Method and apparatus for minimizing inclusions in a glass making process

1. A method for forming a glass sheet comprising:

flowing molten glass over a forming body comprising converging forming surfaces that converge at a bottom of the forming body, the forming body positioned within an enclosure;

heating the forming body with a plurality of heating elements separated from the forming body by an inner wall of the enclosure to form a temperature gradient between a temperature T 1 at a top of the forming body and a temperature T 2 at the bottom of the forming body, an insulating thermal barrier positioned between two adjacent heating elements of the plurality of heating elements;

drawing the molten glass from the bottom of the forming body to form a glass sheet; and

wherein the temperature T 2 at the bottom of the forming body is decoupled by the insulating thermal barrier from the temperature T 1 at the top of the forming body such that a change in T 2 does not cause a substantial change in T 1 .

2. The method according to claim 1 , wherein a 1° C./hour change in T 2 results in less than a 0.5° C./hour change in T 1 .

3. The method according to claim 1 , wherein a thermal resistance of the insulating thermal barrier is greater than about 0.0004 K·m 2 /W.

4. The method according to claim 3 , wherein the thermal resistance of the insulating thermal barrier is greater than about 0.004 K·m 2 /W.

5. The method according to claim 1 , wherein the glass sheet comprises less than about 0.3 inclusions per pound of finished glass.

6. The method according to claim 1 , wherein the glass sheet comprises less than about 0.09 inclusions per pound of finished glass.

7. The method according to claim 1 , wherein the insulating thermal barrier is positioned between a bottom-most heating element of the plurality of heating elements and a vertically adjacent heating element.

8. The method according to claim 1 , wherein the heating comprises radiating more heat from ends of the plurality of heating elements than from centers of the heating elements.

9. The method according to claim 1 , wherein the inner wall comprises an upper inner wall portion and a lower inner wall portion, the method further comprising heating the forming body by passing an electric current through the lower inner wall portion.

10. A method for forming a glass sheet comprising:

flowing molten glass over a forming body comprising converging forming surfaces that converge at a bottom of the forming body, the forming body positioned within an enclosure;

forming a temperature gradient between a temperature T 1 at a top of the forming body and a temperature T 2 at the bottom of the forming body by heating the forming body with a plurality of heating elements separated from the forming body by an inner wall of the enclosure, an insulating thermal barrier positioned between a bottom-most heating element of the plurality of heating elements and a vertically adjacent heating element of the plurality of heating elements;

drawing the molten glass from the bottom of the forming body to form a glass sheet; and

wherein the temperature T 2 at the bottom of the forming body is decoupled by the insulating thermal barrier from the temperature T 1 at the top of the forming body such that a 1° C./hour change in T 2 results in less than a 0.5° C./hour change in T 1 .

11. The method according to claim 10 , wherein the heating comprises radiating more heat from ends of the plurality of heating elements than from centers of the heating elements.

12. The method according to claim 10 , wherein the glass sheet comprises less than about 0.3 inclusions per pound of finished glass.

13. The method according to claim 12 , wherein the glass sheet comprises less than about 0.09 inclusions per pound of finished glass.

14. The method according to claim 10 , wherein the inner wall comprises an upper inner wall portion and a lower inner wall portion, the method further comprising heating the forming body by passing an electric current through the lower inner wall portion.

15. The method according to claim 14 , wherein the upper inner wall portion is separated from the lower inner wall portion by the insulating thermal barrier.

16. A method for forming a glass sheet comprising:

flowing molten glass over a forming body comprising converging forming surfaces that converge at a bottom of the forming body, the forming body positioned within an enclosure;

heating the forming body with a plurality of heating elements separated from the forming body by an inner wall of the enclosure to obtain a temperature T 1 at a top of the forming body and a temperature T 2 at the bottom of the forming body, an insulating thermal barrier horizontally positioned between two adjacent vertically spaced heating elements of the plurality of heating elements;

drawing the molten glass from the bottom of the forming body to form a glass sheet; and

wherein the temperature T 2 at the bottom of the forming body is decoupled by the insulating thermal barrier from the temperature T 1 at the top of the forming body such that a change in T 2 does not cause a substantial change in T 1 .

17. The method according to claim 1 , wherein a 1° C./hour change in T 2 results in less than a 0.5° C./hour change in T 1 .

18. The method according to claim 16 , wherein the insulating thermal barrier is positioned between a bottom-most heating element of the plurality of heating elements and a vertically adjacent heating element of the plurality of heating elements.

19. The method according to claim 16 , wherein the glass sheet comprises less than about 0.09 inclusions per pound of finished glass.

20. The method according to claim 16 , wherein the heating comprises radiating more heat from ends of the plurality of heating elements than from centers of the heating elements.