Infrared sensor for the control of plasma-jet spray coating and electric

Abstract

A multi-purpose optical sensor operates in the medium-to-far infrared wavelength spectral region to sense the surface temperature of plasma-jet spray coating materials. This plasma itself emits little or no radiation in this region and, accordingly, the output signal from the sensor is used to adjust the electrical input and other variables associated with the plasma spray torch to insure that particles arriving at the substrate surface to be coated are, in fact, in a molten state. The sensor employs infrared filters and, additionally, the sensor is used to monitor not only coating and temperature but also plasma beam divergence and particle seeding density to provide other control functions. In another embodiment, the sensor is used to measure the temperature and size of a molten metal pool in the presence of an electric arc, as in the case of the melting and pouring of metal to form ingots, and to control the electric arc and other melting parameters so as to control the size and temperature of the molten pool. It may also be used to locate the position of foreign matter on the surface of the molten pool and to manipulate the arc so as to move the foreign matter away from the pouring region, thereby restricting the amount of such foreign matter which enters the poured metal stream, thus producing cleaner ingots having improved freedom from inclusions.