Four things you need know about glass

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.

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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.

Non-Sheet products

Glass fibre

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

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.

Sheet products

This include  but not limited to the following:

Float glass

The  standard  float  glass  sizes  run from  2 through  25 mm  and with maximum  sheet  sizes  of  3 by  12 metres.

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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).

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Toughened glass

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.

Laminated glass

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).

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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.

Specialist glass

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.


©Copyright 2017

Sources: Materials for Architects and Builders by Arthur Lyons, PhD.


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