Part 3 of our Glass tempering basics series
When it comes to glass tempering, two things often fly under the radar: heating and cooling times and pre-processing quality. Yet, they play a huge role in the result.
Heating and Cooling – It’s all about thickness
The tempering process starts with heating and ends with quenching (rapid cooling). How long does it take? That depends on glass thickness. Furnaces usually work with a set heating time per millimeter, like 40 seconds per mm. So, a 4 mm glass takes about 160 seconds to heat. Simple math, but critical for planning your production.
Moreover, when operating a tempering furnace, the heating time shouldn’t be a fixed number per thickness. The number of glasses you have in a load and the sizes of the glasses also affect the optimal heating time for the batch you’re running.
Pre-Processing – Don’t skip this step
Before heat treatment, all cutting, grinding, and drilling must be done. Why? Because tempering creates internal stress, making post-processing impossible. And here’s the kicker: poor pre-processing = more breakages and lower yield.
- Cutting quality matters: Micro-cracks from excessive cutting pressure can cause breakage during cooling.
- Edge grinding matters even more: A diamond-polished edge allows glass to run at lower furnace temperatures — improving optical quality and reducing roller wave.
Think of pre-processing as the foundation for everything that follows. Better edges, better results.
Your checklist before investing
- Don’t overlook pre-processing machinery.
- Match your equipment to your quality and capacity goals.
- Understand the basics so you can ask the right questions when buying.