Cooling furnace
The cooling furnace is used to cool its contents slowly and in a controlled manner. The resulting mechanical tension in the workpiece is reduced when it cools down to ambient temperature. The cooling furnace is used in the manufacture of glassware . The processing temperature is controlled from approx. 600 ° C to room temperature.
Industrially produced material is moved in roller cooling furnace on steel belts or flat glass as a belt on steel rollers to the downstream packaging equipment.
The cooling process is controlled by continuously regulated cooling and heating, with energy recovery being an important part of the process with the technology used today.
Procedure
Release of tension in the glass
The roller cooling furnace is intended to overcome the temperature difference between the hot forming of the respective glass product and the ambient temperature while relieving the glass product. For example, a thin flat glass produced using the float process passes through a roller cooling furnace as a continuous ribbon of glass after it has been shaped in the float bath. The cooled and relaxed flat glass is then processed further in a product-specific manner. For example, the floated glass ribbon is cut into usually rectangular panes of glass. Roller cooling furnaces have a furnace housing with an inlet and outlet opening for the flat glass, and a motor-driven roller conveyor accommodated therein, with which the flat glass, in particular designed as a glass ribbon, can be transported through the furnace. The roller conveyor comprises a plurality of rollers arranged one behind the other and parallel to one another. With an approximate length of 80 m, the furnace is heated or cooled from above and below in individual zones. The resulting mechanical stresses in the cooled flat glass depend largely on the temperature distribution in the roller cooling furnace. For this purpose, the heating devices can be controlled differently in parallel and transversely to the conveying direction in order to produce one for the respective flat glass, e.g. B. set the floated glass ribbon, favorable temperature distribution in the cooling furnace parallel and transverse to the conveying direction. For high quality glass, it is particularly important that the temperature distribution is perpendicular to the direction of travel of the flat glass, i.e. H. from one border to the other in the net area of a glass ribbon, is as homogeneous as possible. The temperature distribution in the roller cooling furnace results from the heat carried along by the hot flat glass and the heat given off by the heaters. The latter are set via control devices for the heating power, which evaluates the differences between the specified target temperature distribution and the measured actual temperature profile. For this purpose, temperature measuring devices such. B. thermocouples, pyrometers, arranged above and below the glass ribbon.
Tonnage produced
The cooling furnace, also called roller cooling furnace (RKO), not only determines the cutting ability of the glass, but also the tonnage produced and the thickness (thickness) of the flat glass ribbon by means of a very precise speed control of the rollers transporting the glass ribbon. In the past, the roller field was driven centrally by a DC motor and the individual rollers were mechanically connected to one another via a shaft (vertical shaft). Today, each roller is often individually driven by an AC motor controlled by a servo motor. This leads to higher investment costs, but has advantages in the maintenance of the furnace. In order to reduce the transport speed of the glass ribbon with high tonnage and thin glass (e.g. 1.0 mm), kiln widths of around 6.0 m with a glass ribbon width of 4.50 m are built today.
literature
- WH Zachariasen, J. Am. Chem. Soc. 54 (1932)
- AF Holleman, E. Wiberg: Textbook of Inorganic Chemistry, 102nd Edition, Walter de Gruyter Verlag, Berlin, New York, (2007)
- J. Falbe, M. Regitz: RÖMPP Chemie Lexikon, 9th edition, Volume 2, Georg. Thieme Verlag, Stuttgart, (1990)
- H. Scholze: Glass. Nature, structure, properties, 3rd edition, Springer Verlag, (1988)
- G. Jander, E. Blasius: Textbook of analytical and preparative inorganic chemistry, 16th edition, S. Hirzel Verlag, Stuttgart, (2006)
- G. Nölle, Technique of Glass Production Publisher: VEB Deutscher Verlag für Grundstoffindindustrie, Leipzig (1977)
- H.Schulz, the history of glass production Akademische Verlagsgesellschaft Leipzig, (1928)