US1863325A - Core for electric induction coils - Google Patents

Description

Patented June 14, 1932 UNITED STATES PATENT OFFICE LESLIE GIDDENS BBAZIER AN D JAMES URMSTON, 01 LONDON, ENGLAND CORE FOB ELECTRIC INDUCTION COILS No Drawing. Application filed August 28, 1929, Seriallo. 389,096, and in Great Britain September 14,- 1928.

This invention relates to the manufacture of iron cores of electric induction coils, particularly to those coils used in connection with long distance telephony and known as loading I coils.

It is well known that a suitable core can be made by compressing iron powder into a coherent mass, in a suitable mould. Inorder that such a core shall have the required elec- 10 tro-magnetic characteristics, it has been found necessary that the individual grains of iron shall be magnetically separated and preferably also electrically insulated from one another, at the same time the iron grains 15 must be packed as closely to one another as possible. I

It is the object of this invention to produce such cores by the use of an insulating material which is better suited to the requirements of 10 the case than the materials now in use.

The material used for producing the nec essary insulation of the iron grains is one possessing the following properties. It must be in a state of extremely fine subdivision, each individual particle must be capable of resisting shear under pressure, and the material must be a reasonably'good magnetic and electrical insulator.

A .material which .embodies these three properties in a highly efiective degree is a treated form of china clay, known as osmotic kaolin, which is in a state of extremely fine v division. This kaolin is produced by cataphoresis in what is known as the osmotic process and is particularly suitable on account of its extreme purity and fine division.

Kaolin, as it occurs in nature, isa clay consisting of a mixture of particles differing considerably in size. A proportion of these are of colloidal dimensions and a proportion are of materially larger dimension. By cataphoresis it is possible to remove the smaller particles from a suspension in water and separate them from the larger particles. It is with the particles of colloidal, dimensions so separated that the present invention deals. Such particles are taken without mixture with water and are distributed throughout a mass of grains of magnetic material and with 10 or without a binder,'such as shellac, and the whole is consolidated under pressure without employing a temperature approaching the fusion points of the kaolin. By this means the kaolin is in its original form in the final product,.that is to say, the particles retain their natural toughness which peculiarly fits them for the function of separating the magnetic grains during and after consolidation by high pressure. By this means it is ensured that, although the grains of magnetic material are forced very close together, they are still separated by spaces of very small dimensions in which the small particles of kaolin are situated.

The invention accordingly consists in using, as the-insulating material in a core of the kind indicated, kaolin in a state of subdivision in which the particles are of colloidal dimensions, of which osmotic kaolin is an example. The cores are manufactured without the use of high temperatures such as those at which partial or incipient fusion of the kaolin may take place with the aid of a flux.

It has been found that a suitable mixture can be formed containing up to 10% by weight of the treated kaolin, depending to a great extent upon the division of the iron.

The mixing may be carried out in any convenient manner. If the kaolin is thoroughly dried, it can be mixed dry with the iron powder by mechanical agitation, or another method is to suspend the kaolin in an easily evap-- orated liquid, such as alcohol, mix the suspension thoroughly with the powdered .iron and then evaporate off the alcohol.

In order to facilitate the coherence of the mass under pressure a small quantity of shellac or," similar material may be introduced into the mixture, either by dry mixing or by evaporation from solution or by any other known means. This shellac merely fills up the interstices between the grains of iron and kaolin and tends to bind the mass together. It is not relied on in any way for either the ma etic or electrical insulation of the grains 0 iron.

The grains of the kaolin whilst having theproperties of both magnetic and electrical insulation are extremely small, and enable the iron grains to be packed closer together than hitherto, whilst still retaining the necessary insulation from one another. Furthermore the kaolin does not become liquid or 5 lose its propert of resistin shear, which enables extreme y high mou ding pressures to be used without risk of bringing the iron grains in contact one with another.

What we claim as our invention and de 10 sire to secure by Letters Patent is A core for anelectric induction coil com prising powdered magnetic material and in-. sulating material for separating the magnetic grains, mixed together and consolidated by 15 high pressure, in which the insulating material is unfused osmotic kaolin.

In testimony whereof we aflix our signatures.

LESLIE GIDDENS BRAZIER. 2 JAMES URMSTON;