3. ➢Bab ini membahas
✓ Flat rolling
✓ Shape rolling
✓ Pembuatan of seamless tubing & pipe
➢Apa itu proses Rolling? – process of reducing the thickness of a
long work piece
➢Plates – memiliki tebal lebih dari 6 mm
➢Sheets/lembaran – umumnya memiliki tebal kurang dari 6 mm
5. ▪ Metal strip masuk ke 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
▪ Factor2 yang mempengaruhi Rolling Process
▪ Frictional Forces
▪ Roll Force and Power Requirement
6. Friction Forces acting on strip forces
▪ Max Draft
▪ h0-hf = µ2R
Roll Force
▪ F= W0.L.Yavg
▪ L=̃ sqrt{R(ho-hf)}
7. 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
▪ Railroad rails
8. ▪ 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
9. 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
10. 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
11.
12.
13. 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
14.
15. 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
16. 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
17. THREAD ROLLING
▪ Cold-forming process
▪ Straight or tapered threads are formed on round rods by passing
the pipe though dies
▪ Typical products include
▪ Screws
▪ Bolts
18. THREAD ROLLING CON’T
▪ 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
19. 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
20. CONTINUOUS CASTING & INTEGRATED MILLS & MINIMILLS
▪ Continuous casting
▪ Advantages
▪ Highly automated
▪ Reduces product cost
▪ Companies are converting over to this type of casting
21. 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
