Distinguish between bulk rolling of metals and sheet rolling.. Bulk rolling is a metal forming process, where the deformation is naturally three-dimensional. This term - bulk rolling or more generally - bulk forming - is used mainly, to distinguish it from sheet metal processing.
Volumetric and planar deformation
When making stress sheets, which form the metal, are in the plane of the sheet, whereas with volumetric deformation, stresses have components in all three directions of coordinates.
Volumetric deformation, generally speaking, includes such methods of metal forming, how forging, pressing (extrusion), rolling and drawing. It is used for many metals, Firstly, sure, for steel, aluminum and copper.
Metal rolling temperature
Rolling temperature of metals - steel, aluminum, copper - usually subdivided into two main ranges:
- cold working;
- hot working.
Cold rolling occurs at relatively low temperatures in relation to the melting point of the metal. Hot rolling is performed at temperatures above the metal recrystallization temperature. There is also a third temperature range - warm rolling, which is caused by the need to save energy and in some cases is used in industry.
Cold rolling is commonly referred to as plastic deformation of a metal at room temperature.. Phenomena, which are associated with cold working, occur, when the metal is deformed at temperatures around 30 % and below its melting point in the absolute scale of measurement. During cold working, an increasing number of dislocations appears in the metal.. The entanglement of these dislocations causes the hardening of the metal - work hardening or strain hardening. With strain hardening, the strength of the metal increases with deformation..
Annealing the deformed metal
To recrystallize metal, often requires special heat treatment - tempering. During annealing, the strength of the metal can sharply decrease with a significant increase in ductility. This increase in ductility often allows further deformation of the metal without destroying it..
Cold working usually allows for better control over dimensional tolerances of the final product., as well as the quality of its surface, than, hot rolling.
Hot rolling takes place at temperatures 60 % and more from the melting point of the metal on an absolute scale. At elevated temperatures, the metal decreases its strength, which makes it possible to reduce efforts, which are necessary for its plastic deformation. Directly during the deformation of the metal, its recrystallization occurs with the constant formation of new grains. Continuous formation of new grains ensures the preservation of high ductility of the metal. This makes it possible to achieve large deformation values without destruction of the metal.. Controlling the final dimensions during hot working is more difficult due to the formation of dross and volumetric changes during subsequent cooling.
Warm rolling of metals is between hot rolling and cold rolling. It occurs in the temperature range 30-60 % from the melting point of the metal on an absolute scale. Efforts, which are required, to deform the metal when warm rolling above, than hot rolling. The final surface quality and dimensional tolerances are higher, than hot rolling, but not so high, like cold rolling. Although warm rolling has disadvantages, the main incentive for its application is the economy. Heating metal for hot working is very, very expensive. When the rolling temperature is lowered, significant funds are released, which can be used to improve product quality.