What is thermal spraying? What are its characteristics, and what precautions should be taken when using it?

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What is thermal spraying? What are its characteristics, and what precautions should be taken when using it? Thermal spraying is a coating method in which the paint is first heated (usually to 40–60°C) to reduce its viscosity to a level suitable for spraying, after which the spraying process is carried out. Compared to air spraying, thermal spraying includes an additional coating heater and compressed air preheating device to heat the coating and reduce its viscosity; therefore, it is particularly suitable for applying coatings with high viscosity that require large amounts of diluents (such as nitro paints), high-solid-content coatings, and water-soluble coatings. But it is currently mostly used in the coating of vinyl chloride paints and amino paints. Oil-based coatings produce a thicker film with each application, dry more slowly, and are prone to wrinkling; therefore, they are not suitable for application using thermal spraying methods. Characteristics of thermal spraying method: (1) Advantages: By using heating to reduce the viscosity of the coating instead of adding diluents, the amount of diluents required is decreased, which helps to save resources and reduce air pollution ； The solid content of the coating is increased, allowing for thicker coatings to be achieved while reducing the number of spraying sessions required ； The leveling, fullness, and gloss of the coating film have all seen significant improvements; it does not turn white when applied in humid environments, is less affected by climate conditions, and there is no need to adjust the coating process according to the seasons ； Defects such as sagging and dripping are less likely to occur during painting. ⑵There are shortcomings: Despite these advantages, thermal spraying is not widely used with volatile paints. When using this method, it is necessary to modify the original formula by adding an appropriate amount of expensive, high-boiling-point solvents, which increases costs. Moreover, if the solid content is too high, improper thermal spraying can result in excessive crusting of the coating layer. However, it has been put into practical use in the thermal spraying of thermosetting coatings. For example, amino baking varnish can be used for thermal spraying without changing its formula, with either no diluent added or only a small amount of it; it is heated to 45–50°C to achieve a viscosity of 50–70 seconds (according to the Paint-4 viscosity cup). When applying thermal spraying, the following points should be noted: (1) Determine in advance the curve showing how the viscosity of the coating changes with temperature. Only coatings whose viscosity decreases significantly when heated can be coated using thermal spraying. And the most suitable temperature is selected based on the temperature-viscosity curve; generally, the temperature range during which viscosity decreases is chosen as the heating range. ⑵When using thermosetting coatings for thermal spraying, the heating temperature must be below the temperature at which the coating begins to undergo thermal curing; otherwise, the heating during transport or in the heating cycle will trigger a thermal curing reaction, causing the coating to thicken or even gel. ⑶When using electric heating, the voltage of the power supply should not exceed the rated voltage of the heater. If there is no coating in the circuit of the electric heater, it should not be powered on to avoid accidents.