Eddy currents are created in and around a conductive material when it is exposed to a swiftly changing magnetic field – usually an alternating electrical current. The current forms a closed loop that is similar in appearance, when visualized, to the waves of a swirling current in the ocean. The French physicist Leon Foucault discovered eddy currents in the mid-19th century when he discovered that the force needed to spin a metal disk was greater when the disk was positioned between two alternating magnetic poles.
Since Foucault’s discovery, eddy currents have been put to use in many scientific and engineering applications. Here are some of the most common uses of eddy currents in the current day.
Melting Metals
When eddy currents are induced in a conductive material such as metal, they can produce extreme temperatures. For this reason, eddy current induction has become the most prominent way of melting metals in furnaces. Instead of using compostable fuels to create heat – which can induce impurities – induction furnaces use a coil charged with a powerful alternating current to induce eddy currents in the payload metal. A laboratory vacuum induction melting furnace is a type of fully enclosed melting device used in metallurgy labs. They can produce extremely pure liquid metals for the casting of testing samples.
Sorting Coins
When you put a coin into a vending machine, it passes by a series of magnets. If the coin is false – a ‘slug’ then it will contain a different composition of metals. This means that different levels of eddy current will be created, slowing the coin down and allowing it to drop into the rejection chute.
Cooking
Because eddy currents produce heat in conductive materials, they can be used in the induction heating of pans. Electromagnetic coils will not be hot to touch but will swiftly produce heat in metallic pans when they are placed nearby. Induction hobs are used in top-of-the-range domestic cooking appliances.
Metal And Paint Coating Thickness Testing
If an alternating electromagnetic current is passed over a coating, its thickness can be measured by measuring the strength of the eddy current produced.
Brakes
High-speed trains are frequently designed with electromagnetic eddy current brakes, which enable a train to slow down without there being any mechanical connection between brake drums, pads, and wheels. These brakes essentially work on the very same principle that Foucault discovered – that conductive materials will experience resistance when spanning between alternating magnetic poles. A stationary electromagnet is mounted next to a spinning conductive surface – alternating poles and creating an eddy current that provides resistance. Eddy current brakes have no touching moving parts. This means that they do not wear down with friction as much as traditional brake systems and are considered highly reliable.
Rollercoasters use linear eddy current brakes mounted on the side of the track to effectively slow speeding cars. Magnets mounted with gaps in between them create eddy currents in strips of metal mounted on the rollercoaster car itself.
