It is an effect feared by all those who have to toughen glass or work with toughened glass: anisotropy can be a real nightmare if the right precautions are not taken during processing!

Have you ever had a customer ask you if it is possible to completely remove them from tempered glass? Probably, especially if your customers are professionals or other companies who demand a perfect product from you.

Here is how you can answer that question. And how to meet your customers’ demands 100%.

What is anisotropy?

Let’s start with a simple definition of the phenomenon: anisotropy is the appearance of iridescent birefringent areas on the surface of glass. These areas are called ‘temper spots‘ and are often most visible when the glass is viewed from certain angles or with polarised light, while they are not visible at all from other viewing angles or under other conditions.

The formation of these stains on tempered glass is due to a physical phenomenon. Uneven heating or cooling of the sheet can create different stresses between the surface and the core of the glass.

In particular, compressive stresses are created on the outer surface while the core remains in tension, causing shadows or distortions to appear on the surface of the tempered glass.

At the same time, this balance between internal and surface tension is the reason why toughened glass is more resistant to bending and temperature changes, and therefore more difficult to break. Tempering is a thermal process that involves heating the glass to over 600°C and then rapidly cooling it with jets of air.

So is it possible to eliminate anisotropy 100%?

As it is easy to understand, anisotropy is created by the hardening process itself, so it is not possible to eliminate it 100%.

But this does not mean that you have to put up with glass full of shadows or stains: there are specific technologies that can minimise this effect, making it virtually imperceptible. And there are also tricks you can use.

The anisotropy is not only related to the production process, but also to factors such as the following:

– The thickness of the glass: thicker glass tends to show more anisotropy than thinner glass due to the higher internal stresses generated during tempering.

– The chemical composition of the glass: this can change the optical properties of the material.

The use of high quality glass can therefore help to minimise the visual effect of birefringence, and it is also possible to apply coatings to the glass to mask the anisotropy.

But to really minimise the appearance of haze, even in thick glass, it is essential to intervene directly in the tempering process. And that means equipping yourself with a high performance furnace.

Here’s how you can reduce anisotropy by 97%.

A tempering furnace equipped with the right technology can ensure that anisotropy is not a problem for your glass sheets.

For example, all Mazzaroppi systems are specifically designed to:

• Automatic multi-zone control: Thanks to intelligent software, the oven automatically detects the internal areas occupied by the glass pane and can also determine the percentage of these areas. In this way, it is possible to switch on and heat the different areas in a targeted manner, ensuring maximum uniformity of heating and cooling of the glass (and significant energy savings, since no energy is used to heat the empty areas of the furnace!)
• Optimised sheet handling: the intelligent software that manages the operation of all Mazzaroppi plants also controls the movement of each sheet in a punctual and automatic manner, diversifying it according to thickness, type and other characteristics. In this way, different actions are taken for each production batch.

Mazzaroppi technologies reduce anisotropy by 97%, making it virtually negligible.

This is guaranteed on all Mazzaroppi machines, both those designed for large companies and those for small glassworks. In fact, even small furnaces can guarantee very high performances.

Are you afraid that a tempering furnace is too energy-intensive for your work?

With Mazzaroppi ovens you don’t have to worry about this. Thanks to technologies such as the multi-zone control (described a few lines above) or Start&Stop (which allows you to switch off the oven every day when it is not in use and switch it on again in half an hour), you can reduce your consumption by up to 70% compared to many other solutions on the market, without compromising the performance of the machine.

Would you like to know how much energy the ideal Mazzaroppi oven consumes for your needs?

We’ll tell you: ask for a free Mazzaroppi Energy Saving Check and you’ll be amazed at how energy efficient our ovens are!

Give us a call to find out more.