JPH05339021

PURPOSE:To prevent the adhesion of stains by placing a glass plate having poor thermal dimensional stability and/or flatness on a heat resistant glass ceramic plate having good flatness, then putting the glass plate into a specific slow cooling furnace and heat treating the plate. CONSTITUTION:The slow cooling furnace 10 has the construction mounted with a heating element port on its inside wall 11 and a dustproof wall 13 consisting of the transparent heat resistant glass ceramic plate allowing the transmission of a large quantity of heat is formed on the inner side thereof. The dustproof wall 13 is so mounted as to have a hermetic construction and an outside wall 14 consisting of an iron plate is formed on the outer side of the inside wall 11. The glass plate having the poor thermal dimensional stability and/or flatness is placed on the heat resistant glass ceramic plate having the good flatness and is imposed on a transporting conveyor 15 consisting of a heat resisting steel provided in the slow cooling furnace 10. The glass plate is moved at a prescribed speed in the slow cooling furnace 10 set at a prescribed temp. by rotating driving rollers 16 and is taken out. The glass plate is thereafter cooled with water and is dried, by which the glass plate having the good thermal dimensional stability and/or flatness free from the adhesion of the stains on the surfaces is obtd.