EP1981684B1

EP1981684B1 - Method for profiling in cd-direction the surface qualities of a fibrous web to be manufactured/treated in a paper/board machine or in a finishing machine

Info

Publication number: EP1981684B1
Application number: EP20070700287
Authority: EP
Inventors: Tony Lehto; Reijo PIETIKÄINEN
Original assignee: Valmet Technologies Oy
Current assignee: Valmet Technologies Oy
Priority date: 2006-02-01
Filing date: 2007-01-17
Publication date: 2015-05-06
Anticipated expiration: 2027-01-17
Also published as: EP1981684A4; FI20065077L; EP1981684A1; FI20065077A0; CN101374634A; CN101374634B; WO2007088241A1; FI120884B

Description

The invention relates to a method for profiling in cross machine direction, i.e. CD-direction the surface qualities of a fibrous web, such as a paper or board web, to be manufactured/treated in a paper/board machine according to the preamble of claim 1 and to a paper/board machine with a mechanism according to the preamble of claim 6.
Regarding its calendered smoothness and gloss, paper is known to depend strongly on the smoothness of a pressing surface (thermo roll). Replication effect is known from chill rolls, during the wearing of which the calendered gloss falls by several percentage points in terms of Hunter gloss. In SC-paper, among others, it has been experimentally found out, for example, that the roughness change of a thermo-roll surface from Ra-number 0.1 µm to number 0.4 µm degrades the paper's subsequent Hunter gloss by as much as 10 percentage points.
DE 20 2005 018292 U1 shows a generic method for profiling in cross machine direction, i.e. CD-direction the surface qualities of a fibrous web to be manufactured/treated in a paper/board machine according to the preamble of claim 1, said method comprising passing a fibrous web through a treatment zone established by a belt and its backing element, wherein the method comprises controlling the CD-directed surface roughness of at least a single pressing element, working on the fibrous web in the treatment zone, by polishing or roughening the surface of the discussed element selectively in various positions along the CD-direction. Further, DE 20 2005 018292 U1 shows a generic paper/board machine according to the preamble of claim 6 with a mechanism driving a metal belt and comprising a grinding device for grinding the metal belt.
It is an object of the present invention to further develop a method according to the preamble of claim 1 and a paper/board machine according to the preamble of claim 6 such that a novel effective way of working on the surface quality cross-profile (profile in CD-direction, i.e. cross machine direction) of a fibrous web to be manufactured or treated is enabled.
The object of the present invention is achieved by a method having the features of claim 1 and a paper/board machine having the features of claim 6.
Further advantageous developments of the present invention are defined in the dependent claims.
According to a method of the invention, the method comprises controlling the CD-directed surface roughness of at least a single pressing element, working on a fibrous web in a treatment zone, by polishing or roughening the surface of the element selectively in various positions along CD-direction.
The method enables a relatively simple control over the cross-profile regarding surface qualities, such as the gloss and smoothness of a fibrous web to be produced or treated, by polishing and/or roughening said element in contact with the fibrous web selectively in various positions along CD-direction (profiling the surface roughness).
The machining grinding of a belt is preferably performed without removing the belt from the machine, by using for example a crosswise traversing grinding device or laser polishing. It is within the scope of the invention as defined in the appended claims to treat just a portion of the belt surface, or the surface can be treated over its entire lateral dimension to a predetermined crosswise roughness profile. The machining/grinding can also be performed in separation from the machine, which is common practice today. What is essential is that the roughness profile in CD-direction is under control and used for controlling (profiling) the surface quality of paper.
Preferably, the Ra-roughness profile of a surface to be machined is selected such that discrepancies in Ra-roughness between various parts of the surface are not less than 0.01 µm and not more than 1.0 µm.
The method is apt for correcting profile defects of permanent nature, for example for a more intensive calendering of dried-up web edges whenever a sufficient increase of the nip pressure profile is ruled out or undesirable. It is generally useful in situations which call for a local permanent type higher level of smoothness or gloss and which deny the use of a higher line load or temperature. The method provides a new control variable (degree of freedom) for profile "adjustment". The method can be applied in a calender, a metal belt calender, a cylinder dryer section, a Yankee cylinder dryer, a CondeBelt dryer, etc.
In the process of calendering with several nips in succession, it is possible to apply one variation of the method, wherein thermo rolls placed against the opposite sides of paper are deliberately ground to pre-selected and possibly unequal roughness levels. In a multi-nip calender, for example, the thermo rolls present upstream of the deflector nip can be polished for a higher level and the thermo rolls downstream of the deflector nip can be polished to a lower roughness level. The arrangement enables a control over the one-sidedness of gloss (and to some extent smoothness) without proportioning the one-sidedness of temperature or wetting. The method can be applied for multi-nip calenders (Super-, OptiLoad) or soft and machine calenders.
In the process of grinding a metal belt, the method of the invention enables the use of a preferably laterally movable grinding device, which is placed in a liquid-filled chamber, said method comprising the use of a backing element, which is on the opposite side of a belt and which is cooled by means of a fluid flow for effecting the belt grinding at a substantially constant temperature. This solution enables improving the CD-directed grinding tolerance of a metal belt with respect to the currently employed method which gives the belt a major tolerance error in CD-direction, the error being within the range of 5-10 µm.
The invention will now be described in more detail with reference to the accompanying drawings, in which:

Fig. 1: is a schematic side view, showing one metal-belt grinding device of the invention, which is apt for use in a method of the invention,
Fig. 2: is a schematic side view, showing a grinding device of the invention in a second embodiment,
Fig. 3: is a schematic side view, showing a grinding device of the invention in a third embodiment,
Fig. 4: is a schematic side view, showing a grinding device of the invention in a fourth embodiment, and
Fig. 5: is a schematic plan view, showing a grinding device of the invention in a fifth embodiment.

In reference to fig. 1, the grinding device according to a first embodiment of the invention comprises support rolls 8, around which a belt 9 to be ground, disengaged from a fibrous web processing mechanism, is adapted to circle, and a grinding unit 3 disposed on one side of the belt 9 and a backing table 4 disposed on the other side of the belt. The grinding unit 3 comprises a cylinder chamber 10, its internal cavity 6 containing a grinding tool 5 which is adapted to travel crosswise of the metal belt 9 for oscillation along guide bars 5b. The grinding tool 5 includes a grindstone 5a with a horizontal axis of rotation. The cavity 6 is filled with a liquid, e.g. water or an aqueous liquid mixture, delivered into the cavity 6 through an inlet 6a and out of the cavity through an outlet 6b. The cavity 6 has its pressure preferably within the range of 1-20 bars, conveniently at a pressure of about 10 bars. The backing table 4 is also provided with a cooling-fluid filled cavity, said cooling fluid being preferably a liquid or a liquid mixture, e.g. water or an aqueous liquid mixture. The fluid is delivered in through an inlet 7a and out through an outlet 7b. The fluid pressure existing in the backing table's cavity is preferably within the range of about 0 to about 1 bar.
The device operates as follows.
The support rolls 8 are used for tensioning and driving the belt 9. The cylinder chamber 10 is used for pressing the belt 9 against the precision-ground backing table 4, which is preferably provided with small aspiration holes for pressing the belt tightly against the table. The belt is proceeded slowly in a space between the cylinder chamber 10 and the backing table 4 for grinding the belt all over or at desired crosswise spots in order to effect a CD-directed profiling. By using e.g. water or an aqueous liquid mixture in the cylinder chamber and backing table cavities, the temperature of a belt presently in grinding can be maintained equal on either side of the belt, e.g. at a temperature of +23°C. Being ground in a chamber filled with water or other liquid, the belt neither heats up nor vibrates. Moving the grindstone back and forth can be implemented e.g. by way of an NC-control, thus enabling the use of various compensatory contours.
In reference to fig. 2, there is shown a second exemplary embodiment for the grinding device, wherein components like those of fig. 1 are given like reference numerals. The backing table 4 has its top provided with capillary passages 15, whereby the liquid present in the backing table's interior chamber is able to flow into an interspace between the belt 9 presently in grinding and the top surface of the backing table for providing a liquid bearing system. The cylinder chamber 10 has its bottom edge provided with gaskets 14. A discharge line downstream of the outlet 6b is provided with a control valve 11. The cylinder chamber 10 is made movable in vertical direction by means of uprights 12, e.g. by the action of a cylinder 13. The grinding tool 5 is adapted to travel along guide bars 5b and 5c in oscillation crosswise of the metal belt.
In reference to fig. 3, there is shown a third exemplary embodiment for a grinding device of the invention, wherein the backing table comprises a counter-roll 16 provided with an internal cooling fluid circulation. Atop the belt 9, on either side of the grinding unit 3 there are provided auxiliary rolls 17 for guiding the belt along the surface of the counter-roll.
In reference to fig. 4, there is shown a fourth exemplary embodiment, wherein the grinding tool 5a is a face grinder.
In reference to fig. 5, there is shown a fifth exemplary embodiment, wherein the cylinder chamber 10 itself travels in oscillation crosswise of the belt 9 presently in grinding, whereby the fluid pressure inside the chamber 10 can be higher than those in the preceding examples, in which both the cylinder chamber and the backing table or the counter-roll extend across or beyond the entire width of the belt, and it is only the grinding tool present inside the cylinder chamber which travels in lateral direction.
The backing table or the counter-roll can be provided with durable ceramic coatings.
In the process of grinding a new belt, for example, the belt's outermost edge can be left unfinished and the belt can be trimmed to a correct width only after finishing it by grinding. The grinding can be performed e.g. in such a manner that the belt is subjected first to traditional grinding and then to finishing by means of a grinding device of the invention.

Claims

A method for profiling in cross machine direction, i.e. CD-direction the surface qualities of a fibrous web to be manufactured/treated in a paper/board machine, said method comprising passing a fibrous web through a treatment zone established by a belt (9) and its backing element (4; 16), wherein the method comprises controlling the CD-directed surface roughness of at least a single pressing element, working on the fibrous web in the treatment zone, by polishing or roughening the surface of the discussed element selectively in various positions along the CD-direction, characterized in that the method comprises using a laterally movable grinding tool (5), which is placed in a liquid-filled chamber (6), said method comprising the use of the backing element (4; 16), which is on the opposite side of the belt (9) and which is cooled by means of a fluid flow for effecting the belt (9) grinding at a substantially constant temperature.
A method as set forth in claim 1, characterized in that the backing element (4; 16) cooling fluid comprises using water or an aqueous liquid mixture.
A method as set forth in claim 1 or 2, characterized in that the method comprises effecting the roughening and/or polishing without removing a pressing element to be treated from the machine.
A method as set forth in claim 1 or 2, characterized in that the method comprises effecting the roughening and/or polishing by removing a pressing element to be treated from the machine.
A method as set forth in any of the preceding claims, characterized in that the method comprises controlling the roughness numbers of a pressing surface, such that the roughness discrepancy between various parts of the surface lies within the Ra-range of 0,01 µm to 1,0 µm.
A paper/board machine with a mechanism driving a metal belt (9) and comprising a grinding device for grinding the metal belt (9), characterized in that the device comprises a grinding unit (3), disposed on one side of the belt (9) and having a liquid-filled cavity (6) in which is accommodated a grinding tool (5) in use oscillating crosswise of the belt (9) present in grinding, and a backing surface (4; 16) present on the opposite side of the belt (9) and provided with a cooling fluid circulation.