US 4,544,102 A · Differential rate screening

Abstract

Disclosed are differential rate screening processes and apparatuses for continuously screening undersize particles in different size classes to different degrees of incompletion to provide a product having a preselected distribution of particle sizes substantially different from the distribution of particle sizes in a feed of particulate material. A stream of feed is introduced onto a screening member having apertures of sufficient size to pass a plurality of size classes, and is separated into at least a throughs stream and one other stream by causing undersize classes to pass through screen apertures and into a throughs stream in proportions relative to one another substantially different from the proportions of the same undersize classes relative to one another in the feed stream. A sufficient population of undersize particles are provided in each undersize class and differentials between relative proportions of undersize classes in the feed stream and relative proportions of undersize classes in the throughs stream are controlled so as to provide a product having substantially the desired particle size distribution. Various means are provided for causing differentials between relative proportions of undersize classes in the feed and relative proportions of undersize classes passing through the screening member and into the throughs stream, and for controlling these differentials.

Claims79

Dependent claims

A differential rate screening process for continuously screening a feed of particulate material to provide a product having a preselected size distribution substantially different from a predetermined size distribution of said feed which contains particles distributed among a plurality of substreams each of a different size class, said screening process comprising introducing a stream of said feed onto a screening member of a screen means, said screening member having apertures of sufficient size to pass at least one of said substreams as an undersize substream;

separating said feed stream into at least a first throughs stream and one other first stream by causing part of said undersize substream to pass through the apertures of said screening member and into said first throughs stream at a first partial flow rate substantially greater than zero and substantially less than conventional flow rates at which said undersize substream would pass through the apertures of said screening member upon screening said undersize substream to provide essentially complete screening, said first partial flow rate being such as to provide control over the size distribution of said first throughs stream;
and controlling said first partial flow rate so as to provide substantially said preselected size distribution in a particulate product stream comprising at least a portion of at least one of said first throughs stream and said other first stream.

A differential rate screening apparatus for continuously screening a feed of particulate material so as to provide a product having a preselected size distribution substantially different from a predetermined size distribution of said feed which has particles distributed among a plurality of substreams each of a different size class, said screening apparatus comprising screen means having a screening member;

feed means for introducing a stream of said feed onto said screening member, said screening member having apertures of sufficient size to pass at least one of said substreams as an undersize substream;
separation means for separating said feed stream into at least a first throughs stream and one other first stream by causing a part of said undersize substream to pass through the apertures of said screening member and into said first throughs stream at a first partial flow rate substantially greater than zero and substantially less than conventional flow rates at which said undersize substream would pass through the apertures of said screening member upon screening said undersize substream to provide essentially complete screening, said first partial flow rate being such as to provide control over the size distribution of said first throughs stream;
and control means for controlling said first partial flow rate so as to provide substantially said preselected size distribution in a particulate product stream comprising at least a portion of at least one of said first throughs stream and said other first stream.

Dependencies are inferred from the claim text.

Differential rate screening

Life of this patent

Differential rate screening

Life of this patent

Abstract

Claims79