Method of thermally drawing structured sheets
A method of drawing a material into sheet form includes forming a preform comprising at least one material as a large aspect ratio block wherein a first transverse dimension of the preform is much greater than a second transverse dimension substantially perpendicular to the first transverse dimension. A furnace having substantially linearly opposed heating elements one spaced from the other is provided and the heating elements are energized to apply heat to the preform to create a negative thermal gradient from an exterior surface along the first transverse dimension of the preform inward toward a central plane of the preform. The preform is drawn in such a manner that the material substantially maintains its first transverse dimension and deforms across its second transverse dimension.
1. A method of drawing a material into sheet form, the method comprising the steps of:
providing a preform comprising at least one material wherein a first transverse dimension of the preform is greater than a second transverse dimension that is substantially perpendicular to the first transverse dimension, the preform also having a third dimension that is substantially perpendicular to the first and second transverse dimensions and defining a pulling direction;
providing a furnace having at least one heating element on at least one side of the furnace;
energizing the at least one heating element to apply heat to the preform, without the at least one heating element physically contacting the preform, only along an exterior surface of the first transverse dimension to create a thermal gradient of decreasing temperature from the exterior surface inward along the second transverse dimension toward a plane of the preform, wherein the at least one heating element creates approximately uniform temperature distribution along the first transverse dimension;
feeding the preform into the furnace; and
drawing, by pulling in the pulling direction, the preform in such a manner that the material does not substantially deform across its first transverse dimension and deforms across its second transverse dimension while stretching the preform in the third dimension.
2. The method of claim 1 , further comprising preheating the at least one material before the at least one material enters a hottest zone of the furnace and further heating the at least one material after it leaves said hottest zone to gradually bring said at least one material to a lower temperature.
3. The method of claim 1 , wherein heating is applied approximately symmetrically along the second transverse dimension.
4. The method of claim 1 , wherein the at least one material comprises at least one of a thermoplastic polymer, any type of glass, amorphous materials that can be stretched when heated, and metals.
5. The method of claim 1 , wherein the preform comprises two or more materials with similar thermal and mechanical properties.
6. The method of claim 1 , wherein the step of providing a preform comprises providing a first block comprising a first material and embedding in the first block a second block of a second material; wherein, upon completion of the drawing step, the sheet form comprises layers corresponding to said first and second materials.
7. The method of claim 1 , wherein the step of providing a preform comprises providing a first block comprising a first material and embedding in the first block parallel layers of different materials or identical materials with different dopants; wherein, upon completion of the drawing step, the sheet form comprises layers corresponding to said first material and said different materials or identical materials with different dopants.
8. The method of claim 1 , wherein the step of providing a preform comprises providing a first block comprising a first material and embedding in the first block a plurality of vertically aligned secondary material elements centered on a vertical axis of the preform; wherein, upon completion of the drawing step, the sheet form comprises layers corresponding to said first material and said plurality of vertically aligned secondary material elements.
9. The method of claim 1 , wherein the step of providing a preform comprises providing a first block comprising a first material and embedding in the first block a plurality of parallel aligned secondary material elements; wherein, upon completion of the drawing step, the sheet form comprises layers corresponding to said first material and said plurality of parallel aligned secondary material elements.
10. The method of claim 1 , wherein the first transverse dimension of the preform is at least 1.5 times greater than the second transverse dimension.
11. The method of claim 1 , wherein the first transverse dimension of the preform is at least five times greater than the second transverse dimension.
12. The method of claim 1 , wherein the first transverse dimension of the preform is at least ten times greater than the second transverse dimension.
13. The method of claim 1 , wherein the step of providing a furnace comprises providing a plurality of heating elements on one, or both, sides of the furnace, wherein the plurality of heating elements are along opposite exterior surfaces of the first transverse dimension to create a temperature gradient in one direction inward from one of the exterior surfaces along the second transverse dimension towards a plane of the preform that is larger than a temperature gradient in another direction inward from the opposing exterior surface along the second transverse dimension towards the plane of the preform to cause asymmetric drawing.
14. The method of claim 1 , wherein the first transverse dimension of the preform is at least one thousand times greater than the second transverse dimension.