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Mining & Mineral Processing

AC Demagnetising Coils

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Application Summary
Demagnetisation of ferromagnetic particles in the Dense Media / Heavy media separation, Iron Ore Concentration, mineral processing industry
Materials / Commodities
Battery Minerals, Chrome, Coal, diamonds, Iron Ore, PGM

This is an Alternating Current powered electrical device creating an alternating and decreasing magnetic field for the demagnetisation of containing magnetised ferromagnetic particles such as Magnetite or Ferrosilicon recovered by Wet Drum Separators [LIMS] in Dense Media Separation Plants.

Wet Drum Separators [LIMS] are part of the process in “Dense Media Separation” and Magnetite Ore Concentrator plants, magnetic particles discharge from a LIMS in the form of magnetic agglomerates and if not dispersed they can have a detrimental impact on the process and separation efficiency.

In a Dense Media Separation application magnetised particles can increase the viscosity of the medium leading to inefficient separation. In Magnetite Ore upgrading the magnetised particles can entrain non-magnetic particles which are carried from one separation stage to the next, where they can be incorrectly classified as large particle on a screen or in a cyclone. The magnetic agglomerates can be dispersed by passing them through an air cored AC solenoid coil at 50 or 60 Hz

How AC Demagnetising Coils Work?

The magnetic field intensity along the axis of a solenoid coil varies, the maximum value is at the coil centre and minimum value are at the ends. Any slurry and magnetised particles passing through this coil are subjected to a time varying magnetic field of diminishing amplitude which takes them through a series of minor “hysteresis” loops until the particle magnetisation is close to zero, thereby “demagnetising” the particles.

To demagnetise >10μm natural Magnetite or Ferrosilicon, the generally accepted design criteria is 600 oersteds peak magnetic field intensity at the coil centre field decreasing 10-30% each cycle from maximum down to Zero

What Will AC Demagnetising Coils Do?

The MAGQUIP AC Demag coil will effectively demagnetise ferromagnetic particles in a slurry magnetised from a Wet Drum Magnetic Separator [LIMS] thereby ensuring plant operating efficiencies

Why are AC Demagnetising Coils Better?

The advantages of the MAGQUIP demag coil include:

  • Light but sturdy waterproof reinforced fibreglass enclosure and terminal box assembly.
  • No maintenance or spare parts required for long life and reliable operation.
  • Can be supplied with loose TPR “thermistor relay” or alternatively with a Control Panel Thermistor relay in enclosure with indication lights coil healthy coil failure potential free contacts for coil shut down and/or coil failure warning.
  • Supplied with 1m long HDPE pipe section and “Unifit” universal detachable couplings to suit standard flange sizes for flexibility and ease of site fitment.
  • Supplied with “slotted” backing installation plate allowing for easy rotation for coil to desired and optimal installation angle

What Does AC Demagnetising Coils Consists Of?

The coil is wound with class 200 enamel covered copper wire onto a SRBP [bakelite] tube with flanges.

Two temperature sensors [PTC thermistors] are fitted in the coil winding.

The coil is encapsulated in an epoxy filled completely waterproof fibreglass housing.

The housing has two eye bolts for lifting and two studs for bolting to a 20 mm thick nylon support plate.

A slot on the plate allows for coil installation vertical or inclined, a hole at each corner for bolting to support structure.

Coil and thermistor leads are wired to IP66 rating terminal boxes underneath the coil each terminal box includes a compression gland size for 1 for coil leads size 0 for thermistors leads recommended cable size coils 2 core 4 mm² thermistors 2 core 1.5 mm².

Coils are made with bore diameters 102 / 152 /212 mm with corresponding coil lengths being 150 / 200 / 250 mm [optimum length to bore ratio for minimum coil weight]. Custom sizes and designs are available.

The AC Coils are connected to single phase or two phases of three phase AC supply[220/380/525V-50 Hz or 230 /460 /575V- 60 Hz]