US3057475A - Centrifugal air classifier - Google Patents

Description

Oct. 9, 1962 R. MATTHEWS 3,057,475

CENTRIFUGAL AIR CLASSIFIER Filed July 24, 1961 3 Sheets-Sheet 1 Oct. 9, 1962 R. MATTHEWS 3,057,475

CENTRIFUGAL AIR CLASSIFIER Filed July 24, 1961 3 Sheets-Sheet 5 atet Patented Oct. 9, 1962 3,057,475 QENTREFUGAL AIR CLASSIFIER Roy Matthews, Macclesfield, England, assignor to Henry Simon Limited, Stockpcrt, England, a British company Filed July 24, mm, Ser. No. 126,340 Claims priority, application Great Britain Aug. 15, 1960 9 Elaims. ((Cl. 209--144) This invention relates to classifying means of a type wherein materialseparation in accordance with particle size and density is effected in a ring-shaped classifying zone bounded by annular flanking walls between which air is caused to flow in an inwardly moving spiral path into which the material to be classified is directed through an annular slot in one of the flanking walls to form a rotating annular curtain whose rotational motion is in substantially the same direction as the flow of air in the classifying zone. Such classifiers may be used for separating finely divided cereal mill products containing a proportion of proteinaceous material into a fraction containing a higher proportion of protein and a fraction containing a lower proportion of protein.

With such classifiers it is desirable that the inwardly spiral flow of air and entrained material through the classifying zone is not impeded by friction at the surfaces of the zone flanking walls, and to this end it is known to cause the zone annular walls to be rotated about their common axis in the same direction and at substantially the same tangential velocity as that of the air in the zone, such an arrangement being described in U.S. Patent No. 2,990,063 dated June 27, 1961.

In such an arrangement and in orderto prevent loss of efliciency due to the formation of air leakage paths past the classifying zone, it is necessary to provide adequate sealing means between the outlet element of the classifying zone and the duct or chamber which forms a continuation of the path for the air and material entrained therein, and it is a disadvantage of the said arrangement that at their junction the said elements are in relative rotary motion so that the provision of an effective seal entails costly manufacturing processes and careful maintenance.

The object of this invention is to provide a classifying means for cereal mill products which is free from this disadvantage.

According to the invention, a classifier for separating protein containing material from cereal mill stock, or for performing similar separations in accordance with particle size and density in a ring-shaped classifying zone bounded by co-axial substantially annular flanking walls, in which zone air is caused to flow between the flanking walls in a radially unimpeded inwardly moving spiral path into which material to be separated is directed through an annular slot in one of the flanking walls to form a rotating annular curtain whose rotational motion is in substantially the same direction as the flow of air in the classifying zone, the flanking walls thereof being supported from the stationary structure of the machine and pierced by a plurality of orifices through which the jets of air from a source of air of higher pressure than the air in the classifying zone are continuously blown over the zone wall surfaces in such a manner as to lift the boundary layer and thereby reduce the effect of surface friction on the flow of the classifying air as it passes through the classifying zone.

Preferably but not necessarily said orifices form nozzle terminations of holes or slots which are so inclined relative to the zone surface that their discharge angle is substantially tangential to and in the direction of the flow of the classifying air passingthrough the zone.

Particularly for separating protein containing material from cereal mill stock, the shape and relative axial spacing of the annular flanking walls may with advantage be arranged such that the axial distance between the walls at the outer radial extremity of the zone is less than the axial spacing at the inner radial extremity of the zone.

An embodiment of the invention will now be described by way of example, with reference to the accompanying drawings in which:

FIGURE 1 is an elevation partly in section of a classifier,

FIGURE 1b is an enlarged fragmentary sectional view of the classifier shown in FIGURE 1 illustrating details of construction,

FIGURE 2 is a plan view of an annular diaphragm,

FIGURE 3 is a section on the line IIIIII of FIG- URE 2,

FIGURE 4 is an enlarged portion of FIGURE 3.

A vertical cylindrical casing member 1 which forms part of the stator body of a classifying apparatus has at its upper end a closure member 2 having extensions 3 supporting the journals 4 wherein a vertical rotor-shaft 5 is rotatably mounted. A flared extension 6 of the lower end of the rotor-shaft 5 forms a horizontal disc-like element 7 which has on its upper flared surface a plurality of equally spaced radial material-impelling blades 8 supporting a hollow conical upwards extension 9 of the inner portion of an annulus 10 having an inverted substantially L-shaped cross-section, the interior surface of the extension 9 being so spaced from the outer extremity of the disc-like element 7 that there is an annular slot 11 between the adjacent surfaces. The wall of the extension 9 terminates in a short cylindrical section 12 which is coaxial with the vertical rotor shaft 5 and arranged in sealing association with a dependent cylindrical section 13 terminating an inwardly coned extension 14 of the end closure 2 to form an annular guide duct 15 leading from material intake ports 16 (of which only one is shown) in the end closure to the said material-impelling vanes 8 which accelerate the material so that it passes through the annular slot 11 in the form of a rotating annular curtain. On the upper surface of the horizontal portion of the inverted L-shaped annulus 10 there is mounted a plurality of equally spaced radial air impellers 17 arranged so as to support on their upper edges an annular ring 18 whose inner extremity is coaxial with the vertical rotor-shaft and arranged in sealing association with a short cylindrical dependent extension 19 of the inner boundary of an inner annular closure member 20 which isolates the upper portion of the cylindrical casing member from the lower portion thereof except where the short cylindrical extension 19 provides an annular air duct 21 surrounding the previously mentioned annular guide duct 15 and communicating with the radial air impellers 17, so that air entering a tangential port 22 in the said upper portion is passed by the short annular air duct 21 to the impellers 17 which direct it into a circular path Within the casing in a manner which will ensure that when the machine is in operation the tangential velocity of the air in the circular path remains constant substantially irrespective of the quantity of air being passed into the machine.

Below the horizontal portion of the inverted L-shaped annulus 10 and co-axial therewith is a hollow ring 23 of substantially rectangular cross-section whichis mounted on supporting pillars 24 (of which only one is shown) from the fixed structure of the casing in such a manner that there is an operational clearance at those of its surfaces which are adjacent to associated rotating vertical and horizontal surfaces of the L-shaped annulus 10. The said supporting pillars 24 are of streamlined cross-section and at least one of them has a longitudinal bore 25 communicating with the interior of the hollow ring and providing a duct through which air from a compressed air source can be led into the hollow ring the horizontal underside surface 26 of which constitutes the outer part of the upper flanking wall of the classifying zone of the machine. The surface 27 which forms the inner part of the upper flanking wall of the classifying zone is in line with the underside surface of the hollow ring 23 and is provided by the underside surface of the hollow rim 28 of an upwardly flared air-guide member 29 which is mounted on a hollow pedestal 30 from part of the fixed structure of the machine so as to be co-axial with and immediately below the disc-like element 7 of the rotorshaft 5, the hollow interior of the upwardly flared airguide member 29 being closed at its upper end by a sealring plate 31 to provide an air chamber continuation of the hollow part of the supporting pedestal which is arranged to communicate with the source of compressed air which also supplies air to the interior of the hollow ring. Between the air chamber in the air-guide member 29 and the interior of its hollow rim 28 there is a hole 32 or plurality of holes by which the compressed air passes from the air chamber into the said hollow rim the peripheral surface of which forms one boundary of a truncated conical extension 33 of the annular slot 11 of the rotor through which material is passed to the classifying zone. The truncated conical peripheral wall 34 of the hollow rim 28 is pierced by a plurality of holes or slots (not shown) which are so inclined to the rim surface that air blown through them is discharged in a direction which is substantially tangential to and in the direction of rotation of the curtain of material passing through the annular slot 33.

Supported from the fixed structure of the machine so as to be below, and co-axial with, the hollow rim 2% of the air-guide member 29 and its associated hollow ring 23 is a lower annulus 35 which has its inner radial boundary Ri in conformity with the equation -;Z 1.4, being equal to 1.8

where R is the radius of the outer extremity of the horizontal underside surface of the hollow ring. The lower annulus 35 is a hollow component somewhat larger in diameter than the hollow ring 23 and is mounted in such a manner that at its inner boundary Ri, its upper surface is in a plane axially spaced from the underside of the hollow rim of the air-guide member by an amount Hi which lies between 0.1 R0 and 0.35 R0, being equal to 0.26 R0, the upper surface 36 of the lower annulus being dished upwardly from its inner radial boundary so that at radius R0 it is axially spaced from the underside of the hollow ring by an amount H0 such that Ho/Hi is less than 0.7, being substantially equal to 0.15. The foregoing recited values are old, being disclosed in my prior Patent No. 2,990,063 dated June 27, 1961. A suitable air duct 37 is provided to connect the interior of the hollow lower annulus with the same source of compressed air as supplies the air chamber of the air-guide member and the hollow ring. The upper surface 36 of the lower annulus 35 constitutes the lower flanking wall of the classifying zone which in this preferred embodiment of the invention is of the cross-sectional shape, and for the purpose, described in our prior above identified application. It is however to be understood that this invention is not dependent on the employment of that particular zone shape.

The three annular surfaces which constitute the upper and lower flanking walls of the classifying zone and which may be the surfaces of removable annular diaphragm components of their associated members, are pierced by a plurality of holes through which jets of compressed air from the interiors of the annular members are continuously blown during operation of the ma chine so as to lift the boundary layer associated with the classifying air passing through the zone. Such annular diaphragms may be of textile fabric or of porous plastic material, or of sintered metal, or of metal sheet which has been suitably perforated. In the present embodiment of the invention the three annular diaphragms of which one is shown in FIGURES 2, 3 and 4 are of comparatively thin sheet metal 40 formed to produce a plurality of comparatively widely spaced unequal-sided radial serrations 41 the shorter side 42 only of each of which is perforated by a radial row of holes 43 the serrations being arranged so that compressed air blown through the holes to pass over the longer sides of the serrations will travel in substantially the same direction as that taken by the classifying air passing through the classifying zone.

The underside of the lower annulus 35 is fiat and is arranged in fixed sealed association with the top end flange 50 of a stationary cylindrical receiving chamber 51 which is supported from the interior of the cylindrical casing in such a manner as to be substantially co-axial with the vertical rotor shaft, the upper surface of the said top end flange being recessed to provide an annular air duct 52 which is in association with air passages 53 communicating with the hollow interior of the lower annulus. Leading into the said recess at a convenient position is the air duct 37 from the compressed air source. The cylindrical receiving chamber 51 is closed at its bottom extremity by a scroll-channel 54 leading to a tangential outlet duct (not shown) which passes through the wall of the cylindrical casing to provide a channel by which the classifying air and the fines fraction entrained therein leave the machine, the upper central portion of the chamber base inside the scroll-channel forming the seating for the air-guide member pedestal 30.

The cylindrical casing 1 is extended downwardly to form an inverted conical hopper 55 wherein the coarse fraction of the separated material is collected and passed to an outlet port 56 which is closed in conventional manner by a materials feeder of the rotary sealed cell type (not shown).

The rotor is driven at a speed in the range of 800- 3200 R.P.M. by belting 57 or other suitable transmission means from a motor or other available source of rotary motion.

In operation, air is caused to flow through the air inlet port 22 of the machine into the upper portion of the casing (preferably by applying suction to the outlet port for the air and entrained fines fraction) and is then directed, as already described, into a circular path within the casing and from there into the stationary classifying zone through which it passes in an inwardly moving spiral flow to the receiving chamber and outlet duct, its passage through the stationary classifying zone being substantially unimpeded by surface friction at the flanking walls of the zone as a result of the lifting of the boundary layers associated therewith on cushioning air layers formed by the blowing of compressed air through the plurality of openings in the fabric of the said flanking walls. Material fed at the same time into the appropriate intake ports 16 and accelerated in the manner previously described passes into the classifying zone through the annular slot in the upper flanking wall in the form of a rotating annular curtain, the rotational motion of which is maintained in the annular slot by substantially tangential jets of air from openings in the rim of the air-guide member, so that as the curtain of material enters the classifying zone it is rotating in substantially the same direction as the flow of air in the zone.

As the material enters the classifying zone it is immediately subjected to the classifying forces applying therein so that particles smaller than the cut size are entrained in the air, while particles larger than the cut size are expelled from the zone into the lower portion of the cylindrical casing from which it descends into the collecting hopper.

What is claimed is:

1. A classifier for separating protein containing material from cereal mill stock and for performing similar separations of like materials in accordance with partic-1e size and density, comprising a generally cylindrical casing, spaced co-axial substantially annular members mounted in said casing and having flanking walls defining a ring-shaped classifying zone, a source of air under pressure, means to conduct the air under pressure to the classifying zone and cause the same to flow between the flanking walls in a radially unimpeded inwardly moving spiral path, portions of one of said flanking walls defining an annular slot through which material to be separated is directed into the classifying zone to form a rotating annular curtain having a rotational motion in substantially the same direction as the flow of air in the classifying zone, said flanking walls further including portions defining a plurality of orifices therein through which jets of air from a source of air of higher pressure than the air in the classifying zone are continuously blown over the zone wall surfaces to lift the boundary layer of air thereon to reduce surface friction on the flow of the classifying air as it passes through the classifying zone.

2. A classifier as claimed in claim 1 wherein the orifices defined by portions of the flanking walls of said annular members are inclined relative to the classifying zone surface and have a discharge angle substantially tangential to and in the direction of the flow of the classifying air passing through the zone.

3. A classifier as claimed in claim 1 wherein the flanking walls are removable annular diaphragms.

4. A classifier as claimed in claim 3 wherein said diaphragms are comprised of thin sheet metal and include portions defining a plurality of comparatively widely spaced unequal-sided radial serrations, the shorter side only of each of said serrations having portions defining a radial row of holes, said serrations being disposed so that compressed air blown through the holes in the shorter side of one serration passes over the longer sides of adjacent serrations in substantially the same direction as the classifying air passing through the zone.

5. A classifier as claimed in claim 3 wherein said diaphragms are comprised of air permeable material.

6. A classifier as claimed in claim 1 wherein the said spaced coaxial annular flanking walls are disposed relative to each other so that the axial distance between the walls at the outer radial extremity of the classifying zone is less than the axial spacing at the inner radial extremity of said zone.

7. A classifier as claimed in claim 6 wherein the flanking wall having portions defining the slot through which the material is passed into the zone is substantially flat and the other flanking wall is dished.

8. A classifier as claimed in claim 6 wherein; if R0 is the outer radius of the classifying zone, Ri is the inner radius of the zone, H0 is the axial spacing of the flanking walls at radius R0 and Hi is the axial spacing at radius Ri is greater than 1.4, Hi lies between 0.1 R0 and 0.35 R0, and

E is less than 0.7.

9. A classifier as defined in claim 6, wherein; if R0 is the outer radius of the clasifying zone, R1 is the inner radius of the zone, H0 is the axial spacing of the flanking walls at radius R0 and Hi is the axial spacing at radius Ri,

H i=0.26Ro

and

References Cited in the file of this patent UNITED STATES PATENTS 2,990,063 Elias June 27, 1961

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