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100HE high-enthalpy high-speed plasma spraying system
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2008-03-03 00:00
The client company conducted an on-site spraying deposition efficiency test on the 100HE computer closed-loop control plasma spraying system provided by our company. The specific test results are as follows:
Powder feeding amount: 100g/min
Spraying power: 92 kW
Spraying powder: CRO-179 chromium oxide powder
Deposition efficiency: 58.8%
Coating microhardness: HV1350
Coating porosity: 2.5%
Gao Xinhai, professor-level senior engineer, director of coating technology of Advanced Machinery Equipment Co., Ltd.
Abstract: This paper systematically introduces the technical characteristics of the 100HE plasma spraying system. The 100HE plasma spray gun adopts a brand-new gun body structure, and selects the working mode of high voltage and low current. Due to the use of a large proportion of diatomic gas as the working gas, the spray gun has the characteristics of high speed, high enthalpy and high power. Therefore, the 100HE system not only has a wide process window, but also has excellent mass production capacity, and has insurmountable advantages in the large-scale production of high-quality metal, ceramic and cermet coatings.
The 100HE is a true supersonic plasma spray gun
With the continuous advancement of thermal spraying technology, the market demand for high-quality coating products continues to expand, and manufacturers' interest in pursuing high-end coating manufacturing technology and equipment is also constantly increasing. In the process of continuous development, Progressive Technologies has attracted more and more coaters and manufacturers of coated products.
The reliability of the high-end coating is extremely high, which not only meets the requirements in terms of function, but also greatly improves the service life of the coating. 100HE plasma spraying equipment is such high-end equipment for manufacturing high-end coatings. 100HE is a new computer integrated thermal spray (Computer Integrated Thermal Spray - CITS) system, which greatly improves the productivity and controllability of plasma spraying. The 100HE spray gun adopts a new gun body structure design, which successfully realizes the ideal mode of plasma spray gun operating under high voltage and low current, greatly improving the service life of wearing parts. The most important thing is that the spray gun can generate supersonic plasma flames. A series of bright Mach knots and long cluster spray particle streams have become the most notable symbolic features of the 100HE spray gun. Since CITS implements closed-loop control on system power, working gas (argon, nitrogen, helium, hydrogen) and powder feeding gas, the 100HE spray gun can still spray high-quality coatings at high output. CITS has become a global leader in the industry both in terms of technological advancement and process adaptability.
Innovative gun body structure - intensive plasma generator, ideal mode of high voltage, low current and high power
100HE is a plasma spray gun with high power, high heat enthalpy and supersonic speed. What attracts attention is that 100HE is the only commercial high-voltage and low-current plasma spray gun with an energy of 100kW in the international market (formerly Praxair PLAZJET 250 The kilowatt plasma gun is currently discontinued). It adopts an innovative spray gun structure, and successfully realizes people's scientific and technological vision of "increasing the power of the spray gun and reducing the arc current". The benefits of high voltage and low current for plasma torches are obvious.
The main advantage:
1. Under the same power, the arc current can be reduced when the arc voltage is increased. Therefore, the voltage drop and power loss during the transmission of low-voltage direct current can be greatly reduced.
2. Increase the degree of ionization of the gas and increase the enthalpy of the spray gun. Because the gas is more easily ionized by the arc when it passes through the arc column, and the higher the arc voltage, the longer the arc column, the more contact between the gas and the arc, and the more sufficient the ionization, so that the enthalpy value of the plasma flame flow is also greatly increased improve.
3. High flame velocity. The high enthalpy of the plasma flame brings the high speed of the flame. The 100HE spray gun is a supersonic plasma spray gun. A series of bright Mach nodes and long cluster spraying particle stream become its most prominent appearance features.
4. Super long working life of parts. Because the spray gun operates at high voltage, the current of the spray gun is also small under high power, such as when the power on the gun is 90kW, the current is only 380 amps. As a single-cathode spray gun, its current density can even be lower than that of a multi-cathode spray gun. Therefore, the life of consumables is greatly extended. The service life of the anode can be as high as 1000 hours or more.
Although the high-voltage and low-current arc plasma is extremely beneficial to the plasma spray gun, it is very difficult to realize it in engineering.
Technical advantages:
1. Since the voltage of the arc is proportional to the length of the arc column of the arc, the arc current is also proportional to the section size of the arc column. The arc of low voltage and high current is thick and short, and it is easier to stabilize, while the arc of high voltage and low current is thin and long, and the generation, self-sustainment and control of the arc are not easy.
2. In order to obtain a sufficiently high arc voltage, the distance between the cathode and anode of the spray gun is as high as 70mm. It is very difficult to maintain a small current arc and keep it stable in such a long distance and high-speed airflow.
3. The arc used for spraying must be a rigid arc, so this arc plasma also needs to undergo mechanical compression, electromagnetic compression and cold compression in order to obtain the ideal flame flow velocity. The flow characteristics of the gas in the arc channel between the cathode and the anode, the cooling state of the wall, and the slight changes in the geometric dimensions and surface conditions will all affect the stability of the arc.
100HE adopts an innovative spray gun structure and precise electrical control, and is the first to achieve success in high-voltage and low-current plasma spray guns. This article makes a brief introduction to the structure of the 100HE spray gun.
Structure:
1. The schematic diagram of the internal structure of the gun body of the 100HE spray gun is as follows.
图1. 100HE喷枪结构简图
The left side of the picture is the cathode body, the middle part is the insulator and the plasma generator, and the right end is the nozzle.
2. Combined air distribution ring. The end of the protruding part of the front end of the cathode body is a tungsten cathode head, and the side of the protruding part is provided with a groove of a special shape. When combined with the ceramic ring on the insulator in the plasma generator, it forms a gas flow distribution ring that allows the working gas to flow in a programmed pattern. Compared with the air distribution ring specially designed for other spray guns, it has better centering, more accurate positioning and less damage.
3. High assembly precision. The insulator and the plasma generator are installed coaxially with high precision. The plasma generator is a combined type with a unique structure. It is composed of tubular arc compressor, isolator (separator), tungsten 3-ring side-by-side annular anode and other parts.
4. Single cathode/anode structure. When the above two parts are combined, an arc can be formed in the spray gun, and an arc plasma flame is generated for spraying. This structure of 100HE is applicable to all working modes without any changes. That is to say, 100HE does not have many kinds of complicated cathode/anode configurations like some traditional spray guns. It only has this kind of cathode/anode hardware combination in the gun, which simplifies the structure of the spray gun and improves the process adaptability of the spray gun.
5. Discrete nozzle. Conventional commercially available plasma spray guns combine the anode and the nozzle into one. This separate nozzle/anode structure is another innovation of the 100HE. One of the advantages of the discrete structure is that the powder feeding airflow does not interfere with the arc plasma process, and the powder beam does not scour the anode. And the independent nozzle can adapt to more powder injection methods.
6. Various powder delivery methods. There are powder feeding nozzles outside the gun with different apertures, radial powder feeding nozzles inside the gun and axial powder feeding nozzles inside the gun and other combinations of powder feeding modes, which can meet various needs.
100HE adopts the traditional single anode and single cathode structure, and the structure of the spray gun is clear and concise, which makes maintenance and maintenance easier. An intensive plasma generator with patented technology is installed in the gun, and a unique long-arc stabilization technology is adopted to realize a high-voltage, low-current plasma spray gun in a real sense. The high voltage and long arc technology of the plasma spray gun is a major breakthrough in arc plasma technology.
Excellent technical performance: ultra-long arc, large proportion of diatomic gas, high-speed, high-enthalpy plasma flame
The successful implementation of high-voltage and low-current arc plasma has greatly improved the technical performance of the plasma spray gun. The ultra-long DC arc makes it possible to apply a large proportion of diatomic gas, thus greatly improving the energy level of the plasma flame. The 100HE ultra-long arc and the application of a large proportion of diatomic gas make it a high-enthalpy, supersonic plasma spray gun. The main features of the 100HE spray gun are introduced below.
The power of the gun is high
1. Due to the successful implementation of high voltage and low current technology on the spray gun, a large gun power can be obtained under low current (less than 400A), and the maximum power can reach 100kW. This is conducive to spraying refractory materials and improving spraying productivity, especially suitable for spraying production of large roller workpieces.
2. See Table 1 for typical 100HE process parameters.
Table 1: 100HE typical spraying parameters (spraying chromium oxide material)
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等离子喷枪：
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100HE
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喷涂系统：
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CITS, Closed Loop
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喷嘴：
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841121
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等离子气体：
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氩气+氮气+氢气
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等离子气体流量：
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氩气 100～180 scfh
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氮气 80～120 scfh
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氢气 60 ～90 scfh
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喷枪电流：
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380 安
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喷枪电压：
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237 伏
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喷枪功率：
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90 kW
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喷涂距离：
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4.5″
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送粉方式：
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枪内
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涂层材料：
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氧化铬，Praxair214
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送粉速率：
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100 g/min
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粒子温度：
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2550 0C
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沉积效率：
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65 %
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涂层硬度：
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平均1350
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孔隙率：
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平均1.76%
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As can be seen from the table, the content of diatomic gas is nearly 60%, and when the current is 380 amperes, the power on the gun has reached 90 kW.
High enthalpy of the plasma torch
The spray gun can use argon-nitrogen-helium and argon-nitrogen-hydrogen as working gases. Due to the breakthrough of the long arc stabilization technology, 100HE can use a high ratio of diatomic gas in the work, and the ratio of diatomic gas in the working gas can be as high as 60%. A diatomic gas molecule will first dissociate into 2 atoms under the action of an electric arc, so the ionized diatomic gas not only contains the ionization energy after ionization of atoms, but also contains a large amount of dissociation energy after dissociation of molecules. Therefore, the plasma plume generated by a large proportion of diatomic gas has high heat enthalpy and huge energy. When spraying high melting point materials, it not only has high deposition efficiency, but also has strong production capacity.
The high velocity of the plasma plume
The high power and high enthalpy of the 100HE plasma spray gun make the spray gun flame flow obtain high speed. By choosing the right combination of nozzles, the spray gun can obtain supersonic flame flow. At this time, it can be clearly seen that there are multiple bright Mach nodes in the flame flow at the exit of the spray gun, sometimes as many as 7. have the characteristics. The high speed of the flame leads to the high speed of the particles, and the high speed of the particles makes it possible to generate low-stress or even compressive-stress plasma coatings. The particle velocity of 100 HE can be similar to the particle velocity produced by some HVOF equipment, but the spray rate (throughput) and deposition efficiency of 100HE are 2 to 3 times higher than these HVOF equipment. This is because of the enthalpy of the plasma plume High, the temperature is also high.
The working condition is very stable
The 100HE plasma system adopts the CITS closed-loop control system created by Progressive Technologies, and the working state of the plasma spray gun is extremely stable.
The voltage and current of the spray gun are extremely stable. Figure 2 is the measured value of the 100HE plasma spray gun within 16 hours of operation.
Figure 2: Voltage and current variation of 100HE spray gun over 16 hours
It can be seen from the figure that the average value of the current is 370.5 A, and the maximum deviation of the current measurement is less than 0.94%. The voltage is 215.7 V, and the maximum deviation of the voltage measurement is less than 0.09%.
The gas flow of the 100HE system adopts mass flow control, so the flow of various gases is also extremely stable, see Table 2.
Table 2. The flow rate of various gases in the 100HE spray gun within 16 hours
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参数
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设定值
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平均值
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标准偏差
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氩Ar/SCFH
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240
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240
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0.01
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氮N2/SCFH
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100
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100
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0.01
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氢H2/SCFH
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60
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60.7
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0.110
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Long life of parts
Due to the high voltage and low current mode of operation, the most significant advantage is that the service life of the wearing parts in the spray gun is particularly long, because the low current causes very little burning loss to the cathode and anode. Table 3 is the service life of the wearing parts of the spray gun.
Table 3: Lifetime of wearing parts for 100 HE
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易损件
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使用寿命
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阳极
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1000小时
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阴极
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200小时
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电弧压缩器
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200-400小时
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喷嘴
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1000小时
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100HE is a plasma spray gun with innovative structure, high power, high heat enthalpy and high speed. The CITS system adopted has excellent control functions, and the work of the spray gun is extremely stable. The spray gun adopts many types of working gases and the flow rate varies widely, so the process adaptability is unparalleled. Whether it is industrial production or research and development, 100HE is the most ideal plasma spraying system.
Wide process window, superior process adaptability, unmatched coating performance
The inherent characteristics of high-voltage and low-current spray guns are that the working range is large, and the process parameters can be changed and adjusted within a wide range. This is because the long arc has high voltage, as long as the minimum current to maintain the arc is small enough, the range of variation is large enough. In addition, there are many types of working gases, a wide range of flow adjustment, and a variety of powder feeding methods, so 100HE has an extremely wide process window. Table 4 is the application range of the gas flow rate of the 100HE spray gun, and Table 5 is the variation range of the electrical parameters and power of the 100HE spray gun.
Table 4: Flow range of working gas for 100HE spray gun
gas type
SCFH (cubic feet per hour)
SLPM (liter/minute)
Ar
180～400
85～188
N2
90～120
42～56
H2
50～150
24～70
Table 5: Variation range of electrical parameters of 100HE spray gun
Spray gun voltage/V
220～275
Spray gun current/A
375～600
Gun power/kW
20～100
The main advantage of the wide process window is that it has the best process parameter configuration for each spray material. Spraying materials are ever-changing, and the technical requirements of coatings are also varied. Only spray guns like 100HE have such a wide range of process adjustments, and only 100HE can meet various requirements of coating processes. Therefore, the coating sprayed by 100HE has very superior performance.
metal coating
316 stainless steel is a kind of molybdenum-containing stainless steel, which has good corrosion resistance under high temperature conditions, resistance to chloride corrosion, and corrosion resistance to marine and aggressive industrial atmospheres. It is widely used in the industrial production process of chemical industry and papermaking, especially in various valves. The sealing surface of the butterfly valve is sprayed with 316 stainless steel, which can greatly improve the corrosion resistance and sealing performance of the valve.
If this type of coating is sprayed by conventional plasma, it will be difficult to achieve a low porosity. If it is sprayed by conventional HVOF method, the deposition efficiency of the material will be low, and the mass production capacity of both is poor. When spraying with 100HE system, adopt supersonic configuration and powder feeding method outside the gun. The results that can be obtained are:
* Coating bonding strength greater than 8000psi, porosity less than 1.5%;
* Powder feeding rate up to 100g/min;
* The deposition efficiency of sprayed materials is higher than 90%;
* The production capacity is equivalent to 2 conventional HVOF devices;
* Low stress or compressive stress coating, high reliability of the coating.
It can be seen that the coating's bonding strength, porosity and other technical indicators all meet the requirements, and the deposition efficiency is as high as 90%, which can fully meet the various requirements of mass production of high-standard coatings.
Tungsten carbide coating spraying
Since tungsten carbide material is easy to lose carbon during spraying, the hardness of the coating will decrease. Therefore, the supersonic flame (HVOF) method is often used for spraying. But compared with plasma spraying, the deposition efficiency of HVOF is too low. The 100HE system not only has the high speed and coating density of HVOF, but also has the high deposition efficiency of plasma, which is the most competitive choice for tungsten carbide-cobalt material spraying.
For WC-12Co material, the parameters of 100HE spray gun are configured as:
* Gas and flow: argon 142 L/min, nitrogen 56.6 L/min, hydrogen 23.6 L/min;
* Spray gun power: 90kW;
* Powder feeding rate: 80g/min.
The results that can be obtained are:
* The particle speed can reach 430-527m/s, the particle temperature is 1882-2100℃, and the coating deposition efficiency is as high as 81%, more than twice that of ordinary HVOF equipment.
* The average porosity of the coating is 0.58%, and the average microhardness is 1141Hv0.3. The microstructure of the coating is shown in Figure 2.
Figure 2: Metallographic photograph (200×) of 100HE sprayed WC-12Co coating.
It can be seen that the density and hardness of the tungsten carbide coating are comparable to those of the HVOF coating, and the deposition efficiency is as high as 81%, which shows the unique advantages of the 100HE system.
Zirconia Ceramic Thermal Barrier Coating (TBC)
Zirconia ceramic thermal barrier coatings are widely used in aero-engines. Zirconia ceramic materials have a high melting point and low thermal conductivity, making it difficult to spray. In addition, TBC coatings have multiple applications in aero-engines, and their respective technical requirements are also different. Some parts require a slightly higher porosity, some require a dense coating, and some even require quantitative and uniform longitudinal microcracks in the zirconia coating to increase the toughness of the ceramic coating. Since the 100 HE system has a wide process window, it can spray ceramic coatings that meet the requirements according to the actual technical requirements of TBC ceramic thermal barrier coatings.
For ZrO2+7%Y2O3, use the following spray gun parameters to configure spraying:
* Gas and flow rate: Argon 85L/min, Nitrogen 56.6L/min, Hydrogen 66 L/min;
* Spray gun power: 95kW;
* Powder feeding rate: 80g/min.
A TBC coating with a porosity of 10% can be obtained, and the deposition efficiency of the coating can reach 70%.
If you change the spray gun parameter configuration to:
* Gas and flow rate: Argon 85L/min, Nitrogen 56.6L/min, Hydrogen 56.6 L/min;
* Spray gun power: 95kW;
* Powder feeding rate: 50g/min.
Then a relatively dense coating can be obtained. After a certain heat treatment, a coating with uniform longitudinal micro-cracks can be obtained. The crack density (strip/mm) can be controlled, and the deposition efficiency of the coating can be increased to 80%.
Through process control, longitudinal microcracks perpendicular to the thickness direction of the coating are obtained, so that the toughness and reliability of TBC thermal barrier coatings can be greatly improved by using the "microcrack toughening" mechanism.
Chromium oxide coating of ceramic anilox roller:
The anilox roller is a roller that supplies ink to the printing cylinder. The ceramic anilox roller is prepared with a plasma sprayed chromium oxide ceramic coating on the surface, and the coating is engraved with micropores by laser. The surface of the roller carries a thin, uniform film of ink and deposits it on the printing plate.
According to the manufacturing process and operating conditions of the ceramic anilox roller, the requirements for the chromium oxide coating are:
the
*The coating should be dense and well-bonded, and can be finely polished and laser engraved.
*The coating should have excellent consistency and chemical purity to ensure a high quality polished surface and to ensure that the engraved micro-holes are well formed and of consistent size.
*The coating should also have sufficient strength and toughness so that it will not crack and break during engraving.
the
From the coating requirements, it can be deduced that the requirements for spraying equipment should be:
*The equipment can work stably for a long time, and has strong mass production capacity (production capacity and deposition efficiency). Once the roller starts to spray, it is generally required not to stop midway during the spraying process, especially for the production of large rollers.
*Laser engraving requires a good coating consistency, so any metal inclusions in the coating will seriously affect the engraving quality. The deposition of burnt copper foam from the anode nozzle and tungsten particles from the cathode in the coating should be avoided.
The analysis shows that the 100HE system can fully meet these requirements, because among the current commercial plasma spraying equipment, 100HE is in the lead in terms of mass production capacity, and the more critical system is the high voltage, low current operation mode, which will not produce copper in the anode nozzle. Foam flying out and splashing of tungsten particles from the cathode. Therefore, 100HE is an excellent equipment for the production of ceramic anilox rolls.
The parameters of the spray gun for spraying Cr2O3 in the 100HE system are as follows:
*0.45″ nozzle,
*Gas and flow rate: Argon 85L/min, Nitrogen 47L/min, Hydrogen 47 L/min;
* Spray gun power: 95kW;
* Powder feeding rate: 100g/min.
The obtained results are: the melting particle velocity is 245 m/s, the particle temperature is 2673°C, the microhardness is Hv1125, the deposition efficiency DE is 65.5%, and the porosity of the coating is less than 1.3%. The microstructure of the coating is shown in Figure 3.
Figure 3: Microstructural pictures of 100HE sprayed Cr2O3 coatings.
It can be seen that 100HE is an equipment suitable for spraying high-density ceramic coatings. It has large mass production capacity and extremely stable operation, and is especially suitable for large-scale industrial production of ceramic anilox rolls.
Conclusion
100HE has achieved excellent technical performance with its innovative gun body structure. The 100HE plasma spray gun adopts an ultra-long plasma arc and a large proportion of diatomic gas. The spray gun can generate high-speed, high-enthalpy plasma flame flow, and the power on the gun is large , the particle velocity is high. The powerful control function of the CITS system enables the system to work stably for a long time. The 100HE spraying system is especially suitable for the industrial production of large workpieces in factories.
100HE adopts advanced high-voltage, low-current operation mode, which greatly reduces the burning loss of nozzle/cathode, so that the life of wearing parts can be greatly increased.
100HE's innovative spray gun structure, super CITS control function, and variable powder feeding methods enable the spraying system to have an ultra-wide process window, so that 100HE has extraordinary superior process adaptability, and can be applied to each A spray material to find the most suitable process configuration. Therefore, 100HE is especially suitable for the research and development activities of scientific research departments and colleges and universities. It is used to develop new materials for thermal spraying, study new plasma spraying processes for various materials, and new mechanisms and coating combinations of coatings under various parameters. New changes to the layer material.
Completion date: 2008-02-26
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