US3288284A

US3288284A - Method and apparatus for pneumatically classifying solids

Info

Publication number: US3288284A
Application number: US272014A
Authority: US
Inventors: Manley Russell Eugene
Original assignee: Individual
Current assignee: Individual
Priority date: 1963-04-15
Filing date: 1963-04-15
Publication date: 1966-11-29
Anticipated expiration: 1983-11-29
Also published as: DE1482452A1; DE1482452B2; DE1482452C3; NO115653B; GB987671A

Description

v Nov.'29, 1966 R. E. MANLEY 3,288,284

METHOD AND APPARATUS FOR PNEUMATICALLY CLASSIFYING SOLlDS Filed April l5, 1963 '7 Sheets-Sheet l DR/LL ED Fa/P\ BLAST/NG H/GH PRESSURE Nov. 29;, 1966 R. E. MANLEY 3,288,284

METHOD AND APPARATUS FOR PNEUMATICALLY CLAS'SIFYING SOLDS Filed April l5, 1963 '7 Sheets-Sheet 2 10015 im 10AM 10615 INVENTOR.

R. E. MAN LEY Nov. 29, 1966 METHOD AND APPARATUS FOR PNEUMATICALLY CLASSIFYING SOLIDS '7 Sheets-Sheet Filed April l5, 1963 i 000 IJ wsel E322? Nov. 29, 1966 R. E. MANLEY 3,288,284

METHOD AND APPARATUS FOR PNEUMATICALLY CLASSIFYING SOLIDS Filed April l5, 1965 '7 Sheets-Sheet 4 BY 179 n MM J WM@ magg/ Nov. 29, 1966 R. E. MANLEY 3,288,284

METHOD AND APPARATUS FOR PNEUMATICALLY CLASSIFYING SOLIDS Filed April l5, 1963 7 Sheets-Sheet 5 INVENTOR.

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Nov. 29, 1966 R. E. MANLEY 3,288,284

METHOD AND APPARATUS FOR PNEUMATICALLY CLASSIFYING SOLIDS Filed April 15, 1965 fao 7 Sheets-Sheet 6 I N V E NTOR.

Fwse E Nvu/@Ly mi( M 9@ fm@ f @4m R. E. MANLEY Nov. 29, 1966 METHOD AND APPARATUS FOR PNEUMATICALLY CLASSIFYING SOLIDS Filed April 15, 1965 '7 Sheets-Sheet 7 lINVENTOR. wsel afz United States Patent O 3,288,284 METHD AND APPARATUS FR PNEUMA'H- CALLY CLASSIFYING SOLIDS Russell Eugene Manley, 25 Skyline Drive, Box 105i), gden Dunes, Portage, ind. Filed Apr. 15, 1963, Ser. No. 273,014 17 Claims. (Cl. 2&9-135) This invention relates to new and improved apparatus and to a new .method for classifying non-uniform particles. The invention is especially useful for classifying mineral particles and mine run materials, such as sand, which contain particles ranging in size from relatively coarse particles down to line dust.

Various types of `classifying apparatus and classication methods have been employed heretofore. `While their use has filled particular needs more or less satisfactorily, their applications are limited. Consequently, there is an existing need fcr a classification method and apparatus which will rapidly and efficiently classify large quantities of material, will consistently produce a high degree of particle separation and produce a consistent particle size in each separated fraction regardless of the variation in particle size of the feed material. Thus, for example, hydraulic classication has been used for grading particles. The hydraulic methods suffer from low productivity, especially in the finer particle sizes, relatively poor separation and recovery of fine particles, and the need to dry each separated fraction separately. Centrifugal type pneumatic classiers generally separate the material into but two fractions, so that a number of operations must be conducted to produce a corresponding number of fractions, with accompanying equipment and space requirements. Horizontal pneumatic separation has been used, but again as in water separation there is a considerable carry over of particles between grades produced and a wastage of liner particles into the air or wet collector, which wet collector must be used because of the volume of air necessary for this method. The collection of liner particles was not practically possible in such horizontal pneumatic separators. Classification by screening requires a number of screens and separating steps, production is low, and the costs of labor and maintenance are high. Also, angular particles blind the screens. The practice of the best modern screening is to ymake only one separation per machine and, thus, to make the number of separations here attained would require a multiplicity of screens not economically feasible. A variation in amount of feed' to a screen produces a considerable variation in the particle size of the product going over and coming through. A variation in the particle size of the feed produces a similar variation in the over and through fractions. Also, a variation in the particle size of the feed produces a variation in the amount of material that a screen will handle without putting the coarse in the line or vice versa. Other previously proposed apparatus and methods have suffered from one or more disadvantages, including inability to separate material into a number of fractions, poor resolution of the material into fractions concentrated with respect to particle size, and excessive equipment and personnel requirements, among others.

An important object of the present invention is to provide particle classifier apparatus and a method of classifying particles which overcome prior disadvantages and, particularly, which classify granular material in a number 3,238,234? Patentes Nov. as, ieee of concentrated fractions extending over a range of particle sizes. The apparatus and method make it economically and profitably possible to take one or more closely sized fractions from a" given group of particles and leave both liner and coarser near vmesh particles. In so doing, the particle distribution curve can be changed in such a manner as to `be completely different from the base material and meet specifications that previously had been impossible. The method and apparatus allow a `considerable variation in amount of feed Without substantially affecting the sizing, allow a considerable variation in the particle size of the incoming feed without affecting the sizing, and enables one to construct a separating machine that can be adjusted to handle a feed of particles much coarser or liner than a standard feed or change the sized fraction to be coarser or finer or handle materials of different densities or particle shape, all by only simple adjustment of the machine.

A more particular object is to provide apparatus and a method which produce outstanding separation, recovery and classification of valuable nes while also producing a high degree of separation of accompanying coarser particles into a number of fractions.

Another object is to provide apparatus and a method adapted for large scale production while accomplishing the foregoing objects, and which are further adapted for continuous operation.

An additional object is to provide apparatus and a method which are adapted for processing diverse types of granular materials and, especially, which maybe employed to process material as received from its natural source, such as sand pits, quarries, excavations, and so forth.

A further object is to provide apparatus which performs the foregoing classification in but one step involving one pass of the material through the apparatus, and which apparatus is compact and inexpensive, may be operated for long periods of time unattended, and experiences little wear and requires little maintenance, so that the end result is the production of highly refined particle fractions which are much less expensive than heretofore. In particular, fine product fractions are produced and sold at reasonable costs, which previously could not be recovered economically.

These and other objects, advantages and functions of the invention will be apparent on reference to the specification and to the attached drawings illustrating preferred embodiments of the invention, wherein like parts are identified by like reference symbols in each of the views, and wherein:

FIG. 1 is a schematic view illustrating a method and apparatus for processing mine run sand according to the invention, from the sand quarry through the processing operations to final storage of `classiiied material in silos;

FIG. 2 is an enlarged fragmentary vertical cross-sectional view of a hopper for receiving material to tbe classified and for delivering the material to cassifier cells;

FIG. 3 is a schematic side elevational view on a smaller scale of a pneumatic lclassifier cell with a side wall removed, as taken on line 3 3 of FIG. l;

FIG. 4 is a schematic front elevational view of the classifier cell, on the same scale;

FIG. 5 is an enlarged fragmentary vertical longitudinal cross-sectional view of the lower part of the classifier cell, illustrating particularly two collector assemblies and their relationship;

FIG. 6 is a View similar to FIG. 5 but taken at a slightly lower elevation to illustrate the ass-embly of the final collectors and collecting bins therebelow;

FIG. 7 is a fragmentary vertical cross-sectional view on a reduced scale of the feed chute and intermediate collector assemblies in the classifier cell;

FIG. 8 is an enlarged fragmentary vertical transverse cross-sectional view of the lower part of the classifier cell, taken on line 8 8 of FIG. 5;

FIG. 9 is an enlarged horizontal cross-sectional view of an air duct in .the classifier cell, taken on line 9-9 of FIG. 3, particlularly showing air blower propellers therein, in top plan view; and

FIG. l is a vertical cross-sectional View of the duct taken on line 10-10 of FIG. 9 and illustrating the propellers in side elevation.

The invention provides a pneumatic particle classifier which includes means for dropping a stream of particles for pneumatic classification of :the particles, means for collecting individual fractions of the classified particles, means for dropping the collected particle fractions for further pneumatic classification, and means for collecting individual fractions of the further classified particles. The foregoing structure preferably is provided in a classifier cell in combination with other apparatus providing nearly complete recovery of the material undergoing classification in a number of concentrated fractions. The remaining structure includes a particle separator which functions very advantageously to remove entrained fine particles from air leaving the cell. In a preferred assembly, a plurality of classifier cells are operated in parallel.

The new method of the invention may be conducted with the preferred apparatus illustrated and described, or it may be conducted with other apparatus and in other ways. The method involves dropping a stream of particles in free fall, passing a stream of airjtransversely through the particle strea-m to effect a pneumatic classification of the particles, collecting individual fractions of the classified particles, dropping the collected particle fractions in free fall together in a row of adjacent streams in the order in which collected, passing a stream of air transversely through the adjacent particle streams in the same relative direction as the first air stream to effect a pneumatic reclassification of the particles, and collecting individual fractions of the reclassified particles. Additional preferred features of the new method will appear in the course of the description of the invention which follows.

FIG. l of the drawings generally illustrates the equipment used in one preferred application of the invention: A sandstone formation is quarried; sand is washed and dried; dried sand is supplied to a hopper of a classifier; sand is delivered from the hopper to individual cells of a bank of classifier cells for -classification therein; and classified sand is delivered to storage silos.

A typical method of quarrying a sandstone formation 10 is schematically illustrated in the right hand portion of FIG. l. The formation may be found underlying a layer of earth 12 which is removed initially. Thereafter, the formation is disintegrated by blasting, in the course of which explosive charges are inserted in openings 14 drilled in the formation. The material separated from t'ne formation in this manner collects in piles 16 of material which is composed of sandstone in various degrees of disintegration, from large chunks to small particles. The sandstone is friable and may be broken down to small particles by directing a stream of water against the loose material. Water is drawn from a source such as a pool 18. A high pressure pump 28 is used to supply water to a hose 22 directed at the material. A slurry of small sand particles in water flows into a small sump. As the slurry collects, it is removed lby a pump 24 and pumped to a washing and drying building 26. The sand slurry is processed to separate the sand from the water and to dry the sand, in a conventional manner. The dried sand is supplied by a bucket elevator or conveyor 28 to a hopper 32 of a classifier 30.

The mine run sand obtained in this manner is a mixture of particles which may vary from place to place in the formation, and from one formation to another. Particle sizes may vary from 2O mesh down to 20 microns, for example, and the average particle size may vary from run to run, as exemplified by the material used in several runs as set forth hereinafter. The sieve numbers or sizes referred to in the specification and claims constitute the numbers of the U.S. Sieve Series. Other types of sand or other mineral formations or deposits may be quarried or worked in appropriate ways to provide granular material which may be classied employing the appara-tus and method of the invention. Illustrative examples of the classification of additional types of sand are also set forth hereinafter. While the invention is very valuable for classifying sands and other minerals, it will be apparent that a great variety of materials may be classified in like manner.

The dried sand or other material is discharged fr-om the conveyor 28 into the hopper 32, illustrated in greater det-ail in FIG. 2. The hopper supplies the material in parallel streams to a bank of classifier cells 34, arranged in side-by-side relation beneath thehopper. The hopper includes side walls 36, a bottom wall 38, and a number of vertical partitions or dividers 48 which extend upwardly for part of the height yof the side walls. The partitions divide the ihopper into compartments 42 equal in number to the classifier cells 34. A central discharge opening 44 is provided in the bottom wall in the base of each compartment. The openings register with delivery chutes 46, each of which delivers material to one of the classifier cells. A slide valve 48 provided with an opening 50 is mounted in the delivery chute beneath each discharge opening 44. Each discharge opening is opened or closed by the adjacent slide valve, being opened by causing the valve opening Sti to register with the discharge opening and being closed by moving the valve to a position where it blocks the discharge opening, the respective conditions being illustrated successively from the right side of the drawing in FIG. 2. The valves may be controlled manually, mechanically, or electro-mechanically, and other appropriate discharge and delivery apparatus may be employed if desired.

The material delivered by the hopper 32 is pneumatically classified in a plurality of successive stages in each of the classifier cells 34. The particles are caused to fall in streams in the several stages, and air streams are conducted through the cells to classify the particles in the falling streams. In each stage, individual fractions of the classified particle stream are collected. Following each stage except the final stage, the fractions are caused t-o fall in adjacent streamsv in the succeeding stage for further classification in a combined stream. Particles entrained by the air stre-ams in the course of classification are separated therefrom and collected as an additional fraction. The fractions collected in the final stag'e and the fraction of entrained particles are delivered to storage silos.

The classifier cells 34 are constructed alike, and consequently, but one of them is illustrated in detail. Referring to FIGS. 3 and 4, each classifier cell includes a pair of spaced parallel

vertical side walls

52 and 54, a vertical back wall 56, and an upwardly and rearwardly inclined bottom wall 58. The cell includes, from front to back in adjacency, a classifying compartment 60, a particle separator 61 including a baffle compartment 62, and an exhaust compartment or duct 64. The front of the classifier compartment is open for the entry of air and can lcommunicate with the atmosphere or a source of heated air and the like. A suitable framework 66 extends forwardly of the classifier compartment to provide a protective enclosure and is open to the entrance of air.

The classifying compartment 60 is subdivided into four superposed

adjacent wind chambers

68, 79, 72, and 74. A feed hopper 76 is mounted on top of the uppermost wind chamber 68, and it extends across the cell from `one side wall S2 to the other side wall 54. The hopper includes a front retaining wall 77, and a trough composed of a rear bottom wall 78 which is inclined upwardly and to the rear `at an angle close to the angle of repose of the material being separated, and a first bottom Wall Si) which is inclined upwardly and to the front, and is spaced upwardly from the rear bottom wall to permit iiow of granular material therebetween. The rear bottom wall 78 also constitutes a top wall for the classifying compartment t).

Material is delivered from the supply hopper 32 through the delivery chute 415 and collects in a pile of material 82 on the bottom walls '78 and 80 of the feed hopper 76 until the feed chute 46 is full. Material is discharged from the feed hopper at a controlled rate by means of a gate 84 pivotaliy mounted on the front biottom wall 80. An adjusting knob and rod assembly 86 is mounted on the frame 66, and it is operative to move the gate pivotally to or from the rear bottom wall 73. The granular material passes between the bottom walls and .accumulates on the back side of the gate. When the gate is swung forwardly, a stream of particles fiows on the rear bottom wall 78, between it and the gate and since said bottom Wall is at an angle close to the angle of repose, the material rolls down this inclined plane rather than sliding. The position of the gate relative to the rear bottom wall determines the rate of fiow and due to rolling action the finer grains move to the bottom and the coarser to the top of this stream, which places said particles in a pre-classified position.

The granular material is pneumatically classified similarly in each of four successive stages in the wind chambers 68, 7), 72 and '74. In the first stage, the material is stopped by a bumper plate 8S and and reduced to almost zero velocity. It falls by gravity into the uppermost ror first wind chamber 68 through the slot 96 formed by plate 88A, joined to the bottom plate 78, and bumper plate 8S. Said slot 90 is a relatively narrow vertical discharge channel extending across the cell from one side Wall 52 to the other side wall 54. A stream or curtain of particles is dropped through the chute 9*@ in free fall adjacent to the top and to the front o-f the wind chamber. A stream or current of air is passed through the chamber, by means subsequently described, and it passes transversely through the stream of falling particles in the manner represented by arrows in the drawing. The air is conducted upwardly and rearwardly at a rate of fiow suitable to break up the stream of particles and pneumatically classify the material being treated. A closely similar process is conducted in each of the succeeding stages, with variations described subsequently, and the following description is applicable to all stages.

The air stream causes the particle stream to fan out rearwardly according to the physical characteristics of the material, while the particles continue to fall, the distribution being a function of density and/ or surface characteristics and/or terminal velocities of the particles. The largest and heaviest particles are affected the least by the air stream, and the lightest and smallest particles are affected the most, with the intermediate densities and sizes falling therebetween. The air -flow is regulated so that the stream of particles is classi-fied in a succession of transverse strata for subdivisions from front to rear, and nearly all of the particles dlrop to the bottom of the chamber to be collected therein. The a'ir diow is such as to entrain the least possible amount of fine particles while producing the desired classification. The .air stream flows upwardly through the chamber, loutwardly at the rear orf the chamber and is not caused to ow downwardly. A slight amount of fines may nevertheless be er1- trained, and are removed nearly completely by the separator 61, as subsequently described. These results are achieved by employing a relatively low rate of air fiow, |for example, in the range below 500 ,feet per minute in classifying silica or feldspar sands as exemplified hereinafter.

The classifier is constructed to insure constant even non-turbulent flow. In the preferred embodiment illustrated, lit is 4recommended that the width o-f the cells 34, between the side walls 52 and I54, be about one foot to insure that this requirement is met. Provision of a bank of cells affords proper control of the dimensions of the cells while providing for changes in the load or amount of material -conveyed to the supply hopper 32.

The pneumatically classified particles are collected in individual fractions by an assembly of collectors in each wind chamber. A first intermediate collector assembly 92 -or row of collectors is mounted in the -first stage wind chamber 68 and forms the bott-om thereof. The assembly extends transversely from one side W-all 52 to the opposite side wall Se, and longitudinally from the front of the chamber to a position spaced `from and closely adjacent to the separator 6d forming the back of the chamber. Similarly, second and third

intermediate collector assemblies

94 and 96 yform the bottoms of the second and third

stage wind chambers

70 and 72. A final collector assembly 98 forms the `botto-m of the fourth or final stage wind chamber 74. The

intermediate collector assemblies

92, 94, -96 have the same construction, and the -final assembly 98 is similar while being adapted rfor final collection of classified material.

The third intermediate and the final collector assemblies 6 and 98 .are illustrated in greater detail in FIGS. 5, 6 and 8. Referring to the illustrations of the third assembly 96 as representative of the three intermediate assemblies 92, g4, and 95, each `assembly includes eight individual collectors 10d, '102, 104, 1%, 108, 110, 1112, and 114 arranged in a row from the front to the back of the wind chamber. The collectors function to collect successive individual fractions of the classified particles in the direction of air flow in each wind chamber to return their velocities substantial-ly to zero and to drop the collected ,fractions together in -a row of `closely adjacent streams or curtains of particles in the order in which collected, into the succeeding wind chamber for a ifurther pneumatic classification or reclassification therein. The Icollectons are supported in mounting brackets 1&6 and on mounting bars .11S secured to the

opposite side walls

52 and 54 by suitable means, as Aby

respective lbolts

120 and 122. The collectors are preferably constructed of thin-walled sheet material, such as galvanized metal, and they are constructed similarly to each other.

The -first collector 100 at the front of the assembly serves to collect a first particle fraction in each chamber and dischange the fraction into the succeeding chamber. The collector is constructed in front and rear parts i124 and 126 which together form a collecting trough and discharge channel extending yfrom one side wall 52 to the opposite wall S4. 'Phe front part y127A includes an upwardly and forwardly inclined collect-ing chute section 1128, an upstandiing partition section 130 integral with the forward edge of the collecting section, and a vertical downturned discharge chute section 132 integral with the rear edge of the collecting section. The rearwardly disposed remaining :part i126 of the first collector includes an upwardly and rearwardly inclined collecting chute section 134, an 'opstanding partition sect-ion 3.35 integral `with the rear edge of the collecting section, [and a vertical downturned discharge chute section 13S integral with the forward edge of the collecting section.

The partition and collecting sections of the front and rear collector lparts together form a collecting trough. T he front collector part 124 further includes pairs of integral int-urned side flanges and 142 extending respectively from the partition 130 and the collecting section 128 and disposed adjacent to the

side walls

52 and 54, thereby providing How channels or ducts for conveying the parti-cles collected to the discharge section =132. The rear collector part 126 includes similar :pairs of integral inwardly extending side flanges `144 and 146. The

discharge sections

132 and 138 are mounted in closely spaced parallel relation to -form a narrow discharge channel 139. The discharge sections are received in the first two of a series of vertical slots i147 in each of the collector -mounting brackets 116 to support the collector 100. The rear collector part 126 is also seated on the succeeding collector 102, as explained subsequently.

The Vremaining collectors 102-114 are constructed similarly to the rear part 126 of the linst collector '100. Thus, the second collector |162 includes a collecting chute section 148 which is upwardly and rearwardly inclined in parallel to the preceding collecting section =134 and spaced therefrom. Integral inturned side flanges 150 tform a flow channel with the collecting section 148. The flanges also support the preceding section 134 and function as spacers for the sections. An upwardly extending partition |152 is integral with the rear edge of the collecting section 148 of the second collector 102, and inturned side flanges 154 are integral with the .partition section. The partition section is spaced a predetermined distance from the rear partition section '136 of the rst collector 100. The rear part 126 of the first collector and t'he second collector together form a second -trough Ifor collecting a second particle fraction. A vertical discharge Section 156 is integral with the forward edge of the collectling section 148 of the second collector, and is received in a slot |147 1in the mounting bracket. The dischange section :is parallel to and forms a narrow vertical discharge channel 158 with the rear discharge Sectio-n 138 of the first collector, for discharging the second fraction.

The remaining collectors are similarly constructed for successively collecting and discharging third through eighth particle fractions. They extend progressively upwardly and rearwardly, terminating in the eighth collector 114, having a discharge section 160, a collecting section 162 bearing side flanges 163, and a partition section 164 bearing side fianges 165. The collecting section 162 is seated on the mounting bars 118, which thus support the collector assembly. The partition section 164 is in a position adjacent to the separator compartment 61, leaving a space therebetween as indicated at 166 in FIG. 5, for a purpose explained subsequently.

The collecting and discharge sections of the rear part 126 of the first collector and of the succeeding collectors are so spaced as to collect a particular sized particle and the angle of each is such that the particles will enter smoothly and without turbulence. The discharge channels 139 and 153 and the succeeding channels are of equal width, which in the preferred embodiment is about onefourth inch. The preferred angle of inclination of the rearwardly extending collecting sections 134 and 148 and the succeeding sections, and also of the forwardly extending collecting section 128, is in the range of about 34 to 38 degrees from the horizontal, depending upon the angle of repose of the material being separated. The upwardly extending partition sections ofthe collectors are spaced apart for distances which are predetermined according to the fractions to be collected. Except for the partition section 164 of the rearmost collector 114, the partition sections generally extend in the direction of the path of the falling particles in the vicinity thereof, as described subsequently. The entrance openings to the collectors, extending between the partition sections, are generally parallel to the direction of air ow.

Referring to FIGS. 3 and 7, illustrating the dispositions of the feed chute 90 and the intermediate collector assemblies 92-96, the first assembly 92 is arranged with the trough of its first collector 100 disposed beneath but slightly rearward from the feed chute 90. The largest and ing into the wrong collectors.

heaviest particles falling from the feed chute are least affected by the transverse air stream, being displaced only slightly from vertical fall, and consequently, constitute the first fraction collected in the first collector and discharged therefrom. The remaining collectors 102-114 extend in a row in the downstream direction, to collect and discharge fractions of successively smaller and/or lighter particles, which are increasingly displaced horizontally by the air stream. Similarly, the first collector of each of the

successive assemblies

94 and 96 is disposed beneath and slightly rearward of the preceding rst collector 100 and its discharge channel 139, and the former also extends beneath several of the succeeding discharge channels in the assembly thereabove. The remaining collectors in the successive assemblies, like the first assembly, extend in rows in the downstream direction.

Referring also to FIG. 5, the first two partion sections and 136 in each collector assembly are substantially vertical, corresponding to the nearly vertical fall of the larger and heavier particles. The succeeding partition sections of the collectors 102,-112 are inclined forwardly to a progressively greater extent, corresponding to the incerasingly greater horizontal component of motion imparted to the smaller and lighter particles. The rearmost partition section 164 extends substantially vertically to intercept a light fraction of fine particles traveling horizontally to a large extent. Employing the preferred construction of thin-walled collectors, the partition sections have thin upper edges which reduced to a minimum the number of particles striking the edges and possibly bounc- The resulting separation of predetermined fractions is very sharp.

The particle fractions thus separately collected flow down the inclined collecting sections 12S, 134, and 148 and succeeding sections, which converge to the adjacent

vertical discharge sections

132, 138, 156 and succeeding sections, at the front of each wind chamber. In this connection, the above-described angle of inclination for the collecting sections is preferred in the classification of sand particles, so that the particles tend to roll rather than slide as at greater angles. When the particles roll, the larger particles tend to come to the top, thereby moving them towards the front at the time they are dropped. The fractions drop from the discharge channels in closely adjacent streams or curtains into the next wind chamber. Initially, the fractions fall in individual or discrete streams, arranged successively in the same order in which they were collected.

As with chute 90, the particle streams that roll down the rearwardly extending collecting sections have their velocities reduced almost to zero as they enter the discharge channels. It is important that the particles falling through the wind chambers start with approximately equal and low velocities.

It will be seen on reference to FIG. 3 that the particles initially dropped from the feed channel 90 fall in a somewhat different pattern in the rst wind chamber 68 than the pattern of the fall in the succeeding wind chambers when dropped from the intermediate collectors 92-96, owing to the different arrangements of the respective discharge channels. Also, the initial material is a random mixture of particles, Whereas the material dropped from the collectors has been classified according to particle size or density, decreasing in the same order as classified by the air stream. Consequently, the first stage classification is less exact. Employing otherwise substantially the same conditions of air flow, dimensions and spacings in the succeeding

wind chambers

70, 72 and 74, increasingly concentrated or sharp fractions are separated and collected in the successive stages. The finer particles are moved to the rear and the larger particles to the front, until they are properly classified.

Referring to FIGS. 5, 6 and 8, the fina-l collector a-S- sembly 98 includes a row of collectors 100zz-114a, which correspond to the respective preceding collectors 1110-114 and collect corresponding fractions following pneumatic classication in the last stage. The final collectors are constructed as sheet metal panels havin-g side flanges, similarly to the intermediate collectors. Inasmuch as no further classification takes place following the collection, the final collectors are constructed only with upper partition sections for subdividing the falling stream of particles, and lower discharge sections leading into respective collecting bins 1Mb-114]). Thus, the first co-llector 100a has two upwardly extending partition sections 13661 and 136a which form a trough opening disposed beneath the discharge channel 139 of the first collector 100 in the preceding assembiy 96. The second collector 19211 has an upwardly extending forwardly inclined partition section 152a, and so on to the last collector 114a in the row, which lhas a substantially vertical partition 16451. The several partition sections correspond respectively with the

sections

136, 136, 152, and 164 of the intermediate collectors. The first collector 166e is also subdivided into three chutes by two inner spaced

vertical baffles

167 and 168 to force the air to ow over the top of first collector 16th:. The discharge sections of the final collectors, indicated for several of them at 132a, 138a, 1565i, and 162a, are disposed at various angles with respect to the integral partition sections to conduct the collected particles to the bins. The discharge sections, and the lower ends of the collector baffles 167 and 168, Vare received in slots 170 of vertically slotted -mounting bars 172. The bars are secured to the

opposite side walls

52 and 54 by bolts 174.

The rate of air flow in each wind chamber 68-74 preferably is the same as that in every other chamber. The

intermediate collector assemblies

92, 94, and 96 have the same construction, and they and the final collector assembly 98 are arranged to collect corresponding fractions. The vertical spacing between the feed chute 90 and the first assembly 92, the spacings between the several intermediate assemblies 92-96, and the spacing between the third intermediate assembly 96 and the final assembly 98 are the same, preferably providing a drop to the first collector in each row of about nine and one-half inches in processing sands. The horizontal distance from the front of the feed chute 9i) to the back of the classifying compartment 66 is about 14 inches in the illustra-tive embodiment. As previously noted, the width of the classifying compartment is about l2 inches.

As seen most clearly in FIG. 7, the second and

third collector assemblies

94 and 96 are progressively stepped back a short distance in the downstream direction. In the illustrative embodiment, the respective center lines of the first collectors 100 of the

assemblies

92, 94, and 96 are successively displaced about 1%; inch to the rear of the classifying compartment 69. The final assembly 98 is similarly displaced rearwardly relative to the intermediate assembly 96 thereabove, as seen in FIG. 5. This construction effects a countercurrent displacement of the particles falling from one assembly of collectors relative to the collectors in the succeeding assembly, whereby larger particles which in some manner have advanced too far in the downstream direction, are moved forwardly relative to the collectors.

Thus, with the classifier cell in operation, a random mixture of particles drops from the feed chute 9), and particles are collected in fractions in the first assembly 92. The initial classification is less exact, and some particles will be collected further downstream than intended, while others will be upstream of their proper collectors, In the second stage classification, the once classified particles are dropped from the first assembly approximately in their proper classification order, so that the pneumatic reclassification effects a more precise diS- tribution of the particles in the combined falling stream. T-hose particles which initially were too far upstream are moved downstream. Those particles which initially were properly classified remain in their proper subdivisons or strata of the stream. The displacement of the second assembly 94 of collectors permits particles which were too far downstream to, in effect, move upstream towards the front of the assembly, where the larger particles are collected. Thus, for instance, a 50 mesh particle inadvertently entering the mesh fraction can move one collector at a time forward in each subsequent drop and end up in its proper location, by moving from 140 to 100 to 7() to 50 mesh fractions.

The above described rolling of the particles on the col lector sections 134, 148 and successive sections, which causes the larger particles to move to the top and dropped at the front of each small stream, cooperates in establish ing the proper order of particles. Further reclassification in the same manner takes place in the third and fourth stages, with the result that very sharp and concentrated fractions are collected in the final collector assembly 98.

The final collectors 100a-114a register with the respective collecting bins 1Mb-114!) arranged in a row thereunder (see FIGS. 3 and 6). An additional bin 176 is provided at the rear end of the row of bins, and a back panel 178 extends upwardly therefrom, beneath the separator 61. The last collector 11451 is spaced forwardly from the separator, so that material drops behind the collector, as subsequently described. Such material is channeled by the last collector and by the back panel 178, functioning as an additional collector, into the terminal bin 176. As seen in FIGS. 1 and 4, the collecting bins are constructed as ducts havinfy sloping bottoms, in-

dicated at 179. These conduct the separated particles to chutes which extend to a bank of silos 10(3c-114c and 176e, and respectively discharge the collected fractions thereinto. The ducts are beneath the bank of classifier cells 34, yand each collects the Same fraction from all of` the cells for delivery to storage.

Referring to FIGS. 3 and 8, a plurality of spaced parallel flat sheet metal baille plates 180 are mounted in lthe baffle compartment 62, to provide the particle separator 61 on the downstream side of the classifying compartment 60. The separator performs the dual functions of directing the flow of air upwardly through the classifying compartment, and removing entraned particle fines and returning them to the classifying compartment for collection. The baffles extend from one side wall 52 to the opposite side wall 54, which constitute the lateral sides of the baffle compartment, and from the front side of the compartment adjoining the lclassifying -compartment to the back side adjoining the exhaust duct 64. As seen in FIG. 3, the baffles are inclined upwardly from the front side to the rear -side of the baffle compartment at a preferred angle from the horizontal of about 40. As seen in FIG. 8, the bafiies are also inclined upwardly from one side wall S2 to the other side Wall 54 at an angle of about 45. At the respective angles of 40 and 45, the diagonal angle of slope of the baffles from front to rear of the compartment is about 65. The preferred material of construction for the baffles is thin-walled sheet metal such as galvanized metal, as employed in the construction of the collectors.

The bales 180 direct the flow of air uniformly through the several wind chambers 68-74, in an upwardly inclined direction. The baffles also serve to remove entrained fine particles from the air streams, and return them to the classifying compartment 60. The bales are closely spaced apart, about one-half inch in the illustrative embodiment, to provide smooth non-turbulent air flow `and a short drop for the particles. The construction insures that the particles fall onto the baffles rather than being carried away. The particles flow downwardly on the baffles towards the front side of the baffle compartment, due to the front to rear inclination, and also towards one side wall 52, due to the side-tO-side inclination.

With the baflles at the above-described angles, the particles roll rather than slide on the baffles, minimizing abrasive wear of the bailles.

Since the baille spacing is about one-half inch, with an air velocity -of 4 f.p.s., even a 270 mesh parti-cle will fall out of the air as it rises between the baflles. Since the air velocity at the surface of the baffles is approximately zero, these small particles are not restrained from trolling back down the baflles.

The particles thus tend to collect on the baflles at the front of the baffle compartment 62 adjacent to the side wall 52, from where they fall in a stream adjacent to the side wall. The stream of particles falls through the successive wind chambers 68-74, without being particularly affected by the air currents, falling through the spaces between the collector `assemblies and the baffles of the separator 61, as represented at 166 for the final assembly 96. The stream passes behind the last collector 114a in the final assembly, and between it and the back panel 178, and is collected in the terminal bin 176.

The construction of the particle separator 61, particularly the arrangement of the baffles 180, eliminates to a large extent the problem of cascading. With baffles which are inclined only in one direction, from front to rear, the particles falling from each baille `are blown into the space beneath the baille, fall on the succeeding baille, flow 'over its front edge, and so on down the bank of baffles. At each baille some loss in the range of 5% occurs by fines being blown through the baffles and exhausted, and if cascading were allowed the -compounded loss would be excessive. The abrasive action of cascading particles would unduly wear the baflles, and as explained the efficiency of operation would be reduced. Employing the separator of this invention, the particles fall in a relatively quiet zone, adjacent one side wall, and -they also fall in a stream of collected particles, so that Cascading is obviated.

The particle separator 61 recovers a further fraction of very fine particles, down to 20 microns in particle size, and the fraction is collected and stored separately. Previously, it was often very difficult and expensive to separate such a fraction, so that its cost was prohibitive. In addition, the particle separator removes virtually all of the nes from the air streams, so that loss is negligible and the dust problem is alleviated.

Air flows from the separator 61 into the exhaust duct 64, as indicated by the arrows in FIG. 3. The rates of flow through the wind chambers 68-74 yand through the separator communicating therewith are controlled by three

dampers

182, 184, and 186. The dampers constitute plate members pivotally mounted on the separator to divide it into four superposed sections of equal size, vand the dampers extend upwardly of the separator. The tops of lthe lower dampers extend a short distance above the bottom of the damper disposed above it to force the air upwardly and produce an even air flow. The dampers, if adjustment is desired, are operated by adjusting knob and rod assemblies 188 pivotally connected thereto and accessible from the outer side of the back wall 56.

In the preferred manner of operation, each damper is adjusted to a position extending upwardly and outwardly from the separator 61, to produceequal flow rates in the wind chambers, but the dampers can of course be fixed. Thus, the upper first damper 182 is adjustedso that its upper end is located `at about one-fourth of the distance between the separator and the back wall 56. The upper end `of the second damper 184 is located at about one-half of the distance, and the upper end of the third damper 186 is located at about three-fourths of the distance. This distance, the depth of the exhaust duct 64, is about 12 inches in the preferred embodiment, providing a one foot square cross-section for the duct. It will be observed that residual particles which may escape with the air streams and settle out in the exhaust duct will be returned to the separator by gravity, flowing downwardly and to the front on the dampers 182-186 and the bottom wall 58.

In the illustrative embodiment, air is moved through each classifier cell 34 by a blower or fan assembly 190 mounted yadjacent to and partly within the upper end of the exhaust duct 64. The wind chambers, separator, and remainder of the exhaust duct are located on the suction side of the blower. Alternatively, other means for passing air `through the cell may be employed, and the cell may be either under pressure or under suction.

The blower assembly 19) includes a motor 192 mounted on an external panel 194 on the baille compartment. The motor is drivingly coupled with a hub shaft 197, by means of a motor pulley 198, a V-belt 200 and a hub shaft pulley 202. The hub shaft is centrally mounted in a circular tubular section 196 forming the top of the exhaust duct 64, as seen also in FIGS. 9 and 10. The lower square section of the exhaust duct converges to the circular upper section, as illustrated by the converging corner parts 204 in FIG. 9. A grating 206 is mounted in the tube section, and it supports a bearing 208 in which the hub shaft 196 is mounted.

A propeller having blades ZlGa-d is mounted on the hub shaft 197 in the tube section 196. The blades of the propeller are disposed closely adjacent to lthe exhaust tube. With the propeller, the air is exhausted from the duct 64 by a -lifting action which produces smooth nonturbulent flow in the duct and correspondingly smooth flow through -the separator 61 and the classifying compartment 60. The air leaving the exhaust duct may be conveyed by a suitable conduit, not shown, to a conventional -dust collector as schematically represented at 212 in FIG. 1, and a still further fraction of particles, which is quite small, however, collected in this manner. Alternatively, the classifier cell may be exhausted to the atmosphere. I i In operating the classifier 30, one or more cells 34 is placed in operation, depending upon the quantity of material being supplied to the hopper 32. Initially, the first cell is placed in operation, and as material overflows the partitions 4t) (FIG. 2) successive cells may be placed in operation. This may be accomplished automatically, semi-automatically or manually. With the arrangement shown, the entire feed goes to the first cell until its supply bin is filled and the feed will automatically feed over to the second and then successive cells. If at any time there is a shortage in feed, the cells will empty in reverse order. Thus, the only cell having any variation in feed is the rst cell and since the other cells are either fully operative or inoperative, uniformity of output is achieved independently of feed irregularities. Hence, the individual cell loads are maintained relatively constant while providing for variations in the total load. Only the necessary cell capacity is utilized, and consistent uniform classification is obtained.

The results of production runs made with a number of lots of material in a classifier cell 34 as above described are set forth below in tabular form.. The density of the material in each lot was substantially uniform, so that classification was according to particle size. The runs include three made with mine run granular sandstone of three different average particle sizes, a run made with bank sand, and a run made with lake sand. In each case, all particles passed through a Number 20 sieve. The preferred conditions and cell dimensions se-t forth above were employed, with the parts being as shown approximately to scale in FIGS. 5 to 8. The intermediate collector assemblies 92-96 were arranged with their collecting sections such as 128, 134 and 148 at an angle of about 37 from the horizontal. The baffles 180 were at about 40 from the horizontal from front to rear, and about 45 from the horizontal from side to side. The fractions identified as numbers l through 9 were collected respectively in bins ltlflb through 114b and 176.

MINE RUN SANDSTONE-40 AVERAGE SIEVE SIZE, PERCENT OF FRAC- TION ON SIEVE Fraction Percent of Product 3.9 16.9 25.3 12.4 6.4

65 AVERAGE SIEVE SIZE, PERCENT OF FRACTION ON i-. i-. "552i 'i' '55.5' Fraction Percent of Product 2.0 7.0 9.2 18 .6 22.4 28.2 9.6

BANK SAND-BOAVE RAGE SIEVE SIZE, PERCENT OF FRACTION ON SIEVE On Sieve No. Feed #1 #2 #3 #4 #5 #6 #7 #8 #9 .4 34.4 8.2 .4 1.6 46.0 40.6 10.0 .6 6 .6 16 .4 46 .2 67.2 25.2 2.2 .2 19.0 2.0 3 .6 19 .4 46 .6 31.8 18.0 2.8 .2 34.4 .6 .6 2.4 19 .2 47.8 50.0 40.4 17 .8 1 .6 28.2 .2 4 .4 7.6 16.6 28.4 47.2 56 .8 27.8 8.4 .2 2 .2 .8 1.6 3.2 9.4 22.8 57 .8 A l .0 2 .2 11 .4 .2 1 .2 80.0 29 .1 35 .2 41.7 55 .7 69 .1 77.0 90.0 105 .7 136 .2 Fraction Percent of Product 8 2.6 4.2 10.2 22.4 28.0 19.0 6.6 4.4

LAKE SAND- 47 AVE RAGE SIEVE SIZE, PERCENT OF FRACIION ON SIEVE AvereD Fraction Percent of Product In the runs tabulated above, nine concentrated fractions 65 were Vcollected in each case. It is to be observed that each fraction is highly concentrated with respect to either two or three sieve sizes. The average particle sizes collected in the respective fractions is remarkably consistent for diiferent 'mine runs having diierent average particle sizes, 7

and this consistency extends even to different tylpes of sand. The invention enables direct production from the quarry sand of highly concentrated fractions meeting eX- actin-g specications, and which are readily blended to meet particular demands. Production is regulated without 75 change in classiiication lby employing a thank `of cells in parallel. The above sands are especially useful in foundries, for ymaking precision casting molds for the production of special glasses, and they nd other valuable applications.

0 It should be appreciated that in order to have good can be obtained economically even on a large volume basis.

The resistance of a falling stream of particles to penetration by the air stream -varies with the density of the particle stream. By widening the particle stream in the second and subsequent wind chambers, much easier air penetration is achieved resulting in better classification.

Also, I have found that by using several short drops of the particles, lreturning the particles to about zero velocity each time before it is again dropped, this results in the p-articles 'being suspended in and acted upon by the air currents for a longer perio-d of time than a single lon-ger drop with resultant better classification. Also, if large air chambers are used, turbulence is extremely hard to control, and longer drops will not enable the recovery of many of the fine classifications or enable such sharp classification recovery.

The flow of air must be sufficient t-o penetrate and effectively act upon the curtain of fallin-g material to give horizontal velocity to the particles in proportion t-o their size. The falling material will, of course, tend to deflect ythe air stream downward, but it will be noted that the air stream is caused to rise as it passes through the wind chambers and offset any such effect.

With the arrangement shown any misclassification of a particle in the first or second or even third stage can be and is corrected in the subsequent or last stages.

The invention thus provides particle classifying apparatus and a method of classifying particles which accomplishes important objects. Continuous lar-ge scale production of highly classified fractions is achieved, with very small capital investment and space requirements. Personnel requirements are minimized, there being very little operating, cleaning and maintenance requirements. Manufacturing costs are low, and desirable particle fractions are .much less costly than heretofore. Because of the low velocities involved, wear is at a minimum an-d because of the absence of vibration and excessive wear, equipment life is lon-g.

While preferred embodiments of the apparatus and the method of the invention have been described and illustrated, it will be app-arent that various changes and modifications may be made therein within the spirit and scope of the invention. It is intended that such changes and modifications be included within the scope of the appended claims.

I claim:

1. In a pneumatic particle classifier, a classifier cell comprising: superposed wind chambers, a particle separator adjacent to said wind chambers, and an exhaust air duct adjacent to said separator, said wind chambers including a first chamber and a plurality of chambers therebelow; exhaust blower means communicating with said air duct for passing air streams in parallel respectively through said wind chambers and then through said separator; damper means in said air duct for regulating the flow of air through said wind chambers, a feed chute for dropping a stream of particles in free fall in said first wind chamber for pneumatic classificati-on -of the particles therein; a row of collectors in said first wind chamber for respectively collecting individual fractions of the classified particles, said collectors each comprising a sheet material structure including a collecting section inclined upwardly in the downstream direction for collecting a fraction of the falling particles, a partition section extending upwardly therefrom, .and a discharge section extending downwardly therefrom f-or dropping the collected particle fraction in free fall in the wind chamber therebelow, said discharge sections being disposed adjacent to each other and said collecting sections converging thereto for -dropp-in-g said collected fractions together in a row of adjacent streams in the order in which collected for a second pneumatic classi'- fication of the particles; additional rows of said collectors respectively disposed in said plurality of wind chambers for collecting fractions of the particles classified therein and ttor dropping the @Qllisd fractions in wind chambers therebelow for further pneumatic classifications of the particles in corresponding manner; a row of final collectors in a bottom one of sai-d wind chambers for respectively collecting corresponding individual frac-tions of the classified particles, said -final collectors each comprising a sheet material partition; and a 'bank of superposed spaced parallel flat baffles in said separator for removing entrained particles from the air streams leaving the chambers, said baffles being inclined upwardly in the downstream direction and also upwardly in the cross-stream direction, whereby removed particles flow downwardly on said baffles towards one lateral side of said bank and towards said wind chambers, and the removed particles Ifall from said baffles through said wind chambers in a stream adjacent said one side of said bank and are collected as a fraction at said bottom wind chamber.

2. A classifier as defined in claim 1 wherein the inclination of said collecting sections is about 34438" from the horizontal, and the inclination of said baffles in each of said directions is about 40L45 from the horizontal.

3. A classifier as defined in claim 1 and including a plurality of said cells in side-by-side relation, a hopper for supplying material to sai-d cells for classification, compartmeuts in sai-d hopper corresponding in number to said cells, said hopper being adapted for overflowing material from one compartment to the next as the hopper is filled, and a delivery chute for discharging each hopper compartment to the feed chute of one of said cells.

4. In combination with pneumatic particle classifying apparatus including a win-d chamber, means for producing an air stream of predetermined velocity, and particle collecting means in said chamber, a particle separator for removing entrained particles from the air stream leaving the chamber, said separator comp-rising a baille compartment adjacent to said wind chamber, and a bank of superposed spaced parallel flat baffles in said compartment, said bales -being inclined upwardly in the downstream vdirection and also upwardly in the cross-stream direction, whereby removed particles flow downwardly on said bafiles towards one lateral side of said bank and towards said wind chamber, an-d the removed particles fall from said bafiles in said wind chamber in a stream adjacent said one side of said bank. I

5. In a particle separator having means for producing an air stream, a baille compartment having a pair of spaced opposed lateral side walls and front and back sides, and a bank of superposed spaced parallel flat baffles in said compartment, said baffles-being inclined upwardly from the front side to the rear side of said compartment and also upwardly from one side wall to the other, said air producing means directing the air stream from the front side to the rear side of said compartment, and feed means for introducing particles upstream from said baffle compartment whereby when a particle-bearing stream of air is conducted through said bank from front to rear, particles are deposited 'on said batiles and flow downwardly towards said one side wall and towards sai-d front side of said compartment, and the particles Ifall from the front edges of said baffles in a stream adjacent said one side wall. e

6. A particle separator as defined in claim 5 wherein the inclination of said -bafiles in each of said directions is about 40-45 from the horizontal.

7. In a pneumatic classifier, a plurality of superposed wind chambers disposed in spaced relationship, common means for passing air-streams in parallel, respectively through said wind chambers, a hopper lmeans for containing a plurailty of particles of diverse size and having discharge means for dropping a stream of diverse particles in free fall directly and generally transversely through the air-stream of the first `wind chamber for initial pneumatic classification of the diverse particles therein in a plurality of fractions in the direction of the air-streams, a yfirst row of collect-ors in the first wind chamber spaced from the discharge Imeans of said hopper for separately collecting individual fractions of the classified particles, sai-d collectors, each including a collecting and discharge means for collecting an individual fraction of the falling particles in the direction of air fiow to return their velocities to substantially zero and to drop each of the collected particle fractions in a row of adjacent streams of particles in the order in which collected in 'generally free transverse fall through the air-stream of the wind chamber next adjacent the first wind chamber for a partial reclassication in a second row of .particle collectors spaced from the tirs-t row of particle collectors, collecting means in the second particle collectors being disposed adjacent to each other for receipt of partially reclassified streams of particles from said first row of collectors and means for removing classified particles from said second collector.

8. A classifier as defined in claim 7 and including a bank of superposed spaced inclined baies on the downstream side of said Wind chambers for directing the flow of air through the `chambers an-d for removing entrained particles from the air streams leaving the chambers.

9. A classifier as defined in claim 7 wherein at least one of said rows of collectors is displaced in the downstream direction relative to the -ro'w thereabove to effect countercurrent displacement of `the falli-ng particles rrelative to the collectors in said Ione row.

10. A classifier as defined in claim 7 and including a bank of superposed spaced inclined bafiies on lthe downstream side of said wind chambers for directing the flow of air through the chambers and for removing entrained particles from the air streams leaving the chambers, and damper means for regulating the flow of air through said Wind chambers.

11. A plurality of pneumatic classifiers, according to claim 7, including particle feed means for supplying each of the hoppers of the classifiers successively as each classifier becomes fully supplied.

12. A method of classifying non-uniform particles into a plurality of fractions, comprising collecting a mass of particles in a hopper, releasing a stream of particles from the hopper for lgravitation a predetermined distance therefrom directly through an air-stream directed generally transversely With respect to the descending particle stream, the transversely directed air-stream serving to effect a pneumatic first classification of the `free falling particles into a plurality of fractions in the direction of the airstream, separately collecting descending individua-l fractions in a first collecting zone space-d a predetermined distance from the hopper, returning their velocities to substantially zero dropping said collected particle fractions in free fall together in a row of adjacent streams from the first collecting zone in the order in which collected, passing a stream of air transversely through said adjacent particle streams successively in the same relative direction as said first-named air stream to effect a pneumatic reclassification of the first particle fractions and separately collecting individual fractions of the partially reclassified particles in a second collecting zone, spaced from the rst collecting zone.

.13. A method as defined in claim 12 wherein the flow rates of said air streams are about equal.

14. The method of claim 12 including the step of rolling the individual fractions of classified particles down a plane, and substantially stopping the particles before dropping them the second time.

15. The method of claim 12 wherein non-uniform sand particles are classified into a plurality of fractions su'bstantially all of which pass through a 20 mesh sieve.

16. The method of claim 12, wherein the second collecting zone includes a plurality of dischange -outlets disposed in adjacent relationship and the collected fractions are dropped therefrom in free fall together in a row of adjacent streams in the order in which collected through a stream of transversely direct air and into a third collecting zone from which they are dischanged in like manner through additional air-streams and collecting zones until `finally classified.

17. A Imethod as defined in claim 16 wherein said particles are mine nun sand particles substantially all of which pass through a 20-mesh sieve, and said air streams fiow at a rate of about 250 feet per minute.

References Cited bythe Examiner UNITED STATES PATENTS 2,828,011 3/ 195 8 Whithy 209-20 3,044,619 7/ 1962 Knolle 209-33 3,109,807 1 l/ 1963 Sauermann 209-136 3,1 80,492 4/ 1965 Vandenhoeck 209-133 'FRANK W. LUTTER, Primary Examiner.

Claims

7. IN A PNEUMATIC CLASSIFIER, A PLURALITY OF SUPERPOSED WIND CHAMBERS DISPOSED IN SPACED RELATIONSHIP, COMMON MEANS FOR PASSING AIR-STREAMS IN PARALLEL, RESPECTIVELY THROUGH SAID WIND CHAMBERS, A HOPPER MEANS FOR CONTAINING A PLURALITY OF PARTICLES OF DIVERSE SIZE AND HAVING DISCHARGE MEANS FOR DROPPING A STREAM OF DIVERSE PARTICLES IN FREE FALL DIRECTLY AND GENERALLY TRANSVERSELY THROUGH THE AIR-STREAM OF THE FIRST WIND CHAMBER FOR INITIAL PNEUMATIC CLASSIFICATION OF THE DIVERSE PARTICLES THEREIN IN A PLURALITY OF FRACTIONS IN THE DIRECTION OF THE AIR-STREAMS, A FIRST ROW OF COLLECTORS IN THE FIRST WIND CHAMBER SPACED FROM THE DISCHARGE MEANS OF SAID HOPPER FOR SEPARATELY COLLECTING INDIVIDUAL FRACTIONS OF THE CLASSIFIED PARTICLES, SAID COLLECTORS, EACH INCLUDING A COLLECTING AND DISCHARGE MEANS FOR COLLECTING AN INDIVIDUAL FRACTION OF THE FALLING PARTICLES IN THE DIRECTION OF AIR FLOW TO RETURN THEIR VELOCITIES TO SUBSTANTIALLY ZERO AND TO DROP EACH OF THE COLLECTED PARTICLE FRACTIONS IN A ROW OF ADJACENT STREAMS OF PARTICLES IN THE ORDER IN WHICH COLLECTED IN GENERALLY FREE TRANSVERSE FALL THROUGH THE AIR-STREAM OF THE WIND CHAMBER NEXT ADJACENT THE FIRST WIND CHAMBER FOR A PARTIAL RECLASSIFICATION IN A SECOND ROW OF PARTICLE COLLECTORS SPACEE FROM THE FIRST ROW OF PARTICLE COLLECTORS, COLLECTING MEANS IN THE SECOND PARTICLE COLLECTORS BEING DISPOSED ADJACENT TO EACH OTHER FOR RECEIPT OF PARTIALLY RECLASSIFIED STREAMS OF PARTICLES FROM SAID FIRST ROW OF COLLECTORS AND MEANS FOR REMOVING CLASSIFIED PARTICLES FROM SAID SECOND COLLECTOR.