US2185464A - Alumino-thermic mix for making permanent magnets - Google Patents

Description

Patented Jan. 2,

ALQ-THEBWC FOR Hugh A. Howll, Berwyn, 111., gnor to Frank 11 fies, Chicago, Ill.

No Drag. Application December 20, 1937, aerial No. $0,824

3 Claims.

This application is a continuation in part of my application filed June 29, 1937 which issued June 28, 1938 as Patent No. 2,121,799.

This invention relates to permanent magnets,-

% especially permanent magnets of aluminumnickel-iron type, and also to a new process of manufacturing the same.

Castings for permanent magnets of the aluminum-nickel-iron type, when made by the ordinary foundry methods, must be subjected to heat treatment such as normalizing treatment or age hardening, before they are magnetized. Unless this is done, the resulting magnet will be of distinctly inferior quality. A heat treating process is also necessary if the cast alloy contains a fourth element such as cobalt. Such heat treating processes are described in United States patents to Ruder, No. 1,947,274 and No. 1,968,569. The magnets of the above type that contain cobalt are generally superior to those without cobalt, but more costly. In accordance with the teachings of the present invention it is possible to produce a cast permanent magnet comparable in quality with cast permanent magnets of the aluminumnickel-cobalt-iron type, but less costly in that I obviate the need for heat treatment of the casting prior to magnetization, and in some instances also eliminate the cobalt, which is an expensive metal, from the alloy.

The present invention aims at providing a method of making cast permanent magnets easily and cheaply, without the need of a' furnace and without resource to orthodox, foundry methods, materials and equipment. Another object of this invention is the provision of a simple, economical method of producing cast alloys which can later be magnetized and which will acquire and retain a high degree of magnetic power.

The invention will be best understood from reference to the well known chemical reaction between iron oxide and aluminum in a properly divided state based on the equation The reaction is started by igniting the mixture at one spot, and it continues throughout the entire mass without the use of any other heating agency, and results in superheated liquid iron and aluminum oxide or slag. The reaction is completed in less than one half minute, creating a temperature in the neighborhood of 5000 F.

In carrying out my invention, I mix iron oxide in the proper divided state with aluminum. and nickel, with or without the addition of other metals, in an ordinary graphite crucible. This mixture is ignited by a small electric are produced in any convenient manner. While the chemical reaction is taking place, I agitate the mixture by rocking and twirling the crucible, while holding in an upright position, in order to cause the superheated slag to freeze or adhere to the sides of the crucible. After the reaction has been completed, and before the liquid iron has solidified, I chill-cast the metal by pouring all but the slag into an unheated prefabricated mold built up of several parts. The preferred mold is a steel or iron mold lined with carbon or graphite, and quite massive in proportion to the size of the castings'made therein, so that it can conduct a large amount of heat from the cast metal without itself becoming overheated. The mold may be slightly preheated before the casting operation. After the casting has cooled below the red heat, I may remove it from the mold to cool naturally in the open air.

The cast material is then magnetized in a suitable manner, either in one piece or after having been cut or broken into separate parts. Further machining, shaping and finishing may also 32 accomplished either before or after magnetizg.

With a machined carbon mold, castings can be made which compare favorably with die castings in definition and accuracy. A carbon mold built up in parts is particularly desirable in making very small and delicate castings.

In making a magnet alloy of the nickel, iron and aluminum variety, I use the following mixture in my process above described:

Parts by weight Iron oxide scale (F8304) -approximately 40 Fine commercially pure aluminum shot approximately 15 Fine nickel shot ..do 10 With the above mixture and variations of same, I have poured castings weighing as little as five grams, by the above mentioned process.

The above mixture can produce enough metal for a casting of 35 parts by weight, or 87% of the weight of the original iron oxide, and has a chemical composition approximately as follows: iron 62%, nickel 28%. aluminum 10%.

The. presence of other metals, and carbon in reasonably small percentages, does not damage and may improve the permanent magnetic properties of the aluminum-nickel-iron family of alloys. This applies particularly to the addition of small amounts of cobalt, chromium, copper, vanadium, and the like, or zirconium.

Per cent Iron 57.7 Nickel 29 Aluminum 13 Zirconium 0.2

The presence of zirconium in such small amounts, that is, from a trace up to 2%, produces profound eflects in the magnetic properties of the cast permanent magnet. Also, the presence of the zirconium permits magnetization of the casting without heat treatment. Perhaps this is also a result of the alumino-thermic process of making the alloy.

Zirconium is introduced into the mixture which is to be melted in the oxide form, ZrOz, which is a cheap material. A portion of other substances in the mixture being melted combines with the oxygen in some of the zirconia leaving zirconium as a fourth component of the alloy. Other zirconium compounds which are reduced in the alumino-thermic process may be used instead of the dioxide. In order to obtain a given proportion of zirconium in the alloy it is necessary to introduce more than the chemically equivalent amount of zirconia in the mixture that is to be melted, because some of the zirconium appears in the slag.

A further advantage of zirconium together with the aluminum, nickel and. iron is that it permits a complete elimination of heat treatment of chill castings of moderate size and cross section. For example: A chill casting one inch wide and. onefourth inch thick and two inches long made in accordance with the present invention is as good without heat treatment, such as normalizing or age hardening, as the same casting is after it has been subjected tosuch treatment. The presence of zirconium in a proper amount appears to have the effect of magnetically hardening the alloy during the quick cooling of the casting thereby eliminating the subsequent ageing tendencies that would be present when other metals, such as cobalt, form a part of the alloy. Furthermore, the excess zirconium in the melt has a scavenging effect and thereby tends to reduce the amount of impurities which might otherwise find their way into the casting.

I have found that the following mixtures when melted and reduced by the alumino-thermic process outlined above produce fine permanent magnet alloys, In each instance the weight is given in grams.

Mi.\ Mix Mix M ix Mix Mix Mix 1 2 3 4 5 0 7 Iron oxide 180 180 200 200 200 200 200 Aluminum. 00 90 90 90 90 NickeL. c0 60 00 c0 Zirconium oxide. 10 Copper........... 40 40 40 40 (ohalt...... 40 4o Total mixture 315 325 350 390 430 440 400 The iron oxide was scale F8304. The aluminum, nickel, copper, and cobalt were in substantially the pure form. Instead of using hammer scale (Fe3O4) other compounds of iron, which are reduced by the aluminum, may be used, such as the other oxides of iron. If the nickel, copper or cobalt are in a state that requires reduction by the aluminum then a correspondingly larger amount of aluminum must be used. Also, other zirconium compounds may be used in lieu of the dioxide.

Only a trace of the zirconium appears in the cast alloy. The presence of .2% to 5% of zirconium in the alloy produces as great an effect as the presence of 10% to 15% cobalt. In addition cobalt alloy must be heat treated, but the alloys that do not contain cobalt do not require heat treatment before magnetization.

The presence of the copper in the alloy renders the metal being poured more fluid with a lower solidification temperature, enabling a lower pouring temperature and reducing the likelihood of welding of the poured metal to the molds. It also alters the coeflicient of expansion enough to permit the use of mold cavities of more complex shapes.

I have found that the addition of tin to mix number 3 from a trace to an amount sufiicient to produce an alloy containing 2% tin, results in a casting which may be magnetized to produce a satisfactory permanent magnet. However, the presence of the tin causes the casting to require heat treatment before magnetization, as in the case of an alloy containing cobalt. The presence of tin from a trace up to 5% in the mixes containing cobalt lowers the required normalizing or ageing temperature of the resulting alloy.

The cooled magnet alloy will, under practically all conditions, retain a silvery white untarnished finish, especially if carbon molds are used.

Alloys, when made with my process and poured soon enough after the chemical reaction is completed, will be superheated. The molten metal is more fluid than in ordinary foundry practice. I have filled in cavities in carbon molds resulting in fins over one inch square and less than .010 inch .thick, proving the high fluidity of alloy liquid."

When the crucible is whirled, the liquid slag, which will not mix with the metal and evidently has a higher melting point, solidifies in thin strata on the sides of the still relatively cool crucible so that when the thermic action is completed, the liquid metal is easily poured out of the crucible, there being no slag in the pour.

I am aware that many changes may be made in the ingredients and numerous details in the process varied throughout a wide range without departing from the scope of my invention as defined by the appended claims. What I consider new, and desire to secure by Letters Patent is:

1. An alumino-thermic mix for making a permanent magnet containing aluminum, nickel, a compound of iron, and a compound of zirconium, the substances being present in such amounts that after ignition and separation of the slag the remaining melt will contain from 5 to 40% nickel, 7 to 20% aluminum, from an effective amount to 5% zirconium, and the major part of the remainder iron, and which melt will be suitable for conversion into a permanent magnet upon solidification.

2. An alumino-thermic mix for making a permanent magnet containing aluminum, nickel, a compound of iron, and a compound of zirconium, the substances being present in such amounts that after ignition and separation of the slag 5 will be suitable for conversion into a permanent magnet upon solidification.

3. An alumino-thermic mix for making a permanent magnet containing aluminum, nickel, a. compound of iron and a compound of zirconium,

the substances being present in such amounts that after ignition and separation of the slag the remaining metal will contain at least 5% nickel, at least 5% aluminum, an effective amount of zirconium, and a major part of the remainder iron, and which melt will be suitable for conversion into a permanent magnet upon solidification.

HUGH A. HOWELL.

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