Overflow downdraw glass forming method and apparatus

Patent metadata

Field	Value
Publication number	US-9233869-B2
Application number	US-201113190117-A
Country	US
Kind code	B2
Filing date	Jul 25, 2011
Priority date	Aug 8, 2001
Publication date	Jan 12, 2016
Grant date	Jan 12, 2016

Abstract

The present invention discloses improved methods and apparatus for forming sheet glass. In one embodiment, the invention introduces a counteracting force to the stresses on the forming structure in a manner such that the thermal creep which inevitably occurs has a minimum impact on the glass flow characteristics of the forming structure.

First claim

What is claimed is:

1. A method for forming a glass sheet using an improved apparatus, wherein the apparatus includes a trough for receiving molten glass that has sides attached to a wedged shaped sheet forming structure 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 structure and meets at the bottom of the wedge, and wherein the method comprises the steps of:
(a) providing at least one inlet end compression block located at an inlet end of the forming structure, wherein the inlet end compression block is positioned at a bottom end of the forming structure;
(b) providing at least one far end compression block located at an opposite end of the forming structure as the inlet end compression block, wherein the far end compression block is positioned at the bottom end of the forming structure;
(c) applying an inlet end force with an inlet end force applicator to the inlet end compression block such that a bottom of the inlet end of the forming structure is deformed, by thermal creep, in a longitudinal direction; and
(d) applying a far end force with a first far end force applicator to the far end compression block such that a bottom of the far end of the forming structure is deformed, by thermal creep, in a longitudinal direction;
wherein the force applicators apply forces in opposite longitudinal directions to the respective compression blocks such that the bottom of the forming structure is in substantially greater compression than the top of the forming structure such that the bottom of the forming structure, which has a greater resistance to thermal creep than the top of the forming structure, is deformed longitudinally by thermal creep the same magnitude as the top of the forming structure; wherein the inlet end force applicator and the first far end force applicator consistently apply the corresponding inlet and far end forces to remain at a desired level throughout a production campaign such that the bottom of the forming structure deforms under thermal creep by the same magnitude as the top of the forming structure deforms under thermal creep, wherein any deformation of the forming structure that results from thermal creep has a minimal effect on a thickness variation of the glass sheet.

2. The method of claim 1 , wherein a compression stress in the bottom of the forming structure is between 1.25 and 4 times a compressive stress in the top of the forming structure as measured in the middle region.

3. The method of claim 2 , wherein the compression stress in the bottom of the forming structure is between 1.75 and 2.5 times the compressive stress in the top of the forming structure as measured in the middle region.

4. The method of claim 1 , wherein the inlet end force applicator is an inlet end adjustment screw that applies the inlet end force.

5. The method of claim 4 , further comprising the step of periodically adjusting the inlet end adjustment screw to maintain an applied force to the inlet end compression block such that a bottom of the inlet end of the forming structure is deformed, by thermal creep, in the opposite longitudinal direction to the deformation at the bottom of the far end of the forming structure.

6. The method of claim 5 , wherein a compression stress in the bottom of the forming structure is between 1.25 and 4 times a compressive stress in the top of the forming structure as measured in the middle region.

7. The method of claim 6 , wherein the compression stress in the bottom of the forming structure is between 1.75 and 2.5 times the compressive stress in the top of the forming structure as measured in the middle region.

8. The method of claim 4 , wherein the first far end force applicator is selected from the group consisting of a force motor; an adjustable spring; an air cylinder; a hydraulic cylinder; an electric motor; and a weight and lever system that applies the far end force.

9. The method of claim 1 , wherein the inlet end force applicator is selected from the group consisting of a force motor; an adjustable spring; an air cylinder; a hydraulic cylinder; an electric motor; and a weight and lever system that applies the inlet end force.

10. The method of claim 1 , wherein the first far end force applicator is selected from the group consisting of a force motor; an adjustable spring; an air cylinder; a hydraulic cylinder; an electric motor; and a weight and lever system that applies the far end force.

11. The method of claim 1 , further comprising the step of applying a force to a top of the far end of the forming structure with a second far end force applicator to produce a sealing force to counteract the hydraulic pressure of the glass flowing into the forming structure.

12. The method of claim 11 , wherein the second far end force applicator is selected from the group consisting of a force motor; an adjustment screw; an adjustable spring; an air cylinder; a hydraulic cylinder; an electric motor; and a weight and lever system that applies the force to the top of the far end of the forming structure.

13. A method for forming sheet glass using an apparatus, where the apparatus includes a trough for receiving molten glass that has sides attached to a wedged shaped sheet forming structure 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 structure and meets at the bottom of wedge, and wherein the method comprises the steps of:
(a) providing at least one inlet end compression block located at an inlet end of the forming structure;
(b) providing at least one far end compression block located at an opposite end of the forming structure as the inlet end compression block;
(c) applying an inlet end force with an inlet end force applicator to the inlet end compression block such that a bottom of the inlet end of the forming structure is deformed, by thermal creep, in a longitudinal direction; and
(d) applying a far end force with a first far end force applicator to the far end compression block such that a bottom of the far end of the forming structure is deformed, by thermal creep, in a longitudinal direction;
wherein the inlet end compression block and the far end compression block are shaped to distribute force in the forming structure to counteract the effect of the weight of the forming structure such that an applied force subjects the refractory in the middle region of the forming structure to substantially equal thermal compression strain in the longitudinal direction from the top of the middle region to the bottom of the middle region that substantially counteracts the effect of the weight of the forming structure and the molten glass, thus reducing sag in the middle region, and wherein the inlet end force applicator and the first far end force applicator consistently apply the corresponding inlet and far end forces to remain at a desired level throughout a production campaign such that a bottom of the forming structure deforms under thermal creep by the same magnitude as a top of the forming structure deforms under thermal creep, wherein any deformation of the forming structure that results from thermal creep has a minimal effect on a thickness variation of the glass sheet.

Assignees

• Pitbladdo Richard B
• Corning Inc

Inventors

• Pitbladdo Richard B

Classifications

• Y02P40/57

  Improving the yield, e-g- reduction of reject rates · CPC title

• C03B17/067

  combined with thermal conditioning of the sheets · CPC title

• C03B17/064 Primary

  by the overflow downdraw fusion process; Isopipes therefor · CPC title