Encyclopedia of Glass Science, Technology, History, and Culture. Группа авторов. Читать онлайн. Newlib. NEWLIB.NET

Автор: Группа авторов
Издательство: John Wiley & Sons Limited
Серия:
Жанр произведения: Техническая литература
Год издания: 0
isbn: 9781118799499
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7–10 6.0 6.0 16–24 5–11 10–28 1.0 BaO 2.0 3.0 ZnO 3.0 Li2O 0–1 0–1 Na2O 11–15 12–14 8.0 0–2 13–17 1–6 4–8 23–34 K2O 0–2 0–1 0–2 1–6 0–3

      3.1 Viscosity

Viscosity as log η,η in dPa·s Process range, technological meaninga
Melting
2.0 Typical of a soda‐lime silicate glass melt at 1450 °C
3.0 Transfer to forming area Volume relaxation time is <1 s Fixpoint T(3.0) = gob temperature Bushing tip temperature for fiber productionb
Forming
4.0. Upper limit of mechanical working range Fixpoint TWP = T(4.0) = working point
6.0 Lower limit of mechanical working range The difference T(4.0) – T(6.0) is termed the “length” of a glass
Tempering, annealing, and cooling
7.6 Upper limit of macroscopic shape stability Fixpoint TL = T(7.6) = Littleton softening point
11.0c Dilatometric softening point TD Above TD, temperature gradients in a glass object no longer cause thermal stresses A related temperature level is Td = T(11.5) = deformation point Glass objects deform under own weight at rates of a few μm/h
13.0 Technical definition of the glass transition Fixpoint Tg = T(13.0) = annealing point Volume strain relaxation time is 60 s
14.5 Technical definition of ultimate transition to a rigid state Fixpoint T(14.5) = strain point Volume strain relaxation time is 30 min

      a In the earlier days of mechanical forming, empirical indicators were in use. They remain worth to be consulted as empirical guidelines when the complex feature of “workability” is to be kept constant under a compositional change; these indicators read: gob temperature, GT = 2.63·(TLTg) + TL; working range index WRI = TLTg; RMS = relative machine speed = (TL – 450)/(WRI + 80); DI = devitrification index = WRI – 160.

      b Some stonewool processes use T(1.5) as fibrization temperature.

      c Approximation, the exact value depending on the load applied by the dilatometer.

Graph depicts the viscosity–temperature relationship of different glass-forming systems. The pure metallic melts of Ag and Fe are displayed 


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