Paper making and fiber liberation – Processes and products – With measuring – inspecting and/or testing
Reexamination Certificate
2001-09-17
2004-07-27
Fortuna, José A. (Department: 1731)
Paper making and fiber liberation
Processes and products
With measuring, inspecting and/or testing
C162S197000, C162S194000, C162S260000, C162S263000, C162S271000, C162S286000
Reexamination Certificate
active
06767431
ABSTRACT:
STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT
Not applicable.
BACKGROUND OF THE INVENTION
The invention relates to a method for measuring and regulating curl in a paper or board web, in which method the curl of the paper or board web is regulated.
The invention also relates to a paper or board machine line which comprises sections for the manufacture of a paper or board web, which paper or board machine line comprises a means or means for regulating curl in the web.
It is known from experience that if paper is dried one-sidedly, the result is a tendency of curling of the sheet. When paper is dried, for example, by means of normal groups with single-wire draw from the side of its bottom face and if such asymmetric drying is extended over the entire length of the dryer section, the drying takes place so that first the bottom-face side of the paper web is dried and, when the drying makes progress, the drying effect is also extended to the side of the top face of the paper web. The thus dried paper usually curls and becomes concave, when viewed from above.
Reducing the tendency of curling of paper, in particular of fine paper, has become more and more important along with new printing and copying methods, in which methods the paper is heated suddenly, as a rule from one side, so that any internal strains that may have remained in the paper because of different reasons are discharged in the form of its curling. The tendency of paper to curl is affected both by the anisotropies in the different properties of the structure of the paper, such as fibre orientation, filler distribution, and density, and by anisotropies produced in the paper during drying, both in the direction of the plane of the paper and in the z-direction.
As known in the prior art, the tendency of curling of paper is already affected in connection with the forming of the web, in particular at the sheet formation stage by means of the selection of the difference in speed between the slice jet and the wire, and by means of the choice of the former and its mode of running, as well as by means of other running parameters. As known in the prior art, for example, in the case of copying paper, by means of unequal sidedness of drying in the after-dryer, a suitable initial curl form is regulated for the sheet in order that the curling of the paper after one-sided or double-sided copying might be optimized. In the case of copying paper, the reactivity of curling, i.e. the extent to which curling occurs per unit of change in moisture content, is affected to a greater extent by means of a multi-layer structure of the paper, which is produced in connection with the forming of the web in the wet end.
One factor that has a substantial effect on the curling of paper is then one-sided drying of the paper. In drying sections provided with the traditional twin-wire draw, the web can be dried at the same rate from both sides, and the uniformity of drying can be affected, and the tendency of paper to curl can be prevented, by regulating the steam pressures in the upper and lower cylinders. By means of the concept of a dryer section with single-wire draw, said drying at the same rate and said possibility of regulation cannot be accomplished. Attempts are made to prevent unequalsided drying, for example, by means of inverted drying groups, moistening and steam treatment of the web. For example, in connection with calendering, it is possible to employ steam spraying applied to the paper, the effect of which is based on relaxing the strains in the paper fibres by the effect of heat and moisture.
With respect to the prior art related to the invention in connection with regulation of curl and the methods used in it, reference may be made to FI patent 91900, FI patent applications 971301 and 972080 as well as to U.S. Pat. Nos. 5,269,074; 5,542,193; 5,557,860; and 5,592,571. These publications describe various arrangements and devices which are employed for regulation of paper curl. The principles described in said publications can naturally be also used for control of the curl profile in the cross machine direction. The publications also describe dryer sections known in the prior art in which control of curl is essential in order to achieve a good end product.
One problem in the prior art arrangements is that a method that is suitable for on-line measurement of curl is not known, which method has turned out to be an almost compelling need in modern paper manufacture. If curl could be measured on-line, it could also be regulated as quickly as possible as desired.
SUMMARY OF THE INVENTION
Thus, an object of the invention is to provide a method for measuring curl in a paper web, which method is suitable for use in connection with the manufacture of paper, i.e. on-line.
An object of the invention is also to provide a method which is suitable for use at several different locations in connection with a paper or board machine line.
A further object of the invention is to provide a paper or board machine line in which the curl of a web is measured on-line.
With a view to achieving the objectives stated above as well as those coming out later, the method according to the invention is mainly characterized in that, in the method, in connection with the manufacture of a paper or board web, the paper or board web is slit or cut, that the rising/lowering of the edges of a slit/cut gap formed at the slitting/cutting point or the width of the gap is measured by means of a measurement device, and that the curl of the paper or board web is regulated based on the result of measurement.
The paper or board machine line according to the invention is in turn mainly characterized in that the paper or board machine line comprises means for slitting or cutting a paper or board web and for measuring the rising/lowering of the edges of a slit/cut gap formed at the slitting/cutting point or the width of the slit/cut gap in connection with the manufacture of the web in order to regulate the curl of the web based on the result of measurement.
In accordance with the invention, the paper web is slit in its running direction over a suitable length and curl is determined based on the rising/lowering of the slit/cut edges or on the width of the slit/cut gap. The slit/cut edges rise/lower because of the tendency of paper to curl such that the result of measurement of the rising/lowering/width of the slit/cut gap is proportional to the intensity of curl. The necessary correlation may be determined based on laboratory measurements known in themselves. On the basis of on-line measurement, the factors affecting the curling of the paper web or one/some of them can be regulated in order to provide desired curl.
Suitable quick measurement, for example, laser measurement is used in the method according to the invention. The measurement device used is placed above or underneath a web at a location in a suitable way, so that the rising/lowering of the slitting point or of the slit/cut edges or the width of the slit/cut gap can be quickly measured. The measurement device may also be accomplished such that there is situated a light source/detector measurement device which is effective across the slit/cut gap, which device is quick and precise enough to determine the rising/lowering of the slit/cut edges or the width of the gap. Another measurement device known in itself, which can be advantageously utilized in the invention, is formed of a camera and image processing associated therewith.
In accordance with the invention, the curl of the paper web is regulated based on the result obtained from the measurement, for example, by regulating the steam pressure between upper/lower drying cylinders in dryer groups with twin-wire draw in a dryer section, by using a web moistening device or by regulating a device drying the web predominantly from one side. The methods and devices disclosed in the above-mentioned FI patent 91900, FI applications 971301 and 972080 as well as U.S. Pat. Nos. 5,269,074; 5,542,193; 5,557,860; and 5,592,571 can be applied in t
Juppi Kari
Komulainen Antti
Fortuna Jos'e A.
Metso Paper Inc.
Stiennon & Stiennon
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