Tempering furnace for glass sheets

A tempering furnace for a glass sheet, comprising:

• a conveyor configured to convey the glass sheet;
• and
• first convection blow means configured to heat the glass sheet by hot air jets blown on at least one surface of the glass sheet,
• wherein the first convection blow means include:
• a blower configured to pressurize air sucked from the tempering furnace;
• air channels configured to lead air from the blower to blow enclosures, the blow enclosures having, at surfaces of the blow enclosures facing the glass sheet, blow openings from which air is discharged as jets towards the glass sheet;
• and
• electric elements inside the blow enclosures configured for heating air,
• wherein the tempering furnace further comprises:
• second convection blow means configured to aid in leading pressurized air from outside the tempering furnace to blow nozzles from which air is discharged as jets towards the at least one surface of the glass sheet,
• wherein the electric elements and the blow enclosures of the first convection blow means form a plurality of first separately-adjustable blow zones in longitudinal and width directions of the tempering furnace, in which a heating effect of the hot air jets on the glass sheet is adjustable by adjusting a feeding of electric current to the electric elements,
• wherein the blow nozzles of the second convection blow means of the tempering furnace form a plurality of second separately-adjustable blow zones in the longitudinal and width directions of the tempering furnace, in which a heating effect on the glass sheet of the jets discharged from the blow nozzles is adjustable by adjusting a feeding of airflow to the blow nozzles, and
• wherein feed pipes of the blow nozzles of the second convection blow means are arranged to run, in a direction toward the glass sheet, in gaps outside of and between the blow enclosures such that the blow nozzles of the second convention blow means are closer to the glass sheet than a top surface of the blow enclosures of the first convection blow means.