Method of tempering glass sheets of unequal thickness

A method of tempering glass sheets of unequal thickness so as to maintain their surface contours in close correspondence with one another, comprising the steps of:

• placing a relatively thin sheet of glass into a furnace which includes an array of heating means, within which the thin sheet is first subjected to a preheating temperature slightly lower than a temperature suitable for tempering so as to substantially avoid distorting the glass sheet surfaces for a period of time sufficient to heat the thin glass sheet throughout its thickness to approximately said preheating temperature, after which the thin sheet is subjected to a temperature within said furnace higher than said preheating temperature so as to rapidly heat surface portions of the thin sheet to a temperature suitable for tempering at which glass surface distortion may occur;
• removing the thin sheet from the furnace and introducing it into a quenching zone wherein blasts of cooling tempering medium are directed onto the sheet so as to impart a temper thereto;
• in close succession to the treatment of the thin sheet, placing a relatively thick sheet of glass into said furnace, within which the thick sheet is first subjected to said preheating temperature for a period of time sufficient to heat the thick sheet throughout its thickness to approximately said preheating temperature, after which the thick sheet is subjected to a temperature within said furnace higher than said preheating temperature so as to rapidly heat surface portions of the thick sheet to a temperature suitable for tempering at which glass surface distortion may occur;
• removing the thick sheet from the furnace and introducing it into said quenching zone wherein blasts of cooling quenching medium are directed onto the sheet so as to impart a temper thereto;
• whereby the glass sheets experience substantially identical distortion-producing conditions while being subjected to disparate heating schedules in accordance with their thicknesses, so that a thick sheet and a thin sheet tempered in close succession have their surface contours in sufficiently close correspondence with one another to permit them to be laminated together.