Drying and gas or vapor contact with solids – Apparatus – Rotary drums or receptacles
Reexamination Certificate
2000-07-21
2002-09-03
Esquivel, Denise L. (Department: 3744)
Drying and gas or vapor contact with solids
Apparatus
Rotary drums or receptacles
C034S115000, C034S122000, C034S619000, C034S635000, C034S662000, C034S663000
Reexamination Certificate
active
06442865
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application claims priority under 35 U.S.C. § 119 of German patent application No. 199 35 138.4, filed on Jul. 27, 1999, the disclosure of which is expressly incorporated by reference herein in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a drying section of a machine for producing a material web, e.g., a paper or cardboard web.
2. Discussion of Background Information
In conventional multi-cylinder drying sections, the paper web to be dried is guided over a number of steam-heated cylinders or over a configuration involving a number of steam-heated cylinders and screen suction rolls. Particularly at the outset of drying, when the paper web still lacks adequate strength, there are frequently problems with respect to web guidance, which can be attributed in particular to the fact that the still-moist web continues to stick to the smooth contact areas, areas that are urgently necessary for adequate heat transfer. These problems can be reduced by coating the cylinders. Relatively high tension forces are therefore necessary, though this frequently leads to web tears and overstretching of the web edges. Therefore, as a rule, therefore, it is necessary for the drying to proceed more slowly, i.e., with, for example, a lower steam pressure at the beginning, and this means that the required drying section becomes longer overall. The problems discussed above arise to a greater degree at high web speeds.
SUMMARY OF THE INVENTION
The present invention relates to a drying section of the type described at the outset which, at high machine speeds, provides as optimal a drying rate as possible at the beginning of drying, as well as a secure guidance of the web.
Accordingly, the material web, starting at the last press nip of a press section, is conducted in a closed path over at least one straight or slightly curved section, to a larger support roll with an assigned impingement dryer, which is, arranged to subject the material web to an impingement of hot air or hot steam, as it is guided over the support roll. The straight or slightly curved section is provided in the form of an impingement drying section and/or a transfer foil section.
With this design, it is no longer necessary to guide the still relatively moist material web over smooth contact surfaces in order to achieve adequate heat transfer. Because smooth contact areas are avoided at the beginning of drying, the danger of tears in the web and overstretching of the web edges is practically eliminated. Higher drying rates, in particular, are now possible, and this in turn shortens the overall length of the drying section. In principle, impingement drying can also take place in any given transfer foil section. This kind of transfer foil section can be provided in the form of a simple transfer section.
In a preferred embodiment of the drying section according to the invention, the material web is supported at least in the area between the last press nip of the press section, or the removal from the press felt or press belt belonging to the last press nip, and the support roll, by an open, i.e., not smooth, support surface which can be formed, e.g., by a continuous belt or screen. Here, the material web is preferably also supported in the area of the impingement dryer assigned to the support roll by an open, i.e., not smooth, support area, which is being formed either by the surface, or coating or cover, of the support roll or by the surface of a continuous belt or screen guided over the support roll.
It is advantageous for the support roll to have an outer diameter ranging from about 2.5 to about 8 m, and preferably ranging from about 3 to about 5 m.
In a useful practical embodiment, the support roll assigned to the impingement dryer is provided with suction, and a continuous screen is guided over the support roll in order to hold the material web in place. This can be done directly by a suction box located within the device or through openings provided in the jacket surface by an external suction box. When the diameter increases, not only does the circumference of the support roll increase, but the possible angle of wrapping covered by the impingement dryer also increases, and thus the drying area. The impingement dryer can lie above or below the cylinder plane and can be moved for the purpose of transfer and/or cleaning, especially in parts. When the support roll is provided with suction, the roll and the corresponding suction box can contain narrow transfer zones for the purpose of strip transfer.
If impingement flow drying occurs not only in the area of at least one larger support roll but also in that of the straight or slightly curved section, the major part of the impingement drying is ideally taken over by the impingement dryer assigned to the larger support roll.
In principle, a plurality of impingement dryers, each assigned to a given support roll, can also be provided.
In a useful practical embodiment, the material web, following at least one impingement dryer assigned to a given support roll, is conducted to a drying group with at least one drying cylinder. Here, the material web can be fully dried in a single-row or double-row drying group.
On reaching or leaving the first drying cylinder or upon being withdrawn from a smooth heated surface, the material web ideally will already have a dryness content that is greater than about 55 to 65% wt. It is thus possible to avoid pulling the web from a smooth heated area during the time the web has a dryness content of less than about 55 to 65% wt.
In a preferred practical embodiment of the drying section according to the invention, the material web can be moved in the web travel direction and into the cellar, at a point in front of the support roll following the straight or slightly curved impingement drying or transfer-foil section with the assigned impingement dryer, i.e., it can be moved out of the machine (e.g., into the pulper). Thus, refuse removal is provided after the press section.
Here, the material web can be moved into the cellar, e.g., at a point immediately beyond an initial (as viewed in the web travel direction) straight or slightly curved impingement drying section or transfer-foil section.
Alternatively or additionally, the material web can also be moved into the cellar in the vicinity of a pickup roll by which the material web can be removed from a press felt or press belt guided through the last press nip of the press section when the material web is not being conducted into the drying section by the preceding pickup roll.
In certain cases, it is also advantageous if the material web can be moved into the cellar in the area of an additional press roll which lies opposite a deflection roll which is provided for a press felt guided through the last press nip and which is located behind the last press nip of the press section.
As an alternative, the web can also be moved into the cellar in the area of a smooth removal roll which is encircled by the last press felt or belt in such a way that the web runs in conjunction with the roll. A removal scraper is preferably installed on this roll.
It is useful to provide at least one straight or slightly curved impingement drying section or transfer-foil section in which the material web is guided between two screens. In a corresponding straight or slightly curved impingement dryer section or transfer-foil section the material web can be exposed to impingement while passing through the upper screen and/or the lower screen. The screen provided on the blow side should be resistant to high temperatures and be as permeable as possible to the impingement. The material web and the two screens can be supported, e.g., by support rolls, which are only encircled to the extent necessary for paper damage not to arise due to sheering, e.g., an angle of wrapping in a range from about 2° to about 10° can be provided, particularly from about 3° to about 7°. When there is a plurality of impingement dryers, which can be provided in the form of, e
Chau-Huu Tri
Mack Thomas
Mayer Roland
Mayer Wolfgang
Oechsle Markus
Esquivel Denise L.
Greenblum & Bernstein P.L.C.
Shulman Mark
Voith Sulzer Papiertechnik Patent GmbH
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