8.3. Brief technology of glass manufacture
Silicate glass, the basic components of which are SiО2, Al2O3, СаО, MgO, Na2О or К2О, is applied in construction. Thus, there is about 72 % SiО2 in composition of window glass, 10% CaO+MgO and 15% Na2О. Every oxide has the certain destination. Silica creates spatial structure of glass and determines it’s the most important properties. The oxide of sodium accelerates the process of glass formation, reduces the temperature of glass melting, facilitates degassing of glass mass, but promotes the coefficient of expansion and reduces thermal and chemical resistance of glass. The oxides of calcium and magnesium give chemical resistance to glass. Basic components are included in a glass batch with sand, feldspars, soda, limestone, dolomite and other materials. It is possible to enter in a batch up to 60...70 % ash and slags of heat power plants and to get glass of type of marbled glass. Glass on the basis of fuel ash and slags has comparatively low temperature coefficient of linear expansion (54...65×10-7 degree-1), enhanceable strength (80...100 MPa) and water resistance.
The beaten glass, and also auxiliary materials - oxidants, restorers, clouding admixture and others like that are used for improvement glass mass properties and acceleration of melting. Raw materials, applicable to glass mass, are processed to previous preparation. Sands, which contain the enhanceable amount of iron oxides, are beneficated by washing in hydrocyclones or other methods. Dried up and the ground up components of batch are mixed up carefully. To prevent demixing, a batch is briquetted or granulated. Melting of glass can be done in the bath-type furnace of continuous action. It is possible to contain over 2000 tons of glass mass in such bath-type furnace. In bath-type furnace materials continuously move from the loading opening of furnace to the unloading opening; gets in the areas of different temperature and transform into prepared glass mass. The process of glass melting consists of five basic stages: silicates formation, glass formation, degassing, homogenization and cooling for required viscosity.
Glass mass can be produced in different ways depending on the type of products. Sheet glass is obtained by the vertical drawing out on special machines (Fig. 8.4), and rolling on the layer of molten metal.
T
he
last one, so-called fluate-method
is the most progressive method of production of the polished glass.
Its essence is contained
in continuous merging of glass mass from the reservoir of
glass-melting furnace on the surface of molten metal, spreadind on it
like layer of even thickness and transforms into the ribbon of glass
with the polished surface.
Glass blocks are produced by pressing of separate semi-blocks with the their following welding by the special welding automats. At the production of structural glass ribbon, which is made by the continuous horizontal rolling, is stretched out through a forming device for a making of required channel or box-type section. Glass pipes are produced on the production lines of the horizontal or vertical drawing.
Glass fiber is manufactured as filaments from molten glass mass, which stretch through special bushings and winded on a reel which is quickly revolved.
During cooling of glass as a result of overfall of temperature afterstrains are appeared between superficial and internal layers, which can be removed or weakened by special heat treatment of products.