HST (Heat Soak Test) in HTG Polska

The tempered glass of our production is a product of the highest quality. Frequent inspections show that our products have strength exceeding the requirements of PN-EN 12150-1. The characteristics are taken into account, inter alia, mechanical strength, the nature of the crack mesh, dimensions, tolerance and edge finishing.
However, toughened glass has a certain imperfection, we are talking about small particles of nickel sulphide (NiS) that can get into the glass mass during the production process in smelters. As a result of heating the glass in the tempering process, the nickel particles change their volume. Rapid cooling, which causes the glass to harden, prevents the sulfide particle from returning to volume from before the tempering process.
It happens that in glass forms mounted on facades, when they are heated by the sun's rays, the volume of the particle increases, causing an increase in internal stresses. When such a molecule is in the tensile stress zone, there is a high probability that the permissible stress level will be exceeded, which will result in a spontaneous breakage of the glass pane.
More and more of our clients use methods of eliminating this threat. A method that guarantees 99% efficiency is called HST (Heat Soak Test). It consists in heating the toughened glass to a temperature close to 300 C, keeping it for the time specified in the standard, in which, with a probability of 99%, glass panes with nickel sulphide content are revealed by breaking them.