Metal founding – Process – Disposition of a gaseous or projected particulate molten...
Reexamination Certificate
1996-12-10
2001-10-02
Nguyen, Nam (Department: 1722)
Metal founding
Process
Disposition of a gaseous or projected particulate molten...
C164S061000, C164S066100, C164S154400, C164S154800, C164S155300, C164S155600
Reexamination Certificate
active
06296043
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to spraycasting of an atomized molten metal or alloy onto a collector to form a spray deposit with reduced porosity and improved microstructure.
BACKGROUND OF THE INVENTION
A spraycast method is described in U.S. Pat. No. 3,826,301 that involves atomizing a molten metal or alloy and directing the atomized spray onto a collector surface disposed in a spray chamber to form an article. The spray chamber typically is maintained at atmopsheric pressure of argon or other non-reactive gas therein while the molten spray is directed onto the collector.
U.S. Pat. No. 3,826,921, now Reissue 31,767, describes control of the temperature of the spray deposit independent of the temperature of a mold in which an atomized spray is directed to control the structure of the sprayed deposit. To this end, the patent focuses on the conditions of gas atomization of the molten metal or alloy in the atomizing chamber and not the conditions in the spray chamber.
The spraycasting method of making metallic articles continues to suffer from disadvantages that the sprayed deposit includes entrapped argon or other gas that increases porosity of the deposit, that cylindrical spray cast shapes exhibit fissure porosity proximate the inner diameter, and that yields of acceptable spraycast articles are unsatisfactorily low from a commercial production standpoint. Moreover, coarse grain banding is evident in the spraycasting of certain nickel base superalloys, such as IN718.
SUMMARY OF THE INVENTION
The present invention has an object to provide a spraycasting method that overcomes these disadvantages by using spray chamber pressure control technique to provide better thermal control of an atomized spray in flight in the spray chamber and of the sprayed material deposited on a collector in the spray chamber.
The present invention provides in one embodiment a pressure control technique that involves in-situ evacuation of the spray chamber during spray deposition of the atomized metal or alloy on the collector to maintain an inert or non-reactive gas partial pressure no greater than about 400 torr in the spray chamber, preferably a gas partial pressure of from about 10 to less than about 400 torr. Such low spray chamber gas partial pressure provides a higher temperature of the atomized spray in flight in the spray chamber and of the sprayed material deposited on the collector in the the spray chamber. In addition, the amount of entrapped gas in the deposit is reduced as compared to that present in a deposit sprayed at near atmospheric pressure.
In another embodiment of the present invention, the atomized spray of molten metal or alloy is generated by supplying a melt to an atomizing device using atomizing gas, such as argon or other gas inert or non-reactive to the melt, to atomize the melt and direct it as a spray of molten droplets into the spray chamber having an initial (backfilled) inert or non-reactive gas partial pressure of about 400 torr or less therein. Thereafter, the gas partial pressure in the spray chamber is maintained at about 400 torr or less during spray deposition of the atomized spray on the collector by in-situ evacuation of the spray chamber to remove the atomizing gas introduced therein from the atomized spray. For spray cast articles, such as rings and tubes, having rotational symmetry, the collector can be rotated and moved in a single pass relative to the atomizing device to build up a spray deposit thereon.
The spraycasting method of the present invention using the aforementioned low gas partial pressure control technique to provide a higher temperature of the atomized spray and deposited material reduces entrapped porosity in the deposited material, reduces inner fissure voids proximate the collector surface during spray deposition, and provides a uniform grain size across the thickness of the tubular spray deposit as a result of achievement of improved thermal equilbrium conditions in the deposit during spray deposition. Yields of acceptable spray cast components can be improved as a result.
The present invention also envisions a particular embodiment wherein the spray deposit surface is oriented at its leading edge region at a selected acute angle relative to horizontal to improve the quality of the spray deposit by reducing inner diameter fissure porosity. A particular embodiment to this end envisons orienting the collector surface itself at a selected acute angle to horizontal. The present invention envisions in another embodiment actively heating the collector in-situ proximate the leading edge of the deposit at an initial depostion location. The collector is thermally insulated and capable of accommodating thermal expansion of the collector surface in still a further embodiment of the invention. In addition, the scan rate and distance of a scanning atomizer is slaved to the rotational speed of the collector in an additional embodiment of the invention such that actual atomizer dwell time (spraying time) is lessened as the collector rpm is increased.
These and other objects and advantages of the present invention will become more readily apparent from the following detailed description taken with the following drawings.
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Bowen Kim E.
Cook David A.
Dalal Ranes P.
Ingersoll David P.
Potter Douglas S.
Howmet Research Corporation
Lin I.-H.
Nguyen Nam
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