Compositions – Magnetic – With wax – bitumen – resin – or gum
Patent
1986-01-30
1988-01-12
Demers, Arthur P.
Compositions
Magnetic
With wax, bitumen, resin, or gum
252 6251, 252 6253, C04B 3504, H01F 106, H01F 126
Patent
active
047190272
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a shaped article having magnetic properties, particularly to a shaped article comprising particulate material having magnetic properties, to a process for the production of said article, and to a composition for use in such production.
Within the scope of the terms shaped article having magnetic properties, and particulate material having magnetic properties, there are included articles and materials whose properties may be described as ferromagnetic or ferrimagnetic. Both these latter terms include articles and materials which once magnetised remain magnetised when removed from the influence of a magnetic field, and also articles and materials which are capable of being magnetised but which do not remain magnetised when removed from the influence of a magnetic field. Such articles and materials may be considered to be, respectively, permanently and temporarily magnetisable, and are frequently referred to as "hard" and "soft" respectively.
The metals iron, coibalt, and nickel are all ferromangetic. They may be either permanently or temporarily magnetisable depending on the nature of or the amount of additional element or elements with which they may be alloyed.
Materials which are ferrimagnetic include Ba Fe.sub.6 O.sub.19, which is permanently magnetisable, and (Mn, Zn) Fe.sub.2 O.sub.4, which is temporarily magnetisable. Such examples of ferrimagnetic materials are examples of a class of materials referred to as ferrites. The term ferrite is a term well known in the art. Ferrites are magnetic oxides containing iron as a major metallic component and in addition another metal component, e.g. manganese, zinc, lead, strontium, barium, lithium or nickel. The term can include spinels, perovskites, magnetoplumbites, and garnets.
Shaped articles of metals or alloys, for example, iron, cobalt, and/or nickel and/or alloys thereof, may be made by conventional metal shaping techniques, for example, by powder compaction or by casting at high temperature. The present invention relates to the production of shaped articles from particulate materials having magnetic properties, and although it may be applied to the production of shaped articles from metallic particulate magnetic materials, it is also suitable for use in the production of shaped articles from non-metallic particulate magnetic materials, for example ferrites, which may not normally be produced by metal shaping techniques.
Shaped articles of ferrites may be made, for example, by a powder compaction process in which the powdered ferrite is compacted under pressure in a suitably shaped mould and the powder is subsequently sintered by heating at a high temperature which may be in excess of 1200.degree. C. Controlled heating and cooling rates may be required, as may be heating for some hours at the peak temperature. The presence of air or air enriched with oxygen may also be required.
Shaped articles of ferrites may be made from a composition comprising, ferrite powder and a solution of a polymer binder. The article may be shaped, for example, by extrusion, injection moulding, or compression moulding, pyrolysing the polymer binder and finally sintering the ferrite powder.
Shaped articles of ferrites may also be made by filling of plastics materials, although in this case the article generally contains a relatively low proportion of ferrite and thus possesses relatively poor magnetic properties.
Permanently magnetisable materials are used in a wide variety of applications, for example, in motors and in loud speakers. Temporarily magnetisable materials are used in transformers, in antennae rods, in recording heads and in memory cores.
Furthermore, certain ferrites possess the unusual feature of being able to damp vibrations. Articles made in the manner described later may have a good combination of high modulus and good vibration damping.
The present invention relates to shaped articles of particulate materials having magnetic properties, and to the production of such articles by a process which does not involve a lengthy and expensive s
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Battersby Stephen J.
Raistrick James H.
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