Claims
- 1. A method of operating a die casting machine in which a piston which charges molten metal into a die is retracted in a bore in a fill chamber beyond an inlet opening and a vacuum is applied to the fill chamber bore in front of the retracted piston to draw molten metal into the bore of the fill chamber through the inlet opening, the improvement comprising, applying a vacuum behind said piston during application of vacuum in front of the piston.
- 2. The method of claim 1 including introducing a gas at about ambient pressure behind the piston in place of said vacuum as said piston is advanced to charge the molten metal in the fill chamber bore into said die and before said piston clears said inlet opening.
- 3. The method of claim 2 including advancing and retracting the piston in the fill chamber through a piston rod extending out of the fill chamber and providing an enclosure between the fill chamber and the piston rod from which the vacuum applied behind the piston is drawn and into which the gas is introduced.
- 4. The method of claim 3 wherein said gas is an inert gas.
- 5. The method of claim 4 wherein said step of introducing an inert gas at about ambient pressure behind the piston comprises introducing the inert gas into said enclosure and venting said enclosure to atmosphere.
- 6. A vacuum die-casting machine having a fill chamber with a bore for communicating at a first end with a die, a piston extendable in said bore to charge molten metal into the die, a piston rod connected to said piston and extending out of a second end of the fill chamber, and means sealing said second end of said fill chamber characterized by a piston rod seal engaging said piston rod, and enclosure means extending from said fill chamber to said piston rod seal and forming with said piston rod seal an air-tight enclosure at the second end of said fill chamber, said enclosure means being at least laterally flexible to accommodate lateral movement of said piston rod and piston rod seal relative to said fill chamber.
- 7. The vacuum die-casting machine of claim 6 including control means controlling pressure within said enclosure.
- 8. The vacuum die-casting machine of claim 7 wherein said control means includes means selectively generating a vacuum and alternately introducing a gas at about ambient pressure into said enclosure.
- 9. The vacuum die-casting machine of claim 8 wherein said piston rod seal is in sliding engagement with said piston rod and wherein said enclosure means is a bellows.
- 10. The vacuum die-casting machine of claim 8 wherein said fill chamber has an inlet opening through which molten metal is drawn into the fill chamber by vacuum with said piston in a retracted position, said control means generating said vacuum within said enclosure with said piston in said retracted position and introducing said gas at about atmosphere pressure within said enclosure with said piston forward of said inlet opening.
- 11. The vacuum die-casting machine of claim 10 wherein said control means selectively introducing a gas within said enclosure at about ambient pressure includes valve means actuated through forward movement of said piston rod.
- 12. The vacuum die-casting machine of claim 11 wherein said piston rod seal is in sliding engagement with said piston rod and wherein said valve means comprises a valving section of said piston rod having a reduced cross-sectional area which vents said enclosure along said piston rod when said valving section is aligned with said piston rod seal.
- 13. The vacuum die-casting machine of claim 12 including an additional piston rod seal engaging said piston rod beyond the first mentioned piston rod seal and additional enclosure means extending from said first mentioned piston rod seal to said additional piston rod seal forming an additional air tight enclosure, said additional enclosure means also being at least laterally flexible, and wherein said control means includes means generating a vacuum within the first mentioned enclosure with said piston retracted beyond said inlet opening, means introducing an inert gas into said additional enclosure, and valve means connecting the additional enclosure with said first mentioned enclosure to introduce said inert gas into the first mentioned enclosure with said piston forward of said inlet opening.
- 14. The vacuum die-casting machine of claim 13 wherein said valve means comprises a valving section of said piston rod having a smaller cross-sectional area than said first piston rod seal and located on said piston rod such that said valving section is adjacent said first piston rod seal to connect the additional enclosure with the first mentioned enclosure with said piston forward of the inlet opening.
- 15. The vacuum die-casting machine of claim 12 wherein said gas is an inert gas.
- 16. The vacuum die-casting machine of claim 15 wherein said control means includes first valve means introducing said inert gas into said enclosure with said piston forward of said inlet opening and second valve means comprising a valving section of said piston rod having a reduced cross-sectional area which vents said enclosure to atmosphere along said piston rod when said valving section is aligned with said piston rod seal with said piston forward to said inlet opening.
- 17. A vacuum die-casting machine having a die section, a fill chamber having a bore communicating at a first end of the fill chamber with said die section and with an inlet opening adjacent a second end of said fill chamber, a piston slidable in said bore between a retracted position in which molten metal is drawn into said bore of the fill chamber by a vacuum and an extended position in which said molten metal in the bore is charged into said die section, said piston extending out of the bore beyond the second end of the fill chamber, and means sealing said fill chamber characterized by a bellows connected at a first end adjacent the second end of the fill chamber, a piston rod seal connected to a second end of the bellows and slidably engaging the piston rod at a location spaced from the second end of the fill chamber, and pressure control means applying a vacuum within said bellows with said piston adjacent said retracted position and introducing an inert gas into said bellows at about ambient pressure with said piston forward of said retracted position.
- 18. A vacuum die-casting machine having a die section, a fill chamber having a bore communicating at a first end of the fill chamber with said die section and with an inlet opening adjacent a second end of the fill chamber, a piston slidable in said bore between a retracted position in which molten metal is drawn into said bore of the fill chamber by a vacuum and an extended position in which molten metal in the bore is charged into said die section, said piston extending out of the bore beyond the second end of the fill chamber, and means sealing said fill chamber characterized by a bellows connected at a first end adjacent the second end of the fill chamber, a piston rod seal connected to a second end of the bellows and slidably engaging the piston rod at a location spaced from the second end of the fill chamber, pressure control means applying a vacuum within said bellows with said piston adjacent said retracted position, and valve means comprising a valving section of said piston rod, said valving section being aligned with said piston rod seal to allow ambient air pressure into said bellows with said piston forward of said retracted position.
- 19. A vacuum die casting machine having a die section, a fill chamber having a bore communicating at a first end of the fill chamber with said die section and with an inlet opening adjacent a second end of said fill chamber, a piston slidable in said bore between a retracted position in which molten metal is drawn into said bore of the fill chamber by a vacuum and an extended position in which said molten metal in the bore is charged into said die section, said piston extending out of the bore beyond the second end of said fill chamber and means sealing said fill chamber characterized by a first piston rod seal slidably engaging said piston rod at a location spaced rearward of the second end of said fill chamber, a first bellows connected between the second end of said fill chamber and said first piston rod seal, a second piston rod seal slidably engaging said piston rod at a location spaced beyond said first piston rod seal, a second bellows connected between the first piston rod seal and said second piston rod seal, pressure control means applying a vacuum within said first bellows with said piston in said retracted position and introducing an inert gas at about ambient pressure into said second bellows, and valve means comprising a valving section of said piston rod having a reduced cross sectional area, said valving section of said piston rod being aligned with said first piston rod seal with said piston forward of said retracted position to introduce said inert gas at about ambient pressure into said first bellows from said second bellows.
- 20. A vacuum die-casting machine having a die section, a fill chamber having a bore communicating at a first end with said die section and with an inlet opening adjacent a second end of said fill chamber, a piston slidable in said bore between a retracted position beyond said inlet opening toward said second end and an extended position toward said first end, a piston rod connected to said piston and extending out of the bore beyond the second end of the fill chamber, a piston rod seal engaging said piston rod, enclosure means extending from the second end of said fill chamber to said piston rod seal forming an air-tight enclosure, and pressure control means creating a vacuum in the fill chamber bore in front of the piston with said piston in the retracted position to draw molten metal into the fill chamber bore through said inlet opening and simultaneously applying a vacuum to said enclosure behind the piston.
- 21. The die-casting machine of claim 20 wherein said pressure control means includes means to replace the vacuum within the enclosure behind said piston with a gas at about ambient pressure as said piston moves toward said extended position and before said piston clears said inlet opening.
- 22. The die-casting machine of claim 21 wherein said pressure control means includes a valving section on said piston rod having a reduced cross-sectional area which is aligned with said piston rod seal to adjust pressure within said enclosure to about ambient pressure as said piston is extended and before said piston clears said inlet opening.
- 23. The die-casting machine of claim 21 wherein said means to replace the vacuum in said enclosure with a gas at about ambient pressure comprises means introducing an inert gas into said enclosure at about ambient pressure.
- 24. The die-casting machine of claim 23 wherein said means introducing an inert gas into said enclosure at about ambient pressure comprises first valve means introducing said inert gas into said enclosure and means associated with said piston rod venting said enclosure to atmosphere.
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a continuation-in-part of PCT International Patent Application No. PCT/US90/01216 filed on Mar. 6, 1990 designating the United States and now WO90/10516 published Sep. 20, 1990, now abandoned and which in turn is a continuation-in-part of U.S. patent application Ser. No. 07/320,140 filed on Mar. 7, 1989 and now U.S. Pat. No. 5,076,344.
US Referenced Citations (18)
Foreign Referenced Citations (3)
Number |
Date |
Country |
62-207554 |
Sep 1987 |
JPX |
62-296946 |
Dec 1987 |
JPX |
656737 |
Apr 1979 |
SUX |
Non-Patent Literature Citations (4)
Entry |
Abstract of Japanese Patent Publication 53-46779 Published Dec. 16, 1978. |
Abstract of Japanese Patent Publication 62-118955 Published May 30, 1987. |
English Translation of Japanese Patent Publication 53-46779 Published Dec. 16, 1978. |
English Translation of Japanese Patent Publication 62-118955 Published May 30, 1987. |
Continuation in Parts (1)
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Number |
Date |
Country |
Parent |
320140 |
Mar 1989 |
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