the pressure source is a pressure vessel with pressurized liquid or gas.

13. Headbox according to one of the preceding claims, characterized in that a heating device for the pressure medium (liquid or gas) is provided for increasing the pressure of the pressure medium.