Semester

Fall

Date of Graduation

2010

Document Type

Dissertation

Degree Type

PhD

College

Statler College of Engineering and Mineral Resources

Department

Mechanical and Aerospace Engineering

Committee Chair

Larry E. Banta.

Abstract

Drawing of glass fibers is an important industrial process used for manufacture of a variety of materials ranging from optical communications cables to fiber filter media. A variety of machines exist for performing the drawing function, but all share similar problems with control of the fiber diameters and breakage of the fibers during the extrusion process. In many cases, control systems are not configured to monitor the most critical process variables-- temperature of molten glass in the furnace, but instead use only furnace crown temperature. Upsets in disturbance variables such as ambient temperature are compensated manually by operators, usually only after significant problems with fiber breakage occur. This work seeks to provide better understanding of the effects of important process variables on the key quality and production parameters such as fiber diameter and production rates, and to develop an effective control model to monitor molten glass temperature and winder speed for good production quality even if some disturbance happens.;First an analytical model of the glass fiber based primarily on Glicksman's work was developed, with the addition of a radiative heat transfer component and the addition of temperature-dependent relationships for physical properties of soda-lime glass. The model is valid for fibers in the central attenuation region, where most of fiber attenuation and breakage happens. Parametric studies have been done using the model to evaluate the effects of variation in the ambient temperature and variation of the molten glass depth in the furnace. These studies have shown that even modest changes ambient temperature and molten glass depth can generate significant changes in the final diameter of the glass fibers.;Based on those results, a state space model of the furnace has been constructed and used as the basis of a state reduced-order estimator to provide an accurate estimate of the temperature of the molten glass at the furnace bottom. A LQR controller with a reference input was applied in the model for bottom glass temperature control. A winder speed controller has been developed in parallel in order to compensate for the long time delay between application of burner firing rate changes and the response of the thermal system. Then multivariable control analysis was done on variation of ambient temperature and variation of molten glass depth. The control model manipulates both the winder speed and the burner firing rate, bringing the process back to design conditions even if some disturbance occurs, and allows greater flexibility and more accurate quality control for the glass fiber drawing process.

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