The present invention relates to a method of measuring the volume of molten metal liquid pools and in particular noncontacting laser ultrasonic generation and detection at the surface to measure the volume of molten titanium liquid pools.
Currently, vacuum arc remelting is used to produce much of the nation's titanium from Kroll process sponge. However, the process provides only a limited means of removing oxynitride and carbide inclusions from the melt, which can become stress intensifiers in the ingot. An improved quality of the melted product will result in less scrap, and provide industry with the ability to recycle scrap into high value products. The most important aspect, is the capability to produce superior ingots with the potential for designing turbine engines and the like incorporating titanium to be lighter and more efficient.
Plasma and Electron beam hearth melting have the potential to eliminate these stress-intensifying inclusions by increasing the residence time of the molten titanium in the hearth so that the oxynitrides dissolve and the carbides settle out of the melt. These new processes have caused a critical need for an accurate means to measure the volume of the molten metal during hearth melting processes.
At the high operating temperatures of the titanium hearth (1650.degree. c) existing contacting sensors are not practical, and are also a source of melt contamination. Therefore, a noncontacting sensor method using ultrasound wave echo was developed to determine the depth of the titanium melt, which required only melt surface access.
Several types of optical laser-based ultrasonic detectors have been developed for noncontacting measurement of surface motion due to ultrasonic waves. In some cases these devices have been employed at high temperatures to record material properties during heating. However, the majority of these systems depend on phase sensitive detection of the light and require polished surfaces and strict alignment for adequate signal-to-noise ratio, and thus are not suitable for plasma and electron beam hearth melting processes.
It is therefore an object of this novel method to provide a noncontacting means to accurately measure the volume of a molten metal liquid, and further another object of this novel method is to provide a means to accurately measure the volume of molten metal liquid pools without causing a source of melt contamination.
Additional objects, advantages and novel features of the method will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the novel method. The objects and advantages of the method may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve the foregoing and other objects and in accordance with the purpose of the present invention, as embodied and broadly described herein, the novel method of measuring a molten liquid pool volume may comprise the steps of (a). generating an ultrasonic wave echo at the surface of the molten liquid pool; (b). shining a on the surface of the pool; (c). detecting the change in frequency of the light; (d). detecting the ultrasonic wave echo as it reflects at the surface of the pool, after it reflects off the bottom of the molten metal liquid pool; and e). computing the volume of the molten liquid pool by using the frequency change in the light and the time elapsed for the ultrasonic wave echo to reflect off the bottom of the molten metal liquid pool, and return to the surface of the pool.