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Soda lime glass
DIN 8902
Soda-lime glass is the most common type of glass that is produced by melting soda, lime, silica, alumina, and small quantities of fining glass in a furnace at temperatures up to 1675 ° C. Sheets of glass of soda-lime obtained by pouring a layer of molten glass on the surface of the molten tin. This method gives the sheet of uniform thickness and very flat surfaces. Soda-lime glass base material is for most types of glass (colorless, colored and patterned).
Glass relatively inexpensive and readily available, with a wide range of applications. Due to the high thermal expansion coefficient has a low resistance to sudden changes in temperature.
The characteristics of soda lime glass
Characteristics:
- can be chemically strengthened to increase the mechanical strength *
- can be thermally enhanced (tempered) to increase the thermal shock resistance and mechanical strength
- can be machined, coated optically, chemically etched, sandblasted, colored or laminated
- has a good flatness and surface quality
- the lowest cost of manufacture of the glass in sheet form
* Mechanical strength is defined as the overall material's ability to withstand stress and strain. The mechanical strength of tempered glass or chemically reinforced maybe 4 times greater than normal glass.
| SiO2 | 72,60% |
| Na2O | 13,90% |
| CaO | 8,40% |
| MgO | 3,90% |
| Al2O3 | 1,10% |
| K2O | 0,60% |
| SO3 | 0,20% |
| Fe2O3 | 0,11% |
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Typical Modulus of Rupture for 50% Probability of breakage
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Typical Design Stress for 0.8% Probability of breakage
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Spectral Transmission
Properties:
| Density ( @ 18 °C) | 2 500 kg/m3 |
| Mohs hardness | 5 - 6 |
| Modulus of elasticity (Young’s) | 72 GPa |
| Shear modulus | 30 GPa |
| Poisson’s ratio | 0,23 |
| Coefficient of thermal stress | 0,62 MPa/°C |
| Thermal conductivity | 0,937 W/(m K) |
| Specific heat | 0,88 kJ/(kg K) |
| Coefficient of linear expansion | 8,3 * 10 -6 °C |
| Index of refraction (@ 380 - 780 nm) | 1.5 |
| Softening point | 715 °C |
| Annealing point | 548 °C |
| Max. working temperature: | |
| - not toughened | 110 °C |
| - toughened | 150 °C |
| Thermal shock Δ : | |
| - not toughened | 50 °C |
| - toughened | 118 °C |
| Dielectric Constant (@ 20°C) | 7.75 |
| Specific Resistivity: | |
| 1000 Hz | @25°C: 9.7 log R ohm/cm @100°C: 9.1 log R ohm/cm @250°C: 6.5 log R ohm/cm |
| 60Hz | @25°C: 11 log R ohm/cm |
FLOAT glass
Name of glass - float - is, in fact, the name of a technological process in which the liquid glass mass solidifies on the surface of the molten tin. Description of the process is available eg. on page https://en.wikipedia.org/wiki/Float_glass. The name float is typically used for flat soda-lime glass.
Float glass is a product base, which is used to produce other types of specialized glass having improved properties. The way to the final product goes mostly through additional treatment: toughening, annealing, heat strengthening, laminating, and more.
Soda-lime float glass used in technical applications is usually subjected to a toughening process. During toughening, the glass sheet is heated to a temperature of about 700 °C and then quickly cooled with cold air. This changes the microstructure of the glass. An additional effect of toughening is to give a glass the safety features. Toughened glass is very hard on the outside and soft inside, whereby the stresses in the glass structure at the time of breakage cause the disintegration of the glass sheet into small pieces with blunt edges. During the hardening process is to be expected possibility of glass deformation, but no greater than specified in the table below.
Limits for the distortion of glass in the toughening process, measured on the edge of the glass.
| Glass thickness | Max deformation for 1m 1) |
|---|---|
| 3 mm | 3 mm |
| 4 mm - 5 mm | 2 mm |
| 6 mm - 10 mm | 1,5 mm |
1) in proportion to the dimensions. For example, a sheet of glass having a thickness of 8 mm and dimensions 600 x 600 mm due to toughening process has right to deform: 0.6 m × 1.5 mm = 0.9 mm. This fact should be considered at the design stage.
Toughened glass has an increased mechanical and thermal strength in comparison with a "normal" glass (see. tables below).