Induction Heating Handbook

John Davies University of Aston in Birmingham

Peter Simpson Ministry of Defence

McGRAW-HILL Book Company (UK) Limited

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Contents

Preface xi

Chapter 1 Introduction to Induction Heating 1 1.1 The background to induction heating 1 1.2 Induction-heating principles 2 1.3 Applications 5 1.4 Power Systems 5 1.5 Economics, safety, and environment 8

Chapter 2 Through-heating by Induction 10 2.1 Introduction to applications of through-heating 10 2.2 Temperature effects 17 2.3 Heat radiation and convection 24 2.4 Temperature distribution in induction through-heating 26 2.5 Effects of current depth and radiated heat 27 2.6 Temperature distributions in a heating cycle 28 2.7 Selection of frequencies for induction through-heating 30 2.8 Application specifications for coil design 33 2.9 Equivalent circuit coil-design method 43 2.10 Approximate coil-design method 49 2.11 Mechanical construction of coils 55 2.12 Slab reheating 58 2.13 Travelling-wave induction heating 59 2.14 Multi-layer coils 63 2.15 Tapered heating for extrusion 64 2.16 Scale-model analogue methods 65

Chapter 3 Surface Heating by Induction 67 3.1 Metallurgical principles of heat treatment 71 3.2 Quenches and quenching . 77 3.3 Selection of frequency in induction heat treatment 81 3.4 Temperature distribution in induction surface hardening 87 3.5 Application specifications for coil design 89 3.6 Mechanical construction of coils 91

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Chapter 4 Other Applications of Induction Heating 96 4.1 Soldering and brazing 96 4.2 Tube welding 109 4.3 Heating of resin kettles and other vessels 118 4.4 Paintdrying 120 4.5 Induction heating in plastic working 121 4.6 Annealmg and stress relieving 122 4.7 Longitudinal flux induction heating 124 4.8 Transverse flux heating 124 4.9 Semiconductor processing 126

4.10 Miscellaneous uses of induction heating 131

Chapter 5 Induction Melting 135 5.1 Principles of induction meiters 135 5.2 The coreless induction furnace 142 5.3 The Channel furnace 148 5.4 Comparisonof coreless and Channel furnaces 152 5.5 Special features in melting furnaces 155

Chapter 6 Supply-frequency Heating Systems 163 6.1 Advantages and limitations 163 6.2 Load matching 165 6.3 Control and switchgear 168 6.4 Solid-state power regulators 172 6.5 Measurements at supply frequencies 173 0.0 Workhandling equipment 174 6.7 Melting furnace System 177 6.8 Frequency multipliers 178 6.9 Dual-frequency Systems 180

Chapter? Medium-frequency motor^mator Systems 181 /-l Introduction 181 7.2 Principles ofthemedium^requencygenerator 181 7.3 Mechan.cal features ofinductor-alternators 187 7.4 Electncal behaviour of the generator 190 7.5 Load matching and tuning 194 7.6 Control Systems 198

7.7 Automatic voltage regulators 200

Chapter 8 Medium-frequency Solid-state Systems 202

I t r T ^ v * * * * * ^ > solid-state static con-

8 ' 2 a r S S * " ° f m e d l U m ' f r ^ — y induction-heating

8.3 Requirements of the static inverter 203 8.4 Sibcon-controlledrectifiercharacteristics 204 ».:> tSasic inverter Systems 205

8.6 Swept-frequency Systems 207 8.7 Load-resonant System 210

vm

8.8 Comparative efficiencies and impedance characteristics 212 8.9 Control and protection 214 8.10 Construction and layout 216 8.11 Capital and running costs 218 8.12 Comparison between inverters and motor-alternators 219

Chapter9 Radio-frequency Systems 221 9.1 The basis of the radio-frequency generator 221 9.2 Industrial RF heating osciilator valves 229 9.3 The ideal industrial valve characteristics 230 9.4 Construction of industrial triode valves 231 9.5 Magnetically-focused triode 235 9.6 Class C osciilator design 237 9.7 Anode HT power supplies 245 9.8 Control circuits 248 9.9 Power control Systems 249 9.10 Load-matching Output circuits 254 9.11 Radio-frequency metering 260 9.12 Generator reliability 261

Chapter 10 Ancillary Equipment 263 10.1 Measurement technlques 263 10.2 Supply-frequency measurements 263 10.3 Medium-frequency measurements 263 10.4 Radio-frequency measurements 266 10.5 Integrated measurement and control 268 10.6 Temperature measurements 270 10.7 Miscellaneous measurements 272 10.8 Temperature control Systems 273 10.9 Power control and regulation 275 10.10 Cables and busbars 275 10.11 Workhandiing equipment 280

Chapter 11 Economics 292 11.1 Economics and thermal efficiencies of power sources 292 11.2 Cost analysis in hardening and welding 296 11.3 Heating for forging comparisons 298 11.4 Costs of melting furnaces 304 11.5 Miscellaneous economic factors 306

Chapter 12 Theory of Induction Heating 307 12.1 Introduction 307 12.2 Skin effect for semi-infinite siab 307 12.3 Power and flux for semi-infinite slab 314 12.4 Power and flux induced in a wide rectangular slab 318 12.5 Power and flux in a solid cylinder 322 12.6 Power induced in a hollow cylinder 329 12.7 Non-linear theory 335 12.8 Proximity heating 337

ix

Chapter 13 Heat Transfer 341 13.1 Introduction 341 13.2 Reiationship between power m M n t » m

g fe^SF-8"341 J.J.7 Rectanguiar slab 351 13.8 Radiation 352

13.9 Heat transfer durine surfacp h ^ • 11 1ft ftau» •„ . . . g »uriace nardemng 356

ChapKrU Safelyand Environment Conditio« 373

sibilities 374 ' employees' respon-

U 4 f^rnaftionaJ s a f«ty regulations 375

14.4 I E C safety recommendations 375 14.5 Environment and terminology 377

Appendix 1 Eiectroheating Terminology 379

A L I C ^ o n of electroheat e.uipment according to f r e i e n -

AI.2 Terminology 379

Appendix 2 W ^ D B - ^ i n a a b 383

A2 2 f^btheate^ from one side only 383

A2-4 S o a k i n g o f s I a b p r e v i o u s ] y h e a t e d f r o m b o t h s i d e s ^

A ^ I ^ ^ ^ ^ ^ ^ 3 9 4

A3.2 Power plant-quahtyofengineering 394

A3.3 Chcceof power plant for induct.on furnace 397

A3-4 prxs&z^'-zrZ- -Appendix 4 Unit Conversion Tables 407

Appendix 5 Re-stivity, Specific Heat, and Thermal ConH , -Temperature 410 !U d e rma l Conductivity as Functions of

References 412

Appendix 3

A3.5 A3.6

Index 419