Metal Rolling

Chapter 13

Chapter 13

Rolling of Metals

Rolling of Metals

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This chapter describes

This chapter describes

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Flat rolling

Flat rolling

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Shape rolling

Shape rolling

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Production of seamless tubing & pipe

Production of seamless tubing & pipe

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_{Rolling – process of reducing the thickness of a}

_{Rolling – process of reducing the thickness of a}

long work piece

long work piece

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Plates – having thickness greater than 6mm

Plates – having thickness greater than 6mm

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_{Sheets – generally less than 6mm thick} 

_{Sheets – generally less than 6mm thick} 

Introduction

Introduction

 Flat Rolling Process

• Metal strip enters the roll gap

• The strip is reduced in size by the metal rolls

• The velocity of the strip is increased the metal strip is reduced in size • Factors affecting Rolling Process

 –  Frictional Forces

Frictional Forces

Friction Forces acting on strip forces •

Max Draft 

•

h

-h

= µ2R

•

 F= W 

.L.Y 

 Flat-Rolling Practice

 Flat-Rolling Practice

• Hot rolling

 –  The initial break down of an ingot  –  Continuously cast slab

 –  Structure may be brittle

 –  Converts the cast structure to a wrought structure • Finer grains

• Enhanced ductility  –  Reduction in defects •

Continuous Casting 

 –  Is replacing traditional methods  –  Faster & better 

Product of the first hot-rolling operation - Bloom or slab

 –  Square cross section of 150mm (6in) on one side  –  Processed father by shape rolling

• I-beams

Flat-Rolling Practice Cont'd

• Billets – smaller than blooms and rolled into bars and rods • Cold rolling

 –  carried out at room temperature  –  Produces sheet and strip metal  –  Better surface finish – less scale

• Pack rolling – when two or more layers of metal are rolled together 

 Defects in Rolled Plates & Sheets

 Def ects in Rolled Plates & Sheets

 –  Degrade surface appearance  –  Adversely affect the strength • Sheet metal defects include:

 –  Scale, Rust, Scratches, Gouges, Pits, & Cracks  –  May be caused by impurities and inclusions • Wavy edges – result of roll bending

Other Characteristics

Other Characteristics

• Residual stresses – produces:

 –  Compressive residual stresses on the surfaces

 –  Tensile stresses in the middle

• Tolerances

 –  Cold-rolled sheets: (+/- ) 0.1mm – 0.35mm

 –  Tolerances much greater for hot-rolled plates

• Surface roughness

 –  Cold rolling can produce a very fine finish

 –  Hot rolling & sand have the same range of surface finish

• Gauge numbers – the thickness of a sheet is identified by a

Schematic Illustration of Various Roll arrangements

Schematic Illustration of Various Roll arrangements

Schematic Illustration of various roll arrangements : (a) two-high; (b) three-high; (c) four-high; (d) cluster mill

Shape-Rolling Operations

Shape-Rolling Operations

• Various shapes can be produced by shape rolling

 –  Bars

 –  Channels

 –  I-beams

 –  Railroad rails

•

Roll-pass design

requires considerable experience in order 

to avoid external and internal defects

Stages in

Shape Rolling of an H-section part 

 Ring Rolling 

 Ring Rolling 

• A thick ring is expanded into a large diameter ring  –  The ring is placed between the two rolls

 –  One of which is driven

 –  The thickness is reduced by bringing the rolls together  • The ring shaped blank my be produced by:\

 –  Cutting from plate  –  Piercing

 –  Cutting from a thick walled pipe

Various shapes can be produced by shaped rolls • Typical applications of ring rolling:

 –  Large rings for rockets  –  Gearwheel rims

 –  Ball-bearing and roller-bearing races • Can be carried out at room temperature • Has short production time

 RING ROLLING

 RING ROLLING

(a) Schematic illustration of  Ring-rolling operation. Thickness reduction results in an increase in the part diameter.

(b) Examples of cross-sections that can be formed by ring-rolling

Thread Rolling 

Thread Rolling 

• Cold-forming process

• Straight or tapered threads are formed on round rods by passing the pipe though dies

• Typical products include  –  Screws

Thread Rolling Cont'd 

Thread Rolling C ont'd 

• Threads are rolled in the soft condition

• Threads may then be heat treated, and subjected to final machining or  grinding

 Production of Seamless Pipe & Tubing 

• Rotary tube piercing (Mannesmann process)  –  Hot-working process

 –  Produces long thick-walled seamlesspipe

 –  Carried out by using an arrangement of rotating rolls

Continuous Casting & Integrated Mills & Minimills

Continuous Casting & Integrated Mills & Minimills

• Continuous casting  –  Advantages

• Highly automated • Reduces product cost

Continuous Casting & Integrated Mills & Minimills Cont'd 

Continuous Casting & Integrated Mills & Minimills Cont'd 

 Integrated Mills utilize everything from the production of hot metal to the casting and rolling of the finished product

 Minimills

 –  Scrap metal is melted  –  Cast continuously

 –  Rolled directly into specific lines of products

 –  Each minimill produces one kind of rolled product • Rod

• Bar 

Spray Casting 

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 THE END

 THE END