Viscosity

Question 1

What’s the Vogel-Eulcher eqn?

Answer 1

lnN = A = B/(T - Td)

Question 2

What happens when T = Td in the Vogel eqn?

Answer 2

~ N (viscosity) = infinity, elastic solid

Question 3

What are the demarcation temperatures?

Answer 3

1. working point: 1E3 (Pa*s), viscosity where glass is easily shaped
2. softening point: 4E6 (Pa*s), viscosity at which a glass fiber will elongate under its own weight at 1 mm/min
3. annealing point: 1E12 (Pa*s), viscosity where stresses in the glass can be relieved in 15 in
4. strain point: 3.2E13 (Pa*s), viscosity at wich stresses in glass can be relieved in 6 hours

Question 4

What are long and short glasses?

Answer 4

~ long: broad temp range w/ which the glass can be worked (lead silicate)
~ short: solidifies quickly, good for high-speed automated manufacturing (e-glass)