US3015392A

US3015392A - Vertical feed centripetal classifier

Info

Publication number: US3015392A
Application number: US833771A
Authority: US
Inventors: Tibor A Rozsa; Robert O Holmes
Original assignee: Microcyclomat Co
Current assignee: Microcyclomat Co
Priority date: 1959-08-14
Filing date: 1959-08-14
Publication date: 1962-01-02
Anticipated expiration: 1979-01-02

Description

Jan. 2, 1962 T. A. ROZSA ETAL 3,015,392

VERTICAL FEED CENTRIPETAL. CLASSIFIER Filed Aug. 14, 1959 3 Sheets-Sheet 1 FIG. 1

INVENTORS 7180/? A R0 26A BY ROBERTO. HOLMES ATTORNE vs Jan. 2, 1962 1-". A. ROZSA ETAL VERTICAL FEED CENTRIPETAL CLASSIFIER 3 Sheets-Sheet 2 Filed Aug. 14, 1959 ZNVENTORJ 7750;? A. Ro 26A ROBERTO. I'I'OLMEd ArToR/vEYo' Jan. 2, 1962 T. A. ROZSA ETAL VERTICAL FEED CENTRIPETAL CLASSIFIER 5 Sheets-Sheet 3 Filed Aug. 14, 1959 INVENTORS 775 OR A. Ro 26A BY ROBERT O. HOLMES wm ww ATTORNEYS Patented Jan. 2, 1952 3,615,392 VERTICAL FEED CENTWETAL CLASSIFIER Tiber A. Rozsa and Robert 0. Holmes, Minneapolis, Minn, assignors to The Mierocyciomat Co., Minneap olis, Minn a corporation of Delaware Filed Aug. 14, 1959, Ser. No. 833,771 13 Ciaims. (Cl. 209144) This invention relates to a new and improved vertical classifying apparatus and method for the sharp separation of fractions of dry pulverulent material. More particularly, this invention relates to a centripetal classifier for dry pulverulent material having a peripheral inletaxial outlet classifier rotor disposed on a vertical axis provided with a novel and improved large volume peripheral air inlet and positive coarse particle discharge outlet. The classifier is fitted with a classifying rotor of novel design provided with a deck selector means for varying the rotor capacity and varying the product characteristics.

A principal object of this invention is to provide a centripetal classifier of improved efliciency having a peripheral inlet-axial outer classifier rotor disposed on a vertical axis provided with an air inlet structure adapted to supply air evenly and simultaneously to all portions of the classifying zone at the periphery of the rotor.

Another object of this invention is to provide a vertical classifier which eliminates cross paths of coarse and fine particles which interfere with complete coarse discharge by providing positive coarse particle throwout means for quickly and decisively discharging all of the oversize particles from the classifier.

Still another object of this invention is to provide a vertical classifier of overall lower height which is easier to install and which is due to the shortening of the duct between the classifying zone and fine particle discharge because of the elimination of air-inlet means at this point. By shortening the duct between the classifying zone and fine particle discharge, the tendency for the accumulation of deposits of fine particles which unbalance the rotor and cause vibration has been eliminated.

A still further object of this invention is to provide an improved efiicacious method of classifying particles of solid material characterized by the. substantially simultaneous and uniform introduction of air to all parts of the classifying zone whereby the particles to be separated are exposed to uniform and optimum display of opposing forces.

A further object of this invention is to provide a vertical classifier having means for varying the proportion of the rotor which is utilized and for varying the classifier capacity and cut size characteristics of the classifier product thereby.

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

To the accomplishment of the foregoing and related 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 invention, these 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 the same numerals refer to corresponding parts and in which: FIGURE 1 is an elevation in section, through the center of the vertical classifier of this invention;

FIGURE 2 is a horizontal section on the line 22 of FIGURE 1 and in the direction of the arrows;

FIGURE 3 is a horizontal section taken on the line 33 of FIGURE 1 and in the direction of the arrows; FIGURE 4 is an enlarged fragmentary elevation, in

section, through the discharge portion of the classifier showing a modified form of pneumatic seal to prevent intermingling of particles from the coarse and fine discharge passages; and

FIGURE 5 is a further enlarged fragmentary elevation, partly in section, showing in greater detail the air inlet to the modified pneumatic seal means.

Referring to the drawings, the vertical classifier of this invention comprises generally a base platform 10 mounted on supports 11, a fan housing 12 spaced above base platform ill and supported by an annular plate 13, an air inlet scroll 14 whose inside periphery forms a housing for the classifier rotor and a top cover and material feed housing indicated generally at 15. A vertical shaft 16 extends generally from the top to the bottom of the apparatus through the classifying and fan housing sections. The top end of shaft 16 is journaled in a suitable bearing structure 17 supported in a spider structure 18 mounted within the top cover and material feed housing 15. The lower end of shaft 16 is journaled in a suitable bearing structure 19 supported in a ring mount 20 on platform 11 A multiple drive pulley 21 is keyed to the lower end of shaft 16 adapting the shaft to be driven by belts 22 from any suitable motor means.

Vertical shaft 16 is enlarged and reinforced through the part of its length that extends through the classifying and fan housings by a cylindrical tube 23 supported by annular rings 24 and 25 secured to the shaft. The tube structure is reinforced by a further intermediate annular ring 26 secured to the shaft for supporting rotor elements, as described in greater detail hereinafter. An annular top plate 27 is mounted on the top annular ring 24 around the shaft. The top surface of plate 27 is provided with an annular flange 23 having a shoulder at its upper and outer edge which supports the inner periphery of an annular ring 29.- The outer periphery of ring 29 is fitted with a plurality of vertical radiating blades 30 adapted to distribute material feed uniformly for introduction to the classifying zone and, in cooperation with a corrugated lining 31 of housing 15, to break up and reduce agglomerated masses of pulverulent material. Annular ring 29 is maintained rigid and stable by means of a plurality of spacer blocks 32 through which the annular ring is secured to top plate 27. A conical shield 33 is provided to prevent accumulation of material within flange 28 and possible unbalance of the rotor thereby.

An annular bottom plate 34 is disposed about the shaft 16 secured to annular ring 25. A flanged ring 35 is disposed about the shaft 16 and tube 23 between the top and

bottom plates

27 and 34. Flanged ring 35 is supported in part by a plurality of radiating spline members 36 whose threaded inner ends extend through tube 23 and are secured around the periphery of the intermediate annular ring 26. A plurality of vertical pegs or rods 37 are disposed about the shaft 16 and tube 23 to form fan means in the fan housing 12. The pegs or rods 37 extend through and are supported by the upper flange 38 and lower flange 39 of ring 35 and bottom plate 34. To impart additional rigidity to the fan structure, diagonal brace members 49 are desirably used to strengthen the peg or rod members 37.

An annular ring disc 41 is supported on the upper flange 38 of ring 35. A plurality of vertical radiating blades 42 are carried by the periphery of ring disc 41 for the purpose of inducing a slight negative pressure in the annular chamber 43 below the air scroll housing 14 in which the disc and blades rotate. Chamber 43 serves as a positive coarse discharge means, as explained in greater detail hereinafter, and is provided with coarse particle discharge ducts 44.

A heavy mounting ring 45 is disposed about the outer periphery of flanged ring 35 supported by the upper flange 38 on top of the ring disc 41. An annular end plate 46 which forms the bottom plate of the rotor classifying section is supported by and secured to the mounting ring 45. An annular plate 47, which forms the top plate of the rotor classifying section, is supported on the bottom surface of rotor top plate 27. The rotor classifying section supported between the bottom rotor plate 46 and the top rotor plate 47 includes a plurality of slotted vertical blade members 48 interlocked with a plurality of slotted horizontal spaced-apart annular disc members 49. The vertical classifier blades may be flat and disposed to radiate out generally from the axis of the rotor or they may be disposed at an angle between radial and tangential. In a preferred form of construction, as shown in the drawings, the vertical classifier blades are curved. Depending upon operating conditions and the desired classification cut, the blades may be curved in the direction of rotation of the rotor or opposite to the direction of rotation.

The intersecting edges of the classifier blades and classifier discs present the appearance of a cylindrical drum having generally a grilled or honeycombed surface. The

'inner edges of the vertical classifier blades and the inner peripheries of the horizontal classifier discs define the outer periphery of an annular chamber 50 around tube 23 which serves as an axial discharge duct through which classified fine particles are conveyed after separation by the classifying section of the rotor to the fan housing for discharge. A plurality of vertical rod members 51 are supported between the bottom rotor plate 46 and top rotor plate 47 to form a cage structure surrounding and spaced outwardly from the grill structure of the classifier drum formed by the vertical blades and horizontal discs. Additional rigidity is imparted to the cage structure by means of intermediate support brackets 52 spaced about the periphery of the drum structure between the classifying section top and bottom plates.

The air inlet scroll housing 14 surrounds the classifier section of the rotor and is substantially co-extensive in height with it. The air inlet housing comprises an outer scroll housing wall 54 held between a top housing wall 55 and a bottom housing wall 56. A tangential air inlet opening 57 to the scroll housing is provided. A plurality V of interior vertical scroll-

baffle members

58, 59 and 60 tions of the classifying zone surrounding the periphery of the'classifier section of the rotor. One or more horizontal baffle members 61 similarly divide the air inlet housing into vertical sections to insure simultaneous and substantially equal distribution of air vertically along the classifying zone and classifying section of the rotor.

In order that the flow of air from the air inlet housing to the classifying area surrounding the classifying section of the rotor may be uniformly directed, an annular louver curtain wall is disposed in the space between the inner periphery'of the air inlet housing and the outer periphery of the classifying section of the rotor. The louver cur tain wall comprises a plurality of individual louvers 63 which may be stationary or, preferably, as shown in the drawings, adjustable as to pitch; The bottom end of each verticallouver element is provided with a pivot or 7 pin structure 64 by which it is journaled for rotation in an annular ring 65 supported by the inner periphery of the airinlet housing bottom wall 56. The upper end of each louver element 63 is provided with a top pin 66.

The top pin of each louver element is provided with a small spur gear 6 7 each of which meshes with the teeth of a ring gear 68 journaled for rotationin a ring bearing 69 supported within a ring flange 70 on the top of the top plate 55 of the air inlet housing. One of the louver elements is fitted with a'crank 71. Rotation of crank 71 causes rotation of the gear 67 which in turn causes rotation of the ring gear 68 and a corresponding rotation of each of the other louver elements. Crank 71 is provided with a pivoted latch 72 adapted to engage a notched latch plate mounted on the top housing 15. The notches in the latch plate 73 correspond to predetermined pitch angles and permit locking the louver members in the desired predetermined positions.

The classifier top housing 15 rests upon the ring flange 78 on the top wall 55 of the air inlet housing 14 secured by a plurality of clamping fastening means 75 for easy removal when desired. The classifying section of the rotor is designed for easy removal for repair, replacement, inversion to change the direction of the classifier blades, etc. by removal of the top housing without disturbance to the remainder of the apparatus. The top housing is provided with a material feed inlet fitted with one or more feed supply ducts 79.

The fan housing 12 is in the form of a scroll housing having a vertical outer housing wall 80 held between a top housing wall 81, and a bottom wall 82. The top plate 81 of the fan housing is provided with a circular opening in which the flanged ring 35 of the rotor is disposed for rotation and the bottom plate 82 is provided with a similar circular opening in which the flanged bottom plate 34 of the rotor is disposed for rotation. A tangential discharge duct 83 exits from the fan housing.

A vertical scroll housing wall 84 extending between the top plate 81 of the fan housing and the bottom plate 56 of the air inlet housing forms the outer housing Wall for both the coarse discharge chamber 43 and one form of a pneumatic seal chamber 85. The coarse discharge chamber 43 and pneumatic seal chamber 85 are separated by a horizontal plate 86 which forms a common wall of the two chambers; To avoid vibration of the inner peripheries of

plates

81 and 86, they are desirably secured together at intervals by spacer posts 87. The pneumatic seal chamber 85 is provided with one or more dampered inlet openings 88 for controlled admission of air to the pneumatic seal chamber. The inner periphery of the pneumatic seal chamber presents the appearance of an annular slot open except where its top and bottom wall members are made rigid by posts 87. That annular slot surrounds the rotor structure in the annular space between the bottom of ring disc 41 and the upper surface of flange 39. The reduced pressure in coarse discharge chamber 43 and the fan housing 12 causes air to be drawn through the inlet openings 88 into the pneumatic seal chamber and out through the inner annular slot opening from the pneumatic seal into the coarse discharge chamber 43 and fan housing 12 to create a positive inflow of air to prevent accidental migration of particles from the coarse discharge chamber to the fine particle discharge of the fan housing or vice versa.

In order to increase the versatility of the classifier of this invention, it is preferably provided with a deck selector means as described in our co-pending application Serial No. 833,772 filed concurrently. The deck selector means makes it possible for the operator to utilize as much or as little of the axial height of the classifying section of the rotor as necessary or desirable for the particular operating conditions or the particular desired product characteristics. The deck selector means includes an annular ring disc 90 disposed in and adapted to be moved vertically with a sliding fit in the annular axial chamber 50 between the outer surface of shaft tube 23 and the inner periphery of the classifier drum structure. The deck selector disc 90 is supported horizontally for vertical travel within the axial duct 50 by a plurality of threaded shafts 91 disposed symmetrically about and spaced from the shaft tube 23.

The deck selector disc 90 is mounted for movement along the threaded shafts 91 by virtue of threaded collars 92 supported on or in the deck selector disc in number and position corresponding to the number and location of the threaded shafts 91. The upper end of each threaded shaft 91 is journaled for rotation adjacent the outer periphery of annular ring 24. The lower end of each of the threaded shafts 91 passes through the bottom rotor plate 34 but is held against dropping through the bottom plate by virtue of a collar 93 on the shaft immediately above the top surface of the bottom plate 34. To minimize friction, bottom plate 34 is preferably provided with sleeves of bearing material in which the shafts 91 rotate and collar 93 preferably bears against a collar or washer of bearing material. A small pinion gear 94- is keyed to the end of each of the shafts 91 which extends below the bottom plate 34. A sun gear 95 is carried by the collar or sleeve 96 extending from the bottom surface of the bottom rotor plate 34 and is secured by a locking nut or threaded collar 97. The gear 95 is journaled for rotation with the end plate 34 and the rest of the rotor structure but at the same time is adapted for rotation with respect to the rotor for adjustment of the level of the deck selector disc. The teeth of each of the pinion gears 94 mesh with the teeth of the sun gear 95 to form a planetary gear system. Thus when the sun gear 95 is rotated relative to the main shaft 16, each of the planetary pinion gears 94 is rotated to cause rotation of the vertical threaded shafts 91. By virtue of the rotation of the threaded shafts the threaded collars 92. on those shafts supporting the deck selector disc are caused to move vertically up or down along the shaft depending upon the direction of rotation and carry the deck selector disc along with them. The rotation of one threaded shaft causes uniform and simultaneous rotation of each of the other shafts.

When the deck selector disc is at the proper desired level, it is maintained at that level by locking one of the planetary pinion gears 94 against rotation by virtue of any suitable latching means. When pinions 94 are thus locked in position, the gear 95 rotates with the main shaft 16 but since there is no relative movement between the

gears

95 and 94, the deck selector disc remains at the predetermined height. The deck selector disc is solid and imperforate. When it is in position, all of the classifying section of the rotor above the deck selector disc is rendered non-operating. By use of this means, the rotor capacity can be varied without dismantling the apparatus. For a given set of operating conditions, the classification out can be varied to permit the separation of smaller or larger particles by moving the deck selector upwardly or downwardly.

A further peneumatic seal is created at the bottom of the classflier housing 12. The reduced pressure within the fan housing causes a small positive air flow through the circular opening in the bottom wall 82 of the fan housing around the flanged periphery of the bottom rotor plate 34- sufllcient to prevent loss of any Wanted fine particles.

In FIGURES 4 and 5, there is shown a modified form of pneumatic seal. According to this form of seal, the vertical scroll housing wall 8 extending between the top plate 81 of the fan housing and the bottom plate 56 of the air inlet housing is foreshortened to eliminate the space between the positive coarse discharge chamber and the top plate 81 of the fan housing. At the same time, flanged ring 35 is replaced by a cast modified flanged ring 35A and the plurality of vertical pegs or rods 37 disposed about shaft 16 and tube 23 to form fan means in the fan housing 12 are replaced by modified hollow tubes 37A. Tubes 37A continue to function as fan means within the fan housing, but at the same time, according to the modified form of pneumatic seal, they act as air ducts for carrying air to the pneumatic seal means.

The top ends of tubes 37A are set in openings in annular ring 35A. The bottom ends of tubes 37A extend through annular bottom plate 34 and are Welded or similarly attached thereto. The lower ends of tubes 37A which extend through plate 34 are threaded and provided with cylindrical cap means 100. The cap is closed at one end and is provided with a substantial opening 101 in one of its cylindrical side walls. Cap 100 is so positioned on the end of tube 37A that, when the classifier rotor is rotated, opening 101 faces in the direction of rotation and thus permits the cap to function as an air scoop to receive air for passage through the inner channel of tube 37A to the pneumatic seal means. The upper ends of each tube 37A is provided with a substantial slot 102 extending through the tube wall around about half of the periphery of the tube. Slots 102 face outwardly toward the outer periphery of ring 35A and cornmunicate directly with an annular slot 103 cut or otherwise formed in the outer periphery of the ring 35A.

The upper and lower surfaces of annular plate 81 are fitted around the inner periphery of the plate with annular flexible rings 104 secured to the plate and extending inwardly past the inner periphery of the plate so as to just provide running clearance for ring 35A. Seal rings 104 are desirably formed from an inert tough flexible resilient material, such as nylon, polyethylene, rubber or the like. The space between the pair of seal rings 104 disposed on opposite surfaces of plate 81 forms a pneumatic seal chamber 105 which communicates directly with the annular chamber 103 in ring 35A. The upper ends of tubes 37A are desirably filled with plugs 105.

In the operation of the modified form of pneumatic seal means, during rotation of the classifier rotor, the air inlet opening 101 is faced in the direction of rotation of the rotor. The size of the air inlet opening may be adjusted by moving cap 100 up or down on the external threads of the tubes. The velocity of the rotor causes air to be scooped into the cap and forced upwardly through the tubes 37A and out through tube slots 102 into annular slot 103 and chamber 105. This creates a higher positive pressure in the chamber 105 relative to the reduced pressures in the fan housing and coarse discharge chamber 43. The air from chamber 105 thus is forced out between the inner periphery of the seal rings 104- and the outer periphery of ring 35A into and through the spaces between stationary annular plate 81 and rotating annular disc 41 and flange 39A of ring 35A, This pneumatic seal effectively prevents intermingling of coarse particles from the positive coarse discharge chamber 43 and fine particles from the fine discharge fan housing. Where space is a factor, the modified form of pneumatic seal permits lowering of the overall height of the classifier without loss of capacity or loss of efiiciency.

In the operation of the classifier of this invention, reduced pulverulent material is introduced into the feed inlet 78 through one or more supply ducts 79. This material falls by gravity past the spider support for the top shaft bearing and onto the annular ring 29. The rotation of ring 29 causes the material to be thrown centrifugally outwardly. The blades 30 assist in uniformly distributing and dispersing the particles and in cooperation with a corrugated lining ring 31 on the interior of the top housing reduces and separates any agglomerated masses of particles. The dispersed feed material then enters the classification chamber passing through the annular space around the top rotor plate 27 and the classification section top plate 47 and the inner periphery of the channel ring member 74 to drop into the annular chamber between the louver curtain wall and the vertical cage rods of the rotor.

The air inlet surrounds the classifying area surrounding the classifying portion of the rotor and by virtue of the construction of the air inlet housing, air is introduced simultaneously and substantially uniformly to all portions of the classifying zone and the periphery of the classifying section of the rotor. The incoming air is given direction by virtue of the pitch of the louver members 63 comprising the louver curtain wall. The incoming particles are thus subjected to the effect of gravity and the driectional air flow from the air inlet. At'the same time the rotation of the rotor sets up a circular air flow about the periphery of the rotor. The vertical cage members 51 induce a plurality of loose intra-rod vortices and the vertical classifier blades 48 induce a plurality of intra-blade vortices about the periphery of the rotor.

The functioning of intra-blade vortices in the classification of fine particles has been amply explained elsewhere and need not be described here. Sufice it to say that vortices are formed between the blades comprising the classification rotor by which coarser particles are circulated within the rotor sections defined by the blades and discs to a predetermined distance determined by the shape and mass of the particles and finer particles are similarly carried to a greater depth into the rotor. The normal centrifugal throwout effect of the rotor upon the particles of predetermined wanted size is overcome by the application of centripetal drag created by an induced air flow through the rotor and out through the axial duct 54 and out through the fan housing and product discharge duct. The induced centripetal drag is balanced with the centrifugal throwout efiect of the rotor at the place within the rotor that the fine particles of desired size are carried by the intra-blade vortices and into which no particles of larger size are carried.

The increased air inlet capacity permits rapid, thorough and uniform dispersion of the solid particles in air with the efiect that the capacity of a classifier of given size is greatly increased. At the same time separation of particles is greatly facilitated because the particles are exposed to a uniform and optimum display of opposing forces. Formerly in classifiers of this type, the material to be separated and air entered the c1assification in counter-current flows which met in the classification zone. The result was that coarser particles had to fight their way through the counter-current flow of air before they could be discharged from the classification zone and hence were detained unnecessarily long in the classification zone before discharge. According to the method of the present invention, the coarser particles drop by gravity through the classification zone and in the course of their downward travel encounter the entering side flow of air which has the effect of separating finer particles from coarser particles without materially detaining the coarser particles in the classification zone. The coarser particles drop by gravity onto the ring disc 41 below the classification zone and are positively thrown out by the centrifugal effect of the rotating disc into the coarse particle discharge chamber 43 and withdrawn through the the ducts 44.

The peg fan in the fan housing 12 functions primarily to keep the desired fine particles dispersed and airborne. Air flow through the apparatus is induced by conventional means, such as a fan, in communication with the discharge duct 83 to withdraw the desired particles and transport them to an air separator, such as a cyclone separator or the like.

Reduced air pressure is created in the coarse particle discharge chamber 43 by blading 42 carried by ring disc 41 and reduced pressure exists in the fan housing both by virtue of rotation of the peg fan and the outside suction source. Coarse particles might ordinarily be drawn from the coarse particle discharge chamber 7 into the fan housing and fine particle discharge were it not for the presence of the intervening pneumatic seal chamber 85. This pneumatic seal operates by virtue of air drawn into the pneumatic seal'chamber through the accidental contamination of the fine particle product by coarse particles. 7

In the practice of the method of classification according to this invention utilizing the described classification apparatus there are, in general, three possible variations with respectrto gas velocity and rotor speed within the annular classification zone between the circumferential as inlet and rotor periphery. The gas, such as air, may be introduced to the gas inlet to the classification zone at a rate to produce an air vortex having a velocity which is greater than the peripheral velocity of the rotor driven on its shaft. Conversely, the rate of introduction of air and circumferential speed of the rotor may be varied so that the peripheral velocity of the rotor is faster than the velocity of the air vortex in the classifying zone. Intermediate of these is the condition in which the velocity of the air vortex and peripheral speed of the rotor are approximately equal.

For purposes of classification, the first condition wherein the air vortex velocity in the classifying Zone is greater than the circumferential speed of the rotor is to be avoided. Classification of particles is hampered because the particles are forced by the higher velocity air vortex against the back or trailing side of the classifier blades. Coriolis force keeps the particles plastered against the blade walls. Air flow and particle movement is slower along the blade and good classification is not possible.

On the other hand, when the rotor speed is greater than the velocity of the air vortex in the classifying zone, the particles to be clasified are subject to a different set of forces. The particles are hit by the blade faces of the faster moving classifier rotor and the particles move on the front or leading side of the blades. As the particles move inwardly along the blade walls under the influence of air drag, Coriolis force lifts them from the blade face where they are subject to opposing classification forces and flows. These conditions allow for orderly entrance of the particles to the chambers between the rotor blades and discs and provide for orderly exit of the coarse discharge and uniform air flow from one blade to another. These conditions are most acceptable for efficient classification.

The intermediate conditions resulting from the peripheral speed of the rotor and the velocity of the air vortex in the classification zone being substantially the same may be utilized for classification, but are less desirable than those present when the rotor speed is greater than the air vortex velocity. Where the speeds are substantially equal, the particles may enter the rotor anywhere in the space between the blade surfaces in suspension in air and are freely subjected to air drag and centrifugal force balance. Some particles will become plastered on the back walls of the blades due to Coriolis force. Others are suspended and subjected to full air drag and centrifugal forces, but the flows are not as orderly as where the rotor has a greater peripheral 'velocity.

The improved classifier structure according to this in- I vention provides for relatively slow circumferential entrance velocity of the gas into the clasifying zone. The cross section of the gas entrances is adjustable by means of the louver wall arrangement. The gas entrance velocity is uniform along the entire height and around the entire periphery of the classifying zone. The incoming particles are subjected to a gradual exposure of opposing forces. This is largely responsible for the efficiency of the present system. The coarse particles are subjectedto an immediate centrifugal throwout and air draw will pull in only the fine and medium particles closer to the rotor.

As these fine and medium fine particles approach the rotor, they are first subjected to the cage rod members which act as pre-acceleratingrods to accelerate the particles to rotor speed. At the same time the rods act upon the medium particles and throw them out. As a result only the fines and the near fines enter the rotor periphery suspended in air and there are subjected to the full air drag and centrifugal forces to discharge the coarser near fine particles centrifugally outwardly and draw the desired fine particles by air drag inwardly to the axial rotor duct for discharge from the machine to a collectorsystem.

41 and are immediately and positively thrown out centrifugally into the coarse discharge duct 43.

A classifier rotor having backward curved blades is preferred structure. The blades are curved in the direction opposite to the direction of rotation of the rotor. This form of construction reduces tangential air velocity and permits greater energy recovery. At the same time, in this form of rotor construction, during operation of the classifier Coriolis force presses particles on the back surface of the blade walls as the wanted fines move inwardly and the near fines are thrown out.

The invention is further illustrated by the following examples:

A number of tests were conducted under varying operating conditions and utilizing difierent materials. In Examples 1 to 12 a hard wheat flour was processed through the classifier and in Examples 13 to 18, soft wheat flour was processed. In Examples 1 to 6 and 13 to 18, rods 51 surrounding the classifier rotor were in place. In Examples 7 to 12, the rods were removed. In each instance, nineteen rotor decks were utilized. The air setting was maintained constant at 11,000 c.f.m. (cubic feet per minute). The tests were conducted with the louver blades 63 at three different positions. With the louver blades set at 10 from tangential, the velocity of the incoming air was greater than the peripheral velocity of the classifier rotor. With the louver blades set at 20 from tangential, the incoming air velocity was less than the peripheral velocity of the rotor and with the louver blades at 12 from tangential, the air velocity and rotor velocity were substantially equal. The results of the tests are set out in the table below.

Louver Setting Feed Rate Percent Efficiency, Example No. (from tan- (Cwt./Hr.) Pull Out percent gential), of fines degrees It will be noted that good uniformity results from operation of the classifier in spite of widely varying feed rates. The somewhat poorer efiiciency of the classifier in separating soft wheat particles is attributable to the nature of the material which is softer and more moist so that the particles tend to agglomerate.

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 vertical classifier apparatus for dry pulverulent material which comprises a peripheral inlet-axial outlet centripetal extraction classifier rotor journaled for rotation on a vertical axis within a rotor housing, said rotor comprising a plurality of spaced apart hoizontal annular disks and a plurality of vertical blades between the disks, an annular axial discharge duct extending through said rotor, a material feed inlet at the top of said housing, means for distribution of feed for gravitational flow about the cylindrical periphery of said rotor, a scroll housing air inlet to said rotor housing spaced from and surrounding and substantially co-extensive with the classifying section of said rotor for introducing air in a tangential inward flow to the annular zone surrounding said rotor, a fan housing and product discharge in communication with the axial discharge duct of said rotor and fan means on said rotor within said fan housing.

2. A vertical classifier according to claim 1 further characterized in that a vertical annular louver curtain wall is disposed between said air inlet and outer periphery of said classifier rotor.

3. A vertical classifier according to claim 1 further characterized in that said scroll housing air inlet is provided with a plurality of flow unifying vertical scroll bafiies extending successively lesser distances about the periphery of the clasifier rotor.

4. A vertical classifier apparatus for dry pulverulent material which comprises a peripheral inlet-axial outlet centripetal extraction classifier rotor journaled for rotation on a vertical axis within a rotor housing, said rotor comprising a plurality of spaced apart horizontal annular discs and a plurality of vertical blades between the discs, an annular axial discharge duct extending through said rotor, a material feed inlet at the top of said housing, means for distribution of feed for gravitational flow about the cylindrical periphery of said rotor, an air inlet to said rotor housing spaced from and surrounding and substantially co-extensive with the classifying section of said rotor for introducing air in a tangential inward flow to the annular zone surrounding said rotor, a fan housing and product discharge in communication with the axial discharge duct of said rotor, fan means on said rotor within said rotor housing, a coarse particle discharge chamber disposed about said rotor between said air inlet and fan housing, a ring disc on said rotor for rotation in said chamber, vertical blades on the periphery of said disc and a coarse particle discharge duct in communication with said chamber.

5. A vertical classifier according to claim 4 further characterized by the provision of a pneumatic seal chamber disposed between said fan housing and said coarse particle discharge chamber and surrounding said rotor in communication with both said coarse discharge chamber and fan housing.

6. A vertical classifier apparatus for dry pulverulent material which comprises a peripheral inlet-axial outlet centripetal extraction classifier rotor journaled for rotation on a vertical axis Within a rotor housing, said rotor comprising a plurality of spaced apart horizontal annular discs and a plurality of vertical blades between the discs, an annular axial discharge duct extending through said rotor, a material feed inlet at the top of said rotor housing, said material feed inlet being disposed above and about the axis of the classifier rotor, one end of the shaft of said rotor being journaled in a bearing suspended between said material feed inlet and the top of said rotor, means for distribution of feed for gravitational flow about the cylindrical periphery of said rotor, any air inlet to said rotor housing spaced from and surrounding and substantially co-extensive with the classifying section of said rotor for introducing air in a tangential inward flow to the annular zone surrounding said rotor, a fan housing and product discharge in communication with the axial discharge duct of said rotor and fan means on said rotor within said fan housing.

7. A vertical classifier according to claim 6 further characterized in that material feed dispersing means are provided on said rotor between said suspended bearing structure and the top of said rotor, said dispersing means including an annular ring disc having a plurality of radiating vertical blades disposed about its periphery.

8. A vertical classifier according to claim 7 further characterized in that a corrugated annular lining is disposed in said rotor housing about and in cooperation with the vertical blades of said dispersing means.

9. A vertical classifier according to claim 1 further characterized in that the classifying section of said rotor includes a plurality of vertical rod elements spaced outwardly from the outer peripheries of said horizontal annular rotor discs and spaced symmetrically therearound.

10; A vertical classifier according to claim 1 further characterized by the provision within the axial outlet of said classifier rotor ofselector means by which the effective length of the axial outlet duct may be varied.

11. A vertical classifier apparatus for dry pulverulent material which comprises a peripheral inlet-axial outlet centripetal extraction classifier rotor journaled for rotation on a vertical axis within a housing, the classifying section of said rotor including a plurality of spaced-apart horizontal annular ring discs intercepted by a plurality of vertical blade elements spaced apart about the peripheries of said discs, the inner peripheries of said ring discs defining the outer periphery of the axial outlet duct of said rotor, and a plurality of vertical rod elements spaced outwardly from the outer peripheries of said discs and spaced symmetrically therearound; a material feed inlet disposed above and about the axis of the classifier rotor, one end of the shaft of said rotor being supported in a bearing suspended between said material feed inlet and the top of said rotor; material feed dispersing means on said rotor between said suspended bearing structure and the top of said rotor, said dispersing means including an annular ring disc having a plurality of radiating vertical blades disposed about its periphery and a corrugated annular linear disposed in said classifier housing about and in cooperation with the vertical blades of said dispersing means; an air inlet surrounding and substantially co-extensive with the classifying section of said rotor, said air inlet including a scroll housing provided with a plurality of fiow unifying vertical scroll baffles extending successively lesser distances about the periphery of the classifier rotor; a fan housing and product discharge in communication with the axial discharge duct of said rotor and fan means on said rotor within said fan housing; a coarse particle discharge chamber about said rotor between said air inlet and fan housing in communication with the annular chamber between the air inlet housing and outer periphery of said rotor, a ring disc on said rotor for rotation Within said coarse particle discharge chamber, vertical blades on the periphery of said disc, and a coarse particle discharge duct in communication with said'discharge chamber; a pneumatic seal chamber disposed between said fan housing and said coarse particle discharge chamber and surrounding said rotor in communication with both said coarse discharge chamber and fan housing.

12. A vertical classifier according to claim 11 further characterized by the provision within the axial outlet of said classifier rotor of selector means by which the effective length of the axial outlet duct may be varied.

13. A vertical classifier according to claim 1 further characterized in that said scroll housing air inlet is provided with at least one flow unifying horizontal scroll baffle or" successively lesser widths extending about the periphery of the classifier rotor.

References Cited in the file of this patent UNITED STATES PATENTS 2,753,996 Kaiser July 10, 1956 2,762,572 Lykken Sept. 11, 1956 2,774,476 Doyle Dec. 18, 1956 2,796,173 Payne June 18, 1957 2,837,172 Klein June 3, 1958,

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 015 392 January 2 1962 Tibor A. Roz sa et a1.

It is hereby certified that error appears in the above numbered petent requiring correction and that the said Letters Patent should read es corrected below.

Column 1 line 23 for "outer" read outlet column 4v, line 22,, after "bottom" insert housing 7; column 7 lines 32 and 33 after "classification insert zone I column 8 line 62,, for "draw" read drag v Signed and sealed this 1st day of May 1962;

(SEAL) Attest:

ERNEST w SWIDER DAVID L- LADD Attesting Officer Commissioner of Patents