High-molecular coating structure for cavitation erosion protection and preparation method of high-molecular coating structure

Abstract

The invention discloses a polymer coating structure for cavitation protection and a preparation method thereof. The structure is a sandwich structure formed by a material bottom layer, a porous structure layer and a surface layer. The structure is suitable for cavitation erosion protection of the surface of a base material in hydraulic machinery, the structure can be prepared and coated through a high polymer material, the structure can be formed on the surface of the base material after the material is cured, and the structure can also be generated in the form of 3D printing and the like. When cavitation bubbles generated around collapse close to the surface, the structural layer reduces the internal pressure through deformation and surface layer upheaval to balance the low pressure between the cavitation bubbles and the wall surface when the cavitation bubbles collapse, so that the collapse direction of the cavitation bubbles is changed, the impact of micro-jet generated when the cavitation bubbles collapse is remarkably inhibited, the strength of impact waves is reduced, and the cavitation bubbles are prevented from collapsing. Therefore, the purpose of cavitation erosion protection of hydraulic machinery is achieved. The invention provides a novel way with practicability and economical efficiency for cavitation protection of hydraulic machinery.

Description

Technical Field

[0001] This invention belongs to the field of fluid machinery cavitation protection coating technology. Background Technology

[0002] Cavitation erosion is widely considered the "cancer" of hydraulic machinery, and its damage to hydraulic machinery is one of the core issues threatening the safe and stable operation of hydropower stations. Under the action of high-speed water flow, the microjets generated by cavitation collapse and the impact pressure of shock waves can reach hundreds of megapascals, continuously acting on the surface of flow-through components, leading to material fatigue spalling and performance degradation. This not only causes damage to core components such as runners and guide vanes, significantly reducing their service life and mechanical efficiency, but also induces serious faults such as increased unit vibration and perforation of flow-through surfaces, greatly increasing the risk of unplanned shutdowns and maintenance costs.

[0003] Recent studies suggest that air bubbles residing on a substrate surface can reverse the microjets generated by the collapse of nearby cavitation bubbles. Some studies have achieved surface bubble retention through gas generation via surface electrolysis; however, this method is difficult to implement in the actual operating environment of hydraulic machinery, consumes a lot of energy, and lacks economic feasibility. This invention proposes a polymer coating structure and preparation method. By locking internal cavitation bubbles with polymer materials, the reversed microjets generated by the collapse of cavitation bubbles near the coating can be significantly achieved. The coating structure proposed in this invention significantly reduces the intensity of the shock wave generated during surface cavitation bubble collapse and significantly suppresses the impact of microjets, providing a new approach to cavitation erosion protection for hydraulic machinery that is both practical and economical. Summary of the Invention

[0004] This invention provides a polymer coating structure and preparation method for cavitation protection, which can significantly reduce the impact of shock waves generated by cavitation collapse and microjets, thereby achieving cavitation protection for hydraulic machinery.

[0005] This invention discloses a polymer coating structure and preparation method for cavitation erosion protection, characterized in that the coating structure is a sandwich structure composed of an adhesive layer, a structural layer, and a surface layer. The specific steps of the method are as follows: Step 1: Preparation of polyurethane prepolymer 1) Add the polyol monomer solution to a three-necked flask and dehydrate it under vacuum at 110°C for 2 hours to remove water and other small molecules. 2) Pour nitrogen gas for protection and allow it to cool naturally to about 60°C. Add isocyanate and catalyst, then heat to 80°C and stir thoroughly for 2 hours. 3) During the reaction, the NCO content in the prepolymer was determined using the dibutylamine-toluene method. When the content reached the theoretical value, the reaction was stopped, and the resulting prepolymer was vacuum-sealed to remove air bubbles and stored in a sealed container. Step 2: Chain extension and curing of polyurethane prepolymer 1) Take an appropriate amount of prepolymer, put it in a constant temperature oven and heat it to 75°C until it is completely melted, then put it in a defoamer for vacuum degassing until no large bubbles are visible. 2) Then, the curing agent, which has been heated to 120℃ and completely melted, is mixed with the prepolymer in a certain proportion, stirred evenly, and then degassed and stirred. Step 3: Preparation of the coating adhesive layer 1) After thoroughly and evenly mixing the above materials, apply the liquid evenly to the surface of the target substrate, with a coating thickness of 0.1~1mm. 2) The coated specimen is placed in a constant temperature oven for 1 hour for curing, or left to stand at room temperature for 24 hours to obtain the adhesive layer of the target substrate coating. Step 4: Preparation of Coating Structure Layer and Surface Layer 1) Repeat step one, and take an appropriate amount of prepolymer, put it in a constant temperature oven and heat it to 75°C until it is completely melted, then put it in a defoamer for vacuum degassing until there are no large bubbles visible. 2) Then heat the curing agent to 120°C until it is completely melted, and then mix the pore-forming agent and curing agent with the prepolymer in a certain proportion and stir thoroughly and evenly. 3) Spin-coat the thoroughly mixed material evenly onto the substrate adhesive layer, and then place it in a constant temperature environment for 24~48h to fully foam and cure, forming the structural layer and surface layer of the coating. Based on steps one through four above, a polymer coating structure for cavitation erosion protection can be prepared.

[0006] 2. Preferably, the NCO content in the prepolymer is determined by the dibutylamine-toluene method in the range of 3-10%.

[0007] 3. Preferably, the constant temperature vulcanization temperature range is 60~80℃.

[0008] 4. Preferably, the ratio of curing agent to prepolymer is 1:(8~12).

[0009] 5. Preferably, the thickness of the coating structure layer applied to the substrate surface is greater than 2 mm.

[0010] 6. Preferably, the substrate material can be any metal or alloy.

[0011] The beneficial effects of this invention are: This invention provides a polymer coating structure and preparation method for cavitation erosion protection. In this coating structure, the adhesive layer ensures strong adhesion to the substrate, the structural layer consists of widely distributed and relatively uniform cavitation structures, and the surface layer ensures coating toughness. When cavitation occurs near the substrate, the coating can reverse the microjets generated by the collapse of external cavitation bubbles due to the low pressure generated by its internal structure, significantly reducing the intensity of shock waves and achieving cavitation erosion protection for the substrate. This invention features a scientifically simple process, straightforward implementation, and good economic efficiency. Attached Figure Description

[0012] Figure 1 A schematic diagram of the substrate and coating structure, and the behavioral evolution of cavitation bubbles in the vicinity; Figure 2 Scanning electron microscope images of the three parts of the coating structure; Figure 3 The effects of the substrate (left) and coating structure (right) on the microjets generated by surface cavitation collapse (high-speed camera images, shooting rate 180,000 fps, exposure time 0.25 μs) (a. γ = 1.0; b. γ = 1.5; c. γ = 2.0; d. γ = 2.5; e. γ = 3.0; f. γ = 3.5). Figure 4 The effects of the substrate (left) and coating structure (right) on the shock wave generated by the collapse of surface cavitation (high-speed camera images, shooting rate 180,000 fps, exposure time 0.25 μs) (a. γ = 1.0; b. γ = 1.5; c. γ = 2.0; d. γ = 2.5; e. γ = 3.0; f. γ = 3.5). Detailed Implementation

[0013] The technical solution of the present invention will be further explained and illustrated below with specific implementation examples. Example

[0014] 1) Add the polyol monomer solution to a three-necked flask and dehydrate it under vacuum at 110°C for 2 hours to remove water and other small molecules. 2) Pour nitrogen gas for protection and allow it to cool naturally to about 60°C. Add isocyanate and catalyst, then heat to 80°C and stir thoroughly for 2 hours. 3) During the reaction, the NCO content in the prepolymer was determined to be 9% using the dibutylamine-toluene method. When the content reached the theoretical value, the reaction was stopped, and the resulting prepolymer was vacuum-sealed to remove air bubbles and stored in a sealed container. 4) Take an appropriate amount of prepolymer, put it in a constant temperature oven and heat it to 75°C until it is completely melted, then put it in a defoamer for vacuum degassing until no large bubbles are visible. 5) Then, after the curing agent is heated to 120℃ and completely melted, it is mixed with the prepolymer at a ratio of 1:12, stirred evenly, and then degassed and stirred. 6) After thoroughly and evenly mixing the above materials, coat the liquid evenly onto the surface of the stainless steel substrate, with a coating thickness of 0.5 mm. 7) After coating, the specimen is placed in a constant temperature oven for 1 hour for curing, or left to stand at room temperature for 24 hours to obtain the adhesive layer of the target stainless steel substrate coating. 8) Repeat step one, and take an appropriate amount of prepolymer, put it in a constant temperature oven and heat it to 75°C until it is completely melted, then put it in a defoamer for vacuum degassing until there are no large bubbles visible. 9) Then heat the curing agent to 120°C until it is completely melted, and then mix the pore-forming agent and curing agent with the prepolymer in proportion and stir thoroughly and evenly. 10) Spin-coat the thoroughly stirred material evenly onto the adhesive layer of the stainless steel substrate to a thickness of 2mm. Then place it in a constant temperature environment and let it stand for 24 hours to fully foam and cure, forming the structural layer and surface layer of the coating, thus completing the preparation.

[0015] In one of the above embodiments, the invention objective of a polymer coating structure and preparation method for cavitation erosion protection can be achieved, and those skilled in the art can choose according to the actual situation.

[0016] Effect verification The polymer anti-cavitation coating provided by this invention can significantly achieve cavitation erosion protection. In the embodiment described in this example, the microstructure of the completed coating structure under a scanning electron microscope is shown as follows. Figure 2 As shown. The experimental results are as follows. Figure 3 as well as Figure 4 As shown, under different distance parameters (γ represents the ratio of the maximum radius of the cavitation bubble to the distance from the center of the cavitation bubble to the coating surface), the coating structure can significantly change the direction of the microjets generated by cavitation bubble collapse, and also has a significant weakening effect on the generated shock waves. This indicates that the coating structure designed in this invention can significantly repel cavitation bubbles in different ranges, and has a significant effect on cavitation erosion protection.

[0017] The above description is merely an example and illustration of the structure of the present invention. Any modifications or additions made by those skilled in the art to the specific embodiments described herein, as long as they do not deviate from the structure of the invention (the sandwich structure formed by the adhesive layer, structural layer and surface layer) or exceed the scope defined in the claims, shall fall within the protection scope of the present invention.

Claims

1. A high polymer coating structure for cavitation erosion protection and a method of making the same, characterized in that, The coating structure is a sandwich structure composed of an adhesive layer, a structural layer and a surface layer. The specific steps for preparing the structure are as follows: Step 1: preparing a polyurethane prepolymer 1) The polyol monomer solution is added to a three-necked flask and vacuum dehydrated at 110°C for 2h to remove water and other small molecules; 2) Nitrogen is filled for protection, and the temperature is naturally cooled to about 60°C. Isocyanate and catalyst are added, and the temperature is raised to 80°C for 2h of sufficient stirring; 3) During the reaction, the NCO content in the prepolymer is determined by the dibutylamine toluene method; When the content reaches the theoretical value, the reaction is stopped, the obtained prepolymer is vacuum degassed to remove bubbles and sealed for storage; Step 2: chain extension and curing of the polyurethane prepolymer 1) Take an appropriate amount of prepolymer and heat it to 75°C in a constant temperature oven until it is completely melted. Then vacuum degas it in a defoaming device until there are no large bubbles visible; 2) Then mix the completely melted curing agent with the prepolymer at a certain ratio, stir uniformly, and then degas and stir; Step 3: preparation of the adhesive layer of the coating 1) After the above materials are mixed uniformly, the liquid is uniformly coated on the surface of the target substrate, and the thickness of the coating on the substrate is 0.1-1mm; 2) The coated sample is placed in a constant temperature oven for vulcanization for 1h, or left at room temperature for 24h to obtain the adhesive layer of the target substrate coating; Step 4: preparation of the structural layer and surface layer of the coating 1) Repeat the process of step 1, and take an appropriate amount of prepolymer and heat it to 75°C in a constant temperature oven until it is completely melted. Then vacuum degas it in a defoaming device until there are no large bubbles visible; 2) Then heat the curing agent to 120°C until it is completely melted, and then mix the pore former and the curing agent with the prepolymer at a certain ratio, and stir thoroughly; 3) Uniformly spin-coat the thoroughly stirred material on the adhesive layer of the substrate, and then place it in a constant temperature environment for 24-48h to form the structural layer and surface layer of the coating after sufficient foaming and curing; According to the above steps 1-4, a high molecular coating structure for cavitation erosion protection can be prepared.

2. The polymeric coating structure for cavitation erosion protection according to claim 1, wherein The NCO content in the prepolymer is determined by the dibutylamine toluene method, and the range is 3-10%.

3. The polymeric coating structure for cavitation erosion protection according to claim 1, wherein The constant temperature vulcanization temperature range is 60-80°C.

4. The polymeric coating structure for cavitation erosion protection and the method of making according to claim 1, wherein, The ratio of curing agent to prepolymer is 1:(8-12).

5. The polymeric coating structure for cavitation erosion protection according to claim 1, wherein The thickness of the coating structure layer coated on the surface of the substrate should be greater than 2mm.

6. The polymeric coating structure for cavitation erosion protection according to claim 1, wherein The substrate material can be any metal or alloy.

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