Forming V.M. Sglavo – GlassEng - UNITN 2017 · SCHOTT Technical Glasses, 2007 1 – silica 2 –...

V.M. Sglavo – GlassEng - UNITN 2017



Forming

glass:liquidgviscousliquidgsolid

T1/viscosity

working range104 - 107.6 P

1Pas=10PηH2O@25°C=10-2P=1cP

Conventional definitions:

hard & soft glass ÷ ΔT for soda-lime silicate glass

long & short glass (ΔT vs. Δη)




Viscosity

SCHOTT Technical Glasses, 2007

1–silica2–aluminosilicate3–borosilicate4–sodaborosilicate5–soda-limesilicate6–soda-leadsilicate7–leadsilicate

short & long glasses




Viscosity

short & long glasses

€

η =η0 exp QRT#

$ % %

&

' ( (

3

Ceramics and Glasses, Engineered Materials Handbook, vol. 4, ASM international, USA, 2000

Glass science, R. H. Doremus, J. Wiley & Sons, 1994




soda-lime silicate glass

-workingpoint η=103Pas; forming,moulding-softeningpoint η=106.6Pas =lowunderitsownload-annealingpoint η=1012Pas stressesremovedinfewminutes-strainpoint η=1013.5Pas stressesremovedinfewhours;coolingwithoutstresses

log 1

0

Introduction to glass science and technology, J. E. Shelby, The Royal Society of Chemistry, 1997SCHOTT Technical Glasses, 2007




Dilatometric analysis

P = 1 N

l

Δl/l0 vs. T

Δl

Monothonic heating (dT/dt = costant)

Tf

sample

Introduction to glass science and technology, J. E. Shelby, The Royal Society of Chemistry, 1997




DSC analysis

Tg




Viscosity-composition

Silicate glasses

- silica: Tg = 1060-1200°C

- alkaline oxides � η reduction and melt brittleness (non-bridging oxygens)

- alkaline-earth oxides ÷ alkaline oxides � η increase

- PbO � η reduction

- B2O3 � η reduction




Visco-elasticbehaviour

elastic strain viscous strain

τ = G γ τ = η

dvdx

xL = tanγ ≈ γ

dvdx =

ddx

dydt

!

" #

$

% & =

ddt

dydx!

" #

$

% & =

ddtγ

τ = ηdγdt

glassatlowtemperatureglassathightemperature

elasticmodulusviscosity

“Newton’slaw”

Vetri, G. Scarinci, T. Toninato e B. Locardi, Casa Editrice Ambrosiana, 1977




Mix model (Burger)

G1

γ =

τ0G1

+τ0G2

1− e−G2η2

t%

&

' '

(

)

* * +

τ0η3

t

γ1 γ2 γ3

t=0


t=t0

elasticrecovery

retardedelasticrecovery

glassatintermediatetemperature...

-elastic(reversible)-elastic“retarded”(reversible)-viscous(irreversible)

observeddeformations:

viscousfrictionamongmolecules

deform

ation

time




glassatintermediatetemperatures...

onlyviscousterm(T≥Tg)η≈108P,G≈30GPa�tdelay≈3x10-4s

onlyelasticterm(roomtemperature)η≈1014P,G≈30GPa�tdelay≈330s

soda-lime silicate glass


time

deform

ation increasing

temperature

tdelay=η/G

formingtime

Forming V.M. Sglavo – GlassEng - UNITN 2017 · SCHOTT Technical Glasses, 2007 1 – silica 2 –...

Documents

Transcript of Forming V.M. Sglavo – GlassEng - UNITN 2017 · SCHOTT Technical Glasses, 2007 1 – silica 2 –...