2. 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.
3. Types of pass
According to shape wise
Definite passes – those having two equal axes in an x, y
plane (Squares, Rounds)
4. Types of pass
Intermediate passes – those having one axis larger
than the other one (Rectangles – box, Diamonds,
Ovals)
5. 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.
6. Types of pass
Closed passes – The projection of one roll fits into a
groove of the other roll.
7. 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.
8. Number of passes required
No. of Passes= log of co-eff of elongation/log(1.29)
9. 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
11. 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)
12. 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.
13. 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.
16. 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.
19. 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]:
20. 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:
21. Important Formula to Calculate arc
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.
23. 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.
