Rolling of Metals
Introduction
This chapter describes
Flat rolling
Shape rolling
Rolling Mills
Production of seamless tubing & pipe
Defects in rolled products
Introduction
• The Process of Plastically deforming
metal / alloy by passing it between rolls is
known as ROLLING.
• Rolling done either at Hot or cold.
• The metal is drawn into the opening
between the rolls by frictional forces.
• Work piece is subjected to high
compressive forces due to squeezing action
of rolls, resulting in reduced area of cross-
section and increased length.
Cold Rolling Hot Rolling
TERMINOLOGY
INGOT
BLOOM [ 150 x150 mm] or [ 250x300 mm]
BILLET [ 50 x 50] or [ 125 x 125 ]
Slab B = 300-1500 mm
PLATE [ t > 6.35 mm ]
SHEET [ t < 6.35]
STRIP [ t = 6.35 & b = 600 mm ]
FOIL [ t < 1.5 mm & b= 300mm ]
TERMINOLOGY Contd.,
• Angle of contact or Angle of bite – The
Angle subtended at the centre of the roll
by arc AB ( Metal in contact with the roll)
• Rolling Pass – The feeding of material
between the rolls once
• Rolling mill – Consists of rolls ,
bearings& Housings and Drive for
applying power to rolls
Flat Rolling Process
Flat
Flat Rolling Process
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
GEOMETRY OF ROLLING
h0/2 h1/2
CL
B
L
A R
R R-h/2
• The angle of bite α can be expressed as;
tan α = α = L/R
• The length of contact,
L=̃ sqrt{R(h
(2) -h )}
o f
h0 is the strip thickness at start and R is the
roll radius
• h0-hf = µ2R
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
• 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. 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
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
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
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
