US3208675A - Attrition mill apparatus and method - Google Patents

Description

T. w. HoPwooD 3,208,675

Awnmon MILL APPARATUS ANnjMETHon Sept. Z8, 1965 Filed Fb. 8,- 19,63

` 3 Sheets-#Sheet 2 l INVENTOR. 27m/ms M//mmz BY 1/ Sept 23, 41965 T. w. HoPwooD I v ATTRITION MILL APPARATUS AND METHOD 3 Sheets-Sheet 3 Filed Feb. 8, 1963 3,208,675 ATIRITION MILL APPARATUS AND METHOD. Thomas W. Hopwood, Box 538, Giddings, Tex.

' Filed Feb. 8, 1963, Ser. No. 257,267 i 21 Claims. V(CI. 241-5) This invention relates to new Asystems and methods of pulverization by attrition, classification of the powdered product, drying, delamination, chemical treatment, batch mixing and continuous mixing, of materials and to compact arrangements of apparatus comprising efficiently operating combinations of attrition mill, and apparatus used in connection therewith for carrying out these methods.

Centrifugal fluid jet action has been extensively used in apparatus for pulverizing or size reductionof solid material particles. Jets of gaseous fluid are usually introduced at high velocity into an annular grinding zone 'in an outer portion of a treatment chamber of circular cross section, said grinding zone containing material to be pulverized in the form of discreet small particles. The high velocity fluid jets are usually introduced in directions inclined forwardly with respect to the radii of the treatment chamber, so as to maintain the fluid in the chamber whirling rapidly in the direction of such forward inclination, The grinding zone is of limited axial length and is confined by peripheral portions of the chamber walls enclosing said zone at its outer circumference and both axial ends,vand gaseous fluid is continuously withdrawn inwardly from the grinding zone and discharged from the treatment chamber, preferably through a centrally disposed fiuid outlet. The gaseous fluid thus has a generally inwardly spiralling movement within the treatment chamber, andthe material undergoing pulverization is preferably continually supplied to the moving fiuid within the treatment chamber.

The high velocity uid iets effect a reduction of particle size ofthe material under treatment by impact and attrition of particles againstone another and against the chamber walls, while at the same time causing the charge of material to rotate rapidly within the grinding zone in the direction of the whirling movement of the fluid. The material must be prepulverized and predried. Due to the centrifugal effects resulting from the rapid rotation of the charge within the grinding zone, the larger particles are caused to circulate in said zone where they come repeadedly under the influence of the introduced high velocity jets of gaseous fluid and are thus repeadedly subjected'to thesize reducing action produced thereby,` while the material which is sufficiently reduced in size is entrained by the' gaseous fluidas it spirals inwardly toward the centrally disposed fluid outlet. l

' The entraining'action of the inwardly spirallyrgaseous fluid .exerts on thesuspended particles of the circulating material within the pulverizing zone a radially inward component opposing the radiallyoutward component 'of force due to centrifugal action, and continuously removes from the grinding zone particles which are sufficientlyv reduced in size, entraining such particles in its movement toward the fluid outlet and effecting 'a very intense fluidsweeping action of the charge within the chamber, toget lter E with a` high degree of vcentrifugal classification of the 'entrained material. portion of the chamber radial, ly inwardly of the grinding zone usually communicates with an axially extended centrifugal product .collector of smaller diameter than the chamber, which utilizes the States Patent Hice to the product collector or to the central fluid outlet and l attrition in a pulverizing chamber having' means foripro' whirling energy of the gaseous fiuid'entering said'collec- 1 torito separate a considerable portionof the entrained material from the carrier duid, while the duid, more or,Y less freed of such material, may-be discharged through erable distance radially inwardly from the annular grinding zone into which the high velocity fluid jets areintroduced, so that the above described centrifugal classify# ing action is maintained not only within the grinding zone, but also in an intermediate classifying zone, where-y by particles which have not been suicientlyreduced in size are effectively prevented from inward entrainment are caused to recirculate in the grinding zone until sufficiently reduced. In some cases, .the above described centrifugal product collector is omitted and all of the material which is sufficiently reduced is discharged with the entraining gaseous fluid through the centrally disposed outlet and may be separated and collected in any-suitable manner outside the treatment chamber. It is generally convenient and preferable to introduce the material to be pulverized into the treatment chamber at one or more positions inwardly of the zone of action of the high velocity jets,`and preferably adjacent but within the inner boundary of the grinding zone, so that any material which is already sufliciently reducedto be entrained and carried inwardly by the spiralling fluid is not caused to be subjected to further grinding action,

while particles of larger size are caused by centrifugal action to move outwardly into the grinding zone. Furthermore, it is generally convenient to introduce this material into the treatment chamber in suspension in a gaseous fluid having a component of motion in the direction of whirling fluid movement induced by the high' i velocity uid jets.

Various arrangements of fiuid jets'in the grinding zone have been devised in various configurations of the periph'eral walls of the grinding zone. j Generally the apparatus in the prior art required an excessively high rate of gaseous uid supply to provide the necessary jet energy to be transferred to the particles for dissipation in the attrition action and friction of the whirling ow of the fluid. 1

The object of the present invention is toincrease the effectiveness of attrition mill processes by creating a multiplicity of compact counter-turbulence impact currents of the gas-suspended material particles, requiring a minimum of gaseous fluid supply compared to that used by normal jet operation for a comparative rate o tlattrition energy delivered thereby.

'A further object is to provide a high ticle size of a batch of material'whichmay be wet, by

ducing'a multiplicity of high speed eounter-turb`ulen apparatus, means for continuously separating and with vdrawing of the smaller size particles from said chamber,= i Y and classifying flow-inducing means for these particles,

so as to deliverV only those particles which are sufici'e'ntly m reduced in size, to a settling means, and returning theremaining particles to said vpulverizing chamber. and continuously feeding new-raw material to said chamberto v Patented Sept. 28, i965.v

capacity compactapparatus for effectively pulverizing or reducing the parVV v l 3 compensate' for the vamount of material delivered to the settling means.

A further Objectis toprovide an annular paddle wheel i' rotating at right angles and close to high vspeed currents near the bottom of the pulverizing chamber for sweeping and dischargingtany heavy articles which have dropped out of the grinding chamber, back into the chamber for further pulverization,while-'providing a vortex of the lighter particles in the center of the paddle wheel for .axial withdrawal therefrom into the inlet conduit of a classifying means in which the vortex action is continued to maintain. only the liner particles in the central ow of the conduit which leads into the center of a centrifugal iiow inducing'm'eans turning in the same direction as the vortex, the outer annular portion of the How in the conduit leads into the central portion of a similarly driven centrifugal flow inducing means for connection to the return conduit tothe pulverization chamber for recirculation therethru.

A further object is to provide an additional compact classifying means comprising a dual paddle wheel centrifugal fan' for inducing ow therethrough mounted on armsv may be arranged in several radial planes axially spaced on one shaft 42 for passing other arms similarly arranged on one or more other shafts 44, the radial planes Aof which are axially offset with respect to those of the The ends of the beater rods 40 may have uneven or corrugated surfaces so as to increase the ricocheting effect on the particles and the air and to spread its turbulence,

thus to provide a maximum rate of attrition per unit the same drive shaft, one fan wheel portion having a central inlet from the central portion of the inlet conduit of the classifying means for receiving the central portion of the vortex llow in said conduit, the other fan portion having an annular inletfrom the peripheral portion of the conduit for receiving the outer annular portion of the vortex tiows vin theconduit which contains the oversize particles for return to the pulverization chamber.

A further object is to arrange the mill, classifying means and settling means in a common base frame to provide portability to kthe apparatus as a unit, so that it may be transported by at car or truck to placeswhere'it might be needed. e

Other and more specific objects will become apparent in the following detailed description of the apparatus and its method of operation, as illustrated in the accompanying drawings, wherein:

FIG. 1 isa side elevational combination, Y

FIG. 2 isa plan view thereof,

FIGS is a sectional view through the new er the attrition min grinding chamber taken on the line 3-3 in PKG. -2, on an enlargedscale, A FIG. 4 is a sectional view therethrough taken on the line At--Lt in FIG; 3, on a further enlarged scale,

FIG. 5 is an enlarged sectionall view of the paddle wheelin the bottom of the grinding chamber, taken on the lineS--S in FIG. 1,

` FIG. 6 is a detail sectionall view of a portion of the paddle wheel taken on the line 6 6 in FIG. 5,

FIG. 7 isl a detail sectional view of another portionof the paddle wheel takenon the line '7--7 in PIG. 5,'

FIG. '.8 is an enlarged sectional view through one of the fan 'wheels' taken on the lirie 88in FIG. l,

' FIG. 9 is a similar section through the other lfan wheel teken catherine a-sin'FrG. 1, and K FIG;10 is adet'ail sectional 'view taken on the lines lill- 16 inFIGSgS and 9.

inthe-,illustrated embodiment of the invention a parallei-sided grindingchamber 2 0 is provided'with a pocket 22 in its bottom for accommodating 'a paddle wheel 24 with a shaft 26 mounted -in a bearing Z8 on the forward side of the pocket and extending to a pulley 30 at its forward'end for operation by r a motor 32 through belts 34. A base frame 36 provides a support for the motor 32,-' pulverizationchamber structure and other parts of thelcombination comprising the apparatus of the entire mi .t

The material to be pulverized may be fed to the pulverization chamber by a screw conveyor 38 at a suitable rate, and bounces over the tops'of a multiplicity of high speed rotating beater arms 40, their outer ends passing oneanother in closely adjacent radial planes.. The beater volume of chamber space. Only a minimum amount of material is ever sheared by simultaneous impact from its opposite directions, as in normal grinding operations and to some extent in vortex type attrition mills where some gas fluid jets are directed toward thev peripheral wall of the grinding zone and produce a high incidence of crushing the particles circulating in contact with said Wall by the bombardment of the high speed particles in the jet streams against these circulating particles producing a crushing impact thereon between the wall and the ricocheting particles from the jet streams. In applicants novel method, the particles ricochet rapidly against one another and against the beater arms, receiving the high speed impacts only from one side at one time. Thus, while a considerably higher rate of attrition is achieved, frictional and shearing attrition is substantially eliminated. The attrition areas are substantially insulated from the walls of the chamber by more quiescent zones. The gentleness of this attrition method provides some valuable advantages over previous methods. It was found e.g. that the poison glands which are a part of the cotton seed could be separated without damaging the glands in the present attrition method. e

The pocket 22 has a quiescent vortex zone in the central portion of the paddle wheel 24, from which the pulverized material in suspension in this vortex is withdrawn axially from the side of the pocket opposite that through which the shaft 26 extends, into the inlet conduit46 of aclassifying. means 48. The classifying means includes a dual centrifugal fan wheel for withdrawing the core portion of the vortex in the inlet conduit46 with the finer particles in suspension and delivering this portion to the cyclones 52 through the delivery conduit 54, and for withdrawing the annular portion of the vortextlow containing "the heavier particles in this portion and returning it to the v pulverization chamber through return conduit 56, for further pulverization. The classification maybe finely controlled by using a selectedsize of `opening 58 inthe inlet adaptor funnel 60 which is mounted-on the, inlet 62 to the delivery portion. of the fan wheel. A damper valve 64 may be used at times when it is desired to cut ol the vdelivery and recirculate all the material withdrawn from the pulverization chamber. A l

The delivery portion of the fan wheel 50 has fan blades 65 mountedon a backplate 66. The backplate is fixed tothe drive shaft 68 which is mounted in bearings 79. These bearings, like bearings 28; may be spaced away from the casi-ng in'which the fan or paddle wheel operates, so as to insulate the bearings from the heat `in thecasings, which may reach a, temperature vof 1000 F. or more at times. The inlet 62 forms a cylindrical hub foi-,the recirculating flow portion of the fan wheel'50 and is supported byv radial braces 67 on shaft 68 to which it is fixed for common rotation by means of apulley' 72, belts 74 and motor 76. The recirculating tow portion ofthe fan wheel has' fan blades- -78 radially extending from the hub.

The rotation of the tan wheel is in the same directionas of protruding inlet flange 88.

. material .to be"pulv`erized.l

as 1000 F. and more. o of explosive materials, such as sulphur, due to the fact Y that the material is under Vsuction,no't primarily 'under 5. the vortex in the inlet conduit, whereby to assist in maintaining the vortex action to improve the separation to the desired degree in theinlet conduit, in accordance with the size of inlet opening 58 used in the adaptor funnel 60.

To maintain a steady output of the desired quality, an optimum -load of the material is maintained in the pul- `verization chamber for `most'etiicient pulverization, by

feeding the material into the pulverization chamber at substantially the same rate that is delivered to the cyclones, after a proper selection of the size of the inlet opening 58 to the delivery fan portion and proper adjust mentof speeds of operation of motors 32 and 76 have -been made.

The gas uid normally used in the present system is air and the pulverization chamber may be vented to the vatmosphere so as to maintain substantially atmospheric pressure therein. By yrestricting the vent a subatmospheric pressure may be maintained to prevent explosions which could occur under some compression.

ln some instances, as in the case of kpulverizingsubstances like sulphur, it might be desirable to feed some inert gases into this vent to reduce the oxygen ratio in the gas fluid, or even to replace the air entirely by excluding the air and connecting the vent opening to a source of supply of the inert gas at a suitable slow rate. A closed system couldbe used by connecting a return conduit between the exhaust gas llow from the cyclones and the pulverization chamber, to conserve the gas fluid, if it is other than atmospheric air and is too expensive to waste by discharging into the atmospherefrom the cyclones.

Thusthis system lends itself to ecient operation for pulverizing a variety of materials safely and without damage to those materials the minute particles iof whichare vsubject to being spoiled or harmed by harsh frictional scrubbing or crushing impacts.

lThe shafts 42 and 44 to which the beater arms are fixed, are mounted in bearings 80 outside the pulverization chamber and spaced from the opposite sides thereof to insulate them from the high temperatures of the chamber walls.' A motor 82 may be mounted at one end of each shaft for operating the respective beater arm vassembly at high speed in the sarrie direction, preferably away from the recirculating inlet 84 at the top of the chamber.

The inlet conduit 46 is connected to the dual fan casing 90 4by means of a telescopically fitting adaptor sleeve 86 i with end flangesslidably ttingover the inlet conduit and the protruding inlet anges 88 on the fan casing. Thus, the adaptor sleeve 86 may be slid back off the flanges 88, for cleaning and whenever the adaptor funnel 60 has to be changed," The adaptor tunnels 60A have an innerrend ange 92 whichts snugly within the outerl end of inlet sleeve `63, which is rigidly fixed by struts 94 in the center The cyclones 52may be mounted on' the same base framey 36 with the mill and classifying means to form a complete unit that may be readily transported to different sites, where it might be needed,-.cl`ose to the supply of the The present system is ideally suited for Athe dryingand treatment of material at very high temperatures, such It is also suitable for processing characteristics, `due to" the factthat the high velocityand pulverization zone, if sufficient classification is obtained form in the dry powder product, deodorising the product to a degree.

This system is further ideally suited for drying and pulverization -and chemicaltreatment of Wet,',sticky inorganic materials, such as clays of all descriptions, fullers earth, etc.

It is particularly suited for pulverization,` drying and reduction to tine powder of ores of various minerals, providing the same ores are precrushed to a size not larger than about 4" so they may be readily fed by a screw conveyor, and in order that the same ne product can be prepared for flotation and leaching processes, By virtue of use of this type of mill, it is possible to coat particles with any chemicals which would help to speed up the processes of otation and leaching.

The present system is further ideally suited for organic materials havinga high oil content, such as cotton seed,

peanuts, etc., inasmuch as we are able in this instance,

bythe passage of refrigerated air or'other gases, to reduce these o normally oily products to ne powder without clogging the machine. It was also found that in the present method, it is possible to separate the poison gland, which is a part of the cotton seed, from the seed itself without damaging the gland, as is often the case in other harsher milling processes.

This system is extremely well suited for delamination and pulverization of micaceous minerals, the same being processed in a steam medium. l

It is ideally suited for the pulverization and activation of charcoal so that the porosity of charcoal is greatly increased by the removal of extraneous matter from the pores ofthe charcoal.

Also in the drying and pulverization of materials of an abrasive nature, due to the attrition of the particles by other abrasive particles, the abrasion on the machine parts is minimized particularly because the highspeed counterturbulence areas are separated from the chamber walls by more quiescent areas where the particles lose their.

at the center of the paddle wheel vortex by controllingthe size ofthe withdrawal opening. In those cases, the recirculating portion of the fan wheeland the return duct 56 could be omitted. y n l Many other obvious modifications in the details and arrangement of parts in thisv system may be made without tion, as defined in the appended claims.

What is claimed is:

1.- A continuous method of pulverizing material comprising enclosing a quantity of gaseous fluid with said material in a chamber, A j

creating a multiplicity of high speed counter-turbulence currents of particles of the material `by batting and ricocheting them against other particles to reduce the particle size by attrition in closely adjacent zones departing from the spirit and scope ofthe present'inven` throughout a central portion of the chamber space,

' thereby maintaining a relatively quiescent zone ad jacent the walls of said chamber to insulate the walls speed impacts there-V against excessive wear byv high against by stray particles, Y feeding gas and the material to be pulverized into the upper portion of said chamber at a suitable rate,

withdrawing the pulverized material suspended'in said vgaseousiiuid from `the lower portion of said .chamber atv substantially thereto.

the same rate as ,they afregintroduced l 2. A method as definedin claim l, in' which the high vspeed counterturbulence currents are created in a plu rality of closely adjacent planes across the `width of the chamber and in a plurality of closely spaced areas across the lengthv and depth of the central portion of the chammaterial in suspension is vfurther withdrawn and into which the quiescent area -in the lowest portion of the chamber extends.' Y

'5. A method as defined in claim' 4, and trapping any tramp iron vor exceptionally heavy particles of the material in the bottom of said chamber.

6. A method as defined in claim 3, said pulverized material suspended in said gaseous fiuid being withdrawn from the central part of the bottom portion of said chambenrota'ting a large paddle wheel fan at high speed va -pulverzing chamber having a reduction zone with i.

said materialsin turbulent suspension in the central portion of the chamber and a funnel shaped lower portion with a recess in the bottom thereof,

a rotating means having its lower peripheral portion extending into said recess for sweeping' drop-out portions of said materials from said recess in fthe bottom of said chamber back into suspension in said 'central portion, said rotating means. creating a `vortex centrally thereof,

` anoutlet'from the lower portion of saidcliatnhfr at the center of said vortex,

classifying means 'having centrifugal' flow-inducing "means with an inlet conduit connected to saidcharn ber outlet and an outlet conduit for delivering the -flowgof line particles toa separating and collecting means. v

12. Apparatus as definedin claim ll, 'including a separat-ing and collecting cyclone'device connected to said outlet conduit from said classifying means and a come mon platform frame forsupporting all of said apparatus, whereby it may be handled as a portable unit for trans portation on fiat beds to sites .whereitis needed.

and at right angles t'o the v.planesA of said high speed counter-turbulencecurrents, and v the rotation of the high speed paddlewheel fan causing the heavier particles of material removed' to travel ina peripheral path and b'e thrown back into the area of the highfspeed counter-turbulence rcurrents vfor further attrition, and causing the lighter and smaller particles of material to rotate'inlth'e center zone from which area they are withdrawn under suction. 7. A method of reducing the size of particles of raw material to a vfine powder withoutunduly injuring its molecular strncture, comprising v Y subjecting thel material to attrition by a succession of high speed batting and ricocheting impacts onparticles of said. material in turbulent suspension between 'moving parts passing 'each other athigh speeds in parallel planesrvvith small clearances `between them and other batted and ricocheting particles in the 13. Apparatusas' definedin-claim 11, said v classifyingmeans including a dual ow centrifugal famwith concentric inlet conduits, the outer inlet conduitbelngV connected by a vortex' transfer conduit to the said'- chamber outlet, theportion of the fan w'ith'the outer inletcondut 3 having a second outlet conduit which is connected to said pulvcrizing chamber for recirculating the coarser particles received fromthe outer annular part ofthe vortex any run of material.

-center portion of a confined chamber having a funnel shaped bottom portion leading into a recess, said small clearances forming avirtual screen for substantially maintaining the 'larger particles in the upper portion of the Vchamber until they are broken 'up suiciently,

I I crcatinga vortex peripherally sweeping the bottom of the recess and `bringing the particles which have dropped out ofthe turbulent suspension back `into the center portion for continued attrition,v

withdrawing the powdenladen air from thecenter of vsaid vortex in said'reces's, separating the powdei'lof the desired fineness from the coarser powder -in thisair and returning the remaining `coarser powder chamber.

back to the upper portion of the 8. A method as defined in claim 7, and i i I feeding raw material to the' upper portion of the cham' ber at a rate equivalent to the lrate of withdrawal of the'powder of the desired fineness to maintainan optimum loading in saidL chamber. 19.' A method as defined in claim 8, and

maintainingrasuctionin said chamber and throughout the entire apparatus iby controlingsupply :of' air thereto. v 'l `10. A method a's definedin claim 9, operating said method ina closed system and f -using an inertl-gaseouszfiuid-therein in place of air.

il. Apparatus for particle size reduction of. pulverulent materials comprising conduit back intothe chamber for further pulverization'. 14. Apparatus as definedV inclaim 13, anda valve in said inner inlet conduit diverting the entire flowfinto the -recirculating conduit when the valve lis fully closed, for

further batch mixing in the'V pulveri'zing vchamber to obtain homogeneous distribution of minute proportions of important ingredients in the batch.

15. Apparatus as defined in claim 1 3, said inner inlet conduit beingadapted vto receive an exchangeable nozzle selected from a group having different size inlet'srop'enings, whereby the proportion ofthe flow recirculated for further pulverization may be controlled 16.- Apparatus as defined in claim 11, saidpulverizing chamber having high-speed counter-turbulence producing beater means for continuous bombardment of particles against each other vand ricocheting against said beater means producing said turbulence in' the reduction zone `in areasspaced from the walls of said chamber by more quiescent areas. f Y

17. Apparatus as defined inv claim 15, said beater means comprising a pluralityof beater arm wheels rotating in the same direction on spaced axes and having peripheral portions of their radially extending beater arms moving in rna'posite directions in closely adjacent planes.

18. Apparatus as defined in claim 17,*saidbeater arm Awheels having substantiallyl parallel shafts mounted. in

the pulverizing chamberin spaced relation so as togprovide an "overlap vof the peripheries of adjacent wheels, each wheel havinga series of beater arms operating in a plurality of axially spaced radial planes, andthe heater arms of. one wheel having'their planes of operation axially staggered' with relation to those of the adjacent '.wheelso as to move. in closely adjacent planes in opposite directions, when the wheels are rotated inthe same direteion.

19. Apparatus for pulverizing raw material by attrition comprising a. chamber,v al plurality of rotatingbeater assemblies, each assembly having'a plurality'of beater arms operating in closely adjacent planes v with beater -arrnsof yother assemblies rotating on spaced' axesv and t moving past 'each other in oppositejdirectionsat high 4speeds .ina central-portion ofsaid chamber'tocreate .counter-,turbulence "currents of particles `,battedand rico-v as desired for spaced axes are parallel.`

cheted between s aid arms and against eachother, meansfor feeding said material into .the upper portion of said chamber and means for withdrawing puiverized material in suspension from va more quiescent zone Vin the lower portion of saidchamber away from said concerted currents.

21. Apparatus as dened inclam 20, wherein said References Cited by the Examiner UNITED STATES PATENTS l 8/45V Hardinge 24h-48 9/ 56 Lykken et al. .'..v 241-52 3/58 Hale 251-2s-4 2/59 Holm 241-80. 2/61 Lykken et al. 241-5 l/ 63 Quinn 2 :M1-so -f 10 y ANDREW R. JUHASZ,` Primary Examiner.

J. SPENCER ovERHoLsER, Erarm'nrr.Y

Claims (2)

1. A CONTINUOUS METHOD OF PULVERIZING MATERIAL COMPRISING ENCLOSING A QUANTITY OF GASEOUS FLUID WITH SAID MATERIAL IN A CHAMBER, CREATING A MULTIPLICITY OF HIGH SPEED COUNTER-TURBULENCE CURRENTS OF PARTICLES OF THE MATERIAL BY BATTING AND RICOCHETING THEM AGAINST OTHER PARTICLES TO REDUCE THE PARTICLE SIZE BY ATTRITION IN CLOSELY ADJACENT ZONES THROUGHOUT A CENTRAL PORTION OF THE CHAMBER SPACE, THEREBY MAINTAININ A RELATIVELY QUISCENT ZONE ADJACENT THE WALLS OF SAID CHAMBER TO INSULATE THE WALLS AGAINST EXCESSIVE WEAR BY HIGH SPEED IMPACTS THEREAGAINST BY STAY PARTICLES, FEEDING GAS AND THE MATERIAL TO BE PULVERIZED INTO THE UPPER PORTION OF SAID CHAMBER AT A SUITABLE RATE, WITHDRAWING THE PULVERIZED MATERIAL SUSPENDED IN SAID GASEOUS FLUID FROM THE LOWER PORTION OF SAID CHAMBER AT SUBSTANTIALLY THE SAME RATE AS THEY ARE INTRODUCED THERETO.

11. APPARATUS FOR PARTICLE SIZE REDUCTION OF PULVERULENT MATERIALS COMPRISING A PULVERIZING CHAMBER HAVING A REDUCTION ZONE WITH SAID MATERIALS IN TURBULENT SUSPENSION IN THE CENTRAL PORTION OF THE CHAMBER AND A FUNNEL SHAPED LOWER PORTION WITH A RECESS IN THE BOTTOM THEREOF, A ROTATING MEANS HAVING ITS LOWER PERIPHERAL PORTION EXTENDING INTO SAID RECESS FOR SWEEPING DROP-OUT PORTIONS OF SAID MATERIALS FROM SAID RECESS IN THE BOTTOM OF SAID CHAMBER BACK INTO SUSPENSION IN SAID CENTRAL PORTION, SAID ROTATING MEANS CREATING A VORTEX CENTRALLY THEREOF, AN OUTLET FROM THE LOWER PORTION OF SAID CHAMBER AT THE CENTER OF SAID VORTEX, CLASSIFYING MEANS HAVING CENTRIFUGAL FLOW-INDUCING MEANS WITH AN INLET CONDUIT CONNECTED TO SAID CHAMBER OUTLET AND AN OUTLET CONDUIT FOR DELIVERING THE FLOW OF FINE PARTICLES TO A SEPARATING AND COLLECTING MEANS.

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