US3387707A

US3387707A - Permanent magnet assembly

Info

Publication number: US3387707A
Application number: US463706A
Authority: US
Inventors: William C Smith
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1965-06-14
Filing date: 1965-06-14
Publication date: 1968-06-11
Anticipated expiration: 1985-06-11
Also published as: BE682534A; GB1120013A

Description

June 11, 1968 w. c. SMITH PERMANENT MAGNET ASSEMBLY Filed June 14, 1965 5 Sheets-Sheet 1 FIG-3.

INVENTOR William C. Smith BY ATTO NEY June 11, 1968 w c, sMlTH 3,387,707

PERMANENT MAGNET ASSEMBLY June 11, 1968 w. c. SMIII'H 3,387,707

PERMANENT MAGNET ASSEMBLY Filed June 14, 1965 5 Sheets-Sheet 3 3,387,707 PERMANENT MAGNET AfisEMllLY William C. Smith, Blairsville, Pa, assignor to Westinghouse Electric Corporation, Pittsburgh, Pa, :1 corporation of Pennsylvania Filed June 14, 1965, Ser. No. 463,706 10 Claims. (Cl. Elf-223) ABSTRACT OF THE DISCLQSURE A magnetic unit having a pair of poles at a working face, the polarities thereof conferred by a first magnet body, with a pair of magnet bodies remote from the working face connected in series by a soft magnetic member and operating in parallel with said first magnet body.

This invention relates to magnet assemblies particularly useful, by way of example, in magnetic separators for the resolution of magnetic ores into a desired mineral fraction and a gangue fraction. It also concerns apparatus that includes such magnet assemblies.

There are a number of commercial models of magnetic separators available on the market. In these devices, which are of a contacting drum configuration, electromagnets or permanent magnets and pole pieces are arranged relative to an outer surface of the drum, designated the separation surface, to exert a magnetic influence along that surface whereby magnetic mineral constituents of ores, for example, are attracted and held there and can thus be separated from the remaining nonmagnetic constituents, commonly designated as gangue. The separation surface generally is rotated relative to the magnet arrangement in which movement the gangue does not participate and falls away, and the separated magnetic mineral materials are thus removed from the gangue and carried to a place where they can be collected. The present invention is particularly directed to magnetic sep arators employing permanent magnets.

Analysis of the prior art permanent magnet arrangements in these devices demonstrates the existence of significant drawbacks by which about /2 to A of the magnetic flux is not utilized. Thus, in many such devices, substantial spaces such as air gaps are located between the permanent magnets and magnetic flux exists in or passes through those spaces. Since the spaces are within the drum and between adjacent magnets, it is evident that this internal flux constitutes a leakage or a loss of flux compared to the total that should be available to I effect magnetic separation. In still other designs, the spaces between magnets have been eliminated or avoided by placing pole pieces therein and to an extent this eliminates internal flux between adjacent magnets. However, in such arrangements, magnetic flux passes between the pole pieces rearwardly of the magnets. Hence, while a portion of the magnetic flux extends externally of the conveyor surface and is useful, another and significant portion appears rearwardly of the magnet and pole assembly and thus is Wholly removed from any area where it can exert a useful influence for the intended purposes. Such known pole piece arrangement, therefore, simply relocates internal flux leakage and does not eliminate it. Similar problems exist with regard to magnet chucks or assemblies used in conveyors, in sheet spreaders and other applications.

The present invention is an improvement on the device disclosed in the copending applications Ser. No. 254,223, filed Jan. 28, 1963, now Patent No. 3,209,912, and Ser. No. 296,041, filed July 18, 1963, now Patent No. 3,283,- 900, both assigned to the assignee of the present invention.

United States Patent It is the primary object of the present invention to provide a novel arrangement of magnets and pole pieces particularly useful in magnetic apparatus in which an increased field intensity is obtained with improved utilization of magnetic material in that the flux density in all sections of the magnet assembly closely corresponds to that of the maximum energy product.

Another object is to provide magnetic separator, conveying and spreading apparatus including an assembly of permanent magnets and pole pieces providing for an efficient utilization of the maximum amount of the magnetic flux at the separator surfaces in accordance with the foregoing object.

Other objects and advantages of the invention will be apparent from the following detailed description and drawings, in which:

FIGURE 1 is a sectional view of a magnetic unit in accordance with this invention;

FIG. 2 is another embodiment of a magnetic unit in accordance with this invention, a pair of such units is illustrated;

FIG. 3 is a diagrammatic illustration in elevation of a magnetic drum separator;

FIG. 4 is a perspective view showing a permanent magnet assembly for use in a drum separator, the assembly of magnets being arranged in accordance with this invention;

FIG. 5 is a cross-sectional view taken along line V--V of FIG. 6; and

FIG. 6 is a cross-sectional view taken along line VIVI of FIG. 5.

Basically, the objects of increased field intensity and improved magnetic flux distribution are attained in the present invention by a novel magnet unit including at least three bodies of oriented permanent magnet material, two of which are arranged magnetically in series with each other and magnetically in parallel with the third body. As a matter of convenience, the invention will be first described as embodied in a single magnetic unit, and then as embodied in a magnetic assembly which includes a plurality of magnetic units.

The magnetic unit on which this invention is based is a structure composed of soft magnetic pole pieces or members, at least three bodies of permanent magnetic material and a soft magnetic yoke member. These three elements of the magnetic unit are shaped, arranged and assembled to provide at the Working face a first elongated pole face of one polarity, and a second elongated pole face of the opposite polarity spaced from said first pole face and substantially parallel thereto.

More specifically, the magnetic unit of this invention is characterized by a yoke of low reluctance material such as iron having angled arms positioned rearwardly away from the working face of the assembly and having at least two permanent magnet bodies fitted on the forward side of each of the arms thereof. In this unit the arms of the yoke provide a low reluctance path of neutral polarity between the magnet bodies thereby connecting said magnet bodies in series. The pole pieces are arranged at the end of the magnet bodies opposite to the end in contact with the yoke. An additional permanent magnet body is positioned between and in contact with the pole pieces, magnetically in parallel with said first mentioned magnet bodies. For reference purposes, the magnet body positioned between the poles may be called the primary magnet body and the magnet bodies contacting the rear surface of the pole pieces may be called secondary magnet bodies.

The pole pieces and yoke are held in fixed spaced relation to each other and to the bodies of the magnetic material which are associated with them. The bodies of permanent magnet material are positioned so as to confer one polarity upon one magnetic pole piece and the opposite polarity upon the other pole piece. Thus, the yoke supports the rear surfaces of the secondary magnetic bodies abutting it, and a pole piece abuts the forward surfaces of these magnet bodies and the end surface of the primary magnetic body. The magnet bodies are magnetized in a direction that is perpendicular to the planes of the pole surfaces with which they are in contact.

The yoke provides supporting structure for the magnetic unit and has at least two magnet bodies fixed to the forward side of the yoke surfaces extending to the rearward surfaces of the pole piece and to the primary magnet body which is positioned along the working face of the unit. The yoke may alternatively be formed of an angle, solid bar of triangular, square, sector or rectangular cross-section of soft iron or steel or other suitable material. It will be understood that the yoke surfaces may be flat or curved with correspondingly shaped magnet bodies preferably fitting closely thereagainst.

In utilizing the basic unit described, ordinarily a plurality of units will be employed depending upon the number of poles desired. Units assembled adjacent each other will share pole members. For example, a five-pole arrangement may be obtained by empolying four of the described yoke-magnet bodies and pole piece assemblies. In this manner, a magnet assembly is achieved in which a high flux density is attained and the flux density in all sections of the magnet body closely correspond to that of the maximum energy product. Further the efliciency achieved approaches 100 percent, based on the better utilization of the magnetic flux relative to the working face, for the structural and magnetic arrangement of the present invention takes a form in which substantial open spaces between permanent magnets can be greatly reduced or eliminated and concentrates and conducts the magnetic flux into the area where it can be utilized almost entirely to effect a desired object, for example, a magnetic separation.

In one embodiment, the magnetic unit of this invention takes a form in which the yoke is V shaped or angular in cross-section with the arms of the V set at a suitable angle with respect to each other and the apex in the direction of the working face. The pole pieces are bars having, in cross-section, a lower surface thereof generally parallel to a surface of the proximate arm of said yoke. A pair of secondary magnets, or a pair of stacks of slab-shaped magnets, are secured between the adjacent surfaces of the yoke and the pole pieces and a third magnet or primary stack of magnets is secured between the poles of the unit. The secondary pairs of magnets associated with both arms of the yoke are magnetically in series and the yoke provides low reluctance coupling therebetween of neutral polarity. This pair of magnets is magnetically in parallel with the primary magnet or stack of magnets positioned between the poles.

Referring now to the drawings there is shown in FIG. 1 a magnetic unit in accordance with this invention. This magnetic unit has a pair of pole pieces 1, 2 at the working face thereof and a yoke member 3 spaced from the pole pieces having surfaces parallel to the rearward surfaces 4, 6 of the pole pieces. The yoke member 3 has a generally V configuration with the apex of the V in the direction of the working face. Between the spaced poles 1, 2 there is positioned a primary stack of magnets 11 to 16 abutting a lateral face 7 of one pole piece at one end of said stack and abutting a lateral surface 8 of the other pole piece at the other extremity of the said stack.

Between the rearward surface 4 of the pole piece 1 and the parallel surface of the yoke 3 is a secondary stack of magnets 17, 13. A similar stack of

magnets

19, 21 is located between the rearward surface 6 of the other pole piece 2 and the parallel surface of the yoke 3. The magnetic stacks indicated by the

numerals

17, 18 and 19, 21 are magnetically in series, with the yoke 3 providing a low reluctance magnetically neutral path for the flux therebetween This pair of magnet stacks is magnetically in parallel with the primary magnetic stack identified by the numerals 11 to 16.

in FIG. 2 a very similar magnetic unit 3!) is shown paired with an identical magnetic unit 50. In this embodiment of the magnetic unit the yoke forms a very shallow V and consequently, the magnetic stack at the working face 31 to 36 is formed of slabs which are progressively wider as the distance from the poles increases. Thus, in cross-section this stack of slabs forms a deep V which may touch the apex of the yoke as in FIG. 2 or may be remote therefrom as in FIG. 4. The operation of the unit is essentially identical to that of the embodiment shown in FIG. 1. Such magnetic units will ordinarily not be individually employed, but rather, several such units will be employed simultaneously; the magnetic units and in FIG. 2 are shown in assembled relation and clearly, additional units may be added to form an assembly of desired size. The appearance of a plurality of magnetic units of the type shown in FIG. 1 will differ somewhat from an assembly employing a plurality of magnetic units of the type shown in FIG. 3. Thus, around each pole of the FIG. 1 type magnetic assembly, there will be grouped, four magnetic stacks, two primary stacks at the working face of the magnet assembly and two secondary stacks abutting the inclined rearward surfaces of the pole piece. This can be more clearly seen in FIG- URE 4 wherein the two primary magnet stacks 51 to 56 and the two secondary magnet stacks 41 to 48 are positioned about pole 121. When a plurality of units of the type shown in FIGURE 2 are assembled, it will be noted (as shown in FIG. 2) that each pole piece will have associated with it only three magnetic stacks, two primary stacks at the working face of the magnet assembly and the third secondary stack of magnets abutting the rearward surface of the pole piece. Of course, when a plurality of such units are employed the units wiil share pole pieces. While the end slabs of magnetic material in the primary magnetic stack may be of tapered configuration, it is clear that the pole pieces may readily be appropriately shaped so that all magnet slabs have a simple rectangular cross-section.

The invention will be further described in detail with reference to the utilization of magnetic assemblies having magnet units with V-shaped yokes in drum type magnetic separators for resolving magnetic ores. However, it is to be understood that this is for purposes of illustration and is not to be construed as limiting the invention.

The magnetic separator shown in FIGURE 3 comprises a supporting frame 70 on which is mounted the active separator unit indicated generally by the numeral 72. As will be apparent in the detailed description hereinafter, the separator unit structurally comprises a generally cylindrical drum 73 of non-magnetic material (such as stainless steel) surrounding an assembly of magnets and pole pieces located along, but spaced from, a portion of the inside surface 74 (FIGS. 5 and 6) of the cylindrical wall 75 of the drum 73. The magnet arrangement is supported independently of the drum 73 so that the drum can be rotated while the assembly of magnets remain stationary.

Accordingly, the drum '73 is supported on the frame 70 by a shaft '76. A motor 77 operatively connected to the drum 73 through a sprocket and chain arrangement 7-8 attached to the end walls 79 of the drum 73 is also supported on frame 79. Shaft 76 suitably supports the drum 73 by means of bearings 79a attached to the end walls 79.

Internally of frame 70, there is structure by which feed to be resolved is directed to the external surface of the cylindrical wall of the drum of the magnetic separator unit, and by which the fractions into which the feed is resolved can be separately removed. For this general purpose, a conduit 62 leads into an L-shaped chamber 64 at one side of the frame 70. The materials in the feed that are non-magnetic and thus not influenced by the magnet assembly pass downwardly along the L-shaped chamber 64 and are withdrawn through an outlet conduit 65 and are stored or otherwise disposed of as desired. The magnetic materials in the feed are attracted and held to the external surface of the sidewall of the drum until they are carried beyond a point where they could fall into the path to the outlet conduit 65. Once they have been carried beyond this point, they are permitted to drop into a bin or outlet conduit 66 provided to receive them.

Within the drum 73 is the permanent magnet assembly, indicated by the numeral in FIG. 4. The arrangement of the permanent magnets and pole pieces in this embodiment of the invention is shown in FIGS. 4 and 5. This apparatus includes a pair of supporting

end plates

82 and 84 having cross bar means 95 and 96, respectively, associated with each by which the magnet assemblies can be supported. If desired, adjustable means, such as set screws (not shown) may be provided to lock the

end plates

82 and 84 in any desired fixed position on shaft 76. The permanent magnets and pole pieces preferably are maintained as close as possible to the inside surface 74 (FIG. 5) of the drum side wall consistent with the free rotation of the drum relative to the magnet assembly,

The actual width of each magnet body or stack of magnet slabs preferably is determined so that available volume between the yoke and the pole pieces is substantially entirely filled with magnetic material and voids, if any, are minimized. However, it will be understood that in making the magnet slabs. it is difiicult and expensive to provide complicated cross-sections, tapered shapes and other special forms. In many cases then, magnet slabs of simple rectangular cross-section will be employed at some loss in efliciency due to the voids resulting from mismatching of slabs. A pole piece having a rear surface there of abutting a forward surface of a secondary magnet body extends to the working face of the magnet unit. Successive poles define a space in which is positioned a primary magnet body or stack of magnet slabs extending along the working face.

The magnet units as described may be made individually and then assembled with conventional means used to secure several magnet units together to form a magnet assembly. However, in devices employing a plurality of magnet units, it is convenient and desirable to construct the device so that adjacent magnet units share pole pieces and means for securing the elements of the structure together.

In FIGS. 4 and 5, there is shown a five pole magnet strip assembly 80, which includes a plurality of magnet units sharing pole pieces and secured together and afiixed to the

end plates

82 and 84 of the magnetic separator. The device shown is provided with four

magnet units

101, 102, 103, 104 each having a

yoke

110, 111, 112 and 113. The two

middle magnet units

102, 103 share three appropriately shaped

pole pieces

121, 122 and 123 while the end magnet units 101, 104 each have one

pole piece

120 and 124, respectively, which is not shared. The magnetic strip is held together in part by a pluralityof threaded means 85 located between adjacent magnet units which are threaded at one end into the

pole pieces

121, 122, 123 and atthe other end are provided with collars 81 which extend into abutting relation with the rearward edge of adjacent arms of the

yokes

110, 111, 112, 113. It will be noted that by tightening the nut 83, the magnet stacks of adjacent magnet units can be drawn firmly to their respective yokes. The support of the flank magnet stacks of the end magnet units 101 and 104 requires that a hole 86 be drilled in one arm of the yoke and the magnet stack so that the fastening means 35, 83 may effectively draw the pole piece 120, for example, and the magnet stack to the yoke. The magnet slabs in the primary magnet stack may be glued with epoxy cement to each other and to the pole pieces or other suitable means may be employed.

To secure the magnet units to the

end plates

82 and 84, the horizontal cross bars 95 and 96, respectively, are welded or otherwise secured thereto. The cross bar 95 is provided with downwardly extending struts 91 and 92, and the cross bar 96 is similarly provided with struts 93 and 94. The struts are welded or otherwise secured to the cross bars. As will be seen in FIGS. 4 and 5, the ends of the cross bars 95 and 96 closely fit into the angle formed by the rear surfaces of the end yokes 11-0 and 113. The cross bars are preferably welded to the yokes. Downwardly extending struts 91 and 93 closely fit into the angle formed by the rear surfaces of the yoke 111. Similarly, the struts 92 and 94 mate with the rear surfaces of yoke 112. The struts are preferably welded to the yokes. It is clear that an extremely strong structure has thus been provided.

In the embodiment shown in FIG. 4, there are four magnet units that, in the aggregate and in view of their arrangement, contribute five poles. Additional magnet units each contribute one more pole, and accordingly, any odd or even number of poles desired can be easily provided. Where a 360 arc of magnet units is employed, an even number of poles is obtained, for the final magnet unit merely closes and contributes no separate pole. While the magnetic assembly of the invention has been described primarily in terms of a V configuration, in which the yoke arms are fixed at about a angle to each other, other angles, smaller or greater, may be used.

For a drum type magnetic separator of the type being discussed, a diameter of 30 to 36 inches frequently is used and the drum may be as much as 4 to 6 feet in length. The individual permanent magnets used would be functionally of substantially similar length, though that length can be achieved by using a plurality of magnets each of a smaller length so that in the aggregate the 4 to 6 feet of magnets is attained. Of course, the pole pieces also extend the full length, and similarly, the full length required may be achieved by using a plurality of smaller pole pieces in contact with each other.

The materials used to produce the permanent magnets and pole pieces in accordance with this invention can vary widely, as is apparaent to those skilled in the art. Preferably, they are made from ceramic permanent magnet high coercive force materials such as the barium ferrites, or strontium ferrites or other materials of like character, since the arrangement provides a large magnet area in relation to the magnet length. However, the metallic permanent magnet materials such as alnico, and the like can be used. Similarly, the pole pieces can be made of any soft magnetic material desired. Particularly suitable are iron and common soft steel.

While the invention has been described primarily as employing oriented magnetic material, and indeed this is the preferred material, it is also contemplated that isotropic high coercive force permanent magnetic material may be used in the magnetic assembiles of the invention. In using such material, the arrangement is such that directions of strong magnetization of the permanent magnetic material essentially impart one polarity thereof to one of the pole pieces of the magnet assembly, and the other polarity to the other pole piece.

As has already been indicated, the pairs of magnets, or pairs of stacks of magnets in contact with the yoke are magnetically coupled in series. Consequently, if the south pole of one magnet (or stack) is adjacent one pole piece, the north pole of the same magnet is adjacent the yoke, while for the companion magnet (or stack) of the same magnet assembly, the south pole is adjacent the yoke and the north pole is adjacent the other pole piece. These two magnets or stacks of magnets of each magnet assembly are magnetically in series due to their opposite magnetic orientation and to the presence of the yoke which provides a neutral polarity low reluctance path between the stacks. The stack of magnets at the working face etween the lateral surface of the pole pieces is magnetically in parallel with the paired stacks and cooperates with them to increase the flux at each pole.

In consequence of the just described arrangement of pole pieces and magnets, internal flux leakage is minimal because it occurs only at the ends of the magnet assemblies, along one side of each flank magnet assembly, and at bolt locations and mismatched magnet joints. Moreover, there is little flux leakage rearwardly of the magnet arrangement since the flux behind the magnets is concentrated in the yokes and is conducted by the yokes from one of the paired magnets (or stacks) to the other. Hence, the flux is principally located in front of the magnets in an are between the pole pieces and thus substantially all of it, for practical purposes, is available to effect the desired separation.

Operation of a magnetic separator as just described follows that of prior art devices. Thus, where an ore is being separated from a gangue, the ore that is to be resolved is comminuted to a relatively small size, for example, from fines ranging up to particles of A to /2 inch or more. For Wet operation, the finely divided ore, is dispersed in a carrier fluid, normally water, and fed to the separator through the inlet conduit. With the conveyor or drum surface rotating, the feed passes into contact with it and the magnetic material is attracted to and held on the drum surface. The remaining materials pass to the first outlet conduit. The drum surface and its magnet assembly are of such size that the magnetic force is maintained on the particles on the surface until they are carried beyond the area in which they would pass outwardly with the tailings. Once they are beyond that point, the end of the magnetic separator arrangement is reached and the particles fall away from the drum surface under the influence of gravity and the failure, due to remoteness of sufiicient magnetic force to retain them. The falling magnetic particles are directed to a separate outlet conduit provided for them. The alternate polarities of the magnetic poles to which the particles are subjected as the drum surface passes relative to the magnetic drum arrangement, tends to vibrate these particles on the surface, reorientating them and permitting entrapped nonmagnetic material to fall away.

In the resolution of materials with a separator as in this invention by what can be termed :a dry process, the feed usually is arranged to pass over the rotating surface under the influence of gravity. Normallly for dry separations, more magnetic units are used, often covering on the order of 50 percent or more of the surface of the separating drum. In such practice, the feed may be introduced into contact with the separating drum near its top and the feed inlet, commonly a simple funnel arrangement to which a vibrator may be attached if necessary or desirable, is supported from the frame above the drum. The tailings fall free of the drum at its side to an outlet provided for them, while the magnetic particles are held to the surface beyond that point and are separately removed.

Another arrangement, especially suited to dry separations or conveying applications, utilize a drum having magnet assemblies along the entire inner surface of the sidewall of the drum. In such instance, the drum sidewall, which is driven, may provide all or part of the motive power for the conveyor.

Magnet units or assemblies as described are useful for many other industrial applications. For example, they can be used in conjunction with conveyors by which cans may be held to a conveyor and moved as desired. Further, they are useful as spreaders of metal sheets arranged in stacks.

From the foregoing discussion and description, it is apparent that the present invention is a significant advance in magnet units. It will be evident that sizes, number of elements and the like can be changed. Furthermore, the face of the magnet assembly can be made fiat or even concave, rather than convex as shown, for particular applications. Tips can be added to the pole pieces to aid in directing the flux as desired. In all events, the materials of construction for different parts of apparatus with which the magnet assembly is used should be chosen such that no materially adverse influence on the utilization of essentially all the available flux exists.

Having illustrated and described the invention in detail for purposes of exemplification, it should be understood that the invention may be practiced otherwise and is not to be limited by the details expressed.

I claim as my invention:

1. A magnetic unit having a pair of spaced pole pieces at a working face, each pole piece having a front surface at the working face and a rear surface remote therefrom, a primary permanent magnet body positioned at the working face between and in contact with the pole pieces conferring one polarity on one pole piece and the opposite polarity on the other pole piece, a pair of secondary permanent magnet bodies having their polarities magnetically coupled in series through a contacting yoke member of low reluctance material, each member of the said pair of secondary magnet bodies contacting one of said rear surfaces and the primary magnet body, the primary magnet body being magnetically in parallel with the secondary magnet bodies.

2. In a magnet assembly comprising a series of pole pieces spaced along a working face with lateral stacks of slabs of ceramic permanent magnet material filling the space between successive pole pieces, each pole piece having a front surface at the working face and a rear surface remote therefrom, the improvement comprising, rearward stacks of slabs of ceramic permanent magnet material contacting said rear surfaces and extending into contact with said lateral stack to increase the magnetic strength at each pole, a yoke of low reluctance material contacting the rear surface of each of said rearward stacks of slabs connecting them magnetically in series by providing an easy flux path of neutral polarity therebetween and furnishing structural support to the magnet assembly, and the lateral stacks of magnet slabs being magnetically coupled in parallel with said rearward stacks.

3. A magnet assembly comprising a plurality of parallel elongated pole pieces defining a working face, each pole piece having a front surface at the working face, a rear surface remote therefrom and a pair of lateral surfaces joining the front surface to the rear surface, primary oriented permanent magnet bodies contacting the lateral surfaces of said pole pieces and occupying the space between adjacent pole pieces to the working face, secondary oriented permanent magnet bodies contacting the rear surfaces of said pole pieces and the primary magnet bodies, the several oriented magnet bodies about each pole piece conferring a selected polarity thereon with adjacent pole pieces having opposite polarity, a yoke member of low reluctance material contacting the rear surfaces of the secondary magnet bodies connecting them magnetically in series and providing structural support to the magnet assembly, and the primary magnet bodies magnetically coupled in parallel with their associated secondary magnet bodies.

4. A magnet assembly comprising a series of spaced elongated pole pieces defining a working face, the pole pieces lying generally in parallel alignment, each pole piece having a front surface in the plane of the working face and a pair of elongated spaced lateral surfaces extending rearwardly therefrom to join at least one rear- Ward surface, primary bodies of oriented permanent magnet material positioned between and in contact with the lateral surfaces of successive pole pieces thereby filling the space between pole pieces to the working face, secondary bodies of oriented permanent magnet material positioned in contact with the rearward surfaces of said pole pieces and said primary magnet bodies, each pole piece thus being in contact with at least two oriented magnet bodies which cooperate to confer a desired polarity thereupon so that each pole piece has a polarity which is opposite to that of its nearest neighboring pole piece, a yoke member of low reluctance material positioned in contact with the rearward surfaces of said secondary magnet bodies connecting them magnetically in series by providing an easy flux path of neutral polarity therebetween and capable of affording structural support to the magnet assembly, each primary magnetic body being magnetically coupled in parallel with at least two secondary magnetic bodies.

5. An assembly of magnets for use in separating proce dures and conveying applications comprising a pair of elongated magnetic pole pieces of opposite polarity defining between them the working face of said magnet assembly, an elongated yoke member of low reluctance material having a pair of convergent inclined surfaces extending the length thereof, the convergence of said surfaces forming an apex in the direction of said working face, each of said elongated pole pieces lying parallel to and spaced from one of said inclined surfaces, a primary body of oriented permanent magnet material disposed along the working face of said magnet assembly having a direction of magnetization essentially parallel to said working face and substantially filling the space between said pole pieces, a pair of bodies of oriented permanent magnet material each substantially filling the space between one of said inclined surfaces and the pole piece associated therewith and extending to said primary body of oriented permanent magnet material, said pair of bodies of oriented permanent magnet material being arranged with their polarities magnetically coupled in series through the yoke member and the polarities of said pair being magnetically coupled in parallel with said primary body.

6. The magnetic assembly of claim wherein the angle between the convergent surfaces is approximately 90.

7. An assembly of magnets for use in separation procedures having a working face thereon comprising a generally elongated yoke of low reluctance material including a pair of convergent inclined surfaces extending the length thereof, the convergence of said inclined surfaces forming an apex in the direction of the working face of said assembly, a pair of elongated magnetic pole pieces spaced along the working face of the assembly, said pole pieces extending parallel to said yoke and symmetrically spaced therefrom, each of said pole pieces having an inclined surface substantially parallel to one of the inclined surfaces of the yoke with which it cooperates, a primary stack of oriented permanent magnets disposed along said working face having its direction of magnetization essentially parallel to said working face and extending between and into contact with cooperating surfaces of said pole pieces, a secondary stack of oriented permanent magnets positioned between and contacting one of said inclined surfaces of said yoke and the parallel inclined surf-ace of the cooperating pole piece, another secondary stack of oriented permanent magnets positioned between and contacting the other of said inclined surfaces of said yoke and the parallel inclined surface of the pole piece with which it cooperates,

the sevenal stacks of oriented permanent magnets substantially filling the volume between the inclined surfaces of the yoke and the pole pieces and the working face of the assembly, the oriented permanent magnets of the secondary stacks being arranged with their polarities magnetically coupled in series through the yoke, and the oriented permanent magnet of the primary stack being arranged with its magnetic polarity magnetically in parallel to that of the secondary stacks.

8. The magnetic assembly of claim 7 wherein the angle between the convergent surfaces is approximately and the magnets are composed of a ferrite material.

9. In a magnetic separator, a drum having a cylindrical sidewall composed of a non-magnetic material and mounted for rotation on a shaft, a permanent magnet unit having two poles at a working face thereof adapted to attract magnetic material to be separated toward the external surface of the sidewall of the drum and mounted within the drum, said Working face being positioned in close proximity to the internal surface of said sidewall, the magnetic unit comprising a V-shaped yoke of low reluctance soft magnetic material having two arms extending away from the working face thereof, .a pair of pole members of low reluctance soft magnetic material each spaced from and parallel to an arm of said yoke, bodies of oriented permanent magnetic material substantially completely filling the spaces between the arms of the yoke and the pole pieces and extending to the working face of the magnetic unit and comprising a primary body of oriented permanent magnet material disposed along said working face with its direction of magnetization essentially parallel to said working face and extending between and into contact with cooperating surfaces of said pole.

pieces and conferring one polarity on one pole piece and the opposite polarity on the other pole piece, a secondary body of oriented permanent magnet material disposed between and contacting one of the arms of the yoke and one of said pole pieces, and another secondary body of oriented permanent magnet material disposed between and contacting the other arm of the yoke and the other of said pole pieces, the secondary bodies of oriented permanent magnet material being magnetically coupled in series through said yoke and being magnetically in parallel with said primary body.

10. In a magnetic separator in accordance with claim 9, at least two such permanent magnet units adjacent one another and sharing a common pole, the oriented permanent magnet bodies consisting of stacked ceramic permanent magnets in slab form.

References Cited UNITED STATES PATENTS 2,146,588 2/1939 Merrill 2092l9 2,992,737 7/1961 Buus 209223 3,067,366 12/1962 Hofman 335306 3,168,686 2/1965 King 335306 3,209,912 10/1965 Sloan 209--223 3,283,900 11/1966 Sloan 209-223 2,992,736 7/1961 Buus et a1. 2,992,738 7/ 1961 Maynard.

HARRY B. THORNTON, Primary Examiner.

R. HALPER, Assistant Examiner.