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US5144110 - ||||||||||| United States Patent[191 Marantz et...

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Unformatted text preview: ||||||lllllllllllIlllllllllllllllllllIllllIIIII|||||lllllllllllllllllllllll United States Patent [191 Marantz et a1. 9 [54] PLASMA SPRAY GUN AND METHOD OF USE [76] Inventors: Daniel R. Marantz, 25 Cedar La., Sands Point, NY. 11050; Herbert Herman, 30 Waterview Dr., Pt. Jefferson, NY. 11777 [21] Appl. No.: 522,351 [22] Filed: May 11, 1990 Related US. Application Data [63] Continuation-impart of Ser. No. 267,145, Nov. 4, 1988, Pat. No. 4,982,067. [51] Int. Cl.5 ............................... B23K 9/00 [52] US. Cl. .......................... 219/121.48; 219/ 121.47; 219/121.59; 219/121.52; 219/121.5; 427/34 [58] Field of Search ............. 219/121.47, 76.16, 76.15, 219/75, 121.59, 121.48; 427/34 [56] References Cited U.S. PATENT DOCUMENTS Re. 32,908 4/1989 Pfender ........................ 219/121.368 2,806,124 9/1957 Gage .................. 219/75 2,858,411 10/1958 Gage .......... 219/75 3,140,380 7/1964 Jensen 427/348 3,246,114 4/1966 Matvay .......... 219/76 3,312,566 4/1967 Winzeles et a1. ..... 219/76.16 3,472,995 10/1969 Browning et a1. 219/76.16 3,770,935 ll/1973 Tateno et a1. ........ .. 219/121.47 3,947,607 3/1976 Gazzard et a1. .. ....... 427/348 3,989,512 11/1976 Sayce ....................... 75/11 4,341,941 7/1982 Tateno ...... 219/121.48 4,386,112 5/1983 Eaton et a1. .. ...... 427/34 4,668,852 5/1987 Fox et a1. ...... .. 219/76.l68 4,689,468 8/1987” Muehlberger ..... 219/76.16 4,818,837 4/1989 Pfender .......................... 219/121.48 m 'II/fg ‘ ,7]/II{:u.. . ._,_ ”twee t 72 'IIIIIZM' USOOS1441 10A Patent Number: Date of Patent: 5,144,110 Sep. 1, 1992 {11] [45] FOREIGN PATENT DOCUMENTS 51687 11/1987 U.S.S.R. . 959472 6/1964 United Kingdom . Primary Examiner—Mark H. Paschal] Attorney, Agent, or Firm—Dykema Gossett [57] ABSTRACT The plasma generating apparatus and method of this invention is particularly, although not exclusively, suit- able 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 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 plas- mas 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 co- alesced plasma. The second plasma gas may be a con- ventional inert or unreactive plasma gas or more prefer- ably a reactive plasma gas increasing the energy of the free-standing plasma and providing additional advan- tages. The feedstock may then be fed through the bore of the transfer electrode and the free-standing electro- magnetically coalesced plasma, uniformly heating the feedstock and permitting the use of a wide range of feedstock material forms and types, including particu- late feedstock having dissimilar particle sizes and densi- ties, slurries, sol-gel fluids and solutions. 39 Claims, 7 Drawing Sheets “y nfinv ‘ be ,“ .5 g S US. Patent Sep.1,1992 Sheet 1 of 7 5,144,110 76 ..1 r \ 5/ ’l' ~1 a"! / A §\\\\\\\ §\ _‘ \' 76/2 ' M] ' ’2 'IIIIJE\\\'A ‘1 ‘>‘-;.“- ~ 1 \ ‘ 62 I42 58 5,144,110 Sheet 2 of 7 Sep. 1, 1992 U.S. Patent COOLANT IN $11; _ ‘l E“ l , 41.x < ba\\\/\.\\N®\V\u\\\ <‘I‘\§§.§v.fi \s. J COOL /06 US. Patent US. Patent Sep. 1, 1992 Sheet 4 of 7 5,144,110 US. Patent Sep. 1, 1992 Sheet 5 of 7 5,144,110 200 206 2/0 208 K204 a; 2/2 2/6 228 204 232 224 $7 755$ ” %\' Vi? 2‘24 240 2/6 ‘s-fié I§i§ ” égfi : .é‘é 2/6 240 ,. ~11 -\_ _ 5 SI?» 5": . ~ 232 2’36 gig/4%. §W " ”a 7m 236 239 3}};‘ils: {lg ‘5}! aw} éi; (\N 23.9 238 (ll): 5N k4” ~I§Eg ’4‘ k ‘ 238 243 11/121431 3.41” ”L“ ét-fi 243 - a MM :2» ~'III ”2 7156 f ’II'H' ' 4 ”"352 ._~ “ .ar 7‘le 264 {/- ‘4 .“I ’ fl 4N1“ W J I]; :3: " "=:' : i ' ‘ .- ’ m I, 3W mgr/W V4! ‘4'; :64.” 5| .43. .! AVG-RI 268 272 L II\,>>\"~>}8 g:,\'\>>,>4g m ”l." ‘ ~ - ' -\ r 4 23" “y’w’i V/"§§:‘:“ 278288 \\‘ fl ‘ '5‘ ; ..—:_.. 278 L ’1i<\;§\‘ H flrw‘l“ w 346 266 W§\\\\‘ \V" fit“; 347 345 .. \\“‘ “\x 356 - O4 :27" w.\3/6 g 324 306 “‘\“‘V [a \V §._\\\\\V\\ 334 44 .‘s M». Nk‘k "I’llm'l/I/[I/III‘A VI; 7// 340 ' 32.9 /7-7g-/0 US. Patent Sep. 1, 1992 Sheet 6 of 7 5,144,110 5,144,110 Nkm. ES 2 i ) th. Q E5 9... fink! .-.wk\m — — Rom 3,: IEE'II ZGEEEJEE All 0 . ink—“.22: Sheet 7 of 7 Sep. 1, 1992 — mm». NQM. “ka. WWMJ .1 Es 2 III HE g 2:! 2 li Nkm. US. Patent 1 5,144,110 1 PLASMA SPRAY GUN AND METHOD OF USE This application is a continuation-in-part of applica- tion Ser. No. 267,145 filed Nov. 4, 1988, which issued as U.S. Pat. No. 4,982,067 on Jan. I, 1991. BACKGROUND OF THE INVENTION Plasma torches were developed primarily as a high temperature heat source and are now widely used com- mercially for cutting, welding, coating and high tem— perature treatment of materials. Conventional direct current commercial plasma torches or guns include a pointed rod-like cathode generally formed of thoriated tungsten axially located within a bore in the body por- tion of the gun and an annular anode located down- stream of the cathode having a nozzle orifice coaxially aligned with the cathode. A plasma-forming gas, typi- cally argon or mixtures of argon and helium or argon 10 15 and hydrogen, is introduced into the body portion of 20 the gun such that the gas flows in an axial direction around the cathode and exits through the anode nozzle orifice. Plasma generation occurs in the gun in the arc region between the anode and the cathode. The plasma is typically formed by initiating an are between the anode and cathode using a high-frequency starting pulse, wherein the arc heats and ionizes the plasma gas to temperatures of about 12,000 degrees K. The heated and expanded plasma gas is then exhausted at high speed through the nozzle orifice. The gas flow through the gun can be axial 'or introduced in a manner so as to cause a vortex-type flow. The electrical characteristics of the plasma are are determined by the gas flow rate, gas composition, anode nozzle orifice diameter and the electrode spacing. Where the plasma gun is used for spraying a coating, the feedstock is usually in powder form suspended in a carrier gas and injected radially into the plasma effluent, either internally or externally of the nozzle exit depend- ing on the gun manufacturer. Because the temperature drops off sharply in the plasma after it exits the anode nozzle, the powder is preferably introduced as close as possible to the point of plasma generation. US. Pat. No. 2,806,124 is an early disclosure of the basic principles of plasma technology and US. Pat. No. 3,246,114 includes an early disclosure of a commercial plasma gun. Because of the geometry of a plasma gun and poten- tial cathode deterioration, as discussed below, it is not possible to introduce the feedstock material axially through a conventional plasma spray gun, although the potential advantages have long been recognized. In a typical plasma jet coating apparatus, the feedstock pow- ders are introduced radially into the plasma stream downstream from the plasma origin, either perpendicu- lar to the axis or inclined in a direction with or counter- current to the flow of the plasma jet. As will be under- stood, the plasma interferes with particle penetration with a resistance that requires particle momentum suffi- cient to penetrate to the axis of the plasma jet. The particle momentum is provided by the carrier gas. Further, thermal spray powders never have an abso- lutely uniform particle size and generally include a broad distribution of particle sizes. Carrier gas flow rate must further be adjusted dependent upon the particle size, wherein the smaller or lighter particles require a greater carrier—gas flow rate. Nevertheless, the particle injection velocity distribution will be broad even for a narrow particle size distribution and blends or mixtures 25 30 35 45 50 55 65 2 of feed powders have very limited commercial applica- tions. Therefore, heat and momentum transferred to the injected particles will vary over a wide range, resulting in a broad range of velocity and surface temperature distribution upon impact of the particles with the target or substrate. Because of the greater momentum of the larger or heavier particles, the larger particles will pen- etrate through the plasma jet and become entrained in the outer, colder gas region or ejected out of the plasma jet, resulting in unmelted fringe regions of the deposit coating. Very small or light particles of low momentum will fail to penetrate the plasma jet and will also be included in the fringe area. Very small particles which enter the plasma jet core may also overheat and vapor- ize. Therefore, only a fraction of the particles enter the core of the plasma jet and are deposited as a highly dense layer on the target substrate. The unmelted or partially melted particles may affect the density of the deposit. In a typical application, the deposition effi- ciency (i.e., the ratio of material fed into the plasma jet gun compared to the portion which actually forms the coating) is typically low, usually well below 70% for high melting materials, such as oxide ceramics and in- termetallic compounds. Unreactive gases, such as argon or helium, are em- ployed as the plasma gas to avoid erosion or deteriora- tion of the cathode electrode. As described above, the cathode is normally formed of thoriated tungsten and the electrode is operated at temperatures above 1000 degrees Centigrade. Diatomic gases, such as hydrogen or nitrogen, may be added to the inert plasma gas to enhance the power output of the plasma jet torch. How- ever, reactive gases, such as oxygen, cannot be em- ployed because reactive plasma gases would result in oxidation corrosion of the cathode. The use of reactive gases or reactive gas mixtures will cause the cathode to undergo local deterioration, thereby causing the cath- ode point of arc origination to wander, resulting in plasma arc instability or “arc wandering”; however, it would be desirable in a number of applications to utilize certain reactive gases, such as oxygen or oxygen bear- ing gas mixtures as the plasma forming gas. For exam- ple, certain plasma jet applications result in oxygen depletion of the feedstock. The utilization of oxygen, for example, as the plasma gas would result in restora- tion of oxygen in the resulting coating and eliminate the requirement of a post-spray oxygen replacement anneal. It would also be very desirable to raise the operating power level of conventional plasma jet guns without decreasing energy efficiency or deterioration of the electrical components. In a typical plasma jet gun, the energy efficiency decreases as the operating energy level increases because of the inherently high electrical current operation and energy losses in the gun and power cables. Presently, energy is increased in a plasma jet gun by raising the current. Since the power input to a plasma jet gun is a product of the voltage and the current (Power=VxI), it would be desirable to raise the operating power level by increasing the plasma voltage rather than the current. Since the operating voltage is directly related to the plasma-forming gas used, a well as the cathode-anode spacing, it would be desirable to adjust these parameters for optimum operation. How- ever, as described above, plasma forming gas selection is restricted to the group of unreactive or inert gases to avoid cathode deterioration. Cathode-anode spacing is limited due to the problems of initiating and maintaining 5,144,110 3 stable plasma are conditions with large interelectrode spacing. Thus, the present plasma jet technology is limited in at least three important respects. First, radial injection of powdered feedstock results in poor deposition effi- ciency, reduced density of the deposit and requires a narrow range of feedstock particle size where uniform coatings are required. Second, reactive gases or reaCo tive gas mixtures cannot be used as the plasma-forming gas to avoid deterioration of the cathode and are wan- dering. Finally, the operating power level of conven- tional plasma jet guns cannot be significantly increased without decreasing the energy efficiency. Various attempts have been made to avoid the prob- lems of radial feed of plasma jet guns without commer- cial success. The principal solutions proposed by the prior art include (a) hollow cathode plasma guns, (b) RF (radio frequency) guns and (c) a plurality of plasma guns with a single feed. The hollow cathode gun, as the name implies, utilizes a hollow cathode tube, rather than a conventional rod-shaped cathode. The RF plasma gun employs a rapidly alternating electric field generated by a radiofrequency coil which replaces the are as the plasma source. Although the hollow cathode and RF plasma guns have commercial promise, neither system has achieved commercial success. As evidenced by US. Pat. No. 3,140,380 of Jensen, assigned to Avco Corporation, others have tried to merge two or more plasma effluents into a “joint plasma effluent into which a coating material is fed and reduced to substantially molten particles” for deposition on a substrate. In the prior art apparatus disclosed in the Jensen patent, a plurality of plasma guns or “plasma generating means” are “displaced symmetrically” with relation to a common axis such that the “plasma efflu- ents are directed to intercept at a point and merged to form a joint plasma effluent.” The plasma effluents from the individual plasma torches are then fed through a nozzle opening in the common axis and wire or pow- dered feedstock is fed through the nozzle opening in the common axis. As will be understood, this method of forming a “joint plasma effluent" does not result in a single or coalesced free-standing plasma and the im- pinging plasma effluent results in turbulence at the point of impingement through which the feedstock is fed. Further, the temperature of the plasma effluent at the point of impingement through which the feedstock is fed is substantially lower than the temperature of the plasma cores, resulting in lower efficiency than would be obtained for a true axial feed, wherein the feedstock particles are fed into the plasma core. This attempt to provide an axial feed for plasma spraying has not found commercial applications and the thermal spray industry therefore continues to utilize radial feed for plasma torches The prior art also includes other attempts to combine two or more plasmas as disclosed in Tateno, et al U S. Pat. No. 3,770,935. In the plasma jet generator dis- closed in the Tateno, et a1 patent, a positive plasma jet torch is aligned at a right angle to a negative plasma jet torch, such that the plasmas meet and function as a plasma jet torch of straight polarity to achieve a high arc voltage and improved efficiency. However, the plasma jet generator must utilize an inert plasma gas and radial feed of the feedstock. This system has not been introduced commercially and does not overcome the problems with radial feed as described above. 10 15 20 25 30 35 4O 45 50 55 6O 65 4 The prior art also includes numerous examples of transferred arc plasma guns or torches. Transferred arc plasma torches, wherein the substrate is connected elec— trically to the gun, has achieved commercial acceptance in many applications. It is also possible to utilize a sec- ond annular anode electrode, downstream of the pri— mary anode, to transfer the plasma axially as disclosed in Gage US. Pat. No. 2,858,411. Transferred are tech- nology has not, however, resulted in a commercial axial feed plasma gun utilizing powdered feedstock, which is a primary object of the present invention. Thus, although the problems of radial feed in com— mercial plasma spray apparatus have long been recog- nized, the prior art has failed to solve the problems described above in a commercially successful plasma spray system. There is, therefore, a long-felt need for an axial feed plasma spray system which has not been met by the prior art. SUMMARY OF THE INVENTION In its broadest terms, the plasma spray apparatus and method of this invention generates a free-standing elec- tromagnetically coalesced stable plasma permitting true axial feed in a plasma spray system. Feedstock, in partic- ulate or rod form, may be fed through the axis of the free-standing plasma, resulting in improved efficiency, including improved heat transfer and uniform heating of the feedstock, thereby eliminating the problems of radial feed. Further, the plasma generating apparatus and method of this invention may utilize reactive gases or reactive gas mixtures as the plasma forming gas, without resulting in deterioration of the cathode or are wandering. Finally, the operating power level of the plasma jet torch of this invention may be significantly increased, without decreasing the energy efficiency of the system or damaging the electrical components. The plasma spray apparatus of this invention includes at least two, three of more preferably at least four plasma generating means or pilot plasma guns, each generating a plasma of ionized plasma gas, means for extending and electromagnetically coalescing the plas— mas into a free-standing plasma of ionized gas and means for supplying feedstock axially through the free- standing plasma. The pilot plasma guns may be conven~ tional plasma generating torches, each including a pair of electrodes and means supplying a substantially inert ionizable plasma gas between the electrodes, wherein the ionizable plasma gas flows through an are generated between the electrodes, establishing a plasma of ionized gas. In the disclosed embodiment of the plasma spray apparatus of this invention, the pilot plasma guns each include a rod-shaped cathode, an annular body portion surrounding the cathode in spaced relation, an annular anode downstream of the cathode having a nozzle opening axially aligned with the cathode, and means for supplying an inert plasma gas to the annular body por- tion which flows around the cathode and exits the anode nozzle opening. The pilot plasma guns are in one embodiment angularly displaced symmetrically about a common axis, such that the plasmas generated by the pilot plasma guns intersect the common axis. The individual plasmas generated by the pilot plasma guns are extended and electromagnetically coalesced into a free-standing plasma by means of a transferred current established to the main transfer electrode, pref- erably an annular anode having a nozzle bore coaxially aligned with the common axis, such that the plasmas generated by the pilot plasma guns are directed into the 5,144,110 5 nozzle bore of the main transfer anode. The pilot plas- mas are generated in the disclosed embodiment by a , conventional direct current power means connected to the rod-shaped cathodes and the annular anodes, form- ing an electric are through which the inert plasma gas flows, ionizing the gas and forming a plurality of plas- mas which intersect in the throat of the main transfer anode. In the disclosed embodiment, the throat of the main transfer anode is preferably cone-shaped to re- ceive and direct the individual plasmas generated by the pilot plasma guns into the nozzle bore of the main trans- fer anode. ' The power means in one disclosed embodiment fur- ther includes a source of direct current connected to the cathodes of the pilot plasma guns and the main transfer anode establishes a transferred current which electro- magnetically coalesces the pilot pl...
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