By: Karen Wegert
This post is part of our “Tough as Glass” series.
Fireplaces are the centerpiece of many homes, adding warmth and aesthetic appeal. Glass-sealed fireplaces offer the beauty of a natural fire while securing soot, ash, and flames behind a glass-ceramic barrier that must withstand extreme heat and cooling.
In order to ensure that barrier remains intact despite the heat of the fire and the potential for breakage and thermal shock, SCHOTT puts its ROBAX glass-ceramic through three major tests:
When heated too high, traditional tempered glass expands and shatters at temperatures as low as 482 degrees Fahrenheit. ROBAX glass-ceramic, on the other hand, has zero thermal expansion, and therefore can withstand temperatures up to 1400 degrees Fahrenheit without breaking.
Tempered glass also shatters when exposed to sudden changes in temperature. For example, heated tempered glass breaks when exposed to dry ice (-109 degrees Fahrenheit) while heated ROBAX retains its integrity when exposed to extreme cold, such as dry ice or liquid nitrogen (-346 degrees Fahrenheit).
2. ROBAX water shock test.
While most home owners don’t have to fear liquid nitrogen contacting their glass-ceramic fireplace barriers, it’s not hard to imagine spilling water on a glass-sealed fireplace. To ensure ROBAX retains its integrity when contacted with cool water, testers perform the ROBAX water shock test.
In this test, cloths are saturated with water and wiped across a glazing panel heated to maximum temperature. The glass must not shatter under the thermal shock. Next, to simulate a glass cleaning situation, the glass is reheated to maximum temperature and sprayed three times with misted water from the nozzle of a household cleaning spray.
Testers also submerge a heated ROBAX glass-ceramic panel in ice water to ensure it doesn’t break from thermal shock. Glass-ceramic can withstand thermal shocks when heated to 1,292 degrees Fahrenheit while tempered soda lime can only withstand shock up to 365 degrees Fahrenheit.
Glass-sealed fireplaces must not only withstand extreme temperatures, but also stand up to occasional impacts from dropped wood and clumsy fireplace tools. In the ROBAX impact test, testers swing a 2-inch steel ball weighing 1.18 pounds from a pendulum at a height of 16.25 inches directly into the glass-ceramic. The glass must not break under one impact in the center of the pane in order to pass the test.
What should we test next?
Glass must withstand extreme temperatures and high pressures in order to safely serve its numerous roles, and these are just some of the tests we put our glass-ceramic through to confirm its strength before it reaches homes. Any videos you’d like us to make? Leave a comment and let us know.