Thermal tempering and Chemical tempering: what’s the difference?

How can glass be made resistant to impact and mechanical stress? There are two processes to achieve this result: thermal tempering and chemical tempering.

What is thermal tempering?

Thermal tempering is a process that relies on high temperatures. Glass is heated to extremely high temperatures (around 640°C) and then rapidly cooled.

This process alters the internal balance of the glass between tensile and compressive forces, particularly by creating surface compression.

This compressive force makes the glass up to 6 times more resistant not only to impact but also to thermal shock. Additionally, in the event of breakage, thermally tempered glass shatters into small fragments, which is why it is considered safety glass.

What is chemical tempering?

Chemical tempering, or more precisely “chemical strengthening,” is a process based on a chemical phenomenon. This process involves immersing the glass in a bath of potassium salts, causing an exchange of ions on the surface. Sodium ions in the glass are replaced by potassium ions, thereby improving the sheet’s strength and flexibility.

To simplify what happens, sodium ions are replaced by potassium ions, which are much larger than the space they occupy. These oversized ions create the surface compressive force mentioned earlier. The significant difference from thermal tempering lies in the level of compression, which is much higher in chemical tempering.

It is important to note that chemically tempered glass is not safety glass, as it does not break into small fragments when shattered. Therefore, to be considered safety glass, it must always be laminated.

What are the advantages of chemical tempering?

Chemical tempering offers significant advantages over thermal tempering:

• Greater strength and flexibility
• Better optical quality
• Unlimited application to all geometries
• Lighter laminated glass compositions, as it allows achieving the same strength requirements with thinner layers.

What are the main applications of chemical tempering?

The advantages of chemical tempering make it ideal for many projects, ranging from the nautical sector to automotive and design furnishings.

Veneto Vetro is one of the few companies in Italy and Europe capable of offering this exceptional process.
If you want to know more, write to us at sales@venetovetro.com.