WO1998029190A1

WO1998029190A1 - Powder separation

Info

Publication number: WO1998029190A1
Application number: PCT/GB1998/000019
Authority: WO
Inventors: Stephen Fawell; Paul Genner
Original assignee: ERIEZ MAGNETICS EUROPE Ltd
Current assignee: ERIEZ MAGNETICS EUROPE Ltd
Priority date: 1997-01-03
Filing date: 1998-01-05
Publication date: 1998-07-09
Anticipated expiration: 1999-07-03
Also published as: AU5335198A; GB9700081D0

Abstract

In a method of separating a mixture of powders ferromagnetic and non-ferromagnetic materials, the powder mixture passes onto a curved surface which extends over a rotating, cylindrical magnet assembly (16) which comprises a plurality of magnets disposed one after another around the circumference of the assembly, with adjacent magnets presenting alternate poles radially outwards. The powder mixture may be poured onto a conveyor belt (10) trained around a drum (12) concentric with the assembly (16) the belt (10) carries the powder mixture around the upper part of the assembly (16), where it is separated into respective components (20, 22).

Description

POWDER SEPARATION

The present invention relates to a method of separating a mixture of ferromagnetic and non-ferromagnetic powders into their components.

There are various situations in which powders of ferromagnetic and non-ferromagnetic material become mixed together and it is required to separate these. For example, various powders may become contaminated by the presence of ferromagnetic material, particularly iron or steel powder: typically this occurs in the manufacture or processing of powder, due to abrasion of the apparatus being used.

A number of methods have been used hitherto to separate the ferromagnetic (typically iron or steel) powder from the non-ferromagnetic powder being manufactured or processed. One such method uses a grating formed of a plurality of elongate magnet assemblies mounted parallel to each other and spaced apart horizontally: the powder mixture is poured through this grating, the ferromagnetic powder adhering to the magnet assemblies and the non-ferromagnetic material falling through; the separator typically comprises several such gratings mounted one-above-the-other and deflectors are provided to deflect the falling powder mixture to flow over the individual magnet assemblies.

Another known method uses a matrix through which the powder mixture is poured, the matrix being encircled by an electromagnet coil and vibrated by a vibratory drive. The flux produced by the electromagnet is concentrated by the matrix, to cause the ferromagnetic powder to be captured by the matrix.

A further known powder separation method uses a horizontally-mounted drum over which the powder mixture is poured. The drum encloses a permanent magnet: the non- ferromagnetic powder flows over the surface of the drum for part of its circumference and then drops vertically, whilst the ferromagnetic powder is attracted towards the permanent magnet and is held to the surface of the drum for a greater proportion of its circumference before dropping.

However, the above-described separators are of limited effectiveness. A particular problem is that a ferromagnetic particle may be surrounded by non-ferromagnetic particles, such that if the magnetic field of the apparatus is insufficiently strong to retain the overall clump of particles, the whole is passed as if it were non-ferromagnetic. Also, the first two of these separators require additional steps to remove the ferromagnetic powder from the grating or matrix to which it becomes adhered.

We have now devised a method of separating a mixture of ferromagnetic and non-ferromagnetic powders, which is substantially more effective than the above-described methods and does not require additional steps to clean the separator of retained magnetic powder.

In accordance with the present invention, there is provided a method of separating a mixture of powders of ferromagnetic and non-ferromagnetic materials, the method comprising providing a cylindrical magnet assembly which is mounted with its axis horizontal and comprises a plurality of magnets disposed one-after-another around the circumference of said assembly, adjacent said magnets presenting alternate poles radially outwards, rotating said cylindrical magnet assembly around its axis, providing a curved surface which is concentric with said cylindrical magnet assembly and extends at least over an arc of 90° from a point vertically above said axis to a point horizontally aligned with said axis, and causing said powder mixture to move onto said curved surface at its upper region and then move downwardly in a path which follows said surface.

In use of this method, we find that the non- ferromagnetic powder falls more or less vertically downwards when it reaches the point of the curved surface which is horizontally aligned with the axis of the rotating cylindrical magnet assembly. However, the ferromagnetic powder is attracted radially inwards by the magnets, and does not drop from the curved surface until it has travelled to a lower angular position. The non-ferromagnetic and ferromagnetic powders can therefore be collected in separate outlets.

The curved surface may comprise a fixed surface onto which the mixed powder is poured, and over which the mixed powder then slides. Preferably however, the curved surface comprises a drum which is coaxial with the cylindrical magnet assembly, and is rotated in the direction of required movement of the powder. Instead, an endless belt may be trained over a drum and a roller spaced from that drum, the drum being coaxial with the cylindrical magnet assembly: the mixed powder is then poured onto the upper run of the belt, and is then conveyed up to and around the drum.

We have found that this method is very effective in separating mixtures of ferromagnetic and non-ferromagnetic powders of less than 250 micron (and particularly less than 100 micron) particle size. The method is particularly effective in breaking up "clumps" of mixed powders: we believe that this is because, in moving in the curved path coaxial with the cylindrical magnet assembly, the powder is strongly agitated due to the rapidly changing magnetic field to which it is subjected; thus, as the magnet assembly rotates, the magnetic field at each point reverses alternately as the successive permanent magnets pass that point. Preferably the cylindrical magnet assembly is rotated in the opposite direction to the movement of the powder.

Preferably the rotation of the cylindrical magnet assembly produces 500 to 50,000 pole changes per minute. For example, an assembly having 22 magnets disposed one-after- another around its circumference and rotating at 1500 r.p. ., produces 33,000 pole changes per minute. Most preferably the magnet assembly produces 22,000 to 44,000 pole changes per minute.

We have used a magnet assembly of 22 magnets and 12 inch diameter. We have also used a magnet assembly of 10 magnets and 5 inch diameter. In general, the magnet assembly may be of any desired diameter and number of magnets.

The method is intended for use with dry powder but may also be used where the powder is damp. In order to improve the effectiveness of the method, one of the component powders separated by the rotating magnet assembly is guided to a second rotating magnet assembly, which performs a second stage of separation. Likewise, one or more further rotating magnet assemblies may be provided to perform further stages of separation.

An embodiment of the present invention will now be described by way of example only and with reference to the accompanying drawings, in which: FIGURE 1 is a diagrammatic side view of one embodiment of separation for use in carrying out a method in accordance with the invention; and

FIGURE 2 is a diagrammatic plan view of the separator of Figure 1. Referring to the drawings, there is shown a powder separator apparatus which comprises an endless belt 10 trained around a rotatable drum 12 and a roller 14 which are mounted with their axes parallel to each other and horizontally spaced- apart. An electric motor 13 is provided to drive the roller 14 and hence the belt 10 in the direction shown by the arrow A. Within the drum 12, and disposed coaxially with it, is a magnet assembly drum 16 which comprises a plurality of permanent magnets positioned one-after-another around the circumference of the drum, with adjacent magnets presenting alternate poles (N,S) to the outer surface of the drum. An electric motor 17 is provided for rotating the magnet assembly drum 16 in the direction indicated by the arrow B. It will be noted that the direction of rotation of the magnet assembly drum 16 is opposite the direction of rotation of the drum 12. The drum 12 and belt 10 are of plastics or other non-metal material and the spacing between the outer surface of drum 16 and the inner surface of drum 12 is as small as possible.

The apparatus further comprises a feed hopper 18 for holding the mixture of powder to be separated. A mechanical agitator 19 is provided for the hopper so that powder in this feed hopper falls onto the belt 10 and is thus conveyed to the drum 12 and then around the circumference of the drum. Non- ferromagnetic powder falls vertically, generally tangentially of the drum 12. Ferromagnetic powder is retained on the belt 10 for a greater proportion of the drum circumference, being attracted to it by the permanent magnets of the magnetic drum assembly 16. The ferromagnetic powder falls from the belt 10, but at a point or zone spaced somewhat from the point or zone at which the non-ferromagnetic powder falls. The ferromagnetic and non-ferromagnetic powders thus fall into separate outlet ducts 20,22.

The apparatus further comprises an enclosure or housing

24 to contain the powder. Towards the top of this enclosure, an outlet 26 is provided for connection to an extraction fan, for withdrawing air which may be laden with some of the powder.

We have found that the separation method of the present invention is particularly effective. In respect of "clumps" of powder, these tend to be agitated and broken up, so that the ferromagnetic and non-ferromagnetic components of each clump become separated and pass to their appropriate outlets.

It will be appreciated that the method may be used to separate out ferromagnetic powder from non-ferromagnetic powder, but may equally well be used to separate out non- ferromagnetic powder from ferromagnetic powder.

In order to improve the effectiveness of the method, the apparatus may include a second rotating magnet assembly and feed belt, onto which the separated material (either 20 or 22) falls.

Claims

1) A method of separating a mixture of powders of ferromagnetic and non-ferromagnetic materials, the method comprising providing a cylindrical magnet assembly which is mounted with its axis horizontal and comprises a plurality of magnets disposed one-after-another around the circumference of said assembly, adjacent said magnets presenting alternate poles radially outwards, rotating said cylindrical magnet assembly around its axis, providing a curved surface which is concentric with said cylindrical magnet assembly and extends at least over an arc of 90° from a point vertically above said axis to a point horizontally aligned with said axis, and causing said powder mixture to move onto said curved surface at its upper region and then move downwardly in a path which follows said surface.

2) A method as claimed in claim 1, in which said curved surface comprises a fixed surface onto which the mixed powder is poured and over which the mixed powder then slides.

3) A method as claimed in claim 1, in which said curved surface comprises a rotating drum which is generally co-axial with the cylindrical magnet assembly.

4) A method as claimed in claim 1, in which an endless, moving belt is trained over a drum and over a roller spaced from said drum, said drum being coaxial with the cylindrical magnet assembly, and the mixed power is poured onto an upper run of said belt and conveyed up to and around said drum.

5) A method as claimed in any preceding claim, in which said cylindrical magnet assembly is rotated in a direction opposite to the movement of the powder over said curved surface.

6) A method as claimed in any preceding claim, in which the number of said magnets disposed one-after-another around the circumference of said assembly and the rotary speed of said assembly are such as to produce 500 to 50,000 pole changes per minute.

7) A method as claimed in claim 6, in which the number of said magnets and the rotary speed of said assembly are such as to produce 22,000 to 44,000 pole changes per minute.

8) A method as claimed in any preceding claim, in which said powder mixture comprises powders of less than 250 micron particle size.

9) A method as claimed in claim 8, in which said powder mixture comprises powders of less than 100 micron particle size.

10) A method as claimed in any preceding claim, in which said powder mixture is damp.

11) A method as claimed in any preceding claim, in which one of the component powders separated by the rotating magnet assembly is guided to a second rotating magnet assembly, which performs a second stage of separation.