CN113677081B - Reversed polarity plasma spraying gun for ultra-low pressure plasma spraying - Google Patents

Abstract

The invention discloses a reverse polarity plasma spraying gun for ultra-low pressure plasma spraying, comprising a gun body part and an external nozzle part; the gun body part adopts a reverse polarity with a front central through hole cathode and a rear cup-shaped anode. The electrode structure design enables the spray gun to achieve greater power under lower current conditions, reducing the ablation of the electrode and the pollution of the coating; the external nozzle part adopts a graphite nozzle with a straight cylindrical through hole, which is improved by compressing the jet. It increases the jet temperature under low pressure, and greatly prolongs the residence time of the powder in the high temperature jet area, so that the powder can be fully melted and gasified under the condition of low pressure environment and small spray gun power; gas cooling is used to quantitatively cool the graphite spray. The inner wall of the nozzle is at a higher temperature, combined with a larger plasma gas flow, which effectively solves the problem of powder deposition and blockage on the inner wall of the tube wall.

Description

A reverse polarity plasma spray gun for ultra-low pressure plasma spraying

technical field

The invention relates to the field of plasma spraying, in particular to a reverse polarity plasma spraying gun used for ultra-low pressure plasma spraying.

Background technique

Ultra-low pressure plasma spraying is widely used because it can prepare columnar thermal barrier coatings similar to electron beam vapor deposition, which have better resistance and thermal shock resistance than traditional atmospheric spray coatings. It is used in the key hot-end components of aero-engines that require high coating performance. In an ultra-low pressure (50-200 Pa) environment, the plasma jet ejected from the outlet of the gun can expand to 2 m in length and the diameter can be increased to 200-400 mm, but because the density of the plasma jet outside the outlet is significantly reduced, it is also The ability of the external plasma jet to heat the powder is greatly reduced, and it is a huge challenge to achieve partial or complete gasification of high-melting ceramic powders.

The current solutions mainly include two, one is to greatly increase the power of the spray gun to 120-180 Kw by using an ultra-high arc current (2500-3000 A), and send the powder into the inside of the anode about 10-20 from the outlet mm, such as the 03CP spray gun produced by Oerlikon Metco and the MC100 spray gun produced by Medicoat; the other is to add an extended water-cooled horn-shaped nozzle at the outlet of the medium-power atmospheric spray gun, by feeding the powder into a relatively A long water-cooled nozzle is used to prolong the residence time of the powder in the high temperature area of the jet, for example, a spray gun for low-pressure plasma spraying with the authorization announcement number of CN 101954324 B. The above two schemes have the following defects: 1) The above two spray gun electrodes are rod-shaped cathodes and straight cylindrical anodes, and the traditional positive connection method is used with the power supply. Larger power and jet enthalpy can only be achieved by increasing the current, but the increase in current will lead to rapid ablation of the electrode, thereby reducing the service life of the electrode and contaminating the coating, limiting the further promotion and application of the spray gun; 2) Spray The outside of the tube is cooled by cooling water, which will quickly take away the heat of the nozzle, so that the inner wall of the nozzle is in a lower temperature state. The vaporized powder will rapidly cool, solidify and bond, which will block the nozzle and make the spray gun unable to work normally for a long time; 3) The gradually expanding flared nozzle design will reduce the compression effect of the nozzle on the jet to a certain extent, thereby reducing the The heating effect of the jet on the powder makes it difficult to achieve sufficient melting and vaporization of the powder.

SUMMARY OF THE INVENTION

In view of the deficiencies of the above-mentioned prior art, the present invention provides a reverse polarity plasma spray gun for ultra-low pressure plasma spraying. Achieve higher arc voltage and gun power under lower input arc current conditions, and greatly increase the residence time of powder in the high temperature zone of the jet core, while suppressing the powder's turbidity by controlling the plasma gas flow and the inner wall temperature of the graphite nozzle Sedimentation and clogging, to maximize the full melting and gasification of powders in ultra-low pressure environments.

In order to achieve the above objects, the technical solutions of the present invention are as follows.

The invention discloses a reverse polarity plasma spraying gun for ultra-low pressure plasma spraying, comprising a gun body 1 and an external nozzle 10; the gun body 1 comprises a front central through-hole cathode 2 and a rear cup-shaped anode 3 , insulating body 4, main gas intake pipe 5, main gas distribution ring 6, cooling water inlet pipe 7 and cooling water outlet pipe 8; the external nozzle 10 includes a ceramic gasket 11, a graphite nozzle 12, a tungsten bushing 13. Air-cooled sleeve 14, cooling air inlet pipe 15, cooling air outlet pipe 16, powder feeding pipe 17 and thermocouple 18; the gun body 1 and the external nozzle 10 are compressed by the bolts on the air-cooled sleeve 14 Seal the connection.

The graphite nozzle 12, the cathode 2, and the anode 3 are arranged concentrically from front to back, and isolation and insulation are achieved between the cathode 2 and the anode 3 through the PTFE main gas distribution ring 6. The graphite nozzle 12 and the cathode 2 The boron nitride ceramic gasket 11 is used to isolate and insulate between them to prevent the cathode arc root from transferring to the graphite nozzle, thereby ablating the nozzle and contaminating the coating.

The cathode 2 and the anode 3 are provided with a water cooling tank outside, and the cooling water enters from the water inlet pipe 7, flows through the water cooling tank outside the anode 3 and the cathode 2 in turn, and flows out from the water outlet pipe 8 to realize the forced cooling of the cathode 2 and the anode 3. .

A main gas distribution ring 6 is arranged between the cathode 2 and the anode 3, and the plasma forming gas enters from the main gas inlet pipe 5, flows through the main gas distribution ring 6 with a rotating air distribution hole, and then enters the arc chamber channel, and passes through the main gas distribution ring 6. The airflow with the swirling direction stretches and prolongs the initial arc 9 between the cathode and anode, and maintains a dynamic stable state.

The graphite nozzle 12 is inlaid with a tungsten bushing 13, and the tungsten bushing has a high melting point and good mechanical properties, which can effectively reduce the erosion and wear of the nozzle by the powder; The powder feeding hole 19 is communicated with the powder feeding pipe 17, and the powder is fed into the high temperature area of the central jet in the nozzle through the carrier gas and along the powder feeding hole 19.

There is a cooling groove outside the graphite nozzle 12, and a certain flow of inert cooling gas controlled by a mass flow meter enters from the cooling gas inlet pipe 15, and flows out from the cooling gas outlet pipe 16 after passing through the cooling groove, thereby realizing the jetting of graphite. Quantitative cooling and protection of tubes.

The outer two ends of the graphite nozzle 12 are respectively provided with countersinking holes, the bottom of the countersinking hole is 1-2 mm away from the graphite nozzle channel, and the temperature measuring end of the thermocouple is in contact with the bottom of the countersinking hole for temperature measurement, which is adjusted according to the power of the spray gun and the size of the nozzle. The flow rate of the cooling gas outside the nozzle is controlled by the real-time temperature measurement of the thermocouple to control the temperature of the inner wall of the nozzle within the range of 2000-2500°C; therefore, by reducing the temperature difference between the inner wall of the nozzle and the melted and gasified powder , and use a larger plasma gas flow, which can effectively inhibit the deposition and blockage of molten and vaporized powder on the hot wall of the nozzle.

The front central through-hole cathode 2 is connected to the negative pole of the power supply, and the rear cup-shaped anode 3 is connected to the positive pole of the power supply. Through the design of the reverse electrode structure, the arc can be stretched to the greatest extent on the two-pole gun structure. The cathode arc root can be easily stretched and fixed at the cathode outlet, and a larger arc voltage can be achieved, which in turn can achieve a larger gun power at a small current; therefore, this design can increase the jet temperature and enthalpy. At the same time, electrode ablation is reduced, thereby extending the service life of electrodes and spray guns.

The cathode 2 is made of a copper-embedded tungsten bushing, and the anode 3 is made of a copper-embedded molybdenum bushing, so the design can further reduce the ablation of the electrode and the pollution to the coating.

The main gas distribution ring 6 is evenly distributed with 8 air holes with a diameter of 1-2 mm, and the radial rotation angle of the air holes is 45°C. The arc root continues to ablate at one point on the electrode.

The diameter of the powder feeding hole 19 is 1-2 mm, and the distance between the outlet of the powder feeding hole and the cathode outlet is 2-5 mm, so that the powder can be fed into the central high temperature area near the cathode outlet of the spray gun; the outlet of the powder feeding hole is far from the outlet of the graphite nozzle. It is 60-120 mm, which can greatly prolong the heating time of the powder in the high-temperature jet of the nozzle, improve the utilization rate of the jet energy, and make the powder fully melt and gasify.

The central through hole of the graphite nozzle 12 is a straight cylinder with an inner diameter of 4-10mm. The cylindrical flow channel design with a relatively small diameter can effectively compress the jet, increase the temperature of the jet, and make the powder from entering to leaving the nozzle. always in the high temperature jet area.

The external cooling tank of the graphite nozzle 12 is cooled by inert gas such as nitrogen and argon. The use of inert gas cooling can prevent the oxidation and consumption of graphite at high temperature, and greatly prolong the service life of the graphite nozzle.

A reverse polarity plasma spraying gun for ultra-low pressure plasma spraying of the present invention has the following advantages: 1) Under the condition of lower arc current (500 A), the power of the spraying gun can reach 60 Kw, so it can greatly reduce the impact of high current on The ablation effect of the electrode prolongs the service life of the spray gun; 2) The design of the external small diameter straight cylindrical nozzle greatly improves the residence time of the powder in the high temperature area of the jet, improves the utilization rate of the energy of the spray gun, and makes the spray gun in the ultra-low pressure environment. The ceramic powder can also be fully melted and gasified with relatively low power; 3) The design of the external nozzle using gas cooling can accurately control the inner wall temperature of the nozzle, and the higher inner wall temperature combined with the faster plasma jet velocity is effective Solved the deposition and blockage of molten and vaporized powder inside the nozzle.

Description of drawings

In order to illustrate the embodiments of the present invention or the technical solutions in the prior art more clearly, the following briefly introduces the accompanying drawings that need to be used in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only These are some embodiments of the present invention, and for those of ordinary skill in the art, other drawings can also be obtained from these drawings without creative labor.

FIG. 1 is a schematic structural diagram of the present invention.

Reference symbols: 1-gun body; 2-front center through hole cathode; 3-rear cup anode; 4-insulation body; 5-main gas intake pipe; 6-main gas distribution ring; 7-cooling water Water inlet pipe; 8-cooling water outlet pipe; 9-electric arc; 10-external nozzle; 11-ceramic gasket; 12-graphite nozzle; 13-tungsten bushing; 14-air cooling sleeve; 15-cooling air inlet Air pipe; 16-cooling air outlet pipe; 17-powder feeding pipe; 18-thermocouple; 19-powder feeding hole.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work, any modifications, equivalent replacements, improvements, etc., should be included in the protection scope of the present invention. Inside.

As shown in FIG. 1, a reverse polarity plasma spray gun for ultra-low pressure plasma spraying of the present invention includes a gun body 1 and an external nozzle 10; the gun body 1 includes a front central through hole cathode 2, a rear A cup-shaped anode 3, an insulating body 4, a main gas inlet pipe 5, a main gas gas distribution ring 6, a cooling water inlet pipe 7 and a cooling water outlet pipe 8; the external nozzle 10 includes a ceramic gasket 11, a graphite nozzle 12. Tungsten bushing 13, air-cooled sleeve 14, cooling air inlet pipe 15, cooling air outlet pipe 16, powder feeding pipe 17 and thermocouple 18; the gun body 1 and the external nozzle 10 pass through the air-cooled sleeve 14 The bolts on the compress the sealing connection.

The graphite nozzle 12, the cathode 2, and the anode 3 are arranged concentrically from front to back, and isolation and insulation are achieved between the cathode 2 and the anode 3 through the PTFE main gas distribution ring 6. The graphite nozzle 12 and the cathode 2 The boron nitride ceramic gasket 11 is used to isolate and insulate between them to prevent the cathode arc root from transferring to the graphite nozzle, thereby ablating the nozzle and contaminating the coating.

The cathode 2 and the anode 3 are provided with a water cooling tank outside, and the cooling water enters from the water inlet pipe 7, flows through the water cooling tank outside the anode 3 and the cathode 2 in turn, and flows out from the water outlet pipe 8 to realize the forced cooling of the cathode 2 and the anode 3. .

A main gas distribution ring 6 is arranged between the cathode 2 and the anode 3, and the plasma forming gas enters from the main gas inlet pipe 5, flows through the main gas distribution ring 6 with a rotating air distribution hole, and then enters the arc chamber channel, and passes through the main gas distribution ring 6. The airflow with the swirling direction stretches and prolongs the initial arc 9 between the cathode and anode, and maintains a dynamic stable state.

The graphite nozzle 12 is inlaid with a tungsten bushing 13, and the tungsten bushing has a high melting point and good mechanical properties, which can effectively reduce the erosion and wear of the nozzle by the powder; The powder feeding hole 19 is communicated with the powder feeding pipe 17, and the powder is fed into the high temperature area of the central jet in the nozzle through the carrier gas and along the powder feeding hole 19.

There is a cooling groove outside the graphite nozzle 12, and a certain flow of inert cooling gas controlled by a mass flow meter enters from the cooling gas inlet pipe 15, and flows out from the cooling gas outlet pipe 16 after passing through the cooling groove, thereby realizing the jetting of graphite. Quantitative cooling and protection of tubes.

The outer two ends of the graphite nozzle 12 are respectively provided with countersinking holes, the bottom of the countersinking hole is 1-2 mm away from the graphite nozzle channel, and the temperature measuring end of the thermocouple is in contact with the bottom of the countersinking hole for temperature measurement, which is adjusted according to the power of the spray gun and the size of the nozzle. The flow rate of the cooling gas outside the nozzle is controlled by the real-time temperature measurement of the thermocouple to control the temperature of the inner wall of the nozzle within the range of 2000-2500°C; therefore, by reducing the temperature difference between the inner wall of the nozzle and the melted and gasified powder , and use a larger plasma gas flow, which can effectively inhibit the deposition and blockage of molten and vaporized powder on the hot wall of the nozzle.

The front central through-hole cathode 2 is connected to the negative pole of the power supply, and the rear cup-shaped anode 3 is connected to the positive pole of the power supply. Through the design of the reverse electrode structure, the arc can be stretched to the greatest extent on the two-pole gun structure. The cathode arc root can be easily stretched and fixed at the cathode outlet, and a larger arc voltage can be achieved, which in turn can achieve a larger gun power at a small current; therefore, this design can increase the jet temperature and enthalpy. At the same time, electrode ablation is reduced, thereby extending the service life of electrodes and spray guns.

The cathode 2 is made of a copper-embedded tungsten bushing, and the anode 3 is made of a copper-embedded molybdenum bushing, so the design can further reduce the ablation of the electrode and the pollution to the coating.

The main gas distribution ring 6 is evenly distributed with 8 air holes with a diameter of 1-2 mm, and the radial rotation angle of the air holes is 45°C. The arc root continues to ablate at one point on the electrode.

The diameter of the powder feeding hole 19 is 1-2 mm, and the distance between the outlet of the powder feeding hole and the cathode outlet is 2-5 mm, so that the powder can be fed into the central high temperature area near the cathode outlet of the spray gun; the outlet of the powder feeding hole is far from the outlet of the graphite nozzle. It is 60-120 mm, which can greatly prolong the heating time of the powder in the high-temperature jet of the nozzle, improve the utilization rate of the jet energy, and make the powder fully melt and gasify.

The central through hole of the graphite nozzle 12 is a straight cylinder with an inner diameter of 4-10mm. The cylindrical flow channel design with a relatively small diameter can effectively compress the jet, increase the temperature of the jet, and make the powder from entering to leaving the nozzle. always in the high temperature jet area.

The external cooling tank of the graphite nozzle 12 is cooled by inert gas such as nitrogen and argon. The use of inert gas cooling can prevent the oxidation and consumption of graphite at high temperature, and greatly prolong the service life of the graphite nozzle.

This example is used to prepare a columnar-like thermal barrier coating with a high gas phase content of 150-200 um in an ultra-low pressure environment, and the selected powder is 8YSZ with D50=12 um (the Y ₂ O ₃ content is 7-8 % ZrO ₂ powder) nano-agglomerated powder, the matrix is 316L stainless steel with high temperature resistance, and the specific spraying parameters are as follows:

Gun current: 400 A;

Gun voltage: 125 V;

Spray gun power: 50 Kw;

Nozzle length/diameter: 80/6 mm;

Nozzle inner wall temperature: 2000 °C;

Plasma gas flow (argon-hydrogen): 45/15 L/min;

Cooling gas flow (nitrogen): 30 L/min;

Powder feeding amount: 5 g/min;

Spraying distance: 1100 mm;

Substrate temperature: 900-1000 °C;

Ambient pressure: 100 Pa.

Claims (6)

1. a reverse polarity plasma spray gun for ultra-low pressure plasma spraying, characterized in that: comprise gun body (1) and external nozzle (10); Described gun body (1) comprises front center through hole cathode (2), rear cup anode (3), insulating body (4), main gas intake pipe (5), main gas distribution ring (6), cooling water inlet pipe (7) and cooling water outlet pipe (8) ); the external nozzle (10) includes a ceramic gasket (11), a graphite nozzle (12), a tungsten bushing (13), an air cooling sleeve (14), a cooling air intake pipe (15), a cooling air The air outlet pipe (16), the powder feeding pipe (17) and the thermocouple (18); the gun body (1) and the external nozzle (10) are compressed and sealed through the bolts on the air-cooled sleeve (14); The graphite nozzle (12), the cathode (2), and the anode (3) are arranged coaxially from front to back, and the three are insulated from each other; a water cooling tank is opened outside the cathode (2) and the anode (3). , the cooling water enters from the water inlet pipe (7), flows through the water cooling tank outside the anode (3) and the cathode (2) in turn, and then flows out from the water outlet pipe (8); between the cathode (2) and the anode (3) There is a main gas distribution ring (6), the plasma forming gas enters from the main gas inlet pipe (5), flows through the main gas gas distribution ring (6) and then enters the arc chamber; the graphite nozzle (12) is inlaid with tungsten The bushing (13) is provided with a powder feeding hole (19) at the rear end of the nozzle near the cathode outlet, and is communicated with the powder feeding pipe (17); The gas enters from the cooling gas inlet pipe (15), flows through the cooling tank and flows out from the cooling gas outlet pipe (16); the outer two ends of the graphite nozzle (12) are respectively provided with countersunk holes, and the bottom of the countersunk holes is distanced from the graphite jet The pipe channel is 1-2mm, and the temperature measuring end of the thermocouple is in contact with the bottom of the counterbore to measure the temperature, and the temperature of the inner wall of the nozzle is controlled within the range of 2000-2500 ℃ by adjusting the flow rate of the cooling gas; the diameter of the powder feeding hole (19) The distance from the outlet of the powder feeding hole to the cathode outlet is 2-5mm, and the distance from the outlet of the graphite nozzle is 60-120mm. 2. a kind of reverse polarity plasma spray gun for ultra-low pressure plasma spraying according to claim 1, is characterized in that: described front central through hole cathode (2) is connected with power supply negative pole, and described rear cup The anode (3) is connected to the positive pole of the power supply. 3. a kind of reverse polarity plasma spray gun for ultra-low pressure plasma spraying according to claim 1, is characterized in that: described cathode (2) material is copper embedded tungsten bushing, and described anode (3) The material is copper embedded molybdenum bushing. 4. a kind of reverse polarity plasma spray gun for ultra-low pressure plasma spraying according to claim 1, is characterized in that: described main gas distribution ring (6) is evenly distributed with 8 diameters that are 1-2mm The stomata, and the radial rotation angle of the stomata is 45°. 5. a kind of reverse polarity plasma spraying gun for ultra-low pressure plasma spraying according to claim 1, is characterized in that: the central through hole of described graphite nozzle (12) is straight cylinder shape, and inner diameter is 4-10mm . 6. A reverse polarity plasma spray gun for ultra-low pressure plasma spraying according to claim 1, characterized in that: the external cooling tank of the graphite nozzle (12) is cooled by nitrogen gas or argon gas.

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