Hot Rolling: Overview

Hot rolling is the most efficient process of primary forming used for the mass production of steel. The principal effects of hot rolling are the elimination of the cast ingot structure defects and obtaining the required shape, dimensions and surface quality of a product. The main parameter which determines the ability of a rolling process to eliminate the cast structure defects is called the rolling ratio. It is calculated as the ratio of the cross-sections of the initial stock and the final product. The value of the rolling ratio required for obtaining steel structure of a good quality depends on the steel type, e.g. it is about 2 for the structural steels but it can be as high as 12 for tool steels.

The first operation of any hot rolling process is heating of the stock to the proper deformation temperature. During heating and hot forming a scale (oxide layer) forms on the stock surface which must be systematically removed. Descaling can be performed mechanically (by crushing during a hot forming operation) or by spraying with water under high pressure.

During rolling, deformation of material occurs between dies in the form of rotating, driven rolls. It is a stationary process - this means that a deformation zone does not change its position in time. The transporting force during rolling is the friction between rolls and a processed material.

Hot rolling is carried out using various types of rolling mills. The selection of the appropriate rolling technique is made according to the particular hot-rolled product.

For the required geometric product features (such as a shape, dimensions and surface quality) to be obtained, some finishing and (eventual) heat treatment operations are necessary after hot rolling. Typical finishing operations are: cooling, straightening, sizing and surface cleaning. The further stages of the production process are: quality control (it can also be performed during hot forming), marking, piling and preparation for storage and transportation. Some hot-rolled products are coated for protection and/or decoration.

Hot rolling comprises manufacturing technologies for both semi-finished and finished products. Semi-finished hot-rolled steel products are the starting materials for further hot metal forming processes. The following principal hot-rolled product groups can be distinguished:

    * flat products
    * long products
    * seamless tubes
    * specialty products, such as wheels, rings, bars with the periodically varying profile, etc.

Hot-rolled products are often subjected to further processing, such as cold-rolling, forming, machining and joining, in order to achieve a variety of steel products offered for sale.

http://www.steeluniversity.org/content/html/eng/default.asp?catid=30&pageid=2081272061

These are supplementary videos below:

http://www.matter.org.uk/steelmatter/forming/hot_rolling_video_1.html

http://www.matter.org.uk/steelmatter/forming/hot_rolling_video_2.html

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Respectfully,
Henry