Paper making and fiber liberation – Processes and products – Running or indefinite length work forming and/or treating...
Reexamination Certificate
2000-12-22
2003-02-04
Hastings, Karen M. (Department: 1731)
Paper making and fiber liberation
Processes and products
Running or indefinite length work forming and/or treating...
C162S272000, C162S358300, C100S153000
Reexamination Certificate
active
06514385
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application claims priority under 35 U.S.C. §119 of German Patent Application No. 199 62 706.1, filed on Dec. 23, 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 press section of a machine for producing tissue webs, having a shoe press containing a shoe press unit and a counter roll, whose shoe press unit has at least two press shoes and an elastic liquid-impermeable pressing belt guided over these press shoes.
2. Discussion of Background Information
From DE 32 05 664 A1, a shoe roll with at least two press shoes is known for use in a press section of a paper machine, for example. The press shoes are pivotable around an axis parallel to the pressing plan and can differ in their bending radius. This allows optimal press performance to be achieved for the entire thickness spectrum of the sorts of paper produced on a paper machine, i.e., as high a dry content as possible can be achieved.
However, since tissue webs are very thin, the transmission of this knowledge does not result in an improvement of the product quality in the tissue production. Between the different types, only irrelevant thickness differences occur. The application is therefore uneconomical due to the larger investment expense of the described shoe press.
SUMMARY OF THE INVENTION
The present invention provides a press section of the above-mentioned type that allows an economical production of tissue and simultaneously ensures a better product quality.
According to the invention, the two press shoes have different lengths measured in the web travel direction and can each be transferred from an idle position to a press position in which the press shoe in question is positioned opposite the counter roll.
With the press shoe being transferable between an idle position and a press position, press nips of different lengths can be realized quickly and without any reconfiguration expense.
Depending on use, different quality standards are required from tissue products. There are products for which the specific volume (“bulk”) is a deciding quality feature. In other products, it can be more important for economical reasons to accept a lower specific volume in exchange for a high dry content, i.e., a high production. Because of the embodiment according to the invention, it is now possible to change between these types in the tissue production without having to compromise concerning the adjustment of the machine setting and the press setting, as previously necessary. Now the optimal situation can be achieved in each case.
A shoe press roll with a press jacket forming the press belt is provided as the shoe press unit.
For achieving a high specific volume, it is advantageous if at least one press shoe is provided whose length measured in the web travel direction is greater than about 80 mm, greater than or equal to about 100 mm, preferably greater than or equal to about 120 mm. Here, the highest pressure of the pressure progression occurring in a press nip between the press shoe and the counter roll in the web travel direction is preferably selected to be less than or equal to a value of about 2.5 MPa, in particular less than or equal to about 2 MPa, preferably less than or equal to about 1.5 MPa.
On the other hand, it is advantageous for achieving as high a dry content as possible after the press when at least one press shoe is provided whose length measured in the web travel direction is less than or equal about 60 mm and, in particular, less than or equal to about 50 mm and preferably has a value in the range of about 37 mm. Here, the maximal pressure of a pressure progression occurring in a press nip between the press shoe and the counter roll in the web travel direction in a shoe length less than or equal to about 60 mm is preferably selected to be greater than or equal to a value of about 3.3 MPa, at a shoe length less than or equal to about 50 mm preferably greater than or equal to a value of about 4.3 MPa and, at a shoe length in the range of about 37 mm, preferably equal to a value in the range of about 4.8 MPa.
It is particularly advantageous if a heated drying cylinder is provided as a counter roll, particularly a so-called Yankee cylinder that has a considerably larger diameter than the shoe press roll if the shoe press unit is formed by a shoe press roll.
When using the Yankee cylinders, the maximal linear force is frequently limited to a value of about 90 kN/m to 120 kN/m due to excessively large deformations and tensions that occur in a Yankee cylinder. This again limits the maximal pressure for a press shoe designed for high bulk and thus the maximum achievable dry content for the tissue web. This results in a reduction of the machine speed and a higher drying expense at the drying cylinder. By using a shoe press with at least two different press shoes according to the invention, this disadvantage is omitted.
A further increase in dry content can be achieved in that, in a press nip surfaced with felt formed between a shoe press unit and a counter roll, preferably a drying roll, the angle between the tangent coming in contact with the counter roll at the end of the press nip and at least one of the felts leaving the press nip is advantageously greater than or equal to about 10°, in particular greater than or equal to about 15°, in particular greater than or equal to about 18°, and preferably greater than or equal to about 20°. In such a case, particularly, the press belt can be provided with a grooved (ribbed) surface in the circumferential direction that additionally aids in the increase of the dry content. A ribbed press belt is therefore preferably used when a in tissue machine tissues are produced that mainly require a high cry content.
Otherwise, a blind-bored and/or grooved press belt can be used in particular.
The present invention is directed to a press section of a machine for producing webs. The press section includes a shoe press including a shoe press unit and a counter roll. The shoe press unit includes at least two press shoes and an elastic liquid-impermeable press belt guided over the at least two press shoes, and the at least two press shoes have different lengths measured in a web travel direction and each of the two press shoes is arranged for movement between an idle position and a press position facing the counter roll.
In accordance with a feature of the instant invention, the web can include a tissue web.
According to another feature of the invention, the shoe press unit may include a shoe press roll having a press jacket arranged to form the press belt, and the shoe press roll can include the at least two press shoes.
At least one of the at least two press shoes may have a length in the web travel direction greater than about 80 mm. A maximal pressure of a pressure progression occurring within a press nip formed between the at least one press shoe and the counter roll can be less than or equal to a value of about 2.5 MPa.
At least one of the at least two press shoes may have a length in the web travel direction less than or equal to about 60 mm. A maximal pressure of a pressure progression occurring within a press nip formed between the at least one press shoe and the counter roll can be greater than or equal to a value of about 3.3 MPa.
At least one of the at least two press shoes may have a length in the web travel direction less than or equal to about 50 mm. A maximal pressure of a pressure progression occurring within a press nip formed between the at least one press shoe and the counter roll can be greater than or equal to a value of about 4.3 MPa.
At least one of the at least two press shoes has a length in the web travel direction less than or equal to about 37 mm. A maximal pressure of a pressure progression occurring within a press nip formed between the at least one press shoe and the counter roll can be greater than or equal to a value of about 4.8 MPa.
In accordance with a further feature of the pres
Scherb Thomas Thoröe
Schmidt-Hebbel Harald
Greenblum & Bernstein P.L.C.
Hastings Karen M.
Voith Paper Patent GmbH
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