Glass can be produced through either float glass or glass blowing processes. The float glass process involves melting raw materials and allowing the molten glass to float on molten tin, where it cools and is cut. The glass blowing process uses a furnace to melt glass feedstock, after which a gob of molten glass is formed using press-and-blow or blow-and-blow techniques, producing parisons that are blown into molds. Both processes include annealing to strengthen the glass. Inspection and packaging occur after shaping to ensure quality.

1. GLASS
INDUSTRIES
Prepared by :
Al Christian G. Bohol

2. GLASS
■ Non-crystalline amorphous solid that is often
transparent and has a widespread practical,
technological and decorative usage.

3. Glasses that occur Naturally
 obsidian (volcanic silicate glass)
 fulgurites (sand that has been vitrified by a
lightning strike)
 moldavite - green natural glass likely
resulting from meteorite impacts

4. TYPES OF GLASSES

5. Soda glass or soda-lime glass
■ most common
■ is prepared by heating sodium carbonate and
silica.
■ used for making windowpanes, tableware,
bottles and bulbs.

6. Colored glass
■ in demand
■ Small amounts of metallic oxides are mixed
with the hot molten mixture of sand, sodium
carbonate and limestone.
■ used for decorating walls, making
sunglasses, and for making light signals for
automobiles, trains and aeroplanes.

7. Plate glass
■ thicker than ordinary glass
■ has a very smooth surface
■ made by floating a layer of molten glass over
a layer of molten tin
■ used in shop windows and doors.

8. Safety glass
■ shatterproof glass
■ made by placing a sheet of plastic such as celluloid
between sheets of glass.The special quality of this
glass is that in case of breakage the broken pieces
stick to the plastic and do not fly off.
■ used in automobiles & for making bulletproof
screens.

9. Laminated glass
■ bulletproof glass
■ Several layers of safety
glass are bound together
with a transparent
adhesive.The larger the
number of layers used the
greater is the strength of
the glass.
■ stronger than safety glass.
■ used in aeroplanes and
windshields of cars.

10. Optical glass
■ flint glass
■ softer than any other glass
■ Potassium and lead
silicates are used in making
optical glass
■ The main use is in the
manufacture of lenses,
prisms and other optical
instruments.

11. Pyrex glass
■ borosilicate glass
■ highly heat resistant
■ In pyrex glass some of the silica is replaced by boron
oxide. Boron oxide expands very little when heated,
thus, pyrex glass does not crack on strong heating.
■ Uses: Laboratory equipment and ovenware

12. Photo-chromatic glass
■ acquires a darker shade when exposed to bright light
and returns to its original lighter shade in dim light.
■ .This happens because silver iodide is added to this
glass. (silver iodide gets coloured with the intensity
of light.)

13. Lead crystal glass
■ cut glass
■ has high refractive index, and so has the maximum brilliance. It
sparkles and is used for high quality art objects and for
expensive glassware.
■ that it is brittle. It cracks when subjected to sudden changes of
temperature.
■ it is cooled very slowly to prevent brittleness.The process in
which a finished glass article is cooled slowly is called
annealing.

14. PRODUCTION OF
GLASS BY MELTING

15. Production of glass involves
four steps:
■ Batching
■ Batch melting
■ Fining
■ Homogenization

16. Batching
■ It involves selection of raw
materials, calculation of the
concentration of each material,
weighing and mixing powders and
occasionally liquids.

17. Batch Melting
■ Involves the deposition of raw
materials to form the initial melt, and
control the temperature and
atmosphere during the time of
formation of liquid.

18. Finning
■ The removal of bubbles by either bubble rise
or bubble absorption.
■ Bubble rise is assisted by formation of large
bubbles during batch deposition, by low melt
viscosity, and by proper particle sizes for
batch components.
■ Special chemicals, fining agents are often
added to batches to promote fining.

19. Homogenization
■ It requires elimination of heterogeneities
inherent in the producing a melt from the
large variety of components with widely
different properties.
■ Gross defects such as bubbles, seed and
stones are often clearly visible and results to
rejection of most commercial glass .
■ The terms striae and cord are used to
describe variation in local composition in the
glass.

20. ■ Striae – two dimensiona regions, or layers, of
a composition different from the bulk.
■ Cord – are similar regions which are
effectively on dimensional veins in the glass.
■ These region are often detected by visual
observation.
■ Zebra board method is a method use for
detection of optical/visual distortions due to
striae and cord.

21. MANUFACTURING
OF GLASS

22. Two types of Processes
 Float Glass Process
 the Pilkington process (named after the British
glass manufacturer Sir Alastair Pilkington) which
pioneered the technique in the 1950s. It is the
process in which glass is made in sheets.
 Glass Blowing Process
 the process of shaping a mass of molten or
softened glass into a vessel, shape, etc, by
blowing air into it through a tube

23. FOR FLOAT GLASS
PROCESS

24. Stage 1- Melting & Refining
Fine grained ingredients closely controlled for quality, are mixed to make a batch, which flows into the furnace,
which is heated up to 1500 degree Celsius.The raw materials that go into the manufacturing of clear float glass
are:
■ SiO2 – Silica Sand
■ Na2O – Sodium Oxide from SodaAsh
■ CaO – Calcium oxide from Limestone
■ MgO – Dolomite
■ AlSi3O8 – Feldspar
The above raw materials primarily mixed in batch helps to make clear glass. If certain metal oxides are mixed to
this batch they impart colors to the glass giving it a body tint. For e.g.
■ NiO & CoO – to give grey tinted glasses (Oxides of Nickel & Cobalt)
■ SeO – to give Bronze tinted glasses (oxide of Selenium)
■ Fe2O3 –To give Green tinted glasses (oxides of iron which at times is also present as impurity in Silica
Sand)
■ CoO –To give blue tinted glass (oxides of Cobalt)
Apart from the above basic raw material, broken glass aka cullet, is added to the mixture to the tune of nearly
25% ~ 30% which acts primarily as flux.The flux in a batch helps in reducing the melting point of the batch thus
reducing the energy consumed to carry out the process.

25. Stage 2 - Float Bath
■ Glass from the furnace gently flows
over the refractory spout on to the
mirror-like surface of molten tin,
starting at 1100 deg Celsius and leaving
the float bath as solid ribbon at 600 deg
Celsius.

26. Stage 3 - Coating (for making
reflective glasses)
■ Coatings that make profound changes in optical
properties can be applied by advanced high
temperature technology to the cooling ribbon of
glass. Online ChemicalVapour Deposition (CVD) is
the most significant advance in the float process
since it was invented. CVD can be used to lay down a
variety of coatings, a few microns thick, for reflect
visible and infra-red radiance for instance. Multiple
coatings can be deposited in the few seconds
available as the glass flows beneath the coater (e.g.
Sunergy)

27. Stage 4 – Annealing
■ Despite the tranquillity with which the glass
is formed, considerable stresses are
developed in the ribbon as the glass cools.
The glass is made to move through the
annealing lehr where such internal stresses
are removed, as the glass is cooled gradually,
to make the glass more prone to cutting.

28. Stage 5 – Inspection
■ To ensure the highest quality inspection takes place
at every stage. Occasionally a bubble that is not
removed during refining, a sand grain that refuses to
melt or a tremor in the tin puts ripples in the glass
ribbon. Automated online inspection does two
things. It reveals process faults upstream that can be
corrected. And it enables computers downstream to
steer round the flaws. Inspection technology now
allows 100 million inspections per second to be made
across the ribbon, locating flaws the unaided eye
would be unable to see.

29. Stage 6 - Cutting to Order
■ Diamond steels trim off selvedge – stressed
edges- and cut ribbon to size dictated by the
computer. Glass is finally sold only in square
meters.

30. The Float Glass Process

31. FOR GLASS
BLOWING
PROCESS

32. Hot End Processes
■ which typically employ high amounts of heat to
produce and shape a glass container.
■ A furnace is first used to mold molten glass, which
fed to the furnace as glass feed stock. Once the stock
has been fed into the furnace, temperatures inside
can be as high as 1675 degrees Fahrenheit. Next, one
of two method forming methods is applied: press-
and-blow or blow-and-blow.

33. Press-and-Blow
■ is the more commonly used method in glass-container production.
■ When the molten glass reaches between 1050 and 1200 degrees
Celsius it is said to be in its plastic stage, and it is during this phase
that press-and-blow formation begins.A shearing blade is used to
cut and shape the glass into a cylindrical shape, called a gob.The
cut gob falls, and using gravitational force, rolls through the
appropriate passage to reach the moulds. A metal plunger presses
the gob into the blank mold, where it assumes the mould’s shape
and is then termed a parison. Next, the parison is moved into a
final mold, where it is blown into the mould to assume its final
dimensions.This process is typically used for wide-mouthed glass
containers, but can also be used to manufacture thin-necked
bottles.

34. Blow-and-Blow
■ The gob is forced into the blank mould using
compressed air to push the gob into place.The gob,
now a parison, is then flipped into a corresponding
final mould where it is blown again, to form the
interior side of the glass container. Glass bottles of
varying neck thickness can be made using blow-and-
blow formation.
■ A gob is a specific amount of molten glass, which is
eventually formed into a glasscontainer.

35. Annealing
■ heat (metal or glass) and allow it to cool
slowly, in order to remove internal
stresses and toughen it.

36. Cold End Process
■ At this stage in glass production, the bottles or glass
containers are inspected and packaged. Inspection is
often done by a combination of automated and
mechanical inspection, to ensure the integrity of the
final product. Common faults include checks (cracks
in the glass) and stones (pieces of the furnace that
melt off and are subsequently worked into the final
container), which are important to catch because
they can compromise the component. Packaging
methods will vary from factory to factory depending
on the specific type of bottle and the size of the
production run.

37. The Glass Blowing Process