sci course lecture-1
DESCRIPTION
STEELTRANSCRIPT
-
R&D-PRC-SRC
Surface Conditioning & Interaction courseFocus areas: Rolls, Defects & Inspection
Champion: Sudhansu Pathak
Lecturer: Dr Henk Bolt & Dr Lene Hviid
March 2013 - Jamshedpur
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2Surface Conditioning & Interaction course
Time schedule
1. Rolls training2. SIS training
1. Rolls training2. SIS training
1. Rolls training2. SIS training
Two sessionsin plants (choice)
7th of March
15.00 to
16.00
LUNCH
11.30 to
12.45
BREAK
10.45 to
11.30
BREAK
9.00 to 10.30Thursday
Exercise customer defect
complaint
Lec. 8 A3 solving method for defects
Lec. 7Inspection & Coilgrading
Lec. 6 Surface
inspection and control
Lec. 5 Quality controlSDC
6th of March
16.15 to
17.15
BREAK
15.00 to
16.00
LUNCH
11.30 to
12.45
BREAK
10.45 to
11.30
BREAK
9.00 to 10.30Wednesday
Exercise Rolls/lubric. problem
Lec. 4Lubrication
Lec. 3 Rolls failure
& Rolls database
Lec. 2Performance of rolls & surface
Lec. 1Importance of Rolls
5th of March
16.15 to
17.15
BREAK
15.00 to
16.00
LUNCH
11.30 to
12.45
BREAK
10.45 to
11.30
BREAK
9.00 to 10.30Tuesday
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3Rolling Mill Rolls are high-impact key assets
the work horses of any rolling mill
This lecture will highlight the importance & impact of rolls in multiple
aspects costs, product quality, process & daily operations, supply security
A focus on rolling mill rolls within Tata Steel
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Importance of Rolling Mill RollsLecture 1
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5Importance of Rolls
Supply security
Ensure rolls are defect-free & fit-for-purpose
roll shop operations transport, handling, storage
roll inspection
Heart of the rolling process
Harsh operating conditions
Impact on product quality
Cooling/mill hardware & scheduling requirements
High total cost of ownership
Impact on mill operations,downtime, capacity, capability
Roll failure risk
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6 Rolls technology: Core area for Tata Steel mills and R&D Rolls procurement: Strategic function with lead buyer for Tata Steel Group
Rolls: high-impact key assets for rolling mills
High costs roll purchasing roll shop texturing, Cr-platingmill downtime for rollchanges & failuresworking capital tied upin roll fleetstorage space
High impact on
product quality surface defects rougness / texturetransferstrip gauge & shape rollability of product mix
High impact on
operational levelmill scheduling /planned roll changesunplanned roll changessafety aspects, rollfailures & preventionmill pacingmill vibrations, frictioncooling requirements transport/handling
Supply security lead times can be verylong & roll consumptioncan fluctuatemills require tailoredroll properties ratherthan off-the-shelfproducts from rollsuppliers
Roll use = core competency for Tata Steel rolling mills cannot be left / outsourced successfully to third parties
Need for cooperationwith top quality roll suppliers
Importance of rolls
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7 Rolls technology: Core area for Tata Steel mills and R&D Rolls procurement: Strategic function with lead buyer for Tata Steel Group
Rolls: high-impact key assets for rolling mills
High costs roll purchasing roll shop texturing, Cr-platingmill downtime for rollchanges & failuresworking capital tied upin roll fleetstorage space
High impact on
product quality surface defects rougness / texturetransferstrip gauge & shape rollability of product mix
High impact on
operational levelmill scheduling /planned roll changesunplanned roll changessafety aspects, rollfailures & preventionmill pacingmill vibrations, frictioncooling requirements transport/handling
Supply security lead times can be verylong & roll consumptioncan fluctuatemills require tailoredroll properties ratherthan off-the-shelfproducts from rollsuppliers
Roll use = core competency for Tata Steel rolling mills cannot be left / outsourced successfully to third parties
Need for cooperationwith top quality roll suppliers
Importance of rolls
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8Financial impact of roll use in tandem cold strip mills
Roll costs per tonne - year 2003 .
0
2
4
6
8
10
Port Talbot Llanwern CSPY- CM21 CPP-
IJmuiden-
CM11
CPP-
IJmuiden-
CM12
p
o
u
n
d
s
p
e
r
t
o
n
n
e
Miscellaneous, chocks, ..
Roll stock costs
Mill downtime costs
Roll shop costs
Material costs
not included: cost of roll-related coil rejections / repairs / downgrading consequential damage of roll failures (other than loss of roll life)
roll purchasing costs of new rolls constitute only a minority fraction of the total costs of roll usage (TCO = total cost of ownership).
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9Financial impact of roll use in HSMs
total roll-related costs in Corus Hot strip mills;
year=2004
0
2.000.000
4.000.000
6.000.000
8.000.000
10.000.000
12.000.000
14.000.000
16.000.000
18.000.000
20.000.000
HSM
Port Talbot
HSM
Llanwern
HSM2
IJmuiden
t
o
t
a
l
r
o
l
l
-
r
e
l
a
t
e
d
c
o
s
t
s
Mill downtime costs for roll changes
Miscellaneous, chocks, ..
Roll stock costs
Roll shop costs
Roll material costs
roll-related costs per tonne in Corus Hot strip mills;
year=2004
0
1
2
3
4
5
6
HSM
Port Talbot
HSM
Llanwern
HSM2
IJmuiden
r
o
l
l
-
r
e
l
a
t
e
d
c
o
s
t
s
p
e
r
t
o
n
n
e
Mill downtime
costs for roll
changes
Miscellaneous,
chocks, ..
Roll stock
costs
Roll shop
costs
Roll material
costs
roll material costs per tonne
in Corus Hot strip mills; year=2004
0,00
0,50
1,00
1,50
2,00
2,50
3,00
HSM Port Talbot HSM Llanwern HSM2 IJmuiden DSP
IJmuiden
r
o
l
l
m
a
t
e
r
i
a
l
c
o
s
t
s
p
e
r
t
o
n
n
e
Edger & HSB rolls
Back-up Rolls
Rear Finishing Mill Work Rolls (EC/IC)
Early Finishing Mill Work Rolls (HiCr/HSS)
Roughing Mill Work Rolls
roll material costs per km strip
in Corus Hot strip mills; year=2004
10
20
30
40
50
HSM Port Talbot HSM Llanwern HSM2 IJmuiden DSP
IJmuiden
r
o
l
l
m
a
t
e
r
i
a
l
c
o
s
t
s
p
e
r
k
m
s
t
r
i
p
Edger & HSB rolls
Back-up Rolls
Rear Finishing Mill
Work Rolls (EC/IC)
Early Finishing Mill
Work Rolls (HiCr/HSS)
Roughing Mill Work
Rolls
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10
Raw material price development
TSG-SDS raw material prices
0
10
20
30
40
50
60
70
80
90
100
dec-03
jun-04
dec-04
jun-05
dec-05
jun-06
dec-06
jun-07
dec-07
jun-08
dec-08
jun-09
dec-09
jun-10
dec-10
N
i
,
M
o
,
V
p
r
i
c
e
s
i
n
/
k
g
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
C
r
,
s
t
e
e
l
s
c
r
a
p
p
r
i
c
e
s
i
n
/
k
g
NickelMolybdenumVanadiumChrome
Steel Scrap
TSG-SDS raw material price indices
(April-2010 = 100)
0
50
100
150
200
250
300
350
400
dec-03
jun-04
dec-04
jun-05
dec-05
jun-06
dec-06
jun-07
dec-07
jun-08
dec-08
jun-09
dec-09
jun-10
dec-10
p
r
i
c
e
i
n
d
e
x
Nickel
Molybdenum
Vanadium
Chrome
Steel Scrap
Raw material price fluctuations large impact on roll prices
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11
Rolls procurement in TSG (May 2011)
Spend: estimated at US$ 100 Million per annum on rolls in TSG
Since May 2011: Some decrease in roll spend (TSE: less roll consumption & destocking; raw material prices ) Forecast FY14, FY15: again around US$ 100 Million (with bigger share for TSL: more mill output)
Mills/works: > 50 mills/works across TSG using rolls
Items: > 1,000 different roll items across TSG
Delivery times: Ranging from 3 months for small rolls (mainly for long product mills) to >3 years for large (back-up) rolls
$20,800,000
$80,500,000
Asia
Europe
$3,100,000
$18,400,000
$35,500,000
$21,700,000
$22,600,000
Tungsten carbidediscs
Static castrolls/sleeves
Spin cast work rolls
Forged work &intermediate rolls
Cast & forged back-up rolls
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12
Rolls technology: Core area for Tata Steel mills and R&D Rolls procurement: Strategic function with lead buyer for Tata Steel Group
Rolls: high-impact key assets for rolling mills
High costs roll purchasing roll shop texturing, Cr-platingmill downtime for rollchanges & failuresworking capital tied upin roll fleetstorage space
High impact on
product quality surface defects rougness / texturetransferstrip gauge & shape rollability of product mix
High impact on
operational levelmill scheduling /planned roll changesunplanned roll changessafety aspects, rollfailures & preventionmill pacingmill vibrations, frictioncooling requirements transport/handling
Supply security lead times can be verylong & roll consumptioncan fluctuatemills require tailoredroll properties ratherthan off-the-shelfproducts from rollsuppliers
Roll use = core competency for Tata Steel rolling mills cannot be left / outsourced successfully to third parties
Need for cooperationwith top quality roll suppliers
Importance of rolls
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13
Supply security
Unique geometrical designper mill and per roll type
Rolls tailor-made to customers order
Lead times can be very long
+
Fluctuating roll consumption rates
Rolling mill rolls are not available of-the-shelf
Variations in mill output, product mix, rolling process, mill condition, excess
roll consumption
challenging task to ensure that: mills will always have sufficient rolls to keep on rolling
whilst avoiding excessive stock
Once, work rolls were transported
by airplane from Brazil (!) to
The Netherlands to prevent DSP
mill stoppage due to lack of rolls
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14
Supply security tailored rolls
mill-specific roll requirements (microstructural) material properties
A successful roll grade in a certain mill may perform poorly or even fail in a different rolling application
standard roll grades offered by suppliers still need to be fine-tuned
especially for more demanding rolling applications
Maintain fruitful bilateral relations with several key roll suppliers
ensure an adequate level of technology exchange
roll supplier needs to know the mill and grasp its key requirements
roll user should understand the capabilities and limitations of the roll manufacturer
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15
Rolls technology: Core area for Tata Steel mills and R&D Rolls procurement: Strategic function with lead buyer for Tata Steel Group
Rolls: high-impact key assets for rolling mills
High costs roll purchasing roll shop texturing, Cr-platingmill downtime for rollchanges & failuresworking capital tied upin roll fleetstorage space
High impact on
product quality surface defects rougness / texturetransferstrip gauge & shape rollability of product mix
High impact on
operational levelmill scheduling /planned roll changesunplanned roll changessafety aspects, rollfailures & preventionmill pacingmill vibrations, frictioncooling requirements transport/handling
Supply security lead times can be verylong & roll consumptioncan fluctuatemills require tailoredroll properties ratherthan off-the-shelfproducts from rollsuppliers
Roll use = core competency for Tata Steel rolling mills cannot be left / outsourced successfully to third parties
Need for cooperationwith top quality roll suppliers
Importance of rolls
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16
High impact of Rolls on product quality
(1) Gauge & shape
Rolls are the work horses of any rolling mill
The tool to deform slab, bar or strip dimensions required for the customer or for downstream operations.
Gauge & shape control within tight tolerances roll wear (work rolls, intermediate rolls, back-up rolls) has to be sufficiently low and
homogeneous
Work roll change build-up of thermal crown thermal properties of roll important Cold rolling: rapid build-up of a stable thermal crown required to limit length of out-of-
tolerance strip. Hot rolling: shape actuators must be able to compensate for thermal crown
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17
High impact of Rolls on product quality
(2) Surface properties
Work rolls critical influence on surface properties of rolled steel product
transfer of roughness / texture to the strip surface visual appearance processability in downstream/customer operations, coating thickness requirements
Trend: customer expectations requirements regarding strip surface roughness / texture E.g. automotive market: narrow Ra range combined with
high Peak Count (>75 cm-1 at bandwidth 1 m)
Rollrelated surface defects due to roll marks excessive roll wear premature work roll surface degradation
Tata Safari
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18
High impact of Rolls on product quality
(3) Tribological aspects
Work rolls = key component in tribosystem:
strip work roll lubricant (if any) process/loads
strip and the work roll may be coated. This coating may also be an oxide layer.
Lubricant may also be water
Tribo-system governs important parameters such as strip cleanliness and friction level in the mill requires insight in role & properties of work rolls. Some Cold Mills are using Cr-plated work rolls to avoid poor strip cleanliness
Cr-plating from Cr(VI) SHE issue restrictive EU legislation need for alternatives
DSP IJmuiden cannot use certain HSS rolls due to high friction/mill vibrations
Friction level roll properties mill force and power requirements
product rollability limits for a mill (grade/gauge/width-combinations)
Roll design limits can be more restrictive for product rollability than mill power
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19
Rolls technology: Core area for Tata Steel mills and R&D Rolls procurement: Strategic function with lead buyer for Tata Steel Group
Rolls: high-impact key assets for rolling mills
High costs roll purchasing roll shop texturing, Cr-platingmill downtime for rollchanges & failuresworking capital tied upin roll fleetstorage space
High impact on
product quality surface defects rougness / texturetransferstrip gauge & shape rollability of product mix
High impact on
operational levelmill scheduling /planned roll changesunplanned roll changessafety aspects, rollfailures & preventionmill pacingmill vibrations, frictioncooling requirements transport/handling
Supply security lead times can be verylong & roll consumptioncan fluctuatemills require tailoredroll properties ratherthan off-the-shelfproducts from rollsuppliers
Roll use = core competency for Tata Steel rolling mills cannot be left / outsourced successfully to third parties
Need for cooperationwith top quality roll suppliers
Importance of rolls
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20
High impact of Rolls on operational level
(1) scheduled roll changes
Mill operations generally scheduled into rolling campaigns
work roll changes scheduled before each new campaign
maximum # coils & sequence of coils to be rolled within a campaign are strongly determined by the behaviour, capabilities and limitations of the work rolls
some mills: different campaign types with different work roll requirements
ground cambers
surface finish
Work rolls determining factor for mill logistics
Work roll changes = daily routine at mills
frequencies up to several times per shift depending on the mill type and campaign type
Trend in certain markets customers requesting smaller orders with shorter lead times
some mills confronted with shorter average campaign length roll change frequency
due to logistical constraints regarding the coil sequence in a campaign
Aspirational target: Schedule-free rolling
eliminate (majority of) planned work roll changes
allow maximum scheduling freedom
Mills will generally not be able to implement schedule-free rolling with current roll fleet development, trialling and implementation of new work roll types
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21
High impact of Rolls on operational level
(2) unplanned roll changes
unplanned roll changes disturb the normal routine
disproportionally high effect on mill operations
Particularly in cases of roll failure / serious roll damage occurs
extensive mill downtime
effort to remove havoc & get mill ready for restart
Disturbance of upstream operations are also disturbed
E.g: roll failure in DSP / TSCR mill abortion of casting process; slabs in furnace scrapped
Special safety precautions required in cases of spallings or serious damage of a roll type with high residual stresses
compressive stress levels 500 MPa at the hardened barrel surface
forged rolls
CPC-HSS rolls
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22
High impact of Rolls on operational level
(3) roll shop operations
Roll shop comprises large & vital part of operations associated with any rolling mill
Roll shop task: ensure that rolls are prepared correctly & in time for next rolling campaign.
This includes:
Adequate redressing of the barrel surface remove surface layers affected by wear, thermal fatigue and work hardening
Application of the correct ground profile and surface finish
Routine Non-Destructive Testing (NDT) of rolls before each new rolling campaign shield the mill from potential harmful incidents caused by rolls with a defect or remnant damage
from a previous mill incidents
Perform/arrange roll repairs salvaging of damaged rolls arrange repair of rolls with worn journals
Mounting and dismounting of roll sets
(Re)chamfering barrel edges
Roll fleet management
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23
High impact of Rolls on operational level
(4) transport + handling
extensive transport & handling operations associated with roll usage inside roll shops as well as between the roll shop and the mill
Frequent roll changesComprehensive (roll shop)
activities on each roll+
Even more for some mills not located in same building as their roll shop Sometimes routine transport of rolls via public motorways
Some roll shops are serving multiple mills complex logistics, operations & roll fleet management E.g: Cold Strip Mill IJmuiden roll shop, serving:
CM21, CM22, TM21, HDGLines#1,#2,#3 IJmuiden Segal HDGLine in Lige HDGLine in Moerdijk (JV Wupperman/Tata Steel) BUR grinder also in use for other mills
M4 motorway between Llanwern
and Port Talbot (100 km)
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24
High impact of Rolls on operational level(5) implications for mill hardware & process
Work roll cooling essential for all hot & cold rolling mill
Carefully designed cooling systems high, stable & homogeneous heat transfer Optimum coolant flow rates are (a.o.) dependent on work roll properties & rolling speed Inhomogeneous cooling can lead to
premature local roll surface degradation strip surface defects poor strip shape rolling process instability
Roll cooling systems must also exhibit a very high reliability complete roll cooling system failure (e.g. valve not opening) or even partial roll cooling failure (e.g. blocked nozzles)
Hot rolling: additional strip surface cooling devices also required interstand cooling, chilling/skin cooling headers (a.k.a. anti-peeling headers), edge spays
suppress formation of Fe2O3-rich oxide scale abrasive for work roll surface diminish thermal degradation of the work roll barrel avoid roll-in oxide defects on the strip surface.
Also in this respect, work roll properties are important, as they influence the optimum strip cooling requirements, and determine the resilience of the work rolls if the mill is operating outside the optimum window respect to strip
cooling/strip surface temperature
rapid catastrophic roll failure
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25
High impact of Rolls on operational level
(7) friction, chattering, rolling loads limitations
Friction work roll properties A change in work roll material properties can substantially affect the friction coefficient
E.g. HSMs experience: HiCr Iron work rolls HSS work rolls friction
Friction at mill campaign start behaviour of the roll in the grinding process
friction evolution during rolling campaign work roll surface evolution
In some mills, chattering (mill vibrations) is a serious problem related to the previous topic friction and dependent on work roll properties
Roll material strength limits impose maxima to rolling loads
maximum allowable torque, bending force, total and specific rolling forces, rolling pressure, and Hertzian contact stress.
installed mill power can exceed strengthlimits of rolls.
6-high mill with IMR shifting asymmetrical distribution of loads and contact stresses can easily lead to exceeding the rolls Hertzian stress limit.
changes in product mix and/or rolling practice roll fleet still fit-for-purpose?
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26
Roll change reasons Hot Strip Mills (2004)
CSPY - HSM2
8%
5%
8%
0,02%
80%
0,3%
0,27%
5,2%
0,02%
0,09%0,6%
1,1% 0,005%
0,25%
CSPY - DSPheavy bruise
0,1%
medium/heavybanding
9%
Fire cracks0,6%
Defect freeor orange peel
70%
Other30%
tail marks6%
Vibration/grinding lines
0,7%
medium/heavycomets2%
light comets4%
light banding7%
End of programme (EOP)
EOP for logistics
IRC - planned
IRC - extra
BUR change
Shape
Slip / skids / roughness deviation
Vibrations / shudder
Cobble
Pinch / tail marks
Other roll marks / rolling incidents
Roll failure in mill (spall etc.)
Bearing failure
Firecracks
Other reasons
Defect free or orange peel
Fire cracks
light banding
medium/heavy banding
tail marks
heavy bruise
Vibration/grinding lines
light comets
medium/heavy comets
CSP-UK Hot Strip Mill Llanwern
0,11%
14,4%
0,42%
0,48%
0,44%
1,5%
84,2%
0,02%
HSM Port Talbot
0,4%
0,06%
7%
0,03%
0,01%
0,06%
0,04%
0,08%
68%
25%
0,08%
0,02%
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27
CSPY - Cold Mill 21
reasons for work roll changes
2003
End of program / Tonnage
43%
Pinch10%
Roughness
20%
Vibrations / shudder
1%
Bruises / cracks
0%
Burr marks
3%
Strip break
1%
Too fast out ("uitloper")
1%
Slip / skids
1%
Shape1%
Weld break
2%
Lines / streaks
1%
Other marks
(imprints/drag/pits/...)
13%
Other reasons
3%
End of program / Tonnage
Strip break
Weld break
Pinch
Burr marks
Bruises / cracks
Other marks(imprints/drag/pits/...)Lines / streaks
Vibrations / shudder
Too fast out ("uitloper")
Slip / skids
Roughness
Shape
Other reasons
Roll change reasons
Cold Mill 21 IJmuiden
discontinuous sheet mill
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28
Roll Property Requirements - summary
Tensile strength Torsional strength Bending strength Toughness Ductility Fatigue strength Thermal shock resistance
Wear Resistance Cold mills, temper mills: good roughness and texture
retention Hot mills: abrasion resistance, thermal fatigue/
degradation resistance
Resistance to indentation / marks Corrosion resistance / ability to form a stable thin
oxide layer (hot mills) Resistance to bruising Resistance to localised overheating
Resistance to spalling Machinability/Grindability Strip cleanliness not jeopardised
Roll Core Roll Surface
Roll total
Resistance to catastrophic fracture Resistance to roll flattening Fast build-up of steady-state thermal crown Resistance to high contact pressures Value-for-money
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29
Balancing roll requirements
Seemingly conflicting roll requirements need to be reconciled; roll properties need to be balanced for each application:
Roll barrel shell relatively hard; roll core&neck tough Compressive stresses in hardened shell tensile stresses underneath
Barrel hardness:WR (temper mil) > WR (cold strip mill) > IMR > BUR
Use of Cr-plated work rolls: to improve roughness/texture retention particularly for temper mills, sometimes tandem mills
for certain cold rolling mills strip cleanliness is a motivation expensive: not always cost-effective Cr(VI) bath => SHE issue.
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30
Work rolls:
Balance wear resistance and incident resistance
mill / stand mapping
0
2
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6
8
10
0 2 4 6 8 10wear
i
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Mill 1
Mill 2
roll mapping
0
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16
20
0 2 4 6 8 10wear resistance
i
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old rolls generation
current rolls generation
future rolls generation
developmentRoll type 2
Roll
type 1Match mill & roll
Match mill & roll
mill / stand mapping
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2
4
6
8
10
0 2 4 6 8 10wear
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Mill 1
Mill 2
mill / stand mapping
0
2
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6
8
10
0 2 4 6 8 10wear
i
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Mill 1
Mill 2
roll mapping
0
4
8
12
16
20
0 2 4 6 8 10wear resistance
i
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s
i
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old rolls generation
current rolls generation
future rolls generation
developmentRoll type 2
Roll
type 1
roll mapping
0
4
8
12
16
20
0 2 4 6 8 10wear resistance
i
n
c
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s
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old rolls generation
current rolls generation
future rolls generation
developmentRoll type 2
Roll
type 1Match mill & roll
Match mill & roll
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31
Back-Up Rolls:
Cast versus Forged Back-Up Rolls
Primary concerns that affect BUR performance Bruises / impressions Wear Rolling contact fatigue
Lightly loaded mills (e.g. temper mills, DCR mills): cast iron back-up rolls make use of low wear rates offered by these grades
Heavy mill loads forged steel back-up rolls refined grain structure; induced longitudinal grain flow increased fatigue resistance / incident resistance
Cast steel back-up rolls: intermediate case.
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32
Some typical roll chemistries
< 1.5 Nb< 10.2 14 - 51.5 2.53 3.5Enhanced AIC
(super nickel grain iron)
< 0.1< 0.10.2 0.54 - 51.5 2.53 3.5alloy indefinite chill (AIC) iron
(nickel grain iron)
0.21 W0.2 - 12 - 40.5 1.511 - 141.5 - 2Cast HiCr steel
1 - 2
1 - 2
0.2 2
0.5 2
0.5 1.5
Ni
(%)
< 0.1< 0.10.5 217 - 192.8Cast HiCr iron
< 0.1< 0.10.1 - 0.61.5 - 60.7 - 1.0standard forged steel
< 1 W0.5 - 10.5 - 24 - 100.5 - 1.0forged semi-HSS
< 2 W0.5 - 30.5 - 38 - 130.8 - 1.5Forged HSS
2 8 W2 - 82 - 84 - 81 2Cast HSS
W / Nb
(%)
V
(%)
Mo
(%)
Cr
(%)
C
(%)Grade
Each rolling application requires tailored roll properties Wide variety of roll manufacturing routes, chemistries, heat treatments, microstructures
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33
Schematic of Static Single Pour and Static Double Pour
Techniques
Static Single Pour Casting
Static Double Pour Casting
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34
Schematic of Centrifugal Casting
Shell pouring during fast spinning
Solidified shellShell solidifies
Core top poured and spinning decreased
-
35
Schematic manufacturing route for forged rolls
Hardening
ESR (electroslag refining)
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36
Electroslag Refining (ESR)
Molten electro-slag
Water cooled rising mould
Liquid steel
Solidified refined ingot
Benefits: Purification Steel structure
Application of ESR: In case of high content of alloying elements In case of high surface qualityrequirements (e.g. Al foil) For deep hardened rolls For roll conversion
Consumable electrode
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37
Hardening and tempering
Elemental steps in hardening process: Austenising
roll heated above -Fe/-Fe transition temperature Quenching
water quench cryogenic cooling formation of Martensite & a small percentage of retained -Fe roll shell is hard but brittle
Tempering controlled softening; roll becomes less brittle
Differential hardening (neck isolated from barrel)
Hardening furnaces classical furnace static induction hardening dynamic induction hardening (single or double frequency)
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38
Hardness versus tempering temperature
Forged 5%Cr steel rolls
650
700
750
800
850
900
100 150 200 250 300 350 400
Tempering temperature (C)
V
i
c
k
e
r
s
h
a
r
d
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e
s
s
incident
resistance
wear
resistance
-
39
Effect of a rolling incident on roll damage:
influence of the tempering temperature
rolling incidents induce a local temperature peak
the lower the tempering temperature, the more extended the zone where the
microstructure of the roll is affected.
-
40
Explosive failure risk of forged rolls
Explosion risk
Enormous compressive stresses in shell
Compensated by enormous tensile stresses internally
Internal stress levels up to 1000 MPa !!!Crack in roll:
inherent explosion risk
Trend to roll life maximising greater depth of hardening better roughness retention => higher hardness
more critical for explosion risk
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41
Some trends in last decades
Hardening depth increase
roughly from 30 to 120 mm on diameter
i.e. roughly from 15 to 60 mm on radius
Higher barrel hardness
Higher metallurgical purity
Higher alloying content (2%Cr -> 3-8%Cr steel; HiCr iron)
Automated roll inspection
Development of induction hardening techniques
Micro-alloying with strong carbide formers (e.g. 4%Cr-Mo)
Macro-alloying: forged semi-HSS and HSS grades
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42
Breakthrough Technology:
Development & testing of forged HSS rolls
< 1.00.5 1.00.5 2.04.0 - 10.00.5 - 1.0Forged semi-HSS
< 2.00.5 - 3.00.5 - 3.08.0 - 13.00.8 - 1.5Forged HSS
< 0.1< 0.10.1 - 0.61.5 - 6.00.7 - 1.0Standard Forged
W (%)V (%)Mo (%)Cr (%)C (%)Grade
most promising current direction for breakthrough roll technology for cold rolling forged semi-HSS and most particularly forged HSS grades
finely dispersedhard carbides
enhanced wear resistance
high tempering temperature(~ 480C) possible
enhanced incident resistance
-1200
-1000
-800
-600
-400
-200
0
200
400
0 50 100 150 200 250
Depth in radius (mm)
A
p
p
r
o
x
i
m
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t
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t
i
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s
i
d
u
a
l
s
t
r
e
s
s
(
M
P
a
)
Forged HSS
Forged 5% Cr steel
Lower residual stress levels
elimination of explosivefailure risk