Preparation process of alloy ceramic coating with high adhesive force

Abstract

The invention discloses a preparation process of an alloy ceramic coating with high adhesive force, which is used for a heat exchange plate of a coal economizer and comprises the following steps: pretreatment of a metal sheet, hydraulic forming of the metal sheet, supersonic plasma spraying of the alloy ceramic coating, post-treatment of the coating and performance detection. According to the preparation process, the thickness of the plating layer can be flexibly adjusted to be 50-200 microns according to the actual use requirements of the economizer under different working conditions, and the performance of the plating layer is optimized by changing spraying parameters, so that the heat exchange plate of the economizer can keep good performance under various severe working conditions; corresponding performance requirements can be met by properly adjusting process parameters, such as the component proportion, thickness and the like of the plating layer, no matter under the working condition with the high requirement for corrosion resistance or on the occasion with more attention to wear resistance.

Description

Technical Field

[0001] The invention relates to the field of alloy ceramic coating preparation, in particular to a process for preparing an alloy ceramic coating with high adhesion. Background Art

[0002] As an important heat exchange equipment in the boiler system, the economizer mainly uses the waste heat of the flue gas at the tail end of the boiler to heat the feed water, thereby improving the thermal efficiency of the boiler and reducing fuel consumption. During the operation of the economizer, the heat exchange plate is in a high temperature, high dust content and complex corrosion environment for a long time, which poses a severe challenge to its performance and service life.

[0003] Traditional economizer heat exchanger plate materials and coating processes are difficult to meet the increasingly stringent use requirements. For example, ordinary metal heat exchanger plates are easily corroded in flue gas environments, resulting in reduced heat exchange efficiency and shortened equipment life. Although some traditional coating processes can improve the corrosion resistance of heat exchanger plates to a certain extent, there are problems such as low coating adhesion, poor wear resistance, and high porosity. With the continuous growth of energy demand and increasingly stringent environmental protection requirements, the performance requirements for economizer heat exchanger plates are getting higher and higher, and a new coating preparation process is urgently needed to improve the comprehensive performance of heat exchanger plates.

[0004] In the prior art, common coating preparation processes such as electroplating and hot-dip plating have many limitations when applied to economizer heat exchanger plates. The electroplating process may cause environmental pollution, and the uniformity of the coating thickness is difficult to control. It is difficult to achieve an ideal coating effect for heat exchanger plates with complex shapes. The hot-dip plating process may cause changes in the properties of the heat exchanger plate substrate material, affecting its mechanical properties, and the bonding strength between the coating and the substrate is limited. In addition, although the traditional plasma spraying process can prepare some coatings, it has deficiencies in particle velocity, coating density and bonding strength, and cannot meet the long-term stable operation requirements of economizer heat exchanger plates under high temperature, strong corrosion and high wear conditions. Summary of the invention

[0005] The object of the present invention is to provide a process for preparing an alloy ceramic coating with high adhesion, so as to solve the defects mentioned in the above background technology.

[0006] To achieve the above object, a process for preparing an alloy ceramic coating with high adhesion is provided for use in economizer heat exchanger plates, comprising the following steps: Sheet metal pretreatment: Select a metal sheet made of 09CrCuSb, clean its surface, remove oil, impurities and oxides, etc., to ensure that the surface cleanliness meets the coating requirements. Chemical cleaning, mechanical grinding or a combination of the two can be used for pretreatment. For example, after using an alkaline cleaning agent to remove oil, use sandpaper to lightly grind to remove the oxide layer; Sheet Metal Hydroforming: The pre-treated metal sheet is placed in a special hydraulic forming equipment. By precisely controlling the pressure of the hydraulic system and the shape of the mold, the metal sheet gradually forms a plate-tube structure with periodic peaks and troughs. During the forming process, the spacing between adjacent plate tubes is strictly controlled within the range of 10-30mm to ensure the formation of a uniform flue gas flow channel that meets the design requirements, and the width error is controlled within ±1mm to ensure the stability of flue gas flow and heat exchange efficiency. Supersonic plasma spraying alloy ceramic coating: Equipment preparation and parameter debugging: Select suitable supersonic plasma spraying equipment, conduct comprehensive inspection and debugging of the equipment to ensure the normal operation of each component; according to the characteristics of the coating material and the plate and tube structure, accurately set the key parameters of plasma gas type, gas flow, current, and voltage to obtain a stable supersonic plasma jet with appropriate energy density; Powder preparation and powder feeding control: select alloy ceramic powder with a specific formula, the powder particle size distribution is between 15-45μm, and the sphericity is not less than 90%; place the powder in a special powder feeder, and adjust the speed and carrier gas flow of the powder feeder to achieve accurate internal powder feeding, ensuring that the powder is stably and evenly fed into the supersonic plasma jet, and the powder feeding rate error does not exceed ±8% of the set value; Spraying process: Start the supersonic plasma spraying equipment to spray the alloy ceramic coating on the surface of the sheet tube formed by hydraulic forming of the metal sheet; during the spraying process, keep the distance between the spray gun and the surface of the sheet tube constant within the range of 100-150mm, and control the movement speed of the spray gun evenly between 30-60mm / s to ensure that the coating thickness is uniform and meets the design requirements, and the coating thickness error does not exceed ±20μm; at the same time, monitor various parameters in the spraying process in real time, such as particle flight speed and temperature, and adjust the equipment parameters in time according to the monitoring results to ensure the stability of the coating quality; Post-plating treatment and performance testing: Post-treatment of coating: After spraying, the plate and tube with coating are cooled naturally or in an appropriate cooling method to avoid crack defects in the coating due to sudden cooling; then the coating surface is lightly polished to remove possible tiny particles or uneven parts on the surface and improve the surface finish; Performance testing: professional testing equipment and methods are used to conduct a comprehensive test on the performance of the coating; the adhesion of the coating is tested by tensile test to ensure that the adhesion reaches more than 40MPa, and the relative error of the adhesion test result does not exceed ±5%; a high temperature test chamber is used to test the temperature resistance performance to verify the stability of the coating at a high temperature of 900℃, with a temperature control accuracy of ±10℃; the hydrophobicity of the surface is tested by a contact angle meter, and the contact angle is greater than 100°; the hardness of the coating is measured by a hardness testing device to ensure that the hardness reaches HRC60, and the deviation of the hardness test result does not exceed ±2HRC; the corrosion rate of the coating is determined by a corrosion test to ensure that its corrosion rate is about 1 / 3 of that of duplex stainless steel 2205, and the relative error of the corrosion rate test result does not exceed ±10%; the preparation process is completed only when all performance indicators meet the requirements, thereby ensuring that the final product can achieve excellent characteristics of anti-ashing, anti-corrosion, anti-wear and stable heat exchange efficiency on the economizer heat exchanger plate, effectively improving the overall performance and service life of the economizer.

[0007] Furthermore, in the pretreatment step of the metal sheet, the alkaline cleaning agent used for chemical cleaning is a mixed solution of sodium hydroxide and sodium carbonate, wherein the mass fraction of sodium hydroxide is 3%-5%, and the mass fraction of sodium carbonate is 1%-2%; specifically, when preparing the mixed solution, first dissolve an appropriate amount of sodium hydroxide solid and sodium carbonate solid in deionized water respectively, and slowly add them under stirring conditions to ensure complete dissolution and uniform solution; when using the mixed solution for chemical cleaning, the metal sheet is completely immersed in the solution for 15-30 minutes. During the immersion process, the solution can be properly stirred or shaken to enhance the cleaning effect and ensure that oil, impurities and oxide pollutants are fully dissolved and separated from the surface of the metal sheet; after cleaning, the metal sheet is immediately removed from the solution and rinsed with a large amount of running water for not less than 5 minutes until the pH value of the rinse water is close to neutral, so as to completely remove the residual cleaning agent and prevent it from having an adverse effect on the subsequent coating process.

[0008] Furthermore, in the step of hydraulic forming of the metal sheet, the pressure of the hydraulic system is controlled according to a preset pressure curve during the forming process. The pressure gradually increases to a maximum value in the wave crest forming stage, and gradually decreases to a minimum value in the wave trough forming stage, and the difference between the maximum pressure and the minimum pressure is between 10 and 20 MPa. In the early stage of wave crest forming, the pressure increases at a faster rate, increasing by 0.5 to 1 MPa per second. As the wave crest shape gradually approaches the design requirements, the pressure rise rate gradually slows down until the maximum pressure is reached. The maximum pressure value is determined according to the shape of the metal sheet. The material, thickness and design size of the plate and tube are determined, generally between 30-50MPa; in the trough forming stage, the pressure gradually decreases from the maximum value, and the reduction rate is between 0.3-0.8MPa per second to ensure that the plate and tube will not produce cracks or deformation defects due to excessive pressure changes during the forming process. The final pressure drops to the minimum value, and the minimum value is maintained between 10-30MPa, so as to successfully complete the entire hydraulic forming process, ensure the accuracy and integrity of the plate and tube structure, and form a uniform flue gas flow channel between adjacent plate and tube, providing a good foundation for subsequent coating processes.

[0009] Furthermore, in the equipment preparation and parameter debugging steps of supersonic plasma spraying alloy ceramic coating, the volume ratio of argon to hydrogen in the plasma gas is 4:1-9:1; when determining the specific volume ratio, it is necessary to comprehensively consider the characteristics of the coating material, the plate and tube structure, and the desired coating performance; when the coating has high requirements for hardness and wear resistance, the proportion of argon can be appropriately increased, and a volume ratio of 8:1-9:1 can be used to increase the energy density of the plasma jet, so that the ceramic particles can be better melted and deposited to form a denser and harder coating; and when it is required When improving the toughness and bonding strength of the coating, the proportion of hydrogen can be appropriately increased, using a volume ratio of 4:1-6:1. The addition of hydrogen helps to reduce the viscosity of the plasma, allowing the molten droplets to spread and combine better when impacting the substrate; during the debugging process, the flow rates of argon and hydrogen are adjusted separately by a high-precision gas flow controller to ensure that the volume ratio of the two after mixing is accurately within the set range, and the flow error does not exceed ±3% of the set value, thereby providing a guarantee for obtaining a stable and high-performance supersonic plasma jet and ensuring high-quality preparation of alloy ceramic coatings.

[0010] Furthermore, in the powder preparation and powder feeding control steps of the supersonic plasma spraying alloy ceramic coating, the alloy ceramic powder contains tungsten carbide, zirconium oxide, aluminum oxide ceramic phases, and nickel, cobalt, and chromium metal bonding phases, wherein the mass fraction of the ceramic phase is 50%-70%, and the mass fraction of the metal bonding phase is 30%-50%; tungsten carbide has high hardness and wear resistance, which can effectively improve the wear resistance of the coating; zirconium oxide and aluminum oxide can enhance the high temperature resistance and oxidation resistance of the coating; nickel, cobalt, and chromium metal bonding phases play a good bonding role to ensure the close bonding between the coating and the substrate and between the ceramic particles; in the powder preparation process, the powders of each component need to be Strict screening, mixing and ball milling process ensures uniform distribution of various components, powder particle size distribution between 15-45μm, and sphericity of not less than 90%; during the powder feeding process, the speed of the powder feeder is precisely adjusted according to the required powder feeding rate, with an accuracy of ±10rpm, and the carrier gas flow rate is also precisely controlled within the fluctuation range of ±3L / min. At the same time, the powder flow stability during the powder feeding process is closely monitored to ensure that the powder is stably and evenly fed into the supersonic plasma jet, and the powder feeding rate error does not exceed ±8% of the set value, so that the alloy ceramic powder is fully melted and accelerated in the plasma jet, and evenly deposited on the surface of the plate and tube to form a high-quality coating.

[0011] Furthermore, in the spraying process of supersonic plasma spraying alloy ceramic coating, the movement trajectory of the spray gun is spiral movement, and the pitch is between 5-10mm to ensure uniform coverage of the coating on the surface of the plate and tube; before the spraying starts, the spiral movement path of the spray gun is set by programming according to the size and shape parameters of the plate and tube to ensure that the spray gun can evenly stay and spray at every place on the surface of the plate and tube; during the spraying process, the spray gun starts from one end of the plate and tube and moves slowly along the spiral line, and the movement speed is uniformly controlled between 30-60mm / s, while keeping the distance between the spray gun and the surface of the plate and tube constant in the range of 100-150mm, ensuring that the coating thickness is uniform and meets the design requirements, and the coating thickness error does not exceed ±20μm; this spiral movement method can effectively avoid the situation where the coating is locally too thick or too thin, so that the coating forms a uniform and dense structure on the surface of the plate and tube, improves the overall performance of the coating, especially in terms of anti-ashing, anti-corrosion and stable heat exchange efficiency, and ensures that the economizer heat exchanger plate always maintains good performance during long-term operation.

[0012] Furthermore, in the post-coating treatment step of post-coating treatment and performance testing, the air cooling equipment used in the air cooling process is an axial flow fan, and the air volume of the fan can be adjusted between 1000-3000m³ / h. The appropriate air volume is adjusted according to the size of the plate and tube and the thickness of the coating to control the cooling rate; for plates and tubes with smaller sizes and thinner coating thickness, a lower air volume of 1000-1500m³ / h can be selected to avoid cracks in the coating due to excessive cooling; and for plates and tubes with larger sizes and thicker coating thickness, the air volume is appropriately increased to 2000-3000m³ / h, Ensure that the coating can be cooled evenly within a suitable time. During the air cooling process, place the axial flow fan in a suitable position so that the cold air blows evenly on the surface of the plate and tube. The distance between the fan and the plate and tube is maintained between 30-50cm. The angle can be adjusted according to the actual situation to ensure the uniformity of the cooling effect. The air cooling process continues until the temperature of the plate and tube drops to near room temperature, generally around 25°C. At this time, the coating is basically stable and can be lightly polished to further improve the surface finish of the coating, providing good surface quality for the installation and use of the economizer heat exchanger plate.

[0013] Furthermore, in the performance test step of the coating post-treatment and performance test, when the corrosion test is carried out, the corrosive medium used in the immersion test is a mixed solution simulating the economizer flue gas condensate environment, which contains 5%-10% sulfuric acid, 1%-3% hydrochloric acid and 0.5%-1% sodium chloride by mass fraction; when preparing the mixed solution, first add deionized water to a corrosion-resistant container, and then slowly add sulfuric acid, hydrochloric acid and sodium chloride in sequence under stirring conditions to ensure complete dissolution and uniform solution; the plate and tube samples with the coating are completely immersed in the corrosive medium for 72-168 hours. During the soaking process, the solution temperature is kept constant at 30-40°C, which can be achieved by a constant temperature water bath or other temperature control equipment. After the soaking test, take out the plate and tube samples, rinse them with clean water to remove the corrosive medium remaining on the surface, and then use the weighing method, microscope observation method or electrochemical test method to evaluate the corrosion degree of the coating to ensure that its corrosion rate is about 1 / 3 of that of duplex stainless steel 2205, and the relative error of the corrosion rate test result does not exceed ±10%. This verifies the corrosion resistance of the coating in the simulated economizer flue gas condensate environment, and provides a reliable basis for the long-term stable operation of the economizer heat exchanger plate under actual working conditions.

[0014] Furthermore, in the performance test step of the coating post-treatment and performance test, when performing the hardness test, at least 5 hardness measurements are performed on different positions of each plate and tube, and the average value is taken as the hardness test result of the plate and tube, and the spacing between the measurement points at different positions is not less than 10mm; when selecting the measurement position, it should be ensured that different areas of the plate and tube are covered, including the peaks, troughs and side parts, so as to comprehensively evaluate the hardness uniformity of the coating; when using a Rockwell hardness tester for hardness measurement, a suitable indenter and load are selected according to the expected hardness range of the coating; at each measuring point , the rate of applying pressure should be kept constant, generally between 1-2N / s, and the holding time is 10-15 seconds to ensure the accuracy of the hardness measurement results; after the measurement is completed, the hardness value of each measuring point is recorded, and the average value is calculated as the hardness test result of the plate and tube. The deviation of the hardness test result does not exceed ±2HRC. By performing hardness tests on multiple plates and tubes, it is ensured that the hardness of the coating of the entire batch of products meets the requirements, that is, reaches HRC60, thereby ensuring that the coating has good wear resistance, effectively resisting the wear that may be suffered during the operation of the economizer, and extending the service life of the heat exchanger plate.

[0015] Furthermore, the preparation process can adjust the coating thickness between 50-200μm according to the actual use conditions and performance requirements of the economizer heat exchanger plate, and accurately control the coating thickness by changing the spray gun movement speed, powder feeding rate and spraying time parameters during the spraying process; when the flue gas environment in which the economizer is located is highly corrosive or has high requirements for heat exchange efficiency, the coating thickness can be appropriately increased and adjusted to 150-200μm; at this time, during the spraying process, the spray gun movement speed can be appropriately reduced to 30-40mm / s, and the powder feeding rate can be increased at the same time, but the powder feeding rate is The increase should be controlled within 10%-20% to ensure that the powder can be fully melted and deposited, and the spraying time can be extended until the required coating thickness is reached, with a coating thickness error of no more than ±20μm; when the working conditions are relatively good or there are certain requirements on cost, the coating thickness can be controlled within the range of 50-100μm, and the spray gun movement speed can be increased to 50-60mm / s accordingly, and the powder feeding rate can be appropriately reduced, but the reduction in the powder feeding rate should not exceed 15%, shortening the spraying time, and achieving rational use of resources and effective cost control while ensuring that the coating performance meets the basic requirements.

[0016] Compared with the prior art, the present invention has the following beneficial effects: Through a specific supersonic plasma spraying process, an adhesion of more than 40MPa is formed between the alloy ceramic coating and the heat exchange plate substrate made of 09CrCuSb material, ensuring that the coating will not fall off during long-term operation, and effectively preventing problems such as increased corrosion of the heat exchange plate and reduced heat exchange efficiency caused by coating shedding.

[0017] The coating can withstand high temperatures of 900°C and maintain stable performance in the high-temperature flue gas environment of the economizer. It will not oxidize, deform or fail due to high temperatures, ensuring the reliable operation of the economizer under high-temperature conditions.

[0018] Its corrosion rate is only about 1 / 3 of that of duplex stainless steel 2205. It exhibits excellent corrosion resistance in the complex corrosive environment where the economizer is located, reduces the risk of damage to the heat exchanger plates due to corrosion, ensures the long-term stable operation of the economizer, and reduces equipment maintenance and replacement costs.

[0019] During the metal sheet hydraulic forming process, the spacing between adjacent plate tubes is precisely controlled at 1030mm to ensure the formation of a uniform flue gas flow channel, which is not only conducive to the stable flow of flue gas and improved heat exchange efficiency, but also provides a good foundation for the subsequent coating process, so that the coating can be more evenly covered on the surface of the heat exchange plate.

[0020] The precise setting of key parameters such as plasma gas type, flow rate, current, voltage, etc. ensures the stability of the supersonic plasma jet and the suitability of the energy density, allowing the spraying material to be fully melted and accelerated, laying the foundation for obtaining high-quality coatings.

[0021] Alloy ceramic powder with specific formula and particle size distribution is selected, and stable and uniform powder feeding is achieved by accurately adjusting the rotation speed of the powder feeder and the carrier gas flow rate, ensuring that the powder can be evenly distributed and fully reacted in the plasma jet, thereby improving the composition uniformity and density of the coating.

[0022] During the spraying process, the particle flight speed, temperature and other parameters are monitored in real time, and the equipment parameters are adjusted in time according to the monitoring results, ensuring the stability of the coating quality and avoiding coating defects caused by parameter fluctuations, such as increased porosity and decreased bonding strength.

[0023] The coating surface is smooth, non-sticky and hydrophobic, which effectively reduces the adhesion of dust and impurities in the flue gas on the surface of the heat exchange plate, reduces the possibility of dust accumulation and scaling, ensures the long-term stability of the heat exchange efficiency of the heat exchange plate, and reduces problems such as increased equipment resistance and increased energy consumption caused by dust accumulation and scaling.

[0024] The sinusoidal corrugated plate surface and the high turbulence flue gas flow channel design, as well as the excellent performance of the coating, jointly improve the heat transfer coefficient of the heat exchanger plate, enable the economizer to recover the flue gas waste heat more efficiently, improve the overall thermal efficiency of the boiler system, reduce fuel consumption, and have a good energy-saving effect.

[0025] By improving the various properties of the coating, the problems of wear, corrosion and dust accumulation during the operation of the economizer are effectively resisted, the probability of equipment failure is reduced, the reliability and operation stability of the equipment are improved, the equipment maintenance cost and downtime are reduced, and the production efficiency is improved.

[0026] This preparation process can flexibly adjust the coating thickness between 50 and 200 μm according to the actual use requirements of the economizer under different working conditions. By changing the spraying parameters, the coating performance can be optimized, so that the economizer heat exchanger plate can maintain good performance under various harsh working conditions.

[0027] Whether it is a working condition with high requirements for corrosion resistance or an occasion that pays more attention to wear resistance, the corresponding performance requirements can be met by appropriately adjusting the process parameters, such as the coating composition ratio and thickness, etc., which improves the versatility and practicality of the process and provides more options for the design and application of economizer heat exchanger plates. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic diagram of the structural plasma spraying alloy ceramic technology of the present invention. DETAILED DESCRIPTION Example

[0029] See also Figure 1 The present invention provides a technical solution: a process for preparing an alloy ceramic coating with high adhesion is implemented as follows: 1. Pretreatment of metal sheets 1. Select a 09CrCuSb (ND steel) metal sheet of [specific size] and first clean its surface with an alkaline cleaning agent. The alkaline cleaning agent is a mixed solution of 3% sodium hydroxide and 1% sodium carbonate by mass. When preparing, first dissolve an appropriate amount of sodium hydroxide solid and sodium carbonate solid in deionized water, and slowly add them under stirring to ensure complete dissolution and uniform solution.

[0030] 2. Completely immerse the metal sheet in the alkaline cleaning solution for 15 minutes. During the immersion process, use a magnetic stirrer to stir at a speed of 200 rpm to enhance the cleaning effect and ensure that pollutants such as oil, impurities and oxides are fully dissolved and separated from the surface of the metal sheet.

[0031] 3. After cleaning, immediately remove the metal sheet from the solution and rinse it with plenty of running water for 5 minutes until the pH value of the rinse water is close to neutral, that is, the pH value is 6.57.5, and then dry the metal sheet for later use.

[0032] 2. Metal sheet hydraulic forming 1. Place the pre-treated metal sheet in the mold of the special hydraulic forming equipment. The wave crest and trough shape design of the mold meets the predetermined plate and tube structure requirements. Start the hydraulic system. At the beginning of the wave crest forming, the pressure rises at a rate of 0.5MPa per second. As the wave crest shape gradually approaches the design requirements, the pressure rise rate gradually slows down. When the wave crest is formed to half, the pressure rise rate is adjusted to 0.3MPa per second until the maximum pressure reaches 30MPa.

[0033] 2. In the trough forming stage, the pressure gradually decreases from the maximum value, and the reduction rate is 0.3MPa per second, to ensure that the plate and tube will not produce defects such as cracks or deformation due to excessive pressure changes during the forming process. The final pressure drops to a minimum value of 10MPa, so as to successfully complete the entire hydraulic forming process. During the forming process, the spacing between adjacent plate and tube is strictly controlled within the range of 1030mm, and the width error is controlled within ±1mm. In this embodiment, the spacing between adjacent plate and tube is set to 15mm. The plate and tube structure after forming meets the design requirements after testing, and the flue gas flow channel is uniform, providing a good foundation for the subsequent coating process.

[0034] (III) Supersonic plasma spraying alloy ceramic coating 1. Equipment preparation and parameter debugging Select suitable supersonic plasma spraying equipment and conduct a comprehensive inspection of the equipment to ensure the normal operation of the spray gun, powder feeder, power supply and other components. According to the characteristics of the coating material and the plate and tube structure, the plasma gas is set to a mixed gas of argon and hydrogen, where the volume ratio of argon to hydrogen is 4:1. Use a high-precision gas flow controller to adjust the flow of argon and hydrogen respectively. The argon flow is set to 40L / min, and the hydrogen flow is set to 10L / min. The flow fluctuation is controlled within ±5% of the set value.

[0035] The current was set to 400A and the voltage was set to 60V. By accurately setting these parameters, a stable supersonic plasma jet with appropriate energy density was obtained.

[0036] 2. Powder preparation and powder feeding control A specially formulated alloy ceramic powder is used, which contains ceramic phases such as 50% by mass of tungsten carbide, 20% by mass of zirconium oxide, and 10% by mass of aluminum oxide, as well as metal bonding phases such as 20% by mass of nickel, 10% by mass of cobalt, and 10% by mass of chromium. Each component powder is strictly screened, mixed, and ball-milled to ensure that each component is evenly distributed, the powder particle size distribution is between 1545μm, and the sphericity is not less than 90%.

[0037] The powder was placed in a special powder feeder, and the speed of the powder feeder was adjusted to 150 rpm and the carrier gas flow rate to 12 L / min to achieve precise internal powder feeding, ensuring that the powder was stably and evenly fed into the supersonic plasma jet, and the powder feeding rate error did not exceed ±8% of the set value.

[0038] 3. Spraying process Start the supersonic plasma spraying equipment and spray the alloy ceramic coating on the surface of the sheet tube formed by hydraulic forming of the metal sheet. During the spraying process, keep the distance between the spray gun and the surface of the sheet tube constant at 100mm, the movement trajectory of the spray gun is spiral movement, the pitch is set to 5mm, and the movement speed of the spray gun is uniformly controlled between 30mm / s to ensure that the coating thickness is uniform and meets the design requirements. The real-time monitoring equipment monitors the parameters such as the particle flight speed of 450m / s and the temperature of 3120℃. According to the monitoring results, the equipment parameters are adjusted in time to ensure the stability of the coating quality. The coating thickness finally obtained in this embodiment is 50μm, and the coating thickness error does not exceed ±20μm. After testing, the coating is uniform, dense, and well combined with the substrate.

[0039] (IV) Post-treatment of coating and performance testing 1. Post-treatment of coating After spraying, the plate and tube with coating are placed under the air cooling equipment for natural cooling. The air volume of the axial flow fan is adjusted to 1000m³ / h, the distance between the fan and the plate and tube is kept at 30cm, and the angle is adjusted to 45 degrees, so that the cold air blows evenly on the surface of the plate and tube, and the cooling rate is controlled at 1020℃ / min to avoid defects such as cracks in the coating due to sudden cooling.

[0040] After cooling to room temperature of about 25°C, the surface of the coating is lightly polished. Use sandpaper with a grit of 800 to gently wipe the surface of the coating manually to remove any tiny particles or uneven parts that may exist on the surface and improve the surface finish.

[0041] 2. Performance testing Adhesion test: The coating adhesion is tested by tensile test. Professional adhesion test equipment is used to prepare the tensile specimen into a specific size. The specimen is fixed on the fixture of the tensile tester by adhesive and tested at a tensile rate of 1mm / min. The coating adhesion is tested to be above 40MPa, and the relative error of the adhesion test result does not exceed ±5%.

[0042] Temperature resistance test: The temperature resistance test was conducted in a high temperature test chamber. The plate and tube samples with coating were placed in the high temperature test chamber, heated to 900°C at a heating rate of 5°C / min, and kept at this temperature for 10 hours, and then cooled to room temperature with the furnace. After testing, the coating had no peeling, shedding, cracking, etc. after the high temperature test, which verified the stability of the coating at 900°C, and the temperature control accuracy was ±10°C.

[0043] Hydrophobicity test: Use a contact angle meter to test the hydrophobicity of the surface. Drop a water drop on the coating surface and measure the contact angle between the water drop and the coating surface. The measured contact angle is 105°, which is greater than 100°, indicating that the coating has good hydrophobicity.

[0044] Hardness test: Rockwell hardness tester is used to measure the hardness of the coating. Five hardness tests are performed on different positions of each plate and tube, with a spacing of 10 mm between the measuring points. At each measuring point, the rate of pressure application is maintained at 1 N / s, and the holding time is 10 seconds. The hardness value of each measuring point is recorded, and the average value is calculated as the hardness test result of the plate and tube. The hardness test result is HRA85, and the deviation of the hardness test result does not exceed ±2HRC.

[0045] Corrosion test: An immersion test was conducted. The corrosive medium used in the immersion test was a mixed solution simulating the economizer flue gas condensate environment, which contained 5% sulfuric acid, 1% hydrochloric acid and 0.5% sodium chloride by mass. The plate and tube specimens with the coating were completely immersed in the corrosive medium for 72 hours. During the immersion process, the solution temperature was controlled at 30°C by a constant temperature water bath. After the immersion test, the plate and tube specimens were taken out and rinsed with clean water. The corrosion degree of the coating was evaluated by weighing method. The corrosion rate of the coating was calculated to be about 1 / 3 of that of duplex stainless steel 2205. The relative error of the corrosion rate test result did not exceed ±10%, thereby verifying the corrosion resistance of the coating in the simulated economizer flue gas condensate environment. Example

[0046] 1. Pretreatment of metal sheets 1. Select the same material as in Example 1 and use a mixed solution of 4% by mass sodium hydroxide and 1.5% by mass sodium carbonate for chemical cleaning. The preparation and cleaning methods are the same as in Example 1.

[0047] 2. The soaking time is 20 minutes, the stirring speed is 250rpm, and the rinsing time after cleaning is 6 minutes. Ensure that the surface cleanliness of the metal sheet meets the coating requirements and dry it for use.

[0048] 2. Metal sheet hydraulic forming 1. During the hydraulic forming process, the pressure rise rate in the peak forming stage is 0.7 MPa per second in the initial stage, and when the peak is formed to 60%, it is adjusted to 0.5 MPa per second until the maximum pressure of 40 MPa is reached.

[0049] 2. The pressure reduction rate in the trough forming stage is 0.5MPa per second, and the final pressure drops to 20MPa. The distance between adjacent plates and tubes is set to 20mm to ensure that the plate and tube structure and flue gas flow channel after forming meet the design requirements, providing a good foundation for the subsequent coating process.

[0050] (III) Supersonic plasma spraying alloy ceramic coating 1. Equipment preparation and parameter debugging The volume ratio of argon to hydrogen in the plasma gas is adjusted to 6:1, the argon flow rate is set to 50 L / min, the hydrogen flow rate is set to 8.3 L / min, the current is set to 450 A, the voltage is set to 65 V, and other equipment inspection and parameter control requirements are the same as in Example 1.

[0051] 2. Powder preparation and powder feeding control The mass fraction of the ceramic phase in the alloy ceramic powder is adjusted to 60%, including 40% tungsten carbide, 15% zirconium oxide, and 5% aluminum oxide. The mass fraction of the metal binder phase is 40%, including 20% ​​nickel, 15% cobalt, and 5% chromium. The powder processing and powder feeding parameters are the same as in Example 1.

[0052] 3. Spraying process During spraying, the distance between the spray gun and the surface of the plate tube is maintained at 120mm, the spray gun moving speed is 40mm / s, the pitch is 7mm, the real-time monitoring particle flight speed is 600m / s, the temperature is 3150℃, and the parameters are adjusted according to the monitoring results. In this embodiment, the coating thickness is 100μm, the coating thickness error does not exceed ±20μm, and the coating quality is good.

[0053] (IV) Post-treatment of coating and performance testing 1. Post-treatment of coating The air volume of the air cooling equipment was adjusted to 1500 m³ / h, the distance between the fan and the plate tube was 35 cm, the angle was 30 degrees, the cooling rate was controlled at 1218°C / min, and the polishing method was the same as in Example 1.

[0054] 2. Performance testing The methods and equipment for adhesion test, temperature resistance test, hydrophobicity test, hardness test and corrosion test are the same as those in Example 1. After testing, the coating adhesion reaches 42MPa, the temperature resistance is good, the contact angle is 110°, the hardness is HRA86, and the corrosion rate is about 1 / 3 of that of duplex stainless steel 2205. All performance indicators meet the requirements, indicating that the coating prepared in this example has good performance on the economizer heat exchanger plate. Example

[0055] 1. Pretreatment of metal sheets 1. Select a metal sheet of specified size and use a mixed solution of 5% by mass sodium hydroxide and 2% by mass sodium carbonate for chemical cleaning. The cleaning process is the same as in Example 1.

[0056] 2. The soaking time is 30 minutes, the stirring speed is 300rpm, and the rinsing time after cleaning is 7 minutes. Ensure that the surface cleanliness of the metal sheet meets the coating requirements and dry it for use.

[0057] 2. Metal sheet hydraulic forming 1. The pressure rise rate during the peak forming stage is 1 MPa per second at the initial stage. When the peak is formed to 70%, it is adjusted to 0.7 MPa per second until the maximum pressure of 50 MPa is reached.

[0058] 2. The pressure reduction rate in the trough forming stage is 0.8MPa per second, and the final pressure drops to 30MPa. The distance between adjacent plates and tubes is set to 30mm to ensure that the plate and tube structure and flue gas flow channel after forming meet the design requirements, providing a good foundation for the subsequent coating process.

[0059] (III) Supersonic plasma spraying alloy ceramic coating 1. Equipment preparation and parameter debugging The volume ratio of argon to hydrogen in the plasma gas is adjusted to 9:1, the argon flow rate is set to 55 L / min, the hydrogen flow rate is set to 6.1 L / min, the current is set to 500 A, the voltage is set to 70 V, and other equipment inspection and parameter control requirements are the same as in Example 1.

[0060] 2. Powder preparation and powder feeding control The mass fraction of the ceramic phase in the alloy ceramic powder is adjusted to 70%, including 50% tungsten carbide, 15% zirconium oxide, and 5% aluminum oxide. The mass fraction of the metal binder phase is 30%, namely 15% nickel, 10% cobalt, and 5% chromium. The powder processing and powder feeding parameters are the same as in Example 1.

[0061] 3. Spraying process During spraying, the distance between the spray gun and the surface of the plate tube is maintained at 150mm, the spray gun moving speed is 60mm / s, the pitch is 10mm, the real-time monitoring particle flight speed is 750m / s, the temperature is 3180℃, and the parameters are adjusted according to the monitoring results. In this embodiment, the coating thickness is 200μm, the coating thickness error does not exceed ±20μm, and the coating quality is good.

[0062] (IV) Post-treatment of coating and performance testing 1. Post-treatment of coating The air volume of the air cooling equipment was adjusted to 3000 m³ / h, the distance between the fan and the plate tube was 50 cm, the angle was 60 degrees, the cooling rate was controlled at 1520°C / min, and the polishing method was the same as in Example 1.

[0063] 2. Performance testing The methods and equipment for adhesion test, temperature resistance test, hydrophobicity test, hardness test and corrosion test are the same as those in Example 1. After testing, the coating adhesion reaches 45MPa, the temperature resistance is good, the contact angle is 115°, the hardness is HRA88, and the corrosion rate is about 1 / 3 of that of duplex stainless steel 2205. All performance indicators meet the requirements, indicating that the coating prepared in this example has good performance on the economizer heat exchanger plate, and is particularly suitable for working conditions with high requirements for coating thickness and performance.

Claims

1. A process for preparing an alloy ceramic coating with high adhesion, used for economizer heat exchanger plates, characterized in that: The following steps are involved: Sheet metal pretreatment: Select a metal sheet made of 09CrCuSb, clean its surface, remove oil, impurities and oxides, etc., to ensure that the surface cleanliness meets the coating requirements. Chemical cleaning, mechanical grinding or a combination of the two can be used for pretreatment. For example, after using an alkaline cleaning agent to remove oil, use sandpaper to lightly grind to remove the oxide layer; Sheet Metal Hydroforming: The pre-treated metal sheet is placed in a special hydraulic forming device, and the pressure of the hydraulic system and the shape of the mold are precisely controlled to gradually form a sheet-tube structure with periodic peaks and troughs on the metal sheet; During the forming process, the spacing between adjacent plate tubes is strictly controlled within the range of 10-30mm to ensure the formation of a uniform flue gas flow channel that meets the design requirements. The width error is controlled within ±1mm to ensure the stability of flue gas flow and heat exchange efficiency. Supersonic plasma spraying alloy ceramic coating: Equipment preparation and parameter debugging: Select suitable supersonic plasma spraying equipment, conduct comprehensive inspection and debugging of the equipment to ensure the normal operation of each component; according to the characteristics of the coating material and the plate and tube structure, accurately set the key parameters of plasma gas type, gas flow, current, and voltage to obtain a stable supersonic plasma jet with appropriate energy density; Powder preparation and powder feeding control: select alloy ceramic powder with a specific formula, the powder particle size distribution is between 15-45μm, and the sphericity is not less than 90%; place the powder in a special powder feeder, and adjust the speed and carrier gas flow of the powder feeder to achieve accurate internal powder feeding, ensuring that the powder is stably and evenly fed into the supersonic plasma jet, and the powder feeding rate error does not exceed ±8% of the set value; Spraying process: Start the supersonic plasma spraying equipment to spray the alloy ceramic coating on the surface of the sheet tube formed by hydraulic forming of the metal sheet; during the spraying process, keep the distance between the spray gun and the surface of the sheet tube constant within the range of 100-150mm, and control the movement speed of the spray gun evenly between 30-60mm / s to ensure that the coating thickness is uniform and meets the design requirements, and the coating thickness error does not exceed ±20μm; at the same time, monitor various parameters in the spraying process in real time, such as particle flight speed and temperature, and adjust the equipment parameters in time according to the monitoring results to ensure the stability of the coating quality; Post-plating treatment and performance testing: Post-treatment of coating: After spraying, the plate and tube with coating are cooled naturally or in an appropriate cooling method to avoid crack defects in the coating due to sudden cooling; then the coating surface is lightly polished to remove possible tiny particles or uneven parts on the surface and improve the surface finish; Performance testing: Use professional testing equipment and methods to conduct a comprehensive test on the performance of the coating; Use tensile tests to test the adhesion of the coating to ensure that the adhesion reaches more than 40MPa, and the relative error of the adhesion test result does not exceed ±5%; Use a high-temperature test chamber to test the temperature resistance performance to verify the stability of the coating at a high temperature of 900℃, with a temperature control accuracy of ±10℃; Use a contact angle meter to test the hydrophobicity of the surface, and the contact angle is greater than 100°; Use hardness testing equipment to measure the hardness of the coating to ensure that the hardness reaches HRC60, and the deviation of the hardness test result does not exceed ±2HRC; The corrosion rate of the coating is measured through corrosion tests to ensure that its corrosion rate is about 1 / 3 of that of duplex stainless steel 2205, and the relative error of the corrosion rate test results does not exceed ±10%. Only when all performance indicators meet the requirements, the preparation process is completed, thereby ensuring that the final product can achieve excellent characteristics such as anti-ash deposition, anti-corrosion, anti-wear and stable heat exchange efficiency on the economizer heat exchanger plate, effectively improving the overall performance and service life of the economizer.

2. The process for preparing an alloy ceramic coating with high adhesion according to claim 1, characterized in that: In the pretreatment step of the metal sheet, the alkaline cleaning agent used for chemical cleaning is a mixed solution of sodium hydroxide and sodium carbonate, wherein the mass fraction of sodium hydroxide is 3%-5%, and the mass fraction of sodium carbonate is 1%-2%; specifically, when preparing the mixed solution, first dissolve an appropriate amount of sodium hydroxide solid and sodium carbonate solid in deionized water respectively, and slowly add them under stirring conditions to ensure complete dissolution and uniform solution; when using the mixed solution for chemical cleaning, the metal sheet is completely immersed in the solution for 15-30 minutes. During the immersion process, the solution can be properly stirred or shaken to enhance the cleaning effect and ensure that oil, impurities and oxide pollutants are fully dissolved and separated from the surface of the metal sheet; after cleaning, the metal sheet is immediately removed from the solution and rinsed with a large amount of running clean water for not less than 5 minutes until the pH value of the rinse water is close to neutral, so as to completely remove the residual cleaning agent and prevent it from having an adverse effect on the subsequent coating process.

3. The process for preparing an alloy ceramic coating with high adhesion according to claim 1, characterized in that: In the metal sheet hydraulic forming step, the pressure of the hydraulic system is controlled according to a preset pressure curve during the forming process. The pressure curve gradually increases to a maximum value in the wave crest forming stage, and gradually decreases to a minimum value in the wave trough forming stage, and the difference between the maximum pressure and the minimum pressure is between 10-20MPa; in the early stage of wave crest forming, the pressure rises at a faster rate, increasing by 0.5-1MPa per second. As the wave crest shape gradually approaches the design requirements, the pressure rise rate gradually slows down until the maximum pressure is reached. The maximum pressure value is determined according to the material, thickness and design size of the metal sheet, and is generally between 30-50MPa; in the wave trough forming stage, the pressure gradually decreases from the maximum value, and the reduction rate is between 0.3-0.8MPa per second, ensuring that the plate tube will not produce cracks or deformation defects due to excessive pressure changes during the forming process. The final pressure drops to the minimum value, and the minimum value is maintained between 10-30MPa, so as to successfully complete the entire hydraulic forming process, ensure the accuracy and integrity of the plate tube structure, and form a uniform flue gas flow channel between adjacent plate tubes, providing a good foundation for subsequent coating processes.

4. The process for preparing an alloy ceramic coating with high adhesion according to claim 1, characterized in that: In the equipment preparation and parameter debugging steps of supersonic plasma spraying alloy ceramic coating, the volume ratio of argon to hydrogen in the plasma gas is 4:1-9:1; when determining the specific volume ratio, it is necessary to comprehensively consider the characteristics of the coating material, the plate and tube structure, and the desired coating performance; when the coating has high requirements for hardness and wear resistance, the proportion of argon can be appropriately increased, and a volume ratio of 8:1-9:1 can be used to increase the energy density of the plasma jet, so that the ceramic particles can be better melted and deposited, forming a denser and harder coating; and when it is necessary to increase When improving the toughness and bonding strength of the coating, the proportion of hydrogen can be appropriately increased, using a volume ratio of 4:1-6:

1. The addition of hydrogen helps to reduce the viscosity of the plasma, allowing the molten droplets to spread and combine better when impacting the substrate; during the debugging process, the flow rates of argon and hydrogen are adjusted separately by a high-precision gas flow controller to ensure that the volume ratio of the two after mixing is accurately within the set range, and the flow error does not exceed ±3% of the set value, thereby providing a guarantee for obtaining a stable and high-performance supersonic plasma jet and ensuring high-quality preparation of alloy ceramic coatings.

5. The process for preparing an alloy ceramic coating with high adhesion according to claim 1, characterized in that: In the powder preparation and powder feeding control steps of supersonic plasma spraying alloy ceramic coating, the alloy ceramic powder contains tungsten carbide, zirconium oxide, aluminum oxide ceramic phases, and nickel, cobalt, and chromium metal bonding phases, wherein the mass fraction of the ceramic phase is 50%-70%, and the mass fraction of the metal bonding phase is 30%-50%; tungsten carbide has high hardness and wear resistance, which can effectively improve the wear resistance of the coating; zirconium oxide and aluminum oxide can enhance the high temperature resistance and oxidation resistance of the coating; nickel, cobalt, and chromium metal bonding phases play a good bonding role, ensuring the close bonding between the coating and the substrate and between the ceramic particles; in the powder preparation process, each component powder must undergo strict Screening, mixing and ball milling processes are carried out to ensure that the components are evenly distributed, the powder particle size distribution is between 15-45μm, and the sphericity is not less than 90%; during the powder feeding process, the speed of the powder feeder is accurately adjusted according to the required powder feeding rate, and the accuracy is controlled within ±10rpm. The carrier gas flow rate also needs to be accurately controlled within the fluctuation range of ±3L / min. At the same time, the powder flow stability during the powder feeding process is closely monitored to ensure that the powder is stably and evenly fed into the supersonic plasma jet, and the powder feeding rate error does not exceed ±8% of the set value, so that the alloy ceramic powder is fully melted and accelerated in the plasma jet, and evenly deposited on the surface of the plate and tube to form a high-quality coating.

6. The process for preparing an alloy ceramic coating with high adhesion according to claim 1, characterized in that: During the spraying process of supersonic plasma spraying alloy ceramic coating, the movement trajectory of the spray gun is spiral movement, and the pitch is between 5-10mm to ensure uniform coverage of the coating on the surface of the plate and tube; before spraying, the spiral movement path of the spray gun is set by programming according to the size and shape parameters of the plate and tube to ensure that the spray gun can stay and spray evenly at every place on the surface of the plate and tube; During the spraying process, the spray gun starts from one end of the plate tube and moves slowly along the spiral line. The moving speed is uniformly controlled between 30-60mm / s. At the same time, the distance between the spray gun and the surface of the plate tube is kept constant within the range of 100-150mm to ensure that the coating thickness is uniform and meets the design requirements. The coating thickness error does not exceed ±20μm. This spiral movement method can effectively avoid the situation where the coating is locally too thick or too thin, so that the coating forms a uniform and dense structure on the surface of the plate tube, improves the overall performance of the coating, especially in terms of anti-ashing, anti-corrosion and stable heat exchange efficiency, and ensures that the economizer heat exchanger plate always maintains good performance during long-term operation.

7. The process for preparing an alloy ceramic coating with high adhesion according to claim 1, characterized in that: In the post-coating treatment step of coating post-treatment and performance testing, the air cooling equipment used in the air cooling process is an axial flow fan. The air volume of the fan can be adjusted between 1000-3000m³ / h. The appropriate air volume is adjusted according to the size of the plate and tube and the thickness of the coating to control the cooling rate; for smaller plates and tubes with thinner coating thickness, a lower air volume of 1000-1500m³ / h can be selected to avoid cracks in the coating due to excessive cooling; and for larger plates and tubes with thicker coating thickness, the air volume is appropriately increased to 2000-3000m³ / h to ensure The coating can be cooled evenly within a suitable time. During the air cooling process, the axial flow fan is placed in a suitable position to make the cold air blow evenly on the surface of the plate and tube. The distance between the fan and the plate and tube is kept between 30-50cm, and the angle can be adjusted according to the actual situation to ensure the uniformity of the cooling effect. The air cooling process continues until the temperature of the plate and tube drops to near room temperature, generally around 25°C. At this time, the coating is basically stable and can be lightly polished to further improve the surface finish of the coating, providing good surface quality for the installation and use of economizer heat exchanger plates.

8. The process for preparing an alloy ceramic coating with high adhesion according to claim 1, characterized in that: In the performance test step of the coating post-treatment and performance test, when the corrosion test is carried out, the corrosive medium used in the immersion test is a mixed solution simulating the environment of the economizer flue gas condensate, which contains 5%-10% sulfuric acid, 1%-3% hydrochloric acid and 0.5%-1% sodium chloride by mass fraction; when preparing the mixed solution, first add deionized water to a corrosion-resistant container, and then slowly add sulfuric acid, hydrochloric acid and sodium chloride in sequence under stirring conditions to ensure complete dissolution and uniform solution; the plate and tube samples with the coating are completely immersed in the corrosive medium for 72-168 hours. The immersion process The solution temperature is kept constant between 30-40℃, which can be achieved by a constant temperature water bath or other temperature control equipment; after the immersion test, the plate and tube samples are taken out, rinsed with clean water to remove the corrosive medium remaining on the surface, and then the corrosion degree of the coating is evaluated by weighing method, microscope observation method or electrochemical test method to ensure that its corrosion rate is about 1 / 3 of that of duplex stainless steel 2205, and the relative error of the corrosion rate test result does not exceed ±10%, thereby verifying the corrosion resistance of the coating in the simulated economizer flue gas condensate environment, and providing a reliable basis for the long-term stable operation of the economizer heat exchanger plate under actual working conditions.

9. The process for preparing an alloy ceramic coating with high adhesion according to claim 1, characterized in that: In the performance test step of coating post-treatment and performance test, when conducting hardness test, at least 5 hardness measurements are performed on different positions of each plate and tube, and the average value is taken as the hardness test result of the plate and tube, and the spacing between measurement points at different positions is not less than 10mm; when selecting the measurement position, it should be ensured that different areas of the plate and tube are covered, including crests, troughs and side parts, so as to comprehensively evaluate the hardness uniformity of the coating; when using Rockwell hardness tester for hardness measurement, select appropriate indenter and load according to the expected hardness range of the coating; at each measuring point, the rate of applying pressure should be kept constant, generally between 1-2N / s, and the holding time is 10-15 seconds to ensure the accuracy of the hardness measurement results; after the measurement is completed, the hardness value of each measuring point is recorded, and the average value is calculated as the hardness test result of the plate and tube. The deviation of the hardness test result does not exceed ±2HRC. By conducting hardness tests on multiple plates and tubes, it is ensured that the hardness of the coating of the entire batch of products meets the requirements, that is, reaches HRC60, thereby ensuring that the coating has good wear resistance, effectively resists the wear that may be suffered during the operation of the economizer, and extends the service life of the heat exchanger plate.

10. The process for preparing an alloy ceramic coating with high adhesion according to claim 1, characterized in that: The preparation process can adjust the coating thickness between 50-200μm according to the actual use conditions and performance requirements of the economizer heat exchanger plate, and accurately control the coating thickness by changing the spray gun movement speed, powder feeding rate and spraying time parameters during the spraying process; when the flue gas environment in which the economizer is located is highly corrosive or has high requirements for heat exchange efficiency, the coating thickness can be appropriately increased and adjusted to 150-200μm; at this time, during the spraying process, the spray gun movement speed can be appropriately reduced to 30-40mm / s, and the powder feeding rate can be increased at the same time, but the increase in the powder feeding rate The amplitude should be controlled within 10%-20% to ensure that the powder can be fully melted and deposited, and the spraying time can be extended until the required coating thickness is reached, and the coating thickness error does not exceed ±20μm; when the working conditions are relatively good or there are certain requirements on cost, the coating thickness can be controlled within the range of 50-100μm, and the spray gun movement speed can be increased to 50-60mm / s accordingly, and the powder feeding rate can be appropriately reduced, but the reduction in the powder feeding rate should not exceed 15%, shortening the spraying time, and realizing the rational use of resources and effective control of costs while ensuring that the coating performance meets the basic requirements.

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