Magnet Sales and Service Ltd
Sintered Samarium Cobalt rare-earth (SmCo) magnets are manufactured by using powder metallurgy techniques which include stringent process controls and complicated heat treatment cycles. The composition of this alloy is approximately 35% Samarium, 60% cobalt with the balance being Fe & Cu. By varying the percentages of this composition and changing the sintering & heat treatment cycles the two grades 1:5 & 2:17 are produced. The difference between them is in energy product, temperature coefficient and magnetisation force required tosaturate. The 2:17 offers a better performance & lower temperature coefficient, however it is slightly more expensive and requires very high fields to magnetise it.
Both grades exhibit excellent energy, temperature and corrosion resistant properties and should be considered as your first choice of material when a compact high energy field is required at temperatures of over 100°C or hostile environments. Being almost impossible to de-magnetise SmCo magnets have a vast range of applications ranging from servo-motors, robotics, machine tools, to relays, sensors & UHV magnetrons.
Sintered Ferrite Magnets suit a wide range of applications due to their low cost. They are readily available in blocks, rings and discs. Principal applications are DC motors, loudspeakers, reed switch operation, magnetic separator assemblies and general holding devices such as pot magnets. The unmagnetised blocks are machined using diamond cutting machines to match customers' exact specification.
Ferrite has an excellent resistance to demagnetisation and can be magnetised before or after assembly without danger of losing any performance. It can be used in operating temperatures ranging from -40°C to + 250°C. However it does have a poor temperature coefficient losing approximately 0.2% of remanence per degree C when heated above zero.
Aluminium, Nickel, Cobalt also referred to as Alnico 5 and Alnico 500 is manufactured by traditional foundry casting or sintering techniques and was developed in the 1930's. Its principal applications are for triggering of proximity switches such as reeds and hall effects. Other applications include, instrumentation, high temperature 'pot', holding magnets, horseshoe designs for lifting, entry door locks, NDT, magnetic fluid seals, and ferrous separation including sump plugs.
This material offers the best temperature coefficient (0.02% per degree centigrade) of all permanent magnets, thus making it an ideal choice when a constant field over a wide (-270°C to +500°C) temperature range is required.
Bonded Neodymium magnets are produced using compression moulding techniques in simple tools & can be quickly machined into complex shapes. The material is Isotropic offering approximately 10 MGO or 30% of the energy seen in the sintered fully dense material. It has a maximum operating temperature of 120°C and a rather poor temperature coefficient; the Curie temperature is 340°C. Due to its high Iron content these magnets are prone to corrosion and care is needed to avoid moisture or hostile environments. It does have one major advantage over other Rare Earth magnet materials; its Isotropic nature allows it to be magnetised in any direction. It is also possible to have complex multiple pole magnetisation making it an ideal choice for the computer peripheral industries for such applications as small precision motors. Radial and multiple pole magnetisation requires special magnetising fixtures.
NdFeB magnets are again manufactured using a powder metallurgy route. After sintering the material is ground or sliced to size before coating & magnetisation. Sintered NIB magnets offer the highest energy per unit volume of any permanent magnet material, it can lift up to 1000 times its own weight. It is manufactured in numerous energy and temperature grades, current energy levels start at 33 MGO, with up to 50 MGO having been developed in the laboratory. The intrinsic (jHc) coercive force determines the maximum operating temperature, however, it should be noted that even the SH (high coercivity) 150°C degree materials still have a poor temperature coefficient which means that an open circuit magnet can lose about 0.10% of Remanence per °C. These losses are called Reversible Losses and the Remanence will recover as the temperature falls. A vast section of standard disc & blocks sizes are available from stock. Non standard sizes can be manufactured using diamond slicing or grinding techniques at short notice. Apart from temperature difficulties NIB also suffers from corrosion because of its high Iron content and although the magnets are normally supplied coated particular care must be taken to avoid Hydrogen or salt water environments. Although Neodymium offers 30-40% higher energy levels than SmCo alloys and is considerably lower in cost and less brittle, SmCo magnets should still be considered your first choice if either high temperatures & or hostile environments are to be encountered within your application.