Paper making and fiber liberation – Processes and products – With measuring – inspecting and/or testing
Patent
1994-12-13
1996-11-05
Czaja, Donald E.
Paper making and fiber liberation
Processes and products
With measuring, inspecting and/or testing
162111, 162113, 162281, D21F 1112
Patent
active
055713823
DESCRIPTION:
BRIEF SUMMARY
In the manufacture of crepe-type paper, such as toilet paper, tissue paper, cellulose wadding and similar soft paper products, the wet paper web is placed on a large drying cylinder, a so-called Yankee-cylinder, from which the paper web is then removed by means of a doctor blade and rolled into rolls. The peripheral speed of the drying cylinder is somewhat higher than the speed of the downstream web and the proportional difference between these speeds can be defined as the degree of creping. One prerequisite for the manufacture of such papers is that the paper web adheres to the surface of the drying cylinder during the drying process, although this adhesion must neither be too strong nor too weak. The extent to which the web will adhere to the drying cylinder is influenced by the quality of the pulp, the additive substances present therein, e.g. softeners, and also by the nature of the surface of the drying cylinder itself. It is well known to treat this surface continuously, by spraying the same with appropriate chemicals at a position between the doctor blade and the location at which the wet paper web is applied to the cylinder. It is also possible to coat the actual web itself, prior to applying the same, for instance as the web passes a felt, or the felt itself can be treated with such chemicals, which are then taken-up by the web as it comes into contact with the felt. The essential criterion is that these chemicals will be applied to the cylinder surface.
One advantageous method of applying such chemicals is described in U.S. Pat. No. 4,448,818, according to which chemicals are sprayed in the form of airborne droplets, i.e. in an aerosol form. One embodiment hereof is sold by Leckners Verkstads AB, Jonkoping, Sweden, which enables the application of two different chemicals in desired, controllable mixing proportions, e.g. to thereby increase adhesion or facilitate release.
Efficient operation of present-day machines of this kind depends greatly on the expertise of the machine operator and on many years of practice. The operator is able to observe the amount of waste removed by the cleansing doctor blade located downstream of the web-removing blade in order to judge whether or not the chemical coating shall be changed and, if so, how. It is normal to control the degree of creping constantly, by adjusting the motors that drive respective drying cylinders and upstream equipment and also to adjust the speed at which the treated paper web is rolled-up into rolls. If adhesion is too high or too low, the paper web is liable to be torn to pieces, with subsequent stoppages in operation.
An object of the present invention is to provide better possibility of controlling the course of such paper manufacture, either so that the machine operator is better able to judge how web release/adhesion should be adjusted, or preferably to enable release/adhesion to be regulated automatically, so as to enable consistent, uniform production to be achieved, even though the conditions should change somewhat.
Conditions can change in many ways. For example, the quality of the pulp can change during its manufacture; temperature conditions can also change; the doctor blade can be influenced by wear, as also, although slower, the metallic surface of the drying cylinder, which, furthermore, may have a certain "memory" from earlier operations, in that a change in spraying on said coating will not stabilize release and/or adhesion of the paper web respectively until a given length of time has lapsed. Accordingly, it is also an object of the present invention to enable even pulp material to be worked, which is difficult to work.
Contactless arrangements for measuring web tension in paper manufacturing processes are known from U.S. Pat. No. 4,711,133. With constructions of this kind, there is arranged in a fixed surface, against which the paper is drawn, a chamber pressurized via a choke and separate and surrounding thereo a measuring chamber, where the pressure is measured, giving a measure of web tension, being a measure of the mov
REFERENCES:
patent: 3017317 (1962-01-01), Voigtman et al.
patent: 4304625 (1981-12-01), Grube et al.
patent: 4448638 (1984-05-01), Klowak
patent: 4711133 (1987-12-01), Berglund
Czaja Donald E.
Padgett Calvin
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