Teaching goals glass processing - ETH Z...• TS:TG≈3:2 • melt: glass≈ 3:1 • Strongly...

||Institute for Building Materials

Science and engineering of glass and natural stone in construction

Glass processingF. Wittel

1


Teaching goals glass processing:

You will

… recall sheet glass manufacturing processes and get insights into tricky problems

…understand how viscosity – expansion – temperature relations determine processing

…see how prince Rupert drops explode and understand why thermal processing is essential

… will understand crucial steps in processing such as toughening or bending

… get not know novel processing technologies for glass


Short vs. long glasses

TSP

1011.3 dPaꞏs Deformation point,TD

105 dPaꞏs Flow point

TG

short long

Vogel-Fulcher-Tamman-Hesse (Williams-Landels-Ferry in polymers). VFT for TG<T

0VF

B

T Te

Vogel temperature TVF~(TG-50)

TVF


A. Angell (1985)

strong

fragile (non-Arrhenius)

Fragile vs strong glasses


Forming of sheet glass: Methods


Sheet glass production in casting process


Sheet glass production in drawing processes

Cor

ning

-Dow

n-D

raw

-Pro

cess


21 12 2(1 )D raw

mv d L const

t

Incompressible when drawn

L L

Uniaxial stress state

1 2 0V L d d

V L L L

(incompressible)

Cross section is transformed in an affine way.

Sheet glass production in drawing processes


Glass forming: Glass bricks


Hot fracture:4800

1000

2

crit

crit crit

MPa

T K

dv

Cutter:3

2

3,

2

2

cutcrit

critcrit cut

v

d

dv

2 2( ) ( )2

Pv x d x

L

2 maxmax 2

2( 0)

2

L vPv v x d P

L d

Laminar plate flow (Hagen-Poiseuille):

Shear stress: max max

2;

v P Px d v

x L L d


cutter

Free flow Holding of gob




800°C 900°C 1000°C

Cooling due to contact with the mold. hot melts easily flow into corners.

Sticking to the mold when going below certain temperatures. Oil-water emulsion for mold release.


||Institute for Building Materials 400°C

800°C

1200°C

Mold casting is press-forming under self-weight has to be fast.

Chill ripples due to cooling at the mold contacts. warmers volumes overtake.

Glass forming: Glass bricks / casting


Additive methods for 3D printig based on extrusion

http://www.micron3dp.com

Fused filament fabrication (FFF= continuous layers are extruded that fues in theviscouse state bevor the next layer is printed

https://3dprint.com/187824/glass-3d-printing-evolution/


Additive manufacturing crabwise

KIT: Stereolithograpy (SLA) of a glasssuspension with subsequent pyrolysisand sintering steps.

Lawrence Livermore National Laboratory: direct printing of a glass suspension with subsequent pyrolysis and sintering.


Sheet glass manufacturing in flow glass process



Batch house:



Furnace:


Sheet glass manufacturing




Film flow:dm

v d Ldt

,m ax

2 22

,m ax32

cos1 ;

2

h

h h

v

g d xv v v

d

2 3

32

cos

3

3 /

cos

dm g d L

dt

dm dtd

g L

4R e

d v

4-25 laminar1000-2000laminar with ripples

>2000 turbulent



1 2 12( )spP Spreading pressure:

Sn = 6.5g/cm3 = 100°glass= 2.4g/cm3 = 0.3 N/m

0 .356 2 .063

2 (1 cos )

0 .73

glass Sneq

glass Sn glass

cm

dg

cm

Psp>0: spreading; Psp=0: ddeq;Psp<0: contraction



Adjustment of glass thickness:

Equilibrium thickness: 7.3mm

Edge roller:1-12 mm

Fender:4-24mm



Sources for O2: glass and leakagesSolubility in Sn: 630, 95, 5 ppm at 1000, 800, 600 °C

Source for S: glass batch





Cooling: Heat expansionDilatation curves for determining heat expansion coefficientsSlopes are evaluated through a temperature interval, for example 20-300°CDIN-52334 specimen 5x5x50mm, temperature rates 5K/minLarge region of heat expansion coefficients for glasses 0-35 e-6 1/K


Cooling: Heat expansion




Rule of thumb:• TS:TG≈3:2• melt:glass ≈ 3:1• Strongly expanding glasses have low TG

Glass type aL in10-6 K-1

SiO2-TiO2 glass 0.0

Quarz glass 0.54

Borax glass 3.3

Soda-Limeglass

9.4

Lead glass 7



Relation between thermal expansion and chemical composition of glass is rather linear.

Linear model can be used:

pn percentage of weight of each constituent

kn constants

High expansion factors of sodium oxide point at low thermal resistance of soda-lime glass.

3 n nk p

Oxide constant Oxide constant

SiO2 15 MgO 135

Al2O3 52 CaO 489

ZrO2 69 ZnO 21

Na2O 1296 BaO 520

K2O 1170

Adjustment of glass properties: Heat expansion

Values factored by 109 for clarity.


Cooling: Elastic PropertiesEstimation of elastic properties E, , G, K ±2GPa (following Mackenzie):

j V°(j)[cm3/mol]

U°(j)[GPA]

y(j)[-]

x(j)[-]

V°(j)ꞏx(j)[cm3/mol]

U°(j)ꞏy(j)[MPA]

SiO2 28 64.5 0.717 0.709 19.859 45746

TiO2 29.2 86.7 0.001 0.001 0.030 88

ZrO2 30.2 97.1

Al2O3 42.8 134 0.012 0.007 0.307 960

B2O3 41.6 77.8

P2O5 69.6 62.8

MgO 15.2 83.7 0.042 0.062 0.936 5157

CaO 18.8 64.9 0.067 0.071 1.341 4628

BaO 26.2 40.6

ZnO 15.8 41.5

PbO 23.4 17.6

Li2O 16 80.4

Na2O 22.4 37.3 0.149 0.143 3.21 5346

K2O 37.6 23.4 0.004 0.002 0.09 56

S 25.773 61981

3

1

123 .723

Mj j

j

cmm ol

j jj

V x M

y M

1 .086o

oM

Vv

V

67312

0 .2780 .5 0 .244

438233(1 2 )

270552(1 )

o o

o

E v U M Pa

vEK M Pa

EG M Pa


Elastic constants change at glass transition temperature

In the Visco-elastic regime, elastic constants depend on frequency. (US-measurements?)

Above TD the Poisson ratio is 0.5 (Incompressibility condition)

Cooling: Elastic Properties


Cooling: Thermally induced stress

Heat conductivity of glass 0.9-1.2W/(mK) rather low

High temperature gradients result

Perfect deformation constraint:

Estimate with geometry factor fgeo for spheres (2/3), rods (1/2) or plates (1):

Above TD s0

1

T E

Material property=0.9MPaK-1 Soda-lime glass

1geo

T Ef


Cooling: Glass sheet (1D case)

Heat transport:

T

d/2-d/2x

2

0 2T

T Tq

t x

Boundary condition:

0T t q const

inside

2

( 0, ) ( )

( , ) ( )c

ds

T x t T t

T x t T t

Cooling scenario:

1. Constant cooling rate:

2. Cooling in a stationary bath:

3. Quenching:

0( 0 )T t T

, ,T G las T M edium

sT const T

Thermal diffusivity=0.003-0.004 cm2/sSoda-Lime glass T

pc


T

d/2-d/2x

20

0 2TT

qT Tq T const

t x

Parabolic T-profile:

(Symmetry condition)

220( )

2cT

q d xT x T

d

2( )T x ax bx c

Case 1: constantcooling rate

102 ( ) (2 )Ta T x q

0b ( 0) cc T x T

20

2( )8

ds c

T

q dT T x T

Temperature profile

Surface temperature



T

d/2-d/2x

m ax

2

( ) 4 ( )c c s

T

xT x T T T

d

Average temperature:

20

m ax 8c sT

q dT T T

2 202 1

3 30

2( )

24

d

c s cT

q dT T x dx T T T

d

Case 1: constantcooling rate

2m ax3s sT T T T



T [°C]

d/2-d/2x

, ,

0( ) ; ( 0 ) ;T glass T flu id

flu id g lassT x T T t T

Temperature profile:2 2

0( , ) ( )4 4

d dx xT x t T T T erf erf

t t

Case 2: Static bath

0( ) ( )4

s

dT t T T T erf

t

20( ) 2 ( )

4

d

cT t T T T erft

Surface temperature:

Core temperature:

2( ) 1 exp( 4 / )erf x x

Boundary condition:



d/2-d/2

2

10

( ) 4 1sin ( ) exp( )

2 1 2s

Ts

T x T dx t

T T

Temperature profile:

(2 1)

d

Case 3: Quenching

T [°C] withAverage Temperature:

2

2210

8 1exp( )

2 1s

Ts

T Tt

T T

Sort term boundary value:

Long term boundary value:

0 2

81 T

s s

tT T T T

d

2

0 2 2

22

2

8exp

12 exp

Ts s

Ts T

tT T T T

d

tq T T d

d



Low-stress cooling0 .91

EC

0.3(12 )T

C

Useful estimate for soda-lime glass:

200.3surface q d

MPa/K

MPaꞏmin/(Kꞏcm2)

in MPa, q0 inꞏK/min, d in cmResidual stress:

( ) ( )1Ex T T x

Maximaum temerature difference at constant q:2

m ax / (8 )T q d

Residual stress after cooling at constant q:

2

2

81

0 .6

resd qE

d q

res in MPa, q0 inꞏK/min, d in cm

Quality criterion<0.2-2MPa


Thermo-mechanic properties of soda-lime glass

Porperty Value / unit

a Heat expansion coefficient 9∙10-6 K-1

E Young’s modulus 70GPa

s Surface stress 0.34 N/m

n Poisson’s number 0.225

l Heat conductivity 1.3 W/(mK)

r density 2.5 g/cm3

cp Heat capacity 1.3 J/(gK)

b Thermal conductivity (=l/r∙cp) 0.004 cm2/s

TG Glass temperature 550 °C

T14.5 Lower cooling point 520 °C

TD Dillatometric softening point 610 °C

b Depth of surface defects 10 mm


Low-stress cooling

TStart [°C] TFinal[°C] q [K/min] Time [min]

Phase 1heating

300 560 10.8 24.1

Phase 2refining

560 560 0 25

Phase 31st Cooling phase

560 533 -1.1 24.7

Phase 42nd Cooling phase

533 483 -2.2 23.1

Phase 5quenching

483 80 -10.8 37.3

Heating all products to a uniform temperature. qmax must not be exceeded.

Minimization of temperature gradients. Required time Tmax=res/C

Cooling down to T<TG TG-30K with the calculated rate q1

Cooling 50K further (or to T14.5-40K) with 2∙q1

Quick cooling down to the temperature, where a static bath in the environment does not exceed qmax.

Example: =10-6K-1; TG=550°C; =0.003cm2/s; d=1cm; res=2MPa




Glass processing: Technical pre-stressing



Property Toughened safety glass Heat-strengthened glass

Surface compressivestress

100-160 MPa 40-60 MPa

Tensile core stress 50-80 MPa 20-30 MPa

Bending strength (5% fractile)

120 MPa 70 MPa

Allowed sigma 509 MPa 29 MPa

Fracture pattern Small fragments ~1cm2 Larger fractures similar to float glass




Uniform heating to the macroscopic Form stability limit TL=T(7,6) ≈720-750°C

Quenching down to T<TG in ~ 30 seconds







Quenching patterns under certain light conditions visible.

Is part of tempered glass and not a fault.

Patterns emerge by uneven blowing.



Glass processing: Bending of glass


Sag-bending process Press-bending process

Affect on optical properties

Heating to 650°C.Deformation in-between 2 molds.High geometric reproducibility.Large deformations possible.Can be combined with tempering.

Glass processing: Bending of glass


Hungerburgbahn Stop Innsbruck


Vakko Fashion Center Istanbul


Glass processing: Glass cutting


Glass processing: glass cutting with Laser

OWCT: Zero-Width Cutting Technology

• Precise energy input, that leads to crack in cutting direction

• Edge cracks and chipping is avoided Perfect surface quality

• Debonding at microscopic scale

• Small energy for engraving, labeling, drilling…

OWCT

Cutting wheel

Laser drilling


Glass processing: glass cutting with Laser

OWCT

Laser drilling

Laser cuttingLaser engraving


Notch significantly reduces strength


ICc

I

Ka

aYw



• Small gap, glass dust penetrates an avoids closing stress

• Compaction of glass network by pressure stress

• Stress is released by lateral cracks

• Breaking has to be done, while stresses support fracture

• Wetting with water or oil

• Residual stress fractures deviate



Glass processing: Glass cutting by water jet cutting

• Jet nozzle 0.1-0.6mm diameter fine jet

• Ejection at 4000 bar, 1000m/s with abrasive

• Cutting of arbitrary shapes in thick laminated glass

• Often instead of drilling

• Good surface quality


Glass processing: Edge processing

• Cutting leads to damaged surfaces reduces strength in edge zones.

• Edge defects lead to failure of tempered glass.

• For almost all applications finishing treatment of edges needed. automatized

• Corundum / diamond tools.

broken

sanded

polished


Glass processing: Glass edges DIN 1249-11Type Abrevi

ationDescription Drawing

broken KG Raw unfinished glass edge with sharp edges and Wallner’s lines.

edged KGS Broken one with sanded edges

Sanded KMG Sanded to required dimensions. Conchoidal fractures allowed.

Fine-sanded KGN Sanded to required dimensions.

polished KPO Sanded to required dimensions and polished.


Glass processing: Grinding / Abrading Materials

Mineral Hardness (Mohr)

Absolute hardness

Vicker’s hardeness [HV]

Corundum 9 1000 2060

Diamond 10 140.000 10.060

Silicion carbide 9 2600

Soda-lime glass 6-7 400

• Grinding materials rip out small parts from the glass T

• Cooling needed

• Corundum, silicon-carbide, diamond in different graining 40-400 (sieve number = grid mesh/ inch)

• Always bound with clay, polymers, rubbers or metals


Glass processing: grinding and polishing

Essential process for mirror production in the former days

Automatization in grinding and polishing lines like the Twin-process (continuous process)

Abrasives: Quartz sand (SiO2), corundum (Al2O3), silicon carbide (SiC)

Polishing aids: Polishing rouge (Fe2O3), diamond, pumice flower, cork, zinc oxide, cerium oxide


Glass processing: Drilling

• Drilling is grinding into the depth

• Coolants like water, petroleum, turpentine

• Drilling bits with grinding materials

• Diamond tools (hollow drill, drilling bit, segmented drill)

• Laser drilling / water jet drilling


Teaching goals glass processing:

You will

… recall sheet glass manufacturing processes and get insights into tricky problems

…understand how viscosity – expansion – temperature relations determine processing

…see how prince Rupert drops explode and understand why thermal processing is essential

… will understand crucial steps in processing such as toughening or bending

… get not know novel processing technologies for glass


Thank you for your attention.

09.09.2013 67

Date post:	08-Nov-2020
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Teaching goals glass processing - ETH Z...• TS:TG≈3:2 • melt: glass≈ 3:1 • Strongly...

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