First, glass is widely used in building and construction but it no longer tenable to say that people who live in glasshouses should not throw stones because the lay of land has changed vastly since the time this admonition was coined. While standard annealed glass will break into shards easily , building construction glass is often hardened and can withstand the impact of bullets, let alone stones thrown people who do not live in glasshouses. These glass is used as non-load-bearing walls, window panes, doors, clear glass screens, roofing covers and many other uses.
Second, glass is a metallic oxide with silica accounting for lion share of its mass compared with other constituent elements .When these oxides are baked at high temperatures, they fail to re-crystallize when cooled from liquid to a solid-creating glass as we know it. Specifically speaking, glass is manufactured from sand, lime and soda ash. Various metallic compounds are added to the mix to give the glass coloration according to required specification. For example clear glass is formed by adding manganese as a decolourizer to remove the green coloration caused by iron impurities in sand .
Glass is a recyclable material but recycled glass cannot be used to make window glass because it requires pure raw materials.
How glass is manufactured
Third and as I mentioned before, modern glass is manufactured from sand (Silica),Soda ash (Sodium Carbonate) and Limestone (Calcium carbonate) ,with small additions of Calcium sulfate and dolomite. 25% broken glass is added to the mix to accelerate the melting process and helps recycles the production waste.
During production a furnace produces a continuous supply of molten glass at approximately 1000 degrees Celsius, which flow across the surface of large shallow bath of molten tin contained in an atmosphere of Hydrogen and Nitrogen (this prevents oxidation of the surface of the molten metal).
The glass moves across the molten metal ,initially at high temperatures for the irregularities on both surfaces to become evened out ,leaving a flat sheet of glass. The temperature of the glass is gradually reduced as it moves forward, until at the end of molten tin its sufficiently solid at 600 degrees Celsius. The glass thickness is controlled by the speed at which the glass is drawn from the bath of molten tin.
Any remaining imperfections are removed as the glass passes through the annealing furnace, leaving a fire polished material. The glass is then washed and undergo computer controlled cutting. All substandard materials are discarded into rejected bins which provide some of the recycling material.
Float glass used in building and construction is made between 2 mm and 25 mm thick.
Finally, glass can be categorized as non-sheet glass, sheet glass and specialist glass.
Continuous glass fibre is manufactured by constantly feeding molten glass from a furnace into a hearth fitted with 1600 accurately drilled holes through which the glass is drawn at a rate of several thousand per second. The fibre(as small as 9 microns in diameter) pass over size applicator and are gathered together as a bundle prior to being wound up on collet.
The material may then be used as roving ,chopped strands or woven strands mats for the production of glass fibre reinforced material such as GRP(glass-fibre reinforced polyester),GRC(glass-fibre reinforced cement) or GRG(glass-fibre reinforced gypsum)
Glass blocks for non-load bearing walls and partitions are manufactured by casting two half block at 1050 degrees Celsius, joining them together at 800 degrees Celsius followed by annealing at 560 degrees Celsius. They offer a variety of privacy and some are strengthened for vandal and bullet-proofing for building requiring enhanced security.
This include but not limited to the following:
The standard float glass sizes run from 2 through 25 mm and with maximum sheet sizes of 3 by 12 metres.
Georgian wired glass
This glass is produced by rolling a sandwich of 13 mm electrically welded steel wire mesh between two sheets of molten glass. This produces standard wired glass suitable where obstruction is required .In the event of strong impact ,the damage will cause glass to break but the wire mesh will hold in place(see below image).
It’s up-to four to five times stronger than standard annealed glass of same thickness. Its produced by subjecting preheated annealed glass at 650 degrees Celsius to rapid cooling by application of a jet of air. This causes the surface to be compressed tightly together which calls for greater force before I breaking into small granules, unlike annealed glass which break in shards and can easily cause injuries.
It is manufactured by bonding two or more layers of glass together with a plastic inter-layer of polyvinyl butynal (PVB) sheet or a polymethyl methacrylate low viscosity resin. On impact they crack without splintering, being held together as they are, by the inter-layer. Because of this, laminated glass in considered as safety glass. Bullet resistant glass has four or more lamination( see image below – bullet proof glass).
Plastic film laminates
These are transparent or translucent plastic films that are applied to glass internally or externally, for privacy or as manifestation films to prevent people from walking accidentally into clear glass screens or doors.
This include the following:
- One way observation glass-used when unobserved surveillance is required
- Mirror Glass-It’s manufactured by deposition onto a float glass of thin film of silver from aqueous silver and copper salt solutions. The film is the protected with two coat of paints or a plastic layer.
- Alarm glass-it’s incorporated into intruder alarm system which is activated when the glass is broken.
- Stained glass-This is glass that has been coloured and traditionally used on church buildings.
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Sources: Materials for Architects and Builders by Arthur Lyons, PhD.