Slides from my lecture given to 2nd year students in Architecture at the University of Sheffield UK in 2007

1. Glass
Flat Glass Products and
Float Glass Manufacture
Sept 2007
Rick Mitson
Advanced Programme Manager –Pilkington

2. Float Glass Process
Continuous
ribbon of
Cooling
glass Cross
lehr
Float cutters
bath
Melting
furnace
Large plate lift- Small plate lift-
off devices off devices
Raw material
feed

3. What is a ‘glass’ ?
• ‘A supercooled liquid’ - network of silica
molecules is modified by the introduction of
larger metal atoms
• (eg. Sodium, calcium, boron, lead...).
• Most common form -
• Soda Lime Silica
• addition of other metals change the
properties

4. Soda Lime Silica
• Raw materials :
• Silica sand - SiO2 - low impurities, small particle size
• Soda Ash - Na2 CO3 - natural and synthetic grades
• Dolomite - Ca Mg CO3 - mined & crushed
• Limestone - Ca CO3 - mined & crushed
• Minor ingredients - Salt cake Na2 SO4, Aluminium, Carbon, Iron,
Cobalt, …..
SiO2 + Na2CO3 +Ca CO3 ----> 1500 deg C
(Na20)(SiO2)(CaO) + 3 CO 2

5. Flat Glass Products
• 1. Basic - Sheet glass , Float glass, Rolled glass
• Visual appearance - colour, reflection, pattern.
• 2.Safety glass - Laminated - plastic interlayer
- Toughened - pre-stressed
surfaces
• 3. Fire-resistant glass - eg. wired, special laminates.
• 4. Energy control - eg. low emissivity glass coatings,
tinted glass.

6. Basic glass - Clear Float
• Thickness
• 4mm 6mm 10mm
• Light Transmittance 90 % 88 % 87%
• Solar Energy Transmittance 85 % 82 % 78%
• Light Reflectance 8% 8% 8%
• Heat - ‘U’ value W/m2 5.8 5.7 5.6

7. Basic Glass - Tinted Float
• 4mm thickness Light Arctic
• Clear Green Blue
• Light Transmittance 90 % 80% 64%
• Solar Energy Transmittance 85 % 66% 60%
• Light Reflectance 8% 7% 6%
• Heat - ‘U’ value W/m2 5.8 5.8 5.8
• Dark Green, Grey and Bronze similar light transmittance to Arctic
Blue.

8. Fire resistant glass
• Wired glass
• On exposure to fire: glass breaks, but held in place by integral wire mesh
• Example: Pilkington Pyroshield Safety
•
• EN references: EN 572-1 (Definitions etc.), -3 (Polished wired), -6
(Wired patterned), -8 (Supplied and final cut sizes), -9 (Evaluation of
conformity)

9. Fire resistant glass
• Special intumescent laminated glass
• On exposure to fire: layers crack but are held together by the inorganic
intumescent interlayer, which is chemically compatible with glass and
bonds glass layers together
• Examples: Pilkington Pyrostop, Glaverbel Pyrobel
•
• EN references: EN ISO 12543 series (Laminated glass), prEN 14449
(Evaluation of conformity)

10. Low Emissivity Coated Glass
Pilkington Optitherm™ SN is an off-line coated glass for use
in insulating glass units and can be combined with other types of
Pilkington glass.
Pilkington Optitherm™ SN consists of Pilkington Optifloat™
which is provided with a coating on one side. Moreover it is
available as laminated Pilkington Optilam Therm™ and
toughened.
Emissivity of double glazing with low emissivity glass is now
below 1.8 W/ sq.m

11. Self Cleaning Glass
Pilkington Activ™ - same as conventional glass but with a specially
developed coating on the outside. Once exposed to daylight, the
coating chemically reacts in two ways.
Breaking down organic dirt
Using a "photocatalytic" process, the coating reacts with ultra-violet
rays present in natural daylight to break down and disintegrate
organic dirt.
Washing dirt away
The second part of the process happens when rainwater hits the glass.
The coating is "hydrophilic" which means that instead of forming
droplets, the water spreads evenly over the surface and as it runs off
takes the dirt with it. Compared with conventional glass, the water
also dries off very quickly without leaving unsightly "drying spots".

12. How is it made ?
• Basic , Clear & Tinted - Float glass process.
• Coated - On-line in float bath or off-line.
• Laminated - High pressure & temp. in autoclave
• Toughened - Heated with blasts of air in an oven
• Wired & Patterned - Glass formed between rollers

13. Basic Float Costs - 2003 UK delivered
• Raw materials 25 %
• Processing materials 4%
• Process labour 13 %
• Energy 13 %
• Packaging etc. 6%
• Overheads & admin 9%
• Depreciation 13 %
• Marketing, R&D etc. 7%
• Transport 10 %
• Costs £ 300 to 500 per tonne - depending on product

14. Float Glass Process
Continuous
ribbon of
Cooling
glass Cross
lehr
Float cutters
bath
Melting
furnace
Large plate lift- Small plate lift-
off devices off devices
Raw material
feed

15. Spain - Sagunto started up Feb. 2000

16. France Float Glass Plant
started-up November 2001
Batch Plant, Feed conveyor,
Furnace building and chimney

17. Furnace cross-section

18. Raw Material Feed to Furnace
Mixed raw material is
continuously pushed
under the front wall of
the furnace

19. Gas firing into furnace

20. Furnace cross-section

21. Float Glass Process
Continuous
ribbon of
Cooling
glass Cross
lehr
Float cutters
bath
Melting
furnace
Large plate lift- Small plate lift-
off devices off devices
Raw material
feed

22. The Float Bath
Glass Ribbon
Tin
• A bath is typically 60m long and 7m wide
• The tin is about 60mm deep
• Glass enters bath at ~ 1100°C
• Glass leaves bath as a continuous ribbon at ~600°C
• Controlled atmosphere above the glass / tin

23. Flow Over Spout
• Glass flow into bath
controlled by tweel height
• Most of glass flow off spout
goes downstream, a few
percent flows upstream
into ‘wetback’
• Glass in the wetback then
flows out to the edges of
the ribbon

24. Glass Equilibrium Thickness
Forces :
Surface Tension
Hydrostatic
(Gravitational)
At equilibrium all the forces balance
F = nett surface tension
ρg = glass density
ρt = tin density
h = 6.7mm

25. Glass thickness control

26. Thin Glass Manufacture
Top Rolls
Top Rolls:
•Control the speed of the ribbon
•Provide a transverse stretch to the ribbon
•Are used to make glass in thicknesses from 1mm to 8mm

27. Thick Glass Manufacture
Top Rolls
Fenders
Fenders:
•Restrict the spread of the ribbon
•Are used to make glass in thicknesses from 8mm to 25mm

28. On-line coating in float bath
Multi-layer coatings - including Silicon, Tin, Titanium,
Optical systems to control colour in reflection

29. Float Glass Process
Continuous
ribbon of
Cooling
glass Cross
lehr
Float cutters
bath
Melting
furnace
Large plate lift- Small plate lift-
off devices off devices
Raw material
feed

30. Cooling Lehr - Annealing Furnace
• Controlled cooling to avoid internal stress.
• Radiant and convective cooling by air
• Edges stress control by additional heating
• Distortion of polarised light shows stress
levels in glass

31. Glass cutting for market
• Standard glass ribbon width in Europe - 3210 mm
• Largest standard plate size 6000 x 3210 mm - Jumbo plate
• Other standard plates 2800 mm to 3200 mm - Lehr End Sizes
• Some float lines cut small sizes less than 3210 mm wide and
less than 2800 mm long.

32. Glass stacking onto pallets
Large plate stacker Pallet loaded with special grab

33. Storage
Single ‘Standard endcap’
Endcaps should be to
an agreed design and
have been tested and
10 approved by Group
This is unstable MI
Single ‘standard endcaps’
are unstable unless the height
1 is less than 1.5 times the
depth
Ground should be clean and level

34. Manning
Safety Zones
Keep clear of the danger zone!

35. Manning
Keep clear of the
danger zone
Remember
as you lift the
zone gets bigger

36. Glass Transport
• Western Europe - Float lines product mainly
Jumbos and LES sizes.
• Economic transport distance 200km to 600km.
• Processing plants located closer to final customers.
• UK Float lines: 3 Pilkington, St.Helens, Lancashire
• 1 St.Gobain, Eggborough, Yorks.
• 1 Guardian, Hull, Yorks.

37. Global* Flat Glass Capacity and Utilisation
Available Capacity Demand Capacity Utilisation
50 105%
100%
40
95%
Mn Tonnes
30
90%
85%
20
80%
10
75%
0 70%
1999 2000 2001 2002 2003 2004 2005 2006
Estimate Estimate
Calendar Year
Global utilisation continues to tighten
* Worldwide including China

38. Float Glass Process
Continuous
ribbon of
Cooling
glass Cross
lehr
Float cutters
bath
Melting
furnace
Large plate lift- Small plate lift-
off devices off devices
Raw material
feed

39. Glass References
www.pilkington.com
Pilkington Technical Advisory Service
Groupement Europeen des Producteurs de Verre Plat -
info@gepvp.be