US2969191A

US2969191A - Progressive reducing and classifying means

Info

Publication number: US2969191A
Application number: US658455A
Authority: US
Inventors: William H Lykken; Lykken Frances
Original assignee: Microcyclomat Co
Current assignee: Microcyclomat Co
Priority date: 1957-05-10
Filing date: 1957-05-10
Publication date: 1961-01-24
Anticipated expiration: 1978-01-24

Description

-Jam. 24, 1961 H. G. LYKKEN ETAL 2,959,191

PROGRESSIVE REDUCING AND CLASSIFYING MEANS Filed May 10, 1957 INVENTORJ fiE/vR Y 6. L YKKEN BY l/WLL/nM/iLrK/(E/v ATTORNEY;

2 Sheets-Sheet 1 Jan. 24, 1961 H. G. LYKKEN ETAL 2,969,191

PROGRESSIVE REDUCING AND CLASSIFYING MEANS Filed May 10, 1957 2 Sheets-Sheet 2 INVENTORS HENRY G. L YKKEN BY W/LLmMh. L YKKEN 14TToR'NEYf;

United States Patent" signors to The Microcyclomat Co., Minneapolis, Minn., a corporation of Delaware Filed May 10, 1957, Ser. No. 658,455 11 Claims. (Cl. 241-75) This invention relates to the progressive fluid energy reduction and classification of dry solid material in the subsieve particle size range. vention relates to an integrated mill and classifier system including an open rotor fiuid energy mill having multiple closed end rotor units coupled with a peripheral inlet centripetal flow and axial outlet classifier rotor.

Reduction and classification in the subsieve range (that is below about 35 microns particle size) are as yet in their infancy. It is well established, however, that standard practices of reduction and classification to a given sieve dimension are totally inadequate in the subsieve field. It is recognized that there is a marked dividing line between the art of crushing material to a given subsieve particle size and the art of grinding to'a given sieve dimension. The differences become self-evident by the special requirements demanded by the art of subsieve dimension grinding and classifying as set out in this specifi cation.

It is the principal object of this invention to provide'a method and means for the progressive fluid energy reduction and classification of dry solid material in the subsieve particle size range. i

It is a further object of this inventionto provide an integrated mill and classifier system including an open rotor fluid energy mill equipped with multiple closed end rotor units coupled to a peripheral inlet centripetal flow and axial outlet classification rotor. v

Other objects of the invention will become apparent as the description proceeds. a

To the accomplishment of the foregoing and releated ends, this invention then comprises the features hereinafter fully described and particularly pointed out in the claims, the following description'setting forth in detail certain illustrative embodiments of the inventiomthese being indicative, however, of but a few of the various ways in which the principles of the invention may be employed.

The invention is illustrated by the drawings in which line 2-2 of Figure l and in the direction of the arrows.-

The reducing portion of the integrated'mill and classi More particularly, this in-' fier system comprises a lower horizontal axis peripheralf inlet and peripheral discharge closed end rotor indicated generally at 10 made up of an assembly of a plurality of closed end rotor units indicated generally at 11. This rotor has a high axial vacuum proportional to its rotative velocity. The rotor is contained in a reducing chamber enclosed by a housing indicated generally at .12.

Housing 12 is held between two

end plates

13 and 14.

which extend to a base or floor and are afiixed by floor flanges or the like. i 1

A suitable-bearing structure adequately sized to carry 2 i the reducing rotor is mounted at each end of the housing outside of the end plates. .Upon these bearings there is. mounted a shaft 15 which carries the reducing rotor., Shaft 15 is driven by any siutable drive means, not shown.

The shaft is enlarged and reinforced through part of its length by means of a tube 16 supported by heavy'annular rings 17 keyed to the shaft. The shaft tube and heavy annular rings form a rigid unitary structure upon which the reducing rotor units are mounted.

The closed end rotor units 11 are comprised of a slotted.

annular disk 18 perpendicular to the shaft and carrying a plurality of fiat radial blades 19 in the slots around its periphery. The radial blades 19 are positioned per: pendicular to the slotted disk 18 and each pair of rotor, units 11 is separated by an annular disk 20 having a;

diameter reaching to the periphery of .the blades 19. A

series of rotor units is mounted on the rotor between a pair of rotor end disks 21 mounted on each end of tube 16 and secured to the annular rings 17 by means of bolts or equivalent fastening means. The disks Band 20 are held spaced apart by spacers 23. Eachclosed end rotor reducing unit 11 functions independently. The reducing rotor 10 may be made up of any desired number of closed end rotor units 11 depending upon desired capacity;

and other requirements of the material to be reduced and classified.

The reducing rotor 10 develops a relatively. high axial vacuum proportional to its rotative velocity. The axial vacuum is due to a high centrifugal discharge on the forward or leading face of each blade 19 and to the velocity of recession at the back of each blade when the rotor is operated at high rotative speed. This pro- It has been known in so-called jet mills to use high' intensity air flows for grinding. In such mills the release" of energy so far as any individual particle is concerned is a single instantaneous impulse. In contrast, in the reducing means of this invention there is sustained high energy level and continuous impulse action. All reducing action in the mill of this invention is a function ofthe rotor and its peripheral speed. As the larger particles continuously enter and discharge through the periphery of the rotor they are reduced by bursting impact until reduced small enough for final reduction by fiuid energy'f vortex attrition. This is a primary essential in subsieve;

grinding. i

The reducing rotor 10 is mounted in the housing 12 with a running clearance between about 1 and 3 inches and preferably between about 1 /2 to 2 inches running clear-j ance between the periphery of the rotor and the housing wall. The mill load is maintained in a highly fiuidal condition with about one part solids to ten parts an by l This allows each individual particle individual volume. freedom of motion and provides maximum intra-particle velocities.

In the operation of this mill there is no heat generating mass-material action on mass-material nor on the mill housing wall. The more fluidal the mill load the more intense is the mill action. Since this mill produces greater reduction with less heating it therefore requires less than half of the usual power requirements.

The mill reducing rotor acts as a peripheral inlet and. discharge fan which serves to continuously circulate the fluidal mill load about itself in a continuous recirculating flow while at the same time continuously circulating a percentage of scavenging airand discharging the 'fiiies" as reduced from the top of the rotor with every revolution.

The reducing rotor housing 12 is comprised of a generally quarter-cylindrical plate 24 around the lower for ward quadrantof the rotor and a generally quarterc'ylindrical plate 25 around the upper rearward quadrant of the rotor. The lower rearward quadrant of the rotor between

plates

24 and 25 optionally faces upon a troughlike grit trap and coarse discharge indicated generally at 26 in Figure l of the drawings, although for many rnate'rials the grit trap may be omitted and the housing wall 12 then is in the form of a cylinder surrounding. about three-fourths of the periphery of rotor 10.

The mill feed enters the reducing rotor chamber tangentially downwardly at an inlet 27 below the axis of the rotor 10 along the full length of the rotor in a regulated amount from an elongated feed hopper 28. To maintain a desired bulk or weight of material in the circulating riiill load the feed is preferably regulated by an interlock between the motor operating a metering closure 29 of. the feeder and the reducing rotor motor so as to regulate the feeder motor to maintain a uniform mill load. The mill load can thus be set at any desired fluidity or ma terial to air ratio in the circulating flow and as previously pointed out this is desirably about one part solids to ten parts of air by volume. The motor interlock per se forms no part of this invention. Conventional means are available commercially for accomplishing the desired interrelationship and any such unit may be used.

An auxiliary air inlet is provided in air duct 30 for admitting air with the material feed when necessary or desirable. The air inlet 39 is regulated by means of a slide damper 31. Although shown in Figure 1 as being open so as to admit a small amount of air it should be pointed out that in most instances no air need be admitted from this source to maintain the desired fluidal condition of the mill load. The reducing rotor housing 12 is completed by a front wall 32 which defines a portion of the feed hopper and the feed inlet 27 and faces upon the open upper forward quadrant of the rotor 10 to form aduot to the classifying chamber.

The optional grit trap and oversize discharge 26 is useful when the mill is used for differential grinding of materials such as talc, kaolin, earth pigments, etc., contaminated with grit, sand, etc. The grit trap includes a metering closure 33 preferably driven by a motor coupled to the drive motor for the rotor 10 or to the drive motor of a the feed hopper metering closure. 29 so as to discharge some fixed percentage of the total mill load as determined by the material itself and the amount of grit, tramp metal and the like which the material may contain. The discharge'hopper 26, of course, becomes filled with material but this material is maintained in a highly fluid-a1 state by means of high pressure air introduced through an air. duct 34 at the bottom of the rotor housing. The airv entering from duct 34 to the bottom of the reducing chamber is maintained in a highly dispersed state by passing it, for example, through a felt pad 35 held in place by a screen 36 or similar foraminous member. Because of the highly fluidal state of the material in the discharge hopper 26 any dense materials such as grit, tramp metal, oversize particles and the like readily gravitate to the bottom of the hopper and are dispelled by the metering closure 33.

An optional extension plate 37, curved to maintain a. uniform spacing from the periphery of the rotor 10, extends forward from the quarter-cylindrical housing plate 25 over the open upper forward quadrant of the rotor. The function of the extension plate is to retain the material in the reducing chamber for a longer time before discharge to the classifier.

The integrated classifier means is located above the mill rotor and includes a peripheral inlet centripetal flow and axial outlet rotor indicated generally at enclosed in a generally cylindrical housing 41 extending around about two-thirds of' the periphery of the rotor. The classifier housing 41 includes a front forward wall 43 which is, in effect, an extension of the front wall 32 of the reducing rotor housing 12. The classifier housing 41 desirably includes a viewing window 44 in the wall 43. An air inlet 45 is provided at the top of the classifier housing. Air inlet 45 is in communication with an air duct 46. Admission of air through inlet 45 is regulated and controlled by means of a slide damper 4'7. Inlet 65 is the principal source of air for classification and a large volume of air is introduced to maintain the classifier load in a more highly fluid and dispersed state. The material to be classified is preferably present in amounts from about 0.05 to 0.1 percent by volume.

The classifier housing 41 is supported between two

end plates

48 and 49. Spaced apart from the classifying chamber housing 41 is a fan housing 50 including a scroll wall 51 held between an inner end wall 52 and an outer end wall 53. The fan housing scroll communicates with a discharge duct 54 through which classified material is passed to an air separator and collector system, not shown.

A suitable bearing structure adequately sized to carry the classifier rotor and fan is mounted outside of classi fier housing end wall 48 and fan housing end wall 53. A shaft 55 is mounted on these hearings. The shaft may be driven by any suitable drive means. The shaft 55 is enlarged and reinforced through part of its length by a' tube 56 supported by heavy annular rings 57 and 58 keyed to the shaft. The reinforced and enlarged portion of the shaft extends through'both the classifier housing andthe fan housing and carries a classifier rotor end disk 59 secured to annular ring 57 and a fan disk 60 secured to annular ring 58.

The, classifier unit is in the form of a cage which is enclosed between the rotor end plate 59 and a secondary annular end disk 61 parallel to plate 59 and positioned just inside of housing end plate 49. The classifier rotor is subdivided into a plurality of sections by means of a plurality of annular divider rings 62. Each of the

end plates

59 and 61 and the divider rings 62 is provided at its periphery with a plurality of openings for receiving rods63 or other suitable blading which extend the entire length of the classifying zone and formithe cage of the classifying rotor. Rods 63 are parallel to each other and to the shaft 55. It will be noted in Figure 1 that only every other opening provided at the periphery of ring 62 is occupied by a rod.

Spaced inwardly from rods 63 are a plurality of other smaller openings for receiving rods or tie bolts 64 upon which a plurality of circumferential fins or classifying disks 65 are mounted to form a drum-like structure within "the classifying rotor cage. Bolts 64 extend the entire distance between'rotor end. plate 59 and. fan disk 60 and in addition to supporting the classifying disk 65 also support the secondary rotor end plate 61, the dividing disks 62 and an annular disk 66 which rotates between the classifier housing end wall 49and fan housing end wall 52.

The classifier housing end wall 419,and the fan housing end wall 52 are each provided with an enlarged annularopening to receive the cylindrical structure defined generally by the plurality of tie bolts 64. Classify ing disks 65 are held spaced apart by means of spacer washers 67 and the classifier rotor structure is-held spaced apart fromthe fan disk 60 by means of spacer tubes 68. Theannular space defined bythe outer surface of tube 56 and the inner. peripheries of the classifier disks. 65 form an axial outlet from the. classifier rotor to the fan housing. Each classifier unit between the pairs of divider disks operates independently. 'The number of clas} sifier units and length of the rotor are determinedlargely by the desired capacity of the classifier. The reducing,

n li l si y ns tcrs a e, t hc. amq ngth- ,Fan blades 69 are secured to the fan disk 60. The fan blades 69 are relatively small and function primarily to unify the air flow from the axial duct of the classifier rotor to the discharge duct since an outside source of suction is employed to draw the stream of entrained classified particles from the classifier.

The bottom of the classifier 41 includes a fiat bottom wall 70 adjacent to the top of the mill housing 12. Bottom wall 70 has an air inlet opening 71 running the length of the mill and classifier for the admission of supplemental air to the classifying chamber. The air inlets may be slotted, perforated or screened if desired. The admission of air through opening 71 is regulated and controlled by means of a slide damper 72.

For some purposes it may be desirable to withdraw a coarser fraction from the classifier and for this purpose an optional skimmer trough indicated generally at 73 may be provided adjacent to the bottom edge of the cylindrical portion of the classifier housing wall 42. A screw conveyor 74 or similar withdrawal means is provided in the bottom of the skimmer trough 73 for systematic withdrawal of the coarser fraction. The space between the bottom of the skimmer trough 73 and the bottom classifier housing wall 70 provides another supplemental sifting air inlet 75 which extends the entire length of the classifier unit. Air inlet 75 is controlled by means of a slide damper 76.

Fragmentary portions of motor mounts 77 and 78 are shown. These motor mounts are provided for the reducing rotor drive motor and classifying rotor drive motor, respectively. Depending upon the length of the classifier rotor it may be desirable to duplicate the fan and fan housing means at the opposite end of the classifying rotor in order to provide dual discharge ducts from the classifier. Suction is applied to the classifier by means of an independently driven exhaust fan.

The principle of classification calls for subjecting each and every particle of material to be classified individually while in free and individual suspension in a controlled flow of air, such as the centripetal flow into the classifier rotor, to a controlled centrifugal force engendered by rotation of the rotor and applied in the opposite direction. The drag of the air centripetally on a given particle varies as its diameter while the centrifugal efiect varies as the cube of the particle diameter. Because of this a given imbalance of two opposite forces determines precisely the particle size selection. This presupposes that each and every particle must be in individual suspension in the air. The particles must be uniformly distributed in the air and there must be ample dilution of air and ample space between the particles so that they can readily move past one another, either in or out.

The classifier of this invention is designed to separate particles down to one micron particle size and smaller. Classification of particles to one micron particle size involves (25,400) particles per cubic inch of material. However, in the apparatus and method of this invention dealing with this vast number of particles presents no insurmountable problem. In subsieve grinding there must necessarily be a large number of particles and that fact cannot be overlooked.

The material to be classified must first be thoroughly disintegrated and dispersed in air as individual particles. This necessitates thorough aeration to insure that each and every particle is enclose-d in its own individual air film and this condition must be maintained. The presence of the air film lubricates the interplay of particles and is absolutely essential in order to avoid cohesion of particles due to static or other causes.

In addition to stressing uniform distribution and ample dilution of the mass of particles in the air stream it is necessary that the volume of the material to be classified is continuously maintained in the right condition and continuously circulated in the classifier chamber. The ma- 6. terial to the classifier is continuously supplied from the mill below and the oversize is continuously returned from the classifier to the mill rotor for further reduction. It is a function of the classifier rotor to maintain the right condition of the material and its longitudinal distribution.

The peripheral spaced rods 63 of the classifier rotor act as a pre-classifier and continuously and selectively draw the wanted fine particles into the rotor and its axial pickup zone. Classification according to this invention is not a single chance hit-or-miss process. It is a progressive centripetal extraction process in which the wanted particles continuously and repeatedly come to the threshold of acceptance, then go back out repeating continuously until finally accepted and discharged through the axial outlet of the classifier rotor or rejected and returned for further reduction. In order to insure that no oversize particles can get out with the product of desired size the largest of the acceptable particles can afford to go in and out of the rotor repeatedly until it is determined with certainty that they are of proper particle size and withdrawn.

Particle size is regulated by varying the speed of rotation of the classifier rotor or the air flow or both. Air flow is preferably controlled volumetrically in the discharge duct to the independent exhaust fan to obviate variation in the flow due to possible variation in resistance in the mill, classifier or collector system.

For clear understanding of the operation of the mill and classifier system of this invention several various individual air flows and air circulations must be noted. There is first the continuous circulation of the fluidal mill load around the periphery of the reducing rotor. It should be noted that this flow is independent and would exist due to the high speed rotation of the reducing rotor even if there were no air flow into and through the system.

Secondly, there is the continuous circulation of classifiable material around the periphery of the classifier rotor. It should also be noted that this flow is likewise independent and would exist due to the high speed rotation of the classifier rotor even if there were no air flow into and through the system.

Thirdly, there is what may be designated a figure eight circulation starting at the uptake from the grinding chamber, thence up and over the classifier rotor and back down into the reducing rotor discharge, returning the oversize and in part following the circulation around the reducing rotor as scavenging air to pick up the fines from that rotor and carry them back to the classifier uptake.

Fourthly, part of the figure eight circulation shortcircuits above the reducing rotor (as indicated generally in Figure 1 by the upwardly directed arrow above plate 37) and carries with it fines returning with the oversize to avoid return of those fines to the reducing rotor. The returning oversize material is sifted, so to speak, by the air flow entering the bottom of the classifying chamber.

Fifthly, there is a large volume flow of free air entering the top of the classifying chamber which enters around and into the classifier rotor radially inwardly and then axially outwardly to the fan housing and the collector system. This last is the principal air intake to the system.

The air inlet 36 associated with the feed inlet to the reducing rotor is normally closed so that virtually no air enters with the feed. The feed material is introduced to the mill rotor in suificiently small amounts to maintain the desired gas-solid relationship. The high pressure air dispersed through the grit trap 26 at the bottom of the mill housing is primarily for maintaining the feed in the discharge trough highly fluidal and provides a small amount of scavenging air for circulation part way around the mill rotor and removal of fines from the reducing chamber. The auxiliary air which enters from the outside through the bottom of the classifying chamber is primarily for separating desired fine particles from returning oversize on its way back to the mill housing for further reduction in the reducing rotor.

In the operation of theapparatus of this'invention the material to be reduced and classified is continuously fed from-hopper 28 by means of the metering closure 29 and through the material inlet 27 along the entire length of the reducing rotor tangentially into the reducing rotor housing in an amount to establish and maintain the desired air to solid ratio, that is, about ten parts of air to each part of solids by volume as the minimum. The material entering through the material inlet 27 is drawn by the suction created by the reducing rotor which acts as a peripheral fan and is drawn into the continuously circulating air flow around the reducing rotor 10, as previously described and as described in somewhat greater detail in Lykken Patent No. 2,294,920, issued September 8, 194-2.

The material undergoes reduction as a result of intense intra-blade vortex action. The coarser and unreduced material is thrown centrifugally outwardly against the walls of the rotor housing from whence it falls into the oversize discharge 26 at the botom of the rotor housing. The material in the oversize discharge 26 is maintained in a highly fiuidal state by means of air passing into the bottom of the discharge from air duct 34. The denser, heavier oversize particles eventually gravitate to the bottom of the discharge trough and are progressively removed.

The fine particles produced as a result of the reducing action of the rotor it are immediately entrained in a rising air stream which forms part of the figure eight air circulation pattern and are drawn into the continuously circulating flow around the classifying rotor 40. The presence of tne peripheral spaced rods 63 of the classifier rotor creates an intra-blade vortex circulation which acts as a pro-classification circulation into and out of the periphery of the rotor. The finer particles circulate in a path which enters deeper into the rotor while the coarser particles circulate in a path which does not enter so deeply into the rotor. The result is a graded pattern of flows, coarser to finer, depending upon the deptn the path penetrates into the rotor.

Superimposed upon this classifying effect of the rotor 4t) is the flow of air imposed by an external exhaust fan into the top of the classifying chamber, around and into the classifying rotor, through the peripheral rods and classifying disks into the axial discharge duct and through the fan housing and discharge to a collector system. The effect of this large volume superimposed air flow is to greatly dilute the circulating classifier load and to extend and draw inwardly the intra-blade vortex flows. The stretching of the intra-blade vortex flows tends to separate the flow paths of the finest particles from the less fine, the less fine from the coarse, etc. Thus, the paths of the finest particles of desired size are drawn deeply enough into the rotor that the centripetal drag effect of the superimposed air flow exceeds the centrifugal throwout effect of the rotor and the particles of desired si'ze pass through the rotor to the axial outlet duct and thence on through the fan housing to the collector system.

' As pointed out previously, because the particles enter repeatedly into the rotor and repeatedly approach the threshold where the centrifugal throwout effect is overcome there is a wide margin of safety and if a particle of desired size is not picked off and withdrawn the first time it presents itself to the threshold of acceptance, it will eventually be withdrawn on one of its repeated return trips.

The coarsest particles are thrown out centrifugally against the classifier housing wall and return along the wall in the downward leg of the figure eight flow back to the milling area for further reduction. In the course of their passage back to the reducing zone it is possible that some finer particles may be entrained with the oversize and to insure against return of fine particles to the reducing rotor the auxiliary air from inlets 71 and 75 is drawn through the returning stream of oversize and as a result a further separation of fines from oversize takes place. The oversize particles return for'another pass around the reducing'rotor and as part of the same flow there is some scavenger air which passes around the reducing rotortodraw off newly produced fines; The fines which are separated from the oversize in the bottom of the classifying chamber short-circuit the figure eight flow and are immediately returned to the circulating flow around the classifying rotor 40.

For a wide variety of operations it may be desiredlto remove a large portion of the oversize material through the optional by-pass outlet provided by the skimmer trough '73. Where this optional coarse fraction outlet is utilized the amount of oversize which is returned for further reduction is, of course, greatly diminished although the same figure eight circulation is maintained. The oversize material removed by means of the screw conveyor 74 or similar withdrawal means may then be subjected to auxiliary processin, separation, extraction, treatment or the like before being returned to the mill with the regular feed for further reduction.

The integrated mill and classifier is designed for large capacities. A typical large capacity reducing rotor, for example, may have a diameter of 36- inches or more and an axial length of at least '36 inches. The reducing rotor and classifying rotor are of the sarne length. The diameter of the classifier rotor, however, may vary with its volumetric requirements. A classifier rotor of larger diameter is required, for example, in particles size ranges at the small end of the scale, such as one micron and finer.

ror normal operation the speed of both the classifier and reducing rotor are preferably set at a constant value such as in the range from about 1,000 to 2,000 g. at the eriphery of the rotors varying somewhat with the specific gravity of the material and particles size to be extracted. As an example, a rotor 30 inches in diameter rotated at a speed of 1530 rpm. "as a centrifugal force of 1,000 g. at its periphery. With the rotors operating at constant speed particle size control then becomes merely a matter of precise regulation of air volume through the classifier.

It is apparent that many modifications and variations of this invention as hereinbefore set forth may be made without departing from the spirit and scope thereof. The specific embodiments described are given by way of example only and the invention is limited only by the terms of the appended claims.

We claim:

1. A progressive fluid energy reducing and classifying means for dry solid material in the subsieve particle size range which comprises a horizontal axis open rotor fluid energy reducing means enclosed in a mill housing and integrated with a horizontal axis peripheral inlet centripetal flow and axial outlet classifier rotor enclosed in a classifier housing disposed above and in direct fluid communication with said mill housing, a material inlet disposed along the length of the mill housing below the axis of the rotor, an air inlet disposed along the length of the top of the classifier housing and regulatable air flow inducing means associated with the axial outlet of the classifier rotor.

2. A progressive fluid energy reducing and classifying means according to claim 1 further characterized in that said open rotor reducing means comprises an assembly of relatively narrow radial blade closed end rotor units operating as independent peripheral inlet and peripheral discharge fan units in a common housing.

3. A progressive reducing and classifying means according to claim 1 further characterized in that said open rotor reducing means is disposed in said mill housing to operate with a running clearance of from about 1 to 3 inches.

4. A progressive reducing and classifying means according to claim 1 further characterized in that said classifier rotor comprises an assembly of closed end rotor units, each consisting essentially of a plurality of spaced annular disks whose inner peripheries define an axial outlet duct and an outer peripheral ring of parallel spaced rods.

5. A progressive reducing and classifying means according to claim 4 further characterized in that said closed end rotor units are assembled into a rotatable drum of spaced concentric annular disks with an outer cage-like peripheral wall of spaced parallel round rods.

6. A progressive reducing and classifying means according to claim 1 further characterized in that regulatable air inlet means are provided in the bottom wall of said classifier housing.

7. A progressive reducing and classifying means according to claim 1 further characterized in that a coarse fraction skimmer means is provided in the bottom wall of the classifier housing.

8. A progressive reducing and classifying means according to claim 7 further characterized in that screw conveyor means are provided in said skimmer for progressively removing a desired portion of its accumulated coarse fraction.

9. A progressive classifying means for dry solid material in the subsieve particle size range which comprises a horizontal axis peripheral inlet centripetal flow and axial outlet classifier rotor enclosed in a classifier housing, a tangential material inlet disposed along the length of the bottom of the classifier housing, an air inlet disposed along the length of the top of the classifier housing and regulatable air flow inducing means associated with the axial outlet of the classifier rotor, said rotor including an assembly of closed end rotor units, each comprising a plurality of spaced concentric annular disks whose inner peripheries define an axial outlet duct, said disks being assembled into a rotatable drum, and an outer cage-like peripheral wall of spaced parallel rods surrounding said drum.

10. A progressive classifying means according to claim 9 further characterized in that a regulatable air inlet means is disposed along the length of the bottom wall of said classifier housing.

11. A progressive fluid energy reducing and classifying means for dry solid material in the subsieve particle size range which comprises a horizontal axis open rotor fluid energy reducing means enclosed in a mill housing and integrated with a horizontal axis peripheral inlet centripetal flow and axial outlet classifier rotor enclosed in a classifier housing disposed above and in direct fluid communication with said mill housing; said open rotor reducing means comprising an assembly of relatively narrow radial blade closed end rotor units operating as independent peripheral inlet and peripheral discharge fan units in a common housing and disposed in said mill housing to operate with a running clearance of from about 1 to 3 inches; said classifier rotor including an assembly of closed end rotor units each comprising a plurality of spaced annular disks assembled into a rotatable drum, the inner peripheries of said disks defining an axial outlet duct and an outer peripheral ring of parallel spaced rods surrounding said drum; a material inlet disposed along the length of the mill housing below the axis of the rotor, a regulatable air inlet disposed along the length of the top of the classifier housing, a further regulatable air inlet disposed along the length of the bottom wall of said classifier housing and regulatable air flow inducing means associated with the axial outlet of the classifier rotor.

References Cited in the file of this patent UNITED STATES PATENTS 2,270,143 Schaich Jan. 13, 1942 2,717,741 Lykken Sept. 13, 1955 2,762,572 Lykken et al Sept. 11, 1956 FOREIGN PATENTS 833,406 France July 18, 1938 496,783 Great Britain Dec. 6, 1938