AU673076B2

AU673076B2 - A shielded tubular mineral detector

Info

Publication number: AU673076B2
Application number: AU66120/94A
Authority: AU
Inventors: Alan Boyle
Original assignee: APPLIED SORTING TECHNOLOGIES P
Current assignee: Individual
Priority date: 1993-07-05
Filing date: 1994-07-04
Publication date: 1996-10-24
Anticipated expiration: 2014-07-04
Also published as: AU6612094A

Description

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION STANDARD) PATENT 00% Applicants: AV~PLIED SORTING TECHNOL~OGIES PTY LTD S S S S Sq..

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Invention Title: A SHIELDED TUBULA.R MINERAL DETECTOR The following stateme. is a full description of this invention, including the best method of performing it known to me/us: I_ _L1_ I 2 A SHIELDED TUBULAR MINERAL DETECTOR This invention relates to detectors for the automatic sorting or inspection of feed material containing mineralised particles which are electrically conductive, have a magnetically identifiable property, or have both characteristics in some proportion.

In the mining industry, beneficiation of "run of mine" rock particles can be carried out by automatic sorting if the rock particles designated as ore are characterised by a physically measurable quantity such as optical reflectance, radio-activity, electrical conductivity or magnetic permeability. Similarly, the food processing industry uses automated systems that detect a physical parameter, for example electrical conductivity, to 15 indicate the presence of contaminants such as "tramp metal" in a product stream prior to dispatch. The present *invention is thus particularly applicable to the mining and food processing industries, but it could also be used in the pharmaceutical, plastics or timber industries, or in any other area where it is necessary to detect foreign bodies with the intrinsic properties of electrical conductivity and/or magnetic permeability.

Metal detectors presently used in industry have "the serious disadvantage of responding to metallic objects S 25 outside the detection zone or detector, and in some cases to objects of high dielectric constant passing through the detection zone or detector. The undesired response to metal outside the detection zone restricts the proximity of adjacent detectors or other equipment and puts a severe constraint on the position of the detector relative to the associated processing or conveying system.

In addition, the possibility of undesired responses to objects of high dielectric constant passing through the detection zone means that, for example, objects with a high water content can cause the detector to indicate a contaminant when none exists.

staffikylkeepsslr.- P 12 94 23 8 U_ I_ 3 It is an object of the present invention to provide an improved detector which to some extent overcomes these shortcomings.

According to the invention there is provided a mineral detector for detecting a mineral within a feed material, comprising: a fixed electrically conductive tube to receive the feed material, a longitudinal slot in the tube which slot is shorter than the tube and is spaced from both ends of the tube, at least one primary magnetic field coil encompassing the tube between the ends of the slot and 1 energisable to establish within the slotted part of the tube an alternating electromagnetic field, and at least one detector coil encompassing the tube *adjacent to the at least one primary magnetic field coil to detect variations in said alternating electromagnetic field within the slotted part of the tube due to presence of minerals within the feed material.

Said slot may be one of a plurality of longitudinal slots spaced circumferential!, around the Stube.

Preferably said detector coil is one of a pair of detectc.- coils encompassing the tube one to either side of the at least one primary magnetic field coil.

Preferably further the tube is encompassed by an outer tubular member which is electrically conductive so as to serve as confining shield for alternating electric and magnetic fields and the space between the tube and the tubular member is filled with an electrically insulating material, for example an epoxy resin.

The illustrated mineral detector comprises a metallic tube 1, provided with a plurality of longitudinal slots 2 located around the circumference of the tube in the vicinity of the detection zone. The slots are much shorter taftikylfoopespoc6G120 94 238 4 than the tube and are spaced centrally from the ends of the tube. The tube 1 has a circular cross section, but alternatively its cross section could be rolygonal. A cylindrical coil former 3, of an insulating material is located around the tube 1 and also centred on the detection zone. The coil former 3 is provided with three grooves 4, the outer two of which house sensor coils, the inner groove housing a transmitter solenoid. The sensor coils and transmitter solenoid windings are not shown in the drawing.

In use a sample is passed through tube 1. The solenoid is driven by an, alternating current, and generates an alternating primary magnetic field. In this embodiment the alternating current is -f high frequency. In general, however, the frequency will be chosen according to the 15 mineral or contaminant being detected. Eddy currents are formed in the unslotted end portions of tube 1 owing to the *99999 S* presence of the primary magnetic field. The secondary magnetic field developed by the eddy currents opposes the primary field causing an absence of magnetic field in the unslotted end portions, which thus behave as low resistance shorting rings to the flow of the eddy currents. Eddy currents are unable, however, to flow in the slotted portio of the tube 1, so the primary magnetic field is established in this section of the tube 1 unattenuated.

Consequently a magnetic field is established in the sample S. passing through the tube 1, without significantly reducing the shielding provided by the tube 1.

The passage of sample material containing particles which are electrically conductive or magnetically permeable induces changes in the primary magnetic field which are then detected with the balanced sensor coils.

The mineral detector is additionally provided with a cylindrical enclosure exterior to and surrounding the coil former 3 and comprising an outer tubular member formed by two layers 6 and 7. One or both of the layers 6 and 7 is electrically conductive, to ensure that the level stallikykoop'spoc'G6120 94 23 5 of primary magnetic field outside the detector is negligible, and )ne layer is made of a high permeability magnetic material to provide shielding at low frequencies.

By means of the layers 6 and 7 the detector assembly is completely encased in a conductive enclosure, which confines both the alternating electric and magnetic fields, and eliminates the possibility of metal or equipment near the detector giving rise to false detector responses.

The space between the coil former 3 and the enclosure layers 6 is closed with two annular metallic end plates 5, one at each end of layers 6 and 7. The end plates 5 are secured to tube 1 by means of clamping plates 8 and wedge rings The mechanical stiffness of the structure may be 15 improved by filling any or all voids in the assembly exterior to the tube 1, but including the slots 2 in the tube 1, with epoxy resin. Seals 11 are provided to prevent the epoxy resin from escaping during the potting process.

2: Three small holes 9 are provided in layers 6 and 7 to allow the electrical connection of solenoid and sensor coils.

4* .o 4 4 stlaltiikyfkooWispocG6120 4 23 8

Claims

1. A mineral detector for detecting a mineral within a feed material, comprising: a fixed electrically conductive tube to receive the feed material, a longitudinal slot in the tube which slot is shorter than the tube and is spaced from both ends of the tube, at least one primary magnetic field coil encompassing the tube between the ends of the slot and energisable to establish within the slotted part of the tube an alternating electromagnetic field, and at least one detector coil encompassing the tube adjacent to the at least one primary magnetic field coil to "o 15 detect variations in said alternating electromagnetic field S*. within the slotted part of the tube due to presence of Sminerals within the feed material.

2. A mineral detector as claimed in claim 1, wherein said slot is one jf a plurality of longitudinal slots spaced circumferentially around the tube.

3. A mineral detector as claimed in claim 1 or claim 2, wherein said detector coil is one of a pair of detector coils encompassing the tube one to each side of the at least one primary magnetic field coil. 25

4. A mineral detector as claimed in any one of the preceding claims, wherein the tube is of circular cross- section.

A mineral detector as claimed in any one of the claims 1 to 3, wherein the tube is of polygonal cross- section.

6. A mineral detector as claimed in any one of the preceding claims, wherein the tube is encompassed by an outer tubular member which is electrically conductive so as to serve as a confining shield for both alternating electric and magnetic fields.

7. A mineral detector as claimed in claim 6, wherein tlalt&ky'koop.pocCGG120 04 23 8 7 the outer tubular member is both electrically conductive and magnetically permeable.

8. A mineral detector as claimed in claim 7, wherein the outer tubular member is comprised of two layers one of which is electrically conductive and the other of which is magnetically permeable.

9. A mineral detector as claimed in any one of claims 6 to 8, wherein a pair of annular metallic end plates interconnect the outer ends of said electrically conductive tube and said outer tubular member whereby the magnetic field and detector coils are disposed within a conductive enclosure formed by the electricallr conductive tube, the outer tubular member and the metallic end plates.

A mineral detector as claimed in any one of 15 claims 6 to 9, wherein the space between said electrically conductive tube and the outer tubular member is filled with an electrically insulating material.

11. A mineral detector as claimed in claim S: wherein the insulating material is an epoxy resin.

12. A mineral detector substantially as hereinbefore described with reference to the drawing. o DATED THIS 23RD DAY OF AUGUST 19./6 APPLIED SORTING TECHNOLOGIES PTY LTD By Its Patent Attorneys: GRIFFITH HACK CO., S'Fellows Institute of Patent Attorneys of Australia stafllky!koopspocV662094 238 I ABSTRACT The construction of a tubular mineral detector is disclosed wherein the sensing zone is surrounded by a conductive tube which confines both the primary electric and magnetic alternating fields. Establishment of the primary alternating magnetic field within the conductive tube is achieved through the use of a surrounding solenoid, the conductive tube being slotted to avoid cancellation of the alternating magnetic field in the sensing zone of the detector. Conventional balanced sense coils on either side of the primary solenoid are used to detect *a changes in the primary magnetic field as the product passes through the detector. The disclosed invention shows a means of totally shielding the detector from external electric and magnetic fields without compromising its sensitivity to mineral detection. 09 o *0 0S f