Screening device and process

A cyclic screening apparatus (10) and method utilizes multiple air flows and differential air pressures to separate undersize and oversize particles from a mixture of 5 to 50 micron size particles. The apparatus (10) comprises a support (12) including a first conduit (14) connected to a blower (16). A lower undersize particle collecting housing (20) has a secondary air inlet (24) and outlet (26) connected to a suction fan (SF). A screen is clamped between the lower housing and an axially movable and pivotable upper receiving housing. An air distributor rotor (R) is slowly rotated below and directs the first air flow through the screen and into the upper chamber and through a lower portion (40) and against the bottom of lower housing. A rotary nozzle (80), with the help of incoming secondary air flow, disperses particulate material onto the screen below. Oversize particles are periodically vacuumed away by a suction fan (SF') drawing a third flow of air into, through and out a slotted collector arm rotated above the screen. In operation the volume of the first air flow, supplied to the air conduit at a predetermined pressure (P3), is less than the combined volume of the first and second flow drawn out of the lower collecting chamber. Thus, the pressure (P1) in the upper chamber is less than the outside atmospheric pressure but greater than the pressure (P2) in the lower chamber.

TECHNICAL DISCLOSURE 
A cyclic screening device and process utilizing air streams, air 
fluidization and air pressure differentials has the unique ability to 
remove small amounts of oversize particles in the micron size ranges with 
very high degree of precision. 
BACKGROUND OF THE INVENTION 
1. Field of Invention 
The invention relates to an air fluidized screening device and process for 
screening and separating oversize and undersize micron size particles 
uniformily distributed onto a static screen and transported through the 
screen by an air pressure differential assisted gravitational force. 
2. Description of the Prior Art 
The prior art suggests many types of fluidized screening devices and 
processes associated with vibratory feeders and screening mediums which 
have not been entirely satisfactory in the separation of very fine micron 
size particles. 
Fine particulate material has the tendency to easily cake, stick together, 
and hence clog the device due to the presence of but a slight amount of 
moisture, molecular attraction and greater surface area. Thus, the 
particles had to be kept absolutely dry and the fine mesh screen vibrated 
during the screening process. 
The instant invention overcomes the problems of the prior art device and 
processes by the utilization of air fluidization of the particles and 
turbulence to maintain the particles separated and in motion and low air 
differential pressures and sufficient air velocities to draw and pass the 
desired undersize particles through the screen and remove the oversize 
particles from the infeed side of the screen. 
SUMMARY OF THE INVENTION 
A screening device comprising support means including a frame supporting a 
stationary lower housing with a lower collecting chamber therein and a 
fixed or variable speed drive motor and gear reduction unit therebelow 
having an output shaft extending upwardly and rotatable about a central 
vertical axis of the lower housing and device. 
An adjustable air distributing rotor with one or more slotted hollow radial 
arms is keyed to the output shaft and slowly rotates below a static screen 
extending horizontally across the chamber to a peripheral frame clamped to 
an outer flange of the lower housing. Each radial arm is of hollow 
triangular shape, of which the upper apex edge is slotted and the bottom 
wall may or may not be perforated to allow a first air flow forced at a 
predetermined volume into each elongated hollow arm to exit therefrom. At 
least one hollow radial arm has a lower slotted portion or paddle which 
produces turbulences in the air flow. Thus, air can pass simultaneously 
through one or more angularly spaced radial portions of the screen to 
fluidize radial portions of the layer of particles on the screen at any 
one time and downwardly to create air turbulences and fluidize the 
undersize particles collected in the lower chamber. The undersize 
particles are then drawn out of and carried away from the lower collecting 
chamber to a cyclone separater and product collector and then to a 
filtered dust collector with the aid of a second additional air flow of 
lower volume mixing with the first air flow to create a lower differential 
pressure and turbulized by striking the lower slotted portion 40 of the 
rotating hollow radial arm. 
Above the screen is an axially movable and pivotable upper receiving 
housing including an upper receiving chamber and upper outer peripheral 
flange clamped against the screen frame and removably bolted to the lower 
housing flange. The upper housing is connected to swing horizontally about 
the axis of a vertically arranged piston rod of a piston within a fluid 
cylinder supported by the frame and operable to raise and lower the upper 
housing relative to the screen frame and lower housing. 
A second fixed or variable drive motor and gear reduction unit is 
vertically mounted on an upper support housing extending upwardly from the 
upper housing and around the vertical central axis of the device and drive 
shaft of the gear reduction unit. An internal central bearing divides the 
support housing into an upper outlet chamber connected to an outlet and 
lower feed chamber connected to a feed inlet. 
The drive shaft of the gear reducer is coupled to the upper closed end of a 
hollow drive sleeve or tube rotatable within the central bearing and which 
extends to a lower open end supporting a perforated cone or funnel shape 
rotary feed distributor ring or nozzle through which the particles and 
dispersing air can enter. 
Inserted into and or attached to the lower open end of the hollow drive 
sleeve is a vertical tubular leg of an L-shape oversize particle collector 
arm which has a tubular horizontal leg with an elongated slot in the 
bottom thereof into which the oversize particles are drawn by a third air 
flow during operation and rotation thereof above the screen. The oversize 
particles travel upwardly into and out the collector arm and side 
aperatures in the hollow drive sleeve to the upper chamber and outlet 
connected to a cyclone separater and coarse grain collector and optionally 
onto a filter and dust collector and out a suction fan. 
A helical screw feed mechanism is provided surrounded if necessary by a 
heater to dry and feed the particulate material to and for uniform 
distribution by rotating distributor nozzle onto the screen by means of 
gravity aided by a slight dispersion of additional air simultaneously 
drawn into and passing through the nozzle due to a lower differential 
pressure and partial vacuum created by the air flowing through the 
apparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENTS(S) 
In FIG. 1 there is shown apparatus for screening of fine particulate 
material comprising a mixture of particles ranging in size of from 3 to 50 
microns, particularly 3 to 30 microns and preferably from 9 to 18 microns. 
The apparatus comprises a particle screening device 10 about 112 cm (44") 
in diameter and 2.134 m (7 ft.) in height having various air inlets 
connected to a supply of air and air outlets connected to deliver the 
separated particles to additional conventional cyclone separaters, product 
collectors, filters and dust collectors. 
Means to support the apparatus about a central vertical axis comprises a 
support frame F including a plurality of support legs and structural 
members and brackets extending upwardly from a support base B and 
supporting a lower support housing 12 with an air conduit attached thereto 
and to an air inlet duct 14 extending horizontally from an air filter in a 
chamber attached to an adjustable air blower or fan 16, with an air 
intake, attached to a support extending upwardly from the base B. The 
blower 16 supplies a relatively greater volume of air into and creates the 
greater water gauge pressure differential P3 of from 10 to 40 mm of water 
in the air conduit and duct 24. 
Fixed to the lower support wall or bottom of the lower housing 12 are rotor 
drive means comprising a conventional fixed or variable speed drive motor 
and gear reduction unit D from which a vertical drive shaft extends 
upwardly into the air conduit and rotates about an axis aligned with the 
central axis of the screening apparatus 10. 
Mounted upon and fixed to the upper support wall of the lower support 
housing 12 is a lower undersize particle collecting housing 20 including a 
conical shape lower collecting chamber within a truncated cone shape 
bottom or lower wall extending to an outer circular wall fixed to a lower 
outer annular screen support flange 22 about 112 cm (44") in diameter and 
having a screen frame locating and retaining groove or recess in its upper 
surface for the screening means S extending horizontally across the lower 
collecting chamber. 
The lower housing 20 has a filtered air intake duct or conduit 24 extending 
into the bottom of the lower collecting chamber from an air filter and 
chamber situated adjacent the open intake end of the duct 24 and an 
undersize particle outlet duct 26 opposite the intake duct 24. Outlet duct 
26 is also connected to an adjustable motor driven suction fan SF which 
draws air preferably at a greater volume than blower 16 supplies and thus 
a second additional air flow of lower volume is drawn into duct 24 and it 
combines with the first air flow to create a water gauge differential 
pressure P2 of from 5 to 20 mm of water. The fluidized undersize particles 
suspended in the combined air stream are then carried to a cyclone 
separator and collector unit CS which separates and collects a greater 
percentage of the desired heavier and larger undersize or product 
particles from the air stream which carries the lighter and smaller 
undersize particles onto a dust collecting and filter unit DC. 
Adjustably mounted on and keyed to rotate with the drive shaft of the lower 
variable speed drive unit D is an air distributing rotor R including an 
inner central flanged hub 30 and an outer annular hub 32 from which at 
least one and preferably a plurality of angularly spaced slotted radial 
arms or blades 34 extend generally horizontally in the lower collecting 
chamber. As seen in FIGS. 2 and 4 the rotor R preferably comprises four 
(4) equally angularly spaced elongated radial arms 34 each of hollow 
triangular cross sectional shape with an elongated radial slot 36 about 2 
mm (0.080") wide extending through the entire upper horizontal apex edge 
portion thereof situated closely adjacent and spaced from the underside of 
the screening means S. The fine mesh screen S having uniform openings in a 
range of 3 to 50 microns spans the lower chamber and is attached to an 
outer narrow frame about 102 cm (40") in diameter with a projection fitted 
into a locating groove or recess in and clamped to the outer flange 22 of 
the lower chamber 20. 
Each of the arms 34 have, as shown in FIG. 4, oppositely inclined side 
walls diverging from the upper slotted apex edge 36 to a slightly inclined 
bottom wall 38 with or without air passages therein which slopes upwardly 
and radially outwardly at a slight angle from an inner end portion thereof 
attached to the top of the outer annular hub or collar 32. 
Extending downwardly from a perforated bottom wall 38 of at least one of 
the hollow radial arms is as shown in FIG. 4 a lower V-shape channel 
portion 40 defined by oppositely inclined spaced sidewalls extending 
downwardly and converging toward each other to lower spaced, inclined 
edges or lower slotted apex edge portions 42 thereof situated adjacent and 
spaced about 10 mm (0.615") from the inclined conical shape lower or 
bottom wall of the lower housing. The inner side of the V-shape channel 40 
is closed off by the attached collar 32 and hence air must pass out the 
openings in the bottom wall 38 and out the narrow elongated slots about 
1.5 mm (0.060") wide in the lower inclined apex edge portion 42 and 
fluidize the screened undersize particles falling between the arms 34 of 
the rotor R and collecting on the inclined lower wall of the conical lower 
collecting chamber of lower housing 20. 
The outer annular collar 32 is spaced from the central drive hub 30 and 
extends downwardly and rotates around an upwardly projecting central 
annular bearing wall of the air conduit in the lower support housing 20 
and thereby provides an extension of the annular passage or air conduit 
for conveying air from the blower 16, creating the differential pressure 
P3, into the inner open end of each of the hollow triangular shape arms 
34. 
At any one period of time during slow 5 to 20 revolutions per minute (RPM) 
of rotor R, air flowing at a predetermined volume and creating the water 
gauge pressure P3, enters each hollow arm 34, passes out the upper narrow 
elongated radial slots 36 and through adjacent corresponding narrow areas 
of the perforated screen S above to simultaneously fluidize corresponding 
angularly spaced narrow elongated radial portions of the layer of 
particulate material which is collecting on and passing through screen S. 
Likewise, part of the first air flow also passes downwardly through the 
spaced apertures of about 2 mm (0.080) in diameter in the bottom wall 38 
of at least one arm 34, through the V-shape chamber and out the elongated 
slots in the lower inclined apex edge portion 42 of the arm and thereby 
simultaneously fluidize and prevent the screened under size particles from 
collecting on the inclined bottom wall of the lower housing 20. 
The fluidized particles and first air flow are thereafter mixed with and 
carried away from the lower chamber and to cyclone CS with the aid of a 
secondary air flow which are drawn together to create a lower water gauge 
pressure P2 of from 5 to 20 mm in the lower chamber by the conventional 
variable motor driven suction fan SF. This combined first and second air 
flow is also momentarily obstructed every time the lower channel or paddle 
portion 40 of the arm 34 rotates by the inlet and outlet means and thereby 
creates turbulence in the lower collecting chamber and assists in removing 
particulate. 
Mounted upon and clamping the frame of the screen S to the flange 22 of the 
lower housing 20 is an upper conical shape receiving housing 50 comprising 
an upper conical chamber into which the first air flow enters and combines 
with a second air flow to create a water gauge pressure P1 of 2 to 10 mm. 
The chamber is enclosed by an upper inclined wall diverging downwardly and 
outwardly to an outer wall attached to an upper outer annular flange 52. 
The lower surface of the horizontal outer flange 52 is preferably provided 
with a conventional annular seal or O-ring adapted for sealing engagement 
with the frame of screen S maintained by removable bolts extending between 
the lower and upper flanges 22 and 52. Alternatively seals may be placed 
on one or both the lower and upper surface of the screen frame. 
At one side of the upper housing 50, the flange 52 extends radially to 
support a pivot bearing cap or cylinder 56 fixed thereto and attached to a 
fluid pressure actuated pivot piston and cylinder of a displaceable pivot 
means or device 60. The pivot device 60 is adapted to raise and lower the 
upper housing 50 axially off the frame of screen S and allow pivotable 
movement of the upper housing 50 in order to service, replace or change 
the screening means S. 
A vertical support member extending upwardly from the base B also supports 
the end portion of the air duct 14 upon and to which a horizontal base or 
end plate and vertical support cylinder 62 of the displaceable pivot 
device 60 is fixedly attached. 
A piston 64 is slideably mounted for limited axial displacement in a lower 
bore of the support cylinder 62 and has attached thereto an upwardly 
extending piston rod 66. The piston rod 66 is slideably mounted in and 
extends through a smaller upper bore in the upper end of the cylinder 62 
to an upper end portion inserted into the pivot bearing cap 56. A 
conventional two way rotary valve V connectable to a source of fluid under 
pressure such as hydraulic fluid or compressed air, is provided to actuate 
the device. Following unbolting and unclamping of the flanges 52 from 22 a 
partial rotation of the valve V supplies fluid under pressure to the lower 
end of the cylinder bore, which displaces the piston 64 and piston rod 66 
upwardly to a stop shoulder and thereby raises the upper housing 
sufficiently to remove or change the screen S. 
If necessary, the upper housing can also be pivoted about the axis of the 
piston rod 66 relative to the lower housing by disconnecting the quick 
disconnect and connect type coupings provided at the material inlet 74 and 
outlet 76 conduits of the upper support housing 70. 
Rotary material distributor and collector means are provided in and 
supported by an upper central portion of the upper housing 50 for 
distributing and dispersing particulate material fed thereto onto the 
screening means S below and to remove oversize particles accumulated on 
the screen S. 
The rotary distributor and collector means comprises a central cylindrical 
upper support housing 70 fixed to and extending upwardly from a central 
portion of the top or upper wall surrounding a central inlet opening in 
the upper wall of the upper receiving housing 50. 
Between its opposite upper and lower open ends the upper support housing 70 
has extending inwarding from its outer wall an annular web portion 
supporting a central bearing sleeve 72 which together divide the housing 
internally into upper and lower annular chambers. An inclined inlet feed 
conduit 74 extends into the lower annular chamber and an oversize particle 
outlet conduit 76 extends from the upper annular chamber. 
The housing 70 has fixed to its upper open end a second conventional fixed 
or variable speed motor and gear reduction drive unit D' with its output 
drive shaft extending downward and rotatable about a vertical axis 
coinciding with the central axis of the upper and lower housings 20 and 
50. 
Attached to and rotatable with the drive shaft of the upper drive unit D' 
is fixed a hollow elongated shaft or tubular sleeve 78 rotatably engaging 
the central bearing 72. The upper end portion of said hollow sleeve 78 has 
a plurality of outlet passages or apertures in the wall thereof through 
which oversize particles suspended in a third air flow of about 160 M3/hr. 
that creates a differential water gauge pressure P4 of about 1000 mm can 
pass from the interior thereof into and out of the upper annular chamber, 
through outlet conduit 76 to a second oversize particle cyclone separater 
collector unit CS' and, if desired, on to an optionally provided second 
air filter dust collector unit DC' and exhaust air through the second 
variable motor driven suction fan SF'. 
Fixed to and flared upwardly and outwardly from the lower open end portion 
of the sleeve 78 is a perforated cone shape distributor nozzle or funnel 
80 rotatable in the lower annular feed inlet chamber below the material 
feed inlet pipe 74. 
Inserted into and adjustably fastened to the lower end of the rotatable 
hollow sleeve 78 or made an integral part thereof, is the vertical tubular 
leg of a hollow L-shape rotatable collector arm 82 having a horizontally 
extending elongated slotted tubular collecting radial arm or leg. The 
radial collecting arm 82 has as shown in FIG. 3 a continuous narrow 
elongated slot 84 about 3.2 mm (1/8") wide extending through the tube wall 
at the bottom thereof situated directly above and spaced about 6.4 mm 
(1/4") from the adjacent upper side of the static screening means S from 
which accumulated oversize particles are periodically removed during 
rotation of collector arm 82 and operation of the suction fan SF'. On the 
upper side of the horizontal tubular leg of collector arms 82 are inclined 
sides which diverge downwardly and outwardly from the upper horizontal 
apex edge 86 thereof for the purpose of deflecting and preventing the 
accumulation of particles thereon. 
As shown in FIG. 1 the feed inlet pipe 74 and outlet pipe 76 are connected 
to adjacent conduits by an axially movable sleeve type coupling of either 
flexible or rigid construction which can be displaced sufficiently to 
quickly connect or disconnect and swing the upper housing 52, and 
apparatus carried thereby about the pivot support shaft 66 relative to the 
lower housing in order to service the device and screen S. 
Particulate feed means of any conventional type may be provided to feed the 
material to be screened to the inlet pipe 76. The feed means FM shown has 
an optionally heated temperature controlled horizontal housing and channel 
in which a rotatable helical feed screw FS is rotated, at a predetermined 
variable low speed, about a horizontal axis by a train of gears or pulleys 
of predetermined speed ratio driven by a variable speed motor M. A feed 
hopper H at one end holds a quantity of particulate material extruded 
therefrom and advanced at a suitable uniform rate by the rotating helical 
feed screw FS through the channel and heated if needed by an induction 
coil C wrapped about the channel housing. Thus, the particulate material 
containing a mixture of oversize and undersize particles remains in a dry 
powder form during the screening process. 
In the operational screening or production mode the suction fan SF' which 
normally draws a third air flow at 160 M3/hr. and water gauge pressure P4 
of 1000 mm in the collection arm 82 is shut down and no air is drawn 
through the particle collecting vacuum arm 82, outlet 76, cyclone CS' and 
filter DC'. Thus, pressure P4 not present, is equal to P1 in the upper 
chamber during screening. 
During a typical screening operation of material containing up to 30 micron 
size particles the fan 16 forces a first flow of air at about 800 M3/hr. 
which creates a differential water gauge pressure P3 of about 40 mm, into 
each of the hollow arms 34 of the rotor R. The suction fan SF operating at 
1000 M3/hr. draws the first and second flow of additional air of about 200 
M3/hr.; 100 M3/hr. through each of the feed distributor nozzle and duct 
24, into and out of the lower collecting chamber and which combined 
creates the differential water gauge pressure P2 of about 20 mm. The first 
air flow passes out the elongated slots 36, in the arms 34 and through 15 
micron size openings in the screen, to fluidize narrow elongated radial 
portions of the material on the screen and then after a pressure drop 
enters the upper receiving chamber and creates a water gauge pressure P1 
of about 10 mm which is greater than P2. Hence, during screening the 
various sources of air flow are adjusted and regulated to obtain the 
following differential pressures wherein P3&gt;P4=P1&gt;P2. 
Variable speed motors D and D1 are started and adjusted to slowly rotate 
the respective air distributing rotor R at about 12 RPM and the rotary 
distributor 80 and arm 82 at about 25 RPM. Motor M is started and adjusted 
to rotate feed screw FS the desired feed rate and heater coil is operated, 
if necessary, to heat the chamber and dry the material being conveyed to 
the feed pipe 74 and rotating distributor nozzle or funnel 80. Material to 
be screened and secondary air of about 100 M3/hr. passes through the 
perforations in the distributor 80 whereupon the circulation of air 
through the apparatus creates a partial vacuum and a differential air 
pressure P1 in the upper chamber greater than P2 in the lower chamber but 
both lower than the air pressure outside the apparatus. Thus, secondary 
outside air of about 100 M3/hr. is drawn into and helps the nozzle 80 to 
uniformily disperse the particulate material onto the screen S and to mix 
with the first flow of air in the upper receiving chamber. 
Since air pressure P1 above the screens is greater than air pressure P2 
below the screen, the air currents move downwardly and help the 
gravitational force carry the particles onto, and to pass, in this case, 
undersize particles up to 15 microns through the 15 micron openings in 
non-fluidized segments of the screen S situated between the rotor arms 34. 
Particles equal to and of smaller size than the openings in the screen 
then pass with the combined first and secondary air flow into the lower 
chamber and toward the bottom wall of the lower housing. As the rotor 
rotates part of the first air flow passes through the perforated inclined 
bottom wall 38 of preferably one triangular arm 34 and out the inclined 
slot 42 in the lower portion 40 of each arm 34 at a lower pressure than P3 
due to a pressure drop to fluidize the particles collecting on the bottom 
wall. Hence, the combined first and second air flow and the undersize 
particles mix with another portion of the second flow of air of 100 M3/hr. 
passing from inlet 24 and into the lower chamber whereupon they are 
combined and drawn out by suction fan SF at 1000 M3/hr. This exhaust air 
flow is momentarily obstructed by the rotating paddle 40 of at least one 
arm of the rotor and thus causes variations in pressure volume and 
velocity and hence creates air turbulence in the collecting chamber. Thus, 
the particles are carried to the cyclone separator CS by the combined air 
streams whereupon the larger of the undersize particles within a 
predetermined micron size range are separated from the smaller micron size 
fines and dust carried to and filtered from the air stream by the filter 
and dust collector unit DC. 
Following a predetermined period of screening the material feed means FM, 
the second additional air flow and suction fan SF are stopped. The 
oversize particles that have accumulated on the screen are then removed by 
starting up the suction fan drive motor SF', which draws the third 
airstream of about 160 M3/hr. and creates a negative water gauge 
differential pressure P4 of about 1000 mm in the rotating slotted 
horizontal arm of the collector 82. 
The first air flow at pressure P3 continues to enter and flow from the 
slotted rotor arms, through openings in the screen and into the upper 
chamber at a differential pressure P1. Air passing through the screen S 
agitates the coarse or over size particles until picked up and carried 
away by the air flowing into the collector arms 82. At this time pressure 
P4 is less than or equal to the air pressure P2 in the lower chamber. 
The air pressure in the various areas of the apparatus during removal of 
the oversize particle is adjusted and regulated to obtain the following 
differential pressure conditions wherein P3 &gt;P1 &gt;P2 .gtoreq.P4. 
Since the air at pressure P3 emerging from the rotating slotted rotor arms 
is greater than P1 it tends to lift the oversize particles temporarily off 
the screen S after which the reduced air pressure P1, still greater than 
P2, helps gravity carry them back onto the screen whereupon the higher 
volume and lower negative air pressure P4 at rotating collector arm 82 
passing over them draws the oversize particles through the narrow 
elongated slot 84 and carries them out the outlet pipe 76 to the cyclone 
separator CS'. 
The cyclone separater CS' separates and collects the larger oversize 
particles and allows the smaller oversize particles, if any, to continue 
on to be separated from the air by the filter and dust collector unit DC'. 
From the above description it can be seen that various differential air 
pressures P1, P2, P3, and P4, created by the various air streams passing 
through the apparatus are lower than the air pressure outside the 
apparatus and thereby creates a partial vacuum of various degrees within 
the apparatus. 
As many other embodiments and modifications of invention are possible, it 
is to be understood that the embodiment disclosed hereinabove is but an 
example of the many possible embodiments thereof and the invention 
includes all embodiments, modifications and equivalents thereof falling 
within the scope of the appended claims.