US3384238A - Classifying system - Google Patents

Description

May 21, 1968 s. ALPHA CLASSIFYING SYSTEM 5 Sheets-Sheet 1 Filed Feb. 17, 1966 INVENTOR SMITH ALPHA BY W.%.M-

HIS ATTORNEYS y 21, 1968 s. ALPHA CLASSIFYING SYSTEM 3 Sheets-Sheet 2 Filed Feb. 17, 1966 INVENTOR SMITH ALPHA BY 'ZLMY FIG.5.

HIS ATTOR N EYS May 21, 1968 s. ALPHA 3,384,238

CLASSIFYING SYSTEM Filed Feb. 17, 1966 s Sheets-Sheet s F|G.4. l

INVENTOR SMITH ALPHA BY M-%.M= M

HIS ATTORNEYS United States Patent 3,384,238 CLASSIFYING SYSTEM Smith Alpha, Berwick, La., assignor to Air Sifters, Incorporated, Greenwich, Conn., a corporation of Connecticut Filed Feb. 17, 1966, Ser. No. 528,213 4 Claims. (Cl. 209-139) ABSTRACT OF THE DISCLOSURE A centrifugal classifying system including a classifying chamber having a rotary particle rejector in its top and including a fan for drawing air through a pair of diametrically spaced inlets at the bottom of the chamber to develop a rising and rotating column of air in the chamber and draw air through the rejector, the material being classified being introduced directly into the air column by means of a pair of feed conduits to avoid creation of turbulence in the air column, and an outlet centered in the rejector to discharge the air and entrained classified particles through centrifugal separators, the air being recirculated to the inlets from the separators and to a labyrinth seal between the particle rejector and the top of the chamber.

This invention relates to improvements in centrifugal classifying and separating systems for such products as finely divided marble, clay, barites, oyster shell, corn flower, synthetic resins, silica, feldspar, silicon carbon, talc, zinc sulphate, aluminum powder, aluminum oxide, cellulose fibers, granite, mica, iron oxide, carbon black, and the like and, more particularly, to centrifugal classifiers of the particle-rejector type wherein a sharp classification of particles of extremely small size can be obtained.

Centrifugal classifiers of the rotary particle-rejector type are well known and used in industry. While in theory, such rotary particle-rejector classifiers should be capable of producing a 100% separation of fine particles from the larger unwanted particles, in practice, such a sharp separation has not been achieved. The manner in which the material to be classified has been supplied to the particle rejector and the mounting of the particle rejector with respect to the mechanism for promoting flow of air through the classifier have resulted in a maldistribution of the particles in the air stream and leakage of unwanted larger particles through the rejector and mixing with the desired finer particles.

In accordance with the present invention, a particlerejector classifier is provided wherein the particles to be subjected to classification are more uniformly distributed through the flowing column of air in the classifier, the rejector itself is made capable of a sharper separation or classification of the particles and leakage paths are eliminated to prevent passage of contaminating larger particles. Moreover, dual centrifugal separators are included in the system in order to better control the flow rate of air therethrough and more efiicient separation of the fine particles from the air, the waste air from these separators being recirculated through the classifier, together with any particles which are carried over in it, thereby more efiiciently utilizing the air in the system.

In a preferred embodiment of the classifying system, the particles to be classified are admitted at about diametrically spaced zones into a rotating column of air which is drawn through a rotary, vane-type of particle rejector and through a centrally located exhaust duct by means of which the fine particles passing through the classifier are supplied to two centrifugal separators, at reduced air speed or velocity to allow a more effective "ice and efiicient separation of the entrained fine particles from the entraining air. Exhaust air from the centrifugal separators may be returned in part to the particle rejector in two streams supplied to the bottom of the rejector to obtain a better air distribution and utilization therein. Any excess air from the dual centrifugal separators may be passed to a bag filter where any fine particles still entrained in the air can be removed and the waste air exhausted to atmosphere.

With a system of the type described, of a selected maximum size can be separated from a mixture of particles without the presence of any particles larger than the selected size contaminating the end product. By suitably adjusting the speed of the particle rejector, 100% of particles of 6 micron size and smaller can be separated from larger particles. At lower rejector speeds, a sharp classification of larger particles is obtained. In fact, by reversing the direction of rotation of the rejector, 30 mesh particles can be separated from larger particles with high efliciency.

For a better understanding of the present invention, reference may be had to the accompanying drawings, in which FIGURE 1 is a top plan view of a typical system embodying the present invention;

FIGURE 2 is a front elevational view of a portion of the system with parts broken away;

FIGURE 3 is a side elevational view of the system;

FIGURE 4 is a front elevational view partly broken away to disclose details of the particle feed and particle rejector; and

FIGURE 5 is a sectional view on an enlarged scale of the seal between the particle rejector and the classifier housing.

The system disclosed in the drawings is illustrative of the invention but is susceptible to modification as explained hereinafter.

The complete system 10 includes, as best shown in FIGURES l, 3 and 4, a particle-rejector classifier 11, a pair of centrifugal separators 12 and 13, and a bag-type filter 14.

The particle-rejector classifier 11 includes a shell or casing having a generally cylindrical portion 15 connected at its lower end to a downwardly tapering or conical section 16 provided at it lower end with a conical discharge section 17, all in direct communication with each other. Across the top of the shell portion 15 is a closure 18 provided with a centrally located hollow conduit 19 extending above and below the closure 18 and having a top closure 20 in which is mounted a bearing support 21. A shaft 22 extends through the bearing support 21 and is rotatably supported by means of ball bearings or other similar anti-friction bearings 23 and 24 in the bearing support 21. A pulley 25 for driving the shaft is mounted on the upper end of the shaft 22. A centrifugal particle rejector 26 is supported on the lower end of the shaft 22. As shown, the rejector includes a lower disk member 27 which is securely attached to the lower end of the shaft for rotation therewith by means of a nut 28 or similar fastening means. Extending upwardly from the edge of the disk 27 are a plurality of closely spaced thin rejector blades 29 which in a typical system are about of an inch wide and are set at an angle of about 60 to the tangents to the disk 27. The lower ends of the blades 29 may be brazed or otherwise secured in slots (not shown) in the disk 27. An annular top member 30 is secured to the upper ends of the blades 29 and receives in its center aperture 31 the lower end of the shell or housing 19 which has its lower open end located approximately midway of the lengths of the rejector blades 29 and centrally within the rejector 2-6. If desired the rejector 26 can be reinforced by means of addition braces B extending between the members 27 and 30 (FIGURE On the upper surface of the top member (FIGURES 4 and 5) are a plurality of annular lands 31 and interposed annular grooves 32 which cooperate with other alternately arranged annular lands 33 and annular grooves 34 on a plate 35 secured to the closure 18 to form a labyrinth seal. As best shown in FIGURE 4, the plate 35 has a deeper annular groove or passage 36 therein for a purpose to be described hereinafter.

Referring now to FIG. 3, the centrifugal classifier 11 is mounted in a frame 37 of any suitable type which, as shown, includes a substantially square base frame member 38 enabling it to be mounted on the floor 39 or other support in a building with the conical sections 16 and 17 extending below the fioor or support 39. An intermediate, generally square frame section 40 is connected to and supports the shell portion 15, these frame members being interconnected and rigidified by means of suitably interposed vertical supports 41, 42, etc. A platform 43 is supported in spaced relation to the frame 44 also by means of interposed supports 44, 45, etc. to form a rigid supporting structure for the classifier 11. As best shown in FIGURE 2, the platform 43 is disposed above the top 18 of the classifier 11 but below the pulley 25 on the particle rejector drive shaft 22. On opposite sides of the frame 37 are mounted a pair of drive motors 46 and 47 which are connected by means of belts 48 and 49 to the pulley 25 to drive it. The motors 46 and 47 preferably are electric motors although other types of motors or drive means may be used, if desired.

Communicating with the centrifugal classifier 11 through diametrically opposite edges of the top closure 18 are a pair of downwardly extending feed conduits 50 and 51, FIGURES 2 and 4, which are connected at their upper ends with a transverse conduit 52 in which is mounted a conveyor screw 53 for distributing finely divided particles from the inlet conduit 54, at about the mid portion of the horizontal conduit 52. A motor 55 rotates the screw 53 by means of a reducing gear and chain and sprocket drive 56 or the like (FIGURE 2).

Any suitable means may be used for supplying finely divided material to be classified to the inlet 54.

Referring to FIGURE 4, the housing 19 communicates with a conduit 57 connected to the inlet of a centrifugal blower 58 which is arranged to draw air upwardly from the bottom of the classifier 11 through the particle rejector 26 and the housing 19 and discharge the air and entrained particles through divided conduits 59 and 60 into the conventional centrifugal separators 12 and 13 where the finely divided particles are thrown out and discharged through the outlets 61 of the separators (FIG URE 3). Spent air from the separators 12 and 13 is returned by means of conduits 62 and 63 to a common downwardly extending conduit 64 (FIGURE 3) which at its lower end communicates with a pair of conduits 65 and 66 supplying the air to the bottom of the centrifugal classifier between the sections 16 and 17. Inasmuch as the air is supplied through substantially diametrically opposite conduits 65 and 66, a more uniform distribution of the air in the classifier is obtained and any particles carried over by the spent air are returned to the centrifugal classifier for further classification.

Excess air from the separators 12 and 13 may be supplied by the conduits 67 and 68 extending from the top central regions of the separators to the bag-type filter 14 where entrained fine particles in the the air are filtered out and the excess or exhaust air is discharged through the outlet 69 (FIGURE 3).

As shown in FIGURES 4 and 5, air may be supplied either from the atmosphere to the groove 36 in the labyrinth seal or may be supplied, as shown, by means of a pipe or conduit 71 which can be connected to the conduit 63 so that a positive flow of air through the labyrinth seal will be obtained. Air will flow inwardly and outwardly through the labyrinth seal and assures the exclusion of unwanted larger particles which cannot pass the rejector 26 due to centrifugal action of the blades thereof.

In operation, finely-divided material to be classified is introduced through the feed inlet 54 and is distributed substantially equally by means of the screw 53- to the downwardly extending conduits 50 and 51. With the rejector 26 driven at a selected speed by means of the motors 46 and 47, the air in the casing 15, 16 and 17 will be set into rotary motion so that the finely-divided material entering through the conduits 50 and 51 is uniformly distributed into the rising and rotating column of air. Due to the centrifugal action of the rejector 26, only the more finely-divided particles can pass between the blades 29 of the rejector while the larger particles are thrown out by the centrifugal force generated by the rejector. It will be understood that the air is drawn through the rejector by means of the blower 58 which may be driven by a suitable motor 73 either directly coupled to the blower or indirectly coupled as by means of a chain, belt 74 or the like. The air entraining the finely-divided particles is divided into equal streams in the conduits 59 and 60 and supplied substantially equally and at a reduced velocity to the centrifugal separators 12 and 13 where the particles settle out. Spent air from the separators is returned through the conduits 62, 63, 64, 65 and 66 to the bottom of the centrifugal classifier 11 and is recycled therethrough. The larger particles which are rejected and are not entrained in the incoming air are discharged through the outlet cone 17. As explained above, excess or waste air may be discharged into the bag filler 14 where fines are filtered out of the waste air from the system.

Leakage of larger particles between the top of the classifier housing and the top of the rejector is prevented by means of the labyrinth seal as described above, whereby contamination of the fines is avoided.

It will be understood that the speed of rotation of the rejector 26 can be modified depending upon the particle size to be separated. With the system described herein, it has been found that an extremely sharp separation of all of the types of materials referred to above can'be obtained. of particles of 6 micron size, 5 microns or even smaller, can be separated readily. The efiiciency of the applicants classifying system results in part from an excellent distribution of the particles to be classified in the air column, the avoidance of leakage or unwanted particle sizes past the rejector and a better control of the air speed in the centrifugal collectors. A further factor in sharp classifying is the location of the inlet of the housing 19 centrally of the rejector so that the air flow between the blades is substantially uniform from top to bottom, thereby enabling the passage of only a selected size of particles at any place along the length of the slots between the blades 29.

It will be understood that the system is susceptible to considerable modification, as for example, the bag filter may be eliminated, atmospheric air may be supplied to the labyrinth seal rather than positive pressure air through the conduit 71, and other drive means may be provided for the rejector 26, the screw 53 and the blower as may be desired.

Inasmuch as the system is susceptible to modification without departing from the invention, the above described embodiment of the invention should be considered illustrative and not as limiting the scope of the invention as defined in the following claims.

I claim:

1.A classifying system comprising a chamber having a bottom, a top and a side wall, diametrically opposed air inlet means adjacent to the bottom of said chamber for supplying air thereto, an outlet in the top of said chamber, a rotary particle rejector in said chamber substantially concentric with said outlet and adjacent to said top, said rejector having top and bottom circular plates and substantially vertical spaced-apart blades extending between and connected with said plates around their peripheries, means for rotating said rejector, fan means for drawing air through said chamber and said rejector and out of said outlet and establishing a rotating and rising column of air in said chamber, a pair of conduits extending upwardly from said top and communicating with said chamber outwardly of the periphery of said rejector, and means for supplying finely divided material to be classified to said conduits for discharge directly into said rotating column of air.

2. The classifying system set forth in claim 1 comprising a pair of centrifugal separators communicating with said fan means for separating said entrained particles from the air, and means for returning said air to said inlet means.

3. The classifying system set forth in claim 1 in which said outlet comprises a housing extending above and below said top of said chamber and having an open lower end disposed concentrically in said particle rejector and substantially midway of the height of said rejector, said fan means communicating with said housing.

4. The classifying system set forth in claim 1 comprising an annular labyrinth seal having inner and outer peripheries interposed between said top plate of said rejector and said top of said chamber, at least one centrifugal separator communicating with said fan means for separating said entrained particles from said air and means for supplying air drawn out of said outlet by said fan means into said seal about midway between its peripheries.

References Cited UNITED STATES PATENTS 2,269,412 1/ 1942 Sturtevant 209-144 2,276,761 3/1942 Carey 209-144 X 2,939,579 6/ 1960 Hardinge 209-144 2,968,401 1/ 1961 Sheldon 209-144 3,015,391 1/1962 Sharples 209-144 3,089,595 5/1963 Kaiser 209-144 FOREIGN PATENTS 647,888 7/1937 Germany. 497,966 1/ 1939 Great Britain.

HARRY B. THORNTON, Primary Examiner.

TIM R. MILES, Examiner.

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