Roll pass design in continuous bar mills

African Foundries Ltd. Lagos, Nigeria
Presented by
Rahul Kishore

Basics of Rolling
 A rolling mill consist of several, at least two rolls
cylindrical or nearly cylindrical bodies which are
termed as “roll” and which rest in bearings at their
ends.
 The normal and average center distance from the
center of one roll to the center of other determine the
size of mill. Thus 12 inch mill, the distance from center
to center rolls is 12 inch.

Types of pass
 According to shape wise
Definite passes – those having two equal axes in an x, y
plane (Squares, Rounds)

Types of pass
Intermediate passes – those having one axis larger
than the other one (Rectangles – box, Diamonds,
Ovals)

Types of pass
 According to adjustment of rolls
Open passes – The joint between the two rolls is open
or the opening of the pass lies in center.

Types of pass
Closed passes – The projection of one roll fits into a
groove of the other roll.

Pass Design and Groove Details
 This calculation gives the following parameters
for each pass.
Roll groove dimensions.
Roll gap.
Filled width in pass.
Filled area.
Area reduction.
Bite angle.

Number of passes required
 No. of Passes= log of co-eff of elongation/log(1.29)

Thumb rules in rolls pass design
Pass Groove
angle
Bottom
angle
Relief radius Bottom
radius
Box pass 8-10 deg 10
Diamond
pass
>90 deg 18
Square pass 45 deg Around 90
deg
5
Oval pass 60 deg 30 deg 5
Round pass 60 deg 60 deg 0.2 x Bottom
radius
0.5 x dia

Geometrical relation in Rolling

Geometrical relation in Rolling
• A1 x V1 = A2 x V2= A3 x V3…….=1
A1,A2,A3…….. Area of stand 1, stand 2, stand 3…….
V1,V2,V3……..Velocity of stand 1, stand 2, stand 3…….
• Shrinkage factor of steel (1.012 - 1.015)

Thumb rules in rolls pass design
 Fittings from oval to round must be 0.3 to 0.7.
 For ovals width to height ratio must be less than 3.0.

Spread
 When the steel is compressed in the rolls it will
obviously move in the direction of least resistance, so
usually there is not only longitudinal flow but also
some lateral flow. This is called ‘Spread”. it is generally
accepted that beyond a ratio width/height = 5, spread
becomes negligible.

Spread
 The equivalent rectangular approximation into round
oval pass to calculate effective height of the work piece
and the area fraction of work piece and the geometry
of groove.
 H0 – Effective height of outgoing work piece.
 Hi – Effective height of incoming work piece.
 Hi – Height of incoming work piece.
 Reff – Effective Radius of incoming work piece.
 Wi – Width of incoming work piece.
 Bc – Effective Width of work piece.

Spread
 Then maximum spread of a work piece at exit Wmax
was then calculated as.

Spread
 Where y is constant and the value for different pass as
following
Pass y
Square - Oval 0.92
Round - Oval 0.97
Square - Diamond 0.83
Oval - Square 1.06
Oval - Round 0.83
Diamond - Square 0.83
Diamond - Diamond 0.95
Oval - Oval 0.95
With original Shinokura procedure, following spread factors for roll pass design is suggested [1]:

Important Formula to Calculate arc
 To calculate the radius Given an arc or segment with
known width and height:
 The formula for the radius is:

Where:-
 W is the length of the chord defining the base of the
arc .
 H is the height measured at the midpoint of the arc's
base.

Area

Area
 where:
C - is the central angle in DEGREES
R - is the radius of the circle of which the segment is a
part.

Flow Chart to Design Pass For Maximum
Elongation

Important formula to calculate
nominal Weight of bar
Diameter x Diameter
Weight =
162.163

Example
• The Weight of 16 mm Re- Bar
16 x 16 =264
264/162.163 = 1.578 kg
• The Weight of 25mm Re-Bar
25 x 25 = 625
625/162.163 = 3.854 kg

Important formula to calculate
area
 Where Ae = Effective cross-sectional area of bar
L = Length of TMT
W = Weight of TMT

Angle adjustment for twister
guides

Roll pass design in continuous bar mills

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