A real-time control method and system for viscosity of supercritical carbon dioxide spray paint

Abstract

The application discloses a kind of supercritical carbon dioxide spray paint viscosity real-time control method and system, including carbon dioxide supply pipeline, coating supply pipeline, mixed pipeline, cleaning and waste liquid recovery pipeline and PLC, core is replaced with high-priced special viscosity detection equipment by capillary and differential pressure transmitter combination;The method first pressurizes and heats carbon dioxide to supercritical state, while paint is pressurized to the same pressure, after being mixed by micro-mixer, by differential pressure transmitter Collecting pressure difference signal and transmission to PLC, PLC is converted real-time viscosity by built-in viscosity calculation model, closed-loop regulation carbon dioxide flow to regulate mixed fluid viscosity, after pressure stabilization, constant temperature, by high-pressure spray gun Complete spraying, after spraying, pipeline automatic cleaning and waste liquid recovery can be realized.The application can reduce investment cost, stably control paint mixed system viscosity, reduce spraying defects, reduce volatile organic compound emissions, system structure is simple, convenient to operate.

Description

Technical Field

[0001] This invention belongs to the field of coating and spraying technology, specifically relating to a method and system for real-time control of the viscosity of supercritical carbon dioxide sprayed paint. Background Technology

[0002] Supercritical carbon dioxide spraying technology is a rapidly developing green coating process. Carbon dioxide, in a supercritical state with a temperature above 31.1℃ and a pressure above 7.38MPa, combines the diffusivity of a gas with the solubility of a liquid. When mixed with paint, it can reduce the viscosity of the paint. This process can achieve good atomization with only a small amount or even no organic solvents, which can reduce the emission of volatile organic compounds and has significant environmental advantages.

[0003] The viscosity of the mixture formed by paint and supercritical carbon dioxide is highly sensitive to temperature, pressure, and the amount of carbon dioxide added. Even slight fluctuations in temperature and pressure can cause viscosity shifts, leading to coating defects such as uneven coating thickness, surface sagging, and orange peel. To ensure viscosity stability, existing technologies generally employ high-precision Coriolis mass flow meters and high-pressure online viscometers combined with complex temperature and pressure control loops to achieve closed-loop viscosity control. However, dedicated online viscometers and Coriolis mass flow meters capable of withstanding supercritical conditions are expensive, with a single unit costing over 100,000 yuan, resulting in a high initial investment for the entire spraying system. Furthermore, such systems involve complex piping, sensors, and control modules, requiring stringent sensor calibration and routine maintenance, and carrying a high risk of equipment failure, thus hindering the widespread application of supercritical carbon dioxide spraying technology. Therefore, the industry urgently needs a simple, low-cost, and reliable real-time viscosity control method and supporting system for supercritical carbon dioxide spraying paint. Summary of the Invention

[0004] To address the aforementioned problems, the present invention aims to provide a method and system for real-time viscosity control of supercritical carbon dioxide spray paint while ensuring accurate real-time viscosity control and achieving the required spray quality, thereby reducing equipment investment and maintenance costs.

[0005] This invention is achieved through the following technical solution: A real-time control system for supercritical carbon dioxide spray paint viscosity includes a carbon dioxide supply pipeline, a paint supply pipeline, a mixing pipeline, a cleaning and waste liquid recovery pipeline, and a PLC. One end of the carbon dioxide supply pipeline is connected to a carbon dioxide gas source, and the other end is connected to the first inlet of a micro-mixer. Along the fluid flow direction, the carbon dioxide supply pipeline is sequentially equipped with a shut-off valve, a pneumatic diaphragm pump, a first buffer tank, a heater, a first regulating valve, a first pressure sensor, and a first check valve. A first temperature sensor is installed on the heater. The outlet branch of the first buffer tank is connected to a first vent valve. The pipeline between the first regulating valve and the first check valve is connected to the cleaning and waste liquid recovery pipeline via a high-pressure solenoid valve. One end of the paint supply pipeline is connected to a paint tank, and the other end is connected to the second inlet of the micro-mixer. Along the fluid flow direction, the paint supply pipeline is sequentially equipped with a metering pump, a second buffer tank, a second regulating valve, and a first... The second pressure sensor and the second one-way valve are connected to the outlet branch of the second buffer tank, which is connected to the second vent valve. One end of the mixing pipeline is connected to the outlet of the micro mixer, and the other end is connected to the high-pressure spray gun. A capillary tube, a pressure regulating valve, a constant temperature buffer tank, and a third pressure sensor are sequentially arranged along the fluid flow direction on the mixing pipeline. The inlet and outlet ends of the capillary tube are respectively connected to the high-pressure side and the low-pressure side of the differential pressure transmitter. A second temperature sensor is installed on the constant temperature buffer tank. One end of the cleaning and waste liquid recovery pipeline is connected to the outlet of the high-pressure solenoid valve, and the other end is connected to the pipeline between the capillary tube and the pressure regulating valve. A waste liquid collection tank and a third vent valve are sequentially arranged along the fluid flow direction on the cleaning and waste liquid recovery pipeline. The PLC is electrically connected to the first temperature sensor, the first regulating valve, the first pressure sensor, the second regulating valve, the second pressure sensor, the differential pressure transmitter, the second temperature sensor, the third pressure sensor, and the high-pressure solenoid valve.

[0006] Furthermore, the output pressure range of the pneumatic diaphragm pump is 7.5MPa to 14MPa, and the heating temperature of the heater can bring carbon dioxide to a supercritical state with a temperature higher than 31.1℃ and a pressure higher than 7.38MPa.

[0007] Furthermore, the capillary tube is made of stainless steel round tube with an inner diameter D of 0.5mm to 3mm and a length L of 200mm to 1000mm; the differential pressure transmitter has a range of 0 to 1MPa and outputs a 4 to 20mA analog signal to the PLC.

[0008] Furthermore, the micro mixer is a static micro mixer or a T-type micro mixer with an internal microchannel flow structure.

[0009] Furthermore, the constant temperature buffer tank is a pressure-resistant container with a volume of 0.5L to 5L, and has a built-in heating device to maintain a constant fluid temperature. It is equipped with baffles or stirring blades inside.

[0010] Furthermore, the residence time of the mixed fluid in the constant temperature buffer tank is 2s to 10s.

[0011] Furthermore, the metering pump is a high-pressure plunger metering pump, and the output pressure and flow rate can be changed by adjusting the frequency or the plunger stroke.

[0012] Furthermore, the high-pressure solenoid valve is a pulse-type high-pressure solenoid valve.

[0013] Furthermore, the PLC is equipped with a human-machine touch screen for displaying real-time viscosity, pressure, temperature parameters, and input target viscosity values.

[0014] A method for real-time control of the viscosity of supercritical carbon dioxide spray paint includes the following steps: S1. Supercritical carbon dioxide preparation and delivery steps: The carbon dioxide output from the carbon dioxide gas source enters the pneumatic diaphragm pump for pressurization through the shut-off valve, and is then sent to the heater for heating after being stabilized by the first buffer tank to form supercritical carbon dioxide. The supercritical carbon dioxide is then delivered to the micro mixer in sequence through the first temperature sensor, the first regulating valve, the first pressure sensor, and the first one-way valve. S2. Paint pressurization and delivery step: The paint in the paint tank is pressurized by a metering pump to the same pressure as supercritical carbon dioxide, and then delivered to the micro mixer after being stabilized by the second buffer tank, the second regulating valve, the second pressure sensor, and the second one-way valve in sequence; S3. Mixing and differential pressure detection steps: Supercritical carbon dioxide and paint are mixed in a micro mixer to form a mixed fluid. The mixed fluid flows through a capillary tube. The differential pressure transmitter detects the pressure difference between the inlet and outlet of the capillary tube in real time and transmits the pressure difference signal to the PLC. S4. Viscosity Calculation and Closed-Loop Control Steps: The PLC obtains the real-time viscosity of the mixed fluid based on the received differential pressure signal and the preset viscosity calculation model. It compares the real-time viscosity with the preset target viscosity and adjusts the opening of the first regulating valve to change the carbon dioxide flow rate, thereby controlling the viscosity of the mixed fluid. S5. Pressure-stabilized and temperature-controlled spraying steps: The mixed fluid flowing through the capillary tube is stabilized by the pressure-stabilizing valve and then enters the temperature-controlled buffer tank. The mixed fluid is kept at a constant temperature in the temperature-controlled buffer tank and further mixed and dissolved. Then, it is delivered to the high-pressure spray gun through the third pressure sensor to complete the spraying operation. S6. Pipeline cleaning steps: After the spraying operation is completed, open the first vent valve, the second vent valve, and the third vent valve. The high-pressure solenoid valve operates at a pulse frequency, using supercritical carbon dioxide to flush the mixing pipeline and the high-pressure spray gun. The waste liquid is collected into the waste liquid collection tank.

[0015] The beneficial effects of this invention are: 1. Reduce equipment investment: The use of capillary tube + differential pressure transmitter combination to replace expensive special detection equipment significantly reduces the cost of core components and facilitates the promotion and application of this technology.

[0016] 2. Improve viscosity control accuracy: Based on the pressure difference-viscosity correlation model, online real-time detection is achieved. Combined with PLC short-cycle closed-loop adjustment, the viscosity of the mixed fluid can be stabilized, effectively avoiding coating defects such as sagging, orange peel, and uneven thickness.

[0017] 3. Green and environmentally friendly: Relying on the viscosity-reducing properties of supercritical carbon dioxide, the use of organic co-solvents is reduced, and the emission of volatile organic compounds is lowered, which is in line with the development direction of the green coating industry.

[0018] 4. Simple and reliable operation and maintenance: The system piping and control architecture is simple, the number of sensors is small, the calibration and daily maintenance are easy, the failure rate is low, and it is suitable for industrial continuous spraying operation scenarios. Attached Figure Description

[0019] The present invention will now be described in further detail with reference to the accompanying drawings.

[0020] Figure 1 This is a schematic diagram of the overall structure of the supercritical carbon dioxide spray paint viscosity real-time control system of the present invention.

[0021] Reference numerals: 1-Carbon dioxide supply pipeline; 2-Paint supply pipeline; 3-Mixing pipeline; 4-Cleaning and waste liquid recovery pipeline; 5-Carbon dioxide gas source; 6-Stop valve; 7-Pneumatic diaphragm pump; 8-First buffer tank; 9-Heater; 10-First temperature sensor; 11-First regulating valve; 12-First pressure sensor; 13-First check valve; 14-Paint tank; 15-Metering pump; 16-Second buffer tank; 17-Second regulating valve; 18-Second pressure sensor; 19-Second check valve; 20-Micro mixer; 21-Capillary tube; 22-Differential pressure transmitter; 23-Pressure stabilizing valve; 24-Thermostatic buffer tank; 25-Second temperature sensor; 26-Third pressure sensor; 27-High-pressure spray gun; 28-First vent valve; 29-High-pressure solenoid valve; 30-Second vent valve; 31-Waste liquid collection tank; 32-Third vent valve; 33-PLC. Detailed Implementation

[0022] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification.

[0023] It should be noted that the terms “comprising,” “including,” or any other variations are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0024] like Figure 1 This diagram illustrates a real-time control system for supercritical carbon dioxide spray paint viscosity, comprising a carbon dioxide supply pipeline 1, a paint supply pipeline 2, a mixing pipeline 3, a cleaning and waste liquid recovery pipeline 4, and a PLC 33. One end of the carbon dioxide supply pipeline 1 is connected to a carbon dioxide gas source 5, and the other end is connected to the first inlet of a micro-mixer 20. Along the fluid flow direction, the carbon dioxide supply pipeline 1 is sequentially equipped with a shut-off valve 6, a pneumatic diaphragm pump 7, a first buffer tank 8, a heater 9, a first regulating valve 11, a first pressure sensor 12, and a first check valve 13. A first temperature sensor 10 is installed on the heater 9. The outlet branch of the first buffer tank 8 is connected to a first vent valve 28. The pipeline between the first regulating valve 11 and the first check valve 13 is connected to the cleaning and waste liquid recovery pipeline 4 via a high-pressure solenoid valve 29. One end of the paint supply pipeline 2 is connected to a paint tank 14, and the other end is connected to the second inlet of the micro-mixer 20. Along the fluid flow direction, the paint supply pipeline 2 is sequentially equipped with a metering pump 15, a second buffer tank 16, a second regulating valve 17, and a second pressure sensor 18. 8. A second one-way valve 19 is provided, and a second vent valve 30 is connected to the outlet branch of the second buffer tank 16; one end of the mixing pipeline 3 is connected to the outlet of the micro-mixer 20, and the other end is connected to the high-pressure spray gun 27. A capillary tube 21, a pressure regulating valve 23, a constant-temperature buffer tank 24, and a third pressure sensor 26 are sequentially arranged along the fluid flow direction on the mixing pipeline 3. The inlet and outlet ends of the capillary tube 21 are respectively connected to the high-pressure side and low-pressure side of the differential pressure transmitter 22. A second temperature sensor 25 is installed on the constant-temperature buffer tank 24; the cleaning and waste... One end of the liquid recovery pipeline 4 is connected to the outlet of the high-pressure solenoid valve 29, and the other end is connected to the pipeline between the capillary tube 21 and the pressure regulating valve 23. The cleaning and waste liquid recovery pipeline 4 is provided with a waste liquid collection tank 31 and a third vent valve 32 in sequence along the fluid flow direction. The PLC 33 is electrically connected to the first temperature sensor 10, the first regulating valve 11, the first pressure sensor 12, the second regulating valve 17, the second pressure sensor 18, the differential pressure transmitter 22, the second temperature sensor 25, the third pressure sensor 26, and the high-pressure solenoid valve 29.

[0025] The output pressure range of the pneumatic diaphragm pump 7 is 7.5MPa to 14MPa, and the heating temperature of the heater 9 can make carbon dioxide reach a supercritical state with a temperature higher than 31.1℃ and a pressure higher than 7.38MPa.

[0026] The capillary tube 21 is made of stainless steel round tube with an inner diameter D of 0.5mm to 3mm and a length L of 200mm to 1000mm; the differential pressure transmitter 22 has a range of 0 to 1MPa and outputs a 4 to 20mA analog signal to the PLC33.

[0027] The micro mixer 20 is a static micro mixer or a T-type micro mixer, with a microchannel flow structure inside.

[0028] The constant temperature buffer tank 24 is a pressure-resistant container with a volume of 0.5L to 5L. It has a built-in heating device to maintain a constant fluid temperature and is equipped with baffles or stirring blades inside.

[0029] The residence time of the mixed fluid in the constant temperature buffer tank 24 is 2s to 10s.

[0030] The metering pump 15 is a high-pressure plunger metering pump, and the output pressure and flow rate can be changed by adjusting the frequency or the plunger stroke.

[0031] The high-pressure solenoid valve 29 is a pulse-type high-pressure solenoid valve.

[0032] The PLC33 is equipped with a human-machine touch screen for displaying real-time viscosity, pressure, and temperature parameters, as well as inputting target viscosity values.

[0033] This invention indirectly characterizes the viscosity of the mixed fluid through the pressure difference of capillary tube 21, and uses a two-stage formula for joint calculation. All formulas are pre-stored in PLC33 and the calculation is completed automatically. 1. Formula for characterizing fluid viscosity:

[0034] in the formula This refers to the viscosity of the mixture of paint and supercritical carbon dioxide. denoted as the pressure difference between the inlet and outlet of capillary 21, D as the diameter of capillary 21, L as the length of capillary 21, and U as the velocity of the mixed fluid within capillary 21.

[0035] 2. The flow velocity conversion uses Bernoulli's equation:

[0036] In the formula, U is the flow velocity of the mixed fluid in the capillary 21. The pressure difference between the inlet and outlet of capillary tube 21 The density of the mixed fluid.

[0037] Mixed fluid density Between the density of pure paint and the density of supercritical carbon dioxide, the value can be pre-calibrated to be 0.6 to 0.9 times the density of paint according to the working conditions, or it can be estimated in real time according to the pressure, temperature, and component ratio through mixing rules; at the same time, for the characteristics of viscous fluids, the calculation results can be calibrated and corrected through on-site experiments to ensure the accuracy of viscosity calculation.

[0038] The specific steps of a method for real-time control of the viscosity of supercritical carbon dioxide sprayed paint are as follows: S1. System Start-up and Supercritical Carbon Dioxide Preparation: The shut-off valve 6 is opened, and the industrial carbon dioxide in the carbon dioxide gas source 5 enters the pneumatic diaphragm pump 7. The pneumatic diaphragm pump 7 pressurizes the carbon dioxide to 7.5-14 MPa. The pressurized carbon dioxide enters the first buffer tank 8 for pressure stabilization, and then is sent to the heater 9, which heats it to above 31.1°C to make it transform into a supercritical state. The supercritical carbon dioxide passes through the first temperature sensor 10, the first regulating valve 11, the first pressure sensor 12, and the first one-way valve 13 in sequence, and is delivered to the micro mixer 20.

[0039] S2. The paint pressurization and delivery starts the metering pump 15, which draws paint from the paint tank 14 and pressurizes it so that the paint pressure is equal to the pressure of the carbon dioxide supply pipeline 1. The pressurized paint enters the second buffer tank 16 for pressure stabilization, and then passes through the second regulating valve 17, the second pressure sensor 18, and the second one-way valve 19 to be sent into the micro mixer 20.

[0040] S3. Fluid Mixing, Differential Pressure Detection, and Viscosity Calculation: Supercritical carbon dioxide and paint undergo initial mixing within the micro-mixer 20, forming a homogeneous mixed fluid that flows into the capillary tube 21; the differential pressure transmitter 22 detects the pressure difference between the inlet and outlet of the capillary tube 21 in real time. The electrical signal is transmitted to PLC33, which then determines the signal based on the pre-recorded parameters: capillary 21 inner diameter D, length L, and mixed fluid density. Combining the above fluid viscosity characterization formula with Bernoulli's equation, the viscosity of the mixed fluid is calculated in real time and the viscosity value is displayed on the human-machine touch screen.

[0041] S4. Viscosity Closed-Loop Automatic Adjustment: The operator presets a target viscosity value (10 mPa·s ~ 200 mPa·s) on the PLC33 touchscreen. The PLC33 compares the calculated actual viscosity with the target viscosity in real time. If the actual viscosity is higher than the target viscosity, it indicates that the carbon dioxide content is insufficient. The PLC33 outputs a control signal to open the first regulating valve 11, increasing the carbon dioxide flow rate. If the actual viscosity is lower than the target viscosity, the first regulating valve 11 is closed, reducing the carbon dioxide flow rate. The adjustment process is executed in cycles of 0.5 to 2 seconds to continuously stabilize the viscosity of the mixed fluid. When changes in carbon dioxide flow rate cause a pressure shift in the pipeline, the PLC33 synchronously adjusts the frequency or plunger stroke of the metering pump 15 to maintain the pressure balance between the carbon dioxide supply pipeline 1 and the coating supply pipeline 2.

[0042] S5. The mixed fluid flowing through the capillary tube 21 enters the pressure regulating valve 23 to complete the secondary pressure stabilization, and then enters the constant temperature buffer tank 24. The constant temperature buffer tank 24 maintains a constant temperature through the built-in electric heating coil to prevent phase separation of the mixed fluid. The mixed fluid stays in the tank for 2 to 10 seconds, and is further mixed and miscible with the help of the baffle plate to stabilize the outlet flow rate. Finally, the mixed fluid is delivered to the high-pressure spray gun 27 through the third pressure sensor 26 to complete the workpiece spraying operation.

[0043] S6. After the pipeline cleaning and waste liquid recovery spraying operations are completed, close the feed pipeline valve and open the first vent valve 28, the second vent valve 30, and the third vent valve 32. PLC 33 controls the high-pressure solenoid valve 29 to reciprocate at a pulse frequency. Use the residual supercritical carbon dioxide in the pipeline to flush the entire mixing pipeline 3 and the high-pressure spray gun 27 pipeline. The waste liquid generated during cleaning flows into the waste liquid collection tank 31 through the cleaning and waste liquid recovery pipeline 4 for centralized collection, thus completing the cleaning process of the entire set of equipment.

[0044] The scope of protection of this invention is not limited to the technical solutions disclosed in the specific embodiments. Any modifications, equivalent substitutions, improvements, etc., made to the above embodiments based on the technical essence of this invention shall fall within the scope of protection of this invention.

Claims

1. A real-time control system for the viscosity of supercritical carbon dioxide sprayed paint, characterized in that: It includes a carbon dioxide supply pipeline (1), a paint supply pipeline (2), a mixing pipeline (3), a cleaning and waste liquid recovery pipeline (4), and a PLC (33); one end of the carbon dioxide supply pipeline (1) is connected to a carbon dioxide gas source (5), and the other end is connected to the first inlet of the micro mixer (20). Along the fluid flow direction, the carbon dioxide supply pipeline (1) is sequentially equipped with a shut-off valve (6), a pneumatic diaphragm pump (7), a first buffer tank (8), a heater (9), a first regulating valve (11), a first pressure sensor (12), and a first check valve (13). The heater (9) is equipped with a first temperature sensor. The first buffer tank (8) is connected to a first vent valve (28) via an outlet branch of a pressure sensor (10). The pipeline between the first regulating valve (11) and the first check valve (13) is connected to the cleaning and waste liquid recovery pipeline (4) via a high-pressure solenoid valve (29). One end of the paint supply pipeline (2) is connected to the paint tank (14), and the other end is connected to the second inlet of the micro mixer (20). The paint supply pipeline (2) is provided with a metering pump (15), a second buffer tank (16), a second regulating valve (17), a second pressure sensor (18), and a second check valve (19) in sequence along the fluid flow direction. The outlet branch of the second buffer tank (16) is connected to a second vent valve (30); one end of the mixing pipeline (3) is connected to the outlet of the micro mixer (20), and the other end is connected to a high-pressure spray gun (27). A capillary tube (21), a pressure regulating valve (23), a constant temperature buffer tank (24), and a third pressure sensor (26) are sequentially arranged along the fluid flow direction on the mixing pipeline (3). The inlet and outlet ends of the capillary tube (21) are respectively connected to the high-pressure side and the low-pressure side of the differential pressure transmitter (22). A second temperature sensor (25) is installed on the constant temperature buffer tank (24); the cleaning and waste liquid recovery pipeline (4) One end is connected to the outlet of the high-pressure solenoid valve (29), and the other end is connected to the pipeline between the capillary tube (21) and the pressure regulating valve (23). The cleaning and waste liquid recovery pipeline (4) is provided with a waste liquid collection tank (31) and a third vent valve (32) in sequence along the fluid flow direction. The PLC (33) is electrically connected to the first temperature sensor (10), the first regulating valve (11), the first pressure sensor (12), the second regulating valve (17), the second pressure sensor (18), the differential pressure transmitter (22), the second temperature sensor (25), the third pressure sensor (26), and the high-pressure solenoid valve (29).

2. The real-time control system for supercritical carbon dioxide spray paint viscosity according to claim 1, characterized in that: The output pressure range of the pneumatic diaphragm pump (7) is 7.5MPa to 14MPa, and the heating temperature of the heater (9) can make carbon dioxide reach a supercritical state with a temperature higher than 31.1℃ and a pressure higher than 7.38MPa.

3. The real-time control system for supercritical carbon dioxide spray paint viscosity according to claim 1, characterized in that: The capillary tube (21) is a stainless steel round tube with an inner diameter D of 0.5mm to 3mm and a length L of 200mm to 1000mm; the differential pressure transmitter (22) has a range of 0 to 1MPa and outputs a 4 to 20mA analog signal to the PLC (33).

4. The real-time control system for supercritical carbon dioxide spray paint viscosity according to claim 1, characterized in that: The micro mixer (20) is a static micro mixer or a T-type micro mixer with a microchannel flow structure inside.

5. The real-time control system for supercritical carbon dioxide spray paint viscosity according to claim 1, characterized in that: The constant temperature buffer tank (24) is a pressure-resistant container with a volume of 0.5L to 5L. It has a built-in heating device to maintain a constant fluid temperature and is equipped with baffles or stirring blades inside.

6. The real-time control system for supercritical carbon dioxide spray paint viscosity according to claim 1, characterized in that: The residence time of the mixed fluid in the constant temperature buffer tank (24) is 2s to 10s.

7. The real-time control system for supercritical carbon dioxide spray paint viscosity according to claim 1, characterized in that: The metering pump (15) is a high-pressure plunger metering pump, and the output pressure and flow rate can be changed by adjusting the frequency or the plunger stroke.

8. The real-time control system for supercritical carbon dioxide spray paint viscosity according to claim 1, characterized in that: The high-pressure solenoid valve (29) is a pulse-type high-pressure solenoid valve.

9. The real-time control system for supercritical carbon dioxide spray paint viscosity according to claim 1, characterized in that: The PLC (33) is equipped with a human-machine touch screen for displaying real-time viscosity, pressure, temperature parameters and input target viscosity values.

10. A method for real-time control of the viscosity of supercritical carbon dioxide sprayed paint, characterized in that: Includes the following steps: S1. Supercritical carbon dioxide preparation and delivery steps: The carbon dioxide output from the carbon dioxide gas source (5) enters the pneumatic diaphragm pump (7) through the shut-off valve (6) for pressurization, and then is sent to the heater (9) for heating after being stabilized by the first buffer tank (8) to form supercritical carbon dioxide. The supercritical carbon dioxide is then delivered to the micro mixer (20) in sequence through the first temperature sensor (10), the first regulating valve (11), the first pressure sensor (12), and the first one-way valve (13). S2. Paint pressurization and delivery steps: The paint in the paint tank (14) is pressurized to the same pressure as supercritical carbon dioxide by the metering pump (15), and then delivered to the micro mixer (20) after being stabilized by the second buffer tank (16), the second regulating valve (17), the second pressure sensor (18), and the second check valve (19). S3. Mixing and differential pressure detection steps: Supercritical carbon dioxide and paint are mixed in a micro mixer (20) to form a mixed fluid. The mixed fluid flows through a capillary tube (21). The differential pressure transmitter (22) detects the differential pressure at the inlet and outlet of the capillary tube (21) in real time and transmits the differential pressure signal to the PLC (33). S4. Viscosity calculation and closed-loop control steps: PLC (33) obtains the real-time viscosity of the mixed fluid based on the received differential pressure signal and the preset viscosity calculation model. It compares the real-time viscosity with the preset target viscosity and adjusts the opening of the first regulating valve (11) to change the carbon dioxide flow rate, thereby regulating the viscosity of the mixed fluid. S5. Pressure-stabilized and temperature-controlled spraying steps: The mixed fluid flowing through the capillary tube (21) is stabilized by the pressure-stabilizing valve (23) and then enters the temperature-controlled buffer tank (24). The mixed fluid is kept at a constant temperature in the temperature-controlled buffer tank (24) and further mixed and dissolved. Then, it is delivered to the high-pressure spray gun (27) through the third pressure sensor (26) to complete the spraying operation. S6. Pipeline cleaning steps: After the spraying operation is completed, open the first vent valve (28), the second vent valve (30), and the third vent valve (32). The high-pressure solenoid valve (29) operates at a pulse frequency and uses supercritical carbon dioxide to flush the mixing pipeline (3) and the high-pressure spray gun (27). The waste liquid is collected in the waste liquid collection tank (31).

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