US2992737A

US2992737A - Method and means for variation of magnetic strength of permanent magnetic drums

Info

Publication number: US2992737A
Application number: US786873A
Authority: US
Inventors: Harold W Buus
Original assignee: Indiana General Corp
Current assignee: Indiana General Corp
Priority date: 1959-01-14
Filing date: 1959-01-14
Publication date: 1961-07-18
Anticipated expiration: 1978-07-18

Description

July 18, 1961 H. w. BUUS 7 METHOD AND MEANS FOR VARIATION OF MAGNETIC STRENGTH OF PERMANENT MAGNETIC DRUMS Filed Jan. 14, 1959 3 Sheets-:Sheet 1 Harold W Buys July 18, 1961 w, uus 2,992,737

METHOD AND MEANS FOR VARIATION OF MAGNETIC STRENGTH OF PERMANENT MAGNETIC DRUMS Filed Jan. 14, 1959 5 Sheets-Sheet 2 92 3 90 .IEVE 2211?" Harold W. Baas 7 @kgm w jw 5 111 15 y 1961 H. w. Buus 2,992,737

METHOD AND MEANS FOR VARIATION OF MAGNETIC STRENGTH OF PERMANENT MAGNETIC DRUMS Filed Jan. 14, 1959 3 Sheets-Sheet 3 ha 22cm Ham/0 W Buus United States Patent 2,992,737 METHOD AND MEANS FOR VARIATION OF MAG- NETIC STRENGTH F PERMANENT MAGNETIC DRUMS Harold W. Buus, Hales Corner, Wis, assignor to Indiana General Corporation, a corporation of Indiana Filed Jan. 14, 1959, Ser. No. 786,873 10 Claims. (Cl. 209-223) This invention relates to a method and means for adjusting the magnetic field of magnetic separators and particularly relates to means for adjusting the useful magnetic field strength of a permanent magnet separator by adjusting the reluctance of a leakage path for magnetic flux emanating from the permanent magnet assembly of the separator.

The invention is particularly applicable to varying the magnetic field strength of permanent magnetic drums as used for either wet or dry type magnetic separations. Control of the magnetic field strength, in many separations, enables selective separation of materials of varying magnetic responsiveness and the production of either magnetic or non-magnetic products of greater purities.

In a preferred embodiment of the invention, a shorting bar or armature is provided defining an auxiliary path for magnetic lines of flux from the permanent magnet assembly. The presence of the auxiliary path of magnetic material reduces the total magnetic lines of force available in the separating zone. By controlling the amount and/ or position of the magnetic material defining the auxiliary path, the useful magnetic field strength of the separator is varied.

It is therefore an important object of the present invention to provide a simple and flexible mechanical means for varying the magnetic field strength in a magnetic separator.

A further object of the invention is to provide a permanent magnet separator of readily adjustable magnetic field strength.

Another object of the invention is to provide a permanent magnetic separator whose magnetic field over a predetermined separating zone is readily adjusted to pro vide optimum separation under varying conditions.

Other objects, features and advantages of the present invention will be apparent from the following detailed description taken in connection with the accompanying drawings, in which:

FIGURE 1 is a cross sectional view of a drum type permanent magnet separator for use in wet type separations and embodying the teachings and principles of the present invention;

FIGURE 2 is a longitudinal sectional view of the Wet type separator of FIGURE 1;

FIGURE 3 is a cross sectional view similar to FIG- URE 1 but illustrating a modified means for adjusting the useful magnetic field strength of the separator;

FIGURE 4 is a fragmentary somewhat diagrammatic perspective view of a wet type permanent magnet separator and illustrating a further modification of the present invention; and

FIGURE 5 is a cross sectional view similar to FIGURE 1 but illustrating a dry-type permanent magnetic drum separator in accordance with the present invention.

A permanent magnetic separator for wet type separations may have a slurry feed introduced to the separator by means of suitable piping for flow under a submerged lower portion of a separator drum such as indicated at 11 in FIGURE 1, the material to be separated flowing generally in the direction indicated by the arrow 12 in FIGURE 1 into proximity to the lower portion of the drum adjacent the permanent magnet assembly indicated generally by the reference numeral 13. The magnetic solids are attracted to the rotating drum surface by means of the permanent magnet assembly 13 and carried through a series of magnetic fields of successively 0pposite polarity associated with the permanent magnet assembly to final magnetic discharge as indicated by the arrow 15 in FIGURE 1. The non-magnetic solids with the bulk of the water are carried to a tailing discharge as indicated diagrammatically by arrow 16 in FIGURE 1. An operating water level may be maintained in the separating zone as indicated diagrammatically by the dash line 18, for example, with the excess water being carried oif through an overflow discharge as indicated by the arrow 20.

As is well known in the art, suitable means may be provided for confining the flow of the slurry feed introduced as indicated at 12 in FIGURE 1 to a region in close proximity to the drum periphery

adjacent poles

90, 91 and 92. The overflow indicated at 20 may be provided by a vertical wall whose top horizontal edge is at the level indicated at 18 in FIGURE 1 to prevent the liquid level from rising above this level. Suitable means is, of course, provided for collecting the concentrate which is carried by the drum above the Water level for discharge by gravity or other suitable means generally as indicated by the arrow 15.

Referring to FIGURE 2, it will be observed that the drum 11 may comprise a cylindrical shell or material conveyor 30 having an exterior surface for receiving and conveying magnetic material to be separated. The shell 3% is secured to

annular rings

34 and 35 which in turn have

end plates

36 and 37 secured thereto by means of screws such as shown at 38. The

end plates

36 and 37 are journalled on stub shafts 4t} and 41 by means of bearings such as indicated at 43 and 44-. The bearings are retained on the shaft by means of caps 47 and 48 secured to the

end plates

36 and 37 by means of screws such as 50. Suitable seals are indicated at 53, 54, and 56 for protecting the bearings. It will be understood that a sprocket wheel is secured to one of the

end plates

36 or 37 for rotating the drum 11 on stub shafts 40 and 41. Fixed supports for the stub shafts 40 and 41 are indicated diagrammatically at 60 and 61.

The fixed permanent magnet assembly designated generally by the reference numeral 13 may comprise support plates and 71 of non-magnetic material secured by means of

hubs

73 and 74 in fixed relation on the stub shafts 40 and 41. Suitable means may he provided externally of the drum 11 for adjusting the angular position of the stub shafts '40 and 41 to adjust the angular position of the magnet assembly. In operation of the separator, the stub shafts 40 and 41 are fixed. in a predeter mined angular position to maintain a predetermined fixed position of the magnet assembly such as indicated in FIGURE 1. Extending between the

support plates

70 and 71 are a series of fiat holding plates of

non-magnetic material

80, 81, 82 and 83. The

lower margins

85 and 86 of the

support plates

70 and 71 may be of arcuate configuration and define segments of a circular are about the axis of shafts 4t) and 41 so as to be concentric with the interior surface of the shell 30 and spaced from the interior surface substantially only the distance necessary to provide a clearance gap accommodating rotation of the shell 30 relative to the magnet assembly. It will be observed in FIGURE 1 that the holding plates 80-83 define chords of the circular arc defined by the margin 85, so that the holding plates 80-83 are substantially as close as possible to the interior surface of the shell 30.

Also extending between the

support plates

70 and 71 and secured thereto are a series of magnetic pole pieces designated generally by the

reference numerals

90, 91, 92, 93 and 94 formed of strips -118 of magnetic material. It will be observed from FIGURE 1 that the

inner pole pieces

91, 92 and 93 are of generally triangular configuration as seen in cross section. These pole pieces may be formed of a single solid wedge-shaped piece of magnetic steel if desired. By forming the pole pieces of plates or strips such as 102, 103, 104, 105 and 106 for the pole piece 91 which are welded into the triangular configuration, a reduction in the overall weight is achieved and the amount of machining required to form the poles is reduced. Tests have shown that the welded plate type pole piece as shown in FIGURE 1 has sufficient cross sectional area to carry the total flux introduced into these poles by the permanent magnets. It will be observed that the lower margins of the pole pieces are substantially as close to the inner peripheral surface of the shell 30 as possible while still providing the necessary clearance gap as with the holding plates 80-83.

As illustrated, the permanent magnet assemblies are provided by stacks of permanent magnet units such as indicated at 130 of standardized dimensions. In the illustrated embodiment, the permanent magnets are ar ranged in two layers in the radial direction and two rows of stacks in each layer as seen in FIGURE 2. Cover plates are indicated at 131, 132, 133 and 134 in FIGURE 1 extending between the

support plates

70 and 71 and providing covers for the permanent magnets between the successive sets of pole pieces.

In the illustrated embodiment each of the permanent magnet units 130 of a given stack'are magnetized in the same direction through the thickness dimension of the permanent magnet slabs so as to provide directions of magnetization as indicated by

arrows

150, 151, 152 and 153 in FIGURE 1. With these directions of magnetization,

pole pieces

90, 92 and 94 may be considered of south magnetic polarity, While

pole pieces

91 and 93 may be considered of north magnetic polarity. In the illustrated embodiment, all of the permanent magnet units between a given set of pole pieces are magnetized in the same direction to give a magnetic field of the same polarity along the axial length of the drum at the exterior surface of the shell. Material carried along by the exterior surface of the shell during rotation of the drum thus experiences successively a south pole at 90, a north pole at 91, a south pole at 92, a north pole at 93 and a south pole at 94, after which the magnetic material is no longer attracted to the drum surface and is discharged as indi cated by the arrow in FIGURE 1.

It is found highly advantageous to utilize ceramic permanent magnet material for the units 130 such as known by the trademark Indox V. The utilization of permanent magnet materials for the energization source of the magnet assembly is, of course, a distinctive advantage as compared to electromagnetic energization, since no external source of electrical energy is required. The utilization of Indox V ceramic permanent magnets provides an improved energy source, enabling utilization of the total magnetic energy much more efiiciently than prior art structures. The Indox V ceramic permanent magnet units can be suitably made into one specific standard shape enabling the use of multiple numbers of this one shape in various arrangements to eificiently construct magnetic separators of ditferent widths, of different diameter and of different magnetic intensities and field distributions.

A preferred system for varying the magnetic field strength is shown in FIGURES 1 and 2 as comprising a shorting armature or bar 170 mounted by means of a shaft 171 carried within the stub shafts 40 and 41 by means of

bearings

173, 174 and 175. The armature 170 is supported with the shaft 171 by means of

support plates

176 and 177.

Plates

176 and 177 are secured to the shaft 171 by means of collars 180' and 181

receiving keys

183 and 184 which extend into cooperating key ways in the collars and in the shaft 171. Set screws are indicated at and 191 for retaining the keys. An adjusting handle 195 may be provided at the outer end of shaft 171 for adjusting the angular position of the armature 170 relative to the permanent magnet assembly 13.

The armature 170 may comprise a plate of magnetic material such as mild steel curved on a decreasing radius so as to provide shunt paths for magnetic flux from the respective permanent magnet stacks of different reluctance. For example, in the position of the armature 170 shown in FIGURE 1, a portion of the armature is relatively closely spaced to

pole piece plates

106 and 107 to provide a relatively large shunting effect between

poles

91 and 92, thereby decreasing the useful magnetic field strength between these poles at the exterior of the drum. The reluctance of the shunt path is substantially greater between

poles

93 and 94 to provide a maximum field strength between poles 93- and 94 at the exterior surface of the drum 11.

Since the armature is curved on a decreasing radius, it is possible to vary the distance between the armature and the radially inner extremities of strips 101, 102-, 106, 107, 111, 112, 116 and 117 by rotation of the armature. FIGURE 1 shows the armature in three of its possible positions. In the position shown in solid lines in FIG- URE 1, the armature is in close proximity to the poles shorting out the maximum amount of magnetic flux, and thereby providing the minimum magnetic field strength at the exterior surface of the drum. In the position indicated in dot-dash outline at 170a, the armature is positioned substantially out of the influence of the magnetic poles, thereby providing the maximum field intensity at the surface of the drum. The position indicated at 17012 is an intermediate position, shorting out only a small amount of the magnetic flux of the first three

poles

90, 91 and 92, and giving only a slight reduction of the magnetic intensity at these poles with respect to the exterior surface of the drum. The armature may, of course, be positioned in any orientation between the solid line position and the positions indicated at 17% and 17011 to vary the working magnetic field strength anywhere between full strength corresponding to the position indicated at 170:: to a 60% reduction of working magnetic field strength in the position shown in solid lines in FIG- URE 1.

In operation of the embodiment of FIGURES 1 and 2, the cylinder 30 is rotated in the clockwise direction as indicated by arrow 197 and material is fed beneath the first pole 90. Magnetic material is lifted to the rotating cylinder 30 and transported from pole to pole for ultimate discharge upon leaving the influence of the last magnetic pole 94. Experience has shown that the greatest control of quality of magnetic separation occurs in the initial magnetic pick-up zone or through the area of the first three

magnetic poles

90, 91 and 92. This, therefore, is the zone in which the maximum control of magnetic field strength is desired. The last two

poles

93 and 94 are used for transportation of the magnetic material to eventual discharge, so that it is desired to have less reduction of field strength at these last two discharge poles. The configuration of the shorting armature as shown in FIGURE 1 provides the maximum variable control in the initial pick-up zone at poles 90-92. The leakage flux paths between the successive poles are indicated by

arrows

200, 201, 202 and 203, and it will be observed that the reluctance of the shunt flux paths may be substantially continuously varied over a relatively wide range by adjusting the angular position of the armature 170.

FIGURE 3 illustrates a modified armature 210 of magnetic material formed on substantially a constant radius, but with portion 210a thereof having a substantially greater thickness than portion 210!) and portion 21% having substantially twice the thickness of portion 2100 to provide a variable reluctance in the shunt'magnetic paths i dicated by arrows 200-203 in FIGURE 1. FIG- URE 3 is otherwise identical to FIGURE 1, and corresponding reference numerals have been applied to similar parts.

In FIGURE 4, a shorting armature 220 of magnetic material is illustrated which may be formed on a constant radius, but wherein the reluctance of the shunt paths is made variable by virtue of the serrated shape of the armature which provides a progressively decreasing cross sectional area at the regions 220a of the armature. It is also possible to accomplish a variation in the magnetic field strength by mounting the armature of FIGURES 1, 3 or 4 for movement toward or away from the permanent magnet assembly. In this case, the armature would not need to rotate about an axis, but would be mounted in such a manner as to be translated as a unit in a direction along a diameter of the drum, for example.

FIGURE 5 illustrates a second embodiment of the present invention which is generally similar to the embodiment of FIGURES 1 and 2, but involves a dry process for concentrating magnetic materials. In this embodiment, a drum 250 may have the same general construction and mounting as illustrated in FIGURE 2 and may rotate in the direction indicated by arrow 251. Material to be separated in a dry form is delivered by suitable means such as diagrammatically indicated at 253 onto the drum at the top thereof in the direction indicated by arrow 255. The separator may be provided with adjustable division vanes for separating the material falling from the surface of the drum into three discharge streams as indicated by

arrows

260, 261 and 262 in FIG- URE 5.

The permanent magnet assembly designated generally by the reference numeral 270 may be of the same construction described in detail in reference to FIGURE 1 to provide a succession of poles of alternating polarity designated by the reference numerals 280-288. The permanent magnet assembly is essentially the same as that illustrated in FIGURE 1, except that additional stacks of permanent magnet units 130 and additional triangular pole pieces are provided to increase the peripheral extent of the permanent magnet assembly. As described in connection with FIGURE 1, the magnetic poles are each of the same polarity and of uniform strength across the entire axial extent of the drum. In operation, the feed falls on the revolving drum at the first magnetic pole 280 and as it does it receives a definite magnetic polarity. The second magnet pole 281 has a reverse polarity from the first, and as the material passes the second pole, the magnetically responsive fraction of the feed tends to shift and reorient itself. This agitation and reorientation releases some of the entrapped non-magnetic material and permits it to fall free as indicated by arrow 260. The process is then repeated for the third and succeeding magnet poles, and each provides a further magnetic material movement and cleaning. The results is an exceptionally clean magnetic product coming from the concentrate zone as indicated by the arrow 262. The material which does not discharge as tailings as indicated by arrow 260 and yet is not sufficiently magnetic to concentrate may be independently obtained in a middling zone indicated by arrow 261.

As in the embodiment of FIGURES 1 and 2, the permanent magnet assembly preferably comprises stacks of permanent magnet units or slabs.130 of Indox V ceramic material arranged in layers and rows between triangular pole pieces, with the stacks between each set of pole pieces magnetized through their thickness direction as indicated by arrows 290-297 in FIGURE 5.

The leakage flux paths between the successive poles are indicated by arrows 300-307, and as in the embodiment of FIGURE 1, an armature 320 of magnetic material is mounted on a central shaft 321 so as to be angularly adjustable to vary the reluctance of the shunt magnetic flux paths and thereby vary the strength of the working 6 fields between the successive poles at the periphery of the drum.

In the dry magnetic separator of the type shown in FIGURE 5, maximum removal of non-magnetic material and purification of the magnetic material. occurs as the magnetic material is transported by the rotating cylinder beyond the horizontal center line, so that non-magnetic material may drop away by gravity. Therefore, with this type of magnetic separator, the greatest control of magnetic strength is desired in the lower or discharge zone of the magnetic assembly represented by poles 284288. The orientation of the decreasing radius of the shorting armature 320 is therefore opposite to that shown in FIGURE 1 with the radius increasing in the direction of drum rotation in FIGURE 5 rather than decreasing in the direction of drum rotation as in FIGURE 1. This enables a variation of magnetic field strength from the position of minimum magnetic field of the armature shown in solid lines in FIGURE 5 through an intermediate position shown at 320a to a position of maximum working field strength indicated at 32%.

In the commercial application of this invention, some designs have the Indox V magnets operating at a permeance coefficient near the knee of the demagnetization curve. If the magnets are then subjected to low temperatures in shipment or at the operating site, it is possible that the magnets will have a permanent flux drop unless suitable precautions are provided to guard against this flux drop.

The use of the adjustable armature is an excellent precaution against this fiux drop. With the armature in position to provide an auxiliary path for the magnetic flux, the permeance coefficient of the magnets is raised sufliciently above the knee of the demagnetization curve, enabling the magnets to be subjected to temperatures as low as minus 40 F. without experiencing any drop in magnetic flux.

It will be apparent that many modifications and variations may be effected without departing from the scope of the novel concepts of the present invention.

I claim as my invention:

1. In a magnetic separator comprising a conveyor having a surface for receiving material to be separated and a magnet assembly for tending to attract magnetic material toward the conveyor surface for movement therewith to separate the same from non-rnagnetic material, the improvement characterized by means defining a shunt magnetic flux path for magnetic flux from said magnet assembly, and means for adjusting the reluctance of said shunt magnetic flux path without substantially changing the reluctance of the working magnetic flux path of the magnet assembly to adjust the strength of the magnetic field provided by said magnet assembly at the surface of said conveyor.

2. In a magnetic separator comprising a conveyor having a surface for receiving material to be separated and a magnet assembly for tending to attract magnetic material toward the conveyor surface for movement therewith, the improvement characterized by means defining a magnetic flux path of magnetic material at the side of the magnet assembly remote from the conveyor for shunting a predetermined proportion of the magnetic =fiux of said magnet assembly away from the working flux path at said conveyor surface and for selective positioning at a plurality of positions relative to said magnet assembly.

3. In combination with a magnetic separator drum mounted for rotation on a longitudinal axis and a permanent magnet assembly mounted at a fixed angular position within said drum, an armature of magnetic material disposed in said drum in proximity to said permanent magnet assembly, and means for selectively positioning said armature at a plurality of positions for adjusting the reluctance of the magnetic leakage path including said armature for magnetic flux from said permanent magnet assembly while the reluctance of the working magnetic flux path of the permanent magnet assembly remains sub- 'stantially the same.

4. In combination with a conveyor for receiving material to be separated and a magnet assembly for tending to attract magnetic material toward the conveyor for movement therewith, the improvement characterized by an armature of magnetic material disposed adjacent said permanent magnet assembly within the influence of the magnetic field thereof, and means for adjustably mounting said armature to adjust the strength of the useful magnetic field of said magnet assembly.

5. In a magnetic separator comprising a conveyor for receiving and transporting material to be separated and a magnet assembly for tending toattract magnetic material toward the conveyor for movement therewith, said mag net assembly comprising spaced pole pieces extending generally transversely to the conveyor from a point adjacent the inner surface of the conveyor to a point more remote from the conveyor, a series of permanent magnet slabs stacked between the successive pole pieces and magnetized generally in the direction of movement of the conveyor, and means of magnetic material disposed within the magnetic field between the successive pole pieces at the sides thereof remote from said conveyor for diverting magnetic flux from the working flux path of the magnet assembly and for selective positioning at a plurality of positions relative to said poles to selectively adjust the leakage reluctance therebetween.

6. In a magnetic separator comprising a conveyor for receiving and transporting material to be separated and a magnet assembly for tending to attract magnetic material toward the conveyor for movement therewith, said magnet assembly comprising spaced pole pieces extending generally transversely to the conveyor from a point adjacent the inner surface of the conveyor to a point more remote from the conveyor, a series of permanent magnet slabs stacked between the successive pole pieces and magnetized generally in the direction of movement of the conveyor, and means of magnetic material disposed within the magnetic field between the successive pole pieces at the sides thereof remote from said conveyor for diverting magnetic flux from the working flux path of the magnet assembly, and means for adjustably mounting said means of magnetic material to adjust the strength of the useful magnetic field from said permanent magnet assembly.

7. In combination, a magnetic separator drum of nonmagnetic material, a pair of stub shafts mounting said drum for rotation on a longitudinal axis, a permanent magnet assembly mounted within said drum from said stub shafts for angular adjustment by means of rotation of said stub shafts, an armature of magnetic material mounted at the inner side of said permanent magnet assembly for adjusting the useful magnetic field strength thereof, and a shaft extending within one of said stub shafts and mounting said armature for adjustment relative to said permanent magnet assembly to adjust the useful magnetic field strength thereof.

8. In combination, a magnetic separator drum of nonmagnetic material, a pair of stub shafts mounting said drum for rotation on a longitudinal axis, a permanent magnet assembly mounted within said drum from said stub shafts, for angular adjustment by means of rotation of said stub shafts, an armature of magnetic material mounted at the inner side of said permanent magnet assembly for adjusting the useful magnetic field strength thereof, and a shaft extending within one of said stub shafts and mounting said armature for adjustment relative to said permanent magnet assembly to adjust the useful magnetic field strength thereof, said armature comprising a strip of magnetic material of curved configuration and of decreasing radius.

9. In combination, a magnetic separator drum of nonmagnetic material, a pair of stub shafts mounting said drum for rotation on a longitudinal axis, a permanent magnet assembly mounted within said drum from said stub shafts for angular adjustment by means of rotation of said stub shafts, an armature of magnetic material mounted at the inner side of said permanent magnet assembly for adjusting the useful magnetic field strength thereof, and a shaft extending within one of said stub shafts and mounting said armature for adjustment relative to said permanent magnet assembly to adjust the useful magnetic field strength thereof, said armature comprising a curved piece of magnetic material of progressively varying thickness.

10. In combination, a magnetic separator drum of nonmagnetic material, a pair of stub shafts mounting said drum for rotation on a longitudinal axis, a permanent magnet assembly mounted within said drum from said stub shafts for angular adjustment by means of rotation of said stub shafts, an armature of magnetic material mounted at the inner side of said permanent magnet assembly for adjusting the useful magnetic field strength thereof, and a shaft extending within one of said stub shafts'and mounting said armature for adjustment relative to said permanent magnet assembly to adjust the useful magnetic field strength thereof, said armature comprising a curved plate of magnetic material having V- shaped notches therein to provide a progressively decreasing longitudinal cross section at one end thereof.

References Cited in the file of this patent UNITED STATES PATENTS 1,324,529 Ulh'ich Dec. 9, 1919 2,785,801 Laurila Mar. 9, 1957 FOREIGN PATENTS 461,816 Great Britain Feb. 25, 1937