冶金专业英语Unit 16.ppt

Steel rolling is a continuous or stepwise forming with the aid of more than two rotating rolls. The rolls act on the metal primarily through pressure. Therefore rolling is classified among the pressure-forming methods. Steels may be rolled hot or cold. Hot rolling is carried out at an elevated rolling-stock temperature, and cold rolling is performed without heating. Hot-rolling mills are generally divided into the following zones: furnace area (for heat supply prior to deformation), rolling area, and finishing area. Rolling stocks will be homogeneously preheated to defined temperature by socking pits in the furnace area. The rolling area completes the rolling process. Rolling trains are normally adapted to the products to be rolled. Hence, there are very many different types of train, such as roughing trains, intermediate and finishing trains. The most important tasks of the finishing shop are: cutting, straightening, surface protection stacking and retrieving, inspection, checking, sorting, marking, collecting, bundling, packing. The sequence and extent of these jobs will depend on the nature of the product. Cold- rolling mills generally include the following areas: pickling area, rolling train, heat treatment, and finishing area. Steel is cold rolled mainly for producing flat products such as deep-drawing sheet, tin sheet and stainless sheet. Sectional steel products and tubes are also cold rolled. The most wide-spread process is the cold rolling of strip . strip is cold rolled on two-high, four-high or multiple-roll mills. In order to eliminate work hardening after cold rolling, heat-treatment by annealing is frequently applied. A combination of cold forming and heat treatment permits specified technological properties to be obtained. The advantage of hot rolling is that it can be reduced in thickness much more easily. But the surface finish and accuracy are not so good as those obtainable by cold rolling. Th