US2255873A - Magnetic body - Google Patents

Description

y v Patented Sept. 16, 1941v Adolph F. Bandar,

Berwyn, lll., asslznor to Western Electric Company,

Incorporated, New

York, li. Y., a corporation o! New York Application February 25, 1938, Serial No. 192,485

l Claims.

This invention relates to the manufacture of magnetic bodies and more particularly to methods for making magnetic cores of the insulated dust type in which finely divided particles of lmagnetic material are coated with insulation and compressed into form.

In the manufacture of insulated dust magnetic cores the magnetic metal or alloy isusually cast in an ingot and pulverzed to the required ilneness on suitable apparatus, after which the particles are coated with insulation and compressed into required shape. Because the pulverizing action produces internal stresses in the particles which detract from their magnetic properties, the particles are annealed before they are incorporated in a core. It has been customary to anneal the dust in a conventional sealed pot and, as the dust tends to sinter during `this operation, it has generally been necessary to regrind the annealed material before use which results in the restoration of objectionable stresses therein.

An object of this invention is the provision of improved methods for the heat treatment of iinely divided magnetic material' for use in insulated dust cores.

In one embodiment of the invention vcomm'inuted magnetic material in a plurality of shallow trays supported'at spaced intervals in a ventilated container is subjected to a heat treating cycle in a furnace. A cover on the container Fig.l2 is a sectional view of Fig. 1 taken on the line 2 2.

In the preparation of the alloy, molybdenum, nickel and iron 1n suitable proportions, and preferably a small amount of iron sulphide or other embrittling agent, are melted together in a furnace and the resulting alloy is poured into a mold to form an ingot. To develop a-fine grain structure in the alloy the hot ingot is passed successively through progressively reducing rolls, the final reduction being effected at the approximate temperature at which the alloy ceases to be malleable, after which the rolled material is 'quenched in Water at a temperature below` its has a vent in its centralV portion through which gases generated by the magnetic material during one portion of the cycle escape from the container and through which outside air is admitted to the container during another portion of the cycle. The incoming air passes over a sheet of hot iron which removes oxygen from the air. With this procedure and apparatus the dust is effectively annealed without sintering, which precludes regrinding, and the treated dust is more adaptable to subsequently applied -insulation than previous materials, which enables the production of cores having higher permeability values. This process and apparatus are especially suitable for treatingy nickel-iron magnetic alloys of the Permalloy type and have been adapted to a molybdenum Permalloy magnetic alloy, comprising essentially 82% nickel, 16% iron, and 2% molybdenum. For convenience the invention will be described in detail as applied to that material,

Ain conjunction with the appended drawing, in which v- Fig. 1 is an elevation in section of an apparatus for the heat treatment of magnetic dust embodying certain features of the invention, and

malleability range. The resultant ingots are broken into fragments and the fragments are crushed in a hammer mill, or other suitable apparatus, after which the crushed material `is pulverized in an attrition mill or similar apparatus. tionk that will not pass through the sieve is returned to the mill for further pulverizing, this process being repeated until a suiicient quantity of fine dust is obtained.

The dust is then heat treated in the apparatus shown in the drawing, and disclosed in my United States Patent 2,211,311, to relieve the stresses produced by the pulverizing action and otherwise improve the magnetic qualities of the dust.

A measured quantity of dust i0 is placed in a shallow flat-bottomed tray I l or pan having sides extending at an angle ofabout 45 to the plane of the bottom. Inside the vtray and welded or otherwise secured to the bottom thereof are four V-shaped supports l2, conveniently formed from strip steel, which have fiat vtop portions positioned about 1/8" below the top rim of the tray.

The tray can be made of sheet metal and a low carbon steel gives goodI results.

'I'he dust is spread evenly in the tray to a depth governed by the sintering tendency of the particular material under treatment. sintering is a function of temperature and pressure, which vary with the composition and' particle size of the dust, and in eachl case the .depth of the dust in' thick walled container I3 or box of rectangular shape. l'I'he number of trays in each container is The resulting dust ls sieved and any por- 2 i based on handling convenience, but it is advantageous to treat a substantial quantity of dust in i a single container to provide material of uniform 1 quality. I'he lower tray rests on the at con'- tainer floor and the upper trays are successively positioned on the four supports in the adjacently lower tray. On the supports in the top tray is 1 is placed a rectangular sheet of iron llwhich extends over th entire surface of the dust in the tray and extends closely to the tray edges on all sides.

v `placed 'periodically.

the form of a core.

y insulation.

After the trays and sheet iron are positioned in the container, a ilat cover I5 is placed on the container and its edges are sealed thereto with loam I6 or other suitable medium in a continu- 3 ous channel I1 at the top of the container into which a peripheral ange I8 on the cover ex-v tends to provide an eiective seal. At'the approximate center of and extending through the cover'is a vent I9 about one-eighth inch in di- '1 ameter providing an opening into the container. l

The assembled container is placed in a suitl able furnace (not shown) and subjected to a pre Y scribed heat treating routine. For the treatment of the molybdenum Permalloy dust the container 3 is heated to a temperature around850? C. and maintained at that temperature for about one hour. During this period of heat application an l internal pressure is built up in the containerdue to the development of certain gases generated by :heating of the dust. the container through the cover vent and burn i in a tapering llame at the outside of the cover. It is desirable to completely exhaust the gas l generating capacity of the dust during the heating period and therefore the period may be ex- These gases escape Irom tended beyond the prescribed one hour. This is readily controlled by obrvation of the llame at the vent'and if necessary the heating is prolonged until the ilame discontinues.l i After the completion of the heating cycle the `container and contents are cooled at a rate `not exceeding 10 C.fper minute. During this cooling period the gases in the container contract `in volume, and the current iiow is consequently reversed.4 causing air to enter the vent into the container. from the furnace chamber. It is degsirable to prevent oxidation ot the hot dust during this interval'andthls is accomplished by removing oxygen !rom the lincoming air by means :of the heated iron sheet over the top tray, and

the heated trays. Before reaching the dust parmalloy particles treated by applicant's process required 10% less insulation than dust treated -by old methods for equivalent core service. Be-

cause of the sma'ller percentage of insulation present, thenew cores have higher permeability values than the old structures which enhances the utility of the cores when they are used in loading coils and .similar apparatus.

The described methods and apparatus are applicable to various types of magnetic material and modiilcations of the methods and apparatus specically disclosed herein can be readily adapted to a variety .of materials to supply new and useful properties thereto. It is, therefore, to be understood that the invention is restricted only by the scope of the appended claims.

What is claimed is: l

1. A method of treating finely divided magnetic vparticles to improve the magnetic properties and insulatability thereof which comprises heating a mass of the nely divided particlesl in a vented container at such a temperature as to generate and drive oil.' deleterious gases, removing the gas from the particle mass as the gas is formed, subsequently cooling the particles in the container, and removingoxygen from air enter- 35 .ing the vented container during the cooling period.

2. A method of heat treating finely divided magnetic materialto improve the magnetic propi erties. and insulatability thereof which comprises placing the material in a vented container in a layer suiliciently thin to substantially eliminate sintering thereof, heating the container for a period: suihcient to generate and expel gases from said material, exhausting the container during said heating period. cooling the container and material, and removing oxygen from air entering the vented container during the cooling period.

3. A 'method of treating finely divided magnetic material to improve the magnetic properties thereof by heating the ,material to a prescribed temperature and'subsequentlyy cooling the material at a xed rate,y which comprises placing the material in shallow trays, the depth of the material in each tray beingmain'tained within the value at which a sintering pressure i is produced on 'a portion o! the material at the dizing eiectiveness of the labyrinth the trays are cleaned'at suitable intervals to remove any surv face oxide and the iron sheet is cleaned'or re- At the termination oi theveooiing lcyclethe dust 'is removed from the trays and 'the particles are coated with' suitable'insulation mich as thev mixture of magnesium. silicate, sodium silicate `and magnesium hydroxide disclosed in applicants Patent 2,105,070 after which the imulated particles are compressed at high pressure into Magnetic particles treated as described; exhibit new and improved properties that are valuable in insulated dust cores. Formerly, when the'dust was heat treated in a sealed pot any gases gen- Vprescribed temperature, assembling a number of the material containing trays in xed relative positions in a ventilated container, heating the container atthe prescribed temperature, subsequently cooling the container at the flxedrate,

and removing oxygen from air entering the ventilated container .during the cooling period.

y4. A method of. treating 'a lmagnetic nickel iron .alloy in the form or small particles to improve .the properties and' insulatability thereotpwhich comprises the particles in av vented container, heating the container -at such a temperature and period -asvto generate and expel .gases from the particles and the vented containen'cooling the particles in the container,

' and removing oxygen from air entering the container during the cooling period.

.erated by heating were largely reabsorbed dur- 5. A method'of treating nnely divided particles Cores made with molybdenum Perof a magnetic alloy comprising. substantially 82% nickel, 2% molybdenum, and the balance iron for the purpose of improving the magnetic properties of the particles and the insulatabillty thereof, which comprises placing the particles in a vented container, heating the container at a temperature laround 850HC. for two hours, re-

moving generated gases'rom the container during said heating, subsequently cooling the particles in the container at a rate not exceeding 10 C. per minute, and removing oxygen from air entering the container lduring said cooling period.

ADOLPH F. BANDUR.

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