How Do Eddy Currents Separate Nonferrous Metals?
- Starter
- Article
- Ages 10+
- 5 min read
An eddy-current separator takes nonferrous metal, such as aluminium cans, out of a stream of recyclables that a magnet would pass over. According to the Wasatch Integrated Waste Management District, the machine uses a fast-spinning rare-earth magnet to create electromagnetic eddy currents, and those currents push nonferrous metal over a divider into a separate chute.
Contents
- Magnet taking ferrous metal
- Eddy-current separator
- Chute for nonferrous metal
What you will learn
- Say which group of metals an eddy-current separator targets.
- Describe the steps by which the machine pushes an aluminium can out of the stream.
- Place the machine relative to the magnet in the sorting chain.
Before you start
It helps to read the article on magnets first: this one picks up what the magnet leaves behind.
Which metals does an eddy-current separator target?
It targets nonferrous metals, meaning metals without iron. According to Sonoma County Zero Waste, brass, aluminium and copper are in this group, while ferrous metals contain iron and a magnet sticks to them.
This is exactly where a magnet falls short. A question-and-answer page from Physics Van at the University of Illinois says most familiar metals without iron are only very weakly attracted to or repelled by a magnet. For an aluminium can, a different kind of action is needed.
- Ferrous metals pulled
- Aluminium, copper and brass
How does the machine push nonferrous metal out?
It uses a changing magnetic field to induce currents inside the conducting metal itself. According to Princeton University's Joseph Henry Project, an eddy current flows in a loop within a conductor exposed to a changing magnetic field. It produces its own magnetic field opposing the change that created it.
In the machine described by the Wasatch Integrated Waste Management District, a rapidly rotating rare-earth magnet creates the changing field. The aluminium can is not being pulled by a stationary magnet: the induced eddy currents deflect it from its normal fall, over a divider into a separate chute.
Other items, such as plastic bottles or paper, are not pushed, so they fall along the normal path. The stream splits in two: nonferrous metal on one side, everything else on the other.
Machine construction can vary between facilities.
- Spinning drum with magnet
- Divider
- Nonferrous chute
- Chute for the rest
Where does the machine sit in the sorting chain?
In the facility described by the Wasatch Integrated Waste Management District, round items pass a suspended magnet that removes ferrous metal such as soup cans, then an eddy-current separator for nonferrous metal that removes aluminium cans. The eddy-current separator comes after the magnet.
Real-world example
Picture an aluminium drink can and a steel soup can riding the same conveyor. This is a hypothetical walk-through to follow the route. The magnet lifts the steel can out first. The aluminium can travels on to the eddy-current separator, is pushed over the divider and lands in the nonferrous chute.
Common misunderstandings
An eddy-current separator does not pull metal the way a magnet does. It pushes nonferrous metal away, in the opposite direction to a pull.
It does not replace the magnet. The two machines do two jobs: the magnet for ferrous metal, the eddy-current separator for nonferrous metal.
Frequently asked questions
Which metals does an eddy-current separator remove?
Nonferrous metals, for example aluminium. In the facility described, it removes aluminium cans.
Why can't a magnet remove aluminium cans?
Because aluminium has no iron, and most familiar metals of this kind are only very weakly attracted to or repelled by a magnet.
How are the eddy currents created?
By a fast-spinning rare-earth magnet, which creates an alternating magnetic field.
Summary
- The eddy-current separator targets nonferrous metal such as aluminium, which a magnet leaves behind.
- A fast-spinning rare-earth magnet creates eddy currents that push nonferrous metal over a divider into a separate chute.
- The machine comes after the magnet in the described facility's chain for round items.
Terms in this article
English and Vietnamese terms, with the meanings used here. Hover, tap or Tab to a term with a dotted underline for an explanation as you read.
- eddy-current separatormáy tách dòng xoáy
- A machine that pushes nonferrous metals such as aluminium out of a stream of material using an alternating magnetic field.
- eddy currentdòng xoáy điện từ
- A loop of current induced inside a conductor by a changing magnetic field.
- nonferrous metalkim loại màu
- A metal that does not contain iron, such as aluminium, copper and brass.
- ferrous metalkim loại đen
- A metal containing iron, such as steel; common can-sorting examples are attracted by magnets, though iron content does not guarantee strong attraction for every alloy.
- rare-earth magnetnam châm đất hiếm
- A strong kind of magnet made with rare-earth elements.
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Sources
These sources are written for older readers. If they feel hard, read them with an adult.
- Material Recovery and Transfer Facility(opens in a new tab)
Wasatch Integrated Waste Management DistrictTier A: government, standards or research bodiesRead on November 3, 2026
- Metal - scrap(opens in a new tab)
Sonoma County Zero WasteTier A: government, standards or research bodiesRead on November 3, 2026
- Magnets and Iron(opens in a new tab)
Physics Van, University of IllinoisTier A: government, standards or research bodiesRead on November 3, 2026
- Eddy Currents(opens in a new tab)
Princeton University, Joseph Henry ProjectTier A: government, standards or research bodiesRead on November 3, 2026