Float glass production technology annealing lehr

The annealing lehr for quality glass

Flat glass production: Hot End

Once it leaves the tin bath, the glass ribbon enters an up to 200 meter or 656 foot annealing lehr. This is a kind of long kiln in which the glass is cooled slowly from about 600 °C or 1,112 °F to 60 °C or 140 °F. The annealing lehr is a key factor in the glass manufacturing process – this is where the tension and quality of the glass are determined.

The controlled cooling process minimizes stresses in the glass, which is vital when processing the glass afterwards. Therefore, the annealing lehr has a very important role to play. A Grenzebach annealing lehr will contribute to a stable glass. In the closed part of the annealing lehr, heat exchangers are used to prevent cooling with ambient air, which prevents contamination during the process and, in turn, ensures better quality glass. We draw on a customized calculation program with a good, decades-long track record and our expertise from 40 years of annealing lehr technology.


New design revolutionizes annealing lehr

Controlled cooling capacity, improved glass quality and reduced energy consumption

The design of the annealing lehr was completely revised, based on the CNUD EFCO technology. The result: higher glass quality, reduced energy costs and more flexibility in the production.

Advantages of the new Annealing Lehr

Controlled cooling capacity

Separately controllable sections allow the process to be precisely regulated, cooling capacities to be generated exactly as required, and changes to be responded to quickly. Shortened modules lead to shorter control zones, enabling even more precise response to the process. 

Flexible annealing point

Variable temperature curves enable a flexible annealing point. This opens up new possibilities to reach the perfect glass tension for different production scenarios.

Minimized risk of scratches

A segmented drive train with controlled servo drives compensates the contraction of the glass during the cooling process and thereby prevents scratches.

More exact simulations

An improved data situation thanks to more sensors enables a flexible project engineering with optimized adjustment to customer wishes.

Optimized operation and maintenance

Rollers can be changed during operation without having to access the safety areas. The operators also benefit from increased personal protection, a lower noise level and an intuitive control panel.

Up to 70 % less energy consumption

The highly efficient cooling process, optimized insulation and optional heat recovery system for heating and cooling energy increase the energy efficiency.

Ready for automation and digitalization

The new annealing lehr is perfectly prepared for future changes. In this way, for example, the connection to higher-level control systems and the associated automation is possible. A digital twin for even more flexible project engineering and the reduction of development costs is already being worked on.

Structure of an annealing lehr

The right combination between the radiation process and the convection process

In Grenzebach annealing lehrs and especially in the radiation area, ambient air is crossing a battery of heat exchangers that avoids any contamination of the glass. As a result, higher quality glass is ensured and a better control accuracy of the process.

Added value with digitalization

“The data from the annealing lehr help to enhance the production process even further. They are very important for the cold end and specific analysis creates added value thanks to digitalization.”


Statement by Robert Lamy CNUD EFCO GFT
Robert Lamy Sales Director Hot End Grenzebach Belgium bv

Let us help you create a 'thinking' factory.


The future of the glass manufacturing industry is digitization, which means that all stages in the process not only deliver and process data, but also communicate with each other. That’s what we call smart production.

Thickness measurement in the hot area and two-sided temperature measurement are just two of the features involved. The measurement of the glass ribbon’s width offers an additional advantage: by combining the drawing speed of the annealing lehr with the thickness and width of the glass ribbon, it is possible to calculate the tonnage precisely. And by measuring the glass’s position, ribbon swing can be detected and corrected at an early stage. Moreover, the data from the annealing lehr generate conclusions for the entire production process, particularly the cold end. This data gathering and analysis and the resulting conclusions offer real added value for glass producers.

Service for the glass industry


The engineering and commissioning of a new system are the first steps towards a successful glass line. Professional service in daily business is just as important - which is why we are at your side throughout the system’s entire life cycle.


Technology & equipment

For North America

Your contact person: Ron LaBorde

You would like to know what Grenzebach glass solutions can do for you? Call or write us about your challenge. We look forward to hearing from you!

We are here for you

Your contact person: Robert Lamy

Collaboration means dialogue. We support you no matter where you are in the world. Contact us. Send us your enquiry.

Robert Lamy Grenzebach