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Noble material for excellence, glass has a rich history that begins with more than 4,000 years BC. In buildings of all time, glass was used for the transparent, allowing light through and communication with the outside world, much needed housing.

Starting with nineteenth century, glass has become a mark of architectural modernism, being a high technology material, functional and sophisticated, benefiting from its transparent qualities.

Thanks to research efforts in recent decades, the glass has greatly contributed to improving the comfort rooms. Various forms of glass and their functions, offers the designer a greater freedom to build a true architecture of light, which fully meet the demands of modern comfort.

Today, with the advent of new techniques for editing (curtain walls) and the development of glass manufacturing processes (deposits with reflective or low emissivity and solar control), it has widened the scope for facades ansamble, becoming a simple shell or processed, transparent or opaque, reflective or colored.

Because the glass surface occupies most of windows and facades, the way it is chosen in a decisive influence on aesthetics, insulation and soundproofing the whole structure. For this reason we will try to detail the main features for a better determination of the glass required for each project.

Glass is made from a combination of quartz sand (70-72%), sodium carbonate or sulfate form (14%), calcium as a stabilizer and various metal oxides in the case of color. It becomes liquid at high temperatures, at which can be processed. For the manufacture of glass are used (some companies still use yet) technology "shot glass" whose main disadvantage is the image distortions, called "waves".

A current method, with results better than that of the glass "float". Molten glass is poured over a surface of molten tin at 1000 degrees Celsius. Being lighter than metal floats on the bed, resulting in a large sheet and thickness desired. Girls are perfectly polished tin on one side and on the other fire.

The process is illustrated in the following chart:

  • Glass density is 2.5 - which means a mass of 2.5 kg / sq mm thick and flat glass. It follows that a 4mm glass has a weight of 10kg per square meter and insulating glass in a 4-16-4 structure around 20kg per square meter.
  • Compressive strength of glass is very high, namely 1000 N/mm2 (1000 MPa) - which means to break a glass cube of 1 cm is required 10 tons of cargo.;
  • Resistance to bending - A glass surface is subjected to compression flexarii and an extension. Resistance to bending, breaking the order of: 40 MPa for polished glass and 120-200 MPa for hardened glass. It depends on the thickness and type of cutting edge finishing. (The high strength tempered glass, the treatment is because girls are pushing each other very strong glass.);
  • Elasticity - The bottle is a perfectly elastic material (no permanent deformation shows ever), it is fragile at the same time (subject to a bending cross, it breaks without prior cracks);
  • Poisson's ratio "m" - coefficient of lateral contraction. When a piece of material that undergoes a stretching under the influence of mechanical action, there is a thinning of its cross section. Poisson ratio (m) is the ratio between the direction perpendicular direction thinning unit effort in the direction of elongation and unified effort. Building Glass: m = 0.22.
  • Young modulus E - Express traction would be theoretically applied to a piece of glass to transmit an elongation equal to its original length. It is expressed in units of force per unit area. For glass, according to European standards: E = 7.1010Pa = 70 GPa.

Insulation and heat transfer

The glass walls, generally separates two areas at different temperatures. There's therefore a transfer of heat from the warm to the cold. Glazed wall at the same time has the particularity of being transparent to solar radiation that generates heat.

Transfers heat across a wall by conduction, convection and radiation, is expressed by the coefficient "U". It is the heat flow that crosses a wall m2 at a 1grad C temperature difference between outside and inside the room. The higher the coefficient "U" is smaller, so heat losses are lower.

Glazed wall can be done with a simple glass bottle or a double in the second case, obtaining a better thermal insulation. The principle is to close the glass windows between two sheets of glass and building a layer of dry air in order to limit the thermal exchanges by convection and take advantage of low thermal conductivity of air located between two sheets of glass.

To improve the coefficient "U" should be removed heat transfer by conduction, convection and radiation. How it is possible to act on the surface exchange coefficients, this ratio will be improved by reducing exchanges between the two components of double glazing in the following way:
- Transfer by radiation - can be reduced by using low-emissive glass cover
- Transfers by conduction and convection - may be reduced by replacing the air between two sheets of glass with a heavier gas, with a lower thermal conductivity (argon, generally)..
One simple explanation, a simple glass of 4mm has a thermal coefficient of 5.8 W/mp*K, a pack of four structure insulating glass clear float float-16-4 clearly has a heat transfer coefficient 2.8 W/mp*K, one in combination 4float-16-4LowE clearly has a coefficient of 1.4 W/mp*K, and one that has argon instead of air between two sheets of glass of a window 4float-16-4LowE clearly has a coefficient of 1.1 W/mp*K.