US1290010A - Process of making castings of rare-earth metals and their alloys. - Google Patents

Description

A. I M. HIRSCH. PROCESS 0E MAAING CASTINGS 0E RARE EARTH METALS ANO THEIR ALLoYS.

APPLICATION FILED VIAY9-19l8.

Patented Dec. 3l, 1916.

UNITED STATES PATENT OFFICE.

ALCAN HIRSCH AND MARX HIRSCH, OF NEW YORK, N. Y., ASSIGNORS T0 ALPHA PRODUCTS COMPANY, INC., A CORPORATION 0F NEW YORK.

PROCESS 0F MAKING CASTINGS OF BABE-EARTH METALS AND THEIR ALLOYS.

Specification of Letters Patent.

Patented Dec. 31, 1918.

Original application tiled September 17, 1917, Serial No. 191,868. Ilivided and this application illed May 9, 1918. Serial No. 233,452.

To all whom t may concern Be it known that we, ALCAN HIRSCH and M ARX Hmscu, citizens of the United States, and residents of New York, in the county of N ew York and State of New York, have invented certain new and useful Improvements in Processes of Making Castings of Rare- Earth Metals and Their Alloys, of which the following is a specification.

The invention relates to improvements in the manufacture of castings of rare earth metals and their alloys. The improvements are particularly adapted t0 the manufacture of castings of alloys of cerium or lanthanum for sparking purposes. This application is a division of our prior application Serial No. 191663 filed September 17, 1917.

Prior to the present invention it has been considered extremely difficult to cast the desired rods and shapes of cerium and its alloys having a very small cross section and volume with respect to surface, because of the extreme inflammability of the metal on the one hand and its great tendency to chemical reaction with carbon and other substances and to alloyinfg` with metals on the other hand. It was only by the laborious and wasteful process of sawing or turning beneath the surface of oil, or while constantly drenching the fresh surfaces and cuttings with oil, that it was generally known how to make the small commercial shapes necessary for use in lighters, ignition flints, etc.

The present process` has for its object the providing of improvements whereby the rare earth metals and their alloys may be satisfaetorily cast in the various forms desired in commerce and, in many cases, with Sullicient eXact1tude of size to avoid the necess1ty of machining, thereby avoiding not only delay and expense, but much loss of material, which, once powdered. is extremely diflicult to recover in usable shape. Also, according to the present invention, the cast metal or alloy is obtained in a most simple and economical manner and substantially free from objectionable impurities.

Further and more specific objects, features and advantages will more clearly appear from the detailed description given below taken in connection with the accompanying sheet of drawings, which forms a part of this specification.

In the drawing,

Figure l is a vertical -section of a preferred form of apparatus for melting the metals;

Fig. 2 is a top view of a mold into which the molten metal may bepoured for castin g Fig. 3 is a vertical section taken on t e line 3 3 of Fig. 25

Fig. 4 is a vert1cal section taken on the line 4-4 of Fig. 2;

Fig. 5 is a top planview illustrating a modified form of mold; and

Fig. 6 1s a similar view illustrating still another form of mold.

As an illustrative example of the improvements, the preferred process for the manufacture of castings of an allo of cerium, lanthanum, didymium, etc., an iron will be described.

Large pigs of an alloy of cerium, lauthanum and didymium, and possibly small quantities of erbium and thorium, etc., and containing more or less impurities are broken up, as with a hammer, into pieces about one inch diameter. It is preferred to avoid using much smaller pieces than one-half inch in diameter, as they tend to thicken the melt into which they are later put, probably because of the greater amount of oxid formed on the surfaces of the pieces when an equal weight of smaller pieces is used. Larger pieces may be used, especially in the larger melts.

Into a suitable cl'ucible, preferably a Hessian or Battersea Crucible, and suitably heated, a quantity of barium chlorid crystals is put in and melted down. For this purpose, an apparatus such as shown in Fig. l may be used, in which l represents the crucible,

2 a supporting bed portion of fire-brick, pro-y barium chlorid crystals has been evolved and the mass reached a quiet state of fusion, the pieces of metal, consisting mostly of cerium with some lanthanum and small quantities of other metals, are Washed in kerosene or other suitable oil to remove dirt, oxids and carbids thatl may be on the surface thereof, and then they are partially dried, as with news print paper, and then' the piecesof metal are added to the melt of bari rr. chlorid in fairly large batches, that is to say, as many pieces are added at a-time as can be readily shoved under the surface of the barium chlorid. Any kerosene or other oil remaining on the pieces burns off as they go into the molten barium chlorid. The mass should not he stirred, and in adding the metal the melt should be agitated as little as possible. The cerium metal or alloy added should preferably be low in iron, as metal high in iron notV only has a higher melting point, but is apt to contain more of other impurities and these impurities are then far more diflicult to separate. prefer to use a rare earth metal containing about 10% or less of iron. Nhen the metal added has become fluid at the bottom of the crucible, another batch of metal may be added in the same Way and the molten metal batch built up, care being taken not to expose the already molten cerium metal in the melt to the air, which Would rapidly ignite or oxidize it. The heatin of the pieces of metal to melt them shou d be carried out relatively quickly, because, if the operation is carried out slowly, the metal melt does not become as clear and homogeneous, the fused salt above it becomes more viscous and ditlicut to separate from the metal, and much metal is apt to be lost, nor does the metal pour so Well when it is later poured from the crucible. By relatively quickly We mean that the Whole operation of melting, alloying and casting the metal should take not over about two hours, instead of several hours.

When the crucible is about one-half full of molten metal, as illustrated at 6 in Fig. 1, any other metal which it is desired to alloy With it is added. In most cases, it is desirable -to add certain other metals, such as iron, to harden the resulting alloy. This is added in the form of soft wrought iron Wire. It is first cut olf in pieces Weighing, say, 40 to 50 grams and the pieces wound into loose coils or spools. These coils of Wire are poked into the melt under the layer 7 of barium chlorid. If iron alone is used, it is preferred to add sufficient iron so that the resulting alloy contains about 30% of iron. The iron is preferably added periodically in about four batches. The iron becomes hot in the bath and alloys with tlie molten cerium, etc. The layer of barium chlorid prevents oxidation of both metals. If there is We, therefore,

meadow not sucient barium chloridvin the crucible so that portions of the iron Wire protrude, these portions are covered with some barium chlorid to prevent oxidation and the heating continued until they are all melted into the alloy. Before the addition of any subsequent bath of iron, the previous batch of iron should be thoroughly absorbed. During the additi^n of the iron, care should be takennot to stir the batch any more than is absolutely necessary. When all the iron or other metal is added, the temperature may be raised to about 10000 C. which increases the Y fluidity of the molten metal. When the melt is fairly liquid, and about ten minutes before it is poured out., it is thoroughly but gently stirred to lproduce a homogeneous mass. It is important to increase the fluidity in order that, vvhen stirred it shall be thoroughly mixed, .and When poured into the molds the molten metal Will be suiciently iuid not to be congealed prematurely as more clearly pointed out hereinafter. An additional layer of barium chlorid may be added, if necessary.

TWhen the metal is thoroughly molten and homogeneous, the crucible is lifted out of the furnace and a hole poked through the crust, if any, of barium chlorid adjacent the side of the crucible, by means of a hot iron bar or rod. The molten metal is then poured through this hole out into suitable molds. lt is desirable to make up melts of metal of over 350 grams, preferably about 2-3 kilograms, as, if smaller melts, say of 200 grams, are used, difficulty is encountered in pouring the metal.

While any form of molds may be used, it is preferred to maire them of iron or have the casting face of iron or the like. However, graphite and other materials may be used for the molds. The mold, especially if made of solid iron, should he uniformly heated to about 400 C. It should be over 100o C. This heating of the mold permits the pouring of the metal at a temperature so near to the solidifying point that excessive burning is avoided and at the same time permits this metal, near to the point of congelation, to find its way into and lill the mold. The mold should be slowly and uniformly heated to prevent warping thereof. By thus heating the metal mold the residual heat absorbing capacity of the-mold, up to the temperature of congelation of the molten metal is reduced to a point Where it does not materially affect the homogeneity of the resulting casting by causing cracks, breaks, strings and cold shots and similar imperfections in the casting, caused by rapid and uneven cooling of the molten metal. This may be accomplished in other Ways. Instead of heating a heavy metal mold' a thin sheetmetalmold having little heat absorbing capacity may be used to accomplish the same result. In Figs. 2, 3 and 4 there is illustrated an iron mold composed of two parts 10 and 11, the part 10 being a dat iron plate, and the part 11 being a flat iron plate, provided wlth grooves 12, extendlng from the top nearly to the bottom thereof. A connecting groove 13 is provlded at the top. The plates may be held together by four angle bars 14 running along near the top and bottom on the outside of the plates and pulled together by bolts 15. The resulting castings have an unusually small dlameter or 'cross section and relatively great length and the ratio ofthe area in square inches of the molding surface from which withdrawal of heat may take place, to the volume in cubic inches of the casting to be produced, is greater than 16 to 1. In order that this relatively large heat withdrawal surface may not cause premature congelation in the mold of the metal, already near the point of congelation, and prevent the complete How of molten metal near the temperature of incipient congelation, into the mold, the chilling capacity of the mold is reduced as above described, and the fluidity of the molten metal is increased prior to pouring, by stirring and by a slight increase in the temperature thereof, as above described, to permit the molten metal to penetrate the mold cavities with substantial completeness before the stage of incipient congelation is passed.

Before pouring the metal into the mold, the surfaces of the mold may be dusted or otherwise coated with a layer of magnesia or other inert material such as rolling scale or tin plating, so that the pieces of cast metal may be easily removed from the mold. The metal is poured into the connecting slot 13 and runs into the mold slots 12, filling them up. The mold should be allowed to cool slowly, that is, no artificial means are used to hasten the cooling, but the mold is allowed to air cool, so that it cools with suilicient rapidity to prevent any substantial oxidation .of the metal. If the coating of inagnesia has been uniform, a slight tapping of the plate 11, after plate 10 has been removed therefrom,should so loosen the pieces of cast metal that they may be easily removed.

In Fig. 5 is shown a top view of a similar mold adapted to form cylindricalshaped castings or sticks of metal, and in Fig. 6 is shown a vtop view of a similar mold adapted to cast sticks of metal rectangular in crosssection.

The resulting cast sticks of metal as they come from the molds shown in Figs. 2 to 6 are especially adapted for sparkingv purposes and differ materially from the pieces of alloy heretofore used for this purpose and which were made by sawing or turning under oil. The alloy castings made according to our process, have matt unsmeared glassy sur faces where formed adjacent the metal mold surface. While the surfaces may be somewhat rough owing to the presence of some air or blow holes on the surface, yet the surfaces have a characteristic glassy appearance and the metal is not smeared over as is the case when the pieces are formed by sawing or turning. Moreover, especially when cast in the metal molds, it is found that the castings at said surfaces have a superficial skin partly composed of the alloy, but poorer in the rare earth metal than is the alloy in the interior of the cast piece. This probably is due to the alloyV taking up metal or particles from the metal mold surface. This skin serves as a substantially non-corrosive coating or layer while the necessary sparking roperties are not interfered with thereby.

y melting and pouring the alloyed metals from beneath a fused salt as above described, flakes of oxid, which would otherwise be present. in the casting, are substantially eliminated and theresultant casting is extremely homogeneous.

In many cases. it is found that crude metal (chiciiv cerium or lanthanum). as taken from the. electrolytic cell in which it is produced, is so impure or non-homogeneous that a stable and sufficiently air-resistant alloy is not produced by a `single fusion of the crude metal under the purifying bath.

as of barium chlorid. In such case, it is desirable to make two or more successive fusions as described. preferably before alloying (raising the melting point) and casting into final shapes (separating the metal or alloy into small pieces). After each such preliminary purifying fusion, the slagr or fused salt may be removed from the crucible and fresh purifying salt already dehydrated -added to the metal therein, or the metal may be cast into pigs of convenient size (about 1X1x4 inches) for remolding or for breaking into lumps for remelting.

While it has been suggested that in the making of certain brass, bronze and steel alloys, themetal may be melted below a laver of boraX or Waterglass. this a very different proposition from the making of castings of the rare earth metals, such as cerium or lanthanum` and their pyrophoric alloys which congeal readily and pour with diiiculty near their congealing point.. Cerium is not only readily oxidized when heated. but rapidly ignites, and, furthermore` has such a great affinity for oxygen that if melted below such glass as borax or waterglass, would so rapidly combine with the oxygen therein as to cause a violent reaction. With the brass, bronze and steel alloys. there is no such problem. The making of bronze, brass and steel castings is an art distinct and separate from the art of making castings and suitable for commercial use from pyrophoric alloys of cerium and similar rare earth metals in which the active that they earhen iorni @are num under a covering layer of sodium chlothe Working temperature.

,sponding loss of the salt,

' Other methods rid and potassium chlorid, but unless certain additional features or precautions are employed in the process, the results are ver unsatisfactory and even then barium chlorid has distinct advantages not possessed by a mixture of sodium chlorid and potassium chlorid.

Instead of using barium chlorid as a protecting layer for the molten metal, sodium chlorid and other salts inert to the rare earth metal being used, may be used which would prevent oxidation of the metal, but barium chlorid has advantages over certain othe` salts, because of its less volatility at If more volatile not only a carrebut great inconvenience to the Workmen results. Furthermore, it-is believed tlat the surface tension of fused cerium and its alloys against a molten bath high in barium chlorid is farmore advantageous to making homogeneous4 castings and protectingthe surface of the metal from too rapid oxidation. Copper or magnesium may alsobe added to the molten metal lto harden the resulting alloy, or increase the fatness and heat of the spark. preventing oxidation of the melt may be used as by carrying out the fusion in an atmosphere of hydrogen.,

Many other changes and modifications may be made without departing from the spirit and scope of the invention in its broader aspects.

What is claimed as new and desired to he secured by Letters Patent is r 1. In the process of making castings of cerium and similar rare earth metals and their alleys, the steps which consist in melting the rare earth metal and pouring it into molds, the temperature of the metal when poured being sucien-tly close to the congelation temperature to prevent inflammation of the metal.

2. In the process of making casting of cerium and similar rare earth metals and their alloys, the step which consists in pouring the molten rare earth metal or alloy thereof into a mold with a metal molding surface in which the ratio of the area in square inches, of the molding surface from which Withdrawal of heat may take place,

salts are used, there is to the volume in cubic inches of the casting produced, is greater than 16 to 1, the residual heat absorbing capacity of the" mold, up to the temperature of congelation of the molten metal, being reduced to a point where it-does not4 materially affect the homogeneity assenze 4. In the process of making castings of .alloys of ceriumor lanthanum the steps which consist in melting rare earth metal containing mainly cerium or lanthannm andA protecting the molten metal from oxidation and pouring the molten metal into. molds and allowingfthemolds to cool slowly as at room temperature, the residual heat absorblng capacity of the mold, up to the` tempery ature of congelation of the molten metal, being reduced to a po'int where itdoes not materially affect the homogeneity of the r'esulting castings by imperfections in the castrapid and unevenA cooling of' ing caused by the molten metal. K 5. In the process` of making castings of cerium and similar rare earth metals andV alleys thereof, the stepsA which consist in melt-ing therare earth metal or alloy thereof while protecting the molten metal from oxidation, pouring the molten metal into molds, the temperature of the metal when poured being 'suiliciently close to the congelation temperature to prevent inflammation of the rare earth metal, and permittinl the metal to cool inthe mold, with suicient rapidity to prevent Jany substantial oxidation thereof. Y

6. In the process of making castings of cerium and similar rare earth metals and their alloys the steps which consist in melting the rare earth metal and pouring the molten metal into molds heated to about 100 C. or over. Y

7. In the process of makin castings of cerium and similar rare eartlly metals and their alloys the steps which consist in melting the rare earth metal and pouring the moltenV metal into molds heated to about 100 C. or over, and allowing the molds to' cool slowly as to room temperature, the molds being coated with nely divided inert material to render the cast metal more easily removable therefrom.

8.` In the proce of making castings of cerium and similar rare earth metals and their alloys the steps which consist in melting a rare earth metal lWhile protecting the molten metal from oxidation, and pouring the molten metal into molds, the Whole 0peration taking about two hours or less, the residual heat absorbing capacity oi' the mold, up to the temperature of congelation of the molten metal, being reduced to a pint where it dees not materially aect the homogeneity of the resulting castings by perfections in the `casting caused by-rapid and uneven cooling of the molten metal.

9. In the process of making castings of cerium or similar rare earth metals or alloys thereof the steps which consist in melting rare earth metal containingl mainly' cerium or lanthanum and containing about 10% or less of iron, and then melting therewith an alloying metal to harden the resulting alloy,

and pouring the molten rare earth metal or alloy thereof into a'mold with a metal molding surface in which the ratio of the area in square inches, of the molding surface from which withdrawal of heat may take place2 to the volume in cubic inches, of the casting produced is greater than 16 to 1, the residual eat absorbing capacity of the mold, up to the temperature ofcon lation of the molten metal, being reduce Ato a point where it does not materiallyaffect the homogeneity of the resulting casting by imperfectlons in the casting caused 'by rapid and `uneven cooling of lthe molten metal. 10. In the proces of makmgcastn of cerium or similar rare earth metals or a loys -thereof thesteps which consist in melting a point where it does not materially affect the homogeneity of the resulting casting by imperfections in the casting caused by rapid and uneven cooling of the moltenmetal.

L1. In the process of manufacturing castings of rare earth metal alloys the steps which consist in pouring the molten alloy, at Ja temperature near the temperature of incipient congelation thereof, into multiple molds, the mold cavities of which have a ,surface to volume ratio measured in square inches and cubic inches respectively, greater than 16 to 1; and reducing the heat abstract' lng capacity of the molding surface to such` a point that the molten metal penetrates the mold cavitiesgvith substantial completeness before the stage of incipient congelation is passed.

12. In the process of manufacturing castings of cerium and similar rare earth metals or their alloys, the steps which consist in melting` t e rare earth metal or alloy and pouring t e 4molten metal into molds residual heat;` absorbing capacity of which,

Y up to the temperature of congelation of the molten metal, i s` reduced to a point where it does not affect the homogeneity of the resulting casting by imperfections in the cast- 'ng caused by rapid and uneven cooling of the molten metal and permitting the metal to cool in the mold with sufficient rapidity to prevent any substantial oxidation thereof.

Signed at New York, in the county-of New York -andState of New York, this 6th day of May, A. D. 1918.

ALGAN HIRsoH. Y MARX HIRsoH.

Witnesses y Je R. BAILEY,

the A

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