Many companies are looking at the glass industry as their next big market. Sir Alastair Pilkington is the founder of the float glass manufacturing process that quickly became the universal method for producing high-quality flat glass.In India, float glass is typically manufactured using natural gas as the fuel source for the melting furnace. The raw materials used to make float glass include silica sand, soda ash, limestone, and dolomite. These materials are mixed together in the correct proportions and then fed into the melting furnace, where they are heated to a temperature of around 1500 degrees Celsius.
Did you know? Glass can take 1 million years to decompose, making it one of the longest-lasting man-made materials. It can be recycled over and over again.
History of Glass Manufacturing
Until the 1960s, flat glass was produced using sheet and plate manufacturing. These methods were labour-intensive and costly. The surfaces were marked in the plating process since there was glass-to-roller contact. They had to be grounded and polished to bring optical perfection to the finished product.
What is Float glass?
Float glass, commonly known as flat glass, is a highly smooth, distortion-free glass made by floating molten glass on a bed of molten tin. It gives the glass a uniform thickness and a flat surface.
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Raw Materials Required for Glass Manufacturing
Glass manufacturing is a highly energy-intensive industry. Following are the various raw materials used in float glass manufacturing:
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Silica
The primary ingredient in glass making is “sand”, accounting for 60% of a batch. The sand should contain 95-99% silica, which makes up 75% of the Earth’s crust and is relatively inexpensive and readily available. However, the main characteristic of silica is that it is difficult to melt.
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Flux
The high melting point of silica results in the consumption of more energy. To reduce this and protect the furnace, which is also made of silica, a component called flux in the form of soda ash is used.
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Stabilisers
Once silica, together with soda ash, is melted, we get glass. But the resulting component has poor resistance. Thus stabilisers like lime, magnesia and alumina are added to give chemical and mechanical strength to the glass.
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Refining Agent
We use a refining agent called sodium sulphate to remove the carbon dioxide (CO2) from the raw materials. This is done to ensure that the final glass does not contain any CO2 in the form of bubbles.
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Cullet
The glass itself is also an invaluable ingredient. Broken glass pieces called cullets are recovered from the manufacturing process and then crushed before being added to the batch. This will accelerate the melting process and reduce the energy required for melting by 20%.
Different Areas of the Float Glass Factory
Glass and in particular glass manufacturing is an age-old process. Who, how or when glass was discovered is still a mystery to this day.
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Batch
The batch area is where raw materials are received, mixed in the right proportion and delivered to the furnace.
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Furnace
The raw materials are melted in the furnace at a temperature of around 2000 °F and then sent to the float bath.
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Float
In this area, there is a molten tin bath on top of which the glass is made. A top roller machine is used to get the required thickness and width.
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Lehr
This is the area where annealing and cooling of the glass take place.
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Cold End
This is the final stage where the glass is checked, cut to different dimensions and stacked.
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Steps in Float Glass Manufacturing Process
In a standard industrial glass manufacturing process, materials are stored in huge silos and include sand, soda ash, limestone and often iron and carbon.
Step-1: Melting and Refining
All raw materials are fed into a furnace. Natural gas burned in preheated combustion air heats the batch to 2800 °F. Once heated, the batch materials melt and change from semi-molten to molten glass. Melting, refining and homogenizing take place within separate zones of the furnace. Processes within the furnaces are managed from the control room to ensure that the glass is homogeneous and free of bubbles.
Inside the furnace, heat is applied to alternate sides in 15-minute cycles. This assists fuel efficiency by ensuring that combustion takes place in the presence of preheated air. This continuous melting process can last as long as 50 hours. The glass leaves the conditioning end of the melting zone at a temperature of 2000 °F through a narrow canal. This is where it passes to the heart of the process, the tin bath.
Step-2: Tin Bath
The tin bath is around 60 meters long and 4-8 meters wide. The molten glass enters the tin bath and floats on top of the dense molten tin, like oil floating on water. Here the glass spreads out following the exact flatness of the tin so that the upper and lower surfaces remain flat and parallel with accurate spectral properties. The glass is made thicker by confining its initial outward spread to the tin. A controlled atmosphere of hydrogen and nitrogen within the bath prevents the tin from oxidizing.
Step-3: Coating
When it emerges from the tin bath, the glass is sufficiently hard not to be marked by the conveyor rollers. The float glass manufacturing process can produce clear tinted and coated glass products. Online pyrolytic hard coatings are made by depositing microscopically thin layers of metallic oxides using chemical vapour deposition. This process produces extremely durable products that are easily handled, cut, tempered, bent and fabricated.
Step-4: Annealing
During the above processes, some stress is formed in the glass. If the glass is cooled down rapidly, the superficial layer cools down quickly, whereas the inner layer remains hot and creates strain. This can lead to the breaking of glass even due to slight disturbances.The annealing process also improves the thermal properties of the glass, making it less likely to break or crack when exposed to temperature changes. This is important for applications where the glass will be subject to thermal stress, such as in automotive or construction.
Step-5: Inspection
Though the float process is well known for its perfection, inspection is done to ensure that flawless glass is produced.
Step-6: Customisation
Now the glass is snapped to predetermined sizes. Indentations left by the rollers are collected and stored to be used as collets in the melting process. Glass is customised based on customer orders, which might include varying thicknesses, sizes, and coatings.
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Applications of Float Glass
In float glass, raw materials, cullet and decolouriser are finely powdered in grinding machines. These materials are accurately weighed in the correct proportions before they are mixed together.
The following is a list of applications for float glass:
- It is used in the manufacture of windows.
- Due to its crystal clear transparency, it is used to display and protect valuable items, such as watches and jewellery, in shops.
- It is also used in wall panels for creating partitions at home or office cabins. It is both visually appealing and functional.
- Float glass is very popular for constructing architectural exteriors and interiors of a building.
- It is also used in the facades and glazing of commercial structures to create aesthetic effects.
- It is also used in automobiles, medical equipment, etc.
- It is used as a base material for safety, reflective, and self-cleaning glass.
Conclusion:
Glass has been and always will be an integral part of our daily lives. Float glass manufacturing has proved to be the most efficient and cost-effective method. Beyond traditional applications, it is also extending its usage to emerging technologies such as touch screens, refrigeration doors, HD television displays, solar panels, etc.
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