JPH0766871B2 - High-speed and temperature-controlled plasma spray method and equipment - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a plasma arc spray method and apparatus using higher current and higher voltage than conventional plasma spray systems, and more particularly, to The present invention relates to a plasma spray system that extends the service life of an anode portion around a plasma torch nozzle ejection port.

(Problems to be Solved by Prior Art and Invention) In a plasma spray system for injecting powder,
The arc column itself or its ionic body is used as an ultra-high temperature heat source. This utilization plays an important role in the technique of extending the arc column further away from the nozzle jet than in the case of conventional plasma torches. Figure 1 attached
Shown is a conventional plasma spray torch 10 '. The water cooling means has been removed to simplify the drawing. The cylindrical cup-shaped electrical insulator 10 holds a cathode rod 12 extending along the central axis of the insulator 10 at its bottom closure wall. The cathode rod 12 is not in contact with the nozzle member 11 mounted in the opening of the electric insulator 10. The nozzle member 11 has a nozzle hole 11a at the center thereof and provides a plasma spray torch nozzle passage 9. The arc body 17 includes a cathode rod 12 and a nozzle member 11 that acts as an anode.
It is caused by the potential difference between and. The arc body 17 passes between the cathode rod 12 and the inner wall of the nozzle passage 9. Arc body
The length of 17 is extended by the plasma forming gas (G) supplied from the gas supply pipe 15 to the periphery of the cathode rod 12 in the annular manifold 24. Gas supply pipe 15 is an electrical insulator
It is coaxially connected to the insertion hole 15a provided in the cylindrical side wall of the column 10. Inside the cylindrical cup-shaped insulator 10,
A cathode rod (12) which is a transverse partition (13) made of an insulating material such as an insulator (10) is stably supported. A large number of small-diameter through holes 23 are provided in the partition body 13, and the plasma forming gas is sent to the nozzle passage 9 through the periphery of the tapered tip portion 12a of the cathode rod body 12. The powder (P) injected from the nozzle injection port is sent into the gas heated by the arc body 17 at a location beyond the tip portion 18 of the arc body 17. This powder passes from the tube body 16 through the passage 16 ′ leading to the nozzle hole 11a, and the nozzle hole 1
Introduced into 1a under optimal conditions.

A very bright and shining substantially conical arc portion 19 extends slightly from the nozzle portion 9. This arc portion 19 is an extension of the ionized gas body. A large amount of heat exchange is performed in the arc portion 19. The powder particles (P) are further heated in the hot gas stream 25 over the arc portion 19. The powder particles (P) are further accelerated in the high-speed (sonic velocity or less) gas flow 25, and are processed.
A coating film 21 is formed by colliding with the surface of 22.

One example of conventional plasma spray torch 10 ′ Plasma forming gas: Nitrogen (G: 100SCFH) Nozzle passage 9 radius: Approx. 4 mm Operating current: 750 amps Operating voltage: 80 V Conical arc projection length: Approx. 8.5 mm Maximum Achieved power: 60kw Anode / cathode loss voltage: 30V Heating capacity: 37.5kw Actual heating capacity (when heat loss to cooling water is 20%): 30kw Plasma gas enthalpy increase: Approximately 14,500 BTU / lb So-called low voltage arc ( The current plasma system which employs about 80 volts is constructed as shown in FIG. If the material to be sprayed is heat resistant, providing a high temperature heating region is a great advantage. However, if it is a non-heat resistant material,
Such a plasma system has been difficult to use.

The conventional plasma torch heats the powder particles almost instantly when passing through the substantially conical arc portion 19 of FIG. Most (particularly small ones) of these powder particles melt completely and even evaporate. Refractory materials such as tungsten carbide (WC) are decarbonized to form unwanted W ₂ C. The molten particles can also be heavily oxidized.

The device referred to as "D-GUN" provides a much faster, long-lasting heat source at much lower temperatures, unlike conventional flash plasma devices. The low-temperature, high-speed heat source heats and softens the powder particles without melting them. The softened particles maintain their chemical composition and only slightly oxidize when sprayed onto a work piece in the atmosphere.

FIG. 2 is a longitudinal cross-sectional view of an improved non-transfer type plasma arc torch for extending an arc. 2a is the same as FIG.
FIG. 4 is an enlarged cross-sectional view of a nozzle ejection port portion of the torch illustrated in FIG. The improved plasma spray torch 10 has a cylindrical cup body 30 made of an electrically insulating material. Cylindrical cup body
A cylindrical nozzle member 31 is engaged with the opening of 30. The bottom of the cylindrical cup body 30 defines a bottom wall 30a. Bottom wall 30a
Holds a cathode rod body 32 extending along the central shaft portion of the cylindrical chamber 41 inside the cylindrical body 30. Cathode rod
A tip portion 32a of 32 is formed in the nozzle upstream opening of the nozzle hole wall 31a that defines the torch nozzle passage 34, and projects into a substantially conical portion 35 opened in the chamber 41.

The plasma-forming gas flow (G) is supplied into the chamber 41 through the passage 33 from the gas supply pipe 26 provided perpendicularly to the cylindrical chamber 41, becomes a strong vortex, and becomes a substantially tapered cone. The shape portion 35 is further accelerated and guided into the nozzle passage 34. The central core, which has a small diameter of the high-speed vortex, has a lower gas pressure than the gas layer near the nozzle hole wall 31a that is the wall of the passage 34. The arc column 37 extending into the nozzle hole 34a can extend beyond the ejection portion 34a of the nozzle passage 34 by passing through the low pressure center portion thereof. Although this phenomenon has not been elucidated, the critical pressure drop that eliminates the suppression of the arc anode that occurs at subsonic speeds by decreasing the diameter of the passage 34 and / or increasing the arc current. Is created in its transit path to the atmosphere via passageway 34. The arc anode area can be further expanded using supersonic flow.

The extended arc portion 37 (ionization region) is an arc portion having a smaller diameter than the ionized substantially conical arc portion 19 (FIG. 1) of the above-mentioned conventional example, and its length is also overwhelmingly long.

Example of using plasma spray torch 10 Plasma forming gas: Nitrogen (G: 120SCFH) Nozzle passage radius: Approx. 2.4 mm Operating current: 400 amps Operating voltage: 200 V Conical arc projection length: Approx. 30 mm Maximum achieved power: 80 kw Anode / cathode loss voltage: 30 V Plasma gas enthalpy increase: Approximately 27,000 BTU / lb (when heat loss to cooling water is 20%) This enthalpy is almost double that of the previous example.

In the anode ejection portion 36 of the nozzle passage 34 shown in FIG. 2a, the cylindrical nozzle member is heated by the anode and oxygen in the atmosphere.
An erosion portion 39 is formed in the shape of a truncated cone 31 in the portion 31. It takes several hours after the start of use of the apparatus to start the formation, and the erosion rate decreases as the erosion portion 39 expands. It is considered that this deceleration is due to the gas that obstructs the inflow of oxygen into the eroded portion 39. The presence of such an eroded portion 39 is inconvenient and is best excluded.

Therefore, an object of the present invention is to provide a method and apparatus for extending the service life of the anode nozzle portion near the plasma torch nozzle ejection port as described above.

(Means and Actions for Solving the Problems) The present invention relates to an improved plasma arc torch. The plasma arc torch includes a cylindrical insulator that provides a chamber inside. One end of the cylindrical body is a cylindrical nozzle body serving as an anode, and a nozzle passage is provided in a central shaft portion thereof. A cathode rod extends from the closed end along the central axis of the cylindrical inner chamber. The cathode rod is electrically insulated from the anode. The end portion of the nozzle passage facing the tip portion of the substantially conical cathode rod body extends in a substantially conical shape in the chamber, and covers the tip portion of the cathode rod body in a non-contact manner.

Gas supply means for introducing pressurized gas into the internal chamber is provided in the cylindrical body. There is a potential difference between the tip of the cathode rod and the anode, and a plasma arc is created from the anode to the cathode. An annular metal ring body is usually provided around the anode nozzle ejection port. The improvement of the present invention is to provide a discontinuity, that is, a deformed portion in the nozzle passage, which extends the arc column, and the arc column is under sufficient control until reaching the nozzle passage ejection port. Placed.

Suitably, the plasma-forming gas is supplied vertically to the cylindrical insulator inner chamber at a location remote from the anode nozzle passage to form a low pressure vortex core portion extending into the nozzle passage, the low pressure vortex gas core portion being provided in the nozzle passage. A small diameter arc column is formed that extends partially inside. It is preferable that the arc column passes through the nozzle passage by the boundary layer of the vortex gas along the wall portion of the nozzle passage, and the arc portion is provided at the deformed portion of the nozzle passage or immediately downstream thereof.

Such a deformed portion can be formed by inserting an appropriate annular groove forming machine from the ejection port of the nozzle passage or from the other end of the nozzle passage and cutting the inside of the nozzle passage. Alternatively, it is also possible to provide the annular projection inside the passage by processing the nozzle passage in both directions.

Suitably, means are provided for providing the injectable material in the high velocity hot gas stream downstream of the arc column so that the torch does not overheat the injected particles. The deformed portion in the nozzle passage is preferably provided between the end portion of the arc column and the injection material providing means.

(Explanation of the Preferred Embodiment) FIG. 3 is explained. The plasma spray torch 10 ″ extends from the cylindrical cup-shaped electrical insulator 30 and its closed bottom, has a substantially conical tip 32a, and is a cathode rod provided on the central shaft of the electrical insulator 30. 32, a chamber 41 inside the electrical insulator 30, and a cathode nozzle body 31 'provided in an opening opposite the bottom of the cup body 30. Cathode rod body 32.
The substantially conical tip portion 32a of the nozzle passage 54 (nozzle hole 51)
It is inserted in a non-contact type into a substantially conical portion 35 that is opened in a substantially conical shape toward the chamber 41 of the nozzle body 31 'having the. The nozzle body 31 'of the present invention is formed longer than the nozzle body of FIGS. The tip portion (nozzle ejection port) 52a of the nozzle passage 54 of the cathode nozzle body 52 of the present embodiment is provided with a large-diameter nozzle hole portion 57 having a larger diameter than the other nozzle portion on the chamber 41 side. There is. An annular shelf 58 is provided upstream of the large-diameter nozzle hole 57 (opposite the ejection port).
The arc anode ring 59 is formed at a distance from the nozzle tip portion 52a by the action of its shape.

The vortex gas 53 around the cathode rod 32 passes through the substantially conical portion 35 of the nozzle passage 54 and focuses the arc column 55 along the nozzle passage 54. The focused arc column 55 is sent to the downstream tip portion 52 of the nozzle passage 54 and ejected from the ejection port. The annular shelf 58 has a relatively narrow width and is provided at a location where oxygen in the outside air does not reach. The diameter of the large diameter nozzle hole 57 may be 1/10 larger than the diameter of the other narrow nozzle hole 51. In typical high voltage operation, the arc anode ring 59 is formed approximately 95 mm from the cathode rod downstream tip. The nozzle hole 51 in this case is about 129 mm, and the large diameter nozzle hole 57 is about 9 mm.
mm. In a typical plasma arc torch,
The plasma forming gas (G) is nitrogen gas, and the working voltage is
It is 400 volts. By relatively increasing the length of the large diameter nozzle hole 57, it is possible to reduce the operating voltage.

It is worth noting that the narrow width annular ledge 58 allows for sufficient control of the arc length characteristics. This feature makes the plasma spray device of the present invention far superior to conventional plasma spray devices.

It is considered that this improvement phenomenon is due to the disturbance of the peripheral flow along the wall of the anode nozzle hole, whereby the arc forms the arc anode ring 59 with the wall of the nozzle hole immediately after the disturbing point.

Another example of the present invention will be introduced. In this example, the large diameter nozzle hole
An annular groove 60 is provided instead of 57 (Fig. 3a). The depth of the annular groove 60 may be the same as the width of the annular shelf 58. By the action of the annular groove portion 60, the arc column 55 is extended in the nozzle hole 51 under stable control as in the above-mentioned example.

Another example of the present invention is introduced in FIG. 3b. In this example, instead of the large diameter nozzle hole portion 57 or the annular groove portion 60, a small diameter nozzle hole portion 74 having a smaller diameter than the other upstream nozzle hole portion 51 is provided. The width of the upstream annular shelf 75 of the small diameter nozzle hole 74 may be the same as the width of the annular shelf 58.
In this case as well, the arc column 55 is controlled and extended in the nozzle hole 51 by the physical action of the annular shelf 75 as in the above-described two examples.

Still another example of the present invention is introduced in FIG. 3c. In this example, instead of the large diameter nozzle hole portion 57, the annular groove portion 60, or the small diameter nozzle hole portion 74, an annular protrusion portion 76 is provided. The height of the annular protrusion 76 may be the same as the width of the annular shelf 58. Even in this case, the arc column 55 is controlled and extended in the nozzle hole 51 by the action of the annular projection 76 as in the case of the above-mentioned three examples.

Also in the plasma arc torch of all the preferred embodiments of the present invention described above, the injection powder is the same as in the conventional case and the arc column 55.
Is supplied into the high-speed gas stream (ionization region) downstream of the.

In FIG. 4, a further improved version of the four embodiments, especially the embodiment of FIG. 3, is introduced. This plasma arc device further reduces the amount of heat input to the powder for injection.
This device is suitable for further increasing the ejection speed of the thermosoftening particles ejected from the nozzle. This device 10
Includes a cylindrical cup-shaped electrical insulator 30, a cathode rod body 32 having a substantially conical tip portion 32a, and an anode nozzle body 61, and an upstream opening of a nozzle passage 63 of the anode nozzle body 61 is a chamber 41.
It opens in a substantially conical shape toward. The plasma forming gas is vertically supplied to the inner chamber 41 inside the electrical insulator 30, and spirally passes around the cathode rod 32.

A cylindrical large-diameter nozzle portion 65 having a larger diameter than the other nozzle holes 74 on the upstream side is provided in the middle portion of the nozzle hole near the downstream end of the nozzle, and an annular shelf portion is provided on the upstream edge thereof. 66 is formed, and a rounded squeezed part is formed on the downstream edge.
67 is formed. The annular shelf 66 is the annular shelf 5 described above.
8, the annular groove portion 60, the annular ledge portion 75, or the annular projection portion 76 to act in the same manner to create the arc anode ring 62. Narrowing unit
67 is for maintaining the upstream gas flow at a desired gas pressure by accelerating the gas flow. A substantially frustoconical nozzle hole 68 that gradually opens downstream to the nozzle ejection port, which is the nozzle tip, forms a supersonic jet stream 71. The supersonic jet stream 71 forms an intermittent impact portion 72 on the downstream side of the nozzle ejection port.

The powder material 73 for injection is introduced from the tube 69 through the passage 70 into the expanded gas flow in the nozzle hole 68 of the substantially truncated cone shape, and is discharged to the supersonic jet flow 71. The powder particles 73 are mainly affected only by their hot gases, but probably the supersonic jet flow.
It will also be affected by some of the dissociated gas forming 71. Also in this example, there are not enough ionized particles to maintain the arcing phenomenon and form the bright and shiny generally conical shape created in a conventional torch. Even when the temperature in the ionization region reaches as high as 20,000 degrees Fahrenheit, the improved system of the present invention can reduce the number of ionized particles by half.

The danger of UV radiation is eliminated in the system of the invention. However, the temperature of the jet stream is much higher than that of the internal combustion type. Therefore, the transported particles 73 are quickly softened by the time they reach the object to be processed. By adjusting the relationship between the gas enthalpy before colliding with the work piece, the jet velocity and the particle transport distance, the particles 73
Can be brought into an appropriate heat softened state.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of a conventional plasma spray torch used for spray application processing of an object to be processed. FIG. 2 is a vertical cross-sectional view of another example of the non-transfer type plasma arc torch. FIG. 2a is an enlarged sectional view of a nozzle ejection port of the plasma arc torch of FIG. FIG. 3 is a vertical cross-sectional view of the tip of a non-transfer type plasma arc torch according to a preferred embodiment of the present invention. FIG. 3a is a vertical cross-sectional view of a tip portion of a non-transfer type plasma arc torch according to another preferred embodiment of the present invention. FIG. 3b is a vertical cross-sectional view of the tip of a non-transfer type plasma arc torch according to another preferred embodiment of the present invention. FIG. 3c is a vertical cross-sectional view of the tip of a non-transfer type plasma arc torch according to another preferred embodiment of the present invention. FIG. 4 is a vertical cross-sectional view of a tip portion of a non-transfer type plasma arc torch according to still another preferred embodiment of the present invention.

Claims (11)

[Claims] 1. A plasma arc torch comprising a cylindrical electrically insulating container (30), an electrically insulating bottom wall provided at one bottom of the cylindrical container, and at the other bottom of the cylindrical container. And including a nozzle hole (51) extending downstream along the central axis of the cylindrical container,
A conductive nozzle body (52) acting as an anode, the conductive nozzle body (52) protruding from the center of the electrically insulating bottom wall along the central axis of the cylindrical container into the cylindrical container. ) And a cathode rod body (32) electrically insulated from the nozzle body (52) without contacting the nozzle body (52), and the end of the nozzle hole (51) facing the inside of the cylindrical container. Is provided with a substantially frustoconical portion (35) that opens in a substantially frustoconical shape toward the inside of the cylindrical container, and the tip portion of the cathode rod (32) inside the cylindrical container has a substantially conical shape. The shape,
The tip portion of the conical cathode rod body is inserted in the substantially truncated cone shape portion (35) of the nozzle hole in a non-contact manner, and further, a gas for introducing a pressurized plasma forming gas into the inside of the cylindrical container. It is designed so that the pressurized plasma forming gas (53) introduced into the container including the supply means advances spirally around the cathode rod body and reaches the nozzle hole (51). The nozzle hole (5) includes a potential left applying means for applying a potential difference between the cathode rod body (32) and the nozzle body (52).
A plasma arc is created at the tip of the cathode rod body from 1), and is further deformed so as to change the diameter of the nozzle hole in the nozzle hole that is located upstream from the ejection port of the nozzle hole (51). Part is provided, the plasma arc generated in the vicinity of the deformed portion is suitably deformed, and the arc column (55) having an ionization region immediately downstream of the deformed portion is maintained under favorable conditions until reaching the nozzle hole ejection port. , Extending the service life around the ejection portion of the anode nozzle hole, the arc is placed under sufficient control over the entire length of the nozzle hole, and the plasma forming gas is vertically supplied into the container to form the cathode. A low-pressure / high-speed core gas flow is created in the nozzle hole by advancing as a vortex flow around the rod body, and the core gas flow provides a focused arc column (55) with a small diameter up to the middle of the nozzle hole, and the nozzle hole wall To The swirled gas flow layer forms an arc anode ring (59) in the deformed portion or immediately downstream thereof by the action of the deformed portion, and further, at a high speed at the downstream side of the arc column (55), A material supply means for introducing a jetted material into a hot gas stream that does not contain ions, the temperature of the material supply region of the hot gas stream being lower than the temperature of the arc column, and excessive heating of the material. The plasma arc torch is characterized in that 2. The deformed portion is an annular shelf portion (58) provided on an upstream side edge portion of a columnar large-diameter nozzle hole portion (57) extending from the ejection port of the nozzle hole to the inside of the nozzle hole. The plasma arc torch according to claim 1, wherein the diameter of the columnar large-diameter nozzle hole is larger than the diameter of the other nozzle hole on the upstream side. 3. The plasma arc torch according to claim 2, wherein the diameter of the columnar large-diameter nozzle hole portion is larger than the diameters of other nozzle hole portions upstream thereof within the range of 25%. 4. The diameter of the columnar large-diameter nozzle hole is larger than the diameter of other nozzle holes upstream of the column within 40%, and the position of the annular shelf in the nozzle hole is the desired arc voltage. A plasma arc torch according to claim 2, characterized in that 5. The deformed portion is an annular groove portion (60), and the position, depth and width of the annular groove portion in the nozzle hole (51) are determined by the arc anode ring (59) immediately downstream of the annular groove portion. ) The plasma arc torch according to claim 1, characterized in that 6. The deformed portion is an annular shelf (75) provided on the upstream side of a columnar small-diameter nozzle hole (74) having a smaller diameter than the upstream nozzle hole, and the nozzle of the annular shelf is provided. Holes (51)
A plasma arc torch according to claim 1, characterized in that its position within is determined to create an arc anode ring (59) immediately downstream of the annular ledge. 7. The deformed portion is an annular protrusion (76), and the position of the annular protrusion in the nozzle hole (51) creates an arc anode ring (59) immediately downstream of the annular protrusion. The plasma arc torch according to claim 1, wherein the plasma arc torch is determined to be set. 8. The deformed portion is an annular shelf portion (66) provided at an upstream side edge of a columnar large diameter nozzle hole portion (65) provided at an intermediate portion inside the nozzle hole (74), A narrowed portion (67) is provided on the downstream side edge of the columnar large diameter nozzle hole, and a diameter gradually increases from the narrowed portion to the nozzle hole ejection port downstream of the columnar large diameter nozzle hole. 2. A plasma arc torch according to claim 1, wherein a substantially frustoconical nozzle hole portion (68) having a large diameter is provided, and a supersonic jet flow is created at the nozzle hole jet port. . 9. A plasma spray method for a plasma arc torch, wherein the plasma arc torch comprises a cylindrical electrically insulating container, an electrically insulating bottom wall provided at one bottom of the cylindrical container, and the cylindrical shape. A conductive nozzle body that is provided at the other bottom of the container and that extends downstream along the central axis of the cylindrical container and that acts as an anode; and from the center of the electrically insulating bottom wall, the cylinder The cathode rod body that protrudes into the cylindrical container along the central axis of the cylindrical container, does not contact the conductive nozzle body, and is electrically insulated from the nozzle body; The end of the nozzle hole facing the inside of the cylindrical container is provided with a substantially frustoconical portion that opens in a substantially frustoconical shape toward the inside of the cylindrical container, and the cathode rod inside the cylindrical container. The tip of is a substantially conical body with a substantially conical shape The tip end of the substantially conical cathode rod body is inserted into the substantially frustoconical part of the nozzle hole in a non-contact manner, and the plasma spray method of the plasma arc torch includes the inside of the cylindrical container. A pressurized gas is supplied from a gas supply means for introducing a pressurized plasma forming gas into the container, the cathode rod body inside the container is swirled, and a potential difference is applied between the cathode rod body and the nozzle body. A potential difference is created between the two by means of a potential difference providing means, a plasma arc is created from the nozzle hole to the tip of the cathode rod body, and an appropriate size is provided in the nozzle hole at an appropriate distance from the nozzle hole jet port. A deformed portion of a shape is provided, the generated plasma arc is suitably deformed in the vicinity of the deformed portion, an arc anode ring is created immediately downstream of the deformed portion, and an arc column having an ionized region is provided downstream thereof. A full hole inside the nozzle hole, the arc is placed under sufficient control over the entire length of the nozzle hole to extend the service life of the peripheral portion of the anode nozzle hole outlet, and substantially at high speed downstream of the arc column. Surface of the object to be processed by supplying the material particles into the high temperature gas flow by means of a material supply means for introducing the jetting material into the high temperature gas flow that does not contain ions, excluding excessive heating of the material particles. A plasma spray method of a plasma arc torch, characterized in that the softened material particles are processed by colliding at a supersonic speed. 10. The position of the deformed portion within the nozzle hole is determined by the intensity of the desired arc voltage between the anode nozzle body and the cathode rod body. Plasma arc torch plasma spray method. 11. A squeezing section is provided on the downstream side of the deforming section,
An ion-free high-temperature gas is accelerated to supersonic speed, and a substantially frustoconical nozzle section is provided on the downstream side of the narrowing section, the diameter of which gradually increases toward the nozzle ejection port. 11. The plasma spray method for a plasma arc torch according to claim 10, wherein a jetting material is supplied to the nozzle portion.