Classifying – separating – and assorting solids – Sifting – Drum sifters
Reexamination Certificate
2000-02-22
2003-07-01
Walsh, Donald P. (Department: 3653)
Classifying, separating, and assorting solids
Sifting
Drum sifters
C209S283000, C209S306000
Reexamination Certificate
active
06585116
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a screening apparatus used to screen acceptable and rejectable material from a fiber suspension, and, more particularly, relates to such a screening apparatus including a screen basket concentrically positioned relative to a rotor.
2. Description of the Related Art
In the paper-making process, a screening apparatus is typically used to separate foreign matter from a fiber suspension. A typical screening apparatus may include a housing within which a screen basket is mounted around a concentrically positioned rotor assembly. The screen basket may be fabricated from a relatively thin metal plate material although bar or wire materials are also often used and when mounted in a screening apparatus provide a barrier between a screening chamber and an accept chamber. The fiber suspension is transported into the screening chamber by way of a feed inlet. The fiber suspension is introduced to either the inner or outer portion of the screen basket, depending upon the particular type of screening apparatus being used. Material which does not pass through the screen basket flows to an end of the screening chamber away from the feed inlet and is removed through a reject outlet.
One known type of screen basket has circular shaped openings sized to reject unwanted solids and may have support rings located along the length of the basket to provide additional mechanical support. Another type of screen basket has slots having lengths much greater than their widths for separating other types of materials and may have support rings located along the length of the screen basket to provide additional mechanical support. Yet another type of screen basket includes longitudinally extending wires which are attached at each end thereof to respective annular retaining rings. The retaining rings are used to mount the screen basket within the screening apparatus. The retaining rings are bolted to a stationary member to prevent the screen basket from rotating in response to the torsional forces generated by the rotating hydrofoils or drum. Such a mounting arrangement generally places the screen basket in an axially compressive loading condition.
The rotor assembly generally includes hydrofoils or a contoured drum mounted on a rotating shaft in close proximity to the screen basket to sweep past the openings of the screen basket. The hydrofoils or contoured drum may be positioned to sweep over the inner or outer surface of the screen basket. The rotating hydrofoils or contoured drum generate hydrodynamic pulses in the radial direction with enough force and frequency to continuously remove any fiber plugs that occur in the screen basket openings. The localized flows caused by the hydrodynamic pulses are generally in a direction opposite to the flow of the fluid pulp provided to the screen basket under pressure.
As the fiber suspension impacts and passes through the screen basket, the screen basket becomes worn over time and must be replaced. Typically, the quality of the accept material which is transported from the accept outlet of the screening apparatus may be periodically monitored to detect if the quality thereof is degrading. A degradation in quality may be correlated to the wear of the screen basket.
What is needed in the art is a method of more directly, accurately and timely determining a wear state of a screen basket within a screening apparatus.
SUMMARY OF THE INVENTION
The present invention provides a screening apparatus including a sensor which senses a wear parameter which may be directly related to a wear state of a screen basket within the screening apparatus.
The invention comprises, in one form thereof, a screening apparatus for screening acceptable and rejectable material from a pressurized fiber suspension. The screening apparatus includes a housing, a rotor, a screen basket and at least one sensor. The screen basket is positioned generally concentrically around the rotor, and includes at least one screen element. Each sensor is positioned in association with the screen basket. Each sensor is configured for sensing a wear parameter relating to a wear state of the screen element.
An advantage of the present invention is that the wear state of the screen basket may be directly determined through the sensed wear parameter.
Another advantage is that the wear state of the screen basket may be directly sensed using different types of sensors.
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Derwent Abstract 1979-73276B: Ogarkov, SU (Apr. 28, 1977).*
Derwent Abstract 1984-187705: Evstratov, SU (Sep. 3, 1982).*
Derwent Pub. # 1982-J8985E (Abstract of DE 3143779 A, Pub. Date: Jul. 8, 1982; Inventor: Holm, A).*
Derwent Pub. 190 1976-24720X (Abstract of DE 2443548 A, Pub. Date: Mar. 25, 1976; Inventor: Lesk, M).
Doelle Klaus
Hostetter David W.
Lorenz Kurt W.
Rodriguez Joseph
Taylor & Aust P.C.
Voith Sulzer Paper Technology North America Inc.
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