Sheet width control for overflow downdraw sheet glass forming apparatus
A method keeps the width of the manufactured sheet substantially the same by attaching edge directors for the formed sheet to the manufacturing apparatus structure instead of to the forming block. Thus, sheet glass may be manufactured to specification for a longer time with the same forming block. An additional method adjusts the width of the manufactured sheet by changing the distance between the edge directors. Thus sheet glass may be manufactured to different width specifications with the same forming block.
1. A method for manufacturing glass sheets using an apparatus that includes a trough for receiving molten glass that has sides attached to a wedged shaped sheet forming block that has downwardly sloping sides converging at the bottom of the wedge such that a glass sheet is formed when molten glass flows over the sides of the trough, down the downwardly sloping sides of the wedged shaped sheet forming block and meets at the bottom of wedge, wherein the method comprises the step of:
moving a surface of the forming block relative to at least one end edge director fixed to a support structure at that end of the forming block as the forming block changes shape due to thermal creep without changing a distance between a far end edge director at a far end of the forming block and an inflow end edge director at an inflow end of the forming block, such that a width of a glass sheet does not change as a consequence of the surface of the forming block moving relative to the at least one edge director, and then
further comprising the step of adjusting a distance between the inflow end edge director and the far end edge director relative to a moving surface of the forming block as the forming block changes shape due to thermal creep, such that a width of a glass sheet is changed.
2. The method of claim 1 , wherein the method further comprises the step of adjusting a mass flow of glass times a viscosity of glass when changing the sheet width such that a thickness of the glass sheet remains constant.
3. The method of claim 1 , wherein the method further comprises the step of adjusting an angle of the forming block to horizontal when changing the sheet width such that a thickness of the glass sheet remains constant.
4. The method of claim 1 , wherein the method further comprises the step of maintaining a thickness of the glass sheet constant when changing the sheet width.
5. The method of claim 1 , wherein the surface of the forming block at the inflow end is moved relative to the inflow end edge director fixed to a support structure at the inflow end.
6. The method of claim 1 , wherein the surface of the forming block at the far end is moved relative to the far end edge director fixed to a support structure at the far end.
7. The method of claim 1 , wherein the step of moving the surface of the forming block, further includes the step of fixing a location of the inflow end edge director and the far end edge director relative to the surface of the forming block that is moved as the forming block changes shape due to thermal creep.
8. The method of claim 1 , further comprising the step of adjusting a longitudinal position of the forming block relative to the inflow end edge director and the far end edge director to maintain a formed sheet glass thickness profile.
9. The method of claim 1 , wherein the surface of the forming block is moved relative to both the inflow end edge director and the far end edge director.
10. The method of claim 1 , further comprising the steps of:
analyzing a thermal creep deformation via computer simulation finite element analysis; and
analyzing a glass flow distribution resulting from the thermal creep deformation via computer simulation computational fluid dynamics;
such that repeated analytical iterations of thermal creep deformation and glass flow distribution caused by variations in a magnitude and a location of the applied forces yield a configuration such that a thickness of the glass sheet remains substantially constant for a duration of a production campaign.