Casting of Steel Rolling is a metal forming process in which metal  stock is passed through one or more pairs of rolls to reduce the thickness and to make the thickness uniform. Hot Rolling- If the temperature of the metal is above its recrystallisation temperature, then the process is known as hot rolling. Cold Rolling- If the temperature of the metal is below its recrystallization temperature, the process is known as cold rolling.

HOT ROLLING It involves rolling the steel at a high temperature (typically at a temperature over 1700° F) When steel is above the recrystallization temperature, it can be shaped and formed easily, and the steel can be made in much larger sizes. cheaper than cold rolled steel as it is manufactured without any delays in the process

Disadvantage: When steel cools off it will shrink slightly ,giving less control on the size and shape of the finished product when compared to cold rolled. Applications In situations where precise shapes and tolerances are not required. Eg. Rail road tracks and I- beams

COLD ROLLING The steel is processed further in cold reduction mills, where the material is cooled (at room temperature) followed by annealing and/or tempers rolling. This process will produce steel with closer dimensional tolerances and a wider range of surface finishes.

COLD FINISHING Results in higher yield points Following processes can be carried: Cold drawing increases the yield and tensile strength, often eliminating further costly thermal treatments. Turning gets rid of surface imperfections. Grinding narrows the original size tolerance range. Polishing improves surface finish.

Advantages of Cold Finishing superior surface finish, superior tolerance, concentricity, straightness when compared to hot rolled. Disadvantage of Cold Finishing Cold finished bars are typically harder to work with than hot rolled due to the increased carbon content. 

Types of rollers

Types of rollers

Quenching and tempering Quenching and tempering provides the steel with high strength and ductility. Two stage process: Stage 1 : Hardening- temperature increased to 900 deg. C and cooled quickly. Stage 2: tempering the material-It is done by heating the metal to some temperature below the critical point  for a certain period of time, then allowing it to cool in still air. 

Basic principles of Heat Treatment Hardening Annealing Hardening: Application of heat to change a characteristic or condition of the steel.  It increases the metal hardness ,toughness, fatigue resistance, strength.

Annealing Annealing is the process of heating the steel to a particular temperature in the austenite region and cooling down the steel very slowly. Austenite, also known as gamma-phase iron (γ-Fe), is a metallic, non-magnetic allotrope of iron. The nickel alloyed steels and the A series tool steels should be cooled very slowly, as nickel will cause an air-hardening effect.

Normalizing Normalizing is a process that makes the grain size normal. This process is usually carried out after forging, extrusion, drawing or heavy bending operations. The process is designed to: Give improved machining characteristics. Ensure a homogenous structure. Reduce residual stresses from rolling and forging. Reduce the risk of "banding." Help to give a more even response to the steel when hardening.

Grain structure

Parts of a rolling mill Work rolls Backup rolls - are intended to provide rigid support required by the working rolls to prevent bending under the rolling load Rolling balance system - to ensure that the upper work and back up rolls are maintained 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

Mill Configurations(Designs) two-high non-reversing two-high reversing three-high mill (metal fed through two and returned through the other two) four-high or cluster(advantage- less roll in contact with material and so low force and power requirement)

A. 2-high B. 3-high C. 4-high D. 6-high E. 12-high cluster & F. 20-high

Tandem Mill A tandem mill is a special type of modern rolling mill where rolling is done in one pass. There are several stands (>=2 stands) and reductions take place successively. The number of stands ranges from 2 to 18. Tandem mills can be either of hot or cold rolling mill types.

Rolling Defects Surface defects commonly occur due to impurities in the material, scale, rust, or dirt. surface preparation prior to the metal rolling operation can help avoid these. Very serious internal defects are caused by improper material distribution in the final product.