US2885751A

US2885751A - Vacuum casting apparatus

Info

Publication number: US2885751A
Application number: US681406A
Authority: US
Inventors: John N Hornak; William M Thatcher
Original assignee: United States Steel Corp
Current assignee: United States Steel Corp
Priority date: 1957-08-30
Filing date: 1957-08-30
Publication date: 1959-05-12
Anticipated expiration: 1976-05-12
Also published as: DE1154599B; GB843064A; BE570541A; LU36277A1; FR1201749A

Description

May 12, i959 .J. N. HORNAK ETAL 'VACUUM CASTING APPARATUS 2 Sheets- Sheet i Filed Aug. 30, 1957 llllllulllll'l'ul l'llllIl-lll NVENTORS JOHN M HOR/VAK and WILL/AM M. THATCHE'I? MflW May 12, 1959 'J. N. HORNAK ET AL VACUUM CASTING APPARATUS 2 Sheets-Sheet 2 Filed Aug. 30, 195'? /N VE N T 0R5 JOHN IV. HORN/1 K and WILL IAM M THA TCHEI? United States Patent I 2,885,751 VACUUM CASTING'APPARATUS Johri-cN. Homak Homestead: Park, and William M. Thatcher,1 Pittsburgh Pa .assignors to United States Steel Corporation, a corporation of New Jersey Application August 30,1957, Serial-No. 681,406

2fCl'aims. (CI. 22-73) This invention relates to improvements in vacuum, castingaapparatus .and more particularlyto an improved' ingotsintended .for large forgings andthe like is par-, ticularly desirable :but .has ,proven particularly difficult. because of the size of castings involved. Ingotsv of 100' inches or more in diameter and weighing between. 150

and 200 tons are commonly required. To accommodate the necessary mold and mold-stool,. etc., for-such ingots requires a tank or chamber 15 .to. 20feet indiameter and 30 feet or more in height which, for best results, must be evacuatableto anabsolutepressure of less than- 100 microns- 0f mercury. Practical considerations dictate that the molten metal be teemed from a ladle outside this-chamber and supported-atop thereof, thus the'tank or chamber must be capable ofbearing the weight of the ladle and metal of the cast in addition to withstanding the. pressures incident to its evacuation. This has led to the use of extremely heavy-walled chambers accessible only through thetop. The use of such chambers is complicated by the fact that theingots must be left to cool undisturbed for as long as two or three'days: Duringthis period the midportion of ingot mold reaches temperatures as high as 1000 F., and adjacent portions of the chamber are subjected to such varying degrees of heat as to expand unequally and warp. Warping can be prevented by insulating the chamber with refractory materials. However, such refractory linings absorb air and other gases when the chamber is opened; and these occluded gases are given off very slowly during evacuation making it impossible to achieve a vacuum better than 5 mm. of mercury unless uneconomically long times of evacuation are used.

It is accordingly an object of the present invention to provide a large vacuum casting chamber which can be quickly evacuated to very low pressures.

It is a further object of this invention to provide large vacuum casting chambers which can be removed from the cast ingot to permit quick cooling thereof.

It is a further object to provide a casting tank which is relatively light but at the same time is not subject to damaging stresses because of uneven expansion and contraction.

It is another object of this invention to provide a vacuum casting tank which is simple in design and efficient in use.

The foregoing and further objects will be apparent from the following specification when read in conjunction with the attached drawing wherein:

Figure l is a vertical section through the base and bell portions which form the casting chamber of our invention;

Figure 2 is a top view of the chamber with the ladle 2} removed,ithe.,1eft.halfofthevfigure showing the base with; the bell portion removedpand,

Figure 3 is an enlarged detail showing the seal-between the baseandbellportions.

Referring more particularly to, the drawings, the. nu-

meral 2 designates generally the vacuum casting chamber of our invention carrying a suitable ladle L equipped with a conventional stopper and enclosing a suitable moldM. Thechamber 2 comprises a bell portion 6 and a base.8,

the latterdisposed onasuitable foundation, 10. The. base 8 includes a bottom plate 12 and an upstanding rim portion, which terminatesqin a ringmemberr16 having an upwardly facing, bearing surface 18. The rim may be stiffened by a plurality of stub columns 20 and brace plates 22 disposed at intervals about the rim below.

the ringmember thereof and resting upon an extension of the. base. plate. A pipe 24 through the side of rim 14 connects the interior of ,the chamber to a suitable vacuum pump, not shown. A suitable m,old:stool S may be disposedv on a.:suppor.ting.spiderwork of I-beams 26 inside the.rim. and.;carried by the base plate 12. Plates 28.. having an inwardly sloping guide surface27 are disposed atintervalsaboutthering member of. the rim to guide the ;bell portion :6 into proper engagement with bearing The bearing surface 18 is provided with surface 18. annular groove 30 adjacent the inner edge thereofqwhich is ;adapted..to.receive a .compressible. sealing ring 32 formedof .resilientmaterial. such. as natural rubber, neo..- prene. rubber, silicone rubber-or. the.like.. In order to, insure.,.an.;efi"ective..seal this :sealing ring. should be of sufiicient: thickness in:relation to the depth ,of. groove 30.; to be-compressed at least about 20% but not morethan. about 30%.and, .to insure asatisfactory servicelife, the groove and..ring.should..be ofsuchvolume, that the ring; may expand laterally whencompressed and. not overfillu thegroove. The bottom.. plate.12, rim-14 and ring 16;. are joined in a gas tightmanneras by continuous welds..,

The bell portion-6 of,the:chamber comprises a ring;

line bearingplate 36 to which. are :fixedly attached. a plu-.

Disposed. on top, of the. .supports 38 is.aplurality of beams,\.40;. carrying -a plate-42..forming ,a. ,platformfor theladle. L-

rality of columnar; supporting members 38..

which rests thereon on a suitable sealing ring 44.

Disposed within the supporting framework and attached to the bearing ring 36 is a relatively thin gauged cylindrical shell 45 closed at the top by a circular plate 46 having a dished portion 48 adjacent its juncture with the side wall of the shell. Dished portion 48 is preferably of somewhat thinner gauge than the balance of the plate 46 and by reason of its shape and flexibility provides means to compensate for unequal heating and expansion of the shell when teeming molten metal into the mold M and during such time as may elapse between teeming and the removal of the bell portion of the chamber. The cylindrical side wall of shell 45 is relieved of the dead weight of top plate 46 by suspending the latter from the plate 42 of the ladle platform by a plurality of stud bolts 50 carried by the plate 46 and extending through the plate 42. Centrally disposed of

plates

42 and 46 is a tubular member 52 providing a pouring conduit through which molten metal can be teemed from the ladle L into a mold M in the evacuated chamber. Joints between the pouring conduit and

plates

42 and 46, between the plate 42 and the cylindrical side wall of shell 45 and between the shell 45 and bearing ring 36 are made gas tight as by continuous welds.

In using the apparatus the mold M is positioned on the stool S, and the bell section lowered over the base being guided into proper sealing positioned by the plates 28. The ladle L containing at least a portion of the metal to be cast is then placed on plate 42 of the ladle platform to rest on the sealing ring 44 thus completely Patented May 12, 1959 sealing the chamber from the atmosphere. The chamber is then evacuated through pipe 24 to about 100 microns of Hg and teeming of the ingot initiated. The vacuum is maintained until the teeming is complete, care being taken to maintain sufiicient metal in the ladle to seal the system during this operation. In casting of large ingots this may necessitate adding molten metal to ladle L from a transfer ladle or the like from time to time during the casting. When the mold is filled, the vacuum pumps can be shut down and the chamber restored to atmospheric pressure by bleeding-in air through a valve in exhaust line 24. The ladle and bell portion section can then be immediately removed to leave the ingot to cool undisturbed on the base.

Since the structural features of the present apparatus permit opening of the chamber immediately upon completion of casting, the present invention aflords more rapid cooling than heretofore available and the bell section can be used to serve several bases. Further since the structure is such that warping is avoided without the use of insulating linings, lower vacuums can be rapidly achieved and maintained.

The foregoing example illustrates top pouring, the apparatus is of course equally adapted to bottom pouring.

While we have shown and described certain specific embodiments of our invention, we do not wish to be limited exactly thereto except as defined in the following claims.

We claim:

1. Vacuum casting apparatus comprising, a gas tight base member including an upwardly facing bearing surface having a groove therein adapted to receive a compressible sealing ring, a ring of compressible sealing material disposed in said groove, and a bell member supported by said base member, said bell member having a ring-like bearing plate adapted to rest on the rim of said base and compress said sealing ring, a plurality of spaced columnar supports attached to and rising from said hearing plate, a platform carried by said columnar supports and adapted to support a pouring ladle, a gas tight shell comprising a wall portion disposed inside said columnar supports carried by said bearing plate and attached to the latter in a gas tight manner and a top plate suspended from said platform, said top plate including a relatively thinner dished section adapted to flex under expansion and contraction forces, a tubular member carried by said platform centrally thereof extending through and attached to said top plate, and means for evacuating the gas tight chamber formed by said bell member and base.

2. Vacuum casting apparatus comprising, a gas tight base member including a plate and an upwardly extending rim, said rim having an upwardly facing bearing surface having an annular groove therein adapted to receive a compressible sealing ring, a ring of compressible sealing material disposed in said groove having a thickness in the uncompressed condition about 25% greater than depth of the groove and a volume not greater than the volume of the groove, and a bell member supported by said base member, said bell member having a ringlike bearing plate adapted to rest on the rim of said base and compress said sealing ring, a plurality of spaced columnar supports attached to and rising from said bearing plate, a platform carried by said columnar supports and adapted to support a pouring ladle, a gas tight shell comprising a cylindrical wall portion disposed inside said columnar supports carried by said bearing plate and attached to the latter in a gas tight manner and a circular top plate suspended from said platform, said top plate including a relatively thinner dished section adapted to flex under expansion and contraction forces, a tubular member carried by said platform centrally thereof extending through and attached to said top plate, and means for evacuating the chamber formed by said bell member and base.

References Cited in the file of this patent UNITED STATES PATENTS 211,953 Barnum Feb. 4, 1879 1,913,652 Alexander June 13, 1933 2,027,430 Hansen Jan. 14, 1936 2,233,580 Breedon et al. Nov. 4, 1941 2,482,257 Frei Sept. 20, 1949 OTHER REFERENCES The Iron Age Publication, Aug. 14, 1947, 22-73.

Pages 67-70 relied on.

The U.S. Steel Quarterly Publication, May 1956, 22-73.

Page 12 relied on.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No, 2,885,751 May 12, 1959' John N, Hor'nak et a1.

It is herebjr certified that error appears in the-printed specification of the above numbered patent requiring correction and that the said Letters Patent should read ascorrected below.

Column 2, line 69, for "positioned" read position Sig ed and sealed this 1st day of September 1959,

SEAL) Attest:

KARL AXLINE ROBERT c. WATSON Attesting Oflicer Commissioner of Patents