Float glass

Float glass is flat glass, which was in the float process, or even float glass process was prepared. The method is applied industrially since the 1960s, has since been largely displaced most other methods for flat glass production and now supplies about 95 percent of total flat glass all application areas such as window glass, car windows and mirrors.

The term mirror glass is in accordance with DIN 1249 (Flat Glass in building ) and DIN 1259 (glass) for plan and clear glass, but is now often used as a synonym for float glass; as the basis for almost all areas of flat glass is also spoken by base glass.

Production process

The float glass manufacturing is an endlessly - continuous process. The pure refined, at 1100 ° C doughy - liquid glass melt is passed continuously from one side of an elongated liquid tin bath on which the about two-thirds lighter glass floats ( engl. to float) and as a film spreads evenly. Due to the surface tension of tin and molten glass is very smooth surfaces form. The solidified on the cooler end of the bath, approx 600 ° C hot glass is withdrawn continuously and undergoes a cooling furnace in which it is cooled without tension. After an optical quality control the glass cut (: 6000 mm x 3210 mm standard size in Europe) is.

The following table compares production method for transparent flat glass:

The viscosity of the semi- molten glass, and drawing speed of the solid glass is withdrawn from the semi-liquid phase, determines the strength (thickness) of the glass. In many plants are intended to stabilize the glass thickness in the area of the tin bath on the edge of the glass surface (which is later cut off ) on so-called Toproller. To generate higher glass thickness not Toproller come more to the application. In this case, the viscous glass between graphite blocks, called fenders, pulled and thereby folded in higher strengths. The float glass process enables glass thickness from about 0.4 mm. Typically, the global standard thickness 2, 3, 4, 5, 6, 8, 10, 12, 15, 19 and 24 mm are produced.

A float plant is because of the relatively high average tonnages, and therefore large-sized aggregates, very long ( about 300 to 800 m). Zinn and 232 ° C has a low melting point, so it still remains liquid until complete solidification of the glass; also it has in the used 1100 ° C still not high vapor pressure, which could lead to bumps on the bottom side of glass, and behaves almost inert to the glass. The tin must be maintained to avoid oxidation with atmospheric oxygen in an inert atmosphere ( usually nitrogen and hydrogen).

On the molten tin, the glass side is narrow doped with tin. For scientific investigations in laboratory glassware, which depend on particular purity, float glass can not be used under certain circumstances. And subsequent coating methods succeed different on both sides. Identify the bottom on the basis of traces of tin, therefore, is sometimes important for further processing. For the distinction is often exploits the fact that the tin side under short-wave ultraviolet irradiation fluoresces blue-gray.

A float glass plant runs continuously around the clock and produces approximately 11 to 15 years ( When travel ). After a cold repair is required, in which the pot lining is renewed. A larger plant supplies about 3000 m² / h with 4 mm glass thickness and 33 t / h In 2006, about 280 float plants in use worldwide, and the trend is rising.

Identification

Float glass is delivered so far without permanent product identification. Two methods are known, such a designation at or bring:

• Laser Fracking in the glass volume produced minimal optical interference that as a serial code or 2 - can be run or 3-dimensional matrix code.
• Converting the Zinndotierung in a superficial layer of a permanent color or two-dimensional code.

Other labeling method with printing are less durable or Silberbedampfung are no longer in use.

History

Already in the mid-19th century Henry Bessemer had the idea of ​​using liquid tin as a carrier for flat glass. In 1902, William E. Heal received a patent in the U.S. on the production principle of allowing glass continuously run over a tin bath and then to obtain a plane-parallel surfaces. This patent has never been used commercially.

Sir Alastair Pilkington developed the method so far that it was industrially applicable, and put it in front on 20 January 1959, the public. In 1966 the company Pilkington Brothers in St. Helens ( UK ) with the production and awarded following a variety of licenses to other flat glass producers.

The new process replaced the previous flat glass production in casting or blowing off almost completely. Soon came the most flat glass float glass plants worldwide. Transparent sheet glass has since become much cheaper and is now a diverse and large area employed in architectural building material is, the architect is a large playing field and allows energy- saving designs with high transparency. Since the small remaining Zinnspuren some specific applications but contrary to one side of float glass has, for example, the overflow down-draw or fusion method can maintain some relevance for LCD / TFT displays.