High Temperature Capacitance Probes Monitor and Control Windshield Manufacturing Processs

Introduction

Remember the days when windshields were made of flat sheet glass? Not anymore. The complex shapes and designs of today’s windows 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.

Problem

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, 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.

Solution

Limited space, extreme temperatures and excessive vibration had to be considered in the solution design. After careful analysis, MTII Engineers designed a custom, passive capacitance probe capable of operating at temperatures exceeding 500oC. 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 AccumeasureTM 1500 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.

Results

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 1500 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.

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MTI Instruments Inc.
325 Washington Avenue Extension
Albany, NY 12205-5505 USA
Phone: 518-218-2550
Toll Free (US): 800-342-2203
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Measuring Glass Thickness Quench Gap in Glass Making Hearth Process, Precision High Temperature Sensors, Shaping and Tempering of Glass Parts, Automotive Glass Surface and Windshields, Quench Gap Plate Spacing, Automated Monitoring and Measurement