US3233294A

US3233294A - Method and apparatus for casting vertically stacked magnet bodies

Info

Publication number: US3233294A
Application number: US171624A
Authority: US
Inventors: Carpousis Arthur; Robert L Conroy; John J Jesmont
Original assignee: U S Magnet and Alloy Corp
Current assignee: U S Magnet and Alloy Corp
Priority date: 1962-02-07
Filing date: 1962-02-07
Publication date: 1966-02-08
Anticipated expiration: 1983-02-08

Description

Feb. 8, 1966 A. CARPOUSIS ET AL Filed Feb. '7, 1962 3 Sheets-Sheet 1 ROBERT l.. CONROY JOHN J. JESMONT ATTORNEYS Feb. 8, 1966 A. CARPOUSIS ETAL METHOD AND APPARATUS FOR CASTING VERTICALLY STACKED MAGNET BODIES Filed Feb. 7. 1962 FIG. 3c

, FIG. 3a

5 Sheets-Sheet 2 INV EN TORS ARTHUR CARPOUSIS ROBERT CONROY JOHN J. JESMONT ATTORNEYS Feb. 8, 1966 A. cARPoUsls ETAL 3,233,294

METHD AND APPARATUS FOR CASTING VERTICALLY STAGKED MAGNET BODIES 5 Sheets-Sheet :5

Filed Feb. 7, 1962 FIG.4

PLUG RATIO V GATE 00.000 987.65 @oclm INVENTORS ARTHUR CARPOUSIS ROBERT L. CGNROY JOHN J. JESMONT BY M, ATTORNEYS 1N oERsTEDs (lov United States Patent Chico 3,233,294 Patented Feb. s, 1966 The present invention relates to permanent magnets, and more particularly to a method and `mold assembly for casting a plurality of magnet bodies having an improved unidirectional grain structure resulting in increased magnetically anisotropic properties.

It has long been recognized that the magnetic properties of Alnico V alloys containing about 8 percent :by weight aluminum, 14 percent by weightnickel, 24 percent by weightcobalt, 3 percent by weight copper andthe remainder principally iron, can be so cast as to impart a highly directionally oriented grain structure by extracting the heat of the metal from `one or both ends of the mold cavity by direct contact of the metal with a chill member at one orboth ends. After subsequent heattreatment of the cast bodies in a magnetic field coinciding with the longitudinal axis of grain growth, lanisotropic magnets of relatively high maximum external magnetic energy product (BHmaX) are produced.

vlt is the aim of the present invention to provide a method for casting a plurality of vertically stacked magnet bodies having a substantially entirely unidirectionally oriented columnar grain structure for production of permanent magnets having greatly enhanced anisotropic characteristics with high energy content, remanence and coercive force inthe direction of columnar grain growth.

Another aim is to provide a-relatively economical and easily fabricated mold assembly for casting a plurality of vertically stacked magnet'bodies having .greatly improved columnar. grain structure.

Afurther aim is to provide a method and `mold assembly to produce lsubstantially entirely unidirectionally oriented, vertically stacked magnet bodies which will have vertically diterentiated and improved columnar grain structure and resulting enhanced magnetically anisotropic properties upon subsequent heat-treatment in a magnetic field.

Other aims and advantages of our invention will 'be readily apparent from the following detailed description and claims and by reference to the attached drawings wherein:

FIG. 1 is a vertical section ofastacked mold assembly embodying the present invention;

FIG. -2 is 1a yplan v'iewof fa mold tier of fthe lmold assembly in FIG. l;

FIG.' 3a is a representation of the grain 'structure o'f the -magnet bodies produced bythe lowermost -mold tier; FIG. 3b `is Va representation of the grain structure of the magnet bodies produced by the --intermediate mold tier;

`FlG. Sciis `a `representation of the grain structure'of the magnet bodies produced by fthe uppermost mold-tier;

FIG. 4 Aisa plot offthe -eect of the Aratio of mold volurne/'gate volume against -percentag'eof columnar crystalliz'atiom and FIG. 5 is -a graph vshowing Ademagne'tization curves of typical Alnico V magnets producedfcommerci-ally according tothe present invention `and of directionally grained magnets commercially produced according-tothe practice heretofore utilized.

It lhas now been found that the foregoing and related objects can be attained by a method using Ya mold assembly of a plurality of tiers Aof heated refractory molds eachihaving a'plurality of closely spaced apart mold chambers seated upona chill member '.with .the mold chambers of the lowermost tier-extending upwardly from the chill Vmember and -the lmoldchambers of the-several tiers lbeing interconnected by centrally disposed, `vertical gate V passages of lesser vcross-section than the cross-section of the mold chamber. The mold assembly should also provide a `reservoir 'of 'molten metal above the uppermost mold chambers `to ensurea'steep thermal gradient during chilling ofthe metal inthe mold chambers andto 'provide a reservoir of heat. The superheat and heat of solidication of the metal is extracted by the chill member throughthe metal in the cavities of the lowermost moldtier andthe metal in the gate passages acts'as a conduit'for heat extraction from'the metal of the upper tiers. Since the grains in the cast `bodies have been "oundto decrease in frequency and size as the distance of the mold tier from the chill member increases, it is considered thatthe column of metal in'the upper vtiers dened by the cross-section of the vertical Vgate passages chillsmore quickly than the remaining metal in the mold chambers and thereby acts as a directionally crystallized core and chilling reservoir for the remainder of the metal to enhance the formation of directionalized columnar grainsin the magnet'bodies of theupper tiers.

By the present invention ishas'been found that the unidirectional columnar grain growth of various anisotropic permanent magnet alloys can be enhanced Ythroughout the various tiers of the mold assembly. Under commercial operating conditions, Alnico V ,magnets frequently have been produced with a BHW,x of 8.0 to 83x106 gauss-oersteds. Under more closely controlled conditions, Alnico V magnets having anenergy product of as TABLE ONE Energy products of verticallystacked magnets Br Hu BHmx Dimension Tier Gausses Oersteds Gauss- Oersteds Lower 13, 000 800 6. )(10*l 0.725' DiameterX0i470' Length Middle 13, 380 831 7. 64)(106 Upper 13, 400 S39 7. 85X10 Lower 13, 790 6. 8X10 0.79 DiameterX0.560' Length lMiddle 13, 200' 800 7. 2)(10 Upper 13, 330 889 7. 9X'100 Lower 13; 850 760 7.' GX10 0.870' DiameterXOO' Length Middle 13, 900 762 7. 2 106 Upper 14, 070 784 7. 7X10 Lower 13, 200 '782 7. 1X10 0.950' Diameter 0.575' Length {Mddle 13, 500 795 7. 6X1()a Upper 13, 686 810 8. 2)(106 Lower 13, 20() 750 7. 2)(10e 1.10" Dameter 0.670' Length Middle 13, 350 770 7,'4X10 Upper 13, 500 780 7. 9 10 alignment.

continues up through the gate passages 12a.

high as 8.5 106 gauss-oersteds have been produced. Macroscopic exam-ination has shown as few as 4 to 10 columnar crystals in the magnet bodies produced in the upper tier of the mold assembly.

Significantly, within the operating ranges set forth herein, the process has proven highly effective even when sub- Jected to the variables of commercial foundry operation. Indicative of this efticacy is the data set forth in Table YOne tab-ove wherein magnet bodies of Alnico V `alloy -were cast in commercial foundry operation.

For a more specific understanding of t-he apparatus and method, reference is made to FIGS. 1 and 2 of the attached drawings wherein a mold assembly embodying the present invention is illustrated. Assembled on top of the metal chill plate 2 are three

refractory mold tiers

4, 6 and 8, each of which has a plurality of `closely spaced apart

mold chambers

16a, 10b and 10c, respectively, which extend upwardly from the lower face of the mold and terminate inwardly of the upper face. Extending from the upper ends of the

mold chambers

10a, 10b and 10c to the upper face of the mold are centrally disposed

vertical gate passages

12a, 12b and 12C, respectively, which thus provide a continuous vertical passage or column through the several tiers. In assembling the tiers, the

gate passages

12a, 12b and 12C and thereby the mold chambers, are vertically aligned, and a hightemperature adhesive (not shown) is placed about the periphery of the mold junctures to secure them in proper To distribute metal into the mold cavities, a riser 14 having an enclosed chamber 15 or reservoir and a funnel 16, both fabricated from refractory material, are placed on top of the several mold tiers and secured .in place by high temperature adhesive (not shown).

Initially, the assembly of refractory molds, riser and funnel is preheated to a temperature of about 1200 to 2700 F. and preferably 1800 to 2700 F. and then is placed upon the chill member 2 after which the superheated magnet alloy is introduced into the funnel 16 to till up the mold chambers 10, the gates 12 and extend up into and preferably fill the reservoir of the riser 14, as illustrated in the attached drawing, to provide a reservoir of superheated metal above the uppermost mold chambers 10c.

The molten magnet alloy in the lowermost mold chambers lila is quickly chilled by the extraction of heat through the chill member 2 and the soliditication process Since a steep temperature gradient is effected between the chill plate 2 and the superheated molten alloy, the metal in the central portion 18 of the mold chamber 10b defined by the cross-section of the gate 12a and indicated by the dotted lines in FIG. 1 rapidly chills to form a columnar grain structure directionalized in the direction of heat ilow. The chilled metal in the central portion of the mold chambers 10b then extracts the heat from the surrounding metal in the mold chambers and produces a columnar grain structure similarly oriented but of even larger size because of the lower rate of solidification in this chamber. Similarly, the process of chilling proceeds upwardly through the gate passages 12b into the central portion of the mold chambers 10c to effect chilling of the alloy therein. The reservoir of molten metal in the riser 14 maintains the steep thermal gradient in the column 18 of alloy dened by the cross-section of the gate passages 12 to ensure the continued extraction of heat by the chill member 2 at the bottom thereof which in turn produces the desired directional grain growth.

It will also be noted that the molten alloy initially flowing through the upper mold tiers heats the refractory material thereof to minimize further the tendency for transverse heat loss therein.

The molds, riser and funnel are fabricated of refractory material which will maintain its strength and dimensioning at the preheating-temperatures of 1200V to 2700 F.

In practice, metallic oxides such as aluminum oxide, forsterite, Zircon and mullite have proven advantageous when bonded by alkali metal silicates. Other bonding agents which @have been used in mold production are oxychlorides, phosphates, organic silicates and metalloorganic compounds.

. The chill member may be a metal plate fabricated from a high temperature resistance and corrosion resistant alloy and may utilize a collant medium such as water, liquid metal or gasses, to aid in heat dissipation if so desired. v

Upon cooling of the molds, they may be disassembled by striking them with a mallet and solidified metal will fracture readily in the area of vertical gate portions due to the brittleness thereof.

As best seen in FIGS. 3a, b and `c, representing the grain structure of magnet bodies of an Alnico V alloy obtained commercially by a three-tier mold assembly, lthe grain structure is entirely unidirectional in the plane and the number of grains decreases with attendant increase in the size of the grains as the distance from the chill member increases.

The demagnetization curves of three tiers of magnets commercially produced according to the present invention from Alnico V alloy are shown in FIG. 5 in comparison with the demagnetization curve (X) of Alnico V-DG magnets commercially produced according to prior art processes. The curves A, B and C represent the magnets obtained from the lowermost, middle and uppermost tiers, respectively. It can be seen that the magnetic properties of the uppermost tier (C) are most greatly enhanced.

The relationship of the mold chamber to the gate passage is extremely important to proper functioning of the present invention. Initially, the cross-sectional area of the mold chamber must be 1.75 to 64 times that of the cross-sectional area of the gate passage, and .preferably 9 to 16 times, in order to provide thenecessary capacity for heat extraction commensurate w1th a hlgh degree of effective columnarization of the metal 1n the mold chamber area surrounding the vertical column defined by the 4cross-section of the gate passage.

Similarly, the relationship of the volume of themold chamber to the volume of the gate passage is significant as shown in FIG. 4 of the attached drawings wherein the degree of columinarization rapidly falls as the volume ratio is increased above 35:1. Accordingly, the mold chamber volume should be not greater than about 40 times that of the gate passage in order to effect optnnum thermal extraction from the metal in the upper mold tiers, and the molds are preferably dimensioned to provide a mold chamber/ gate passage volume ratio of l0 to 35:1 for optimum efficacy and economy in utilization of the mold material commensurate with sucient strength.

Similarly, the eifective height of the magnet column must not be so great as to exceed the capacity for the chill plate of the assembly to extract the heat of solidification of the molten alloy prior to the onset of significant heat loss transversely of the molds and interference with the growth of the unidirectional columnar crystals of increasing size. Thus, an effective upper limit for the magnet column height is l0 times that of the maximum transverse dimension of the mold chamber. The optimum relationship will vary somewhat with the conditions of operation but is preferably in the range of 1 to 6:1.

As pointed out in the copending application of Robert L. Conroy, lohn I. Iesmont and Samuel Weimersheimer, Method and Apparatus for Casting Magnet Bodies, Serial No. 171,664, filed February 7, 1962, the thermal factors of the molten alloy and the mold must be very closely controlled to ensure that the chill member at the bottom of the mold assembly Will extract substantially all of the superheat and latent heat necessary to chill the molten alloy. In this application, it is pointed out that the crosssectional area of the mold chambers must be greater than about one-third that of the mold pattern area, and further that the mold (and riser and funnel) should be preheated to a temperature of about 1200 to 2700 F. and preferably 1800 to 2700 F. Also, the molten magnet alloy should be superheated at least about 200 F. above the liquidus point so as to provide a steep thermal-gradient in the molds relative to the chill member by providing a large reservoir of heat in the upper portion ofthe mold during heat extraction and also by minimizing the effect of heat loss transversely of the mold through the side refractory material.

The terminology cross-sectional area of the mold chambers as usedherein refers to the area of the horizontal cross-section taken through the mold chamber cavity and to the sum of such cross-sectional areas in any given mold.

The terminology cross-sectional area of the mold pattern portion as used-herein refers to the area of the cross-section of that portion of the mold having its margins defined by the outermost portions of the outermost mold cavities in any given mold and including the area of the mold cavities therewithin, but not including the reinforcement area of the mold pattern which extends about the outer margins ofthe mold pattern, i.e., the outer peripheral portion.

The term steep thermal gradient as used herein refers ,toa large difference between the temperatures of the solidifying metal and the molten metal spaced upwardly therefrom.

By proper selection of the metal temperature, mold temperature, and mold? dimensions as hereinbefore set forth, it has been found that a number of anisotropic magnet alloys can be cast into bodies having a totally or highly unidirectionally oriented columnar grain structure with resulting enhanced magnetic properties. Thus, the invention has been found not only highly effective with Alnico V alloys containing 6 to 11 percent by weight aluminum, 16 to 30 percent cobalt, 12 to 20 percent nickel, up to 7 percent copper, and the remainder principally iron, but also with the Alnico VI B alloys additionally containing up to 2 percent titanium.

The term magnet alloy as used herein refers to ferrous alloys capable of developing a high degree of anisotropy during heat-treatment in a magnetic field coinciding with the' axis of. columnarization and particularly to ferrous base alloys containing aluminum, nickel, cobalt and iron known as Alnico V and Vl alloys.

The term superheated as used herein` refers to magnet alloys which are heated to temperatures at least 200 F. above the liquidus temperature but below the temperature at which twin grain formation occurs, which temperature is sutlicient to permit the extraction of the heat of the molten metal substantiallyentirely by the chilll member to enable the columnar grain growth in combination with preheated refractory molds and process of the present invention.

For example, the superheated temperature range effective in the present invention for casting Alnico V alloy is 2880 to 3450 F. and preferably 3200 to 3450 F., and that for casting Alnico VI alloys is 2950 to 3500o F. and preferably 3200 to 3500 F.

InV practice, it hasbeen foundthat high metal and mold temperatures produce the optimum results. Generally speaking, the thermal' gradient or difference in temperatures between the metal and the mold is found to affect optirntun performance in that a lesser gradientl tends to improve'the resultant magnetic properties. In accordance with the preferred aspect of the invention, the molds are preferably preheated to temperatures of 1800 to 2700" F., and the metal is preferably heated to a temperature above 3200 F. but below the point at which twin grain formation takes place.

d As specific examples of alloys which have p'r'ov'eniparticularly advantageous in the practice of the present invention are the following:

ALNICO V Element Preferred Specific Com- Range position,

Percent Percent Aluminum 8. 0-8. 8 8. 3 Nickel 13. 044. 0 13. 3 Cobalt- 23. 5-25. 0 24. 5 Copper 1. 5-3.5 2. 9 Columblum.. O. 15-0. 5 0. 2 Titanium 0. 15-0. 5 0. 3

Remainder principally iron with minor impurities.

ALNICO VI Preferred Spoeic Com- Element Range, position,

Percent Percent Aluminum 8. 0-8. 5 8. 5 Nickel lll-7. 15. 5 15.5 COOSlL 23. 5-25. 0 24. 3 Copper 2. 5-3. 5- 3.0 Coluinhlum 0. 5-1. 5 0. 8 Titanium 0. 5.-1. 5 1.1

Remainder principally iron with minor impurities.

Illustrative of the eicacy of the present invention are the following specific examples wherein superheated magnet alloy was cast in stacked refractory molds according to the present invention.

EXAMPLE @NE Molds having a plurality ofV mold chambers as illustrated in FIGS. 1 and 2 wereiprepared from aluminum oxide using sodiumsilicate as a binder. The' mold charnbers wereV 0.870 inch in diametery and 0.650'inch in height and the gate passages were 0.200 inch in diameter and 0.375 inch in height, providing a volume ratio of about 312:1. The mold chambers were closely spaced apart to provide an area ratio of mold chamber cross-section to mold pattern area of about 1:25;

Three molds were then assembled with the gate passages in vertical alignment and bonded together with a high temperature adhesive (Liquag'rip, a product ofy Whitehead Brothers, New York, New York); A refractory riser and pouring funnel were then placed thereon and secured inr place by high temperature adhesive.

This refractory assembly was' initially preheated tol a temperature of about 2000" F. and then placed on top of a steel chill plate 1 inch in thickness.-

The magnet alloy containing 8.14 percent by weight aluminum, 24.25 percent by weight cobalt, 13.5 percent by weight nickel, 2.9 percent by weight copper, 0.15 percent by Weight titanium, 0.45 percent by weight columbium and the remainder principally iron- [Ainico V (with silicon and carbon impurities of about 0.13-percent)] was superheated to a temperature of about 34.00 F. and poured into the preheated mold assembly to fill the riser. The superheat and heat of solidifcation were extracted through the chill plate. After the metal had solidified and the molds had cooledV suiliciently',Y the components were disassembled and the magnet bodies removed. Upon fracturing, the magnets from the several tiers were found to be unidirectional in grain orientation and the grains were found to increase insize from the lowerrnost to the upper moldtier.

The castings were then normalized atl about l700 F. for one-half hour and cooled in a magnetic field parallel to the axis of grain orientation for about fifteen minutes. The magnet bodies were then subjected to coercive aging at a temperature of about 1100 F. for about two hours and at about 1025 F. for twenty hours.

The magnets thus produced were determined to have the following magnetic properties:

A mold assembly similar to that in Example One was prepared except that it utilized only two tiers of molds.

The mold assembly was similarly preheated to a temperature of about 2000 F., placed upon a steel chill plate An alloy containing 8.3 percent by weight aluminum, 13.3 percent by weight nickel, 24.5 percent by weight cobalt, 3.0 percent by weight copper, 0.2 percent by weight columbium, 0.3 percent by weight titanium, and the remainder principally iron (with about 0.12 percent by weight carbon and silicon impurities) was preheated and introduced into the mold assemblies in an amount sufficient to ill the riser. In the instances of the first and third groups of Amold assemblies, the temperature of the metal was 3450" F., and the temperature of the metal introduced into the second group of assemblies was 3400 F.

After chilling, the castings were heat-treated similarly to those in Example One. The magnet-ic properties of the several groups of magnets were as follows:

and the alloy of Example One which was similarly super- M01 d Metal Bq heated to aboutv3400 F. was introduced thereinto in an Magnets Temi,y Tem,y Br Gausses Heoergds Gflg'gf amount sufficient to fill the riser. F- F- OGISGdS Upon cooling, the magnet bodies were heat-treated to h Exa e an l1 "t netic Group r slmarly t ose m. mple On d t e mg Lowor 1,800 3,450 13,200 700 0.75 10 properties were determined as follows: Midd1o 1, 800 3, 450 13, 300 810 7 2 1Oo Upper 1, :300 3, 450 13, 000 B40 7. 0 10 Group II: BHmx Lower 2, 200 s, 40o 1s, 250 780 6. 9 1Gf1 Tier Br Gausses I-IoOersteds Gauss- Middle 2,200 3,400 13, 500 790 13x10 Oerstods Uppor. 2, 200 3, 400 13, 550 820 7. 8x10@ Group III:

Lowor 2, 400 3, 450 13, 400 700 6. 9 10a Lower 13,250 A'700 0.8 10 Middle 2,400 3, 450 13,400 f 780 7.5 10u

Upper

13, 3 800 7. 1X1()a Upper 2, 400 3, 450 13, 680 840 8. 3 10 EXAMPLE THREE A three-tier mold assembly was similarly prepared to that in Example One. The mold chambers had a diameter of 0.85 inch and a length of 5.0 inches to provide an L/D ratio of 6:1. The gate passages had a diameter of 0.50 inch and a length of 0.50 inch to provide a volume ratio of 33:1. The ratio of the cross-sectional area of the mold chambers to that of the mold pattern area was approximately 1:2. The refractory mold assembly was preheated to a temperature of 2000 F. and placed upon a metal chill plate.

An alloy containing 8.3 percent by weight aluminum, 13.5 percent by weight nickel, 24.3 percent by weight cobalt, 2.8 percent by weight copper, 0.2 percent by weight columbium, 0.3 percent by weight titanium, and the remainder principally iron (with about 0.12 percent by weight carbon and silicon impurities) was preheated to a temperature of 3100 F. and introduced into the mold assembly in an amount sutiicient to lill the riser.

Upon cooling, the magnet bodies were removed and heat-treated similarly to those in Example One. The resultant magnets were found to have the following magnetic properties:

BH... u Tier Br Gausses Ho Oersteds Gauss- Oersteds 13, 500 800 7. 3 100 13,490 830 7. 5)(10 Upper 13, 480 844 7. 7 X105 EXAMPLE FOUR To indicate the effect of lesser thermal gradient between the temperature of the metal and of the mold, three y that of the mold pattern area was about 2.5: l.

One group of mold assemblies was preheated to a temperature of 1800 F., the second group to 2200 F., and the third group to 2400 F.

We claim:

l. A process for casting a plurality of stacked metallic bodies having directionally oriented columnar grain structure comprising: providing an assembly having a chill member, a plurality of tiers of refractory molds vertically disposed thereon and a riser member upon the uppermost of said tiers, said tiers each having a plurality of closely spaced apart mold chambers, the mold chambers of adjacent tiers each being interconnected by centrally disposed vertical gate passages of lesser cross-sectional area than the mold chambers and the mold chambers of the tier adjacent said chill member extending upwardly therefrom, said riser member providing a reservoir chamber substantially closed to atmospheric heat loss communicating with and disposed above'the mold chambers of the uppermost of said mold tiers, said mold tiers each having a mold pattern portion deiined by the periphery of the outermost mold chambers and a reinforcing portion extending thereabout with a ratio of mold chamber crosssectional area to the area of said mold pattern portion of greater than about, 1:3, preheating said tiers of molds and riser member to a temperature of about 1200-2700 F.; introducing superheated anisotropic ferrous magnet alloy into said mold chambers and said reservoir chamber in an amount sucient to till said mold chambers and provide a reservoir of superheated alloy above said mold chambers, said alloy having been superheated to a temperature of at least 200 above the liquidus point but below the point at which twin grain formation occurs, said mold and alloy temperatures being selected to provide a steep thermal gradient during extraction of the superheat and heat of solidication of the alloy in said mold chambers while minimizing transverse heat loss therefrom, said reservoir of superheated alloy in said reservoir chamber providing a reservoir of heat for the metal in said mold cavities to avoid premature chilling thereof and to enable solidiication to occur through extraction of the heat from the molten metal in said mold chambers through said chill member; and allowing said metal to cool by extraction of heat through said chill member to form magnet bodies having a unidirectionally oriented columnar grain structure.

2. The process in accordance with claim 1 wherein said ferrous magnet alloy contains essentially 6-11 percent by weight aluminum, 12-20 percent by we-ight nickel, 16-30 percent by weight cobalt, up to 7 percent by weight copper and the remainder principally iron, and wherein said alloy is at a temperature of about 28803450F.

3. The process in accordance with claim 2 wherein said ferrous magnet alloy contains 1-2 percent by Weight titanium.

4. rll`he process in accordance with claim 1 wherein the cross-sectional area of said mold chambers is 1.75-64 times that of the cross section of said gate passages.

5. The process in accordance with claim 1 wherein the upper end of the mold chamber in the uppermost of said mold tiers is spaced from said chill member a distance not greater than times the maximum transverse dirnension of the mold chamber.

6. A process for casting a plurality of stacked metallic bodies having directionally oriented columnar grain structure comprising: providing an assembly having a plurality of tiers of refractory molds and a riser member on the uppermost of said tiers, said tiers eac-h having a plurality of closely spaced apart mold chambers with the mold chambersof the lowermost tier extending upwardly from the lower surface thereof and the mold chambers of adjacent tiers each being interconnected by vertically aligned, centrally disposed vertical gate passages, said mold chambers having a cross-sectional area 1.75-64 times that of the gate passages and a volume not greater than about 40 times that of said gate passages, said riser member providing a reservoir chamber substantially closed to atmospheric heat loss communicating with and disposed above the mold chambers of the uppermost of said mold tiers, said mold tiers each having a mold pattern portion defined by the periphery of the outermost mold chambers and a reinforcing portion extending thereabout with a ratio of mold chamber cross-sectional area to the area o f said mold pattern portion of greater than about 1:3; preheating said mold assembly to a temperature of about 1200-2700 F.; placing said preheated mold assembly upon a chill member with said mold chambers vertically oriented, the mold chambers of the lowermost tier opening directly thereon; introducing superheated anisotropic ferrous magnet alloy into said mold assembly in an amount sutlicient to ll said mold chambers and said reservoir chamber and provide a reservoir of superheated alloy above the alloy in said mold chambers, said alloy having been superheated to a temperature of at least 200 F. above the liquidus point but below the point at which twin grain formation occurs, said mold and alloy temperatures being selected to provide a steep thermal gradient during extraction of the superheat and heat of solidication of the alloy in said mold chambers while minimizing transverse heat loss therefrom, said reservoir of superheated alloy in said reservoir chamber providing a reservoir of heat for the alloy in said mold chambers to avoid premature chilling thereof and to enable solidification to occur by extraction of the heat from the molten alloy in said mold chambers through said chill member; and allowing said metal 'to cool by extraction of heat through said chill member to form magnet bodies having a unidirectionally oriented grain structure.

7. The process in accordance with claim 6 wherein said ferrous magnet alloy contains essentially 6ll percent by Weight aluminum, 12-20 percent by weight nickel, 16-30 percent by weight cobalt, up to 7 percent by weight copper, and the remainder principally iron, and wherein said alloy is at a temperature of about 2880-3450 F.

8. The process in accordance with claim 6 wherein said ferrous magnet alloy contains essentially 6-ll percent by weight aluminum, 12-20 percent by weight nickel, 16-30 percent by weight cobalt, up to 7 percent by weight copper, l-2 percent by weight titanium, and the remainder principally iron, and wherein said alloy is at a temperature of about 2900-3500 F.

9. A process for casting a plurality of stacked metallic bodies having directionally oriented columnar grain structure comprising providing an assembly having a plurality of tiers of refractory molds and a superimposed riser member, said tiers each having a plurality of closely spaced apart rnold chambers extending upwardly from the lower surface of the mold tiers but terminating inwardly of the upper surface of said mold tiers and vertically aligned centrally disposed vertical gate passages extending from the upper end of said mold chambers to the upper surface of said mold tiers, said mold chambers having a cross-sectional area 1.75 to 64 `times that of the gate passages and a volume not greater than about 40 times that of said gate passages, said riser member providing a reservoir chamber substantially closed to atmospheric heat loss and disposed above and communicating with the mold chamber-s of the uppermost mold tier, said reservoir chamber distributing molten magnet alloy to the mold chambers of the several tiers, the upper end of the mold chambers in the uppermost tier being spaced from said chill member a distance not greater than l0 times the maximum transverse dimension of the mold chambers, said mold tiers each having a mold pattern portion defined by the periphery of the outermost mold chambers and a reinforcing portion extending thereabout with die cross-sectional area of said mold chainbers being not less than 1/3 that `of the cross-sectional area of the mold material in the mold pattern area; preheating said assembly to a temperature of about 1200 to 2700 F.; placing said preheated assembly upon a chill member with the mold chambers vertically oriented, the mold chambers of the lowermost m-old opening directly thereon; introducing superheated anisotropic ferrous magnet alloy into said riser member for distribution into the mold chambers of the several tiers, said superheated magnet alloy `being suilicient to provide a reservoir of superheated alloy in said riser member above said mold chambers, said alloy having been superheated to a temperature of at least 200 F. above the liquidus point but below the point at which twin grain formation occurs, said mold and alloy temperatures being selected to provide a steep thermal gradient during extraction of the superheat and heat of solidification of the alloy in said mold chambers while minimizing transverse heat loss therefrom, said reservoir of superheated alloy in said reservoir chamber providing a reservoir of heat for the alloy in said mold chambers to avoid premature chilling thereof and to enable solidiiication to occur through extraction of the heat from the molten alloy in said mold chambers through said chill member; and allowing said metal to cool by extraction of heat through said chill member to form magnetic bodies having a unidirectionally oriented columnar grain structure.

l0. The process in accordance with claim 9 wherein said superheated ferrous magnet alloy contains essentially 6 to ll percent by weight aluminum, 16 to 30 percent by weight cobalt, 12 to 20 percent by weight nickel, up to 7 percent copper, and the remainder principally iron and wherein said alloy is at a temperature of 2880 to 3450 F.

11. The process in accordance with claim 10 wherein said superheated ferrous magnet alloy additionally contains .l5 to .50 percent by weight titanium, and .l5 to .50 percent by weight columbium.

12. The process in accordance with claim 10 wherein said alloy contains l to 2 percent titanium.

13. A mold assembly for casting stacked magnet bodies having unidirectional grain structure comprising a chill member; a plurality of tiers of refractory molds disposed vertically thereon, said tiers each having a plurality of closely spaced apart mold chambers with the mold chamers of the lowermost tier extending upwardly from the chill member and the mold chambers of adjacent tiers each being interconnected by centrally disposed vertical gate passages, said vertical mold chambers having a cross-sectional area about 1.75 to 64 times that of the cros-s-sectional area of the gate passages and a volume not greater than about 40 times that of the gate passages, said Imold tiers each having a mold pattern portion defined by the periphery of the outermost mold chambers and a reinforcing portion extending thereabout with a ratio of mold chamber cross-sectional area to the area of said mold pattern portion of greater than about 1:3; and a riser member upon the uppermost of said tiers providing a reservoir chamber substantially closed to atmospheric heat loss communicating with and disposed above the mold chambers of the uppermost of said mold tiers.

14. A mold assembly for casting stacked magnet bodies having unidirectional grain structure comprising a chill member; a plurality of tiers of refractory molds disposed vertically thereon, said molds each having a plurality of cl-osely spaced apart mold chambers extending upwardly from the lower surface of the mold tier but terminating inwardly of the upper surface of the mold tier and centrally disposed vertical gate passages extending upwardly therefrom to the upper face of the mold tier to interconnect the mold chambers of adjacent tiers, said vertical chambers having a cross-sectional area about 1.75 to 64 times that of the cross-sectional area of the gate passages and a volume not greater than about 40 times that of the mold chambers, said mold tiers each having a mold pattern portion defined by the periphery of the outermost mold chambers and a reinforcing portion extending thereabout with said mold chambers having a cross-sectional area not less than about 1/3 the cross-sectional area of the mold material in the pattern area; and a riser member upon the uppermost of said tiers providing a reservoir chamber substantially closed to atmospheric heat loss communicating with and disposed above the mold chambers of the uppermost of said mold tiers.

15. A mold assembly for casting stacked magnet bodies having unidirectional grain structure comprising a chill member; a plurality of tiers of refractory molds disposed vertically thereon adapted to be preheated to temperatures of about 1200 to 2700 F., said molds each having a plurali-ty of closely spaced apart mold chambers with the mold chambers of the lowermost tier extending upwardly from the chill member and the mold chambers of adjacent tiers each being interconnected by centrally disposed vertical gate passages, said mold tiers each having a mold pattern portion dened by the periphery of the outermost mold chambers and a reinforcing portion extending thereabout with said vertical chambers having a cross-sectional area about 1.75 to 64 times that of the cross-sectional area of the gate passages and a volume not greater than about 40 times that of the mold chambers, the ratio of mold chamber cross-sectional area to the area of said mold pattern portion being greater than about 1:3; and a superposed riser member having a reservoir chamber therein substantially closed to atmospheric heat loss communicating with and disposed above the mold chambers of the upper mold tier for distribution of molten metal to the mold chambers of the several mold tiers.

16. A mold assembly for casting stacked magnet bodies having unidinectionai grain structure comprising a chill member; a plurality of tiers of refractory molds disposed vertically thereon adapted to be preheated to temperatures of about 1200 to 2700 F., said molds each having a plurality of closely spaced apart mold chambers extending upwardly from the lower surface of the mold tier but terminating inwardly of the upper surface of the mold tier and aligned, centrally disposed vertical gate passages extending upwardly therefrom to the upper surface of the mold tier to interconnect the mold chambers of adjacent tiers, said mold tiers each having a mold pattern portion defined by the periphery of the outermost mold chambers and a reinforcing portion extending thereabout, said vertical mold chambers having a crosssectional area about 1.75 to 64 times that of the crosssectional area of the gate passages and a volume not greater than about 40 times that of the mold chambers, said mold chambers having a cross-sectional area not less than about 1/3 the cross-sectional area of the lmold pattern area, the upper end of the mold chambers in the upperv most mold tier being spaced from said chill member a distance not greater than ten times the maximum transverse dimension of the mold chambers; and a superposed riser member having a reservoir chamber therein substantially closed to atmospheric heat loss for distribution of molten metal to and disposed above the mold chambers of the several mold tiers, the Vertical gate passages of the uppermost mold tier opening into said reservoir chamber.

17. The assembly in accordance with claim 16 wherein said molds and riser member are fabricated of metallic oxide :refractory material bonded by talk-ali meta-l silicate.

References Cited by the Examiner I. SPENCER OVERHOLSER, Primary Examiner'.

MARCUS U. LYONS, MICHAEL V. BRINDISI,

Examiners.

Claims

1. A PROCESS FOR CASTING A PLURALITY OF STACKED METALLIC BODIES HAVING DIRECTIONALLY ORIENTED COLUMNAR GRAIN STRUCTURE COMPRISING: PROVIDING AN ASSEMBLY HAVING A CHILL MEMBER, A PLURALITY OF TIERS OF REFRACTORY MOLDS VERTICALLY DISPOSED THEREON AND A RISER MEMBER UPON THE UPPERMOST OF SAID TIRES, SAID TIERS EACH HAVING A PLURALITY OF CLOSELY SPACED APART MOLD CHAMBERS, THE MOLD CHAMBERS OF ADJACENT TIERS EACH BEING INTERCONNECTED BY CENTRALLY DISPOSED VERTICAL GATE PASSAGES OF LESSER CROSS-SECTIONAL AREA THAN THE MOLD CHAMBERS AND THE MOLD CHAMBERS OF THE TIER ADJACENT SAID CHILL MEMBER EXTENDING UPWARDLY THEREFROM, SAID RISER MEMBER PROVIDING A RESERVOIR CHAMBER SUBSTANTIALLY CLOSED TO ATMOSPHERIC HEAT LOSS COMMUNICATING WITH AND DISPOSED ABOVE THE MOLD CHAMBERS OF THE UPPERMOST OF SAID MOLD TIERS, SAID MOLD TIERS EACH HAVING A MOLD PATTERN PORTION DEFINED BY THE PERIPHERY OF THE OUTERMOST MOLD CHAMBERS AND A REINFORCING PORTION EXTENDING THEREABOUT WITH A RATIO OF MOLD CHAMBER CROSSSECTIONAL AREA TO THE AREA OF SAID MOLD PATTERN PORTION OF GREATER THAN ABOUT, 1:3, PREHEATING SAID TIERS OF MOLDS AND RISER MEMBER TO A TEMPERATURE OF ABOUT 1200-2700* F.; INTRODUCING SUPERHEATED ANISOTROPIC FERROUS MAGNET ALLOY INTO SAID MOLD CHAMBERS AND SAID RESERVOIR CHAMBER IN AN AMOUNT SUFFICIENT TO FILL SAID MOLD CHAMBERS AND PROVIDE A RESERVOIR OF SUPPERHEATED ALLOY ABOVE SAID MOLD CHAMBERS, SAID ALLOY HAVING BEEN SUPERHEATED TO A TEMPERATURE OF AT LEAST 200* ABOVE THE LIQUIDUS POINT BUT BELOW THE POINT AT WHICH TWIN GRAIN FORMATION OCCURS, SAID MOLD AND ALLOY TEMPERATURES BEING SELECTED TO PROVIDE A STEEP THERMAL GRADIENT DURING EXTRACTION OF THE SUPERHEAT AND HEAT OF SOLIDIFICATION OF THE ALLOY IN SAID MOLD CHAMBERS WHILE MINIMIZING TRANSVERSE HEAT LOSS THEREFROM, SAID RESERVOIR OF SUPERHEATED ALLOY IN SAID RESERVOIR CHAMBER PROVIDING A RESERVOIR OF HEAT FOR THE METAL IN SAID MOLD CAVITIES TO AVOID PREMATURE CHILLING THEREOF AND TO ENABLE SOLIDIFICATION TO OCCUR THROUGH EXTRACTION OF THE HEAT FROM THE MOLTEM METAL IN SAID MOLD CHAMBERS THROUGH SAID CHILL MEMBER; AND ALLOWING SAID METAL TO COOL BY EXTRACTION OF HEAT THROUGH SAID CHILL MEMBER TO FORM MAGNET BODIES HAVING A UNIDIRECTIONALLY ORIENTED COLUMNAR GRAIN STRUCTURE.