Low-temperature degreasing system and method for coating pretreatment

Abstract

The present invention relates to the field of the purification and reuse of a degreasing solution for automotive coating pretreatment. Provided is a low-temperature degreasing system for coating pretreatment. The low-temperature degreasing system for coating pretreatment comprises: a degreasing tank (1) provided with a workpiece inlet end A and a workpiece outlet end B; a heating module (9) arranged at the bottom of the degreasing tank (1) for heating the degreasing solution in the degreasing tank (1); a first hydrodynamic cavitation module connected to the degreasing tank (1); a temperature-raising demulsification oil-water separator (4) connected to the degreasing tank (1); and a second hydrodynamic cavitation module connected to the temperature-raising demulsification oil-water separator (4). By combining heating demulsification with the hydrodynamic cavitation technology, a better degreasing and oil removal effect can be achieved at temperatures lower than those for traditional high-temperature heating demulsification; and the degreasing solution can maintain the same cleaning ability under reduced degreasing tank operating temperatures, thereby reducing energy consumption and prolonging the replacement cycle of the degreasing tank solution.

Description

Low-temperature degreasing system and method for pre-coating treatment Technical Field

[0001] This invention relates to the field of purification and reuse of degreasing solution in automotive pre-coating treatment, specifically to the field of low-temperature degreasing systems for pre-coating treatment. Background Technology

[0002] Degreasing is a crucial step in the pretreatment line of an automotive painting workshop. The purpose of degreasing is to clean the surface of welded workpieces of grease, dirt, and dust, providing a clean surface with good contact with the workpiece for phosphating (or silane coating), ensuring the formation of a complete phosphating film (or silane film). Incomplete degreasing during pretreatment not only hinders the formation of the phosphating film (or silane film) but also affects the adhesion, decorative properties, and corrosion resistance of the coating during post-phosphating painting. Degreasing relies on the dissolving and saponifying effects of degreasing agents on contaminants, and the wetting, penetration, and dispersion effects of surfactants on contaminants, removing contaminants from the metal surface and allowing clean cleaning agents to adhere to the surface, thus achieving the purpose of cleaning the metal surface.

[0003] The automotive painting production line is highly automated and uses a medium-high temperature degreasing process, which means that the degreasing working temperature is maintained at 50-60℃ during production. To maintain this process temperature for degreasing, the workshop needs to consume a lot of heat energy.

[0004] As oil carried by the car body continuously mixes into the degreasing system during the production process, the oil content of the degreasing solution gradually increases, severely affecting the degreasing effect and leading to poor paint quality. How to separate oil and dirt from the degreasing tank solution and maintain its cleanliness and degreasing capacity is an important research topic for automotive painting plants and painting equipment manufacturers. The requirements for the degreasing system are: to ensure that oil in the tank solution can be promptly removed and centrally recycled to maintain the cleaning capacity of the degreasing solution; and to minimize the amount of degreasing wastewater carried to the wastewater treatment plant, reducing the pressure on the wastewater treatment plant.

[0005] The current solution involves installing a high-temperature demulsifier / oil-water separator to remove oil from the degreasing tank. The principle is to heat the tank liquid to a certain temperature (80-90°C), causing the oil particles in the emulsion to aggregate and accelerate their floating or settling. While heating can accelerate oil-water separation, in some cases, especially when the emulsion is very stable, it may require a longer time and higher temperatures to achieve the desired separation effect. This process requires a large amount of energy, leading to extremely high energy costs, particularly when processing large volumes. Furthermore, strict safety measures are necessary during the heating process to prevent fire and explosion accidents.

[0006] Traditional degreasing and oil removal technologies all use high-temperature heating to break up emulsions, combined with chemical agents, which has the following drawbacks: (1) High energy consumption. The degreasing tank solution needs to be maintained at 50-60℃ through circulating heating to clean the car body. The floating oil on the surface of the tank solution overflows into the traditional oil-water separator, which operates at a high temperature of 70-90℃ for demulsification and oil-water separation; (2) Low oil removal efficiency. Due to the limitations of the process and technology itself, the traditional high-temperature heating demulsification oil-water separator can only solve the problem of oil in a small portion of the overflowing tank solution. It cannot solve the problem of oil in the tank solution of the degreasing tank. In addition, the high temperature of 70-90℃ will also damage the performance of the degreasing agent and increase the consumption of the degreasing agent; (3) Large amount of degreasing wastewater discharge. As the number of vehicles cleaned increases, the oil content of the degreasing tank solution becomes higher and higher, making the degreasing and oil removal performance unable to meet the process quality requirements. The production line must be shut down to replace the degreasing tank solution. A car painting workshop will generate hundreds to thousands of tons of degreasing oily wastewater per year. Degreasing wastewater is classified as hazardous waste and cannot be treated by traditional water treatment processes, requiring companies to incur significant costs for its disposal. Technical issues

[0007] The current process for degreasing tanks in the pretreatment stage of automotive painting, which involves heating to break up the emulsion and then separating the oil using a traditional oil-water separator, is characterized by high energy consumption, low oil removal efficiency, and large amounts of degreasing wastewater discharge.

[0008] To address the aforementioned issues in pre-coating degreasing solution treatment, this invention provides a low-temperature degreasing system and method for pre-coating treatment. By combining heating demulsification with hydraulic cavitation technology, it achieves better degreasing and oil removal effects at temperatures lower than those of traditional high-temperature heating demulsification. It also maintains the same cleaning capacity of the degreasing solution while lowering the operating temperature of the degreasing tank, thereby saving energy and extending the degreasing tank solution replacement cycle.

[0009] The pre-coating low-temperature degreasing system includes:

[0010] The degreasing tank has a workpiece inlet end A and a workpiece outlet end B;

[0011] A heating module is installed at the bottom of the degreasing tank to heat the degreasing liquid in the tank.

[0012] The first hydraulic cavitation module is connected to the degreasing tank;

[0013] A heated demulsifying oil-water separator is connected to the degreasing tank;

[0014] The second hydraulic cavitation module is connected to the heated demulsifying oil-water separator.

[0015] Preferably, the first hydraulic cavitation module includes a first high-pressure pump and a first cavitation generator connected in sequence; the first high-pressure pump is connected to the workpiece inlet A, and the first cavitation generator is connected to the workpiece outlet B; a positive pressure gauge is connected between the first high-pressure pump and the first cavitation generator; the first cavitation generator is provided with a negative pressure port, and the negative pressure port is connected to a negative pressure gauge.

[0016] Preferably, the workpiece inlet A is provided with a liquid intake port of the first hydraulic cavitation module, and the liquid intake port is located in the middle and lower layer of the degreasing tank; the workpiece outlet B is provided with a first liquid outlet manifold of the first hydraulic cavitation module; the first liquid outlet manifold is close to the liquid surface of the degreasing tank.

[0017] Preferably, the degreasing tank is provided with a second liquid outlet manifold on each side of its width direction. The outlet of the second liquid outlet manifold is inclined at a certain angle to the length direction of the degreasing tank and faces the workpiece inlet A.

[0018] Preferably, the heated demulsifying oil-water separator is connected to an oil collector, which is positioned on the liquid surface at the inlet end A; the heated demulsifying oil-water separator is provided with a return end, which is connected to the degreasing tank.

[0019] Preferably, the heated demulsifying oil-water separator includes:

[0020] A heating tank, wherein a heater is provided inside the heating tank, and the heating tank is connected to the degreasing tank;

[0021] A cavitation tank is connected to a second hydraulic cavitation module, the second hydraulic cavitation module including a second high-pressure pump and a second cavitation generator arranged in sequence;

[0022] The settling tank is equipped with a second oil collection tank and a return tank;

[0023] The heating tank is connected to the cavitation tank.

[0024] Preferably, the heating tank is provided with a partition in the middle, which divides the heating tank into a first tank and a second tank. The heater is provided in the first tank. The partition is provided with a through hole that connects the first tank and the second tank. The second tank is provided with a first oil collection tank. The second tank is provided with a U-shaped pipe that connects to the cavitation tank.

[0025] Preferably, the cavitation tank is provided with a baffle that divides the cavitation tank into a first cavity and a second cavity; the distance between the baffle and the bottom of the cavitation tank is greater than zero, and the U-shaped tube extends into the second cavity.

[0026] Preferably, the second chamber is connected to a second high-pressure pump; the first chamber is connected to a second cavitation generator; a positive pressure gauge is connected between the second high-pressure pump and the second cavitation generator; the second cavitation generator is provided with a negative pressure port, and the negative pressure port is connected to a negative pressure gauge.

[0027] Preferably, an overflow port is provided between the cavitation tank and the settling tank; the settling tank is provided with an outlet pipe, the outlet pipe is connected to the return liquid tank, and an adjustment pipe is provided at the upper end of the outlet pipe.

[0028] Preferably, an oil separation device is also connected to the liquid surface at the workpiece inlet A of the degreasing tank.

[0029] The low-temperature degreasing method for pre-coating using the aforementioned low-temperature degreasing system for pre-coating, the method comprising:

[0030] S1. The degreasing tank heating module heats the degreasing tank liquid to maintain the working temperature of the degreasing tank; it performs hydraulic cavitation treatment on the degreasing tank liquid, breaking the oil-water interface of the emulsified oil through hydraulic cavitation, so that the emulsified oil is converted into floating oil.

[0031] S2, the liquid outlet manifold of the hydraulic cavitation module pushes the oil floating on the liquid surface from the workpiece outlet end B to the workpiece inlet end A. An oil collector is provided at the workpiece inlet end A. Using the oil collector, the oil with high oil content on the surface of the degreasing tank liquid is pumped to the heating demulsification oil-water separator.

[0032] S3. The heated demulsifying oil-water separator first heats and initially skims off the oil. Then, the initially skimmed liquid is introduced into the cavitation tank through a U-shaped tube. In the cavitation tank, hydraulic cavitation treatment is carried out. The cavitation liquid overflows into the settling tank. In the settling tank, the oil and liquid are further separated. The oil enters the oil collection tank and is introduced into the oil drum. The clean liquid enters the return liquid tank and is introduced into the degreasing tank.

[0033] Furthermore, the pre-coating low-temperature degreasing method further includes S4, after separating the oil with a high oil content on the surface of the degreasing tank liquid through a heated demulsifying oil-water separator, the remaining floating oil is further collected and separated into oil and water using a floating oil separation device.

[0034] Compared with the prior art, the beneficial technical effects of the present invention are as follows: Beneficial effects

[0035] 1. By incorporating hydraulic cavitation technology into the existing process, the friction and shearing mechanical action generated by cavitation changes the morphology of molecular clusters in the multiphase mixture in the solution, transforming large molecular clusters into smaller ones, enhancing the activity of solution molecules, reducing the viscosity and surface tension of the solution system, improving the solubility and permeability of the solution system, and enhancing the wettability of the solution system, thereby enhancing the degreasing ability of the solution.

[0036] 2. The instantaneous local high temperature and pressure generated by hydraulic cavitation are accompanied by strong shock waves and mechanical effects such as microjets with speeds of up to 1400 m / s or more, during which a large amount of energy is released. These effects can cause the oil-water interface of the emulsified oil to be squeezed or impacted and destroyed. The emulsified oil is broken into small oil droplets, which carry microbubbles and rise rapidly. Due to the sufficient number of bubbles, the collision coefficient increases, and the small oil droplets collide and aggregate into large oil droplets, completing the transformation into floating oil. At this time, the floating oil is removed by the floating oil collection and separation technology, which significantly improves the oil removal and purification capacity.

[0037] 3. This system combines heating demulsification with hydraulic cavitation technology, achieving better degreasing and oil removal effects at temperatures lower than traditional high-temperature heating demulsification; it also maintains the same cleaning capacity of the degreasing liquid while lowering the operating temperature of the degreasing tank; thus saving energy and extending the degreasing tank liquid replacement cycle.

[0038] 4. The liquid intake port of the first hydraulic cavitation module is located in the middle and lower layer of the degreasing tank. It can perform cavitation treatment on the degreasing liquid in the middle and lower layer of the degreasing tank, which can not only remove the floating oil on the surface, but also remove the emulsified oil in the degreasing tank liquid, ensuring a good cleaning effect on the workpiece. Attached Figure Description

[0039] Figure 1 is a schematic diagram of the system flow of the processing system of the present invention.

[0040] Figure 2 is a schematic diagram of the system flow structure of the processing system of the present invention.

[0041] Figure 3 is a schematic diagram of a low-temperature demulsifying oil-water separator.

[0042] Figure 4 is a top view of the degreasing tank.

[0043] Figure 5 is a top view of another type of degreasing tank. The best embodiment of the present invention

[0044] As shown in Figure 1, the pre-coating low-temperature degreasing system includes a degreasing tank, which is connected to a heating module, a first hydraulic cavitation module, and a heated demulsifying oil-water separator. The heated demulsifying oil-water separator is connected to a second hydraulic cavitation module and is also connected to an oil tank.

[0045] As shown in Figure 2, the pre-coating low-temperature degreasing system includes a degreasing tank 1, which has an inlet end A and an outlet end B; a heating module 9, which is located at the bottom of the degreasing tank 1 to heat the degreasing liquid in the degreasing tank 1; a first hydraulic cavitation module, which is connected to the degreasing tank 1; a heating demulsifying oil-water separator 4, which is connected to the degreasing tank 1; and a heating demulsifying oil-water separator 1, which is connected to the second hydraulic cavitation module.

[0046] As shown in Figure 2, the degreasing tank 1 is also equipped with a degreasing agent inlet, which is connected to the degreasing agent feeding area 8. The heating module 9 includes a pump, a filter 90, and a heat exchanger 91 arranged in sequence. The heat exchanger continuously exchanges heat with the degreasing liquid in the degreasing tank through steam or hot water, thereby raising the temperature of the degreasing liquid.

[0047] In this embodiment, the workpiece is an automotive sheet metal part. As shown in Figure 2, the automotive sheet metal part enters from side A of the degreasing tank 1 according to the workpiece entry direction, is immersed in the degreasing tank 1, and the grease and dirt on the surface of the automotive sheet metal part are cleaned, and it exits from side B of the degreasing tank 1.

[0048] As shown in Figure 2, the first hydraulic cavitation module includes a first high-pressure pump 3 and a first cavitation generator 2 connected in sequence; the first high-pressure pump 3 is connected to the workpiece inlet A, and the first cavitation generator 2 is connected to the workpiece outlet B; a positive pressure gauge is connected between the first high-pressure pump 3 and the first cavitation generator 2, and the first cavitation generator is provided with a negative pressure port, which is connected to a negative pressure gauge.

[0049] As shown in Figure 2, the inlet A of the degreasing tank 1 is provided with a liquid intake port of the first hydraulic cavitation module, located in the lower middle layer of the degreasing tank 1. As shown in Figure 4, the outlet B is provided with a first liquid outlet manifold 20 connected to the first cavitation generator 2. The first liquid outlet manifold 20 consists of a row of pipes with multiple liquid outlets. The first liquid outlet manifold 20 pushes the oil with a high oil content in the upper layer of the degreasing tank from the outlet B to the inlet A. As shown in Figure 2, the outlet of the first liquid outlet manifold 20 maintains a certain inclination angle with the liquid surface. The first liquid outlet manifold 20 is located at the upper end of the degreasing tank 1 close to the liquid surface and sprays liquid at an angle towards the liquid surface, which is beneficial for pushing the oil in the upper layer of the degreasing tank 1 towards the inlet A.

[0050] As shown in Figure 5, for degreasing tanks with large volume and length, second liquid outlet manifolds 21 are provided on both sides of the width direction of the degreasing tank 1. The outlets of the second liquid outlet manifolds 21 are inclined at a certain angle to the length direction of the degreasing tank 1 and face the inlet end A. The oil collector 70 is located on one side of the inlet end A, and the outlet of the heating demulsifying oil-water separator is located on the other side of the inlet end A; this causes the floating oil to gather and be collected at the location of the oil collector 70.

[0051] As shown in Figure 2, the heated demulsifying oil-water separator 4 is connected to the oil collector 70, which is set on the liquid surface at the inlet end A; the heated demulsifying oil-water separator 4 is provided with a return end, which is connected to the degreasing tank 1.

[0052] In this embodiment, the oil collector 70 is a floating oil suction device.

[0053] As shown in Figure 3, the heated demulsifying oil-water separator includes: a heating tank 40, which is equipped with a heater 401 and connected to an oil collector 70; a cavitation tank 41, which is connected to a second hydraulic cavitation module, which includes a second high-pressure pump 5 and a second cavitation generator 6 arranged in sequence, with a positive pressure gauge 60 between the high-pressure pump 5 and the second cavitation generator 6, and the second cavitation generator 6 having a negative pressure port connected to the negative pressure gauge 61 and a one-way valve; a settling tank 42, which is equipped with a second oil collection tank 422 and a return tank 420; and the heating tank 41 and the cavitation tank 42 are connected. Embodiments of the present invention

[0054] Example 2;

[0055] The heating tank 41 is provided with a partition 402 in the middle, which divides the heating tank 1 into a first tank 403 and a second tank 404. The heater 401 is located in the first tank 403. The partition 402 is provided with a through hole 4020 that connects the first tank and the second tank. The second tank 404 is provided with a first oil collection tank 4040. The second tank 404 is provided with a U-shaped pipe 410 that connects to the cavitation tank.

[0056] The heating tank 41 is configured as two tanks, with the heater placed in a separate space, which improves the heating efficiency. The heated liquid is introduced into the second tank through the through hole 4020, and oil and water are separated through the first oil collection tank 4040, which allows for the initial skimming of oil from the heated liquid.

[0057] A baffle 411 is provided inside the cavitation tank 41, dividing the cavitation tank 41 into a first chamber 412 and a second chamber 413. The distance between the baffle 411 and the bottom of the cavitation tank 41 is greater than zero. A U-shaped tube 410 extends to the second chamber 413, and the outlet of the U-shaped tube is located in the second chamber 413. The second chamber 413 is connected to a second high-pressure pump 5; the high-pressure pump 5 is connected to a second cavitation generator 6, and the first chamber 412 is connected to the second cavitation generator.

[0058] An overflow port 414 is provided between the cavitation tank 41 and the settling tank 42; the liquid that has undergone cavitation treatment in the cavitation tank overflows into the settling tank 42 through the overflow port 414; the settling tank 42 is provided with an outlet pipe 421, which is connected to the return liquid tank 420, and an adjustment pipe 4210 is provided at the upper end of the outlet pipe 421.

[0059] The cavitation treatment fluid in the cavitation tank overflows into the settling tank. The overflow of floating oil into the second oil collecting tank 422 is regulated by changing the height of the regulating pipe 4210. When the outlet height of the regulating pipe 4210 is higher than the opening of the second oil collecting tank 422, the settled floating oil overflows into the second oil collecting tank 422. When the outlet height of the regulating pipe is lower than the opening of the second oil collecting tank 422, oil is drained from the second oil collecting tank 422. The lower layer of purified liquid in the settling tank is introduced into the return liquid tank 420 through the outlet pipe 421, further separating the oil and water in the degreasing liquid and significantly reducing the oil content returning to the degreasing tank.

[0060] The first and second cavitation generators each include a container with an inner diameter that decreases from top to bottom. The container has a tangentially oriented inlet pipe and an outlet pipe in the middle. The outlet pipe contains a Venturi tube structure, and a guide component is located below it. A high-pressure pump injects liquid at a certain pressure into the hydraulic cavitation generator. Upon entering the generator, the liquid forms a swirling flow resembling a hurricane within the container cavity. The laminar flows rub and shear against each other. As the swirling flow rotates downwards within the cavity, it accelerates, increasing in speed. At the venturi tube throat, a negative pressure environment is created, passively dissolving gas and generating cavitation bubbles. Then, the pressure rapidly recovers, the cavitation bubbles burst, releasing energy and producing the hydraulic cavitation effect.

[0061] The working principle of the low-temperature degreasing system for pre-coating treatment in this embodiment is as follows:

[0062] The workpiece is immersed in degreasing tank 1 along the workpiece infeed direction. After cleaning and degreasing, the grease, dirt, and dust on the surface of the workpiece are cleaned, while the oil and dirt remain in the degreasing tank. The heating module continuously heats the degreasing liquid in degreasing tank 1 to maintain the working temperature of the degreasing liquid; at the same time, the degreasing liquid undergoes hydraulic cavitation treatment to further break up the emulsified oil-in-water mixture, causing impurities and fine particles to float to the surface. The first outlet manifold 20 of the first cavitation generator 2 pushes the degreasing liquid with floating oil on the surface of the degreasing tank toward the workpiece inlet A. An oil collector 70 is provided on the surface of the liquid at workpiece inlet A. The oil collector 70 collects the floating oil and fine particles with some liquid and pumps them to the heated demulsifying oil-water separator 4. In the heated demulsifying oil-water separator 4, the oil is first skimmed off by heating, and then it passes through the second cavitation generator for hydraulic cavitation treatment. The liquid that has been skimmed off is further demulsified by cavitation. The demulsified liquid overflows into the settling tank 42 and is settling. Then, it is separated into oil and water again. The floating oil enters the second oil collection tank 422, and the clean liquid enters the return tank 420. The return tank 420 is the return end of the heated demulsifying oil-water separator. The return end sends the clean liquid to the degreasing liquid tank.

[0063] Example 3;

[0064] Unlike Example 1, this example adds an oil separation device 7 to the surface of the liquid at the workpiece inlet A of the degreasing tank. The oil separation device 7 is connected to an oil collector 70. The structure of the oil separation device 7 is prior art, and its technical information can be found in patent CN201921892786.7, "Oil Skimmer." This oil separation device can collect a small amount of floating oil from the surface of the degreasing tank and further separate the oil and water, keeping the liquid surface clean so that automotive sheet metal parts do not carry grease when entering from the workpiece inlet A.

[0065] The low-temperature degreasing method for pre-coating using the aforementioned low-temperature degreasing system for pre-coating, the method comprising:

[0066] S1. The degreasing tank liquid is heated using the degreasing tank heating module to maintain the working temperature of the degreasing tank; the degreasing tank liquid is subjected to hydraulic cavitation treatment, which breaks the oil-water interface of the emulsified oil and transforms the emulsified oil into floating oil.

[0067] S2, the outlet manifold of the hydraulic cavitation module pushes the oil floating on the liquid surface from the outlet end B to the inlet end A. An oil collector is provided at the inlet end A. Using the oil collector, the floating oil with some liquid on the liquid surface is pumped to the heated demulsifying oil-water separator.

[0068] S3. The heated demulsifying oil-water separator first heats and skims off the oil, then introduces the skimmed liquid into the cavitation tank through a U-shaped tube. The cavitation tank is then subjected to hydraulic cavitation treatment, and the cavitated liquid overflows into the settling tank. In the settling tank, the oil and liquid are further separated. The oil enters the oil collection tank and is introduced into the oil drum. The clean liquid enters the return liquid tank and is introduced into the degreasing tank.

[0069] The pre-coating low-temperature degreasing method further includes S4, where the oil with a high oil content on the surface of the degreasing tank is separated by a heated demulsifying oil-water separator, and then the remaining floating oil is further collected and separated into oil and water using a floating oil separation device. Industrial applicability

[0070] This invention provides a low-temperature degreasing system and method for pre-coating treatment, which combines heating demulsification with hydraulic cavitation technology. Specific implementation methods are provided, and those skilled in the art, upon learning of the disclosed technical solution, can implement and apply this technology. This application can solve the problem of excessively high oil content encountered in existing pre-treatment processes in coating workshops; it can achieve better degreasing and oil removal effects at temperatures lower than traditional high-temperature heating demulsification; it can maintain the same cleaning capacity of the degreasing solution while lowering the operating temperature of the degreasing tank; thereby saving energy and extending the degreasing tank solution replacement cycle.

Claims

1. A low-temperature degreasing system for pre-coating treatment, characterized in that, include: The degreasing tank has a workpiece inlet end A and a workpiece outlet end B; A heating module is installed at the bottom of the degreasing tank to heat the degreasing liquid in the tank. The first hydraulic cavitation module is connected to the degreasing tank; A heated demulsifying oil-water separator is connected to the degreasing tank; The second hydraulic cavitation module is connected to the heated demulsifying oil-water separator.

2. The low-temperature degreasing system for pre-coating treatment according to claim 1, characterized in that, The first hydraulic cavitation module includes a first high-pressure pump and a first cavitation generator connected in sequence; the first high-pressure pump is connected to the workpiece inlet A, and the first cavitation generator is connected to the workpiece outlet B; a positive pressure gauge is connected between the first high-pressure pump and the first cavitation generator; the first cavitation generator is provided with a negative pressure port, and the negative pressure port is connected to a negative pressure gauge.

3. The low-temperature degreasing system for pre-coating treatment according to claim 1, characterized in that, The workpiece inlet A is provided with a liquid intake port of the first hydraulic cavitation module, and the liquid intake port is located in the middle and lower layer of the degreasing tank; the workpiece outlet B is provided with a first liquid outlet manifold connected to the first hydraulic cavitation module; the first liquid outlet manifold is close to the liquid surface of the degreasing tank.

4. The low-temperature degreasing system for pre-coating treatment according to claim 3, characterized in that, The degreasing tank has a second liquid outlet manifold on each side of its width direction. The outlet of the second liquid outlet manifold is inclined at a certain angle to the length direction of the degreasing tank and faces the workpiece inlet A.

5. The low-temperature degreasing system for pre-coating treatment according to claim 1, characterized in that, The heated demulsifying oil-water separator is connected to an oil collector, which is positioned on the liquid surface at the inlet end A. The heated demulsifying oil-water separator is provided with a return end, which is connected to the degreasing tank.

6. The low-temperature degreasing system for pre-coating treatment according to claim 1, characterized in that, The heated demulsifying oil-water separator includes: A heating tank, wherein a heater is provided inside the heating tank, and the heating tank is connected to the degreasing tank; A cavitation tank is connected to a second hydraulic cavitation module, the second hydraulic cavitation module including a second high-pressure pump and a second cavitation generator arranged in sequence; The settling tank is equipped with a second oil collection tank and a return tank; The heating tank is connected to the cavitation tank.

7. The low-temperature degreasing system for pre-coating treatment according to claim 6, characterized in that, The heating tank is provided with a partition plate, which divides the heating tank into a first tank and a second tank. The heater is installed in the first tank. The partition plate is provided with a through hole that connects the first tank and the second tank. The second tank is provided with a first oil collection tank.

8. The low-temperature degreasing system for pre-coating treatment according to claim 6 or 7, characterized in that, The cavitation tank is equipped with a baffle that divides the cavitation tank into a first cavity and a second cavity. The distance between the baffle and the bottom of the cavitation tank is greater than zero. The heating tank is equipped with a U-shaped tube that connects to the cavitation tank and extends to the second cavity.

9. The low-temperature degreasing system for pre-coating treatment according to claim 8, characterized in that, The second chamber is connected to the second high-pressure pump; the first chamber is connected to the second cavitation generator; a positive pressure gauge is connected between the second high-pressure pump and the second cavitation generator, and the second cavitation generator is provided with a negative pressure port, which is connected to the negative pressure gauge.

10. The low-temperature degreasing system for pre-coating treatment according to claim 6, characterized in that, An overflow port is provided between the cavitation tank and the settling tank; the settling tank is provided with an outlet pipe, which is connected to the return liquid tank, and an adjustment pipe is provided at the upper end of the outlet pipe.

11. The low-temperature degreasing system for pre-coating treatment according to claim 1, characterized in that, An oil separation device is also connected to the liquid surface at the workpiece inlet A of the degreasing tank.

12. A low-temperature degreasing method for pre-coating using the low-temperature degreasing system according to any one of claims 1-11, characterized in that, The method includes: S1. The degreasing tank heating module heats the degreasing tank liquid to maintain the working temperature of the degreasing tank; it performs hydraulic cavitation treatment on the degreasing tank liquid, breaking the oil-water interface of the emulsified oil through hydraulic cavitation, so that the emulsified oil is converted into floating oil. S2, the liquid outlet manifold of the hydraulic cavitation module pushes the oil floating on the liquid surface from the workpiece outlet end B to the workpiece inlet end A. An oil collector is provided at the workpiece inlet end A. Using the oil collector, the oil with high oil content on the surface of the degreasing tank liquid is pumped to the heating demulsification oil-water separator. S3. The heated demulsifying oil-water separator first heats and initially skims off the oil. Then, the initially skimmed liquid is introduced into the cavitation tank through a U-shaped tube. In the cavitation tank, it undergoes hydraulic cavitation treatment and oil-liquid separation again.

13. The low-temperature degreasing method for pre-coating treatment according to claim 12, characterized in that, In step S3, the cavitation treatment liquid overflows into the settling tank; in the settling tank, the oil is further separated; the oil enters the oil collection tank and is introduced into the oil drum; the purified liquid enters the return liquid tank and is introduced into the degreasing tank.

14. The low-temperature degreasing method for pre-coating treatment according to claim 12, characterized in that, The pre-coating low-temperature degreasing method further includes: S4. After the oil with high oil content on the surface of the degreasing tank liquid is separated by the heated demulsifying oil-water separator, the remaining floating oil is further collected and separated into oil and water using a floating oil separation device.

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