GB2166129A - Method for making cores and the like - Google Patents

Abstract

A method for preparing cores and the like such as magnetic recording head cores. They are made from metallic alloy oxides such as ferrite and used as electrical, electronic, or magnetic elements of electrical appliances such as tape recorders and televisions. The method is characterized by covering alloy compacts partly or wholly by silver and then baking them in an oxygen atmosphere for a predetermined time and at a predetermined temperature, whereby constituents of the alloy compacts are converted to oxides under strict control. Silver covered baked cores may be utilized for attaching terminals.

Description

SPECIFICATION Method for making cores and the like This invention relates to a method for making cores and the like made from metallic oxides.

Such cores made in accordance with this invention are most advantageously employable as electrical,. electronic, or magnetic elements for various appliances.

Molds made from oxides of specific alloys are widely used today as electrical, electronic, or magnetic elements of electrical appliances.

A typical example of such molds is ferrite.

Molds of this kind have been made generally by roasting a metallic alloy, prefiring it and molding its powders to a compact, and then firing it again. As these manufacturing steps, especially the roasting, prefiring and firing steps thereof, are largely influenced by oxygen, it is essential for producing molds of uniform electrical characteristics to take great care of the amount of oxygen which is utilized in the various steps. However, in practice, control of the amount of oxygen is extremely difficult, though not impossible. In fact, molds thus produced by conventional methods are all checked in respect of their characteristics. As their characteristics vary from each other and by each lot, a sampling inspection can hardly be adopted.

In view of the above drawbacks of the conventional methods, the present invention aims to provide an improved method for making electrical, electronic, or magnetic cores and the like made from metallic oxides and having stable and uniform structures and characteristics.

The present invention provides a method for making cores and the like made from metallic oxides for electrical, electronic, or magnetic elements for appliances; which comprises preparing alloy compacts of a desired configuration having metallic constituents which form said metallic oxides when they are baked, covering the said alloy compacts partly or wholly by filmy silver or an alloy thereof, and baking the alloy compacts at least partially covered with the filmy silver in an oxygen atmosphere for a predetermined time and at a predetermined temperature.

The method of the invention comprises roasting a metallic alloy for oxidation after having at least partially wrapped it by a filmy silver. This filmy silver may be made from pure silver or internally oxidizable silver alloy, and the metallic alloy be any metal alloy which can be internally oxidized under a partial pressure of oxygen and at a comparatively high temperature.

The method of this invention is utilized having regard to the following explanation.

While silver absorbs therein oxygen at an elevated temperature, it exhales oxygen at room temperature and becomes pure silver which has a high electric conductivity though it is non-magnetic. Since the partial pressure of oxygen which has been dissolved into silver an an elevated temperature is comparatively low, and since an amount of oxygen which diffuses through a silver or silver alloy is constant at a predetermined specific temperature and under an oxygen atmosphere of a predetermined specific pressure, an amount of oxygen- which shall be diffused into a core metal or metal alloy via silver for oxidizing the former by affiliating thereto, can readily and freely be controlled.

In addition to this advantage, as the oxygen in this instance is given to the core metal through silver and consequently at a selected direction of paths of oxygen, crystalline grains oxidized and precipitated in the core metal are not arranged at random but can be prismatically aligned in the paths of oxygen.

In the method of this invention, a metallic core of a desired configuration which is to be wrapped or sandwiched by filmy silver and then internally oxidized can be made by powder metallurgy, that is by molding and sintering constituent metal powders of the core into the desired configuration. However, it is preferable to make the metallic core from a molten metal alloy, because it will not then have such porosity as is often observed in one made powder metallurgically and which prevents the growth of crystalline grains beyond a certain size. For example, when soft ferrite is made from Ni-Zn-Fe powders by the aforementioned conventional method, the desired magnetic permeability is not obtained sometimes.This is because while the magnetic permeability is often a function of the size of oxidized crystalline grains in the soft ferrite, they cannot attain a desired size on account of the porosity inherent to molds made by powder metallurgy.

The invention will be further described with reference to the following illustrative Example.

A molten alloy of Ni 15%-Zn 35%-Fe 50% was prepared, from which an ingot was made. The ingot was hot rolled to a sheet.

This sheet was sandwiched between a pair of sheets of pure silver, and rolled to an integral wafer sheet. Chips were cut off from this sheet. The chips were baked in an 02 atmosphere for 3 hours.

In order to examine metallurgical structures, several chips sampled from the baked ones were cut vertically, and observed by a microscope of 200 magnifications. Crystalline grains observed there were about 108 Their permeabilities were evenly about 100at, and they did not vary substantially from each other: The chips or cores thus obtained can be used as magnetic recording head cores, magnetic erasing head cores, El & U cores, convergence cores for colour TVs, thermo-switch cores, irradiation absorbers for electric cookers, flyback cores for colour TVs, and so on, when their outer silver films are removed by washing them by acid. When wire terminals are brazed to their outer silver films, they can be employed as noise filters for SCR noise, line noise filters for TV receivers, inductors for stereo loud speakers, and so on.

In the above example, the alloy sheet which has been rolled to a wafer, can be covered by filmy silver by not dipping.

As described above, by the method of this invention, cores made from metallic oxides for electrical appliances can be obtained under strict control of their electrical characteristics and capacities. Filmy silver covering cores can be removed by machining or chemically when desired. Alternatively, the filmy silver can be utilized as it is for connecting the cores to wire terminals.

It shall be noted that "cores" used throughout this specification includes chips or sheets of any configuration and of any dimensions.

Claims (5)

1. A method for making cores and the like made from metallic oxides for electrical, electronic, or magnetic elements for appliances; which comprises preparing compacts of a desired configuration having metallic constituents which form said metallic oxides when they are baked, covering the said alloy compacts partly or wholly by filmy silver or an alloy thereof, and baking the alloy compacts at least partially covered with the filmy silver in an oxygen atmosphere for a predetermined time and at a predetermined temperature.

2. A method as claimed in claim 1, in which the filmy silver is removed partly or wholly from the baked alloy cores.

3. A method as claimed in claim 1 or 2, in which the filmy silver at least partially covering the baked alloy cores is attached with terminals.

4. A method as claimed in any of claims 1 to 3, in which the alloy compacts are made from molten alloy thereof.

5. A method according to claim 1, substantially as herein described in the foregoing Example.