In order to maintain proper profile and thickness within a glass furnace the extrusion plate spacing must be maintained at a predetermined gap. Unfortunately, due to process changes and temperature swings this gap can fluctuate significantly in short periods of time. This variation causes the glass thickness to change (check out our glass thickness measurement devices to accurately measure thickness), producing uneven temperature gradients and creating potentially weak glass panels. To control this critical parameter the manufacturing process requires automated active feedback control sensors installed into a very harsh environment.

The complex shapes and designs of today’s windshields complicate the manufacturing process and significantly increase quality control measures. Maintaining a constant shape and thickness is required to reduce the possibility of failure from stress induced during the quenching process. Proper profile and thickness within a glass furnace the extrusion plate spacing must be maintained at a predetermined gap variation causes the glass thickness to change, producing uneven temperature gradients and creating potentially weak glass panels. To control this critical parameter the manufacturing process requires automated active feedback control sensors installed into a very harsh environment. MTI Engineers designed a custom, passive capacitance probe capable of operating at temperatures exceeding 600°C. The probes featured “fail-safe” construction, eliminating the possibility of catastrophic failure should the probe cement be compromised from excessive vibration. The passive design removed all active elements from the measurement area allowing for stable control of the extrusion gap. MTII selected the Accumeasure capacitance system, which allowed multiple measurement and control points. The high frequency response and minimum phase delay made it the ideal choice for closed loop control.

The final probe configuration was a custom ASP-100-CTA sensor with a 0.5” (12.5mm) measurement range. Although the gap only fluctuated by +/-0.005” (125 µm) the large measurement range allowed for an increased probe operating distance and reduced the probability of probe damage. At 500 Hz frequency response the Accumeasure system resolved measurements to less than 50 µin (1.25 µm) and provided continuous monitoring and real-time feedback control. This significantly improved product quality and virtually eliminated any scrap, saving $1000’s in the first month alone.