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Publication numberUS3313908 A
Publication typeGrant
Publication dateApr 11, 1967
Filing dateAug 18, 1966
Priority dateAug 18, 1966
Publication numberUS 3313908 A, US 3313908A, US-A-3313908, US3313908 A, US3313908A
InventorsByram Robert F, Robert Unger
Original AssigneeGiannini Scient Corp
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Electrical plasma-torch apparatus and method for applying coatings onto substrates
US 3313908 A
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Description  (OCR text may contain errors)

April 11, 1967 R. UNGER ETAL ELECTRICAL PLASMA-TORCH APPARATUS AND METHOD FOR APPLYING COATINGS ONTO SUBSTRATES Original Filed April 14, 1965 3 Sheets-Sheet 1 FIG.3A

I N VIEN'I'ORS.

(/NGEIQ 2055B 7' 205527 F: BYE/4M April 11, 1967 R. UNGER ETAL 3,313,908

ELECTRICAL PLASMA-TORCH APPARATUS AND METHOD FOR APPLYING COATINGS ONTO SUBSTRATES Original Filed April 14, 1965 3 Sheets-Sheet 2 FIG.3 Q 755%" CUEIQEN T INVENTORS. SOMQCE 2055/2 7 (W952 205.52 r E B e/2M A7 TO/Q/VEYS' A April 11, 1967 R. UNGER ETAL 13,908

ELECTRICAL PLASMA-TORCH APPARATUS METHOD FOR A LYING v COATINGS ONTO SUBS TES Original Filed April 14, 1965 3 Sheets-Sheet 5 INVENTORS. 205527 (/NGEE ROBE/Q T E B Y/Qfl/W Y Q- Unite States atent 3,313,998 Patented Apr. 11, 1967 Free ELECTRICAL PLASMA-TORCH APPARATUS AND METHOD FOR APPLYING COATINGS ONTO SUBSTRATES Robert Unger, Dana Point, and Robert F. Byram, Santa Ana, Califi, assignors to Giannini Scientific Corporation, Amityville, N.Y., a corporation of Delaware Continuation of abandoned application Ser. No. 448,065, Apr. 14, 1965. This application Aug. 18, 1966, Ser. No. 573,431

18 Claims. (Cl. 219-76) The present patent application is a continuation of copending application Serial No. 448,065, filed April 14, 1965, for Electrical Plasma-Torch Apparatus and Method for Applying Coatings Onto Substrates, now abandoned.

This invention relates to a plasma-torch apparatus and method for creating extremely high particle velocities and thereby depositing superior-quality metal and/ or ceramic coatings on substrates of various types. The invention further relates to a plasma torch incorporating improved arc [gas-introduction means, improved electrodes of the insert type, and improved cooling means.

A primary object of the present invention is to provide an apparatus and method for effectively and efiiciently adhering coatings onto substrates, such coatings being characterized by a high degree of density, smoothness and other desirable characteristics.

A further object is to provide a method of eifecting high-velocity spraying of particles of metals and ceramics onto substrates, in a manner achieving'numerous important results including effective collimation of the jet, minimum loss and wastage of powder, high deposition rates and efficiencies, absence of undesired chemical effects, smooth coating surfaces, high coating density, and superior adherence to the substrate.

An additional object is to provide a plasma-torch apparatus and method which may be readily adapted for optimum operation relative to either ceramic spray or metal spray.

Another object is to provide a plasma-torch apparatus and method wherein the arc gas is introduced in different ways in accordance with whether such gas is monatomic or diatomic, both ways producing a swirl or vortex action, and both achieving benefits including increased electrode life.

A further object is to provide an electrical plasma-jet torch having front and rear electrodes formed as inserts which are inexpensive to manufacture and use, and which may be replaced in a very short period of time.

Another object is to provide a plasma torch incorporating an improved water-circulating system effecting a better degree of cooling of the electrodes and other-torch components.

Another object is to provide a high-velocity powder spray apparatus and method wherein a cover-gas shield is employed in conjunction with the nozzle element to effect improved collimation of the jet, in addition to achieving benefits such as prevention of undesired (or creation of desired) chemical eifects, cooling of the workpiece, and removal of any loosely-adherent spray particles.

These and other objects will become apparent from the following detailed description taken in connection with the accompanying drawings in which:

FIGURE 1 is a side elevational view illustrating the plasma torch of the invention as employed in spray-depositing a coating onto a substrate, and showing various gas and powder sources in schematic form;

FIGURE 2 is an enlarged elevational view showing the front end of the torch, looking upwardly in the showing of FIGURE 1;

FIGURE 3 is a longitudinal central sectional view taken on line 33 of FIGURE 2;

FIGURE 3A is a longitudinal form of nozzle insert;

FIGURE 4 is a transverse sectional view on line 4-4 of FIGURE 3;

FIGURE 5 is a transverse sectional view on line 55 of FIGURE 3;

FIGURE 6 is a sectional view, on line 66 of FIG- URE 3, illustrating the arc gas inlet means which is employed for monatomic gases;

FIGURE 7 is a sectional View, on line 77 of FIG- URE 3, showing the arc gas inlet means which is employed for diatomic gasses; and

FIGURE 8 is a sectional view schematically indicating a powder feed mechanism employed in the present method and apparatus.

Proceeding first to a description of the entire apparatus the electrical plasma torch is illustrated to comprise an insulating handle and easing 1d the lower portion of which is adapted to be gripped by the operator, and the upper portion of which is adapted to contain various housing and electrode elements next to be described. One such element contained within the upper portion of insultating handle 10 comprises a cup-shaped insulating body l l, formed of a phenolic or other suitable substance, such body being suitably grooved at the peripheral portions thereof to receive the rims of generally cup-shaped rear and front housing elements 12 and 13, respectively. Such housing elements, and the remaining portions of the torch (excepting for the seals, and unless otherwise noted), are formed of copper, brass, tungsten, or other suitable metals.

The rear housing element 12 has a central tulbular stem 14 which extends through a corresponding axial opening in the insulating body 11. Inserted into such stem in close-fitting relationship is the cylindrical body of a rear electrode element 16. Such cylindrical body merges through a forwardly-convergent frustoconical portion, and a second and smaller-diameter cylindrical portion, with a generally conical arcing tip section 17 having a rounded forward or apex end. Such arcing tip 17 is disposed in the nozzle passage to be described, whereas the rear electrode sections between the arcing tip and the stem 14 are disposed in a gas-vortex chamber. The vortex chamber is defined by a cup-shaped liner 19 which nests closely in the cup-shaped insulating body 11. The liner is suitable maintained in position as by screws 20'.

Rear electrode element 16 is maintained in position by means of an externally-threaded plug 21 which is seated against the enlarged head or rear end 22 of such element. Plug 21 and head 22 are disposed in an internally-threaded section of hollow stem 14, but only the plug is shown as being threadedly associated with the stem.

The portion of insulating handle and casing 10 axially adjacent plug 21 is provided with an opening 23, so that the plug 21 may be unthreaded (as by inserting a wrench into a hexagonal socket therein) in order to remove the entire rear electrode 16. In the described manner, therefore, the rear electrode may be replaced easily and in a very short period of time. A cover plug, not shown, may be removably mounted in opening 23.

The above-indicated liner 19 for the gas-vortex chamber 18 may be formed of a suitable insulating material such as asbestos cement. The internal wall of such liner is cylindrical and concentric with the axis of the torch apparatus. Provided in the insulating body 11 between the bottom (rear) wall of liner 19 and the bottom wall of the body 11, and around stem 14, is an annulus or counterbore 24.

Defined between the bottom wall of rear housing 12 and the adjacent (radial) wall of body 11 is a coolant sectional view of one 3 chamber 26 through which water or other coolant for the rear electrode is passed as will be described subsequently. The front housing element 13 also defines therein, on opposite sides of a water separator to be described, several coolant chambers adapted to cool the nozzle element and adjacent portions of the torch.

The front and rear housings 13 and 12 face in opposite directions, the rims thereof being seated over annularlygrooved portions of body 11 as previously indicated. Such rims are suitably secured to the body 11, as by screws 27 some of which are indicated in FIGURE 5. Such screws, and cooperating O-rings 28 and 29, effectively maintain the parts in assembled relationship and prevent leakage of water or other coolant from the housmgs.

A powder-injection, cooling and electrode-supporting member 31 is mounted to front housing 13 as by screws 32 (FIGURE 2) which extend through a radial flange 33 of such member. On the forward side of flange 33, and preferably integral therewith, is a relatively large-diameter cylindrical portion 34 of the element 31. Integrally formed on the other side of flange 33 is a relatively smalldiameter cylindrical portion 36 having axially-spaced radial flanges 37 and 38 at the inner end thereof.

The forwardmost of the two flanges 37 and 38 on smalldiameter cylindrical portion 36 is numbered 37. Such flange seats a generally frustoconical hollow water separator or partition 39 which extends outwardly therefrom and seats against the forward face of insulating body 11 adjacent the interior surface of housing 13. Thus, forward and rear coolant chambers 41 and 42 are defined on opposite sides of separator 39, within housing 13 and radially-outwardly of the cylindrical portion 36.

The inner or rearward one 38 of the indicated flanges on portion 36 seats against the forward edge of the liner (or wall member) 19 for the arc chamber 18. Furthermore, such flange 38 engages the interior surface of the cup-shaped body 11. An O-ring 43 provided at such interior surface, and a second O-ring 44 provided around stem 14 and engaging the body 11, insure against leakage of gas from the arc chamber 18.

Provided continuously through both the forward and rear portions 34 and 36 of the powder-injection, cooling and electrode-supporting member 31 is a cylindrical passage or bore 46. A nozzle and front electrode insert 47, having a cylindrical surface, is mounted in such bore 46. The nozzle insert is mounted in close-fitting but removable relationship, being secured by means of the set screw 48 indicated in FIGURE 4. Such set screw 48 is threaded radially through the relatively large-diameter cylindrical section 34 of element 31, and has a conical inner end which seats in a conical recess in the periphery of the nozzle insert 47. The positions of the set screw and recess are such that insert 47 will be maintained in a predetermined desired position within element 31, the position being such that powder-injection passage (to be described hereinafter) will register precisely.

The nozzle and electrode insert member 47 has formed therethrough a plasma and powder passage having a cylindrical forward portion (or bore) 49 and a-frustoconical rear portion 51. Both of such portions are coaxial with chamber 18 and with rear electrode 16. The cylindrical forward portion 49 is relatively long, for purposes to be described. The rear portion 51 is sufficiently large in diameter to receive the conical forward or arcing section 17 of the rear electrode. Such electrode section 17 is much smaller in diameter than is the adjacent region of passage portion 51, so that are gas may flow forwardly and tangentially (helically) from vortex chamber 18 into passage portion 49.

There will next be described the remaining portions of the passages and chambers through which water (or other coolant) is circulated in order to cool effectively the described nozzle insert 47 and also the rear electrode 16..

Water from a suitable source is conducted inwardly through an inlet pipe or conduit 52. which extends through insulating handle 10 and communicates with the abovedescribed chamber 41 on the forward side of water separator 39. From chamber 41, the water circulates forwardly into and through two circumferentially-spaced water passage 53 (FIGURES 3 and 4) in member 31. Such passages 53 communicate with an annular chamber 54 which is formed at the forward end of the large-diameter portion 34 of member 31. Chamber 54, in turn,

communicates with a large number of circumferentiallyspaced water passages 56 (FIGURES 3 and 4), such passages having relatively small diameters and extending longitudinally of the torch and closely adjacent the outer cylindrical wall of nozzle insert 47. Thus, such insert 47 is effectively cooled by the water which flows (in opposite directions) over and through the member 31.

Passages 56 communicate with the above-described chamber 42 on the rear side of separator 39. From such chamber 42, the water flows rearwardly through a substantial number of circumferentially-spaced longitudinal passages 57 (FIGURES 3 and 5) in the insulating body 11. The water is thus conducted to the described chamber 26 at the rear of the torch, and discharges through a water-outlet pipe or conduit 58 in handle 10.

Leakage of water from the coolant circuit is prevented by the previously-indicated O-rings and also by an additional O-ring 59 which is provided bet-ween the radial front face of housing 13 and the adjacent flange 33 of member 31.

Electrical power may be supplied to the torch in any suitable way, but is preferably delivered through the 7 Water inlet and outlet conduits 52 and 58, in order that the power conduits will be water cooled and thus prevented from overheating. For this purpose, the conduits may be formed of metal but, preferably, are formed of flexible insulating material and contain flexible electrical conductors (not shown) in the water passages. As shown in FIGURE 3, a suitable current source 61 is connected through a lead 62 to water-outlet conduit 58, and through a second lead 63 to the water-inlet conduit 52.

Current source 61 is preferably a DO. source adapted to deliver very high currents, the lead 63 being connected to the positive terminal and lead 62 to the negative. Thus, the nozzle insert and electrode 47 is normally the anode, whereas the rear electrode 16 is normally the cathode. It is to be understood, however, that reverse polarities may in some cases be employed, as may alternating current, pulsating current, high-frequency current, combination DC. and superimposed high-frequency current, etc.

The current source 61 operates, after use of a suitable high-frequency, high-voltage or other arc-starting means (not shown), to maintain a high-current electric are 65 (FIGURE 3) between the tip or forward end of rear electrode portion 17 and the wall of cylindrical nozzle insert portion 49. Preferably, the gas-flow and other conditions are caused to be such that the are (at the downstream footpoint thereof) engages the wall of passage portion 49 at a region which is spaced a very substantial distance rearwardly from the downstream (forward) end of insert 47. Such downstream arc footpoint is located upstream of the powder-injection port to be described. It is to be understood that the are 65 is indicated only in schematic fashion.

Proceeding next to a description of the means for introducing arc gas into vortex chamber 18, this includes first and second ports or inlet openings 66 and 67 which are formed in the chamber liner 19 as shown in FIG- URES 3, 6 and 7. The first port 66 is located in the bottom (rear) corner of the liner 19 and communicates radially, through a passage portion 68 (FIGURE 7) in insulating body 11, with an internally-threaded fitting receptacle or socket portion 69 also formed in such body.

The second port, number 67 is disposed forwardly of port 66 and communicates through an oblique passage portion 71 with the indicated fitting receptacle 69. Such oblique portion 71 is directed radially-inwardly and forwardly, and is preferably at an angle of between about 60 degrees and about 70 degrees relative to the longitudinal axis of the plasma torch apparatus.

Both of the ports 66 and 67 are olfset substantial distances from a vertical plane intersecting the longitudinal axis of the torch, so that the gas introduction is generally tangential relative to the gas-vortex chamber 18. Referring to FIGURE 6, when the gas is flowing through passage 71 and port 67 the gas flows not only tangentially but also forwardly and helically, the pitch or lead of the helix being relatively great. On the other hand, when gas is flowing through passage 68 and port 66 there is a substantially purely tangential manner of gas introduction, with much less forward inclination and with a resulting helical gas fi'ow characterized by less lead or pitch in the helix.

First and second externally-threaded fittings 73 and 74 are adapted to be selectively inserted into the internally-threaded fitting receptacle or socket 69, to thereby cause inflow of gas either through passage 68 and port 66, or through passage 71 and port 67. The first such fitting is shown in FIGURE 7 and has an axial bore 76 communicating directly with radial passage 68 and thus with the described port 66. The fitting 73 extends radially-inwardly sufficiently far to prevent flow of gas to passage 71.

The second fitting 74 is shown in FIGURES 3 and 6, having an axial passage 7-7 and a plurality of radial ports 78, at least one of the latter being in communication with passage 71 regardless of the rotated positon of fitting 74. Fitting 74 also has a solid or blind tip 79 (FIGURE 6) which is inserted into passage 68 toprevent flow of gas therethrough to port 66. i

The fittings 73 and 74 are connected selectively to a conduit 80 leading to a suitable source 81 (FIGURE 1) of gas under pressure. When the gas source 81 contains a monatomic gas, such as argon or helium, the fitting 74 (FIGURES 3 and 6) is employed in order to cause the gas to be introduced through passage 71 and port 67. Thus, a vortical or helical flow is created having a large for-ward or axial component. When the gas source 81 contains nitrogen, hydrogen or other diatomic gas, fitting 73 (FIGURE 7) is employed to effect flow of gas through passage 68 and port 66. Thus, as described above, the inflow of gas is substantially radial, there being only a small axial component. When the source 81 contains a mixture of diatomic and monatomic gases, the fitting selection is normally determined by the gas which predominates in the mixture. Thus, if the mom atomic gas (such as argon) predominates, fitting 74 is employed.

It has been found that the described selective use of different types of tangential-inlet ports (for dilferent gases) produces important results, including substantially increased electrode life.

Proceeding next to a description of the very important means for injecting coating material into nozzle insert 47, for entrainment into the plasma resulting from heat ing of the arc gas by are 65, this comprises a passage or port 82 (FIGURE 3) which is formed generally radial ly through insert 47 and communicates with passage. portion 49 in spaced relationship from the downstream end thereof. The inlet into passage 49 from radial port 82 is spaced substantially farther from the downstream end of insert 47 than is the case relative to conventional plasma-spray apparatus. Such increase in the distance through which powder passes within passage portion 49 permits adequate heating and accelerating of the powder despite the fact that the gas flows at very high velocities as will be stated hereinafter. The region of passage portion 49 downstream from port 82 should not be divergent, so that the high gas and powder velocities will be maintained in such region.

It has been found that the radial passage 82 should incline slightly, in a forward or downstream direction (FIG- URE 3), in order to achieve desirable entrainment of the powder into the plasma without creating undesired backpressure, plugging or other effects. More specificially, the passage 82 may be at an angle of approximately degrees from the longitudinal axis of passage portion 49 (10 degrees from a plane which is perpendicular to the axis of passage portion 49). As indicated, the inner end of passage 82 is closer to the downstream end of the nozzle passage than is the outer end of the passage 82. The axis of passage 82 preferably intersects the longitudinal axis of passage portion .49 (both lying in a vertical plane).

Passage 82 communicates with an additional passage 83 which is formed through the member 31, is being assured that these passages register because of the above-indicated set screw 48 (FIGURE 4) and cooperating conical recess in the insert 47. Passage 83, in turn, communicates with a powder-injection conduit 84 leading to a suitable powder source 86 which is schematically shown in FIGURE 1. A source of carrier gas for the powder from source 86 is indicated schematically at 87 in FIGURE 1, being connected to powder source 86 through a conduit 88. Thus,

powder from source 86 is entrained into gas passed therethrough from gas source 87, and the combination gas and powder are conducted through conduit 84 and passages 83 and 82 to nozzle passage portion 49. One desired form of powder source 86 will be described subsequently with reference to FIGURES.

Referring next to FIGURE 3A, a second nozzle insert 47a is illustrated. Such insert may be identical to that shown in FIGURE 3, except that the diameter of the downstream passage portion 49a.is somewhat larger than in the case of passage portion 49 of FIGURE 3. Insert 47a is employed when it is desired to spray ceramics, as distinguished frommetals, the reason being that the largerdiameter passage portion 49a decreases the gas pressure somewhat and thus permits the ceramic powder to be maintained in portion 49a for an additional period of time required to permit effective and adequate heating thereof. Instead of employing diiferent inserts 47 and 47a for metals and ceramics, it is within the scope of the invention to change other factors, including gas pressure and power level.

Mounted on the forward or downstream end of the torch, namely on the large-diameter cylindrical portion 34 of member 31, is a generally cup-shaped gas conductor 90 having a large-diameter cylindrical upsteam section 91, a frustoconical intermediate section 92, and a smallerdiameter cylindrical downstream section 93. The inner diameter of upstream section 91 corresponds generally to the outer diameter of portion 34, so that the gas conductor may telescope over portion 34 as indicated. Thus, conductor 90 is locked in position by means of a set screw 96, gas leakage being prevented by an O-ring 97.

The smaller-diameter or outlet portion 93 of the gas conductor 90 defines a round outlet opening 98 (coaxial with passage portion 49) the diameter of which is much larger (for example, approximaly 2 times larger) than the diameter of nozzle passage portion 49. Furthermore, opening 98 is spaced away from the downstream (forward) end of insert 47 by a considerable distance, such distance being shown as somewhat greater than the spacing between powder inlet 82 and the downstream end of insert 47. The interior wall of gas conductor 90 at the smaller-diameter outlet end 93 thereof is shown as being rounded, as viewed in section, in the general manner of a nozzle.

An additional gas source, indicated at 99 in FIGURE 1, communicates through a conduit 100 with the gas conductor 90. More specifically, conduit 100 communicates with a port in the large-diameter cylindrical portion 91 at a slightly forwardly-inclined angle.

of conductor 90, such port being located radially outwardly from a protuberant or axially-extending downstream end of insert 47. As illustrated, such. downstream end extends a considerable distance away from the front face of member 31. V

The gas conductor 90 performs important functions relative to aiding in collimating the plasma which discharges from passage portion 49, preventing undesired oxidation or other effects relative to the powder entrained in such discharging plasma, cooling the workpiece or substrate, and blowing away any loosely-adherent particles from the workpiece or substrate so that the adherence of the coating to the substrate is improved.

It is'emphasized that the set screw 96 facilitates removal of the gas conductor 90, for example when it is desired to change nozzle inserts 47 by loosening the set screw 48 (FIGURE 4). When the gas conductor 90 is in mounted condition, it conceals and prevents loosening of the outer end of the set screw 48.

Method of high-velocity spraying Stated generally, the method of the invention comprises increasing the mass flow and enthalpy of an areheated gas to such values that a coating substance entrained therein will be accelerated to a velocity of at least 250 feet per second, introducing into the gas a coating substance adapted to be accelerated thereby to at least such velocity, and impinging the entrained coating substance against a workpiece or substrate. Stated more specifically, the coating substance is in the form of a fine powder having a particle size on the order of 75 microns or less.

The method further comprises introducing the coating powder into the nozzle passage at a point a relatively long distance upstream from the outlet end thereof, and Furthermore, the method comprehends employing an auxiliary gas-conductor downstream from the nozzle passage and passing auxiliary gas through such conductor for purposes including improving the collimation of thepowder particles in the discharging plasma, protection of the powder from oxidation and other effects, cooling of the workpiece, and removal of loosely-adherent particles from the workpiece. Additionally, the method comprehends employing nozzles having different size passages in accordance with whether the entrained powder is metal or ceramic. The gas is passed through the nozzle passage in a vertical or helical manner.

The enthalpy, powder-injection point, gas flow, and other factors should be so regulated and correlated that the spray powder is melted but not vaporized. The melted particles, in impinging against the workpiece at high velocity, form an extremely dense and smooth coating which adheres effectively to the substrate. Using the present method, coatings have been formed which are smooth to within less than 10 microinches (less than 10 microinches difference after finishing between peaks and valleys of the coating surface).

The are gas is selected from a group consisting of argon, helium, nitrogen, hydrogen and mixtures thereof. A preferred are gas (introduced through vortex chamber 18) comprises a mixture of argon and hydrogen, with the argon predominating. The hydrogen produces the effect of increasing the enthalpy of the plasma and thereby accelerating the spray powder particles to a much greater extent than would otherwise be the case. The mixture is preferably about 90 percent argon, 10 percent hydrogen. However, the mixture may also comprise (for example) 65 percent argon and 35 percent hydrogen, or 50 percent argon and 50 percent hydrogen.

As indicated above, the spray powder is introduced in finely-divided form, less than 75 microns particle diameter. The particle size may also be only a few microns, ,or even less than one micron. The decrease in particle size permits melting of the particles in a very short period of time, and increases the particle-acceleration effect because of the low particle mass.

The manner of feeding and injecting the spray powder is important to the method. The powder-introduction port or passage 82 may be, for example, approximately /8 inch from the downstream end of passage portion 49 (FIGURE 3) when the diameter of such portion 49 is on the order of 0.21-0.28 inch. As previously indicated, the smaller diameter of nozzle bore 49 is employed for particles which are more readily melted, for example metals, because the residence time of the particles in the plasma is decreased. For more refractory materials such as oxides, the insert 47a (FIGURE 3A) having a larger bore 4% (such as 0.28 inch) is employed because the larger bore decreases gas velocity somewhat and thus increases residence time and heating effect.

The amount of gas employed to entrain powder and carry the same to port or passage 82 should be maintained at a minimum. For this reason, it is preferred that a screw-type powder source 86, not an aspirator-type, be employed. Referring to FIGURE 8, a powder hopper 101 containing powder 102 is provided with a feed screw 103 rotated by motor 184. Screw 103 feeds the powder at a predetermined rate from hopper 101 to a chamber 185 into which argon or other powder-carrier gas is supplied by the above-indicated pipe or conduit 88. The powder-gas mixture then flows through a venturi or restrictor 106 and a suitable mixing device 107 (such as a cyclone mixer) to the above-indicated conduit 84 leading to passage 83 and thus port 82 (FIG? URE 3). With the described apparatus, and equivalent apparatus, a predetermined rate of powder feed may be achieved with relatively low requirement for argon or other carrier gas. i

As an example, the amount of carrier gas for the powder may be on the order of about one cubic foot per minute at a pressure of about 5 psi. gauge.

To achieve high particle velocities, the mass flow is caused to be high as above stated. For example, the arc gas may be fed through chamber 19 at a rate on the order of 2 c.f.m. at a pressure of 20 p.s.i.g. Much higher pressures and flow rates may be employed.

The current supplied by source 61 (FIGURE 3) should be high, for example on the order of 275450 amperes or higher, the voltage being on the order of 60 volts. Thus, the power in the illustrated torch apparatus may be in the range of about 16 kw. to about 27 kw. or more.

The flow of gas through the auxiliary gas-conductor may be on the order of 3545 s.c.f.h. (standard cubic feet per hour). In some cases, no gas is fed through conduit and the auxiliary conductor 98 except that which emanates from the nozzle bore 49. Nevertheless, the auxiliary conductor 90 performs important shielding and other effects. The gas passed through conduit 108 is normally inert, such as argon. However, in some cases such gas may be one adapted to create a desired chemical reaction, as distinguished from preventing oxidation.

The relationships are caused to be such that, as above indicated, the particle velocity at a region three inches from the nozzle outlet is at least 250 feet per second. The velocity may also be much higher, for example 800 feet per second, or sonic.

Referring to FIGURE 1, the workpiece or substrate is indicated at W, and the applied coating at C. The work may be located a few inches from opening 98. It is a feature of the invention that the discharging plasma is characterized by a surprisingly small cone angle. Thus, spraying may be efiected precisely, on any desired small or large area, without waste or overspray. Access to various interior surfaces is also greatly facilitated.

It is to be understood that many of the advantages of the invention may be achieved with particle sizes larger than those indicated. It is also possible to employ a majority of particles in the indicated range, mixed with a certain percentage of particles of larger sizes.

It is within the scope of the invention to connect an additional (or alternative) power source between electrode 16 and/or 47 and the substrate W. Also, it is within 2. An electrical plasma torch, which comprises:

an elongated nozzle electrode insert having a passage therethrough,

a rear electrode,

nozzle means to mount said insert and said rear electrode in the scope of the invention to provide one or more addicoaxial relationship, tional powder-injection ports 82, and inject therethrough said last-named means including an insert-mountthe same or a different powder than that being passed ing element adapted to removably receive said through the illustrated port 82.. Thus, for example, alloyinsert, 1ng may be achieved in the plasma et. means to maintain a high-current electric are between As specific examples of the present method and apparasa1d rear electrode and said insert, tus, reference is made to the following table giving repmeans to pass gas through sa1d nozzle passage in said lggsentittive IdataI.I In all Ifases, the arc voltage is about insert, an; 1 f

vo ts. n a cases, t e arc gas is 90 percent argon, means to e ect continuous circu ation 0 water in op- 10 percent hydrogen, whereas the gas passed through con- 5 posite directions and radially-outwardly of said induits 84 and 100 is argon. Gas may be introduced sert, through the auxiliary conductor 90 at a rate of about 35 said last-named means being such that said water s.c.f.h. The table represents use of the method withthe flows over at least a portion of the exterior of illustrated apparatus, including the screw-type powdersaid insert-mounting element and also flows feed means shown schematically in FIGURE 8. through a plurality of passages 111 said insert- Current Are Gas Through Powder Deposition Deposition Powder (amperes) Chamber 18 Carrier Gas R tFefl/hr Rate,1b./hr. Izlfiiciengg a e, percen Tungsten Carbide (12% Cobalt)" 275 1.2 c.t.m. at 20 p.s.i.g 0.8 0.1. 8. 5 3.4 40. 0 D0 300 1.2 e.f.m. at 20 p.s.i.g. 0.8 c.f. 12.0 6. 4 53. 3 Tungsten.-. 450 1.2 e.f.m. at 20 p.s.i.g 0.8 c.f. 12.4 2.8 22. 6 Nichrome V 275 1.2 c.f.n1. at 20 p.s.i.g 0.8 c.f. 5. 8 2. 6 44. 9 D0 250 1.2 c.f.m. at 20 p.s.i.g 0.8 e.f. 6.8 3. 4 50.0 Zirconium Oxide 275 1.2 c.f.m. at 15 p.s.1.g 0.3 e.f. 6.7 0.5 7. 5 Aluminum Oxide. 400 1.2 c.f.m. at 15 p.s.i.g- 0.3 e.l. 4. 7 0.8 17.7 NichromeV 275 1.2 c.f.m. at 15 p.s.i.g 0.3 c.f. 8.6 6.4 74. 5

The particle velocity measurements recited in the presmounting element, ent specification and claims were made in the ambient said passages being disposed adjacent the exatmosphere, 3 inches from the forward or outlet end of terior surface of said insert. the nozzle insert 47. Such velocities are much less than 3. An electric plasma torch, which comprises: those to which the particles are accelerated as they leave, a nozzle electrode having a nozzle pass-age therethe nozzle passage. The velocity recitations in the apthrough, pended claims refer to such velocities 3 inches from the 40 a rear electrode, nozzle outlet. A means to define a gas-vortex chamber communicating The foregoing detailed description is to be clearly un- Withsaid nozzle passage and coaxial therewith, derstood as given by way of illustration and example sa1d gaSV0rt X am having a Wall Which is only, the spirit and scope of this invention being limited surface of revolution about the central axis of solely by the appended claims. said nozzle passage,

We claim: 7 first inlet means communicating generally tangentially 1. A method of operating a gas-vortex electrical plasma 'With said gas-vortex chamber and disposed in a plane torch on different types of gases and in such manner that which is generally perpendicular to the common axis benefits including maximum electrode life are achieved, of said chamber and said nozzle passage, which comprises: second inlet means communicating generally tangenproviding an electrical plasma-jet torch having a gastjally ith id gaswortex h b Vortex chamber commumcetmg axlany Wlth a nozzle said second inlet means being inclined forwardly P a relative to said common axis whereby gas introsaid torch alsohaving an elongated rear electrode duced through Said Second inlet means flows t i i i of siald ig a b helically in said gas-vortex chamber and with mam ammg. an 6 cc me are m Sal mom 6 passage ea relatively long lead between turns of the helix, tween said rear electrode and another electrode, and means selectively adapted at different t1me periods introducing, dur1ng periods when 1t is desired to opert t duce tian diam i 0a th u h ate the torch with a gas which is essentially diatomic, h 5 t an 3 y i s an essentially diatomic gas into said gas-vortex rs m e {means an essen la y monlormc e through said second inlet means, and means to malnchamber and generally tangentially thereof,

said gas flowing vortically and helically in said gasvortex chamber and discharging through said nozzle passage, and

tain a high-current electric are between said rear electrode and another electrode. 4. The invention as claimed in claim 3, in which said means to introduce gas selectively through said first and second inlet means comprises a plurality of gas-inlet fitsaid rear housing element having a central stem portion inserted through said body into said vortex chamber,

an elongated rear electrode insert disposed in an axial passage in said central stem portion,

a removable plug threadedly inserted into said rear housing element and adapted to lock said rear electrode insert in position,

a front housing element having a rim portion mounted to said insulating body,

an electrode-mounting and coolant-conducting element mounted to said front housing element,

said last-named element having formed therethrough a nozzle insert-receiving bore,

said last-named element also having formed therethrough a plurality of longitudinally-extending circumferentially-spaced coolant passages disposed adjacent said bore,

coolant separator means extending between said electrode-mounting and coolant-conducting element and the interior wall of said front housing element,

said coolant-separator means dividing said front housing element into front and rear coolant chambers,

means to introduce coolant into said front coolant chamber for circulation forwardly and exteriorly along said electrode-mounting and coolant-conducting element and subsequent circulation in a rearward direction through said circumferentially-spaced passages to said rear coolant chamber,

means to conduct coolant from said rear coolant chamber through said insulating body to a coolant chamber defined by said rear housing element rearwardly of said insulating body,

means to drain coolant from said last-named chamber,

a nozzle electrode insert removably secured in said bore in said electrode-mounting and coolant conducting element,

means to pass gas through said vortex chamber for outflow through said nozzle electrode insert, and

means to maintain a high-current electric are between said rear electrode insert and said nozzle electrode insert.

6. A method of forminga dense, smooth coating on a substrate, which comprises:

providing an electrical plasma-jet spray torch having an elongated, generally cylindrical nozzle passage,

effecting flow of gas in said torch and through said nozzle passage to the ambient atmosphere,

maintaining a high-current electric arc in said torch at such location therein that at least the downstream footpoint of said are is located in said nozzle passage and is spaced a substantial distance from the downstream end of said nozzle passage,

injecting a finely-divided particulate coating material into said nozzle passage laterally through a wall portion thereof and at a location between said downstream footpoint and said downstream end,

regulating said gas flow and the power in said are in such manner that the velocity of said particles, when measured at a location in the ambient atmosphere three inches from said downstream end, is at least 250 feet per second, and

directing said particles against a substrate to form a dense and smooth coating thereon.

7. The invention as claimed in claim 6, in which said method further comprises effecting vortical flow of said gas in said nozzle passage about the axis thereof.

8. The invention as claimed in claim 6, in which said gas flow and the power in said are are also regulated in such manner that said particles of coating material are softened but not vaporized.

9. The invention as claimed in claim 6, in which the majority of said particles of coating material have diameters no greater than 75 microns.

10. The invention as claimed in claim 6, in which said gas comprises a mixture of argon and hydrogen.

11. The invention as claimed in claim 6, in which said method further comprises effecting said injection of coating material at a location spaced upstream from said downstream end of said nozzle passage.

12. Apparatus for effecting high-velocity spray deposition of a dense, smooth coating onto a substrate, which comprises:

first wall means to define a gas-vortex chamber,

the interior surface of said first wall means being a surface of revolution about a predetermined axis,

means to introduce gas into said chamber generally tangentially thereof whereby to effect vortical flow of said gas in said chamber about said axis,

second wall means to define an elongated nozzle passage communicating with said chamber,

the interior surface of said second wall means also being a surface of revolution about said axis, the portion of said nozzle passage adjacent said chamber being generally frustoconical and converging in a direction away from said chamber, the portion of said nozzle passage remote from said chamber being generally cylindrical,

said cylindrical passage portion extending from the small-diameter end of said frustoconical passage portion to the ambient atmosphere, an elongated rear electrode extending axially of said chamber into said frustoconical passage portion,

the forward end of said rear electrode being spaced radially-inwardly from said interior surface of said second wall means, means to maintain a high-current electric are between said forward end of said rear electrode and an arcing region of said interior surface of said second wall means,

said arcing region being spaced a substantial distance upstream from the downstream end of said cylindrical passage portion,

a powder-injection port provided in said second wall means between said arcing region and said downstream end of said cylindrical passage portion, and

means to inject through said port into said cylindrical passage portion a finely divided spray powder adapted to be applied to a substrate,

said gas-introduction means and said arc-maintaining means effecting softening but not vaporizing of said injected spray powder, and further effecting acceleration of said powder to such velocity that said powder when passed through the ambient atmosphere at a distance three inches from said downstream end of said cylindrical passage portion is traveling at a velocity of at least 250 feet per second.

13. The invention as claimed in claim 12, in which said forward end of said rear electrode is also generally frustoconical and coaxial with said axis, the surface of said forward end converging in a direction away from said chamber.

14. The invention as claimed in claim 12, in which said powder-injection port is spaced a substantial distance upstream from said downstream end of said cylindrical passage portion.

15. The invention as claimed in claim 12, in which said means to inject spray powder through said port includes a passage communicating directly with said port and extending generally radially of said axis, said power passage being somewhat inclined relative to a plane which is perpendicular to said axis and extends through said port, .the direction of incline being such that the portion of said powder passage adjacent said port is more remote from said chamber than is the portion of said powder passage remote from said port.

16. The invention as claimed in claim 12, in which an auxiliary gas conductor is provided around said second wall means and has an annular mouth portion coaxial with said axis, said mouth portion being spaced downstream from said downstream end of said cylindrical passage portion, the diameter of said mouth portion being much larger than that of said cylindrical passage portion, and in which means are provided to introduce gas into said auxiliary gas conductor independently of said gasvortex chamber.

17. The invention as claimed in claim 12, in which water-cooled Wall means are provided around said second wall means, and in which said second wall means is a 14 metal insert removably secured in said water-cooled wall means.

18. The invention as claimed in claim 17, in which first and second ones of said metal inserts are provided, said second metal insert having a cylindrical passage portion the diameter of which is substantially greater than that of the cylindrical passage portion of said first insert.

No references cited.

ANTHONY BARTIS, Primary Examiner. RICHARD M. WOOD, Examiner.

Non-Patent Citations
Reference
1 *None
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Classifications
U.S. Classification219/76.16, 219/76.11
International ClassificationH05H1/26, B05B7/14, B05B7/22, H05H1/42, B05B7/16
Cooperative ClassificationB05B7/144, H05H1/42, B05B7/226
European ClassificationB05B7/22A3, H05H1/42, B05B7/14A8