Before HST, the glass undergoes tempering to strengthen it. Tempered glass is heated to about 620°C (1150°F) and then rapidly cooled, inducing compressive stress on the surface and tensile stress within. This makes the glass significantly stronger but also more sensitive to internal defects like NiS.
Heating: The glass is placed in a heat soak oven, where it is gradually heated to 280–300°C (536–572°F). This temperature is chosen because it accelerates the transformation of NiS inclusions from their unstable phase to a stable phase, causing them to expand.
Holding Period: The glass is held at this temperature for 2-4 hours to allow any latent defects to manifest.
Cooling: The glass is then cooled to ambient temperature before further inspection or shipping.
Glass with critical NiS inclusions will typically shatter during this process due to the stress caused by the NiS expansion. Broken panes are discarded, and only the defect-free glass moves forward.
Prevents spontaneous breakage of large, installed panes that could endanger pedestrians below.
Ensures glass used in overhead applications won’t fail unexpectedly.
Maintains structural integrity and user safety in glass barriers or railings
Enhances reliability in architectural glass used for external building envelopes
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