Paper making and fiber liberation – Apparatus – Running or indefinite length product forming and/or treating...
Patent
1989-01-25
1994-04-19
Dang, Thi
Paper making and fiber liberation
Apparatus
Running or indefinite length product forming and/or treating...
162343, 162344, 162346, 162347, D21F 102
Patent
active
053042859
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a stock-inlet or head box for a papermaking machine. Among the essential components of this stock-inlet are two converging flow-guidance walls which are as wide as the machine and which, together with a rear wall and with two lateral walls, define a nozzle-like outlet-channel as wide as the machine. Located at the downstream end of the flow-guidance walls, which are also known as the lower lip and the upper lip, is an outlet-gap as wide as the machine, from which the paper-stock emerges, in the form of a jet as wide as the machine, onto a circulating wire-screen upon which the paper web is formed.
Known stock-inlets of this kind are described in the following publications:
1. C.A.-PS 849,817,
2. U.S. Pat. No. 3,373,080,
3. U.S. Pat. No. 4,198,270 (=DE 27 26 709),
4. U.S. Pat. No. 4,455,197,
5. U.S. Pat. No. 4,552,619,
6. U.S. Pat. No. 2,920,699,
7. U.S. Pat. No. 3,846,229 (=DE 23 02 196)
One serious problem with such stock-inlets is maintaining the internal width of the above-mentioned outlet-gap constant over the width of the machine. It has been found, in practice, that the presence of local deviations from the desired width of the gap impairs the quality of the resulting strip of paper. More particularly, it produces an irregular weight-per-unit-of-area transverse profile. For instance, it has been found that a specific change in gap-width increases the weight per unit of area of the strip of paper by a factor of 10.
Another problem is that certain changes in gap-width may occur only when the machine is in operation and thereafter disappear only partly. Such changes are brought about by temperature fluctuations, for example, especially if, after a shut-down, the papermaking machine is started up again with heated stock. In this case, the flow-guidance walls assume only gradually the higher temperature of the stock.
Changes in gap-width which occur in different degrees at different locations over the width of the machine are particularly troublesome. For instance, a flow of cold air entering the mill (such as, when a door is opened) may cause a one-sided change in gap-width. Other uneven changes in gap-width appear to be caused by stiffening ribs which are used, in certain known designs, to reinforce the flow-guidance walls.
In Publication 1, a description is given of a stock-inlet, the lower flow-guidance wall of which is supported on a foundation by a hollow carrier. The problem upon which this publication is based is that the upper part of the hollow carrier, adjoining the flow-guidance wall, assumes a higher temperature than the lower part. The top, therefore, expands more than the bottom and the lower flow-guidance wall, therefore, becomes warped. In-order to overcome this problem, it is suggested that the lower part of the hollow carrier be kept at the same temperature as the upper part by means of a heating device.
In the case of the stock-inlet according to Publication 4, a bundle of pipes, and flow-guidance walls attached thereto, runs through the interior of a hollow stock-inlet housing. A pivotably mounted upper lip is formed by one of the walls of a cross-sectionally triangular hollow carrier. In order to keep the parts of the stock inlet at a specific temperature, water is passed through the interior of the stock-inlet housing and through the upper-lip hollow carrier, separate from the paper-stock, of course. According to FIG. 6, a rectangular hollow carrier is built onto the triangular hollow carrier, which, according to FIG. 1 serves to support the adjusting spindles. In order to ensure that, in the event of a change in temperature a corresponding change in length of the triangular hollow carrier can take place unimpededly, rectangular hollow carrier 54 in FIG. 7 is divided into sections distributed over the width of the machine.
In the stock-inlet described in Publication 5, the flow-guidance walls are again reinforced by hollow carriers. As in Publication 1, steps are taken to ensure that the hollow carrier, and thus the flow-guidance
REFERENCES:
patent: 4197159 (1980-04-01), Newns et al.
patent: 4373993 (1983-02-01), Fujiwara
patent: 4406740 (1983-09-01), Brieu
patent: 4426257 (1984-01-01), Antikainen et al.
Egelhof Dieter
Meinecke Albrecht
Dang Thi
J.M. Voith & GmbH
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