Case study of profiles of electrical steel

1

A REPORT ON

CASE STUDY OF PROFILES OF ELECTRICAL STEEL

BY

G PRANAY RAJ (2011B4A4630H)

K GAUTHAM REDDY (2011A8PS364G)

AT

ROURKELA STEEL PLANT

A Practice School-I Station Of

BIRLA INSTITUTE OF TECHNOLOGY & SCIENCE, PILANI

(JUNE-JULY, 2013)

2

A REPORT ON

CASE STUDY OF PROFILES OF ELECTICAL STEEL

BY

G PRANAY RAJ 2011B4A4630H

MSc. Math + B.E.MECH K GAUTHAM REDDY 2011A8PS364G

B.E. ELECTRONICS & INSTR

Prepared in partial fulfillment of the

Practice School-I Course No BITS C221/BITS C231/BITS C241/BITS GC221/BITS

GC231

AT

ROURKELA STEEL PLANT

A Practice School-I Station of

BIRLA INSTITUTE OF TECHNOLOGY & SCIENCE,

PILANI

(JUNE-JULY, 2013)

3

BIRLA INSTITUTE OF TECHNOLOGY AND SCIENCE

PILANI(RAJASTHAN)

Practice School Division

Station: ROURKELA STEEL PLANT Centre: ROURKELA

Duration: From 12th June 2013 to: 7th July 2013

Date of Submission: 8th July 2013

Title of the Project: Case study of profiles of electrical steel

ID No. Name(s) of student(s) Discipline

2011B4A4630H G PRANAY RAJ MSc MATH + B.E. MECH

2011A8PS364G K GAUTHAM REDDY B.E. ELECTRONICS & INSTR.

Name(s) of expert Designation

Mr. Muthuswamy DGM, R&C LAB

Mr. CHANDAN SAMAL Sr. Manager, Metallography department, R&C LAB

Name of the PS Faculty: Mr. TUFAN CHANDRA BEHRA & Mrs. MONALISA MISHRA

Key Words: PROFILE, CRNO STEEL, BUCKLING, OVERCURING

Project Area: SILICON STEEL(ELECTRICAL STEEL)

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Abstract: Quality is a major concern for a very big industry like the Rourkela steel plant. Since RSP is the only steel plant that produces silicon steel in the whole country it needs to have proper quality assurance standards, so as to satisfy the costumers and also diminish their losses. One of the major factors that contribute to the silicon steel’s quality is its profile (it’s a systematic study of the variation of the coils thickness along its width). Our project includes the study of profiles of 20 coils, and observe the changes its undergoing through the silicon steel mill and relating it to the final product and its quality to understand its importance, and also understand the amounts of steel which is wasted in the process and suggest measures to be taken to prevent events like buckling, scratches, overcuring, black surface and coil breakages over the surface of silicon steel.

Pranay Raj

Gautham Reddy

Signature(s) of Student(s) Signature of PS Faculty

Date 7-07-2013 Date

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ACKNOWLEDGEMENT

We thank Mr. Tufan Chandra Behera and Mrs. Monalisa Mishra for

guiding us through this practice school. They have been really helpful

in making the stay in Rourkela memorable and our experiences rich.

We are also thankful to Mr. Muthuswamy (DGM, R&C lab) and Mr.

Chandan Samal for spending their valuable time and giving us this

great opportunity to work under their guidance. We would also like

to thank Mr. Saroj Das and Mr. K.K.Biswal for guiding us throughout

the project and the opportunity to learn about the silicon steel mill

and its functioning, and we are also thankful for their patience and

their interest in letting us know things. Finally, we thank the PS

division for giving us this wonderful opportunity of working in

Rourkela Steel Plant.

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INDEX

ABOUT ROURKELA STEEL PLANT ………………………………………………………………… 7

1) INTRODUCTION ……………………………………………………………………………………… 8

1.1) DESCRIPTION OF PROCESS AT HOT STRIP MILL …………………………………. 8

1.2) DATA FROM HOT STRIP MILL …………………………………………………………….. 10

1.3) Material flow chart that takes place at hot strip mill…………………… 11

2) BRIEF DESCRIPTION OF PROCESS THAT TAKES PLACE

AT SILICON STEEL MILL……………………………………………………………………. 12

2.1.1) BUST LINE………………………………………………………………………………. 12

2.1.2) ANNEALING AND PICKLING LINE…………………………………………….. 12

2.1.3) COLD REVERSING MILL………………………………………………………….. 13

2.1.3.1) HEAT GENERATION IN THE COLD ROLLING PROCESS………. 14

2.1.3.2) DYNAMIC HEAT EXCHANGE IN THE MOVING

STRIP AND ROTATING ROLL……………………………………………. 15

2.1.3.3) Heat Balance…………………………………………………………………. 16

2.1.4) TA OR DECARB LINE…………………………………………………………….. 17

2.1.5) SLITTER LINE……………………………………………………………………….. 17

2.2) PROCESS FLOW CHART THAT TAKES PLACE AT SILICON STEEL MILL. 18

3) PROFILE………………………………………………………………………………………….. 19

4) OBSERVATIONS MADE IN THE BUST Line………………………………………. 20

5) OBSERVATION MADE IN THE SLITTER LINE………………………………………. 23

6) GRAPHS OF PROFILES OF COILS……………………………………………………….. 25

7) OBSERVATION AND ANALYSIS………………………………………………….......... 31

8) CONCLUSION......................................................................................... 34

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ABOUT ROURKELA STEEL PLANT

SAIL-Rourkela Steel Plant (RSP), located in Rourkela, Odisha the first

integrated steel plant in the public sector in India, was set up with German

collaboration with an installed capacity of 1 million tonnes in 60s.

Subsequently, its capacity was enhanced to 2 million tonnes. The RSP has

various firsts to its credit. It is the first plant in Asia to adopt the energy-

efficient LD process of steel making and the first integrated steel plant of SAIL

which adopted the cost effective and quality centred continuous casting route

to process 100% of steel produced. The plant has also, for the first time in

India, had adopted external desulphurisation of hot metal by calcium carbide

injection process. RSP is one of the unique steel units under the SAIL umbrella

with a wide variety of special purpose steels.

The Republic of Germany provided technical knowhow for the construction of

the steel plant. German metallurgical firms Mannesmann, Krupp,

Demag, Siemens and Voestalpine provide machinery and consultancy to the

plant among others. Rourkela Steel Plant was the first steel plant in Asia to

utilize the LD (Linz-Donawitz) process of steel-making. Rourkela Steel Plant also

has an associated Fertilizer Plant that produces nitrogenous fertilizers using

ammonia feedstock (from its coke oven plant).

RSP presently has the capacity to produce 2 million tonnes of hot metal, 1.9

million tonnes of crude steel and 1.67 million tonnes of saleable steel. It is

SAIL’s only plant that produces silicon steels for the power sector, high quality

pipes for the oil & gas sector and tin plates for the packaging industry. Its wide

and sophisticated product range includes various flat, tubular and coated

products.

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1) INTRODUCTION

In metalworking, rolling is a metal forming process in which metal stock is

passed through a pair of rolls. Rolling is classified according to the temperature

of the metal rolled. If the temperature of the metal is above its recrystallization

temperature, then the process is termed as hot rolling. If the temperature of

the metal is below its recrystallization temperature, the process is termed as

cold rolling. In terms of usage, hot rolling processes more tonnage than any

other manufacturing process, and cold rolling processes the most tonnage out

of all cold working processes.

Rourkela Steel Plant, a unit of Steel Authority of India Limited (SAIL) took the

lead & achieved the distinction of being the first in the country to start

commercial production of CRNO. Equipped with the state of the art

technology, Silicon Steel Mill with installed capacity to produce 73,500 tpa of

CRNO was set up with technical collaboration of M/s A.K.STEELS (Formerly

ARMCO), USA, a pioneer in the field of electrical steel. Silicon Steel Mill is ISO –

9001 & ISO –14001 Unit. The CRNO stream has been awarded ISO - 9001, the

International Quality Assurance System, certified by M/s RWTUV, Germany in

September 1996. And ISO –14001 Environmental Management System,

certified by M/s BIS, India in October 2000.

Meeting international standards with respect to magnetic properties,

insulation coating properties, insulation resistivity, dimensional tolerance &

lamination factor is the credo at Silicon Steel Mill. Various facilities have been

added with a view to keep pace with the latest technology. The notable

features are external desulphurisation of hot metal, high purity steel making,

vacuum degassing, continuous casting, and highly accurate hot rolling mill &

Cold Rolling Mill complex incorporating the most advanced technology for

manufacturing CRNO steel strips. The unit has a modern Magnetic Testing

Laboratory, which is one of its kinds in the country.

For the production of CRNO steel, slabs produced in SMS is firstly processed in

hot strip mill to produce HR coils of desired thickness and width which are the

sent to silicon steel mill for further processing.

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1 .1) Brief description of process that takes place at hot strip mill:

1) Walking Beam Furnaces:

• Each Furnace has 6 zones

• Slabs are put on charging side roller table with the help of depiler crane

• slab is extracted from furnace by extractor and is placed on the

discharge roller table and sent to Ro/Vo

2) Primary Descaler:

• To remove the scale formed on the surface of slabs during its heating

inside furnaces

• Water jet at high pressure of 145-160 Bar is applied on top and bottom

surface of slabs.

3) Roughing Stand:

• R0/V0: Heated slabs reduced to desired thickness and sent to R1. Slabs

after rolling at R0/V0 are called Intermediate Transfer Bars

• ROUGHING STAND-I (R1) :Bars from Ro given 3 to 5 passes and reduced

to desired thickness

• ROUGHING STAND-II (R2):The thickness of the bar from R1 reduced

further

4) Coil Box:

• The Intermediate Transfer Bar is coiled and subsequently uncoiled to

feed tail end of transfer bar into the Finishing Mills.

5) Finishing Mill:

• Reduction is given to the bar in each of the 6 stands.

• The strip temperature is controlled on Run Out Table (ROT) having 4

cooling banks

6) Coilers:

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• The strip gets coiled in one of the two hydraulic down coilers

• The hot coils are circumferentially strapped on the body by Automatic

Strapping Machine and marked for identification.

• Necessary samples are cut from the coils for its testing.

• Coils are then transferred to coil yard and are allowed to cool before

they are sent for further processing in different units of RSP

7) Dividing Line:

• Hot Rolled Coils meant for converting into HR plates are uncoiled in

Uncoiler and levelled in Leveler-I

• Sheared at Dividing Shear to the required lengths

• Then plates are levelled once again in Leveler-II and piled in Pilers

1.2) Data from hot strip mill:

Coiling temperature: 660-770 C

Rolling temperature: 1040-1050 C

Finishing temperature: 860-880 C

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1.3) Material flow chart that takes place at hot strip mill:

12

2) BRIEF DESCRIPTION OF PROCESS THAT TAKES PLACE AT SILICON STEEL

MILL:

Cold Rolled Non-oriented (CRNO) steel produced here is the energy efficient

steel, is an essential raw material recognized the world over for manufacturing

electrical equipment like generators, motors, relays, small transformers etc.

Used primarily in special rotating and static electrical equipment, the CRNO

steel is characterized by low watt loss (core loss) and high permeability

Silicon steel mill receives inputs from hot strip mill as HR coils with initial width

of 1055mm and initial thickness between 2.2 to 2.5mm.

2.1.1) BUST LINE:

Firstly it is processed in the BUST line (build up and side trim line) where side

trimming of the coil takes place where the width of the coil is reduced from

1055 mm to 1025/975/925mm.

Line Features:

1. Coil Wt. 15 Mt (max)

2. Coil I.D. 510 & 710 mm, Width: 600 To 1150 mm

3. Electronic Weigh Bridge

4. Line speed 15 to 125 mpm.

5. Jog speed 15 mpm

6. Line tension 1.75 Kg / mm2

2.1.2) ANNEALING AND PICKLING LINE:

This line is used for pickling of HR coils after BUST line.

Line Features:

1. Hydrochloric acid pickling (HCL) 5 tanks for pickling.

2. Acid conc. 8 To 12 %. Salt conc. 12 % max.

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3. Acid bath temp. 70 +/- 3oC

4. Annealing of M-36 / M-27 & higher grades.

5. Gas fired & electric heating zones 3 each.

6. Annealing temp. 950 +/- 10oC

7. Anti-rust oil coating after pickling.

8. Taylor - Winfield shifting head seam welding m/c

9. Line speed 10-35 mpm (Entry-90 / Process 60 / Exit 90 mpm )

10. Tension - Entry - 0.35 to 1.05 Kg/mm2

Furnace - 0.35 to 1.05 Kg/mm2

Pickling - 1.05 Kg/mm2

Exit - 2.5 Kg/ mm 2

11. Pickling Tanks - 5 (L - 25. 7 m, W - 2.13 m, Depth - 1.207 m)

Capacity - 36,000 Lts each (1 to 3) 4A – 16800, 4B-19600 lts.

12. Cascade rinse unit 3 compartments.

2.1.3) COLD REVERSING MILL:

Cold rolling occurs with the metal below its recrystallization temperature

(usually at room temperature), which increases the strength via strain

hardening up to 20%. It also improves the surface finish and holds tighter

tolerances. Commonly cold-rolled products include sheets, strips, bars, and

rods; these products are usually smaller than the same products that are hot

rolled. Because of the smaller size of the work pieces and their greater

strength, as compared to hot rolled stock, four-high or cluster mills are used.

Cold rolling cannot reduce the thickness of a work piece as much as hot rolling

in a single pass.

After annealing and pickling the coil goes to cold reversing mill where the

thickness of the coil is reduced from 2.2 to 2.5 mm to 0.5 mm in 5 to 6 passes

14

by applying pressure. Here in each pass the thickness is reduced not more than

33%.

2.1.3.1) HEAT GENERATION IN THE COLD ROLLING PROCESS

The Area of Contact (roll and Strip) between the hard work roll surface and the

softer steel strip surface is where friction is created, deformation occurs and

heat is generated. The “Area of contact” is defined by the strip width in the

transverse plane and the circumferential “Arc of Contact” (AoC) between the

roll and strip.

The area of contact varies with the changing AoC and the strip width thus a

small reduction gives a short arc of contact and combined with a narrow strip

with gives a smaller area of contact and vice versa.

The heat generated at the frictional interface (Area of Contact) and through

the energy used in deformation is transferred into both the strip and the roll in

the roll bite. In this mill as pressure is applied, heat is generated so hot water is

used as a coolant.

(i) 4 Hi Mill Roll Stack (iii) Area of Contact

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2.1.3.2) DYNAMIC HEAT EXCHANGE IN THE MOVING STRIP AND ROTATING

ROLL

In the rolling process where the area mass ratio is higher because the gauge is

“thin” a large proportion of the “strip heat” is lost to air with further losses to

such things as coolant wash-over, however, heat absorbed by the rotating roll

is subject to a more complex thermal mechanism.

Heat will continuously migrate to cooler zones in and out of the roll body due

to the localized elevated temperature in the area of contact (bite) and localized

“chill zones” created in the impingement areas of coolant sprays on the

surface.

This localized heat input / output process results in a non-uniform distribution

of heat, circumferentially around the roll and transversely across the roll body.

Additionally the roll is subjected to Thermal and Mechanical Fatigue during

rolling:

i) Thermal fatigue as the roll cycles through the elevated temperatures in the

roll bite and the lower temperature zones cooled under the coolant spray

footprints.

ii) Mechanical Fatigue by mechanical compression (flattening) and physical

distortion (deflection) caused by the rolling force and the necessary torque

applied by the motor.

High reduction schedules combined with the requirement to produce a

widening range of material cross-sections and a more varied range of softer

and harder materials, results in increasingly greater challenges in the control of

roll temperature and the effective transfer / extraction of heat.

16

Given the more diverse range of thermal conditions it is important to install

efficient and robust roll cooling systems that can establish both heat balance

and controllable thermal conditions around the work roll as well as across its

width by controlled selective cooling and efficient heat transfer.

2.1.3.3) Heat Balance:

To establish heat balance it is imperative that heat transferred into the roll is

transferred out, however as the heat input and output is not distributed

uniformly the fundamental requirement to achieve effective heat extraction is

to ensure

i)The roll surface temperature range around the circumference is minimized

which reduces thermal fatigue and roll surface degradation as well as lowering

the potential for surface defects, impaired lubricant performance and roll

wear.

ii)The transverse temperature distribution is controlled to assure strip flatness

is not affected by excessive thermal crowning or excessive localized expansion

across the rolling width and in particular at the edges (edge waves).

The average roll temperature is difficult to establish during the rolling process

but the difference in the temperature at the exit of the roll bite will represent

the highest value in the range and the temperature after the final cooling zone,

17

in the area ahead of the entry bite should represent the lowest in the range

around the circumference: it is necessary to apply coolant and configure sprays

such that the difference in those two values is minimized.

It is also imperative to establish the same “temperature profile” on both top

and bottom rolls as a pair to avoid differential thermal crowns and transverse

profiles

2.1.4) TA OR DECARB LINE:

Then it goes to TA or decarb line where carbon content is reduced firstly and

then coating takes place which can either be organic, inorganic or semi

organic.

2.1.5) SLITTER LINE:

Then it finally goes into the slitter line where the final inspection of the coil

takes place for any defects like buckling, coil breakage, over curing, black

surface, scratch etc. and side trimming is done as per the requirement of the

customer.

Then it is packed and finally dispatched to the customer.

18

2.2) PROCESS FLOW CHART THAT TAKES PLACE AT SILICON STEEL MILL:

19

3) Profile

Profile is made up of the measurements of crown and wedge. Crown is the

thickness in the center as compared to the average thickness at the edges of

the work piece. Wedge is a measure of the thickness at one edge as opposed

to the other edge. Both may be expressed as absolute measurements or as

relative measurements. For instance, one could have 2 mil of crown (the

center of the work piece is 2 mil thicker than the edges), or one could have 2%

crown (the center of the work piece is 2% thicker than the edges). It is typically

desirable to have some crown in the work piece as this will cause the work

piece to tend to pull to the center of the mill, and thus will run with higher

stability.

We have examined a sample of 20 coils of different grades like 60A,70B,53C

near the BUST line(build up and side trim line )and took the data of defects in

them such as buckling, coil breakage, scratch, black surface etc. in the slitter

line and observed which profile of the coil causes defects like buckling and

others.

20

4) Observations made in the BUST line (profile measured from operator side

to other side in mm at 5 points in mm at beginning, middle and end of

the coil):

From operator side to other sideS NO HSM NO SSM NO TA and DECARB no PROFILE

head1 mid1 centre mid2 head2

1 91790 70B-3425 TA-4160 2.41 2.41 2.41 2.43 2.42

2.4 2.41 2.41 2.41 2.39

2.39 2.41 2.41 2.42 2.41

2 91785 70B-3426 TA-4124 2.65 2.63 2.61 2.66 2.65

2.39 2.39 2.4 2.41 2.4

2.33 2.34 2.34 2.36 2.35

3 91791 70B-3427 TA-4148 2.58 2.59 2.59 2.59 2.57

2.36 2.37 2.37 2.38 2.38

2.45 2.46 2.45 2.46 2.45

4 91770 60A-4496 DE-4424 2.71 2.71 2.71 2.71 2.71

2.45 2.45 2.44 2.45 2.45

2.4 2.4 2.4 2.42 2.42

5 91772 60A-4497 TA-4140 2.32 2.32 2.32 2.32 2.32

2.32 2.33 2.31 2.32 2.32

2.4 2.42 2.42 2.41 2.41

6 92266 60A-4508 TA-4150 2.38 2.36 2.41 2.4 2.4

2.45 2.45 2.42 2.42 2.42

2.47 2.47 2.46 2.46 2.45

7 92267 60A-4509 TA-4151 2.34 2.33 2.33 2.34 2.33

2.33 2.32 2.32 2.31 2.3

2.41 2.39 2.39 2.38 2.38

21

8 92289 70B-3434 DE-4324 2.53 2.53 2.51 2.52 2.5

2.6 2.56 2.54 2.56 2.54

2.52 2.53 2.51 2.52 2.53

9 92284 60A-4510 DE-4326 2.57 2.56 2.55 2.55 2.54

2.53 2.54 2.54 2.55 2.54

2.65 2.66 2.66 2.66 2.64

10 92269 60A-4511 TA-4161 2.55 2.52 2.52 2.53 2.51

2.54 2.53 2.52 2.52 2.51

2.65 2.64 2.63 2.6 2.61

11 93099 53A-4656 TA-4196 2.68 2.65 2.61 2.59 2.56

2.46 2.44 2.43 2.42 2.41

2.3 2.3 2.3 2.3 2.3

12 93133 60A-4544 DE-4348 2.39 2.42 2.42 2.45 2.46

2.26 2.28 2.29 2.29 2.29

2.53 2.55 2.57 2.57 2.56

13 93098 53A-4657 TA-4261 2.61 2.6 2.6 2.59 2.56

2.29 2.28 2.29 2.3 2.29

2.56 2.55 2.56 2.57 2.57

14 93142 60A-4545 TA-4175 2.42 2.42 2.44 2.43 2.41

2.22 2.23 2.24 2.24 2.23

2.53 2.52 2.5 2.52 2.49

15 93100 53A-4658 TA-4191 2.46 2.46 2.45 2.45 2.44

2.28 2.27 2.27 2.27 2.21

2.53 2.52 2.52 2.51 2.49

16 93097 53A-4659 2.57 2.55 2.57 2.58 2.58

2.29 2.29 2.29 2.29 2.28

2.35 2.34 2.34 2.33 2.31

22

17 93103 60A-4546 DE-4366 2.66 2.67 2.66 2.64 2.59

2.32 2.32 2.33 2.33 2.32

2.35 2.35 2.35 2.36 2.37

18 93146 60A-4547 TA-4234 2.19 2.2 2.21 2.21 2.2

2.42 2.43 2.44 2.44 2.42

2.51 2.53 2.54 2.56 2.55

19 93141 60A-4548 2.28 2.3 2.3 2.3 2.3

2.45 2.44 2.43 2.43 2.43

2.46 2.48 2.48 2.48 2.48

20 93114 60A-4549 2.56 2.57 2.57 2.57 2.56

2.42 2.43 2.42 2.43 2.43

2.72 2.72 2.7 2.72 2.7

23

5) Data collected from the slitter line (defects like buckling, coil breakage

etc.):

S NO TA and DECARB no parts prime(mt) seconds(mt) REASONS

1 TA-4160 1 5.6 COIL BREAKAGE

2 4.9

2 TA-4124 1 5.6 NO DEFECTS

2 5.2


2 5.4

4 DE-4424 1 5.6 NO DEFECTS

2 5.2


2 4.8


2 5.2


2 4.7

8 DE-4324 1 4.1 BUCKLING

2 6.1 BLACK SURFACE

9 DE-4326 1 5.3 SCRATCH

2 4.3 BLACK SURFACE

3 1.8

10 TA-4161 1 2 BUCKLING

2 2.3 OVER CURING

3 5.3

24


2 3

12 DE-4348 1 5.6

2 5.1 SCRATCH

13 TA-4261 1 4.5 BUCKLING

2 4


2 5


2 5 OVERCURING

3 4.1

16 BUST LINE COIL NOT PROCESSEDYET PROCESSED

17 DE-4366 1 2.1 BUCKLING

2 COIL BREAKAGE


2 5

3 4.1

19 BUST LINE COIL NOT YET PROCESSED

20 BUST LINE COIL NOT YET PROCESSED

25

6) GRAPHS OF THE PROFILES OF THE COILS WE EXAMINED (middle part):

X AXIS: 5 EQUIDISTANT POINTS ALONG THE WIDTH OF THE COIL

Y AXIS: THICKNESS OF THE COIL AT THAT POINTS (in mm)

2.38

2.385

2.39

2.395

2.4

2.405

2.41

2.415


TA-4160

TA-4160

2.38

2.385

2.39

2.395

2.4

2.405

2.41

2.415


TA-4124

TA-4124

26

2.35

2.355

2.36

2.365

2.37

2.375

2.38

2.385


TA-4148

TA-4148

2.434

2.436

2.438

2.44

2.442

2.444

2.446

2.448

2.45

2.452


DE-4424

DE-4424

2.3

2.305

2.31

2.315

2.32

2.325

2.33

2.335


TA-4140

TA-4140

27

2.405

2.41

2.415

2.42

2.425

2.43

2.435

2.44

2.445

2.45

2.455


TA-4150

TA-4150

2.285

2.29

2.295

2.3

2.305

2.31

2.315

2.32

2.325

2.33

2.335


TA-4151

TA-4151

2.51

2.52

2.53

2.54

2.55

2.56

2.57

2.58

2.59

2.6

2.61


DE-4324

DE-4324

28

2.52

2.525

2.53

2.535

2.54

2.545

2.55

2.555


DE-4326

DE-4326

2.495

2.5

2.505

2.51

2.515

2.52

2.525

2.53

2.535

2.54

2.545


TA-4161

TA-4161

2.38

2.39

2.4

2.41

2.42

2.43

2.44

2.45

2.46

2.47


TA4196

TA4196

29

2.245

2.25

2.255

2.26

2.265

2.27

2.275

2.28

2.285

2.29

2.295


DE-4348

DE-4348

2.27

2.275

2.28

2.285

2.29

2.295

2.3

2.305


TA-4261

TA-4261

2.21

2.215

2.22

2.225

2.23

2.235

2.24

2.245


TA-4175

TA-4175

30

2.16

2.18

2.2

2.22

2.24

2.26

2.28

2.3


TA-4191

TA-4191

2.314

2.316

2.318

2.32

2.322

2.324

2.326

2.328

2.33

2.332


DE-4366

DE-4366

2.41

2.415

2.42

2.425

2.43

2.435

2.44

2.445


TA-4234

TA-4234

31

7) Observation and analysis:

So in the above table part of the coils which have no defects came under

prime which means it has a good surface and the coil which has defects like

buckling, BS etc. and doesn’t have a good surface finish will come under

seconds(non-prime).

Non-prime (Second & Defective) steel products may be defined as:-

i) Products of non-standard dimensions: provided they do not show the

defects or the physio-chemical faults of downgraded products, and that they

are sold and delivered in different or heterogeneous formats with no

guarantee or indication of quality.

ii) Downgraded products

Downgraded products means iron and steel products having:

(a) Surface defects

Some of the surface defects are:

Waviness / Buckling

Lack of flatness consisting of undulation (including waves and buckles) in the

surface of a sheet or plate. Troughs and crests on rolled products which may

occur along with waviness of edges.

Cracks

Discontinuity, usually of the hairline type:

- Longitudinal - parallel to rolling direction,

- Transverse-perpendicular to rolling direction,

- With scale or Y-shaped (forked).

Scratches

Scratches (single or multiple) of mechanical origin on the surfaces of products

that can be felt by hand/ nail.

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Straightness and profile:

Defects whereby the section or its cross- section depart from the required

dimensions and straightness by more than the tolerances specified in

international technical standards.

(b) Internal faults

Physio-chemical faults concern the analytical and structural composition of the

steel and/or presence of presence of radioactive elements in the steel.

These faults are internal defect and make the product unusable in the

corresponding commercial quality. In general, these defects- such as

inclusions, split ends, piping, off chemistry etc. Cannot be seen with the naked

eye. These defects are detected by ultrasonic methods, by mechanical and/ or

chemical tests. Presence of radioactive elements, if any, may be detected by

radiation meter.

As in the case of products with the surface defects, the importer must declare

products with physio- chemical faults and supply documental evidence.

Customs checks on these faults may be carried out with the assistance of a

competent verification agency including accredited chemical laboratory.

(c) Characteristics not conforming to the values specified in the National /

International standards specification with regard to:

chemical analysis i.e. off chemistry,

mechanical properties i.e. off mechanical properties,

Dimensional tolerances i.e. off size.

Magnetic properties, stacking factor, insulation resistivity etc. in case of

electrical steel grades.

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The latter relates to one or more of the following aspects: length, width,

thickness, flatness, straightness, section.

The deviation from complete flatness is the direct result of the work piece

relaxation after hot or cold rolling, due to the internal stress pattern caused by

the non-uniform transversal compressive action of the rolls and the uneven

geometrical properties of the entry material.

So out of 17 coils we examined who’s total weight turns out to be 172.2T,

36.7 T has defects which accounts for 21 %.

So it is observed that coils that has defects has showed either or both of the

below profile trend

i) Coils with the thickness between adjacent points is greater than or equal to

0.02mm.ex: TA-4348

ii) coils with profile increasing or equal from head1 to mid2 and then there is a

sudden decrease of thickness at head2(last part of the coil).ex:DE-4234

2.245

2.25

2.255

2.26

2.265

2.27

2.275

2.28

2.285

2.29

2.295


DE-4348

DE-4348

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So in order to avoid defects it is recommended to take measures to avoid the

above two kinds of profiles in HR coils

8) CONCLUSION:

• Proper rolls are to be selected in the rolling mill.

So as to reduce the expansion of the rolls and to avoid any kind of

changes in the diameter which in turn affects the profile of the coils

• Proper surface finish and temperatures are to be maintained.

Maintenance of temperature with efficient cooling systems prevents

uneven expansion of the rolls.

• Proper lubrication and coolants are to be used.

Lubrication avoids unnecessary bonding between the surface of the rolls

and the coils and prevents and diminishes frictional impact. Making the

coil-making process under control. And coolants maintain the proper

temperature and help the rolls and coils avoid any kind of fatigues.

2.41

2.415

2.42

2.425

2.43

2.435

2.44

2.445


TA-4234

TA-4234

35

• Effective header geometry to be maintained.

Headers should be properly placed such that the coolant absorbs the

heat generated from the rolling process. It should be placed at an ideal

distance.

• Geometrical symmetry to be practiced.

Geometrical symmetry ensures that both sides of the coil are exposed to

similar conditions and prevents any kind of mechanical defects which

can be caused to the coils.

• Equal flows

Equal flows of coolants and lubricants ensure thermal symmetry in the

rolls. Subjecting both sides of the coil to similar thermal conditions.

Education

Case study of profiles of electrical steel