How can supersonic spraying technology improve coating quality?

How can supersonic spraying technology improve coating quality?

Supersonic spraying technology is a surface coating preparation technique that can improve coating quality through various methods, including:

Optimize spraying process parameters

Controlling spraying speed: In supersonic spraying, the speed of sprayed particles is crucial for coating quality. Appropriately increasing the spraying speed can give particles higher kinetic energy when they collide with the substrate surface, thereby better deforming, spreading, and embedding, forming a denser and more cohesive coating. However, excessive speed may lead to excessive particle fragmentation and rebound, affecting the quality of the coating. Therefore, precise control of the spraying speed is required, generally between 300m/s and 800m/s, to achieve good coating quality.

Adjust spraying distance: Spraying distance refers to the distance from the nozzle outlet to the substrate surface. The appropriate spraying distance can ensure that the sprayed particles collide with the substrate in the state and form a coating. If the distance is too close and the particle kinetic energy is too high, it may cause damage to the substrate, and the coating is prone to overheating, oxidation, and other problems; The distance is too far, resulting in excessive loss of particle kinetic energy and inability to fully deform and embed, leading to a decrease in coating adhesion and an increase in porosity. Usually, the distance for supersonic spraying is between 100mm and 300mm, and the specific distance can be determined through experimentation and adjustment.

Accurate control of powder feeding amount: The powder feeding amount directly affects the thickness and density of the coating. Reasonably control the powder feeding amount, so that the sprayed particles can uniformly impact the surface of the substrate within a unit time, forming a coating with uniform thickness and dense structure. Excessive or insufficient powder feeding can lead to a decrease in coating quality. Excessive powder feeding can cause defects such as porosity and delamination in the coating, while insufficient powder feeding can result in the inability to achieve the expected coating thickness and performance. Accurately adjust the powder feeding amount according to different spraying materials and substrate requirements, usually by adjusting the speed of the powder feeder or the flow rate of the powder feeding gas.

Select appropriate spraying materials

High purity materials: Choosing high-purity spray coating materials can reduce the impact of impurities on coating quality. Impurities may form defects in the coating, reducing its density, adhesion, and corrosion resistance. For example, when spraying metal ceramic coatings, using high-purity metal and ceramic powders can improve the hardness, wear resistance, and oxidation resistance of the coating.

Appropriate particle size distribution: The particle size distribution of the sprayed material also has a significant impact on the quality of the coating. Generally speaking, finer powder particles can result in smoother and denser coatings, but overly fine particles may cause problems such as powder agglomeration and poor flowability; Coarse particles can improve the deposition efficiency of the coating, but may increase the surface roughness and porosity of the coating. By optimizing the particle size distribution of powders, such as using bimodal or multimodal particle size distributions, the advantages of powders with different particle sizes can be comprehensively utilized to improve coating quality. For example, in the supersonic flame spraying of WC Co coatings, the use of bimodal particle size distribution powders ranging from 10 μ m to 45 μ m can result in the coating having both good density and high deposition efficiency.

Good flowability and sphericity: The spraying material should have good flowability and sphericity, so that it can be evenly and stably delivered to the spray gun during the powder feeding process, and better accelerated and focused during the spraying process. Powder particles with good sphericity are more prone to deformation and spreading upon impact with the substrate surface, resulting in better quality coatings. For example, spherical powders prepared by atomization method have good flowability and sphericity, and can obtain high-quality coatings in supersonic spraying.

Improving substrate surface pretreatment

Thoroughly clean the surface: Before spraying, the substrate surface must be thoroughly cleaned to remove impurities such as oil stains, rust, and oxide scales. These impurities can affect the adhesion between the coating and the substrate, leading to defects such as coating peeling or flaking. Chemical cleaning, mechanical polishing, sandblasting and other methods can be used for cleaning to ensure that the substrate surface is clean and shiny, providing a good foundation for the adhesion of the coating.

Surface roughening treatment: Proper roughening treatment of the substrate surface can increase the contact area between the coating and the substrate, and improve the bonding strength. The commonly used roughening methods include sandblasting, shot blasting, etc. By forming a certain roughness on the surface of the substrate, the coating can be better embedded in the pits and grooves on the substrate surface. However, the degree of roughening should be moderate, as excessive roughening may lead to surface damage to the substrate and uneven coating. Generally speaking, the surface roughness Ra of the substrate should be between 3 μ m and 10 μ m.

Preheating the substrate: Preheating the substrate before spraying can reduce the thermal stress between the coating and the substrate, improve the adhesion and density of the coating. The preheating temperature is generally determined based on the properties of the substrate material and coating material, usually between 100 ℃ and 300 ℃. Preheating can evaporate the moisture on the surface of the substrate, reduce pores and defects in the coating, and keep the substrate in a state of thermal expansion. During the cooling process after spraying, it will shrink in line with the coating, reducing problems such as coating peeling caused by thermal stress.

Using spray guns and equipment

High performance spray gun: Choosing a high-performance supersonic spray gun is the key to improving coating quality. Spray guns have better acceleration and focusing capabilities, which can enable sprayed particles to obtain higher speed and more concentrated energy, thereby improving the quality of coatings. For example, a spray gun designed with a Laval nozzle can accelerate the spraying gas to supersonic speed, allowing the spraying particles to achieve higher velocity and better focusing effect under the action of high-speed airflow, forming high-quality coatings.

Accurate control system: Equipped with a precise control system, it can monitor and control various parameters in real-time during the spraying process. By controlling the system, it is possible to accurately adjust parameters such as spraying speed, spraying distance, and powder feeding amount to ensure the stability and consistency of the spraying process. At the same time, the control system can also accurately control the movement speed and trajectory of the spray gun, achieving uniform spraying and improving the quality and uniformity of the coating.

Online monitoring and feedback: By utilizing online monitoring technologies such as laser velocimeters, high-speed cameras, etc., the speed, temperature, morphology, and other parameters of sprayed particles can be monitored in real time, as well as the formation process and quality status of coatings. According to the monitoring results, adjust the spraying parameters in a timely manner to achieve feedback control and continuously optimize the coating quality. For example, when the deviation value of the spray particle velocity is detected by a laser velocimeter, the working parameters of the spray gun can be adjusted in a timely manner to restore the particle velocity to the zj range, ensuring stable coating quality.

Through the application of the above comprehensive measures, supersonic spraying technology can improve the quality of coatings and play a more important role in many fields such as aerospace, mechanical manufacturing, and energy, meeting the high-performance requirements of coatings in different application scenarios.