Methods and apparatus for forming a glass ribbon
A roll forming apparatus includes at least one forming roll being spaced from a forming body to define a gap. The forming roll includes a working zone portion having a working zone surface with a length extending along a rotation axis of the forming roll and a thermal resistance boundary extending at an acute angle relative to the rotation axis. In further examples, methods include the step of feeding a stream of molten glass through the gap to form a glass ribbon including a formed thickness. The thermal resistance boundary facilitates substantial uniform radial expansion of the working zone surface relative to the rotation axis across the length of the working zone surface in response to heating of the working zone portion by the molten glass.
1. A method of forming a glass ribbon with at least one forming roll and a forming body spaced to define a glass forming gap between the forming roll and forming body, wherein the forming roll comprises a working zone portion comprising a working zone surface including a length extending along a rotation axis of the forming roll, wherein the working zone portion is defined by a first thermal resistance boundary extending at a first acute angle relative to the rotation axis of the forming roll and a second thermal resistance boundary extending at a second acute angle relative to the rotation axis of the forming roll, and the first acute angle and the second acute angle face away from one another in opposite directions of the rotation axis, the method comprising:
supplying a stream of molten glass; and
feeding the stream of molten glass through the gap to form a glass ribbon including a formed thickness, wherein the first thermal resistance boundary and the second thermal resistance boundary facilitate substantial uniform radial expansion of the working zone surface relative to the rotation axis across the length of the working zone surface in response to heating of the working zone portion by the molten glass
wherein the working zone portion comprises a circumferential dovetail portion that includes a trapezoidal cross-sectional portion flared in a radial direction extending away from the rotation axis of the forming roll, and the circumferential dovetail portion is defined by the first thermal resistance boundary and the second thermal resistance boundary.
2. The method of claim 1 , wherein the working zone portion comprises a frustoconical end surface defined by the first thermal resistance boundary.
3. The method of claim 1 , further comprising cooling the forming roll with a fluid.
4. The method of claim 3 , wherein the cooling of the forming roll includes flowing the fluid through a cooling passage extending along the rotation axis of the forming roll.
5. The method of claim 3 , wherein the cooling of the forming roll includes flowing the fluid against an internal central portion of the forming roll to facilitate substantial uniform expansion of the working zone surface across the length of the working zone surface in response to heating of the working zone portion by the molten glass.
6. The method of claim 1 , further comprising directing heat to outer peripheral edges of the working zone portion to facilitate substantial uniform expansion of the working zone surface across the length of the working zone surface in response to heating of the working zone portion by the molten glass.
7. The method of claim 1 , wherein the first acute angle is from about 30° to about 60°.
8. The method of claim 1 , wherein the first thermal resistance boundary extends between the working zone surface and the rotation axis.
9. A method of forming a glass ribbon with at least one forming roll and a forming body spaced to define a glass forming gap between the forming roll and forming body, wherein the forming roll comprises a working zone portion comprising a working zone surface including a length extending along a rotation axis of the forming roll, wherein the working zone portion comprises a circumferential dovetail portion that includes a trapezoidal cross-sectional portion flared in a radial direction extending away from the rotation axis of the forming roll, and the circumferential dovetail portion is defined by a first thermal resistance boundary and a second thermal resistance boundary, the method comprising:
supplying a stream of molten glass; and
feeding the stream of molten glass through the gap to form a glass ribbon including a formed thickness, wherein the first thermal resistance boundary and the second thermal resistance boundary facilitate substantial uniform radial expansion of the working zone surface relative to the rotation axis across the length of the working zone surface in response to heating of the working zone portion by the molten glass.
10. The method of claim 9 , wherein the working zone portion comprises a frustoconical end surface defined by the first thermal resistance boundary.
11. The method of claim 9 , further comprising cooling the forming roll with a fluid.
12. The method of claim 11 , wherein the cooling of the forming roll includes flowing the fluid through a cooling passage extending along the rotation axis of the forming roll.
13. The method of claim 11 , wherein the cooling of the forming roll includes flowing the fluid against an internal central portion of the forming roll to facilitate substantial uniform expansion of the working zone surface across the length of the working zone surface in response to heating of the working zone portion by the molten glass.
14. The method of claim 9 , further comprising directing heat to outer peripheral edges of the working zone portion to facilitate substantial uniform expansion of the working zone surface across the length of the working zone surface in response to heating of the working zone portion by the molten glass.
15. The method of claim 9 , wherein the first thermal resistance boundary extends at a first acute angle relative to the rotation axis of the forming roll.
16. The method of claim 15 , wherein the first acute angle is from about 30° to about 60°.
17. The method of claim 9 , wherein the first thermal resistance boundary extends between the working zone surface and the rotation axis.