Most of the coatings used in the industry are dried by heating, and the main drying methods are as follows:
1. Hot air convection heating
The cold air passes through the heat exchanger in the hot air circulation system to turn it into hot air, and then sends it to the drying room. In this way the temperature of the drying room rises gradually to reach the temperature required by the process. This method is called hot air . Convection heating. Its biggest advantage is that the temperature in the drying room is uniform, especially suitable for the condition of natural gas, coal gas or oil as the heat source, so it is widely used in most European countries. In addition, the exhaust gas in the drying chamber can be directly sent to the combustion furnace for burning, which not only saves energy, but also does not require a special exhaust gas treatment device. Convection heating is very suitable for drying the coating film of workpieces with complex shapes. Electricity is the most used energy in most factories in our country. If only convection drying is used, the energy utilization rate is low, so other methods should be used.
2. Radiant heating
Using the infrared beam emitted by the heating element itself to directly heat the object is called radiant heating. Experiments show that the coating has a weak absorption ability to visible light and near-infrared light (wavelength 0.38-2.5 μm) radiated by the heating element, but has a strong absorption ability to far-infrared light (wavelength 2.5-25 μm ). According to the principle of matching absorption, the coating absorbs far-infrared waves during the drying process, and at the same time causes the internal molecules to generate a resonance effect, and generates , so the coating dries quickly and effectively.
The biggest advantage of radiation heating is to save energy. Experiments have proved that radiation heating has obvious , and it can save energy by 20% to 30% compared with hot air convection heating. However, the heat distribution is uneven, and the radiation energy is inversely proportional to the square of the distance from the heated body, so it is not suitable for heating workpieces with complex shapes. For example, if the car body coating is simply heated by radiation, the temperature of the car body will be uneven, the drying will be uneven, and there will be over-baking, and some parts will not be completely dry, resulting in different colors and affecting the appearance quality of the car body.
3. Convective radiation heating
According to the advantages and disadvantages of hot air convection and radiation heating, we learn from each other, that is, the method is the most satisfactory. This method is used for baking large and medium-sized coatings with complex shapes (such as car bodies). This can not only make the temperature of the lower drying chamber more uniform, ensure the quality of the coating film, but also save energy. This form was the most widely used in Japan and CHINA's auto industry a few months ago .
