US3670802A

US3670802A - Vacuum casting apparatus

Info

Publication number: US3670802A
Application number: US793335*A
Authority: US
Inventors: David M Krick; Lawrence D Koltz; Warren C Williams
Original assignee: Wisconsin Centrifugal Inc
Current assignee: Wisconsin Centrifugal Inc
Priority date: 1969-01-23
Filing date: 1969-01-23
Publication date: 1972-06-20
Anticipated expiration: 1989-06-20
Also published as: GB1242978A; CH519358A; DE1961517A1

Abstract

A centrifugal casting machine is mounted in a vacuum chamber, a vacuum furnace, a vacuum pump is selectively connectable to the furnace and to the vacuum chamber, and a nozzle assembly for the vacuum furnace is connected to the vacuum chamber by a flexible seal.

Description

[451 June 20, 1972 United States Patent Krick et al.

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Primary Examiner-J. Spencer Overholser Assistant Examiner-V. K. Rising [21] Appl.N0.: 793,335

AttorneyRonald E. Barry and James E. Nilles A centrifugal casting machine is mounted in a vacuum T m T S B A 7 5 ma 72 6 M5 B7 3 3 8 5 2 5 6 4 6 [58] FieldofSearch....................

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chamber, a vacuum furnace, a vacuum pump is selectively connectable to the furnace and to the vacuum chamber, and a f 1 Re emnces C ted nozzle assembly for the vacuum furnace is connected to the vacuum chamber by a flexible seal.

UNITEDSTATESPATENTS 2,625,719 Moore...................................164/258 19CIaims,4DrawingHgu1-es VACUUM CASTING APPARATUS BACKGROUND OF THE INVENTION Certain alloys containing reactive elements, such as titanium, columbium, molybdenum and the like, must be cast in a vacuum to prevent reaction of the molten metal with the gases in the atmosphere. Efforts to vacuum cast these metals have generally involved the use of a single vacuum chamber to enclose both the furnace and mold. A considerable amount of time is required to evacuate the chamber, since the metal cannot be melted until a complete vacuum is present in the chamber. A two step operation generally employed in this type of a system requires the molten metal to be initially poured from the furnace into a billet and allowed to cool. The billet is then remelted and cast in its final form.

SUMMARY OF THE INVENTION The centrifugal casting apparatus of this invention can be used to cast such metals in a single operation in a relatively short period of time. The time required to melt and cast the metal is reduced by providing a separate vacuum chamber for the centrifugal casting machine and using a conventional vacuum furnace to melt the metal outside of the vacuum chamber. A vacuum pump is selectively connected to the furnace and to the vacuum chamber to evacuate the fumace and chamber in sequence. A vacuum furnace can be evacuated in a relatively short period. During the time that the metal is being melted in the furnace, the vacuum chamber is evacuated also in a relatively short time because of its reduced size. The molten metal is cast in a single operation through a nozzle assembly mounted on the pouring spout of the furnace and projecting through a flexible seal on the vacuum chamber. Premature opening of the furnace is prevented by using a cap removing assembly that will remove the cap from the nozzle assembly only when the pressure on each side of the assembly is approximately equal.

Other objects and advantages of the present invention will become apparent from the following detailed description when read in connection with the accompanying drawings, in which:

FIG. 1 is a view of the centrifugal vacuum casting assembly.

FIG. 2 is a section view of the nozzle assembly.

FIG. 3 is a view of the noule assembly in the pouring or tilting position.

FIG. 4 is an enlarged section view of the nozzle assembly.

DESCRIPTION OF THE INVENTION Although the disclosure hereof is detailed and exact to enable those skilled in the art to practice the invention, the physical embodiments herein disclosed merely exemplify the invention which may be embodied in other specific structure. The scope of the invention is defined in the claims appended hereto.

Referring to FIG. 1 of the drawings,-the vacuum casting assembly includes a vacuum chamber for a centrifugal casting machine 12 and a vacuum furnace 14 supported by means of stanchions 15 for tilting motion about an axis 70. The furnace 14 is a conventional tilt type furnace and is tilted to pour molten metal from the furnace 14 into the mold 13 of the casting machine 12 by a conventional tilt mechanism. The vacuum furnace has a pouring spout 18 extending angularly upwardly through the pivot axis 70 between the stanchions 15. A vacuum is maintained between the furnace l4 and vacuum chamber 10 during a pouring operation by means of a nozzle assembly 16 mounted on the pouring spout 18 of the vacuum furnace l4 and connected to a nozzle housing 20 on the vacuum chamber 10 by means of a flexible seal assembly 22. The vacuum chamber 10 and vacuum furnace 14 are evacuated by means of a vacuum pump 24 connected to selectively evacuate the furnace l4 and the vacuum chamber 10.

In this last regard, the vacuum pump 24 must be of a size sufficient to evacuate readily the larger of the vacuum chamber 10 or the furnace 14. The pump 24 is connected to the vacuum chamber 10 and vacuum furnace 14 by means of a duct 28 having control valves 30 and 32 located on each side of the pump 24. A second duct 34 is connected to the furnace l4 and is closed by means of a manual valve 36 to allow for the tilting of the furnace 14. A seal 38 is. provided between flange 40 on duct 34 and flange 42 on duct 28 to maintain the vacuum in the furnace 14. Control valve 30 is closed and control valve 32 is opened when air is being evacuated from the furnace 14. Valve 32 is then closed and valve 30 opened to evacuate the chamber 10.

The vacuum in the fumace 14 is maintained by means of the nozzle assembly 16 mounted on the pouring spout 18 for the furnace 14. The furnace 14 is a conventional type electric induction furnace enclosed and sealed by a cover 17. The nozzle assembly 16 (FIG. 4) includes a cylindrical housing 40 made of a heat conductive material such as copper secured to a flange 48 provided on the pouring spout 18 by means of bolts 44. The housing 40 is sealed to the flange 48 by means of 0- ring 46 provided between the housing 40 and the flange 48. The housing 40 is insulated by means of a stainless steel liner 49 press fitted into reduced diameter sections 50 and 52 in the housing 40 to provide gap 51 between the housing 40 and liner 49. The open or pouring end of the housing 40 is closed by means of a cap 56 having an annular flange 55 that laps the outwardly projecting end 45 of the liner 49. The cap 56 is sealed to the housing 40 by means of an O-ring 58 provided in the flange 55 to engage the housing 40. The cap 56 is protected from the radiant heat of the molten metal in the furnace by means of a refractory lining 60 provided on the internal surface of the cap 56 within the annular flange 55. When a vacuum is drawn in the furnace, the cap 56 will be held in tight sealing engagement with the open end] of the housing 40 by atmospheric pressure on the end of the cap 56.

The nozzle assembly 16 projects into the nozzle housing 20 through an opening 21 and is sealed in the opening 21 by means of the flexible seal assembly 22 to maintain the vacuum during pouring. The seal assembly 22 includes an annular boot 61 secured to the outer surface of the housing 40 by means of a ring clamp 62 and to a flange 64 in the opening 21 in the housing 20 by means of a ring clamp 68. A lip or rib 65 can be formed on each edge to aid in holding the boot on the nozzle. The nozzle assembly 16 is arranged on. the pouring spout 18 to pivot about the pivot point 70 so that the boot 61 is not subject to any tension or stretching but is merely displaced as the nozzle assembly is pivoted from one position to the other. The boot is made of a material which is heat resistant, sufficiently flexible to move with the nozzle and having sufficient strength to withstand the pressure difference between the atmosphere and casting chamber. A Buna N type rubber has been used for the boot.

The boot 61 is protected from the heat of the molten metal in the housing 40 by means of a water coil and a heat radiation shield 72. The water coil 80 is mounted on the outer surface of the housing 40 between the portion of the boot 61 secured to the housing and the flange 48 where the greatest amount of heat is conducted to the housing 40 during the pouring cycle. Any heat in this portion of the housing 40 will be carried away by water circulated through the coils 80 and will maintain the temperature of the housing low enough to prevent burning of that portion of the boot 61 clamped to the housing.

During tapping the boot 61 is protected from the radiant heat of the molten metal by means of a shield or flange 72 provided on the end of the housing 40. When the nozzle assembly is rotated to the position shown in FIG. 3, the shield 72 will be located between the molten metal in the mold 13 and the boot 61. It is also possible to provide a flexible heat shield on the inner surface of the boot 6].

Back splash of molten metal poured into the nozzle housing 20 is prevented by means of a tundish positioned within the nozzle housing 20. The tundish 100 includes a shell 102 having outwardly sloped sidewalls and a refractory lining 104 on the end walls 107. The flow of molten metal through tundish 100 is controlled by

arcuate surfaces

106 and 108 provided on each side of nozzle 110. The

arcuate surfaces

106 and 108 provide a smooth flow path for the molten metal eliminating any splashing of the molten metal that could land on the boot and burn a hole in the boot.

The cap 56 is removed from the nozzle prior to pouring metal from the fumace by means of a pneumatic or hydraulic clamp assembly 82 mounted in the top portion of nozzle housing 20. The clamp assembly 82 includes a cylindrical housing 84 having an internal flange 86. A ram 88 is mounted for axial motion in a cylindrical sleeve 90 supported by the flange 86 and has a magnet 92 positioned to engage the cap 56. The magnetic force of the magnet 92 is sufficient to lift the cap 56 from the nozzle assembly when the pressure on each side of the cap is substantially equal. A pneumatic or hydraulic piston and ram assembly 94 is connected to move the ram 88 toward and away from the housing 40.

In operation, the furnace 14 is initially evacuated of air by opening valve 32, closing valve 30 and starting the vacuum pump 24. The cap 56 will be held in position on the housing 40 by the vacuum in the furnace 14. After the air has been evacuated from the furnace 14, the

valves

32 and 36 are closed and valve 30 opened to start evacuating air from chamber 10. The furnace 14 is energized to melt the metal while the air is being evacuated from chamber 10. Once the cap 56 has been removed, the centrifugal casting mold 13 is rotated on pedestal 11 by a conventional drive mechanism indicated at 19. Water is circulated through coil 80 continuously by any conventional tilting arrangement. The furnace 14 is tilted on the stanchions 15 by means of a conventional tilting system. The nozzle assembly 16 will pivot about the pivot point 70 until the molten metal pours into the noule housing 20.

, Although a centrifugal casting machine has been shown within the vacuum chamber 10, it is also possible to cast metal in static type molds with this assembly.

What is claimed is:

1. Vacuum casting device comprising a vacuum chamber,

a tilt type vacuum furnace having a pouring spout extending into said chamber through an opening in said chamber, mold means for casting metal in said vacuum chamber,

a vacuum pump connected to selectively evacuate said furnace and said vacuum chamber,

and flexible seal means for connecting said pouring spout to said chamber to maintain a vacuum in said chamber and to permit tilting motion between said spout and said chamber whereby molten metal under vacuum can be poured from said furnace into said mold means.

2. A device according to claim 1 including a nozzle assembly mounted on said pouring spout, and including a removeable cap on said assembly to seal said furnace from said vacuum chamber.

3. A device according to claim 2 including means mounted in said vacuum chamber for removing said cap.

4. A device according to claim 3 wherein said cap removing means is operative when the pressure on each side of said cap is substantially equal.

5. A device according to claim 1 including a nozzle assembly on said pouring spout and said flexible seal means includes complementary connecting parts mounted on said nozzle assembly and said vacuum chamber.

6. A device according to claim 5 wherein said nozzle assembly includes a removeable cap to seal said furnace from said chamber.

7. A device according to claim 5, wherein said nozzle assembly includes means for protecting said flexible seal means from the heat of the molten metal.

8. A device according to claim 7 wherein said protecting means includes a radiation shield supported by said nozzle assembly.

9. A device according to claim 7 wherein said protecting means includes a water coil mounted on said noule assembly.

10. A device according to claim 7 wherein said protecting means includes a flexible shield provided on the inner surface of said flexible seal means.

11. An apparatus for pouring molten metal from a tilt type vacuum furnace having a pouring spout into a centrifugal casting machine positioned in a vacuum chamber, said apparatus comprising a nozzle assembly extending through an opening in said chamber, said assembly including a cap positioned in said chamber,

means for sealing said cap to said spout, and

flexible means for sealingly connecting said assembly to the vacuum chamber and for permitting tilting motion between said spout and said chamber,

said cap being removable from said assembly.

12. An apparatus according to claim 11 wherein said connecting means comprises a flexible boot having an outer section connected to said housing and an inner section connected to said assembly.

13. An apparatus according to claim 1 1 wherein said nozzle assembly includes means for cooling said pouring spout.

14. An apparatus according to claim 11 including means for protecting said flexible means from radiant heat while pourmg.

15. An apparatus according to claim 11 including means in the vacuum chamber for removing said cap from said housing.

16. An apparatus according to claim 15 wherein said removing means includes a magnet mounted in said chamber for movement into engagement with said cap.

17 A vacuum casting assembly comprising a vacuum chamber,

a centrifugal casting apparatus sealed in said vacuum chamber,

an external tilt type vacuum furnace external of said vacuum chamber, having a pouring spout extending through an opening into said chamber,

a vacuum pump connected to selectively evacuate said chamber and said furnace,

and flexible seal means for connecting said pouring spout on said furnace to said vacuum chamber and for permitting tilting motion between said spout and said chamber while maintaining the vacuum therebetween.

18. An assembly according to claim 17 wherein the tilting axis of said furnace is located in the plane of said flexible seal means.

19. An assembly according to claim 17 including means on said pouring spout for controlling the flow of molten metal into said casting apparatus.

Claims

1. Vacuum casting device comprising a vacuum chamber, a tilt type vacuum furnace having a pouring spout extending into said chamber through an opening in said chamber, mold means for casting metal in said vacuum chamber, a vacuum pump connected to selectively evacuate said furnace and said vacuum chamber, and flexible seal means for connecting said pouring spout to said chamber to maintain a vacuum in said chamber and to permit tilting motion between said spout and said chamber whereby molten metal under vacuum can be poured from said furnace into said mold means.

9. A device according to claim 7 wherein said protecting means includes a water coil mounted on said nozzle assembly.

11. An apparatus for pouring molten metal from a tilt type vacuum furnace having a pouring spout into a centrifugal casting machine positioned in a vacuum chamber, said apparatus comprising a nozzle assembly extending through an opening in said chamber, said assembly including a cap positioned in said chamber, means for sealing said cap to said spout, and flexible means for sealingly connecting said assembly to the vacuum chamber and for permitting tilting motion between said spout and said chamber, said cap being removable from said assembly.

13. An apparatus according to claim 11 wherein said nozzle assembly includes means for cooling said pouring spout.

14. An apparatus according to claim 11 including means for protecting said flexible means from radiant heat while pouring.

17. A vacuum casting assembly comprising a vacuum chamber, a centrifugal casting apparatus sealed in said vacuum chamber, an external tilt type vacuum furnace external of said vacuum chamber, having a pouring spout extending through an opening into said chamber, a vacuum pump connected to selectively evacuate said chamber and said furnace, and flexible seal means for connecting said pouring spout on said furnace to said vacuum chamber and for permitting tilting motion between said spout and said chamber while maintaining the vacuum therebetween.