## 4 Conclusions  
In this study, we designed a catalytic infrared curing system by combining catalytic infrared technology and coating curing equipment. The radiative characteristics of the catalytic infrared equipment were tested, and the applicability of this curing system for curing powder coatings was investigated. Finally, a one-dimensional heat transfer model was established. The following conclusions were obtained:  
1. The maximum surface temperature of the radiation panel was 475 \({}^{\circ}\)C, and its infrared wavelength range was 2-25 \(\upmu\)m. The infrared absorption wavelengths of most of the functional groups of the polyester/TGIC powder coatings were in this region. Thus, the coatings were quickly cured with catalytic infrared radiation;
2. The optimal curing parameters for this catalytic infrared curing process were 230 \({}^{\circ}\)C for 2 min and 220 \({}^{\circ}\)C for 3 min. The mechanical properties of the coatings became  
Figure 23: Heating times required for the coating temperature to reach 220 \({}^{\circ}\)C and 230 \({}^{\circ}\)C with different substrate thicknesses. Figure 22: Predicted coating temperatures with varying substrate thickness. stronger as the temperature and time increased. However, the gloss of the coatings appeared to decrease. When the temperature was too high, the color of the coatings became dark;
3. An internal heat source was introduced in the simulation model. This model could accurately predict the temperature change in the coating. The total efficiency \(\eta_{\rm tot}\) was determined to be 0.4;
4. According to the numerical simulations, when the substrate thickness was 1 mm, the optimal coating curing temperature was 230 \({}^{\circ}\)C. For substrate thicknesses \(\geq\) 2 mm, a coating curing temperature of 220 \({}^{\circ}\)C was more efficient. This study showed that catalytic infrared radiation can be used to cure polyester-based coatings efficiently, and that the coatings can meet engineering quality requirements. Using the catalytic infrared optimal curing parameters determined in this study, the yield can be increased by four to nine times with the same production time compared to the hot-air curing parameters provided by the coating manufacturer. Compared to the curing parameters provided in the literature [7; 9] for polyester-based coatings, the yield can be increased by 6.5 times with the same production time. The simulation model reported in this work can be used to predict the shortest time required to cure coatings with different substrate thicknesses. This work is a significant reference for the design of production processes and catalytic infrared curing production lines. The catalytic infrared curing method is more suitable for application with high-temperature-resistant coatings, ensuring efficiency and savings in energy. Future research should focus on controlling the wavelength of catalytic infrared radiation to ensure a good match between the radiation wavelength and the infrared absorption band of the coating when producing different types of coatings, thus further reducing energy consumption and increasing yield. Conceptualization, S.P. ; Methodology, Y.Y. ; Software, Y.Y. ; Validation, Y.Y. ; Formal analysis, Y.Y. and T.W. ([PERSON]); Resources, L.L. ; Writing--original draft, Y.Y. ; Writing--review & editing, T.W. ([PERSON]), L.X., Y.L., X.W. and T.W. ([PERSON]); Visualization, Y.Y. ; Supervision, S.P. and L.X. All authors have read and agreed to the published version of the manuscript. The research was funded by the 13 th Five-Year National Science and Technology Major Project of China (grant nos 2016 YFC0801706 and 2017 YFC0702202) and the National Natural Science Foundation of China (grant no. 51578011). The authors are grateful for the financial support from the Key Laboratory for Comprehensive Energy Saving of Cold Regions Architecture of the Ministry of Education. The authors are also grateful for the financial support from the International Science and Technology Cooperation Center in Hebei Province (no. 20594501D).