Paper making and fiber liberation – Apparatus – Running or indefinite length product forming and/or treating...
Reexamination Certificate
2001-04-09
2003-03-04
Hastings, Karen M. (Department: 1731)
Paper making and fiber liberation
Apparatus
Running or indefinite length product forming and/or treating...
C162S358200
Reexamination Certificate
active
06527916
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application claims priority under 35 U.S.C. §119 of German Patent Application No. 100 22 087.8, filed on May 8, 2000, the disclosure of which is expressly incorporated by reference herein in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention concerns a pressing section for pressing water out of a paper web. Pressing sections have become known in numerous configurations. The invention relates to such pressing sections in which at least two pressing stations are present, of which at least the second pressing station is formed of a so-called shoe press and in which the paper web is pressed between two felts.
2. Discussion of Background Information
Such pressing sections have already been used for a long time in the production of thicker packaging papers. Such papers are produced at medium speeds. Here, the above-mentioned pressing sections have proven themselves. See Wochenblatt für Papierfabrikation [Paper Manufacturing Weekly], No. 6, 1999; p. 380-385, in particular FIG. 19. It is possible to use relatively coarse felts for these packaging papers that do mark the paper web, but have a high air permeability.
More recently, the attempt has been made to use pressing sections of the above-mentioned type in a slightly modified construction for the production of thinner papers, which are produced at higher speeds, for example, printing papers. They are described in “Wochenblatt für Papierfabrikation” [“Paper Manufacturing Weekly”], No. 2, 1999; p. 94 to 99, FIGS. 7, 11, and 16 as well as in Wochenblatt für Papierfabrikation [Paper Manufacturing Weekly], No. 11/12, 1999; p. 745 to 752, figure of the PM 5 Compact Lang Papier, Ettringen on page 746. It has been shown that pressing sections of the type mentioned above are advantageous because both sides of the paper web have printing properties that are approximately identical in quality. However, the results have not been completely satisfactory up to now. Specifically, the problems are as follows:
Insufficient dry contents were achieved with pressing sections of the type mentioned above. Thus, the paper web is still relatively moist after leaving the pressing section. Furthermore, the dry content of the paper web is not even across the web width.
The separation of the paper web from one or the other felt after passing through the individual pressing stations is critical; occasionally, tearing of the edges of the paper web occurs. Besides the higher speeds, these problems are also connected to the fact that the felts for thin papers must be denser and smoother due to the quality requirements of the paper surfaces to be printed. Thus, their dewatering becomes more difficult. The function of the suction felt guide rolls becomes less certain. They are supposed to hold the paper web safely on the felt provided for further transport during the separation of the two felts. However, this latter is only successful when the transport felt is sufficiently open and air permeable.
SUMMARY OF THE INVENTION
The present invention provides a pressing section that includes a first and a second pressing station, a common lower felt arranged to run through the first and the second pressing stations, and an first upper felt and a second upper felt arranged to run through the first and second pressing stations. The second pressing station includes a shoe press roll located above a lower roll, and a pressing plane of the second pressing station is oriented one of essentially vertically or inclined at an angle &bgr;, which is a maximum of about 20° to a vertical reference. Moreover, according to the instant invention, the pressing section is more efficient to use for thinner papers at higher machine speeds as well, in particular for printing papers. Thus, such a pressing section should have its own advantages with respect to the even printability properties on both sides of the web. Moreover, it should be free from the above-mentioned disadvantages and should by all means allow a longer felt service life. It should also prevent the problem of tears in the edges of the paper web and reduce the number of suction felt rolls, their energy use, and their noise level.
Accordingly, the present invention also includes a common lower felt that is sufficiently dense to be essentially air impermeable even in its new state after moistening, and that is sufficiently open to allow water through at pressures greater than about 5 bar. The first and second upper felts are sufficiently open to allow air through in their moistened, uncompressed state, and a pressing plane of the first pressing station being oriented at an angle &agr;, which is greater than angle &bgr;, and preferably where angle &agr; is greater than about 20° to the vertical reference.
Specifically, the inventor recognized the following:
For the purpose of better printability, the felts must have as smooth a surface as possible. Further, the water tightness of the felts is an extremely critical parameter. It must be set in such a way that a rewetting of the paper by the belts cannot occur after each pressing station. The lower felt must be made sufficiently watertight that it is not only air impermeable, but also, in the case of small differences in pressure and by capillarity, returns as good as no water to the paper web during a contact period of approximately 0.1 to 0.2 seconds after each of the two pressing sections.
Moreover, the upper felts must be open and air permeable so that the paper web remains securely adhered to the lower felt (to which it adheres due to its lack of air permeability) when the felts are being separated after the pressing stations and, as a result of the air flowing in from above, separates itself from the upper felt. Here, the contact time between the paper web and the upper felt after each pressing station should be minimized so that the reverse moistening of the paper web by the upper felt remains low.
The combination of features according to the invention provides an elegant selection from a plurality of features that leads to success. Specifically, the following advantages can be attained:
The web leaves the pressing section with a greater dry content than before, which leads to fewer tears in the paper web. This increases the production capacity. Further, there are no strips of different degrees of dryness (moist strips) in the web cross profile, and the felts need to be dewatered to a lesser degree. The necessary energy for providing the vacuum as well as the number of suction rolls can be reduced while increasing the service life of the felts, since the latter can be more specialized for one single purpose. Moreover, the number of felts itself is reduced such that the machine is also more accessible, especially in the cellar of the machine, and the noise level of the machine and the energy consumption of the press section during operation are reduced.
The following is specifically achieved in accordance with features of the instant invention:
The common lower felt being sufficiently dense to be essentially air impermeable even in its new state after moistening, and the first and second upper felts being sufficiently open to allow air through in their moistened, uncompressed state allow an essentially flawless separation of the web from the upper felt upon exiting the pressing station; the web reliably follows the lower felt, which is desired. The common lower felt being sufficiently open to allow water through at pressures greater than about 5 bar ensures the evenness of dewatering of the paper web towards both of its surfaces, which is essential for printability. A pressing plane of the first pressing station which is oriented at an angle &agr;, which is greater than angle &bgr;, and preferably which is greater than about 20° to a vertical reference contributes to the prevention of reverse moistening of the paper web by the upper felt upon exiting the pressing station.
In further embodiments, the jacket of the first upper pressing roll is grooved or blind bored
Greenblum & Bernstein P.L.C.
Hastings Karen M.
Voith Paper Patent GmbH
LandOfFree
Pressing section for a paper machine does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Pressing section for a paper machine, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Pressing section for a paper machine will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3074142