How Is a Permanent Magnet Made

A permanent magnet is a type of magnetic material that generates its own constant magnetic field. Without permanent magnets there would be no electric motors, loudspeakers, computers, hard disc drives or smartphones, to name just a few of the modern everyday appliances that depend on magnetic field strength.

The most commonly used permanent magnets are made from neodymium, iron and boron in alloys such as NdFeB, NiB and Neo, although some rare earth magnets, including the popular ferrite and Samarium Cobalt (SmCo) magnets are also produced. They are often coated in order to improve their performance.

How do they make them?

Neodymium and ferrite magnets are manufactured using the powder metallurgy process. In this method, a suitable mixture of the desired metals and binder is mixed, milled to a fine powder and then compressed or compacted into shapes before heating to cause densification via liquid phase sintering. The result is a magnet with a uniform surface and dimensions.

Electromagnets are similar to a permanent magnet but they do not produce their own magnetic field and therefore require a current of electricity to be applied to them in order to generate one. However, they are not always as durable and can be easily damaged if the current is interrupted.

Generally, they are not as strong or durable as the permanent magnets and should not be used to hold heavy items. They are also more prone to corrosion and should not be utilised as structural components as they will corrode quickly.

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They can be shaped into many different forms such as rings, bars and discs plus custom shapes such as trapezoids, arcs, mitres and the famous ‘top hat’. They are usually supplied with a coating to help prevent rust and corrosion and can be produced in various colours.

The process for forming these alloys into magnets is essentially the same as making any other metal or ceramic part. After the mixture is calcined and the particles are wet ball milled, they are then compacted or press fired to produce the final shape. This can either be done in a vacuum or at room temperature depending on the specific alloy being produced.

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Once the shape has been achieved, it is packaged in boats and loaded into a vacuum sintering furnace. The specific temperatures and presence of vacuum or inert gas are determined by the type of rare earth alloy being produced and the grade required for optimum performance.

After the sintering process, the magnet is then subjected to a tempering heat treatment. This is to soften and prepare the magnet for a more demanding role in a production process.

Some electromagnets are cast from a steel or copper alloy. These are typically more common in the commercial sector and may be available in standard sizes or can be designed with a range of special shapes to suit customer requirements.

All of the above methods can be used to make a wide range of permanent magnets, the most popular of which are made from neodymium, ferrite and samarium cobalt. Other materials such as boron and iron can also be used to produce magnetic components but these are not as common or durable as the neodymium or ferrite alloys.

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