Manufacturing float glass
Float glass is made by floating molten glass on a bed of molten metal, typically tin.
This method produces glass sheets with a very flat surface and uniform thickness.
The float process step by step:
Through a complex system of silos, weighing hoppers, conveyors, mixers, dust extractors and diverters, the batch house receives, stores, weighs, mixes and transports materials to provide a consistent quality of float glass.
Four main raw materials are used in the composition of clear glass (SGG PLANILUX®): sand (60%), soda-ash, limestone, feldspar (and up to 25% of cullet – broken glass - used to lower the temperature of the melting point).
At this early stage, metallic oxides can also be incorporated in the batch to obtain body tinted float glass (SGG PARSOL® bronze, green, blue etc…).
Glass is prepared by melting down these raw materials in the furnace at high temperature (around 1550°C) to remove any impurities and bubbles.
The furnace is a wide tank lined with refractory materials capable of holding up to 2200 tons of molten glass.
Natural convection ensures the homogeneity of the preparation.
The glass is fired from the top of the furnace, each side alternating every 20 min, using natural gas; and reusing waste gases to preheat the air on the opposite side.
Molten glass from the furnace flows on the surface of a bath of molten tin under a controlled atmosphere.
The glass spreads over the tin forming a ribbon of uniform thickness and viscosity.
Tin is used because of its low reactivity with the glass.
The bath contains ~260 tons of tin.
In this way, the glass produced has perfectly flat and parallel surfaces.
The natural thickness of the glass ribbon is about 6.5 mm.
To make thicker or thinner glass, mechanical forces must be applied to the ribbon in the float bath.
Top rollers positioned above the molten tin are used to control both the thickness and the width of the glass ribbon.
The thickness of the ribbon thus depends on the speed, angle and penetration of the top rollers as well as the speed through the lehr.
The ribbon is then pulled through the float to the lehr continuously.
The glass ribbon flows out of the float bath at 600°C.
At this stage, a transparent layer of metallic oxides can be deposited onto the hot glass to enhance its properties.
This special coating is called “Pyrolitic” or “online” coating and totally fused into the surface of the glass.
This technique ensures both a strong and highly durable coating.
SGG REFLECTASOL®, reflective solar control glass is produced in this way.
Once the glass reaches the end of the float, it has cooled to a rigid enough state to be lifted from the float to the lehr via lift-out rollers.
The annealing lehr is a sealed air-filled environment over 190m long where the glass is gradually cooled in a controlled way to release any internal stresses.
Glass which has not been annealed properly is likely to shatter or crack when subjected to a relatively small temperature change or a small impact.
This will decrease the overall strength of the glass.
The annealing step is critical to the durability of the glass.
Once cooled, the glass ribbon is ready to pass through the cutting area.
A system of conveyors takes the glass ribbon through different quality machines and technological devices.
First, the glass thickness and the presence of defects are monitored by online laser detection systems.
The defects are located and classified according to size and type.
Glass sheets are optimized with any defective glass dropping down the cullet return system.
Based on a standard criterion, a quality code will be assigned to the glass depending on the final application requirements: mirror, automotive or building quality.
The ribbon is automatically cross-cut (once the roller marked edges have been removed and recycled) into standard sheet dimensions: 6000x3210 mm, 3210x2250 mm...
7-Stacking and transport
Each sheet is lifted using suction cups.
The capacity of the fully-automated stacking equipment is 25 ton/hour: sheets are detected in exactly the right position, then picked up by robots and laid down on the rack.
A thin layer of interleafing Lucite powder is applied between each sheet to avoid scratches during transportation and prevent the sheets from sticking to each other.
The sheets are then stored on racks or packed in wooden boxes for export markets or specific needs and ready to be sent to the customer.
Fully automated, the Saint-Gobain Glass Egypt facility is equipped with the latest innovations.
Many detectors, cameras and setting devices placed right along the production line are followed centrally, from the control room, and monitored on the line.
All parameters are carefully controlled and fine-tuned to obtain the highest quality of glass: from the temperature in the furnace, to the temperature profile across the cooling zone, including the control and adjustment of the
thickness, the flatness, the internal stresses etc...
Added to these online tools, the quality lab carefully controls the optical, mechanical and chemical proprieties of the glass produced.
Saint-Gobain Glass Egypt plant manufactures:
SGG PLANILUX® - High quality clear glass
SGG PLANILUX® is the clear annealed glass by Saint-Gobain Glass.
Manufactured by the float process, the glass produced has perfectly flat, parallel surfaces.
SGG PLANILUX® is a multi-purpose clear glass, suitable for a wide variety of applications: external and internal glazing; from indoor furniture to fully-glazed facades.
SGG PLANILUX® is the substrate glass used to manufacture most other processed glass products: double-glazed units, coated glass, mirrors, decorated, screen-printed, acid-etched, sandblasted, lacquered, laminated, toughened...
SGG PLANILUX® comes in a range of thicknesses, from 2 mm to 19 mm.
SGG PARSOL® - Unique body tinted glass
SGG PARSOL® is a body-tinted glass with perfectly even surfaces made, like SGG PLANILUX® clear glass, using the float process.
SGG PARSOL® has a coloured appearance and basic solar control properties.
Saint-Gobain Glass has strict tolerances on its coloured glass and ensures through precise quality control that the tinted glass is the same within a batch and across batches - year after year.
SGG PARSOL® is intended for universal applications: interior applications for decoration, glass partitions, glass doors, furniture, table tops; external applications in single or double glazing, for facades and overhead glazing.
When an attractive appearance is needed, SGG PARSOL® gives colour to the space.
When basic solar control properties are required, SGG PARSOL® is the solution, with low light reflection.
SGG REFLECTASOL® - Reflective solar control glass
SGG REFLECTASOL® is a reflective solar control glass, carefully designed to meet the requirements of hot countries as it provides functional benefits such as solar control, glare reduction and great exterior appearance.
Furthermore, its reflective quality creates a one way observation effect under certain lighting conditions, transmitting light and at the same time screening vision for the purposes of privacy.
SGG REFLECTASOL® is suitable for most types of façade glazing.
The coating applied during the float process is known as ‘Online pyrolytic coating’.
When the glass is still hot, metal oxides fuse onto the glass surface.
This process completely fixes the coating into the surface of the glass, giving it greater strength and stability over time.
Thanks to the Saint-Gobain Glass worldwide network of 35 float lines and 14 offline coaters, Saint-Gobain Glass Egypt is also able to supply a wide range of glass products for both internal and external applications: extra-clear float glass, high performance solar control and low-E coated glass (online and offline coating) for temperature control, patterned glass, back painted glass and special glass products such as fireproof glass, and many more.