Temper Mill Process- Cold Rolled Steel
Temper Mill after annealing, the steel has been so thoroughly relieved of internal stresses that it has a tendency not to bend uniformly, resulting in localized strains (similar in appearance to stretch marks in human skin) during subsequent forming operations. To counter this, a light reduction, between ½ and 3½ percent of the thickness, is taken at the Temper Mill. Similar in some ways to the 5-stand, the Temper Mill is made up of two ‘4-Hi’ rolling mill ‘stands’ arranged in series. The tandem arrangement gives operators the flexibility to improve the flatness of the product and to allow a ‘matte’ surface finish to be applied by the shot-blasted work-rolls while meeting the targeted reduction, or ‘extension’. Work rolls are changed each day or so, after which the widest scheduled coils are processed. As at the 5-stand, coils are rolled from wide-to-narrow in a ‘come-down’.
Unlike the 5-Stand, power is delivered from the four mill motors to the backup rolls, which turn the work rolls, which in turn roll the steel. The reductions are much smaller, so less tension is held between stands and the roll coolant / solution system is not normally used. Operators at the temper mill are relied upon to make most adjustments based on the rolling parameters and product appearance.
Oil can be electro-statically applied either ‘lite’ or ‘heavy’ by coating the top surface of the coil as it is wound onto the tension reel. If necessary to make the customer’s coil weight requirements, coils can be split with a shear at the exit of the last stand. At the exit side of the second mill, a gamma-ray thickness measurement device uses radioactive material to record the gauge of the steel. Footage counters at both the entry and exit ends consist of rubber-coated wheels that are turned by the strip; each revolution is counted and translated into a length measurement. These instruments record the coil footage for TMW billing, as well as the extension achieved during temper rolling.