Alnico Magnets

Alnico magnets can be manufactured in one of two ways. The most common method is by casting, but there are times when sintering is also suitable in production. Aluminium, Cobalt, Nickel, Copper and Iron are the components that make up this alloy. Due to its brittle nature, Alnico magnets are not really suitable for structural use. Despite this, it’s still a very hard substance, so drilling and machining it can be a challenge.

Regardless of the method of production (casting or sintering), it can be used for various applications in its “off the shelf” state. However, a smoother surface can be created by precision grinding, which will increase its tolerance and usefulness still further, but as you might expect, this is more expensive.

Due to the nature of production (if casting, sand moulds need to be made and if sintering, the process will need die presses), ordering a small amount of the magnets is usually cost prohibitive. It can be done, but is likely to feature increased charges or at the very least a minimum quantity order requirement.

There are various grades of Alnico available at Bunting Magnetics, although the main standard grade is Alnico 5. The different production methods will also present slightly different finishes to the magnet structure, for example, if they have been cast, there will be tiny air holes present, whereas those produced by sintering will not have these holes. They also sometimes have a protective coating added. This is generally considered unnecessary because the corrosion resistance is already very high. If not for protection, there will sometimes be a coating added to simply make it “look nicer”. The Alnico Red Magnet range is, as the name suggests, after a red coating has been added to the product.

The high Br values present in Alnico magnets are very similar to those found in NdFeb (Neodymium Magnets) and SmCo. However, Alnico is slightly more versatile in the sense that it can be cast into different, complex shapes. In addition, it can actually be magnetised during the heat treatment stage. It is this part of the procedure, which gives Alnico its completed magnetic values. When possible and for performance purposes, it’s common for it to be magnetised during this final part of assembly in order to allow the aforementioned versatility to come into play – this is what makes the horseshoe magnet pattern a possibility.

There are many common uses for this particular kind of magnet, including things like sensors, generators, loudspeakers, electric meters and even dc motors. Alnico is likely to be suited to anything requiring high field output and operation at really high temperatures.

Alnico magnets shouldn’t really be used when temperatures exceed 500°C but are ideal for temperatures over 350°C when, in contrast, SmCo magnets migrate out of the structure at this sort of level, which actually results in an irreversible loss of magnetic output. On the other end of the scale, -75°C is deemed to be the lowest temperature for Alnico to still be 100% effective. At -190°C we begin to see permanent losses (about 10%) in performance. The actual losses for Alnico are a function of the magnet geometry, total magnetic circuit and the BH curve shape.

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