Chapter 13

1 / 22

# chapter 13 - PowerPoint PPT Presentation

Rolling of Metals. Chapter 13. Introduction. This chapter describes Flat rolling Shape rolling Production of seamless tubing &amp; pipe Rolling – process of reducing the thickness of a long work piece Plates – having thickness greater than 6mm Sheets – generally less than 6mm thick.

I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.

## PowerPoint Slideshow about 'chapter 13' - Leo

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript

Introduction

• This chapter describes
• Flat rolling
• Shape rolling
• Production of seamless tubing & pipe
• Rolling – process of reducing the thickness of a long work piece
• Plates – having thickness greater than 6mm
• Sheets – generally less than 6mm thick

Flat Rolling

Flat Rolling Process

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
• Roll Force and Power Requirement
Frictional Forces

Friction Forces acting on strip forces

• Max Draft
• h0-hf = µ2R

Roll Force

• F= W0.L.Yavg
• L=̃ sqrt{R(ho-hf)}
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 Con’t
• 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

Changes in grain structure during hot-rolling

Defects in Rolled Plates & Sheets
• Undesirable
• 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
• Alligatoring – complex phenomenon
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 gauge number
Schematic Illustration of various roll arrangements : (a) two-high; (b) three-high; (c) four-high; (d) cluster mill
Shape-Rolling Operations
• Various shapes can be produced by shape rolling
• Bars
• Channels
• I-beams
• Roll-pass design requires considerable experience in order to avoid external and internal defects

Stages in Shape Rolling of an H-section part. Various other structural sections such as channels and I-beams, are rolled by this kind of process.

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
• Close dimensional tolerances
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

• Cold-forming process
• Straight or tapered threads are formed on round rods by passing the pipe though dies
• Typical products include
• Screws
• Bolts
• Threads are rolled in the soft condition
• Threads may then be heat treated, and subjected to final machining or grinding
• Uncommon or special-purpose threads are machined
Production of Seamless Pipe & Tubing
• Rotary tube piercing (Mannesmann process)
• Hot-working process
• Produces long thick-walled seamless pipe
• Carried out by using an arrangement of rotating rolls
• Tensile stresses develop at the center of the bar when it is subjected to compressive forces
Continuous Casting & Integrated Mills & Minimills
• Continuous casting
• Highly automated
• Reduces product cost
• Companies are converting over to this type of casting
Continuous Casting & Integrated Mills & Minimills Con’t

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
• Structural steel
Spray Casting : In spray casting the molten metal is sprayed over a rotating mandrel to produce seamless tubing and pipe