US2915179A - Aerodynamic classifier - Google Patents

Description

Dec. 1, 1959 H. G. LYKKEN 2,91 ,179

AERODYNAMIC CLASSIFIER Filed Feb. 17, 1954 4 Sheets-Sheet l E INVENTOR.

Ila/Ry (rm/(EN UM W Arrazmsls Dec. 1, 1959 H. G. LYKKEN 2,91

AERODYNAMIC CLASSIFIER Filed Feb. 17;, 1954 4 Sheets-Sheet 2 FIE E INVENTOR. Ila/m 4-! LVKAEN lrronms s Dec. 1, 1959 HQ G. LYKKEN Filed Feb. 17, 1954 AERODYNAMIC'CLASSIFIER 4 Sheets-Sheet 3 FIEI4 INVENTOR. l/EA/R 6. l YK/(E/V aymoqwyfi 4 rroawzys Dec. 1, 1959 H. G. LYKKEN 2,915,179

AERODYNAMIC CLASSIFIER Filed Feb. 17, 1954 4 Sheets-Sheet 4 :IIIIIIIIIIIIIIIIE IIIIIIIIIE INVEN TOR. #5402 Y 6% l. YAKEA/ Arronusys .Ufl sd w s en AERODYNAMIC CLASSIFIER Henry G. Lykken, Minneapolis, Minn., assignor to The Microcyclomat C0., Minneapolis, Minn, a corporation of Delaware I This invention relates to methods and apparatus for classifying dry pulverent material to any desired particle size range. More particularly thisinvention relatesto a classifier which is a self-contained power-driven machine for separating fines of any specified particle size and finer from an unclassified feed'of v dry pulverulent material; The separated fines are removed from the classifier to a-collector witha circulating gas stream. The oversize particles are discharged at the bottom of the machine. I v a The classifier of this invention is so constructed that it can be adjusted to produce a product of any specified fineness with no oversize-particles and nearly complete extraction of fines in the range from all minus one micron and finer through all minus 100.0 microns and finer. This aerodynamic classifieris a compact, horizontal rotor machine which may be built in any desired size and capacity. It is based upon a unique principle of classification, the result'of years-of experimentation and-development, requiring subjecting the dry pulverulent material suspended in a gaseous stream to three successive aerodynamic reactions. 4 I v I i Theprincipal, object of this invention isthus to pro- :vide aerodynamicsrnethods and apparatus for classifying dry pulverulent material arranged and regulated to separate out and extract'as the fine product, withno oversize,material in the range of all minusone micron to all minus 1000 microns on a precisionbasist suchas, for example, all minus 2 microns, all minus 5 microns, 10, 30, 60 microns or the like as may be..required. i

It is the object of this invention to provide methods and apparatus for classifying dry pulverulent material in which dry particles and gas are fed into theclassifier at a controlled .and regulated rate and subjected to a series of specific controllable and controlled aerodynamic actions that segregate out thefiner material from coarser material where, classification is based upon particle size, the finer material going out with the gas flow .to a collector system and thecoarser fraction remaining in the classifier long enough to' get .a complete or nearly complete extraction of. the fines with the oversize material dropping to the :bottom of the classifier from which it is continuously removed .at a regulated rate.

It is another object of this invention to provide methods and apparatus for classifying dry pulverulent material in which dry particles and gas are fed intothe classifier at a regulated rate and subjected to a seriesaof specific controllable and controlled} aerodynamic actions that segregate the material .of lower .specific gravity from material of higher specific gravity where classification is based upon weight differentials of uniform size particleS, the lighter material going out with the gas flow to a collector system' and the' heavier fraction remaining in the classifiert long enough as, get a complete or nearly complete extraction'of the light particles with the heavier particles dropping to the bottomof the,class'ifi'er from which'they are cont'nuously removed at arcgulatedrate.

An object o'f'this invention is to provide a classifying 7 2,915,179 Patented Dec. 1, 1959 apparatus disposed on a horizontalaxis having a centripetal classifier rotor within an involute scroll housing and a centrifugal fan rotor within a housing.

7 Another object of this invention is to provide a method and apparatus for removing and separating unwanted hard or dense materials occurring in natural substances from the wanted portions.

Itis a further object of this invention to provide a classifying apparatus and method adaptable to a wide variety of purposes, materials and classification over a wide range of particle sizes.

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

To the accomplishment of the foregoing and related ends, this inventionthencomprises the features hereinafter fully described and particularly pointed out in the .claims, the-following description setting forth in detail certain, illustrative embodiments of the invention, these being indicative, however, of but a few of the various ways in which the principles of employed. j

The invention is illustrated with reference to the drawings in which corresponding numerals refer to the same the invention may be parts and in which:

, ,fan housing of the apparatus taken along the line 3 -.3

and in the direction of. the arrows of Figure 1;

rotor;

Figure 5 is a transverse. sectional view'through the classifying zone of the apparatus as in Figure 2 showing in simplified and diagrammatic form the intra-blade vortex flow in the classifying zone due to the action of the classifying rotor alone;

Figure 6 is a transverse sectional view of the classifying section as in Figure 5 showing in simplified and diagrammatic form the vortex fiow in the classifying zone due to the action of the classifying rotor and the additional draft of air due to the action of the impeller fan unit and v i Figure Tis a fragmentary'transverse sectional view similar to Figure 2 but showing an alternative form of particulate material from the bottom of the classifier.

Broadly defined, the aerodynamic classifier of this in.- vention comprisesv a horizontal classifier housing con taining a classifier rotor and an exhaust fan on the same shaft...IIhe classifier rotor isa newly developed centripetal flow type rotor with axial flow to the fan. The classifier is provided with a feeder and a tailings removal mechanism, each having a variable speed drive. a

The classifier housing is a 360 involute scroll in which the classifier rotor is mounted for rotation in reverse of the direction of theexpanding involute, or opposite to the direction of rotation of a centrifugal scroll fan. Thus, the opening which would normally be the discharge of a fan scroll becomes the inlet of the classifier scroll for both the gaseous stream and the pulverulent feed. Both the gas and the feed enter the classifier tangentiallythe full length of the housing and in a downward direction.

A substantial clearance is provided under the rotor allowing for the accumulation of a shallow bed of material maintained at a substantially constant depth or level over the tailings outlet in the bottom of the involute scroll housing. The level of the bed may be maintained by automatically varying the rate of feed to compensate for variation inpercentage of oversize in the feed with the bottom discharge adjusted to a fixed rate.

The first aerodynamic reaction takes place at this point. All coarser and heavier particles, particularly sand, crystalline silica and other grit drop out at this point. The bed of pulvernlent material at the bottom of the classifier, due to the pulsating air action induced by the rotor, is fluent and turbulent providing a difierential settling effect. The larger and heavier particles sink to the bottom of the bed as the fines and near fines ebulla te upwards and are swept around the rotor. Since only fines and near fines can enter the rotating rotor, all oversize materials and heavier particles necessarily accumulate in the bed from which they are progressively removed.

The periphery of the rotor is provided with spaced blades, preferably in the form of round rods, forming with the rotors end disks a cylindrical cage which is subdivided into sections by intermediate disks. The spacing of these blades is selective in design to cover a wide range in particle size and density of material. The rotor has an axial duct connected to the exhaust fan for maintaining a controlled centripetal suction and gas fiow though the rotor. When revolved, such a rotor cage will produce an intrablade vortex flow. Air is drawn into the rotor along the trailing side of each blade or rod and discharged outward along the forward side of the following blade or rod. This forms a closed vortex action having an accelerated forward velocity extending beyond the periphery of the rotor and a diminishing for- Ward velocity within the periphery. j

Initially, such a rotor provides a uniform positive centrifugal barrier at its periphery, insuring a uniform distribution of gas and material suspended in the gas axially and peripherally, as well as uniformity of flow into the rotor.- The highest centripetal velocity of the jecting each particle in distributed suspension in gas to a controllable high tension centrifugal throwout and a uniform controllable centripetal air drag. Theoretically, 'all but the wanted particle size may be prevented from entering the rotor by controlling the gas flow. But, to attain the highest possible commercial efiiciency, both fines and near fines, i.e., material several microns oversize, are allowed to enter the rotor to ensure easy entry of all the fines, and to provide classification in depth. The instant the gas and pulvernlent material break through the barrier back to the blade its forward velocity is largely reversed by the outward suction of the blade. The MV of the material is greatly reduced. The radial drag of the gas is diverted and its radial component greatly reduced. It becomes, in fact, a closed loop except'for that percentage of the gas actually drawn into and through the rotor by the exhaust fan.

It must be noted here, that there are two gas flows in the rotorthe gas that is drawn through the rotor by the exhaust fan and the recirculating gas forming the looping flow of the intra-blade vortices, a function of the rotor blading and rotor speed. The rotor induced flow and aerodynamic reactions are independent of the gas flow drawn through the rotor, except for the inwar expansion of the loops within the rotor. v j

A precision classification takes place within the loops of the intra-blade vortices. Particles of a given mass or size can enter radially only so far into a rotor of primary classification.

given design when no gas is being drawn through the Y rotor. This includes even submicron material. The finer particles go in farther, inversely proportional to their mass or size, in a graded sequence. The pulvernlent material is continuously entering the rotor a distance inversely proportional to its mass in a graded sequence and continuously reversing flow. Classification is then merely a matter of drawing out the wanted size with a controlled suction at the point the wanted size reverses its flow.

A wide factor of safety is allowed for since the particles of the desired size enter the rotor several hundred times per second, so even a ten percent pickupofthe desired particles on each looping trip into the rotor will sut'fice to give precise, but commercially efiicient and economical, classification. The suction intake can be located farther back in the rotor and the suction intensity reduced for double insurance against picking up any oversize. A wide range of specific particle sizes can be obtained by merely regulating the gas suction through the rotor bya damperin the exhaust fan discharge.

In order to equalize the suction and minimize turbulence', an annular drurn built up of spaced annular disks is interposed between the classification zone in the rotor and its axial outlet duct. The diameter of the disks comprising the rotor drum'and their spacing may be varied to accommodate differing materials of difiering particle sizes. The spaces between the annular disks form annular chanels between the classification zone or the rotor and its axial outlet. One function of the drum is to provide a resistance barrier that will equalize the radial flow through the annular channels, equalizing suctionat theintake ports in the periphery of the drum and minimizing turbulence. Another function of the drum is to position the intake ports in proper relation to the circulating particles of wanted size. 7

The aerodynamic reactions and gas flows in the space between the housing and the rotor provide the first and All of the harder and heavier co-.taminating material, as well as most of the oversize, are here thrown out, leaving only material nearly fine enough to enter the rotor. Also all of the fines and near fines are maintained in a constant, uniformly distributed suspension in the circulating gas about the periphery of the rotor.

The aerodynamic reactions and flows that produce the in and out recirculating flow of fines and near fines through the periphery of the rotor and radially into the ,rotor a distance inversely proportional to the par ticle size comprise the second step of the classification process and the first step in the final selective classification.

The aerodynamic reactions and flows that selectively pick up the wanted particle size and fines and withdraw this desired product through the rotor to the exhaust fan, rejecting the oversize, make up the third and final step in the process. Classification according to this invention is a progressive sequential series of steps, each controllable by design of the apparatus and regulation of gas flow for precision classification and volume output.

Referring now to the drawings and particularly to Figures 1 to 4, the exemplary form of the apparatus shown in these figures consists of aclassifier having a horizontal axis with ;a centripetal classifier rotor and its housing at one end and a centrifugal fan rotor and its'housing at the other end. The classifier housing, indicatedgenerally at 10, is a 360 centrifugal fan type scroll (involute) enclosed between two end plates 11 and 1 2. Plates 11 and 12 are disposed at either end of the housing 10 and extendto a base or floor where they are held fixed by floor flanges 14 and 15. The fan housing, indicated generally at 16, is slightly spaced apart fromthe classifier housing and is .likewise enclosed between two end plates 17 and 18. @End plate 11 of the classifier housing is provided witha large circular opening 19 and end plate 12 is provided with a somewhat smaller circular opening 20 which ,is concentric with 19. "Plate 18 of the fan housing is provided-with 'a 'large circular opening 21 slightly larger in size than 19 :and plate 17 is provided with a somewhat smaller circular'opening 22. In the form here illustrated the fan housing 16 is held spaced apart 'from the classifier housing 10 by means of radial spacer bars '24 welded to plates 11 and 18. This spacing may, of course, be widely varied and externally mounted fan means .or other suction means for drawing'a' gas through the classifier maybe used. For ease in'asse mbling and disassembling the apparatus and providing access {for cleaning, repair and the like, it is preferred that plates 11,12, 17 and 18 be formed in two parts, flanged ,at their juncture and bisecting the circular openings.

A bearing structure indicated generally at 25 is mounted outside the fan housing disposed opposite circular opening-22 mounted upon a flange "26 on end plate 17.

A sirnila-r bearing structure indicated-generally at 27 is disposed at the opposite end of the apparatus adjacent circular opening and mounted on flange 28 on end plate 12. The details of construction ofthe bearings and 27 are within-the province of mechanical design and need not be further explained here except to state that they are preferably of the ball or tapered-roller type and they are adequately sized to carry the rotor of the'classifier at the speeds desired and are adequately protected against the entrance of abrasive material into the hearing; Upon the bearings 25 and 27 there is mounted a shaft 29 for passage through openings 19, 20, 2.1 and 22 and rotation concentrically with the axis of the classifier and fan structure. The shaft may be rotated by means of -a pulley (not shown) mounted at either end of the apparatus on the projecting end of-the shaft and belted to any suitable motor or the shaft may be directly connected to a motor of suitable design or driven by a variable speed motor.

"The shaft 29 is enlarged and reinforced by a tube 30 Welded or otherwise secured to annular rings 31 and 32 which in turn are welded or otherwise secured to shaft 29. The shaft 29, annular rings 31 and 32 and tube 30 form a rigid unitary base for the rotor structure and all rotative elements are mounted on and driven from this rotor structure base. The rotor structure base is further reinforced by an external annular ring 34 welded "to the outside of tube 30. Ring 34 is provided with a plurality of radial slots 35 into which splines 36 may fit for supporting one end of the classifier rotor.

The exhaust fan disk 37 is bolted or riveted or otherwise mounted on ring 34. The peripheral edge of disk t blades 41 alternating. The fan structure is completed by an annular ring 42 supported by the opposite edges of the fan blading and mounted by rivets or other means on a collar member indicated generally at 44.

The collar member 44 comprises generally an annular ring 45 having an outside diameter just slightly smaller than the diameter of annular opening 21 and lying partially within that opening, and a tubular ring member 46 having an outside diameter just slightly smaller than the diameter of annular opening 19 and lying partially within that opening. One end of tubular member 46 fits within ring 45 and the two are held together in a composite collar member by means of a reinforcing ring 47 riveted to ring 45 and welded to tube 46, or otherwise suitably secured. The inner surface of collar member 44 is supported by the edges of radial splines 36. The end of collar member 44 which projects through opening 19 is of reduced thickness providinga-shoulder 48 upon which an end plate 49 rests. :Plate 49 is Welded to collar member 44 and forms one secondary end plates 51 and 52 and the divider rings 54 are provided at theirperipheries with a plurality of round openings for receiving rods or pins 55, or other suitable blading, which extend theentire length of the classifying zone and form the cage of the classifying rotor. Rods or pins-55 are parallel to each other and -to shaft 29. Spaced inwardly from these rods or pins are a pluralityof other smaller openings for receiving rods 56 upon which circumferential fins or classifying Jdisks'57 are'imounted to form a drum-like structure'within the classifying rotor. Rods 56 are threaded at one end to be received into threaded-openings in secondary end plate 52 and serves to secure all of the elements forming the classifier into a unitary rotor assembly which may be readily removed and replaced by other similar assemblies. alternately by means of spacer disks or washers 58 which encircle only rod 56 and by annular spacer rings 59 which encircle the entire rotor structure.

Plates Stand '52, divider rings 54 and classifying disks 57 are all mounted perpendicular to shaft 29 and projecting radially out- "ward therefrom. The inner diameters of divider rings 54 and classifying disks 57 are substantially greater'than the outside diameter of tube '30 such that an annular axial passage 60 is formed by the outer surface of tube 30 and the inner edges of rings 54 and disks 57. Thus, the classifier rotor comprises generally an outer cage formed of the rotor blades and an inner drum formed-of spaced annular disks forming an annular axial passage or duct 60 around tube 30 of the rotor shaft.

A generally frusto-con'icalspacer ring 61 fits around the rotor structure tube 30 within annular passage 60, tapering inwardly toward the fan housing for the purpose of equalizing flow of gaseous fluid through the sections of the classifying unit. A spacer disk 62 secured to fan housing end plate 17 fills out the fan housing.

As shown in Figure l the classifier is provided with a feeder 64, which may be rotary orof another type, but which is perferably-provided with a variable speed drive. The feeder is -mounted on the top of inlet 65 (Figure 2) for feeding through opening 67 tangentially into the classifier housing. The feed inlet is provided with a port 68 provided with a slidable damper 69 to regulate the amount of air or other gaseous fiuids which may enter the feeder.

The involute classifier housing is provided with an inner liner 70 which forms part of the involute scroll and is adjustable through its upper quadrant adjacent the feed inlet to vary the spacing between the classifying rotor and the housing wall. Means '71 are provided for adjusting the position of the movable portion of the liner Wall and holding it fixed in its adjusted position for the desired running clearance of the rotor.

An outlet for oversize and denser particles is provided along the length of the bottom of the classifier housing. The outlet comprises a discharge opening 72 in the bottom wall of the housing. with a slide-out damper 73 by which the size of the opening may be varied. Positioned immediately under the discharge opening is a means for continuously and constantly removing the oversize material as it accumulates in the classifier. In the form here shown this means comprises an endless flexible belt'74 carried on rollers Classifying disks 57 are held spaced apart Opening 72 is provided 75 and 76, one of which is connected to suitable drive means, preferably a variable speed motor. The belt 74 fits tightly against discharge opening '72 supported on a fiat guide member 77. The outersurface of belt 74 is provided with a plurality of slats or cleats for dragging out the oversize material. Although belt 74 is driven at a constant rate it is preferably provided with a variable speed drive means so that the rate of removal of oversize material may be varied depending upon the material being treated, the rate of extraction and the like.

In the operation of the classifier a fluent bed of pulverulent material is maintained at the bottom of the classifier housing. The pulsating air action of the rotor maintains the bed in a constant fluid state and provides a differential settling effect. The bed is preferably maintained substantially constant at a predetermined optimum depth. This depth of bed may be maintained automatically by means of pressure sensitive elements 78 and 79 set in the walls of the classifier housing on opposite sides of the bottom by detecting and measuring the pressure differential between points A and B and by means of a suitable conventional relay amplifier varying the feeding rate of the feeder 64. The periphery of the rotor, and end walls of the housing and the surface of the bed define a channel of given cross-sectional area of gas flow. As this area reduces by an increase in the thickness of the bed the pressure differential between points A and B greatly increases, and conversely.

One method of interlocking the depth or level of the bed and the rate of feed is based on this pressure drop. The pressure sensitive elements 78 and 79 may be connected to a mercury U-tube so as to produce a fluctuation in the levels of the mercury corresponding to the pressure drop. By suitably placed electrical contacts within the mercury tube an electrical signal may be transmitted which may be translated into energy by which the feed mechanism may be made to start and stop or to be driven at variable speeds. In one form of operation thefeeder mechanism may be adjusted to a constant rate slightly in excess of capacity of the classifier, but on an intermittent flow basis. This intermittent flow may then be stopped and restarted by electrical impulses from the control tubes as the level of the bed fluctuates. Similar results may be obtained by the use of commercially available pressure sensitive electronic control units.

If the percentage of oversize and dense particles in the material fed varies greatly, necessitating constant change in the rate of oversize withdrawal to maintain a bed of uniform thickness, the pressure drop or differential over the bed may also be used to regulate this rate of withdrawal.

An alternative form of oversize withdrawal means is shown in Figure 7. In the form here illustrated a corrugated or similarly toothed roller 80 is positioned in the mouth of discharge opening 72A and driven at a regulatable rate for continuous withdrawal of the oversize and dense material into a tailings box 81 mounted below the discharge opening in the housing wall. The discharge of this material from the tailings box out through spout 82 may be regulated by adjustment of slide 84 in which the spout is carried.

A supplemental air intake may be provided into the bottom of the classifier housing for assisting in maintaining the bed of pulverulent material in a fluent state. The bottom Wall of the housing, adjacent to the discharge opening is provided with a plurality of slots 85 or similar perforations. An air intake housing 86 in the form of a pendent box covers the perforated area of the housing wall and is provided with spout means 87 for connection to a pressurized air supply. A screen 88 is preferably provided over the perforations in the housing wall. The air supply may be regulated by means of a sliding damper 89. This supplemental air supply makes possible a highly activated fluid bed under the rotor, desirable for certain purposes andtypes of classification.

of the classifier.

As shown in Figure 3, a scroll housing is provided around the fan impeller unit, said housing being composed of an outer spiral plate 90 of gradually increasing radius in the clockwise direction. Attention is again called to the fact that the direction of rotation of the classifier rotor in its involute scroll housing is the reverse of the direction of rotationof the fan in its scroll housing, which is normal. The fan housing is provided with an outlet 91 from which the classified particles are discharged .to a suitable collector for separation from the gaseous carrier. A damper 92 is provided for varying the size of the outlet opening.

Broadly stated, the operation of the apparatus of this invention comprises the steps of feeding a controlled supply of dry pulverulent solid material and air (or other reactive or inert gaseous carrier) tangentially to the involute classifying area and subjecting the solid material to three successive aerodynamic reactions. The first of these aerodynamic reactions is a primary classification and takes place in the space between the rotor and the classifier wall due principally to differential settling within a fluid bed of the particulate material at the bottom of the classifier housing adjacent to the feeder inlet. As the stream of pulverulent material and air is fed tangentially intothe classifying zone it is initially subjected to turbulence andcomplete dispersal of the pulverulent material as the pulverulent material falls to the bed at the bottom In this area, between the feed inlet and the bed of particles at the bottom of the housing, the clearance between the rotor and the housing wall is greatest so that the action of the rotor has little direct effect on any but the finest particles.

' In reality, the fluent bed at the bottom of the classifier is the source of supply upon which the rotor feeds. At this point the action of the rotor above the bed maintains thebed in a pulsating turbulent fluid state which has a differential settling effect upon the paricles. The coarse, hard-and dense particles settle to the bottom of the bed where they may be removed. This effect may be heightened and the turbulence of the bed activated by introducing additional air into the bottom of the housing and up through the bed. The unwanted oversizes are preferably withdrawn through the discharge outlet at the constant rate allowing the oversize material to remain in the bed long enough that substantially all of the fines and near fines may be extracted by the rotor from the oversizes before they are withdrawn.

The differential settling effect in this initial stage of the classification process will cause the formation of a bed of graded particle sizes. The top layers will be composed of substantially all fines and near fines with substantially no oversizes, graduated down through layers of near fines and some oversizes, oversizes with some fines and then finally to the bottom which is made up of a layer which is substantially all coarse, hard and dense material with a minimum of wanted fines and near fines. This substantially complete extraction of the fines and near fines from the oversize may be achieved by allowing the oversize to remain in the bed for a sufiiciently long time, care being taken, however, to prevent the accumulation of oversize at the bottom of the bed from substantially increasing the depth of the bed.

The rotation of the rotor cage formed by the spaced peripheral blades produces a plurality of intra-blade vortex flows as indicated in a greatly simplified and diagrammatic form in Figure 5. These intra-blade vortex flows comprise generally constantly circulating air streams into and out of the rotor cage in the form of distorted loops 94. The forward motion of each blade creates a vacuum behind that blade. Thus, immediately behind the blade there is an immediate inrush of air to fill the vacuum. This air has an accelerated forward motion. The next following blade advancing toward the vacuum compresses the air directly in front of the blade tending to push that air radially outward. This air in am n turn tends 'to rush in to fill the vacuum behind "the forand contributes to the accelerated forward motion of the air around the periphery of the rotor cage. The result of these several forces plus the centrifugal throwout effect of the rotating rotor cage contribute to form the plurality, of distorted circular high speed vortices or loops having an accelerated forward motion extending beyond the periphery of the rotor and a diminishing forward velocity within the periphery of the rotor.

As the rotor cage rotates above the fluid bed of particles at the bottom of the classifier housing and the outer faces of the vortex flows circulating at high velocity beyond .theperiphery of the rotor come into contact with the fines and near fines ebullating at the surface of the turbulent fluid bed, these fines and near fines are picked up and carried into the intra-blade vortex flow. Be cause the rotor provides a uniform positive centrifugal barrier at its periphery only the fines and near fines can enter the rotor. Any oversize material picked up by the vortices is immediately rejected and returned to the fluid bed at the bottom of the classifier where it may settle out and be withdrawn. Although all but the wanted fines could theoretically be prevented from entering the rotor, both fines and near fines are permitted to enter the rotor in order to insure easy entry of all of the fines and to provide classification in depth so as to attain the highest possible commercial efficiency.

The grading and separation of the particles of gradually differing sizes within the intra-blade vortex flows constitute the second aerodynamic reaction of the classifying process and the first step in the final selective classification. The throwout effect of the particles is a function of rotor speed. In this process a rotor speed providing a resistance through the centrifugal barrier ofabout 1000 to 1200 G is generally used, but may, of course, be varied widely depending upon varying needs. The pulverulent material in the air attains its maximum throwout effect or MV immediately behind each blade. Thus, as shown in the drawing the coarser of the fine and near fine material, indicated by the coarser arrows 9 5, is prevented from breaking through the barrier back [of the blade and its flow is immediately reversed. The somewhat finer particulate material, here indicated by intermediate arrows 96, because of its lesser mass, breaks through the barrier back of the blade but its forward velocity is largely reversed by the outward suction of the following blade. The verywfi-nest particles, indicated by the fine arrows 97, break through the resistance barrier and because the MV of this material is greatlyreduced -it is carried back farther into the rotor. Here the radial drag of'the air is diverted and its radial component is greatly reduced so that the inner vortex flow becomes, in fact, a closed loop as illustrated diagramrnatically.

Thus, it is seen that the second aeuodynamicreaction is a sorting and grading action caused by the vortex flows between the blades of therotor. The loop formed by the intra-blade vortex is in fact made up of a plurality of circulating streams of graded particle sizes. The inner portions of these circulating streams, behind the resistance barrier created by the rotor blades, are graded strictly according to particle size .With the path of the finest particles extending farthest into the rotor, the path of the next finest particles being just inside the outermost loop, and so on in a great number of precisely this grading reaction presented in Figures and 6, is

,greatly over-simplified and that the graduation of particle sizes within the vortex loops is infinitely finer and more precise than illustrated.

leaves the mill. extend out to the zone where the wanted size of solid When a further air flow is superposed on the vortex loops by suction through the rotor created by the exhaust fan, the effect is to elongate and further distort the intrablade vortex loops. This effect is shown in simplified and diagrammatic form in Figure 6 where the air flow induced bysuction is represented by arrows 98 distorting the loops as indicated at 94A. By drawing the intra-blade vortex loops into the periphery of the drum of disks within the rotor cage, that is, into "the intake ports formed by the spaced annular disks mounted inside of the rotor cage, it is possibleto disrupt or break the fiow of the outer edges of the vortex loop and withdraw at least part of the fine particles circulating in this flow. This constitutes the third aerodynamic reaction in the classification process. I l i As shown in Figure 6, the radially innermost position of the vortex loop, where the particles of the desired size are circulating, is sucked into the rotor drum. The suction applied by the exhaust fan is controlled to be sufficient at this point to overcome the centrifugal throwout effect of the rotor and break the edge of the vortex loop pulling at least some of the wanted particles into the axial annular duct and out through the fan housing. At the normal operating motor velocities the desired size particles enter the rotor carried in the vortex loops hundreds of times a second. Thus, a wide factor of safety is provided for since only a small percentage of the desired particles need be picked up from each cycle into the rotor. Five to ten percent pick-up will suflice since the wanted particles passed over in one cycle may be picked up on the next.

By varying the spacing of the blades forming the rotor cage and the velocity of the rotor a preferred vortex shape for any given material and size range may be obtained. It will'be observed that allof the material entering the rotor attains a high centrifugal energy. This is a function of peripheral velocity and can be varied at will. Classification as to particle size is due to the outward pull of gravity against the inward drag of air flow in diametrically opposite directions. T o obtain an adequate differ- .ential between these two forces in the case of subsieve -material it is therefore necessary to increase as much as possible the centrifugal force as between particles of different sizes. The normal difference between theforce of gravity upon the mass of a 1 micron particle and a 2 micron particle as to air drag or air velocity is negligiwithin a range for any given material and classifier arrangementQ The blading of the rotor cage performs these functions. The radial depth of the graded zone of particle size distribution may be increased and the vortex loops expanded inwardly as much as may be desired by the fan unit which draws a regulatable amount of air through the classifier against the resistance of the classifier rotor.

The principal function of the inner rotor drum formed by the spaced annular disks isto position the intake ports between the annular disks-in proper relation to the circulatingwanted particle size, that is, to provide a predetermined cut-oif point where the outgoing material actually The annular channels of the drum must its .annular' channels equalizing suction at its intakeports and minimizing turbulence. The air flow may be further regulated and 'controlledby varying the spacing between 11 the disks, the diameters of the disks, the the spacer rings 61 and the like. 7

Because of the pattern of flow of air in the intra-blade vortex loops a relatively dead air space exists behind each blade of the rotor cage as best illustrated in Figure 6. The existence of this relatively dead air space causes a build up of particles behind each of the rotor blades in the form of an air foil tail as indicated at 99. The presence of this accumulation of particles behind the blades of the cage in no way adversely affects the classifying action of the machine.

The aerodynamic classifier of this invention is adaptable to the classification of a great many pulverulent materials, such as, for example, grain flours, talc, clays, kaolin, frits, pigments, graphite, paper and paint fillers, insecticides, various chemicals, metal powders, foodstuffs such as cocoa and the like.

In processing talc, clays, graphite and the like the material is normally first reduced in a ball or rod mill to about 325 mesh. The wanted material, such as talc, generally grinds down more and finer than the crystalline gangue and other grit. This material is classified fine enough to get out as much as possible of the wanted product, but more important to eliminate all the heavy crystalline material. The oversize is reground to recover more or all of the wanted material and classified. This progressive reduction in grinding in two or more steps is particularly advantageous when the feed is contaminated with material which is harder to grind and other undesirable material in the product. Progressive reduction and classification saves power and mill wear. Every time the fines are removed the mill etficiency increases. The product is better, being substantially free from contamination and capable of being classified to any desired fineness.

If the feed is a heterogeneous material, which contains a softer and more valuable product that reduces more readily. and finer, it can be extracted in the grinding process. if one part of the heterogeneousmixture has substantially less mass weight it can be separated out by first classifying the mixture into particles of substantially the same particle size.

In many types of grinding the wanted product must not exceed a specified particle size and contain a minimum of super fines. This calls for a properly selected mill operating in series with the classifier operating on the principle of progressive reduction. The mill product is continuously passed through the classifier for the continuous removal of the wanted size at a rate which will reduce overgrinding to a minimum. The oversize is continuously re- \turned to the mill. Such progressive grinding is desirable for most grinding problems from the standpoint of milling efliciency since it permits increasing capacity with decreasing power cost and maintenance due to wear.

As many apparently Widely difierent embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that I do not limit myself to the specific embodiments herein.

What I claim is:

l. A classifier for dry pulverulent solid material comprising an involute scroll classifier housing and a fan housing spaced apart therefrom, a rotor journaled for rotation horizontally in said classifier housing opposite to the direction of the involute scroll, multi-stage centripetal extraction classifier means comprised of a plurality of closely spaced radial annular discs mounted between ananular end plates on said rotor within said housing, said rotor carrying a plurality of spaced vortex flow-inducing members surrounding and spaced outward from the peripheries of the discs, the inner end of the involute scroll classifier housing wall being adjustable for varying the running clearance of the rotor, radial fan means in said fan housing and an axial duct leading from said classifying means longitudinally to said fan.

2. The combination of an involute scroll classifier housing, a tangential material and air inlet to said housdistribution of ing, a multi-stage centripetal extraction classifying rotor comprised of a plurality of closely spaced radial annular discs mounted between annular end plates, said. rotor carrying a plurality of spaced vortex flow-inducing members surrounding and spaced outward from the peripheries of the discs, said rotor journaled for rotation horizontally in said housing opposite to the direction of the involute scroll, said tangential inlet being disposed horizontally along the length of the housing at substantially the level of the axis of the rotor, an axial duct running lengthwise of said rotor, the inner end of the involute wall of said classifier housing being adjustable for varying the running clearance of the rotor, a fan having spaced radial passages therein exterior of the classifier housing, said radical fan passages being in direct communicationwith said lengthwise axial rotor duct, and a housing enclosing said fan, said housing being spaced apart from said classi fier housing.

3. A classifier for dry pulverulent solid material coniprising an involute scroll classifier housing, a tangential material and air inlet to said housing, feeder means for controlling the feed of material, a multi-stage centripetal extraction classifying rotor comprised of a plurality of closely spaced radial annular discs mounted between annular end plates, said rotor carrying a plurality of spaced vortex flow-inducing members surrounding and spaced outward from the peripheries of the discs, said rotor journaled for rotation horizontally in the housing, said tangential inlet being disposed horizontally along the length of the housing at substantially the level of the axis of the rotor, the involute walls of said classifier housing providing for substantial clearance around said rotor at the bottom of the classifier housing to permit the'accumulation of a substantial bed of material at the bottom or" the housing, a horizontal longitudinal discharge opening in the wall of the classifier housing adjacent the bottom thereof for removing relatively coarse and dense particles from said classifier, an axial duct in said rotor in direct communication with radial fan passageways at one end thereof and a housing enclosing said radial fan passageways forming a fan housing.

4. The apparatus according to claim 3 further characterized in that movable over-size removing means are mounted horizontally outside of the housing adjacent to said discharge opening as a metering closure therefor for removing relatively coarse and dense particles from said classifier and maintaining a bed of material of optimum thickness in the bottom of the classifier.

5. Apparatus according to claim 4 wherein said movable means is an elongated longitudinally corrugated roller.

6. Apparatus according to claim 4 wherein said movable means is an endless belt having shallow spaced apart cleats on its outer surface.

7. A classifier for dry pulverulent solid material comprising an involute scroll classifier housing, a tangential material and air inlet to said housing, feeder means for controlling the feed of material, a multi-stage centripetal extraction classifying rotor comprised of a plurality of spaced radial annular discs, said rotor carrying a plurality of longitudinal rods parallel to therotor shaft spaced about the periphery of the rotor, said rotor being sectionalized by spaced annular plates mounted on said rotor, said rotor journaled for rotation horizontally in the housing, said tangential inlet being disposed horizontally along the length of the housing at substantially the level of the axis of the rotor, the involute walls of said classifier housing providing for substantial clearance around said rotor at the bottom of the classifier housing to permit the accumulation of a substantial bed of material at the bottom of the housing, a horizontal longitudinal discharge opening in the wall of the classifier housing adjacent the bottom thereof for removing relatively coarse and dense particles from said classifier, an axial duct in said rotor in direct communication with radial fan passageways at one end thereof and a housing enclosing said radial fan passageways forming a fan housing.

8. The apparatus according to claim 7 further char acterized in that the axial duct of said classifying rotor is defined by the inner edges of the plurality of, spaced annular disks projecting radially within the hous ng, the spaces between the discs forming a plurality of radiating annular slot passageways in direct communication with said duct.

9. The apparatus according to claim 3 further characterized in that said feeder means is provided with drive means whereby it feeds solid material to said classifier housing synchronously with the withdrawal of solid material. from the housing, said feeding drive. means being controlled by detecting means in said housing wall sensitive to the pressure differential over the bed of accumulated solid material at the bottom of the housing.

' 10. The combination of an involute scroll classifier housing, a tangential material and air inlet to said housing, closures at each end of the housing, one of said closures having a circular opening, a rotor journalled for horizontal rotationwithin the; housing opposite to the direction of said involute scroll and projecting through said circular opening, the inner end of the involute scroll classifier housing wall being adjustable for varying. the running clearance of the. rotor, a horizontal longitudinal discharge opening in the wall of the classifier housing adjacent the bottom thereof for removing relatively coarse and dense particles from said classifier, an axial duct running lengthwise of the rotor, a plurality of annular plates mounted on said rotor, a plurality of longitudinal rods parallel to the rotor shaft spaced about the peripheries of said annular plates forming a rotor cage, an inner axial drum comprising a plurality of spaced annular disks mounted on said rotor between said annular plates projecting radially outward from the said axial duct, a fan portion having radial passageways mounted at the end of the rotor projecting through said circular opening and in direct communication with said lengthwise axial duet, a housing for said fan portion spaced apart from the classifier housing, a discharge outlet in said fan housing for said solid material and a damper for controlling air fiow through the classifier.

11. A classifier for dry pulverulent solid material comprising an involute scroll classifier housing, a tangential material and air inlet to said housing, means for controlla ily feeding material into said inlet, closures at each end 01. said housing, one of said closures having a circular opening, a rotor journalled for horizontal rotation in the housing opposite to the direction of said scroll and projecting through the circular opening, the inner end of the involute scroll classifier housing wall being adjustable for varying the running clearance of the rotor, a horizontal lo lgitudinal discharge opening in the wall of the classifier housing adjacent the bottom thereof for removing relatively coarse and dense particles from said classifier, a plurality of annular plates mounted on the rotor within the housing and carrying a plurality of rods adjacent their outer perimeter forming a rotor cage, said rods being substantially perpendicular to said plates and parallel to said rotor, an inner axial drum comprising a plurality of thin spaced annular disks within the housing between said annular plates, an axial duct in said rotor in direct communication from the annular slots between the spaced annular disks to radial fan passageways in the rotor at the end thereof projecting through the circular opening, a housing enclosing said radial fan passageways forming a fan housing, said fan housing being spaced apart from the classifier housing, a discharge outlet in said fan housing for said solid material and a damper in said outlet for controlling air through the classifier.

12. An involute scroll classifier housing comprising two end closures, means for journalling a classifying rotor for horizontal rotation between said end closures, said rotor comprising a plurality of closely spaced radial '14 annular discs mounted between annular end plates, said rotor carrying a plurality of spaced vortex flow-inducing members surrounding and spaced outward from the pe ripheries of the discs, the walls of said housing forming an involute scroll around said rotor between said end walls pro-vidingfor substantial clearance around said rotor at the'bottom of said housing to permit the accumulation of a substantial bed of material at the bottom of said housing, an elongated horizontal tangential inlet mounted on one side of said housing at about the level of theaxis of the rotor for controllably feeding solid material to be classified and a gaseous carrier therefor tangentially into .said housing and a central circular opening in one of said end closures forming an outlet from said housmg.

13. The apparatus according to claim 12 further characterized in that a horizontal longitudinal discharge opening is provided in the wall of the classifier housing adja cent the bottom thereof for removing relatively coarse and dense particles from said classifier, said discharge opening extending the length of the classifier housing.

' 141. The apparatus according to claim 13 further characterized in that movable over-size removing means are mounted horizontally outside of the housing adjacent to saiddischarge opening as a metering closure therefor for removing relatively coarse and dense particles from said classifier and maintaining a bed of material of optimum thickness. in the bottom of the classified.

15. The apparatus according to claim 12 further characterized in that said feeder means is provided with drive means whereby it feeds solid material to said classifier housing synchronously with the withdrawal of solid ma terial from the housing, said feeding drive means being controlled by detecting means in said housing wall sensitive to the pressure differential over the bed of accumulated solid material at the bottom of the housing.

16. A method of classifying dry pulverulen-t solid materials which comprises subjecting said material to a sequence of individually controllable aerodynamic reactions, said method comprising feeding a controlled supply ofdry solid-material and gas tangentially'into a horizontally disposed generally involute classifying zone for substantially uniform distribution longitudinally thereover, differentially settling out and removing the coarser and denser pulverulent material by maintaining the feed material initially in a pulsating fluent bed at the bottom of the classifying zone, continuously whirling a fiuidal stream of the remaining finer particles of the solid material centrifugally at' high speed in a generally arcuate path of gradually diminishing cross-sectional area around the outer periphery of the involute classifying zone, said fiuidal stream of particles being comprised of a plurality of smaller fiuidal streams of particles of the solid material entrained in the gas whirling at high speed around the inner periphery of the involute classifying zone setting up a plurality of inner vortex flows, said inner vortex fiows being composed of a plurality of circulating streams of particles in precisely graded sequence, further separating the finer particles of solid material from the coarser particles by superimposing upon the fiuidal streams of particles suction from axially of the involute classifying zone to distort and elongate the paths of said vortex flows radially inward, continuously and repeatedly withdrawing centripetally at least part of the desired fine particles from the inner vortices by further distorting and elongating the inner vortex fiows radially inwardly and by overcoming their centrifugal action by added suction whereby the paths of the particles of desired size may be intercepted and classification of the. wanted particle sizes is obtained.

17. A method of classifying dry pulverulent solid materials which comprises subjecting said material to a se' quence of individually controllable aerodynamic reactions, said method comprising feeding a controlled sup ply of dry solid material and air tangentially into a horizontally disposed generally involute classifying zone for substantially uniform distribution longitudinally thereover, differentially settling out and removing the coarser and denser particles of said material by maintaining the feed material initially in a pulsating fluent bed at the bottom of the classifying zone, continuously whirling a fluid-a1 stream of the remaining finer particles of the solid material centrifugally at high speed in a generally arcuate path of gradually diminishing cross-sectional area around the outer periphery of the involute classifying Zone, said fluidal stream of particles being comprised of a plurality of smaller fluidal streams of particles of the solid ma terial entrained in the air whirling at high speed in arcuate paths in narrow segregated radial zones around the inner periphery of the involute classifying zone setting up a plurality of looping inner vortex flows, said inner vortex flows being composed of a plurality of circulating streams ofparticles in precisely graded sequence, further separat ing the finer and lighter particles of solid material from the coarser and denser particles by drawing air radially inwardly from the periphery of the involve classifying zone thereby superimposing suction upon the fiuidal streams of particles to distort and elongate the paths of said looping vortex flows radially inward, intercepting the paths of the thus distorted vortices in an inner cylin drical zone in which at least part of the circulating particles are of the desired size and density and continuously and repeatedly centripetally withdrawing at least part of these desired particles by drawing the outer periphery of the vortices in which the desired particles circulate radially inwardly by added suction imposed upon the fiuidal streams of particles to overcome their centrifugal ac tion whereby particles of the desired size and density are uniformly and completely removed from the classifying zone.

18. The method of claim 17 further characterized in that the pulsating fluent bed of, pulverulent solid material maintained at the bottom of the involute classifying zone is comprised in part of unwanted coarse and dense particles which unwanted particles are continuously removed from the bottom of said classifying zone and the solid material to be classified is introduced synchronously with the accumulation of said material in said bed as determined by the pressure difierential over said bed, thereby maintaining the bed at a substantially constant level.

19. A classifier for dry pulverulent solid material comprising an involute scroll classifier housing and a fan housing spaced apart therefrom, a rotor journaled for rotation horizontally in said classifier housing and multi: stage centripetal extraction classifying means mounted on said rotor within the housing, said classifying means comprising a plurality of closely spaced radial annular discs mounted between annular. end plates, said rotor carrying a plurality of vortex flow-inducing members sur rounding and spaced outwardly from the peripheries of the discs, the inner end of said involute classifier housing wall being movable and adjustable for varying the running clearance of the classifier rotor, means for adjusting said involute scroll housing, radial fan means in said fan housing and an axial duct leading from said classifying means to said fan.

References Cited in the file of fl'iis patent UNITED STATES PATENTS 661,086 Stebbins Nov. 6, 1900 690,652 James Jan. 7, 1902 844,842 Anderson Feb. 19, 1907 850,959 Och Apr. 23, 1907 1,356,384 Marshall Oct. 19, 1920 1,420,593 Titchmarsh June 20, 1922 1,787,079 Lykken Dec. 30, 1930 1,920,117 Tenney July 25, 1933 2,214,434 Nelms Sept. 10, 1940 2,255,206 Duncan Sept. 9, 1941 2,361,758 De Flique Oct. 31, 1944 2,403,740 Muench July 9, 1946 2,597,333 Jindrich May 20, 1952 2,706,088 Paul Apr. 12, 1955 2,754,967 Lykken July 17, 1956 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No, 2,915,179 December I, 1959 Henry C1,, Lykken It is hereby certified that error appears in the-printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1, line 16, for "pulVereni" read pulverulent column 3, line 27, for "though" read through column 4, line 53, for "fines" read finer column 6, line 1, for "fits" read fi'b column 12, line- 15, for "radical" read are radial column 14, line 26, for "coa'se" read me coarse line 28, for "classified" read classifier column 15, line 21, for "involve" read involute Signed and sealed this 24th day of May 1960.,

(SEAL) Attest:

KARL H. AXLINE ROBERT C. WATSON Attesting Officer Commissioner of Patents

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