Paper making and fiber liberation – Processes and products – Running or indefinite length work forming and/or treating...
Reexamination Certificate
1997-12-22
2001-07-17
Chin, Peter (Department: 1731)
Paper making and fiber liberation
Processes and products
Running or indefinite length work forming and/or treating...
C162S210000, C162S306000, C162S358100, C162S349000, C162S358300, C162S358400, C162S360200
Reexamination Certificate
active
06261416
ABSTRACT:
CROSS-REFERENCE OF RELATED APPLICATIONS
The present application claims priority under 35 U.S.C. §119 of German Patent Application No. 196 54 195.6, filed Dec. 23, 1996, and of German Patent Application No. 197 05 030.1, filed Feb. 10, 1999.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a device for draining a web, e.g., a paper web, in a paper production machine having a press section with at least one press nip (opening) through which the web is guided and thereby drained and smoothed. However, in accordance with an exemplary embodiment of the present invention, one side of the web is more strongly smoothed than the other side.
Further, the present invention relates to a method for draining a web, e.g., a paper web, in a paper production machine, in which the web is guided through at least one press nip (opening) in which the web is drained and thereby smoothed. However, in accordance with this exemplary embodiment, one side of the web in the press nip is more strongly smoothed than the other side.
2. Discussion of the Background Information
The drainage of a paper web in a press section normally takes place with the aid of felt belts which are guided through the press openings together with the paper web. The water which is pressed out of the paper web is absorbed and removed by the felt sheets. Because the felt sheets are usually guided in loops, these felt sheets must be conditioned to maintain their water-absorbing capabilities.
With devices in use today for draining paper webs, usually one side of the web is more frequently pressed in contact with the felt than the other. Out of concern for a well-supported sheet guidance and an undesirable remoistening of the paper web, the web is guided together with only one felt belt through at least the last press opening. For example, in a known press section having three press nips, the upper web side is pressed in contact with the felt three times, while the lower web side is pressed in contact with the felt in the first press nip and against an outer surface of a smooth roll in the other two openings. As a result, a significant difference in roughness values between the upper and lower sides of the raw paper occurs after the press nip. Such a difference in the roughness leads, in particular, to differing printing characteristics for the paper and, thus, is often not desired.
It is already known how to balance differing roughness values between the two sides of a paper web that is caused by differing smoothing in the web draining device, e.g., by performing a unilateral smoothing of the paper web on a side opposite to a previous unilateral smoothing, i.e., after the press section in the end treatment of the paper. It is also known how to avoid a unilateral, greater smoothing of the paper web by arranging a same number of rolls for smoothing both sides of the paper web. Such an even arrangement of smoothing rolls is, however, not always possible or desirable. In addition, the unilateral smoothing in the opposite direction during the end treatment of the paper web is relatively costly.
SUMMARY OF THE INVENTION
Thus, the present invention provides device similar in general to the type mentioned above that enables, in a relatively simple manner, draining the paper web while ensuring an essentially equal degree of roughness on both sides of the web.
Further, the present invention presents a method similar in general to the type mentioned above that enables draining the web and ensuring an essentially equal degree of roughness on both sides of the web after the draining.
The device of the present invention may include a device for roughening a side of the web that was more smoothed in the press section.
The method of the present invention may include roughening the web on its smoother side.
Unlike the previously known devices for draining a web, an additional smoothing of an upper side of the web, which was less smoothed in the press section, does not take place according to the invention. Rather, the more-smoothed side of the web is roughened such that, upon leaving the press section, a substantially even-sided roughness of both sides of the web results. This result is favorable not only from a structural standpoint for the device, but also provides the advantage that, if desired, an over-smoothing of both sides of the web can be prevented. The device in accordance with the present invention can be used, e.g., when it is not possible or desirable to arrange a same number of smoothing rolls on both sides of the web. In addition, the device in accordance with the present invention can be used advantageously when it is not possible or desirable to smooth the web in the opposite direction in the post-treatment phase.
In a preferred exemplary embodiment of the present invention, a pre-press device may be positioned before the press section for roughening the web. The pre-press device may be designed to produce a higher degree of roughness on the more-smoothed side of the web than the other side. In particular, the roughness difference may be selected such that the web exhibits an essentially equal degree of roughness on both sides after leaving the press section. A pre-positioned pre-press device, which may be formed or created, e.g., by two rolls forming a press nip between them and a roughness compensation for partially draining the web even before entering the press section. Because of the higher dry content of the web achieved upon entry to the press nip, drainage in the press section is improved.
According to a further embodiment of the present invention, the pre-positioned pre-press device may include a screen belt guided through the press nip together with the web such that the screen belt is positioned on the side of the web to be roughened. The screen belt, preferably guided in a loop, causes a roughening of the side of the web lying against it as the web is guided through the pre-press device. Thus, in a preferred embodiment, the paper-production screen may be utilized as the pre-positioned screen loop because it is already positioned before the press section for the purpose of draining the web. A press device is additionally arranged in this screen loop such that the web is guided through the press nip with the screen belt.
According to the present invention, it may be particularly advantageous to position the press device behind (with respect to a circumferential direction of the screen loop) a screen suction roll present in the screen loop.
According to a further embodiment of the present invention, the pre-press device may include at least one felt belt guided through the press nip with the web. Water pressed out in the pre-press device may be advantageously removed by the felt belt. By positioning a felt belt inside of the screen loop, i.e., on a side of the screen belt opposite the web, the screen belt may be supported on its running side and water pressed out of the web may transported out of the press zone.
The felt belts are also preferably guided in loops. Conditioning devices can be utilized to advantageously maintain the water absorption capability of the felt belts.
Instead of a felt belt guided through the press nip of the pre-press device, the pre-press device can also include a roll with a felt covering. Water pressed out can thereby be removed. It is further preferred that a conditioning device be provided, e.g., a felt-washing press device for the felt covering, to maintain the water absorption capability of the felt cover.
By utilizing a suction contact roll in the pre-press device, the web may be advantageously separated from the screen belt and guided in a suitable manner to a subsequently-arranged press section.
According to further embodiments of the present invention, the pre-press device may include a roll with recesses, e.g., grooves or blind holes, formed in the roll sleeve surface. In this manner, the water absorption of the roll may be increased, thus, improving the drainage capability of the pre-press device. The pre-press device can also include a roll with
Esslinger Klaus
Kotitschke Gerhard
Mayer Wolfgang
Meschenmoser Andreas
Mohrhardt Gunther
Chin Peter
Greenblum & Bernstein P.L.C.
Voith Sulzer Papiermaschinen GmbH
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