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In the steel plants after the production of liquid steel, thick flat sheets and rolls are produced.
Such thick products are then converted into thinner products by passing them in Hot or Cold Rolling Mill .
A Rolling Mill is a metal forming line in which metal stock is passed through a pair of rolls to reduce its thickness. Rolling is classified according to the temperature of the metal rolled. If the temperature of the metal is above its recrystallization temperature, then the process is termed as hot rolling. If the temperature of the metal is below its recrystallization temperature, the process is termed as cold rolling.
A Rolling Mill consists of:
Work rolls – touching the material to be rolled.
Backup rolls - are intended to provide rigid support required by the working rolls to prevent bending under the rolling load .
Intermediate rolls- between Work Rolls and Back-up rolls in case of a 6-high rolling mill.
Rolling balance system - to ensure that the upper work and back up rolls are maintain in proper position relative to lower rolls .
Roll changing devices - use of an overhead crane and a unit designed to attach to the neck of the roll to be removed from or inserted into the mill.
Mill protection devices - to ensure that forces applied to the backup roll chocks are not of such a magnitude to fracture the roll necks or damage the mill housing .
Roll cooling and lubrication systems .
Pinions - gears to divide power between the two spindles, rotating them at the same speed but in different directions Gearing - to establish desired rolling speed
Drive motors - rolling narrow foil product to thousands of horsepower
Electrical controls - constant and variable voltages applied to the motors
Coilers and uncoilers - to unroll and roll up coils of metal
Various rolling configurations are: 2-high, 4-high , 6-high and Cluster Mills.
The two-high reversing mill has rolls that can rotate in both directions.
To minimize the roll diameter a 4-high, 6-high or a cluster mill is used. A small roll diameter is advantageous because less roll is in contact with the material, which results in a lower force and energy requirement. The problem with a small roll is a reduction of stiffness, which is overcome using backup rolls. These backup rolls are larger and contact the back side of the smaller rolls.
A 4-high mill has four rolls, two small and two large.
A cluster mill has more than 4 rolls, usually in three tiers.
A tandem mill is a special type of rolling mill where rolling is done in one pass.
In a traditional rolling mill rolling is done in several passes, but in tandem mill there are more than 2 stands and reductions take place successively.