Surface Compression Comparative Measurements on Tempered Glass with Different Instruments

The Surface Compression Stress (SC) data, collected by Stazione Sperimentale del Vetro, were analysed to compare the measurements carried out by Scalp-05, Scattered Light Polariscope, and Laser Gasp, Strainoptics’ GASP® Polarimeter. The first one (Scalp) measures the SC at the tin and air side. It is a compact scattered light polariscope for depthwise stress measurement in sheet glass. SCALP-05 contains diode laser, optics and camera. Recording of the data and stress calculation is done by PC. The second one (Laser Gasp) is also well known at glass industry and it is able to measure the SC at the tin side, giving an information of the point surface stress. Also a research was focused on measurements of opportunely thermally treated glass, for which the thermal process was set to create an asymmetric Surface Compression Stress, and consequently an induced small curvature. The SC measurements were carried out on both the surfaces by Scalp-05 and on tin side with Laser Gasp, according ASTM 1279 Then the specimens were broken to evaluate: 1. bending strength according EN 1288-3; 2. fragmentation according EN 12150.