Glass forming sheet drawing

Glass, machine drawn A flat glass sheet formed by drawing. See also Glass, float. 

The amorphous PEN resin pellets are first dried at 180 °C and then extruded at 290-300 °C through a die, formed into a sheet, which is then followed by a two-step orientation (forward draw and sideway draw process) just above the glass transition temperature (Tg) (>120°C). After the orientation process, the PEN film is conveyed between rollers at 210-220 °C to induce crystallization. At the end of the orientation and crystallization process, the film is cut and rolled into widths and lengths to suit individual customers [14-16], Two of the process used to produce such films are shown in Figure 10.3. 

Viscoelasticity is the phenomenon of time-dependent strain. Often, it is also referied to as anelasticity. Glassy materials, above the glass transition temperature show Newtonian viscosity, i.e. the stress is proportional to the strain rate. This property is exploited in the drawing of fiber and sheet forms. We can write, in terms of normal stresses and strains. 

Drawing is used to form long glass pieces that have a constant cross section, such as sheet, rod, tubing, and fibers. 

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