Influencing the jet velocity in the multilayer headbox

Paper making and fiber liberation – Apparatus – Running or indefinite length product forming and/or treating...

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162216, 162344, D21F 102

Patent

active

056226039

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The invention concerns a multilayer headbox of a paper machine with a slice nozzle subdivided by lamellae of flexible installation, in which slice nozzle there is for each stock suspension an aperture space provided which extends across the machine width. Furthermore, the invention concerns a method for adjusting the relative velocities of the individual stock suspensions at the nozzle exit.
A headbox of that type is known, e.g., from DE-OS 37 04 462. Its aperture spaces being supplied independently from one another with stock suspensions, said headbox serves the manufacture of multilayer paper webs. To adjust different velocities and pressures of the stock suspension in the individual spaces, the lamellae between individual aperture spaces are pivotable about their longitudinal axis and are manually adjusted from outside. Disadvantageous is here that, when the quantity passing through the headbox changes, the interrelationship of stock suspension velocities between individual layers changes, requiring readaptation by manual adjustment. A further disadvantage is that the necessary accuracy of adjustment cannot be achieved at all or only at extraordinary expense.
Moreover, reference is made to patent document DE 31 01 407 A1. This document depicts a multilayer headbox whose built-in lamellae are installed flexibly. The lamellae shown there, however, aim to maximally equalize the flow velocities of the different layers.
Hence, it is also known to fashion the lamellae in the aperture space flexible across their entire length, allowing them to automatically adjust in such a way that equal pressure prevails at any point in all aperture spaces. A flow adjustment in the individual nozzle spaces and a mutually independent adjustment of the exit gaps for the individual paper layers, however, is not possible thereby.
For some time now it has been desired to influence the velocities of the individual jets of a multilayer headbox in such a way that the differential velocities between individual jets will change. In the cited prior art this is carried out by manual adjustment of the individual lamellae. It shows here, however, that it is very difficult to adjust the lamellae, which are up to 10 meters long, to the necessary accuracy of a few hundredths of a millimeter against the forces of flow in a fashion which is constant across the machine width. Furthermore, altering the conditions of throughput leads to different velocity ratios between individual layers, whereby readjustment becomes necessary.


SUMMARY OF THE INVENTION

Reasons for the necessity of influencing the velocity of the individual stock suspension layers are: individual stock suspension layers. The variation of shear forces possible thereby, between liquid layers, generates turbulences which affect the formation, which allows an influencing of the paper web formation that may be desired. orientation and lengths of the semiaxes of the break length ellipses of the paper web, depending on the size of the jet angle and the jet-wire speed differential. Said break length ellipses, in turn, correlate with the orientation and statistical distribution of the fibers about the major direction in the outer layer. Possible is thus an influencing of the mechanical properties of the paper web. the fiber orientation, that is, it deforms at moisture changes in accordance with this property. With the fiber orientation and distribution differing in the outer layers of a paper web, the so-called "curl," that is, the tendency of a paper to roll at moisture changes, of a sheet will be favored. Therefore, the curl tendency can be influenced as well by velocity changes.
The problem underlying the invention is to provide a method for influencing the flow velocities of the individual layers of a multilayer headbox which is broadly independent of the amount of stock suspension throughput through the headbox. A further problem of the invention is to provide a multilayer headbox for application of the aforementioned method.
These problems are solved b

REFERENCES:
patent: 3598696 (1971-08-01), Beck
patent: 3843470 (1974-10-01), Betley et al.
patent: 4181568 (1980-01-01), Pfaler
patent: 4376014 (1983-03-01), Bergstrom
patent: 4765868 (1988-08-01), Fujiwara
patent: 5074965 (1991-12-01), Keskiivari et al.
patent: 5431785 (1995-07-01), Bubik et al.

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