AU2013200967A1 - Magnetic separator - Google Patents

Abstract

A magnetic separator for extracting magnetically susceptible items from bulk conveyed material being conveyed in a predetermined direction by a conveyor is disclosed. The magnetic separator includes a magnet arrangement spaced from the conveyed material where the magnet arrangement providing a magnetic field generally extending from an operating face of the magnet arrangement to attract the magnetically susceptible items to the magnet arrangement. The magnet arrangement is adapted to dynamically change the magnetic field experienced by the conveyed material for facilitating removal of the magnetically susceptible items by moving the magnet arrangement with respect to the conveyor.

Description

1 MAGNETIC SEPARATOR TECHNICAL FIELD [0001] The present invention relates to magnetic separators for extracting magnetically susceptible material such as iron and the like from conveyed bulk material. In a particular form, the present invention relates to magnetic separators for removing tramp iron. BACKGROUND [0002] Magnetic separators are used with respect to conveyors that carry bulk materials such as mineral ores, coal, sugar cane, plastics, chemicals, grain and food products to remove unwanted iron and steel from these products. This protects downstream processing equipment such as pulverisers, crushers, mills and the like given that the introduction iron or steel items to equipment of this type is likely to result in significant damage and downtime. Similarly, magnetic separators are employed to prevent unwanted product going to customers, or in some cases, to limit sparks and resulting fire hazards. [0003] Magnetic separators, which are variously known in the art as tramp iron or tramp metal magnets, conveyor magnets or over-band magnets typically involve either an electromagnet or permanent magnet arrangement that is suspended over the bulk material that is being conveyed in a configuration such that the conveyed bulk material passes through the operable magnetic field region of the magnetic arrangement. Any magnetically susceptible items, such as tramp iron, will then be attracted to the magnet arrangement as they pass through the operable magnetic field region of the magnet separator. In another configuration, the magnetic separator may be suspended over the trajectory of the bulk material as it discharges from the conveyor. There are also self-cleaning magnetic separators having a belt that is driven in close proximity to, or across the face of, the magnet arrangement where it then collects the magnetically susceptible material for disposal. [0004] The size and strength of the required operable magnetic field region will be largely determined by the width and velocity of the conveyor and the associated depth of burden of material. This in turn will determine the size and strength of the required magnet arrangement. Accordingly, in some bulk handling applications such as a coal loading facility, it is not unknown to have magnet arrangements weighing in excess of 80 tonnes. Clearly, the capital and infrastructure costs involved in a magnetic separator installation of this size are at one extreme but as a general principle reducing the size and strength of the magnet arrangement for effectively the same operable magnetic field strength as determined by its ability to attract magnetically susceptible material will lead to costs savings as smaller and less stronger magnets or less powerful electromagnets may be used. This is apart from the infrastructure costs savings that arise from using smaller magnetic separators.

2 [0005] One attempt to address this issue has been to momentarily increase the strength of the magnetic field of the magnet arrangement based on a signal from an associated metal detector which alerts the magnetic separator that there may be magnetically susceptible material in the section of bulk material being conveyed in proximity to the separator. The primary disadvantage of this system is that it is only applicable to electromagnetic magnet arrangements whose magnetic field strength can be increased by increasing electrical power to the magnet arrangement. [0006] There is therefore a need to increase the effectiveness or separating ability of magnetic separators for a given size or magnetic field strength and/or to provide consumers with an alternative choice. SUMMARY [0007] In a first aspect the present invention accordingly provides a magnetic separator for extracting magnetically susceptible items from conveyed material being conveyed in a predetermined direction by a conveyor, the magnetic separator including: a magnet arrangement spaced from the conveyed material, the magnet arrangement providing a magnetic field generally extending from an operating face of the magnet arrangement to attract the magnetically susceptible items to the magnet arrangement, wherein the magnet arrangement is adapted to dynamically change the magnetic field experienced by the conveyed material for facilitating removal of the magnetically susceptible items by moving the magnet arrangement with respect to the conveyor. [0008] In another form, the magnet arrangement is movable with respect to the conveyor to dynamically change an orientation of the magnetic field with respect to the predetermined direction of the conveyed material. [0009] In another form, the magnet arrangement is rotatable about a vertical axis defined substantially perpendicular to the operating face of the magnet arrangement. [0010] In another form, the magnet arrangement is rotatable in an oscillatory motion following an arcuate path about the vertical axis. [0011] In another form, the magnet arrangement is continuously rotatable about the vertical axis. [0012] In another form, the magnet arrangement is movable with respect to the conveyor to dynamically change the magnetic field gradient experienced by the conveyed material. [0013] In another form, the magnet arrangement is tiltable about a horizontal axis.

3 [0014] In another form, the magnet arrangement is tiltable in an oscillatory motion defined substantially parallel to the operating face of the magnet arrangement and either in line with or substantially perpendicular to the predetermined direction of travel of the conveyed material. [0015] In another form, the distance extending between the magnet arrangement and the conveyed material may be dynamically varied. [0016] In another form, the magnet arrangement is movable with respect to the conveyor to dynamically change the magnetic field to increase the exposure time experienced by a magnetically susceptible item being conveyed in the conveyed material. [0017] In another form, the magnet arrangement is movable from an initial position in the direction of the conveyed material at substantially the same speed as the conveyed material. [0018] In another form, the magnet arrangement is retractable to the initial position. [0019] In another form, the magnetic separator further includes a detector for detecting the presence of magnetically susceptible items in the conveyed material. [0020] In another form, on detection by the detector of a magnetically susceptible item in the conveyed material, the magnet arrangement is moved with respect to the conveyor to dynamically change the magnetic field experienced by the conveyed material arrangement to facilitate removal of the magnetically susceptible item from the conveyed material. [0021] In a second aspect the present invention accordingly provides a magnetic separator for extracting magnetically susceptible items from conveyed material being conveyed in a predetermined direction, the magnetic separator including: a magnet arrangement spaced from the conveyed material, the magnet arrangement providing a magnetic field to attract the magnetically susceptible items to the magnet arrangement, a detector for detecting the presence of magnetically susceptible items in the conveyed material; wherein on detection by the detector of a magnetically susceptible item in the conveyed material; the magnet arrangement is adapted to increase the exposure time that the magnetically susceptible item experiences with respect to the magnet arrangement to facilitate removal of the magnetically susceptible item from the conveyed material. [0022] In another form, the magnet arrangement is movable from an initial position in the direction of the conveyed material at substantially the same speed as the conveyed material on detection of the magnetically susceptible item. [0023] In another form, the magnet arrangement is retractable to the initial position.

4 [0024] In a third aspect the present invention accordingly provides a magnetic separator for extracting magnetically susceptible items from conveyed material being conveyed in a predetermined direction by a conveyor, the magnetic separator including: a magnet arrangement spaced from the conveyed material, the magnet arrangement providing a magnetic field to attract the magnetically susceptible items to the magnet arrangement, wherein the magnet arrangement is adapted to dynamically change the magnetic field gradient experienced by the conveyed material for facilitating removal of the magnetically susceptible items by moving the magnet arrangement with respect to the conveyor. [0025] In a fourth aspect the present invention accordingly provides a method for extracting magnetically susceptible items from conveyed material, including: conveying the conveyed material in a predetermined direction; applying a magnetic field to the conveyed material by a magnet arrangement to attract the magnetically susceptible items to the magnet arrangement; moving the magnet arrangement with respect to the conveyed material to dynamically change the magnetic field experienced by the conveyed material for facilitating removal of the magnetically susceptible items. [0026] In another form, moving the magnet arrangement results in an orientation of the magnetic field dynamically changing. [0027] In another form, moving the magnet arrangement results in a gradient of the magnetic field dynamically changing. [0028] In another form, moving the magnet arrangement results in an increase in the exposure time that a magnetically susceptible material experiences. BRIEF DESCRIPTION OF DRAWINGS [0029] Illustrative embodiments will be discussed with reference to the accompanying drawings wherein: [0030] Figure 1 is a side figurative view of a magnetic separator in accordance with an illustrative embodiment; [0031] Figure 2a is a top view of the magnetic separator illustrated in Figure 1; [0032] Figure 2b is an underside view of the magnet arrangement illustrated in Figure 1.

5 [0033] Figures 3a and 3b are underside and side views respectively of an alternative magnet arrangement. [0034] Figures 4a and 4b are underside and side views respectively of yet another alternative magnet arrangement. [0035] Figure 5 is an end view of a magnetic separator in accordance with another illustrative embodiment; [0036] Figure 6 is a side view of a magnetic separator in accordance with a further illustrative embodiment; [0037] Figure 7 is a side view of a magnetic separator in accordance with yet another illustrative embodiment; and [0038] Figure 8 is a front perspective view of the magnetic separator illustrated in Figure 7. [0039] In the following description, like reference characters designate like or corresponding parts throughout the figures. DESCRIPTION OF EMBODIMENTS [0040] Referring now to Figure 1, there is shown a side figurative view of a magnetic separator 100 according to an illustrative embodiment of the present invention operating to extract magnetically susceptible items from conveyed material in the form of bulk material 210 being conveyed in a conveyor 200 in direction 300. Magnetic separator 100 includes a magnet arrangement 120 configured to provide an operable magnetic field region 110 extending from an operating face 122 through the bulk material 210 beneath magnetic separator 100 to attract magnetically susceptible items to the magnet arrangement 120. [0041] In this illustrative embodiment, magnet arrangement 120 consists of a series of permanent magnets in a North, South, North configuration and positioned so that the magnetic field lines extend across the width of the conveyor 200 (as best shown in Figure 2b depicting an underside view of magnet arrangement 120) and generally providing a gradient magnetic field as required with field lines in this illustrative embodiment extending across the direction of travel 300 of the conveyor 200. [0042] Referring now to Figure 2a, there is shown a top view of magnetic separator 100, where the magnet arrangement 120 has been adapted to dynamically change the magnetic field experienced by the conveyed material 210 by moving the magnet arrangement 120 with respect to the conveyor 200. In this illustrative embodiment, the orientation of the operable magnetic field region 110, as indicated by cross- 6 hatched area (as best shown in Figure 1), is dynamically changed with respect to the direction 300 of the conveyed material 200. In particular, the magnet arrangement 120 rotates or turns about vertical axis V defined substantially perpendicular to operating face 122 and following an arcuate or part circular path A (as indicated) in an oscillatory manner to facilitate removal of magnetically susceptible items. [0043] A magnetically susceptible item found in bulk material such as a piece of tramp iron, except in the case of a perfectly symmetrical object such as a ball bearing, will have an elongate axis defining the dimension which has the greatest physical extent from end to end of the object. In many cases, particularly in mining and/or quarrying applications, the magnetically susceptible item will be a piece of ferrous rod or bar-shaped material that is substantially elongate in one direction. These magnetically susceptible items will be distributed in the bulk material with random orientations. [0044] A magnetically susceptible item in a magnetic field will first attempt to align its elongate axis with the field lines of the magnetic field that extend between the poles of the magnet arrangement. Once oriented along the field lines of the magnetic field, the magnetically susceptible item will then tend to move along any gradient in the magnetic field strength and be attracted to the magnet arrangement. [0045] While these two different movements of the magnetically susceptible item (ie first orientation and then attraction) may be close to simultaneous, it is observable that there is a distance at which rotation or reorientation of the item will begin to occur prior to the item moving towards the magnet arrangement as it experiences the gradient magnetic field. As such, the initial orientation of a magnetically susceptible item as it compares to the orientation of the magnetic field lines will determine in part how readily it may be attracted to the magnet arrangement with those items already aligned with the magnetic field gradient being preferentially attracted to the magnet arrangement. [0046] As any magnetically susceptible item will only be exposed to the operable magnetic field region 110 for a limited amount of time, as determined by the velocity of the conveyor belt and the size of the field region, an item that is say perpendicular to the alignment of the magnetic field lines may not have sufficient time to first reorient and then be attracted to the magnet arrangement. This would typically be addressed by employing a stronger magnet arrangement providing higher magnetic field gradients with its attendant size increase and cost implications. [0047] The Applicant has found that by dynamically changing the orientation of the operable magnetic field region and hence the direction of the field lines, a magnetically susceptible item will be preferentially attracted to the magnet arrangement at the instant its elongate axis is substantially aligned with the field lines of magnet arrangement 120. Put another way, by rotating the magnet arrangement 120 the chance that a magnetically susceptible item will find itself in alignment with the magnetic field lines of the magnetic field is increased leading to enhanced recovery and extraction of these items as compared to a statically operated magnetic separator.

7 [0048] Changing the orientation of the magnetic field in this manner will also assist in extracting a piece of magnetically susceptible material, particularly of rod or bar shape which may be lying partially beneath a piece of non-magnetic product in a manner and orientation that prevents its removal. In accordance with this embodiment, the magnetically susceptible item may be caused to oscillate or change its direction as it aligns itself with the dynamically changing field lines until it finds itself in an orientation where it may be more readily extracted from the bulk material. In this manner, improved recovery of magnetically susceptible items which ordinarily would not be removed even given the largest magnet arrangements may be achievable. [0049] Referring now to Figures 3a, 3b, 4a and 4b there are shown some other commonly utilised magnet arrangements 120A, 120B that may be adapted in accordance with the embodiments described here. It will be appreciated that the various magnet arrangements are depicted by way of example only and other types of magnet arrangements suitable for use as a magnetic separator are contemplated to be within the scope of the invention. Figure 3a shows the underside of magnet arrangement 120A consisting of three magnets having a North, South, North configuration extending along its length as best shown in Figure 3b which depicts a side view of magnet arrangement 120. Figure 4a shows an alternative magnet arrangement 120B based on an electromagnetic arrangement consisting of a central South pole (which may be either circular or rectangular) and an outer North pole. [0050] While in this illustrative embodiment, magnet arrangement 110 moves in an oscillatory motion, in other embodiments magnet arrangement 110 may rotate continuously at a constant or variable rate. As would be appreciated by those of ordinary skill in the art, the rate and direction of rotation, whether it be oscillatory or constant, will be determined by factors including, but not limited to, the strength, size and extent, and magnetic field gradient of the operable magnetic field region, the depth and type and density of bulk material being conveyed, the expected size and distribution of magnetically susceptible items and the velocity of conveyor. These factors and how they affect the configuration and operation of a magnetic separator are often defined based on a user requirement specification which might specify as an example that at least 90% of tramp iron corresponding to an M25 hex nut or larger must be removed from the conveyed material. [0051] Referring now to Figure 5, there is shown in yet another illustrative embodiment, a magnet arrangement 120 that has been adapted to dynamically change the magnetic field experienced by the conveyed material 210 by moving the magnet arrangement 120 with respect to the conveyor 200 to dynamically change the magnetic field gradient experienced by the conveyed material 210. In particular, magnet arrangement 120 is adapted to tilt or be rocked about a horizontal axis J defined substantially parallel to operating face 122 of magnet arrangement 120 and in line with the direction of travel of conveyed material 210 and following an arcuate or part circular path D as depicted in Figure 5. Alternatively, magnet arrangement 120 may be adapted to tilt or be rocked about a horizontal axis defined substantially parallel to operating face 122 but substantially perpendicular to the direction of travel of 8 conveyed material 210. These axes may be located external to the magnet arrangement 120 resulting in the entire magnet arrangement 120 following an arcuate or part circular path analogous to a cradle being rocked. [0052] By dynamically tilting magnet arrangement 120 in this manner, a given location in the conveyed material 210 will experience changes in the magnetic field gradient as this gradient is not uniform throughout the operable magnetic field region 110 as shown in Figure 5. As a result, a given location is more likely to experience a higher magnetic field gradient then otherwise would be the case for a static magnet arrangement and as such any magnetically susceptible material is more likely to be attracted to magnet arrangement 120. [0053] In further embodiments, magnet arrangement 120 may be both rotatable and tiltable to further facilitate the removal of magnetically susceptible material from conveyed material 210. In yet another embodiment, the distance between the conveyed material 210 and magnet arrangement 120 may be varied by in this case dynamically raising and lowering magnet arrangement 120. [0054] Referring now to Figure 6, there is shown a magnetic separator 500 according to another embodiment. Magnetic separator 500 once again is operable to extract magnetically susceptible items from bulk material 210 being conveyed in a conveyor 200 in direction 300. In this illustrative embodiment, the magnet arrangement 520 is adapted to dynamically change the magnetic field experienced by the conveyed material by moving the magnet arrangement with respect to the conveyor 200 to increase the exposure time that a magnetically susceptible item experiences with respect to the magnetic field of magnet arrangement 520. In particular, magnet arrangement 520 is adapted to be moveable from an initial position 565 to be advanced in a forward direction 560 in the direction 300 of the conveyed material. [0055] In this illustrative embodiment, magnetic separator 500 includes a magnet arrangement 520 and a detector 530 for detecting the presence of magnetically susceptible items in the bulk material 210. Furthermore, magnet arrangement 520 is operable to be also retractable in the reverse direction 570 with respect to direction 300 to its initial position 565. [0056] On detection of a magnetically susceptible item 220 by detector 530 and allowing for a delay for the magnetically susceptible material 220 to reach the initial position of magnet arrangement 520, magnet arrangement 520 is then actuated to move in the direction and at substantially the same speed as the conveyed material for a predetermined distance, thereby increasing the exposure time to the magnetic field of magnetic arrangement 520 that magnetically susceptible item 220 experiences which in turn facilitates the removal of the magnetically susceptible item 220 from bulk material.

9 [0057] Magnet arrangement 520 may then be retracted in the reverse direction 570 to initial position 565 until the next magnetically susceptible item is detected by detector 530 in which case it will again travel in the direction of the conveyed material 200. In another embodiment, magnetic arrangement 520 may be retracted rapidly in the reverse direction 570 to the initial position 565 should a further magnetically susceptible item 220 be detected by detector 530 while magnet arrangement 520 is travelling in the forward direction 560 so that the next magnetically susceptible item 220 can be followed. As would be appreciated by those skilled in the art, this arrangement will still increase the exposure time for any given magnetically susceptible item as compared to a magnet arrangement that does not move in the direction 300 of the conveyed material 200. In another embodiment, travel of magnetic arrangement 520 may be halted in the unlikely event that multiple magnetically susceptible items are detected by detector 530 in a short period of time. [0058] Where magnet arrangement 520 is an electromagnet, the strength of the magnetic field may also be increased on detection by detector 530 by increasing the electrical power to the magnet arrangement 520. The combination of increased exposure time and magnetic field strength will further facilitate the recovery of the magnetically susceptible item. While in this illustrative embodiment, the use of a detector 530 has been shown in combination with the travelling magnet arrangement depicted in Figure 4, equally it may be employed in combination with the magnet arrangements depicted in Figures 1 to 3, wherein the rotating and tilting actions described are actuated on detection of a magnetic susceptible item by a detector. [0059] Referring now to Figures 7 and 8, there is shown a magnet separator 600 according to another illustrative embodiment of the present invention directed to the recovery of tramp iron from a horizontal conveyor 610 such as would be found typically in the quarrying and mining industries. Magnet arrangement 620 which may be a permanent or an electro magnet of either the manual or self-cleaning style, is suspended over conveyor 610 on suspension frame 640 incorporating a motorised suspension trolley 650 supporting an annular ring arrangement 680. [0060] In this illustrative embodiment, motorised trolley 650 is driven forward and back along the suspension frame 640 in via a rack and pinion type system driven by in this example an electric motor 655. Annular ring arrangement 680 on its upper surface includes a concentric annular toothed rack or rail 686 on which toothed gear-wheels 685 from which the magnet arrangement 620 is suspended can be driven in either direction around the annular ring 680 by means of electric motor 687. [0061] In an alternative embodiment, annular ring arrangement 680 may be incorporated on the motorised trolley apparatus 650. Motorised trolley 650 and/or annular ring arrangement 680 are operable based on a detection signal received from metal detector 630 which in this illustrative embodiment is positioned upstream and over the conveyor to detect the presence of any tramp iron in the conveyed material.

10 [0062] In one example, metal detector 630 upon detection of an item of tramp iron within the burden (not shown) on conveyor 610 will send a detection signal to either or both of motorised trolley 650 or annular ring arrangement 680 to cause them to operate to drive their respective apparatus. In this illustrative embodiment, motorised trolley 650 supporting both the annular ring arrangement 680 and the magnet arrangement 620 is driven forward in direction 660 at a speed at or near that of conveyor 610 and retracted in direction 670 at a higher speed. [0063] The forward and backwards movement of the magnet arrangement 620 as provided by motorised trolley 650 and the rotational movement of the magnet arrangement 620 as provided by annular ring arrangement 680 may be made to function simultaneously or independently as required. The movement of the gear wheels 685 may be operable to either cause magnet arrangement 620 to rotate about a vertical axis either in an oscillatory motion or through a full revolution. In yet another embodiment, the geared track 686 on the annular ring arrangement may feature a rise and fall, hill and hollow profile around its circumference to cause the magnet arrangement 620 to tilt or rock about a horizontal axis as the magnet arrangement 620 travels about the annular ring arrangement 680. [0064] While in this illustrative embodiment, electric motors have been employed to drive motorised trolley 650 and annular ring arrangement 680 equally other driving arrangements such as hydraulic, pneumatic or the like may be employed depending on requirements. As an example, hydraulic or pneumatic pistons may be attached to the corners of the magnet arrangement 620 to cause it to rotate or tilt as required. [0065] The embodiment described in Figures 7 and 8 functions to dynamically change the magnetic field experienced by the conveyed material by moving the magnet arrangement 620 with respect to the conveyor 610 in a number of ways. By rotating the magnet arrangement 620, the orientation of the magnetic field experienced by the conveyed material is changed and to a lesser degree the magnetic field gradient. By tilting or rocking the magnet arrangement 620 the resulting magnetic field gradient experienced by the conveyed material is changed. By moving the magnet arrangement 620 along with the conveyed material the exposure time for a potential magnetically susceptible item is changed. As has been described above, moving the magnet arrangement with respect to the conveyor as exemplified by one or more of the aspects described above, whether considered individually or in combination, can be seen to facilitate the removal of magnetically susceptible items from the conveyed material. In addition, the magnetic separator arrangements described above may be employed with either permanent magnets or electromagnets. [0066] Although the conveyors depicted in the various embodiments of the invention are shown travelling in a horizontal direction, it will be understood that the invention may equally be applied to conveyors operating in inclined configurations. As such, references to "horizontal" and "vertical" axes as indicated above are in relation to the configuration of the magnet arrangement and in particular to the I1 operating face of the magnet arrangement as the entire magnetic separator may be configured to operate in an inclined or tilted configuration. [0067] Throughout the specification and the claims that follow, unless the context requires otherwise, the words "comprise" and "include" and variations such as "comprising" and "including" will be understood to imply the inclusion of a stated integer or group of integers, but not the exclusion of any other integer or group of integers. [0068] The reference to any prior art in this specification is not, and should not be taken as, an acknowledgement of any form of suggestion that such prior art forms part of the common general knowledge. [0069] It will be appreciated by those skilled in the art that the invention is not restricted in its use to the particular application described. Neither is the present invention restricted in its preferred embodiment with regard to the particular elements and/or features described or depicted herein. It will be appreciated that the invention is not limited to the embodiment or embodiments disclosed, but is capable of numerous rearrangements, modifications and substitutions without departing from the scope of the invention as set forth and defined by the following claims.

Claims (22)

1. A magnetic separator for extracting magnetically susceptible items from conveyed material being conveyed in a predetermined direction by a conveyor, the magnetic separator including: a magnet arrangement spaced from the conveyed material, the magnet arrangement providing a magnetic field generally extending from an operating face of the magnet arrangement to attract the magnetically susceptible items to the magnet arrangement, wherein the magnet arrangement is adapted to dynamically change the magnetic field experienced by the conveyed material for facilitating removal of the magnetically susceptible items by moving the magnet arrangement with respect to the conveyor.

2. The magnetic separator of claim 1, wherein the magnet arrangement is movable with respect to the conveyor to dynamically change an orientation of the magnetic field with respect to the predetermined direction of the conveyed material.

3. The magnetic separator of claim 2, wherein the magnet arrangement is rotatable about a vertical axis defined substantially perpendicular to the operating face of the magnet arrangement.

4. The magnetic separator of claim 3, wherein the magnet arrangement is rotatable in an oscillatory motion following an arcuate path about the vertical axis.

5. The magnetic separator of claim 3, wherein the magnet arrangement is continuously rotatable about the vertical axis.

6. The magnetic separator of any one of the preceding claims, wherein the magnet arrangement is movable with respect to the conveyor to dynamically change the magnetic field gradient experienced by the conveyed material.

7. The magnetic separator of claim 6, wherein the magnet arrangement is tiltable about a horizontal axis defined substantially parallel to the operating face of the magnet arrangement and either in line with or substantially perpendicular to the predetermined direction of travel of the conveyed material.

8. The magnetic separator of claim 7, wherein the magnet arrangement is tiltable in an oscillatory motion about the horizontal axis.

9. The magnetic separator of claim 6, wherein the distance extending between the magnet arrangement and the conveyed material may be dynamically varied.

10. The magnetic separator of any one of the preceding claims, wherein the magnet arrangement is movable with respect to the conveyor to dynamically change the magnetic field to increase the exposure time 13

11. The magnetic separator of claim 10, wherein the magnet arrangement is movable from an initial position in the direction of the conveyed material at substantially the same speed as the conveyed material.

12. The magnetic separator of claim 11, wherein the magnet arrangement is retractable to the initial position.

13. The magnetic separator of any one of the preceding claims, further including a detector for detecting the presence of magnetically susceptible items in the conveyed material.

14. The magnetic separator of claim 13, wherein on detection by the detector of a magnetically susceptible item in the conveyed material, the magnet arrangement is moved with respect to the conveyor to dynamically change the magnetic field experienced by the conveyed material arrangement to facilitate removal of the magnetically susceptible item from the conveyed material.

15. A magnetic separator for extracting magnetically susceptible items from conveyed material being conveyed in a predetermined direction, the magnetic separator including: a magnet arrangement spaced from the conveyed material, the magnet arrangement providing a magnetic field to attract the magnetically susceptible items to the magnet arrangement, a detector for detecting the presence of magnetically susceptible items in the conveyed material; wherein on detection by the detector of a magnetically susceptible item in the conveyed material, the magnet arrangement is adapted to increase the exposure time that the magnetically susceptible item experiences with respect to the magnet arrangement to facilitate removal of the magnetically susceptible item from the conveyed material.

16. The magnetic separator of claim 15, wherein the magnet arrangement is movable from an initial position in the direction of the conveyed material at substantially the same speed as the conveyed material on detection of the magnetically susceptible item.

17. The magnetic separator of claim 16, wherein the magnet arrangement is retractable to the initial position.

18. A magnetic separator for extracting magnetically susceptible items from conveyed material being conveyed in a predetermined direction by a conveyor, the magnetic separator including: a magnet arrangement spaced from the conveyed material, the magnet arrangement providing a magnetic field to attract the magnetically susceptible items to the magnet arrangement, wherein the magnet arrangement is adapted to dynamically change the magnetic field gradient experienced by the conveyed material for facilitating removal of the magnetically susceptible items by moving the magnet arrangement with respect to the conveyor.

19. A method for extracting maaneticallv susceDtible items from conveyed material. including: 14 conveying the conveyed material in a predetermined direction; applying a magnetic field to the conveyed material by a magnet arrangement to attract the magnetically susceptible items to the magnet arrangement; moving the magnet arrangement with respect to the conveyed material to dynamically change the magnetic field experienced by the conveyed material for facilitating removal of the magnetically susceptible items.

20. The method of claim 19, wherein moving the magnet arrangement results in an orientation of the magnetic field dynamically changing.

21. The method of claim 19, wherein moving the magnet arrangement results in a gradient of the magnetic field dynamically changing.

22. The method of claim 19, wherein moving the magnet arrangement results in an increase in the exposure time that a magnetically susceptible material experiences.