US2714236A - Apparatus for centrifugally casting titanium - Google Patents

Description

2, 1955 o. w. SIMMONS 2,714,236

APPARATUS FOR CENTRIFUGALLY CASTING TITANIUM Filed March 5, 1954 2 Sheets-Sheet 1 if Q 79 Q I INVENTOR. g F|G,2 omen w. smmows ATTORNEYS! 2, 1955 o. w. SIMMONS 2,714,235

APPARATUS FOR CENTRIFUGALLY CASTING TITANIUM Filed March 5, 1954 2 Sheets-Sheet 2 77 as a/ 49 55 I3 63 /5 95 2! 75 /7 I a 29 A 51 A I 5 L #4 FIG. 3

FIG.4.

1N VEN TOR.

ORIEN W. SIMMONS BY 5m, QMQM #Mmm ATTORNEYS:

APPARATUS FGR CENTRIFUGALLY CASTING TITANIUM Grien W. Simmons, Beaver, Pa., assignor to the United States of America as represented by the Secretary of the Army Application March 3, 1954, SerialNo. 413,978

1 Claim. (Cl. 22--65) (Granted under Title 35, U. S. Code (1952), sec. 266) The invention described herein may be manufactu and used by or for the Government for governmental purposes without payment of any royalties thereon.

This invention relates to an apparatus for fabricating titanium and, more particularly, to the production of contaminate-free titanium castings.

A great deal of popular interest has developed in recent years with respect to the possible substitution of titanium for the more common metals in many widely divergent applications. Acting as an incentive to this interest is the comparative availability of titanium ore, as Well as the highly desirable properties possessed by titanium metal in many of its alloys. They are light, strong, ductile, corrosion resistant, and have good mechanical properties over the range of 75 to 800 F. However, titanium also has some properties which are extremely perverse. One of the perverse properties of titanium is its extreme reactivity in the molten condition which makes the casting of a contaminate-free titanium article very difficult.

Titanium melts at a high temperature, 3150 F., and in the molten condition reacts with just about everything it contacts. Furthermore, many of these products of reaction have considerable effect on the properties of the titanium alloys containing them. At the present time, no known refractory will resist attack by molten titanium. Graphite, for example, has been used for crucibles and although carbon is thereby introduced into the metal, graphite is more satisfactory for this purpose than some of the other available refractory materials. High carbon, such as 0.5 to 1.0%, is undesirable in cast or welded titanium because large dendrites of brittle titanium carbide are formed in the titanium matrix. The atmosphere, reacting with the molten titanium, imparts even more impurities to the metal.

It is, therefore, an object of this invention to provide an apparatus for casting titanium which will overcome the aforementioned dimculties.

An additional object of this invention is to provide an apparatus for rapidly transferring molten titanium to a mold cavity so as to insure delivery of molten metal to all extremities of the mold before it solidifies, whereby the percentage of incompletely formed castings is reduced.

Another object of this invention is to provide an apparatus for centrifugally casting titanium.

A further object of this invention is to provide an apparatus for melting and casting titanium in a continuously maintained contaminate-free, inert atmosphere.

A still further object of this invention is to provide apparatus for melting and casting titanium quickly and in such a manner as to reduce contamination of the molten titanium by the associated apparatus.

in carrying out these objects, advantage is taken of the favorable fluidity characteristics of titanium. Although titanium does have a high melting point, only a slight superheat is required to impart excellent fluidity to both titanium and its alloys. Thus, casting may be carried out as soon as suflicient molten metal is obtained without the uni necessity of super-heating the melt. These factors permit a mold to be filled very rapidly at a relatively low temperature.

Accordingly, the apparatus which I propose, employs an interconnected crucible and mold which permit the titanium to be melted in the crucible and delivered to the mold under the influence of a continuously maintained inert atmosphere. The crucible and mold are supported on a centrifuge which is operative to impart rotation to the entire assembly as soon as the titanium has reached a fluid state, to thereby introduce the melt or molten metal to the mold by centrifugal force. During the entire melting and molding steps a continuous inert atmosphere is maintained to prevent contamination of the melt.

All of the foregoing as well as other objects and advantages of this invention will become apparent from a study of the following specification, taken in conjunction with the accompanying drawings, wherein like characters of reference indicate corresponding parts throughout the several views and wherein:

Figure 1 is a front elevational view of apparatus provided, in accordance with this invention, for centrifugally casting titanium, certain parts also being shown in broken lines to designate an alternative position,

Figure 2 is a plan view taken along line 22 of Figure 1, with parts of the mold broken away,

Figure 3 is a sectional view, taken along line 3-3 of Figure 2 showing the construction and arrangement of certain parts of the apparatus, and,

Figure 4 is a sectional view, with parts of the crucible broken away, taken along line 4-4 of Figure 3, showing the construction of the crucible and the manner in which it is supported on the centrifuge.

With particular reference to Figure l, the apparatus is shown, generally, to include a centrifuge 1 which has a column 3 adapted to be rotatably driven by a suitable motor (not shown) in response to actuation of the on button of the control switch 5'. A T-shaped yoke '7', having a sleeve 3 which is rigidly affixed to the column 3, provides a stable support for the casting apparatus. The diametrically opposed ears 9 of the yoke are apertured to receive a pair of parallel rods 11, 11, which are rigidly attached thereto by locknuts 12, on which a crucible l3 and a mold 15 are supported by means of special brackets 17, 19 respectively. By spacing the mold a greater distance than the crucible from the axis of rotation of the centrifuge, centrifugal force is operative upon actuation of the centrifuge to force-feed the contents of the crucible to the mold cavity in a manner hereinafter described. The leg 21 of the yoke supports a counterweight 23 in an adjusted position to counterbalance the weight exerted by the casting apparatus on the opposite side of the column. The counterweight is fixed in its adjusted position in any suitable manner, such as by a set screw 25. The crucible supporting bracket 17 comprises a flat plate having acircular opening 29 at its center, the bounding portions of which support an enlarged circular flange 31 of the crucible. Fixed to opposite ends of the bracket 17, such as by machine screws 33, are a pair of rod- engaging sleeves 35, 35. These sleeves slidably engage the support rods 11 and are held in an adjusted position along the length thereof by means of associated set screws 37.

The mold supporting bracket 19 comprises a pair of plates 39, 40, between which a split-type mold 15 is clamped, as shown in Figures 1 to 3. Each of these plates is provided with a plurality of apertures, each of which slidably receives a bolt 41. The nuts 43 associated with each bolt thus afford a satisfactory means for clamping the mold between the two plates 39, 40. Flanges 45, 46 extending outwardly of the plates 39, 40 respectively, are each provided with a threaded aperture which threadingly engages a support rod 11, as shown in Figure 2.

Accordingly, this engagement affords a means for adjusting the position of the mold supporting bracket 19 such that the mold 15 may be placed in any position along the length of the support rods 11.

As shown in Figures 3 and 4, the crucible 13 is provided with a graphite liner 47, having a central axial cavity, which is thermally insulated from the outer jacket 51 with powdered graphite 53. Refractory cement 49 is used to retain the powdered graphite and liner in proper assembly. The top of the liner is closed by means of a removable cover 55 which is also made of graphite, as is a horizontal sprue 57. One end of the sprue 57 extends through a port 59 in the side wall of the crucible, in a direction normal to the axis of rotation of the centrifuge, into communication with the cavity of the graphite liner. The other end of the sprue 57 extends through a centrally located opening 61 in the adjacent plate 39 of the mold support bracket and into engagement with the gate 63 of the mold 15, such that direct communication is had between the metal receiving portion of the crucible liner 47 and the mold cavity 65. The metal receiving portion of the graphite liner 47 is preferably made in the form of an inverted truncated cone, having a longitudinal axis normal to the plane of rotation of the crucible, to facilitate the upward movement of the melt from the bottom thereof to the level of the sprue 57 under the action of centrifugal force during the casting operation.

It will be apparent that a refractory cement (not shown) may be used to seal the connections of the cover 55 and sprue 57 to the graphite liner 47, as well as the connection of the sprue to the gate of the mold; the primary purpose of such a cement is to assure a seal against the entrance of air at these connection points which would otherwise cause contamination of the melt during casting.

As shown in Figure 1, an induction heating coil 67 is supported on the base 69 of the centrifuge, removed from the path of rotation of the crucible, in a normal position (full lines) in which it is inoperative to supply heat to the crucible. An actuating lever 71 is operative, upon movement from its initial position (full lines) at one extremity 70 of an associated cam slot 72 to its second position 71' (broken lines) at the other extremity 73 of the cam slot, to cause upward movement of the coil 67. In raised position (broken lines) the coil 67' is operative to supply a melting heat to the metal stock contained within the crucible.

Associated apparatus is provided to supply an inert gas to the crucible and mold during the melting and casting operation to prevent contamination of the melt by v the air which would otherwise envelop the metal. This apparatus includes a swivel coupling 74 which is supported on the rotatable column of the centrifuge. The

coupling 74 comprises a housing 75 which is fixed by v means of a machine screw 77 to the sleeve 8 for rotation therewith. A closure member 79 provided with an axial bore 81 is inselted in the top of the housing 75 and is held against rotation therewith by means of a rigid delivery tube 83 which. disposed out of the path of rotation of the centrifuge, communicates with a supply tank 85 of an inert gas, such as argon. Sufficient clearance is provided between the closure member 79 and the inner wall of the housing 75 to permit the housing to rotate relative to the closure member. A lubricant such as silicone grease may be used to facilitate this relative rotation and to further provide a substantially complete hermetic seal therebetween. The bore 81 in the closure member communicates with a chamber 87 in the bottom of the housing 75. Also communicating with this chamber 87, through a port 88 in the side wall thereof, is a supply tube 89, the opposite end of which in turn communicates with a port 91 in the cover 55 of the crucible.

It will thus be apparent, that upon opening the valve 93 of the supply tank 85, gas will fiow through the delivery tube 83, into the chamber 87 of the swivel coupling 74 through the port 88 of the housing into the supply tube 89, and then into the metal receiving portion of the crucible liner 47 through the port 91 in crucible cover 55. Passing through the sprue 57 which is associated with the port 59 in the side of the crucible, the gas will then flow into the mold cavity 65, from which it will be exhausted to atmosphere by means of the vent 95 at the distal extremity of the mold. After the passage of an interval of time, depending upon the rate of flow, the inert gas will flush the air out of the entire system. Continued flow of the gas will thus provide an inert atmosphere which will prevent contamination of the metal before and during the melting and casting operation. By virtue of the swivel coupling 74, it is possible to effectively and continuously flush the system with inert gas prior to and during the melting of the metal, and during the centrifugal casting operation, without interruption.

In preparing the apparatus for use, the mold 15 is first clamped between its bracket plates 39, 40 and the support rods are threaded into the associated apertures of the plates. The crucible 13 is then placed in its bracket 17 and, with the sprue 57 in engagement with both the gate 63 of the mold and the port 59 of the crucible, the crucible bracket 17 is clamped in position on the support rods 11 by means of the set screws 37. The crucible is then charged with the desired constituents and the cover 55 is placed in position. Refractory cement can at this time, if desired, be used to seal the aforementioned connections.

The gas supply tube 89 is then connected to the crucible cover 55 and the swivel coupling 74; the gas delivery tube 83 is connected to the supply tank and the swivel coupling 74. With all the components so arranged, the counterweight 23 is adjusted on the leg 21 of the support yoke relative to the axis of rotation of the centrifuge to effect a balance of the apparatus.

The apparatus, as such, is now ready for the melting and casting operation. However, it has been found desirable to first purge the confines of the crucible and mold of air before melting the metal to reduce contamination of the melt and casting. This may be done by maintaining a constant supply of inert gas to the system, as hereinbefore described, during the entire procedure, from a time shortly before the melting heat is applied to the crucible.

After a brief interval of purging the air from the sys tern and without interrupting the supply of gas, the heating coil 67 is raised into operative association with the crucible by moving the actuating lever 71 from its first to its second selective position, whereby the parts will assume the broken line position 67' illustrated in Figure 1. Power is then supplied from a source (not shown) to the induction coil 67 whereby it is operative to deliver a melting heat to the contents of the crucible. Sufficient heat having been supplied to liquefy the contents, the coil 67 is returned to its original position out of the path of rotation of the crucible, and the cen- I: the melt to the mold is very rapid and, consequently,

assures delivery of molten metal to the entire mold cavity before it solidifies. As a result, castings of irregular configurations are facilitated.

Obviously the rate and duration of inert gas supply, speed of rotation of the centrifuge and other variable factors to be considered in carrying out the aforementioned operation will vary depending upon the size of the object being casted and upon the size of the respective elements of the apparatus. By way of illustration, however, in casting a titanium object of a size which would require a crucible charge of approximately three ounces, satisfactory results are obtained by supplying argon gas at the rate of 5 cu. ft., per hour continuously from about 20 minutes before the melting heat is applied to the charged crucible until the entire casting operation is completed and the casting is solidified. This assures a contaminate-free atmosphere during the entire operation. Where it is possible to prepare the charge from titanium sponge which has been previously melted to remove the volatile magnesium and magnesium chloride, which would otherwise form dross in the mold if permitted to enter the melt, even better castings may be obtained. For an object of the size now being described, operation of the centrifuge at about 300 R. P. M. with the mold spaced approximately 12 inches from the axis of rotation would produce sufficient force to properly feed the titanium melt to the mold.

It will become apparent to those skilled in the art that other and different arrangements may be used within the purview of this invention. could incorporate an integral heating means to provide more uniform and sustained heat application to the melt during the centrifugal casting operation; likewise any inert gas could be used to prevent contamination of the metal. It is, therefore, to be understood that the form of the invention herewith shown and described is to be taken as a preferred example of the same and that changes in the shape, size and arrangement of the parts may be reverted to without departing from the spirit of the invention. the form disclosed be taken as illustrative and not as limiting. Furthermore, I do not wish to be limited beyond the limitations which may be imposed by the following claim.

I claim:

In apparatus for centrifugally casting titanium and titanium alloys under an inert atmosphere comprising: a rotatable column constituting an axis of rotation; a T-shaped yoke sleeved upon the column in rigid rela- For example, the crucible Accordingly, it is desired that tion therewith, having three radially extending members spaced in 90 relation with respect to one another; a counterweight adjustably carried on the central yoke member; means for locking said counterweight in a selected position; a pair of spaced parallel bars fixedly supported at one end at their adjacent extremities one in each of the lateral radially extending yoke members; a crucible adjustably positioned proximate to said column; an apertured closure for said crucible; means for suspending the crucible between said bars and in rigid relation therewith at a selected distance from said column; an open-ended heating coil below and concentric with said crucible; means for placing said heating coil in operative relation with said crucible when the latter is stationary; a vented split mold positioned remotely of the said column between the said bars; means for clamping and supporting the said mold adjustably with respect to said crucible; a conductor for linking the cavities of said crucible and said mold; a cylindrical housing having an open end and an apertured wall, positioned upon said rotatable column; means for securing said housing to said column for rotation therewith; an apertured stationary closure member in sealing engagement within the open end of the said rotatable housing and in frictional relation therewith; a source of inert gas; a conductor between said source and said stationary closure member for conducting the gas through the stationary closure member and into said rotatable housing; and a conductor between the housing and said crucible closure for conducting the gas into the crucible.

References Cited in the file of this patent UNITED STATES PATENTS 2,009,489 Fritzsche July 30, 1935 2,174,904 Taylor Oct. 3, 1939 2,359,524 Lane Oct. 3, 1944 2,509,670 Capita et al. May 30, 1950 2,557,971 Iacklin June 26, 1951 2,586,027 Gray Feb. 19, 1952

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