An improved plasma gun coaxially injects particles of ceramic materials having high melting temperatures into the central portion of a plasma jet. This results in a more uniform and higher temperature and velocity distribution of the sprayed particles. The position of the cathode is adjustable to facilitate optimization of the performance of the gun wherein grains of the ceramic material are melted at lower power input levels

Zaplatynsky, Isidor

English

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United States Patent 1191 [ill Patent Number: 4,990,739 
ZaplatYnskY [MI Date of Patent: Feb. 5, 1991 
PLASMA GUN WlTH COAXIAL. POWDER 
FEED AND ADJUSTABLE CATHODE 
Inventor: 
Assignee: 
Appl. NO.: 
Filed: 
Isidor Zpplatynsky, Fairview Park, 
Ohio 
The United States of America as 
represented by the Administrator of 
the National Aeronautics and Space 
Adminiptrn tion, Washington, D.C. 
376,488 
Jul. 7,1989 
Int. Cl .5  ................................................ BSIC 9/00 
US. Cl, .......................... 219/121.47; 219A21.52; 
219A21.48; 219/75; 219/76.16; 427/34 
Field of sevch ........... 219/76.12, 121.59, 121.48, 
219A21.49, 121.5, 121.52, 129.47, 75; 427/34, 
32 
References Cited 
U.S. PATENT DOCUMENTS 
2,922,869 1/1W Giannini et al. ............... 219A21.47 
3,055,591 9/1%2 Shepard .......................... 219A21.47 
3,562,486 2/1971 Hatch et al. .................... 219A21.52 
3,710,070 1/1973 Hirt et al. ....................... 219/121.47 
3,803,3 80 41 1974 
4,142,089 211979 
3,894,209 7/1975 
4,540,121 9/1985 
4,621,183 1 h 9 8 6  
4,627,990 12/1986 
4,739,146 4/1988 
4,788,408 11/1988 
4,818,837 4/1989 
4,650,953 311987 
4,780,591 10/1988 
Ragaller ......................... 219/121.47 
Fairbairn ......................... 219/121 P 
Lau et al. ........................ 219/121 P 
Browning ............................. 239/13 
Takeuchi et al. ............... 219/121 P 
Saga et al. ............................. 427/10 
Eger et al. .................... 219/121 PQ 
Lindland et al. ............. 219/121 PY 
Bernecki et al. ............... 219/121.52 
Wlodarczyk et al. ......... 219/121.52 
Pfender .......................... 219/121.52 
Primary Examiner-M. H. Paschal1 
Attorney, Agent, or Firm-Gene E. Shook; John R. 
Manning; James A. Mackin 
1571 ABSTRACT 
An improved plasma gun coaxially injects particles of 
ceramic materials having high melting temperatures 
into the central portion of a plasma jet. This results in a 
more uniform and higher temperature and velocity 
distribution of the sprayed particles. The position of the 
cathode is adjustable to facilitate optimization of the 
performance of the gun wiierein grains of the-ceramic 
material ?e melted at lower power input labels. 
4 Claims, 3 Drawing Sheets 
10 
https://ntrs.nasa.gov/search.jsp?R=19910016561 2020-03-24T07:01:14+00:00Z
U.S. Patent Feb. 5, 1991 Sheet 1 of 3 4,990,739 
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Fig. 1 
Sheet 2 of 3 US. Patent Feb. 5, 1991 
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4,990,739 
U.S. Patent Feb. 5, 1991 Sheet 3 of 3 4,990,739 
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4,990,"^^ 
1 
PLASMA GUN WITH COAXIAL POWDER 
AND ADJUSTABLE CATHODE 
FEED 
ORIGIN O F  THE INVENTION 
The invention described herein was made by an em- 
ployee of the United States Government and may be 
manufactured and used by or for the Government for 
governmental purposes without the payment of any 
royalties thereon or therefor. 
TECHNICAL FIELD 
This invention is concerned with plasma spraying 
materials having high melting temperatures. The inven- 
tion is particularly directed to an improved plasma gun 
for spraying ceramic materials. 
Several models of arc plasma guns are used at the 
present time to spray metallic or ceramic coatings. All 
share a similar design. More particularly, in one prior 
art gun the particles to be sprayed are injected orthogo- 
nally to the plasma jet externally. In another prior art 
gun these particles are injected through a hole or holes 
in the nozzle. 
A major disadvantage in using these prior art plasma 
guns is that only a portion of the particles penetrate to 
the central region of the jet. A significant portion of the 
injected particles is entrained in the external region of 
the plasma jet which is the cooler portion. Conse- 
quently, the injected particles acquire a spectrum of 
velocities and temperatures. In the case of a ceramic 
material, such as zirconia, some of the particles are only 
partially melted while others are not melted at all. 
It is, therefore, an object of the present invention to 
provide an improvqd plasma gun wherein the particles 
to be sprayed are injected into the central portion of the 
plasma jet for optimum heating. 
Another object of the invention is to provide an im- 
proved plasma jet in which the position of the cathode 
with respect to the anode can be adjusted to optimize 
the performance of the gun for a given application. 
BACKGROUND ART 
U.S. Pat. No. 3,894,209 to Fairbairn discloses a nozzle 
for an energy beam system. This nozzle utilizes a hol- 
low radio frequency electrode housed in an inner sleeve 
that is telescopically mounted within an outer sleeve. 
One or more powders or aggregates are selectively fed 
axially through a bore in this hollow electrode while a 
gas is selectively fed through the space around the elec- 
trode. 
U.S. Pat. No. 4,142,089 to Lau et a1 is directed to a 
pulsed coaxial thermal plasma sprayer comprising an 
elongated conductive tube having an electrode position 
coaxially therein. Inert gas, such as helium, is mixed 
with a powdered material, such as a ceramic or a metal, 
and a controlled amount is injected evenly into the tube. 
U.S. Pat. No. 4,650,953 to Eger et a1 describes a 
plasma torch having an electrode secured to a liquid 
cooled electrode holder and formed with a flow passage 
communicating with a central outlet for delivering an 
ionizable gas. A nozzle body which surrounds the elec- 
trode serves to conduct gas along the outside surface of 
this electrode. 
DISCLOSURE O F  T H E  INVENTION 
The objects of the invention are achieved and the 
problems of the prior art are solved by a plasma gun 
wherein particles are injected coaxially into the central 
5 
10 
15 
20 
25 
30 
35 
40 
45 
ISY 
portion of the plasma jet. This produces a more uniform 
and higher temperature and velocity distribution of the 
sprayed particles. 
At the same time, the length of the path of the parti- 
cles in the plasma jet is increased. Also, the feed gas acts 
as a coolant for the cathode, thus extending its life. 
An important feature of the invention is that the posi- 
tion of the cathode is adjustable to facilitate optimiza- 
tion of the gun performance. Tests have shown that 
zirconia grains plasma sprayed with the new gun can be 
melted at considerably lower power input levels when 
compared with commercially available guns of the 
prior art. 
BRIEF DESCRIPTION O F  THE DRAWING 
2 
The details of the invention will be described in con- 
nection with the accompanying drawing wherein 
FIG. 1 is a rear elevation view of an arc plasma gun 
embodying the features of the invention: 
FIG. 2 is a simplified axial sectional view taken along 
the line 2-2 in FIG. 1; 
FIG. 3 is a photomicrograph showing the morphol- 
ogy of zirconia particles sprayed into water using a 
commercially available plasma gun; and 
FIG. 4 is a photomicrograph showing the morphol- 
ogy of zirconia particles sprayed into water using a 
plasma gun embodying the features of the present in- 
vention. 
BEST MODE FOR CARRYING OUT THE 
INVENTION 
A plasma gun 10 constructed in accordance with the 
invention is shown in FIGS. 1 and 2. The body of the 
gun comprises a housing 12 in the form of an elongated 
cylindrical insulator having oppositely disposed end 
faces 14 and 16. An axial bore 18 extends from the rear 
end face 16 toward the forward end face 14. A recess 20 
extends from the forward end face 14 into the housing 
12. An enlarged cylindrical bore 22 extends from the 
bottom of the recess 20 toward the rear of the housing 
and meets the bore 18. An enlarged chamber 24 having 
a diameter substantially equal to the diameter of the 
recess 20 is formed in the housing 14 rearwardly of the 
enlarged bore 22. 
An anode 26 is secured to a metal base 28 mounted on 
the forward face 14. The base 28 has a rearwardly fac- 
ing boss 30 which extends into the recess 20 in the hous- 
ing 12. A suitable sealing ring 32 is Drovided between - -  
50 the boss 28 and the housing 12. A'similar ring 34 is 
positioned between the base 28 and the housing 12. 
These rings are of a suitable sealing material, such as 
rubber. 
The base 28 has a pair of oppositely disposed recesses 
55 36 and 38 connected by a centrally disposed opening 40. 
The recess 36 extends inwardly from the forward face 
of the anode 28, while the recess 38 extends inwardly 
from the face of the boss 30. The opening 40 is in sub- 
stantial alignment with the bore 18 in the housing 12. 
The anode 26 has a base mounted in the recess 38 in 
the boss 30 by suitable screws (not shown), and the 
anode extends into the bore 22 in the housing 12. A 
sealing ring 42 is positioned between the anode 26 and 
the wall of the bore 22. The outermost surface of the 
65 anode 26 engages the end face of a tubular refractory 
insulator 44 positioned in the bore 22. 
A cathode 46 has a base threadably mounted on a 
hollow support 48 carried by a base 50 secured to the 
60 
4,990,739 
3 4 
rear face 16. The support 48 protrudes from the base 50 Experimental work with the gun 10 has shown that 
into the housing 12 along the axial bore 18. Suitable zirconia grains plasma sprayed with the gun after opti- 
sealing rings 52 and 54 are provided between the sup- mization of the arc were melted at considerably lower 
port 48 and housing 12 in the bore 18. input levels when compared with commercially avail- 
As shown in the drawing, the support 48 extends 5 able guns. This is illustrated by the 200 magnification 
through the axial bore 18 into the enlarged bore 22. The photomicrographs in FIGS. 3 and 4. The input power 
support 48 further extends into the bore of the refrac- to each gun was 20KW while the arc gas flow was 60 
tory insulator 44. SLM. The zirconia powder was fed to each gun at a 
The tubular refractory insulator 44 is inserted into the rate of 50 grams/minute. 
bore 22 in the housing 12 prior to mounting on the 10 While the preferred embodiment of the invention has 
anode 26. A groove 56 machined or  cast in the outer been described, it will be appreciated that various struc- 
peripheral surface of the refractory insulator 44 forms tural modifications can be made to the arc plasma gun 
an annular chamber for receiving an ionizable gas from without departing from the spirit of the invention and 
a paswge 58 in the housing 12 that is connected to a the scope of the subjoined claims. By way of example, it  
suitable source 60. A plurality of passages 62 extend 15 is contemplated that the manual cathode adjustment 
from the inner surface of the refractory insulator 44 to mechanism of this embodiment may be replaced with a 
this chamber to form a gas ring around the cathode 46. remote control. 
'The temperature of &e p l i m a  gun 10 is controlled 
by a suitable cooling fluid which passes through the 
various components from a supply line 64 to a discharge 2o 
line 66 as shown in FIGS. 1 and 2. The cooling fluid 
from the supply line 64 enters a circular chamber 68 in 
the anode base 28 and flows into the recess 20 through 
passages 69. This fluid then flows through a plurality of 
passages 70 into the chamber 24 which surrounds the 25 
cathode support 48. 
An interior chamber 72 in the cathode support 48 is in 
communication with the chamber 24 through a plurality 
of passages 74. The cooling fluid then flows from the 
chamber 72 into another cooling chamber 76 in the 
cathode base 50 through passages 78. This cooling fluid 30 
is then discharged through the line 66. 
In operation, the flow of cooling fluid is started and 
arc gas flow is started through the passage 58. A DC 
potentia1.k established between the cathode 46 and a 
conical surface 80 on the interior of the anode 26. The 35  
ring of passages 62 supplies the ionizable gas to this 
charged space between the cathode and anode to form 
a plasma jet which extends through a central bore 82 in 
the tip anode 26 to the aligned opening 40. 
of a centrally disposed passage 84 that extends axially 
through the cathode 46 and its support 48. This passage 
84 is placed in communication with.a suitable source 86 
of ceramic powders. These particles are carried by a gas 
and are injected into the plasma jet by way of this coax- 45 
ial passage 84 so that the particles are injected coaxially 
into the central portion of the plasma jet. This coaxial 
injection results in a more uniform and higher tempera- 
' ture of the sprayed particles. This improved injection 
causes the particles to achieve higher and more uniform 50 
velocity. 
At the same time, the length of the path of the parti- 
cles in the plasma jet is increased, In addition, the feed 
gas from the ring of passages 60 acts as a coolant for the 
Another feature of the invention is the novel mount- 
An important feature of the invention is the provision 4o 
cathode 46, thus extending its life. 55  
I claim: 
1. An arc plasma gun comprising, 
a housing in the form of an elongated insulator having 
oppositely disposed end faces and an axial bore 
forming a chamber extending therethrough be- 
tween a forward end face and a rear end face, said 
chamber having a forward portion adjacent to said 
forward end face having a major diameter and a 
rear portion adjacent to said rear end face having a 
smaller diameter. 
an anode having an opening therein, 
a metal base mounted on said forward end face, said 
base having a rearwardly facing boss extending 
into said forward portion of said axial bore for 
mounting said anode with said opening in substan- 
tial alignment with said chamber, 
an elongated cathode assembly extending into said 
chamber from the rear and face of said housing 
toward said anode whereby an arc may be gener- 
ated, said cathode assembly comprising 
a base portion adjacent to said rear end face, 
an elongated body portion extending from said base 
portion through said rear portion of said chamber 
into said forward portion, and 
a cathode mounted on an end of said body portion 
opposite said base portion, 
at least one passage in said housing in communication 
with a source of ionizable gas for supplying the 
same to said anode and cathode to maintain an arc, 
a bore extending through said cathode in communica- 
tion with a source of ceramic powders in a feed gas 
for feeding said powders to said arc, and 
a plurality of threaded members extending from said 
rear end face for operable engagement with said 
base portion of said cathode assembly whereby said 
elongated body portion and said cathode are selec- 
tively moved in said axial bore toward and away 
from said anode for optimizing the performance of 
said gun. 
2. An arc plasma gun as claimed in claim 1 including 
ing of the base 50 of the cathode 46 on the housing 12 so 
that the spacing between the cathode 46 and the anode 
26 is adjustable. This novel mounting provides for opti- 
mization of the performance or efficiency of the gun 10 
for a given set of gun operating parameters such as 
power input, arc gas flow, feed gas flow, powder feed 
rate, and particular material being sprayed. 
More particularly, a plurality of studs 88 extend from 
the rear face 16 of the housing 12 through the base 50 of 
the cathode. Axial movement of the cathode 46 is ac- 
complished by adjusting a plurality of nuts 90 on the 
studs 88. 
a conical surface on the interior of said anode facing the 
outermost end portion of said cathode in said forward 
portion of said axial bore. 
3. An arc plasma gun as claimed in claim 2 including 
a refractory insulating member mounted in said housing 
in said forward portion of said axial bore for enclosing 
said conical interior surface of said anode and said cath- 
ode. 
4. An arc plasma gun as claimed in claim 3 including 
means in said refractory insulating member for forming 
a ring of ionizable gas around said arc. 
60 
65 
* * * * *  


Plasma gun with coaxial powder feed and adjustable cathode

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