Alnico magnets have now been manufactured for over 100 years, in which time the process has not drastically changed.
Alnico magnets are permanent magnets that are primarily made up of a combination of aluminium, nickel and cobalt but can also include copper, iron and titanium.
In this blog we will be explaining the manufacturing process of Cast Alnico, a larger Alnico magnet weighing tens of kilograms which will nearly always be produced by casting.
Step 1 – Foundry Furnace
Each grade of Alnico has a special recipe in terms of the percentage of aluminium, nickel, cobalt and iron used.
Quantities of the individual elements are put into an induction furnace and melted at over 1750oC. Extra aluminium than what is actually required to form the final magnet is added because some is wasted as it melts at a much lower temperature, generally around 680oC.
During the melt and before casting, a sample is taken, cooled and analysed using an x-ray spectrometer to confirm that the exact ratios of materials are correct and to allow any last minute adjustments to be made.
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Step 2 – Casting
The molten material is poured into a shell mould or larger green sand moulds. As the molten metal cools, the shell moulds start to burn and by the time the magnets are cold, the shell is almost disintegrated. A shell mould is made using a pattern plate and a moulding machine.
Patterns are a similar size to the required magnet size but with an additional allowance for shrinkage and machining to size.
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Step 3 – Fettling
The newly cast magnets are harvested from the moulds before they are then fettled on grinding wheels to remove the runner gates.
Step 4 – Heat Treatment
The magnets are then heated to a very high temperature and are placed into magnetisers so that they can start to cool down whilst in the presence of a very strong magnetic field. This process is known as hardening the magnets.
The magnets are then placed in large tempering ovens for a few days to temper and stabilise the magnets.
The heat treatment stage of the process, in conjunction with the foundry mix of alloys, gives the magnetic material its temperature handling characteristics and its final magnetic properties.
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Step 5 – Grinding
The magnets often need finish grinding to tight tolerances. As the magnets are very hard, this is done by grinding.
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Step 6 – Testing
Alnico magnets can be tested with an hysteresis graph testing machine, gauss meter or flux meter.
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Step 7 – Coating/Painting
If a specific coating is required, this is done right at the end of the process. The poles of the magnets may be fettled to leave them bright and shiny.
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Step 8 – Magnetising
Magnets are inserted into a coil or solenoid magnetiser and in one fifth of a second, the electrical pulse generates the necessary field needed to fully magnetise the magnets.
Finally, every magnet sold by FIRST4MAGNETS is quality assured before it is dispatched to the customer to be used in hundreds of different applications.
If you have any questions or queries then be sure to get in touch with our team of experts who are available on 0845 519 4701 or sales@magnetexpert.com and are always happy to help.
