Horizontal non-contact slumping of flat glass

Abstract

This paper continues the work of M. Akilian and A. Husseini on developing a noncontact glass slumping/shaping process. The shift from vertical slumping to horizontal slumping is implemented and various technologies required for the horizontal slumping process are developed. In the horizontal slumping process, a thin sheet of glass is placed in between two horizontal ceramic air bearings with a bearing to glass gap of about 50 pm, and the assembly is heated up to 600*C. The glass is unconstrained in the horizontal plane and must be positioned without any solid contact. Specifically, the technologies developed are: an optical distance sensor for positioning of the glass, glass position control via air bearing fluid shear force and tilt of device, and device mechanisms for operation in 600*C. Glass was slumped horizontally with bearing-to-glass gaps of >50 [mu]m, 36±2.5 pm, and 30.5±2.5 [mu]m. The best flatness achieved was 6.7/3.6+0.5 [mu]m for front/back of the glass sheet, with a gap of 36+2.5 [mu]pm. It was discovered that 600*C is hotter than necessary and that 550*C is still too hot for optimal slumping conditions. In addition, an important shift is made from using an oven, which heats the entire device, to using in-line pipe heaters, which supply heated air. This allows for much quicker heating and cooling times, which decreases slumping time to less than 30 minutes (10 minutes heating, 5 minutes slumping, 10 minutes cooling).