Float glass production technology annealing lehr

The annealing lehr for quality glass

Float 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.

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
Smart glass production through digitalization
Data gathering and analysis in glass production

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.

Waste heat recovery system in the cooling process

Heat is valuable. Why not make full use of it?

Waste heat recovery system

An intelligent solution: we transfer the heat that is discharged during the cooling process via pipelines to the warehouse area, where it serves to maintain the required minimum glass temperature during the cold season. At the same time, this reduces heating costs in the warehouse.

WHR systems
Service for the glass industry

Partnership and service that go the extra mile.

Our service for the glass industry

Construction and commissioning of a new glass production line is only the first stage in a good customer relationship. Professional service in daily operation is just as important: We want your investment to be profitable without any interruption – that’s why our engineers are there for you with guidance and support over the entire life cycle of the plant.

We Service

Technology & equipment

Float glass production

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