Endless belt

Details Endless belt Endless belt

1999-05-19

2001-01-16

Bidwell, James R. (Department: 3651)

Conveyors: power-driven

Conveyor section

Endless conveyor

C198S846000, C162S351000

Reexamination Certificate

active

06173831

ABSTRACT:

CROSS-REFERENCE OF RELATED APPLICATIONS
The present application claims priority under 35 U.S.C. § 119 of German Patent Application No. 198 23 948.3, filed May 28, 1998, the disclosure of which is expressly incorporated by reference herein in its entirety.
1. Field of the Invention
The present invention is directed to an endless belt. More specifically, the present invention is directed to an endless belt for use in a drainage section of a machine that manufactures a web of fibrous material, such as paper, cardboard, or tissue.
2. Discussion of the Background Information
In the forming section of a paper making machine, endless belts circulate through the machines relative to wire belts. The endless belts are mounted on the side of a wire belt opposite the side that supports a pulp suspension. Wear caused by stationary elements (e.g., rails, foils, etc.) is therefore supposed to be prevented.
DE 35 90 589 C2 discloses a forming section having two wire belts that form a so-called double-wire zone in which the pulp suspension is drained toward both sides of the belt. To improve the paper characteristics, part of the drainage section is covered with a water-impermeable belt to prevent drainage in that section. A disadvantage of this structure is that, because of the covered area, the length of the entire drainage section must be relatively large, and is not very efficient.
DE 44 20 801 C2 discloses a double-wire zone in which a belt supports a wire belt, which may be either water-permeable or water-impermeable. The water-impermeable belt impairs paper quality by an entrained boundary layer of air, and prevents two-sided drainage. While a water-permeable belt (e.g., perforated) certainly permits drainage, a large amount of water can accumulate in the initial drainage zone, which can undesirably mark the web due to the high flow speeds.
DE 44 11 621 A1 discloses a paper making machine in which a pressing belt in the forming section has an adjacent pressing felt, which absorbs part of the water. The remaining water is stored in the grooves of the pressing belt. Here, the ratio of the surface area of the grooves to the overall surface of the belt should be as small as possible to obtain an adequately large support surface necessary for low belt wear. Such a belt design is suitable for high press pressures and low drainage rates. However, greater drainage flows, such as occurring in the forming section, cannot be properly managed. Increasing the belt thickness would increase the water absorption, but would produce a belt with excessive flexural rigidity tat prevents the required uniform drainage over the width of the belt.
DE-A-196 34 349 discloses, on the side of the wire belt opposite the suspension, a profiled belt running at right angles to the wire belt. The profiled belt is provided with a plurality of holes, borings, or slots, and is thus mostly open. The profile belt may also have a rough, ribbed, or otherwise profiled outer surface facing the wire belt, which may be water impermeable.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to overcome the drawbacks of the prior art.
It is also an object of the invention to provide an endless belt with two-sided uniform drainage without impairing the quality of the web of fibrous material.
The above and other objects are met by providing an endless belt that is substantially closed on one side, and is substantially open on the opposite side. A water storage capacity of the belt is at least approximately 5 l/m
2
, particularly within a range of from approximately 5-25 l/m
2
, and preferably within a range of from approximately 10-18 l/m
2
. A mean flexural rigidity in the circumferential direction and in the transverse direction, based on a distance of 1 meter in each direction, is less than or equal to approximately 10 Nm
2
per one meter distance.
The mean flexural rigidity in the circumferential direction may be the same as the mean flexural rigidity in the transverse direction. However, the flexural rigidity in the circumferential direction and the flexural rigidity in the transverse direction may also be different from each other.
The belt of the present invention may be provided with grooves, particularly on its open side. At least some of the grooves may run generally in the circumferential direction and/or generally the transverse direction. According to an exemplary embodiment of the belt according to the invention, grooves run generally in both the circumferential and cross-wise directions. In principle, the grooves may also be arranged to form a spiral.
In an exemplary embodiment of the belt according to the invention, at least some of the grooves have a depth which is within a range from approximately 5-25 mm, and particularly within a range from approximately 12-20 mm, to provide the necessary water storage capacity.
On its open side, the belt may also have a plurality of knobs or be formed by a plurality of such knobs. This structure reduces flexural rigidity in the circumferential and the transverse direction while providing a high water storage capacity. These may, for example, be disposed in rows running generally in the circumferential direction and generally in the transverse direction. A spiral arrangement of the knobs is also possible. The drainage wire in question is then carried by the contact surface of the knobs coming into contact with the wire.
Because of this design, not only is marking-free two-sided drainage possible, but it ensures that the flexural rigidity in the circumferential direction and in the transverse direction is small enough to be able to set optimal drainage conditions over the entire width.
In an exemplary embodiment of the belt according to invention, the outer contact surface of the knobs which can be brought into contact with a wire is on the whole less than or equal to approximately 50% of the entire surface of the belt particularly within a range of approximately 15-30% and preferably within a range of approximately 20-25% of the entire surface of the belt.
The individual contact surfaces of the knobs preferably have a maximum dimension of approximately 6 mm in any direction. The maximum dimension of the individual contact surfaces of the knobs is thus preferably restricted to a value which is less than or equal to approximately 6 mm, and particularly approximately 2 mm for any individual contact surface.
The individual contact surfaces of the knobs may, for example, have around, square, or rectangular shape, whereby the contact surfaces of the various knobs may be the same or different.
It is also preferable if the belt has compressibility of approximately 100 to 2000 kPa.
The base of the belt may also have a reinforcement on which the knobs are disposed. The reinforcement may include reinforcement fibers, which are preferably embedded in a matrix and run in both the circumferential and transverse directions. The matrix may be made of polyurethane, or a combination of polyurethane and other materials.
To minimize manufacturing expenses, it is preferable that the knobs are formed by machining a base to remove excess material.
Preferably, the base has a thickness within a range of from approximately 0.5-8 mm, and particularly 4 mm thick. The thickness of the wire in contact with the belt is preferably approximately 0.7 mm.
The knobs also preferably include an internal gas cushion, such as an air cushion. This gas cushion may be ventilated from the side and/or toward the closed side of the belt.
To improve the wire carrying function of the belt, the contact surfaces of the knobs may be formed at least partially by spikes embedded in the knobs. By appropriate design and purposeful selection of material of the spikes, belt wear and the tendency toward marking may be reduced. The spikes can be slotted at least in the region of the contact surface, whereby the contact surface bearing the associated wire is further reduced. Such a slotted design is particularly advantageous when the individual contact surfaces of the knobs have a maximum dimension of approximately 2 mm i

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