IntroductionIntroduction

Annealing of a Stainless steel is in order to Annealing of a Stainless steel is in order to improve machinability, refine grain size, to improve machinability, refine grain size, to remove internal stresses develops during remove internal stresses develops during the forming etc.the forming etc.Whereas pickling is an aggressive Whereas pickling is an aggressive chemical removal of oxides scale that chemical removal of oxides scale that develops during heat treatment and/or develops during heat treatment and/or surface contaminantssurface contaminants

Line SpecificationLine SpecificationMaterial to be Processed AISI 200,300, 400Material to be Processed AISI 200,300, 400Strip Thickness Strip Thickness 0.3 mm – 3 mm 0.3 mm – 3 mm Strip Width Strip Width 600mm – 1300 mm600mm – 1300 mmCoil ID; (In & Out) Coil ID; (In & Out) 610 mm610 mmCoil OD; (In & Out)Coil OD; (In & Out) 1800 mm (Max.)1800 mm (Max.)Coil WeightCoil Weight 28 MT (Max.) 28 MT (Max.) Hand of LineHand of Line Right to Left Right to Left Product MixProduct Mix AISI 200 – 60%, AISI 200 – 60%,

AISI 300-30%, AISI 400-10%AISI 300-30%, AISI 400-10%

Line SpecificationLine Specification

Total length of line 320 meters

Height of equipment from 10.36 meters (app.)

+ 0 mill floors level

Depth of cellar from 5 m (exit lopper) (app.)

+ 0 mill floors level 7.5 m (sump pit) (app.)

Crane hook height 10.935 m

Line specificationLine specification

Product Width 1030mm – 25%1270 MM-75%

Reference strip 1.2 x 1150 mmTV Value of Furnace 80 mm.mpm Max. Line Speeds Entry – 120/160 MPM

Process– 80/120 MPMExit – 135/200 MPM

Production at Ref Strip 40.88 Ton / HrAnnual Production 2,50,000 MTPA Furnace having Flox Burner by LPGPickling by Electrolytic Na2SO4,

Electrolytic HNO3,Mix Acid

AccumulatorsAccumulators

(i) Entry: - Strip storage capacity - 600 meters (app.) Looper car travel - 100 meters (app.)

(ii) Exit: - Strip storage capacity - 565 meters (app.)

Looper car travel - 142 meters (app.)

(iii) Creep: - Strip storage capacity - 60 meters (app.) Looper car travel - 30 meters (app.)

Line SpecificationLine Specification

2 Hi Skin Pass Mill with Max. 1.5% Reduction On Line Tension leveller and provision for side trimmerLine Bay 30mx350m with adjacent Coil Storage bay of 24mx350m

Line Consists OfLine Consists Of

Entry Equipments with LooperWelding machine from Guild,USADegreasing UnitAnnealing furnacePickling sectionSkin pass mill with Creep looperOn-line Tension leveller and provision for side trimmer.Exit equipments with looperAll Auxiliaries which includes Acid Storage, ETP, WT, DM water plant Etc.

PROCESSPROCESSUncoiling of CRFH

Coil at uncoilerWelding Degreasing

Entry looperAnnealingin furnaceCooling section

Pickling Exit looper Skin pass mill

Tension levellerCreep looperRecoiling of

CRAP coilat exit

Entry EquipmentEntry Equipment2 Uncoiler with CPC unitPaper winder with tension feedback unitPinchrolls,5 roll flatteners,Up cut shears,belt conveyorsFlat leader end handling system by vacuum stacker;Bottom side shiftableBridles;deflector,steering rolls;PU coated roll dia 1000 mmx1600 mmAutomatic seam welding machine from Guild USA; Welding time #4 min..Coil car, coil centering system

WELDING SECTIONWELDING SECTION Type -Guild Model QMM 125-54, Quick lap Seam Welder Material 200,300,400 CRSS Max. Strip Width 1300mm Min. Strip Width 600 mm Max. Strip Thickness 3.0mm Min. Strip Thickness 0.3mm Electrics 415/3/50Weld Process Continuous Seam

Degreasing sectionDegreasing section (i) First degreasing stage - Spray degreasing machine (ii) Second degreasing stage - Chemical scrub brush (iii) Rinsing section - 3 –Stage cascade rinsing (iv) Length of degreasing section – 18.15 meters (approx)

ANNEALINGANNEALING

Annealing is done to: 1. To regain grain structure 2. To increase malleability and ductility. 3. To attain mechanical properties.

ANNEALING STAGES 1. Recovery 2. Recrystallization 3. Grain growth

Furnace sectionFurnace section

Length of Section is 135 m10 Air Jet Cooling Chamber 2nd & 9th Jet Cooling chamber is having Mist cooling also to assist avoiding carbide precipitation..Length of Cooling Section 52.5 mBurners 92 Nos with Turndown ratio 10:16 burner control Zone

Furnace sectionFurnace section

3 Radiation Pyrometer at Exit of each Chamber.4 Optical Pyrometer at Jet Cooling SectionRadar Type Furnace sensor.Burner Flame sensor, Ionization TypeFurnace Pressure Sensor.Fuel Consumption 22 kg/Ton.Temperature of Strip AISI 200 – 950 C

AISI 300 – 1020-1140 CAISI 400 – 740-870 C

Recuperator; Air out temp will be ~ 600 C.Air Curtains at Exit of FurnaceThreading SystemRoll removal RigRetraction Cooling Section.

Furnace sectionFurnace section a) TV valve (m/min, mm) for 304 annealing 80 b) TV valve (m/min, mm) for 430 annealing 60 c) Max furnace operating temp 1250ºc d) Setting range of air/gas ratio 1.1 – 1.6 (i) Total length of the furnace 73,900 m (ii) Total length of the cooling section 52,500 m (iii) Length of unfired preheating section 21,000 m (iv) Height of strip pass line above support floor 2500mm

(v) Furnace chamber 04 chambers 1st chamber: - unfired preheating section 2nd chamber: - unfired + 1st fired zone 3rd chamber: - 02 fired zones 4th chamber: - 03 fired zones (vi) No. of burner's – 92 (26/36/30) Burner input / chamber – 22.6 MW (7.6 / 9.2 / 6.1MW)

Stable combustion without a flame and Stable combustion without a flame and defined recirculation of hot combustion defined recirculation of hot combustion productsproducts

Flox burners

Flox and flame temperature fieldFlox and flame temperature field

PICKLINGPICKLING

The function of pickling is to dissolve/ remove/ peel off oxide layer on surface of strip. Such oxide layers are formed during hot rolling and in case of cold rolled strip during annealing operation.

IN AP-4 PICKLING IS DONE IN 3 SECTIONS Neolyte electrolytic pickling section Nitric electrolytic pickling section Mixed acid pickling section

Neolyte electrolytic pickling sectionNeolyte electrolytic pickling section

Aqueous solution of sodium sulphate is used.Strip is descaled with help of electric current.

(i) No. of tank - 01 (ii) Length of tank – 50 metes (approx) (iii) Rectifier - 8 sets(2 x 5500A) (iv) Electrode - No of sets – 24

(8 anode sets, 16, cathode sets)

8 Cells with combination of Cathode-Anode-Cathode.Tank made of MS lined with Brick & RubberTank covers made of PP2 Pair of Squeeze roll at Entry & ExitSupport roll arranged such as the strip moves in

a zigzag manner.

Neolyte electrolytic pickling sectionNeolyte electrolytic pickling section

Chemical reactions

Equilibrium reactions H2O = OH- + H+

Na2SO4 = 2Na+ + SO4-

Anode process 2OH- = H2O + 1/2O2 + 2e- 2H+ + SO4- = H2SO4 Fe2O3 = 2Fe++ + 3/2O2 + 6e- Fe = Fe+++ + 3e- Cr2O3 + 5H2O = 2CrO4- + 10H+ + 6e- Cr + 4H2O = CrO4- + 8H+ + 6e-

Cathode Process 2H+ + 2e- = H2

2OH- + 2Na = 2NaOH

Nitric electrolytic pickling sectionNitric electrolytic pickling sectionHORIZONTAL RUTHNER ZIG ZAG DESIGN (i) No. of tank - 01 (ii) Length of tank – 14 meters (approx) (iii) Rectifier - 01 sets (2 x 5500A) (iv) Electrode - No of sets - 06

(02 anode sets, 04 cathode sets)

Pickling is effected in nitric acid by alternate anodic and cathodic polarization of strip.Low current density is used to just remove the passivation layer from the strip so that the chemical reaction between HNO3 and strip surface is enabled.Disadvantage of the NITRIC acid being electrolyte is that a higher current density NOx is produced.DeNOx system is used for NOx emissions.

Mixed acid pickling sectionMixed acid pickling sectionRUTHNER SHALLOW TANK DESIGNLittle acid amount but with high acid circulation.Mixed acid tanks.

(i) No. of tank - 02 (ii) Length of tank – 36

meters approx (18 meters each)In this section residual scale is removed, chromium depleted layer is pickled and brightening of strip surface is achieved.HF is used because pure nitric acid would form a passivation layer, thus preventing further metal dissolution.

Me + 4HNO3 = Me(NO3)2 + NO + 2H2O Me(NO3)3 + 3HF = MeF3 + 3HNO3

Me + HNO3 + 3HF = MeF3 + NO + 2H2O

COIL AFTER PICKLINGCOIL AFTER PICKLING

Skin Pass MillSkin Pass MillSkin passing is done to

1. To improve strip shape 2. To impart the desired surface finish to steel from 2D to 2B 3. To produce desired mechanical properties. 4. To eliminate minor surface blemishes. 5. Masking of yield point

2 Hi MillElongation 1.5%Roll Cleaning systemBottom Roll having Hydraulic Gap ControlQuick Roll Changing device;

Roll changing time ~ 8 minutesRoll changing is possible during runningHigh Pressure Hydraulic system2 High roll – 800mm (max.) /

750mm (min.) x 1500mm barrel length. Roll force – Max. 10,000 KN

Tension LevellerTension LevellerThe purpose of tension levelling is to bring all the fibres

in the metal to equal lengthTo achieve Desired strip elongation(0-2%) and strip flatnessTension leveller consists of Entry bridle, Tension leveller wet

type process, Exit bridles Type – wet type.

Design – One set of bending roll cartridge

Two sets of anti cross bow roll cartridge Tension – 350 KN (max.)

Roll configuration. Bending roll module: 6 – High Anti cross bow roll module: 3 – High Roll sizes. Bending: - work roll – 35mmØ x 1600mm Intermediate roll - 50mmØ x 1600mm Back up roll - 60mmØ x 130mm Anti cross: - work roll – 150mmØ x 1600mm Back up roll - 60mmØ x 130mm

Tension

Bending Combination ofBending and Tension

Anti-Cross BowBending

Effect

Function

MODULES AND EFFECT OF TENSION LEVELLING

Module Anti-Cross Bow

Hydraulic cylinder with integrated linear transducer

Monobloc Frame

Passline roll

Dry air nozzle pipe

Bending cartridge with support rolls protected by purging air

Anti Cross Bow cartridge with support rolls

Adjustable upper cartridge

Cartridge clamping cylinders

Servo valves

Fully enclosed Scale Breaker frame

Adjustable in and outlet

Scale removal motor with auger conveyor (Option)

LEVELLER IN MONOBLOC DESIGNLEVELLER IN MONOBLOC DESIGN

Exit EquipmentsExit Equipments1 Recoiler with EPC UnitPaper unwinder with Tension feedback unitPinch Rolls, Up Cut Shears, Belt Conveyor.Bridles, Deflector, Steering rolls; PU coated

Roll dia 1000 mm x 1600mm.Coil car with a provision to travel in other bay4 Strands Dolly Type Looper; Storage capacity 566 m.On line Weighing, Manual StrappingHydraulics & Pneumatic Systems