US3201835A - Casting refractory metals - Google Patents

Description

Al1g- 24, 1955 D. E. COOPER ETAL 3,201,835

CASTING REFRACTORY METALS Filed March ll, 1963 3 Sheets-Sheet l .n ri sl" JNVENToRs. Donold E. Cooper Schuyler A. Herres Al1g 24, 1965 D. E. COOPER ETAL 3,201,835

CASTING REFRACTORY METALS Filed March ll, 1965 5 Sheets-Sheet 2 INVENTORS. l Donald E. Cooper Schuyler A. Herres Allg 24, 1965 D. E. COOPER ETAL CASTING REFRACTORY METALS 3 Sheets-Sheet 3 Filed March ll, 1963 JNVENToRs. Donald E.Cooper Schuyler A. Herres United States Patent Oliice 3,201,835 Patented Aug'. 24, 1965 3,201,835 CASTING REFRACTORY METALS Donald E. Cooper, Las Vegas, Nev., and Schuyler A. Herres, Murray Hill, NJ., assignors to Titanium Metals Corporation of America, New York, NSY., a corporation of Delaware Filed Mar. 1l., H63, Ser. No. 267,071 8 Claims. (Cl. 22-68) This application is a continuation-in-part of our application Serial No. 43,205 led July l5, 1960, now abandoned.

This invention relates to die casting of metals, and more particularly to die casting refractory metals.

Die casting has heretofore been widely used for casting relatively low melting point metals such as magnesium, zinc, aluminum, tin and lead base alloys. Eut the same type of machine design and proce-ss used in making die castings of such low melting point metals cannot generally be used to produce die castings of refractory metals, because such refractory metals 'have higher melting points and are often reactive in nature, particularly at their melting temperatures.

It is therefore an object of this invention to produce a die casting of a refractory metal. Another object of this invention is to provide a die casting machine useful for producing a casting of refractory metal. These and other objects of this invention will be apparent from the following description thereof and from the annexed drawings in which:

FIG. l shows a general top view of a die casting machine embodying features of this invention.

FIG. 2 shows a central vertical section of the die casting machine of FIG. 1 taken along the line 2--2.

FIG. 3 shows a front view, partly broken out, of the portion of the machine comprising the electrode actuating mechanism and the melting crucible.

FIG. 4 shows a side View, also partly broken out, of the same portion of the machine shown in FlG. 3.

FIG. 5 shows a horizontal sectional View of the portion of the machine containing the melting crucible, taken along the line 5-5 in FlG. 2.

FIG. 6 shows how the melting crucible shown in FIG. 5 is tilted in operation.

FIG. 7 shows enlarged, and in some detail, the portion of the machine comprising the injection mechanism and the die blocks. Y

Referring now particularly to FIGS. l and 2 the machine is partially enclosed in a gas tight shell indicated generally at lil and which is composed of a bin l2, an

f injector housing 14, a crucible housing i6 having its top'electrically insulated from the sidewalls thereof by interposition of insulating gasket i7, and an electrode housing le?. Attached to the top of electrode housing 19 preferably by removable bolts l@ (see FIG. 3) is horizontal plate 2o to which are xedly attached vertical guide rods 2.2. Lower bearing plate 24 is attached to the tops of guide'rods 22 and carries suitable spaced bearings 26 through which projects the tops of screw shafts 2S, the lower ends of screw shafts 2S being suitably seated and maintained in similarly spaced foot bearings 36, which are attached to and carried on the upper surface of plate 20.

Spanning screw shafts 28 is lower cross head 32 which is provided with fixed nuts 34 where it is transfixed by screw shafts 28. Also attached to lower cross head 32 are spaced quick acting uid cylinders 36 (see FlGS. 3 and 4), which may be air or hydraulic, whose piston rods 38 are fxedly attached to upper cross head dil which is provided with suitable openings through which the screw shafts 28 pass freely. Upper cross head 4d is maintained in vertical alignment above lower cross head 32 by guide rods 22, which slidably pass through suitable openings in the upper and lower cross heads 4t) and 32. Fixedly attached to and depending from upper cross head 4t? is electrode ram 42 which extends downwardly and passes freely through a suitable opening in lower cross head 32, and also passes through an opening in plate Ztl and into electrode housing 18. An electrode, supported by the ram 42 and attached thereto at the lower end thereof by any suitable means, as by a temporary weld at 43, is shown at 44. Where ram 42 passes through plate 2d, a suitable gas tight sliding seal, as at 46, is provided.

The top ends of `screw shafts 2S, projecting through lower bearing plate 24 are attached to pinion gears 43 which in turn mesh with central spur gear 50, suitably ixed on vertical drive shaft 52 which is journalled through an upper bearing plate 54. Bevel gear 56 is iixedly attached to the portion of drive shaft 52 which projects above upper bearing plate 54, and is in turn driven by meshed bevel gear 5S fixedly attached to the shaft 6d of electric motor 62.

Thus it will be seen that as lower cross head 32 is moved up and down by rotation of screw shafts 28, in response to actuation by motor 62 through the gear train described, upper cross head 40 will also move up and down correspondingly vsince the assembly of pistons 36 and piston rods 33 will ordinarily maintain the two cross heads in fixed relationship. Upper cross head 40 will thereby move electrode 44 correspondingly up and down since these elements are connected by ram 42. The direction of rotation and control of motor 62 is best accomplished by automatic means dependent on the melt- -ing arc characteristics; such means, including often an amplidyne circuit, `are well known in the art and since they form no part of this invention per se, will not be described in detail. In addition to this movement control, the upper cross head lil may be moved rapidly up and down, for reasons explained hereinafter in more detail, with respect to lower cross head 32 by action 'of cylinders 36, to extend or retract their piston rods 38, this being accomplished by introduction or bleeding of compressed iiuid such as air through flexible hoses 64, with the air passage therethrough controlled by suitable means, such as valve 66.

Referring now particularly to FIGS. 3, 4, 5 and 6, it will be seen that electrode 44 is arranged to be lowered into or raised with respect to a cavity 68 in a crucible 7i) which is provided in its top rim with indented pouring spout 72. Preferably, but not necessarily, crucible 70 is fabricated as a heavy wall body of a good heat conducting metal such as copper. lt is supported inside crucible housing 16 so that it may be tilted in order for molten metal therein to be poured. This is accomplished in the embodiment illustrated by provision of saddle 74, which is generally U shaped and which is provided internally with la duct 76, through which may be circulated a cooling fluid such as water. Crucible 'lil is maintained in position in saddle 74 resting on the bottom part of the U and is attached thereto as by bolts 78. Bracing members 8i) are iixedly attached at their ends to the upper part of saddle 74, and encircle a top portion of crucible 74B to which they are each attached -as by bolts 82. Projecting outwardly from the tops of the vertical arms of saddle 74 are hollow ltrunions 84 which are journaled through sealed bearings S6 in a side wall of crucible housing 16. Cooling iiuid pipes 38 pass through the hollow trunions 84 extending outwardly therefrom and are preferably connected by ilexible hoses 9i) to .a suitable source of water supply and drain, not shown.

At the exterior end of one of the hollow trunions 84 is iixedly attached crank arm 92, with its end pivotably attached, as at 94, to the piston rod 96 of air cylinder 98 which itself is suitably mounted on base plate 160, at tached :to an adjacent portion of the crucible housing 16 as by Welded bracket 102. Compressed air is supplied through connecting hoses 104from a source of supply,r

not shown, so that by appropriate action of air cylinder 93, piston rod 96 may be lextended or retracted and act Welding at 110, it being understood that an aperture is provided above funnel 1116 as at` 112 to allow free passage 106 leads through a short connecting pipe 114 into horizontal feed tube 116 which comprises liner 117 of graphite carried inside, support steel tube 11S. Slidable in feed tube 116 is closely fitting steel plunger 120 which is iixedly attached to the internal end of a plunger rod 1722.1 Sliding seal 12,4 protects and maintains a gas tight passage of l plunger rod 122 through the side wall of injector housing v 1. die block 18,0 and movable ldie block 184. It will also be seen Vthat feed tube 116 is arranged to pass through or transix stationary'die block v181i so that it communicates 'with casting cavity y192 through runner 19t) and gate 183.

The entire shell is.y designed lto be gas tight and provision for evacuation is made through nipple 194 which is set intow and througha sidewall thereof, as shown through fa sidewall of injector housing 14, and maybe yof metal poured from Crucible 70. The bottom of funnelv 14. The endk of plunger rod 122 is connected to actuating means such as extending piston rod 126 of hydraulic cylinder 128,' which itself is supported and xedly attached to plate 130 which is attached across the outer ends of supporting bars 132 vsecured to the injector housing 14.

The inner end of feed tubeV 1,16 isdisposed toV extend through a suitable aperture in front plate 134 and Vis attached thereto by flange 136 which is attachedto the supf port tube 118 as by welding, and to front plate, 134 byY bolts 138. Front plate 134 is suitably supportedby cross brace 140 fixed between opposite sides of housing 14 and attached as kby nuts "142 tothe ,interior ends of spaced machine bars*V 144 which extendv through the side wall of injector housing `14 and are attached at their outer ends to back plate 146. Machine bars 1'44k are sealed Where they pass through the side wall of injector housing 14 preferably being iirmly attached thereto as by Welding at 148. Mounted on machine bars 144, inside the injector housing 14, is sliding plate 150, to which is attached sliding plate rod 152 Which'is suitably sealed with a sliding seal at 154 where it passes through the side wall of V'injector housing 14. The exterior end of sliding plate rod 152 is pivotably attached to toggle links 156 which in .turn are pivotably attached `to toggle links 158, Whose exterior -ends are pivotably mounted, on backplate 146 as at ,161). The center pivotv connecting togglelinks 156 and 158 is also attached at 162 to verticallink 164`which in turn is at?j tached to the piston rod 166 of vfluid cylinder 168. A suitable base plate 170 supports fluid cylinder 168 and is itself supported and connectedlto machine bars 144 by rods 172. f 4 K The'oor of injector housing 14 is provided with an aperture 174 below the Afront p1ate'134 and sliding plate 150, and which forms a passage into bin 12.- The side 4connected by pipingvln, Vor other'convenient means, to a vacuum pump 198 driven suitably by electric motor 260. A bleed valve 2%2is arranged, as shown through a side- Wall Yof Crucible housing 16, so that air may be let into shell 10 when it is desiredto break vacuum. Power connections for supplying melting currentlbetween electrode 44 and metal in crucible-'tl are arranged conveniently, as by provision of tlexiblecable 204 attached to'cross head 4h which lis in direct contact through ram 42 with electrode v'44, andflexible cable 206 attached to trunion S4 which is attached 4and connected to'saddle 74 which is in turn attached and connected to the bot.- tom of crucible 7l). Power Vleads 204 and 206` are connected with suitable and conventional control means to a ysource of high amperage4 electric power (not shown).

' It must be realized that production of die castings of refractory and reactivemetals such as titanium, zirconium, and high alloy steels, is a somewhat different operation than producing inexpensive castings of the lower melting point, and often cheaper rmetals.A In production of die castings of zinc or aluminum, for example,y rapidity of operation, volume of production and long die life are essential to profi-table business'.Y In making titaniumV castings, for example, the surface nish and soundness of the casting is important and the high priceof the metal and limitedriield of usefulnesswould Yordinarily tend to limit the number, of parts required from a set of dies. The

Y valueY of Vaflinished casting Vwould tend to.'l make each v ing their required life.

walls of bin 12 are preferably fabricated in two sections which may be disconnectably kattached as by bolts 176l so that finished castings deposited inthe b in 12 may be f removed at intervals. For convenience the bin V12 is provided with supporting Wheels17 8. f f

As is customary in die casting'machines the dies are split andseparable. As will be seen'by reference to FIG. 7, they are composed of a stationary die block 186, whichv is attached to front p1ate134 as by bolts 182, and a movf able die block 184 which is attached to sliding *plateV 150 as' by bolts186. It willbeapparentthat die blocks 18) and 184 may be separated, or.locked into'face-to-face relationship,` by means of the mechanism previously described actuating sliding plate 151) yto rwhich movable die block 184 is attached. In thev embodiment illustratedy lt willbe noted by thoseiskilled in the art that the die casting machine illustrated and described herein does not contain many of the refinements and auxiliary devices at'A times incorporated in machines heretofore proposed and used in the Vmaking .of die castings.v This permits a cleaner.presentation,l for vgreater clarity and understanding `of the important and unique features of the machine vof this invention. It is to be'un'derstood, however, that such minor variations .as employing conventional and well 'known parts to providejejccto'r pinlmechanis'm for separatingV castingsv from Aa die, cores, and'cooling means for dies, plates, Yand plunger'may be incorporated if necessary or desirable. y a Y Operation of the die casting machine -of this invention I will be described; forillustration with reference to production cfa casting rof titanium metal. y First the ,electrode housing 13 is detached from the remainder yof .the apparatus -by Yloosening Vand removing bolts 17y and with the associated electrode control structure'arranged in' accessible position,'the electrode ram 42 is run down by'actuation of the electrode control mechanism operated by motor y62. Apreviouslyprepared electrode o-f titanium metal 'as at 44'is temporarily attached ,to the bottom of the velectrode-ram as bywelding at 43, so that it may besupported in arc melting relationship to a body ofrefractory metal in cru-cibler'Tt when the .electrode housing 13 is again assembled inroperativerelation with thehousing `16. A starting Charge of titanium sponge or chips is placed in the bottom of Crucible '70 which is adjusted into upright position lby suitable actuation of air cylinder '93. With the electrode 44 now `attached to the ram 42 it is run up into the electrode housing 18 and the whole electrode control yassembly -is replaced on top of Crucible housing 16 and the bolts 17 replaced and tightened. Conveniently at this stage the electrode control cylinders 36 are actuated so that the upper cross head 40 is run down close to lower Cross head 32 for reasons which will hereinafter be explained in' more detail.

Suitable dies 180 and 184 with recesses to form at least one casting cavity 192, to produce ythe required casting are bolted in place against plate 134 and sliding plate 150 respectively. 'Phe dies yare then locked together by actuation of hydraulic Cylinder 168 to straighten out and align toggles 156 and 158. Plunger 120 is withdrawn to the outer end of feed tube 116 Iby suitable actuation of hydraulic cylinder 128, thus providing a free open passage through the funnel 106 and connecting pipe 114 into the horizontal feed tube 116. All bolts are tightened and joints Checked for leaks and then the entire shell is evacuated by action of vacuum pump 198.

When the pressure in the shell 10 has reached beow about 5 millimeters and preferably below about 1 millimeter of mercury absolute, and it is apparent that there are no deleterious leaks in the shell, power is turned on through power leads 204 and 266 and the electrode 44 is lowered by suitable control of motor 62 operating ram 42 through the screw shafts 28 and Cross head 32 until an arc is struck between the bottom end of electrode 44 and, initially, the starting charge of titanium metal in Crucible 70. Following this, maintenance of the arc between electrode 44 and a pool of molten metal in Crucible '79 is accomplished by suitable control of rotation of screw shafts 28 to raise or lower electrode 44, by, for example, a control unit customarily employed, based on maintenance of a uniform voltage across the arc. Under these conditions electrode 44 is progressively melted into a pool of molten titanium metal in Crucible 70, with the pool being contained in a skull of solid titanium metal in Contact with the inner wall of Crucible 70. When the pool amounts to suicient metal to produce the required casting together with its runners and sprue, melting power is shut olf and electrode 44 is rapidly raised by actuation of cylinders 36 to lift cross head 40 with respect to Cross head 32 thereby to lift the end of electrode 44 quickly out of the way of Crucible 70 when tilted. Without delay,

during which additional metal in the pool Could be solidied in Crucible '70, the Crucible is quickly tilted by actuation of air cylinder 98 so that the pool of molten titanium metal in the skull inside Crucible 70 is poured into funnel 106 and through tube 114 into the feed tube 116. As soon as the molten metal is received in feed tube 116, plunger 120 is, at high velocity, actuated by hydraulic cylinder 128 to force the molten metal through gate 188 and runner 190, and into the die cavity 192.

After a suitable time period to allow the casting to solidify in cavity 192, hydraulic cylinder 168 is actuated to raise central pin 162 between toggles 156 and 158, thereby to unlock and separate the die blocks by moving sliding plate 150 and its attached die away from plate 134 and the fixed die block 180. By reason of the attachment of the sprue of metal remaining in feed tube 116 and gate 138, the casting will ordinarily remain with the xed die block 180. Plunger 120 may thereupon be again actuated inwardly by hydraulic cylinder 128 to force the casting and attached sprue and runner out of die block 180 to a position where the Casting will fall by gravity into bin 12.

To produce another casting, cylinder 168 is actuated to Close and lock the dies 130 and 184 together. Cylinder 128 is actuated to withdraw plunger 120 to the outer end `of the feed tube 116, and Crucible 70 is returned to upright f position.

position by actuation of cylinder 98. Then cylinders 36 are actuated so that upper Cross head 441 is lowered close to lower cross head 32 and this will place the electrode 44 in the cavity in Crucible 70 in approximate melting Power between the electrode 44 and the Crucible 7d is then turned on through power leads 294 and 206 and the electrode melt control system put into operation to actuate motor 62 to maintain a melting arc so that additional metal of electrode 44 is melted to form another pool or body of molten metal in Crucible 70, and the steps above described are repeated.

After a suitable number of castings have been produced by a repetition of the above described cycle, which may be when all of the metal in the consumable electrode 44 has been melted into Crucible 70, and the castings are suliiciently Cool, the atmosphere is allowed to enter housing 10 by opening bleed valve 2112. With the interior of shell 10 at atmospheric pressure, bolts 176 are then removed and the lower portion of bin 12 separated from the upper portion thereof and the finished castings removed from the bin.

Production of die castings having good surface finish and proper qualities is dependent on a number of important factors. The melting of the Charged metal must be accomplished so that the molten pool in Crucible 7i) is enclosed in a skull of solid metal which is not so thick as to restrict the amount of metal available for pouring and Casting. The heavy mass of the Crucible '70 as shown and described is ideal for producing melting conditions under which a desirable pool of molten metal will be formed in side a thin skull. Fabrication of a heavy wall Crucible 7l) of copper will provide sufficient heat sink capacity so that the Crucible itself will absorb sufficient heat during melting without the necessity for additional or external cooling. The arrangement described, in which a cooling duct 76 is provided in Crucible saddle 74, makes possible the cooling of Crucible 7@ between pourings. It will be apparent that the heat sink capacity of the Crucible 7l) obviously will have a delinite limit and it is a unique and valuable safety feature that the Crucible itself can maintain proper operating conditions during melting without the introduction of a cooling liuid, such as water, into the furnace in this vicinity. Any leak or disruption of the Cooling water system could result in contact of water with molten titanium or other reactive metal at high temperature and result in a disastrous explosion. Therefore, provision of cooling duct 76 in saddle 74, through which Cooling water can be circulated at intervals when the melting operation is not in progress, enables the Crucible 70 to be adequately cooled under safe operating Conditions.

The metal used for die Casting may be melted in Crucible 7@ employing either a Consumable or nonconsumable electrode. lf Consumable, the electrode 44 is fabricated of the metal to be melted and is progressively consumed and transferred into Crucible 70 according to principles well known in the art. If a non-Consumable electrode is employed at 44 it may conveniently be fabricated of tungsten and the metal to be melted may originally, or by suitable means be progressively, charged into Crucible 7i) as desired. In any event, the electrode 44 is raised or lowered with respect to the metal in Crucible 7@ to maintain a desirable and properly operating melting arc. Control devices for accomplishing this are well known and will not herein be described in detail. They often operate in response to a signal feed back which maintains the distance between the electrode tip and the pool of molten metal so as to keep the arc voltage Constant. ln the case of a Consumable electrode the electrode ram 42 and the electrode 44 will be gradually lowered as the electrode 44 is progressively consumed. ln the Case of a non-Consumable electrode this may be raised or lowered but will 'oe generally raised to maintain proper arc Conditions between its tip and a gradually rising pool of molten metal in Crucible 7l). In any event,

embodiment illustrated, comprise screw shafts 28 which 'drive cross head 32 and crossvhead 4dii, and electrode ram 42 which supports electrode A44, and which are actuated by motor 62 through gears 4S and Sil, are designedv to maintain a melting arc between electrode ed and refractory metal in Crucible 7d during the melting operation. inherently the type of mechanism involved will not be suitable for rapid or almostrinstantaneous move ment of electrode 44. Therefore, auxiliaryelectrode raising means comprisingv` fluid cylindersV 36 acting on upper cross head 4t) are'arranged to rapidlyfraise ram,

d2 and electrode 44 independently of any position in which the cross head 32 may be-'situated Thus, at the4 properstage during the melting of metalin crucble7fl, when it is apparent by consideration of the time oi melting, or the quantity of metal melted, the power may l be disconnected betweenV electrode 44 and crucible 711, and electrode 44 raised out of the Crucible cavity, and the crucible immediately tiltedto pour the pool of molten metal therein into funnel 106. The sequence of these steps must be rapid and uninterrupted.

It has been found advantageous to fabricate funnel 106` of, or line it with, a suitable material, preferably one that will not react to any appreciabley degree'with the molten metal passing therethrough. Graphite has' been found to be suitable, and the vtime of contactvof the molten metal 'with the graphite funnel 1116 has not been found to result in appreciable contamination of the molten metal.

The specific construction of the feed tube116and its cooperatingplunger 12) is a key feature of this invenn tion. As described, the feed tube 116 is fabricatedwith steel outer support tube 118 and a graphite liner 117.l

The problems in design of a workable feed ytube assembly involve providing a temporary holding cylinder Within which the plunger 120 can operate, the molten refractory" metal in the holding cylinder being at extremely Vhigh temperature compared to the temperature when molten of metals heretofore and lnormally used 'in die casting processes. The molten metal in feed tube 116 must not be allowed to solidify, obviously, and the feed tube ma'- terial must not be such as to alloy with or contaminate the refractory metal, `We haven found that liner'117 fabricated of graphite of a grade described in commerce Vas extruded graphite of good structuralfquality, medium grain size, pitch treated and of high bullr'density, will operate advantageously inside a strong steel'support tube 118. Graphite has heretofore often been proposed and used 'as a Crucible or mold material even for castings of refractory metals. Its use in the feed tube of the die casting machine of this invention, however, becomes successful for quite different reasons; the application and purpose isl quite different. Graphite in liner 117 acts as a material to maintain the -rnolten condition ofv rek fractory metal contained therein even though its `thermal iconductivity'is greater than adjacent or normallyl cn sidered materials of construction such as steel.` In a sense; graphite liner 11'7 acts as a thermal Vinsulator inspite of the fact that its thermal conductivity is higher than that j of steel support tube 118. Our workY leads us to be- Y lieve that when molten refractory metal enters feed tube 116 and contacts liner 117, the high thermal conductivityI lof the graphite of liner 117 results inV freezing of a thin skin of solid metal around the molten metal body. Soliditlcation of this Vskin results in a shrinkage of the molten metal bodytrwhich shrinks away from the graphite liner wall, thus destroying the physical contact (except perhaps along a line at the bottom) and with loss of physical contact, the'overall heat transfer'isv substantially reduced. Additionally, graphite is ycharacterized by v a thermal capacity only about one'quarter; that of steel so that it actually acts to'provide an initial chilling to freeze a surface skin without causing excessive heat loss from the yrnain body of liquid metall, The thinskin of'solid metal is readily rammed by the'v plunger A120 into the mass or biscuit remaining fat the end of the freed tube and which is discharged attached by the vspi-ue tothe casting.

In addition, graphite resists thermal shock, isV highly refractory and provides some lubricating effects when the plunger travels through it. This is'probably in par-t the result of a wearing away of a minute amount of surface graphite with each plunger stroke.. Even so'V and with a Vshort' contact time, the graphite liner 117 does not diele'teriously contaminate Vthe refractory lmetal being die cast. i p The stel-support tube 118 providesk strength to the feed tube assembly enablingV the weaker graphite liner 117 to resist the pressures and forces exerted by plunger 120. p

The t of plunger 126) in liner '117 is also important and the t should be close enough so that the plunger V126i wipes the interior surface of liner 117` clean of refractory metal with each stroke. Clearance tolerance is low and should not exceed .005 .inch all around. Preferably the .Vt between, plunger 121i` and liner 117 Vis tight plunger 120 through liner 117 will ream out its interior Vto desired close fit size. f

' It will be yevident that graphite liner 117 ldue to fit requirements Vandrigorous use will not be long lived. It should be replaced when clearance between its interior and plunger 120 becomes sloppy.Y It'will, however, we have yfound,function efficiently for an acceptable number of ramming and casting cycles. 5

Immediately on transfer of the molten metal into the feed tube 116, plunger 120 :is actuated to force the molten metal into the die cavity. Againthis step must follow theprevious step in rapid and uninterrupted sequence so that from the time the electrode is raised out of the'cavity in crucible '70 until the plunger 120 operates to force the molten metal from feed ltube 116 into the die cavit-ies,rmay be of the order of onlil a few seconds.

It is necessary that operation of plunger 124i beextremely fast` so that a very high velocity is imparted to the molten fmetal in the feed tube 116. Apparently high velocity is necessary to produce wellV defined and sound castings; howevenextremely high pressures maintained particularly after the metal hasentere'd the die cavities, are

not necessary, as when dietcasting lower melting point Y- metals, such as Zinc and aluminum; Contributing to the tory for producing `,satisfactory Vcastings of mostrrefractory metals.. However, when casting metals such as tita-k nium and zirconium which are in addition highly reactive, particularly with atmospheric gases( at elevated temperature, the pressurev in shell 10 should be preferably no vgreater than 'lf millimeter Y, of mercury.l VIt will be appreciated that since'the' die cavitiesV are highly evacuated no displacement of gases occurs when molten metal is forced thereinto. Thus, the cavities forming the die cast body may rapidly be filled by molten metal forced thereinto by high velocity, and no venting of the die cavities is required; and no porosity permeated with atmospheric gases occurs in the so-produced castings. The melting, pouring and casting accomplished according to this invention under vacuum, results in a beneficial degassing of the metal employed and lack of porosity in finished castings not obtainable when such processing is carried out in the presence of appreciable amounts of atmospheric, or even inert, gases, that is above the pressures recited.

The location of bin 12 within the shell 10 provides a receptacle for holding the finished castings still under vacuum until they are sufliciently cool and ready to be exposed to the atmosphere. After casting, the metal is preferably maintained between the die blocks 180 and 184 until the formed casting has essentially solidified. At this point the die blocks may be separated and it may be removed from the die and deposited into the bin below. However, it may still be above the temperature at which exposure to air might be deleterious. Therefore, the arrangement described in the embodiment illustrated provides for cooling the finished castings to a safe temperature in an atmosphere devoid of contaminating gases to insure the best possible surface condition.

The following examples illustrate the production of die casting according to this invention.

Example 1 Apparatus embodying features of this invention as described hereinbefore, was employed. A l-inch diameter tungsten inert electrode was used to melt a charge of commercially pure titanium in a heavy copper crucible using an arc current of about 2,000 amperes at about volts. After a pool containing about 1/2-pound of molten titanium had been formed in a skull of solid titanium in the Crucible, the electrode was rapidly raised and the molten titanium poured into the graphite feed tube by tilting the Crucible and then immediately forced by a fast acting plunger into casting cavities in a pair of mild steel die blocks. The casting cavities were in the form of specimen shapes used for tensile strength testing and were connected by runners leading to a common gate. The casting was cooled and removed from the die casting machine shell with all the above operations being carried out under vacuum of about 200 microns of mercury absolute.

The runners were removed from the cast tensile specimens. The ash at the die block parting line was ground olf. The die cast specimens had a bright, smooth surface finish free from oxide or nitride contamination and were an accurate reproduction of the configuration of the cavities in which they were cast.

The die cast specimens were then pulled in a tensile testing machine and showed the following mechanical properties:

Ultimate tensile strength 100,000 p.s.i. Yield strength (0.2%) 88,000 p.s.i. Elongation in 1 inch 20%. Reduction in area 30%.

Sections of the specimens showed no discernible porosity and the castings were sound and solid.

Example 2 The same process steps described in Example 1 were followed using the same die blocks to cast specimens of Type 316 stainless steel. Similar quality die cast tensile specimens were produced which showed the following mechanical properties:

Ultimate tensile strength 82,500 p.s.i. Yield strength (0.2%) 42,000 p.s.i. kElongation in 1 inch 63.5%.

Reduction in area 70%.

` Similar tests were performed producing the same grade and quality die castings -of mild steel and A-286 (composition disclosed and claimed in U.S. Patent No. 2,641,540) alloy steel.

The term refractory metal as employed herein is intended to include those metals having a melting point above 1200 C. Such metals include titanium, zirconium, steel, alloy steels, molybdenum, tungsten, tantalum, columbium, vanadium, nickel, cobalt, as well as high melting point alloys of these metals and so-called superalloys. Alloys are intended to be included within the term metal provided they have the required high melting point to be considered refractory.

The die casting machine of this invention is useful for production of castings having good surface finish and sound metallurgical properties. Such castings may be suited for many applications without additional surface treatment, such as machining. The normal amount of flash resulting from the split dies as customarily employed, may readily be removed by a grinding operation as is well known in the art, and separation of runner and sprue may also be accomplished by clipping, sawing or other known method of separation. The finished castings may be used in applications where their form and characteristics of the metal from which they are fabricated make them particularly adapted; for example, titanium die castings may be employed in production of aircraft parts where their strength and light Weight may be advantageous or they may be empoyed in the manufacture of marine hardware where their resistance to corrosion is a valuable characteristic.

We claim:

1. In apparatus for die casting a refractory metal including a gas tight shell, a pair of separable die blocks inside said shell recessed to form a casting cavity therein and means for melting a body of molten metal in a tiltable crucible in said shell the improvements which comprise;

(a) a horizontal feed tube inside said shell communicating with the casting cavity in said die blocks, said feed tube having a graphite liner, Y

(b) means for transferring molten metal `from said -tiltable Crucible into said feed t-ube through the top thereof, and,

(c) a plunger inside said feed tube closely fitting the liner therein and actuated by means external of said shell to force molten refractory metal from said feed `tube into the casting cavity in said die blocks.

2. Apparatus according to claim 1 in which the said feed tube has a graphite liner and an outer steel support tube.

3. Apparatus according to claim 1 in which the clearance ,between the said plunger and the said graphite liner in the feed -tube does not exceed .005 inch all around.

4. Apparatus according to claim 1 in which the fit between said plunger and said feed tube is obtained by fabricating said plunger and said graphite liner of precise matingsize.

5. A method for producing a die casting of a refractory metal which comprises;

(a) Imelting said refractory metal in a cold Crucible by striking and maintaining an electric arc between an electrode and refractory metal in said crucible thereby to form `a Ibody of molten refractory metal within a skull of solidied refractory metal in said crucibie,

(b) breaking said are between said electrode and said molten refractory metal in said crucible when said lbody of molten metal in said crucible is sufficient 11 Y 12 (e) said steps (c) and (d) tol-lowing step (b) in chamber evacuated to a pressure below 5 millimeters of rapid and uninterrupted sequence therebyto prevent mercury absolute. v further solidic-ation ofsaid 'body of molt'eri'refrac- 8. 'A method according to claim 5 in which the retory metal in ysaid orucible and to prevent deletefractory metal is titanium.

rious solidicaton of said refractory metal in said "5 l feed tube and contamination of said molten refracv *References Cited by the Examiner tory Vmetal by the materialr of 'said feed tube, yand UNITED STATES rPATENTS v steps (a), (b), (c) and (d) being rried fout Under 2,610,372 -9/52 schroeder 22-#73 XR vauuml s Y 2,727,937 172/55 Beyer 7510 6. A method according to claim '5 in which steps (a), 10 2,795,644V 6/57 Kuhn 22....69 10b), (c) Iand (d) are `carried Gut in 'a cominonch'amber' y"2,799,066 7/57l Federman et A@151. 22-73 evacuated to a pressure below 5 Ymillimeters of mercury 2,904,861 9/59V vMorgenstern 22-68 XR absolute. j' 3,019,495 2/62 kCornell 22-618 '7. A method according to claim 5 in which steps (a),r Y (fb), (c) `and (d) and an add-itionalstep of cooling the 15 MARCUS U-LYQNSPWWWY Emmmeff so-produced-die castings are carried out in a commou MICHAELV BRlNDISLExamner.

Claims (1)

1. IN APPARATUS FOR DIE CASTING A REFRACTORY METAL INCLUDING A GAS TIGHT SHELL, A PAIR OF SEPARABLE DIE BLOCKS INSIDE SAID SHELL RECESSED TO FORM A CASTING CAVITY THEREIN AND MEANS FOR MELTING A BODY OF MOLTEN METAL IN A TILTABLE CRUCIBLE IN SAID SHELL THE IMPROVEMENTS WHICH COMPRISE; (A) A HORIZONTAL FEED TUBE INSIDE SAID SHELL COMMUNICATING WITH THE CASTING CAVITY IN SAID DIE BLOCKS SAID FEED TUBE HAVING A GRAPHITE LINER, (B) MEANS FOR TRANSFERRING MOLTEN METAL FROM SAID TILTABLE CRUCIBLE INTO SAID FEED TUBE THROUGH THE TOP THEREOF, AND

Images