Glass Manufacturing Process
The procedure adopted in the manufacture of glass may broadly be divided into the following five
stages.
1. Collection of Raw Materials
Depending upon the type of glass to be manufactured, suitable raw materials are collected. Table 141 shows the raw materials required for each type of glass.
Notwithstanding the unrefined components, the cullet and decolourisers are additionally added for
each kind of glass.
The cullet demonstrates squander glass or bits of broken glass. They increment the fusibility of glass
and forestall loss of soluble base by volatisation during the response in shaping new glass. They
additionally decrease the expense.
The unrefined components for the most part contain hints of the iron mixtures. The ferrous oxide
confers a green tone to glass and ferric oxide bestows an extremely light yellow color. To keep away
from such impacts, the decolourisers are added. The typical substances utilized as decolourisers are
antimony oxide (Sb2O3), arsenic oxide (AS2O3), cobalt oxide (CoO), manganese dioxide (MnO2) and
nickel oxide (NiO).
2. Preparation of Batch
The raw materials, cullet and decolouriser are finely powdered in grinding machines. These
substances are correctly weighed in correct proportions earlier than they are combined together. The
blending of these materials is accomplished in mixing machines until a uniform aggregate is acquired.
Such a uniform combination is known as the batch or frit and it's far taken for further process of
melting in a furnace.
3. Melting in Furnace
The batch is melted either in a pot furnace or in a tank furnace. The heating is sustained till the
evolution of carbon dioxide, oxygen, sulphur dioxide and different gases stops.
(i) Pot Furnace
In this furnace, the pots are adopted as units. A typical glass melting pot is shown in fig. 14-1.
A pot is a vessel made of hearth-clay. This procedure resembles the crucible metal system. These pots
are positioned in mainly prepared holes inside the furnace. The charging and accumulating doorways
are saved projecting out of doors in order that raw materials may be delivered and molten glass can
be taken out with ease.
The pots are packed with uncooked substances. The furnace is heated through producer gasoline.
When the mass has melted down, it's miles removed from the pot and it's miles taken for the
subsequent operation of fabrication. The melting of glass via pot furnace is an intermittent process. It
is used to soften small quantities of glass at a time or to put together special styles of glass.
(ii) Tank Furnace
This furnace resembles the reverberatory furnace adopted for puddling of the wrought-iron. Fig. 14-2
indicates the phase of a tank furnace followed for the melting of glass. It is constructed with
strengthened masonry. The roof is given unique form to deflect the flames of heated gas.
The ports are furnished for the access of preheated manufacturer fuel. The doors are furnished for
charging and for getting rid of the molten glass. A bridge separates the tank into unequal
compartments.
The batch is heated in huge compartment and it incorporates truly impure glass. It flows thru
commencing of bridge into small compartment. The gall or floating impurities are gathered at the top
of huge compartment. The refractory lining is furnished to the interior surface of tank.
The tank is full of raw materials. The furnace is heated via permitting manufacturer gasoline via ports.
The charging of raw substances and taking out of molten mass are simultaneous. This is a non-stop
technique and it's far followed to melt large quantities of glass at a time.
4. Fabrication
The molten glass is given suitable shape or form in this stage. It can either be done by hand or by
machine. The hand fabrication is adopted for small scale production and machine fabrication is
adopted for large scale production.
Following are the different ways of fabrication
(i) Blowing
For this reason, a blow-pipe is used. Its diameter is ready 12 mm and its period is about 1.Eighty m.
One quit of the blow-pipe is dipped within the molten mass of glass and a lump of about 50 N weight
is taken out. This lump of glass will then lengthen to some extent via its very own weight.
The operator then blows vigorously from other cease of blow pipe. It can also be carried out with the
assist of an air compressor. This blowing reasons the molten mass to count on the shape of a cylinder.
It is then heated for few seconds and is blown once more. The blowing and heating are persisted until
the cylinder of required length is shaped. It is then placed on an iron plate and it is disconnected from
blow pipe. The cylinder is then reduce vertically by way of a diamond. It falls into a skinny plate by
using gravity.
(ii) Casting
The molten glass is poured in moulds and it's miles allowed to calm down slowly. The huge pieces of
glass of simple design may be organized by this technique. It is likewise followed to prepare mirrors,
lenses, and so on.
(iii) Drawing
This procedure consists in truely pulling the molten glass either by hand or by mechanical gadget. An
iron bar is dipped sideways in the molten mass of glass. It is lifted up horizontally and in doing so, it
catches up a sheet of molten glass. This sheet is then allowed to bypass over a huge rotating roller.
The roller enables the molten glass to spread in the shape of a thin sheet.
(iv) Pressing
In this technique, the molten glass is pressed into moulds. The pressure may additionally both be
applied through hand or by using mechanical means. This procedure is followed for decorative articles,
hole glass articles and so on.
(v) Rolling
There are techniques of rolling. In one method, the molten mass of glass is surpassed between heavy
iron rollers and flat glass plate of uniform thickness is received. In every other approach, the molten
mass of glass is poured on a flat iron casting desk and it's far then became flat with the useful
resource of a heavy iron curler.
(vi) Spinning
In this manner, the molten glass is spun at high pace by means of a machine to shape very fine glass
fibres. This glass has tensile energy identical to that of mild steel. It does not fade, decay or decrease.
It isn't attacked by means of acids, fireplace and vermins. It is very smooth and flexible. It is used for
supplying insulation towards warmth, electricity and sound.
5. Annealing
The glass articles, after being manufactured, are to be cooled down slowly and steadily. This method
of gradual and homogeneous cooling of glass articles is known as the annealing of glass.
The annealing of glass is a totally critical process. If glass articles are allowed to cool down rapidly, the
superficial layer of glass cools down first as glass is a horrific conductor of warmth. The indoors
element stays relatively hot and it is therefore in a state of stress. Hence, such glass articles break to
pieces under very mild shocks or disturbances.
Following are the two methods of annealing
(i) Flue Treatment
In this method, a long flue is provided and it's miles constructed in the sort of way that there may be
gradual lower in temperature from one end of flue to the alternative. The crimson-warm articles of
glass are allowed to enter at the recent end of flue and they may be slowly moved on travelling bands.
They emerge as cool when they reach the cool give up of flue. This approach is useful for big scale
production.
(ii) Oven Treatment
In this approach, the pink-hot glass articles are located in ovens in which arrangement is made to
govern the temperature. After articles are located within the ovens, the temperature is slowly added
down. This approach is beneficial for small scale manufacturing.