US3540947A - Method of manufacturing a permanent magnetic alloy - Google Patents

Description

Nov. 17, QO

Filed Oct. 23, 196'? SDAECHH KMKI METHOD OF MANUFACTURING A PERMANENT MAGNETIC ALLOY santafe 2 Sheets-Sheet 1 INVENTOR JHM/CIN fO/Y/P/f/ ATTORNEYS Nom l?, i970 sADAlcl-il Kon/@AKH 3,540,9?

METHOD OF MANUFACTURING A PERMANENT MAGNETIC ALLOY Filed Oct. 23, 1967 2 Sheets-Sheet 2 chill plate OOOOOO OOOOOO OOOCOO OOOOOO OOOOOO Fig. 6@

lagging magnetic alloy products portion 1N VENTOR SRM/CHI nor/mw BY J J ATTORNEYS 3,540,947 METHOD F MANUFACTURING A PERMANENT MAGNETIC ALLOY Sadaichi Komaki, 2-20-5 Kaga, Itabashi-ku, Tokyo, Japan Filed Oct. 23, 1967, Ser. No. 677,307 Claims priority, application Japan, Oct. 25, 1966, 41/69,970 Int. Cl. C21d 1/04; H01f 1/02 U.S. Cl. 148-103 2 Claims ABSTRACT 0F THE DISCLOSURE A method of manufacturing a permanent magnetic alloy formed with columnar crystals oriented parallel to the axis of the alloy, characterized by steps of melting and casting in a mould a permanent magnetic alloy blank comprisng cobalt, nickel, aluminum, copper, titanium and iron, applying a coat of sulphur to the surface of said blank, inserting the blank in a non-magnetized sheath, passing the blank containing sheath through a heat area defined by an electromagnetic induction coil energized by an alternating current of frequency to progressively heat the zones of the blank passing through said area to such a degree as to destroy original crystalline structure and cause recrystallization, and thereafter passing said sheath into a cooling liquid so as to progressively quench said blank to thereby produce substantially completely unidirectionally oriented crystals in said blank.

Advances in the progress of modern industries have brought about improved performance of electronic equipment and other machines and instruments which have become more efficient in operation and compact in size than ever before. Magnetic materials which constitute the nucleus of various equipment have also made progress by leaps and bounds. Particularly noteworthy have been the improvements made in the properties of permanent magnetic alloys.

The present inventor has carried out research on permanent magnetic alloys for some time past. His inventions in this lield of art have been granted I apanese Pats. Nos. 458,293, 447,358 and 466,178, and permanent magnetic alloys are now manufactured by the methods of the patented inventions on an industrial scale, making no small contributions to the progress of industries.

Meantime, there are no bounds to advance in the progress of electronic equipment, and the development of integrated circuits has accelerated a further improvement in performance and made it possible to obtain a compact overall size in these equipments. This has made it necessary to make further efforts in improving the properties of permanent magnets.

Improvements in the magnetic properties of permanent magnetic alloys generally rest in the following three points:

(l) Increased residual magnetism (Br); (2) Higher coercive force (HC); and (3) Higher (BH)maX.

The three patented inventions referred to above substantially satisfy the requirements 'set forth above. However, there has since been made a demand to increase coercive force still further. In an effort to satisfy this demand, various proposals have been made to increase coercive force of permanent magnetic alloys.

Methods proposed for increasing coercive force of permanent magnetic alloys include addition of titanium. Typical of the permanent magnetic alloys containing titanium is an Alnico 8 alloy which contains 8% of aluted States Patent ICC.

minum, 14% of nickel, 35% of cobalt, 3% of copper, 5% of titanium, and the remainder iron. It has a residual magnetism Br of 8,000 to 9,000 gauss, a coercive force HC of 1,200 to 1,400 oersteds, and a maximum energy of 3.0 to 4.5 106 gauss oersteds. It will be seen that the alloy shows substantially marked improvements in coercive force over alloys of the prior art and has a satisfactory value of HC. However, it is relatively low in maximum energy, the value thereof being less than half the values shown by the permanent magnetic alloys according to the patented inventions of the present inventor mentioned above.

Efforts have hitherto been made to bring about an improvement in maximum enregy of permanent magnetic alloys of high coercive force and high titanium content, of which Alnico 8 is the mainstay. However, there have been many obstacles that have to be overcome in manufacturing permanent magnetic alloys of higher maximum energy because of the fact that permanent magnetic alloys of high titanium content tend to have a very nely shaped and brittle crystalline structure. To obviate Ythis problem, the invention of Japanese patent appln.

publn. No. 9,284/ 66 has been made, but method of this invention has not been carried into practice on an industrial scale for reasons listed below, in spite of the fact that three years have already elapsed since the application for patent was tiled. The defects of said method are as follows:

(1) A columnar crystalline structure cannot be obtained unless by a high temperature casting technique. The Official Gazette of Japanese patent appln. publn. No. 9,284/66 contains on p. 2. the following statement: A macro structure is shown that has been obtained by the so-called chill casting technique by which a magnetic body is cooled starting from the bottom surface. From this statement, it would seen that a columnar crystalline structure can be obtained by using a chill plate in the conventional manner. However, there is a description on p. 3 of said Official Gazette to the effect that melt in the atmosphere in a high-frequency furnace, and cast in a heated mould. The alloy obtained by this process is said to have the following magnetic properties: Br, 10,500 gauss; HC, 1,310 oersteds; (BH)maX.,

gauss oersteds, with the convexity ratio of magnetization curves being 52.4%. From this statement, it will be evident that the attainment of a maximum energy of the order of 7.0 to 7.2 106 in a permanent magnetic alloy is impossible unless a heated mould is used and the magnetic material is quenched starting from its bottom surface. The present inventor has conducted experiments on this process, and the results obtained show that the process entails a lot of labor and expenses. Typical of the techniques involving the use of a heated mould is the Show process patented in Great Britain which also requires a lot of expenses and a long interval of time to manufacture permanent magnetic alloys, so that the process is not suitable for industrial production because of high production cost. So long as the production of permanent magnetic alloys relies on the use of heated moulds it would be almost impossible to obtain magnets at low cost on a mass production basis. As shown in FIG. 6 of said Official Gazette, a heated mould is honeycombshaped, wtih the upper part of the mould being formed as a heating water basin, as shown in FIG. 6a of said Official Gazette, in which is placed a number of waste magnetic alloys to prevent the magnetic alloys to be manufactured from being cooled starting from above for the purpose of obtaining a columnar crystalline structure in the magnetic alloys. This process has a low yield of magnetic alloys as illustrated in FIG. 6c of said Ofcial Gazette, resulting'in higher production cost. It lwill be understood that it is only in the middle portion that a suddent reduction in temperature is less likely to occur, because the circumferential portion cools olf quickly. Since the portion of alloys nearer the chill plate cools off quickly, the magnetic alloy blanks obtained tend to have a columnar crystalline structure which is composed in three stages as shown in FIG. 1 of said Official Gazette.

(2) Columnar crystals are very small and unstable. Assuming that a columnar crystalline structure is obtained by the high temperature casting process mentioned above, the columnar crystals formed will be very small, with the crystals being needle crystals of small width and a length of the order of to 50 millimeters. The above statement is based on information obtained from the report made by the inventor of the quoted Japanese patent in the Journal of tle Japan Institute of Metals, 1966, vol. 30, No. 4, on p. 315. As for the magnetic properties of permanent magnetic alloys produced by a high temperature casting process or a heat generating casting process, there are many other reports in the literature which show that the maximum energy (BH)mx of the alloys are of the order 7.0 to 7.2. It is to be noted that the columnar crystals formed in these alloys are not necessarily oriented in a given direction, but that there are unstable columnar crystals which prevent the magnetic alloys from having a higher maximum energy.

(3) Columnar crystals vary in pattern in the upper and lower portions of the magnetic alloy. The description in the aforementioned Ofiicial Gazette of Japanese patent shows that the columnar crystals formed in a permanent magnetic alloy (a rod-shaped magnetic body 13.8 millimeters in diameter and millimeters in length) obtained by the high temperature casting process are arranged in three different patterns. The lowermost portion of the magnet nearest the chill plate has very small crystals which are needle crystals having a height of 5 to 7 millimeters. The crystals in the center portion are larger than in the lowermost portion, while the crystals only in the uppermost portion of the magnet which is suciently heated are satisfactory for practical purposes and have a length ranging from 11 to 13 millimeters.

The portion of the columnar crystalline structure of the magnet near the chill plate has a maximum energy of 4.6 106 gauss oersteds, which is a very low value. This does not show the effect of addition of sulphur in the alloy and the use of a chill plate technique. The upper portion of magnet which exhibits the best columnar crystals obtained has a maximum energy of 8.0 106 gauss oersteds, which is substantially equal to or below the values obtained with the methods of patented inventions of the present inventor. In view of this, this process will never be used for manufacturing permanent magnetic alloys on a mass production basis; if ever the process were used for the purpose mentioned; its use would be limited to the production of those magnetic alloys which are designed for special application.

On the other hand, the magnet in its overall length of 25 millimeters has a maximum energy of the order of 7.0)(166 gauss oersteds, which is a very low value indeed. It only shows a fairly high value in coercive force, which is 1,400 oersteds. If itis desired to obtain a magnet having a maximum energy of the order of 8.0 106 gauss oersteds, nearly one-half portion of the magnet having a length of 25 millimeters would have to be cut olf and discarded. This would mean that the magnet obtained is very high in cost.

(4) The magnetic alloy should be subjected to retreatment so as to render the crystals larger. If, as stated in the preceding paragraph, about half the magnetic alloy blank in length should be discarded in order to obtain a magnet having a maximum energy of 8.0 106 gauss oersteds, it would be required to provide means whereby the crystals of the magnetic alloy blank could be rendered larger. The aforementioned Official Gazette of Japanese patent describes on p. 3 the necessity of heating the blank at temperatures above 1,200o C. by means of a high frequency electric current, gas or the like. This heating operation is performed after the blank has been formed with a columnar crystalline structure by means of a high temperature casting processa repetition of heating opeartions which increases production cost. Assuming that the crystals have been rendered larger at the cost of labor and expense, the magnetic properties of the magnet obtained in the atmosphere are, in the maximum, as follows: Br, 10,600 gauss; HC, 1,350 oersteds, and (BH)maX, 8.6 106 gauss oersteds. These values are fairly good, and if the magnet could be manufactured at low cost on a mass production basis, it would be of value. However, it would be impossible to manufacture this magnet on a mass production basis.

(5) It is required to treat the magnet in an argon atmosphere. The Oicial Gazette of Japanese patent appln. publn. No. 9,284/ 66 referred to above states, on p. 3, that in rendering the crystals of the magnet larger and cleaner as a forementioned, the values representing the magnetic properties of the magnet have been obtained after treating the magnet in an argon atmosphere. And the values obtained as the result of argon treatment are listed in said patent appln. publn. as Br, 11,000 gauss; HC, 1,380 oersteds, and (BH)mX, 10.3 106 gauss oersteds.

It is known in the art of permanent magnetic alloy manufacture how diicult it is to treat magnetic alloy blanks in a gaseous atmosphere of any sort in mass production operations. It would be needless to provide examples to establish the fact. If it is required as a prerequisite to subject magnetic alloy blanks to this kind of treatment, the results obtained in industrial production will be substantially the same as the results obtained in experiments. If, therefore, a method is available which permits to manufacture permanent magnetic alloy blanks having a maximum energy of 10.3 106 at low cost on a mass production basis, the method may be said to be worth patenting.

From the foregoing description, it will be understood that the method of manufacturing permanent magnetic alloys of the patented invention referred to above has many disadvantages which prevent the method from being carried into practices on a mass production basis. The factors responsible for the defects of the method can be found in the steps taken for rendering the crystals larger in nickel-cobalt-aluminum-copper-iron permanent magnetic alloys of high titanium content, in which one or more elements of sulphur, carbon and selenium are added in proper amounts to the alloy and melted together, the molten metal being cast in a predetermined mould (for example, a high temperature mould or a heat generating mould) and then quenched by means of a chill plate and the like starting from one end surface of the casting.

The method of the patented invention mentioned above is based on the fundamental concept that melting the alloy together with sulphur, carbon, and/or selenium and casting the molten metal in a mould will produce a magnetic alloy which has large columnar crystals. Stated differently, the method has two prerequisites for producing large columnar crystals in permanent magnetic alloys containing titanium: one is that the alloy should contain sulphur, carbon, and/ or selenium in certain amounts, and the other is that transfer of heat should be controlled so as to be directed in a given direction. If this hypothesis is correct, it will follow that large crystals cannot be produced in permanent magnetic alloys containing titanium if the crystals do not contain sulphur, carbon and/or selenium. It is to be noted that the method of this patented invention comprises, as essential steps, melting the alloy together with sulphur, Carbon, and/or selenium added in suitable amounts by weight to the alloy, and then casting the melten metal in a mould.

The method of the present invention is different from the aforementioned method in which sulphur, carbon, and/ or selenium are added in suitable amounts by weight to known permanent magnetic alloys containing titanium and melted together, and the molten metal is cast in a predetermined mould. And the permanent magnetic alloys obtained by the method of the present invention are different from the permanent magnetic alloys containing element added according to the aforementioned method. The method of the present invention obviates the aforementioned disadvantages of the prior art method.

According to the present invention there is provided a method of manufacturing a permanent magnetic alloy of large columnar crystals having excellent magnetic properties which compares favorably with a single crystals magnetic comprising the steps of casting a magnetic alloy material of high titanium content in a suitable mould, ap-

plying a coat of sulphur by suitable means to the surface of a casting obtained (magnetic alloy blank), inserting a number of such magnetic alloy blanks each with a coat of sulphur thereon into a non-magnetized sheath and passing same at a constant speed through a high frequency induction magnetic field to progressively heat and melt the blanks to such a degree that the original crystalline structure is destroyed and re-crystallization takes place in the blanks, and thereafter progressively quenching with a cooling liquid the portion of the blanks which is disposed at a position spaced apart a predetermined distance from a high frequency coil used for heating and melting the blanks, whereby unidirectional cooling by heat transfer into said liquid occurs to produce substantially completely unidirectionally oriented columnar crystals (or at right angles to the cooling liquid level) in the blanks which have a (100) direction parallel to the axis of the blanks.

In the known method of manufacturing permanent magnetic alloys of high titanium content described, one or more. elements of sulphur, carbon and/or selenium are added to the alloy and heated and melted together in an electric furnace for to 15 minutes, in order to obtain permanent magnetic alloys of higher quality. The defect of this method will be explained, for example, with reference to the addition of sulphur. Since melting occurs in the atmosphere, the molten metal is repeatedly displaced by convention on the surface of the high frequency electric furnace. In other words, the molten metal has an infinitely large surface which is brought into contact with atmosphere. If sulphur is added to the alloy, it will instantly be burned by heat, and part of the sulphur will ind its way into the molten metal. The sulphur in the molten metal will be brought to the surface of the electric furnace by convention at the next instant to thereby combine with air. This process will be repeated. It is believed that the sulphur will also combine with O2 (oxygen) and N2 (nitrogen) in the molten metal. Thus, large amounts of sulfides will be produced. The sulphur will naturally combine with O2 and N2 in the atmosphere. Aluminium and titanium have been known to have strong deoxidizing and denitrifying actions in steel making reactions. It will be understood that in the Alnico 8 alloy which has a high titanium content, there are substantial amounts of aluminium oxide, oxides of titanium and/or nitrates of titanium formed therein. The formation of these compounds has been a factor which has hitherto prevented the provision of an anisotropic crystalline structure in permanent magnetic alloys by the addition of sulphur according to the prior art method.

The present invention obviates all the disadvantages of the prior art methods. The invention will now be explained with reference to the accompanying drawings, in which:

FIGS. 1a and 1b are a view in explanation of the arrangement of columnar crystals formed in a known nickelcobalt-aluminium-copper-iron permanent magnetic alloy of high titanium content by casting same in a high temperature mould and quenching same starting from below and a diagram showing BH-HC curves of different portions of the alloy;

FIG. 2a is a view in explanation of a magnetic alloy blank having a coat of sulphur applied thereto according to the method of this invention;

FIG. 2b is a view in explanation of the magnetic alloy blank of FIG. 2a as it is inserted in a sheath;

FIG. 3a is a view in explanation of the chemical reaction of sulphur taking place in the method of this invention;

FIG. 3b is a detailed view of FIG. 3a;

FIG. 4 is a view in explanation of columnar crystals formed in a permanent magnetic alloy provided by the method of this invention;

FIG. 5 is a view in explanation of variations caused in columnar crystals by changes in the amount of sulphur applied to a permanent magnetic alloy by the method of this invention;

FIGS. 6a and 6b are a longitudinal sectional view and a plan view of a mould of the high temperature casting method; and

FIG. 6c is a view in explanation of the results of casting in the mould of FIGS. 6a and 6b.

EXAMPLE 1 (l) An Alnico 8 permanent magnetic alloy blank having a composition of 35% cobalt, 7% aluminium, 14% nickel, 4% copper, 4.5% titanium, and the remainder iron and impurities is melted in a high frequency electric furnace, and a cylindrical magnet for a loudspeaker 21 millimeters in outer diameter and 16 millimeters in height is cast in a mould. The molten metal cast in a mould does not contain sulphur at all. Accordingly, a permanent magnetic alloy blank 1 shown in FIG. 2a has very finely shaped crystals therein. A coat of oxide 2 as described in the specification of Japanese Pat. No. 447,358 is applied to opposite end surfaces (shown as a circular portion in a plan) of the blank. The coat applied generally has a very small thickness which is of the order of 0.001 to 0.003 millimeter. In this exmple, however, the coat applied has a thickness in the range from 0.05 to 0.1 millimeter for experiments sake, the thickness in this embodiment being 50 to 100 times as large as the thickness of a coat generally applied to the magnet.

A thick coat of sulphur ranging in thickness from 0.5 to 0.7 millimeter is further applied over the first coat of oxide on opposite end surfaces of the magnet, the sulphur applied to opposite sides weighing about 1.0 to 1.5 grams. In applying a coat of sulphur, sulphur in a solid form at room temperature is put into a suitable vessel and heated gradually on an electric heater. The sulphur will be melt-ed gradually into a molten state. If opposite ends of a permanent magnetic alloy blank are inserted into the molten sulphur by turns, a suitable amount of sulphur will be attached to opposite end surfaces of the blank. Upon drying immediately after getting attached to the blank, the sulphur Will be firmly deposited on the blank. FIG. 2a shows a magnetic alloy blank with a coat of sulphur deposited on opposite end surfaces thereof.

(2) A number of permanent magnetic alloy blanks treated as aforementioned are inserted in a non-magnetized sheath 5 as described in the specification of Japanese Pat. No. 458,293 and in the manner as shown in FIG. 2b. Needless to say, the sheath must be formed of such material as can withstand heating at elevated temperatures and also do not show changes, such as a rise in temperature for example, upon exposure to a high frequency induction magnetic field. Preferably, the sheath is made of porous material and has a multitude of small openings therein. In the uppermost portion of the sheath is put the so-called waste magnet, which is to `be severed and discarded after the blanks have been processed through operations. The waste magnet may -be Alnico 3 which is not costly. The waste magnet is shown at 4 in FIG. 2b.

(3) The blank-containing sheath is lowered progressively and moved at a speed of 11 millimeters per minute throu-gh a coil 6 as shown in FIG. 3. A high frequency current (about 400 kilocycles) is passed through the coil. The coil is mounted at a distance of about 75 millimeters above the level of a cooling water bath 8 in a tank 9. The sheath is suspended by means of a cord 7. The bottom of the sheath is closed by a soft steel plate so as to prevent the molten magnetic alloy blanks from owing out of the sheath.

If the value of high-frequency current passed to the coil is increased gradually, zones in each Iblank are progressively melted in the form of bands. Each of the melted portions is only 15 to 20 millimeters in length, so that part of said portion is in a heated condition and at elevated temperature, through the rest of the portion is at normal temperature. Thus, very small bluish-white flames will be seen near the upper portion of the coil as at 10.

(4) The chemical change which the blanks undergo in the process will be explained in detail with reference to FIG. 3b. The coat of oxide of a thickness ranging from 0.05 to 0.1 millimeter as shown in FIG. 2a will be competely removed by the oxidizing action of sulphur deposited on said oxide coat, said sulphur is heated and burned when the magnetic alloy blanks melted, with a small quantity of sulphur finding its way into the magnetic alloy blanks. This phenomenon is quite a novel discovery and forms the basis on which the present invention is found.

As stated previously, aluminium and titanium show excellent deoxidizing and denitrifying actions in steel making reactions. If, however, the treatment as disclosed in Japanese Pat. No. 447,358 is given to magnetic alloy blanks without applying sulphur thereto, the magnetic alloy blanks will be made into discrete magnetic bodies ea-ch 2l millimeters in diameter and 16 millimeters in length and having a perfect crystalline structure of an anisotropic character.

If sulphur is applied to opposite end surfaces of an individual magnetic alloy blank to such a degree that it has a thickness of 0.5 to 0.7 millimeter on one end surface (weighing about 1.0 to 1.5 grams in total) before subjecting the magnetic metal blanks to heating and melting, sulphur will act as a potent deoxidizing agent t thereby completely remove the coat of oxide applied to the blanks previously. This shows that the oxygen O2 contained in the permanent magnetic alloy blanks is also nearly completely removed. The most advantageous phenomenon is that in the portion of the blank shown in FIG. 3b, sulphur shown at 3 is heated and converted into a fluid condition, so that it ows into a space 11 between the blank 1 and the sheath 5. Since the portion of the magnetic alloy blank disposed below the coil 6 is already in a molten state, there is no space between the blank and the sheath in this portion of the blank. Thus, the sheath is completely filled with a molten metal in this portion without any space therein. The portion of sulphur burned and owing out of the sheath in a gaseous state (shown as flames at is very small in amount.

It will be noted that the major portion of sulphur will thus be converted into a gaseous state upon heating at high temperatures and acts only in the portion of sheath which is completely lled with molten metal as aforementioned. At the same time, no fresh supply of oxygen O2 or nitrogen N2 will be delivered to this portion of sheath because there is no communication maintained with atmosphere. This leaves the sulphur to act freely and strongly on oxygen 02, nitrogen N2 and their compounds in the permanent magnetic alloy blanks in a molten state to thereby deoxidize and denitrify them. Thus, the magnetic alloy blanks are perfectly cleansed and moved into cooling zone, so that large columnar crystals oriented parallel to the axis of the blanks can `be formed continuously.

The novel characterizing feature of this chemical reaction is that sulphur, instead of being added to and contained in the blanks, is supplied in such a manner that it can act as a catalyst for forming crystals in the magnetic alloy blanks of high titanium content the instant they are formed, so that fresh and clean molten alloy can be continuously provided.

In the known methods of manufacturing permanent magnetic alloys, the quantity of sulphur contained in alloys has been held responsible for the formation of crystals in the magnetic alloys. It should be emphasized that the present invention is based on an entirely different technical concept. In this embodiment of the invention, sulphur is 2.2 to 3.3% by weight of each blank which Weighs about 45 grams. On the contrary, samples of alloy blanks of high titanium content which showed formation of very large columnar crystals contained 0.05 to 0.33% by weight of sulphur, which is less than 10% of the amount applied. This shows that formation of very large columnar crystals of the size formed in the Alnico 8 magnetic alloy depends not on the amount of sulphur retained in the alloy but the amount of sulphur released to atomsphere. If sulphur were added to an alloy blank in a proportion of 2.2 to 3.3% by weight when the alloy is iirst melted by a conventional method, the amount of sulphur remaining in the alloy would be 0.88 to 1.32% by Weight because the amount of Sulphur retained in the alloy is over 40% of the amount added.

However, it is known that (BH)mx shows an optimum value when the amount of sulphur remaining in the alloy is in the range from 0.2 to 0.25% by weight. It will be evident, therefore, that if there were 0.88 to 1.32% by weight of sulphur remaining in the magnetic alloy, it would have very poor magnetic properties. It will be appreciated from the foregoing that this is a case of antimony: if the amount of sulphur added in an initial melting operation to an alloy is increased, the magnetic body produced will have poor magnetic properties because of a large amount of sulphur retained therein; if the amount is reduced to improve the magnetic properties of the magnetic body, no large columnar crystals would be formed.

It should be noted that according to the method of the present invention, sulphur acts merely as a catalyst for forming crystals in a magnetic alloy blank, with activated sulphur or compounds thereof being stuck to the inner surface of the sheath as impurities in the form of black masses.

The large columnar crystals formed by the process described above are oriented parallel to the axis of the sheath and cover a distance of 300 millimeters which is identical with the length of the sheath. The crystals have a length which is in the range from to 100 millimeters, not in the range from 15 to 50 millimeters as shown in FIG. 4. As stated preciously, a cheaper magnetic alloy blank is disposed at the uppermost portion of the sheath. This uppermost blank portion contains all the impurities that have been removed from the underlying blanks, so that said blank portion is severed and discarded as waste material after magnetization operations are completed.

FIG. 5 further illustrates the feature of this invention. A center portion 15 of the magnetic alloy shown in FIG. 5 is l5 millimeters in length, which is identical with the length of a magnetic alloy blank inserted initially in the sheath. Said portion has finely shaped crystals formed thereon which are exactly like the ones formed when it is cast in a mould. Said alloy blank portion had a coat of sulphur of 0.25 to 0.3 millimeter in thickness, which is half the thickness of coat generally applied, applied to opposite end surfaces thereof. It Will be seen that the paucity of sulphur as a catalyst is responsible for the granular crystals formed in this blank portion.

It will be noted that the blank portions 14 and 13 above and below said blank portion 15 have large columnar crystals oriented substantially parallel `to the axis of the magnetic body. This shows that when sulphur is applied to opposite ends of each of the magnetic alloy blanks in a proportion ranging from 1.5 to 3.3% by weight, an excellent columnar crystalline structure can be provided. An interesting finding is that when these different blank portions 13, 14 and 15 were analyzed chemically, their compositions were substantially equal to one another. This shows that the amount of sulphur retained in the magnetic alloy has no infiuence on the formation of large columnar crystals; the most important thing in forming large columnar crystals oriented parallel to the axis of the magnetic body is to provide means whereby conditions favorable for the formation of columnar crystals can be created. The method of this invention can provide this means for accomplishing the object of manufacturing permanent magnetic alloys with large columnar crystals on an industrial scale at low cost.

The magnetic alloy obtained by the method of this invention as aforementioned is rod-shaped with a length of 300 millimeters and a diameter of 21.0 millimeters. The magnetic body may be cut into suitable lengths by discharge processing or the like.

The magnetic alloy obtained by the method of this invention as aforementioned is subjected to most suitable magnetic field cooling (for example, isother-mal magnetic field cooling), and then to annealing at 580 C. for 10 hours. After these treatments, the magnetic alloy shows the following magnetic properties: residual magnetism Br, 1,300 gauss; coercive force HC, 11,390 oersteds; and maximum energy (BHLMX, 10.5 106 gauss oersteds. These values are not so unfavorable when compared with the values hitherto obtained experimentally with single crystals magnetic bodies which are: Br. 11,500 gauss; HC, 1,350 oersteds; and (BHLMX, 11.0 106. It might be said that these values are the highest obtainable for magnetic alloys manufactured industrially at low cost. These values are obtained, of course, in the atomsphere.

EXAMPLE 2 In this embodiment, the coat of oxide 2 is replaced by a coat of nitride, with sulphur being applied at 3 in exactly the same manner as in Example 1. The magnetic alloy blanks are converted into a rod-shaped magnetic alloy as in Example 1. This shows that the sulphur has stronger deoxidizing and denitrifying action than aluminium and titanium.

EXAMPLE 3 A permanent magnetic alloy blank consisting of cobalt, 14% nickel, 7% aluminium, 3% copper, 5% titanium, 0.25% sulphur, and remainder iron by weight is melted and cast into a rod-shaped magnetic body 300 millimeters in length and 21 millimeters in diameter. The casting is treated in accordance with the method of Japanese Pat. No. 458,293 granted to the present inventor.

Examination of the magnetic alloy obtained shows that the crystals formed therein are not a conglomeration of finely shaped crystals existing since before the treatment. They are, to be sure, columnar crystals oriented parallel to the axis of the magnetic body. The crystals, however, are very finely shaped, their lengths varying from one another. After optimum magnetic field cooling and suitable annealing, the majority of the magnetic Ibodies obtained have a maximum energy of 7.0 to 7.6 106 gauss oersteads, some showing a value of 8.0 106, though very small in number.

The results show that magnetic alloys with a perfect anisotropic crystalline structure can never be manufactured by adding a certain proportion of sulphur to an alloy prior to melting to provide a permanent magnetic alloy blank and then re-treating said alloy blank to obtain an anisotropic crystal formation in the alloy. The reason for this is that since sulphur is contained in the magnetic alloy blank, it exists in the form of compounds, by combining with copper or iron to provide iron sulfide, for example,

in the blank when the latter is re-treated. Attention must be paid to the fact that a very small amount of free sulphur is contained in the alloy.

It is known that melting by a zone melting technique is quite different from the so-called melting of metals. The results obtained in this example show that sulphur is rarely activated by re-treatment. Stated differently, it will be appreciated that it is impossible to obtain active sulphur or its compounds, such as sulphur diode for example from sulphur originally present in an alloy.

In this example, it has been established that it is almost impossible to manufacture on an industrial scale permanent magnetic alloys of high titanium content and excellent magnetic properties substantially equal to single crystal magnets by treating magnetic alloy blanks containing sulphur by the method of Japanese Pat. No. 458,293, for this method cannot provide large columnar crystals oriented in the axial direction of the magnetic alloys.

From the foregoing description, it will be appreciated that the method of the present invention enables to manufacture on an industrial scale permanent magnetic alloys of high titanium content which show excellent magnetic properties substantially equal to those of single crystal magnetic alloys by means of a simple technique no one has ever thought of before.

The alloy according to this invention has compositions which are determined in such a manner as to increase the yield of magnetic bodies as much as possible and at the same time to obtain optimum values of Br, HC and (BH)m,.x by taking into consideration fragility and external appearance of the magnetic bodies manufactured. It has been found that the magnetic alloys commercially most advantageous in manufacturing same on a mass production basis have a maximum energy of 9.5 to 10.5 106 gauss oersteds.

What I claim is:

1. A method of manufacturing a permanent magnetic alloy formed with columnar crystals oriented parallel to the axis of the alloy, characterized by steps of melting and casting in a mould a permanent magnetic alloy blank comprising cobalt, nickel, aluminium, copper, titanium and iron, applying a coat of oxide of 0.001 to 0.003 millimeter in thickness to the opposite end surfaces of said blank, applying a coat of sulphur to the surfaces of said oxide coating, inserting the blank in a non-magnetized sheath, passing the blank containing sheath at a constant speed through a heat area defined by an electromagnetic induction coil energized by an alternating current of frequency to progressively heat the zones of the blank passing through said area to such a degree as to destroy original crystalline structure and cause recrystallization, and thereafter passing said sheath into a cooling liquid so as to progressively quench the portion of said blank disposed at a position spaced apart a predetermined distance from said area to thereby produce substantially completely unidirectionally oriented crystals in said blank.

2. A method of manufacturing a permanent magnetic alloy formed withcolumnar crystals oriented parallel to the axis of the alloy having improved magnetic properties in the axial direction which are substantially equal to the magnetic properties of a single crystal magnet, such method being characterized by steps of melting and casting in a predetermined mould a permanent magnetic alloy blank comprising 25 to 40% cobalt, 10 to 20% nickel, 6 to 12% aluminium, 0 to 6% copper, 2 to 10% titanium, and remainder iron by weight, applying a coat of oxide of 0.001 to 0.003 millimeter in thickness to the opposite end surfaces of said blank, applying a coat of sulphur of 1.5 to 3.3% of the blank weight to the surfaces of said oxide coating, inserting a number of such blanks in a nonmagnetized sheath, moving said blank containing sheath at a constant speed downwardly through a high frequency induction magnetic field to progressively heat the blanks to such a degree as to destroy original crystalline structure and cause recrystallization, and thereafter passing said 11 12 blank containing sheath into a. cooling liquid so as t0 FOREIGN PATENTS pitogressi/ ely quenih the tportlor (tyf said lllnls dispfosed 158,672 8/1951 Australia a lplfson Space atf hpfebe efme Snttlln 821,624 10/1959 Great Britain. a 1g requenFY Col 0 efe? Pro ce s S.a1a.y 987,636 3/1965 GrearBritain. completely unldlrectionally orlented crystals 1n said 5 blanks- L. DEWAYNE RUTLEDGE, Primary Examiner References Cited UNITED STATES PATENTS 2,578,407 12/1951 Ebeling 148-103 U.S. C1. X.R. 3,450,580 6/1969 Hadeld er al. 148-103 X 10 14S- 31.57, 108

G. K. WHITE, Assistant Examiner

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