US 2373405 A
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April l0, 1945., R. LowlT 2,373,405
PROCESS OF MAKING SEAMLESS HOLLOW BODIES OF REFRACTORY METALS Filed Feb. 14, 1941 warm/6 0.//7 6.44m caff INVENTOR. /U' 0W/7 ATTORNEY Patented pr. l0, 1945 NETE@ STATES maar ottica PROCESS 0F MAKING SEAMLESS HOLLOW BODIES 0F REFRACTORY METALS Rudolf Lowit, Union City, N. l., assignor to Callite Tungsten Corporation, Union City, N. d., a oorporation of Delaware l Claims.A
The present invention relates to the manufacture of seamless tubes of refractory metals such as tungsten, molybdenum, tantalum and columbium.
It is an object of this invention to provide seamless tubes, tubular parts, or hollow bodies of various cross-sectional shape, which are useful in operations Where high temperatures are encountered. For this purpose the high melting point metals above mentioned are distinctly suitu able but hitherto no practical method has been devised for manufacturing them .in tubular form.
it is contemplated by the present invention to form a hollow body of the metals contained in the group including' tungsten, molybdenum, tan taluni, and their alloys or composite bodies of said metals, by pressing a body from the metallic powder about a forming core. The pressed body is then subjected to a sintering process during which the metallic powder sinters and frits into a coherent body capable oi being forged, rolled or swaged, and subsequently drawn. The forming core may be removed as an incident to the temperatures employed in sintering or :ritting the metallic body, which 'temperatures are suiilciently high to melt or volatilize out the material of which the forming core is made.
lr' the forming core be of metal, it should ordinarily have a melting point considerably dlerent from that of the metal of which the tube is to be formed. lt should also have a coeicient of expansion not greater than said tube metal and preferably considerably lower. Furthermore, the core material, if metal, should either be of a metal that will not readily alloy nor form compounds with the tube metal or else it should be coated or sleeved with such va metal or other compound to prevent such alloying or reaction. Suitable for such cores are alloys of nickel, iron, chromium, etc., and particularly the alloy of nickel and steel known as Invar which has a nickel content of 36% and a very low coedicient of expansion.
I have found various compounds of silicon, such as quartz, pyrex glass, or other boro-silicate glasses, to be especially suitable for use as a formingv core. Sillimanite and carborundum may also be satisfactorily used.
According to the preferred method of the invention, a die of the desired shape is partially lled with a refractory metal in nely divided form. This is then tamped down and a rod, which is to be the forming core, is placed centrally on this metal, More of the same metal powder is then placed in the die in such manner that the forming core is disposed Within the mass. 55
The whole assemblage is then subjected to considerable pressure so as to form the metal powders into a compact body about the forming core. This body is then removed and subjected to a preliminary sintering at a temperature suflicient to bring the metallic powders into a coherent body with the forming core still disposed therein in a neutral or reducing atmosphere or in a vacuum. At this point the metallic body attains sufficient coherence to be handled, and it is then placed between electric termini and electric current is passed directly through it until it is heated .to a point short of the fusing temperature. This heating may be done by passing a current directly through the body, or by any other means such as by high frequency induction. During this treatment the core crops out, melts out, or distils ofi according to its nature, through a properly provided opening, and there results a coherent, strong, hollow, metallic body.
The drawing presents a flow diagram showing the various steps of the process.
es shown in the diagram, the die or mould is i'lrst filled approximately half ull of finely divided metal such as molybdenum which is tamped down. A rod of borosilicate glass is then centered in the die on top of the metal powder. More of the metal powder is then added to lill the die, the glass rod remaining in the center' thereof. The metal powder thus in the die is then subjected to a high pressure, hydraulic or otherwise, ci the order of l@ or 213 tons per square inch, or even higher, in order to compress and densely compact the metal powder as uniformly as possible. The compacted mass with the glass core stili in place is then sinte'red by placing lt in a furnace in a neutral or reducing atmosphere or in a vacuum. rIhe body may be mounted during the sintering step in a vertical position between two electrodes and heated by direct pas sage of current to slightly below the meltingpclnt of the metal. Below this temperature the glass rod melts and flows out or drops out, leaving a smooth, clean passage through the metal body.
The molybdenum body with the cylindrical opening so formed by the removal of the borosilicate glass rod is then removed from the furnace. A rod. which may be of metal or other suitable material, is then inserted in the hole in the center of the body and the assemblage so formed is then introduced into a swaging machine and swaged down in known manner. When the tubing has been reduced to the desired size, the core is removed, mechanically-or otherwise, and there results a strong molybdenum tube of fibrous *VVeonstruenon-i innescare! swinging; thezbodymay 1 1 v t @internmlybzlemm,v thereby1s,inf rr1eSaid 1 f 1 I f 1 be relied or: forsean Thermal stier may bei draw-g 1 1drlwnzbvdyand meltingrwt ,Seid bOQSH-f 11 m511iv1-1--irv -*rvf1 fff categlasscorepinsertingafmetalrodinto'the i '11' IfiThe procedure sbeveideseribed for molybdenum 1 'hollowleft by'siaidfe: endiswaeng @WMO fie-11 11 1 *Ywithslightlmodincationsasltotemneratureandv/Siredsze@ 1 1 1 i ienne; win: 'also' apply for mngsten; cantslum,1 ed.1 l 1 1 1 12; method of; making aI seamless :tope @f1 1 1 1 f iiunlloium,1 composite :bodies of i 'said metals; my f v 1molyhdemim,v tungsten nr; like refractory metal f their rim-emi? metal o 2 Hnweyer, if f tungsten, y 1 1comprisinspressinggseid refractory meter about imetiis :usedand:aipyrexgiasseorethere wo111d-1i a1borosilicategiassmdsnteringsaid: pressed 1 ne little,1 iff any; change necessarmvl'yrex'glaiss; i metal in 1 a neutral; or; 1 educing atmospliereI by 1 forinstiance,- will; melt Eand Iflow;atlabout; i200? i I mounting said body between electrodes and pass'.v
wriesiiicen oxide distiisiouti at temperetureso i ing 1'ciurrent throfueh Iseid:sirnre'red body, thereby s 1 l "theorder of 1BGD" C orhighen r: 1 1 1vheating; i1, toia temperature slightlybelowlthe 1 1 y 1 1 y z 1 y 1 l f 1 It; is witlriin the lconteignplation of the irivveifltiong I melting point of: the metal@ at the same timemeltf i "'that the forr'ning core'mayevenbef ois.1 metal 'l5 ing outy the Iborosilioate1glass rod; then inserting l f i v iraving a melting pointashign :aslorzhignerthan: 1 t 1 i a rodofmetaiinthe passage formedby the said f Ithe meltingpoint of ItheI tube metal; It 'snouicLI 1 1 1 1 1 f vnd;drawing1 said 1 sus@ I 1 Iimameiong and zshrmid niet @berofametaiithat woud; 1 i 1 r 13. @'Ihemethod: of making@ Seamless tubing ie! l *alloy with thetube' metal; For instance, if; the 291 dense molybdcnummetalcom rising the :steps o1 i tube metal ismolybderium,it Wouldbe quite prac-5' 1' cnmpaeting, molybdenum 1 I 1er.l 1 powder u 1 e 1 l Itical and within the souper of@ the' invention to use i 1 pressure; of the ,order of; 101tof21l1tons perso 1 r l f a rod of tungstenproperlyfcoated lorsleeved; with i i 1 inch; about 1a 1 core of orosilieate glass; heating 1 highI melting point oxides susha's, the oxidego` 1 1 said body so ffoi'med to a, temperaturejustbelow i i beryllium; magnesiom1,izirconium,; ori thorium; ias@ i251 the v1r eltizns paint iof molybdenum and above Ithe f v 1 the forming' leere; iaitho'u'gh tungstenhas La cm1-2 i i me? l point Ofi the said elassfcord thereby :sine f1siderablyhigherimelting poiritthan has molyb-1 wtering the powdered molybdenum andmelting :out l l deniim; Its coefficient of expansion; lfilowever,v isi the 1saidglasscore1; inserting 1a metal rod into the 1 f close vto that 'olfI pyrex glass 1and because ofI itsk l opening left by Saidmeltedoutcore;mechanically 1 i vcoatingit; Wilinot: ailoywith molybdenuinp "Ihere 301 WOIkine Said sintered body; about said metal rod@ 1 l are Icertain practical advantages in 'usinga tung l 1 i until Said bodyis reduced tovdensve metallic conel 1 `fsten'rodinitnisimannersiricethe:tube:maybe1I ldition? and thenzremovinggseidmetal rod.1 .11 i y 11 1 1 formed g about lit anda lafterlthe sintering step, the l 1 whole assembly centered; about? the tungsten ,coi-el i 1 which stili rerlnainsmay he swaged; :forged: rolled 1 i and drawnw'ithout: the necessity 1 ofzremovng the 1 core; and inserting; a newI rodi in place thereof.: 1 After the sw'aging,v rolling,1 forging and drawing l inea die of raisuitabl fllmll filling Sdlde ap* 1 isI completed; however; 1rthe tungsteri1 core kmay l proximately lhalfI fullI withnelyj divided rerse I be removed mechanically; 1I may :also vuse ias a i 4i@ tory metalicenterng: a rod of borosiiiceteI glass;
core material, Where the body material is molybupon said metal in said die, completely filling denum, a rod of molybdenum coated with high said die with more of the nely divided refractory melting point oxides. metal with the glass rod remaining centered Having thus described my invention, what I 45 therein, subjecting the powdered metal in said claim is: l 1 die to a pressure of approximately 10 to 20 tons 1. The method of forming a seamless molybper square inch, and then heating to a, temdenum tube which comprises pressing nely perature slightly below the melting point of the divided molybdenum powder in a die about av metal, thereby sintering said metal and melting borosilicate glass core, heating said pressed body 50 out said rod of borosilicate glass. so formed to a temperature just below the melt- RUDOLF LOWIT.
o 14; 11i/retired of making; a Is1eam111ess1 mbe sf tu group; consisting 1 off 1 tungsten, f molybdennm "1 tantaium; columbium and the alloys; and com: posite bodiesI ofi said metals capable :or beine i lmechenieallrworkd that consists ,in first Pmi/id