Method of heat treating moving glass sheets on modified gas bed

A method of tempering glass sheets comprising:

• heating a glass sheet to a temperature sufficient for tempering;
• passing the heated glass sheet through a first cooling zone wherein each of the opposite surfaces of the glass sheet is subject to a plurality of thin, discrete, spaced-apart, parallel, laminar streams of relatively cool tempering medium angularly directed toward the glass surface so as to cool each portion of the glass sheet passing therethrough at a relatively high rate of heat transfer to rapidly harden the surfaces of the glass sheet and thereby substantially reduce subsequent formation of optical distortion in the glass, exposing each portion of the glass sheet to the laminar streams for a sufficiently limited period of time to substantially avoid inducing fluttering of the glass sheet, and withdrawing the glass sheet from the first cooling zone before the desired degree of temper is fixed in the glass;
• immediately passing the incompletely tempered glass sheet from the first cooling zone into a second cooling zone wherein each of the opposite major surfaces of the glass sheet is subjected to a plurality of diffuse patterned streams of relatively cool tempering medium which provide a relatively lower heat transfer rate and a relatively flutter-free support for the glass sheet, and maintaining each portion of the glass sheet in the second cooling zone until the desired degree of temper is fixed in the glass.