US3887458A

US3887458A - Permanent magnet strong field separator

Info

Publication number: US3887458A
Application number: US362305A
Authority: US
Inventors: Erkki A Laurila
Original assignee: BERMECO Oy
Current assignee: BERMECO Oy
Priority date: 1972-05-26
Filing date: 1973-05-21
Publication date: 1975-06-03
Anticipated expiration: 1992-06-03
Also published as: DE2325322C3; CA990686A; FI48535C; NO134934B; FI48535B; DE2325322A1; SE384146B; NO134934C; DE2325322B2

Abstract

For concentrating particularly weakly magnetic minerals there is provided a rotating cylinder or drum having at its circumference a number of magnetic pole gaps created by pole shoes and adjacent permanent magnets having a great coercive force. Inside the cylinder there is provided a separate permanent magnet system causing an essential change in the magnetic field within the gaps as the section in question of the cylinder circumference passes a certain point. Said change in the field releases the magnetic material attached to the cylinder by the magnetic force. The separate magnet system preferably comprises a second cylinder provided with magnets at equal distances from each other as those at the outer working cylinder and rotating in synchronism with said outer cylinder.

Description

United States Patent Laurila June 3, 1975 PERMANENT MAGNET STRONG FIELD SEPARATOR Primary Examiner-Robert Halper Attorney, Agent, or Firm-Browdy and Neimark [75] Inventor: Erkki A. Laurila, Helsinki, Finland Bermeco 0y, Helsinki, Finland May 21, 1973 [57] ABSTRACT For concentrating particularly weakly magnetic miner- [73] Assignee:

Filed:

Appl.

,305 als there is provided a rotating cylinder or drum having at its circumference a number of magnetic pole gaps created by pole shoes and adjacent permanent [30] Foreign Application Priority Data May 26, l972 Finland.....

magnets having a great coercive force. Inside the cyl 1436/72 inder there is provided a separate permanent magnet system causing an essential change in the magnetic field within the gaps as the section in question of the cylinder circumference passes a certain point. Said 02 a 3 1 B Q12 9 0 &3 2N w "m m a m in "m0. 9 "0 m nmf L C min UI-F 111 2 oo 555 [ll change in the field releases the magnetic material at- 209/220 tached to the cylinder by the magnetic force. The separate magnet system preferably comprises a second cylinder provided with magnets at equal distances from each other as those at the outer working cylinder and rotating in synchronism with said outer cylinder.

335/295 lsraelson.................v...... 335/295 x Clams 2 Drawmg F'gures 3,223.898 3,231,789 l/l966 Engelsted.... 3,4523 I0 6/1969 PERMANENT MAGNET STRONG FIELD SEPARATOR BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to magnetic separators and more particularly to separators for weakly magnetic minerals, wherein concentrating takes place at the circumference of a rotating cylinder or drum.

2. Description of the Prior Art The attraction ofa magnetic field on a ferromagnetic or paramagnetic particle is known to be proportional to the product of the absolute value H of the magnetic field strength and its gradient, i.e., the quantity [Hl grad lH l Thus, the separators used for separating weakly magnetic minerals must have both a strong field, which is the reason for the name strong field separator, and means with which this field can be strongly reversed at appropriate points, while the separation of strongly ferromagnetic materials is easier.

In one known apparatus for separating the latter materials, concentrate is fed onto the circumference of a rotating cylinder which has been provided with permanent magnet bars at regular intervals so that their magnetic fields are radial and alternately reverse. The magnetic material is separated by means of a smaller cylinder which has been fitted outside the principal cylinder and rotates synchronically with it. The peripheral surface of the smaller cylinder has been respectively fitted with iron rods which, when coming close to the said permanent magnet bars, momentarily strengthen the magnetic field and cause the magnetic material to pass from the surface of the cylinder provided with magnet bars onto the separation cylinder, from where the said strongly magnetic part is then recovered.

The known separators for weakly magnetic materials have usually been provided with electric magnets to provide a sufficiently extensive field. In addition, these separators have been provided with some moving part which, when it is in the magnetic field, causes the field to converge at certain points and, when it comes outside the range of the field, loses its magnetism, thereby making it possible for the magnetic mineral which has become attached to the convergence points to become detached.

SUMMARY OF THE INVENTION The present invention provides a magnetic separator of the character previously described, comprising a rotating cylinder or drum on the outer surface of which the concentrate is separated,

a number of pole gaps created on the cylinder surface by means of pole shoes linked to magnetic possessing a great coercive force, and

a separate multi-pole system with permanent magnets provided inside said cylinder for causing an essential change of the magnetic field within the pole gaps as they pass a certain point at the cylinder circumference.

The object of the present invention is thus a strong field separator structure in which the magnetic field is created with permanent magnets. In principle, any permanent magnet materials with a sufficiently high energy product are practicable, but it is essential to resort to oxide magnets which are magnetically hard, i.e., possess a great coercive force. For example, ceramic barium ferrite and strontium ferrite magnets, such as Ferroxdure 330, Indox 5, lndox 8 etc., already make a very practical structure possible, but the construction principle set forth in the invention proves even more advantageous when, for example, CoSm or other lanthanide magnets with a coercive force of more than 5000 Oe and an efficiency of IO 20 million GsOe are used.

Thus. according to the invention, a great number of pairs of poles, in the field between which the quantity IHl grad [H l is high, are created with such magnets in the working area, such as a cylinder surface. The essential point of the invention is the arrangement by which the magnetic field, at an appropriate stage, is entirely extinguished or at least weakened to the extent that the weakly magnetic mineral concentrate which has become attached to the field can be released. In some cases it may be advantageous even to momentarily reverse the magnetic field at the concerned point at the cylinder circumference.

This change of the magnetic field, or actually the conduction of the flux along another path, takes place according to the invention with the help of a reversely magnetized system consisting of permanent magnets. The system may preferably include another cylinder which is situated inside the working cylinder, rotates synchronically with it, and touches or very nearly touches it at an appropriate point and which has been respectively provided with magnetic poles at the same intervals as on the working cylinder.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I shows an apparatus according to the invention with two cylinders linked to each other one inside the other, and

FIG. 2 shows a detail of FIG. 1 on an enlarged scale.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the apparatus according to the figures, the actual working unit consists of a cylinder 1 which has a relatively long diameter and rotates in the direction indicated by the arrow. Pole gaps parallel to the side line of the cylinder have been created on the cylinder surface according to the construction principle indicated in the figure. It would also be possible to make the pole gaps parallel to the cylinder circumference. The active parts are permanent magnets 2 made of an oxide or Ianthanide magnet material and which are alternately magnetized in reverse directions. T-shaped iron rails 3 form the pole shoes; a sufficiently strong field strength can be obtained in the narrow gaps between the pole shoes, for example over 10 k0, while the field gradient receives a very high value. When some granular material or suspension is fed onto the cylinder surface, ferromagnetic and paramagnetic particles become attached to the cylinder surface at the pole gaps. By using blowing, or water sprays when a suspension is concerned, a considerable portion of the accompanying non-magnetic material can be removed so that finally only a relatively pure concentrate remains attached to the pole gaps. FIG. 1 illustrates the feeding of suspension with feeding trough 4, the suspension outlet with its thresholds 5 where the concentrate particles which remain in the outflowing suspension still have an opportunity to become attached to the magnetic field of the cylinder, and washing system 6 consisting of water sprays. It is natural that in this wet separator the rotative velocity of the cylinder is so low that the water and suspension flow downwards against the rotational direction of the cylinder. The concentrate which has become attached at the magnet gaps between the pole shoes on the cylinder surface is removed with second magnetic cylinder 7. Magnets 8 (FIG. 2) have been provided on its circumference so that the mutual distance between their pole shoes 9 or magnet ends is the same as the distance between pole shoes on the surface of cylinder 1. When the cylinders rotate in the directions indicated by arrows, opposite poles will always face each other. As explained in more detail in the description relating to FIG 2, the field then disappears from the magnet gap between pole shoes 3 when permanent magnet 2 is in the position closest to the surface of cylinder 7, if magnets 8 of cylinder 7 have appropriate dimensions. This appropriate dimensioning can be calculated on the basis of the general theory concerning magnetic circuits. The magnetic potential corresponding to the state of magnets 8 at a given moment must be sufficient to create the necessary flux over the magnet gap between the cylinders. The width of the pole shoe 3 edges inside and in a tangential direction of the cylinder 1 is chosen to be more than l/n of the width of permanent magnets 2 measured in the direction of cylinder 1 radius, where n indicates the ratio between the saturation induction of the pole shoe material and the remenant induction of the permanent magnet material. When the field disappears in a magnet gap between pole shoes 3, the concentrate attached to it becomes detached either owing to centrifugal force (in dry separators) or in the manner indicated in the figure with the help of water spray ll directed from between bridge l and the surface of cylinder 1. The detached concentrate is then removed along bridge 10.

To diminish constructional problems, the diameter of cylinder 7 is preferably less than half the inner diameter of cylinder 1. The placement of counter-cylinder 7 inside the working cylinder provides mainly two advantages which are closely linked to each other. The magnet gap between the cylinders can then be small and the extinction of the magnetic field in the pole distances on the cylinder surface can be achieved without the magnets of cylinder 7 having to become unreasonably oversized. Constructionally it is also very advantageous that there are no devices which inconvenience the flow and treatment of material on the outer surface of the cylinder or in its vicinity. This would be the case if the counter-cylinder were placed outside the working cylinder. FIG. 2 shows an enlarged section of the contact point between the cylinders. The arrows indicate the directions of the the internal magnetic fields of permanent magnets 2 of outer cylinder 1 and permanent magnets 8 of inner cylinder 7. When the point in question on the outer cylinder is far from the circumference of the inner cylinder, the magnetic path on the outer cylinder is closed mainly owing to the narrow magnet gap between the expanded ends of pole shoes 3. When, again, the point in question comes essentially in contact with the magnets on the circumference of the inner magnets, as shown in the figure, these two magnet systems form a closed magnet circuit, i.e., the entire flux of a working cylinder magnet runs through the respective counter-cylinder magnet, and thereby the flux and field in the magnet gap on the cylinder surface are extinguished. By an appropriate dimensioning of the magnets and the poles the flux in the said magnet gaps can even become momentarily reversed.

One prerequisite for an appropriate operation is now that the flux corresponding to the remanent induction of the magnets on cylinder 7 is greater than the flux corresponding to the remanent induction of magnets 2. The continuous attraction between opposite magnetic poles ensures the synchronic rotation of cylinders l and 7.

What is claimed is:

1. A permanent magnet separator particularly for separating weakly magnetic materials from nonmagnetic materials, comprising:

a first hollow rotating cylinder, having inner and outer surfaces, composed of a plurality of substantially rectangular solid permanent magnets each arranged in a parallel relation to the side line of said cylinder and a plurality of pole pieces each substantially identically shaped and spaced intermediate said permanent magnets, thereby forming on said inner surface alternate substantially parallel sections consisting of said magnets and pole pieces, said permanent magnets being alternately reversely magnetized; and

shunting means, including a separate rotating multipole permanent magnet eccentrically mounted within said first cylinder, for shunting the magnetic field of said pole pieces of said first cylinder by cooperation between said shunting means and said pole pieces of said first cylinder as said pole pieces of said first cylinder come into a certain position in relation to said shunting means;

said separate permanent magnet comprising a second rotating cylinder with alternating reversely magnetized permanent magnets and pole pieces in which the distance between the magnetic pole pieces is the same as the distance between the magnetic pole pieces of said inner surface and wherein the remanent flux of said permanent magnets on said second cylinder is greater than the remanent flux of said permanent magnets on said first cylinder, said second cylinder being synchronized with said first cylinder so that said magnetic pole pieces thereof always face oppositely magnetized pole pieces on said first cylinder at said certain position.

2. The separator of claim 1, wherein the width of each of said pole pieces inside and in tangential direction of said first cylinder is more than 1/n of the width of each of said permanent magnets measured in the direction of said first cylinder radius, where it indicates the ratio between the saturation induction of the pole shoe material and the remenant induction of the permanent magnet material.

3. A separator according to claim 1, wherein said magnets on said first and second cylinders are oxide permanent magnets.

4. The separator of claim 3 wherein said oxide permanent magnets are composed of barium ferrite.

5. The separator of claim 3 wherein said oxide permanent magnets are composed of strontium ferrite.

6. A separator according to claim 1, wherein said magnets on said first and second cylinders are lanthanide permanents magnets.

7. A separator according to claim 1, wherein the magnetic strength of said permanent magnets of said second cylinder in relation to the magnetic strength of said permanent magnets of said first cylinder is such that shunting essentially weakens the magnetic field of said pole pieces of said first cylinder at the said certain position.

8. A separator according to claim 1, wherein the magnetic strength of said permanent magnets of said second cylinder in relation to the magnetic strength of said permanent magnets of said first cylinder is such that shunting essentially extinguishes the entire magnetic field of said pole pieces of said first cylinder at the said certain position.

9. A separator according to claim 1, wherein the magnetic strength of said permanent magnets of said second cylinder in relation to the magnetic strength of said permanent magnets of said first cylinder is such that shunting momentarily makes the magnetic field of said pole pieces of said first cylinder weakly reverse at the said certain position.

10. The separator of claim 1 wherein the said pole pieces on said first cylinder are formed in substantially the shapes of a T and are arranged in a spaced relation to the said solid rectangular permanent magnets such that the cross of the T's form the outer circumference of the said first cylinder and said crosses of said T's of adjacent ones of said pole pieces do not abut one another, thereby forming with said permanent magnets substantially parallel slots in the outer surfaces of said first cylinder.

Claims

1. A permanent magnet separator particularly for separating weakly magnetic materials from non-magnetic materials, comprising: a first hollow rotating cylinder, haviNg inner and outer surfaces, composed of a plurality of substantially rectangular solid permanent magnets each arranged in a parallel relation to the side line of said cylinder and a plurality of pole pieces each substantially identically shaped and spaced intermediate said permanent magnets, thereby forming on said inner surface alternate substantially parallel sections consisting of said magnets and pole pieces, said permanent magnets being alternately reversely magnetized; and shunting means, including a separate rotating multipole permanent magnet eccentrically mounted within said first cylinder, for shunting the magnetic field of said pole pieces of said first cylinder by cooperation between said shunting means and said pole pieces of said first cylinder as said pole pieces of said first cylinder come into a certain position in relation to said shunting means; said separate permanent magnet comprising a second rotating cylinder with alternating reversely magnetized permanent magnets and pole pieces in which the distance between the magnetic pole pieces is the same as the distance between the magnetic pole pieces of said inner surface and wherein the remanent flux of said permanent magnets on said second cylinder is greater than the remanent flux of said permanent magnets on said first cylinder, said second cylinder being synchronized with said first cylinder so that said magnetic pole pieces thereof always face oppositely magnetized pole pieces on said first cylinder at said certain position.

2. The separator of claim 1, wherein the width of each of said pole pieces inside and in tangential direction of said first cylinder is more than 1/n of the width of each of said permanent magnets measured in the direction of said first cylinder radius, where n indicates the ratio between the saturation induction of the pole shoe material and the remenant induction of the permanent magnet material.