Drying and gas or vapor contact with solids – Process – Diverse types of drying operations
Reexamination Certificate
2000-05-01
2001-07-24
Wilson, Pamela (Department: 3749)
Drying and gas or vapor contact with solids
Process
Diverse types of drying operations
C034S355000, C034S392000, C034S560000, C034S561000, C034S071000, C034S095000, C034S116000
Reexamination Certificate
active
06263589
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a method of drying a fiber web, in which the fiber web is dried by a drying apparatus comprising two endless bands that are impermeable to air, first turning rolls, around which the first band is arranged to turn, and second turning rolls, around which the second band is arranged to turn, the first and second bands being arranged to run part of the way in parallel such that they define a drying zone between them, the first band being heated and the second band being cooled, a fiber web and at least one felt or wire being arranged to run between the bands such that the fiber web is in contact with the first, heated band, and the felt or wire is between the fiber web and the second, cooled band; and the position of the edge of the band is measured.
The invention further relates to an arrangement in a fiber web drying apparatus comprising two endless bands that are impermeable to air, first turning rolls, around which the first band is arranged to turn, and second turning rolls, around which the second band is arranged to turn, the first and second bands being arranged to run part of the way in parallel such that they define a drying zone between them, the first band being arranged to be heated by heating means, and the second band being arranged to be cooled by cooling means, a fiber web and at least one felt or wire being arranged to run between the bands such that the fiber web is in contact with the first, heated band, and the felt or wire is between the fiber web and the second, cooled band; the arrangement comprising means for measuring the position of the edge of the band.
BACKGROUND OF THE INVENTION
Many patent publications, such as WO 96/11300 and U.S. Pat. No. 4,461,095, teach the drying of a fiber web between two parallel metal bands moving in the same direction such that the fiber web is in contact with the heated metal band and that there is a wire between the fiber web and the second, cooled metal band, whereby the steam separated from the fiber web by heating condenses to the wire by the effect of the cold metal band. The basic idea is that two endless metal bands are arranged to run around turning rolls and that against the inner surface defined by the loops that the bands form are provided pressure chambers containing hot steam and water, respectively, such that the pressure produced presses the hot and cold bands, respectively, against the fiber web and the felt running between them. Together with seals, the bands located between the pressure chambers form one side of the pressure chambers such that the steam and water can directly affect the bands. The operation of the apparatus is fully known per se and has been disclosed, for example, in the above patent publications, which are incorporated herein by reference.
A piece of information needed in the above-described control and adjustment of the drying apparatus is the position of the bands crosswise of the machine direction. The position of the edge of the band is measured using a sensor that forms a fork, inside which the edge of the band can move. In both branches of the fork there are optical fibers that form a kind of light nozzle. The light travels from the light-transmitting fiber ends through the air to the light-receiving fiber ends, unless there is a band edge preventing the light from travelling. The edge of the band partly covers the light nozzle, whereby the output signal of the sensor is proportional to the area covered by the band. In the fiber web drying apparatus environment, impurities, however, may cover the light nozzle and the ends of the fibers, and this may change the readings of the sensor, i.e., the sensor will no longer be reliable: it is prone to malfunction and requires much maintenance. The vertical motion of the band is also rather restricted, since the band damages the fibers when it comes into contact with them. Further, the sensor is difficult to adjust, and its readings are not reliable. The settings of the sensor are not stable, which is another reason why the sensor requires much calibration and maintenance. Further, the sensor is rather expensive.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a method and an arrangement in which the above drawbacks can be avoided.
The method of the invention is characterized in that the position of the edge of the band is measured by bringing a sliding block into contact with the edge of the band, the material of the sliding block being harder than that of the band.
Further, the arrangement of the invention is characterized in that the means for measuring the position of the edge of the band comprise a sliding block, which is made of harder material than the band and which is arranged to come into contact with the edge of the band.
The essential idea of the invention is that the edge position of two endless bands one heated, one cooled—running in parallel in the same direction and forming a loop is measured by contacting the edge of the band. The contact is so light that the edge of the band is not damaged. Another essential idea is that the block coming into contact with the edge of the band is substantially harder than the band. In a preferred embodiment, the block coming into contact with the edge is arranged by means of springs in a rod whose mass is greater than that of the block. In another preferred embodiment, a damper is arranged in the rod for damping and preventing oscillation of the rod.
The advantage of the invention is that the sensor is reliable, gives accurate results, and does not require much maintenance. The block coming into contact with the edge of the band keeps the edge of the band clean, but it does not wear nor damage the band. The measuring system is also simple, accurate and reliable, and also inexpensive. When the block coming into contact with the edge of the band is connected by means of springs to a rod whose mass is greater than that of the block, the transfer of any minor roughnesses from the edge of the band to the measuring sensor can be prevented, whereby the measuring sensor can define the displacement of the band fairly evenly. The oscillation and vibration of the rod can be prevented by the dampers arranged in the rod.
REFERENCES:
patent: 4461095 (1984-07-01), Lehtinen
patent: 4719707 (1988-01-01), Klapp
patent: 5071513 (1991-12-01), Bluhm et al.
patent: 5594997 (1997-01-01), Lehtinen
patent: 5619806 (1997-04-01), Warren
patent: 5706587 (1998-01-01), Lehtinen et al.
World Intellectual Property Organization, Int'l Application No. PCT/FI95/00559, Int'l Publication No. WO 96/11300, Int'l. Publication Date Apr. 1996.
Alston & Bird LLP
Metso Paper Inc.
Wilson Pamela
LandOfFree
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