Classifying – separating – and assorting solids – Sifting – With liquid treatment
Patent
1998-05-28
2000-09-19
Walsh, Donald P.
Classifying, separating, and assorting solids
Sifting
With liquid treatment
209306, 209397, 2105121, B07B 104, B01D 120, B01D 149, B01D 2126
Patent
active
061198676
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a screen cylinder. In particular the invention relates to a screen cylinder intended for screening fiber suspensions in the wood processing industry.
The wood processing industry uses two basic types of screen drums. One type is a drum made of a metal plate in which screen apertures, either holes or slots, have been manufactured with a desired spacing while the plate is planar after which the plate has been bent cylindrical and the edges have been welded together to form a cylinder. During the past two decades screen plates having certain kinds of grooves machined thereto before the manufacture of the screen apertures have become very popular, the grooves being located in a finished screen drum on the side facing the rotor and substantially parallel with the axis of the drum and the screen apertures are located at the bottom of the grooves.
WO-A-8703024 discloses a straining means which comprises a screen plate having an injection side and an acceptance side for straining of suspensions of cellulose fibers. The screen plate has grooves on both sides thereof and openings through the screen place connecting the grooves on the opposite surfaces of the plate. The openings are either inclined or perpendicular to the screen surface.
EP-A2-0 236 843 discusses a screen plate resembling very much to the screen plate of U.S. Pat. No. 4,529,520. In other words, the screen plate has grooves with an inclined first side surface, an upright second side surface and a bottom surface between the side surfaces. The bottom surface is substantially parallel to the screen plate surface. The only exception to the US patent is that there are two openings one after the other through the bottom surface.
U.S. Pat. No. 5,073,254 discloses yet another version of the so called contoured screen plates. In this version the groove has curved side and bottom surfaces and the openings through the screen plate are positioned to the lowermost part of the groove.
U.S. Pat. No. 5,000,842 discusses a screening apparatus having a screen drum and a rotatable rotor inside the screen drum. The document concentrates mainly on the structure of the rotor but gives a number of different alternatives to the contoured screen plate.
The other basic type of screen drums, the so-called wire screen drums, are usually 10 manufactured by securing support wires to a cylindrical jig onto which the screen wire is wound up with a certain pitch from a reel by rotating the jig. The screen wire supplied from the reel is secured to the support wires by welding. When a wire surface of the desired size has been formed the cylinder having the screen wires on the outer side and the support wires on the inner side is detached from the jig. After this the cylinder is cut open in its axial direction and bent to form a planar surface and further, the planar surface is bent in the opposite direction to form a cylinder so that the screen wires extend essentially in the axial direction and the support wires are parallel with the frame.
The other basic type of screen drums, the so-called wire screen drums, are usually manufactured by securing support wires to a cylindrical jig onto which the screen wire is wound up with a certain pitch from a reel by rotating the jig. The screen wire supplied from the reel is secured to the support wires by welding. When a wire surface of the desired size has been formed the cylinder having the screen wires on the outer side and the support wires on the inner side is detached from the jig. After this the cylinder is cut open in its axial direction and bent to form a planar surface and further, the planar surface is bent in the opposite direction to form a cylinder so that the screen wires extend essentially in the axial direction and the support wires are parallel with the frame.
Until recently the wire used as the screen wire has in most cases had a symmetric cross section as regards its securing point. FIG. 1 illustrates how a line C.sub.L which has been drawn via the center lines of the sides 6 and 8 of a screen
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Ljokkoi Risto
Wathen Pertti
Ahlmstrom Machinery Oy
Martin Brett A
Walsh Donald P.
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