CA1176599A - Arc plasma generator and a plasma arc apparatus for treating the surfaces of work-pieces incorporating the same arc plasma generator - Google Patents
Arc plasma generator and a plasma arc apparatus for treating the surfaces of work-pieces incorporating the same arc plasma generatorInfo
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- CA1176599A CA1176599A CA000400130A CA400130A CA1176599A CA 1176599 A CA1176599 A CA 1176599A CA 000400130 A CA000400130 A CA 000400130A CA 400130 A CA400130 A CA 400130A CA 1176599 A CA1176599 A CA 1176599A
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- plasma
- arc
- cathode
- electromagnet
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Abstract
ABSTRACT OF THE DISCLOSURE
An arc plasma generator comprises a consumable cathode, a cylindrical anode, and a focusing solenoid arranged coaxially with the consumable cathode. A power unit for maintaining the arc is electrically connected to the con-sumable cathode and the anode. In accordance with the in-vention the arc plasma generator further comprises a tubular plasma guide connected to an end face of the anode and an electromagnet. The electromagnet is arranged in the tubular plasma guide on the axis thereof and is enclosed in a housing made of a nonmagnetic material and having a cross-sectional area sufficient to conceal the cathode from the viewer's sight, looking in the direction of the cathode through the plasma guide. Also, the focusing solenoid is arranged on the tubular plasma guide and is connected in opposition with the coil of the electromagnet. A plasma arc apparatus for treating the surfaces of work-pieces comprises an arc plasma generator of the invention and an assembly for holding the work-piece to be treated. The assembly is a cover having a centrally-disposed opening. The cover is fixed on the end face of the plasma guide. The apparatus is also provided with a disk coil attached to the cover and connected in an aiding manner with the focusing solenoid. The invention provides for an effective removal of macroparticles from the plasma flow to improve the treatment of the surfaces of work-pieces.
An arc plasma generator comprises a consumable cathode, a cylindrical anode, and a focusing solenoid arranged coaxially with the consumable cathode. A power unit for maintaining the arc is electrically connected to the con-sumable cathode and the anode. In accordance with the in-vention the arc plasma generator further comprises a tubular plasma guide connected to an end face of the anode and an electromagnet. The electromagnet is arranged in the tubular plasma guide on the axis thereof and is enclosed in a housing made of a nonmagnetic material and having a cross-sectional area sufficient to conceal the cathode from the viewer's sight, looking in the direction of the cathode through the plasma guide. Also, the focusing solenoid is arranged on the tubular plasma guide and is connected in opposition with the coil of the electromagnet. A plasma arc apparatus for treating the surfaces of work-pieces comprises an arc plasma generator of the invention and an assembly for holding the work-piece to be treated. The assembly is a cover having a centrally-disposed opening. The cover is fixed on the end face of the plasma guide. The apparatus is also provided with a disk coil attached to the cover and connected in an aiding manner with the focusing solenoid. The invention provides for an effective removal of macroparticles from the plasma flow to improve the treatment of the surfaces of work-pieces.
Description
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.
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.).
~ 7~ 5~ ~
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.
~ 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 _5_- .
~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 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 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 ~'7~ 5~ g 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.
_9_ ~'~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.
~ 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.
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 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.
~14-
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.).
~ 7~ 5~ ~
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.
~ 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 _5_- .
~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 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 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 ~'7~ 5~ g 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.
_9_ ~'~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.
~ 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.
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 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.
~14-
Claims (8)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS
FOLLOWS:
1. An arc plasma generator comprising:
- a consumable cathode having the form of a cylinder of a smaller diameter and made of a plasma forming material;
- an anode having the form of a cylinder of a greater diameter, arranged coaxially with said consumable cathode and electrically connected thereto;
- a power unit for maintaining the arc, forming said electrical connection between said consu-mable cathode and said anode and having there-fore at least two terminals, one of which being connected to said consumable cathode and the other to the anode, - a tubular plasma guide connected with one of its end faces to an end face of said anode, - an electromagnet arranged in said tubular plasma guide and coaxially therewith, a housing for said electromagnet made of a non-magnetic material, enclosing the electromagnet and having a cross-sectional area sufficient to conceal the cathode from the viewer's sight, looking in the direction of the cathode through the plasma guide, and - a focusing solenoid disposed about said tubular plasma guide and connected in opposition with the coil of the electromagnet.
- a consumable cathode having the form of a cylinder of a smaller diameter and made of a plasma forming material;
- an anode having the form of a cylinder of a greater diameter, arranged coaxially with said consumable cathode and electrically connected thereto;
- a power unit for maintaining the arc, forming said electrical connection between said consu-mable cathode and said anode and having there-fore at least two terminals, one of which being connected to said consumable cathode and the other to the anode, - a tubular plasma guide connected with one of its end faces to an end face of said anode, - an electromagnet arranged in said tubular plasma guide and coaxially therewith, a housing for said electromagnet made of a non-magnetic material, enclosing the electromagnet and having a cross-sectional area sufficient to conceal the cathode from the viewer's sight, looking in the direction of the cathode through the plasma guide, and - a focusing solenoid disposed about said tubular plasma guide and connected in opposition with the coil of the electromagnet.
2. An arc plasma generator as set forth in claim 1 wherein an insulating liner is placed between said tubular plasma guide and said anode.
3. An arc plasma generator as set forth in claim 1 wherein the inner surface of said tubular plasma guide is provided with ribs extending at an angle to an expected flow of plasma.
4. An arc plasma generator as set forth in claim 1 wherein said electromagnet has an axially streamlined form and said housing has a similar form.
5. An arc plasma generator as set forth in claim 4 wherein said electromagnet has the form of a cone whose vertex is facing said consumable cathode.
6. An arc plasma generator as set forth in claim 4 wherein said electromagnet has the form of two cones abutting each other on their bases.
7. An arc plasma generator as set forth in claim 1 wherein the number of turns per unit length of said fo-cusing solenoid on said tubular plasma guide behind said electromagnet in the direction of an expected flow of plasma is greater than on the remaining portion thereof.
8. A plasma arc apparatus for treating the surfaces of work-pieces, comprising an arc plasma generator of claim 1, an assembly for holding the work-piece to be treated, constructed as a cover fixed on an unsupported end face of said plasma guide, made of a nonmagnetic material and having an opening for holding the work piece to be treated, and a disk coil attached to said cover and connected in an aiding manner with the focusing solenoid.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000400130A CA1176599A (en) | 1982-03-31 | 1982-03-31 | Arc plasma generator and a plasma arc apparatus for treating the surfaces of work-pieces incorporating the same arc plasma generator |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000400130A CA1176599A (en) | 1982-03-31 | 1982-03-31 | Arc plasma generator and a plasma arc apparatus for treating the surfaces of work-pieces incorporating the same arc plasma generator |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1176599A true CA1176599A (en) | 1984-10-23 |
Family
ID=4122476
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000400130A Expired CA1176599A (en) | 1982-03-31 | 1982-03-31 | Arc plasma generator and a plasma arc apparatus for treating the surfaces of work-pieces incorporating the same arc plasma generator |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1176599A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN106880401A (en) * | 2017-03-28 | 2017-06-23 | 成都美创医疗科技股份有限公司 | A kind of plasma debridement surgical knife |
-
1982
- 1982-03-31 CA CA000400130A patent/CA1176599A/en not_active Expired
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN106880401A (en) * | 2017-03-28 | 2017-06-23 | 成都美创医疗科技股份有限公司 | A kind of plasma debridement surgical knife |
| CN106880401B (en) * | 2017-03-28 | 2023-05-26 | 成都美创医疗科技股份有限公司 | Plasma debridement scalpel |
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