Mr. Jorma Vitkala GPD Chairman [email protected] +358

Mr. Jorma VitkalaGPD Chairman

[email protected]+358 40 553 2042

Tempering process

2

∆t

Source: www.gii.fi © Jorma Vitkala GPD

Annealed vs. tempered glass

3Source: www.gii.fi © Jorma Vitkala GPD

4

Physical principles of temperingGlass is amorphous material, no fixed melting or freezing pointThermal expansion is not linear


Physical principles of tempering

5

Thermal contraction in transition range during cooling depends on cooling power

temperature

fast cooling

slow cooling

volume

surface

mid plate


Quenching / Cooling Process Control

T1

T2

∆t ~ 130 °C

T1

∆t

6

Tempering stresses development



Glass is heated up to 600…640 °C While heated to the transition range (~600 °C)• molecular structure starts to loosen• viscosity changes quickly• volume grows → density decreases

Fast cooling• surface cools quickly and solidifies• center cools slower, continues to contract, harder

surface resists the contraction of center• result is: surface in compression,

center in tension

7

tension

compression

glas

s th

ickn

ess

surface

mid plate



In quenching, glass is cooled down from 630°C to about 500°Cso that temperature difference between glass surface andmid-layer is about 120°C.

8

0

100

200

300

400

500

600

700

0 2 4 6 8 10 12 14 16 18 20

Time (s)

Tem

pera

ture

(C)

MIDPLATE

SURFACE

TEMPERATURE DIFFERENCE

QUENCHING COOLING


Tempering pressure

6 mm: 1000…1600 Pa3 mm: 23 000 Pa

9

∆t

∆t

6 mm

3 mm


Glass Tempering Process –Stress During Cooling

10

Temperature distribution Stress distribution

t = 3 mm , T0 = 630°C, h = 700 W/m2K

0

100

200

300

400

500

600

700

-1.5 -1 -0.5 0 0.5 1 1.5

T / °

C

z / mm

0 s

0.5 s

3 s

5 s

10 s

TG

-100

-80

-60

-40

-20

0

20

40

60

-1.5 -1 -0.5 0 0.5 1 1.5

/ M

Pa

z / mm

0 s

0.5 s

3 s

5 s

10 s

TG

(Aronen A., 2014)

Source: Antti Aronen TUT

Temperature and stress distributions during cooling. Glass thickness is 3 mm, T0 is 650 °C and h is 600 W/m2K. (Aronen A., Modelling of Deformations and Stresses in Glass Tempering, Dissertation, 2012)

-100

-80

-60

-40

-20

0

20

40

60

-1.5 -1 -0.5 0 0.5 1 1.5

/ M

Pa

z / mm

0 s

0.5 s

3 s

5 s

10 s

TG

11Source: Antti Aronen TUT

Quenching / Cooling Process Control

T1

T2

∆t ~ 130 °C

T1

∆t

12

Tempering stresses development


18.3

.201

6

14

Calculation of Strains and Stresses

Iteration of T, k, cp, S

Iteration of Tf,

Calculation of , G, K, th

Calculation of

),()()( xTSxTTk

xtTTcpg

Iteration of 0, , z

tTx

tTx

TRHt

fref

11exp tt

tttTttTtT

i

fiifi

tTCtT fi

n

iif

1

ttTtTttTtTt gffglth

t

dttt0

''

i

n

ii

twGGGtG11

10 exp

i

n

ii

twKKKtK21

20 exp

t

kkijij

t thkk

ij

ij

dtdt

ttd

ttG

dtdt

ttdttK

t

0

0

´´

3'

')´(2

´´

'3')´(

2

2

,h

h

Ndztz

2

2

,h

h

Mzdztz

zyx 0

1,

2,1 coscoscoscos

cos44

2121

11,,,,

),(kjki

ji xLaxLaxaxa

Lam

mjibjib

mimimimi

mi

eeeee

TTFTTFxTS

0zPlane stress

Source: Antti Aronen TUT

Heating and cooling times


17

Radiation heating: First generation


Combination radiation/forced convection – 2nd generation

• Air jets inside furnace to control equal heat transfer on both sides of glass• Necessity with low-e coatings• Helpful with all glasses 20


Heat transfer in tempering furnace

Thermal conduction and internal radiation

Radiation

Radiation

Convection

Convection

Contact heat transfer

Roller

Glass

Heating glass in tempering furnace


Radiation

Radiation

Convection

Convection


Roller

Glass


Low-E

Low-E glass heating

0 50 100 150 200 250 300

1Thickness

Tem perature (C )

B ottom

C lear g lass 4m m Low -e g lass 4m m

No forced convection

Tim e-step is 5 seconds

Top

22

Balanced heating from both sides can be achieved with convection

Source: www.gii.fi © Mikko Rantala Glaston Finland

Balanced heating from both sides can be achieved with convection

0 5 0 1 0 0 1 5 0 2 0 0 2 5 0 3 0 0 3 5 0 4 0 0

1Thickness

T e m p e r a t u r e ( C )

B o t to m

C le a r g la s s 4 m m L o w - e g la s s 4 m mF o r c e d c o n v e c t io n

t o p : 6 5 W /m 2 C , 1 0 0 W /m 2 Cb o tt o m : 5 0 W /m 2 C

T im e - s te p is 5 s e c o n d s

T o pWith forcedconvection


Radiation

Radiation

Convection

Convection


Roller

Glass


23

Low-E

Source: www.gii.fi © Mikko Rantala Glaston Finland

Latest convection technology


26

Thermal imageOne end colder


Thermal image

Longitudinal gaps cause hot spots in other glasses

direction of travelSource: www.gii.fi © Jorma Vitkala GPD

Heat treatment of glass in tempering

29

top surface

bottom surface

∆t

∆t


Heat transfer in tempering process


Glass tempering cooling


Cooling air jets Discharging flow

Forced convection on glass surface

Heat flux between air and glass plate depends on:

• Cooling pressure

• Nozzle diameter, shape

• Nozzle to plate distance

• Nozzle to nozzle spacing

• Air removal

32Source: www.gii.fi © Mikko Rantala Glaston Finland

Cooling glass in tempering

Thermal conduction

Radiation

Radiation

Convection

Convection

Roller

Glass

20C

20C30 – 60C

30 - 60C

Temperaturedistributions

roller roller


Fragmentation test

• EN 12150-1• Fragment sizes are proportional

to in-glass tenstion• Fragment is conted 50 x 50 mm²

area

18.3

.201

6


Roller wave optical disturbion

18.3

.201

6


Straight glass flatness

• prEN 12150-1• Over roll bow• Roller wave• Edge lift

18.3

.201

6


EDGE KINK – FRAME EFFECT

• Reason:• Edges overheat the

coating starts to bend the glass

• How to fix it:1) By using individual heater

profile or convection profile (less heat for the edges or less convection for the edges) it is possible to reduce the length wise edge kink. Leading and tailing edges can be controlled by shortening heating time.

2) Shorter heating time3) Lower temperature

44

BURNED COATING

• Reason• Overheating• Too high temperature at the

beginning of heating cycle

• How to fix it• Decrease the temperature

and/or heating time• Heater profile (less heat at

the edges of the glass)• Convection profile to

prevent burning on edges

45

FLATNESS

• Bi-stable glass• This means that glass can be

bended either way by just pressing it

• Reason behind this is that center of glass has heated slower than edges and thus the glass has different stress levels between center and edge

• In specially edge deleted thin low-e production it is very crusial that tempering line is able to control the heat between center and edges accurately and that this power can be adjusted. 46

WHITE HAZE – LENSE EFFECT

47

• Lens mark in the middle is caused by same effect as “white haze”

• The glass is not heated up evenly from top and bottom

• When bottom side is heating faster than top, the glass bends upwards in furnace and this creates a lens mark to coating

• Too low convection • Low-e coating is designed to

reflect radiation and for this reason top convection system is needed

• If the top convection system in not accurate or powerful enough glass will always have lens mark in the middle

FLATNESS

• Overall flatness• To gain the best overall

flatness top and bottom surface needs to have same stress level

• In low-e production this is more challenging as the coated side reflects also the cooling effect

• Independent nozzle control helps to get best overall flatness in low-e production

48

Roller wave + edge kink

Glass optical issues

50

GPD

Nav

i 201

4 D

ubai

Gla

ston

Gen

uine

Car

e

52

Quality monitoring systems

SCANNER GLASTON QUALITY MANAGEMENT REPORT

Anisotropy

53

tempered glassthe stress distributionof the differencesaccentuated lightingpolarization


Anisotropy, iridescence, birefringence

Glass image as seen by using polarising filtersGlass stopped at early stage of quenching


NiS-inclusion


Large glass needs special handling equipment -Tvitec Spain

56Summary of GPD – 2015, J.VitkalaSource: www.gpd.fi ©Tvitec

57

Thank you

[email protected]+358 40 5532042

Documents

Mr. Jorma Vitkala GPD Chairman [email protected] +358