Roll Pass Design Process

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y->'

•

•

..·, ...

~

j

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---- ..

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INTRODUC T/ON - 113

Main factors affecting the rolling parameters • ENTRY- EXIT SHAPES AND DIMENSIONS

Geometrical factors

_ _..,.

• CONTACT LENGTH AND CONTACT AREA • ENTITY OF REDUCTION (STRAIN)

Rolling speed

• SPEED OF DEFORMA TION (STRAIN RATE)

• CHEMICAL COMPOSITION

Steel under rolling and rolling temperature

• MECHANICHAL PROPERTIES • THERMAL PROPERTIES •

• CHEMICAL COMPOSITION (mechanical- thermal properties)

Rolling rolls

• ROLLS TEMPERATURE AND SURFACE WEAR •DIAMETER • FRICTION BETWEEN ROLLS AND STEEL UNDER ROLLING

Other factors

• SCALE THICKNESS ON THE BILLET SURFACE • RECRYSTALLIS ATION AND GRAIN STRUCTURE EVOLUTION • TENSION BETWEEN THE STANDS

This document contains proprietary information of Danieli & C. S.p.A., not disclosable, not reproducible. All Rights Reserved.

2

.,,., ..,.

IN TR OD UC TIO N- 213

A good rolling mill simulation pr og ram mu st have •Thern1o-mechanical properties for different steels

Mechanical model

Thermal model

Deformation model

•Yield stess model • Rolling force - torque - pow er calculation models

- - - - i....

Dro p of temperature during the rolling process due to: • interstand cooling (radiation) • water cooling effect • contact with the rolls • deformation heat

Calculation of grooves shape and dimensions on the stands: • spread model • geometrical model

This document contains proprietary information of Danieli & C. S.p.A., not disclosable, not reproducible . All Right s Reserved.

3

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,.

'

INTRODUC TION- 313

IN ANYCA SE '

All the calculation models must be tuned

•USING ROL •USING FEM

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4

YIELD STRESS -1114

THE STEEL YIELD STRESS IS FUNCTI ON OF: • Chemical composition of the steel • Strain entity of deformation • Strain rate speed of deformation • Temperature

This document contains proprietary information of Danieli & C. S. p.A., not disclosable, not reproducible . All Rights Reserved.

5

YIELD STRESS- 2114

STRAIN DEFINITION 2 DEFINITIONS 1 1 h¡

1 1

1 \ dh h, ho rph &h-

ho

L-

," , ,

/ / /

/

,

h.

o

=

ho

- 1 b¡ db - b, - bo rpb &b-

bo

b o

bo

h ho

= ln(h¡' ho '

•

b¡~db

/

/

dh

= b¡)

= ln( b,)

b

bo

11

~dl l¡ 1 \. dl ll -lo &, = ln( ) rp,= lO /. • l lo lo 0 lo

From the law of constancy of volume V 0=V 1 --> h0b010=h 1b 111

With the logarithmic stains it' s possible to have a better description of the state of deformation With the logarithmic stains it' s possible to follow a multiphase deformation as we find on the rolling milis This document contains proprietary information of Danieli & C. S.p.A. , not disclosable, not reproducible. All Rights Reserved .

6

YIELD STRESS- 3114

INFLUE NCE OF STRAIN ON YIELD STRESS Kan

hu

This document contains proprietary information of Danieli & C. S.p.A., not disclosable, not reproducible. All Rights Reserved.

7

YIELD STRESS- 41 14

STRAIN RA TE DEFINITION •dt: time spent to complete the deformation •d 100 s- 1. This document contains proprietary information of Danieli & C. S.p.A., not disclosable , not reproducible. All Rights Reserved .

9

YIELD STRESS- 6114

INFLUENCE OF TEMPERATURE ON YIELD STRESS

~h

T: temperature

With an increase in temperature the yield stress decrease. The injluence of temperature is very strong and affects also the strain rate influence. The temperature has also directs effects on the steel structure with phase changes and recrystallisation phenomena and injluences also the friction coefficient va fue .. This document contains proprietary information of Danieli & C. S.p.A., not disclosable, not reproducible. All Rights Reserved .

10

YIELD STRESS- 7/14

EXAMPLE of yield stress curve for a low carbon steel

S;2100

::t::1 h0 *v0

vn

hn = Dw(l-cos8)+h 1

=

hn *vn= h 1 *v 1 --->v1>vn>v0

vrcos6

Forward slip: S= f

V -V

1

V

r

r=

V V

1_1 r

s = f

hn cosb" _ 1 h1

.

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20

FORC E -3/7 Kwr

in flat rolling plain deformation

In this case: • Free spread and very small ~W •Ratio wlh very high (~30-40) • Entry and exit geometry well known •11=1.15

friction (Kr) 1 o

~vr

1

o

1 o

ho -------- -------- - ; -----

• Pressure distribution on the width is constant • 11 *Kof can be considered constant along the contact length. • The term ~ has not a constant distribution along the contact length with a maximum on the neutral plane • Kwr

----1-r-

roll~g

direction

1 o

1

.------- ----· neutral plane o

0

1 o

Wo

--------

W¡

------------- --------·

-------··--~

is calculated considering a mean value for

~

(with friction coefficient constant along the contact length).

o

R: roll radius h0 : entry height h 1: exit height lct: contact length

w 0 : entry width w 1 : exit width Fct: contact area

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21

FORC E -4/7 Kwr

in long products rolling (3-axial strain)

In genera l all the calcula tion formul ae to calcula te Kwr have been develo ped for flat rolling and must be correct ed for long produc ts rolling.

In this case are not satisfie d the condit ions seen before for flat rolling, in fact: • NOT free spread in sorne cases, where there is a strong constra int of the lateral spread due to the groove d rolls, and almost free spread in other cases. • Ratio w/h small compa red to flat rolling (~1 also