US3822016A

US3822016A - Magnetic separator having a plurality of inclined magnetic separation boxes

Info

Publication number: US3822016A
Application number: US00244786A
Authority: US
Inventors: G Jones
Original assignee: Individual
Current assignee: Individual
Priority date: 1972-04-17
Filing date: 1972-04-17
Publication date: 1974-07-02
Anticipated expiration: 1991-07-02

Abstract

A separator device for separating magnetic particles from a fluid current containing magnetic and non-magnetic particles in which separation of the magnetic particles is effected by passing the fluid through a separation device in the form of a number of parallel plates to which the particles will adhere under the action of a strong magnetic field applied to the separator device, the plates of the separator device being inclined at a small angle to the horizontal, the separator being cyclically operated to cause zones of strong and substantially zero magnetic field whereby separation of the magnetic particles from the remainder of the fluid current is effected.

Description

United States Patent 119 Jones [11] 1 3,822,016 1451 Jul 2, '1974 PLURALITY OF INCLINED MAGNETIC SEPARATION BOXES [76] Inventor: George Henry Jones, Connor Downs, Hayle, Cornwall, England [22] Filed: Apr. 17, 1972 [21] Appl. No.: 244,786

[52] US. Cl .1 209/222, 209/223 R, 209/232 [51] Int. Cl. 1303c U04 1 [58] Field of Search 209/223, 222, 221, 220, 13 9 12243 225,, 3212192 1 210/222, 223

[56] References Cited UNITED STATES PATENTS 832,825 10/1906 Wait 209/222 1,024,045 4/1912 Weatherby 209/224 1,462,111 7/1923 Jobke 209/222 1,601,658 9/1926 Ullrich 209/223 R 1,683,780 9/1928 Mulsmeyer 210/223 2,760,638 8/1956 Annettwj. 210/222 2,771,995 11/1956 Noel 3,221,882 12/1965 Frantz 3,326,374 7/1963 Jones 209/232 X 3,346,116 10/1967 Jones ....210/222 3,693,792 9/1972 Lang 209/219 FOREIGN PATENTS OR APPLICATIONS 105,831 9/1898 Germany ..209/222 252,034 5/1926 Great Britain ..209/222 768,451 2/1957 Great Britain ..209/223R Primary Examiner-Robert I-lalper 5 7 ABSTRACT A separator device for separating magnetic particles from a fluid current containing magnetic and non magnetic particles in which separation of the magnetic particles is effected by passing the fluid through a separation device in the form of a number of parallel plates to which the particles will adhere under the action of a strong magnetic field applied to the separator device, the plates of the separator device being inclined at a small angle to the horizontal, the separator being cyclically operated to cause zones of strong and substantially zero magnetic field whereby separation of the magnetic particles from the remainder of the fluid current is effected.

8 Claims, 15 Drawing Figures MAGNETIC SEPARATOR HAVING A PLURALITY OF INCLINED MAGNETIC SEPARATION BOXES FIELD OF THE INVENTION The present invention relates to a means for separating solid magnetic particles from a fluid in which they are suspended. I

PRIOR ART I s In known separators, such as are described in the Specifications of my British Pat. No. 768,451 and my US. Pat. No. 3,326,374 a fluid current, carrying magnetic particles of a solid such as iron, is passed vertically through one or more plate-boxes.

In both cases the method of magnetic separation comprises at least two principal steps in each cycle, namely the passing of particle carrying fluid through a zone of strong magnetic field which include magnetizable plate-like members so that the magnetic particles in the fluid adhere thereto, and thereafter passing a flow of scouring fluidthrough said same zone after the magnetic field has been reduced to zero. An additional step of washing the magnetic particles whilst they are adhering to the plate-like members may be provided between the feed and scour periods. The magnetic field which is applied to the zone in which the plate-like members are situated is applied transversely to the flow of the particle carrying fluid. In the former patent the plate-like members are stationary and the value of the magnetic field varied between maximum and zero. In the latter patent, the plate-boxes are mounted in a circle and rotatable about a central axis so as to pass into and out of zones of magnetic field which are not themselves varied.

If it is required to separate very small magnetic particles or particles which are only slightly magnetic then difficulty is encountered since, in the present state of technology, there is a limit to the strength of magnetic field economically attainable.

SUMMARY OF THE INVENTION According to the present invention there is provided means for magnetically separating solid magnetic particles from a fluid current including a magneticparticle separation device having parallel plates arranged therein and spaced apart to enable a fluid current to flow therethrough, said separation device being in clined at an angle to the horizontal to assist the flow of fluid therethrough; means for applying a magnetic field transversely to the flow of fluid through the inclined separation device so as to cause the magnetic particles to adhere to the sides of the plates; means for applying to the upper end of the separation device in cyclic rotation the fluid feed current from which the magnetic particles are to be removed and a flow of wash fluid to remove the magnetic particles after the magnetic field has been reduced to zero.

BRIEF DESCRIPTION OF DRAWINGS The present invention will now be described in greater detail by way of examples with reference to the accompanying drawings, wherein:

FIGS. la to 1c. are side elevation, end elevation and plan view respectively of a plate-box for use in a separator; e I

FIG. 2a is a side elevation of a first embodiment of separator;

FIG. 2b is a section of part of the separator shown in FIG. 2a;

FIG. 3 is a schematic diagram, in front elevation, of a second embodiment of separator;

FIG. 4 is a longitudinal section of a separation device which can be used in any of the separators herein described;

FIG. 5 is a'longitudinal section of a modified form of plate-box for use in a separator;

FIG. 6 is a section through a third embodiment of separator;

FIG. 7 is a section through a fourth embodiment of separator;

FIG. 8 is a schematic plan view of a rotary separator such as that shown in FIG. 6 or FIG. 7;

FIG. 9a is an end elevation of an alternative form of plate-box for use in a separator; FIG. 9b is a schematic diagram, in front elevation, of a fifth embodiment of separator;

FIG. 10a is a section through part of a sixth embodiment of separator; and

FIG. 10b is a schematic diagram, in front elevation, of the sixth embodiment of separator part of which is shown in FIG. 10a.

DESCRIPTION OF PREFERRED EMBODIMENTS surface of each of the plates 3, run longitudinally of the plate-box 1, from one open end to the other. Twelve bolts 5 are provided for holding the casing 2 together, the casing 2 being made up of four rectangular plates 6. Two locating rods 7 are provided for maintaining the plates 3 in position. The non-grooved major surface of the plates 3 are uppermost and each is in contact with the apices of the grooved surface of the next upper adjacent plate. The plates 3 are made of a readily magnetizable material. The top and bottom of the casing 2 is made of magnetic material, whilst the sides are made of a non-magnetic material such as brass.

Referring to FIGS. 2a and 2b a separator 8 for magnetically separating solid magnetic particles from a fluid has two electromagnetseach consisting of a coil 9 anda pole-piece 10. A non-magnetic central rectangular section 11 separates the pole-pieces 10, one of which is arranged vertically above the other. In the gap separating the pole-pieces l0 and within the rectangular section 11 there is arranged a plate-box separation device 12 which incorporates the plate-box 1. As can be more clearly seen in FIG. 2b the pole-pieces 10 are shaped so that their mutually registering faces are inclinedto the horizontal, so as to be parallel to the flow of fluid in the plate-box 1. The separation device 12 is located between these inclined faces of the pole-pieces 10, the device 12 sloping from the input end downwardly to the output end, a variable-position funnel 13 being provided at the output end. A half-butterfly valve 14 is also provided at the output end to minimize the velocitydifl'erences between the layers of fluid flowing Three cam-operated valve stems 16 (only one of which is shown) are provided at'the input end for controlling inlet valves to the plate-box 1.

Referring to FIG. 3 there is shown a second embodiment in which two separators 8 are mounted side by side. There are four coils 9 arranged on the arms of U- shaped magnetic pieces 17 (only the upper of which is shown, the lower being hidden by other parts of the separator). The receptacle is in the form of an inclined longitudinal trough which leads to storage tanks (not shown). A fluid feed arrangement consisting of a supply pipe 18, an impeller 19 and a circulating pipe 20, is connected up to each of the separators 8. A wash water tank 21 is connected via an associated nonretum valve 22 to the separators 8. A scour-supply pipe 23 is similarly connected via a scour valve 24. The camoperated valve stems 16 (FIG. 2) are driven by means of a shaft (not shown) which is coupled by means of a chain to a pulley 25 which is driven by means of a drive gear assembly 26. The funnels 13 are variably positioned in synchronism with the valve stems 16 by means of a shaft 27.

Referring to FIG. 4 a separation device 12 is shown having a modified form of plate-box 28 in which the plates 3 are held by means of a part-wedge member 29 which is held in the plate-box 28 by means of a screwthreaded member 30. The screw-threaded member 30 is engaged in a flange 31 of the casing of the device 12.

Rotation of the member 30 causes it to push the member 29 into the plate-box 28 so jamming the plates 3 in position, or causes it to withdraw the member 29 from the plate-box so that plates can be removed for cleaning, repair or any other reason. A guide member 32 is secured to the casing of the device 12 and serves to guide the outflowing fluids from the plate-box 28 into the funnel 13.

At the inlet end of the device 12 each valve stem 16 operates a valve 33. The valve 33 shown controls entry of water from a chamber 34. A water-supply pipe 35 communicates with the chamber 34 to supply water to the chamber. The valve 33 is lined with a layer 36 of a resilient plastics material or rubber. Alternatively, it

may be lined with a metal. A fluid feed supply pipe 37 is shown adjacent the chamber 34 but cut off from it.

Referring to FIG. 5 there is shown a second form of plate-box 38 in which two dividing plates 39 are provided. A chute member 40 is formed integral with the casing 41 of the plate-box 38. The plate-box 38 is otherwise similar to the plate-box 1. The dividing plates 39 extend from the assembly of plates 3 in the plate-box 38 and so form three supply troughs 42 for three layers of plates 3. When fluid is supplied from a pipe 43 it flows into the uppermost of the three supply troughs 42. The intermediate supply trough 42 is only supplied with fluid when the uppermost supply trough overflows. Similarly the lowermost supply trough 42 is only supplied with fluid when the intermediate supply trough 42 overflows. The dividing plates 39 therefore substantially equalize the pressure head of fluid flowing through the plates 3. This eliminates the necessity for the half-butterfly valve 14 when the plate-box 38 is used in place of the plate-box l.

Referring to FIGS. 1 to 5, in operation the separation process is carried out in three successive stages. Firstly the cam operation opens a first valve 33 which allows fluid feed which is being continuously circulated through the pipe 20 in order to prevent settling of solids in the pipe, into the plate-box for a certain length of time. During this time the coils 9 are energized by a DC. current so that magnetic particles in the fluid flowing through the plate-box are attracted to the plates 3 due to the pole-pieces l0 magnetizing the plate-box. As can be seen from FIG. lb the apices of the triangular grooves 4 are uppermost so that the magnetic flux is concentrated at the edges of the grooves 4 where one plate 3 contacts the next lower adjacent plate 3. Thus most of the magnetic particles are held at those points of concentrated flux.

Secondly, after the flow of fluid feed has been cut off due to the first valve 33 closing, a second valve 33 opens and allows wash water to enter the plate-box so that non-magnetic contaminants are washed away. During this time the coils 9 are kept energized and the supply of wash water is of low pressure.

Thirdly, after the second valve 33 is closed, a third valve 33 is opened allowing scouring water to be passed through the plate-box. The half-butterfly valve 14 is turned so as not to impede flow. The coils 9 are deenergized or they can be energized by a current flowing in a direction reverse to the previous direction of energization current so as to counteract the remanent field on de-magnetization as disclosed in my British Patent 963,193. Thus the magnetic particles are no longer magnetically held in the plate-box and are carried out of the plate-box in a current of scouring water.

The output from the separator during the three stages is guided by the funnels 13 into three respective compartments of the receptacles 15.

This three-stage cycle is carried out repetitively giving a cyclic separator.

Referring to FIG. 6 there is shown a rotary separator in which separation devices 12 are carried on arms 44 of a spider-rotor 45 of a non-magnetic material and which is rotatably driven by a vertically arranged shaft 46. There are two pairs of magnetizing stations 47 (only one pair of which is shown) arranged so that there are magnetizing stations 47 at intervals around the rotor 45. Each pair of magnetizing stations 47 is formed by a pair of U-shaped magnetic pieces 17 which are juxtaposed one on top of the other, in spaced relationship to define air gaps in which separation devices 12 can be accommodated. Support members 48 are provided for supporting the upper magnetic piece 17. The air gaps formed by the pieces 17 slope outwardly downwards from the rotor so that output from the rotary separator is received at points around the outer perimeter of the separator. A drive motor 49 is coupled by means of a gearbox 50, mounted on the upper U-shaped magnetic piece, to the shaft 46 which runs in a lower bearing 51 supported on the lower magnetic piece 17.

Referring to FIG. 7 which also relates to a rotary separator, instead of a non-magnetic spider-rotor 45, a solid discoidal magnetic rotor 52 is provided so eliminating the need for a lower magnetic piece 17. As can be seen from FIG. 7, the discoidal rotor is horizontally arranged and supported on a base member housing the gearbox 50. The rotor has a central flat circular area surrounded by a downwardly inclined area on which the separator boxes 12 are located therearound. The drive motor 49 and gearbox 50 located with a supporting base plate are now arranged under the separator. The rotor 52 serves to complete the magnetic circuit of between magnetizing stations 47.

In operation the separation devices on the rotor can either be placed in the magnetizing stations singly or in groups. The separation process is carried out, as previously described, in three stages. The feeding of fluid and washing away of non-magnetic contaminants is done in those devices 12 during magnetization of the the magnetizing stations 47 while the scouring operation is carried out in those devices 12 during little, non or reverse magnetization of the magnetizing stations 47. The rotor can either rotate in one direction continuously or in steps. Also the rotor can oscillate from one position to another and back again to the first position. The rotor 53 can be either a non-magnetic spider or a magnetic solid discoidal rotor.

Referring to FIG. 9a another form of plate-box is shown. The main difference between this plate-box and that shown in FIG. lb resides in the construction of the casing 2 and, in particular, in the plate 6 which forms the top plate of the casing 2, i.e., that plate on which the upper magnetic piece 17 bears. This top plate is formed as a piston member 106 having at one end a radially extending peripheral flange 107 which serves to limit the inward stroke of the piston member into the plate-box. The piston member 106 is dowelled to plates 6' forming the sides of the casing 2 by means of dowels 108. Between the edges of the plates 6 and the flange 107 there is provided a soft tubular packing 109 which serves to seal the plate-box. The weight of the upper magnetic piece 17 augmented by the force of magnetic attraction serves to push the piston member 106 into the plate-box so as to compress the plates 3 together.

Referring to FIG. 9b there is shown an embodiment in which the plate-box shown in FIG. 90 could be used. In this embodiment the upper magnetic piece 17 is mounted on rods 110 supported by an arch-support lll. Lifting jacks 112 are fixed on top of the arch support 111 for acting on the rods 110, which pass through apertures (not shown) in the support 111, to raise the upper magnetic piece 17 which in the normal operational position rests on the plateboxes. Thus the plateboxes can be removed for cleaning or repair whenever it is desired to do so.

Referring to FIGS. 10a and 10b there is shown a sixth embodiment of a magnetic separator, in which the plate-box shownin FIG. 9a could be used. In this embodiment the pole-pieces of the magnetic pieces 17 present pole faces inclined to the horizontal. The platebox is inserted between the inclined pole faces. To pre-' vent the upper magnetic piece 17 sliding on the inclined surface presented by the plate-box and so causing damage to the rods 110 and other parts of the separator, guide bars 113 are provided.

The inclination of the separation devices 12 in all the examples of separator described is between 0 and 90 being preferably in the range 5 to 45. A small inclination results in a low rate of flow of the fluid and water through the plate-boxes giving a high proportion of the 6 magnetic particles separated from the fluid. A larger inclination gives, a fast flow with a decrease in the proportion of magnetic particles extracted.

Although the plates 3 in the plate-boxes described had their non-grooved major surfaces uppermost, they can clearly be arranged with their grooved major surfaces uppermost in the plate-boxes. Also various shapes of groove, other than triangular can be used.

The plates 3 may be of iron, steel, magnetic stainless steel or cobalt iron alloy (Permendur etc.) and may be unprotected against wear and corrosion or protected by chromium plating, chromium diffusion or other suit able method. The plates 3 are preferably made of low carbon steel or stainless steel containing approximately 13 percent chromium with little or no nickel, one variety of which is known as stainless: iron.

The grooved plates 3 may be replaced by other members of magnetic material, e.g. steel wool, expanded metal, wire gauge, steel balls, steel rods of circular or other suitable section, or twisted bars of square, triangular or other suitable section.

It should be appreciated that when grooved plates 3 are used they tend to move within the plate-boxes because of large changes in magnetic field due to switching on and off and reversal of the field.

Clearly although the operation of the separators has been described as being a three-stage process, the washing operation could be omitted to give a two-stage operation.

In all the separators the feeding and washing take place in a magnetic field whilst the scouring can take place in a very reduced or zero magnetic field strength, or in a reversed magnetic field. The flow of scour water may be at a pressure between 10 and 60 pounds per square inch.

Instead of the magnetic air gaps being inclined using the shaped pole-pieces 10, the entire magnetic fieldproducing structure can be tilted.

Instead of the screw-threaded member 30, a spring may be provided to keep the part-wedge member 29 in place in the plate-box 28.

The switches controlling the energization of the coils 9 may be controlled by the same cam arrangement as controls the valve stems 16.

The operation of the device could be hydraulically, solenoid or compressed air controlled instead of being controlled by a cam arrangement.

In a preferred arrangement a number of cams on a rotating shaft control electrical switches directly and may control some valves directly and other valves indirectly by means of solenoids or air valves or a combination of both.

Clearly in the rotary separators permanent magnets could be used in place of the electromagnets made up of the magnetic pieces 17 and coils 9.

The above described magnetic separators will remove particles of metallic iron, biotite, tourmaline, iron oxides, nickel-iferous pyrrhotite or serpentines, ilmenite, compounds intermediate between rutile and ilmenite, iron oxide, manganese oxides, iron carbonates, iron silicates, garnets, epidote, chromite, Wolfram or compounds containing iron from mixtures containing particles of quartz, felspar, bauxite, clay, phosphates, apatite, magnesite, strontium, or barium sulphides, scheelite, or carbonates or other non-magnetic substances.

What I claim and desire to secure by Letters Patent is: v

1. A rotary magnetic separator for separating solid magnetic particles from a fluid current, comprising a rotatable horizontally arranged non-magnetic spider rotor having a plurality of inclined arms sloping outwardly downwardly from the center of the rotor; a plurality of magnetic separation boxes arranged on the arms of the spider rotor; a series of flat plates located in each magnetic separation box, said plates having triangular grooves on the lower major surface thereof, the apices of said grooves contacting the upper major surface of the next lower plate; upper and lower U-shaped magnetic pieces; means for supporting the upper magnetic pieces in relation to the lower magnetic pieces to form a pair of air-gaps therebetween and between which said separation boxes pass as the rotor rotates, said air gaps being inclined outwardly downwards to correspond to the inclination of the separation boxes; energizing coils located on the ends of the U-shaped member for providing when energized a magnetic field across the air-gap so as to strongly magnetize the plates of a separation box located therein; and means for rotating said spider rotor in cyclic stepped manner for alternately moving each separation box into a zone of strong magnetic field within the air-gap for fluid current to be fed thereinto and thereafter into a zone of zero magnetic field, located midway between the pair of air-gaps defined by said U-shaped magnetic pieces, for the application of scouring fluid to remove the magnetic particles left adhering to the plates of the separation box.

2. A rotary magnetic separator according to claim 1, wherein said spider rotor is carried on a vertically arranged central shaft which runs in a bearing located on the lower U-shaped magnetic piece and wherein a drive motor and gearbox are mounted on the upper U- shaped member to drive said shaft which extends therethrough.

3. A rotary magnetic separator for separating solid magnetic particles from a fluid current including a rotatable horizontally arranged solid discoidal magnetic rotor having a central flat circular area, surrounded by a downwardly inclined annular area; a plurality of magnetic separation boxes carried about said annular area of the discoidal rotor; a series of flat plates located in each magnetic separation box, said plates having triangular grooves on the lower major surface thereof, the apices of said grooves contacting the upper major surface of the next lower plate; a U-shaped magnetic piece having outwardly downwardly inclined ends; means for supporting the U-shaped piece such that the inclined ends thereof are located over diametrically opposite separation boxes thereby forming an air-gap between the top of the separation boxes and the outwardly downwardly inclined ends; energizing coils located at end portions of said U-shaped member for providing a magnetic field across the airgap to strongly magnetize the plates of a separation box located therein; and means for rotating said discoidal rotor in cyclic stepped manner for each separation box in turn to first be moved into a zone of strong magnetic field within the air-gap and secondly into a zone of substantially zero magnetic field whereby the fluid current containing magnetic particles to be separated therefrom is first fed into the separation box in a zone of strong magnetic field whereafter scouring fluid is fed into the separation box in a zone of substantially zero magnetic field so as to remove the magnetic particles left adhering to the plates of the separation box.

4. A rotary magnetic separator according to claim 3, wherein there are sixteen magnetic separation boxes arranged in equi-spaced relation around the annular area of said discoidal rotor, and wherein two additional zones of strong magnetic field are provided to form additional air-gaps at relationship to said first pair of air-gaps, said four air-gaps each being of such a width that two magnetic separation boxes can be accommodated therein simultaneously whilst a pair of separation boxes on each side thereof is in a zone of zero magnetic field.

5. A magnetic separator for separating solid magnetic particles from a fluid current including a pair of magnetic separation boxes; a series of flat plates located in each magnetic separation box, said plates having triangular grooves on the lower major surface thereof, the apices of said grooves contacting the upper major surface of the next lower plate; upper and lower U-shaped magnetic pieces; means for supporting the upper magnetic piece in relation to the lower magnetic piece to form a pair of air-gaps therebetween in which the magnetic separation boxes are located in inclined relation to the horizontal; energizing coils carried at end portions of the U-shaped members for providing a magnetic field across the air-gap when said coils are energized thereby to strongly magnetize the plates of the separation box for removing magnetic particles from a fluid current, during a fluid current feed cycle, said removed magnetic particles adhering to said plates; a main supply of electric current for said coils for strong magnetization of said plates; means for passing a small electric current reverse to that of said main supply through said coils for reducing the remanent magnetic field to substantially zero when said main supply is interrupted during a scouring period to thereby remove the magnetic particles adhering to the plates of the separation box; and jacking means for raising the upper U- shaped magnetic piece in relation to the lower magnetic piece to facilitate removal of the separation boxes from said air-gaps.

6. A magnetic separator according to claim 5, wherein said upper U-shaped magnetic piece is carried by a pair of rods, and wherein an arch-support carries a pair of lifting jacks to which the ends of respective rods are attached.

7. A. magnetic separator according to claim 6, wherein the top-plate of the separator box is formed as a piston member having a radially extending peripheral flange, the face of the upper U-shaped magnetic piece bearing on the piston member, a packing member being provided between the walls of the separator box and the piston member, and guide bars being provided to cooperate with the upper U-shaped magnetic piece to prevent it sliding on the inclined surface of the separator boxes.

8. A magnetic separator according to claim 5, wherein each separator box includes two dividing plates located between the triangular grooved plates so as to divide said plates into three groups within said separator box, said dividing plates being longer than the triangular grooved plates and arranged to extend out of the inlet side of the separator box in an upwardly inclined direction owing to the inclination of the separator box, said dividing plates thus forming together with a chute extending from the base of the separator box, three supply troughs for the three groups of triangular grooved plates.

Claims

1. A rotary magnetic separator for separating solid magnetic particles from a fluid current, comprising a rotatable horizontally arranged non-magnetic spider rotor having a plurality of inclined arms sloping outwardly downwardly from the center of the rotor; a plurality of magentic separation boxes arranged on the arms of the spider rotor; a series of flat plates located in each magnetic separation box, said plates having triangular grooves on the lower major surface thereof, the apices of said grooves contacting the upper major surface of the next lower plate; upper and lower U-shaped magnetic pieces; means for supporting the upper magnetic pieces in relation to the lower magnetic pieces to form a pair of air-gaps therebetween and between which said separation boxes pass as the rotor rotates, said air gaps being inclined outwardly downwards to correspond to the inclination of the separation boxes; energizing coils located on the ends of the U-shaped member for providing when energized a magnetic field across the air-gap so as to strongly magnetize the plates of a separation box located therein; and means for rotating said spider rotor in cyclic stepped manner for alternately moving each separation box into a zone of strong magnetic field within the air-gap for fluid current to be fed thereinto and thereafter into a zone of zero magnetic field, located midway between the pair of air-gaps defined by said Ushaped magnetic pieces, for the application of scouring fluid to remove the magnetic particles left adhering to the plates of the separation box.

2. A rotary magnetic sepparator according to claim 1 wherein said spider rotor is carried on a vertically arranged central shaft which runs in a bearing located on the lower U-shaped magnetic piece and wherein a drive motor and gearbox are mounted on the upper U-shaped member to drive said shaft which extends therethrough.

3. A rotary magnetic separator for separating solid magnetic particles from a fluid current including a rotatable horizontally arranged solid discoidal magnetic rotor having a central flat circular area, surrounded by a downwardly inclined annular area; a plurality of magnetic separation boxes carried about said annular area of the discoidal rotor; a series of flat plates located in each magnetic separation box, said plates having triangular grooves on the Lower major surface thereof, the apices of said grooves contacting the upper major surface of the next lower plate; a U-shaped magnetic piece having outwardly downwardly inclined ends; means for supporting the U-shaped piece such that the inclined ends thereof are located over diametrically opposite separation boxes thereby forming an air-gap between the top of the separation boxes and the outwardly downwardly inclined ends; energizing coils located at end portions of said U-shaped member for providing a magnetic field across the air-gap to strongly magnetize the plates of a separation box located therein; and means for rotating said discoidal rotor in cyclic stepped manner for each separation box in turn to first be moved into a zone of strong magnetic field within the air-gap and secondly into a zone of substantially zero magnetic field whereby the fluid current containing magnetic particles to be separated therefrom is first fed into the separation box in a zone of strong magnetic field whereafter scouring fluid is fed into the separation box in a zone of substantially zero magnetic field so as to remove the magnetic particles left adhering to the plates of the separation box.

4. A rotary magnetic separator according to claim 3, wherein there are sixteen magnetic separation boxes arranged in equi-spaced relation around the annular area of said discoidal rotor, and wherin two additional zones of strong magnetic field are provided to form additional air-gaps at 90* relationship to said first pair of air-gaps, said four air-gaps each being of such a width that two magnetic separation boxes can be accommodated therein simultaneously whilst a pair of separation boxes on each side thereof is in a zone of zero magnetic field.

5. A magnetic separator for separating solid magnetic particles from a fluid current including a pair of magnetic separation boxes; a series of flat plates located in each magnetic separation box, said plates having triangular grooves on the lower major surface thereof, the apices of said grooves contacting the upper major surface of the next lower plate; upper and lower U-shaped magnetic pieces; means for supporting the upper magnetic piece in relation to the lower magnetic piece to form a pair of air-gaps therebetween in which the magnetic separation boxes are located in inclined relation to the horizontal; energizing coils carried at end portions of the U-shaped members for providing a magnetic field across the air-gap when said coils are energized thereby to sttrongly magnetize the plates of the separation box for removing magnetic particles from a fluid current, during a fluid current feed cycle, said removed magnetic particles adhering to said plates; a main supply of electric current for said coils for strong magnetization of said plates; means for passing a small electric current reverse to that of said main supply through said coils for reducing the remanent magnetic field to substantially zero when said main supply is interrupted during a scouring period to thereby remove the magnetic particles adhering to the plates of the separation box; and jacking means for raising the upper U-shaped magnetic piece in relation to the lower magnetic piece to facilitate removal of the separation boxes from said air-gaps.

7. A magnetic separator according to claim 6, wherein the ttop-plate of the separator box is formed as a piston member having a radially extending peripheral flange, the face of the upper U-shaped magnetic piece bearing on the piston member, a packing member being provided between the walls of the separator box and the piston member, and guide bars being provided to cooperate with the upper U-shaped magnetic piece to prevent it sliding on the inclined surface of the separator boxes.