Method for controlling the thickness of a substrate
A method for controlling the thickness of a glass ribbon and an article produced thereby are provided. The method includes: providing a glass ribbon by drawing from a melt or redrawing from a preform; predefining a nominal thickness of the glass ribbon; determining the thickness of the glass ribbon over its entire net width; determining at least one deviation of the thickness of the glass ribbon from the predefined nominal thickness; identifying the area of the thickness deviation in the glass ribbon; and heating the area of the at least one thickness deviation in the glass ribbon using a laser, so that the glass ribbon attains the predefined thickness.
1. A method for controlling thickness of a glass ribbon, comprising:
providing a glass ribbon by drawing from a melt or redrawing from a preform with a drawing rate (v GB ) and an average thickness (D) in a net portion;
predefining a nominal thickness of the glass ribbon;
determining a thickness of the glass ribbon over an entire net width (B);
determining at least one deviation of the thickness from the nominal thickness;
identifying an area on the glass ribbon of the at least one deviation; and
heating the area using a laser beam to cause the area to attain the nominal thickness, wherein the heating further comprises controlling at least a power of the laser beam, a duration of irradiation of a laser beam, or a wavelength of the laser beam as a function of the thickness,
wherein the laser is equipped with a scanning head configured to scan the entire net width of the glass ribbon; and
wherein the following relationship applies between the entire net width (B), the drawing rate (v GB ), a beam diameter (D) of the laser beam, a scanning rate of a laser (v Las ), and a correction factor k:
2· k·v GB ·B<D·v Las , and
wherein the correction factor k is at least equal to or greater than 1 and the entire net width and the beam diameter are given in meters and the drawing rate and the scanning rate of the laser are given in meters per second.
2. The method as claimed in claim 1 , wherein the correction factor k is at least equal to or greater than 10.
3. The method as claimed in claim 1 , wherein, prior to the heating, the area has a viscosity in a range between 10 4 and 10 9 dPa·s, and wherein areas of excessive thickness are subjected to a greater laser power than areas of appropriate or undersized thickness.
4. The method as claimed in claim 1 , wherein the scanning head has an optical lever or a length of the optical path between the glass ribbon and a scanner mirror of between at least 1.8 m and at most 5.0 m.
5. The method as claimed in claim 1 , wherein the laser power is at most 3000 W.
6. The method as claimed in claim 1 , wherein the laser beam acts on a deformation zone of the glass ribbon.
7. The method as claimed in claim 1 , wherein the step of providing the glass ribbon by drawing or redrawing comprises drawing or redrawing by virtue of a weight of the glass ribbon.
8. The method as claimed in claim 1 , wherein the laser is a CO 2 laser.
9. The method as claimed in claim 1 , wherein the step of determining of the thickness comprises measuring selected from the group consisting of an interference measurement, a chromatic confocal measurement, a white light topography measurement, a white light interferometry measurement, and combinations thereof.
10. The method as claimed in claim 1 , further comprising directing the laser beam by a galvanometer scanner and/or a polygon mirror wheel.