This is our second episode of the #AskGlaston video series. I’ve been amazed by the number and quality of questions we are getting. Thanks to you, we can say that this series will have a long-lasting place in Glastory. Today, we’ll cover an interesting topic that glass users and processors question from time to time. Which produces the best quality: tempered or heat-strengthened glass?
#AskGlaston question #3:
“You nicely handled the topic of roller waves in tempered glass in one of the previous posts. My follow-up question is: are these worse on toughened glass or on heat-strengthened glass? And why? Some people think roller waves on toughened glass is worse. To me, it is virtually the same as the glass softens during the heating, which is the same for both processes… if anything, heat strengthened may be riskier as the glass takes longer to cool… Thoughts?”
If you first want to refresh your memory about how to reduce roller wave, take a look at the previous article.
Generally, there is no difference between tempered or heat-strengthened (HS) glass when it comes to roller wave. In both cases, the glass heating process is the same. However, when we go to the limits of the heat-treatment process, small differences occur.
Roller wave depends primarily on the glass temperature. The higher the glass temperature when the glass exits the furnace, the worse the roller waves. The glass temperature can be slightly higher in the tempering process, especially with thicker glass, than in the HS process. This can have a negative impact on the glass in terms of the roller waves. However, we are talking about only very minor differences.
Also, the higher the glass quality, the lower the glass breakage in the furnace (tempering line yield). That is also one of the reasons why some processors may provide the same quality both with tempering and HS, even though there is a possibility to run with a slightly lower temperature when the glass is heat-strengthened.
It is also worth noting that the pre-processing quality affects the minimum possible temperature of the tempering process. The better the pre-processing (grinding and cutting) quality, the lower the heat-treatment temperature can be.
Thanks again for the question!
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