Presentation on theme: "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."— Presentation transcript:
1 ROLLINGRolling 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.
2 ROLLING The gap between rolls < thickness of entering bar Friction force necessary to bite the bar and to pull it through the rollsMetal bar gets squeezed, and elongated while its c/s area decreasesThe most important industrial metal forming operationsa machine rolling:ROLLING MILLIn a typical rolling mill:A pair of rolls is driven by an electric motor which transmits torque through gearRolls are mounted in a stand with a screw-down mechanism.
3 TYPES - based on work temperature: ROLLINGTYPES - based on work temperature:– Hot Rolling:most common due to the large amount of deformation required– Cold rolling:produces finished sheet and plate stockHot 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.
4 TYPES -based on work-piece geometry: ROLLINGTYPES -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.
5 ROLLING Microscopic View: Coarse grain becomes finer in size Gets elongated along the direction of rollingIn order to refine the grains, heat treatment performed immediately after rolling, which results in recrystallization after rollingAPPLICATION: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
6 ROLLING Analysis: DRAFT: amount of thickness reduction, d = t o - t f R=roll radiusL=contact arc lengthLp=projected arc lengthhf= strip final thicknessVr=velocity of the rollVf=velocity of the strip at roll exitho=strip initial thicknessN=neutral pointα=angle of biteVo=velocity of strip at entrance to rollAnalysis:DRAFT:amount of thickness reduction, d = t o - t fToo much & too little??REDUCTION:draft expressed as a fraction of starting stock thickness, r = d / toCONTACT ARC LENGTH:Smaller rollers have small length of contactSide view of flat rolling, indicating before and after thicknesses, work velocities, angle of contact with rolls, and other features.
7 ROLLINGMILLS & EQUIPMENTSDriving Power per Roll: PR = T x wT=FXR/2
8 ROLLING MILLS & EQUIPMENTS Points to remember: Two horizontal rolls revolving at the same speed but in opposite directionRolls are supported on bearings housed in sturdy upright side frames called standsSpace between the rolls can be adjusted by raising or 1owering the upper roll.
9 ROLLING MILLS & EQUIPMENTS Points to remember: Three parallel rolls, arranged one above the otherIt is used for rolling of two continuous passes in a rolling sequenceThis results in a higher rate of production than the two-high rolling mill.
10 Two high would result in wavy rolled plates or sheets unevenly thick Points to remember:It is essentially a two-high rolling millTwo middle rolls are smaller in size than the top and bottom rollsSmaller size rolls (working rolls) concentrate the total rolling pressure over the workpiece.The larger (back-up rolls) prevents the deflection of the smaller rollsROLLINGMILLS & EQUIPMENTSTwo high would result in wavy rolled plates or sheets unevenly thick..\TEACHING\SUBJECTS\Manufacturing\FORMING\Video\2-3-4 high rolling mill.wmv
11 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
12 ROLLING MILLS & EQUIPMENTS It is suitable for continuous & mass production
13 ROLLING PROCESSES & APPLICATIONS Thread and gear rolling: ..\TEACHING\SUBJECTS\Manufacturing\FORMING\Video\Thread Rolling.mp4ROLLINGPROCESSES & APPLICATIONSThread and gear rolling:Forms threads on cylindrical parts by rolling them between two diesCommercial process for mass producing bolts and screws because of higher production rates & stronger threadsPerformed by cold working in thread rolling machines
14 ROLLING PROCESSES & APPLICATIONS Shape Rolling: Blooms are usually taken as raw materials for shape rollingMultiple steps are required in shape rollingStructural sections such as I-sections, rails, channels can be rolled using set of shaped rolls
15 ROLLING PROCESSES & APPLICATIONS Ring Rolling: Applications: ball and roller bearing races, steel tires for railroad wheels, and rings for pipes, pressure vessels, and rotating machineryDeformation process in which a thick-walled ring of smaller diameter is rolled into a thin-walled ring of larger diameterTwo circular rolls, (idler roll and driven roll )are used, they move closer to each other, thereby reducing the thickness of ring and increasing its diameterA pair of edging rollers are used for maintaining the height constant...\TEACHING\SUBJECTS\Manufacturing\FORMING\Video\Ring Rolling.mp4
16 ROLLING PROCESSES & APPLICATIONS Tube piercing or, seamless tubing: : ..\TEACHING\SUBJECTS\Manufacturing\FORMING\Video\Hot piercing billet process.mp4Rotary 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.