Strengthened glass article and process for making

Claim 1

In a process for strengthening curved alkali metal containing flat glass articles by softening a glass sheet at a temperature near its softening point, bending said glass sheet to a desired configuration, and subsequently strengthening said glass article by exchange of relatively large ions from an external source for smaller alkali metal ions of the glass while maintaining said glass below its strain point for a sufficient period of time to achieve a useful surface compressive stress, the improvement comprising the use of a glass consisting essentially of the following composition: SiO2 59-62 percent by weight Al2O3 18-23 percent by weight Li2O 4-5.5 percent by weight Na2O 7-9 percent by weight B2O3 3-5 percent by weight and having a log 10 viscosity of 4.0 at a temperature below about 2900* F., having a maximum solubility in 0.5 weight percent H2SO4 at 100* C. of about 0.06 milligram per square centimeter per hour, including fining the glass in a molten state at a temperature slightly above the melting temperature but below 2900* F. and forming the flat glass at a temperature of from about 1850* F. to about 2100* F. by a conventional method of forming flat glass.

Claim 2

A method of producing strengthened, flat glass having a maximum solubility in 0.5 weight percent H2SO4 at 100C. of about 0.06 milligram per square centimeter per hour, comprising: a. melting at a temperature of about 2500* F. to about 2700* F. a glass base of a composition consisting essentially of: SiO2 59-62 percent by weight Al2O3 18-23 percent by weight Li2O 4-5.5 percent by weight Na2O 7-9 percent by weight B2O3 3-5 percent by weight b. fining said molten glass at a temperature slightly above the melting temperature but below 2900* F.; c. forming sheets of said molten glass maintained at a temperature of from about 1850* F. to about 2100* F. by a conventional method of forming flat glass; d. annealing said glass sheets; and e. strengthening said annealed glass sheets by exchanging a relatively large metal ion from an external source for a smaller ion of the glass while maintaining said glass below its strain point for a sufficient period of time to achieve a surface compressive stress.

Claim 5

A method of producing strengthened, flat glass having a maximum solubility in 0.5 weight percent H2SO4 at 100* C. of about 0.06 milligram per square centimeter per hour, comprising: a. melting at a temperature of about 2500* F. to about 2700* F. a glass base of a composition consisting of: SiO2 59-62 percent by weight Al2O3 18-23 percent by weight Li2O 4-5.5 peRcent by weight Na2O 7-9 percent by weight B2O3 3-5 percent by weight b. fining said molten glass at a temperature slightly above the melting temperature but below 2900* F.; c. forming sheets of said molten glass maintained at a temperature of from about 1850* F. to about 2100* F. by a conventional method of forming flat glass; d. annealing said glass sheets; and e. strengthening said annealed glass sheets by exchanging a relatively large metal ion from an external source for a smaller ion of the glass while maintaining said glass below its strain point for a sufficient period of time to achieve a surface compressive stress.