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GlassCon Global 2016 technical sessions include a range of topics covering many different fabrication and design issues. Jeff Nixon with Glass Coatings & Concepts led one presentation that looked at mitigating thermal stress breakage in heat-strengthened spandrel glass.
As Nixon explained, architectural designs have evolved and the industry is seeing unprecedented thermal stresses in spandrel. Many current designs promote thermal stresses. These can include double and triple insulating glass units; super low-E; little or no ventilation, etc.
Some of the factors that influence thermal stress can include, among others, environmental issues, such as temperature build up and gradients, as well as design factors.
Speaking of design factors, these can include conditions with the outer lite, for example. He explained that highly transparent outer lites result in a greater solar energy incident upon the inner lite. In addition, reflective coatings on surface one of the glass result in less solar energy reaching the inner lite. Another consideration, Nixon said, is colored glass absorbs much of the light, which also results in less solar energy on the inner lite.
“The outer lite is an important design factor,” Nixon said. “Color is also a design factor – this can make a difference …”
Other design factors can include framing (shading and thermal properties); interior corners (or other additive configurations); as well as surface flaws, which can be an influence.
Nixon added that ceramic frit can also influence the strength. Different frits, for example, affect the glass in different ways. This can include thermal expansion as well as quality of the frit. These both lead to a big range in effects on the frit. He explained that a frit with a high thermal expansion can lead to breakage; contamination in the frit can cause issues as well.
The session also covered some mitigation strategies. As far as the environmental factors, Nixon pointed out that the lower the solar radiation the better. “Remember, cold morning light is the issue, not the heat; the morning sun creates that thermal gradient,” he said.
Design factor considerations include addressing areas such as framing, interior corners and the color of the interior lite, among others.
Nixon concluded with a few points, reminding everyone that extreme thermal stresses can result in breakage of heat-strengthened spandrel glass. Increasing the glass strength to fully tempered, which can approximately double the strength, can help. This, he added, only needs to be done to the inboard lite.
GlassCon Global 2016 continues through tomorrow. Stay tuned to USGNN for more news and reports.
