#AskGlaston Episode 9: How to eliminate specific quality problems with tempered glass?

Thank you for your excellent questions! This latest #AskGlaston episode will answer two of your questions regarding specific quality problems with tempered glass.

1. How to eliminate the rainbow effect and white smoke spots?
2. How to obtain consistent results from our tempering line?

Watch our video response here. I hope you’ll get new insights, share those with your colleagues and raise your quality level. Keep your questions coming, and we’ll keep answering them!

How to eliminate the rainbow effect and white smoke spots?

You’re facing a problem with 6 mm clear tempered glass. Glass first gets a rainbow effect, then it turns into white smoke spots. Later on, these detach in the form of a film.


Looking at the picture you sent us, we can see that there’s been some kind of washing material in the glass before it entered the furnace, which then burned onto the glass during the heat treatment. So, your problem is related to pre-processing, particularly to glass washing. It actually has nothing to do with the heat treatment.

How to obtain consistent results from our tempering line?

You’re finding it difficult to obtain consistent results from your tempering line. It seems that the cooling nozzles are slightly irregular in the height from the glass. Your Chinese manufacturer has advised you to use the furnace continuously to obtain a consistent result. Also, the manufacturer is saying that for a given thickness, the parameters for tempering must always be changed for all areas of the loading section, even for the same glass thickness. Your glass tempering results are now totally unpredictable. Also, the furnace doesn’t have an IR sensor, but you’ve used a handheld temperature sensor and found the heat distribution fairly consistent, with a temperature difference between 10 to 15 °C.

Overall, it seems you have both mechanical and process-related issues. It also shows that the comparison between the different tempering furnaces might be difficult. You get some values from the manufacturers, but the reality might still be totally different.

As a first step, we advise you to adjust the height of the nozzles to the same level. Use a handheld pressure-measuring device to make sure the pressure level is uniform.

Also, we recommend that you buy an IR scanner. This gives your operators a great tool to monitor the heating of the glass, and it also gives feedback on how well the tempering has succeeded.

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Kimmo Kuusela

Joined Glaston in 2005 and has worked in different positions since then. Kimmo has and gathered extensive hands-on experience on practically all parts of the glass processing chain. Currently working as Sales Director for Glaston in North America.