Paper making and fiber liberation – Processes and products – Running or indefinite length work forming and/or treating...
Reexamination Certificate
1999-09-23
2001-04-10
Silverman, Stanley S. (Department: 1731)
Paper making and fiber liberation
Processes and products
Running or indefinite length work forming and/or treating...
C162S336000, C162S190000, C162S264000, C162S322000, C162S343000
Reexamination Certificate
active
06214170
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a process for cleaning or maintaining the cleanliness of a low-consistency branch of a stock density-regulated headbox system including the constant part of a paper or cardboard machine with at least one high-consistency branch and a low-consistency branch, where the final concentration output by the headbox onto a wire or between two wires is determined by the mixing ratio of high-concentration and low-concentration suspension flows.
The invention further relates to a headbox system including the constant part of a paper or cardboard machine with a stock density regulation that is sectioned across the machine width by variably mixing a high-consistency suspension and a low-consistency suspension, having a high-consistency branch and a low-consistency branch.
2. Discussion of Background Information
Sectional stock density-regulated headbox systems are generally known from countless patent applications and disclosures. For example, reference is made to Applicant's German Patent Disclosure Document DE 40 19 593 A1, which discloses a sectional stock density-regulated headbox with two branches of individual supplies that are distributed across the machine width and are for two stock suspensions that have different concentrations. In this instance, paper stock and backwater are used as the suspensions with the different consistencies. With variances in the basis weight cross section of the paper web at a particular point of the web width, which is associated with a particular section of the headbox, the concentration C
M
of the relevant section flow is corrected by changing the quantity ratio of regulating flows that are supplied to a mixer and have different solids contents Q
H
/Q
L
. This type of basis weight cross section regulation is very advantageous with regard to a simultaneously good fiber orientation cross section and causes very favorable results with regard to the basis weight cross section.
The disclosure of this previously cited reference and Applicant's earlier Patent Applications DE 37 41 603 A1, DE 44 22 907 A1, DE 42 37 304 A1, and DE 42 11 291 A1, particularly with regard to the possibilities for density regulation of the final concentration of stock suspensions by mixing suspensions that have different concentrations, are herein incorporated by reference in their entireties. In particular with regard to the cited prior art, it should be emphasized that possible basis weight changes that are produced by metering particular fibrous materials or fibrous material contents can be compensated for in the known headboxes by means of a corresponding regulation mechanism that influences the sectional concentration of the stock suspension. The cited prior art discloses in detail how the supply to the headbox of stock suspensions that have different properties can be carried out and how the basis weight cross section of the material web can be kept uniform.
In practice, with the above-cited stock density-regulated headbox systems, the desired final concentration is usually regulated by means of a more or less intensive admixing of backwater I or clear filtrate to a slightly over-concentrated stock suspension, where backwater I is understood to mean all of the circulating backwater. In this connection, it has turned out that increased scale and slime deposits can occur in the supply lines of the low concentrate. As a result of this, on the one hand, the regulation mechanisms can be impaired, because the hydraulic resistances of the lines change; on the other hand, there is also the danger of quality losses due to the sudden freeing of such scale and/or slime deposits. At present, if scale or slime deposits of this sort occur, the attempt is made either to clean the scale and/or slime deposits during operation with the aid of expensive chemical additives or additives that impair the manufacturing process or to carry out a mechanical cleaning when the machine is shut down.
SUMMARY OF THE INVENTION
Other exemplary embodiments and advantages of the present invention may be ascertained by reviewing the present disclosure and the accompanying drawing.
An object of the invention is to provide a different process for cleaning or maintaining the cleanliness of the low-consistency branch of a stock density-regulated headbox system including the constant part of a paper or cardboard machine which can also be carried out during operation without side effects interfering with the production. A further object is to provide a headbox system that is suitable for performing this process.
The inventors have recognized that the scale and/or slime deposits on the walls of lines and devices in the vicinity of low-consistency suspension paths essentially occur because, in contrast to the high-consistency suspensions, few solids are entrained. As a result of this, when left undisturbed, a relatively thick boundary layer accumulates on the walls at low flow speeds, as a result of which, the adhesion and cohesion forces become greater than the flow-induced shear forces and scale and/or slime deposits occur.
In order to prevent the process explained above, a process is provided for cleaning or maintaining the cleanliness of the low-consistency branch of a stock density-regulated headbox of a paper or cardboard machine. The headbox has at least one high-consistency branch and one low-consistency branch. The final concentration output by the headbox onto a wire or between two wires is determined by the mixing ratio of high-concentration and low-concentration suspension flows to the effect that an increased content of solid particles is supplied to the low-consistency branch. Due to interferences, the supply of solid particles produces a reduction of the boundary layer thickness and thus an increase in the shear forces in the wall region. As a result of this measure, a cleaning effect is produced which breaks down existing scale and/or slime deposits or assures that the formation of scale and slime deposits is hindered or prevented.
A process is provided for cleaning or maintaining the cleanliness of the low-consistency branch of a stock density-regulated headbox system comprising a constant part of a paper or cardboard machine having at least one high-consistency branch and one low-consistency branch, possibly sectioned. The process includes mixing a ratio of high-concentration and low-concentration suspension flows to determine a final concentration output by the headbox onto a wire or between two wires; and supplying the low-consistency branch with an increased content of solid particles.
According to another advantageous embodiment of the process provides that, at the same time as the increase of the solid content in the low-consistency branch, the corresponding solid particle content in the high-consistency branch is reduced or that, in a particularly advantageous manner, the sum of the supplied solid particle contents in the low-consistency branch is equal to the sum of the reduced solid particle contents of the high-consistency branch. By means of this, the process can be used for continuous production without disadvantage because no greater interference with the basis weight occurs.
It is particularly advantageous if the mass of the supplied solid particle content of one section in the low-consistency branch is equal to the reduced mass in this section of the solid particle content of the high-consistency branch. This not only maintains the average of the basis weight of the paper or cardboard web produced, but also maintains the basis weight cross section of the web produced.
Is also possible to supply both the low-consistency branch and the high-consistency branch in a controlled fashion, i.e., controlled or regulated, such that, to increase the solid particle content in a section in the low-consistency branch, the quantity distribution between the high-consistency branch and the low-consistency branch in this section is changed.
Another advantageous embodiment according to the invention provides that so
Begemann Ulrich
Humberg Holger
Greenblum & Bernstein P.L.C.
Halpern Mark
Silverman Stanley S.
Voith Sulzer Papiertechnik Patent GmbH
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