African Foundries Ltd. Lagos, Nigeria

Presented byRahul 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 passIntermediate 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 passClosed 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 designPass 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 calculation in round

Spread calculation in Oval

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

Spread Where y is constant and the value for different pass as

following

Pass ySquare - 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:

Important Formula to Calculate arcWhere:-

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.

Important Formula to Calculate arc Area

Important Formula to Calculate arc 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

Thank You