Flat glass

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Fragment of a Roman window pane from the 1st to 4th centuries
Principle of vertical drawing of flat glass according to the Fourcault process. A rail floating on the weld pool acts as a shaping nozzle. When the rail is pressed down, a little glass will come out of the central slot and freeze. This solid edge can then be pulled upwards, while liquid glass flows in continuously from below.

As flat glass each is glass referred to in the form of discs, regardless of the applied manufacturing process. The most common manufacturing processes for flat glass are the float glass process , the rolling or casting of flat glass, and other processes that are mainly historically significant, such as the Libbey-Owens or cylinder blowing processes . The products are panes which are mainly used in the building industry for window or architectural glass . Another large area of ​​application for flat glass is automobile glazing , mirrors , solar glass for photovoltaics , solar thermal energy and also greenhouses as well as display glass for computer screens, televisions and smartphones. For most of these applications, the glass produced is subjected to further refinement steps in order to adapt it to the respective conditions of use.

history

See also: History of glass production
Large quantities of flat glass were already produced in ancient times. Many public buildings such as baths had glass facades measuring several square meters. For this purpose, liquid glass was molded into sand molds of approx. 40 cm × 40 cm. The resulting panes had a wavy edge and were rough on one side and therefore cloudy. The disks were placed in a grid-shaped holder and held on the edge by four clamps. The process was lost in the course of the mass migrations, as there was a lack of customers and sales channels for this type of glass for several centuries.

In the Middle Ages, new methods of manufacturing flat glass were discovered. The oldest of these is the throwing of heated glass balls at the glassmaker's pipe to make moon glass . This produced circular disks up to 1.2 m in diameter. Due to the production process, the center piece of the pane, to which the moon glass stuck to the glassmaker's pipe, was thickened - the so-called "slug".

From the 17th century, evenly thick slices of up to 1.5 m were achieved by rolling. From 1904, panes of almost any dimension could be “drawn”. The float glass process was first used in 1959 for industrial use; it makes up the majority of flat glass today. Embossed glass, which can also have complex relief patterns, is produced using the rolled glass process. During this process, a wire mesh can be inserted and wired glass can be produced.

Used glass products

Transport frame on trailer

Flat glass serves as the basis for numerous further processing.

Toughened safety glass (ESG)
is thermally toughened glass (according to DIN 12150-1). In the case of thermally toughened glass, the glass is heated to temperatures above its transformation temperature , to around 630 degrees Celsius, and then quickly cooled by blowing off with cold air. Since glass is a poor conductor of heat , when it cools, the surface - and the core, too - of the pane is cooled down first. When the pane has completely solidified (at approx. 530 degrees Celsius), the core is still significantly warmer than the surfaces. With further cooling, the viscosity increases very sharply, which is why stresses can no longer be relieved by relaxation processes. Since the core of the glass sheet remains in the temperature range of the transformation temperature for a longer period, it can contract further than the surfaces of the glass. This creates compressive stresses in the surface and tensile stresses in the glass volume. The compressive stresses on the surface make crack growth more difficult, which is why the strength and thermal shock resistance of ESG is significantly higher than that of untreated flat glass. Tempered safety glass can no longer be mechanically processed afterwards. If the cracks get too deep and enter the tensile stress zone, the frozen stresses are suddenly released and the glass crumbles into small crumbs. The edges of the glasses are naturally particularly sensitive. ESG glasses are used for car side windows, shower partitions, all-glass doors, facade glasses and so-called alarm glasses .
Partially toughened glass (TVG)
according to DIN EN 1863 is also thermally toughened glass. However, the pre-tensioning is not as high as with single-pane safety glass and therefore the breaking behavior is different. The pane is also stronger than normal float glass and breaks with long cracks that run from the point of failure to the edge of the glass.
Laminated safety glass (VSG)
according to DIN EN ISO 12543-2, a laminate made of alternating layers of glass and plastic film ( polyvinyl butyral - PVB or ethylene vinyl acetate - EVA). In the event of breakage, the glass splinters or shards should stick to the film. Safety glass with a thickness of about 25 mm is called armored glass and is used, for example, for shop windows, showcases and car windows. If the layer thickness is increased accordingly, one speaks of bulletproof glass. Laminated safety glass can consist of combinations of different types of glass (float, ESG, TVG).
Laminated glass (VG)
according to DIN EN ISO 12543-3, a laminate of at least two panes and organic intermediate layers, mainly made of cast resin
Multi-pane insulating glass (MIG)
according to DIN 1259-2, consists of at least two panes and an edge seal with space between panes (SZR), which can be gas or air-filled. Also referred to as insulating glass or heat protection glass for short .
Fire protection glazing
A system that meets the requirements of a fire resistance class according to DIN 4102. Fire protection glazing can be single or double glazing. Fire class
Solar control glass
A special type of glass, mostly insulating glass , which has improved sun protection properties thanks to its absorbent and reflective coating.
Bulletproof glass with a bullet test
Wired glass made of cast glass
is regulated according to DIN 1249. When producing wired glass, a wire mesh is inserted into the shaped glass ribbon during the shaping process. This prevents the disintegration of the glass and the falling of parts in the event of a break, similar to laminated safety glass .
Difference between a normal and a hydrophobic glass surface
Glass with self-cleaning properties
are available in different versions. One possibility is that the glass has a special coating on the outside. This initially dissolves organic dirt under the influence of UV light . (Rain) water, which is distributed in a thin film on the pane due to the hydrophilicity of the glass surface, washes away the loosened dirt.
Another possibility for self-cleaning properties of glass surfaces is a special finishing technique based on the model of the lotus flower , the so-called lotus effect . Using a special process, the hydrophobic (water-repellent) and dirt-repellent properties of the lotus flower are transferred to a glass surface. With this surface modification, glass-typical material chemically bonds with the glass surface. This makes the finish resilient and insensitive to UV light ( daylight ). Hydrophobic, usually organic, layers, however - unlike pyrolytically applied self-cleaning oxidic layers - usually have a low durability and must therefore be renewed after some time.
Smart glass
Electrically switchable glass whose light transmission can be changed by applying a voltage. Various technologies and fields of application are summarized under the generic term "intelligent glass". Depending on the design, these glasses can serve as sun protection (glass remains transparent) or act as a privacy screen (glass becomes opaque ).

Flat glass manufacturing process

The groundbreaking principle for the industrialization of sheet or window glass production was the mechanical drawing process, in which a flat glass ribbon is drawn from the melting tank. The Englishman Clark was the first to design such a process in 1857, but it could not be used any more than that of the Frenchman Vallin , who had been granted a patent for it in 1871. The Belgian engineer and manager of the Frison & Cie glass factory, Émile Fourcault (1862–1919) , had success . Before 1900, the Belgian glass furnace designer Gobbe approached him with the suggestion that Frison & Cie try a method for the machine production of window glass.

Fourcault method

The process of the same name developed by him in 1904 made it possible for the first time to draw flat glass directly from the molten glass. In this process, the molten glass swells through a rectangular drawing nozzle embedded in the molten glass, and immediately afterwards it is gripped by the side and pulled vertically upwards. Pairs of rollers convey the solidifying glass mass through an 8.00 m high vertical cooling furnace. During the pulling process, the melt cools down, which also creates a horizontal wave movement due to the gravitational pull. This pattern is still visible later in the window pane. In order to reduce this disturbing effect, these glasses were always used with a horizontally running wave direction.

Libbey-Owens method

In 1899, the American Irving W. Colburn began to develop a method for producing flat glass using the drawing process. The Libbey-Owens process was patented by him in 1904. However, it was not until 1913 that the first successful results came about. By the time Colburn had already sold the patent to the Toledo Glass Company. Three years later the process was fully developed. Since the company had meanwhile changed its name to the Libbey-Owens Sheet Glass Company, the method was named Libbey-Owens Process in 1917. Today it is no longer used. Similar to the Fourcault method, the ribbon of glass was first drawn horizontally upwards from the free surface of the glass melt, but after approx. 70 cm it was bent over a polished steel roller and drawn vertically. Instead of a drawing nozzle, a catching device was used, which had the advantage of avoiding drawing strips and waves, as triggered by the nozzle of the Fourcault process. The glass then passed through a cooling duct up to 60 m long, where it cooled to around 30 ° C. Then it was cut. Glass thicknesses between 0.6 and 20 mm can be adjusted via the pulling speed. The width of the glass ribbon that could be produced was 2.50 m.

Pittsburgh process

From 1928 the Pittsburgh Plate Glass Company used a combination of the Libbey-Owens and the Fourcault process: the glass melt was removed from the free surface as in the Libbey-Owens process, the drawing machine of the Fourcault process drew the glass in up to 12 m high cooling shaft. In this process, further processing took place on a platform approx. 10–15 m above the level of the hut.

Float glass process

All of these processes have been replaced by the float glass process, at least in Europe, USA, and Asia. In the float glass process, the molten glass is directed onto a layer of liquid tin . The glass floats on the specifically heavier tin and forms smooth surfaces. The main advantages of the float process are the better quality of the two surfaces, the higher throughput of the system, the higher glass bandwidth and the better quality of the manufactured product. These factors far outweigh the investment costs, which are higher for a float system than for the old process.

Glass processing techniques

Flat glass surface defects are: scratches ( vandalism , incorrect glass cleaning, transport damage) or due to cement deposits and hydrofluoric acid burns (vandalism). In principle, such damage can only be repaired by carefully removing glass as evenly as possible in the area of ​​the defect.

There are two repair methods: 1. Combination of grinding and polishing , 2. Polishing.

In the first method, the glass is removed using a grinding process in several stages. Here, an angle grinder with a flexible mounting plate is used, which is equipped with grinding disks of different grain sizes or with a polishing disk. The first stage of the grinding wheel has the task of removing the glass required by scraping off the glass. The finer grinding stages have the task of reducing the surface roughness to such an extent that the polishing stage can restore the original transparency .

  • Advantages: The repair is possible in the installed state.
  • Disadvantages: The repair quality depends on the repairer's experience. Uneven glass removal creates the risk of unnecessary optical distortions. If the repairer does not succeed in replacing the first two grinding structures evenly with the last grinding structure, remnants of the first two structures remain visible (cloud formation).

To reduce these quality risks, there are processes in which a mechanical machine guide is applied to the glass by means of suction cups.

In the second process, the required glass removal is carried out using a very intensive polishing process. The glass components (approximate composition: 75% SiO 2 , 13% Na 2 O, 12% CaO) are hydrated and dissolved in water. The original transparency of the glass is not changed during polishing. The following conditions are required for this intensive polishing process:

  • aqueous polishing suspension with optimal polishing agent (cerium oxide)
  • Special felt (toboggan structure)
  • high polishing pressures
  • high speed

This method uses a negative pressure system between the polishing suspension tank and the polishing machine in order to supply or remove the polishing agent from the polishing machine and to guide the machine plane-parallel over the glass.

  • Disadvantages: not known
  • Advantages: The repair is possible in the installed state.
  • The transparency of the glass is not changed during the repair.
  • Minimized, even glass removal and thus minimized optical distortion.

Glass constructions

Glass facade of the New Kranzler Eck , designed by Helmut Jahn
The articles glass holder and flat glass # glass constructions overlap thematically. Help me to better differentiate or merge the articles (→  instructions ) . To do this, take part in the relevant redundancy discussion . Please remove this module only after the redundancy has been completely processed and do not forget to include the relevant entry on the redundancy discussion page{{ Done | 1 = ~~~~}}to mark. TomAlt ( discussion ) 10:54, Oct. 15, 2012 (CEST)
  • Glazing with linear support is glazing in which the panes are continuously supported in lines.
  • Point-mounted glazing is glazing that is connected to a substructure at points. The point support can:
    • In bores or cutouts using continuous point fixings or
    • Take place at the corners or edges of the pane using clamp holders.
  • Structural glazing facades (SSGS facades) are bonded all-glass facades
  • Vertical glazing is glazing that is less than 10 ° inclined to the vertical.
  • Overhead glazing is glazing that is inclined by more than 10 ° to the vertical.
  • Walkable glass is glazing that is walked on as planned.
  • Accessible glass is glazing that is only entered for maintenance and cleaning purposes.

See also

Web links

Wiktionary: Flachglas  - explanations of meanings, word origins, synonyms, translations