#AskGlaston Episode 48: How to avoid edge kink in tempered glass?

This week, we will comprehensively look into the following hot question:

  1. How to avoid edge kink in tempered glass?

How to avoid edge kink in tempered glass?

That is an excellent question, and we get that question almost every day from our customers. And before I go into the details of how you can avoid it, it’s very important to understand what is actually causing the issue.

The edge kink is mainly caused during the heating phase of the tempering process. Particularly, when the glass temperature is above its transition point, and the glass is starting to become very soft. The higher the temperature and the longer the time the glass bends in that temperature, the worse the issue could become.

There are three main reasons that are actually causing edge kink. The first is that the glass is creeping between the furnace rollers. And this is the same thing that is also causing a roller wave on the glass. But the phenomenon becomes more visible and more severe on the edge areas of the glass. Therefore, if you heat the glass too much, there’s more chance you will see this issue on the glass edges.

The second reason is that your furnace or tempering line rollers could be leveled unevenly. So the reason for these could be, for example, improper installation or improper maintenance. So it is worth checking that all your conveyors are properly leveled if you are seeing a lot of edge kink on your glasses.

The third reason is turbulent air movement in the chiller. In the newer lines, there are a lot of technologies that help to control this issue. But if you are running an older line, you might have to consider having some kind of an upgrade done there so that you have more tools for the control.

And regarding how to avoid or control edge lift, the first thing is that you need to have is a capable furnace. Your furnace needs to have enough heating control and enough heating power so that you can ensure that all your glasses are evenly heated and you do not end up heating the edge areas more than the center area of the glass. And if you have the technology to enable you to do that, then you just have to check your recipe settings to make sure that you are not overheating the glass on the edges. A thermal scanner, for example, is a very handy tool in helping you make sure that the glass is evenly heated.

The second thing is to tell your maintenance team to check the leveling of the conveyors. And the third one would be a new edge control technology that can significantly help you reduce this effect. We were demonstrating the edge control technology at Glasstec 2018, where we were running live demonstrations of the technology right here in Tampere. We were able to significantly reduce edge lift on all of the glasses that we produced. And we were seeing values of lower than 0.1 mm in 4-mm glass, for example. This is something that has not been seen before in the glass industry.

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About the author

Riku Färm

With a background in industrial engineering and management, Riku is Director of Heat Treatment Product Management & Sales Engineering at Glaston. He is keen on working with customers and developing new business- and technology-related things – which makes product management a natural fit for him. In everything Riku does, he aims to ensure that glass processing customers are as successful as possible. This drives Riku and challenges him every day to think about what could be done better. Riku is an e-sports enthusiast. Aside from watching, he also enjoys playing the games that he actively follows.

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