A method for preparing a shear-enhanced polyurethane composite coating for erosion resistance

Abstract

The application discloses a preparation method of a shear reinforced polyurethane composite coating for erosion resistance. The preparation method is as follows: taking polyurethane as a base material, adding a shear hardening gel obtained by polymerization reaction of hydroxyl-terminated polydimethylsiloxane and boric acid as an additive, and blending and polymerizing to prepare the composite coating. The composite coating introduces a dynamic boron-oxygen bond, so that the mechanical properties of the composite coating can be self-adaptively changed and transiently responded to the impact conditions of the sand-containing water flow particles. Under low-speed impact, the composite coating relies on viscoelasticity and molecular chain segment movement to buffer and consume energy, and to relieve erosion. Under high-speed impact, the composite coating keeps toughness through elastic chain segments, and the modulus is suddenly increased through the shear hardening effect of the dynamic boron-oxygen bond, so that the composite coating can be cooperatively prevented from tearing and falling off, and the base can be reliably protected. The application provides a new way with practicability and economy for improving the erosion resistance of hydraulic machinery.

Description

Technical Field

[0001] This invention belongs to the field of anti-erosion protective coating technology for fluid machinery. Background Technology

[0002] As the core equipment of hydropower generation, the safe and reliable operation of water turbines is crucial for ensuring power supply and the stability of the power system. However, based on the experience of operational hydropower stations, erosion and wear caused by sediment have consistently been significant factors threatening unit safety and affecting unit lifespan. Erosion and wear result in material loss and morphological changes on the flow surface, leading to decreased unit operating efficiency and secondary problems such as excessive vibration and noise. In severe cases, it can even cause safety accidents such as blade breakage. Coating protection is an important technical means to improve the wear resistance of hydraulic machinery. However, existing hard coatings often become brittle due to a lack of toughness when subjected to high-speed, sediment-laden water flow, while elastomeric coatings are easily torn due to insufficient strength. Composite coatings with hard particles added to the elastomer can, to some extent, balance strength and toughness, but face the problem of interfacial incompatibility. Practice shows that the interfacial adhesion between the elastomeric coating and the runner material, as well as the strength of the coating itself, still need improvement. Under high-speed sediment impact or strong cavitation, it is prone to tearing and peeling, limiting its application in the protection against sediment wear in large hydraulic machinery.

[0003] This invention proposes a method for preparing a shear-reinforced polyurethane composite coating. This composite coating forms an interpenetrating polymeric network structure through shear-hardening gel and elastomer molecules, exhibiting good compatibility and imparting shear-hardening properties to the elastomer. This allows the composite coating to adapt its modulus to external impacts. Under high-speed sediment conditions, the elastomer molecules exhibit high toughness through chain segment motion, while the gel molecules exhibit high strength through dynamic boron-oxygen bonds, achieving more effective impact energy dissipation and significantly improving the erosion resistance of the composite coating. Simultaneously, the composite coating's modulus increases sharply due to the shear-hardening effect of dynamic boron-oxygen bonds, thereby synergistically preventing coating tearing and peeling, achieving reliable protection of the substrate. This invention provides a new, practical, and economical approach for erosion protection of hydraulic machinery. Summary of the Invention

[0004] This invention provides a method for preparing a shear-reinforced polyurethane composite coating for erosion resistance. The composite coating contains dynamic boron-oxygen bonds (BO), which significantly improves surface toughness, reduces surface impact, and enhances adhesion, thereby achieving efficient protection of hydraulic machinery under erosion.

[0005] This invention provides a method for preparing a shear-reinforced polyurethane composite coating for erosion resistance. Its core feature is the preparation of dynamic boron-oxygen (BO) bonds to achieve an instantaneous structural change and thus significantly improve protective performance. The specific steps for preparing this composite coating are as follows: Step 1: Preparation of polyborosiloxane polymer 1) Weigh a certain amount of hydroxyl-terminated polydimethylsiloxane (PDMS-OH), and add boric acid (H3BO3) in a ratio of 1:(0.3~0.5). Stir thoroughly in a beaker to ensure uniform mixing. 2) The above mixture was polymerized in an oil bath at 180°C with continuous stirring to ensure uniform reaction. After the polymerization reaction was completed, it was taken out and cooled to room temperature for later use. By controlling the hydroxyl content (i.e. molecular weight) in PDMS-OH and the proportion of boric acid added, polyborosiloxane polymers (PBDMS) with different borylation crosslinking densities can be obtained. Step 2: Preparation of polyurethane prepolymer 1) Place the measured polyol monomer into a three-necked flask, set the temperature to 110℃ and maintain a vacuum state for 2 hours to thoroughly remove trace amounts of moisture and volatile small molecules from the system, and then introduce nitrogen gas as a protective gas. 2) When the system cools down naturally to around 60°C, add the isocyanate component and catalyst, raise the reaction temperature to 80°C, and maintain the constant temperature and stir for 2 hours. 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 vacuumed to remove bubbles and sealed for storage. 3) Weigh a certain amount of prepolymer and place it in a 75℃ constant temperature oven to melt it completely. Then transfer it to a vacuum defoaming device for treatment until no obvious bubbles are visible to the naked eye. At the same time, heat the curing agent to 120℃ to a molten state and mix it with the prepolymer in proportion. After the mixture is thoroughly stirred, vacuum degassing and stirring are performed again to form a polyurethane prepolymer. Step 3: Preparation of Composite Coating 1) Weigh a certain amount of PBDMS as an additive and mix it with polyurethane prepolymer at a mass ratio of 1: (4~5). Then add vulcanizing agent and stir slowly and continuously under a water bath at 25°C until PBDMS is completely dissolved in polyurethane prepolymer to obtain reaction material. 2) After the above reactants are evacuated to a vacuum in a vacuum dryer to remove air bubbles, they are sprayed onto the surface of alloy steel sheets that have been pre-treated by sandblasting roughening and plasma activation, and then placed in a 70°C oven until fully cured. The shear-reinforced polyurethane composite coating is obtained through steps one through three.

[0006] 2. Preferably, the NCO content in the prepolymer is determined by the dibutylamine-toluene method in the range of 3-11%.

[0007] 3. Preferably, the mass ratio of curing agent to prepolymer in the step is 1:(6~10).

[0008] The beneficial effects of this invention are: This composite coating introduces dynamic boron-oxygen bonds into the polyurethane elastomer, enabling its mechanical properties to adaptively change with the impact conditions of sediment-laden water flow. Under the impact of low-velocity sediment particles, the composite coating exhibits a typical viscoelastic state, preventing sediment abrasion of the flow surface through molecular chain segment movement, similar to other polymer coatings. Under the impact of high-velocity sand particles, the coating maintains its toughness through the movement of elastomer molecular chain segments and achieves a rapid increase in its modulus through the shear hardening effect of the transient response of the dynamic boron-oxygen bonds, thus preventing tearing and detachment. Attached Figure Description

[0009] Figure 1 Schematic diagram of the erosion protection principle of composite coatings against low-speed and high-speed particles; Detailed Implementation The technical solution of the present invention will be further explained and illustrated below with specific implementation examples.

[0010] Example 1) Weigh a certain amount of hydroxyl-terminated polydimethylsiloxane (PDMS-OH) and add boric acid (H3BO3) in a ratio of 1:(0.3~0.5). Stir thoroughly in a beaker to ensure uniform mixing. 2) The above mixture was polymerized in an oil bath at 180°C with continuous stirring to ensure uniform reaction. After the polymerization reaction was completed, it was taken out and cooled to room temperature for later use. By controlling the hydroxyl content (i.e. molecular weight) in PDMS-OH and the proportion of boric acid added, polyborosiloxane polymers (PBDMS) with different borylation crosslinking densities can be obtained. 3) Place the measured polyol monomer into a three-necked flask, set the temperature to 110℃ and maintain a vacuum state for 2 hours to thoroughly remove trace amounts of moisture and volatile small molecules from the system, and then introduce nitrogen gas as a protective gas. 4) When the system cools down naturally to around 60°C, add the isocyanate component and catalyst, raise the reaction temperature to 80°C, and maintain the constant temperature and stir for 2 hours. During the reaction, the NCO content in the prepolymer is determined by the dibutylamine toluene method. When the content reaches the theoretical value of 10%, the reaction is stopped, the obtained prepolymer is vacuumed to remove bubbles and sealed for storage. 5) Weigh a certain amount of prepolymer and place it in a 75℃ constant temperature oven to melt it completely. Then transfer it to a vacuum defoaming device for treatment until no obvious bubbles are visible to the naked eye. At the same time, heat the curing agent to 120℃ to a molten state and mix it with the polyurethane prepolymer at a mass ratio of 1:10. After the mixture is thoroughly stirred, vacuum degassing and stirring are performed again to obtain the polyurethane prepolymer. 6) Weigh a certain amount of PBDMS as an additive and mix it with the polyurethane prepolymer at a mass ratio of 1: (4~5). Then add the vulcanizing agent and stir slowly and continuously under a water bath at 25°C until the PBDMS is completely dissolved in the polyurethane prepolymer to obtain the reaction material. 7) After the above reactants are evacuated to a vacuum in a vacuum dryer to remove air bubbles, they are sprayed onto the surface of alloy steel sheets that have been pre-treated by sandblasting roughening and plasma activation. The sheets are then placed in a 70°C oven until fully cured to obtain the shear-reinforced polyurethane composite coating.

[0011] In one of the above embodiments, the invention objective of a method for preparing a shear-reinforced polyurethane composite coating for erosion resistance can be achieved, and those skilled in the art can choose according to the actual situation.

[0012] Effect verification The shear-reinforced polyurethane composite coating provided by this invention can significantly achieve erosion protection. In the embodiment described in this example, under normal conditions and low-velocity silt particle impact, the internal boron-oxygen bonds (BO) of the composite coating are relatively weak, exhibiting a viscoelastic state. When high-speed shear occurs, these bonds are forcibly elongated, broken, and rapidly recombine with adjacent molecular chains to form a stronger and more rigid temporary cross-linked network. This process instantly and significantly increases the material modulus (hardening), thereby dispersing and dissipating the enormous impact energy and preventing the coating from being punctured or torn. However, when the high-speed shear force disappears, the internal boron-oxygen bonds can quickly return to a weakly connected state, achieving effective protection against particle erosion.

[0013] 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 dynamic boron-oxygen bond (BO) design in the composite coating of the invention or exceed the scope defined in this claim, shall fall within the protection scope of the present invention.

Claims

1. A method for preparing a shear-reinforced polyurethane composite coating for erosion resistance, characterized in that, The core of this process is to prepare dynamic boron-oxygen bonds (BO) to achieve an instantaneous structural change and thus significantly improve the protective performance. The specific steps for preparing this composite coating are as follows: Step 1: Preparation of polyborosiloxane polymer 1) Weigh a certain amount of hydroxyl-terminated polydimethylsiloxane PDMS-OH, add boric acid H3BO3 in a ratio of 1:(0.3~0.5), and stir thoroughly in a beaker to ensure uniform mixing; 2) The mixture was polymerized in an oil bath at 180°C with continuous stirring to ensure a uniform reaction. After the polymerization reaction was completed, it was removed and allowed to cool naturally to room temperature for later use. By controlling the hydroxyl content (molecular weight) and the boric acid addition ratio in PDMS-OH, polyborosiloxane polymers PBDMS with different borylation crosslinking densities can be obtained. Step 2: Preparation of polyurethane prepolymer 1) Place the measured polyol monomer into a three-necked flask, set the temperature to 110℃ and maintain a vacuum state for 2 hours to thoroughly remove trace amounts of moisture and volatile small molecules from the system, and then introduce nitrogen gas as a protective gas. 2) When the system cools down to 60°C naturally, add the isocyanate component and catalyst, raise the reaction temperature to 80°C, and maintain the constant temperature and stir for 2 hours. During the reaction, the NCO content in the prepolymer is determined by the dibutylamine toluene method. When the content reaches 3~11%, the reaction is stopped, the obtained prepolymer is vacuumed to remove bubbles and sealed for storage. 3) Weigh a certain amount of prepolymer and place it in a 75℃ constant temperature oven to melt it completely. Then transfer it to a vacuum defoaming device for treatment until no obvious bubbles are visible to the naked eye. At the same time, heat the curing agent to 120℃ to a molten state and mix it with the prepolymer at a mass ratio of 1:(6~10). After the mixture is thoroughly stirred, vacuum degassing and stirring are performed again to obtain polyurethane prepolymer. Step 3: Preparation of Composite Coating 1) Weigh a certain amount of PBDMS as an additive and mix it with the polyurethane prepolymer at a mass ratio of 1: (4~5). Then add the vulcanizing agent and stir slowly and continuously under a water bath at 25°C until the PBDMS is completely dissolved in the polyurethane prepolymer to obtain the reaction material. 2) After the above reactants are evacuated to a vacuum in a vacuum dryer to remove air bubbles, they are sprayed onto the surface of alloy steel sheets that have been pre-treated by sandblasting roughening and plasma activation, and then placed in a 70°C oven until fully cured. The shear-reinforced polyurethane composite coating is obtained through steps one through three.

2. The shear-reinforced polyurethane composite coating prepared by the method described in claim 1 is used in hydraulic machinery erosion resistance.

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