Ultrasonic time-of-flight measurements for inline gas analysis and process monitoring in the phenolic urethane cold box process

Abstract. The phenolic urethane cold box (PUCB) process is widely employed for sand core production in the foundry industry. It allows high production rates of sand cores, which are later used for producing complex metal castings. The process begins by shooting a sand–binder mixture into a core box to define the core geometry. During the subsequent curing stage, catalysts are introduced to harden the binders and are then removed by blowing dry compressed air through the sand core. In order to optimize this complex and highly dynamic production process for efficiency and core quality, there is a need for measurement systems that can reliably monitor the curing stage. In this study, we present a measurement system capable of capturing the dynamics of the PUCB core-curing stage via ultrasonic time-of-flight measurements. By measuring the speed of sound, the concentration of the catalyst in the exhaust airstream is determined. Volumetric flow rate and temperature are measured simultaneously. The measurement system is validated, and measurement uncertainties are discussed. We demonstrate the measurement system in a PUCB core-making machine using N,N-dimethyl-n-propylamine (DMPA) as the catalyst. DMPA concentrations of up to 3.6 % ± 0.5 % (coverage factor k=1) were found in the exhaust airstream. The measurements provide insights into the dynamics of the curing stage, and we showcase the potential for the optimization of catalyst removal. Integrating this measurement system into core-making machines enables automation strategies, potentially enhancing efficiency and product quality in foundry operations.