Knowing Alnico magnets
Alnico is an acronym referring to an alloy of Aluminium (Al), Nickel (Ni) and Cobalt (Co).It is basically an iron alloy which has Al, Ni and Co other than iron ore. It was first manufactured in Japan.
They are a category of strong permanent magnet with excellent temperature stability, high residual induction, and relatively high energy and are physically hard and brittle. Their shapes are mainly round and rectangle. However, many other shapes can also be manufactured using different foundry techniques.
Alnico has a low coercive force and can get easily demagnetized if it is not handled carefully. Despite that they can be pretty easily re-magnetized even if they lose partial magnetization. Also some types of Alnico magnets are homogenous so they can be magnetized in any direction whereas the others are non-homogenous and therefore can be magnetized in only one specific direction. The latter have a greater magnetic capacity than the former.
One of the most useful properties of an Alnico magnet is that it is the only magnet that has useful magnetism even when heated red-hot. They are also one of the most stable magnets.
The creation of Alnico magnets
Alnico magnets can be produced by either casting or sintering process. The Manufacturing process of cast magnets is an elaborate one involving the pouring of a molten metal alloy into a mold and later treating the resultant material to heat in cycles. The magnet that is formed is dark grey in color with a rough surface.
However, machining of the surfaces can give them a shiny appearance like that of steel. Sintered magnets, on the other hand, are prepared by the compaction of fine grained Alnico powder by pressing and then produced compacted powder is sintered into a solid magnet.
Alnico is brittle, and therefore can easily chip or crack. To machine this material it is imperative to use special machining techniques. Cast Alnico materials contain some imperfections which can be exposed by finish machining.
According to the MMPA standard which provides specifications for Permanent Magnet Materials these magnets are mainly used for their magnetic properties rather than for physical use and hence it is imperative that during the manufacturing process some imperfections might creep in.
It is therefore recommended by the standard that these magnets not be used for structural purposes.
The applications of Alnico magnets
Alnico magnets are in wide use in the industry in sectors where strong permanent magnets are used. They are used in various appliances such as electric motors, loudspeakers, microphones etc.
However, in many applications they are being superseded by rare earth magnets, whose stronger fields and larger energy products allow smaller size magnets to be used for a given application.