This week, we’re dealing with questions about the dots on a glass surface that appeared after tempering and the equipment that can measure the glass flatness:

1. We have a furnace made in China and have a lot of dots on the glass surface after tempering. The dots appear only on one side of the glass, the side that has contact with the rollers. Can you give any advice?
2. What type of equipment is used to measure the flatness of the glass in addition to a standard straight-edge ruler?

For this week’s questions, see our full video response below!
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We have a furnace made in China and have a lot of dots after tempering on the glass surface. The dots appear only on one side of the glass, the side that has a contact with the rollers. Can you give any advice?

As we can see in the picture, those defects are all around the glass. That tells us that there is something happening or some mistakes or errors happening all around the furnace. There are many sources for this kind of challenge.

From the furnace side, it can be that:

• The rollers / roller surfaces have some fractures.
• The insulation from the sides or the roof is coming down in small residual parts, which causes this effect on the glass.
• The rollers are vibrating. In this case, please check the quality of the bearings and also that they are installed correctly.

When it comes to the loading side, the following aspects need to be considered:

• • It’s essential that the loading side is very clean. It can be, for example, that the first rolls have some friction with the insulation, so the insulation is then taken forward to the furnace, which leads to these mistakes on the glass.
  • It can also be that the glass itself is hitting the inside insulation to cause this.

On the chiller side:

• Air pressure may be blowing through the exit door into the furnace.

What type of equipment is used to measure the flatness of the glass in addition to a standard straight-edge ruler?

There are a lot of online measurement tools available on the market for the local bow. For example, iLooK online quality measurement system measures all the values online when the glass is processed and transferred to the unloading section of the tempering line. Unfortunately, for the overall bow of the glass, there is no reliable automatic online measurement device. A longer straight-edge liner can be used to check the overall bow of the glass.

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