EP0523214B1 - Headbox - Google Patents

Abstract

PCT No. PCT/EP92/00208 Sec. 371 Date Sep. 8, 1992 Sec. 102(e) Date Sep. 8, 1992 PCT Filed Jan. 31, 1992 PCT Pub. No. WO92/13995 PCT Pub. Date Aug. 20, 1992.A headbox includes a nozzle type stock channel with an outlet gap. The nozzle type stock channel is defined by two flow guide walls. Arranged on the discharge end of the upper flow guide wall is a movable aperture to which attach numerous adjustment spindles which are arranged distributed across the machine width. Each adjustment spindle has on its end away from the aperture a spindle drive. Provided on the upper end of each spindle is a measuring device serving the determination of the local position of the aperture. The measuring device has a measuring housing and a measuring element movable in it. The measuring element is connected positively with the aperture, independently of the spindle, by way of a measuring rod. The measuring housing is positively connected with the area of the flow guide wall on the near side of the aperture, by way of an oblong tubular measuring reference.

Description

The invention relates to a headbox for a machine for the production of fibrous webs, e.g. Paper webs, in particular with the features a) to e) of claim 1, which are known from the Voith brochure "Headboxes" No. p 2503. Such a headbox has two flow guide walls; these converge towards each other in the direction of flow and thus (together with side walls) form a nozzle-like, machine-wide fabric channel, which has a machine-wide fabric outlet gap. At least one of the two current-carrying walls is movable or has a movable part; this allows a rough adjustment of the inside width of the material outlet gap.

In addition, there is a device for fine adjustment of the clear width of the outlet gap, namely in the form of a strip that extends along one of the two flow guide walls (e.g. on the movable flow guide wall) along the fabric outlet gap over the entire machine width and relative to this flow guide wall transversely to the outflow direction is adjustable and deformable locally. To be more precise, the aforementioned current-carrying wall is divided into a rigid main part and the adjustable and locally deformable bar. This rigid main part can be a rigid, ie immovable part of the headbox or as the above-mentioned flow guide wall (or a movable flow guide wall part) which is movable relative to the rest of the headbox.

Numerous adjusting spindles arranged over the machine width are provided for adjusting the mentioned bar. Each of these adjustment spindles can be moved individually along their axis by means of a spindle drive. The bar can thus experience a small local deformation using each of these numerous adjusting spindles. Of course, you can also operate several adjacent adjusting spindles at the same time. The goal is usually to set the clear width of the outlet gap as precisely as possible across the machine width, so that the result is that the paper web produced on the machine receives properties that are as constant as possible (in particular constant weight per unit area) over the machine width. However, it may sometimes also be desirable to place the web width at a certain point, e.g. at the edges, deliberately causing a deviation from the normal path properties by adjusting individual spindles. Exceptionally, it can also happen that all adjustment spindles are actuated simultaneously in order to adjust the bar evenly over the entire machine width.

The mentioned strip can be designed differently: It is preferably designed as a so-called diaphragm, which has the shape of a ruler and is arranged at the outlet-side end of the relevant current guiding wall (i.e. on the stiff main part of the current guiding wall). Such a diaphragm is - seen in longitudinal section through the headbox - adjustable transversely to the longitudinal extent of the flow guide wall and locally deformable.

Another embodiment of the movable bar can be realized in that the outlet-side end of the current guide wall in question is connected to the rigid main part of the current guide wall via a thin point. In this case, the outlet-side end of the current-carrying wall can itself be adjusted or locally deformed.

In addition to these known features, the following can also be seen from the Voith brochure mentioned above: In order to be able to read their local position along the entire length of the strip at any time during operation, numerous measuring devices are provided which are distributed over the machine width. A preferred embodiment is shown in which each adjusting spindle has such a measuring device at its end remote from the bar. According to Figure 9, the measuring devices are designed as preferably mechanical measured value indicators. According to Figure 5, a so-called "displacement sensor" is additionally provided on each spindle. This is a measuring device which is designed as an electrical signal transmitter. The entirety of these signal transmitters is used to remotely display the position or the state of deformation of the bar mentioned, and also (if required) to transmit corresponding data to a process control system which, among other things. controls the adjustment spindle drives in such a way that the paper web receives the desired basis weight cross section.

The well-known headboxes have proven their worth in practice. However, it was found that with the previous arrangement of the measuring devices, the accuracy of the measurement of the position or the state of deformation of the bar mentioned is not sufficient in all cases.

The invention is therefore based on the object of taking measures by means of which the accuracy of the measurement of the position and the state of deformation of the strip can be further improved in the headboxes described at the outset.

This object is achieved by the characterizing features of claim 1.

The invention is based i.a. on the result of a difficult and lengthy investigation of the causes of the measurement inaccuracies observed so far. Here it had to be taken into account that, for example, the mechanical measured value indicators have been arranged as follows: Their stationary housing rests on the housing of the spindle drive, which in turn is attached to the rigid main part of the current supply wall in question (according to Figure 5 of the Voith brochure mentioned, the relevant one is Current guide wall stiffened by a so-called upper lip support). In addition, the movable measuring element of the measuring device rests positively on the end of the spindle which is remote from the bar. In other words, the current position of the relevant part of the bar can only be communicated to the measuring device via the spindle.

For this reason, a measurement error often arises from the fact that some of the adjusting spindles are under tensile stress, while others are under compressive stress. The cause of these stresses is the deformation resistance of the bar. It can also happen that the tension in one or more adjustment spindles changes from tension to compression or vice versa. In other words: the adjustment spindles of a headbox suffer different and changing elastic deformations in the form of changes in length during operation. Similar elastic deformations can e.g. occur in the housings of the spindle drives or in the current guide wall in question or in the stiffening beam belonging to it. All of these mechanical deformations and any additional thermal deformations falsify the result of the measurement of the local position of the bar.

A headbox is known from US Pat. No. 4,342,619, at the outlet gap of which in turn an adjustable and locally deformable strip (15), designed as a ruler-shaped diaphragm, is provided. At only a short distance from the exit gap, numerous measuring devices (21) are provided which are distributed over the width of the machine and are designed as electrical signal transmitters. Each of these measuring devices has a movable measuring element (23) which, independently of the adjusting spindles (17), is positively connected to the bar (15) via a measuring rod (23A). Each measuring device also has a measuring housing (22) which is positively connected to a rigid part (12A) of the current carrying wall (12). With this known device, it may be possible to obtain relatively precise measured values about the local position of the bar (15). One difficulty, however, is that the measuring devices cannot be protected with 100% certainty from contamination or from occasional flooding. You will probably disguise the measuring devices with the help of a cover; However, this cannot be kept permanently sealed due to the mobility of the bar (15). The use of such a measuring device located in the vicinity of the outlet gap had to be rejected.

• 1. Das bewegliche Meßglied jeder Meßeinrichtung muß (wie aus der schon genannten US-PS 4,342,619 bekannt) unabhängig von den Verstellspindeln über einen separaten Meßstab formschlüssig mit der Leiste verbunden sein. Hierdurch wird beim Übertragen der Meßgröße der störende Einfluß des wechselnden Spannungszustandes der Verstellspindeln eliminiert.
• 2. Das Meß-Gehäuse jeder Meßeinrichtung darf nicht mit einem von der Leiste entfernten Teil der betreffenden Stromführungswand (oder gegebenenfalls eines dazugehörenden Versteifungsträgers) verbunden werden.
  Statt dessen muß das Meß-Gehäuse über ein langgestrecktes, und sich parallel zum Meßstab erstreckendes Bindeglied mit dem leisten-nahen Bereich der Stromführungswand (genauer gesagt: des steifen Hauptteils der Stromführungswand) verbunden sein. Das genannte Bindeglied wird nachfolgend "Meßreferenz" genannt, weil es der Meßeinrichtung die korekte Bezugsgröße liefert. Wesentlich ist, daß die langgestreckte Meßreferenz nur mit dem leisten-nahen Bereich des steifen Hauptteils der Stromführungswand verbunden ist. Dadurch ist sie über ihre ganze Länge unabhängig von örtlichen elastischen Verformungen der Stromführungswand oder des Versteifungsträgers und gegebenenfalls von elastischen Verformungen der Spindel-Antriebsgehäuse. Somit werden alle diejenigen Meßfehler eliminiert, welche bisher durch derartige Verformungen (infolge Änderung des Belastungszustandes oder infolge örtlicher TemperaturSchwankungen) verursacht wurden.

The invention is based on the knowledge that an arrangement of the measuring devices removed from the bar must be maintained and that the following must be provided in order to increase the measuring accuracy:

• 1. The movable measuring element of each measuring device (as is known from the already mentioned US Pat. No. 4,342,619) must be positively connected to the bar independently of the adjusting spindles via a separate measuring rod. In this way, the disturbing influence of the changing voltage state of the adjusting spindles is eliminated when the measured variable is transmitted.
• 2. The measuring housing of each measuring device must not be connected to a part of the current guiding wall in question (or, if applicable, an associated stiffening beam) removed from the strip.
  Instead, the measuring housing must be connected to the area of the current-carrying wall (more precisely: the rigid main part of the current-carrying wall) by means of an elongated connecting link that extends parallel to the measuring rod. The link mentioned is referred to below as the "measurement reference" because it provides the correct reference variable for the measuring device. It is essential that the elongated measurement reference is only connected to the area of the rigid main part of the current guide wall close to the strip. As a result, it is independent over its entire length of local elastic deformations of the current-carrying wall or of the stiffening support and, if appropriate, of elastic deformations of the spindle drive housing. This eliminates all those measurement errors that have previously been caused by such deformations (as a result of changes in the load condition or as a result of local temperature fluctuations).

The invention is applicable to many different headbox designs. It is irrelevant, for example, whether the outflow direction runs horizontally through the outlet gap or is inclined downwards or upwards relative to the horizontal. A vertical, preferably upward outflow direction is also possible. If one of the two power supply walls has a moving part (which will be the case in most cases), then this part can be pivoted in a joint; or it can be moved at an angle to the outflow direction his. With some headboxes, this part can be moved and swiveled. The bar provided for fine adjustment of the clear width of the outlet gap can, as already mentioned above, be designed as a displaceable, linear-shaped diaphragm or as the bendable, outlet-side end of one of the two flow guide walls. If, according to US Pat. No. 4,783,241 (file: P 4356), a displaceable screen is combined with a bendable outlet-side end of a current-carrying wall, the measuring devices according to the invention are assigned to the screen.

The measuring devices of the headbox according to the invention can be arranged spatially separated from the adjusting spindles according to the model of US Pat. No. 4,342,619. In this case it is possible that the number of measuring devices deviates from the number of adjusting spindles. However, the number of measuring devices is preferably made equal to the number of adjusting spindles as before. The known feature is preferably also retained, according to which the individual measuring device is arranged coaxially with the associated adjusting spindle. This results in an important further idea of the invention, according to which the measuring reference and the measuring rod extend through the interior of the adjustment spindle, which is now tubular, and preferably also through the interior of the spindle drive. The elongated measuring reference is preferably also tubular, so that the measuring rod can extend through the interior of the measuring reference.

The invention is applicable to headboxes which have measuring devices arranged exclusively on the spindles and designed as (preferably mechanical) measured value indicators. However, the invention can also be used when the headbox has only measuring devices which are designed as electrical signal transmitters for remote display.

However, it is preferably provided that in a known manner both a measured value indicator (for the direct reading of the measured values) and an electrical signal transmitter (for the purpose of remote display and / or data transmission to a computer) is provided on each adjusting spindle.

This has the advantage that the electrically measured data can be checked at any time by means of the mechanical measured value indicators, and that the headbox can continue to be operated using the mechanical measured value indicators even in the event of a fault in the electrical measurement. However, it is also conceivable that electrical devices are used both for local display of measured values and for remote data transmission.

According to a further important concept of the invention, which is also important, the electrical signal transmitter is arranged on each adjusting spindle between the spindle drive and the mechanical measured value indicator. The electrical signal transmitter is located at a location that can be extremely well protected against disruptive influences (e.g. contamination). It is conceivable that a common housing is provided for the electrical signal transmitter and the mechanical measured value indicator. In any case, it can be expected that the electrical signal transmitter will withstand the rough continuous operation of a paper machine with much greater certainty than with the arrangement according to Figure 5 of the Voith brochure p 2503.

The accuracy of the measured value acquisition can be increased even further by eliminating those disturbances which can be caused by thermal changes in the length of the measuring rods and measuring references. For this purpose, it is useful, for example, to measure the measuring rods and measuring references from materials with the same thermal expansion coefficient (preferably so from the same material). In addition, it is advisable to maintain the already known measure described below: namely, the adjustment spindles are arranged - and thus also all measuring rods and measuring references within a closed and isothermally kept room. This space is preferably formed by the interior of the box-shaped stiffening girder of the current conduction wall in question mentioned above. This means that temperature differences that occasionally occur in the vicinity of the paper machine cannot have a negative effect on the measurement.

Die Figur 1

ist ein Teillängsschnitt durch einen Stoffauflauf.

Die Figur 2

ist eine Teilansicht in Richtung des Pfeiles II der Fig. 1.

An embodiment of the invention is described below with reference to the drawing.

Figure 1

is a partial longitudinal section through a headbox.

Figure 2

is a partial view in the direction of arrow II of FIG. 1st

The headbox shown has two converging flow guide walls 11, 12 which delimit a nozzle-like and machine-wide material channel 10. This ends in a machine-wide fabric outlet gap 9. The outgoing paper stock arrives in the usual way on a paper machine screen 8 which runs over a breast roll 7.

The lower flow guide wall 11 (in the example shown) is part of the stationary headbox housing. The upper current-carrying wall 12 comprises a likewise stationary part 12a, a movable but stiff main part 12b (connected to the part 12a via a joint 12c) and a ruler-shaped bar, hereinafter referred to as "aperture" 13. In order to stiffen the main part 12b, it is welded to a hollow stiffening support 18 which is attached. This is known in Way connected to a bending beam 21. Between the two supports 18 and 21 there is a pressure cushion 22, with the aid of which the movable main part 12b of the current guiding wall 12 can be held together with the stiffening support 18 without deflection. Because you have to keep in mind that all of the previously mentioned parts 11, 12, 13, 18, 21 and 22 extend perpendicular to the plane of the drawing over the entire machine width and thus have a length of up to 10 m. A lifting device 23 engages at each of the two ends of the stiffening support 18 for the purpose of rough adjustment of the clear width of the outlet gap 9.

The aforementioned linear-shaped diaphragm 13 is provided for fine adjustment of the outlet gap 9. It can be adjusted transversely to the direction of flow, in the example shown obliquely from top to bottom. They can be adjusted in their entirety if necessary. Most of the time, however, it is only adjusted by local deformation, namely by amounts that can be smaller than 1/100 mm.

For this purpose, the diaphragm 13 is positively connected to numerous adjustment spindles 14, 14 ', 14''(FIG. 2) which are distributed over the machine width; the positive connection is made by a so-called spindle foot 24, in which a window 25 is provided. Each of the adjusting spindles 14 extends diagonally through the stiffening support 18 and is provided with a spindle drive 20 at its upper end. In a known manner, this comprises a gear housing 20a fastened to the stiffening support 18 and a worm wheel 20b rotatably mounted therein, the worm wheel of which is not visible can be driven by means of a handwheel 20c and / or by means of a motor 20d. A rotation of the worm wheel 20b produces a longitudinal displacement of the spindle 14 by means of a thread and thus a corresponding local deformation of the diaphragm 13.

Motor 20d may be a stepper motor; then the smallest possible stroke of the spindle is 3/1000 mm.

During operation, the local position of the diaphragm 13 (or in other words: the state of deformation of the diaphragm) must be continuously monitored on each spindle 14. For this purpose, the position of the diaphragm 13 is measured on each spindle 14 relative to the area of the stiffening support 18 close to the diaphragm and thus of the rigid main part 12b of the current-carrying wall 12. A measuring device 15 serving this purpose is arranged above the gear housing 20a. There it is easily accessible for the operating personnel; it can also be used there easily, e.g. be protected from contamination by means of a transparent hood 26.

The following is provided for connecting the measuring device 15 to the orifice 13 and the area of the current-carrying wall 12 close to the orifice: A tubular measurement reference 19 extends through the tubular adjusting spindle 14 and is connected at its lower end by means of a tubular base 27 to the stiffening support 18 and on it upper end is positively connected to a measuring housing 17. The tubular base 27 is located in the already mentioned window 25 of the spindle base 24. A measuring rod 16 extends through the interior of the tubular measuring reference 19 and is held in direct contact with the upper side of the diaphragm 13 by means of a compression spring 28. At its upper end, the measuring rod 16 extends into the interior of the measuring housing 17. An electrical measuring coil 30 is arranged there and there the measuring rod has a soft iron core 29. It should be noted that the measuring housing 17 is centered in the gear housing 20a, but axially relative to it Direction is easily displaceable. The measuring housing 17 therefore does not follow any deformations of the gear housing 20a and the upper region of the stiffening support 18. Rather, it always represents the exact position of the lower, area close to the diaphragm of the stiffening support 18 and the rigid main part 12b of the current-carrying wall 12. The measuring rod 16 also remains completely unaffected by the deformations mentioned, so that the soft iron core 29 represents the exact position of the diaphragm 13. This is measured by the measuring device 15 relative to the rigid main part 12b of the current-carrying wall 12, in the form of an electrical signal which is forwarded via lines 31 to a remote display device 32 and / or to a computer (not shown).

In addition, a mechanical measured value indicator 33 is provided. This has a housing 34 which is positively connected to the measuring housing 17 and a movable measuring member 35. This is held in contact with the upper end of the measuring rod 16 by the (very small) force of a spring (not shown) or by a screw connection not shown. Thus, the measured value indicator 33 works with the same precision as the electrical measuring device 29, 30, 31, 32. The smallest measurable adjustment of the diaphragm 13 is approximately 1/1000 mm.

1 also shows that the diaphragm 13 is pressed in a known manner by means of a pressure hose 36 onto the outer end of the main part 12b of the current-carrying wall 12. The pressure hose 36 rests in an abutment 37 screwed to the stiffening support 18. The interior of the stiffening support 18 is hermetically sealed from the surroundings by welded or screwed-on covers 38 and 39, respectively. In order to avoid thermal deformations of the main part 12b of the current guiding wall 12 and the stiffening support 18 as far as possible, a lower temperature control channel 40 and an upper temperature control channel 41 are provided in the interior of the stiffening support 18. These temperature control channels also extend across the entire machine width; they become liquid of the same temperature flows through. By all of these measures, the stiffening beam 18 and the main part 12b of the flow wall 12 can be kept isothermal.

2, the cover 39 and the abutment 37 are omitted. Shown is the linear diaphragm 13 and the lower end of one of the adjusting spindles 14 with the spindle foot 24 (which has a window 25). In the window 25 there is the tube base 27 of the measuring reference 19 and the compression spring 28 with which the measuring rod 16 is at the top the aperture 13 is pressed. Only the center lines of the two adjacent spindles 14 'and 14' 'are shown.

Claims (13)

1. A headbox for a manufacturing machine of lengths of fibre material, for example lengths of paper, comprising the following features:

   a) a jetlike material channel (10) as wide as the machine, which forms an outlet gap (9) as wide as the machine, is defined by two converging flow-guiding walls (11 and 12);

   b) one of the two flow-guiding walls (for example 12) comprises a stiff main element (12b) and an adjustable and spatially deformable ledge (13), which is arranged at the material outlet gap (9) and which extends over the width of the machine and which is engaged by a plurality of adjustment spindles (14) which are spaced over the width of the machine;

   c) each adjustment spindle (14) has a spindle drive (20) at its end remote from from ledge (13);

   d) the ledge (13) is connected to a plurality of measuring devices (15), which are spaced over the width of the machine and also arranged remote from the ledge (13) and which serve to determine the local position of the ledge (13) and of which each comprises a measuring housing (17) and a measuring element (29) which is movable therein;

   characterized by the following features:

   e) each of the movable measuring elements (29) is positively connected, via a measuring rod (16) and independently from the adjustment spindles (14), to the ledge (13);

   f) each measuring housing (17) is positively connected, via an elongated connecting element, the so-called "measuring reference" which extends parallel to the measuring rod (16), to the area near the ledge of the aforementioned stiff main element (12b) of the flow-guiding wall (12).
2. A headbox according to claim 1, characterized in that the measuring rod (16) extends through the interior of the tubularly arranged measuring reference (19).
3. A headbox according to claim 1 or 2, characterized in that the measuring reference (19) and the measuring rod (16) extend through the interior of the spindle (14).
4. A headbox according to claim 3, characterized in that the measuring reference (19) and the measuring rod (16) extend through the interior of the spindle drive (20).
5. A headbox according to one of claims 1 to 4, characterized in that each measuring device is designed as a mechanical measuring-value indicator (33).
6. A headbox according to one of claims 1 to 4, characterized in that each measuring device (15) is designed as an electric signal emitter (29, 30).
7. A headbox according to one of claims 1 to 4, characterized in that both a measuring-value indicator (33) and an electric signal emitter (29, 30) is arranged on each adjustment spindle (14).
8. A headbox according to claim 7, characterized in that the housing (34) of the measuring-value indicator (33) and the housing (17) of the electric signal emitter (29, 30) are rigidly connected to each other and to the measuring reference (19).
9. A headbox according to claims 4 and 8, characterized in that the electric signal emitter (29, 30) is arranged between the spindle drive (20) and the measuring-value indicator (33), and the measuring rod (16) or an extension of it extends up to the movable measuring element (35) of the measuring-value indicator (33).
10. A headbox according to one of claims 1 to 9, characterized in that the ledge (13) is in a conventional manner designed as a straightedge diaphragm.
11. A headbox according to one of claims 1 to 10, characterized in that all measuring rods (16) and all measuring references (19) are made of materials of identical heat expansion coefficients.
12. A headbox according to one of claims 1 to 11, characterized in that all measuring rods (16) and all measuring references (19) are arranged in a sealed and isothermally kept space.
13. A headbox according to one of claims 1 to 12, characterized in that the adjustment spindle (14) is connected to the ledge (13) via a spindle base (24) which comprises a window (25), and that the measuring reference (19) is connected to the area of the flow-guide wall (12) near the ledge via a tubular base (27) which is arranged in the window (25).

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