US3013663A

US3013663A - Spiral track centrifugal separator

Info

Publication number: US3013663A
Application number: US826073A
Authority: US
Inventors: Vane Zdenek
Original assignee: Individual
Current assignee: Individual
Priority date: 1959-07-09
Filing date: 1959-07-09
Publication date: 1961-12-19
Anticipated expiration: 1978-12-19

Description

Dec. 19, 1961 Z. VANE SPIRAL TRACK CENTRIFUGAL SEPARATOR 3 Sheets-Sheet 1 Filed July 9, 1959 6%, WVE/WU/i Dec. 19, 1961 2. VANE 3,013,663

SPIRAL TRACK CENTRIFUGAL SEPARATOR Filed July 9, 1959 5 Sheets-Sheet 2 WVE/VTUF Dec. 19, 1961 z. VANE 3,013,663

SPIRAL TRACK CENTRIFUGAL SEPARATOR Filed July 9, 1959 5 Sheets-Sheet 3 United States Patent G 3,013,663 SPIRAL TRACK GENTRIFUGAL SEPARATOR Zdenek Vane, Box 225, Postal Station D, Ottawa, Ontario, Canada Filed July 9, 1959, Ser. No. 826,673 24 Claims. (61. 20-144) This invention relates to a method of and means for centrifugal separation of suspended solids in a fluid flow, and deals more specifically with separations performed in a continuous helical track. This application is a continuation-in-part of my application Serial No. 470,496 filed November 22, 1954, now abandoned.

Separations by centnifugal force, conducted in a free vortex, are satisfactory wherever the handled material is fine enough to traverse the separator without choking the same. Separable materials however, with components which differ greatly in size and density as, for instance, the grain product of a threshing machine, cannot be separated economically in a free vortex type apparatus, if the carrier fluid flow is intercepted by the edges of separating members in axial direction and said edges project forward into the oncoming flow of the separable material. A constant risk of choking and plugging narrow passages, coupled in cyclones with a large pressure drop, exclude free-vortex type separators from a separation work of this kind.

1 have found that the advantages of centrifugal separation can be employed for the above mentioned separable materials when, instead of a free vortex, a closed continuous spiral path is used for subjecting the treated material to centrifugal tension, wherein narrow egress passages for the fine separated components have such a direction that they cannot be choked by much coarser particles flowing past them, and a continuous separation work is thus made possible. A spiral conduit with .a nearly straight trajectory for the handled material, combined with separating members having passages slanting backward from the main path for the treated material, enable the use of centrifugal force for separations of materials nonsuitable for a free vortex. The purpose of this invention is to provide a method of multiple separations and a separator free from choking risks; the pressure drop is lower than that of a cyclone, but the centrifugal tension therein developed can be compared to that of a cyclone.

In general, it is an object of this invention to provide a method and an apparatus for multiple separations of components having disparate grain sizes and densities.

Another object of the invention is to provide a separator for grain size classification and density separation with variable means of controlling the grain size and density of components during the operation.

Still another objectis to provide a method of this kind with steps and means for keeping the separating members clean during the operation when materials with a choking tendency and a sticky, clogging character are treated.

In this invention, the flowing fluid is compelled to follow a helical path, defined by a closed continuous spiral track. At desirable locations along the path, selected components of the fluid carrier may be removed by the centrifugal tension developed in the fluid to drive portions thereof through apertures in the conduit .walls; for this purpose, the conduit .has a helical direction and is provided with slots to allow Stratified layers to be filtered ofi, roughly along a radius from the helix axis. Slots in the outer conduit wall connect to a collecting conduit to separate heavy materials. Slots in the inner conduit wall provide an outlet for the lighter component to a conduit adjacent the helix axis. In order to compensate'for a pressure drop in the main conduit'due to continuous ice losses through these collecting slots and to assist the separation of components into such collecting conduits, an additional fluid is fed into the circuit, across the main conduit, through feed slots facing said collecting slots. The separating operation may be performed in the direction of the radius either inwardly, if it is desired to collect the lighter component, or outwardly if the heavier component of the fluid is to be collected. In this second type, the slots in the inner wall of the main conduit are feed slots and lead to a tfluid compensation supply, while the slots in the outer wall lead to a collecting space. In the first type, the slots in the outer wall of the helical conduit lead to a fluid compensation supply, while those in the inner wall connect to a collecting space. Thus, in each case there is -a lateral flow of the additional fluid across the main conduit, passing from feed slots to collecting slots.

In the drawings which illustrate embodiments invention FIGURE 1 represents a partly cut-away elevation of the separator,

FIGURE 2 is a diagram explaining schematically the function of the separating members of the apparatus in FIGURE 1,

FIGURE 3 shows variable means for control of the separator,

FIGURE 4 is a modification of the apparatus in FIG- URE 1,

FIGURE 5 is a diagram explaining the function of the apparatus in FIGURE 4, and

FIGURE 6 represents a combination of both variation of the separator. 1

Generally, a system of three parallel conduits is so up in each variation of separator, wherein one of the conduits is the helical path for spinning a carrier fluid carrying a separable mixture, another conduit collects the separated components, and a third conduit supplies an additional fluid flow of clean carrier to promote the of the separation. The number of components separated is not limited, since the receiving conduit may be divided lengthwise into any desired number of sections, each section separating one selected component from the treated mixture. The exchange of the carrier between the three conduits and the egress of the separated components is conducted in the direction of the radius of the spin. The separation itself may proceed either in a radially inward or outward direction. Only one of the three conduits must have a spiral direction since it has to produce a centrifugal tension in the treated material. i

The separator, shown in FIGURE 1, separates radially inwardly; it consists of a hollow standard 11, fixed in a base 12, and having a top outlet opening 13, controllable by a bathe 14. This baflle is a valve of any well known type, represented in the drawings by a's'ymbol only, and its purpose is to vary the cross-section area of the outlet 13, without closing it completely. The standard 11 fHIlC- tions as a receiving conduit of the system;its' inner space 15, defined by a bottom 16, is a collecting space for the the standard wall 11' and the wall 19, is divided by a vertical partition 20 into two parallel conduits, of which thenumeral 21 designates the outer, and'thenumeralzz the inner conduit. 1 Each of them is provided atthe'base 12 with a feed spout, numeral 23 for the conduit 21, and numeral 24 for the conduit 22. Both conduits are supplied with a suitable carrier fluid as air, either from one common source, or from two separate pressure sources, not shown in the drawings. A separable mixture is fed into the carrier fluid flow in the conduit 22 by a hopper 25. The outer conduit, 21, has a progressively decreasing cross-section area, from the base to the top of the separator; its purpose is to supply an additional carrier fluid needed to enhance the separation by a lateral, inwardly deflecting carrier flow, and this additional flow is dis continued at the point where the separating members end. This point is marked by numeral 26, and shows the end of the conduit 21 in dotted line. The outlet 27, provided with a volume control baflle 28, belongs to the conduit 22, the conduit 21 being closed at the point 26. A separating area is provided in the wall of the standard 11, represented by series of openings 29, provided at that part of the wall which is adjacent to the conduit 22; these openings 29 allow the egress of the separated components into the collecting space 15. There are other series of openings numeral 30, similar to the first ones, provided in the vertical partition 20, radially adjacent to or a little ahead, in the direction of flow, of the series of openings 29. Their purpose is to direct a flow of additional carrier fluid across the helical path of the conduit 22, thus acting against the centrifugal tension, to sweep away lighter components from the treated mixture through the egress openings 29 into the collecting space 15. As the exact position of the respective series of openings cannot be clearly seen either from the elevation, or from a plan view, a part of the system of the three conduits is developed in FIGURE 2 in one plane. The resulting diagram illustrates the separating area, which can be partly seen in FIGURE 1: separating openings 29 have, when viewed in the direction of flow shown by an arrow, clear backwardly slanting spacers 31 the angle of which, marked by A, formed with a tangent drawn to the inside periphery of the conduit 22, being a measure of protection against choking said openings 29 by coarse material passing by. The flow through the separating openings 29 is controlled by the

baflles

14 and 28. The feed openings 30 have a forward slant. It will be noted that all conduits are sealed off from the outer space and from each, except the feed inlets, separating passages and evacuating outlets shown in the drawings.

In operation, the separable mixture fed from the hopper 25 into the carrying fluid and passing through the conduit 22 is rotated on the helical path thereof, and all particles heavier than the carrier are driven by centrifugal tension outwardly to the wall defining said conduit 22, i.e., to the partition 20. By proper controlling of the flow in the

outlets

13 and 27, a radially directed inward flow of additional carrier fluid of any desired force is set up from the series of openings 30 in the conduit 21 toward the series of openings 29 in the space of the hollow standard,

and sweeps from the outer periphery of the conduit 22 that part of the suspended solid mixture which is specifically lighter and cannot resist such a lateral pressure. When a fine mixture of kernels and dirt, produced in a thresher for grain, is propelled by an air flow, all the fine dust and chafl particles are separated in this separation area through openings 29, and are collected in the space 15 to be evacuated by the outlet 13. The remaining part of the mixture which is heavier and composed of kernels of good and medium quality and which resisted the lateral pressure of the additional air flow because of its greater momentum, continues its travel along the conduit 22, to be evacuated by the outlet 27. It is obvious that a clean carrier fluid only is fed into the feed spout 23.

The angle A which the openings 29 form with the tangent tg drawn to theinner periphery of the helical path in the conduit 22, protects said openings against plugging. Said angle may be varied during the operation along with the shape and the size of said openings, by a device shown in FIGURE 3a. Fine laminae 32 define egress openings 33 of the separating member 34; they are pivotally mounted, by means of fine suspension journals 35, in a larger passage cut out in the standard wall 11. Each lamina is activated by another journal, numeral 36, to perform a pivoting movement, the resulting new posit-ion being shown by dotted lines. All journals 36 of a separating member are joined by a narrow steel belt 37, provided with slightly elongated holes 38, in which journals 36 may pivot in a short spiral movement. The belt 37 is then connected to a lever 39, activated outside of the standard 11. This system of variable openings works in a similar way as the Venetian blind. In FIGURE 3b, another type of variable openings 40 is shown, wherein the included angle A is fixed, the size alone of the openings being made variable. A fine steel belt 41 is punched so as to produce parallel holes, the punched material is bent on one side of the hole to form a directing vane 42 having a desired angle with the remaining part of the belt, and this belt is slidingly fastened on a series of similar holes provided in the standard 11, one side of which may also be bent to form another vane 42', so as to increase or reduce the passage formed thereby, when the belt is changed from position lengthwise. Obviously, the belt may be punched also by plain holes only, thus leaving the passages without directing

vanes

42, 42. The herein described system of variable openings, which assume a form of gratings similar to a concave of a thresher, are able to replace advantageously an expensive and complex system of screens used normally in threshcrs. The protection against choking of such gratings, and the possibility of changing the quality of the product during the operation by only varying the lateral flow through said gratings, without ofi periods, will be appreciated especially in thresher like machines wherein any change of the product quality requires normally an exchange of screens. It is obvious that the conduit 21 for the additional fluid need not have a helical direction, and may be given any other suitable form; the size of openings 29 must be large enough to intercept the selected components in their full helical speed. The

bafiles

14 and 28 are to vary the crosssection area of the respective outlets, said outlets never being closed completely, since no separation would then be possible.

In order to take advantage of all possibilities of quality control for separated components, the additional fluid flow should be controlled also in its pressure source before entering the spout 23. The size alone of separating openings 29 is not decisive of the separating result, since the density of particles entering said openings will depend rather from the angle A and from the lateral pressure exerted by the additional fluid flow: the readiness of a par ticle to change its direction and to enter a slot 29 increases with the increasing angle A and with the increasing force of the lateral pressure. When product density is concerned, varying the passages for the fluid carrier in

outlets

13 and 27 has the same effect as if the size of the respective separating openings were varied. Varying the size alone of openings 29 will influence chiefly the size of separated particles if the other means of control remain unchanged. The smaller the angle and the sharper is the curvature of the trajectory for a particle entering the slot; this means a lower density of the separated particles and a smaller risk of plugging the slot.

The apparatus shown in FIGURE 1 separates particles in a radially inward direction, thus acting against the centrifugal pressure, thereby subjecting the treated material to a severe density test. In FIGURE 4, a modification of said apparatus is shown wherein the separable particles move radially outward from the main flow, to be pcrmanently separated. The additional fluid flow enhancing the separation acts here in the same way and direction as the centrifugal force does. This modified separator consists of a hollow standard 43 fixed in a base 44 and supporting the other structure parts. The upper end of the arated components is shown by smaller arrows.

standard 43 is closed by a cover 45; a sloped bottom 46 defines, along with the cover 45, the inside space 47 in the standard, as a conduit for the additional fluid, introduced by a feed conduit 48. A closed spiral track is coiled on the standard 43, said track being formed by two flat spirals 49 and 50, joined by a vertical spiral partition 51, thus defining a helical conduit 52, provided with a hopper 55, and the outlet 54 with a volume controlling baffle 56. Parallel with the helical conduit 52 is mounted a collecting conduit 57, defined by an outer wall 58 and the two spirals '49, 50; this conduit 57 is to receive a flow of carrier fluid with therein suspended particles separated from the material traveling in the main helical conduit 52, and extends from the outset point 59, near the bottom 46, to the end point 60, near the cover 45. This collecting conduit 57 is thus shorter than the helical conduit 52,

and is further divided lengthwise by a tight partition 60' in two parts, to collect two different separated components from the treated mixture; each part is then provided with an outlet pipe to drain the separated product. The lower half of the conduit 57 is drained by the outlet 61, having a volume control baflie 61', and the upper half has an outlet pipe 62 with a baffle 62'. The spiral partition 51 contains two gratings, each having a series of separating openings, the series numeral 63 being for said lower part of conduit 57, and the series numeral 64 for the upper part thereof. To each of these series of openings in the partition 51 corresponds, in the opposite wall of conduit 52, a series of openings in the wall of the standard 43, slightly ahead in direction of flow, to discharge a lateral deflecting flow radially outward, thus increasing by its effect the centrifugal pressure of the spinning fluid and material on the partition 51. Said series of openings in standard 43 is marked by numeral 65 for the lower part, and by numeral 66 for the upper part of the conduit 57. The separating members containing the

openings

63 and 64 are constructed for classification according to grain size, as gratings of a sufiicient thickness to resist the wear by abrasion, resulting from a considerable friction of the handled material against said members. The size of openings 64 is larger than that of the openings 63. All other details are the same as in FIGURE 1. The FIGURE is a diagram showing the position of the separating members in the apparatus of FIGURE 4, when developed in one plane.

In operation, a separable mixture is fed by the hopper 55 into the feed inlet 53 along with a flow of a carrier fluid entering said inlet from a pressure source, not shown in the drawing. The mixture is rotated on the helical path of the conduit 52, and is driven toward the spiral partition 51 by centrifugal tension. All heavy and fine particles are traveling along said partition 51, being pressed thereon by a layer of coarser and lighter components of the same mixture, traveling in the central part of the cross-section of conduit 52. The frictional contact with the partition 51 reduces the velocity of the traveling fine part ofthe mixture, thus increasing its readiness to enter a separating opening in a radially outward direction. This readiness to change its trajectory is further enhanced by the lateral flow of fluid coming from openings 65, when the treated mixture enters the Zone between the two series of openings 63 and 65. The position of the laminae in the gratings 63 is seen in FIGURE 5, the directionof the main flow being marked by a large arrow, while the trajectory of the sep- Such change of direction is made possible for the fine part of the mixture by a reduced speed due to friction, and by a draft through said openings of the fluid, adjustable by a proper volume control in the outlet 61, by the baffle 61. It is obvious that all structure parts participating in this separation must be tight enough, having no communication whatsoever with the outside space, except by controllable outlets. Any desired speed and pressure then can be used. When a mixture produced by the cylinder of a thresher, containing coarse straw, kernel bearing ears, chaff, kernels and fine dust, is fed into the hopper 55, and a flow of air is propelled by conduits 48 and 52, the combined action of the centrifugal tension and of the pressure caused by the additional air in a radially outward direction, will separate all fine dust, chaff and kernels in the first stage of separation, in the first separation area of this separator, defined by the openings of series 63 and 65, while the remaining mixture of coarse straw and some kernel bearing ears which, due to their larger size, were unable to pass through the slots of the first separating member, continues its travel along the helical conduit 52, to meet the second separating area, series of openings 64 and 66, having openings of larger size, wherein the heavier kernel bearing ears are separated from the coarse light straw in a similar way as the finer components in the first stage of separation. For these separations, the width of the slots is about one inch for the first, and one inch and one half for the second stage of separation. As in the case of separator in FIGURE 1, the size of separating openings alone does not determine the expected result,since the draft through said gratings is of prime importance. The clean straw remaining from the second stage of separation is evacuated by the outlet 54, while the kernel bearing ears are directed by the outlet pipe 62 to the machine for re-threshing. The fine mixture separated according to grain size in the first stage of separation by openings 63/ 65, will be object of a new separation according to density in an apparatus shown in FIGURE 1, along with a fine part of grain separated by the concave of the thresher itself. It is known that the concave of a modern thresher separates up to percent of the fine grain from the coarse straw, so that this apparatus, FIGURE 4, has only a small part thereof to separate. In standard threshers however, this small part, to be correctly separated, requires a very important and expensive screen structure.

The two separator variations of FIGURES l and 4 are shown in FIGURE 6 combined in one structure, wherein the centrifugal force performs, in two successive steps, a complete separation work required in threshing operations, with all advantages of the above single separators. This lighterand space saving combination in FIGURE 6 is made possible by using a helical wall 67 to divide the inner space of the hollow standard 68 in two

parallel conduits

69 and 70, one of which, numeral 69, is closed by the bottom of standard and has an inlet 71, and functions as an additional fluid feed conduit for a separating coil 72 which separates radially outwardly; the other one, numeral 70, serves as a collecting conduit for a coil 73, separating radially inwardly. Thus, the

coils

73 and 72 function in the same'way as the two separator variations described in FIGURES -l and 4 respectively, and FIGURE 6 shows an elevation of the combined separator with the dividing wall 67 in dotted lines. Said wall is formed by a helically twisted strip inserted and tighty fastened by its edges in the hollow standard 68 so as to seal off the two

conduits

69 and 70 from each other. At the outset point B the wall 67 forms a large conduit 69 which takes at this point all the cross-section area of the inner space of standard 68; the conduit 70 starts at the same point B with a zero cross-section area, to increase progressively its crosssection, thus reducing the conduit 69, until at the point '0 each of them occupies one' half of the cross-section area within the standard 68. This progressive changes goes on between the points C and D,'until at D the con,

in one plane, and would appear in an elongated rec- 'tangle of the standard 68 as a diagonal.

The two

auxiliary conduits

69 and 70 follow a helical path at the same pitch and direction as the two main coils 72 and. 73, and each of said auxiliaries in standard 68 communi 3 cates with its respective main conduit throughthecommon wall of the standard provided with slots of the same kind as shown in FIGURES 1 and 2, numeral 29, and in FIGURES 4 and 5, numeral 65. All the other parts of the structure in FIGURE 6 are also derived from the structures in FIGURES l to 5. The coil 72 is provided with an inlet 76 and a hopper 77 to receive therethrough respectively a flow of air and a mixture of coarse straw, dirt, kernels and kernel bearing cars. This coil 72 classifies the materials according to grain size, and has an outlet 78 at its top end, with a volume control valve 79, to discharge the coarse straw, while the finer part of the mixture is collected by a collecting conduit 80 adjacent the coil 72 from outside and divided by a vertical partition 81' in two parts, the lower one being provided with an outlet spout 82 for kernels and fine dirt, while the upper half thereof is provided with an outlet spout 83 for kernel bearing ears. Both outlet spouts 82 and 83 have suitable variable valves, not shown in the drawings, to control the flow of air passing therethrough. The coil 72 has a common wall with the collecting conduit 80, partition 84, which is slotted at suitable points, not shown in the drawing, to allow the egress of the separated components. The slots are equivalent of those shown in FIGURES 4 and 5, numeral 63. The coil 73, equipped to separate materials radially inwardly according to density, in this case the fine dust and chafl from heavy kernels, is provided at the base with an inlet 85 and a hopper 86 for introducing respectively an air flow and a mixture to be separated, and at the top with an outlet 87 and a volume controlling valve 88. Adjacent thereto is an auxiliary feed conduit 89 with an inlet 90 to supply an additional air flow directed from outside through suitable slots, not shown in the drawing, in the common wall, partition 91 between the two

conduits

73 and 89; said slots are equivalent to those in FIGURES l and 2, numeral 39. Radially adjacent to such slots are located other slots in the wall of standard 68, corresponding to those in FIGURES l and 2, numeral 29, to receive said additional air carrying light parts of the mixture and coming across the main conduit of the coil 73 into the collecting spaceauxiliary conduit 70, wherefrom it is evacuated by outlet 74. The heavy kernels which resisted, in this density test, the lateral pressure of the added air flow travel along the periphery of the coil 73, due to centrifugal tension, and are evacuated at 87. The cross-section area of the auxiliary feed conduit 89 is decreasing progressively from the inlet 90 to the end point 92.

In operation, the parts of this combined separator perform the same functions as in the above single apparatus: in the first stage, the coarse output of a thresher is treated by the coil 72 between its

points

76 and 78; the spout 82 yields the fine dirt with good kernels, to be treated again in the coil 73, and the spout'83 yields kernel bearing ears which are to be re-threshed. In the second stage, the coil 73 handles, between its

points

85 and 87, the finer part of the thresher output separated by the concave, along with that yielded by the outlet spout 82, and evacuates the separated dirt by outlet 74, and the clean kernels by outlet 87.

It will be noted that the common walls,

partitions

84 and 91, on which the treated mixture is pressed by centrifugal tension, may be given a more or less sloped position as in a tunnel, to keep the mixture evenly spread on the screening surfaces. It depends on the flow velocity and on the kind of the handled materials, what an angle this slope shall be given. The vertical position of the partitions shown in the drawings is that suitable for the highest velocities. The outer

auxiliary conduits

80 and 89 need not be helical. The dividing wall 67 need not be helically twisted either if the

coils

72 and 73 make only a half a turn.

Any variation of the separator shown hereabove may be constructed for separations of various materials. In many cases, the possibility of varying'and adjusting the size and density of the separated product during the operation is an appreciable advantage. Some separable materials show a tendency to clog on narrow passages, thus changing the separating capacity of the separating members. Very small diflerences of this kind may be corrected in this apparatus by adjusting the flow rate in respective outlets, to keep the product quality constant. This way of correcting the result may be combined with a change of size, shape and angle of the separating openings in the active members, as shown above. Finally, the clogging of materials may be avoided by adding, to the separable material, particles of a suitable size and weight, which produce a scrubbing effect on the helical surfaces and the separating members, thus removing constantly the therein clogging material and reintroducing it into the circuit. For instance, an apparatus of this type, used in flour milling operations for screening the finely ground grain kernels having a certain degree of humidity, necessary for a correct comminuting, can be supplied with an air flow with the addition of small steel balls sweeping the passages constantly and keeping them clean; the balls, of course, are separated at the end of the trajectory for the screened material and re-introduced into the circuit by a feedback system.

I claim:

1. A method of centrifugal separation into fractions of suspended separable materials comprising the steps of: conveying a first fluid carrier carrying separable materials in suspension along a helical path in a first bounded space shaped in the form of a continous spiral, thus subjecting said materials in suspension to centrifugal force during a spin of said fluid carrier along said helical path, introducing an additional fluid carrier into said first fluid carrier from a second bounded space radially adjacent to said first space deflected substantially in chordal directions of said spiral so as to shift, in a chordal direction, a part of said first fluid carrier with a fraction of said separable materials from said first space into a third bounded space adjacent said first space radially opposite from said second space with respect to a longitudinal was of said spiral.

2. The method of claim 1 with the added step of introducing said additional fluid carrier into said first space at an acute angle, said angle being included substantially within a downflow interval between a tangent drawn to the periphery of the helical path on one side, and the radius at the point of tangency on the other side, and the step of removing said fraction of said separable materials in suspension with said part of said carrier fluid substantially at said acute angle into said third space, said acute angle being a means of controlling the density and the grain size of said separated fraction, and a measure of protection against blocking of passages by that part of said treated materials in suspension which continue traveling along the helical path in said first bounded space.

3. The method of claim 2 with the added step of varying the cross-sectional flow area of said additional fluid carrier so as to vary the volume of said separated fraction, and the density and the grain size of the therein separated materials.

4. The method of claim 3 with the added step of varying said acute angle so as to control the density and the grain size of materials separated in said fraction.

5. The method of claim 1 in which said additional fluid carrier is introduced into said helical path in a radially inward'direction thus exerting a lateral deflecting pressure upon said first fluid carrier against said centrifugal force and shifting a fraction of lower density materials from said first space into said third space, with the step of controlling the flow rate of said additional fluid carrier to vary the density of said separated fraction by varying said lateral deflecting pressure exerted upon said materials in suspension.

6. The method of claim 1 in which said additional fluid carrier is introduced into said first space substantially radially outwardly, thus, in the direction ofcentrifugal force and shifts a fraction of said materials in suspension of smaller grain size and higher density from said first space into said third space, with the step of controlling the flow rate of said additional fluid carrier to vary the volume of said separated fraction, and the density and the grain size of separated materials.

7. The method of claim 1 with the added step of feeding said additional fluid carrier in flows directed into said first space at an acute angle, said angle being included substantially within a downflow interval between a tangent drawn to the periphery of the helical path on one side. and the radius at the point of tangency on the other side, and the step of removing separated fractions of said materials in suspension with a part of said fluid carrier from said first space in a substantially radial direction in flows directed at said acute angle, said additional fluid carrier thus exerting a lateral deflecting pressure on said first fluid carrier across said helical path, said acute angle being a means of controlling the density and the grain size of said separated fractions and a measure of protection against blocking of passages by that part of said treated materials in suspension which continue traveling along the helical path in said first bounded space.

8. The method of claim 1 with the added step of conveying with said suspension, generally non-separable particles having a higher density than said separable materials, said higher density particles exerting a scrubbing effect on said helical path so as to sweep away and reintroduce into circulation any parts of said materials having clogged to said path.

9. The method of claim 5 with the step of introducing said additional fluid carrier at more than one point of the helical path into said first fluid carrier and removing at each of such points a part of said fluid carrier containing one fraction of said separated materials from said helical path, said lateral deflecting pressure exerted by said additional fluid carrier being graduated from one such point to the other of said helical path so as to remove fractions of treated materials in partial flows the density of which increases from one point of removal to the other.

10. The method of claim 9 in which said acute angle and cross-section areas of said flows are made variable so as to control the density of fractions separated at any one of said points of removal.

' 11. The method of claim 6 with the step of introducing said additional fluid carrier at more than one point of the helical path into said first fluid carrier and removing at each of such points a part, of said fluid carrier containing one fraction of said separated materials from said helical path, said lateral deflecting pressure exerted by said additional fluid carrier being graduated from one such point to the other of said helical path soas to remove fractions'of materials treated in partial flows the density of which decreases and the grain size of therein suspended particles increases from one point of removal to the other. 1

12. The method of claim 11 in which said angle and cross-section areas of said partial flows are made variable so as to control the density and the grain size of particles of fractions separated at any one of said points of removal.

13. A separator of the charatcer described comprising in combination: a closed helical walled main conduit having a center and a longitudinal axis of a helix, said axis being located outside said main conduit, said main conduit having an inlet and an outlet portion, and having two intersections of said main conduit with any one radius of said helix normal to said axis and passing through the center of said main conduit, the two intersections being located in two portions of the wall of said main conduit which are substantially opposite to each other in said that the shape of said openings and said acute variable.

10 main conduit, aseries of feed apertures in said main conduit in a portion of the wall thereof which is substantially adjacent to one of the two intersections of said main conduit with said radius of said helix, a series of egress slots in said main conduit in a portion of the wall thereof adjacent to the other of said'intersections and substantially radially opposite to said series of said feed apertures, said series of feed apertures being thus substantially radially aligned to said series of said egress slots in said main conduit, a closed auxiliary feed conduit radially adjacent to said main conduit and extending from a point of said main conduit where said series of feed apertures begins to that point of said main conduit where said series of feed apertures ends, a closed auxiliary collecting conduit radially adjacent said main conduit but substantially radially opposite to said auxiliary feed conduit and extending from a point of said main conduit where said series of said egress slots begins to'that point of said main conduit where said series of said egress slots ends, means connecting a fluid carrier supply source to said auxiliary feed conduit and to said inlet portion of said main conduit, means to supply materials to be treated into said fluid carrier in said main conduit, and a fluid carrier outlet connected to said auxiliary collecting con duit.

14. The separator of claim 13 wherein said egress slots are defined by directing vanes and include an acute angle with a tangent drawn to the helix of the main conduit,

said helix being defined by any one of said portions of said wall in which said slots may be located, said angle being included within a downflow interval between said tangent on one side andthe radius at the point of tangency on the other side, said vanes thus having a clear backward slope in the helical direction of the main conduit so that edges of said vanes adjacent said main conduit cannot accroach coarse materials traveling down said main conduit.

15. The sepanator of claim 14 wherein said feed apertures areprovided with similar directing vanes as said egress slots at a susbtantially similar angle to the direction of saidmain conduit and arranged in symmetry with said egress-slots vanes.

16. The separator of claim 13 wherein each of said slots and apertures has a variable cross-section area, said area being defined by the correspondence between a fixed opening in the main conduit wall and an opening in a steel belt adapted to slidingly overlie the fixed openlugs.

17. The separator of claim 15 wherein said directing vanes are pivotally mounted on journals lodged in the walls of said main conduit, said vanes being further provided with journals fixed to said vanes and joined with a belt to operate a pivotal movement of said vanes so angle are 18. The separator of claim 13 having more than one series of egress slots arranged in spaced relation to each other along said main conduit and having an auxiliary collecting means divided lengthwise i'ntoportions sealed from each other so that each of said series of egress slots has its own collecting means provided with-amoutlet for one separated fraction, said main conduit being provided with more than one series of feed apertures so that each of said series of egress slots is faced, across said main conduit, with a series of feed apertures substantially ra-' dially opposite thereto, said series of feed apertures having a common closed auxiliary feed conduit, said feed conduit having one end thereof connected to a fluid carrier supply source while said feed conduit is closed at the other end, said series of egress slots being arranged so that said slots are increasing in size from one series to the other. i

19. The separator of claim 18 having two series of egress slots in a spaced relation along the inside periphery of said main conduit and auxiliary collecting means in the form of a hollow standard, said standard supporting the separator structure and enclosing the helical axis of the main conduit, said main conduit being coiled around said standard, each one of the two series of said egress slots discharging into one portion of said collecting means defined by said standard, each of said sections being further provided with an outlet and with a flow rate control for one separated fraction, an auxiliary feed conduit radially adjacent said main conduit on the outer periphery thereof and having two series of feed apertures connecting said feed conduit with said main conduit, one series of said apertures being located slightly ahead of said first series of egress slots, the second series of said apertures located slightly ahead of said second series of egress slots.

20. The separator of claim 18 having two series of egress slots in spaced relation on the outside periphery of said main conduit and auxiliary feed means in the form of a hollow standard, said standard supporting the separator structure and enclosing the helical axis of the main conduit, said main conduit being coiled around said standard, each one of said series of egress slots discharging into one section of said collecting means located substantially radially adjacent to the outer periphery of said main conduit, each of said collecting-means sections being further provided with an outlet and a flow rate control means for one separated fraction, and auxiliary feed means defined by said standard, said hollow standard being closed at its bottom and at its top, said standard having an inlet connected to a fluid carrier supply source and two series of feed apertures in a wall common with said main conduit.

21. A separator of claim 13 having said series of egress slots shaped as gratings constituted by fixed slots punched in the wall of said collecting conduit with a steel belt having similar slots to slidingly overlie said fixed slots in the main conduit wall, said fixed slots having one side of punched material bent to form a directing vane on one side of said fixed slot, while said belt contains slots with punched material bent on the other side of said slots so that each completed slot has two directing vanes at a fixed tangential angle and enabling said slot to have a variable cross-section.

22. The separator of claim 21 with slots having only one side provided with directing vanes.

23. The separator of claim 21 with slots constituted by plain holes only.

24. A centrifugal separator of the character described comprising: a hollow standard supporting two helicalwalled main conduits coiled around said standard, said standard enclosing a helix axis for the two main conduits, each of said main conduits having that part of their walls which is nearest to said axis common with said standard, said standard defining an inner space which is divided lengthwise in the part thereof adjacent to said common walls into two parallel inner conduits by a metal strip sealing ofi said two inner conduits from each other in such a manner that the first of said inner conduits extends over the entire cross-section area of said inner space at the direction of the helical axis to the profit of the second inner conduit, but decreases progressively said area in the direction of the helical axis the profit of the second inner conduit until said second inner conduit extends over the whole cross-section area of said inner space while said first inner conduit ends by zero cross-section area at the end point of said common walls, said first inner conduit being provided with an inlet and means for connecting to an additional fiuid carrier supply source at that point where said first inner conduit occupies the whole area of said inner space and where said second inner conduit begins; a series of feed apertures in the common wall between the first of said main conduits and said first inner conduit, said series of feed apertures extending along the whole length of said common wall of said first inner conduit with said first main conduit; a series of egress slots in said common wall between said second main conduit and said second inner conduit, said second inner conduit being provided with an outlet for one separated fraction of materials treated; an outer collecting means radially adjacent said first main conduit and radially opposite to said first inner conduit, said outer collecting means being divided in two sections to collect two different fractions of materials treated, a first series of smaller egress slots connecting said first main conduit with the first of the two sections of said outer collectiug means to collect a first fraction of separated materials of relatively small grain size, said first series of egress slots being substantially radially aligned with the first half of said series of said feed apertures in said first main conduit; a second series of larger egress slots connecting said first main conduit with the second section of said outer collecting means to collect a second fraction of separated materials of larger size, said second series of larger egress slots being substantially radially aligned with the second half of said feed apertures in said first main conduit, each of said two sections of said outer collecting means being further provided with an outlet for one separated fraction of materials treated; an outer and radially opposite to said second inner conduit, said outer feed means extending from the outset point of said common wall to the end thereof, a series of feed apertures connecting said outer feed means with said second main conduit, said series of feed apertures in said second main conduit being substantially radially aligned with said series of egress slots connecting said second main conduit with said second inner conduit; means to feed a fluid carrier into said second main conduit and means to feed into said fluid carrier in said second main conduit other materials to be treated; an inlet in said outer feed means and means connecting said inlet in said outer feed means with an additional fluid carrier supply source, and tight closing means on the end point of said outer feed means.

References Cited in the file of this patent UNITED STATES PATENTS 1,023,750 Morscher Apr. 16, l9l2 1,666,476 Stebbins Apr. 17, 1928 1,675,941 Lindsay July 3, 1928 1,861,247 Stebbins May 31, 1932 2,709,397 Banning May 31, 1955 2,762,610 Puhe-Westerheide Sept. 11, 1956 2,829,771 Dahlstrom Apr. 8,1958