Paper making and fiber liberation – Processes and products – With measuring – inspecting and/or testing
Reexamination Certificate
2000-05-18
2003-02-18
Fortuna, Jose A. (Department: 1731)
Paper making and fiber liberation
Processes and products
With measuring, inspecting and/or testing
C162S198000, C162S190000, C162SDIG004, C700S128000
Reexamination Certificate
active
06521089
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application claims priority under 35 U.S.C. §119 of German Patent Application No. 199 22 817.5, filed on May 19, 1999, the disclosure of which is expressly incorporated by reference herein in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a device and process for controlling or regulating the basis weight of a paper or cardboard web in a manufacturing process.
2. Discussion of Background Information
An essential quality factor of a paper or cardboard web lies in the uniformity of the basis weight of the web produced. In the manufacturing process of a web of this kind, numerous interference factors occur that can have a negative influence on the uniformity of the basis weight viewed across the machine width and also in the machine direction. These interference factors include, for example, temperature fluctuations, pressure fluctuations, and manufacturing tolerances, but also include errors in the embodiment or adjustment of the paper machine during the manufacturing process. In order to eliminate these negative interference factors to the greatest degree possible and to achieve a uniform manufacture of the paper web, devices and processes are used to control and regulate the basis weight in the lateral and longitudinal direction of the web.
The published, unexamined German Patent Disclosure DE 20 19 975 discloses how, with the aid of two sensors for measuring the basis mass in a traveling web, the actual basis weight cross profile and the actual basis weight longitudinal profile can be extracted from a measured diagonal profile and longitudinal profile and can be used for controlling or regulating the basis weight of a web.
The Patent Document DE 35 35 849 discloses changing the width of the outlet gap of a headbox at particular locations on the web width so that the flow rate of the stock suspension correspondingly changes locally. If the flow rate of the stock suspension changes locally with the same concentration across the machine width, then this influences the quantity of solids at this point in the web with regard to the web width and thus produces a change in the basis weight at this point or at this strip of the web.
The Patent Application DE 40 19 593 A1 discloses a device and a process for regulating the basis weight cross profile of a paper web. According to this document, the concentration of the stock suspension flow at this location is changed using a variation of the basis weight cross profile of the paper web at a particular location on the web width. In order to achieve this, the proposal is made to section the headbox at least partially across the machine width and to supply it with individually adjustable concentrations with the aid of regulated sectional flows. The individual adjustment of the concentration of each sectional flow takes place by a regulation of the inflow conditions of two individual flows with constant, but different, concentrations. As a result of the different solids content of the sectional flows, a change in the basis weight is produced at the corresponding location on the web width.
In the regulating process used here, the basis weight cross profile of the paper web is measured at the end of the paper machine and, through the use of a control circuit, the aperture on the headbox is regulated or the inflow conditions of the individual flows are regulated with different concentrations for the respective sections.
A regulating process of this kind with the measurement of the basis weight cross profile has been disclosed, for example, by the Patent Applications DE 40 05 281 or DE 42 38 037. In both of the above-mentioned documents, the basis weight cross profile of the paper web is measured at the end of the paper machine and, by a process guidance system, the necessary adjustment of the actuators is produced in order to sectionally influence the basis weight.
The disclosures of the above-cited prior art are expressly incorporated by reference herein in their entireties, with particular emphasis on the regulation techniques and regulation mechanisms disclosed.
The problem with this prior art is that the known regulation of the basis weight has a relatively sluggish behavior with long reaction times.
SUMMARY OF THE INVENTION
The object of the invention is to develop the known paper machine with a regulation of the basis weight and the corresponding process so that the reaction times of the regulation are significantly shortened and influence can therefore also be exerted on fluctuations in the paper manufacturing process which in their chronological course, have a shorter wavelength than the travel time of the paper web through the paper machine.
The object of the invention is attained by an additional control circuit having at least one sensor for detecting the concentration of the incoming backwater. According to the process, another control circuit can be provided such that, after the detection of a retention change, the retention change is counteracted by influencing the concentration of the stock suspension that is placed onto the wire or introduced between the wires.
Consequently, we propose improving the known device for controlling or regulating the basis weight of a paper or cardboard web in the manufacturing process of a paper or cardboard machine, having a first control circuit for adjusting the basis weight with at least one adjustable device for influencing the basis weight and at least one basis weight sensor so that another control circuit with at least one sensor for determining the concentration of the incoming backwater is provided.
Advantageously, the at least one device for influencing the basis weight can be embodied as a multitude of adjustable element which are arranged distributed across the width of the machine. For example, this corresponds to a paper machine with a dilution water-regulated headbox, which has mixers or valves distributed across the width of the machine, which sectionally regulate the stock suspension concentration by different mixture ratios of backwater and high-consistency pulp.
It can also be advantageous for the at least one adjustable device for influencing the basis weight to be provided as an actuator for the second control circuit.
In another embodiment of the invention, the at least one sensor for the concentration of the backwater can be arranged before or in a backwater container or also in a line for supplying backwater to the headbox. In this connection, however, the control path can be shorter the closer to the extraction of the backwater, i.e., to the wet section, the measurement is carried out. However, by a measurement after an intermediary buffer, for example, a backwater container, small fluctuations can be eliminated which could lead to erroneous regulating actions.
It is also advantageous for the additional control circuit to be connected to the actuators of the first control circuit. This embodiment can save on the number of actuators.
On the one hand, the sensor for measuring the basis weight and, optionally, the moisture, can be positioned at the end of the drying section or between the press section and the drying section, preferably at the end of the press section. If the sensor is positioned at the end of the press section, then the control path is shortened by approximately 90% in comparison to a measurement at the end of the drying section. Furthermore, errors and interruptions are detected in a significantly more rapid fashion and consequently can be eliminated or influenced in a significantly more rapid fashion, by which unproductive operating times can be significantly curtailed.
With regard to the process, the inventor proposes improving the known process for controlling or regulating the basis weight of a paper or cardboard web in the manufacturing process with a first control circuit which adjusts the basis weight of the web with the aid of at least one basis weight measurement and at least one device for influencing the basis weight so that, in another control circ
Griech Wolfgang
Thomas Dirk
Fortuna Jos'e A.
Greenblum & Bernstein P.L.C.
Voith Sulzer Papiertechnik Patent GmbH
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