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Bonded ferrite magnets are manufactured using injection moulding techniques which are fully automated and particularly suitable for high volume production. Isotropic and anisotropic properties can be obtained in parts with a wide variety of shapes and sizes. One of the greatest advantages of the injection moulding process is that a high degree of shape complexity is possible, eg. gears, snap fits and undercuts. It is also possible to incorporate shafts, bushes and other inserts into the process thereby greatly simplifying magnetic assemblies.

Bonded  ferrite materials are composite materials consisting of  ferrite powders (BaO.6Fe2O3 or SrO.6Fe203) dispersed in an engineering thermoplastic matrix. Polyamides are the most commonly used as the matrix materials in bonded  ferrite compounds, but for applications operating above 120ˇăC, polyphenylene sulphide (PPS) can be used (up to 200ˇăC).

Tailoring of the desired magnetic performance can be achieved by varying the proportion of ferrite powder to polymer matrix. Very high volume fractions of magnet powder are possible.

The magnetic temperature stability is controlled by the ferrite powder, with coefficients of Br = -0.19 %/ˇăC and HcJ = + 0.3 %/ˇăC. With very low temperatures there is a risk of permanent de-magnetisation in magnet systems with low working points. Corrosion resistance of both the ferrite and matrix material is good.

PROCESSING
Processing begins with the controlled mixing and dispersal of the  ferrite powder into molten thermoplastic matrix material. This mixing is conducted on highly specialised state of the art compounding equipment because of the high volume fraction of filler being used. The resultant pelletised compound is the feedstock for the injection moulding process.

Injection moulding is carried out on specially adapted machines. The process commonly operates fully automatically with components being collected and separated directly from the moulding machine. Anisotropic properties can be achieved in axial, radial, diametrical or multipolar orientations during moulding with the presence of the appropriate magnetic fields in the mould tool.

Very precise dimensional control is achieved in this process and the component should not require further machining.

Components may be magnetized before final inspection, packing and despatch.

                              

                                                                  

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