Note: Descriptions are shown in the official language in which they were submitted.
B~CKGROUND 0~ '~HE INVE~TTION
1. ~ield of the Invention
The presen,J invention relates ~-o plasma e~gineering
and more particularly it comprehends an arc plasma generator
and a plas~a arc apparatus for treating the surfaces of
v~ork~pieces l~corporatin~ the same arc plasma generator.-
The inve~tion may prove most advantageous in surfacing,cleaninO and etching metal surfaces in vacuum. Specifically,
vacuum condensation of the plasma of metals is used to
produce antifriction, corrosion-resistant, abrasion-resistant,
~eat-resis~ant, superconducting, optical" and other coatings.
2. ~escription of the Prior Art
Heretofcre attempts to treat the metal surfaces havi~
the rou~hness height from 0. 02~ to 0.5 ~ m b~ pla~a strea~s
produced by the arc plasma generators have failed to re~ain
~he roughness number of the surfaces. q'his is due 'o the
presence ol an appreciable number of macroparticles - dro~lets
and solid fra~ments of the cathode material - in ~he plas~a
stream genera~ed by the cathode spot. Apart from worsening
~he surface finish of the coatin~s applied by the plasma
technique the macroparticles give rise to punctures ~nd
b~ild-up portions in the condensates to thereby degrade
mechanical, electrical, optical and other properties of the
coatings and in practice the expected ad~antages of
applying v~rious coatings are not gained in full (resista~ce -
to wcar, supe~ior antifriction and corrosion-resist~nt pro-
perties, etc.).
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I~nowll in -the art is an arc plasma generator disclosed
in US Patent No 35625~848. ~his generator comprises a
consumable cathode arranved inside the anode in axial
a'ignrlent therewith, a means ~or exciting an arc between
the cathode and the anode (ignition means), and a power
unit ~or maintaini~g -the arc electrically connected to the
anode and the cathode. ~he ignition means initiates an
arc discharge between -the cathode and the anode. ~he cathode
generates a plasma comprising atoms and ions of the cathode
rl.aterial. ~s has alread~T been stated the plasma stream
contains an appreciable number o~ macroparticles - droplets
and solid ~ragmen-ts of the cathode material - ~uhich are
undeslrable since they impair the ~uality of the coatings.
~ he macroparticles in the plasma stream are the result
of a local and the general superheati~g o~ the active sur~ace
of the ca-thode by such a powerful and concentrated thermal
source as -the cathode spot is (the spot's temperature is
several thousand degrees, current density is as great
as from about 106 to about 107 A/cm2).
~ nown in the art is also an arc plasma generator
(~.S.Gilmour, D~ ochwood, Pulsed metallic-plasma genera-
tors. Proc. GEE~ vol. 60, ~o 8, 1972, p.977) comprisi~g a
consumaDle cathode arranged coaxially with a cylindrical
anode, an igniting electrode for initiating an arc between
the cathode and -the anode connected to an ignitiDg pulse
generator, and a pov~er unit for maintaining the arc. ~he
arc plasma generator fur-ther comprises a focusing solenoid
arra~ged on the anode.
~~he arc plasma ge~erator is put into operation bJ
appl~in$ a fî~ing pulse tG the igniti~g electrod~ with a
raquency OL the order oP a -Pew tens of Hertz. The plas~a
stream is generated a-t the same frequency as soon as a
pulsed arG discharge between the anode and the ca-thode is
ixcited. ~he macroparticles in the metallic plasma present
a problem ~it~ this arc plasma generator. The direction o-P
the velocity vector oF the charged components of the s~ream
can be varied by turning the axîs of the focusing solenoid
through an an~le with respect to the axis of the system. In
-this case a number o~ macroparticles are removed ~rom -the
plasma s-tream as a result of a certain separation of the
streams of macroparticles and charged components (ions and
electrons) in space. However, the prior art generator does
not e~clude all the macroparticles ~rom reaching the generator
outlet and, conse~uently, from hi-tting a substrate since the
ran~e o~ turnir~ the ~ocusing solenoid (15 and up) makes
the s~Jstem transparent from the cathode to -the generator
outlet for the macropar-ticles rus~ir~ in the same direc-tion.
S~ARY 0~ TIIE I~VE~TIO~
A ~eneral object o~ the inven-tion is to provide an
arc plasma generator and a plasma arc apparatus for
~reating the surfaces of work-pieces, incorporating the same
arc plasma generator wherein the electromagnetic system
is so constructed that by separating in space the components
of the plasma stream in a ma~7netic field an efPective removal
of macroparticles from the plasma stream is achieved.
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~ hese and other objects of the invention are accomplished
by an arc plas~a ~enerator comprisin2 a consumable cathode,
a cylindrical anode, and a Docusing solenoid bo~h arra~ed
co~xially -~vith the con~umable cathode, and a power unit for
main~ai~ln~ the arc electrically connected to the consumable
cathoQe and the anode 3 wherein according to the in~ention
there is a tubular plasma guide connected to an end face
OL ~he anode as v~ell as an electroma~net arranged in the
tu~ular plasma gu~de on the a~is thereof and enclosed in
a housing made of a nonma~netic material and havinO a cross-
-~ecJional area s-~fficient to conceal the cathode from the
v~ev)~r's sight, looking in the direction of thé cathode
throush the plasma guide, ~3hereas the focusing solenoid
is arra~ed on the tubular plasma guide and is connec~ed
in opposit on with the coil of the electroma~net.
In such an arranvement the macroparticles fly apart
from the end face of the cathode to stri~e against-the
alls of the ~ousiPg of the electrom~gnet or those of -the
~las~a guide and will never reach the outlet of the ~enerator.
The char~ed components of the ~lasma stream (ions and
elec~ro~s) follow the path alo~g the lines of force of the
magnetic Iield induced by the focusin3 sole~oid and the
electromagnet, both bei~g connected in opposition to each
o~her, to fly round the electromagnet and easily reach the
outle~ of the generator. ~herefore the ou~let plasma is
co~pletely free of any macroparticles and can be used, by
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~7~59~
USi1~ SUC~ a ~enerator~ for treating the sur~aces ol work-
-l~ieCeS (to apply coatin~s, to ractice a plasrr~a cleaning
and ionic etchin~) withou-t ag~ra~ati~ -their surface finish
o~ rou~hness heir~ht not exceedi~g 0.025 to ~.05 ~m.
lt is pr~lerred -to insulate -the plasma guide ~rorr~
the anode by rneans o~ an insulating liner, which feature
makes fox an increase in the efliciency o~ plasma stream
passing throuOh the plasma guide.
Charged particles are known to ~ollow the magnetic lines
of i`orce only when the ~armor radius o~ the particle is
small as compared with the sys-tem dimensions. ~he ions
o~ the majori-ty of metals emit-ted from the cathode spot
in a vacuum have the energy of some tens of electron volts.
'~herefore these ions can pass through -the generator of the
invention having a giap of 10 cm between the plasrna guide
and the housing o~ the electromagnet only when the magnetic
~ield strength is several kilo-oersteds. ~ormally such magnetic
f'ields are difficult to induce. However, when the magne-tic
system is I'illed with a vacuum plasma this difficulty is
rernoved since passin~ of -the ion component throu~h the
~enerator OL the invention in this case is possible with a
substan-tially lower magnetizing force, which is only SULD-
~icient to magnetize the io~s of -the plasma. In this case
the electron conduction in the plasma, while being retained
alon~ theA rnaænetic lines o~ force, is sharply decreased
la~e ally. 'l'he electric field passes throu~h the plasma.
T'ne electric field in the system is induced by electron
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t:; ri~
potelltials when the electrons are crossed b~ ma~netic lines
o~ force. ~s tnis takes place the magnetic lines o- fo~ce
acquire the potential of the electrodes or o~ the walls
oli the sys-te~ which they cross. ~hus~ when the plasma guide
is at posi~ive potential rela-tive the cathode there is an
electric field induced in the plasma flow and directed to
i~s axis. '~his field provides for constriction (focusing)
OL the plasma flow to decrease posi-tive-ion loss on the
walls of uhe ~lasma ~ruide and -to increase the number of
ions a-t the outlet~i.e., the ions that have passed the
annular ~a`p between the ?lasma guide and the electromaOnet.
With a di~lectric liner between the plasma guide and the
anode due to high-velocity ion bombardment the plasma ~uide
acquires a higher po-uential -~han does the anode~ '~he electric
field near the walls of the plasma guide becomes stronger
ar.d the plasma flow along the plasma guide beco~les more
effec-tive.
In order to avoid passage of macroparticles that rebound
~rom the walls of -the plasma guide to the ou-tlet thereof
it is advi~able that the inner sur~ace of the tubular plasma
~uide be provided wi-th ribs extendin~ at an an~le to an
expected flow of plasma.
It is desirable to construct -the electroma~net arran~ed
in -t~e plasma guide so -that it has an axially streamlined
form and the ~ousing has a similar form. '~his facilitates
en-try of the plas~a flow in-to an annular ~ap `~etween the
plasma ~uide and the electromagnet and, consequently, increases
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5~g
~ile .lolv o~ rpla-?na at the ou-tlet of the genera-~orO
li prcl`crred ~oLIm oP -the hOUSil~ and inneL solenoid
is that ol` a cone or two cones abuttin3 each other on the-r
bases.
lt is also desirable -tha~ -the ~um~er OL turns per unit
ler,^O~ll o the focusing solenoid on the tubular plasma
,uide oehind the electroma~net in the direction o~ an expected
rlow o~ plasma be greater than on the remaining portion
OL vhe plasma ~uide n'his enables focusing of the outcom-Lng
plas;na Ilow, resul~s i~ higher densit~ and, conse~uently7
makes ~or an increase in -the rate of applying coatings.
~ o the accomplishment o~ the ~oregoing and related ends
the invention also consists in the provision of a plasma
arc appara~us for t~eating the surfaces of work-pieces7
comprising an arc plasma genera-tor and an assembly for holdin~
-the ~Jork-~iece to be treated, wherein according to the in-
vention the arc plasma generator is constructed according
to any one o~ the above claims, -the assembly for hold-
ing the work piece is a cover fixed on an unsupported end
face o~ the plasma guidel made o~ a nonmagnetic material
and having an opening fox holdin~ -the work-piece to be
trea-ted, and a disk coil attached to the cover and connected
in an aiding manner ~th the focusing solenoid.
As used herein the term "disk coil" means a coil whose
radial dimension is greater than the longitudinal (a~ial)
dimensîon. ~he ~ork-piece is to be held on the axis of the
generator betv~een the cover and the ho~sing o-f the electro-
magnet. ~agnetic lines of force, in this case, make sharo
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be~ds before the cover to approach the gene~ator axisthat is why the plasma flow is also direc-ted toward -the
axis oi the generator ~ollowil~g its passage through the
anrlular gap between the plasma guide and -the housing of the
electromaOnet to thereby s-trike the side surfaces of the
~ork-piece. ~his obviates the need -to axially rotate tne
work-piece, which technique provides for a consiaerable simpli-
fication of the generator construction takinO into account a
forced cooling of the work-piece and applying a high current
to it as it is su~jected to ionic cleaning and surfaciL~g.
Since the work-piece is stationary taking temperature is
also simplified as the work-piece is being subjected to sur-
facing.
B:RIE~ )ESCRIP~rI ON Ol~ r~l~ DR~iVJINGS
~ he invention will be described further, by way of
example, with reference to the accompanying drawings, of
which: -
~ ig. 1 is a diagrammatical view o~ an arc plasma gene-
rator of the inven-tion shown in an axial section;
~ ig. 2 is a diagram showing fundamentals of separation
of the components in a plasma flow as it takes place in the
generator of the inven-tion~
~ ig. 3 is a diagrammatical view, in longitudinal sec-
tion, of a portion of a plasma arc apparatus for treating
-the surfaces of work-~ieces, incorporating the arc plasma
generator of the invention.
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~'~SCRIP~IOl~ OF mI~ P~EF~R~ D Ei~JI~ODII~T
L~e~errinO to ~ig~ 1 of the accor,lpanying drawi~rs~ an
a,~c l)lasma genera~or comprises a consumable cathode 1 having
the form of a cylinder with a 60 mm diameter~ the dimensions
bein~ in~ica-ted fcr purposes of illustration only, and made
o~ a plasma forming ma-terial, for example, titan of Graae
~T-1, a cylindrical anode 2, which may have the form of a cup
VJith a ce~urally disposed opening in its bottom for axiall~
mou~ti~g the cathode 1 inside the anode 2 (the anoda is
2~ mm long and of 26~ mm in diameter).
The unsupported end face of the anode 2 carries a tubular
plasma ~uide 3 attached thereto, having a 36~ mm len~th
and a 26~ mm diametcr, and made of a nonma~netic steel.
To make the flow of plasma through the plasma ~uide 3
more effecti~e an insulating liner ~ is placed between the
plasma guide 3 and the anode 2 (the liner is made, e.g. of
an acrylic plastic). In this case due to a bombardment of
the plasma guide by the highest velocit~ ions the plasma
guide ac~uires a higher potential than does the anode. ~he
electric ~ield near the walls of the plasma guide becomes
s-tro~er and the plasma flow along the plasma ~uide becomes
more e~fective.
It is desirable that the inner surface of the plasma
guide 3 be provided with ribs 5 extending at an angle
to an expected flow of plasma. ~his makes it possible to
avoid passage o~ macroparticles that rebound from t~e walls
oi the plasma guide 3 to -the outlet thereof. The most accep-
table are the ribs made in the form of rinOs arranged one
~ 17t~X~3
a~er ano-tller in parallel plancs ~Jhich are perpendicular
to the axis oD the plasma ~uide 3.
'~rithin the plasma guide ~ and axially with it there
is arranæed an electromaOnet 6 which.is enclosed in a 'nousing
7 made o~ a nonma~netic s~eel.
'~hc electromagnet 6 and the housing 7 ma~ have a cylindri-
cal -form as in ~ig. 2, but a streamlined form, for exa~ple
conical, is preferred (not shown), it may well be composed
oi two cones (~ig. 1) a~u-tting each o-ther on their bases
(the base diame-ter is 10~ mm and the heigh-t of each cone
is 18~ mm). ~ests have shown that such form o~ the electromag-
net facilita~es en~ry o~ -the plasma flow into an an~ular
gap bet~Jeen the plasma guide 3 and the electroma~net 6 and~
consequen-tly, increases the flow o~ plasma a-t the outlet
of the generator~
A distance from the end face at the outlet of the
plasma guide ~ ~o the cen-ter of -the housi~g 7 is 175 mm.
'~ith this specific construc-tion and with the dimensions
specified in the plasma guide 3, the housing 7, the cathode
1 and their relative position the housing 7 has a cross-
-sectional area sulD~icient to conceal the cathode from
the viewer's sight, looking in the direction o~ the cat~ode
through the plasma guide 3.
~ he housing 7 is held in position by means of a hollow
prop 8 through which electric current is supplied -to -the
coil of the elec-tromagnet 6 via leads 9.
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~ he cathode 1, the anode 2, the plas~a guide 3, and
the electroma2net 6 are water cooled (-the cooli~g system
not shown).
An ignition elec-trode 11 having the form of a rod,
wiiich may be made of molibdenum, abuts the side surface
o~ the cathode 1 through a ceramic connecting strip 10.
~ eference numerals.12 and 13 in Fig. 1 designate leads
~or supplying ignition pulses to the spar~ gap be-tween the
cathode 1 and the ignition electrode 11 from an ignition
pulse generator 14.
It is to be appreciated that the arc between the anode
and the cathode can be ignited by any conventional means
other than that specified. A power unit 15 ~or maintaining
the arc has one of i~s terminals connected to -the consumable
cathode 1, and the other o~e to the anode 2. ~he leads 12,
13 are passed into the anode 2 through openings in the bo~tom
of the anode 2 and through vacuum-tight dielectric seals 16.
~ he plasma guide 3 is encornpassed by a focusing solenoid
17. It is desirable herewith tha-t the number of turns per
unit leng-th o~ the focusing solenoid 17 on the tubular
plasma guide 3 behind the electromagnet 6 be greater than
on the remaining portion thereof. ~his enables the most
effective focusing o~ the outcomin~ plasma flow, results
in higher density and, consequently, makes for an increase
in the rate o~ applying coatings if the generator is used
~or surfacing work-pieces.
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9~
~ e~erence numc~al 18 designates a work-piece -GO be
treated (~igs 2 and 3). ~i~. 3 shows a plasma are apparatus
for treating the sur~aces of work-pieces, comprisin~ the above-
described arc plasma generator and an assembly for holdi~
the work-piece to be -treated in the form of a cover 19 made
ol a nonmagne~tic steel and attached to the end of the plasma
guide 3. ~he cover has on its outer side a disk coil 20
of a 260 mm diameter and 60 mm -thick, which is connected
in an aidi~ ~anner with the focusing solenoid~ In this
case a base carrier 22 is received in the plasma guide 4
through the central opening 19 and an insulator 21.
In operation, power sources (not shown) for ~eeding
the Yocusing solenoid 17 a~d the electromagnet 6 are switched
on and an electric ~ield is induced to have the lines of
force pattern as shown by dotted lines in ~ig. 2.
The power uni-t 15 and-the pulse generator 14 are a~so
switched on. With a high-voltage ignition pulse supplied to
the ignition electrode 11 a spark discharge appears in the
gap between the electrode 11 and the cathode 1 over the
ceramic connecting strip 10. The spark discharge initiates
an arc discharge be-tween the cathode 1 and the anode ~
and a cathode spot appears on the e~fective sur~ace 23 of
the cathode 1j which cathode spot genera-tes a flow of plas~a
o~ the material of the cathode 1. ~he ions a~d the electrons
contained in the plasma flow follow the magnetic lines o~
orce pas-t the housi~g 7 o~ the electromagnet 6 and through
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the outlet portion of the plasma ~uide ~ reach t'ne sur~ace
ol the work-piece 18. Arrows in Fi3. 2 show the direction
o~ the charged components of the plasma flow (ions and
electrons).
Neu-tral vapor and the macroparticles follow the strai~ht-
line path(dash-and-dot lines in Fig. 2) and adhere to the
surfaces of the plasma guide 3 and the housing 7. Therefore
at the outlet of the generator and, consequently, close
to the surface of the work 18 -the plasma flow is free of
the macroparticles.
In the case of -treating the outer surfaces of -the bodies
of revolution the disk coil 2~ deflects the magnetic lines
of ~orce toward the work sur~ace (do~ted lines in Fig. 3),
That is why the ionized component of the plasma flow is
also deflected toward -the system axis and reaches the work
surface. The macroparticles are screened from passage onto
the work surface by the housing 7.
~ hough the invention has been described herein by way
of preferred embodiments thereof other forms are possible
within the scope of the appended claims.
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