bsp project (based on continuous casting) [final]

•~~aiiq;~~STEELAUTHORITY OF INDIA LIMITED

~~~BHILAI STEEL PLANT

Preparation of 5 Roll Assembly

Sets of CCS in MARS-2

&

26.05.14 - 21.06.14

Under the Guidance of

Arindum HalderRoll No: - P 14/2214

Aritra Chatterjee Roll No: - P 14/2216

Subham Shit Roll No: - P 14/2215

Mr. Gitesh Dewangan

Department of Mechanical Engineering

INDIAN INSTITUTE OF ENGINEERING SCIENCE AND TECHNOLOGY, SHIBPUR

Assistant Manager, MARS-2, BSP By

[email protected]

Typewritten text

Project on :

[email protected]

Typewritten text

STEEL AUTHORITY OF INDIA LIMITED

[email protected]

Typewritten text

(FORMERLY BENGAL ENGINEERING AND SCIENCE UNIVERSITY, SHIBPUR)

[email protected]

Typewritten text

BHILAI STEEL PLANT

Acknowledgement

We would sincerely like to thank the Human Resource Department, of Bhilai Steel Plant,

SAIL for their constant assistance to help us achieve this project work successfully. Our

sincere regards to Mr. S.K. Marathe for helping us realise the do’s and don’ts pertaining to

this specific project report and also helping us in all other sort of ways throughout the entire

duration of our project work. We would like to thank Mr. Gitesh Dewangan , Assistant

Manager of MARS-2, BSP who opted to become our project guide and it was owing to

him only that our project has become a piece of tangible reality from just a dream. It is only

owing to his sincere help, guidance and hours of teaching and learning we gained from him

that we have finally been able to jot down this project report. We are sincerely indebted to

him, for the large chunks of time he spent every now and then to answer all of our doubts

and questions and scrutinise our reports, pointing our mistakes and guiding us to the correct

path. We would also like to pay our sincere gratitude to Mr. M.L. Soni, the person who

was referred to, by none other than our own project guide, Mr. Dewangan, for further

clarifying our doubts, with his year long experience and it was only owing to him that we

came to know how the practical field work is done in the industry, how various

machines are operated, the technique for dismantling, operation and measurements, which

one cannot find in any sort of books or in internet. Last, but not the least, we would like to

thank and send our sincere regards to Mr. Samiran Sikdar, who has remained one of the

key figures behind this project report. It was only owing to him that we obtained the lion’s

share of the information which we used for this very project report. We are extremely

thankful to him for all the minute details he provided us regarding our project and it was

only due to him that we could obtain the basic idea required to understand our project topic.

It can truly be stated that without his help, our report and ideas would have been incomplete.

Lastly, we would like to thank all other various persons and workers of BSP, who have

helped us in one way or another during this month-long project based training of ours.

Contents

INTRODUCTION

Introduction to Bhilai Steel Plant I – II

1. CHAPTER 1: A REPORT ON MARS-2

1.1 Introduction to MARS-2 1

1.2 Annual production in MARS-2 5

1.3 Cost control of MARS-2 during 2013-14 6

2. CHAPTER 2 : AN OVERVIEW OF CONTINUOUS CASTING

2.1 Introduction 9

2.2 Components involved in the Continuous Casting Process 10

2.3 General Overview of Continuous Casting Machines 14

2.4 Development And Principal Types of Casting Machines 15

2.5 Processes Involved in Continuous Casting 16

2.6 Causes of Defects in The Cast Product And Prevention 20

3. CHAPTER 3: A BRIEF DISCUSSION ON FIVE ROLL SET

3.1 Introduction & General Overview 22

3.2 Location of Five Roll Set 23

3.3 Different Parts Present in a Five Roll Assembly 24

4. CHAPTER 4: PREPARATION OF 5 ROLL SET

4.1 Introduction 42

4.2 Description of the Process 42

4.3 Various Instruments Used in the Reassembling Process 47

5. CHAPTER 5: FAILURES IN 5 ROLL SET AND MEASURES FOR

VVVVVVVX.PREVENTION

5.1 Introduction 50

5.2 Failures in Bearings : Causes and Cures 50

5.3 Failures in Rollers : Causes and Cures 54

CONCLUSION 56

REFERENCE 57

I

An Introduction to Bhilai Steel Plant Bhilai Steel Plant - a symbol of Indo-Soviet techno-economic collaboration, is one of the first

three integrated steel plants set up by Government of India to build up a sound base for the

industrial growth of the country, The agreement for setting up the plant with a capacity of 1

MT of Ingot steel was signed between the Government of erstwhile U.S.S.R. and India on 2nd

February, 1955, and only after a short period of 4 years, India entered the main stream of the

steel producers with the commissioning of its first Blast Furnace on 4th February, 1959 by the

then President of India, Dr Rajendra Prasad. Commissioning of all the units of 1 MT stage was

completed in 1961. A dream came true-the massive rocks from the virgin terrains of Rajhara

were converted into valuable iron & steel.

In the initial phase the plant had to face many teething problems, mostly unknown to the

workforce at the time. But by meticulous efforts and teamsprit, these problems were

surmounted and the rated capacity production was achieved only within a year of integrated

operation of the plant.

Thereafter, the plant was expanded to 2.5 MT capacity per year, and then to 4 MT of crude

steel per year, with Soviet assistance.

BSP is the sole manufacturer of rails and producer of the widest and heaviest plates in India.

Bhilai specializes in the high strength UTS 90 rails, high tensile and boiler quality plates, TMT

bars, and electrode quality wire rods. It is a major exporter of steel products with over 70% of

total exports from the Steel Authority of India Limited being from Bhilai. The distinction of

being the first integrated steel plant with all major production units and marketable products

covered under ISO 9002 Quality Certification belongs to BSP. This includes manufacture of

blast furnace coke and coal chemicals, production of hot metal and pig iron, steel making

through twin hearth and basic oxygen processes, manufacture of steel slabs and blooms by

continuous casting, and production of hot rolled steel blooms, billets and rails, structural,

plates, steel sections and wire rods. The plant's Quality Assurance System has subsequently

been awarded ISO 9001:2000.

Not content with the Quality Assurance system for production processes, Bhilai has one in for

ISO 14001 certification for its Environment Management System and its Dalli Mines. Besides

environment-friendly technology like Coal Dust Injection System in the Blast Furnaces, de-

dusting units and electrostatic precipitators in other units, BSP has continued a vigorous

afforestation drive, planting trees each year averaging an impressive 1000 trees per day in the

steel township and mines.

A leader in terms of profitability, productivity and energy conservation, BSP has maintained

growth despite recent difficult market conditions. Bhilai is the only steel plant to have been

awarded the Prime Minister's Trophy for the best integrated steel plant in the country seven

times.

Bhilai Steel Plant, today, is a panorama of sky-scraping chimneys and blazing furnaces as a

modern integrated steel plant, working round the clock, to produce steel for the nation. Bhilai

has its own captive mines spread over 10929.80 acres. We get our iron ore from Rajhara group

of mines, 85 kms south-west of Bhilai. Limestone requirements are met by Nandini mines, 20

kms north of Bhilai and dolomite comes from Hirri in Bilaspur district, 135 kms east of the

plant. To meet the future requirement of iron ore, another mining site Rowghat , situated about

100 km south of Rajhara, is being developed; as the ore reserves at Rajhara are depleting.

II

Bhilai expanded its production capacity in two phases - first to 2.5 MT which was completed

on Sept. 1, 1967 and then on to 4 MT which was completed in the year 1988. The plant now

consists of ten coke oven batteries. Six of them are 4.4 metres tall. The 7 metre tall fully

automated Batteries No 9 & 10 are among the most modern in India. Of Bhilai's seven blast

furnaces, three are of 1033 cu. metre capacity each, three of 1719 cu. metre and one is 2000

cu. metre capacity. Most of them have been modernized incorporating state-of-the-art

technology.

Steel is made through twin hearth furnaces in Steel Melting Shop I as well as through LD

Convertor -continuous Casting route in SMS II. Steel grades conforming to various national

and international specifications are produced in both the melting shops. Production of cleaner

steel is ensured by flame enrichment and oxygen blowing in SMS I while secondary refining

in Vaccum

Arc Degassing ensures homogenous steel chemistry in SMS II. Also in SMS II is a 130 T

capacity RH (Ruhshati Heraus) Degassing Unit, installed mainly to remove hydrogen from rail

steel and Ladle Furnace to meet present and future requirements of quality steel. Bhilai is

capable of providing the cleanest and finest grades of steel.

The rolling mill complex consists of the Blooming & Billet Mill, Rail & Structural Mill,

Merchant Mill, Wire Rod Mill and also a most modern Plate Mill. While input to the BBM and

subsequently to Merchant Mill and Wire Rod Mill comes from the Twin Hearth Furnaces, the

Rail & Structural Mill and Plate mill roll long and flat products respectively from continuously

cast blooms and slabs only. The total length of rails rolled at Bhilai so far would circumvent

the globe more than 4.5 times.

To back this up, there is Ore Handling Plant, three Sintering Plants – of which one is most

modern, two captive Power Plants with a generating capacity of 110 MW, two Oxygen Plants,

Engineering Shops, Machine Shops and a host of other supporting agencies giving Bhilai a lot

of self-sufficiency in fulfilling the rigorous demands of an integrated steel plant. Power Plant

No.2 of 74 MW capacity has been divested to a 50:50 SAIL/NTPC joint venture company. The

plant has undertaken massive modernization and expansion plan to produce 7.5 MT of hot

metal by the year 2010.

More than the machinery and processes, it is the men i.e. the engineers, technicians, skilled and

unskilled workers behind them that constitute the flesh and blood of this steel plant.

Bhilai at present has around 34000 persons to run this pulsating giant. The culture which has

today become the hallmark of Bhilai is a result oriented approach to work. It is their effective

and co-operative working relationship nurtured in a spirit of dedication and enthusiasm that

has shaped Bhilai's image today.

Adjoining the plant, a modern township - Bhilai Nagar, having the spaciousness of a village

and the cleanliness of a modern town is spread – over in 17 self-sufficient sectors with schools,

markets, parks and other facilities. Free Medical aid is given to all the employees and their

dependents through a network of health centers, dispensaries and hospitals. Medical facilities

are extended to retired employees & their spouses also. The Education Department runs a

number of higher secondary, middle, primary, and pre-primary schools in Bhilai and also in

the mines townships at Rajhara, Nandini and Hirri.

Thus together with all this facilities the Bhilai Steel Plant has not only become the leading steel

plant in the country but also has set a standard so high that other industries strive to achieve.

A REPORT ON MARS-2 Introduction, Annual Production & Cost Control of

Machining, Assembly & Re-Engineering Services-2

Chapter 1

Page | 1

MARS-2

1.1 INTRODUCTION TO MARS-2

• MARS-2 is popularly known as Machine Shop-2. MARS-2 stands for Machining,

Assembly & Re-Engineering Services-2. MARS-2 was established during 4 MT

expansion project to take care of machining & assembly jobs of Convertor,

Continuous Casting Shop & Plate Mill. The shop has got two machining bays

(Light bay and Heavy & Medium bay 78 x 24 M each), and one Assembly bay (72

x 24 M) which forms a Tee with the machining bays.

Working Area of the shop : 5161m2

Electrical Power : 1 MVA

• Past & Present:

MARS-2 started with manpower of 128. The present strength is only 86. Initially

MARS-2 was dedicated for 4 MT expansion area but presently it is dealing with

almost all the major shops of BSP.

• Specialization:

MARS-2 has two MACHINE BAY

1. LIGHT BAY- for Light Machining

2. HEAVY BAY- for Heavy Machining

MARS-2 has one ASSEMBLY BAY for assembly work.

• Capacity :

Annual machining capacity: 2200 T

Annual assembly capacity: 6000 T

Main assemblies done are 5-roll set, 8-roll set, 10-roll set, and Pinch rolls used in

Slab Caster of Continuous Casting Shop.

• Machining Jobs:

Following important high value items are machined:

1. Slide Block of Plate Mill

2. Inserts for Continuous Casting Shop

3. Hammer Plates of Sintering Plant-2 & 3

4. Top Tie Rod of Coke-oven

5. New Wheels of Various Departments.

Page | 2

• Repairing & Reclamation Jobs:

Following items are repaired & reclaimed:

1. Pinch Roll of Slab & Bloom Caster

2. Truing of Dia. 230 Roller of Continuous Casting Shop

3. Roll Table Cylindrical Roller Of Plate Mill

4. Reclamation of Various Wheels

5. Partening of Magnet of Continuous Casting Shop & Plate Mill

6. Reclamation of Ribbed Roller of Plate Mill

• Assembly Jobs:

Following important items are dismantled & reassembled in MARS-2

1. 5 ROLL SET OF CONTINUOUS CASTING SHOP

2. 10 ROLL SET OF CONTINUOUS CASTING SHOP

Page | 3

3. TONG ASSEMBLY OF CONTINUOUS CASTING SHOP

4. BREAST ROLL ASSEMBLY OF PLATE MILL

5. MUDGUN BARREL ASSEMBLY OF BLAST FURNACE

Page | 4

6. MUDGUN COLUMN ASSEMBLY OF BLAST FURNACE

7. DEDUSTING FAN OF SINTERING PLANT-3

• MARS-2 Assembly Jobs:

Following important items are dismantled & reassembled:

Input/ Output Shaft Assembly

Wheel Assembly

Eccentric Shaft Assembly

Reducer Assembly etc.

• Main Equipment(s):

MARS-2 is one of the most well equipped machine shop in BSP. It boasts of series of

highly useful machines like- Vertical Boring machine (1 No), Horizontal Boring

Machine (1 No), HMT Lathe (8 Nos.). MARS-2 also consists of 1 Cylindrical

Grinding Machine, 1 Heavy Duty Lathe, 1 Plano Milling Machine, 1 HMT Horizontal

Milling Machine, 1 HMT Universal Milling Machine etc. Beside these, it has 2

Slotting Machine, 1 Shaping Machine, 1 Thread Cutting Machine, and 1 Auto Welding

Machine of 10 T too.

MARS-2 Crane Details:

MARS-2 has 3 overhead cranes each in Heavy, Light & Assembly Bay:

Assembly Bay Crane- 50 / 20 T Capacity

Heavy Bay Crane- 20 / 10 T Capacity

Light Bay Crane- 20 / 10 T Capacity

Page | 5

1.2 ANNUAL PRODUCTION IN MARS-2

Manufacturing of High Value Items :

S.N. Name of Items Qty. Total Value (Rs.)

1 Slide Block (Insert) of CCS 68 81,600

2 Slide Block (PMM- 548) for Plate Mill 18 2,61,000

3 Slide Block of Plate Mill Main Stand 27 54,00,000

4 Hammer Plates of SP – 3 1176 19,20,408

5 Machining of New Wheels 46 9,27,406

6 Tie Rod Size M48X16 Mtr. of Coke Oven 22 3,85,000

Total Value (Rs.) 89,75,414

Repair & Reclamation of High Value Items :

S.N. Name of Items Qty. Total Value

(Rs.)

1 Vertical Roll of R & S Mill 27 10,12,500

2 Pinch Roll of CCS 156 2,24,07,216

3 Breast Roll of P/Mill 6 13,33,332

4 Motorized Tong Assembly Of CCS 3 9,00,000

5 Welding of Various Sizes Wheels 168 34,99,944

6 Hydraulic Mud Gun Assembly 4 20,00,000

7 Dia. 230 Roller of 8- Roll set 176 68,74,912

8 Reclamation of Dia. 450 Cylindrical Roller of Plate

Mill 16 32,00,000

9 Reclamation of Dia. 300 Roller of Plate Mill (Welding

& Machining) 6 20,66,670

10 Reclamation of Dia. 350 & 450 Ribbed Roller of Plate

Mill 18 72,00,000

Total Value (Rs.) 5,04,94,574

Page | 6

Important Assemblies for CCS Operation :

5 Roll Set Assembly - 91 Sets



So, total no. of sets for CCS Operation = 138 Sets

1.3 COST CONTROL OF MARS-2 DURING 2013-14

Saving in Bearings :

S.N. Name of

Items

Bearing

Used

New

Bearing

Reclaimed

Bearing

Value

Per

Piece

Total

Saving

1

5 Roll Set

Bearing No.

6212

5460 1415 4045 419 16,94,855

2

8 Roll Set

Bearing No.

22220

384 42 342 3564 12,18,888

3

10 Roll Set

Bearing No.

22213

2800 773 2027 2000 40,54,000


Steps taken to Save Bearings :

By removing old bearing from the sets.

By cleaning properly then checking.

By assembling properly with sufficient grease.

Cost Control in Maintenance :

S.N. Name Of Items Qty. Total Value (Rs.)

1 Saving Of Head Stock Of Lc-100 Lathe Machine

By Sleeving Bearing Seating. 1 50,000

2 In-House Repair Of Lubrication Oil Pump Of L-

45 Lathe Machine 1 20,000

3 Repair Of Feed Mechanism Of Horizontal Boring

Machine 1 30,000


Page | 7

Total Saving :

1. Saving in Manufacturing of High Value Items = 89,75,414

2. Saving in Repair & Reclamation of High Value Items = 5,04,94,574

3. Saving in Bearing = 69,67,743

4. Saving in Maintenance = 1,00,000

So, the Total Saving = 6,65,37,731.

Saving In Power Consumption :

Total Consumption of Electricity during 2013-14 -648500 KWH

Total Consumption of Electricity during 2009-10 -750690 KWH

Saving in Power consumption during last 4 year– 102190 KWH

Steps Taken For Power Reduction :

Over Hauling of Heavy Duty Motors & Generators.

Switching off Machines, Fans, and ACs & Coolers etc. during idle time.

Switching off of MG Sets.

Saving In Oil Consumption :

Total Oil Consumption during 2012-13 - 4430 Ltrs.

Targeted reduction in Oil consumption for 2013-14 – 3390 Ltrs.

Saving in oil consumption in current year - 1040 Ltrs.

Steps Taken For Reducing Oil Consumption :

By stopping leakages from Machines.

By properly handling in Oil store room.

By taking care at the time of pouring oil in machines.

• MARS-2 Certification:

MARS-2 has following important Certifications:

OHSAS: 18001

SA:8000

ISO:14001

Page | 8

Manpower Statistics in MARS-2:

• MARS-2 Awards & Rewards:

MARS-2 has got following awards:

NATIONAL SAFETY AWARD for various categories.

BEST HOUSEKEEPING AWARD.

2005-06 2006-07 2007-08 2008-09 2009-10 2010-11 2011-12 2012-13 2013-14

Executive 4 4 4 4 4 3 3 3 3

Non-Executive 107 106 102 101 99 91 88 86 82

0

20

40

60

80

100

120

Ma

np

ow

er

Years

Manpower over the Years

Non-Executive Executive

AN OVERVIEW OF

CONTINUOUS CASTING Continuous Casting Process, Parts of CCM, Types,

Processes Involved & Casting Defects

Chapter 2

Page | 9

CONTINUOUS CASTING

2.1 INTRODUCTION Continuous casting of steel is a process in which liquid steel is continuously solidified into a

strand of metal. Depending on the dimensions of the strand, these semi-finished products are

called slabs, blooms or billets. The process was invented in the 1950s in an attempt to increase

the productivity of steel production. Previously only ingot casting was available which still has

its benefits and advantages but does not always meet the productivity demands. Since then,

continuous casting has been developed further to improve on yield, quality and cost efficiency.

This process also known as ‘strand casting’ is used most frequently to cast steel (in terms of

tonnage cast). Aluminium and copper are also continuously cast. Sir Henry Bessemer, of

Bessemer converter fame, received a patent in 1857 for casting metal between two contra-

rotating rollers. The basic outline of this system has recently been implemented today in the

casting of steel strip.

Liquid steel is supplied to the continuous caster from the secondary steelmaking shop. The

ladle is usually delivered by crane and positioned into a ladle turret, which subsequently rotates

the ladle into the casting position. A slide gate in the bottom of the ladle is opened to allow the

liquid steel to flow via a protective shroud into a tundish, a vessel that acts as a buffer between

the ladle and the mould. As the tundish fills, stopper rods are raised in order to allow the casting

of steel into a set of water-cooled copper moulds below the tundish. Solidification begins at the

mould walls and the steel is withdrawn from the mould by a dummy bar. As it leaves the mould,

the strand of steel requires a sufficiently thick solid shell to carry the weight of the liquid steel

that it contains, i.e. the ferrostatic pressure.

Fig. 2.1: Continuous Casting Machine in action

Page | 10

Throughout the entire casting process, the mould oscillates vertically in order to separate the

solidified steel from the copper mould. This separation is further enhanced by introducing a

mould powder into the mould. The strand is withdrawn from the mould by a set of rolls which

guide the steel through an arc until the strand is horizontal. The rolls have to be positioned

close enough together to avoid bulging or breaking of the thin shell.

As the steel leaves the mould, it has only a thin solidified shell which needs further cooling to

complete the solidification process. This is achieved in the so-called secondary cooling zone,

in which a system of water sprays situated between the rolls are used to deliver a fine water

mist onto the steel surface. At this point, the steel, solidified shell and liquid center, is called

the strand. After the strand has been straightened and has fully solidified, it is torch-cut to pre-

determined product lengths. These are either discharged to a storage area or to the hot rolling

mill.

Continuous Casting has evolved from a batch process into a sophisticated continuous process.

This transformation has occurred through understanding principles of mechanical design, heat-

transfer, steel metallurgical properties and stress-strain relationships, to produce a product with

excellent shape and quality. In recent years, the process has been optimized through careful

integration of electro-mechanical sensors, computer-control, and production planning to

provide a highly-automated system designed for the new millennium.

2.2 COMPONENTS INVOLVED IN THE CONTINUOUS

XX.CASTING PROCESS

Components Primary Task Secondary Task

Ladle Transport and hold the liquid steel Facilitate inclusion removal

Ladle Turret Position full ladles over the tundish

and remove empty ones.

Free the cranes for higher

productivity.

Tundish Act as a buffer between the ladle

and the mould. Facilitate inclusion removal

Mould Cool down the liquid steel to form

a solidified shell

Rolling Strand Further cool the strand to fully

solidified and straighten it

The above table provides a brief idea about the various components involved in the continuous

casting process and states their actions briefly. However a further detailed overview of the

various parts is given below:

Ladle

Molten metal is tapped into the ladle from furnaces. After undergoing any ladle treatments,

such as alloying and degassing, and arriving at the correct temperature, the ladle is transported

to the top of the casting machine. Usually the ladle sits in a slot on a rotating turret at the casting

Page | 11

machine. One ladle is in the 'on-cast' position (feeding the casting machine) while the other is

made ready in the 'off-cast' position, and is switched to the casting position when the first ladle

is empty. From the ladle, the hot metal is transferred via a refractory shroud (pipe) to a holding

bath called a tundish.

Ladle Turret

One very important part of a continuous casting plant is the ladle turret. It holds the pouring

ladles, which weigh up to 300 ton. By means of the ladle turret, the pouring ladles are

alternately slewed into pouring and charging position. This function ensures the uninterrupted

option of the continuous casting plant. While one ladle is being emptied a full ladle is provided

on the other side.

The bearings of the ladle turret, in spite of being subjected to high forces and considerable

tilting moments, have prolonged service life. The ladle turret serves for sequential casting.

Tundish

From the ladle, the hot metal is transferred via a refractory shroud (pipe) to a holding bath

called a tundish. The tundish allows a reservoir of metal to feed the casting machine while

ladles are switched, thus acting as a buffer of hot metal, as well as smoothing out flow,

regulating metal feed to the moulds and cleaning the metal. The shape of the tundish is typically

rectangular, but delta and "T" shapes are also common. Nozzles are located along its bottom to

distribute liquid steel to the moulds. The tundish also serves several other key functions:

Enhances oxide inclusion separation

Provides a continuous flow of liquid steel to the mould during ladle exchanges

Maintains a steady metal height above the nozzles to the moulds, thereby keeping steel flow

constant and hence casting speed constant as well (for an open-pouring metering system).

Provides more stable stream patterns to the mould(s).

Fig. 2.2: Intermediate ladle of Continuous Casting Machine:

1 – Steel Jacket; 2 – Metering Nozzle; 3 – Metal Reservoir;

4 – Gunned Layer; 5 – Concrete

Page | 12

Tundish Nozzle

Two basic types of tundish nozzles are used: (1) a metering or open nozzle and; (2) a stopper

rod-controlled nozzle. Metering nozzles, a simpler system, have been generally employed in

billet and small bloom casters, producing silicon-killed steels. Metal discharge rate is

controlled by the bore of the nozzle and the ferrostatic pressure (metal height in the tundish)

above the nozzle. Different bores are selected depending on the section size cast and casting

speed required. Stopper rod-controlled nozzles are used for casting slabs and large sections

when aluminum-killed steels are produced. In this application, metal discharge rate through the

nozzle is controlled manually or automatically by the setting of the stopper head in relation to

the nozzle opening. Originally, over-sized nozzles were used for casting aluminum-killed

steels: as alumina build-up occurred, the stopper head was raised to compensate for a reduction

in flow rate.

Mould

The main function of the mould is to establish a solid shell sufficient in strength to contain its

liquid core upon entry into the secondary spray cooling zone. Key product elements are shape,

shell thickness, uniform shell temperature distribution, defect-free internal and surface quality

with minimal porosity, and few non-metallic inclusions.

The mould is basically an open-ended box structure, containing a water-cooled inner lining

fabricated from a high purity copper alloy. Mould water transfers heat from the solidifying

shell. Although the material of construction of the inner lining is usually a high purity

cold-rolled copper, copper with small amounts of silver is commonly used to obtain increased

elevated-temperature strength. The working surface of the liner is often plated with chromium

or nickel to provide a harder working surface and also to avoid copper pickup on the surface

of the cast strand.

There are two types of mould designs; tubular moulds and plate moulds. Tubular

moulds conventionally consist of a one-piece copper lining that usually has relatively thin walls

and is restricted to smaller billet and bloom casters. Plate moulds consist of a 4-piece copper

lining attached to steel plates. In some plate mould designs opposite pair of plates can be

adjusted in position to provide different section sizes. For example, slab width can be changed

by positioning the narrow-face plates, and the slab thickness changed by altering the size of the

narrow-face plates. The plate mould is inherently more adaptable than the fixed-configuration,

tubular mould. In addition to permitting size changes, changes can also be made to the mould

taper (to compensate for different shrinkage characteristics of different steel grades) as well as

ease of fabrication and reconditioning.

Mould heat transfer is both critical and complex. Mathematical and computer modeling are

typically utilized in developing a greater understanding of mould thermal conditions. Heat

transfer is generally considered as a series of thermal resistances as follows:

Heat transfer through the solidifying shell

Heat transfer from the steel shell surface to the copper mould outer surface

Heat transfer through the copper mould

Heat transfer from the copper mould inner surface to the mould cooling water

Page | 13

Rolling Strand

In the mould, a thin shell of metal next to the mould walls solidifies before the middle section,

now called a strand, exits the base of the mould into a spray chamber. The bulk of metal within

the walls of the strand is still molten. The strand is immediately supported by closely spaced,

water-cooled rollers which support the walls of the strand against the ferrostatic pressure

(compare hydrostatic pressure) of the still-solidifying liquid within the strand. To increase the

rate of solidification, the strand is sprayed with large amounts of water as it passes through the

spray-chamber; this is the secondary cooling process. Final solidification of the strand may

take place after the strand has exited the spray-chamber.

It is here that the design of continuous casting machines may vary. This describes a 'curved

apron' casting machine; vertical configurations are also used. In a curved apron casting machine,

the strand exits the mould vertically (or on a near vertical curved path) and as it travels through

the spray-chamber, the rollers gradually curve the strand towards the horizontal. In a vertical

casting machine, the strand stays vertical as it passes through the spray-chamber. Moulds in a

curved apron casting machine can be straight or curved, depending on the basic design of the

machine. In a true horizontal casting machine, the mould axis is horizontal and the flow of steel

is horizontal from liquid to thin shell to solid (no bending). In this type of machine, either strand

or mould oscillation is used to prevent sticking in the mould.

After exiting the spray-chamber, the strand passes through straightening rolls (if cast on other

than a vertical machine) and withdrawal rolls. There may be a hot rolling stand after withdrawal

to take advantage of the metal's hot condition to pre-shape the final strand. Finally, the strand

is cut into predetermined lengths by mechanical shears or by travelling oxyacetylene torches,

is marked for identification, and is taken either to a stockpile or to the next forming process.

In many cases the strand may continue through additional rollers and other mechanisms which

may flatten, roll or extrude the metal into its final shape.

Fig. 2.3: Continuous Casting Mould with Ceramic Insert:

1 – Secondary Oxidation Protector; 2 – Ceramic Insert; 3 – Porous Ring;

4 – Ultrasonic Transducer; 5 – Copper part of the Mould

Page | 14

2.3 GENERAL OVERVIEW OF CONTINUOUS

XX.CASTING MACHINES

Casting machines can be classified into several main groups depending on the section shape

produced: billet, bloom, round, slab and beam blank. In some cases, overlaps occur where the

moulds on a particular machine can be changed to cast other shapes; for example, billets or

blooms, blooms or small slabs, and blooms or rounds. In addition, machines exist where special

shapes, such as rectangles and dogbone structural sections can be cast as well as billets or

blooms.

Billet:

Billet machines, which cast section sizes up to approximately 5 inches square, are multi-strand

machines that are widely used in the mini-mill sector of the industry but only to a relatively

limited extent in fully integrated plants. This has occurred because of practical considerations

which are related to the heat size, casting rate per strand (tons/minute) and casting time. In

general, casting times are limited to approximately one hour for each heat because of heat

losses in the ladle. It is practical, for example, to cast a 50 net-ton heat on a 2-strand machine

or a 100 net-ton heat on a 4-strand machine. However, the number of strands required for

casting heat sizes in excess of 200 net tons, which are common in integrated steel plants,

becomes impractical.

Bloom:

Bloom casters have been more widely installed by integrated plants because the casting rate

for the larger section size is higher than for billet sizes and, consequently, larger heat sizes can

be cast with relatively fewer strands. Bloom section sizes cast can vary, for example, from 7

in. sq., cast on a 6-strand machine from 150 net-ton heats, up to as large as 14.6 in. x 23.6 in.,

cast on a 3-strand machine from 180 net-ton heats.

Round:

The installation of machines for casting rounds, principally for seamless tube production, has

been relatively slow. Although a 4-strand caster was installed, for example to produce 125 and

210-mm (4.9 and 8.3 in.) diameter rounds from a 30 metric-ton (33 net ton) heat in 1965,

potential surface cracking problems delayed the introduction of round casting. Some

modifications were made later for an existing 6-strand billet/bloom caster, for example, to

produce 152-mm (6-in.) diameter rounds in 1980s. The installations of the modified caster

included the 640,000 metric tons (700,000 net tons) per year U.S. Steel machine at Lorain,

which is a 6-strand caster producing up to 232-mm (9 and 1/4 in.) diameter rounds.

Slab:

There are a large number of slab casters throughout the world which, although operated

principally in integrated steel plants, are also used for producing stainless and specialty steel.

These machines are generally high production units with rated annual capacities of up to 1.4

Page | 15

million metric tons (1.5 million net tons) and above. They are usually either single or

twin-strand machines casting large heat sizes. A wide variety of low carbon, low alloy, alloy

and stainless steel grades are cast for sheet, strip, plate and specialty applications. Successful

examples of the slab casters are the CSP technology developed by then SMS, and ISP from

then Mannesmann Demag, both in Germany. (The two companies have merged as

SMS Demag). Beam Blank and Special Shapes: Beam blanks are cast to be subsequently rolled

into I beams. Other special shapes are also cast to produce near-net shapes for various final

products. . The new technology has been developed to cast beam blank with thinner web, such

as 50 mm and less.

2.4 DEVELOPMENT AND PRINCIPAL TYPES OF

XX.CASTING MACHINES

One of the major objectives in the design of continuous casting machines has been to reduce

the capital cost of the installation while at the same time maintaining or improving the quality

of the cast product. This objective has been achieved by a progressive reduction in the height

of the machine which has resulted in a reduction in the size of the supporting structure, building

height and foundation. It has led to the development of five principal types of casting machines

which are essentially applicable to all section shapes cast whether billets, blooms, slabs, etc.

Chronologically, these types, illustrated schematically are:

1. Vertical machine with a straight mould and cutoff in the vertical position.

2. Vertical machine with a straight mould, single-point bending and straightening.

3. Vertical machine with a straight mould, progressive bending and straightening.

4. Bow type machine with curved mould and straightening.

5. Bow type machine with curved mould and progressive straightening.

Fig. 2.4: Various Section Shapes Produced in Continuous Casting

Page | 16

The choice between these types of casting machines depends on a complex optimization of the

specific facility requirements for caster productivity, product quality and machine complexity,

and cost. With the introduction of the newer designs there has been an increasing adoption of

the bow-type machines with curved moulds for slab casters and to a lesser extent for billet and

bloom machines. Curved machines are usually simpler to build (i.e., lower cost) and maintain

than vertical with bending machines, as the bender is eliminated. However, for some grades of

steel, for example, plate grades, quality and casting speed limitations were previously more

restrictive on these curved machines. Recently, technical developments such as "clean" steel

practices and electromagnetic stirring have been applied to curved machines to overcome these

restrictions. In general, the complexity of the casting process and machine varies greatly

between the type of product being cast (e.g., billet, bloom, or slab). This is due both to

the thermo-mechanical characteristics of these cast sections, and to the different applications

of the cast product.

Billet sections are self-supporting in

the secondary cooling zone, while

slabs are usually not. Generally,

billet casters have tended to be

simple in design, with open-pouring

streams, limited automatic controls,

and no roll support in the secondary

cooling zone. Conversely, slab

casters are complex and use the total

range of subsystems such as total

stream shrouding, computer controls,

and total roll containment

throughout the machine. Bloom

casters are intermediate between

these two extremes.

2.5 PROCESSES INVOLVED IN CONTINUOUS

XX.CASTING

To start a cast, the mould bottom is sealed by a steel dummy bar, which is held in place

hydraulically by the Straightener Withdrawal Units. This bar prevents liquid steel from flowing

out of the mould. The steel poured into the mould is partially solidified, producing a steel strand

with a solid outer shell and a liquid core. In this primary cooling area, once the steel shell has

a sufficient thickness, about 0.4 - 0.8 inches (10 to 20 mm), the Straightener Withdrawal Units

are started, and proceed to withdraw the partially solidified strand out of the mould along with

the dummy bar. Liquid steel continues to pour into the mould to replenish the withdrawn steel

at an equal rate. The withdrawal rate depends on the cross-section, grade and quality of steel

Fig. 2.5: Principal Types of Casting Machines

Page | 17

being produced, and may vary between 12 and 300 inches per minute. Casting time is typically

1.0 - 1.5 hours per heat to avoid excessive ladle heat losses.

Upon exiting the mould, the strand enters a roller containment section and secondary cooling

chamber in which the solidifying strand is sprayed with water, or a combination of water and

air (referred to as Air-Mist) to promote solidification. This area preserves cast shape integrity

and product quality. Larger cross-sections require extended roller containment (Figure 3). Once

the strand is fully solidified and has passed through the Straightener Withdrawal Units, the

dummy bar is disconnected, removed and stored. Following the straightener, the strand is cut

into individual pieces of the following as-cast products: slabs, blooms, billets, rounds, or beam

blanks, depending on machine design.

Liquid Steel Transfer

There are two steps involved in transferring liquid steel from the ladle to the moulds. First, the

steel must be transferred (or teemed) from the ladle to the tundish. Next, the steel is transferred

from the tundish to the moulds. Tundish-to-mould steel flow regulation occurs through orifice

devices of various designs: slide gates, stopper rods, or metering nozzles, the latter controlled

by tundish steel level adjustment.

Primary Cooling

Metal is drained from the tundish through another shroud into the top of an open-base copper

mould. The depth of the mould can range from 0.5 to 2 metres (20 to 79 in), depending on the

casting speed and section size. The mould is water-cooled to solidify the hot metal directly in

contact with it; this is the primary cooling process. A lubricant can also be added to the metal

in the mould to prevent sticking, and to trap any slag particles—including oxide particles or

scale—that may be present in the metal and bring them to the top of the pool to form a floating

layer of slag.

Mould Oscillation

Mould oscillation is necessary to minimize friction and sticking of the solidifying shell, and

avoid shell tearing, and liquid steel breakouts, which can wreak havoc on equipment and

machine downtime due to clean up and repairs. Friction between the shell and mould is reduced

through the use of mould lubricants such as oils or powdered fluxes. Oscillation is achieved

either hydraulically or via motor-driven cams or levers which support and reciprocate (or

oscillate) the mould.

Mould oscillating cycles vary in frequency, stroke and pattern. However, a common approach

is to employ what is called "negative strip", a stroke pattern in which the downward stroke of

the cycle enables the mould to move down faster than the section withdrawal speed. This

enables compressive stresses to develop in the shell that increase its strength by sealing surface

fissures and porosity.

Page | 18

Secondary Cooling

Typically, the secondary cooling system is comprised of a

series of zones, each responsible for a segment of controlled

cooling of the solidifying strand as it progresses through the

machine. The sprayed medium is either water or a

combination of air and water. To increase the rate of

solidification, the strand is sprayed with large amounts of

water as it passes through the spray-chamber; this is the

secondary cooling process. Final solidification of the

strand may take place after the strand has exited the spray-

chamber.

Three (3) basic forms of heat transfer occur in this region:

Radiation: The predominant form of heat transfer in the upper regions of the secondary

cooling chamber, described by the following equation:

Q = σEA(Ts4 − Ta

4) [3.5.1]

Where σ is the Stephan-Boltzmann constant, E is the emissivity constant (≈0.8), A is the

surface area, Ts and Ta are steel surface and ambient temperatures respectively.

Conduction: As the product passes through the rolls, heat is transferred through the shell

as conduction and also through the thickness of the rolls, as a result of the associated contact.

This form of heat transfer is described by the Fourier Law:

Q =KA(Ti − To)

∆X [3.5.2]

For conductive heat transfer through the steel shell, k is the shell's thermal conductivity,

whereas A and ∆X are the cross-sectional area and thickness of the steel shell, respectively,

through which heat is transferred. Ti and To are the shell's inner and outer surface

temperatures, respectively.

Convection: This heat transfer mechanism occurs by quickly-moving sprayed water

droplets or mist from the spray nozzles, penetrating the steam layer next to the steel surface,

which then evaporates. This convective mechanism is described mathematically by

Newton's Law of Cooling:

q = hA(Ts − Tw) [3.5.3]

Where h is a constant coefficient of heat transfer, A is the surface area, Ts and Tw are the

steel surface and spray water temperature.

Fig. 2.6: Secondary Cooling

Process

Page | 19

Shell Growth

Shell growth can be reliably predicted from Fick's Law:

L = V (D

k)

2

[3.5.4]

D = shell thickness; L = Cast distance from mould steel meniscus from where solidification

begins; V = Casting speed; k is an empirical constant determined from cast grade and machine

design.

Metallurgical Length

Metallurgical length, is

defined as the distance from

the mould at which the strand

becomes totally solid. It is a

parameter which depends

upon the casting speed and

secondary cooling rate. The

metallurgical length is a

complex function of steel

composition, casting speed,

cooling rate and strand

dimensions.

Strand Containment

The containment region is an integral part of the secondary cooling area. A series of retaining

rolls contain the strand, extending across opposite strand faces. Edge roll containment may also

be required. The focus of this area is to provide strand guidance and containment until the

solidifying shell is self-supporting. In order to avoid compromises in product quality, careful

consideration must be made to minimize stresses associated with the roller arrangement and

strand unbending. Thus, roll layout, including spacing and roll diameters are carefully selected

to minimize between-roll bulging and liquid/solid interface strains.

Strand support requires maintaining strand shape, as the strand itself is a solidifying shell

containing a liquid core that possesses bulging ferrostatic forces from head pressure related to

machine height. The area of greatest concern is high up in the machine. Here, the bulging force

is relatively small, but the shell is thinner and at its weakest. To compensate for this inherent

weakness and avoid shell rupturing and resulting liquid steel breakouts, the roll diameter is

small with tight spacing. Just below the mould all four faces are typically supported, with only

the broad faces supported at regions lower in the machine.

Bending and Straightening

Equally important to strand containment and guidance from the vertical to horizontal plane are

the unbending and straightening forces. As unbending occurs, the solid shell outer radius is

under tension, while the inner radius is under compression. The resulting strain is dictated by

Fig. 2.7: Diagram illustrating Metallurgical Length

Page | 20

the arc radius along with the mechanical properties of the cast steel grade. If the strain along

the outer radius is excessive, cracks could occur, seriously affecting the quality of the steel.

These strains are typically minimized by in-corporating a multi-point unbending process, in

which the radii become progressively larger in order to gradually straighten the product into

the horizontal plane.

After straightening, the

strand is transferred on

roller tables to a cut off

machine, which cuts the

product into ordered

lengths. Sectioning can be

achieved either via torches

or mechanical shears. Then,

depending on the shape or

grade, the cast section will

either be placed in inter-

mediate storage, hot-

charged for finished rolling

or sold as a semi-finished

product. Prior to hot rolling,

the product will enter a

reheat furnace to adjust its

thermal conditions to

achieve optimum metal-

urgical properties and

dimensional tolerances.

2.6 CAUSES OF DEFECTS IN THE CAST PRODUCT

XX.AND PREVENTION

There are five categories of failure for the strand:-

1. Internal Cracking

2. Surface cracking

3. Center segregation

4. Inclusion Content

5. Oscillation Marks

Fig. 2.8: Diagram illustrating Bending and Straightening Zone

Page | 21

Internal cracking and surface cracking is decided by the strains and stresses in strand during

casting. Possible measures to prevent crack formation are optimizing mould powder and mould

oscillation to result in an oscillation mark depth < 0.2mm and to provide good maintenance

regarding misaligned rolls.

Center segregation can be reduced by choosing a combination of casting speed and secondary

cooling rate so that the point of solidification is well within the soft reduction zone. Having

done so the next step of optimization is to increase the soft reduction level further to achieve a

greater thickness reduction.

Inclusion content can be lowered by making sure that the residence time for liquid steel in

tundish is as long as possible. This is achieved by maintaining a high level of steel in the tundish

and/or casting at lower speeds.

In order to minimize the depth of the oscillation marks it is essential to properly optimize the

oscillation settings. The negative strip time should be as close to 0.11 s as possible combined

with a stroke that results in the smallest possible oscillation mark depth. The negative strip time

(hatched areas) is the main influencing factor for the formation of oscillation marks. Increasing

negative strip time is accompanied with increasing depth of oscillation marks.

A breakout will occur if the ferrostatic pressure exceeds the strength of the strand shell. It is

avoided by ensuring the shell thickness at any given point in the strand is sufficient to carry the

weight of the liquid steel above this point .Since the probability of breakout increases with a

decreasing shell thickness, it is very important to maintain a high steel level in the mould and

to have as low superheat as possible. This allows the shell to solidify to an adequate thickness

before the steel leaves the mould. Given that a thin shell might break under the pressure of the

liquid steel, oscillation marks should be kept as shallow as possible.

Depending on its precise composition, the linepipe steel grade can either be peritectic or hypo-

peritectic. Peritectic compositions are very crack sensitive, and so require more careful casting

to avoid cracks forming and propagating through the shell to cause breakout.

A BRIEF DISCUSSION ON

5 ROLL SET General Overview, Location, Different Parts Present

in 5 Roll Assembly & Description

Chapter 3

Page | 22

A BRIEF DISCUSSION ON

5 ROLL SET

3.1 INTRODUCTION & GENERAL OVERVIEW 5 roll sets are an integral component of the traditional slab caster machines used for continuous

casting process. Although 5 roll sets may not find their application in the latest forms of the

continuous casting machines yet they still form an integral part in the traditional slab casters

still widely used in most steel plants. The 5 roll set design has been introduced by the aid of

the Russian technologies since the 1970’s and are still adopted by SAIL.

5 roll sets form the first of the numerous sets of rolling assemblies used in the rolling strand of

slab caster. Located just below the mould, the chief function of 5 roll sets is to provide better

support to the slab being cast in the earlier stages of the continuous casting process. As the Cast

Slab starts to solidify at the mould, 95% of the slab remains in hot liquid form and only rest

5% solidifies at the surfaces of the Slab-wall. So, if the support is less, then it is more prone to

break-out. Break-out means the extraction of liquid hot metal from any leakage or crack

developed on the solidified walls of the cast slab. So it is mandatory to provide more support

points to the cast slab when it is not fully solidified i.e. having maximum liquid hot metal inside

it in the earlier stage of Continuous casting.

Also 5 roll sets play an integral part in the secondary cooling process of the cast slab. The

process of primary cooling starts in the mould and the secondary cooling starts in the 5 roll

assembly of the rolling strand. The 5 roll sets in a rolling strand are provided with supply of

water through a network of water pipes attached to the assembly which spray water on the cast

slab while it is supported by the 5 roll set and thus secondary cooling is achieved. 5 rolls thus

have several usage in a slab caster and it is used in radial type slab caster or single point bending

continuous casting machines. In this report we discuss the preparation of 5 roll assemblies used

in slab caster and a detailed study of its individual components their production, application,

failure and reclamation.

Fig. 3.1: 5 Roll Assembly Set of CCS

Page | 23

3.2 LOCATION OF 5 ROLL SETS

The arrangement of rollers in the slab caster is described in the diagram above. The sequence

of the rollers along with their brief details is stated below:

The mould is situated on top of the rolling strand. In case of radial slab caster machines the

curvature starts from the mould part itself.

Just below the mould the 5 roller assembly set is situated which marks the beginning of the

rolling strand. The roller diameter is generally 140 mm in this section.

The ten roller assembly set follows the 5 roll assembly set. The ten roll assembly provides

further support to the cast slab. The roller diameter is generally kept 180 mm.

Four types of Radial Pinch rolls are situated after the ten roll assemblies. The four types of

pinch rolls used are described below:-

1. Pinch roll 320 (the rollers are having diameter ϕ 320 mm). Six sets of such rollers are

used in each machine, with each set consisting of four rollers. One roller is connected

to the driver motor hence called the drive roller while the rest three are idle rollers.

2. Pinch roll 360 (the rollers are having diameter ϕ 360 mm). Four sets of such rollers are

used in each machine, with each set consisting of four rollers. The arrangement of drive

roller and idle roller is the same.

3. Pinch roll 400 (the rollers are having diameter ϕ 360 mm). Four sets of such rollers are

used in each machine, with each set consisting of four rollers. The arrangement of drive

roller and idle roller is the same.

4. Pinch roll 450 (the rollers are having diameter ϕ 450 mm). Three sets of such rollers

are used in each machine, with each set consisting of four rollers. The arrangement of

drive roller and idle roller is the same.

Fig. 3.2: Location of 5 Roll Assembly Set in CCM

Page | 24

The pinch roller assemblies complete the radial zone. The radius of curvature is maintained

at 12 metres.

After the radial section the straightening zone begins. This is the terminal part of the rolling

strand as the slab enters the unbending zone followed by the horizontal section. 5 sets of

rollers are used in this portion with a roller diameter of approximately 480 mm.

3.3 DIFFERENT PARTS PRESENT IN A 5 ROLL

XX.ASSEMBLY

A 5 roll assembly generally consists of the outer frame to which the rollers are attached. The

frame which is generally made of mild steel or fabricated steel generally consists of a number

of parts like the big radius , the small radius, the pressure plates ,column etc. Along with this

various parts like the L-plates , Lock plates , End Cover and Ring are inlcuded in the working

drawing of the 5 roll sets.

Each 5 roll set consists of 30 rollers altogether with a diameter of 140 mm and length 648 mm

approximately. The rollers consist of the following parts:-

i) Axle

ii) Bearings

iii) Inner ring

iv) Outer ring

v) Steel clips

Detailed sescription of various parts of the 5 roller assembly along with their working drawing,

materials used along with their chemical composition and certain design criterias to be

considered during production are mentioned in this context.

Fig. 3.3: Various Parts of Dismantled Roller

Page | 25

L-Plate

The above diagram shows the working drawing of the L-plates used in 5 roll sets.

The material used in manufacturing of the L-Plates is generally termed as Fe410WA under the

standard of IS 2062-92. Fe410WA is a kind of structural steel with IS standard. The carbon

content in this steel is less than 0.2% and hence they are used to roll sections. The rolled

sections are higly bendable, ductile and easily weldable. Thus it can be easily understood why

Fe410WA is often the first choice while dealing with the materials for various equipments of

5 roll sections.

The weight of the specimen is about 0.54 kg. Dimensions are taken from the actual part. The

roughness of the specimen is generally indicated by the roughness symbol ∇ which indicates

the reference Ry/Rz length is about 8 mm. The Ra value varies from 25 – 12.5 mm and the

roughness grade number used can be N11 or N10.

Page | 26

Lock Plate

The above diagram shows the working drawing of the Lock plates used in 5 roll sets.

The Lock plates are used in roller bearing assemblies to hold the roller bearing end cap to the

outer end of an axle journal in order to prevent the accidental removal of the capscrews and

hence they are an integral component of the 5 roller sets. The Locking plate is held in place

by a grease fitting extending through the aperture and threaded into the end cap.

The material used in manufacturing of the Lock Plates is generally termed as Fe410WA under

the standard of IS 2062-92. Fe410WA is a kind of structural steel with IS standard. The carbon

content in this steel is less than 0.2% and hence they are used to roll sections. The rolled

sections are higly bendable, ductile and easily weldable. Thus it can be easily understood why

Fe410WA is often the first choice while dealing with the materials for various equipments of

5 roll sections.



the reference Ry/Rz length is about 8 mm. The Ra value varies from 25 - 12.5 mm and the


Page | 27

Ring

The above diagram shows the working drawing of the rings used in bearings of the rollers used

in the 5 roll sets.

The rollers are guided by a flange on the inner ring. This stops the rollers from sliding out at

high speed due to their momentum.The roller bearings ususally consist of the following

components:- the outer ring, inner ring and the roller assembly.

Page | 28

The material used in the manufacturing of these rings is ‘Heat resistant Low Alloy Chromium

Cast Iron’. Such irons have high abrasive rsistance and also they can show high resistance to

impact loading. They also have high corrosion resistant properties due to their chemical

composition.

The purpose for such chemical composition of low chromium alloy cast iron are explained

below:

i) The high carbon content (3.0 to 3.7% approx.) is prescribed when maximum abrasion

resistance is desired.

ii) Silicon is needed for two reasons. Fristly a minimum amount of silicon is required to

enhance fluidity of the melt. However it has further importance due to its effect on as-

cast-hardness. Increased amount of silicon increases the amount of martensite and the

resulting hardness.

iii) Manganese is typically held to a maximum value of 0.8 ~ 1 %. While it provides

increased hardenen-ability to avoid pearlite formation, it is also a more potent austenite

stabiizer than nickel and promotes increased amount of retained austenite and lower

as-cast-hardness.

iv) Chromium is primarily added in order to offset the graphitizing effects of nickel and

silicon.

v) Sulphur improves the machinability properties but has little effects on the longitudinal

mechanical properties

vi) Phosphorous increases strength and hardness but at the expense of ductility and impact

to toughness.

The chemical composition of such type of iron used is given below:

i) Carbon(C) – 3.0 to 3.7%

ii) Silicon(Si) – 1.3 to 2.5%

iii) Manganese(Mn) – 1.0 Maximum %

iv) Sulphur(S) – 0.12 Maximum %

v) Phosphorous(P) – 0.3 Maximum %

vi) Chromium(Cr) – 0.3 to 1.1 %

Hardness HB 163-210

The following things should be noted during the production and designing of rings:-

i) Casting should be free from all casting defects

ii) Non-perpendicularity of the surface with respect to the axis of ϕ 113 should not be more

than 0.3 mm



the reference Ry/Rz length is about 8 mm. The Ra value varies from 25 – 12.5 mm and the


Page | 29

End Cover -1

The above diagram shows the working drawing of the end covers used in the 5 roll sets.

End covers are available for roller bearing units fitted at shaft ends. In addition to protecting

the shaft ends of bearing arrangements, they also play a key role in preventing accidents.The

Page | 30

designation of appropiate end covers are generally available in the product tables (SYNT series,

FYNT series). The permissible length of the shaft end and the allowable protrusion dimensions

of the end cover are also provided. Sometimes end covers are used to replace the complete seal

at that side of the bearing.

According to the standrads set by SKF the end covers can be broadly categorised in to two

different units:-

i) End covers for metric SKF ConCentra units

These end covers can be snapped easily intp the recess of the housing bore, on the

mounting collar side.

ii) End covers for Inch SKF ConCentra units and units with a locking collar

End covers in this series are mounted with an interference fit on the housing bore.They

are always supplied together with the bearing units.


Cast Iron’. Such irons have high abrasive rsistance and also they can show high resistance to

impact loading. They also have high corrosion resistant properties due to their chemical

composition.

The chemical composition of such type of iron used is given below:

i) Carbon(C) – 3.0 to 3.7%






Hardness HB 163-210

The following things should be noted during the production and designing of end cover:-

i) Radial runout of bore ϕ 60 A4 with respect to its axis should not be more than 0.05 mm.

ii) Taper & ovality of bore should not be more than half the tolerances on diameter.

iii) Non-perpendicularity of the surface ‘S’ with respect to the axis of Φ60 A4 should not

be more than 0.05 mm on ϕ 79.5.


roughness of the specimen in the periphery is generally indicated by the roughness symbol ∇∇

while the rest is given by the roughness symbol ∇. ∇∇ symbol corresponds to Ra values of 6.3,

3.2, 1.6 (N9, N8, N7) while for ∇ symbol Ra values vary from 25 to 12.5 (N11, N10).

Page | 31

End Cover -2

The above diagram shows the working drawing of the end covers used in the 5 roll sets.


Cast Iron’.The chemical composition of such type of iron used is given below:

i) Carbon(C) – 3.0 to 3.7%






Hardness HB 163-210

The following things should be noted during the production and designing of end cover:-

i) Radial runout of ϕ 110 X3 with respect to its axis should not be more than 0.06 mm.

ii) Non-perpendicularity of the surface ‘R’ with respect to the axis of ϕ 113 X3 should not

be more than 0.05 mm on Φ110 X3.


roughness of the specimen in the periphery is generally indicated by the roughness symbol ∇∇

while the rest is given by the roughness symbol ∇. ∇∇ symbol corresponds to Ra values of 6.3,

3.2, 1.6 (N9, N8, N7) while for ∇ symbol Ra values vary from 25 to 12.5 (N11, N10).

Page | 32

Axle-1

The above diagram shows the working drawing of the axle used in the rollers of the 5 roll

assemblies.

The Axle is the component which sustains the roller when it is assembled into the troughing

set supports. It is made from drawn steel, cut and machined by automatic numerically

controlled machines. The axle is the load carrying component of the roller and must be sized

in relation to the load and the roller length. It is important not to overload the roller due to the

resultant excessive deflection of the spindle which in turn places irregular pressure on the

bearing, and reduces, as a consequence, the roller life.

Axles are generally round or hexagonal shaped. Hexagonal axles are specified by the length

across the flats. Round axles are specified by their diameter. The most common axle sizes are

7/16" hex and 11/16" hex. Axles are mostly made from either Mild Steel or Stainless Steel.

Axles are generally retained by a spring or cotter pins. Springs are held in place with dimples

stamped into the material .Cotter Pins are put into holes drilled thru the axle. Other axle

retention methods include:

i) Hog Rings

ii) Spring Both Ends

iii) Fixed or Staked

Axle machining offers other options for retaining the axle. Some of the axle operations include

the following processes:-

i) Drilled and Cut

ii) Threaded

iii) Milled slot for keeping bar

Page | 33

iv) Milled flat

v) Turned

vi) Snap Ring Groove

The material used in the manufacturing of these axles is termed as ‘40Cr1’ under the Indian

Standard IS 1970. This is a kind of alloy steel which is used in axle manufacturing.

The table given below enlists the properties of 40Cr1 in hardened and tempered condition:

Designation

of Steel

Tensile

Strength

(kgf/mm2)

Yield

Stress

Minimum

(kgf/mm2)

Normalizing

Temperature

℃

Hardening

Temperature

℃

Quenching

Medium

Tempering

Temperature

℃

40 Cr 1 80-95 60 850-880 850-880 Oil 550-660

The chemical composition of such type of ally steel used is given below:

i) Carbon(C) – 0.35 to 0.45%


iii) Manganese(Mn) – 0.50 to 0.80%




Hardness HB 220-250.

The following things should be noted during the production and designing of axles:-

i) Radial runout of ϕ 60 Xn with respect to its axis should not be more than 0.05mm.

ii) Non-concentricity of the surfaces P and Q (ϕ 60 Xn) with respect to each other should

not be more than 0.025 mm.

iii) Ovality and taper of the surfaces P and Q (ϕ 60 Xn) should not be more than 0.02 mm

in diameter.

iv) Radial runout of ϕ 58 X3 with respect to the axis of ϕ 60 Xn should not be more than

0.05 mm.

v) Non-perpendicularity of the surface G with respect to the axis of ϕ 60 Xn should not

be more than 0.025 mm.


roughness of the specimen in the periphery is generally indicated by the roughness symbol ∇∇∇

and at some of the edges by the roughness symbol ∇∇. The rest of the surface roughness is

denoted by the roughness symbol ∇. From the various charts regarding roughness symbols and

roughness grade numberswe can conclude that the roughness symbol ∇∇∇ corresponds to the

roughness value (Ra) value of 0.8, 0.4, 0.2 and the roughness grade numbers concerned are N6,

N5, N4. ∇∇ symbol corresponds to Ra values of 6.3, 3.2, 1.6 (N9, N8, N7) while for ∇ symbol

Ra values vary from 25 to 12.5 and the roughness grade numbers concerned are namley N11

and N10.

Page | 34

Axle-2

The above diagram shows the working drawing of the axle used in the rollers of the 5 roll

assemblies.

The material used in the manufacturing of these axles is termed as ’40Cr1’ under the Indian

Standard IS 1970. This is a kind of alloy steel which is used in axle manufacturing.

The following things should be noted during the production and designing of axles:-

i) Radial runout of ϕ 60 Xn with respect to its axis should not be more than 0.05mm.

ii) Non-concentricity of the surfaces P and Q (ϕ 60 Xn) with respect to each other should


iii) Ovality and taper of the surfaces P and Q (ϕ 60 Xn) should not be more than 0.02 mm

in diameter

iv) Radial runout of ϕ 58 X3 with respect to the axis of ϕ 60 Xn should not be more than

0.05 mm

v) Non-perpendicularity of the surface G with respect to the axis of ϕ 60 Xn should not

be more than 0.025 mm

Hardness HB 220-250.




denoted by the roughness symbol ∇. The roughness symbol ∇∇∇ corresponds to the roughness

value (Ra) value of 0.8, 0.4, 0.2 (N6, N5, N4). ∇∇ symbol corresponds to Ra values of 6.3, 3.2,

1.6 (N9, N8, N7) while for ∇ symbol Ra values vary from 25 to 12.5 (N11, N10).

Page | 35

Rollers

The above diagram shows the working drawing of the rollers of the 5 roll assemblies.

Technical requirments regarding manufactuing of the specific rollers:-

1. Material Specification and other technology requirements shall be as per RDCIS, SAIL-

RANCHI No. RD/SCR/FF-95 Dt. 10-12-96

2. Ovality and taper of Bore ϕ 110 An should not be more than half of the tolerance on

diameter.

3. Non-concentricity of Bore ϕ 110 An marked ‘P’ & ‘Q’ with respect to each other should


4. Non -perpendicularity of the surface ‘R’ & ‘S’ with respect to axis of ϕ 110 An should


5. Radial runout of surface ϕ 110 An should not be more than 0.05 mm.

6. Radial runout of surface ϕ 140 G with respect to axis of ϕ 110 An should not be more than

0.05 mm.

7. Annular groove of ϕ 120, 2 mm depth on both faces of the roller, is provided for

identification of these rollers, among rollers produced earlier.

8. This plain roller as per RDCIS recommendation is the modified version of the earlier

grooved roller as per DRG. No. CC-90-017.2.

Page | 36

Although the main purpose of rollers used in 5 roll sets is for providing better support to the

cast slab, the rollers also have a host of other applications. Below are listed some common

situations and the ways in which rollers are specialized to best handle these conditions. Keep

in mind that a particular application may include several of the following scenarios.

i) Gravity Applications

Rollers are not directly driven and only rotate when product passes over them. For light

products rollers are light-weight and bearings are lightly oiled to reduce rotational friction.

Bearings may be grease packed for heavier products that can easily overcome rotational

friction.

ii) Powered Applications

Rollers are directly driven by belts, chains, or other means. Rollers may be rotating even when

product is not present. Bearings are grease packed to maintain lubrication through more

continuous use.

iii) High Speeds

Rollers are subjected to operating speeds above 250 RPM. Rollers are built with light weight

tubes that are straightened to tight tolerances to reduce imbalances and prevent bouncing.

Bearings are semi-precision or precision for prolonged service life. When operating speeds

exceed 400 RPM rollers are built using only precision bearings.

iv) Heavy Loads

Rollers are subjected to large live loads during normal use. For small, light-duty rollers, a heavy

load may be less than 100 lbs. For large, heavy-duty rollers, a heavy load may be more than

1000 lbs. Rollers are built with components that are large enough to resist deflection. At long

BF’s a Center puck may be added to the axle to prevent the axle from deflecting too far and

rubbing along the inside of the tube.

v) Stationary Loads

Rollers are subjected to long periods of being loaded but not rotating. Rollers are built with

thicker tubes to prevent denting from prolonged loading on just one side of the tube. Bearings

feature hardened raceways to resist denting and cages, or retainers, that keep the balls evenly

spaced around the bearing to evenly distribute the load. Bushings may also be used due to their

high static load capacities.

vi) Impact Loads (Shock Loading)

Rollers are subjected to objects colliding with them. Products may have uneven bottoms that

cause them to bounce along the rollers or products may be dropped or thrown while being

loaded onto the rollers. Rollers are built with heavy walled tubes to resist denting. Bearings are

high capacity to reduce the risk of damage. Bushings may be used due to their lack of moving

(breakable) parts.

vii) Dirty/Gritty Environment

Rollers are subjected to small particles of dirt or dust that can contaminate bearing lubrication

and prevent the bearings from rotating. Bearings feature contact seals and shields that prevent

Page | 37

particles from entering. Bearings may also be regreaseable so that lubrication can be regularly

flushed. Bushings may also be used due to their lack of moving parts or need for lubrication.

The material used in the manufacturing of the rollers is generally high chromium steel having

chromium content as high as 13%. Addition of chromium increases the corrosion resistance

greatly.

The specification for forged quality foot rolls and 5 set rolls are given below:-

1. Scope:

The specification covers the requirement of forged and heat treated top rolls (140 mm

dia.) of continuous slab casting machines.

Composition (%):

C = 0.25 - 0.30 Ni = 1.0

Mn = 0.80 max. Mo = 0.60 – 0.80

Si = 0.70 max. P = 0.040 max.

Cr = 12 - 14 S = 0.025 max.

2. Forging Operation:

Forging shall be made as per IS: 1570 Pt. V – 72 and will be supplied duly deal treated

and in finish machined condition as per drawings. The forging could be produced in

multi-piece blanks which must be parted of into individual rolls before final hardening

treatment. The forging will have following mechanical properties in hardened and full

tempered condition;

UTS > 950 MPa %E > 10%

YS > 750 MPa BHN = 280 – 320

3. Processing Parameters:

A. Forging Temperature Range = 1100 – 900 ℃

(Charge hot forgings for controlled furnace cooling before the temperature falls

before - 650℃)

B. Soft Annealing (8 hrs.) = 720 – 730 ℃

(Furnace cool up to 250℃)

C. Hardening Treatment:

All forging will be rough machined including bores with heat treatment allowance

& subjected to total surface inspection to ensure freedom from any surface defects

including bore before hardening as per the following:

i) Preheating (2 hrs.) – 700 – 720℃

ii) Cooling – Air/oil/salt bath (60 minutes)

iii) Austenitising (2 hrs.) – 980 + 5℃

(After hardening immediately charge for tempering treatment. Any of the electric

furnace/ salt bath furnace or gas fired furnace should be utilized for heat treatment.

Finish machining/grinding allowance so be left on rough machined forgings before

hardening treatment should be decided on the basis of type of I I.T. furnace used)

D. Tempering Treatment:

Hardness – HB: 280 – 320 = 620 + 5℃ (12 hrs.)/air cool

Page | 38

4. Finish Machining:

All forging after heat treatment shall be finish machined / grind as per dimensions and

other instructions given in the drawings.

5. Ultrasonic Testing:

All forging shall be ultrasonically tested after heat treatment with test frequency more

than 2 MHz. The forging shall be from ultrasonic defects except isolated flow echo with

maximum level of 50% with 100% back echo.

The following things should be noted during the production and designing of rollers:-

i) After hot forging the forged blanks must be controlled, cooled in furnace and in no

case these will be allowed to cool in air below 650℃.

ii) After cooling the forgings will be inspected for surface quality and shall be finally

soft annealed before rough machining.

iii) All the annealed forgings must be rough machined including bore with heat

treatment allowances (2 – 3 mm) on the surface and will be visually inspected for

any surface flaw on outer as well as bore surfaces. Preferably few sample pieces in

the developmental stage could be magnaflux tested to ensure freedom from any

surface defect.

iv) The other processing norms and metallurgical parameters may be kept as per

standard operating practices.

The weight of the specimen is about 46 kg. Dimensions are taken from the actual part. The



denoted by the roughness symbol ∇. From the various charts regarding roughness symbols and

roughness grade numberswe can conclude that the roughness symbol ∇∇∇ corresponds to the

roughness value (Ra) value of 0.8, 0.4, 0.2 and the roughness grade numbers concerned are N6,

N5, N4. ∇∇ symbol corresponds to Ra values of 6.3, 3.2, 1.6 (N9, N8, N7) while for ∇ symbol

Ra values vary from 25 to 12.5 and the roughness grade numbers concerned are namley N11

and N10.

Page | 39

Bearings

The above diagram shows the working drawing of the bearing used in the rollers of the 5 roll

assemblies.

The materials from which the bearing components are made determine to a large extent the

performance and reliability of rolling bearings. For the bearing rings and rolling elements

typical considerations include hardness for load carrying capacity, fatigue resistance under

rolling contact conditions, under clean or contaminated lubrication conditions, and the

dimensional stability of the bearing components. For the cage, considerations include friction,

strain, inertia forces, and in some cases, the chemical action of certain lubricants, solvents,

coolants and refrigerants. The relative importance of these considerations can be affected by

other operational parameters such as corrosion, elevated temperatures, shock loads or

combinations of these and other conditions.

Contact seals integrated in rolling bearings can also have a considerable impact on the

performance and reliability of the bearings. The materials they are made of have to offer

excellent oxidation, thermal or chemical resistance. In order to meet the needs of various

applications, SKF uses different materials for bearing rings, rolling elements, cages and seals.

Furthermore, in applications where sufficient lubrication cannot be achieved or where an

electric current passing through the bearings has to be prevented, SKF bearings can be supplied

with special coatings.

The bearing which is generally used in the rollers of 5 roll sets is of bearing 6212 type.

According to the bearing nomenclature rules the inner diameter of such bearing is 5 times the

last two digits of the bearing name and hence the inner diameter of bearing 6212 is 60 mm.The

type of bearing used is deep groove ball bearings,single row hybrid bearings.

Principal Dimensions Basic Load Ratings Speed Ratings Mass Designation

Inner

Dia.

Outer

Dia.

Breath Dynamic

Load

Limit

Static

Load

Limit

Fatigue

Load

Limit

Reference

Speed

Limiting

Speed

d D B C Co Pu

mm mm mm KN KN KN r/min r/min kg

60 110 22 55.3 36 1.53 17000 4000 0.71 6212-2RS1/

HC5C3WT

Page | 40

Bearings are manufactured to take pure

radial loads, pure thrust loads, or a

combination of the two kinds of loads.

The nomenclature of a ball bearing is

illustrated in the adjoining figure which

also shows the four essential parts of a

bearing. These are the outer ring, the inner

ring, the balls or rolling elements, and the

separator. The bearings are the parts

which give virtually frictionless rotation

to the tube body with respect to the fixed

spindle. Bearings are the most complex

and critical part of a roller. Bearings come

in a wide variety of sizes, shapes, and

features that all offer different

performance characteristics. Bearing

capacity does not dictate roller capacity.

Roller load capacity is usually dictated by axle or tube deflection. Higher capacity bearings in

a long roller will not necessarily change the load capacity of the roller. Bearing capacity is

usually the limiting factor of roller capacity only at short BF’s. In a rolling bearing the starting

friction is about twice the running friction, but still it is negligible in comparison with the

starting friction of a sleeve bearing. Load, speed, and the operating viscosity of the lubricant

do affect the frictional characteristics of a rolling bearing.

Fig. 3.4: Nomenclature of Ball Bearing

Fig. 3.5: Various Types of Ball Bearing

Page | 41

The various types of ball-bearings are shown in the above figure. The single-row deep-groove

bearing will take radial load as well as some thrust load. The use of a filling notch in the inner

and outer rings enables a greater number of balls to be inserted, thus increasing the load

capacity. The angular-contact bearing provides a greater thrust capacity. Single-row bearings

will withstand a small amount of shaft misalignment of deflection, but where this is severe,

self-aligning bearings may be used. Double-row bearings are made in a variety of types and

sizes to carry heavier radial and thrust loads. Sometimes two single-row bearings are used

together for the same reason, although a double-row bearing will generally require fewer parts

and occupy less space. The one way ball thrust bearings are made in many types and sizes. All

these bearings may be obtained with shields on one or both sides. The shields are not a complete

closure but do offer a measure of protection against dirt. A variety of bearings are manufactured

with seals on one or both sides. When the seals are on both sides, the bearings are lubricated at

the factory. Although a sealed bearing is supposed to be lubricated for life, a method of re-

lubrication is sometimes provided.

The following things should be noted during the production and designing of 6212 bearings:-

i) Deep groove geometry for high speeds and supporting both radialand axial loads.

ii) “Light” bearing design for use in limited space applications or for average loads.

iii) C3 radial clearance allows thermal expansion for continuous opeating temperatures up to

120 degrees C/248 degrees F.

iv) Sheet steel cage evenly spaces balls for reduced friction , vibration, and noise.

v) Open bearing for lubrication applied in place.

Preloading of straight roller bearings may be obtained by:

i) Mounting the bearing on a tapered shaft or sleeve to expand the inner ring,

ii) Using an interference fit for the outer ring,

iii) Purchasing a bearing with the outer ring pre-shrunk over the rollers.

Ball bearings are usually preloaded by the axial load built in during assembly. The permissible

misalignment in bearings depends on type of bearing and the geometric and material properties

of the specific bearing. The object of preloading is to remove the internal clearance usually

found in bearings, to increase the fatigue life, and to decrease the shaft slope at the bearing.

In general, cylindrical and tapered roller bearings require alignments that are closer than deep-

groove ball bearings. Additional protection against misalignment is obtained by providing the

full shoulders recommended by the manufacturer. Also, if there is any misalignment at all, it

is good practice to provide a safety factor of around 2 to account for possible increases during

assembly. The life of the bearing decreases significantly when the misalignment exceeds the

allowable limits.

Felt seals may be used with grease lubrication when the speeds are low. The rubbing surfaces

should have a high polish. Felt seals should be protected from dirt by placing them in machined

grooves or by using metal stampings as shields. The commercial seal is an assembly consisting

of the rubbing element and, generally, a spring backing, which are retained in a sheet-metal

jacket. These seals are usually made by press fitting them into a counter bored hole in the

bearing cover. Since they obtain the sealing action by rubbing, they should not be used for high

speeds.

PREPARATION OF

5 ROLL SET Introduction, Description of Process, Instruments

Used in Reassembling

Chapter 4

Page | 42

PREPARATION OF 5 ROLL SET

4.1 INTRODUCTION

In earlier chapters the description of the various components of the 5 roll assembly sets of

Continuous Casting were discussed. The damaged and rejected parts of the 5 roller sets, once

they are no longer fit to be used, are removed from the rolling strand and they are sent to the

respective repairing and reassembling workshops for their reclamation and to be made fit for

further usage. MARS-2 is established for repairing of the damaged or malfunctioning

equipment of the machines of various shops including Continuous Casting Shop. In MARS-2

the repairing of 5 Roller Assembly Set of Continuous Casting Shop is done in several steps. In

this chapter we discuss about the various processes undertaken by the workshop for reclamation

of the damaged parts and preparation of new parts for the 5 roll assemblies.

4.2 DESCRIPTION OF THE PROCESS

The whole process can be classified into three basic processes:

A. Dismantling & Separating the Parts

B. Repair or Reclamation of Parts

C. Assembling the 5 Roll Assembly Set

A. Dismantling & Separating the Parts

This process involves several steps which are discussed below:

1. First of all, the set must be placed in a proper place and cleaned by removal of all the

impurities and dust particles that have accumulated inside the rollers and the frame. In

Continuous Casting Process, the semi-solidified metal chips got stuck in the assembly

set and often rollers got stuck. So, dedusting is necessary before further Dismantling

process can be started. In this case, by blowing high pressure air all dust particles are

removed and the semi-solidified metal chips are often removed by oxy-acetelene flame

cutting.

2. After cleaning the assembly set, the entire

assembly is placed with the help of the crane

in such a way that the Big Radius remains in

the upward direction and the Small radius in

downward direction. This particular position

of the assembly is necessary because the big

radius is separated first by shifting it with the

help of crane and placing it in another place. Fig. 4.1: Use of Crane for Shifting Big Radius

Page | 43

3. In order to separate the big radius from the assembly,

firstly the bolts [4×2×2 =16; Dimensions: M48×200

for 200 mm gap & M 48×300 for 250 mm gap],

clamping Big Radius and Small Radius must be

unbolted and kept at a proper place. Each of the Big

Radius and Small Radius have eight bolts each. This

bolts are used to keep the big radius and small radius

attached firmly to the frame. Before removal of the

rollers, separating of the Big Radius and Small Radius

is necessary such that the removal process of rollers

become easier.

4. In order to separate the big radius and small radius, a proper sling is used. The sling is

tightly attached to the Big Radius manually and then the sling is hooked up with the help

of the hook (having capacity of 10 T) of the crane of the Assembly Bay [Fig. 4.1].

5. Once the Big Radius is hooked up, it must be kept at a proper place to remove its rollers.

The Big Radius is oriented in vertical position as per the Fig. 4.2.

6. After that, the bolts of the rollers and L – Plate, Lock Plates are removed. Then, all

rollers [3×5 = 15] are separated from the frame by applying external force with the help

of a rod and are arranged in a place in order.

7. Now, once the rollers are removed from the frame the axle is the first to be removed.

The axle extends out on both side and so manual hammering is enough to take it out.

After the axle is removed the outer rings are removed by fixing a rod from the other side

and hammering is done. Along with outer rings comes out the inner ring and bearing.

The same is done for the other side also. If the bearing gets stuck inside due to damage

or increase in friction due to dust, so oxy-acetylene arc is used for metal gas cutting.

8. Thereafter the Small Radius frame must be placed properly so as to dismantle its rollers

[3×5 = 15] and plates present in the frame, then it must be properly clamped. Following

the same way, the roller’s nuts and bolts, axles must be carefully dismantled of Small

Radius.

Fig. 4.2: Orientation of Big Radius

Fig. 4.3: Separated Parts of the Roller

Page | 44

In this way, all parts of the 5 roll assembly set are dismantled properly with the help of

various instruments and machines.

B. Repair or Reclamation of Parts

The parts of damaged or malfunctioning rollers can be treated in two manners depending

upon its use and damage:

1. Reclamation & Reuse of parts

2. Rejection & Replacement of parts

The bearings, axle that are undamaged should be cleaned and properly greased to be reused

again. This method of reusing is known as reclamation. In this case, the bearings are

generally heated in oil bath to remove any soil, dust or grease whatever is stuck in side of

the bearing dissolves and comes out of it. So, the bearing gets cleaned and can be reused

again.

Lubrication in Bearing:

If rolling bearings are to operate reliably they must be adequately lubricated to prevent

direct metal-to-metal contact between the rolling elements, raceways and cages. The

lubricant also inhibits wear and protects the bearing surfaces against corrosion. The choice

of a suitable lubricant and method of lubrication for each individual bearing application is

therefore important, as is correct maintenance.

A wide selection of greases and oils is available for the lubrication of rolling bearings and

there are also solid lubricants, e.g. for extreme temperature conditions. The most favorable

operating temperatures will be obtained when the minimum amount of lubricant needed for

reliable bearing lubrication is provided. However, when the lubricant has additional

functions, such as sealing or the removal of heat, additional amounts of lubricant may be

required.

Fig. 4.4: Rejected Rollers

Page | 45

The lubricant in a bearing arrangement gradually loses its lubricating properties as a result

of mechanical work, ageing and the build-up of contamination. It is therefore necessary for

grease to be replenished or renewed and for oil to be filtered and changed at regular

intervals.

Defects in Rollers:

The rollers are dusted to remove any surface impurities and metal flux. If the cracks in

rollers are observed the rollers are rejected. Often the rollers get flattened brings about a

change in curvature, due to the high temperature and pressure. In this case, the rollers are

rejected because they increase the number of contact points that may become a cause of

break-out. If any crack is noticed in axle, then it is also replaced with new one. If the axle

becomes deformed or bends due to hammering or any kind of other pressure, then it is

subjected to grinding operation in order to bring its correct shape. In general, defects in

rollers are due to defective bearing damaged by soil, dust and grease. To remove these,

bearings are heated in oil-bath; thus the dust, soil are precipitated and grease dissolves in

the oil. Then the bearings are cleaned & regreased and in this way bearings become

reusable. This process is called ‘Reclamation’.

C. Assembling of the 5 Roll Assembly Set

The steps to assemble the 5 roll assembly set are the following:

1. The process of assembling the frame starts by assembling of roller. The rollers are

assembled in the way the rollers are dismantled. The sequence of assembling follows the

procedure similar to dismantling, i.e. one that goes out last is the first to be inserted. The

inner, outer rings along with bearings are attached to roller first on both sides. The inner

rings are attached then the bearings and after that the outer rings. Hence the axle is

assembled. The bearings are attached with steel clip to remove slip.

2. In the sequence of placing rollers in frame, the rollers of the Big Radius are attached first.

While placing rollers in roller place they must be provided with correct sling and kept on

frame following methods/commands of only one person. The rollers are fixed to the frame

by using L-clamp and bolts for fixing it with pedestal.

3. The rollers of the two end rows are fixed first. These two rows are aligned with the help of

a straight edge. The height of the rollers from the base of the Big Radius is 310 mm when

the Big Radius is oriented in such a way that the rollers are above. Their height from the

Fig. 4.5: Assembling the Rollers

Page | 46

surface in contact with pressure plate is 264 mm. The bolts used for bolting the two end

rows are M20×120 mm.

4. Next, the central three rows are fixed with the help of two aligned side rollers and a

template. This template is a measure to make the 5 roll set get the exact curvature of 12 m.

The template has a radius of 12 m, of dimensions 1650×150 (mm). The bolts used in these

three rows M20×140 mm. The three rows in the middle are provided with pegging, often

of 1-0.5 mm thickness at the bottom for increased height and thus 140mm length bolts are

used as they have to cover a further depth. The rollers are adjusted with lock plates. The

three rows in the middle are movable or replaceable but those at the periphery are fixed.

5. Then the Big Radius and Small Radius are both assembled to reconstruct the frame. The

separated parts are again placed upon one another in the correct position and then they are

assembled together by means of clamping and bolting together. The bolts used here are

M48×200 –for 200 mm gap and M48×300 – for 250 mm gap. The pressure plates used

vary as 20 mm –for a 200 mm slab, 70 mm –for a 250 mm slab and two plates of 70 mm

are used one on top and other at bottom for 320 mm slab. The washers used are of 52 mm

diameter.

6. While placing rollers in Small Radius frame the rollers are adjusted with the aligned Big

Radius maintaining the optimum distance with a micrometer.

The distance between the corresponding rollers of big radius and small radius must be

maintained. The distances vary as:

a. 1st roller after mould – 251.70 mm

b. 2nd roller after mould – 251.58 mm

c. 3rd roller after mould – 251.47 mm

d. 4th roller after mould – 251.33 mm

e. 5th roller after mould – 251.20 mm

7. Finally this distances are checked by Micrometer. The extra width is provided between the

rollers prior to 250 mark in order to provide the much needed clearance and to also ensure

that the cast slab does not get stuck within the rollers. The extra width is provided with the

help of pegging’s which have minimal thicknesses.

Fig. 4.6: Rows of Rollers

Page | 47

The total frame dimension is 3400X800 mm. The total distance between the rolls is

2000mm and the slab that is rolled has a width of 1500mm.

4.3 VARIOUS INSTRUMENTS USED IN THE

XX.REASSEMBLING PROCESS

1. Inside Micrometer

The micrometer is a precision measuring instrument, used by engineers. Micrometer use the

principle of a screw to amplify small distances (that are too small to measure directly) into

large rotations of the screw that are big enough to read from a scale. The accuracy of a

micrometer derives from the accuracy of the thread- forms that are at its heart. The amount of

rotation of an accurately made screw can be directly correlated to a certain amount of axial

movement (and vice versa), through the constant known as the screw’s lead. A screw’s lead is

the distance it moves forward axially with one complete turn (360).

Parts of Micrometer:

Frame – The thick body that holds the anvil and barrel in constant relation to each other. It is

thick because it needs to minimize flexion, expansion and contraction, which would distort the

measurement. It is heavy to increase the thermal mass, to prevent substantial heating up by the

holding hand/fingers.

Fig. 4.7: Complete Assembly of 5 Roll Set

Fig. 4.8: Diagrams of Micrometer

Page | 48

Anvil – The shiny part that the spindle moves toward, and the sample rests against.

Sleeve/barrel/stock – The stationary round part with the linear scale on it.

Lock nut/ thimble lock – The knurled part that one can tighten to hold the spindle stationary.

Screw – It is inside the barrel.

Spindle - The shiny cylindrical part that the thimble causes to move toward the anvil.

Thimble – The part that one’s thumb turns.

Ratchet stop – Device on end of handle that limits applied pressure by slipping at a calibrated

torque.

The spindle of an ordinary metric micrometer has 2 threads per millimeter, and thus one

complete revolution moves the spindle through, a distance of 0.5 millimeter. The longitudinal

line on the frame is graduated with 1 millimeter divisions and 0.5 millimeter subdivisions. The

thimble has 50 graduation, each being 0.01 millimeter. Thus, the reading is given by the number

of millimeter divisions visible on the scale of the sleeve plus the particular division on the

thimble which coincides with the axial line on the sleeve.

2. Template

The template is a measuring instrument used to measure the radius of curvature of the rolling

strand including the 5 roll set. In case of 5 roll sets, the template is used to check whether it is

properly aligned with the exact radius of curvature of 12 m. The template has a radius of 12 m,

of dimensions 1650×150 mm. The template is used to check the alignment of the three set of

rollers in the middle while that at the two edges are checked with the help of straight edges.

The bolts used in these three rows M20×140 mm.

This instrument is used in MARS-2 during the assembling of the 5 roll sets to align the rollers

of Big Radius in the curvature of radius 12 m. Then, Template is again used in Continuous

Casting Shop to recheck its alignment after placing the 5 roll assembly set in the slab caster

machine below the mould before the machine is started.

Fig. 4.9: Diagram of Template

Page | 49

3. Straight Edge:

Straight Edge is a tool with and edge free from curves, or straight, used for transcribing straight

lines, or straight, used for transcribing straight lines, or checking the straightness of lines. If it

has equally spaced markings along its length it is usually called a ruler.

Straight edges are used in the automotive service and machining industry to check the flatness

of machined mating surfaces.

True straightness can in some cases be checked by using a laser line level as an optical straight

edge; it can illuminate an accurately straight line on a flat surface such as the edge of a plank

or shelf.

We use the straight edge for aligning the two rollers on the periphery. These two rollers are

aligned at a height of 310 mm from the base of Big Radius when oriented such that the rollers

are facing up.

Fig. 4.10: Diagram of Straight Edge

FAILURES IN 5 ROLL SET

AND MEASURES FOR

PREVENTION Introduction, Failures in Bearings and Rollers, Their

Causes and Cures

Chapter 5

Page | 50

FAILURE IN 5 ROLL SETS AND

MEASURES FOR PREVENTION

5.1 INTRODUCTION As discussed earlier the 5 roll sets are located just below the mould in the rolling strand and

hence they have to withstand prolonged exposure to very high temperatures close to the melting

point of steel around 1500-1600ºC. As a result of such extreme conditions the 5 roll sets;

especially the rollers are prone to very high thermal stresses, stresses developed during

contraction and cooling on water treatment ,formation of fire cracks and also wear, tear and

friction. All these phenomena lead to the failure of the rollers and as a result decreases the

working efficiency of the 5 roll assemblies and as a whole the entire continuous casting

machine. Also the roller bearings may also undergo failure or get damaged due to a host of

reasons like overloading, internal cracking etc. In this chapter we describe the various causes

that lead to the failure of the rollers, the bearings and other components present in the 5 roll set

and also discuss the various measures that can be undertaken in order to prevent the failure of

the parts so affected.

5.2 FAILURES IN BEARINGS – CAUSES AND CURES

Precision ball bearings are designed to have a long and useful life. Assuming the application is

correct to begin with, maximizing longevity means bearings must be properly installed,

lubricated and maintained. Poor operating environments, particularly moist or contaminated

areas and improper handling practices invite premature bearing failure.

When a bearing does fail, it is important to determine the exact cause so appropriate

adjustments can be made. Examination of the failure mode often reveals the true cause of

failure. This procedure is complicated by the fact that one failure mode may initiate another.

For example, corrosion in a ball race leaves rust-an abrasive-which can cause wear, resulting

in loss of preload or an increase in radial clearance. The wear debris can, in a grease-lubricated

bearing, impede lubrication resulting in lubrication failure and subsequent overheating.

The major causes that have been earmarked for causing bearing failures are namely:-

1. Excessive Load: - Premature spalled area in ball path.

2. Overheating: - Discoloration of rings, balls, cages.

3. False Brinelling: - Elliptical wear marks at each ball position.

4. True Brinelling: - Ball indentations in raceways.

5. Normal Fatigue Failure: - Spalling or flaking of material from contact surfaces.

6. Reverse Loading: - Balls show grooved wear band

7. Contamination: - Denting of bearing raceways or balls

8. Lubricant failure: - Discoloured ball tracks and balls

9. Corrosion: - Chemical attack results in reddish/brown discolouration.

10. Misalignment: - Raceway ball track not parallel to raceway edges

11. Loose Fits: - Circumferential wear and/or discolouration of mounting surfaces.

12. Tight Fits: - heavy ball wear path at bottom raceways.

Page | 51

A brief description of these various causes of failure in bearings is described in the nest part of

this chapter along with a brief insight to the various methods which are undertaken in order to

prevent the bearing failures and to enhance bearing working life.

Excessive Loads Excessive loads generally cause premature fatigue. Tight fits,

Brinelling and improper preloading can also bring about early

fatigue failure. This type of failure looks same as normal fatigue,

although heavy ball wear paths, evidence of overheating and a

more widespread spalling (fatigue area) are usually evident with

shortened life.

The solution is to reduce the load or redesign using a bearing with

greater capacity.

Overheating Symptoms are discoloration of the rings, ball, and cages from gold to

blue. Temperatures in excess of 400°F can anneal the ring and ball

materials. The resulting loss in hardness reduces the bearing capacity

causing early failure. In extreme cases, balls and rings will deform.

The temperature rise can also degrade or destroy lubricant.

Common culprits are heavy electrical heat loads, inadequate heat

paths and insufficient cooling or lubrication when loads and speeds

are excessive. Thermal or overload controls, adequate heat paths, and

supplemental cooling are effective cures.

False Brinelling False Brinelling -elliptical wear marks in an axial direction at each

ball position with a bright finish and sharp demarcation, often

surrounded by a ring of brown debris indicates excessive external

vibration. A small relative motion between balls and raceway

occurs in non-rotating ball bearings that are subject to external

vibration. When the bearing isn't turning, an oil film cannot be

formed to prevent raceway wear. Wear debris oxidizes and

accelerates the wear process. Correction is done by isolating

bearings from external vibration, and using greases containing anti

wear additives such as molybdenum disulphide when bearings

only oscillate or reverse rapidly and in actuator motors.

True Brinelling Brinelling occurs when loads exceed the elastic limit of the ring

material. Brinell marks show as indentations in the raceways which

increase bearing vibration. Severe brinell marks can cause

premature fatigue failure. Any static overload or severe impact can

cause brinelling. Examples include: using hammers to remove or

install bearings, pressing bearing onto a shaft by applying force to

the outer ring. Install bearings by applying force only to the ring

being press fitted, i.e., do not push the outer ring to force the inner

ring onto a shaft.

Page | 52

Normal Fatigue Failure Fatigue failure-usually referred to as spalling-is the fracture of

the running surfaces and subsequent removal of small. Discrete

particles of material. Spalling can occur on the inner ring, outer

ring, or balls. This type of failure is progressive and once

initiated will spread as a result of further operation. It will

always be accompanied by a marked increase in vibration,

indicating an abnormality. The remedy is to replace the bearing

or consider redesigning to use a bearing having a greater

calculated fatigue life.

Reverse Loading Angular contact bearings are designed to accept an axial

1oading in one direction only. When loaded in the opposite

direction, the elliptical contact area on the outer ring is

truncated by the low shoulder on that side of the outer ring.

The result is excessive stress and an increase in

temperature, followed by increased vibration and early

failure. Corrective action is to simply install the bearing

correctly. Angular contact bearings must be installed with

the resultant thrust on the wide face of the outer ring and

opposite face of inner ring.

Contamination Contamination is one of the leading causes of be failure. Contamination

symptoms are denting of the bearing raceways and balls resulting in high

vibration and wear.

Contaminants include airborne dust, dirt or any abrasive substance that

finds its way into the bearing. Principal sources are dirty tools,

contaminated work areas, dirty hands and foreign matter in lubricants or

cleaning solutions.

Clean work areas, tools, fixtures and hands help reduce contamination

failures. Keep grinding operations away from bearing assembly areas and

keep bearings in their original packaging until you are ready to install

them. Seals are critical-damaged or inoperative seals cannot protect

bearings from contamination.

Lubricant Failure Discoloured ball tracks and balls are symptoms of lubricant failure.

Excessive wear of balls, ring, and cages will follow, resulting in

overheating and subsequent catastrophic failure. Ball bearings depend on

the continuous presence-of a very thin-millionths of an inch-film of

lubricant between balls and races, and between the cage, bearing rings,

and balls. Failures are typically caused by restricted lubricant flow or

excessive temperatures that degrade the lubricant's properties. Suitable

lubricant and quantity to Also, any steps taken to correct improper fit.

Control preload better, and cool the shafts and housings will reduce

bearing temperatures and improve the lubricant life.

Page | 53

Corrosion Red/brown areas on balls, raceways, cages, or bands of ball

bearings are symptoms of corrosion. This condition results from

exposing bearings to corrosive fluids or a corrosive atmosphere.

The usual result is increased vibration followed by wear, with

subsequent increase in radial clearance or loss of preload. In

extreme cases, corrosion can initiate early fatigue failures. Correct

by diverting corrosive fluids away from bearing areas and use

integrally sealed bearings when- ever possible. If the environment

is particularly hostile, the use of external seals in addition to

integral seals should be considered. The use of stainless steel

bearings is also helpful.

Misalignment The most prevalent causes of misalignment are bent shafts, burns or

dirt on the shaft or housing shoulders, shaft threads that are not

square with shaft seats, and locking nuts with faces that are not

square to the thread axis. The maximum allowable misalignment

varies greatly with different applications, decreasing, for example,

with speed. Misalignment can be detected on the raceway of non-

rotating ring by a ball wear path. Appropriate corrective action

includes: inspecting shah and housings for runout of shoulders and

bearing seats; use of single point-turned or ground threads on

nonhardened shaft and ground threads only on hardened shafts and

using precision grade locknuts.

Loose Fits Loose fits can cause relative motion between mating parts. If the

relative motion between mating parts is slight but continuous,

fretting occurs. Fretting is the generation of fine metal particles

which oxidize, leaving a distinctive brown colour. This material is

abrasive and will aggravate the looseness. If the looseness is

enough to allow considerable movement of the inner or outer ring,

the mounting surfaces (bores, outer diameters, faces) will wear and

heat, causing noise and runout problems.

Tight Fits A heavy ball wear path in the bottom of the raceway around the entire

circumference of the inner ring and outer ring indicates a tight fit.

Where interference fits exceed the radii clearance at operating

temperature, the balls will become excessively loaded. This will result

in a rapid temperature rise accompanied by high torque. Continued

operation can lead to rapid wear and fatigue. Corrective action includes

a decrease in total interference better matching of bearings to shafts and

housings-taking into consideration the differences in materials and

operating temperatures. Increased radial clearance also increases

bearing life in such cases.

Page | 54

5.3 FAILURES IN ROLLERS – CAUSES AND CURES

The roll surface is crucial for work rolls in hot rolling mills. We have to deal with wear,

oxidation, firecracks, sticking and friction. These are the major causes which cause damages

to rollers and thus eventually lead to the roller failure. Some of these causes leading to the roller

failure are discussed below:

Wear Work roll in hot strip mills wear due to friction between roll surface and hot strip. (Back up

rolls wear as well, but under pressure with elastic deformation, the friction is much less.) The

wear is uneven from one end of the barrel to the other. The oxide layer of the work rolls shears

off more or less completely at least on the strip entry and exit side. The oxide particles may

increase the wear. When the oxides are sheared off, there is direct friction between roll and

strip material, the work roll wears. Wear is similar to that of cutting tools and the development

of roll materials for hot rolling mills follows the development of cutting tools. Wear of hot-

mill work-roll material depends strongly on the type and content of carbides, rather than on

hardness. The reason for better roll wear performance should be suspect in the changed

temperature distribution in the strip and related strain.

Oxidation Oxide layers cover the surfaces of work rolls in hot strip mill and give them a colourful

appearance, somehow between yellow and black, especially in the early stand. These oxide

layers may have different thickness for various roll grades. This raised the question again and

again, whether these oxides are originating from the sheet or the rolls. Many people carried out

tests to prove the oxidation rates of different roll materials. However, we have to keep in mind:

1. The oxide layer builds up already after the first revolution(s)

2. In the rolling gap oxygen has no access to the roll surface

3. The temperature of the roll surface in the rolling gap does normally not exceed 700 C

4. The time in the rolling gap at “high” temperatures is only a fraction of a second in each

revolution, see Figure 6.

5. The time when the strip is between descaler and F 1 or between the stands is much longer

than in the rolling gap.

6. Oxygen has access to the strip everywhere outside the rolling gap.

7. Strip temperature is normally in the range of 900º to 1100º C.

In case the layers get too thick, the sheared off oxides may not stick any more to the surface or

they are washed away from the roll cooling water, especially where the water flow is disturbed,

for instance at the cross-points of the fire-crack network. Rolling heavy gauges with low

reduction and high speed in the critical stands often repairs the oxide layers on the roll surface.

Firecracks Mill people know firecracks are forming during normal rolling in hot rolling mills for flat and

long products. Fire-cracks appear in cold rolling mills only occasionally after rolling accidents.

Fire-cracks on rolls develop only, when a “hot” roll surface is cooled/quenched rapidly,

normally by cooling water. Fire-cracks are not “bad” in itself, but often they may cause spalls,

initiate banding/peeling and change friction. Plastic deformations due to the thermal expansion

at the roll surface in the rolling gap should cause whatever and finally create fatigue cracks. At

given crack depth the distance from crack to crack – the size of the fire-crack pattern – is

proportional to the strength of the roll material.

Page | 55

The major features prevalent in firecrack formation are: -

1. Firecracks in the finishing mill decrease in depth and size of the network from the first

stand to the last stand, they are almost invisible in the very last stand(s).

2. Firecracks develop during the first contact(s) with the strip, no fatigue problem, the most a

(very) low cycle fatigue.

3. Firecracks form due to the maxima stress and are perpendicular to the surface (brittle

fractures).

4. The worst condition for forming firecracks are mill stalls with strip in the stands; deep

cracks and a coarse network pattern may lead to unproductive loss of roll stock.

Procedures/strategies to reduce the firecracks due to mill stalls are available and often

neglected.

5. Firecracks in AIC develop more easily into spalls (fatigue) than those in High Chrome rolls.

HSS behaves probably similar to HCr in this respect.

6. The old theory for fire cracks based on plastic deformation and fatigue, however, evidence

was never found or proved.

Sticking Sticking happens when under high pressure (favourable low temperatures of the strip) matrix

material under friction welds to the strip. The smaller the areas of homogeneous matrix material

are the lower the risk of sticking becomes. The microstructure of roll material and strip are

crucial for sticking. Sticking of strip material to the rolls happens, if at all, in general in the

very last stand(s). HSS should not stick with smaller areas of homogeneous carbide free matrix.

Friction Without friction, rolling is impossible. The coefficient of friction between steel and any roll

grade is very similar, no big variations. Lubrication of the rolling gab of course reduces friction.

For normal ground rolls, friction dictates the maximum bite angle as a function of rolling speed.

In case the bite angle for a given rolling speed is too high, (or vice versa the rolling speed is

too high for a given bite angle) shatter will happen. Lubrication helps to overcome actual

friction problems, but it is the wrong way to attack this issue. As soon, as the fire-cracks are

under control, discussions about the coefficient of friction will stop. After rolling some strips

without water-cooling, they turn on cooling water and a nice firecrack pattern develops

immediately. The friction improves, not the materials are changed but the roughness is

increased and this increases friction as well.

While discussing of friction the following points must be noted: -

The coefficient of friction of different roll materials is very similar.

The roll surface in the mill has high impact on friction between roll and strip, which is

something different from a coefficient of friction of roll materials.

The rolling conditions are crucial for the roll surface.

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Page | 56

CONCLUSION Continuous Casting has evolved from a batch process into a sophisticated continuous process.

This transformation has occurred through understanding principles of mechanical design, heat-

transfer, steel metallurgical properties and stress-strain relationships, to produce a product with

excellent shape and quality. In recent years, the process has been optimized through careful

integration of electro-mechanical sensors, computer-control, and production planning to

provide a highly-automated system designed for the new millennium.

In conjunction with growing demands to operational efficiency of continuous-casting

machines, technological functions of intermediate ladle become more and more extensive

including additional metallurgical processes: removal of non-metallic inclusions, addition of

components, and calcium modification of steel. Today, the duration of steel teeming from one

intermediate ladle of continuous-casting machine reaches by two technology factors:

deterioration of metering nozzles and wear of intermediate ladle lining in jet falling area. Mold

tubes of modern continuous-casting machines are made with high dimensional precision, and

their working surface is coated with a special anti-wear covering on the basis of Cr, Ni and

other metals.

The Five roll sets though are still an integral part of the continuous casting machines used in

most of the Indian steel plants, however with the advent of latest technology they have fallen

behind the pecking order. The Five roll sets used in Bhilai Steel Plant, Sail were borne with the

aid of the Russian technologies in the early 1970’s. The five roll sets are used in the traditional

slab casters with a radius of curvature of 12 m. The traditional slab casters are part of single

point bending continuous casting machines which provides less support to the semi-solid cast

slab while it solidifies. In such machines the mould itself is a part of the 12 metre radius of

curvature followed by five roll sets. However such machines are slowly becoming outdated

and are being replaced by more efficient multiple point bending unbending continuous casting

machines. This machines generally have a radius of curvature of 9 m and the mould is

completely vertical in these cases. The Five roll sets are replaced in these slab casters by a new

six roll sets which can provide larger contact points to the semi-solid cast slab. Also five roll

sets with their traditional design and structure can surround the cast stab only from two sides

while the new slab casters have rolling strands equipped with the facility of supporting the cast

slab from all the four sides.

In the working procedure of continuous casting, equally important to strand containment and

guidance from the vertical to horizontal plane are the unbending and straightening forces. If

the strain along the outer radius is excessive, cracks could occur, seriously affecting the quality

of the steel. These strains are typically minimized by incorporating a multi-point unbending

process, in which the radii become progressively larger in order to gradually straighten the

product into the horizontal plane. In five roll sets, minimizing the effect of strains is much more

difficult to tackle.

Thus, five roll sets are facing a lot of competition from the modern slab casters with advanced

and better equipped designs of rolling strands and may well face a scare of running outdated.

However, despite their age old design and lesser efficiency the five roll sets used in the

continuous casting shops of Bhilai Steel Plant, SAIL still produce an annual yield of 1.5 million

tonne per year and it is with the help of these traditional technologies that BSP still remains

one of the leading industries of India.

Page | 57

REFERENCES:

Books:

i) Shigley’s Mechanical Engineering Design; 9th Edition By Richard G. Budynas and

J.Keith Nisbett.

ii) Degarmo’s Materials and Processes in Manufacturing By J.T Black, Ronald and

Kohser.

Websites:

i) www.wikipedia.org

ii) www.skf.com

iii) www.concastmachine.com

iv) www.steel.org

v) www.steeluniversity.org

vi) www.metalpass.com

vii) www.gangsteel.net

viii) www.wikianswers.com

ix) www.google.com

Research Papers and Scholarly Articles:

i) “Frequently Asked Questions about Hot Strip Mill Work Roll Surface” (wear,

oxidation, fire cracks, sticking and fiction) by Dr. Karl Heinrich Schroeder

ii) Continuous Casting simulation, Version 1.60 User Guide by steeluniversity.org

iii) Current Continuous Casting Machines: Potentials for Technological & Equipment

Development by A.N Smirnov and A.L Podkorytov

iv) Gateway of BSP 2008

v) Roller Manual by Omni Metalcraft.corp

vi) Working Drawings and information from design department of BSP, SAIL

http://www.wikipedia.org/

http://www.skf.com/

http://www.concastmachine.com/

http://www.steel.org/

http://www.steeluniversity.org/

http://www.metalpass.com/

http://www.gangsteel.net/

http://www.wikianswers.com/

http://www.google.com/

bsp project (based on continuous casting) [final]

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