GLASS INDUSTRY INFORMATION

HISTORY

- It has been around since at least 5000 BC when glass making was discovered by accident when
the heat from fires melted the basic ingredients of glass together.
- Naturally occurring glass such as obsidian had been used by people before they learned how to
make glass. Obsidian was used to produce knives, arrowheads, jewelry, and money.
- About 3500 BC, man-made glass was used in glazing clay pots and for making vases.
- According to archaeological evidence, the first man-made glass was found in Eastern
Mesopotamia and Egypt around 3500 BC. About 1500 BC, the first glass vessels were made. For
300 years, the glass industry increased rapidly, and then declined. It was revived in 700 BC,
Mesopotamia and in 500 BC, Egypt.
- During the last century BC, Syrian craftsmen invented the glass forming technique called
glassblowing. The technique can also be called as blow pipe. This discovery made the glass
production cheaper, easier, and faster.
- Glass production flourished in the Roman Empire and spread to all other countries under its
rule.
- In 1000 AD, the Egyptian city of Alexandria was the most important center of glass production.
- By the time of Crusades, the glass production was developed in Venice and became the
glassmaking center in the western world.
- In the 13th and 14th centuries, the art of making stained glass on churches and cathedrals across
Europe became popular. Examples are the Chatres and Conterbury cathedral windows.
- In 1765, “crystal glass” production became a new era in glass industry
- In the early 1800s, crown glass was in great demand.
- In the 1820s, the age of blowing bottles, flasks, and glasses was ended by the invention of hand-
operated machines.
- In the 1870s, the first semi-automatic bottle machine was introduced.
- After 1890, manufacturing developments and applications of glass industry increased very
rapidly.
- In 1903, Michael Owens, engineered the first automatic bottle blowing machine. It could
produce millions of light bulbs a day and could produce 2500 bottles per hour
- In the 1960s, Sir Alastair Pilkington invented the “float” method of glass making which
revolutionized the industry. He had the idea in early 1950s, but it took seven years of hard work
to prove he was right.

DEFINITION

- Glass is from all-natural sustainable raw materials.

- Glass is commonly called as “soda-lime” glass. Containers made of glass are commonly made
with a combination of various oxides or oxygen-based compounds.
- Chemically, “glass is a super cooled liquid formed from the union of non-volatile inorganic
oxides resulting from the decomposition and fusing of alkali and alkaline earth compounds, sand
and other constituents, ending in a product with random atomic structure.
- Properties of glass: sterile when new, hard and smooth surface (thus easy to clean), odorless,
impermeable to odors, vapors, steam, gases, and liquids., inert, non-toxic, some are
transparent, brittle, heavy
- Glass is not a solid, not a gas, and not also a liquid. It is classified as a rigid liquid. It maintains
liquid properties while acting like a solid. With the application of certain amount of heat, it can
return to its liquid and workable form. This makes the glass easy to reuse and recycle.
- “A glass is by definition a liquid at all temperatures. Compositionally, a typical glass consists of
the network formers or glass formers, fluxes or alkaline metals, and the network modifying
alkaline earths (PbO, CaO, BaO)”
- Principle Raw Materials of Glass Industry:
a. Silica sand (Glass sand) (SiO2) – of all the materials, sand is the hardest to melt. It is the
backbone of the glassy phase. It must be almost pure quartz. The iron content must also be
low since it produces color in glass. In the Philippines, it is usually mined in Palawan.
b. Sodium carbonate (soda ash) (Na 2O) – it is a fluxing agent – gives fluidity and lowers the
melting point of the silica sand. It also causes the finished glass to be water soluble which is
not desirable in glass making. It is usually found in the ash of certain plants but now it is
derived from table salt. In the Philippines’ Glass Industry, soda ash is usually imported from
Europe, Japan, & Europe.
c. Dolomite (limestone) (CaO٠MgO٠2CO2) – it is the source of lime and it improves the
homogeneity of the glass. It also speeds up the solidification and cooling of the glass. It is
also the source of magnesium oxide (MgO), which decreases the viscosity of glass, reduces
the devitrification temperature (devitrification is the crystallization of glass molecules), and
improves thermal resistance.
d. Feldspar (calcium alumina) (CaAl2O3٠6SiO2) - Al2O3 is a refractory material that gives
durability to the glass. It also increases the viscosity and the workability of the melt.
Feldspars are also additional sources of SiO2 and fluxing agents.
e. Cullet – it is also called recycled glass. It is plant generated, recycled or processed and its
current average use is about 37%. It improves furnace efficiency and helps saving energy
consumption. Cullet usually undergoes a process to remove non-glass contaminants and to
create size uniformity. Some of these contaminants are labels, aluminum caps, and non-
magnetic metal.
- Minor Ingredients: (table)
a. Gypsum and Saltcake – used as fining agents and sources of SO 2 gas and Na2O or CaO
b. Iron Pyrite – used as a coloring agent – source of iron and sulfur in amber
c. Iron Chromite – used as a coloring agent to produce emerald green glass
d. Cobalt Oxide – used as a coloring agent to produce blue glass and a decolorizing agent in
flint
e. Sodium nitrate – oxidizes iron to make it less noticeable n the finished glass
f. Selenium – decolorizes colored contaminants
g. Arsenic trioxide – it facilitates the removal of bubbles
h. Nickel oxide – it is used to give grey tinted glasses
- Kinds of glass
a. Soda-lime glass – most common variety of glass, which the main components are soda ash,
limestone, and silica. Widely used for the manufacturing of bottle containers, window
panes, tableware, and bulbs. It does not melt at high temperatures. The least expensive
form of glass.
b. Lead glass – made up of lead oxide (at least 20% of the batch), silica and alkali. It is used for
optical products because of its high refraction and dispersion. Its high refractive index gives
a brilliance that may be exploited by cutting. Its surface is cut into decorative patterns to
reflect light thus can be called cut glass. It is also favored for electrical applications because
of its excellent insulating properties. Examples of electrical applications are light bulbs and
neon lights. This glass is brittle because it cannot withstand high temperature or sudden
changes in temperature. This glass is also called as lead crystal glass because lead oxide is
used as flux in crystal glasses.
c. Borosilicate glass – any silicate glass that contains 5% boric oxide in its composition. it has
excellent resistance to temperature, chemical corrosion, shocks, and electricity. It expands
very little when heated thus it does not crack immediately on strong heating. It is not that
convenient to fabricate unlike soda-lime or lead glass. This glass is best for scientific
glassware and oven ware. It is also called Pyrex glass. Borosilicate glass shouldn’t be
recycled because of its high resistance to heat thus it is difficult to melt with the silica san
and other raw materials.
d. Aluminosilicate glass or Alumina-silica glass – has high concentration of aluminum oxide in
its total composition. it has greater chemical durability and can withstand higher operating
temperatures compared to borosilicate glass. It is also more difficult to fabricate than
borosilicate glass. It can be used as resistors for electronic circuitry if coated with an
electrically conductive film.
e. Ninety-six percent silica glass – a borosilicate glass, melted and formed by conventional
means. It is then processed to remove all the non-silicate elements from the batch. The
resulting pores are consolidated when reheated to 1200˚C. It is a type of glass that can resist
heat shock up to 900˚C. It is used for industrial items such as furnace sight glasses and for
outer windows on space vehicles where the glass must withstand the heat of reentry into
earth’s atmosphere.
f. Fused silica glass – consists simply of silica in the non-crystalline or amorphous state. The
difficulty of its fabrication makes it very expensive of all glasses and number of available
shapes is limited. It has the maximum resistance to heat shock. The highest allowable
operating temperature is 900˚C for longer periods and 1200˚C for shorter periods. It is
restricted to applications such as astronomical telescopes, optical waveguides and crucibles
for growing crystals.
g. Special glasses – have the same components as the ones above mentioned but with some
chemicals are added depending on the purpose of the glass. The following are some
examples of special glasses:
 Colored glass – the choice of the metallic oxide to be added is determined by the
desired color because different metallic oxides give different colors to the glass. It is
used for decorating walls, making sunglasses, and for making light signals for
automobiles, trains and aero planes. This type of glass is in demand.
 Glass-ceramics – they begin their existence as glasses then are converted into
dense, fine-grained crystalline ceramics. Special glass-ceramics with high
temperature resistance and qualities make it machinable with ordinary
metalworking tools. It is the material that is chosen for the shuttle’s tile retainers.
- MANUFACTURING PROCESS

Glass Industry has many products thus wide and important applications. The products of this
industry can be found almost everywhere. It can be found from households to markets,
industrial spaces, and even applications for space craft. It is one of the most sustainable
materials ever produced in the world thus recycling and reusing are remarkable processes of
this industry.

Common products of the glass industry are flat glass, container glass, and pressed & blown
glass. The manufacturing process of these products are almost the same except for the forming
and finishing. Flat glass can be formed by float process, drawing process, or rolling process.
While container glass and pressed & blown glass are formed by using press method, press &
blow method, or blow & blow method. These products are usually a soda-lime type of glass and
it constitutes a greater percentage of total glass production.

The following definitions are commonly found in Glass Industry:

a. Float Process – It is invented by Sir Alastair Pilkington which produces clear, tinted and
coated glass for buildings, and clear and tinted glass for vehicles. Before, it can only
manufacture 6mm thick glass, but because of innovations and research, it can already
manufacture glass as this as 0.4mm and as thick as 25mm. It uses a molten tin bath which
the molten glass floats on it, spreads out and forms a level surface.
b. Press and Blow Method – this method is applied for producing wide neck packaging or
containers. This is done by shaping the parison by pressing the glass against a blank mold
with the metal plunger.
c. Blow and Blow method – this method is applied for producing narrow thick neck walled
packaging or containers. This is done by forming the parison by compressing air.
d. Drawing Processes
 Danner process – glass flows from a furnace forehearth in the form of a ribbon
 Vello Process – glass flows from a furnace forehearth into a bowl which is then
shaped

There are other processes for manufacturing glass industries. Some of those are preserved from
the 19th century methods but already enhanced. Some glasses are made with semi-automatic
equipment and some are still made by mouth-blown manufacturing and even hand-painted by
artists. The above-mentioned processes are the processes which are commonly used today by
small, medium, and large glass manufacturing plants.
 The following flowchart and step by step process show the manufacturing of glass containers or
bottles:

predetermined quantities of silica sand, soda ash, limestone and feldspar are
blended in a mixer
cullet is added to hasten the process.
the mied raw materials are brought to the batch house or batch bin for
temporary storage.
BATCHING the mixed batch is conveyed and charged into a furnace - a continuous melting
tank by means of a batch charger

the furnace is made up of a special kind of cement resistant to glass corossion

and high temperature
heated to 1500˚C
heating takes place 9-14 days
MELTING
all batch materials in the furnace are melted and refined

from the other end of the furnace, molten glass is drawn out into forehearths
the temperature in forehearths are lowered to 1200˚C
the molten glass is fed to the bottle forming machine by the feeder
FORMING the formed bottle will be taken out by an automatic holder into the moving table

the bottles are heated above a critical temperature and gradually cooled to room
temperature
ANNEALING

this process allows bottles to be printed wit ceramic labels by means of a

stenciling machine
the decorated bottles are made to pass through decorating lehrs where
temperature is high enough to enable the label to fuse into the bottle
DECORATING after going through the lehrs, the bottles are cooled down to room temperature
once cooled, they are sorted out, inspected, and packed for delivery
The first step, BATCHING, is where the raw materials measured and mixed. The second step, MELTING, it
is where the mixed raw materials are melted at a very high temperature. On the third step, FORMING or
can be also called SHAPING, this is where the molten glass is drawn out into forehearths where the
temperature is lower than the furnace. This is when the molten glass becomes more viscous, having a
pseduoplastic behavior. This molten glass is fed to the bottle forming machine by a feeder. This feeder
has a plunger and a shear which assists in the flow of the molten glass. the molten glass is then pushed
by the plunger to the opening with the size controlled by the shear. This will automatically cut the
molten glass into a gob. At last, the gob is delivered through a metal guide into the bottle forming
machines. This machine consists of 6 independent section machines. This means that they work
independently and do not affect others if they have defects. The following list is the steps undergone by
the formation of the bottles in the IS machines:

1. Gob is fed into the blank mold which starts the formation of the bottle in an inverted postion;
2. A plunger in the settle blow drops from the top whereupon compressed air forces the glassijnto
the finished form of the mouth;
3. The mold is closed on top and air is injected in the counter blow through the newly formed
mouth forming the parison, a partly formed bottle;
4. The parison is transferred to the blow mold in an uptight position;
5. The bottle is finally blown to its final form;
6. The formed bottle is taken out by an automatic holder into the moving table;
7. Each machine can produce 30-70 bottles per minute. In the stacker, the bottles are arranged
side by side, moving after one another in preparation for the annealing process.

For the fourth step, ANNEALING, it is technically heating and gradually cooling the bottles. The purpose
of this is to allow the molecules composing the glass to realign themselves. The bottles were formed out
by forces which results to the disarrangement of the molecules. Annealing helps to strenghten the
bottles to be less brittle. Gradually cooling the bottles to room temperature prevents thermal shicks and
residual strains. Lastly, DECORATING. This is only optional when the company or the customer wants it
to be decorated or labelled. Ceramic labels are applied into bottles by means of a stenciling machine.
After the labels are applied, the bottles pass through decorating lehrs which have a temperature high
enough to fuse the label into the bottle. After, the bottles are cooled and ready to be sorted out,
inspected and packed for delivery.
The following flowchart and step-by-step process show the manufacturing of float glass:

CUTTING
RAW MATERIALS
ANNEALING
UNLEADING

CULLET MIXING FORMING

INSPECTION

MELTING REFINING
PACKING

SHIPPING

Silica sand, soda ash, dolomite, limestone, feldspar and other raw materials needed are proportionally
weighed and mixed. The mixed batch with the cullet is conveyed to the silo tanks, ready for the feeding
into the furnace. The process melting is where the raw materials are fused into molten glass at a
temperature of 1500˚C to 1600˚C using bunker fuel oil. A bunker oil is a type of liquid fuel which is
fractionally distilled from crude oil. Glass Forming or also called Float Process is where the molten glass
at a temperature between 1100˚C to 1150˚C is formed over a molten tin bath. It is to produce a
distortion. After forming the molten glass, the now semi-rigid glass passes through the Lehr Chamber for
removing undesired strains in the glass to produce a strong and well-balanced annealed Flat Glass.
Annealing can be called as controlled cooling. After the annealing process, the Flat Glass is thoroughly
washed, and it is then inspected of its quality and cut into desired sizes and shapes. The finished Flat
Glasses are then packaged for distribution. Float glass is usually sold only in square meters.

Float glass cannot be easily distorted because of its precise surface flatness which provides excellent
through-vision lenses. Its surface is naturally fire-finished which is shows sparkling and brilliant luster
than sheet glass or polished plate glass.

Clear float glass has many applications. One of which is the architectural glass – exterior and interior
window and door openings – are just some of the applications used in the architectural world. It is also
used as curtain walls and showcase windows. They can be found in home furniture like tabletops and
dressers.
Different treatments or additions to float glass’ properties are also existing. One example is the heat
treatment in which float glass is heated to around 650˚C to produce toughened glass or commonly
known as tempered glass. after heating the float glass to such temperature, it is then quenched with air
jets so that the surfaces are cooled quickly, and the core more slowly. Tempered glass is used in safety
glazing in buildings.