Method and apparatus for minimizing inclusions in a glass making process
An apparatus for forming a glass sheet with reduced zircon inclusions in the glass sheet is disclosed. In one embodiment, the apparatus comprises heating elements distributed vertically between the weirs of a forming wedge and the root of the forming wedge, and wherein a thermal barrier is disposed between adjacent heating elements. A method of using the apparatus is also disclosed.
1. An apparatus for forming a glass sheet comprising:
a forming wedge comprising weirs at the top of the forming wedge and forming surfaces below the weirs that converge to a root at the bottom of the forming wedge;
a plurality of heating elements disposed proximate to the forming wedge, at least one of the heating elements comprising a center portion disposed between end portions, wherein the end portions of the at least one heating element have a higher resistance than the center portion of the at least one heating element and the end portions of the at least one heating element radiate a greater amount of heat than the center portion of the at least one heating element;
an enclosure disposed about the forming wedge, the enclosure comprising an inner wall separating the forming wedge from the plurality of heating elements; and
an insulating thermal barrier positioned in the enclosure and horizontally disposed between an adjacent pair of heating elements, wherein the insulating thermal barrier thermally isolates heating elements positioned above the insulating thermal barrier from heating elements positioned below the thermally insulating barrier.
2. The apparatus according to claim 1 wherein a thermal resistance of the insulating thermal barrier is greater than about 0.0004 K*m 2 /W.
3. The apparatus according to claim 1 further comprising a cooling element disposed between the root and the weirs and separated from the forming wedge by the inner wall.
4. The apparatus according to claim 1 further comprising a plurality of insulating thermal barriers disposed between an adjacent pair of heating elements.
5. The apparatus according to claim 1 wherein the inner wall comprises segments separated by the insulating thermal barrier.
6. The apparatus according to claim 5 wherein a segment of the inner wall comprises a heating element.
7. The apparatus according to claim 1 wherein the insulating thermal barrier comprises a plurality of layers.
8. The apparatus according to claim 7 wherein the plurality of layers comprises a structural layer and an insulating layer.
9. The apparatus according to claim 1 wherein the end portions of the at least one heating element have reduced cross sectional areas relative to the center portion of the at least one heating element.
10. The apparatus according to claim 1 wherein the at least one heating element is formed from a plurality of different electrically conductive materials, wherein each of the electrically conductive materials has a different resistivity.
11. An apparatus for forming a glass sheet comprising:
a forming wedge comprising weirs at the top of the forming wedge and forming surfaces that converge to a root at the bottom of the forming wedge;
a plurality of heating elements disposed at an elevation above the root, at least one of the heating elements comprising a center portion disposed between end portions, wherein the end portions of the at least one heating element have a higher resistance than the center portion of the at least one heating element and the end portions of the at least one heating element radiate a greater amount of heat than the center portion of the at least one heating element;
an enclosure disposed about the forming wedge, the enclosure comprising an inner wall separating the forming wedge and the heating elements;
an insulating thermal barrier positioned in the enclosure and horizontally disposed between a bottom-most heating element of the plurality of heating elements and a vertically adjacent heating element, wherein the insulating thermal barrier thermally isolates the vertically adjacent heating element from the bottom-most heating element.
12. The apparatus according to claim 11 wherein the end portions of the at least one heating element have reduced cross sectional areas relative to the center portion of the at least one heating element.
13. The apparatus according to claim 11 wherein the at least one heating element is formed from a plurality of different electrically conductive materials, wherein each of the electrically conductive materials has a different resistivity.
14. The apparatus according to claim 11 further comprising a plurality of insulating thermal barriers disposed between the heating elements.
15. The apparatus according to claim 11 wherein a thermal resistance of the insulating thermal barrier is greater than about 0.0004 K*m 2 /W.
16. The apparatus according to claim 14 wherein the plurality of heating elements comprises a plurality of horizontally aligned heating elements and a plurality of vertically aligned heating elements, and wherein each of the horizontally and vertically aligned heating elements is separated from an adjacent heating element by an insulating thermal barrier.