US3011637A - Float discharge device for rotatable type heavy-media separators - Google Patents

Description

Dec. 5, 1961 H. J. FELSCH ETAL 3,011,637 FLOAT DISCHARGE DEVICE FOR ROTATABLE TYPE HEAVY-MEDIA SEPARATORS FiledJuly 24, 1958 3 Sheets$heet 1 INVENTORS AQNS (luau/0v 5430/ $064 F QPAHf/Q ATTORNEYS Dec. 5, 1961 H. J. FELSCH ETAL 3,011,637

FLOAT DISCHARGE DEVICE FOR ROTATABLE TYPE HEAVY-MEDIA SEPARATORS Filed July 24, 1958 5 Sheets-Sheet 2 ATTORNEYS Dec. 5, 1961 H. J. FELSCH ETAL 3,011,637

FLOAT DISCHARGE DEVICE FOR ROTATABLE TYPE HEAVY-MEDIA SEPARATORS Filed July 24, 1958 3 Sheets-Sheet 5 fi? 79 92 & {a -i n m I 39 I 3; if

INVENTORS ATTORNEYS United States Patent Oflfice 3,011,637 Patented Dec. 5, 1961 3,011,637 FLOAT DISCHARGE DEVICE FOR ROTATABLE TYPE HEAVY-MEDIA SEPARATORS Hans Joaquin Felsch, Paio Alto, and Reuel F. Pray, Jr., San Francisco, Calif., assignors to Western Machinery Company, San Francisco, Calif., a corporation of Utah Filed July 24, 1958, Ser. No. 750,821 21 Claims. (Cl. 209-1725) This invention relates to heavy-media separation of solid particles and is more particularly concerned with an improved drum type separating apparatus and methods for handling and separating particle mixtures of materials of different specific gravities.

in recent years, industries have recognized the advantages of separation of solid particles by their differences in specific gravity. In such processes, a mixture of particles having different specific gravities is immersed in a fluid having a density approximative and usually intermediate of the gravities of the particles to be separated. Thus, the particles of lesser specific gravity than the fluid are separated in a float fraction while the particles of greater specific gravity are separated into a sink fraction. The present invention is primarily concerned with such types of operation utilizing rotating drum separatory vessels.

One of the primary requisites of the heavy-media sepa ration is that the size range of the particles to be separated must be capable of being handled by the apparatus. With certain materials, the particles sizes vary over an extremely wide range. For example, some types of coal contain coarse float particles as large as 8 inches in diameter while the fine float pieces are composed of granular material. The usual practice is to remove all of the float particles from the separating bath by discharging a measured amount of the separatory fluid over a weir. To this end, it has been necessary to provide at the separatory vessel float fraction discharge weir an overfalling stream of fluid or uappe having a depth equal to or slightly exceeding the maximum float particle size in order to facilitate removal of the entire float fraction. This head of fluid above the crest of the weir required to accommodate the removal will directly affect the approach velocity of the separatory fluid (the cross flow velocity of the liquid through the drum) and therefore the retention time of any given particle as it moves from the feed end toward the discharge weir.

The retention time has a vital influence on the quality and accuracy of separation inasmuch as it predetermines the time available for a heavier particle to sink within the medium to a zone where it will not be subject to evacuation by the overflow suction along with the float fraction. Thus, reduction of the depth of the nappe of the overflow ing stream of the separatory fluid increases the retention tirne of the particles in the separatory vessel. Reducing the depth of the nappe to a dimension which is less than the dimension of the submerged portion of the larger float particles, however, will prevent these particles from being discharged in the overfalling stream. These particles will abut the crest of the Weir and consequently will establish a residence in the separatory vessel for a length of time sufficient to form a dam across the weir. The dam consisting of the larger float particles then raises the level of the media within the separatory vessel. When the fluid pressure behind the dam increases sufliciently to break up the dammed up particles, the particles are discharged in a single surge of fluid. The surge of fluid precipitates a sudden lowering of the level of the media to its normal level which engenders a momentary increase in velocity in the form of a pulsating wave. This sudden velocity increase causes sink particles which are still sinking in the medium to be carried out with the pulsating wave for discharge with the float particles. It is evident therefore that these surges which cause sink and float particles to intermingle and to be discharged together, results in a poor, uneflicient metallurgical separation. Thus to improve the quality of separation of materials so treated it has become desirable to reduce the depth of the nappe and still be able to discharge large size float particles.

Several attempts have been made in the past to achieve this end. Some devices require additional crushing or grinding to reduce the size of the particles. This solution, however, has not been found to be practical since the resultant product will be composed of an excessive amount of fines. Other devices have incorporated additional separating structure to remove the coarse float particles apart from the finer float pieces. Such devices aside from their complicacy often interfere with the laminar flow of t.e overfalling stream at the discharge weir producing turbulence that tends to upset the hydraulic balance in the separatory vessel.

With the present invention, a novel discharge device is incorporated in the separatory apparatus to facilitate the removal of oversize particles by hydraulic evacuation in the overfalling stream having a nappe depth which is less than the diameter of the particle. This special device comprises a curved segment arranged to scoop into the medium immediately adjacent to the medium discharge weir to mechanically increase the buoyancy of any large size particles in its path by imparting a lifting action thereto.

With the foregoing considerations and purposes in mind, it is the major object of this invention to provide a novel process and apparatus for improving the separation of particles of different specific gravities.

It is a further object of this invention to provide for a novel process and apparatus for facilitating gravity separation of particles in a heavy medium stream While maintaining relatively stable hydraulic conditions within the principal zones of separation and particle discharge.

t is a further more specific object of this invention to provide for an improved rotatable heavy media gravity separator embodying a novel discharge device for mechanically increasing the buoyancy of oversized float particles.

It is further an object of this invention to provide for a novel heavy media separatory apparatus for improving the quality of separation by increasing the retention time of the float particles being separated in the apparatus.

It is further an object of this invention to provide in an improved heavy media separatory apparatus which separates a particle mixture into a float fraction and a sink fraction, a novel discharge device for mechanically in creasing the buoyancy of oversized float particles to facilitate their discharge and imparting a tumbling motion to the oversized particles to further stimulate their discharge.

It is further an object of this invention to provide in an improved heavy media separatory apparatus which separates a particle mixture into a float fraction and a sink fraction, a novel discharge device for mechanically increasing the buoyancy of oversized float particles to facilitate their discharge and for imparting tumbling and spiral motions to the oversized particles to further stimulate their discharge.

It is further theobject of this invention to provide an improved heavy media separatory apparatus having a novel float particle discharge device of simple and durable construction and comparatively inexpensive to manufacture.

Further objects will presently appear as the description proceeds in connection with the appended claims and the annexed drawings wherein:

FIGURE 1 is a front elevation illustrating the heavy media separator with the end plate partially removed;

FIGURE 2 is a section substantially along line 22 of FIGURE 1;

FIGURE 3 is an enlarged fragmental section ,of a portion of FIGURE 2 more clearly illustrating the float removal scoop shown in FIGURES 1 and 2;

FIGURE 4 is an enlarged. perspective view illustrating the 'float removal scoop assembly shown in FIGURES 1-3;

FIGURES 57 are simplified diagrammatic elevations illustrating the progressive action of the float removal scoop as viewed from within the separatory chamber; and

FIGURE 8 is an enlarged perspective view illustrating a further embodiment of the float removal scoop assembly similar to'FIGURE 4.

Referring now to the drawings and more particularly to FIGURES 1 and 2, a drum separator is there illus-.

trated which is generally designated at 10. This separator comprises a hollow, cylindrical shell or drum 12 mounted on the base 14 having a horizontal deck 16 supported by longitudinally extending channels 18 and transversely extending channels 20, The drum 12 is mounted for rotation about its longitudinal axis on the base 14 by means of two steel tires 22 which circumscribe and are joined to the periphery of the drum near opposite ends thereof as by welding or other suitable means. Each tire 22 rides on a pair of support rollers 24 one on each side of the separator equidistant from the drum axis as best shown in FIGURE 2. Each of these rollers 24 is provided with trunnions 26 which are journalled in bearings 28 formed in the brackets 36*. The

rackets 30 in turn are fixed to the base 14 by welding or other suitable means. In addition to the support provided by rollers 24, there are provided antifriction rollers 25 (FIGURE 2) which are mounted on the base one on each side of each tire to bear against the sides of the associated tire for maintaining its longitudinal position on the support rollers 24. The drum is rotatably driven by means of a sprocket 32 which circumscribes the drum and is secured to the periphery thereof by suitable means such as welding or the like. The sprocket 32 is drive connected to a suitable drive (not shown) and may be driven any predetermined speed depending upon the character of material being separated.

The ends of the drum 12 are partially closed by annular frustoconical end plates 36 and 38 joined to the drum, one at each end, and having circular openings 37 and 39 thereof coaxial with the longitudinal axis of the drum. The circular opening 39 of plate 38 constitutes in effect an overflow weir for the separatory fluid and float fraction of the separation and is of larger diameter than the circular opening 37 in plate 36;

Referringnow more particularly to FIGURE 2, the drum is provided with a plurality of longitudinally extending perforated sink lifters'40. These lifters 41 are spaced apart circumferentially uniformly about the inner surface of the drum 12, and are secured thereto by axi- ,surface of the'drum. These partitions 48 are secured at 50 to brackets 52 fixed to a stationary framework 54.

The partitions extend below the liquid level to prevent floated light material from reaching the lifters 40 as they are rotated and from becoming trapped therein, while their flexible character allows passage of large chunks of sink particles carried by the lifters. V V

The framework 54 supporting the partitions 48 com-' prises a pair of spaced vertical angles 56 mounted on the base 14 at each end'of the drum and reinforced by. gussets 58. Spaced horizontal angles '69, which are sup ported by the vertical angles 56, extend axially through 4 the drum 12 through the openings 37 and 39 provided in end plates 36 and 38.

An inlet trough or chute 62 is supported by the framework 54 to which it may be secured in any suitable manner. This trough extends through the circular opening 37 in the end plate 36 and has a downwardly extending discharge end terminating just below the normal liquid level of the pool of heavy medium within the drum in the proximity of the end plate' I A heavy fluid separating medium of selected specific gravity is supplied to the drum by means of a pipe 64 from a supply source (not shown) and intimately admixes with the feed supplied through trough 62. The rate of fluid flow in the supply pipe 64 is controlled by valve 65. The heavy medium with the light or float fraction of the separation overflows the weir formed by the circular opening 39 in the end plate 38 to a float fraction discharge launder 66 shown in outline form. A discharge launder 68 for the heavy or sink fraction of the separation extends longitudinally into the drum and is, for the most part, above the central horizontal axis of the drum and below the point where the lifters 40 pass the pocket discharge position in their revolution. This discharge trough 68 is supported from the framework 54 by brackets 76 or other suitable means. A fluid separating medium is introduced into the upper end of discharge trough 68 by a supply pipe 72 which communicates with the interior of the discharge trough through an opening 74 formed in the base of the trough. The supply pipe 72 is provided with a control valve 76 for measuring the amount of fluid being introduced into the trough.

In accordance with this invention, a float discharge scoop indicated at 78, FIGURES 13 and at 89, FIG- URE 8 is provided immediately adjacent to the discharge weir 39 or the periphery of the portformed in annular end plate 38 for facilitating removal of oversized float particles, the diameters of which approach or are greater than the depth of the overfalling stream indicated at 79QFIGURE 3. This is accomplished by mounting the scoop on the end plate 38 to revolve with the drum 12 so that a lifting'action Will be imparted to the particles by the scoop as it rotates with the drum as will be described. In operation of the separatory apparatus, the scoop does not lift the float particles completely out of the heavy media bath for discharge but rather functions primarily to mechanically increase the buoyancy of the oversized particles for hydraulic evacuation by the stream 79 overfalling the weir 39. By mechanically increasing the buoyancy. of the oversized float particles therefore, it is understood that the magnitude of immersion of these particles is reduced by mechanically raising the oversized float particles so that each of the particles are buoyed up or sustained with a predetermined submerged dimension by a mechanical force in addition to the hydraulic force established by the particle displacement of fluid. Thus, as scoop 78 revolves with drum 12 it passes under the oversize float particles and imparts a lifting action thereto to reduce the degree of immersion of these particles. in the fluid and to thereby facilitate their discharge over weir 39 by the forward motion of the stream overfalling the weir. Depending on the amount of oversized particles'present in the drum =feed, the separatory apparatus may be provided with a single scoop or a plurality of spaced apart scoops mounted around the periphery of the overflow discharge opening in. endplate-SS. Inasmuch as the percentage of large particles is usually small, it is usuallysuflicient to equip the drum with a single scoop. This is desirable in that it avoids interference with the steady overflow current which may lead to an'undesirable pulsating effect.

Referring particulariy to FIGURES 14, one embodiment of the scoop is therein illustrated and is generally designated at 78, comprising a rigid arcuately shaped plate 86 having a constant radius of curvature and mounted on the end plate 38 for rotation with the drum 12 by bolted clips 82 and 84. The bolted clip 84 is provided with an elongated bolt hole' 86 to facilitate adjustment of the leading angle of the scoop. The scoop is thereby mounted so that its leading edge is at a greater distance from the longitudinal axis of the drum 12 than its trailing edge. The clips 82 and 84 further position the scoop at an acute angle with the end plate discharge opening for imparting to the buoyed up particles a tumbling action in the direction of the discharge opening 39, thus further facilitating their evacuation in the overfalling stream 79.

The arcuately shaped plate 80 as illustrated in FIG- URES l-4 is provided with spaced apart elongated perforations 88 for stimulating the outward skid of any scooped up particles. These perforations 88 are slanted to form an acute angle between the sides of the perforations facing the leading edge of the scoop 78 and the end plate 38, so that there is a minimum of interference with the laminar overflow stream. The stimulation of the outward skid of the particles is accomplished by the passage of media through the perforation 88 which urges against the scooped up particles to impart an additional force to the float particles in forcing them over the weir. Thus, by passing the media through the slots, the full velocity of the fluid stream is utilized in pushing the float particles over the weir.

Referring now to FIGURE 8, the alternative scoop illustrated therein and generally indicated at 89 is substantially identical with the scoop 78 shown in FIGURE 4 and described in connection therewith, with the exception that the scooping plate 90 in addition to being curved, is also spiralled. This configuration imparts a spiralled motion to the particles in the path of the scoop in addi tion to the tumbling and skidding motions caused respectively by canting the plate with respect to the discharge opening and the slanted perforations 88.

The operation of the apparatus is believed to be apparent from the foregoing description. The mixture of particles to be separated is fed to the inlet trough 62 where it is pre-wetted by separatory fluid withdrawn from supply conduit 64. The pre-wetted mixture is then introduced into the separatory fluid within the chamber formed by the drum 12. Due to the selected intermediate density of the separatory fluid, the more dense fraction of the mixture gradually settles to the bottom of the chamber and accumulates at the bottom side of the drum 12. Rotation of the drum 12 at a selected speed (about 0.8 rpm. for a foot drum) in the manner previously described causes concomitant movement of the sink lifter blades 40 in the direction of the arrow 45 (FIGURE 1) so that the sink fraction accumulated at the bottom of the separatory chamber are picked up by the blades and raised in a concentric path up through the separatory fluid to the upper part of the chamber. It is preferable that the speed of the drum be maintained as slow as possible to prevent the medium from being churned, while at the same time providing for adequate lifting capacity to discharge the separated sink particles. The minimal speed at which the separatory vessel rotates, therefore, is determined by the number of sink particles carried by each lifter blade 40 and hence by the size of the sink particles and the number of lifter blades.

In the progress of rotation of the drum, the lifter blades 40 become inverted to drop the entrapped sink fraction into the inclined discharge trough 68 whence it is conveyed to other points of usage. To insure movement of the discharged sink fraction along the discharge trough 68, measured amounts of fluid medium are introduced to the trough by conduit 72,

The float fraction of the mixture which is less dense than the heavy medium rises gradually to the surface and is evacuated from thedrum in the overfalling stream 79 of excess heavy medium overflowing from the drum 12 into the discharge launder 66.

In accordance with the invention, the buoyancy of certain of the float particles 92 which are oversized (having diameters greater than the depth of the nappe and which cannot be discharged by the overfalling stream alone) is mechanically increased by scoop 78 to facilitate hydraulic evacuation by the overfalling stream 79. The scoop 78 as it rotates with the drum 12 scoops into the medium (FIGURES 6-8) so that as it enters the fluid, it averts the development of fluid currents which would tend to disturb the laminar flow of the stream. The oversized particles in the path of the scoop are moved along from the leading edge to the trailing edge having their buoyancy mechanically increased to raise them snfliciently to clear the edge of the weir as they are evacuated in the overfalling stream. The scoop, to stimulate removals, further imparts a tumbling and skidding motion to the oversized particles concomitant with the lifting action imparted thereto. The embodiment of FIGURE 8 in which the scooping plate is spiralled imparts a spiral motion to the particles in addition to increasing the buoyancy and imparting tumbling and skidding motions to the oversized particles to further facilitate their discharge from the separatory chamber.

While the foregoing descriptions have been largely concerned with the elements of the particular apparatus, it is obvious that the invention is not necessarily restricted thereto and that functional equivalents may be employed to carry out the method of particle separation. For example, ditferent supporting and rotary drive systems may be used. The configuration of the separatory drum and consequently the chamber formed thereby may vary, other means for lifting the sink fraction may be employed such as buckets and similarly, other means may be employed for accomplishing each or" the functions of the scoop.

Thus, in accordance with the invention, the method of carrying out the particle separation is started by passing a stream of separatory fluid of selected specific gravity through the separatory chamber and discharging it over a Weir as an overfalling stream having a selected nappe depth to predetermine the approach velocity or the fluid stream within the chamber. The particle mixture to be separated is introduced into the fluid stream flowing through the chamber whereupon the particles of lesser specific gravity than the fluid separate into a float fraction rising slowly to the fluid stream surface while the particles of greater specific gravity are separated into a sink fraction and settle to the bottom of the chamber. As the particles of the mixture are being separated into their respective fractions, they are carried forward by the velocity of the stream. In order to achieve a complete separation of the particle mixture before any of the particles are discharged in the overfalling stream, the nappe depth of the overfalling stream, which controls the velocity of the fluid stream flowing through the chamber, is maintained sufliciently low to retain the particle mixture in the chamber until the separation is completed. The sink fraction is then removed from the float stream without admixing with the float fraction which is progressing towards the overflowing stream. Particles of float fraction having lesser dimensions than the depth of the nappe are hydraulically evacuated in the overflowing stream. Particles of float fraction having greater dimensions than the depth of the nappe and which, owing to their physical size, cannot be discharged from the chamber by hydraulic evacuation alone, are mechanically buoyed up so that the dimension of the portion of each oversized particle which is below the surface of the fluid is decreased, thereby facilitating hydraulic evacuation of those particles over the weir. In order to further facilitate the evacuation of these oversized particles in the overflowing stream, tumbling and skidding motions are imparted to the particles simultaneously with the mechanical buoying of the particles. To still further facilitate the removal of the oversized particles, a spiraling motion (FIGURE 8) is imparted to motions.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered. in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

What is claimed and desired to be secured by United States Letters Patent is:

1. In combination, a horizontally oriented rotatably mounted separatory vessel having an inlet, a sink fraction discharger outlet and a float fraction discharge weir substantially concentric with the vessel rotation axis, means for introducing a separatory fluid and solids to be separated into said vessel through said inlet for flow at a predetermined rate through said vessel to overflow over said discharge weir in a nappe of a predetermined height, and means for enabling passage in a single stream with the separatory fluid over said Weir of float particles having dimensions larger than the depth of the separatory fluid nappe at said weir.

2. In combination, a horizontally oriented rotatably mounted separatory vessel having an inlet, a sink fraction discharge outlet and a float fraction discharge weir substantially concentric with the vessel rotation axis, means for introducing a separatory fluid and solids to be separated into said vessel through said inlet for flow at a predetermined rate through said vessel to overflow over said discharge weir in a nappe of a predetermined height, and evacuation means for enabling passage with the separatory fluid over said weir of oversized float particles having dimensions larger than the depth of the separatory fluid nappe at said weir, said evacuation means being mounted adjacent said Weir for rotation with said vessel and arranged relative to said weir to mechanically increase the buoyancy of said oversized particles in the float fraction for hydraulic evacuation by the fluid stream overfalling said weir.

3. in the apparatus defined in claim 2 wherein said evacuation means comprises at least'one curved plate having a-trailing edge immediately adjacent said weir and a leading edge at a greater distance from the axis of said shell means than said trailing edge for scooping into the separatory fluid during rotation of said vessel, said leading edge being rotatable in a closed path to penetrate into the separatory fluid to a maximum depth that is closer to the surface of said fluid stream than to the bottom thereof.

4. In the apparatus defined in claim 3 wherein said curved plate is mounted on said vessel at an acute mgle with the interior surface thereof adjacent said weir for imparting a tumbling action to oversized particles in the direction of said weir.

5. In the apparatus defined in claim 3 wherein said curved plate is spiralled for imparting a spiralled motion to the oversized particles.

6. In the apparatus defined in claim 5 wherein said plate is provided with elongated perforations for stimulating the outward skid of the scooped up particles.

7. m me apparatus defined in claim 3 wherein said curved plate is arcuately shaped with a constant radius of'curvature. v e

8. In the apparatus defined in claim 7 wherein said plate is provided with elongated perforations for stimulating the outwardskid of the scooped up particles.

9. lna heavy media separatory apparatus, a separatory a Weir in one endthereof, means for-introducing particles to be separated into said vessel, means forintroducing V a separator-y fluid into said vessel near the vother end thereof for flow at predetermined rate through said vessel and over said weir separating said particles into a float fraction and a sink fraction, means mounted to rotate with said vessel for lifting the sink fraction without admixing it with the float fraction, means for discharging the separated sink fraction, means for rotating said vessel whereby the sink fraction is carried forward by said lifting means to be deposited in said discharge means and means mounted adjacent to the periphery of the discharge opening for rotation with said shell means to mechanically increase the buoyancy of oversized particles in the float fraction for hydraulic evacuation by the fluid stream overfalling said weir.

10. In a heavy media separatory apparatus, a drum mounted for rotation about a substantially horizontal axis and'forming a separating chamber having a discharge opening at one end thereof and an inlet opening at the other end thereof, means for introducing particles through said inlet to be separated into a float fraction and a sink fraction in said drum, means for introducing a separatory fluid into said chamber through said inlet for flow at predetermined rate through said chamber to overflow through said discharge opening in a nappe of a predetermined height which is less than the maximum potential size of the float particles, means for rotating said drum and means for separately removing said sink fraction and said float fraction including such particles of maximum potential size from said chamber-Without disturbing the hydraulic conditions of separatory fluid flow through said drum and for enabling passage of said float fraction in a single stream with said separatory fluid overflowing said discharge opening.

11. In a heavy media separatory apparatus, a drum mounted for rotation about a substantially horizontal axis and forming a separation chamber having a discharge opening at one end thereof and an inlet opening at the other end thereof, means for introducing particles through said inlet to be separated into a float fraction and a sink fraction in said drum, means for introducing a separatory fluid into said chamber through said inlet for flow at a predetermined rate through said chamber to overflow through said discharge opening in a nappe of a predetermined height which is less than the maximum potential size of the float particle, means for rotating said drum, and evacuation means for separately removing said sink fraction and said float fraction including such particles of maximum potential size from said chamber, said evacuation means comprising at least one curved scoop member movable in a concentric path with said drum adjacent said discharge opening for mechanically increasing the buoyancy of oversized float particles too large to be discharged in the stream of separatory fluid overflowing through said discharge opening such that said oversized float particles are raised only partially out of said stream, the path ofsaid scooped member extending into said stream to a maximum depth that is closer to the surface of said stream than to the bottom thereof.

12. In the apparatus defined in' clairn 11 wherein said scoop member comprises a arcuately shaped plate having a trailing edge immediately adjacent to the discharge opening and a leading edge at a greater distance from the horizontal axis of said drum than the trailing edge for scooping into the separatory fluid during rotation of said drum. 7

13. In the apparatus definedin claim 12 wherein said plate is mounted at an acute angle with the discharge opening for imparting a tumbling motion to particles scoopedup in the direction of said discharge opening.

' 14. In the apparatus defined in claim 12 wherein said plate'is provided with elongated perforations for stimulating the outward skid of the scooped up particles.

15. In the apparatus defined in claim 11 wherein said scoop member comprises a curved spiralled plate having a trailing edge immediately adjacent to the discharge opening and a leading edge ,ata greater distance from the horizontal axis of said drum for scoopin into the separatory fluid during rotation of said drum.

16. In the apparatus defined in claim wherein said plate is mounted at an acute angle with the discharge opening for imparting a tumbling motion to particles scooped up in the direction of said discharge opening.

17. In the apparatus defined in claim 15 wherein said plate is provided with elongated per-formations for stimulating the outward skid of the scooped up particles.

18. In a heavy media separat-ory apparatus for use in separating a mixture of particles having different specific gravities into float and sink fractions, a horizontally oriented rotatably mounted separatory vessel having a particle mixture inlet, a sink fraction discharge outlet and a float fraction discharge weir, means for establish ing a nappe of separatory fluid overfailing said weir of predetermined height and means for moving particles of said float fraction having submerged dimensions larger than the depth of the separatory fluid nappe over said weir in a single stream with said nappe of separatory fluid such that the height and velocity of said nappe remains substantially free of disturbance.

19. In a heavy media separatory apparatus for use in separating a mixture of particles having diiierent specific gravities into float and sink fractions, a horizontally oriented rotatably mounted separatory vessel having a particle mixture inlet, a sink fraction discharge outlet and a float fraction discharge Weir, means for establishing a nappe of separatory fluid overfalling said weir of predetermined height and evacuation means for moving particles of said float fraction having submerged dimensions larger than the depth of the separatory fluid nappe over said weir, said evacuation means being mounted adjacent said Weir for rotation with said vessel to mechanically increase the buoyancy of said float fraction particles having dimensions larger than the depth of said separatory fluid nappe such that said float fraction particles having dimensions larger than the depth of said separatory fluid nappe are raised only partially out of said separatory fluid nappe.

20. In a heavy media separatory apparatus for use in separating a mixture of particles having different specific gravities to float and sink fractions, a horizontally oriented rotatably mounted separatory vessel having a particle mixture inlet, a sink fraction discharge outlet and a float fraction Weir, means for establishing a nappe of separatory fluid overfalling said weir of predetermined height and evacuation means for moving particles of said float fraction having submerged dimensions larger than the depth of the separatory fluid nappe over said weir, said evacuation means being mounted adjacent said weir for rotation with said vessel to mechanically increase the buoyancy of said float fraction particles having dimensions larger than the depth of said separatory fluid and being arranged to allow the full velocity of said separatory fluid overfalling said weir to be imparted to said mechanically buoyed up particles to stimulate the outward skid thereof.

21. In a separatory apparatus for use in separating a mixture of particles having different specific gravities into float and sink fractions, a vessel having a particle mixture inlet at one end and a float fraction discharge weir at the other end, means for establishing a stream of separatory fluid flowing through said vessel and overfalling said weir and having a nappe of predetermined height and means mounted for movement substantially transversely of said nappe for moving particles of said float fraction having submerged dimensions larger than the depth of the separatory fluid nappe over said weir in a single stream with said nappe of separatory fluid While maintaining the depth and velocity of said nappe constant irrespective of the size of the particles of said float fraction, said means for moving said float fraction particles penetrating into said stream to a maximum depth that is closer to the surface of said stream than to the bottom thereof.

References Cited in the file of this patent UNITED STATES PATENTS 792,778 Koneman June 22, 1905 1,525,300 Herbert Feb. 3, 1925 1,824,688 Rigler Sept. 22, 1931 2,624,461 Falconer Jan. 6, 1953 FOREEGN PATENTS 489,970 Italy Jan. 29, 1954

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