Overflow downdraw glass forming method and apparatus

Patent metadata

Field	Value
Publication number	US-2016264445-A1
Application number	US-201514978681-A
Country	US
Kind code	A1
Filing date	Dec 22, 2015
Priority date	Aug 8, 2001
Publication date	Sep 15, 2016
Grant date	—

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

1 - 17 . (canceled)

18 . A method for reducing the sag rate of a forming trough having a longitudinal axis, a middle region, a first end, and a second end opposite the first end, said method comprising:
a) restraining the forming structure at a lower portion of the first end; and b) applying a force to a lower portion of the second end such that all material in a middle region of the forming structure is subject to a force distribution which produces substantially equal thermal compression strain in the longitudinal direction from top to bottom to produce a force distribution in the forming structure that substantially counteracts the effect of the weight of the forming structure and the molten glass, thus reducing sag in the middle region.

19 . The method of claim 18 , further comprising the step of supporting the forming structure at the first end and the second end.

20 . An improved apparatus for forming sheet glass, 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 improvement comprises:
a) at least one inlet end compression block located at an inlet end of the forming structure; and b) at least one far end compression block located at an opposite end of the forming structure as the inlet end compression block; 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 creates compressive forces at a bottom of the forming structure that are equal to or greater than compressive forces at a top of the forming structure, as measured at the longitudinal center of the forming structure; such that any deformation of the forming structure that results from thermal creep has a minimal effect on a thickness variation of the glass sheet.

21 . The apparatus of claim 20 , wherein the applied force is greater than a force necessary to put a bottom of the forming structure into compression.

22 . A method for reducing the sag rate of a forming structure having a longitudinal axis, a middle region, a first end, and a second end opposite the first end, said method comprising:
a) restraining the forming structure at a lower portion of the first end; and b) applying a force to a lower portion of the second end such that compressive forces measured at a bottom of the forming structure are greater than or equal to compressive forces at a top of the forming structure, as measured at the longitudinal center of the forming structure, to produce a force distribution in the forming structure that substantially counteracts the effect of the weight of the forming structure and the molten glass, thus reducing sag in the middle region.

23 . The method of claim 22 , further comprising the step of supporting the forming structure at the first end and the second end.

24 . An improved apparatus for forming sheet glass, 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 wedge, and wherein the improvement comprises:
a bottom of the wedge shaped sheet forming structure having a continuously parabolically curved shape in a convex upward direction such that the sheet formed from the apparatus is flat.

25 . The apparatus of claim 24 , wherein the inverted slope of the wedge shaped forming structure is at a constant angle with respect to vertical.

26 . The apparatus of claim 24 , wherein the inverted slope of the wedge shaped forming structure has a lesser angle with respect to vertical at the inlet end and the far end than at a center of the wedge shaped forming structure.

27 . An improved apparatus for forming sheet glass, 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 wedge, and wherein the improvement comprises:
a bottom opening of the chamber containing the apparatus having a width that varies in a longitudinal direction such that a magnitude of radiant heat loss in a vertical direction from the chamber containing the apparatus is controlled to different values in the longitudinal direction.

28 - 39 . (canceled)

40 . An improved apparatus for forming sheet glass, 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 improvement comprises:
a) at least one inflow measurement device that measures a mass flow of air into a muffle door chamber; and b) at least one outflow measurement device that measures a mass flow of air out of the muffle door chamber; wherein the outflow measurement device regulates cooling air flowing out of the muffle door chamber equal to a measured value that flows into the muffle door chamber such that no air leaks through cracks and openings between the muffle door chamber and the glass flowing off a bottom of the wedged shaped sheet forming structure.

41 . The apparatus of claim 40 wherein the inflow measurement device regulates cooling air flowing into the muffle door chamber to a constant value such that energy loss in a muffle door zone is constant.

42 - 45 . (canceled)

Assignees

• Corning Inc

Inventors

• Pitbladdo Richard Bruce

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