Production Analysis by Modelling of Unfinished Product Generation in Rolling Mill of Steel Industry

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Production Analysis by Modelling of Unfinished Product Generation in Rolling Mill of Steel Industry

Sneha Dewangan1*

Shri Shankaracharya Engineering College,

Dept. of Electronics & Telecommunication (A.I.C.T.E. Approved), Junwani Durg Pin-490006, Chhattisgarh, India.

Chandradutta Verma2

Shri Shankaracharya Engineering College,

Dept. of Electronics & Telecommunication (A.I.C.T.E. Approved), Junwani Durg Pin-490020, Chhattisgarh, India

Satyendra Kumar Dewangan3

Bharti Engineering College,

Dept. of Civil Engg. (A.I.C.T.E. Approved), Durg Pin-491001, Chhattisgarh, India

Abstract Every Steel Industry produces unfinished products along with finished products. In Merchant Mill of a Steel Plant uses hot rolling process to produce Merchant Products like Angles, Channels, Beams, Bars and T.M.T. bars, etc. In this process billets are heated at 1200 ± 50 0C in Reheating Furnace and passes between rollers of stand. Merchant Mill sometimes generates unfinished products (Cobbles), which results in failure of the process technology. This problem is responsible for Mill trip which thus stops the rolling for some time. It is observed approximately 2 to 4 cobbles generated per day in rolling hour. We found, there is increase in load of stand and decrease in temperature of heated billets. Hence for minimization of cobbles, Radiation Pyrometer is installed after rolling stand in existing system. The data such as temperatures of billets and corresponding load of the stand are collected through the adaptive control system through monitor and are analyzed by software IBM SPSS Statistics 20. Result of the analysis consists of Mean, Standard deviation, Correlation and Regression coefficient of load and temperatures. The finding shows that there is a significant negative relationship between Load and Temperature i.e. load is inversely proportional to the temperature. Hence optimum temperature must be required for continuous & uniform rolling process in steel industry. By this modification there is increased productivity, quality parameter of the merchant products and profit of the Mill.

Key words: Cobble, Radiation Pyrometer, Angles, Channels, Rolling.

  1. INTRODUCTION

    Merchant mill operation is based on hot rolling process, which produces, Angles, Channels, Beams Bars, TMT Bars. In this study we measure the load and temperature of heated soaked billets before and after passing between the rolling stands. For load measurement, ammeter instrument is installed in the process & for measurement of temperature of billets uses thermocouple. For the data collection related to generation of unfinished products Instrumentation method is applied, we use Radiation Pyrometer instrument which measures surface temperature of the heated billets, which is passed between the rollers while rolling. It is a non- contact temperature sensor that

    infers the temperature of an object by detecting its naturally emitted thermal radiation by the surface of very hot object. An optical system collects the infrared thermal radiation of the heated object and focuses it on detector. The detector converts the heat energy into electrical signal to drive the temperature display. Also we found the impact of load on rollers by instrument Ammeter.[8]

    1. Merchant Mill

      The Merchant Mill is semi continuous high capacity mill, which is designed to roll 0.5 to 1.0 MT per annum of finished products.[8] The mill consists mainly three sections as-

      • Re-heating furnace

      • The mills stands and cooling beds

      • Finishing zone & shipping

        Raw materials used are billets of size (in mm) 90×90, 95×95, 100×100, 110×110, 105×105 and length ranging from 5 m to 6 meter. Billets are supplied from stock yards by Electromagnetic Cranes to the loading device, to push the billets on the furnace approach roll table. It is designed to receive billets from the loading device and deliver them to the furnaces. The furnace charging pusher, pushes the billets after evolving from the approach roll table into the furnace and moves the entire charge inside the furnace and thus pushing the heated billets on to the delivery roll table at the discharge side of the furnace.[9]

    2. Reheating furnace and its process-

      In merchant mill there is a Continuous Pusher Type Reheating furnaces, Gas fire burners, 3 zone Furnaces ( Soaking Zone, Heating Zone, Preheating Zone), capacity 60 ton/hrs ( heated billets supply for Rolling).In reheating furnace, the cold billets are loaded in loading device by overhead crane (O.H.C.) from billets yard as per quality requirement of mill. By delivery roll table, the billets has been sending into charging side of the furnace, after this the billets are charged by use of charging device, through pulpit operation manually (electrical & mechanical device)

      in standard manner.[1] The charged billets are heated and soaked in furnace at 1200 ± 50 0C after this; heated billets are pushed by charging pusher mechanism than discharged heated billets on delivery roll table. These heated billets are passed between rollers (mechanical stand) and by hot rolling process it gives finished merchant products.

      Fig. 1. Cross-section of R.H.F. [7]

      • To analyze the relationship between the Heating zone temperature and load on motor of stand.

      • To develop a model under the Production of bar and Angle.

    D. Research frame work:

    TMT 25

    ANGLE 50

    TMT 25

    ANGLE 50

    TEMPERAT URE OF BILLETS

    LOAD ON MOTOR

    (Rolling- Stand)

    LOAD ON MOTOR

    (Rolling- Stand)

    (Rolling – Stand)

    TEMPERAT URE OF HEATING ZONE

  2. RESEARCH METHODOLOGY

    1. Problem Identified

      The Merchant Mill of Steel Plant produces finished products as per Customers & Market Requirement. But sometimes produces unfinished product (cobbles) due to unexpected problem in Hot Rolling Process. These problem arises due to failure of lubrication system in rolling stands, cooling system in stands, electric failure, uneven temperature of billets, mechanical problem and high rolling speed etc. This problem impact production qualitatively as well as quantitatively, loss of Human effort, raw material wastage and cause breakdown of mill. Furthermore it takes a lot of time to start rolling again and hence cause high production loss.

    2. Statement of Problem:

      The Mill was undergoing loss of production due to variations in Hot Rolling process Parameters. Following problems were identified:-

      • Variability in quality standards of finished products in same profile.

      • Change in operational parameter during rolling process of mill.

      • Increasing the cobbles in rolling stands, it gives unfinished product.

      • Roll breakage due to uneven rate of rolling & lack of maintenance.

      • Generation of excess load in rolling stand during operation.

      • High speed rolling gives different types of breakdowns.

      • Uneven temperature of heated billets supply from furnace.

    3. Research Objective:

      • To analyze the relationship between the temperature and load of billets at stand.

    The data are collected for TMT 25mm bar and Angle 50mm production .Under these conditions, the Billet temperature at 2nd stand during passes between roller, Heating zone temperature and Load on Stand 2 motor are measured with the help of Control devices. These data are analyzed in order to determine he relationship between them.

  3. DATA COLLECTION AND ANALYSIS

    The primary data is collected directly from the Fixed Type Radiation Pyrometer installed near stand 2 of the reheating furnace & mill operation. The variables measured in the process of data collection are as follows:-

    • Temperature of Billet at stand 2 in 0C = Ts

    • Temperature of heating zone in 0C = Th

    • Load of roller in Ampere = L

      Where, Load of roller (L) is dependent on other two variables i.e. Temperature of billet in stand 2 (Ts) & Temperature of heating zone (Th). Hence, Load of roller (L) is considered as Dependent variable and other two are Independent variables.

    • Heating zone temperature (Th): The temperature of reheating furnace in which the billets are heated at desired rolling temperature (hot rolling process).

    • Temperature of billet at stand 2 (Ts): It is the measured temperature of billets at the point when the billets are passing from stand 2.

    • Load of roller (L): The usage of current to drive the motor of stand 2 which is used to rotate the roller and to transfer the billets for further process. It is measured in Ampere.

    These variables are measured for the merchant products of TMT-25mm and No. of observation taken under each condition is N = 30

    TABLE I. Data collection during production of TMT 25 mm bar

    S.no.

    Load of Rollers (Ampere)

    Billet Temperature at (stand 2) 0C

    Heating zone Temperature 0C

    1

    825

    1048

    1250

    2

    847

    1052

    1248

    3

    852

    1065

    1252

    4

    844

    1047

    1260

    5

    870

    1061

    1240

    6

    905

    1070

    1242

    7

    897

    1072

    1238

    8

    875

    1078

    1230

    9

    847

    1085

    1241

    10

    910

    1092

    1247

    11

    842

    1103

    1250

    12

    825

    1110

    1253

    13

    832

    1103

    1260

    14

    839

    1097

    1265

    15

    915

    1082

    1267

    16

    918

    1087

    1270

    17

    925

    1067

    1253

    18

    947

    1073

    1148

    19

    951

    1045

    1228

    20

    910

    1049

    1232

    21

    893

    1035

    1233

    22

    857

    1038

    1242

    23

    872

    1042

    1244

    24

    885

    1043

    1247

    25

    891

    1029

    1252

    26

    905

    1045

    1255

    27

    915

    997

    1203

    28

    925

    970

    1237

    29

    870

    968

    1240

    30

    910

    1080

    1248

    S.no.

    Load of Rollers (Ampere)

    Billet Temperature at (stand 2) 0C

    Heating zone Temperature 0C

    1

    718

    1047

    1226

    2

    720

    1042

    1220

    3

    716

    1050

    1228

    4

    717

    1052

    1218

    5

    715

    1057

    1228

    6

    715

    1062

    1252

    7

    725

    1063

    1222

    8

    735

    1074

    1221

    9

    711

    1068

    1218

    10

    754

    1067

    1220

    11

    729

    1080

    1211

    12

    711

    1082

    1203

    13

    720

    1058

    1210

    14

    722

    1057

    1220

    15

    757

    1053

    1210

    16

    720

    1047

    1221

    17

    750

    1053

    1225

    18

    745

    1055

    1232

    19

    725

    1058

    1230

    20

    715

    1077

    1235

    21

    712

    1080

    1233

    22

    711

    1082

    1245

    23

    715

    1078

    1240

    24

    712

    1082

    1230

    25

    715

    1083

    1222

    26

    722

    1075

    1228

    27

    718

    1077

    1231

    28

    725

    1052

    1229

    29

    717

    1078

    1233

    30

    735

    1073

    1215

    S.no.

    Load of Rollers (Ampere)

    Billet Temperature at (stand 2) 0C

    Heating zone Temperature 0C

    1

    718

    1047

    1226

    2

    720

    1042

    1220

    3

    716

    1050

    1228

    4

    717

    1052

    1218

    5

    715

    1057

    1228

    6

    715

    1062

    1252

    7

    725

    1063

    1222

    8

    735

    1074

    1221

    9

    711

    1068

    1218

    10

    754

    1067

    1220

    11

    729

    1080

    1211

    12

    711

    1082

    1203

    13

    720

    1058

    1210

    14

    722

    1057

    1220

    15

    757

    1053

    1210

    16

    720

    1047

    1221

    17

    750

    1053

    1225

    18

    745

    1055

    1232

    19

    725

    1058

    1230

    20

    715

    1077

    1235

    21

    712

    1080

    1233

    22

    711

    1082

    1245

    23

    715

    1078

    1240

    24

    712

    1082

    1230

    25

    715

    1083

    1222

    26

    722

    1075

    1228

    27

    718

    1077

    1231

    28

    725

    1052

    1229

    29

    717

    1078

    1233

    30

    735

    1073

    1215

    TABLE II. Data collection during production of ANGLE – 50mm

    1. Data Analysis

      The tool used for the analysis of data collected at different conditions is IBM SPSS Statistics 2.0. The tool is used to analyze the following:

      • To determine the Descriptive analysis of the readings.

      • To determine Correlation between all the variables.

      • To perform Multiple regression analysis. This is used to formulate formula under these 2 conditions.

        1. Analysis of TMT 25 mm bar:

          TABLE III. Descriptive analysis

          Descriptive Statistics

          N

          Range

          Minimu m

          Maximu m

          Mean

          Std. Deviation

          Load of Rollers (Ampere)

          30

          126

          825

          951

          883.30

          36.321

          Heating zone Temperature

          30

          122

          1148

          1270

          1242.5

          0

          22.261

          Billet Temperature at (stand 2)

          30

          142

          968

          1110

          1057.7

          7

          35.064

          TABLE IV. Correlation analysis

          Correlations

          Load of Rollers (Ampere)

          Billet Temperatur e at (stand 2)

          Heating zone Temperatu re

          Load of Rollers (Ampere)

          Pearson Correlation

          1

          -0.261

          -0.442*

          Sig. (2-tailed)

          0.164

          0.015

          N

          30

          30

          30

          Billet Temperature at (stand 2)

          Pearson Correlation

          -0.261

          1

          0.238

          Sig. (2-tailed)

          0.164

          0.206

          N

          30

          30

          30

          Heating zone Temperature

          Pearson Correlation

          -0.442*

          0.238

          1

          Sig. (2-tailed)

          0.015

          0.206

          N

          30

          30

          30

          • Correlation is significant at the 0.05 level (2-tailed).

          With the help of Correlation, we can determine how strong the relationship exists between these variables. As we can observe from the table:

          • There is a weak negative linear relationship between load of rollers (L) and billet temperature at stand 2 (Ts) i.e. -0.261.

          • There is a moderate negative linear relationship between load of rollers (L) and temperature of heating zone (Th) i.e. -0.442.

            TABLE V. Regression analysis

            Fig. 2. Bell shape curve graph for regression analysis

            Bell shape curve in histogram fulfills the assumption of multiple regressions that is normality of the error term distribution.

            According to regression coefficient table we can formulate the formula for the relationship between load of rollers (L) in term of Temperature of billet at stand 2 (Ts) and temperature of heating zone (Th)

            Load of roller (L) = a + b1 x1 + b2 x2 L = 1879.938 -0.171 × Ts -0.657 × Th

            where 1879.938 is constant called intercept and is denoted by a.

        2. Analysis of Angle

          Descriptive Statistics

          N

          Range

          Minim um

          Maximu m

          Mean

          Std.

          Deviation

          Load of Rollers (Ampere)

          30

          46

          711

          757

          723.40

          12.939

          Billet Temperature at (stand 2)

          30

          41

          1042

          1083

          1065.4

          0

          12.982

          Heating zone Temperature

          30

          49

          1203

          1252

          1225.2

          0

          10.526

          Valid N (listwise)

          30

          Descriptive Statistics

          N

          Range

          Minim um

          Maximu m

          Mean

          Std.

          Deviation

          Load of Rollers (Ampere)

          30

          46

          711

          757

          723.40

          12.939

          Billet Temperature at (stand 2)

          30

          41

          1042

          1083

          1065.4

          0

          12.982

          Heating zone Temperature

          30

          49

          1203

          1252

          1225.2

          0

          10.526

          Valid N (listwise)

          30

          TABLE VI. Descriptive analysis

          TABLE VII. Correlation analysis

          Correlations

          Load of Rollers (Ampere)

          Billet Temperat ure at (stand 2)

          Heating zone Temperature

          Load of Rollers (Ampere)

          Pearson Correlation

          1

          -.291

          -.302

          Sig. (2-tailed)

          .118

          .105

          N

          30

          30

          30

          Billet Temperature at (stand 2)

          Pearson Correlation

          -.291

          1

          .142

          Sig. (2-tailed)

          .118

          p>.454

          N

          30

          30

          30

          Heating zone Temperature

          Pearson Correlation

          -.302

          .142

          1

          Sig. (2-tailed)

          .105

          .454

          N

          30

          30

          30

          With the help of Correlation, we can determine how strong the relationship exists between these variables.

          As we can observe from the table:

          • There is a weak negative linear relationship between load of rollers (L) and billet temperature at stand 2 (Ts) i.e. -0.291.

          • There is a moderate negative linear relationship between load of rollers (L) and temperature of heating zone (Th) i.e. -0.302.

        TABLE VIII. Regression analysis:

        According to regression coefficient table we can formulate the formula for the relationship between Load of rollers (L) in term of Temperature of billet at stand 2 (Ts) and Temperature of heating zone (Th).

        Load of roller (L) = a + b1 x1 + b2 x2 L = 1393.2910.253× Ts 0.327 × Th

        Where 1393.291 is constant called intercept and is denoted by a

    2. Production Analysis

    We have collected the data of amount of monthly production of merchant mill & respective unfinished products, before and after the installation of radiation pyrometer i.e. on Nov 2018. These are as follows:-

    i. Data Collection & Analysis before installation of Radiation Pyrometer

    TABLE IX. Data Collection of Unfinished Product before installation of Radiation Pyrometer (2018-19)

    iii. Graphical Analysis

    Total unfinished product/year (Ton)

    S.no.

    Month

    Productio n/ year (Ton)

    Total unfinished product/year (Ton)

    Percentage of Unfinished product/year (%)

    1.

    Apr 2018

    54283

    232.50

    0.42

    2.

    May 2018

    54639

    255.39

    0.46

    3.

    June 2018

    52399

    200.27

    0.38

    4.

    July 2018

    34476

    199.84

    0.57

    5.

    Aug 2018

    51906

    209.14

    0.40

    6.

    Sept 2018

    52208

    223.58

    0.42

    7.

    Oct 2018

    45934

    189.50

    0.41

    8.

    Nov 2018

    51216

    242.42

    0.47

    Total

    395061 T

    1752.64 T

    ——

    Average

    49382.6 T

    219.08 T

    0.44%

    S.no.

    Month

    Productio n/ year (Ton)

    Total unfinished product/year (Ton)

    Percentage of Unfinished product/year (%)

    1.

    Apr 2018

    54283

    232.50

    0.42

    2.

    May 2018

    54639

    255.39

    0.46

    3.

    June 2018

    52399

    200.27

    0.38

    4.

    July 2018

    34476

    199.84

    0.57

    5.

    Aug 2018

    51906

    209.14

    0.40

    6.

    Sept 2018

    52208

    223.58

    0.42

    7.

    Oct 2018

    45934

    189.50

    0.41

    8.

    Nov 2018

    51216

    242.42

    0.47

    Total

    395061 T

    1752.64 T

    ——

    Average

    49382.6 T

    219.08 T

    0.44%

    300

    200

    100

    0

    Total unfinished product/year (Ton)

    Data Analysis

    We found that the generation of unfinished product in 8 months (from April 2018 to Nov 2018) is 1752.64 Ton which is on average 219.08 Ton/month. Percentage of Cobble (unfinished products) generation was 0.44 % of total finished products. Total production in 8 months was 395061 Ton/month i.e. 0.395 MT. Other reasons are not included here, which impact production. Hence there was a loss incurred-

    Approximate Mean Production Loss (before installation) =

    219.08 Ton / Month

    ii. Data Collection & Analysis after installation of Radiation Pyrometer

    TABLE X. Data Collection of Unfinished Product after installation of Radiation Pyrometer ( 2018 -19)

    S.no.

    Month

    Production

    / year (Ton)

    Total unfinished product / year (Ton)

    Percentage of Unfinished product/year (%)

    1.

    Dec 2018

    45566

    140.94

    0.30

    2.

    Jan 2019

    55286

    123.58

    0.22

    3.

    Feb 2019

    52222

    129.32

    0.24

    4.

    Mar 2019

    59207

    112.18

    0.18

    5.

    April 2019

    41075

    102.48

    0.24

    6.

    May 2019

    55026

    80.75

    0.14

    7.

    June 2019

    35609

    98.62

    0.27

    8.

    July 2019

    54228

    70.84

    0.13

    Total

    398219 T

    858.71 T

    ——

    Average

    49777.4 T

    107.33 T

    0.215 %

    Data Analysis after installation IMPAC Radiation Pyrometer

    A Digital Fixed type Radiation Pyrometer was installed on 27 Nov 2018 near stand 2, merchant mill, B.S.P. Data was collected from the product Log book of mill and monthly report of production .We found that the generation of unfinished product in 8 months (from Dec 2018 to July 2019) is 858.71Ton which is on average 107.33 Ton/month). Percentage of Cobble (unfinished products) generation was 0.215 % of total finished products. This Data shows the decrease in cobble generation.

    Fig 3. Bar graph representation of Cobble generation before installation of Radiation Pyrometer

    Total unfinished product / year (Ton)

    150

    100

    50

    0

    Total unfinished product / year (Ton)

    150

    100

    50

    0

    Fig 4. Bar graph representation of Cobble generation after installation of Radiation Pyrometer

    iv. Analysis of Increased Production

    Increased Production or Cobble reduction = Cobble generation before installation Cobble generation after installation

    Increased Production or Cobble reduction = Cobble generation before installation Cobble generation after installation

    Increased Production (Ton / month) = 219.08 107.33 =

      1. Ton/month, i.e.0.23%

  4. RESULT & DISCUSSIONS

    Analysis of the collected data after installation of fixed type Digital Raiation Pyrometer model no. IMPAC IBA-5, signifies the load is inversely proportional to the temperature. This gives the new formula for calculating the generated load on rollers of stand. Also, Continuous monitoring the temperature of heated billets shows the minimum safe rolling temperature and safe load limit which must be set and maintained for continuous rolling.

    TABLE XI. Observed Load data after installation of Radiation pyrometer

    Profile

    Process Load (°C)

    Safe Load setting

    (Amperes)

    Angles

    800 ± 50

    1100

    Bars

    800 ± 50

    1250

    Benefits of analysis after installation of radiation pyrometer-

        • Continuous monitoring the temperature of heated billets.

        • Increased the productivity 111.75 Ton/month and decreasing the production of unfinished product.

        • Increased Production per year is 1341 Ton/yr.

  5. CONCLUSION

    The generation of unfinished products along with the finished products gives loss of productivity. It was due to excess load generation in motor to operate rollers in rolling stand because of less temperature of heated billets in furnace. This problem solved by installation of Radiation pyrometer hence continuous & uniform observation became possible. After this installation increased productivity is observed approximately 111 Ton/ month and subsequent decrease in Cobbles. Also financial impact on the company is around 5.7 Crore Rs/ year by increased production.

    Also our analysis with the help of tool IBM SPSS Statistics 2.0 of data load and temperature, made it possible to standardize the present system in the merchant mill. The tool determined the correlation and multiple regression analysis, hence derived standard formula for all the products in the mill.

  6. FUTURE SCOPE

This instrument radiation pyrometer can be used as control process parameters for rolling in any steel industry. Formula derived in this study for the different profiles (angles, channels and bars) can be used to maximize production in the Rolling mill of Steel Plant

ACKNOWLEDGEMENT

I am very thankful to express my gratitude towards to Mr.

    1. Nanda, Manager. Instrumentation Department, SAIL Bhilai Steel Plant, for guiding me during this research work.

      REFERENCES

      1. (2007). Annual Review. In Heat Stress & Public Health, Bhilai Steel Plant.

      2. Burgees, G. K. (1919). Report of Pyrometer. Washington D.C. Chicago: Committee of National Research Council, Washington

        D.C. Chicago meeting.

      3. Eckert, E. &. (1959). Heat & Mass Transfer. Mc Grew Hill Book Company .

      4. Raghvan, V. (1989). Material science and engineering. prentice hall of India private ltd, Delhi .

      5. Savin, L. (1977). Industrial furnaces. Mir publishers Moscow.

      6. Shigeru, E. Development of thermo mechanical control process and high performance steel in JFE Steel. Technical report JFE.

      7. W.Trinks. (1962). Industrial Furnaces. John Wiley & Sons, New Delhi .

      8. (2008). Work Visit Notes. In Training & Management Development Department, Bhilai Steel Plant.

      9. Yun-gingGu. (2016). Experiment research on Hot Rolling Processing of non smooth pit surface. Applied Bionics & Biomechanics.

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