The following are some specific methods to ensure the thickness stability of high-temperature resistant coatings through process adjustments:
Coating process adjustment
Choose the appropriate coating method:
Spraying method:
Parameter optimization: For air spraying, it is necessary to accurately adjust parameters such as the air pressure of the spray gun, the amount of paint sprayed, the distance between the spray gun and the coated substrate, and the speed of the spray gun movement. For example, increasing the air pressure appropriately can make the coating atomize finer and distribute more evenly, but excessive pressure may cause the coating to rebound, affecting thickness uniformity. Generally, it is more appropriate to control the air pressure between 0.3-0.6 MPa; The distance between the spray gun and the substrate is generally maintained at 15-30 centimeters, and adjusted reasonably according to the viscosity and other characteristics of the coating to ensure uniform adhesion and stable thickness of the coating.
Selection of Spray Gun Types: In thermal spraying technology, different types of spray guns such as plasma spraying and supersonic flame spraying are suitable for different coating materials and substrate conditions. For example, plasma spraying is suitable for spraying ceramic high-temperature resistant coatings. By adjusting the power and gas flow rate of the plasma arc, the coating particles can collide with the substrate surface at an appropriate speed and state, forming a uniform and stable coating thickness.
Brushing method: Select a suitable brush and control the brushing force and direction according to the shape of the substrate and coating requirements. During the brushing process, it is necessary to maintain even force to avoid locally brushing too thick or too thin. The amount of paint dipped each time should also be relatively fixed to ensure that the coating can reach a stable and uniform thickness after multiple brushing. It is commonly used for coating small components with complex shapes and low precision requirements for coating thickness.
Dip coating method: Strictly control the viscosity of the coating, dip coating time, and the immersion and extraction speed of the components during dip coating. For example, increasing the viscosity of the coating can thicken the coating, but too high viscosity can cause uneven surface and thickness of the coating, which needs to be reasonably adjusted according to the coating material and desired thickness; The immersion coating time generally ranges from a few seconds to tens of seconds, and the optimal duration should be determined through experiments to ensure that the surface of the component can uniformly adhere to a suitable thickness of coating. It is commonly used for coating large quantities of small components with regular shapes.
Multi layer coating strategy: Adopting a multi-layer coating method, each layer of coating is controlled at a thin and uniform thickness, which can better alleviate the internal stress of the coating and reduce the problem of thickness instability caused by excessive thickness in a single coating. For example, when planning to apply a high-temperature resistant coating with a total thickness of 300 microns, it can be applied in 5-6 layers, with each layer thickness controlled at around 50-60 microns. After each layer is applied, appropriate drying or curing treatment should be carried out according to requirements before applying the next layer. This method makes the overall thickness of the coating more uniform and stable, and can improve the bonding strength between the coating and the substrate as well as between each layer of the coating.
Optimization of pretreatment process
Surface treatment of substrate:
Cleaning treatment: Thoroughly remove impurities such as oil stains, dust, and rust from the surface of the substrate. A combination of chemical cleaning (such as using organic solvents to remove oil stains, acid washing to remove rust, etc.) and mechanical polishing (such as sandpaper polishing, sandblasting, etc.) can be used to ensure that the surface of the substrate is clean and the roughness is appropriate, creating good conditions for uniform adhesion of the coating and avoiding the influence of poor surface cleanliness or roughness on the stability of the coating thickness. For example, by sandblasting to control the surface roughness of the metal substrate between Ra1.6 and Ra6.3, the coating can better bite and adhere evenly, ensuring stable thickness.
Activation treatment: Using methods such as chemical plating, ion implantation, plasma treatment, etc. to activate the surface of the substrate, increase the active sites on the surface, and form a stronger chemical bond between the coating and the substrate. This helps the coating to adhere evenly and stably to the substrate, reducing thickness changes caused by poor bonding during use. For example, after plasma treatment on some plastic substrates, the adhesion effect of the coating is significantly improved, and the thickness can be maintained more stable in subsequent use.
Application of primer coating: Before applying the main coating, a layer of primer coating (primer or transition layer) is first applied. Its function is to adjust the difference in thermal expansion coefficient between the substrate and the main coating, improve compatibility, and provide a smoother and more adhesive surface for subsequent coatings, thereby ensuring the stability of the thickness of the main coating. For example, when coating ceramic high-temperature resistant coatings on aluminum alloy substrates, a layer of organic silicon aluminum powder paint is first applied as the base coating, which can effectively reduce the stress caused by different thermal expansion coefficients and make the thickness of the ceramic coating more uniform and stable during subsequent coating.
Curing process control
Accurate adjustment of curing temperature: The curing temperature is strictly set according to the requirements of the coating material, and high-precision temperature control equipment is used for temperature control to ensure minimal temperature fluctuations. Because curing temperatures that are too high or too low can affect the degree of curing and structural stability of the coating, leading to changes in coating thickness. For example, for epoxy modified high-temperature resistant coatings, the curing temperature requirement is between 120 ℃ and 150 ℃, with an error control of ± 5 ℃. Curing within this temperature range can fully crosslink the coating to form a stable structure and maintain a stable thickness.
Reasonable setting of curing time: Based on the characteristics of the coating material and factors such as coating thickness, accurately determine the curing time. Insufficient curing time, incomplete chemical reactions inside the coating, poor strength and stability, and easy thickness changes; If the curing time is too long, it may cause the coating to cure excessively, resulting in internal stress and also affecting the thickness. For example, when the coating thickness of a certain organic silicon high-temperature resistant coating is 100 microns, the curing time should be set to 2-3 hours to ensure sufficient curing and stable thickness of the coating.
Improved post-processing technology
Polishing and trimming: After the coating is cured, the surface is appropriately polished to remove possible protrusions, burrs, and other uneven parts, making the coating surface smoother. At the same time, the coating thickness can also be checked to see if it meets the requirements. For areas with insufficient local thickness, touch up can be applied and then polished again to further ensure the stability and uniformity of the final coating thickness. This method is commonly used for components with high requirements for surface flatness and thickness accuracy.
Quality inspection and feedback adjustment: Use coating thickness gauges, microscopes and other testing tools to comprehensively inspect the thickness and microstructure of the coating, and compare and analyze the test results with the design requirements. If it is found that the thickness does not meet the requirements or there are problems such as uneven thickness, timely feedback and adjustment of corresponding process parameters, such as coating parameters, curing parameters, etc. Through continuous testing and process optimization cycles, the coating thickness is always in a stable and compliant state.
Through the comprehensive application of the above process adjustment measures, the stability of the thickness of high-temperature resistant coatings can be effectively improved, enabling them to better perform protective and other functions during use.

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