Classifying – separating – and assorting solids – Sifting – Elements
Reexamination Certificate
2000-04-27
2001-07-10
Walsh, Donald P. (Department: 3653)
Classifying, separating, and assorting solids
Sifting
Elements
C209S363000, C209S370000, C209S392000, C209S406000
Reexamination Certificate
active
06257413
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a screen for screening fiber material. More particularly, the present invention is directed to a screen panel for such a screen.
BACKGROUND OF THE INVENTION
During the screening of fiber material, such as fiber suspensions of cellulosic material, the object is generally to separate coarse particles in the form of shives, fiber bundles or other impurities from the fiber material. The screening is usually carried out in a screen with a screening cylinder, which can be stationary or rotary. The screening cylinder is generally provided with holes or slits, through which the fiber, but not the impurities, can pass.
Screening cylinders of this type are usually manufactured by drilling holes or milling slits in a metal sheet, which is then formed into a cylinder. In order to obtain an open area, i.e. that portion of the cylinder surface which is perforated as much as possible, the holes or slits must be arranged in a tight relationship. At the same time, the strength of the cylinder must be maintained. This therefore requires high precision work.
Particularly during the manufacture of slitted cylinders, which in certain cases are more advantageous than cylinders with holes which are drilled, difficulties concerning the strength arise, because the material between the slits will become rather thin. The slits, therefore, must be made short and arranged at a certain relationship from each other. This, in turn, results in a certain restriction of the open area.
One way to solve this problem is to form the cylinder from a great number of bars, which are kept in place by annular strips. This, however, is a complicated and expensive way of manufacturing a screening cylinder. It is, furthermore, difficult to provide the slits with a uniform width across the entire cylinder.
SUMMARY OF THE INVENTION
In accordance with the present invention, this and other difficulties have been solved by the invention of a screen panel adapted to constitute a portion of a screening cylinder for the screening of fibrous material, the screen panel comprising a unitary screen panel of wear-resistant material having a first surface, a second surface, an upper edge, a lower edge, and a pair of side edges, the first surface including a plurality of axially extending grooves, a plurality of slit-shaped screening orifices disposed at the bottom of the plurality of axially extending grooves, at least one support ring extending circumferentially across the first surface and being integral with the screen panel, and assembly means for assembling the screen panel into the screening cylinder without the use of welding. Preferably, the screen panel includes a plurality of the support rings.
In accordance with one embodiment of the screen panel of the present invention, the screen panel includes a plurality of recesses on the second surface of the screen panel at a location directly in front of the plurality of axially extending grooves.
In accordance with another embodiment of the screen panel of the present invention, the plurality of slit-shaped screening orifices have a slit width of between about 0.5 and 1 mm.
In accordance with another embodiment of the screen panel of the present invention, the assembly means comprises at least one flange formed on one of the pair of side edges. Preferably, the assembly means further comprises additional fastening members disposed along the top and bottom edges of the screen panel.
According to the present invention, these problems are thus solved by forming the screen from a number of screen panels, which together form a screening cylinder, i.e. each screen panel constitutes one portion of the circumference of the screening cylinder. One screen panel can possibly extend around the entire circumference of the screening cylinder. The screen panels are manufactured individually by being formed in one piece, whereafter the screen orifices are provided in the panels. Several panels are thereafter assembled to form a screening cylinder.
The forming of the panels can be carried out by casting, compression molding or the like, of a material which is a suitable wear-resistant metal alloy or ceramic material, for example alumina. Such material is not weldable. The screen panels, thus, must be joined together without welding.
Each panel is formed with a curvature radius, which substantially corresponds to the radius of the screening cylinder. The panel is also formed with a great number of substantially axial grooves and a number of support rings, which extend substantially in the circumferential direction. These support rings are formed as an integral part of the panel. These rings are located on the same side of the screen panel as are the grooves. On the opposite side of the panel recesses are preferably formed, which are located directly in front of the grooves. The panel is also formed with edge flanges, by means of which several panels can be assembled in the circumferential direction. Fastening means can be formed along the curved edges for attaching the panels axially to one another.
After their forming, the panels are provided with screening orifices, which are cut in the form of substantially axial slits. This is preferably carried out by precision grinding, by means of which a slit width of about 0.1 to 1 mm can be obtained. The slits are placed in relation to the grooves, preferably at the bottom thereof. The screening orifices are cut out from the opposite side in relation to the grooves and support rings, so that the slits extend through the panel to the bottom of the grooves, but not through the support rings. Thereby a maximum open area is obtained, and at the same time the strength of the screen panel is maintained.
REFERENCES:
patent: 4374729 (1983-02-01), Frykhult
patent: 4986900 (1991-01-01), Mason
patent: 0 287 267 A2 (1988-10-01), None
patent: 0 357 382 A2 (1990-03-01), None
patent: 0357382-A2 (1990-03-01), None
patent: 441 108 (1985-09-01), None
Beauchaine Mark
Lerner David Littenberg Krumholz & Mentlik LLP
Valmet Fibertech AB
Walsh Donald P.
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