In-Situ Sensors for Liquid Metal Quality

The development of effective methods for directly measuring liquid metal quality, prior to casting and final solidification, has long been a goal for Process Metallurgists. For aluminum, which is generally much cleaner than steel, it is first necessary to concentrate the inclusions by filtering the metal through a porous frit, before then freezing the remaining metal, and subjecting it to microscopic examination (e.g. PoDFA). An alternative method is to take a sample of metal, freeze it, and then dissolve the metal to release the particles (inclusions) through elutriation (the Slime Technique). The only true on-line, in-situ, methods are the Ultrasonic Liquid Metal Sensors (such as the Mansfield Molten Metal Sensor), and the Electric Sensing Zone Methods (such as LiMCA and ESZ-pas). Currently, perhaps the most reliable, but least satisfying, technique is to wait for customer complaints to identify problems. JFE has developed an ultrasonic, on-line, system that registers larger inclusion clusters in rolled steel sheets as they are produced. Alternatively, many steelmakers will use PDA (Pulse Discrimination Analysis) on a small surface of solid steel, to arrive at conclusions concerning inclusions less than 10 microns. Unfortunately, this ignores the much larger inclusions normally present within a steel melt that are responsible for compromising metal properties. The late Professor Iwase was a strong believer in the development of good techniques and methods to monitor and control metallurgical processes, including those related to metal quality. This review is dedicated to his memory, and to his strength of perseverance.