Glass substrate for vehicle glazing, in particular for the windscreen of a vehicle

A method for producing a glass substrate for vehicle glazing, comprising:

• hot forming a borosilicate glass to have an average thickness from 0.3 mm to 5 mm in a hot forming section;
• stretching the borosilicate glass in a flow direction or in a longitudinal direction of movement of the borosilicate glass to not exceed 10 mm/s and to not undershoot a value of 3 mm/s to maintain an aging velocity (Av) of the borosilicate glass, at least during the stretching,
• wherein the following applies to the aging velocity (Av):
• Av=Nf/(t*Hsl)
• where:
• Nf is a new surface area of a main surface that is newly formed during the hot forming process;
• t is a time passed in the hot forming section during the hot forming;
• and
• Hsl is a length of hot forming section along which the borosilicate glass is stretched;
• maintaining a width of the borosilicate glass to be hot formed in the hot forming section so that the width is altered by less than 3% in the hot forming section
• adjusting a viscosity of the borosilicate glass to be between log (η/dPa·s)=4.8 and log (η/dPa·s)=5.5 at a beginning of the hot forming section by temperature control,
• wherein the temperature control comprises a heat absorbing chamber upstream of a throughput control component and ceiling heaters of a float bath furnace that has a tin bath onto which molten glass to be hot formed into the borosilicate glass is transferred through the throughput control component,
• wherein the heat absorbing chamber comprises fluid flow areas forming a metallic pipe system through which water flows and which absorb heat from the molten glass to be hot formed,
• wherein the metallic pipe system comprises a heat-absorbing dye or a temperature-resistant paint on a surface thereof;
• and
• adjusting the viscosity of the borosilicate glass to be between log (η/dPa·s)=7.1 and log (η/dPa·s)=7.6 at an end of the hot forming section.

A method for producing a glass substrate for vehicle glazing, comprising:

• hot forming a borosilicate glass to have an average thickness from 0.3 mm to 5 mm in a hot forming section;
• stretching the borosilicate glass in a flow direction or in a longitudinal direction of movement of the borosilicate glass, to maintain, at least during the stretching, a ratio of a new surface area (Nf) of a main surface that is newly formed during the hot forming process to a length (Hsl) of the hot forming section in the flow direction or longitudinal direction of movement of the borosilicate glass and to a time (t) passed in the hot forming section during the time of hot forming does not exceed 10 mm/s and does not undershoot a value of 3 mm/s;
• maintaining a width of the borosilicate glass to be hot formed in the hot forming section so that the width is altered by less than 3% in the hot forming section;
• adjusting a viscosity of the borosilicate glass to be between log (η/dPa·s)=4.8 and log (η/dPa·s)=5.5 at a beginning of the hot forming section by temperature control,
• wherein the temperature control comprises a heat absorbing chamber upstream of a throughput control component and ceiling heaters of a float bath furnace that has a tin bath onto which molten glass to be hot formed into the borosilicate glass is transferred through the throughput control component
• wherein the heat absorbing chamber comprises fluid flow areas forming a metallic pipe system through which water flows and which absorb heat from the molten glass to be hot formed,
• wherein the metallic pipe system comprises a heat-absorbing dye or a temperature-resistant paint on a surface thereof;
• and
• adjusting the viscosity of the borosilicate glass to be between log (η/dPa·s)=7.1 and log (η/dPa·s)=7.6 at an end of the hot forming section.