Lehrs / Float- and display glass annealing lehr

Robot Technology for Lehrs Stacking

Lehrs / Float- and display glass annealing lehr


In the classical Float and Solar Glass lehr design the rollers are driven by a centralized shaft, which provides the same rotational speed for each roller. This system is basically safe, but in the event of a disturbance (failure) very critical for the rollers themselves. Technologically the system with its open sprockets and oil pans has been state of the art 25 years ago.

The main disadvantage is to be seen in the same rotational speed of each roller. The glass enters the lehr at a temperature of approx. 600°C and cooled to approx. 70°C. During this process it thermally shrinks and will lead to a relative movement of the glass on the rollers itself. This will result in a scratching of the glass surface (Micro Scratches). Due to the reduction of the rotational speeds (offset) of the rollers, according to the temperature of the glass, such effect may be avoided, whereas the LOR’s are operated as the master drives.


  • Glass ribbon width of up to 4,5m (15’)
  • All tunnels zones (A,B, C, D and RET) with inner linings, manufactured from heat and chemical resistant stainless ssteel
  • Electric radiation heating
  • Electrical heating system operated by thyristor controls
  • Six heating control loops across glass ribbon width
  • Heating elements and semi indirect cooler units are manufactured from high temperature resistant stainless steels
  • Integrated, electronically movable edge heaters
  • Indirect and semi indirect cooler inserts in annealing zones (A to C)
  • Six cooling control loops across the glass ribbon width
  • Special design down flow cooling fans in cooling zones (RET) to mix the internal air with cooling air
  • Modular zones with side wall inserts, for flexible installation of heating and indirect/semi-indirect cooling units
  • Special design for over and under ribbon heaters
  • Double lateral wall system with stainless steel surface
  • Use of ceramic rollers for glass transport for scratch minimization (low SO2)
  • Individual drives, one unit per roller (no open sprockets/oil pans)
  • Drive configuration by inverters, to compensate the glass shrinkage of ribbon
  • Additional backup inverters for operational roller drive safety
  • Roller support arranged by zones, for easier alignment and higher accuracy
  • Fully insulated lehr (all tunnel zones) with approx. 350mm (14”) ceramic fiber and mineral wool
  • Fully automatic air inlet damper systems for temperature curve control
  • Control of the lehr exit temperatures, required for optimal cutting results
  • Individual inverter controlled cooling banks (decentralized) in F zones
  • Optional automatic internal cullet removal system (patent pending) for RET and F zones
  • Automatic process control for the control and monitoring of temperatures by PLC and backup system
  • Optional communication processor (Ethernet or others) for link to plant process control
  • Electronic control of the internal air movements (drift system) for a minimization of the energy consumption
  • Optimal temperature distribution across the lehr width
  • Full scope supply incl. control and field wiring