Methods and apparatus for spray forming, atomization and heat transfer

Abstract

The present invention is directed to methods and apparatus that use electrostatic and / or electromagnetic fields to enhance the process of spray forming preforms or powders. The present invention also describes methods and apparatus for atomization and heat transfer with non-equilibrium plasmas. The present invention is also directed to articles, particularly for use in gas turbine engines, produced by the methods of the invention.

Description

RELATED APPLICATIONS [0001] This application claims priority to and is a divisional application of U.S. patent application Ser. No. 10 / 913,361, filed Aug. 9, 2004 which claims priority to and is a divisional of 09 / 882,248, filed Jun. 18, 2001, now U.S. Pat. No. 6,772,961, which claims priority to U.S. Provisional Application No. 60 / 212,122, filed Jun. 16, 2000, all of which are incorporated herein by reference.FIELD OF THE INVENTION [0002] The present invention is directed to methods and apparatus that use electrostatic and / or electromagnetic fields to enhance the process of spray forming preforms or powders. The present invention also describes methods and apparatus for heat transfer using non-equilibrium plasmas and for atomization. BACKGROUND OF THE INVENTION [0003] Spray forming is a process by which a stream of molten metal is atomized by a gas stream impinging upon it. The resulting atomized droplets are then directed to a target by the gas stream, or the resulting atomized dr...

AI Technical Summary

Benefits of technology

[0008] The present invention overcomes the limitations of the conventional powder process by permitting a significantly larger melt to be manufactured to powder, thereby eliminating the blending steps. They also are melted and atomized in a ceramicless system, thereby minimizing the contamination from the furnace linings. They are atomized in vacuum, thereby eliminating the need for screening and handling. They can either be containerized and sealed in a vacuum or rapidly solidified to form a solid preform in vacuum, thereby eliminating sources of handling and hence possible contamination. Finally, the present invention will have considerably fewer handling steps than conventional powder making, and thus will be more cost effective.

[0015] Accordingly, in various embodiments, non-equilibrium plasmas are advantageously employed to effect optimal heat transfer, and the non-equilibrium plasma must act with a heat sink / source that has a thermal conductivity capable of removing the desired quantity of heat. While two or more electrodes have been used in the past to produce a plasma in a region of high heat, such as a weld zone, so that the plasma would serve to conduct heat outward from the weld zone, thereby increasing the surface area for heat, embodiments of the present invention are directed to the discovery that a non-equilibrium plasma may be used to introduce heat into a workpiece as well as from a workpiece. It has further been surprisingly discovered that under the correct conditions a non-equilibrium plasma can be used to efficiently transfer heat in a vacuum.

Problems solved by technology

Producing powders by typical prior spray forming methods results in a yield loss of 10-15%, and much of the loss is associated with powder being trapped in various areas of the apparatus rather than being delivered to the collection vessel during the process.

In producing solid workpieces, known as preforms, typical prior spray forming methods result in a yield loss of 25-40%, and a significant portion of the loss is usually caused by over-spray and particles bouncing off the surface due to their angular impact relative to the normal of the preform surface.

Various methods have been described to recover and reuse overspray powder, such as, for example, U.S. Pat. No. 5,649,993, but these are not wholly satisfactory.

Because many powders and preforms are susceptible to damage to their chemical structure by air and oxygen, they are often produced in a shield gas environment of nitrogen or argon.

Thus, any powder or preform remaining in the chamber becomes contaminated and unusable when air and oxygen enter the spray forming apparatus after the flow of shield gas is turned off.

This method of manufacture is not efficient because several small melts are required for blending, melts are made in conventional ceramic lined furnaces and hence result in oxide contamination, several powder handling operations offer opportunity for contamination, and many steps in the process make the production operation costly.

Heat transfer using non-equilibrium plasmas has heretofore been poorly understood and often incorrectly or inefficiently applied.

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