Bent Architectural Glass
Architects and designers love to interrupt nowadays straightness, corners and curves with soft curves. That’s why there are, next toin addition to rounded, interior glass products and accessories, glassy living and working accessories also ,curved glass façade s. Already inBy the middle of the 19th century, was the bent architects’ were beding glass developed in England and till todaythis exists today in a slightly modified version. only slightly modified. For In the applications of the building envelope, glass is generally bent through a thermal gravity process. building glass is generally a thermal gravity bending applied. Thereby The procedure is as follows: a plain pane is laid over a bending form and in the bending oven heated up to 550 – 620 °C. After having reached the softening point the plain pane descents descends (due to thethrough gravity) slowly into the bending mould and adopts its shape. The following cooling down defines the originating kindshape of the glass. Slow cooling down, free from residual stress, produces a glass which can be further processed, whereas fast cooling off originates creates a partial or fully pre-tempered glass which is not applicable for further processing (see > chapter 7.1).
|Schritt 1: Bauen einer Biegeform und Auflegen des ebenen Rohlings||Step 1: Build a bending die and placement of the flat blank|
|Schritt 2: Erwärmen des Glases auf 550 bis 620 °C||Step 2: heating the glass at 550 to 620 ° C.|
|Schritt 3: Der Rohling sinkt in die Biegeform ein||Step 3: The blank sinks to the bending die|
|Schritt 4:||Step 4:|
|Langsames Abkühlen bei Floatglas (mehrere Stunden)||Slow cooling of float glass (several hours)|
|Schnelles Abkühlen bei thermisch vorgespannten Gläsern||Rapid cooling in heat treated glass|
|Abb. 1: Prinzipielle Herstellungschritte||Figure 1: Main schematic fabrication steps|
Generally,bent glass is not a regulated building material, but andmust guarantee functionality like heat-, solar- and noise protection glass. In addition, it must and has as well to meet the requirements of the building laws, such as like fall preventing prevention measurements and load bearing regulations.
To prove this and thus to be allowed to install bent glasses, the manufacturers in Germany must supply an abZ (general approval by a construction supervising body), in Europe an ETA (European Technical Approval) or a permittance has to be obtained in each single case before the construction has been startedcan begin. Comprehensive norms for bent glasses are at present not available at present, nevertheless the full usability has to be stated always.
8.4.2 Glass types
Principally In principal, are all plane ordinary types of glass which are used in constructions are bendable. Also such types in slightly restricted quantity which are equipped with combination-function coatings. The individual parameters like bending radii, bending forms as well as glass thicknesses and coatings have to be aligned in advance with and on each other. Bent glasses are indeed high tech special products and need therefore alreadycareful consideration in the early planning stadium stages very careful preparation and consensus of by all people involved. In addition to the already mentioned types of glass, normal glass, TVG and ESG, also bent VSG and insulating glasses can be produced in this manner. Especially for the last two mentioned, increased tolerances have to be considered for the installation. It must also be generally taken into account of the varying reflection characteristics of plain and bent glasses. Same Identical glasses standing side by side will have different optical appearance. For larger projects it is recommended to make a 1:1 sampling. Also the design possibilities for the glass areas mentioned under 8.9 may be applied with some restriction, depending on the bending.
Basically all coated architectural glass from type Guardian SunGuard® and many from type Guardian ClimaGuard® can be bent or have a flexible alternative. Guardian will directly inform you about the restrictions of the individual types concerning ways and shapes of bending.
8.4.3 Kinds of bending
A distinction is generally made between bent glass, slightly bent glazing with a radius of more than two meters and heavily bent ones glass with small radii. Moreover there is a difference between glass which is bent cylindrically and the one which is bent spherically. Cylindrically speicis species bending over one axis and spherically over two axes.
Float glass allows generally for all these bending shapes. Due to the production technology, ESG and partially pretempered glass allow principally thefor mainly cylindrical bending. This process is also recommended for glasses with coating, as the production process is short and thereby coat more gentle. Spherical and conical bending requires long lasting production and is therefore normally unsuitable to be used as coated glasses.
The smallest possible bending radius is approx 100 mm for glasses with a thickness < 10 mm and about 300 mm for > 10 mm thick glasses. These possibilities depend however on the manufacturer and have to be checked in advance.
8.4.4 Determination of shape
Exact descriptions of the dimensioning dimensions are required for the shape determination of bent glass. In addition to thickness of the glazing, the height of the panes and the width of at least another two of the five dimensions needs to be determined in the following drawing for inner and outer execution. It always has to be considered that, with the exception of the opening angle, all data refer to the same surface (concave = inside, convex = outside).
|Bemaßbung Innenmaße||Interior Dimensions|
|Biegeradius (mm)||Bending radius (mm height)|
|Abwicklung (mm)||Processing (mm height)|
|Sehnenlänge (mm)||Filament length (mm)|
|Stichhöhe (mm)||Pitch height (mm height)|
|Biegewinkel (°)||Bending angle (°)|
|Bemaßung Außenmaße||External dimensions|
The standard bending is the cylindrical execution to which refer alsoreferred to in the definitions. these definitions. All other geometrical shapes, such as like spherical bends, must be dimensioned estimated by an exact drawing, so that shape and size can be determined without doubt. Already Llinear elongations of cylindrical shapes (b1, b2) are to be displayed separately.
Special tolerances and production technical shape conditions, which must be strictly considered, apply to bent glasses:
220.127.116.11 Local disruptions
The local disruptions of ESG and TVG may differ from the specifications for plain glasses, as glass geometry, -size and -thickness may have more influence on bending than on plain design. In any case, tThey have tomust be settled with the manufacturer. in any case.
18.104.22.168 Outline precision
|Abb. 2: Schematische Darstellung Konturtreue (PC)||Fig. 2: Schematic illustration of contour accuracy|
|Abb 3.: Geradheit der Höhenkante (RB)||Fig. 3: Straightness of the edge height (RB height)|
|Abb. 4: Schematische Darstellung Verwindung (V)||Fig. 4: Schematic illustration of twist (V)|
22.214.171.124 Edge offset
|Abb. 5: Kantenversatz bei VSG (d)||Figure 5: offset in VSG (d height)
Figure 6 offset in insulating glass (d height)
|Abb. 6 Kantenversatz bei Isolierglas (d)|
126.96.36.199 Tangential junctions
The tangent is the straight line which starts at a defined point of the curve. It stands then perpendicularly to the radius of the curve. Without this tangential joint there would be a bend at this spot. This is feasible with glass but can not be recommended. There are generally larger tolerances at a bend point than at tangential continuations.
|Mit tangentialem Übergang||With tangential transition|
|Ohne tangentialen Übergang||No tangential transition|
|Abb. 7: Tangentiale Übergänge||Figure 7: Tangential transitions|
8.4.6 Static specifics
Deformation and bend stress glazing can be defined through finite-elements models with the aid of the theory of shells. The coving, depending on the storing conditions of monolithic glasses, can have a positive consequence thanks to the shell bearing impact, namely in the direction of thinner glasses. Insulating glass, however, does not have fully have this effect. Due as due to the coving of the glass, the bending strength is increased and thus extremely high climatic loads can arise. This has to be considered, especially when units have tangential attachment pieces at a coving. The result can be broader edge seals, which thus affect later glass installation.