Paper making and fiber liberation – Processes and products – With measuring – inspecting and/or testing
Reexamination Certificate
1998-01-26
2001-09-04
Silverman, Stanley S. (Department: 1731)
Paper making and fiber liberation
Processes and products
With measuring, inspecting and/or testing
C162SDIG004, C162SDIG004, C162S183000, C162S212000, C162S216000, C162S252000, C162S259000, C162S263000
Reexamination Certificate
active
06284100
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method of controlling one or more cross-direction property profiles of a paper web manufactured by a paper machine, which method employs a control system for regulating a headbox or headboxes of the paper machine and in which method the property profile(s) is/are measured by a measurement system. A measurement signal obtained from the measurement system is supplied to the control system. Each headbox is supplied with at least two feed streams which contain feedstuffs for the paper to be manufactured suspended in aqueous solution and which feed streams are divided into feed zones in cross-machine sections of the headbox, the feed zones each being supplied with combinatory streams of the feed streams.
In addition, the present invention relates to apparatus for controlling one or more cross direction property profiles of a paper web manufactured by a paper machine, which apparatus comprises a control system for regulating a headbox or headboxes of a paper machine, a measurement system for measuring each property profile, means for feeding a measurement signal obtained from the measurement system to the control system, means for supplying at least two feed streams to each headbox, which feed streams contain feedstuffs for the paper to be manufactured in aqueous solution, and means for dividing the feed streams into feed zones in cross-machine sections of each headbox, which feed zones are each supplied with combinatory streams of the feed streams.
BACKGROUND OF THE INVENTION
As is known in the prior art, systems for controlling the cross-direction grammage of paper manufactured by paper machines operate in the following manner. The flow of thickstock coming into a wire pit of a paper machine is regulated by a grammage valve based on grammage measurement at the dry end of the paper machine. The grammage of the paper web is measured by means of measuring sensors traversing in a cross direction thereof, and the measurement result of the cross-direction grammage profile is averaged and passed as a feedback signal of a control system. The flow of thickstock is passed from the grammage valve, as known in prior art, to the wire pit, into which white water from the wire section of the paper machine is also passed. The thickstock flow and white-water are mixed in the wire pit and the thus-obtained diluted stock flow is passed, as known in itself, through pulp cleaning and deaeration devices to an inlet header of a headbox and therefrom, further through a distribution tube bank of the headbox, possibly through an equalization chamber and a turbulence generator to a slice channel of the headbox. A pulp suspension jet is discharged from the slice channel onto a forming wire or into a forming gap defined between forming wires.
In the prior art, the cross-direction grammage profile of paper manufactured by paper machines may be regulated by profiling the height of a slice opening in a headbox based on the aforesaid grammage measurement at the dry end of the paper machine. Recently, so-called dilution regulations have also become more common in which dilution water, usually white-water or a stock that is more dilute than the headbox stock, is supplied to individual feed points situated in the cross-direction in connection with a headbox. This dilution water feed system serves to profile the cross-direction grammage profile of a slice jet together with the regulation of a profile bar, or without it. A special advantage of dilution regulation is that the headbox can be operated with a slice opening having a uniform height so that the cross-direction flows in the slice jet and after it, caused by the profiling of the height of the slice opening, as well as distortions of the fiber orientation profile of paper resulting from them, may be avoided.
Prior-art dilution headboxes are subdivided into several feed zones across the headbox. Additionally, there may be more than one layer of such feed zones. Two or more streams of feedstuff supply each layer of feed zones, and each stream of feed stuff may supply one or more layers of feed zones. Each feed zone in each layer is equipped with means for controlling the combinatory proportions of streams fed to that feed zone, normally using a suitable valve arrangement. Additionally, there may be one or more layers of feed zones which are supplied by only one feed stream, or are supplied by plural feed streams without means for controlling combinatory proportions of feed streams fed to each feed zone.
Commonly, two feed streams are provided, one supplying the main feedstuff, and the other supplying a feedstuff of different properties. Normally, the second stream is more dilute than the main stream, but this need not always be so. The dilute feedstuff is normally white-water taken from the wire pit or short circulation, often with some processing, such as deaeration, cleaning, or filtration. The main feedstuff also normally contains white-water, to which a thickstock is added. In some cases, clarified water may be used instead of white-water as the dilute feedstock.
More than two feed streams may be provided, where each feed stream supplies feedstuffs of different material composition. For instance, both white-water and clear water streams may be supplied as well as the main feedstuff stream. Alternatively, two main feed streams may carry different feedstuffs, with a third feed stream carrying a dilute feedstuff However, it is also possible that more than one stream contains the same feedstuff; in this case, all streams carrying an identical feedstuff are treated as a single consolidated stream for the purposes of the invention described below. Applicability of this invention requires that not all streams cany exactly the same feedstuff, as described more fully below.
The streams fed to each feed zone are mixed together in any of several ways in the feed zone, producing an aggregate stream. The aggregate streams from all feed zones are merged, forming a single jet discharged across the whole headbox. There may be some mixing between streams in adjacent feed zones in this merging.
An example of a dilution headbox is the Valmet Sym-Flo D™.
With respect to different details of structures of dilution headboxes, reference is made to the following patents and patent applications: Finnish Patent No. 92229 (corresponding to European Patent Application No. 0 633 352 and U.S. Pat. No. 5,674,363) and U.S. Pat. No. 5,560,807.
In some cases, multiple conventional (non-dilution) headboxes may be operated as if their combination formed a dilution headbox. This is possible if the headboxes do not all have the same feed streams, and there is a difference in composition between some of the feed streams being fed to the individual headboxes. In this case, modulating the slice lip profiles has the effect of changing the combinatory proportions of the feed streams at each location across the web. However, the streams are not mixed, so the effect is similar to operation of a multilayer dilution headbox.
Feedstuffs, White-water, Retention
It should be noted that the feedstuffs used in the paper industry are of complex composition, containing many distinct material components suspended in an aqueous solution The principal material components are fibers of different kinds, with properties which depend on the fiber source (Norway spruce, silver birch, Eastern hemlock, bagasse, kenaf, etc.), and pulping process used. Resins and synthetic polymers, as well as various clays, minerals (ash), and other inorganic material may be added. Substances such as dyes, brighteners, anti-brighteners, bleaches, and opacity agents may occur in quantities which have negligible effects on the weight, strength, or other material properties of the web, but which have major effects on color, brightness, opacity, and other optical properties of the web. There may also be solutes dissolved in the aqueous solution, affecting its pH and other chemical properties, thus modulating the effect of other feedstuff components on properties of the web.
As known in
Kniivilä Juha Antero
Nyberg Petri
Shakespeare John Francis
Halpern Mark
Silverman Stanley S.
Steinberg & Raskin, P.C.
Valmet Corporation
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