US 4,544,101 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. An input stream of feed material 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 input stream. The overs, throughs or both from one rate screening member may be introduced as an input stream onto another rate screening member. A sufficient population of undersize particles are provided in each undersize class and differentials between relative proportions of undersize classes in an input stream and relative proportions of undersize classes in a 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 an input stream and relative proportions of undersize classes passing through a screening member and into a throughs stream, and for controlling these differentials. An output stream from one rate screening member may be blended with an output stream from another rate screening member and at least a portion of an output stream from one rate screening member may be recycled to a crusher and then sent to the same or a different rate screening member.

Claims94

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 first stream of said feed onto a first screening member of a screen means, said first screening member having apertures of sufficient size to pass at least two substreams of said feed stream as first undersize substreams;

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

1 more element

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 first screening member and a second screening member;

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

2 more elements

Dependencies are inferred from the claim text.

Differential rate screening

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Differential rate screening

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Abstract

Claims94