US2294921A - Mechanism for delivering pulverized material - Google Patents

Description

P 2a H. e. LYKKEN 2,294,921

mmcmmsm FOR DELIVERING PULVERIZED MATERIAL Filed Aug. 31. lsa 3 SheetQ-Sheet 1 ATTORNEY.

Patented Sept. 8, 1942 2,294,921 MECHANISM FOR DELIVERING PULVEBIZED V 7 MATERIAL s 1 7 Henry G. Lykken, Minneapolis, Minn. ADplicationAugust 31,1938, Serial lilo. 227,610

3 Claims (Cl. 83-11) My invention relates to anew and improved I method of andmechanism fordelivering pulverized material classified to a selected particle size. In such machines, exact and efiicientclassification implies the removal of all particle sizes below a given size, with no oversize particles in the finished product.

In the following disclosures there is shown, among other things, a-mill in 1whichboth a pulverizing action and aclassifyingaction areaccomplished in the same chamber; 'I'he'pulverizing action takes place by means of a rotor created pulverizingair vortex such as .is described in my Patent No. 1,838,560 issued December 29, 1931, but, as is well understood, such a vortex can be created by currents of air projectedtangentially (non-radially) into a chamber, as covered by my Patents No. 1,768,621 issued Julyil,

1930, and No. 1,756,254isslled April 29,1930. As

the description proceeds it will be apparent that the principles of and mechanism-for classificoa tion can .be used separately from, or in conjunction with any type of pulverizing machine, and

may or may not be a part of that machine.

Where air is referred to in this specification it will be understood that the term is used generically to include other gaseous media that may, ease of pul-' be'iound useful in the particular verization and classification.

Heretofore, there have been proposeda wide variety of methods of classifying pulverized material, including simple sortingdevices depend-.

ingupon the carrying capacity of an air stream, centrifuges, multiple chambers, screens, etc. In such prior classification devices, substantial quantities of finished product, i. e., material pul-' ve'rized to the desired size, has been returned to the pulverizing apparatus along with the oversize material rejected in the classifier. This amounts to not only ine'fiicient classification insofar' as decreased output for the machine :is

- concerned, but even a small percentage of such finished product, including fines, returned: to the pulverizer will. greatly reduce the efiiciency of the pulverizer (as much as -fifty percentiabe cause such material cushions, retardsand interferes with the pulverizing action upon. the

material yet to be reduced. The sufficiently .re-"

duced material that failed to be removed in the classifier is carried ofi in several different forms.

that is, it may be clinging to an'oversize particle, several finished particles may be clustered together making a larger mass, the particles may reach the outer wall of the chamber and be gathered up by a group of oversize returns, etc.

It is, broadly, an'object of this invention. to remove in the classifier practically all of the material that is sufiiciently pulverized so that only material actually requiring further reduction in size is rejected and returned tof the pulverizing chamber, while all the finished product is de'- livered towhatever collection system that is connected'to the classifier.

A further seriousdefect with existing types a classifiers is that while themechanism may be adjusted to deliver from the machine a selected maximum particle size the classifier will nevertheless permit larger'par'ticles to pass out with the finished product and in'many case this is unsatisfactory even commercially.

Again, the conditions for the return, of over-v size particles from the classifier for further pulverization' have been such thatthematerial is returned intermittently thus imposing intermittent loads upon the pulverizer.

It is also, broadly, anotherfobject of this V vention to overcome thexforegoing' as well as to be rejected is reduced, and removing'the ished product from the center of thevortex or of the rotor as rapidly as the same'is separated" other defects interfering with higher Iemciency of the mechanism.

Also in prior devices dependingiup on air theclassificatlon, the drag of the outgoingair on the material'is generally at a right angle to the centrifugal or other force participating in the classification action. 'L Q A further object of this invention is to subject the pulverized material particles which are in troduced into the classifier chamber to the drag ofan outgoing current of air, carrying, the particles of desired size, and to an opposing centrifugal force.

Still further objects of this invention are to subject the material which is introduced into f the classifier chamber while suspended in air to theKwhirling action of avortex, to the pulsating action of a closed-end rotor, to increasing centrifugal force as the size of. theoversizeparticles fromthe oversize material.

Still other objects of my invention comprise subjecting the material in the classifier to a continuousscavenging with large quantities oi air; and allowing the entering stream'of, air and suspended material to promptly expand at the action; and'aeratingff the rejected oversize material immediatelybebeginning of the classifier.

fore it leaves the classifier.

Even otherobjects of this invention :consist j in providing a unitary pulverizing and classifying machine in one chamber so arranged that the material being pulverized is subjected to two different vortex actions, is continually and promptly scavenged with large amounts of air, in both the pulverizer chamber and in the classifier chamber, the oversize material rejected in the classifier is returned to the pulverizing chamber continuously for further reduction without causing intermittent loading of the pulverizing chamber, and the returned oversize is subjected to a specially imparted downward component.

- fier apart from any pulverizing mechanism.

Referring to Figs. 1 and 2, in the embodiment chosen to illustrate the principles of this invention, the combined pulverizer and classifier comprises a cylindrical shell llqsupported upon a base l2 and closed at the top by a plate [3. The

material to be pulverized may be fed into the casing from 'a hopper ll by; means of a feed screw l5 working in the sleeve l6 and opening into the casing as indicated at IT. The feed screw is driven from a motor l8 through vari- Air is admitted to the pulverizing chamber beneath the bottom plate 24 of the rotor, and all 7,

The entry' around the periphery of the rotor. of the air to the chamber 21 is facilitated by a plurality of fan blades 33 that are mounted on the underside of the bottom plate 24 of the rotor, as shown. The number of these blades will vary, as will be understood. It will be noted that these fan blades are shaped to cooperate with the contour of the bottom plate 28 and that there is but a narrow-opening 34 for the air as it enters the chamber 21. This arrangement likewise provides an air seal against material in the pulverizing.

' rotor 2|, and the material fed into the chamber able speed reduction gearing enclosed in the 7 housing l9, and which may be of any suitable type, and may or may not be supplemented by a chain and sprocket drive 19A. Obviously, other forms of feeding mechanisms may be used.

In the embodiment illustrated, a pulverizing air vortex is set up by the closed-rend rotor, indicated generally at 2|, and. comprising a hub 22, top and bottom plates 23 and 24 and a pluralityof spaced apart radial plates 25. The number of blades and the spacing thereof around the rotor will be governed by the pulverization requirements, and the desirability'of maintaining a pulverizing air vortex peripherally of the rotor. The rotor hub is mounted upon the shaft 26 which is supported by suitable bearings in the top l3 and bottom [2 of the machine; the shaft being driven ,by a motor or other source of power (not'shown) and in any appropriate manner for the 'speed required. The areaof the casing H in which the rotor 2| operates is known as the pulverizing chamber or zone, and is indicated generally by the arrow-21. The pulverizing chamber is closed at the bottomloy the dished plate 28 having a central opening 29.

above the bottom l2 of the mill; and in that lower portion of the casing I I is -a large open ing 39 through which air is admitted to the space 3|, and from. there into the mill through the' opening, 29. The latter opening may be covered .by a slidable shutter 32 to regulate the amount of air admitted. into the pulverlzing chamber as one means of control thereof. ,It may be said that with the machine as here shown and the '60 'The plate 28 is spaced a substantial distancev principles set forth in this applicationlarge quansize.

is reduced in size 'adequately' I In the mill as illustrated the pulverizing chamthrough the opening I! is picked up and carried in, this air vortex. The material is therefore subjected to the centrifugal forces of the vortex, the particles smash into each' other with great force and rub against each other as they rotate in the vortex. Under these violent impacts and attritions the particles are reduced in Of course as the sizes of the particles change the effect of centrifugal force thereon .varies and the newly created'particles'seek other strata-like positions, thus causing further collisions and rubbings, and so on until the material ber 21 is shown as provided with a corrugated lining the use of which isoptional to facilitate the formation of a bed of material upon the wall of the pulverizing zone so that additional pulverization occurs atthe walloi the chamber by material" striking the material held there, rather than dry material striking the walls of the chamber. Some bed of material will be formed under most conditions, and its depth will be-increased by the use of the corrugated lining.

Also in the mill as illustrated it is noted that the pulverizing rotor 2| is larger in diameter atthe bottom than at' the top so that the rotor tapers inwardly at the top of the mill. This construction has been found of advantage whe'n pu l-- verizing some of the heavier materials, and for other reasons; However, it will be understood that the pulverizing vortex could be created by a rotor which is not tapered'at all, or" which is tapered in the opposite direction, depending upon the desires of the mill designer and the problems encountered in connection with a particular material or requirement.

7 Of course theair vortex need not be set up by a rotor at all but may be created by any other suitable means such as high pressure air, superheated steam, et'c'., appropriately directed into the chamber toset' up the pulverizing vortex.

Efficient action of the pulverizing mechanism requires thorough and complete scavenging of the material being pulverized'preferably by a cross-currentof air, to constantlyjremove from' the entire pulverizing zoneall material which is sufliciently reduced in size; and as fast as the verized product suspended in the air, passes out of the pulverizing chamber at the top; I prefer to remove from the pulverizing zone even a substantial quantity of oversized or insufllciently reduced material so as to be sure to'remove all of the finished material as promptly as possible.

Of course the oversize material must be separated from the finished material and returned to the pulverizing zone for further pulverization while the finished product should be removed from the mill. That is the function of the new and improved classifier about to be described.

a The portion of the casing immediately 7 above the pulverizing chamber 21 may be termed theclassification chamber and is indicated'generally at 4|. The upperportion of the classification chamber is closed partially by the fiat ring 42 which is supported upon the annular shoulder 43. In-the classification chamber is a rotor indicated generally at 44 and comprising a central hub 45, mounted upon shaft 25 'and rotor which has a large diameter at the top. and

is progressively smaller in diameter to the bottom thereof. The classifier rotor also sets up an annular vortex action in chamber 4|, b'utus- .ually this vortex will have speeds of'a much lower order than the speeds of vortex.

Before describing the classifier action,"the arrangement for withdrawing air and final material from the classifier chamber 4| will be described. 1

The opening 5| in the ring "is disposed close the pulveriz'ing to and axially of the classification rotor 44 and constitutes the outlet from the classification take of therotor 44 is from its periphery. and

its discharge is from its axis. v As has been described, the material discharged from the pulverization zone contains a considerable quantity of oversize materialas well as" the finished material, and is rotating in a rapid but confined vortex. By the arrangement of the classification rotor as shown and described this vortex is permitted to immediately expand in the bottom of the classification zone, and the vortex is at oncesubstantiallylreduced in speed. Such an immediate expansion also at once spreads the material and subjects it to the scavenging action of the air beingcontinually drawn through the mill so that particles that have been sufficiently reduced .in size tend at once to carried toward thehub of the rotor and out of the mill. It will be understood of course that not nearly all of the finished product is immedi- 7 ately removed. from'the classification chamber.

A very substantial part of it remains yet to be classified and'that action occurs under the inchamber 4| into the upper chamber 52 of the mill. The latter chamber may be described as the outlet chamber, and has the discharge duct 53 (Fig. 2-) of the mill communicating therewith.

(This duct preferably connects with a suitable collection system, not shown) In the embodiment shown in the drawings thechamber 52 has a fan 54 located therein, the purpose of which is to continuously draw from the classification chamber 4| and into the outlet chamber '52 the air and finished material. The fan shown comprises a hub 55 mounted upon the shaft 25, which hub terminates in the fiat disk' 56. A ring-shaped plate 51 is appropriately secured to the diskand. to the bottom of that plate are secured a plurality of fan blades 58 which are very narrow and do not extend down' beyond the depth of the disk 56. It will be understood of course that any other construction of'suction fan, centrifugal or otherwise, may be used in place of the fan that has been described, and also the fan need not be located in the mill at all but may be anentirely separate element, where used. I

The suction action of the fan is effective throughout the entire mill. Accordingly, the finished material is being constantly withdrawn inwardly from the vortex throughout the height of the chamber 4|, through the rotor and along fluence of the classification rotor which is designed to continue the vortex of reduced speed and to subjectthe material inthat vortex to repeated sorting actio-ns,'or pneumatic fsieving" actions.

That is to say, as each rotor blade advances in the direction of rotationthere is a suction created behind theblade which draws air ,and material toward the center of the rotor, and asthe rotor advances thereis pressure created by the advancing face of the following blade which forces the air and material out of the rotor. Accordingly the material in the vortex goesinand out of the rotor around the several blades as the rotorrotates and thisconstant pulsating action causes the material to spread out and to, approach the center of the rotor- 56 that-the-air leaving the chamber throughfthe opening 5| "willcarry with it the finished'product. The particles to' centrifugal force which of course, acts upon a particle according to its mass. This force opthat are thrown out by the rotor are'subjected poses the for-cc or drag of the air carrying the particle out of the chamber, and the proportioningof theseiorces determines the selected particle size.

In the'present machine, the gradually increasiing width of the rotor blades toward thetopof the machine increases the centrifugalforce exerted by-the rotor blade. Accordingly thematerial that travels upwardly in the classification chamber 4| which is near, but yet above the desired particle size will have added centrifugal force imparted to it to keep it out of the outlet" opening, and force it to the Wall of the chamber I from where it will be returned to the pulverizing chamber. The repeated pulsations ocf-the material by the rotor blades frees all-material that has been suificiently reduced in size, andrejec'ts all oversize rmateri-al.- I, The oversize material is thrown to the outer wall of the chamber 4|. 'It has'been found that even with appropriate precautions it is not, as'v a' practical matter, possible to prevent particles which are a proper size irom reaching the outer. 7 wall of the classification chamber 4| and there To ,Iree,

be'mixed with the 'oversized material.- all such material I"provide means to create a turbulence-in the materialon and near the w'all" of the casing II and before it leaves the classifier. Hence anyparticles which are of a propersize .35 the shaft2 6. or the axis of the vortex as it may i be termed, into the opening 5|.j Thus, the in-- is provided withcorrugations El. that these corrugations are inclined downwardly will be freed from the oversize and work inwardly,

' finally escaping through the discharge outlet ii.

In the illustrated embodiment, the lower portion of the wall of the classification chamber ll It will be noted in the direction of rotation of the vortex. The oversize material that is thrown outwardly in the classifier .vortex reaches the wall of the chamber and slides down the same, both that above the corrugations as well as that oppositethe corrugations. Accordingly the'incline of the corrugations in the direction of rotation of the vortex gives a downward component to the returning material so that the vortex is intact aiding the return of the oversize material to the pulverlzing chamber. This return action goes on continuously, and together withjthe reduced vortex at the bottom of the classifier chamber, there is no accumulation of the oversize material there, and no periodic loading 'of the pulverizing rotor. At the same time the action of the air in the corrugations providing a disturbing turbulence in the air and material there permits the rising spiral of air in the vortex to free any finer material which may be mingled with the oversize.

deep and spaced on about one inch centers, while the corrugations in the 'classifier chamberhave been approximately one inch deep and spaced on between three and four inch centers, with an inclination of thirty degrees, following of course the contour of the well. These spacings will vary from mill to mill according to the requirements for each and it will be apparent that different lengths of corrugation may be used, depending upon the particular conditions in the classifier, while under certain circumstances the corrugations may be vertical.

. in the number of fines in the finished product so that the large majority of particles ultimately collected are very close to'the selected top size. For example with the mechanism adiustedfor a 15 micron top size mostof th particles will be within the range of '10 to 15 microns. The same ratio holds even'for sizes below 15 -micron top size. a

It will be appreciated that-the mechanism is readily adaptableto the handling of" different materials and even different particle sizes of the same material by changes in the volume of air, by changes in the suction fan, and by simple changes in therotors to vary the number of blades or the contour of the blades, including using straight blades or those curved either in the direction of rotation or in the opposite direction. The .size of the outlet opening II can be readily changed by replacing the ring 42 with another having a different sized opening. In place of varyingthe air opening by means of the slide 32, the outlet duct 53 from the machine to the collection system may be controlled by means of a damper indicated at'5ll.

Other modifications are illustrated in the further figures of the drawings, now to be described. v Figure3 illustrates a modified form of classifier rotor in which the rotor 8| has an upper portion 92 which is of uniform diameter, and

below which is an inwardly and downwardly ta-- pered portion. Around the outer edges of the portion 92- of the'rotor blades is a large mesh screen 94; The mesh of this screen may be two or three openings to the inch. v

While it has not been illustrated, I have found that fiat, spaced apart, ringshaped plates or wire bands or hoopsmay be substituted for the screen and with equivalent operating effect, which has been found desirable with some materials and in some instances. 1

o The purpose of the screen or other arrangement is to introduce a certain interference with It should be pointed out that there is no definite relationship between the .number of blades on the pulverizing rotor 2i and th number of blades upon the classifier rotor 44. The two rotors act independently of each other, andin each case the number of rotor blades, size, shape and spacing is chosen by the designer in accordance with the particular pulverizing" or classifying problem with which he is faced. Materials vary in weights, in degrees of hardness or friability, and the requirements of users vary as to the top particle size desired. These and other factors determine what will be the construction of the respective rotors.

It also may be pointed out that the ring 4a cooperates with the ring 42 to constitute a running seal to prevent the discharge of material between the rings and to the opening 5 I.

With the construction and arrangement of parts which have been illustrated and described it has been found that the parts, the volume of air, etc. can be proportioned and balanced so that any particle size can be selected as the top particle size.- And it has further been found that with the described mechanism removal from the-pulverizing chamber of sufficiently reduced material is so rapid that there is a substantial reduction the normal in and out fiow of air and mate,- rial caused by the rotor blades and to thus modify tosome extent the pulsating action laterally. Thus the passage of the particles through the classifier zone and out of the chamber will be retarded sufliciently to complete the rejection of undesired oversize particles.

Of course, the part of the rotor of uniform diameter could be of difierent'proportions and height than those illustrated in Fig; 3 by way of example. I

Figure 4 illustrates a classifier that is separate and apart from the pulverizer. In this case the material enters the casing H through pipe 12 in the direction of a vortex in the casing. The material may be suspended in air, or not, as suits the individual case. Air also may be introduced into the classifier chamber through the lower opening 13, below the rotating plate I4, and on thebottom of which are a plurality of fan blades 15. The classifier rotor'lB creates and maintains a vortex of air and suspended material in the chamber ,H. In this case there is shown a design of=rotor which is somewhat like that shown in Fig. 3 in that the rotor comprises a central hub 16 carrying a plurality of radial blades 11, the upper portion of which, to the point 8|, is of uniform diameter and then the blades taper downwardly and inwardly as indicated at '2. At the upper ends the blades carry the annular angle iron 18 to which is fastened the stop ring plate 19.

The operation of the classifier of Fig. 4 is substantially the same as that described in connection with the classifier of Fig. 1. The finished product is discharged from the mill through the central opening 83 formed by the ring-shaped plate 84 which divides the classifier chamber from the outlet chamber 85 in which there is shown a suction fan 86 that also discharges the material through an outlet 81. The fan 86 and the rotor I6 and the plate 14 are all mounted upon a shaft 88 supported in appropriate bearings in the top and bottom plates of the mill, the shaft being driven by any suitable source of power (not shown).

The rejected oversize material passes from the mill through one or more outlets 89 located at the bottom of the classifier opposite the air inlet. Thus, even the rejected oversize is subjected to a final aeration or scavenging action to release any particles that have been sufilciently reduced and which may be among the oversize particles.

Of course it will be apparent that the described mechanisms may be used to classify into two or several classes of particle sizes, as well as the operation described in this specification.

The types of rotors shown have been found to be particularly useful when classifying material to very small particle sizes, for example, less than five microns and in classifying lightweight materials, as well as with other materials and larger particle sizes. The number of blades and the spacing thereof are chosen to suit the particular conditions.

While all the rotors that have been described have had a tapered portion, it is practical and satisfactory to, in'some instances, have rotor blades for the classifier which are of uniform width and in such cases the blades also may be surrounded by the wire or similar arrangements, if desired.

With devices such as have been hereinabove described, I have successfully pulverized and classified numerous materials on a commercial scale. With a classifier chamber twenty-four inches in diameter containing a rotor of fifteen inches maximum diameter rotating at 2600 R. P. M, crystalline calcite has been pulverized and classified to a top size of twenty-five microns atthe rate of two hundred fifty pounds per hour. By increasing the rotative speed the maximum particle size delivered was five microns. Increasing the height of the classifier has enabled the obtaining of a maximum particle size less than five microns.

of delivered particles has been obtained by other variations in the classifier rotor such as the diameter, or the shape and number of the blades, and by adding the screen or disks to the rotor as heretofore described.

Modifications in the arrangement and location of parts may be made within the spirit and Likewise increase in fineness scope of my invention and such modifications are intended to be covered by the appended claims.

I'claim:

1. A machine for delivering material of a selected. maximum particle size which comprises a casing having a bottom and a top, means for admitting air through the bottom of the casing, a rotor mounted for rotation in the casing. means for operating the rotor so as to set up and maintain in the casingabout the rotor an intense, high-speed, pulverizing vortex of air and sus-- pended material, means for' feeding material to the casing and vortex, means for withdrawing air and pulverized material from the vortex at the upper end of the rotor and into a classifying chamber, a rotor mounted for rotation in the latter chamber, the rotor being tapered outwardly and upwardly from adjacent the pulverizing rotor to the upper end of the chamber and arranged so as to set up and maintain in the chamber a less intense vortex and to subject the pulverized material therein to repeated lateral movements back and forth as the same spirals upwardly in said casing, and an outlet for selected material and air located axially in the end of the rotor near the upper end of the casing.

2. A machine for segregating particles of pulverized material comprising a chamber having an axial outlet at one end thereof, means for feeding material and air into the chamber, a rotor mounted in the chamber and causing the air.and material to whirl in a vortex in which the material is suspended in the air, the rotor having an end plate adjacent the outlet and a plurality of spaced apart radial blades extending from the axis of the rotor and a major part of theheight of said chamber below said outlet, the rotor end plate having an opening therein registering with said outlet, the suspended material moving inwardly and outwardly of the rotor repeatedly as the same spirals through the casing toward the outlet, and means for continuously removing the selected material through said outlet and opening.

3. In a machine for deliveringpulverized material of a selected maximum particle size, a casing, a bladed rotor mounted therein of less diameter than the casing and of substantially a corresponding length, the rotor also being of substantially less diameter at one end and tapering toward the opposite end, means for feeding air and suspended material into said casing near the smaller end of said rotor and into the space around said rotor, a plate closing the larger end of said rotor except for an outlet for selected material in the central portion thereof, and means for drawing air and selected material through said outlet.

HENRY G. LYKKEN.

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