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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
Source: www.gii.fi © Jorma Vitkala GPD
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
Source: www.gii.fi © Jorma Vitkala GPD
Quenching / Cooling Process Control
T1
T2
∆t ~ 130 °C
T1
∆t
6
Tempering stresses development
Source: www.gii.fi © Jorma Vitkala GPD
Physical principles of tempering
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
Source: www.gii.fi © Jorma Vitkala GPD
Physical principles of tempering
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
Source: www.gii.fi © Jorma Vitkala GPD
Tempering pressure
6 mm: 1000…1600 Pa3 mm: 23 000 Pa
9
∆t
∆t
6 mm
3 mm
Source: www.gii.fi © Jorma Vitkala GPD
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
Source: www.gii.fi © Jorma Vitkala GPD
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
15Source: www.gii.fi © Jorma Vitkala GPD
17
Radiation heating: First generation
Source: www.gii.fi © Jorma Vitkala GPD
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
Source: www.gii.fi © Jorma Vitkala GPD
Heat transfer in tempering furnace
Thermal conduction and internal radiation
Radiation
Radiation
Convection
Convection
Contact heat transfer
Roller
Glass
Heating glass in tempering furnace
Thermal conduction and internal radiation
Radiation
Radiation
Convection
Convection
Contact heat transfer
Roller
Glass
Heating glass in tempering furnace
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
Thermal conduction and internal radiation
Radiation
Radiation
Convection
Convection
Contact heat transfer
Roller
Glass
Heating glass in tempering furnace
23
Low-E
Source: www.gii.fi © Mikko Rantala Glaston Finland
Latest convection technology
25Source: www.gii.fi © Jorma Vitkala GPD
26
Thermal imageOne end colder
27Source: www.gii.fi © Jorma Vitkala GPD
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
Source: www.gii.fi © Jorma Vitkala GPD
Heat transfer in tempering process
30Source: www.gii.fi © Jorma Vitkala GPD
Glass tempering cooling
31Source: www.gii.fi © Jorma Vitkala GPD
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
33Source: www.gii.fi © Jorma Vitkala GPD
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
35Source: www.gii.fi © Jorma Vitkala GPD
Roller wave optical disturbion
18.3
.201
6
36Source: www.gii.fi © Jorma Vitkala GPD
Straight glass flatness
• prEN 12150-1• Over roll bow• Roller wave• Edge lift
18.3
.201
6
37Source: www.gii.fi © Jorma Vitkala GPD
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
Source: www.gii.fi © Jorma Vitkala GPD
Anisotropy, iridescence, birefringence
Glass image as seen by using polarising filtersGlass stopped at early stage of quenching
54Source: www.gii.fi © Jorma Vitkala GPD
NiS-inclusion
55Source: www.gii.fi © Jorma Vitkala GPD
Large glass needs special handling equipment -Tvitec Spain
56Summary of GPD – 2015, J.VitkalaSource: www.gpd.fi ©Tvitec