Fluid sprinkling – spraying – and diffusing – With means fusing solid spray material at discharge means
Reexamination Certificate
2001-06-18
2004-08-10
Hwu, Davis (Department: 3752)
Fluid sprinkling, spraying, and diffusing
With means fusing solid spray material at discharge means
C239S003000, C239S690000, C239S132000, C239S132100
Reexamination Certificate
active
06772961
ABSTRACT:
FIELD OF THE INVENTION
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
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 droplets are cooled to form a powder. 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. The flow of shield gas, however, must be turned off to allow workers to enter the chamber for cleanup, changeover and maintenance. 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.
Previously, gas streams or jets have been used to direct the path of the particles involved in the spray forming process. The gas streams typically consist of argon or nitrogen as the means of directing the particles, and heat is removed from the workpiece through conduction or convection.
Current processes for making powder metal products, particularly in materials used for critical aerospace applications, use a conventional gas atomizing process. In this process, high-pressure gas is directed at a molten metal stream to break it into smaller droplets. The droplets solidify as powder. For critical applications, the resultant powder is then blended with batches of powder from other small melts. The blend is screened to a small mesh size (325 mesh), canned and consolidated by extrusion into product suitable for manufacture into an aircraft component. 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. There is a need in the art for methods and apparatus that improve the yield and quality of powders and preforms produced by spray forming. The present invention is directed to these, as well as other, important ends.
SUMMARY OF THE INVENTION
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.
In one embodiment, the present invention describes apparatus comprising dispensing means, collecting means, and means for directing molten particles from the dispensing means to the collecting means comprising an electrostatic field and/or an electromagnetic field. Optionally, the apparatus may further comprise atomization apparatus and/or non-equilibrium heat transfer apparatus.
In another embodiment, the present invention describes spray forming methods comprising directing molten particles from dispensing means to collecting means by producing an electrostatic field and/or electromagnetic field between the dispensing means and the collecting means. Optionally, the apparatus may further comprise atomization apparatus and/or non-equilibrium heat transfer apparatus.
In another embodiment, the present invention is directed to apparatus comprising a melt chamber that comprises at least one orifice; a means for expelling a molten material through the at least one orifice in the melt chamber; and a means for applying a rapid electrostatic charge to the molten material. Preferably, the means for forcing the molten material through the at least one orifice in the melt chamber is a mechanical or electromechanical actuator or a pressure means. In a preferred embodiment, the apparatus further comprises a means for cooling the molten particle. Preferably, the means for cooling the molten particle comprises a means for generating a non-equilibrium plasma.
In another embodiment, the present invention describes methods for forming particles comprising producing a first molten particle; and applying a rapid electrostatic charge to the first molten particle, wherein the rapid electrostatic charge causes the first molten particle to form at least one smaller second particle. Preferably, the first molten particle is expelled through at least one orifice in the melt chamber via mechanical means or by a pressure means. In a preferred embodiment, the at least one smaller second molten particle is cooled, preferably by a non-equilibrium plasma.
In another embodiment, the present invention is directed to apparatus for transferring heat between a heat-transfer device and a workpiece comprising the heat-transfer device, wherein the heat-transfer device is electrically charged or held at a potential; the workpiece, wherein the workpiece is mechanically separate from the heat-transfer device; and means for transferring heat between the workpiece and the heat-transfer device comprising a means for generating a non-equilibrium plasma. The heat-transfer device can be either a heat sink or a heat source.
In yet another embodiment, the present invention is directed to methods of transferring heat between a heat-transfer device and a workpiece comprising producing a non-equilibrium plasma capable of transferring heat between the heat-transfer device and the workpiece, wherein the heat-transfer device is electrically charged or held at a potential, and wherein the heat-transfer device is mechanically separate from the workpiece. The heat-transfer device can be either a heat sink or a heat source.
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.
The novel methods of the present inv
Conrad Helmut Gerhard
Conrad Wayne
Forbes Jones Robin M.
Kennedy Richard L.
Phillips Andrew Richard Henry
ATI Properties Inc.
Hale and Dorr LLP
Hwu Davis
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