Group Members

1- Haider Ali2- Saad Hassan

Rolling of Metal

TOPICS

Rolling Types of Rolling Flate Rolling Shapes rolling Ring rolling Rolling mill

Rolling…… process of reducing the thickness of a long work piece.

OR The process of plastically deforming metal by

passing it between the rolls is known as rolling.

Rolling (metalworking)

• Rolling….. Is widely used to convert steel ingots into blooms, billets, and slabs, and subsequently into plates, sheets and strips.

Rods

Advantages:

Provides high throughput. Provides good control over the dimensions

of the finished product.

Rolling Process

Rolls transfer energy to the strip through friction. As the strip is dragged by the rolls into the gap between them, it decreases in thickness while passing from the entrance to the exit. Meanwhile its speed gradually increases from the entrance to the exit.

V0 = input velocityVf = final or output velocityR = roll radiushb = back height hf = output or final thickness

Rolling process

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Hot rolling Cold rolling

Classification of Rolling Process

Hot rolling

Hot working ---- above the re-crystallization temperature.

It is employed where large reduction in cross-sectional area is required.

Used for to produce bars, rods, rails etc.

Advantages:

Machanical strength is increase. Porosity is reduce.

Dis-Advantages:

Poor surface finish. Loss of precise dimension.

Cold rolling

Cold working ---- below the re-crystallization temperature.

Employed for finishing the metal to given specification of sizes and surface quality.

Produces sheets, strips and foils.

with good surface finish increased mechanical strength.

Advantages:

Re-crystallization

Re-crystallization is a process by which deformed grains are replaced by a new set of undeformed grains.

Re-crystallization temperature can be defined as the temperature at which destroyed grains of a crystal structure are replaced by the new strain grains

→ Solvent added (clear) to compound (orange) → Solvent heated to give saturated compound solution (orange) → Saturated compound solution (orange) allowed to cool over time to give crystals (orange) and a saturated solution (pale-orange

Flat Rolling

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

Flat Rolling

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

Product of the first hot-rolling operation - Bloom or slab Square cross section of 150mm (6in) on one side Processed further by shape rolling

I-beams Railroad rails

Flat-Rolling 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.

Changes in grain structure during hot-rolling

Defects in Rolled Plates & SheetsDefects in Rolled Plates & Sheets

Undesirable Degrade surface appearance Adversely affect the strength

Sheet metal defects include: Scale, Rust, Scratches, Pits, & Cracks May be caused by impurities and inclusions

Wavy edges – result of roll bending

Other CharacteristicsOther 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 finish 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 Schematic Illustration of Various Roll arrangementsarrangements

Shape-RollingShape-Rolling Structural shape rolling, also known as shape rolling and

profile rolling. It is a metal forming process where structural shapes are passed

through rollers to bend or deform the workpiece to a desired shape while maintaining a constant cross-section.

Structural shapes that can be rolled include: 1) I-beams 2) H-beams 3) T-beams 4) U-beams 5) channels 6) railroad rails 7) pipes

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.

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

Ring RollingRing 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

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 ROLLINGRING 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

ROLLING MILLS: A rolling mill consists basically of rolls, bearings, a housing

for containing these parts, and a drive for applying power to the rolls and controlling there speeds.

Rolling mills can be conventionally classified with respect to the number and arrangement of the rolls.

Classification of rolling mills:

i) Two-high millsii) Tow-high reversing millsiii) Three-high millsiv) Four-high millsv) Cluster millsvi) Continuous millsvii) Planetary mills

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

Continuous Casting & Integrated Mills & MinimillsContinuous Casting & Integrated Mills & Minimills Continuous casting

Advantages Highly automated Reduces product cost Companies are converting over to this type of casting

Continuous Casting & Integrated Mills & Minimills Con’tContinuous 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

ROLLED PRODUCTSi) Bloom: First breakdown product of ingots with a minimum

cross-sectional area of 36 in2. Generally, square in cross-scetion.ii) Billet: Further reduction of bloom by rolling results in a billet. Cross-sectional area 1.5 in. X 1.5 in.iii) Slab: A hot rolled ingot with a width to thickness ratio of 2:1

at least. Cross-sectional area over 16 sq. in. **Blooms, billets and slabs are known as semi-finished products

because they are subsequently formed into other mill products.

iv) Plate: It has thickness greater than ¼ in.

v) Sheet and Strip: Generally have thickness lesser than ¼ in.

vi) Foil: Thickness is very small just as 0.002 in.

* Billets and other unfinished rollings are further rolled to I-sections, T-sections, Angles, Channels, Girders etc.

Application Of Rolling in Pakistan Industry.

BATALA STEEL PRODUCTS

Mughal Steel Products

PAKISTAN STEEL MILL

PAKISTAN STEEL MILL also produced Sheets, Strips and Plates.Uses.Pipes for Gas/Water/Oil.Storage Tanks, Vessels, Containers.Ships, Launches & Floating Structures.Steel Flooring.

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