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. An improved apparatus for forming sheet glass, wherein the apparatus includes an inflow pipe for delivering molten glass, 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 the wedge, wherein the improvement comprises:
a) a first inflow end compression block inserted into a first cavity at an inflow end of the forming block; and
b) a second far end compression block inserted into a second cavity at a far end of the forming block;
such that a longitudinal compressive force is applied to a bottom of the first cavity and a bottom of the second cavity to counteract a thermal creep effect of a gravitational force from a weight of the forming block.
2. The improved apparatus of claim 1 , wherein a depth of the first cavity and a depth of the second cavity are independent and range from 0 to 35 percent of a length of the bottom of the wedge.
3. The improved apparatus of claim 1 , wherein a depth of the first cavity and a depth of the second cavity are independent and range from 10 to 35 percent of a length of the bottom of the wedge.
4. The improved apparatus of claim 1 , wherein a depth of the first cavity and a depth of the second cavity are independent and range from 20 to 25 percent of a length of the bottom of the wedge.
5. The improved apparatus of claim 1 , wherein the improvement further comprises a third compression block at the inflow end that applies a portion of the inflow end compression force such that a thickness profile of a glass sheet remains substantially constant.
6. The improved apparatus of claim 5 , wherein the improvement further comprises a fourth compression block at the far end that applies a portion of the far end compression force such that a thickness profile of a glass sheet remains substantially constant.
7. The improved apparatus of claim 6 , wherein the improvement further comprises a sum of the longitudinal forces applied to the forming block by the second compression block and the fourth compression block at the far end being greater than a sum of the longitudinal forces applied to the forming block by the compression blocks at the inflow end such that a sealing force is applied between the inflow pipe and the forming block at the inflow end.
8. The improved apparatus of claim 1 , wherein the improvement further comprises a third compression block at the far end that applies a portion of the far end compression force such that a thickness profile of a glass sheet remains substantially constant.
9. The improved apparatus of claim 1 , wherein the improvement further comprises the longitudinal force applied to the forming block by the second compression block at the far end being greater than the longitudinal force applied to the forming block by first compression block at the inflow end in order such that a sealing force is applied between the inflow pipe and the forming block at the inflow end.
10. An improved apparatus for forming sheet glass, wherein the apparatus includes an inflow pipe for delivering molten glass, 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 the wedge, wherein the improvement comprises:
a) an inflow end compression block at an inflow end of the forming block; and
b) a far end compression block at a far end of the forming block;
wherein a far end longitudinal compression force at the far end of the forming block is larger than an inflow end longitudinal compression force such that a sealing force is applied between the inflow pipe and the forming block at the inflow end.