US3676638A - Plasma spray device and method - Google Patents

Abstract

An improved plasma spray device which deposits heat fusible material onto a substrate to form a continuous film. The plasma is effected by passing an ionizable gas between two electrodes which support an electric arc. The material to be deposited on the substrate is added to the plasma during its passage through a large nozzle. The gas is directed into a helical path by a plurality of conduits formed in a large disk. The material rides on the cylindrical surface of the revolving gas before being ejected from either a nozzle with a constant interior diameter or a gradually changing diameter.

Description

United States Patent Stand July I 1, 1972 s41 PLASMA SPRAY DEVICE AND 3,145,287 8/1964 Siebein er al ..2l9l76 x METHOD 2,960,594 ll/l960 Thorpe ....2l9/l2l P 2,973,426 2/1961 Casey ..2l9l76 X 1 Milk NW York. 3,061,710 l/l967 Browning et al.. ..2|9/1s [73] Asian: sum Comm Mammomck1 No 3,179,784 4/1965 Johnson ..2l9/76 [22] Filedi JI 1971 Primary Examiner-J. V. Truhe Assistant Examiner-Gale R. Peterson [21 1 Appl' 109369 Attorney-James M. Heilman and l-leilrnan 8c Heilman Related US. Application Data [57] ABSTRACT [63] Continuation-impart of Ser. No. 834,292, June l8,

1969, abandoned. An improved plasma spray device whlch deposits heat fusible material onto a substrate to form a continuous film. The 521 0.5.0 ..219/121| 219/76 P'asma is by inilabl 51 int.Cl nz'sk 9/00 electmdes which am N deposited on the substrate is added to the plasma during its Field l t [58] 0 Search 219/76 121 P 74 7s R passage through a large nozzle. The gas ts directed Into a helllhnn cal path by a plurality of conduits formed in a large disk. The [56] R m CM material rides on the cylindrical surface of the revolving gas n' 1- ATES PATENTS before being ejected from either a nonle with a constant interior diameter or a gradually changing diameter. 3,l H.826 12/1963 Sullivan et al. ..2l9/76 3,l67,633 1/1965 Fonberg ..2l9/75 lsClalrns, Drawing Figures as m Pomoert 3| IO 27x m 2 30I7 2| Z; 35 a POWDER m PATENTEDJUL 1 1 m2 SHEU 3 SUPPLY MILLE STAND INVENTOR a? ATTORNEY PLASMA SPRAY DEVICE AND METHOD This application is a continuation-in-part of the Stand application Ser. No. 834,292, filed June 18, 1969 entitled Plasma Spray Device and Method," assigned to Sealectro Corporation, now abandoned. This application is related to Stand US. application Ser. No. 835,876, filed June 4, I969, entitled Method of Depositing Heat Fusible Material and Apparatus Therefor," issuing into US. Pat. No. 3,591,751, granted July 6, 197 l and to Stand U.S. application Ser. No. 834,293, filed J une I8, 1969, titled Spray Nozzle for Plasma Guns," issuing into US. Pat. No. 3,627,204, granted Dec. l4, l97l and also to Stand and Streicher US. application Ser. No. 868,487filed Oct. 22, l969, titled Powder Feeding Assembly, issuing into U.S. Pat. No. 3,606,48 l, granted Sept. 20, l97l. All the foregoing applications are incorporated by reference herein in their entirety, and these applications and the present application are assigned to the same assignee, i.e., Sealectro Corporation.

This application pertains to an improved plasma spray device which deposits heat fusible material onto a substrate to form a continuous film. The plasma is effected by passing an ionizable gas between two electrodes which support an electric arc. The material to be deposited on the substrate is added to the plasma during its passage through a large nozzle. The gas is directed into a helical path by a plurality of conduits formed in a large disk. The material rides on the cylindrical surface of the revolving gas before being ejected from either a nozzle with a constant interior diameter or a gradually changing diameter.

The use of insulating films of plastic material deposited on metal, ceramic, and other substrates is becoming more important in modern technology. New coating materials, such as polytetrafluoroethylene, i.e., PTFE, or TFE, more commonly known by its specific trademarks Teflon" (Dupont Company), "Halon" (Allied Chemical Company), Fluon" (lrnperial Chemical Industries, Ltd.). "Hostaflon" (Farbwerke Hoechst), and other high temperature plastics, all referred to hereinafter generally as PTFE, are now being applied to many types of base materials to lower friction, increase protection, and provide a chemically inert surface. When these materials are deposited as a paste or in powdered form they may be melted by inserting the substrate into a furnace and applying heat to melt the material. When the substrate cannot withstand the high temperature necessary to melt the powder, or is too big and awkward to be handled efficiently, some other method must be used. The present invention supplies both the device and the method. PTFE powder can also be sprayed onto cloth where it coalesces in a continuous film without injuring the fabric. Also metal powders of various kinds can be successfully sprayed onto various substrates.

One of the features of the present invention is the use of a revolving plasma jet within the spraying device. The path taken by the gas retains the powder material on or near its outer surface next to the nozzle. Another feature is a smoothly curved modified nozzle which produces a venturi effect. For a better understanding of the present invention, together with other details and features thereof, reference is made to the following description taken in connection with the accompanying drawings.

FIG. I is a cross sectional view of the preferred form of the plasma spray device taken along an axial line.

FIG. 2 is a side view of the large plate or disk with its conduits.

FIG. 3 is a partial cross sectional view of the large disk taken along line 3-3 of FIG. 1.

FIG. 4 is a cross sectional view showing an alternate form of the spray device with the insulating means positioned at a different location.

FIG. 5 is a side view of an insulator plate with its gas directing conduits.

FIG. 6 is a partial cross sectional view of the insulator plate taken along line 66 of FIG. 4.

FIG. 7 is a cross sectional view of an alternate form of curving nozzle used to broaden the flame and to deposit a more even coating.

HO. 8 is a side view of the plasma gun device with covers thereon.

FIG. 9 is a diagram of connections showing how the spray device may be powered from a standard A C supply line.

FIG. 10 is a detailed view of one of the preferred relationship between the electrodes. Referring to FIGS. 1, 2 and 3, the plasma device includes an outer retaining insulatingcylinder 10, several cylindrical liners ll, 12, and 13, the latter being an extension of thenozzle portion 14. Thenozzle 14 is a hollow cylinder having astraight bore 15 formed with astep 16 adjacent to a plurality ofinjection conduits 17. The injection conduits are positioned at an acute angle to the cyiinder axis in order to propel a stream of powdered material intobore 15 without disturbing the flow of gas in the bore.Conduits 17 are connected toflexible powder tubes 18, which may be made of a plastic material such as polyethylene, rubber, or other suitable material.

Theextension cylinder 13 is formed with a coneshaped cavity 20, the surface of which acts as one electrode of an electric arc discharge. Asmaller cone 21 at the end of asolid cylinder 22 acts as the other electrode for the arc discharge, the actual position of the are being at the edge of thecone 2!. Copper may form the anode, and tungsten the cathode, for example.Cylinder 22 may be supported bylarger cylinders 23 and 24, the latter cylinder being held in alignment by ametal disk 25.

More effective results are obtained when the angles between the electrodes are different. The best results are obtained when the difference between the angles is between 10 30, and for example, a cone angle of approximately l20 and a cone shaped cavity of approximately all as illustrated in FIG. 10.

Current for the electric arc is furnished by agenerator 26, one terminal being connected to thenozzle 14 and the other terminal being connected tocylinder 24. Aswitch 19 is used to apply power to the spray device.

Ajacket 27 is formed by ashort cylinder 28 and aflange 30 for distributing gas around the edge ofdisk 25. Gas is admitted to the device by aconduit 31 and is then distributed around the disk by acircular edge slot 32. A plurality ofconduits 33 direct streams of gas from thevertical slot 32 into the space aroundcylinders 23 and 22, and then through the arc discharge and intonozzle cavity 15.

Theconduits 33 direct the gas generally toward the axis of thenozzle opening 15 as shown by the angular direction in FIG. I. They also direct the flow of gas into a slight off-axis" direction as shown by FIGS. 2 and 3. The result is a combination of helix-directed streams which blend and form a rotating gas cylinder, moving along thenozzle cavity 15. When the gas moves through the electric arc, it is heated and ionized. If the resulting temperature is 4,000 F. or over, the gas remains in its ionized condition until cooled. A plasma jet may be obtained of l0,000 15,000 F. By regulating the amount of power applied at the arc and controlling the rate of gas flow to the arc, the temperature of the plasma may be confirmed to a level below l0,000 F. and maintained there within a fairly narrow range.

Powder conveying conduits 17 are each bored at an angle which is substantially parallel to acorresponding gas conduit 33. The powder is thereby injected into the revolving hot gas stream at a direction which has no tendency to divert or change the direction of the gas flow. The injected plastic particles ride on the outside surface of the gas stream and are retained in that position because of centrifugal force. Since the direction and placement of the injected particles remain fixed, it is easy to adjust the ratio of flow and the arc current so that all the particles will emerge from the spray device at a desired temperature. Since the particles revolve with the gas, they traverse a longer path from the point of injection to the end of the nozzle and therefore have sufficient time to be heated to a predetermined temperature by the hot gas. Any non-corrosive insert gas may be used. Nitrogen, argon, carbon dioxide, and helium have given good results. Oxygen probably should be avoided because it tends to attack the electrode material adjoining the arc.

Referring now to FIG. 4, 5, and 6, a plasma spray device is shown similar to the device of H68. 1, 2, and 3 but including a metal cylinder A which may be grounded and which is used as one of the terminals for the electrical power. The disk A which directs the gas toward its helical motion is made of any type of insulator material such as Bakelite" (Union Carbide Corporation). The action is the same, except that only thecentral electrode 21, 22, 23, 24, is the cathode, all other metal parts being grounded.

in the views shown in FIGS. 1 and 4 no cooling means are indicated. The device generates considerably heat so water cooling is generally part of the apparatus. Annular spaces between elements I1 and 12 have been used for cooling purposes. Such cooling methods are old in the art.

The nozzle 14A shown in FIG. 7 is similar to the nozzle of FIGS. 1 (and 4) except that it is shorter and contains a nozzle space which is curved and stream-lined. Theentrance cone 20A is preferably approximately at 45 angle has a rounded portion to reduce turbulent gas flow at this point. Also, the nozzle throat is gradually increased in cross sectional area up to a point near the exit portion so that the nozzle acts like a venturi. Theconduits 17A which carry the powder have their exit ports close to the maximum diameter of the nozzle. The result is a longer flame with increased diameter. With such a larger nozzle it is possible to deposit a uniform film of PTFE as thin as 0.001 inch thick on aluminum, stainless steel, etc.

While specific dimensions may vary, one form of nozzle which has given excellent results, for example, has an entrance diameter of 0.712 inches, upstream from the arc space. The downstream constriction adjoining arc space is 0.312 inches and the exit end of the nozzle gradually increases to 0.538 inches in diameter. in this figure the powder to be sprayed is entered through short conduits 175 which may be vertical as illustrated or at approximately a 30 forward angle to the vertical, making a total angle of approximately 461: withconduit 17A, and having a smoothly curved junction point.Conduits 17A are preferably approximately 1630 to the horizontal. The diameters ofconduits 17A and B are preferably approximately 0.l", Certain of these representative dimensions are shown in the drawings.

The powder is then propelled through the angularly disposedconduits 17A to join the plasma flame. As a convenience in manufacture,conduits 17A are first drilled from thesurfaces 54, then these entrances are plugged and new entrance conduits !7B are drilled so that the inlet powder pipes 18 (FIG. 4) may be attached.

The particle size varies considerably with the powder used. For the best deposits of metals, such as copper and stainless steel, the particle size should be small, about 0.002 inch in diameter. For PTFE and other plastics, which have a lower melting point, the particle size can be in the range of 0.0l0 to 0.025 inches.

F IG. 8 shows the assembled plasma spray device with ahandle 36 and acover 37. The powder is entered throughpipe 16 and water cooling entrance andexit tubes 40 and 42 are secured to the lower portion of the main body. Aflame 42 of plasma with powdered material is shown delivering material to asubstrate 43 of any commercial material.

If it is desired to generate the direct current power from the standard A C supply lines, a rectifier circuit, as shown in FIG. 9 may be employed. The circuit is conventional and includes atransformer 45 having a primary winding 46 connected in series with avariable resistor 47. A secondary winding 48 is connected to afull wave rectifier 50 including four semiconductor diodes 51. Anammeter 52 is connected in series with the load conductor and avoltmeter 53 is connected across the load. These instruments are necessary for adjusting the arc to the right intensity since the arc is inside the device and cannot be seen.Switch 19 connects the rectifier circuit to the arc terminals.

Powdered PT FE, polyethylene, and polypropolene have been sprayed onto a substrate to form an integral continuous film. Also, metal powder such as aluminum, copper, tin, and lead have been successfully sprayed by the device described above.

While there has been described and illustrated a specific embodiment of the invention, it will be obvious that various changes and modifications can be made therein without departing from the field of the invention which should be limited only by the scope of the appended claims.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

I. A plasma spray device for depositing powdered heat fusible material carried by a plasma onto a substrate comprising, means to produce a rotating plasma, a nozzle having a conduit for the passage of the powdered heat fusible material mixed with a plasma, an opening leading into said nozzle conduit for supplying powdered material to the hot plasma, said opening disposed at an angle to the nozzle conduit for tangently directing the powder into a rotating plasma and mixing with the surface layer thereof, said nozzle formed with a flared conical surface at its interior end which forms a first electrode for an electric are, an axial cyiinder secured adjacent to said conical surface for forming a second electrode, said first and second electrodes defining an arc space, a gas distribution disk mounted around a supporting structure which disk holds the axial cylinder in place, an annular space in said gas disk connected to a source of gas supply, and a plurality of angular eject conduits in said disk so constructed that the gases issuing therefrom will rotate as they pass through the arc space and through the nozzle.

2. A spray device as claimed in claim I wherein said openings which supply powdered material and said eject conduits are disposed at approximately the same angular relationship to the nozzle conduit axis.

3. A spray device as claimed in claim 1 wherein said disk is secured to the nozzle and to said axial cylinder whereby an electric potential is established therebetween for supporting an electric arc.

4. A spray device as claimed in claim 1 wherein a series of openings are provided for supplying powdered material to the nozzle, said openings being mounted opposite to each other in the nozzle cylinder.

5. A spray device as claimed in claim I wherein said axial cylinder is formed with a conical end, the angle of said cone being greater than the angle of said flared conical surface.

6. A spray device as claimed in claim 5 wherein the difference between the angle of said cone and the angle of said flared conical surface is between therange l0 30.

7. A plasma spray device to produce a rotating plasma for depositing powdered heat fusible material carried by the plasma onto a substrate comprising a nozzle, two electrodes spaced apart and defining an arc space therebetween, a disk associated with said electrodes, a source of gas supply leading to said disk, said disk formed with a plurality of first angular eject conduits so constructed that the gas issuing therefrom rotates through the arc space and the nozzle, and a plurality of second conduits in the nozzle for supplying powdered mate rial into the rotating plasma, said first and second conduits disposed at the same angular relationship to the nozzle conduit axis.

8. A spray device as set forth in claim 7 wherein the angular eject conduits are spaced substantially in a circle around the entire area of said disk, and said angular eject conduits are set at such angles that the gas passing therethrough will immediately rotate.

9. A spray device as set forth in claim 7 wherein the angle of said electrodes defining the arc space has a difference of approximately 10 30.

10. A spray device as set forth in claim 7 wherein said disk is an insulator and electrically separates the electrodes from each other.

I l. A spray device as set forth in claim 7 wherein said disk is metal and is electrically conductive.

12. A spray device as set forth in claim 7 wherein said disk is made of conductive metal and the external jacket is an insulator and electrically separates the electrodes from each other.

13. A spray device as set forth in claim 5 wherein said cone is connected to the positive terminal of a source of direct current power and said flared conical surface is connected to the negative terminal.

14. A spray device as set forth in claim 1 wherein said plurality of angular conduits in the gas distribution disk direct the gas toward the nozzle axis and at the same time direct the flow at an angle to the axis to provide a cylindrical gas mass which rotates as it passes outwardly through the nozzle.

15. A spray device as set forth in claim 1 wherein the nozzle includes a conduit space defined by a smooth curving bore leading from the arc space to a point adjacent to the nozzle exit port to permit laminar flow of the hot gasses.

[6. A spray device as set forth byclaim 14 wherein the arc space is connected to the nozzle bore by a smooth curved surface to avoid turbulent flow.

17. A spray device as set forth byclaim 16 wherein the side of the cone shaped cavity is at an angle approximately 45' to the longitudinal axis of the extension nozzle cylinder. and the conduits for supplying powdered material into the rotating plasma are at an angle of approximately I6Va to said nozzle cylinder.

18. A spray device as set forth byclaim 14 wherein the arc space is adjoining an upstream cavity having a diameter of substantially 0.712 inches. a downstream constriction of substantially 0.312 inches, and said nonle having an exit diameter of substantially 0.538 inches.

4! i l I i

Claims (18)

1. A plasma spray device for depositing powdered heat fusible material carried by a plasma onto a substrate comprising, means to produce a rotating plasma, a nozzle having a conduit for the passage of the powdered heat fusible material mixed with a plasma, an opening leading into said nozzle conduit for supplying powdered material to the hot plasma, said opening disposed at an angle to the nozzle conduit for tangently directing the powder into a rotating plasma and mixing with the surface layer thereof, said nozzle formed with a flared conical surface at its interior end which forms a first electrode for an electric arc, an axial cylinder secured adjacent to said conical surface for forming a second electrode, said first and second electrodes defining an arc space, a gas distribution disk mounted around a supporting structure which disk holds the axial cylinder in place, an annular space in said gas disk connected to a source of gas supply, and a plurality of angular eject conduits in said disk so constructed that the gases issuing therefrom wilL rotate as they pass through the arc space and through the nozzle.

2. A spray device as claimed in claim 1 wherein said openings which supply powdered material and said eject conduits are disposed at approximately the same angular relationship to the nozzle conduit axis.

3. A spray device as claimed in claim 1 wherein said disk is secured to the nozzle and to said axial cylinder whereby an electric potential is established therebetween for supporting an electric arc.

4. A spray device as claimed in claim 1 wherein a series of openings are provided for supplying powdered material to the nozzle, said openings being mounted opposite to each other in the nozzle cylinder.

5. A spray device as claimed in claim 1 wherein said axial cylinder is formed with a conical end, the angle of said cone being greater than the angle of said flared conical surface.

6. A spray device as claimed in claim 5 wherein the difference between the angle of said cone and the angle of said flared conical surface is between the range 10* - 30* .

7. A plasma spray device to produce a rotating plasma for depositing powdered heat fusible material carried by the plasma onto a substrate comprising a nozzle, two electrodes spaced apart and defining an arc space therebetween, a disk associated with said electrodes, a source of gas supply leading to said disk, said disk formed with a plurality of first angular eject conduits so constructed that the gas issuing therefrom rotates through the arc space and the nozzle, and a plurality of second conduits in the nozzle for supplying powdered material into the rotating plasma, said first and second conduits disposed at the same angular relationship to the nozzle conduit axis.

8. A spray device as set forth in claim 7 wherein the angular eject conduits are spaced substantially in a circle around the entire area of said disk, and said angular eject conduits are set at such angles that the gas passing therethrough will immediately rotate.

9. A spray device as set forth in claim 7 wherein the angle of said electrodes defining the arc space has a difference of approximately 10* - 30* .

10. A spray device as set forth in claim 7 wherein said disk is an insulator and electrically separates the electrodes from each other.

11. A spray device as set forth in claim 7 wherein said disk is metal and is electrically conductive.

12. A spray device as set forth in claim 7 wherein said disk is made of conductive metal and the external jacket is an insulator and electrically separates the electrodes from each other.

13. A spray device as set forth in claim 5 wherein said cone is connected to the positive terminal of a source of direct current power and said flared conical surface is connected to the negative terminal.

14. A spray device as set forth in claim 1 wherein said plurality of angular conduits in the gas distribution disk direct the gas toward the nozzle axis and at the same time direct the flow at an angle to the axis to provide a cylindrical gas mass which rotates as it passes outwardly through the nozzle.

15. A spray device as set forth in claim 1 wherein the nozzle includes a conduit space defined by a smooth curving bore leading from the arc space to a point adjacent to the nozzle exit port to permit laminar flow of the hot gasses.

16. A spray device as set forth by claim 14 wherein the arc space is connected to the nozzle bore by a smooth curved surface to avoid turbulent flow.

17. A spray device as set forth by claim 16 wherein the side of the cone shaped cavity is at an angle approximately 45* to the longitudinal axis of the extension nozzle cylinder, and the conduits for supplying powdered material into the rotating plasma are at an angle of approximately 16 1/2 * to said nozzle cylinder.

18. A spray device as set forth by claim 14 wherein the arc space is adjoining an upstream cavity having a diameter of substantially 0.712 inches, a downstream constriction of substAntially 0.312 inches, and said nozzle having an exit diameter of substantially 0.538 inches.

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