US 2232352 A
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Patented Feb. 18, 1941 UNITED STATES PATENT OFFICE am-saessm s is:
assignments, to Radio Corporation of America, New York, N. Y.. a corporation of Delaware No Drawing.
Application April 26, IQS'L'SQI'III No. 139,000. Iii Germany April 29, 1938 SCIaims.
It is common to produce magnetic cores for intermediate and high frequency purposes from finely powdered magnetic material, such as iron or ferromagnetic alloys, by compressing the particles by means of a bindingagent to form a solid material. For the purpose of avoiding conductive relative contact between the'said particles, various methods have been proposed according to' thereto, a film of a phosphoric acid metal compound is mounted on the magnetic particles without these particles assisting genetically in the tack of the surface since the rate and the uniiormity of the chemical attack per particle canonly be controlled with difiiculty. The fact that in accordance with the invention no gas development as a result of chemical reaction arises is also conducive to uniformity.
The invention is consequently particularly adapted for use with magnetic particles the di-- mensions of which are in the order of magnitude to a few a, the thickness of the insulating films to be obtained notexceeding 20 ma. 0
Since in accordance with the invention the magnetic particles have been provided with a thin insulating film, the magnetic powder thus obtained can be given any shape by compression. I
In order to increase the mechanical strength of the magnet core a binding agent may be used with advantage in a manner known per se after the insulating film is mounted. For this purpose, use may be made, for example, of a synthetic resin which may be capable of being hardened.
In the use of a resin capable of being hardened.
even distribution of the magnetic particles in the final product may be assisted by grinding the material after mixture ,with the resin, by next giving it at ordinary temperatures the desired shape and by then heating it to cause it to harden.
Example I I 1 kg. of magnetic powder is introduced into 1 litre of a 2 normal solution of aqua-ammonia containing 60 milliequivalents of zinc ion and 60 milliequivalents of phosphate ion. The excess of aqua-ammonia is then removed by boiling while shaking continuously so that all the zinc phosphate present in the solution is precipitated on the surface of the particles. After being filtered and dried, the powder is squeezed into the desired shape at a pressure of about 5000 kgJcm.
zinc ion and 45 milliequlvalents of phosphate ion per 100 cm. The paste thus obtained is kneaded while evaporating the excess of aqua-ammonia and water, which may be efi'ected while heating.
to a low extent or in vacuo at ordinary temperatures. The material is then completely dried and ground to form a powder which is mixed with an alcohol solution containing 60 grams of a hardening phenoli'ormaldehyde condensation product. Alter volatilisation of the solvent the powderlng operation is renewed and the powder is then squeezed at 150 C. into the desired shape, it being possible to apply a squeezing pressure of 1500 k8./cm.
In order to avoid the presence of other electrolytes which would affect the properties of the core, the ammoniacal zinc phosphate solution may be obtained by newly precipitated zinc hydroxidebeing dissolved in a concentrated solution of aqua-ammonia, by a dilute phosphoric 1 kg. of magnetic powder is intimately mixed with about 100 cm. of a weakly-acid ferric phosphate solution containing 30 mllliequivalents of ferri-lon and milliequivalents of phosphate 7 tained is reduced to the form of a powder and mixed with an acetone solution containing grams of the commercial resin known under the registered trade mark "plastopal H. Alter volatilisation of the solvent, the material is squeezed into the desired shape at ordinary temperatures, it being possible to apply a pressure of 5000 kg./cm.
1 kg. of magnetic powder is intimately mixed with about 100 cm. of a 2 normal solution of aqua-ammonia containing 30 milliequivalents of cupri-ion and 45 milliequivalents or phosphate ion per 100 cm. and the mixture is evaporated to dryness and powdered, while-kneading, in the manner described in the second example. The powder is agitated in a solution containing grams of a hardening phenolformaldehyde condensation product and is then evaporated to dryness while shaking. The material thus obtained is reduced to the form of a powder and then squeezed at ordinary temperatures at a pressure of about 5000 lrg./cm. The cores thus obtained are hardened in a furnace by heating for three hours at 130 C.
The quantities, indicated in the examples described, of the substances used are chosen to accord with the specific weight of the iron and an average size of the particles 01 3 a as possessed by certain known commercial powdered iron by means of which the invention yields particularly favourable results.
What we claim is:
1. A process of providing particles of ferromagnetic-metallic material with a coating of insulation material substantially entirely by precipitation of phosphoric acid metal compound from a dispersion which has substantially no chemical reaction with the magnetic material itself whereby the original size of the magnetic particles is substantially unafiected during the process, which consists in intimately mixing comminuted ferro-magnetic-metallic material with a compound comprising weakly-acid ferric phosphate solution containing substantially equal molecular amounts of ferri-ion and phosphateion to form a paste, drying the mixture while subjecting it to a kneading action and thereafter comminuting the resulting material.
2. The process described in the next preceding claim characterized by that each kilogram of ferro-magnetic-metallic material is mixed with approximately cubic centimeters of weaklyacid ferric phosphate solution containing 30 milliequivalents of ferri-ion and 30 milliequivalents of phosphate ion.
3. The steps in a process of providing particles of Ierro-magnetic-metallic material with a coating of insulation material which consist in intimately mixing comminuted ferro-magnetic-metallic material with a compound comprising weakly-acid ferric phosphate solution containing substantially equal molecular amounts of ferri-ion and phosphate-ion, and drying the mixture while subjecting it to substantially continuous agitation.
EVERT JOHANNES WILLEM VERWEIJ. JAN HENDRIK DE BOER. THEODORUS ANTHONIUS SPOOR.