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Eddy current separators

Application

Eddy current separators, or non-ferrous separators, separate non-magnetic (non-ferrous) metals. They purify large bulk streams and/or separate non-ferrous metals for reuse. Eddy current separators have many uses. They can handle high capacities, because the conveyor belt separates and carries away non-ferrous metals continuously and fully automatically. An important factor for good separation is an even flow of material, supplied by a vibrating feeder or conveyor belt for example. This results in a uniform distribution across the belt, so that the material arrives as a monolayer: this means that the supplied layer thickness is about as thick as the largest piece, and thus that there are no pieces lying one on top of the other. This is especially important with smaller fraction sizes. Goudsmit separators are robustly built so they can remain operational day and night in even the most demanding applications, such as incinerator slag reprocessing. Application examples include:

  • removal of aluminium caps for the glass recycling industry;
  • removal of brass rivets and hinges in the wood recycling industry;
  • removal of non-ferrous metals from slag from waste incineration plants;
  • processing of scrap, electronics waste or household waste;
  • elimination of impurities from recycled plastic streams for protection of injection moulding machines;
  • clean-up of mining and mineral streams, e.g. removal of broken-off excavator teeth;
  • recovery of casting residues in the metal casting industry.

Working principle

Goudsmit has been producing eddy current separators for many years. Market and customer wishes are focal points for the design of a robust, reliable machine line.

How eddy current separators work

Eddy current separators have a conveyor belt system with a high-speed magnetic rotor at the end. The rotation speed of the magnets generates an induction field, creating a rapidly changing magnetic field (see animation). The separation is based on the principle that every electrically conductive particle located in an alternating magnetic field is temporarily magnetized.

Simply put: for a brief moment all metals that pass the magnetic roller become magnetized themselves, causing them to be ejected.
This enables us to separate a huge number of non-ferrous metals and their alloys, including aluminium, copper and brass.


Material

Electrical conductivity

Density

Conductivity/Density

 

σ = [1/Ω ⋅ m]

ρ = [kg/m3]

σ/ρ = [m2/ kg ⋅ Ω]

 

x106

 

x103

Non-magnetizable metals

Aluminium

37,0

2700

13,7

Magnesium

21,7

1740

12,5

Copper

59,9

8960

6,7

Silver

62,1

10500

5,9

Zinc

16,9

7140

2,4

Gold

41,7

19320

2,2

Brass

15,2

8500

1,8

Cadmium

13,3

8650

1,54

Tin

8,7

7300

1,2

Chrome

7,7

7190

1,07

Bronze

7,1

8900

0,80

Solder 50-50

6,7

9000

0,74

Titanium

2,3

4510

0,52

Platinum

9,4

21450

0,44

Lead

4,8

11360

0,42

Stainless steel

1,4

7800

0,18

Magnetizable metals

Cobalt

17,2

8850

1,95

Nickel

14,3

8890

1,61

Steel

5,6

7800

0,71

 

 

 

 

Material

Some non-ferrous metals are more easily separated than others; this has to do with the physical properties. This table lists non-ferrous metals categorized on the basis of three factors. The first column shows the electrical conductivity of the material: a measure of how easily a material conducts electricity. The second column indicates the density of the material; this is important for the effect of gravity on the ejected piece of metal. After all, the eddy current forces generated by the magnetic rotor must overcome these forces. The last column shows the ratio between these two factors. The greater the electrical conductivity and the lower the density, the better a material can be separated with the eddy current technique.

Size and shape

The fraction size (i.e. the size of the particles in the flow of material) is also a very important factor for achieving good separation. Eddy currents induce repulsive forces in a piece of metal that cause it to be ejected with a certain trajectory. As a result, the non-ferrous metals have a different ejection trajectory than the other residue and inert materials in the product stream. This ultimately results in a range of trajectories for inert and non-ferrous material. The larger the volume, the more widely separated ('a') the ejection trajectories of a chunk of inert material and a non-ferrous metal object of the same volume. This is why it is easier to separate aluminium cans (or pieces of them) than small copper wires.

Size plays a role, as does the shape. For example, a ball has less air resistance than a tangle of copper wire or a bent piece of sheet metal. This also affects the range of trajectories, as shown here.

Machine operation

Thus eddy currents affect the trajectory of non-ferrous metals. A rapidly rotating magnetic rotor creates these eddy currents. This rotation can be either concentric or eccentric.

 Trajectory of an Eddy current separator

Concentric vs eccentric

All Goudsmit eddy current separators are based on an eccentric design. This means that the magnet rotor rotates eccentrically inside an outer jacket. Systems of this type have a number of advantages over concentric systems:

  • Concentric systems suffer from a problem referred to as 'burn-in’. This phenomenon occurs when the product stream still contains iron or ferrous particles and these end up under the conveyor belt. The eddy currents heat up these magnetic particles, just like an induction hob. The hot magnetic particles then burn through the protective jacket, causing permanent damage. Eccentric systems are not susceptible to this problem because they are not magnetic around the entire circumference of the roller and therefore magnetic particles do not remain attached around the entire perimeter.
  • Influencing the ejection angle: the magnetic rotor can be tilted inside the drum, changing the moment at which the non-ferrous metals are ejected. For more information on adjusting the machine, please contact our application specialists.

HI (High Intensity)

Some Goudsmit magnetic rotors, such as the 22HI and 38HI, feature a HI (High Intensity) magnet configuration. This is a Goudsmit exclusive, which generates extremely high magnetic forces. The HI magnetic rotors are therefore also suitable for small fractions that are difficult to process and weakly magnetic non-ferrous particles that are difficult to separate.

Ferromagnetic separation

Because product streams often contain pieces of iron (ferrous elements), the Goudsmit eddy current systems include a deferrization module. This allows removal of pieces of iron via a separate route, before the actual non-ferrous separation takes place. Possible solutions include a vibrating chute in combination with a drum magnet, or a conveyor belt in combination with a magnetic head roller separator. Both systems can be built with various magnetic strengths, for separation of strongly magnetic or even weakly magnetic metals (such as stainless steel). See animation.

Separation partition/splitter

For the final, definitive separation of the two product streams we place a partition between the inert and non-ferrous streams. There are different types to ensure maximum separation or purity of your product stream.


Location

Eddy current separators are normally placed at the end of the production line. Prior to that, in chronological order, the following processing steps take place:

  • shredding/crushing of the material;
  • sieving of the various fractions;
  • iron and ferrous separation;
  • non-ferrous separation;
  • possibly supplemented by sensor separation.

Type

Separation partition relative to range of trajectories

EddyCan logo

Trajectory of an EddyCan, Eddy current separator

EddyXpert logo

Trajectory of an EddyXpert, Eddy current separator

EddyFines logo

Trajectory of an EddyFines, Eddy current separator

 

 

The non-ferrous fractions contain all the valuable and precious metals; the non-ferrous separation is therefore the processing step that recovers the value from the product stream. In theory, everything prior to this is pre-processing or preparation, to maximize the efficiency of the non-ferrous separation. Depending on the product stream and sales contract, you can choose between 'optimum in recovery' or 'optimum in grade'. For questions concerning these terms please feel free to contact our sales representatives. They will be happy to advise you.

Suitable for fraction
Working width
Magnetic system

Products

EddyCan - Eddy current separator

Lightweight, simple eddy current separator. For the separation of aluminium cans, and similar 'coarse' products.

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EddyXpert - Eddy current separator

All-rounder; robust eddy current separator. Many possible combinations for desired application.

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EddyFines - Eddy current separator

Advanced, robust eddy current separator. For separation of the smallest non-ferrous particles.

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