Plasma spray gun and method of use

• US 5,144,110 A
• Filed: 05/11/1990
• Issued: 09/01/1992
• Est. Priority Date: 11/04/1988
• Status: Expired due to Fees

• Current Assignee: Daniel R. Marantz, Herbert Herman
• Original Assignee: Daniel R. Marantz, Herbert Herman
• Inventors: Herman, Herbert, Marantz, Daniel R.
• Primary Examiner(s): Paschall, Mark H.
• Application Number:
  US07/522,351
• Time in Patent Office: 844 Days
• Field of Search: 219/121.47, 219/76.16, 219/76.15, 219/75, 219/121.59, 219/121.48, 427/34
• US Class Current: 219/121.48
• CPC Class Codes: H05H 1/42 with provisions for introducing materials into the plasma, e.g. powder, liquid arc stabilising or constricting arrangements H05H1/3405; coaxial protecting fluids H05H1/341; electrostatic spraying, spraying apparatus with means for charging the spray electrically B05B5/00 ; cf. B23K9/324, B05B7/22
• CPC Class Codes: H05H 1/44 using more than one torch

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 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 feedstock 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 particulate feedstock having dissimilar particle sizes and densities, slurries, sol-gel fluids and solutions.

Claims

1. A plasma spray apparatus, comprising:

an anode;

means for generating a first plasma stream of ionized plasma gas said first plasma generating means including a first plasma deflecting means coupled to said anode and adapted to receive said first plasma stream and to direct said received stream to said anode;

means for generating a second plasma stream of ionized plasma gas intersecting said first plasma stream within aid anode, said second plasma generating means including a second plasma deflecting means;

means for extending and electromagnetically coalescing said first and second plasma streams into a free-standing plasma of ionized plasma gas; and

means for supplying feedstock into said free-standing plasma, whereby said feedstock is heated and accelerated.

2. The plasma spray apparatus defined in claim 1, characterized in that said means for extending and electromagnetically coalescing said first and second plasma streams includes a main transfer electrode having a bore, and said means of generating said first and second plasma streams comprise pilot plasma spray guns for generating a plasma into said main transfer electrode.

3. The plasma spray apparatus defined in claim 2, characterized in that said spray apparatus includes power supply means for supplying electric power to said plasma spray guns to generate said first and second plasma streams of ionized gas and for supplying electric power to said main transfer electrode to extend and electromagnetically coalesce said first and second plasma streams to form said free-standing plasma.

4. The plasma spray apparatus defined in claim 2, wherein said means for generating said first and second plasma streams further includes a first plasma gas supply means for supplying an inert plasma gas to said pilot plasma spray guns, and said means for extending and electromagnetically coalescing said first and second plasma streams includes a second plasma supply means for supplying a reactive plasma gas to said main transfer electrode.

5. The invention recited in claim 1, wherein said first and second pilot plasma generating means are angularly related to one another.

6. The invention recited in claim 1, wherein said first and second pilot plasma generating means are parallel to one another.

7. An axial feed plasma spray apparatus, comprising:

at least two pilot plasma guns, each of said plasma guns having a rod-shaped cathode with a free end, each of said pilot plasma guns further having an annular body portion surrounding said cathode in spaced relation, each of said annular body portions having an annular anode with a nozzle opening and an angularly disposed outlet portion, and means for supplying a plasma-forming gas to said annular body;

said pilot plasma guns being disposed in a housing and being displaced about a common axis with said cathode free ends extending substantially parallel to said common axis;

a main transfer anode located downstream of said pilot plasma guns having a bore coaxially aligned with said common axis;

means for supplying an electrical bias to said cathodes and said pilot plasma gun anodes to generate an electric arc between said cathodes and said pilot plasma gun anodes thereby generating first and second plasmas of ionized plasma gas exiting said nozzle openings, and for supplying electric power to said cathodes and said main transfer anode thereby extending and electromagnetically coalescing said first and second plasmas into a free-standing plasma within said transfer anode bore;

means for receiving said first and second plasmas of ionized plasma gas and for directing said received plasma gas to said main transfer anode; and

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 anode bore.

8. The axial feed plasma spray apparatus defined in claim 7, characterized in that said apparatus further includes means for supplying a second plasma-forming gas to said main transfer anode bore, thereby generating said free-standing plasma in said main transfer anode bore.

9. The axial feed plasma spray apparatus defined in claim 7, wherein said pilot plasma guns are symmetrically disposed about said common axis.

10. The axial feed plasma spray apparatus defined in claim 7, wherein said pilot plasma guns are parallel to said common axis.

11. The axial feed plasma spray apparatus defined in claim 7, wherein the outlet of said bore of said main transfer anode has a diameter larger than the diameter of the inlet of said bore.

12. The axial feed plasma spray apparatus defined in claim 11, characterized in that said main transfer anode includes a throat having a cone-shaped portion opening to said bore which receives said first and second plasmas.

13. The axial feed plasma spray apparatus defined in claim 7, characterized in that said apparatus includes three equally and symmetrically spaced pilot plasma guns each generating a plasma directed into said main transfer anode bore.

14. The axial feed plasma spray apparatus defined in claim 7, characterized in that said apparatus includes four equally and symmetrically spaced pilot plasma guns generating a plasma directed into said main transfer anode bore.

15. The axial feed plasma spray apparatus defined in claim 7, characterized in that said means for supplying electric power includes a source of electric power connected to said cathodes and said pilot plasma gun anodes and to said cathodes and said main transfer anode and sequencing means first impressing an electric current between said cathodes and said pilot plasma gun anodes, thereby generating said first and second plasmas, and then impressing an electric current between said cathodes and said main transfer anode, thereby extending and electromagnetically coalescing said first and second plasma into said free-standing plasma.

16. The axial feed plasma spray apparatus defined in claim 7, wherein said plasma spray apparatus includes a powder feedstock supply tube extending between said pilot plasma spray guns and coaxially aligned with said common axis to feed powdered feedstock into said free-standing plasma.

17. The axial feed plasma spray apparatus defined in claim 7, characterized in that said feedstock supply means includes a continuous rod of feedstock and means feeding said rod through said common axis into said free-standing plasma.

18. The axial feed plasma spray apparatus defined in claim 17, characterized in that said means for supplying electric power includes means connected to said rod of feedstock and to said first and second plasmas of ionized plasma gas.

19. The axial feed plasma spray apparatus defined in claim 17, characterized in that said pilot plasma guns are parallel to a common axis and said means for supplying feedstock is coaxially aligned with said common axis.

20. The axial feed plasma spray apparatus defined in claim 17, wherein said second gas supply means supplies a reactive ionizable plasma gas to said main transfer electrode bore.

21. An axial feed plasma spray apparatus, comprising:

a transfer electrode having a nozzle bore therethrough;

at least two 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 therewith and a second annular electrode downstream of said rod-shaped electrode free end;

first power supply means including a source of electric current connected to said rod-shaped electrode and said annular electrode to generate an electric arc therebetween;

means for supplying a substantially inert plasma gas to said annular body portion around said rod-shaped electrode, said first power supply means thereby generating first and second plasmas of ionized gas;

a main transfer electrode defining a bore for receiving said first and second plasmas;

deflection means for receiving said first and second plasmas and for directing said received plasmas to said main transfer electrode;

second power supply means including a source of electric current connected to said rod-shaped electrodes of said pilot plasma guns and to said main transfer electrode;

a second gas supply means for supplying plasma gas to said main transfer electrode bore,

said second power supply means energizing said main transfer electrode thereby extending and electromagnetically coalescing said first and second plasmas and ionizing said second plasma gas forming a free-standing plasma in said main transfer electrode bore; and

means supplying feedstock to said free-standing plasma in said main transfer electrode bore, thereby heating and accelerating said feedstock in particulate form.

22. A method of plasma spraying, comprising the following steps:

introducing a first plasma of ionized plasma gas into a chamber defined by a housing by coupling a first channel to said chamber and adapting said first channel to receive said first plasma and to transport said received first plasma to said chamber;

introducing a second plasma of ionized plasma gas into said chamber and intersecting said first plasma by coupling a second channel to said chamber and adapting said second channel to receive said second plasma and to transport said second plasma to said chamber so as to allow said second plasma to intersect said first plasma within said chamber;

extending and electromagnetically coalescing said first and second plasmas with an anode into a free-standing plasma of ionized gas; and

feeding a feedstock into said chamber through said intersection of said first and second plasmas into said free-standing plasma, said free-standing plasma heating and accelerating said feedstock in particulate form as a spray suspended in said plasma gas.

23. The method of plasma spraying defined in claim 22, wherein said method includes feeding and ionizable plasma gas into said free-standing plasma.

24. The method defined in claim 23, wherein said method includes feeding said ionizable plasma gas tangentially into said free-standing plasma thereby generating a vortex constricting said free-standing plasma.

25. The method of plasma spraying defined in claim 23, wherein said ionizable plasma gas is a reactive ionizable plasma gas and wherein a substantially inert ionizable plasma gas is used to form said first and second plasmas.

26. The method of plasma spraying defined in claim 24, wherein said method includes feeding a reactive ionizable plasma gas into said free-standing plasma, and ionizing said reactive plasma gas.

27. A method of plasma spraying comprising the following steps:

providing a chamber;

generating first and second angularly related plasmas of ionized plasma gas intersecting a common axis by coupling a first channel to said chamber and adapting said first channel to receive said first plasma and to direct said first plasma to said chamber and by coupling a second channel to said chamber and adapting said second channel to receive said second plasma and to direct said second plasma to said chamber so as to allow said second plasma to intersect said first plasma within said chamber;

extending and electromagnetically coalescing said first and second plasmas in a free-standing plasma;

simultaneously feeding an ionizable plasma gas into said free-standing plasma thereby extending said free-standing plasma; and

feeding a particulate feedstock through said intersection of said first and second plasmas into said free-standing plasma, said free-standing plasma heating and accelerating said particulate feedstock as a spray.

28. A method of plasma spraying, comprising the following steps performed in sequence:

generating first and second plasmas each generated by flowing an ionizable plasma gas between a pair of electrodes and generating an electric arc between said electrodes;

providing a anode;

providing a first channel between said anode and said pair of electrodes, said first channel being adapted to receive said first plasma and to direct said first plasma to said anode;

providing a second channel between said anode and said pair of electrodes, said second channel being adapted to receive said second plasma and to direct said second plasma to said anode so as to allow said second plasma to intersect said first plasma within said anode;

extending and electromagnetically coalescing said first and second plasmas and forming a free-standing plasma coincident with said common axis by generating an electric arc between said intersecting first and second plasmas and said anode and flowing a second plasma gas through said anode; and

feeding a feedstock along said common axis through the intersection of said first and second plasmas into said free-standing plasma, wherein said free-standing plasma heats and accelerates said feedstock in particulate form.

29. 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 defining a passage, and means for supplying a first plasma-forming gas to said annular body circulating around said rod-shaped electrode and passing through said passage;

said pilot plasma guns displaced about a common axis;

a main transfer electrode located downstream of said pilot plasma guns having a bore 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 ionized plasma gas passing through said passages, and for supplying electric power to said main transfer electrode for extending and electromagnetically coalescing said first, second, third, and fourth plasmas into a free-standing plasma within said main transfer electrode bore;

deflection means in communication with said passages and said main transfer anode for receiving said first, second, third, and fourth plasmas and for transporting said received plasmas to said main transfer electrode;

means for supplying a second plasma-forming gas into said bore of said main transfer electrode; and

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.

30. The invention recited in claim 29, further including 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.

31. The invention recited in claim 29, wherein said rod-shaped electrodes are cathodes, said annular electrodes are anodes and said main transfer electrode is an anode.

32. The invention recited in claim 29, wherein said pilot plasma guns are displaced symmetrically about said common axis.

33. The invention recited in claim 29, wherein said pilot plasma guns are oriented parallel to said common axis and wherein each of said annular electrodes has a plasma deflecting portion for deflecting said plasmas toward said common axis.

34. The invention recited in claim 29, wherein said electric power supply means includes four DC power supplies and one high frequency supply.

35. A plasma spray apparatus, comprising:

a housing defining a chamber;

means in association with said housing for generating a first plasma along a first axis, said first plasma generating means having first means for deflecting said first plasma stream along a second axis;

means in association with said housing for generating a second plasma along a third axis, said second plasma generating means having second means for deflecting said second plasma along a fourth axis, said fourth axis intersecting with aid second axis such that said first and second plasmas intersect;

a transfer electrode defining a passage, said transfer electrode being disposed in relation to said first and second plasma generating means such that said plasmas enter said electrode passage; and

means in association with said transfer electrode for extending and electromagnetically coalescing said first and second plasma into a free-standing plasma of ionized gas; and

means for supplying a feedstock into said passage of said electrode and into the path of said free-standing plasma.

36. The invention recited in claim 35, wherein said first and second axes are substantially parallel to one another.

37. A plasma spray apparatus, comprising:

a housing defining a chamber;

means attached to said housing for introducing a first plasma of ionized plasma gas into said chamber;

means attached to said housing for introducing a second plasma of ionized plasma gas into said chamber;

a transfer electrode having a passage for receiving said first and second plasmas;

means for supplying an electric current through said first and second plasmas to said transfer electrode to extend and electromagnetically coalesce said first and second plasmas into a free-standing plasma of ionized gas; and

transporting means, coupled to said passage, for receiving and transporting said first and second plasmas to said chamber;

means for supplying feedstock into said chamber and through said passage of said electrode;

whereby said feedstock is heated and accelerated.

38. A plasma spray apparatus, comprising:

a housing defining a chamber;

first plasma generating means for generating a first plasma of ionized plasma gas issuing into said chamber;

second plasma generating means for generating a second plasma of ionized plasma gas issuing into said chamber and intersecting said first plasma stream;

a transfer electrode defining a passage for receiving said first and second plasmas;

transporting means, coupled to said first and second plasma generating means for transporting said first and second plasmas to said chamber and for allowing said first and second plasmas to intersect within said chamber;

gas introducing means for introducing a plasma-forming gas into said passage of said transfer electrode;

means for supplying an electric current through said first and second plasmas to said transfer electrode to extend and electromagnetically coalesce said first and second plasmas into a free-standing plasma of ionized gas; and

means for supplying a feedstock into said passage of said transfer electrode.

39. An axial feed plasma spray apparatus comprising:

four pilot plasma guns mounted on a housing which defines a chamber, 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, and means for supplying a first plasma-forming gas to said annular body such that said plasma-forming gas circulates around said rod-shaped electrode, and exits 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 between said rod-shaped electrodes of said pilot plasma guns and 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;

deflection means, coupled between said rod-shaped electrode and said main transfer electrode for receiving said first, second, third and fourth plasmas and for transporting said received plasmas to said main transfer electrode;

means for supplying a second plasma-forming gas which enters said bore of said main transfer electrode; and

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.