AUTOMATIC CONTROL OF INTERFACE BOUNDARIES IN VERTICAL FREEZEPRODUCTION PROCESSES

A KEY CONSIDERATION IN A VARIETY OF MANUFACTURING PROCESSES IS CONTROLLING EITHER THE POSITION OR SHAPE OF AN INTERFACE DEFINED AS THE BOUNDARY BETWEEN LIQUID AND SOLID MATERIALS OF DISSIMILAR COMPOSITION OR DENSITY TO WITHIN CERTAIN ALLOWABLE TOLERANCES. EXAMPLES OF SUCH DIVERSE PROCESSES ARE VERTICAL FREEZE BRIDGMAN AND CZOCHRALSKI CRYSTAL GROWTH AND ELECTROSLAG REMELTING FOR METAL REFINEMENT. AUTOMATING THESE PROCESSES REQUIRES THE ABILITY TO MONITOR AND MAINTAIN THE CRITICAL GROWTH INTERFACE PARAMETERS THROUGHOUTAN ENTIRE LENGTHY BATCH PROCESS USING AN APPROPRIATE PROCESSFEEDBACK CONTROL ALGORITHM. A TECHNIQUE BASED ON GAMMA RAY TRANSMISSION IS IDEAL TO PROVIDE INFORMATION REGARDING INTERFACE POSITION AND CURVATURE. HOWEVER, EXISTING METHODSTHAT PROVIDE POSITIONAL INFORMATION ARE NOT SUITABLE FOR APPLICATION TOWARDS INDUSTRIAL AUTOMATION. THE RESEARCHERS PROPOSE TO DEVELOP A METHOD TO MONITOR AND SUBSEQUENTLY CONTROL AN INTERFACE BOUNDARY USING AN APPROPRIATE GAMMA RAYEMITTING RADIOISOTOPE AND A RUGGED SEMICONDUCTOR DETECTOR. THE DETECTOR WILL BE EITHER A MODIFIED VERSION OF AN EXISTING DEVICE OR A NEW UNIT, DEVELOPED IN-HOUSE, WITH SUPERIOR DETECTION PERFORMANCE CAPABILITIES. PHASE I WILL INCLUDE RESEARCH ON THE DEVELOPMENT OF GAMMA RAY TRANSPORT MODELS AND ALGORITHMS THAT WILL ALLOW THEM TO DECIDE WHAT ARE THE IDEAL COMPONENT PROPERTIES NEEDED TO FULFILL THEIR SPECIFIC REQUIREMENTS IN TERMS OF POSITION RESOLUTION, DETECTION EFFICIENCY, AND A TIMELY PRESENTATION OF THE MEASURED GAMMA RAY INTENSITY. EXPERIMENTS WILL BE PERFORMEDTO DEMONSTRATE MEASUREMENT CAPABILITIES SUCH AS SENSITIVITY TO SMALL CHANGES IN EITHER INTERFACE CURVATURE OR DENSITY.