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Limits and evolution of needs in the simulation of flat product rolling Eliette Mathey
Presented by Nelson Souto
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Context
2/12
ArcelorMittal – Flat product rolling research:
Hot strip mills
Cold rolling mills
Temper mills
2 complementary approaches for simulation
1) Complex models (finite element or other “heavy” numerical models)
• Understand phenomena during rolling
– improvement of process & solving of problems (only R&D models)
• Models with several interactions (strip models/roll deformation models) – Thermal, mechanical, microstructural, tribological phenomena
• Low constraints on computational time (hours OK)
• Reference models to develop simplified models
2) Simplified models (replace supplier models in plants)
• Models for setup & control – On-line models or R&D offline models to run many times
• Strong constraints on computational time – Just few msec for multiple computations on each strip during rolling campaign
• Regression of complex models (lower dimension, fewer interactions…)
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Introduction Simulation needs in hot rolling
Thickness : 220-260mm Length : 10-15m Width : 800 – 2200 mm Discharging temp: ≈ 1200°C
Width reduction Thickness down to 25-35mm
Thickness : 1.5-25mm Length : 400-1500m Width : 800 – 2200 mm Finishing rolling temp : ≈800-950°C
Cooling down to coiling temp ≈ 550-750°C
Typical tolerances on final product: Thickness : +/- 0.1 mm Crown : 40-60µm at 40mm from edge
3/12
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Introduction Simulation needs in hot rolling
Thickness : 220-260mm Length : 10-15m Width : 800 – 2200 mm Discharging temp: ≈ 1200°C
Width reduction Thickness down to 25-35mm
Thickness : 1.5-25mm Length : 400-1500m Width : 800 – 2200 mm Finishing rolling temp : ≈800-950°C
Cooling down to coiling temp ≈ 550-750°C
Typical tolerances on final product: Thickness : +/- 0.1 mm Crown : 40-60µm at 40mm from edge
Combustion, energy consumption, temp. homogeneity, productivity
Temperature, scale
Force, temperature, shape (microstructure)
Force, temperature, shape, flatness, microstructure
Temperature, flatness, microstructure
4/12
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Lam3: strip model
Very performant unique stationnary formulations
- Visco-Plastic & Elasto-Visco-Plastic material behavior
- Low computation time for simulation of stationnary process
Can use high anisotropic mesh without precision loss
- very well adapted for simulation of very thin strip rolling
User can define friction, strip behavior, microstructure
evolution laws
Tec3: roll deformation model
Very accurate work roll deformation prediction
Almost no computation cost
- no need for 3D roll simulation
y
z
Roll 1 (WR)
Roll 2 (shiftable IR))
Roll 3 (BUR)
Contact line 0
Contact line 1
Contact line 2
f0
f1
f2
Ftot/2 Ftot/2
Fwrb/2 Fwrb/2
Complex models Lam3-Tec3 R&D rolling model
ArcelorMittal is co-owner of LAM3-TEC3 source code with Constellium 5/12
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Surface quality defect:
displacement of slab corner on top & bottom surfaces
during roughing (succession of vertical & horizontal passes)
Simulation of H/V passes to predict corner movement
Optimization of width reduction schedule
Optimization of edger roll shape (flat, groove shape)
After roughing mill, edge line defect up to 40mm product edge
Horizontal pass (H) Vertical pass (V)
Initial corner position
Final corner position
Complex models Lam3 application: Reduction of edge line defect in the roughing mill
6/12
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Complex models Lam3-Tec3 application: Effect of crown & flatness actuators (FM)
Finishing mill (FM):
Strip crown and flatness is consequence of work roll deformation and actuators like
bending forces, roll shape…
Coupled Lam3-Tec3 simulations provide accurate prediction of strip crown and flatness
less strip crown latent flatness
Effect of bending forces
+
-
+
-
Non-homogeneous stress (latent flatness)
1st stand of finishing mill (example)
wavy edges
center buckle
Accurate 3D computation for strip + roll deformation
Only a few minutes CPU
7/12
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Recrystalized fraction
850°C
However some questions remains:
1) How to take into account flatness defect at the entry of the stand
geometrical defect not possible with stationary simulation
stress distribution applied on the entry section will evolve before the roll bite…
2) Chaining of passes: how to take into account interstand phenomena
effect of creep on stress distribution
proper chaining residual stresses between passes
3) Effect of microstructure evolution in the interstand
Recrystalization influences interstand creep rate and might have effect on stress, flatness
and width evolution [M.Zhang, PhD 2014]
Complex models Lam3-Tec3: Difficulties and Limits
8/12
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Limited evolution of Lam3-Tec3 in the last 20 years
Chaining/coupling with flatness models (PhD thesis S. Abdelkhalek, R. Nakhoul, K. Kpogan)
but huge loss of competencies to use these developements
Coupling with microstructure models (Internship)
needs to be updated, adapted to multipass rolling
Parallelisation of Lam3 solver (Internship + Open Engineering)
limited improvement (only for resolution of linear system)
‘‘Aging’’ code
Mainly interfaces developement (Open Engineering)
to ease the use of the model but remains difficult to master
Limited internal ressources & competencies to modify code
Other finite element software used (Abaqus, Forge, etc.)
Complex models Lam3-Tec3: Difficulties and Limits
9/12
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Simplified models Force Prediction
Estimate rolling force in FM for setup, capability estimation…
- Temperature evolution (usually 1D model)
- Roll deformation : Hitchcock model (analytical model)
- Force/Torque/Power estimation: from simple models (Sims) to more elaborate 2D models (Von Karman, Orowan)
- 2 main unknown data:
• Product yield stress acording to temperature Compression trials according to temperature or microstructure model
• Friction coefficient on roll bite still difficult to estimate beforehand (evolution of roll surface, lubrication…)
However tuning and adaptation allow accurate estimations (but measurements needed!)
Temperature/Force/Torque prediction along FM (example)
Before tuning
After tuning on a database of the
same grade
10/12
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Simplified models Threading refusal model
Estimate threading refusal risk for setup based on ½ analytical model
Incremental computation on evolution of the strip kinetic energy
Energy balance between deformation and friction
Increasing friction better threading Decreasing s0 easier threading
Unknow data: Product yeld stress and friction coefficient
Good prediction of risk with back-calculated data
Calculation time only 0.1 sec
but
0
0.05
0.1
0.15
0.2
0.25
0.3
0 10 20 30 40 50 60 70 80 90
Position in campaign
Lim
it f
rictio
n c
oe
ffic
ien
t
Laminés - µ Calculé Laminés - µ Limite Patinages - µ Limite
137B
Back-calculated friction
Limit friction to avoid threading
Coils with slippage at threading
11/12
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Simplified models Difficulties and Limits
On-line models in plants based on regression of complex models
Fitting of linear models based on experimental plans
Lam3 or Tec3 simulations
Very fast computations
just few ms
Model cannot be easily modified when changes are made on the plant or new grade
are produced
adaption will over-compensate or reach unrealistic values
Fast models with phisical basis needed nowadays
strip models for 3D applications (widening, flatness)
friction evolution
12/12
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Conclusions
Complex models
• Finite element modelling remains reference for understanding
• Lam3-Tec3: “relatively fast” stationary model with roll deformation
Simple models (needed)
• With physical background
• Fast computation
• Easy to maintain & roll out in mills
Both models
• Parameters still difficult to estimate beforehand (friction, yield stress)
• Assumptions difficult to validate (temperature distribution, stress distribution…)
13/12
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Thank you for your attention !
Limits and evolution of needs in the
simulation of flat product rolling
Eliette Mathey
(Presented by Nelson Souto)