Methods and apparatus for producing toughened glass

Claim 1

A METHOD OF TOUGHENING GLASS IN SHEET FORM, COMPRISING THE STEPS OF HEATING THE GLASS SHEET TO A TEMPERATURE NEAR THE SOFTENING POINT OF THE GLASS, RAPIDLY CHILLING THE GLASS SHEET BY DIRECTING STREAMS OF CHILLING MEDIUM SIMULTANEOUSLY OVER BOTH SURFACES OF THE GLASS SHEET AND SIMULTANEOUSLY WITH SAID RAPID CHILLING, GENERATING RADIATIONS IN THE WAVELENGTH RANGE OF 2.75 MICRONS TO 4.5 MICRONS, TO WHICH RADIATIONS THE GLASS IS PARTIALLY TRANSPARENT, AND DIRECTING SAID RADIATIONS AT SAID SURFACES AS SAID SURFACES ARE BEING RAPIDLY CHILLED, WHILE SUBSTANTIALLY PREVENTING THE DIRECTION AT SAID SURFACES OF THE GLASS SHEET, RADIATIONS HAVING A WAVELENGTH GREATER THAN 5 MICRONS, TO WHICH RADIATIONS THE GLASS IS OPAQUE, SAID GENERATING, DIRECTING AND PREVENTING STEPS BEING CONTINUED LONG ENOUGH TO PRODUCE A TEMPERATURE DIFFERENTIAL BETWEEN THE INSIDE AND THE SURFACES OF THE GLASS SHEET, GREATER THAN WOULD BE PRODUCED IN THE ABSENCE OF SAID GENERATING, DIRECTING AND PREVENTING STEPS, WHEREBY A TOUGHENED GLASS SHEET HAVING A MODIFIED STRESS DISTRIBUTION IS OBTAINED.