Method and apparatus for tempering glass sheets

An apparatus for tempering glass sheets, said apparatus comprising:

• a furnace,
• rolls in the furnace which are configured to be rotated back and forth for moving the glass sheets back and forth,
• a quench unit including a first and a second quenching zone,
• first cooling air boxes with their nozzles in the first quenching zone, second cooling air boxes with their nozzles in the second quenching zone, means for conducting the cooling air separately into the first and second cooling air boxes, and
• conveyor rolls in the quenching zones,
• wherein the nozzles of the first cooling air boxes are slit nozzles and the rolls of the first quenching zone are adapted to be rotated continuously in one direction and the rolls of the second quenching zone are adapted to be rotated back and forth.