STATISTICAL APPROACH TO MINIMIZE WASTE IN  TYRE MANUFACTURING PROCESS: A CASE STUDY        R.K.Dilrukshi   108804H        Degree of Master of Science in Business Statistics              Department of Mathematics  Faculty of Engineering  University of Moratuwa  Sri Lanka      I    DECLARATION OF THE CANDIDATE I hereby declare that the work presented here in genuine work done originally by me except as cited in the reference and has not submitted elsewhere for the requirement of degree programme or published any time before. Signature: Date: R.K.Dilrukshi DECLARATION OF THE SUPERVISOR The above candidate has carried out research for the Master Dissertation under my supervision. ……………………….. ………….. Signature of the Supervisor Date Prof. T.S.G Peiris Professor in Applied Statistics Department of Mathematics Faculty of Engineering University of Moratuwa Sri Lanka       II    ABSTRACT The main focus of this study was to assess the wastes occurring because of defect tyres in air tyre manufacturing process in the Loadstar Pvt. Limited. This lost accounts for 37.75 million during the last five months. In this study a complete statistical analysis about defect tyres were carried out for five tyre types in air tyre manufacturing process by means of Parato diagram. The average run lengths were found for each tyre type. Explanatory statistical analysis revealed that the defect tyre cost is high due to factors such as under cure, bladder pleat, air bubble in, plate damage, air bubble lug, low pressure and less side wall thickness. These statistical analyses are recommended to help manufacturers to identify the exact issues in the manufacturing process and rectify those. Keywords: Average run length, Chi-square test, NP chart, Parato diagram, P chart, X-bar chart III    ACKNOWLEDGEMENT First I would like to thank to my supervisor Professor T.S.G. Peiris, Head, Department of Mathematics, Faculty of Engineering, University of Moratuwa for his valuable guidance and advice for enriching my knowledge and skills through his experience. I glad to express my gratitude to Mr. A.M Razmy, Senior Lecturer in Statistics, South Eastern University of Sri Lanka for his help for enriching my knowledge through his experience. I would like to thank all my colleagues from the quality control department of the Loadstar Pvt. Limited for their favorable facilitation on their official ground as well as in personally. My special gratitude offered to whom that I couldn’t mention here and involved directly and in directly on this manner. Finally I would like to thank my farther, husband, daughter and teachers who provided me a good guidance to perform my activities up to this level.     Dilrukshi                                                     IV    TABLE OF CONTENTS Page Declaration i Abstract ii Acknowledgement iii List of Tables vii List of Figures ix             Chapter 1: Introduction 1 1.1 Description of the company 1 1.2 Air tyre production process 1 1.2.1 Tyre building area 1 1.2.1.1 Pocket machine 3 1.2.1.2 Tyre building machine 3 1.2.1.3 Inflating machine 3 1.2.1.4 Brushing Machine 3 1.2.1.5 Warming and tread rolling mill 3 1.2.1.6 Tread shaping and drilling machine 4 1.2.1.7 Air bag inserting machine 4 1.2.2 Tyre curing area 4 1.2.2.1 Curing in ovens 4 1.2.2.2 Curing in presses 4 1.3 Categorization of tyres. 5 1.3.1 First choice tyres. 5 1.3.2 Defect tyres. 5 1.4 Objective of the study. 6 Chapter 2: Literature Review 7 2.1 Introduction. 7 V    2.2 Scrap tyre disposal related to problems 8 2.3 Major methods and reasons of recycling tyres. 9 2.4 Historical perspectives. 9 2.5 Scrap tyre disposal statistics 10 2.6 Rubber recycling. 10 2.7 Background of the information. 11 2.8 Theory 12 2.8.1 Control chart 12 2.8.1.1 How to check the process 12 2.8.1 .2 Variable control chart 12 2.8.1.3 Attribute control chart 12 2.8.2 Chi-square test 13 2.8.3 Parato diagrams 13 2.8.3.1 Count parato 14 Chapter 3: Description of the Data and Methodology 15 3.1 Description of the data 15 3.2 Methodology 16 Chapter 4: Results and Discussion 17 4.1 Relationship between number of defectives and total cost 17 4.2 Reasons for Defectives. 21 4.3 Results 22 4.3.1 Tyre type I 22 4.3.2 Tyre type II 36 4.3.3 Tyre type III 52 4.3.4 Tyre type IV 63 4.3.5 Tyre type V 74 VI    Chapter 5: Conclusion and Recommendations 87 References 89 Appendix 90   .        VII    LIST OF TABLES  Page Table 3.1 Few data of Data set 15 Table 4.1 Number of defectives of each Tyre type 17 Table 4.2 Cost of defectives of each Tyre type 18 Table 4.3 Reasons of defectives of Tyre type I 26 Table 4.4 Reasons for tyre type I Bladder pleat defect 28 Table 4.5 Reasons for tyre type I Bladder leak defect 29 Table 4.6 Reasons for tyre type I Under cure defect 30 Table 4.7 Reasons for tyre type I Thin bead defect 31 Table 4.8 Reasons for tyre type I Plate damage defect 32 Table 4.9 Reasons for tyre type I Low pressure defect 33 Table 4.10 Reasons for tyre type I Air bubble lug defect 34 Table 4.11 Reasons for tyre type I Pressure leak defect tyres 35 Table 4.12 Chi-square test of Tyre type I 46 Table 4.13 Reasons of defectives of Tyre type II 40 Table 4.14 Reasons for tyre type II Under cure defect 42 Table 4.15 Reasons for tyre type II Bladder leak defect 43 Table 4.16 Reasons for tyre type II Pressure leak defect 44 Table 4.17 Reasons for tyre type II Two color defect 45 Table 4.18 Reasons for tyre type II Low Pressure defect 46 Table 4.19 Reasons for tyre type II Foreign matter defect 47 Table 4.20 Reasons for tyre type II Short mould side wall defect 48 Table 4.21 Reasons for tyre type II Air Bubble side wall defect 49 Table 4.22 Reasons for tyre type II Less under tread thickness defect 50 Table 4.23 Chi-square test of tyre type II 51 Table 4.24 Reasons of defectives of tyre type III 55 Table 4.25 Reasons for tyre type III Under cure defect 57 Table 4.26 Reasons for tyre type III Plate Damage defect 58 Table 4.27 Reasons for tyre type III Air Bubble in defect 59 Table 4.28 Reasons for tyre type III Less side wall thickness defect 60 VIII    Table 4.29 Reasons for tyre type III Low pressure defect 61 Table 4.30 Chi-square test of tyre type III 62 Table 4.31Reasons of defectives of tyre type IV 66 Table 4.32 Reasons for tyre type IV Under cure defect 68 Table 4.33 Reasons for tyre type IV Air Bubble in defect 69 Table 4.34 Reasons for tyre type IV Air Bubble lug defect 70 Table 4.35 Reasons for tyre type IV Flash open defect 71 Table 4.36 Reasons for tyre type IV Hose leak defect 72 Table 4.37 Chi-square test of Tyre type IV 73 Table 4.38 Reasons of defectives of tyre type V 77 Table 4.39 Reasons for tyre type V Plate damage defect 79 Table 4.40 Reasons for tyre type V Less under tread thickness defect 80 Table 4.41 Reasons for tyre type V Less side wall thickness defect 81 Table 4.42 Reasons for tyre type V Under cure defect 82 Table 4.43 Reasons for tyre type V Air bag leak defect 83 Table 4.44 Reasons for tyre type V Low pressure defect 84 Table 4.45 Reasons for tyre type V Foreign matter defect 85 Table 4.46 Chi-square test of tyre type V 86                                 IX    LIST OF FIGURES                             page                    Figure 1.1 Process layout of tyre building area 2 Figure 4.1 Number of defectives vs cost of defect tyre 20 Figure 4.2 P Chart of tyre type I 22 Figure 4.3 NP Chart of tyre type I 23 Figure 4.4 X bar chart of tyre type I 24 Figure 4.5 Parato Diagram of tyre type I 27 Figure 4.6 Reasons for tyre type I Bladder pleat defect tyres 28 Figure 4.7 Reasons for tyre type I Bladder leak defect tyres 29 Figure 4.8 Reasons for tyre type I Under cure defect tyres 30 Figure 4.9 Reasons for tyre type I Thin bead defect tyres 31 Figure 4.10 Reasons for tyre type I Plate damage defect tyres 32 Figure 4.11 Reasons for tyre type I Low pressure defect tyres 33 Figure 4.12 Reasons for tyre type I Air bubble lug defect tyres 34 Figure 4.13 Reasons for tyre type I Pressure leak defect tyres 35 Figure 4.14 P Chart of tyre type II 37 Figure 4.15 NP Chart of tyre type II 38 Figure 4.16 X bar chart of tyre type II 38 Figure 4.17 Parato Diagram of tyre type II 41 Figure 4.18Reasons for tyre type II Under cure defect tyres 42 Figure 4.19 Reasons for tyre type II Bladder leak defect tyres 43 Figure 4.20Reasons for tyre type II Pressure leak defect tyres 44 Figure 4.21 Reasons for tyre type II Two color defect tyres 45 Figure 4.22 Reasons for tyre type II Low pressure defect tyres 46 Figure 4.23 Reasons for tyre type II Foreign matter defect tyres 47 Figure 4.24 Reasons for tyre type II Short mould side wall defect tyres 48 Figure 4.25 Reasons for tyre type II Air Bubble Side Wall defect tyres 49 Figure 4.26 Reasons for tyre type II Less under tread thickness defect tyres 50 Figure 4.27 P Chart of tyre type III 52 Figure 4.28 NP Chart of tyre type III 53 X    Figure 4.29 X bar chart of tyre type III 54 Figure 4.30 Parato Diagram of tyre type III 56 Figure 4.31Reasons for tyre type III Under cure defect tyres 57 Figure 4.32 Reasons for tyre type III Plate damage defect tyres 58 Figure 4.33 Reasons for tyre type III Air bubble in defect tyres 59 Figure 4.34 Reasons for tyre type III Less side wall thickness defect tyres 60 Figure 4.35 Reasons for tyre type III Low pressure defect tyres 61 Figure 4.36 P Chart of tyre type IV 63 Figure 4.37 NP Chart of tyre type IV 64 Figure 4.38 X bar chart of tyre type IV 64 Figure 4.39 Parato Diagram of tyre type IV 67 Figure 4.40 Reasons for tyre type IV Under cure defect tyres 68 Figure 4.41 Reasons for tyre type IV Air bubble in defect tyres 69 Figure 4.42 Reasons for tyre type IV Air bubble lug defect tyres 70 Figure 4.43 Reasons for tyre type IV Flash open defect tyres 71 Figure 4.44Reasons for tyre type IV Hose leak defect tyres 72 Figure 4.45 P Chart of tyre type V 74 Figure 4.46 NP Chart of tyre type V 75 Figure 4.47 X bar chart of tyre type V 76 Figure 4.48 Parato Diagram of tyre type V 78 Figure 4.49Reasons for tyre type V Plate damage defect tyres 79 Figure 4.50 Reasons for tyre type V Less under tread thickness defect tyres 80 Figure 4.51 Reasons for tyre type V Less side wall thickness defect tyres 81 Figure 4.52 Reasons for tyre type V Under cure defect tyres 82 Figure 4.53 Reasons for tyre type V Air bag leak defect tyres 83 Figure 4.54 Reasons for tyre type V Low pressure defect tyres 84 Figure 4.55 Reasons for tyre type V Foreign matter defect tyres 85           XI    LIST OF ANNEXES  Page Annex – A Production detail of elected tyre types 94 Failure probability results Annex – B ARL and additional cost values due to defectives 95 Chi-square test results Annex – C Reasons for defect of tyre type III and IV 96 Annex – D Reasons for defect of tyre type I and II 97 Reasons for defect of tyre type V Annex – E Main reasons for defectives of five tyre types 98 Annex – F Total cost of defectives for the period of past five months 97 Total cost of defectives for the period of past five months (cont)    98