Abstract The plasma generating apparatus and method of this invention is particularly, although not exclusively, suitable for plasma spraying. The plasma spray apparatus and method of this invention generates a free-standing electromagnetically coalesced stable plasma through which feedstock may be fed, eliminating problems with conventional radial feed plasma guns. The plasma spray apparatus of this invention includes a plurality of pilot plasma guns preferably angularly displaced symmetrically about a common axis and a main transfer electrode located downstream of the pilot plasma guns having a nozzle bore coaxially aligned with the common axis. The plasmas generated by the pilot plasma guns are directed into the throat of the main transfer electrode bore and a second plasma gas is supplied to the throat of the main transfer electrode bore which is ionized and coalesced with the plasmas generated by the pilot plasma guns, generating a free-standing electromagnetically coalesced plasma. The second plasma gas may be a conventional inert or unreactive plasma gas or more preferably a reactive plasma gas increasing the energy of the free-standing plasma and providing additional advantages. The feestock may then be fed through the bore of the transfer electrode and the free-standing electromagnetically coalesced plasma, uniformly heating the feedstock and permitting the use of a wide range of feedstock material forms and types, including particular feedstock having dissimilar particle sizes and densities, slurries, sol-gel fluids and solutions.
An axial feed plasma spray apparatus comprising: four pilot plasma guns, each including a rod-shaped electrode having a free-end, an annular body portion surrounding said rod-shaped electrode in spaced relation including an annular electrode having a nozzle opening axially aligned with said rod-shaped electrode and means for supplying a first plasma-forming gas to said annular body circulating around said rod-shaped electrode and exiting said annular electrode nozzle opening; said pilot plasma guns displaced about a common axis; a main transfer electrode located downstream of said pilot plasma guns having a bore coaxially aligned with said common axis; means for supplying electric power to said rod-shaped electrode and pilot plasma gun annular electrodes to generate an electric arc between said rod-shaped electrode and said pilot plasma gun annular electrode generating first, second, third, and fourth plasmas of plasma gas exiting said nozzle openings, and for supplying electric power to said main transfer electrode extending and electromagnetically coalescing said first, second, third, and fourth plasmas into a free-standing plasma within said main transfer electrode bore; means for supplying a second plasma-forming gas which enters said bore of said main transfer electrode; axial feedstock supply means for feeding feedstock along said common axis into said free-standing plasma, thereby heating and accelerating said feedstock in particulate form through said main transfer electrode bore.
Claim 2
Dependent Claim
219 words
An axial feed plasma spray apparatus comprising: four pilot plasma guns, each including a rod-shaped electrode having a free-end, an annular body portion surrounding said rod-shaped electrode in spaced relation including an annular electrode having a nozzle opening axially aligned with said rod-shaped electrode and means for supplying a first plasma-forming gas to said annular body circulating around said rod-shaped electrode and exiting said annular electrode nozzle opening; said pilot plasma guns displaced about a common axis; a main transfer electrode located downstream of said pilot plasma guns having a bore coaxially aligned with said common axis; means for supplying electric power to said rod-shaped electrode and pilot plasma gun annular electrodes to generate an electric arc between said rod-shaped electrode and said pilot plasma gun annular electrode generating first, second, third, and fourth plasmas of plasma gas exiting said nozzle openings, and for supplying electric power to said main transfer electrode extending and electromagnetically coalescing said first, second, third, and fourth plasmas into a free-standing plasma within said main transfer electrode bore; means for supplying a second plasma-forming gas which enters said bore of said main transfer electrode; axial feedstock supply means for feeding feedstock along said common axis into said free-standing plasma, thereby heating and accelerating said feedstock in particulate form through said main transfer electrode bore.