Imaging pyrometer for monitoring the surface temperature of a spray-formed steel billet

摘要

A two-wavelength, imaging pyrometer was developed for real-time measurement of the surface temperature distribution of a spray-formed steel billet. This new spray-forming process is used to deposit bulk steel on a ceramic substrate in a surface temperature range of 300 deg C to 400 deg C, using four, twin-wire arc plasma torches. These steel billets are used as tools in metal forming processes, injection molding and die casting tools, and other processes that may need hard tooling, such as the automotive industry. The steel billet must be formed with a uniform, surface temperature distribution to minimize the thermal stresses within the steel, throughout the process. The imaging pyrometer uses a near-IR InGaAs CCD camera with high quantum efficiency from 0.95 to 1.75 microns. The wavelengths of 1.40 and 1.65 microns were selected to sense the low temperature billet. The camera has a format of 320 X 240 pixels with a pixel spacing of 30 microns and an integral 12-bit A/D converter with both video and digital outputs. The design of the pyrometer provides a working distance of 2.2 meters and a field of view of 0.6 meters. This technical paper describes the calibrations and initial measurement results obtained in a spray forming facility at the Ford Research Laboratory. The calibration provided intensity ratio measurements for surface temperatures ranging from 200 deg C to 300 deg C, the expected range of operation. The initial measurements described here depict the surface temperature distribution of the steel billet throughout the spray forming process, typically lasting several hours.