ROLLING Rolling is a process of reduction of the cross-sectional area or shaping a metal piece through the deformation caused by a pair of metal rolls rotating in opposite directions. Rolling is the plastic deformation of materials caused by compressive force applied through a set of rolls.

ROLLING The gap between rolls < thickness of entering bar Friction force necessary to bite the bar and to pull it through the rolls Metal bar gets squeezed, and elongated while its c/s area decreases The most important industrial metal forming operations a machine rolling: ROLLING MILL In a typical rolling mill: A pair of rolls is driven by an electric motor which transmits torque through gear Rolls are mounted in a stand with a screw-down mechanism.

TYPES - based on work temperature: ROLLING TYPES - based on work temperature: – Hot Rolling: most common due to the large amount of deformation required – Cold rolling: produces finished sheet and plate stock Hot rolling results in residual stress-free product. Scaling is a major problem, due to which dimensional accuracy is not maintained. Cold rolling of sheets, foils etc is gaining importance, due to high accuracy and lack of oxide scaling. Commonly conducted after hot rolling when good surface quality and low thickness tolerance are needed. Cold rolling also strengthens the product due to work hardening.

TYPES -based on work-piece geometry: ROLLING TYPES -based on work-piece geometry: – Flat rolling: used to reduce thickness of a rectangular cross section – Shape rolling: square cross section is formed into a shape.

ROLLING Microscopic View: Coarse grain becomes finer in size Gets elongated along the direction of rolling In order to refine the grains, heat treatment performed immediately after rolling, which results in recrystallization after rolling APPLICATION: Hot rolling: rails, sheets, structural sections(I-beams, L-beams, and U-channels), round and square bars and rods, plates etc. Cold Rolling: Sheet metal work

ROLLING Analysis: DRAFT: amount of thickness reduction, d = t o - t f R=roll radius L=contact arc length Lp=projected arc length hf= strip final thickness Vr=velocity of the roll Vf=velocity of the strip at roll exit ho=strip initial thickness N=neutral point α=angle of bite Vo=velocity of strip at entrance to roll Analysis: DRAFT: amount of thickness reduction, d = t o - t f Too much & too little?? REDUCTION: draft expressed as a fraction of starting stock thickness, r = d / to CONTACT ARC LENGTH: Smaller rollers have small length of contact Side view of flat rolling, indicating before and after thicknesses, work velocities, angle of contact with rolls, and other features.

ROLLING MILLS & EQUIPMENTS Driving Power per Roll: PR = T x w T=FXR/2

ROLLING MILLS & EQUIPMENTS Points to remember: Two horizontal rolls revolving at the same speed but in opposite direction Rolls are supported on bearings housed in sturdy upright side frames called stands Space between the rolls can be adjusted by raising or 1owering the upper roll.

ROLLING MILLS & EQUIPMENTS Points to remember: Three parallel rolls, arranged one above the other It is used for rolling of two continuous passes in a rolling sequence This results in a higher rate of production than the two-high rolling mill.

Two high would result in wavy rolled plates or sheets unevenly thick Points to remember: It is essentially a two-high rolling mill Two middle rolls are smaller in size than the top and bottom rolls Smaller size rolls (working rolls) concentrate the total rolling pressure over the workpiece. The larger (back-up rolls) prevents the deflection of the smaller rolls ROLLING MILLS & EQUIPMENTS Two high would result in wavy rolled plates or sheets unevenly thick ..\TEACHING\SUBJECTS\Manufacturing\FORMING\Video\2-3-4 high rolling mill.wmv

ROLLING MILLS & EQUIPMENTS Points to remember: Two smaller working rolls are backed up by two or more of the larger back-up rolls. For rolling hard thin materials, work rolls of very small diameter and considerable length needed. This type of mill is generally used for cold rolling work

ROLLING MILLS & EQUIPMENTS It is suitable for continuous & mass production

ROLLING PROCESSES & APPLICATIONS Thread and gear rolling: ..\TEACHING\SUBJECTS\Manufacturing\FORMING\Video\Thread Rolling.mp4 ROLLING PROCESSES & APPLICATIONS Thread and gear rolling: Forms threads on cylindrical parts by rolling them between two dies Commercial process for mass producing bolts and screws because of higher production rates & stronger threads Performed by cold working in thread rolling machines

ROLLING PROCESSES & APPLICATIONS Shape Rolling: Blooms are usually taken as raw materials for shape rolling Multiple steps are required in shape rolling Structural sections such as I-sections, rails, channels can be rolled using set of shaped rolls

ROLLING PROCESSES & APPLICATIONS Ring Rolling: Applications: ball and roller bearing races, steel tires for railroad wheels, and rings for pipes, pressure vessels, and rotating machinery Deformation process in which a thick-walled ring of smaller diameter is rolled into a thin-walled ring of larger diameter Two circular rolls, (idler roll and driven roll )are used, they move closer to each other, thereby reducing the thickness of ring and increasing its diameter A pair of edging rollers are used for maintaining the height constant. ..\TEACHING\SUBJECTS\Manufacturing\FORMING\Video\Ring Rolling.mp4

ROLLING PROCESSES & APPLICATIONS Tube piercing or, seamless tubing: : ..\TEACHING\SUBJECTS\Manufacturing\FORMING\Video\Hot piercing billet process.mp4 Rotary tube piercing is used for producing long thick walled tubes. A pair of skewed rolls are used for drawing the work piece inside the rolls. A mandrel is used for expanding the central hole, and sizing the inner diameter.