US1887380A - Process of and apparatus for standardizing magnetic cores - Google Patents

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Vii. J. POLYDCROFF PROCESS OF AND APPARATUS FOR STANDARDIZING MAGNETIC GORES REQ VD Filed June 27, 1931 Patented Nov. 1932 I UNITED STATES PATENT; OFFICE 'WLADIMIR J. PQLYDOROFF, OI CHICAGQ'ILLINQIS, ASSIGNOB JOHNSON LABORA- TORIES, INCL, OF CHICAGO, ILLI ENOIS, A CORPORATION OF ILLINOIS rnocnss or AND APPARATUS non Application filed June 27,,

The invention relates to methods of manufacturing, and apparatus for testing mag netic cores, said cores being made of 001m minuted and insulated magnetic particles to reduce'the losses to desired minimum in cir cuits in which said. cores are employed. Because of necessary standardizing of several magnetic cores when used for simultaneous alteration of inductance coils, it may be necessary to maintain these losses at a'very uni-- form level in the production of cores. Practics shows that in the production of'cores, especially in compressed form, the Variations in radio-frequency resistance from the de sired level may be so great that several cores will be rejected because of high loss character. v

To avoid waste, the primary magnetic material has to be of such characteristics, that the highest loss cores obtainable will still be acceptable for high-frequency operation, which in turn would impart to a majority of the cores undesirably low core losses.

The present invention involves a new methnot of increasing the radio-frequency resistance' ofa core by a controllable increase of eddy-current losses after said'core has been completely finished. The insulation of individual particles is found necessary to reduce saidlosses, and, therefore, by de-insulating or bringing several particles in close contact, the losses may be conveniently increased.

The invention will be better understood if reference is made to the accompanying drawing, which shows a convenient electrical arrangement. 1 is a core whose losses are measured in the solenoidal winding 2 which is a partoi a radio-frequency series resonant circuit, consisting of said winding 2, a condenser 3, an ammeter 4, and E. M. F. of a certain frequency. Y

Said circuit is made resonant to the ,applied frequency, either by choosing inductance of the winding 2 on the core 1, or by "adjustment of the condenser 3. Thecurrent in resonance is indicated by the ammeter 4 and the magnitude of it is inversely pro ortional to the radio-frequency resistance of the circuit. With a certain value of E. M. F. the amplitude of current, resonance, may

STANDARDIZING MAGNETIC COBES 1931. Serial resume.

be set as the standard of resistance to which i value all the cores should be adjusted.

Higher current amplitude indicates lower than standard resistance.

Another circuit, which consists of a source of high potential 5 and two electrodes 6, is applied directly on the core. Sufficiently high potential to break the individual insulation of the magnetic particles is applied to any section of the core where it may be desirable to increase the losses. An electric discharge from the electrodes produces conductive paths as indicated by zigzagged lines on the core, which paths increase the eddy-current losses, manifested by increase of radio-frequency resistance of the core, with corresponding decrease of the amplitude of the amrneter 4.

Practice shows that this treatment can be efiectuated 1n the core inside the winding 2, while the radio-frequency c rcuit 18 in oscil=' lating condition.

The direction of discharge, as indicated by the solid-line circuit, is transverse to the magnetic flux direction and, therefore, does not afiect the permeability of the core.

The direction of discharge, as indicated I by thedotted-line circuit, is the same as that of the flux, and the application of discharge may increase both core losses and ermeability, the latter because of decrease magnetic reluctance.

If the discharge is transversely of the core, the core may be rotated while it is being standardized, in order that the electrical dis-- said core until the desired standardization is efiected.

, 3. The process of decreasing the specific resistivity of any portion of a compressed magnetic core having insulated magnetic particles, which consists in passing a current of electricity through said portion, to thereby increase the core losses of said portion.

4., The process of increasing the permeability of a compressed core having insulated magnetic particles,which consistsin pass'inga 1 current of electricity through said corein the flux-direction of said core.

5. The process of measuring the electrical characteristics of and treating a mag netic core having insulated particles, which consists in measuring the core-losses introduced by said core into an alternating-current circuit, and increasing the core losses to a desired standard in said circuit by decreasing the specific resistivity of said core by coincidently breaking down some of the insulation between the particles.-

6. The process of standardizing a magnetic 'core containing insulated finely divided particles, which consists in rotating the core relatively to while subjecting it toan electrical discharge.

7. An apparatus for standardizinga magnetic core containing finely-divided insulated particles, including means for transmitting a dischargethrough said core, an induction coil in the field of said core, and an ammeter in circuit with said coil for indicating the increase of losses of said core.

8. An apparatus for standardizing a magnetic core containing finely-divided insulated particles, including means for transmitting a selective discharge through said core, an induction coil in the field of said core, an ammeter in circuit with said coil for indicating the increase of losses of said core, and a variable condenser.

9. The process of decreasing the specific resistivity of a compressed comminuted material having individually-insulated particles of conductive material, which consists in passing an electrical dischargethrough any portion of said material, thereby partially breaking down the insulation.

10. The process of decreasing the specific re'sisistivity ofa compressed comminuted material having individually-insulated particles of conductive material, which consists in passing an electrical discharge through any portion of said material, thereby partially breaking down the. insulation and bringing certain of said particles into electrical con tact with each other. i

In testimony whereof, I afiix my signature.

WLADIMIR J. POLYDOROFF.

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