Abstract: A tempering furnace for a glass sheet, and method for assembling the tempering furnace. The furnace comprises a first furnace portion and a second furnace portion attached successively one after another in the lengthwise direction of the furnace. Each of said furnace portions comprises a division channel arranged in the lengthwise direction of the furnace for dividing air to blow enclosures. The first furnace portion is provided with a blower pressurizing air sucked from the tempering furnace and feeding said air to the division channel of said first furnace portion. The division channel of the first furnace portion is connected to the division channel of the second furnace portion for leading air from the blower to said division channel of the second furnace portion.

Abstract: In a method for tempering a glass sheet, based on identified glass sheet properties, a tempering furnace temperature and/or glass sheet heating time are adjusted, the blowing pressure and/or distance of cooling unit air jets are adjusted, the glass sheet is heated in a tempering furnace, the achieved temperature is thereafter measured from the glass sheet surface, and the glass sheet is cooled. The development of the thickness direction temperature profile of the sheet during the tempering cooling is calculated, the residual stress profile achieved in the glass sheet during tempering is calculated, a reference variable for the glass sheet tempering level is selected and the selected reference variable is compared to a predetermined threshold value. If the comparison between the reference variable and the threshold value fulfils a predetermined criterion, an alarm is created and/or the glass sheet is found not to qualify as safety glass.