Single-Pane Safety Glass (ESG)
“Transparent insulation” was therefore designed to offer unique economic and environmental benefits, but it alsowhile guarantees providing both comfort and convenience. In this process, the basic glass is thermally treated (tempered), which gives it three outstanding characteristics: it has a four to five times greater tensile strength than before it was tempered and can therefore handle much higher suction or blunt impact forces. Tempering also makes glass more resistant to severe, short-term fluctuations in hot and cold temperatures, as well as more able to handle large differences in temperature within the pane of glass itself. However, should failure occur due to overloading, then the glass will disintegrate into a blunt-edged mass of loosely connected pieces of glass that pose a lesser risk of injury than the sharp-edged shards produced by shattered conventional glass. conventional glass produces when it shatters.
The only blanks that reach the tempering unit are the onesthose cut from basic glass. These blanks are precisely measured, the edges have already been worked, and the drilled holes and boundary cuts have already been made. These panes are heated up to approx. 600 °C using controlled and even heating, are then next rapidly cooled down using cold air, and are thenfinally “quenched” by being rapidlyquickly being brought back to room temperature.
|Auflegen||Float (the molten glass)|
|Erhitzen > 600 °C||Heat|
|Abnehmen||Lift the cooled glass off|
This “quenching” or, stated in professional terms, “blowing off”, makes the glass surface cool down faster that the centre of the glass, which creates a durable tensile strength in the glass. The tensile stress increases from glass surface, which is under compression stress, to the core of the glass section.
|Zugspannung||Nominal tensile strength|
|Spannungsverteilung||Tensile strength distribution|
|Zug||Drawing or pulling tension|
|Druck||Pressure or compression|
|Ohne Belastung||No load applied|
|Bei leichter Durchbiegung||Slight bending pressure applied|
|Bei erhöhter Durchbiegung||Increased bending pressure applied|
This tension dynamic gives the plate of glass its outstanding features, and also explains why all machining must be carried out on the plate of glass in advance. If drilling, for example, is carried out on the glass after it has been tempered, the entire plate of glass will shatter. The reason for this is that the drilling procedure breaks up, or interrupts, the tension structure, which causes the glass to break apart. The tension zones are visible under polarized light and can be viewed at certain angles as collared, optical effects.
7.1.2 Building physical characteristics
Thermal conductivity, light and energy permeability, thermal expansion, compressive strength and elastic modulus remain identical in the basic glass, as does the weight, the sound insulation characteristics as well as the chemical properties. Other parameters, however, will vary tremendously.
7.1.3 Resistance to impact and shock
ESG is resistant to shocks from soft, deformable objects like the human body, and is in acc. with EN 12 600 (the pendulum impact test for glass in buildings). The respective field of application determines the required glass thickness.
7.1.4 Tensile bending strength
ESG can be made out of various basic types of glass and is additionally coated with ceramic colours. The tensile bending strength must therefore be classified as per the design:
– ESG made from float glass o = 120 MPa
– ESG made from ornamental glass o = 90 MPa
– ESG made from enamelled plane glass, whereby the enamelled side is under tensile stress o = 75 MPa
7.1.5 Reliability despite impact from balls being thrown
At 6 mm thick, ESG glass is especially suitable for use in large surface glass applications in gyms and sports halls as is typical in countries such as Germany (in acc. with DIN 18 032 “Test for safety against throwing balls”).
7.1.6 Heat influence
ESG is capable of resisting temperatures exceeding 300 °C for brief periods of time, and temperatures exceeding 250 °C for extended periods of time. The resistance versus temperature differences within a glass pane, between the centre and the edge of the pane, for example, is very high, at 200 Kelvin (K), compared with 40 K for float glass.
These are unavoidable irisation appearances on thermally tempered glass due to the internal stress distribution in each pane. Depending on the angle of view, dark-coloured rings or stripes are visible in polarized light.
7.1.8 Optical quality
Minor surface changes can occur in the ESG, since it will be moved about on wheels during its manufacturemanufacturing. These minor surface changes are referred to as “roller waves”, and have a physical basis due to technical reasons and cannot be prevented. This is the same reason why, in exceptional cases, dots – “roller pickup” – can also form on the glass surface, and are visible under adverse lighting conditions.
7.1.9 Moisture film on ESG
The wettability of the surface can be toughened by different impressions from rolls, suction cups, trowelling compounds or lubricants. In subsequent formation of a moisture film on the glass surface, this varying wettability within a glass surface is visible, but does not indicate any deficiency.
Each ESG plate of glass must be clearly and permanently marked in accordance with EN 12 150.
Heat-soaked and toughened safety glass and tempered ESG-H
In each basic glass there are extremely low quantities of nickel sulphide crystals that are inevitably introduced into the glass via the raw materials. In normal float or ornamental glass, these crystals do not have any relevance.
The extremely fast cooling off period during ESG production “freezes” the NiS particles in a high temperature crystal modification. When heat is later applied through solar energy absorption, for example, this crystal structure may change because the volume of the crystals change, i.e. increases, and this may cause the glass to suddenly burst apart as soon as the particles exceed a critical size.
Therefore, all safety-relevant glazing and panes such as façade glass, that are going to be exposed to high temperature alternations must be subjected to the additional heat-soak test.
This test is carried out acc. to EN 14 179 and has to be documented. This test forces the nickel-sulphide crystals that may be present to react quickly. Those panes of glass that do have these invisible crystals are intentionally destroyed during this test. For that purpose, the ESG panes are heated up to a defined 290 °C ± 10 % for at least 2 hours – in Germany, this test is carried out according to the local list of construction rules, so that the test may even go for as long as 4 hours – in order to achieve the regulated building product ESG-H.
|erstes Glas, das 280 °C erreicht||Initial glass that reaches 280 °C|
|letztes Glas, das 280 °C erreicht||Last batch of glass that reaches 280 °C|
|erstes Glas erreicht 280 °C||Initial glass reaches 280 °C|
|letztes Glas erreicht 280 °C||Last batch of glass reaches 280 °C|
This process is controlled using internal and external controllers; and each supplied pane has to be permanently documented. Moreover these panes have to be declared additionally to the ESG standard identification visibly.
7.3 Partially tempered glass (TVG)
According to EN 1863, as single pane, TVG is not classified as safety glass, but as a combination element for forming glass, indispensable in the glazing construction business.
Production is the same as for ESG, but the cooling-off process is slower, which means that the stress differences in the glass are lower. You could even rank TVG between float and ESG glass. The values for the alternating temperature resistance as well as the flexural tensile strength are proof of this. The structure after a fracture occurs is similar to the that of a float glass pane. The fracture radiates outward from the point where the impact/fracture occurred to the edges of the pane.
Thanks to TVG’s fracture characteristics, which are different from that of ESGESG’s, a single unit of laminated safety glass has excellent residual load-bearing properties.
(Foto VSG-ESG + VSG-TVG – Guardian?)
In case of failure of one pane out of two TVG panes in VSG there is only a minor deflection, contrary to the sagging of VSG and ESG. That is why TVG replaces ESG more and more in laminated glass when increased flexural tensile strength and alternating temperature loading are required.
A slower cooling down during the production process avoids the risk of a spontaneous breakage by NiS inclusions.
7.3.2 Tensile bending strength
– TVG of float glass o = 70 MPa
– TVG of ornamental glass o = 55 MPa
– TVG of enamelled plane glass whereby the enamelled side is under tensile stress o = 45 MPa
7.3.3 Heat influence
The failure strength of a TVG against temperature differences in the glass space can be assessed at 100 K.