Glass tempering
Applied heat treatment methods
- Tempering - ESG
- Heat Soak Test - HST
- Annealing - TVG
- Curving and bending of glasses
These operations are carried out in tempering and bending furnaces and laminating machines.
Tempering: During tempering, the glass is heated and then rapidly cooled to increase its strength and heat resistance.
Tempered glass:
- Cannot be cut, drilled or milled
- More resistant to breakage and sudden temperature changes
- Breaks into small, non-sharp pieces when broken
- The surface becomes more wavy
Tempering conditions:
- Hairline cracks can form during the cutting of the glass, making tempering more difficult
- The minimum machining of glass sheets is edge grinding
The process:
- The glass is transferred from the loading table to the furnace.
- The glass is heated in the furnace by alternating movements.
- In the cooling unit it cools down rapidly.
- The finished glass is placed on the unloading table.
Quality control:
- "Zebra" test
- Overall curvature test
- Local bend test
- Mechanical strength test
- Fracture test
All tests must be carried out at each change of glass thickness and glass type.
Local bend measurement:
Local bend can be measured with a gauge, with a maximum deviation of 0.5 mm over a length of 300 mm.
- Tempered glass: 0,5 mm / 300 mm
- Tempered glass: 0,3 mm / 300 mm
Total deflection: Max. deflection 3 mm/m.
Fracture test: On standard 360 x 1100 mm specimens, the glass is broken by point-concentrated force.
- 4-12 mm thickness: min. 40 pieces per block
- 3 mm: min. 15 pieces
- 15-19 mm: min. 30 pieces
Mechanical strength test: the glass is subjected to a standard load.
Heat Soak Test (HST): The HST filters out nickel sulphide inclusions that cause spontaneous breakage. The glass is heated to over 290°C and held there, then cooled back to filter out latent defects.
Heat-strengthened glass: is produced in a similar way to toughened glass, but the re-cooling is longer and less intense. After breaking, the glass sheet retains its structure and does not break. No risk of spontaneous breakage, no HST required.
Bending and Embossing: Bent glass technology is a process in which glass sheets are shaped into the desired shape by heating and bending. This technology is particularly useful in applications where curved or specially shaped glass surfaces are needed, such as vehicle windshields, architectural glass surfaces, or design elements.
During the process, the glass is first heated to a high temperature (usually between 600-700°C), which allows the material to become pliable. Subsequently, the glass is passed through precision rollers that bend it into the specified shape.
The glass is then cooled rapidly, which strengthens the material, making it more resistant to mechanical impacts. The technology allows for the unique, complex shaping and high-precision manufacturing of glass while maintaining its optical clarity and structural integrity. These bent glasses can be incorporated into insulating or laminated structures.
