Experimental studies on a combined near infrared (NIR) curing system with a convective oven

Near-infrared (NIR) curing recently became viable for the rapid curing of coating layers in several industries that require much faster line speeds to both increase production and reduce the system size, thereby saving on the overall curing cost. Previous works have revealed how NIR penetrates and efficiently heats the coating layer on top of a steel substrate. Despite these great efforts, the industry still requires more experimental evidence, data collection and system optimization to replace conventional hot air dryers with NIR dryers in the near future. Hence, we aim to develop a highly efficient NIR heating module, investigate its basic performance and suggest its optimized operation for the coil coating industry. First, we design and develop a NIR dryer integrated with a heating module, conveyor and waste heat recirculation loop. Second, we investigate the dynamic temperature response of the targeted steel substrate for various optical properties of coatings, such as absorption, reflectance and transmittance. Third, the curing performance is also observed in the NIR dryer for different coatings and operating conditions. We then discuss why NIR heating alone cannot meet the successful curing of a coating on substrates in terms of surface adhesion and resistance testing. Finally, we suggest a robust and stable operation method that combines NIR and convective oven heating, which allows for successfully cured outputs.