Method for heat treatment of glass plate to strengthen its peripheral region

Abstract

The invention relates to heat treatment of a glass plate for strengthening only a peripheral region of the glass plate while annealing the major region. The glass plate is heated to a temperature of 550.degree.-650.degree. C. and placed on a ring-like holder which is maintained at a temperature lower than the temperature of the glass plate by 100.degree. to 600.degree. C. such that the peripheral region of the glass plate makes contact with a ring-like upper surface of the holder. Then glass palte on the ring-like holder is kept in an annealing chamber maintained at a temperature in the range from 50.degree. to 500.degree. C. and not higher than the initial temperature of the ring-like holder. After that the glass plate is allowed to cool down to room temperature. This method is applicable to either flat glass plates or curved glass plates and very suitable for treating glass plates ranging from 1.5 to 3.0 mm in thickness.

Dependencies are inferred from the claim text.