Classifying – separating – and assorting solids – Sifting – Elements
Patent
1995-03-31
1997-06-17
Bollinger, David H.
Classifying, separating, and assorting solids
Sifting
Elements
B07B 149
Patent
active
056389604
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention concerns a screen, specifically a screen basket for sorting fiber suspensions. Known from U.S. Pat. No. 4,717,471 is a screen where the entrance area of the perforations is heavily flared in the shape of a funnel, the opening of the funnel having a very large angle, of more than 120 degrees, and perforations being round holes or orifices.
There are also screens formed by a parallel arrangement of rods, which form the screen duct or leave appropriate voids between them (DE 3,327,422).
A similar screen is known from U.S. Pat. No. 4,193,503, where the outlet side of the screen element is rounded in a convex fashion. But this screen type can only be used in conjunction with a virtually ribbed screen surface where the ribbing extends transverse to the major direction of flow along the screen surface. This arrangement imparts a wavy movement to the fiber suspension to concentrate the fibers and other more lightweight materials in an upper layer, i.e., at a greater distance from the screen surface, thus preventing these lightweight substances from passing through the screen perforations. This effect is contrary to the effect desired by the present invention, which is to sort the fibers--notably paper or cellulose fibers--out through the screen perforations, but prevent particles having dimensions greater than the desired fibers from passing through the screen surface.
The screen of DE 3,327,422 is susceptible to cloggings on the screen edges formed by the tilted rods. With such screens it is known that the throughput and the sorting integrity decrease with the sharpness of the profile while the susceptibility to clogging, for instance to cellulose buildup, increases.
The problem underlying the present invention is to reduce the susceptibility to clogging and increase sorting integrity during the sorting operation.
SUMMARY OF THE INVENTION
The inventional solution to the problem is characterized by a screen having a plurality of screen perforations having a funnel design wherein at least a part of the perforation ingress area is rounded to a convex curvature.
The convex design of at least part of the ingress area of the screen perforation results in a cross-sectional constriction in the direction of flow. The constriction increases the velocity of the liquid directed through the aperture, and thus improves the removal of lightweight paper or cellulose fibers by the screen perforations. The rounding in the ingress area offers the further advantage of reducing the flow resistance to the fiber suspension passing through the screen, with fibers of paper and cellulose contained in it. Owing to the favorable cross-sectional transitions, a stoppage of the fiber suspension flow through the screen perforation can be greatly avoided. Moreover, the inventional design of the screen perforation makes it possible to avoid clogging of the perforations. The screen surface remains smooth and is not wavy as in the prior art. The rounding may also feature approximate shapes, for instance of partial ellipses rather than radii. The screen perforation ingress area is the area extending from the screen entry in the pass-through direction, while the egress area is the area which is located in the area of discharge. No specifications are made, however, as regards the relations between the two areas.
The convex shape of parts of the ingress area, or of the entire ingress area, can be described by at least one radius or a plurality of different, successive radii. Viewed cross-sectionally, the convex areas may have the shape of a circular arc, partial areas of ellipses etc.
The distance between the centers of the screen perforations is preferably at least 3.5 times the cross section of the perforation at its narrowest point, specifically transverse to the generatrix of the peripheral surface of the screen basket (envelope). Transverse to the perforation, the spacing may be less, so that for instance the rounding radii of adjacent holes touch tangentially, or even less. The rounding may also be ef
REFERENCES:
patent: 4193503 (1980-03-01), Connolly
patent: 4529520 (1985-07-01), Lampenius
patent: 4717471 (1988-01-01), Winkler
patent: 5255790 (1993-10-01), Einoder
Beuermann Karl-Heinz
Rienecker Reimund
Bollinger David H.
J.M. Voith & GmbH
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