Power and Temperature Control in Electric Forehearths

Temperature control of the glass in a forehearth determines quality of the glass and affects percent pack. The forehearth provides the last opportunity for temperature conditioning. Temperature control in this area demands a close scrutiny as to means of sensing temperature, introduction of energy and the control instrumentation to accomplish this. Electricity as a forehearth energy source provides unique features and capabilities, including conductance or resistance measurement and control of glass temperature. Conductance measuring of fuel-fired forehearths is also a viable option to eliminate the nuisance factor of failed thermocouples. SCR controllers provide the most effective means of controlling electric energy for forehearths, boost or all-electric melting. SCR control systems can be stand-alone instruments or can be incorporated into digital control systems for selecting output levels and monitoring the process. Uniformity of temperature within the forehearth cross-section is best achieved by using conductance measuring with SCR-controlled electric energy.