Drying screen and process for using the same

Details Drying screen and process for using the same Drying screen and process for using the same

1998-06-24

2001-03-06

Chin, Peter (Department: 1731)

Paper making and fiber liberation

Processes and products

Running or indefinite length work forming and/or treating...

C162S306000, C162S358100, C162S358200, C162S361000

Reexamination Certificate

active

06197158

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATIONS
The present application claims priority under 35 U.S.C. §119 of German Patent Application No. 197 26 933.8, filed on Jun. 25, 1997, the disclosure of which is expressly incorporated by reference herein in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a drying screen having a supporting structure composed of a web, mesh, or similar arrangement. The drying screen may be utilized in dryer sections for the manufacture of fibrous pulp webs.
2. Discussion of Background Information
Drying screens of the type generally described above are utilized to press a fibrous pulp web onto a corresponding dryer cylinder and to guide the fibrous pulp web between dryer cylinders, guide rolls, etc. However, when the fibrous pulp web is to be transferred from a smooth roll, e.g., a press roll or a dryer cylinder, undesirable longitudinal elongations of the fibrous pulp web may occur due to adhesion of the fibrous pulp web to the smooth roll surface.
SUMMARY OF THE INVENTION
The present invention improves the adhesion of the fibrous pulp web to the drying screen during a transfer of a fibrous pulp web from a roll.
The present invention provides an elastic coating layer having a shaped or profiled surface on at least portions of a side of the supporting structure facing the fibrous pulp web.
When the drying screen is stressed or compressed, i.e., when it is pressed against a supported fibrous pulp web, the surface area of the shaped surface of the supporting structure coating is reduced. Further, the fibrous pulp web can be supported by an especially smooth roll, e.g., in the press section, and the drying screen can be pressed onto the roll via screen tension or via an additional contact element acting on the drying screen.
Due to the elasticity of the coating, subsequent relaxation of the drying screen results in an enlargement or expansion of the shaped surface on the supporting structure. In this manner, an expansion of void spaces formed between the fibrous pulp web and the shaped surfaces of the coating occur. A low vacuum is formed in these void spaces that leads to an increased adhesion of the fibrous pulp web to the coating and, therefore, to the drying screen. As a result, an improved and secure transfer of the fibrous pulp web from the supporting element, e.g., press roll, is provided. As the fibrous pulp web proceeds beyond the supporting element, the vacuum created in the void spaces will become smaller as air is sucked into the voids through the fibrous pulp web and through a gap between the web and the coating until the vacuum dissipates or disappears. Once the vacuum in the void spaces has dissipated or disappeared the fibrous pulp web can be transferred to a subsequent unit, e.g., dryer section, without any problems.
The coating may be, e.g., an open-pore, elastic foam of polyurethane or rubber. Alternatively, the coating may include an elastic base material in which hard particles are embedded and that protrude from the surface in an unstressed state. These hard particles may effect the shape of the coating.
The coating with hard particles may be manufactured by applying an elastic base material together with the hard particles to the side of the supporting structure adapted to face the web and then removing an outer portion of the elastic base material using a chemical method, e.g., chemical solvent materials that do not attack the hard particles.
A circumference, location, and manufacture of the coating may be determined according to the type of drying screen or support structure, and to the degree of desired adhesion. Thus, the drying screen can be single-layered or multi-layered, symmetrical or asymmetrical, and/or formed as a spiral screen or fiber web or include a formed fabric.
The drying screen may be particularly suited for transferring the fibrous pulp web from smooth surfaces made of ceramic, mold casting, polyurethane, or rubber.
In particular, when the entire or large portions of the side of the support structure facing the fibrous pulp web is to receive an elastic coating, the surface may be prepared by spraying the coating onto the support frame.
Should the support structure be formed of a fiber web, the fibers are to be at least partially coated. It is also possible to coat only individual fibers and/or to form the fibers in the shape of a belt and coat only the side facing the fibrous pulp web.
In the event that the fibers are to be completely coated, it is advantageous to produce the coating for the fibers prior to manufacturing the drying screen, e.g., in a dip bath.
Moreover, with drying screens of this type, it may be possible to improve the transfer of the fibrous pulp web between two drying screens within a dryer section. This may be achieved by allowing the receiving drying screen to have a softer coating than the transferring drying screen. In this regard, the increased flexibility of the softer coating results in an increased vacuum in the void spaces, which leads to increased adhesion to the receiving drying screen.
The present invention is directed to a drying screen for a fibrous pulp web. The drying screen includes a support structure composed of one of a web or mesh, and an elastic coating having a shaped surface provided on a side of the support structure adapted to face the fibrous pulp web.
In accordance with another feature of the present invention, the coating includes an elastic base material having embedded hard particles that protrude from the shaped surface in an unstressed state.
In accordance with another feature of the present invention, the coating includes an open-pore, elastic foam. Further, the elastic foam includes one of polyurethane and rubber.
In accordance with still another feature of the present invention, the elastic coating is provided on an entire side of the support structure adapted to face the fibrous pulp web.
In accordance with a further feature of the present invention, the support structure includes a fiber web, and fibers of the fiber web are at least partially coated with the elastic coating. Further, individual fibers of the fiber web are coated with the elastic coating. Alternatively, the fiber web is a belt and only a side of the belt adapted to face the fibrous pulp web is coated with the elastic coating.
In accordance with still another feature of the present invention, the support structure includes a formed fabric positioned on the side adapted to face the fibrous pulp web, and the fibers of the formed fabric are coated with the elastic coating.
In accordance with another feature of the present invention, the drying screen is adapted for use in a dryer section of a machine to manufacture a fibrous pulp web such that the drying screen receives the fibrous pulp web from a preceding press section and guides the fibrous pulp web to the dryer section.
In accordance with a still further feature of the present invention, the drying screen is adapted for use to transfer the fibrous pulp web to a second drying screen within a dryer section, the second drying screen comprising a coating having a greater elasticity than the transferring drying screen.
In accordance with a further feature of the present invention, the drying screen is adapted to be guided through a press nip of a press section with the fibrous pulp web to drain the fibrous pulp web.
The present invention is directed to a process for applying an elastic coating to a support structure of a drying screen composed of one of a web or mesh. The process includes applying an elastic base material together with the hard particles to a side of the support structure adapted to face a fibrous pulp web, and chemically removing an outer portion of the elastic base material. The chemical removal does not affect the hard particles.
The present invention is also directed to a drying screen that includes a support structure composed of a plurality of fibers, and an elastic layer, located on a side of the support structure adapted to receive a fibrous pulp web, adapted to create a

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