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Handbook of Induction Heating Second Edition

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Handbook of Induction Heating Second Edition

Valery Rudnev Don Loveless Raymond L. Cook

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CRC Press Taylor & Francis Group 6000 Broken Sound Parkway NW, Suite 300 Boca Raton, FL 33487-2742 © 2017 by Taylor & Francis Group, LLC CRC Press is an imprint of Taylor & Francis Group, an Informa business No claim to original U.S. Government works Printed on acid-free paper International Standard Book Number-13: 978-1-4665-5395-8 (Hardback) This book contains information obtained from authentic and highly regarded sources. Reasonable efforts have been made to publish reliable data and information, but the author and publisher cannot assume responsibility for the validity of all materials or the consequences of their use. The authors and publishers have attempted to trace the copyright holders of all material reproduced in this publication and apologize to copyright holders if permission to publish in this form has not been obtained. If any copyright material has not been acknowledged please write and let us know so we may rectify in any future reprint. Except as permitted under U.S. Copyright Law, no part of this book may be reprinted, reproduced, transmitted, or utilized in any form by any electronic, mechanical, or other means, now known or hereafter invented, including photocopying, microfilming, and recording, or in any information storage or retrieval system, without written permission from the publishers. For permission to photocopy or use material electronically from this work, please access www.copyright.com (http://www​ .copyright.com/) or contact the Copyright Clearance Center, Inc. (CCC), 222 Rosewood Drive, Danvers, MA 01923, 978-7508400. CCC is a not-for-profit organization that provides licenses and registration for a variety of users. For organizations that have been granted a photocopy license by the CCC, a separate system of payment has been arranged. Trademark Notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation without intent to infringe. Visit the Taylor & Francis Web site at http://www.taylorandfrancis.com and the CRC Press Web site at http://www.crcpress.com

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This book is dedicated to the customers of Inductoheat Inc. and Inductotherm Group Companies who through the years have provided the opportunity to study, learn, and develop the themes presented in this text. This includes customers of the past and present who have had the courage to venture into sometimes uncharted waters in the area of induction heating design and development in order to reap the projected gains provided by this technology.

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Contents Preface to the Second Edition of the Handbook of Induction Heating............................... xvii Authors.......................................................................................................................................... xxi 1. Introduction..............................................................................................................................1 2. Industrial Applications of Induction Heating...................................................................9 2.1 Heat Treatment by Induction..................................................................................... 12 2.1.1 Hardening........................................................................................................ 12 2.1.1.1 Surface Hardening.......................................................................... 14 2.1.1.2 Through Hardening........................................................................ 20 2.1.1.3 Selective Hardening........................................................................ 21 2.1.2 Tempering and Stress Relieving...................................................................22 2.1.3 Normalizing.................................................................................................... 24 2.1.4 Annealing........................................................................................................ 25 2.1.4.1 Full Annealing and Homogenization.......................................... 25 2.1.4.2 Intercritical Annealing................................................................... 26 2.1.4.3 Subcritical Annealing..................................................................... 27 2.1.4.4 Spheroidized Anneal or Spheroidizing.......................................30 2.1.5 Induction Heat Treating of Nonferrous Metallic Materials...................... 30 2.2 Induction Mass Heating.............................................................................................. 32 2.2.1 Bar, Rod, and Billet Reheating...................................................................... 33 2.2.2 Thixoforming Applications........................................................................... 37 2.2.3 Tube, Pipe, and Vessel Heating..................................................................... 37 2.2.4 Wire, Rope, and Cable Heating..................................................................... 38 2.2.5 Slab, Plate, Rectangular Bar, and Bloom Heating...................................... 39 2.2.6 IH of Strips, Thin Slabs, Plates, Films, and Sheets..................................... 40 2.2.7 Coating............................................................................................................. 41 2.2.7.1 Curing of Paints and Varnishes.................................................... 41 2.2.7.2 Preheating before Thermal Spraying...........................................42 2.2.7.3 Galvannealing, Galvanizing, and Galvaluming........................42 2.3 Special Applications of IH..........................................................................................43 2.3.1 Joining, Friction Welding, Brazing, Bonding, Soldering, and Sealing....43 2.3.2 Shrink Fitting and Disassembling...............................................................44 2.3.3 Motor Rotor Heating...................................................................................... 45 2.3.4 Seam Annealing.............................................................................................. 46 2.3.5 Induction-Assisted Laser Materials Processing......................................... 46 2.3.6 Food Industry.................................................................................................. 47 2.3.7 Papermaking................................................................................................... 47 2.3.8 Wool and Wood Processing.......................................................................... 47 2.3.9 Chemical Industry.......................................................................................... 47 2.3.10 Cap Sealing...................................................................................................... 47 2.3.11 Miscellaneous.................................................................................................. 48 2.4 Induction Melting........................................................................................................ 48 2.4.1 Induction Channel-Type Melting Furnace.................................................. 48 vii

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2.4.2 Induction Crucible-Type (Coreless) Furnace............................................... 48 2.4.3 Induction Vacuum Melting........................................................................... 49 2.5 Induction Welding....................................................................................................... 49 2.6 Conclusion..................................................................................................................... 50 3. Theoretical Background....................................................................................................... 51 3.1 Basic Electromagnetic Phenomena in IH................................................................. 51 3.1.1 Electromagnetic Properties of Metallic Materials...................................... 53 3.1.1.1 Electrical Resistivity (Electrical Conductivity)........................... 53 3.1.1.2 Magnetic Permeability and Relative Permittivity (Dielectric Constant)....................................................................... 55 3.1.2 Skin Effect........................................................................................................ 60 3.1.3 Electromagnetic Proximity Effect................................................................ 66 3.1.4 Electromagnetic Slot Effect............................................................................ 69 3.1.5 Electromagnetic Ring Effect.......................................................................... 71 3.1.6 Electromagnetic Force.................................................................................... 72 3.1.7 Introduction to Electromagnetic End and Edge Effects............................ 78 3.1.7.1 Electromagnetic Longitudinal End Effect................................... 79 3.1.7.2 Helix Effect....................................................................................... 85 3.1.7.3 Electromagnetic Transverse Edge Effect.....................................85 3.1.7.4 Electromagnetic Effect of Joined Materials with Different Electromagnetic Properties (EEJ Effect)....................................... 88 3.2 Thermal Phenomena in IH.........................................................................................90 3.2.1 Thermal Properties of the Materials............................................................ 90 3.2.1.1 Thermal Conductivity....................................................................90 3.2.1.2 Heat Capacity and Specific Heat................................................... 91 3.2.2 Three Modes of Heat Transfer...................................................................... 92 3.2.2.1 Thermal Conduction....................................................................... 92 3.2.2.2 Convection Mode of the Heat Transfer........................................ 93 3.2.2.3 Radiation Mode of the Heat Transfer........................................... 94 3.3 Estimation of the Required Power and Dynamics of IH....................................... 95 3.3.1 Estimation of the Required Power for IH.................................................... 95 3.3.2 Intricacies of the Dynamics of IH................................................................. 99 3.4 Advanced Induction Principles and Mathematical Modeling............................ 102 3.4.1 Mathematical Modeling of the Electromagnetic Field............................ 103 3.4.2 Mathematical Modeling of the Thermal Processes................................. 109 3.4.3 Numerical Computation of the Process..................................................... 111 3.4.3.1 Traditional Methods of Calculation........................................... 111 3.4.3.2 Finite Difference Method............................................................. 112 3.4.3.3 Finite Element Method................................................................. 119 3.4.3.4 Mutual Impedance Method......................................................... 126 3.4.3.5 Boundary Element Method......................................................... 129 3.4.3.6 Coupling of the Electromagnetic and Thermal Problems...... 130 3.4.3.7 Comparison of Different Numerical Techniques and Final Remarks Regarding Computer Modeling............... 132 3.4.4 Limitations of Generalized All-Purpose Commercial Programs.......... 133 3.4.5 Crucial Tips Executives Must Know Regarding Computer Modeling of IH.............................................................................................. 136

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4. Heat Treatment by Induction............................................................................................ 139 4.1 The Basics of Metallurgy and Principles of Heat Treatment of Steels and Cast Irons............................................................................................................. 139 4.1.1 Crystalline Structures and Critical Temperatures................................... 140 4.1.2 Fe–Fe3C Phase Transformation Diagram and Steel Classifications....... 145 4.1.2.1 Classifications of Steels................................................................. 146 4.1.2.2 Steel Identification Systems......................................................... 149 4.1.2.3 Phases of the Equilibrium Fe–Fe3C Diagram............................ 150 4.1.3 Time–Temperature Transformation Diagram and Continuous-Cooling Transformation Diagram................................ 153 4.1.4 Steel’s Trace (Residual) Elements and Alloying Elements...................... 163 4.1.5 Hardenability................................................................................................ 169 4.1.5.1 Through Hardening...................................................................... 169 4.1.5.2 Induction Surface (Case) Hardening.......................................... 176 4.1.5.3 Summary of the Limitations of Standard Forms of Hardenability Tests.................................................................. 178 4.1.6 Effect of Heat Intensity (Heating Rate) and Prior Structure on Induction Heat Treatment Results in Steels........................................ 180 4.1.7 Super-Hardness Phenomenon.................................................................... 188 4.1.8 Inclusions....................................................................................................... 190 4.1.9 Grain Boundary Liquation (Incipient Melting)........................................ 192 4.1.10 Specifics of Induction Hardening Stainless Steels and Bearing Steels............................................................................................................... 194 4.1.10.1 Physical Properties........................................................................ 196 4.1.10.2 Hardening Specifics...................................................................... 196 4.1.11 Induction Heat Treatment of Cast Irons.................................................... 198 4.1.11.1 Gray Cast Irons.............................................................................. 203 4.1.11.2 Ductile Cast Irons.......................................................................... 205 4.1.11.3 Specifics of Electromagnetic and Thermal Properties............. 208 4.1.11.4 Good Practices in Induction Hardening of Cast Irons and Closing Remarks.................................................................... 210 4.1.12 Specifics of Induction Hardening of Powder Metallurgy Materials..... 218 4.2 Induction Hardening: Subtleties of Machine Design and Process Recipe Selection.......................................................................................................................222 4.2.1 Hardness Case Depth Definitions..............................................................225 4.2.2 Induction Hardening Methods................................................................... 227 4.2.2.1 Scan Hardening............................................................................. 227 4.2.2.2 Continuous or Progressive Hardening...................................... 248 4.2.2.3 Single-Shot Hardening.................................................................254 4.2.2.4 Static Hardening............................................................................ 263 4.2.2.5 Pulse Heating Mode..................................................................... 267 4.2.3 Specialty Inductors....................................................................................... 267 4.2.3.1 Pancake, Split-Return, Butterfly, and Hairpin Inductors........ 268 4.2.3.2 Specifics of Designing Inductors for Heating Interior Surfaces........................................................................................... 272 4.2.3.3 Proximity Induction Heating of Flat and Plane Surfaces........ 275 4.2.3.4 Inductors with Inserts.................................................................. 275 4.2.3.5 Clamshell or Split Inductors........................................................ 276 4.2.3.6 Profiled Inductors.......................................................................... 278

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4.2.4

4.3

4.4 4.5

4.6

Fabrication and Cooling of Hardening Inductors.................................... 280 4.2.4.1 Material Selection.......................................................................... 280 4.2.4.2 Fabrication Techniques................................................................. 282 4.2.4.3 Surface Conditions........................................................................ 286 4.2.4.4 Water Cooling of Hardening Inductors..................................... 289 4.2.5 Frequency Choice and Power Selection..................................................... 293 4.2.5.1 Through Hardening...................................................................... 293 4.2.5.2 Surface Hardening........................................................................ 294 4.2.5.3 Heat Duration................................................................................ 296 4.2.6 Inductor Mounting Styles............................................................................ 297 4.2.7 Quenching and Spray Quench Designs.................................................... 299 4.2.7.1 Introduction................................................................................... 299 4.2.7.2 Quench Media............................................................................... 301 4.2.7.3 Quench Methods...........................................................................304 4.2.7.4 Part Cleaning before Heating and after Quenching................ 306 4.2.7.5 Quench Systems Design and Controls....................................... 307 4.2.8 Striping (Striation) Phenomena, Barber-Pole Effect, and Snakeskin (Soft-Spotting) and Fish-Tail Phenomena.................................................. 310 4.2.8.1 Striping Phenomena and Barber-Pole Effect............................. 310 4.2.8.2 Snake-Skin Effect and Soft-Spotting Phenomena.................... 314 4.2.8.3 Fish-Tail Effect (Field-Fringing Phenomenon).......................... 315 Holes, Keyways, Grooves, Undercuts, and Other Geometrical Irregularities..... 316 4.3.1 Longitudinal (Axial) Holes and Longitudinally Oriented Hollow Areas............................................................................................................... 317 4.3.2 Transverse (Radial) Holes............................................................................ 318 4.3.3 Angled Holes................................................................................................. 320 4.3.4 Other Factors................................................................................................. 321 Control of Distortion and Prevention of Cracking................................................ 324 Accessory Equipment and Work Handling for Heat Treating............................ 335 4.5.1 Robots, Gantries, and Pick-and-Place Units.............................................. 335 4.5.2 Hoppers and Magazines.............................................................................. 336 4.5.3 Conveyors...................................................................................................... 336 4.5.4 Rotary Tables................................................................................................. 337 4.5.5 Unscramblers and Bar Feeders................................................................... 337 4.5.6 Cylindrical Part Feed Mechanisms............................................................ 337 4.5.7 Pipe and Tube Handling Equipment......................................................... 337 4.5.8 Basket-to-Basket Systems for Long Products............................................ 338 4.5.9 Strip Heating Mechanisms.......................................................................... 338 4.5.10 Accessory Systems for Processing Large Steel Plates.............................. 338 4.5.11 Work Holding Centers................................................................................. 339 Tempering of Induction-Hardened Components.................................................. 339 4.6.1 General Comments Regarding Tempering............................................... 339 4.6.2 Self-Tempering (“Slack Quenching”).........................................................344 4.6.3 Induction Tempering and Its Features....................................................... 347 4.6.3.1 Coil Design and Process Parameters.......................................... 349 4.6.3.2 Flux Manager Technology for Stress Relief of Oil Country Tubular Goods............................................................................... 356 4.6.3.3 C-Core Inductors........................................................................... 370 4.6.4 Final Remarks................................................................................................ 374

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4.7

4.8

4.9

Magnetic Flux Control Techniques: Concentrators, Intensifiers, Shunts, and Shields.................................................................................................................. 376 4.7.1 Electromagnetic Shields............................................................................... 377 4.7.2 Magnetic Shunts............................................................................................ 379 4.7.3 Magnetic Flux Concentrators...................................................................... 379 4.7.3.1 Physics of the Magnetic Flux Concentration............................. 380 4.7.3.2 Design and Application Features............................................... 381 4.7.3.3 Selection of the Flux Concentrator Materials............................ 383 4.7.3.4 Advantages and Drawbacks of Using Magnetic Flux Concentrators................................................................................. 386 Heat Treating Equipment Maintenance.................................................................. 389 4.8.1 Power Supply................................................................................................. 390 4.8.1.1 Visual Inspection........................................................................... 390 4.8.1.2 Mechanical Test............................................................................. 390 4.8.1.3 Ohm-Meter Tests........................................................................... 390 4.8.1.4 Power Measurements (Meter or Oscilloscope)......................... 391 4.8.1.5 Meters and Limit Lamps.............................................................. 391 4.8.1.6 Audible and Visual Observation................................................. 391 4.8.2 Heat Station, Bus Connections, and Inductor Foot.................................. 392 4.8.2.1 Visual.............................................................................................. 392 4.8.2.2 Mechanical Test............................................................................. 393 4.8.2.3 Ohm-Meter/Capacitor/Meter/Load Frequency Analyzer...... 393 4.8.2.4 Audible and Visual Observation................................................. 393 4.8.3 Water Recirculating System........................................................................ 394 4.8.3.1 Visual.............................................................................................. 394 4.8.3.2 Meter Measurement...................................................................... 394 4.8.3.3 Pressure Flow and Temperature Measurement........................ 394 4.8.3.4 Audible and Visual Observation................................................. 395 4.8.4 Quench Recirculating System..................................................................... 395 4.8.4.1 Visual.............................................................................................. 395 4.8.4.2 Meter Measurement...................................................................... 396 4.8.4.3 Pressure Flow and Temperature Measurement........................ 396 4.8.4.4 Audible and Visual Observation................................................. 396 4.8.5 Heat Treating Inductor Maintenance and Storage................................... 396 4.8.5.1 Consistent Workpiece Holding................................................... 396 4.8.5.2 Keeping the Inductor Clean......................................................... 396 4.8.5.3 Visual Inspection........................................................................... 397 4.8.5.4 Maintain Electrical Contacts....................................................... 397 4.8.5.5 Maintaining Spares....................................................................... 398 4.8.6 Flux Concentrators........................................................................................ 398 4.8.7 Heat-Treating Machinery Maintenance.....................................................400 4.8.7.1 Visual..............................................................................................400 4.8.7.2 Audible and Visual Observation.................................................400 4.8.7.3 Safety Circuits................................................................................ 401 Review of Selected IHT Applications..................................................................... 401 4.9.1 Gear, Pinion and Sprocket Hardening...................................................... 401 4.9.1.1 Material Selection and Required Gear Conditions before Heat Treatment.................................................................. 403

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4.9.1.2 Overview of Hardness Patterns..................................................404 4.9.1.3 Coil Design and Heating Mode.................................................. 406 4.9.2 Hardening of Steering Racks...................................................................... 421 4.9.3 Induction Hardening Raceways for the Wind Energy Industry...........422 4.9.4 Induction Hardening of Crankshafts........................................................425 4.9.4.1 Introduction...................................................................................425 4.9.4.2 Technologies for Crankshaft Heat Treating.............................. 426 4.9.4.3 Summary Regarding SHarP-C Technology.............................. 435 4.9.5 Induction Hardening of Camshafts........................................................... 436 4.9.5.1 Scan Hardening............................................................................. 437 4.9.5.2 Single-Shot Hardening................................................................. 438 4.9.5.3 Static (Nonrotational) Hardening...............................................440 4.10 Solutions for Solving Typical IHT Problems: Questions and Answers.............442 4.10.1 Case Study #1. The Power-Scan Rate-Hardness Relationship................442 4.10.2 Case Study #2. Cryogenic Coil Cooling.....................................................443 4.10.3 Case Study #3. Chain Hardening...............................................................443 4.10.4 Case Study #4. Hardness at Diameter Change in Scan Hardening of Stepped Shafts..........................................................................................444 4.10.5 Case Study #5. Quenchant pH and Corrosion..........................................445 4.10.6 Case Study #6. Copper Coil Wall Thickness vs. Coil Life.......................445 4.10.7 Case Study #7. Residual Magnetism..........................................................446 4.10.8 Case Study #8. Heating with Variable Axial Gaps between Long Rods................................................................................................................448 4.10.9 Case Study #9. Hallow Shafts with Holes and Splines...........................448 4.10.10 Case Study #10. Graphs of Hardened Case Depth vs. Power................. 450 4.10.11 Case Study #11. Induction Tempering and Residual Stress Distribution.................................................................................................... 451 4.10.12 Case Study #12. Soft Spots after Grinding................................................ 453 4.10.13 Case Study #13. Safety Warning for People with Pacemakers, Metallic Implants, etc................................................................................... 453 4.10.14 Case Study #14. Re-Hardening of Already Hardened Parts................... 455 4.10.15 Case Study #15. Etched vs. Unetched Samples in Crack Detection....... 456 4.10.16 Case Study #16. Induction Heating of Ultra-Thin Conductive Coatings.......................................................................................................... 457 4.10.17 Case Study #17. Distortion of Shafts in Induction Hardening............... 457 4.10.18 Case Study #18. Uniform Heating of Steel Plates..................................... 459 4.10.19 Case Study #19. Circumdeferential Hardness Variation Using Single-Shot Inductors................................................................................... 460 4.10.20 Case Study #20. Non-Martensitic Structures in Induciton Hardened Parts............................................................................................. 461 5. Joining Applications...........................................................................................................463 5.1 Brazing and Soldering by Induction.......................................................................463 5.1.1 Overview........................................................................................................ 465 5.1.2 Types of Joints............................................................................................... 466 5.1.3 Size and Shape Factors................................................................................. 467 5.1.4 Frequency Selection...................................................................................... 468 5.1.5 Types of Inductors and Coil Design Features........................................... 469 5.1.6 Overview of Filler Materials and Flux Selection...................................... 473

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5.1.7 Fixturing and Handling.............................................................................. 475 5.1.8 Summary........................................................................................................ 477 5.2 Bonding....................................................................................................................... 478 5.3 Cap Sealing................................................................................................................. 481 5.4 Shrink Fitting.............................................................................................................. 482 5.5 Motor Rotor Heating..................................................................................................484 6. Induction Mass Heating..................................................................................................... 487 6.1 Applications, Design Approaches, and Fundamental Principles of Induction Mass Heating before Metal Hot and Warm Working.................... 487 6.1.1 Hot and Warm Working Steels................................................................... 488 6.1.2 Stainless Steels and Superalloys................................................................. 490 6.1.2.1 Stainless Steels............................................................................... 490 6.1.2.2 Superalloys..................................................................................... 492 6.1.3 Steel Surface Oxidation and Scaling.......................................................... 495 6.1.4 Target Temperatures. Factors Associated with Steel Overheating........ 502 6.1.5 Design Concepts........................................................................................... 507 6.2 In-Line IH of Long Cylinder Bars and Rods.......................................................... 516 6.2.1 Electrothermal Nature of In-Line IH......................................................... 516 6.2.2 Longitudinal and Transverse Cracks......................................................... 522 6.2.3 Transient Processes and Nose-to-Tail Temperature Profiles.................. 522 6.2.4 Energy Efficiency of In-Line Cylinder Bar and Rod Heaters................. 525 6.3 Billet Heating.............................................................................................................. 527 6.3.1 IH of Steel Billets........................................................................................... 527 6.3.1.1 Progressive Heating of Billets..................................................... 527 6.3.1.2 Maximizing Flexibility of Induction Billet Heaters................. 536 6.3.1.3 Static Heating of Billets................................................................ 539 6.3.2 IH of Nonferrous Billets............................................................................... 547 6.3.3 Hybrid Designs: Induction + Gas Furnace versus Gas Furnace + Induction........................................................................................................ 551 6.3.3.1 Induction Is Followed by Gas Furnace....................................... 551 6.3.3.2 Gas Furnace Is Followed by an Induction Heater.................... 551 6.4 Bar/Billet/Rod End Heating.................................................................................... 552 6.5 Billet/Slug Heating for Semisolid Processing........................................................ 556 6.5.1 Nature of Semisolid Processing and Basic Phenomena.......................... 557 6.5.2 Shortcomings of Mathematical Modeling of IH for Semisolid Casting............................................................................................................ 559 6.5.3 Technological Aspects of Commercial IH Systems for SSM Forming.... 561 6.6 Intricacies of Induction Wire/Cable/Rope Heating.............................................. 562 6.6.1 Specifics of Design Criteria and Coil Arrangements............................... 562 6.6.2 Energy Efficiency.......................................................................................... 565 6.6.2.1 Frequency Selection...................................................................... 565 6.6.2.2 Ferrous and Nonferrous Wires................................................... 565 6.6.2.3 System Geometry Factor.............................................................. 566 6.6.3 Commercial Aspects of Induction Wire, Cable, and Rope Heaters....... 567 6.7 Tube and Pipe Heating.............................................................................................. 568 6.7.1 Specifics of IH of Tubular Products............................................................ 568 6.7.2 In-Line IH of Tubes and Pipes and Their Applications.......................... 571

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6.7.3

6.8

6.9

Selective Heating of Tubular Products: Case Studies of Typical Applications................................................................................................... 574 Slab, Plate, Bloom, and Rectangular Bar Heating................................................. 578 6.8.1 General Remarks........................................................................................... 578 6.8.2 Longitudinal Electromagnetic End Effects of Rectangular Workpiece..... 581 6.8.2.1 Nonmagnetic Slab......................................................................... 581 6.8.2.2 Magnetic Slab................................................................................. 582 6.8.3 Electromagnetic Transverse Edge Effect................................................... 583 6.8.3.1 Transverse Edge Effect of Nonmagnetic Slab........................... 583 6.8.3.2 Specifics of the Transverse Edge Effect of a Magnetic Slab.... 585 6.8.3.3 Dynamics of Transverse Edge Effect during the Heating Cycle................................................................................................ 586 6.8.4 Design Concepts of Heating Rectangular Workpieces: Case Studies of Commercial Installations................................................ 586 6.8.4.1 Static Heating................................................................................. 586 6.8.4.2 In-Line Continuous Heating........................................................ 588 6.8.4.3 Oscillating Heating....................................................................... 589 In-Line IH of Strip, Sheet, Plate, Thin Slab, and Transfer Bar.............................. 591 6.9.1 Strip-Coating Processes............................................................................... 591 6.9.1.1 Metallic Coating of Strips (Galvanizing, Galvaluming, Galvannealing, and Tinning)...................................................... 591 6.9.1.2 Nonmetallic Coatings................................................................... 598 6.9.2 Coil Design Concepts for Heating Strips, Plates, Sheets, and Thin Slabs................................................................................................................ 598 6.9.2.1 Longitudinal Flux Inductor (Solenoid Coil).............................. 599 6.9.2.2 Transverse Flux Induction Heater.............................................. 603 6.9.2.3 Traveling Wave Induction Heater............................................... 606 6.9.2.4 Channel-Type Edge Heaters........................................................ 607 6.9.2.5 C-Core Edge Heaters.....................................................................608 6.9.2.6 Doorless Technology for Strip Processing Lines...................... 609

7. Power Supplies for Modern Induction Heating............................................................ 611 7.1 Power–Frequency Combinations............................................................................. 611 7.2 Elements of Power Electronics................................................................................. 611 7.2.1 Inductors........................................................................................................ 613 7.2.2 Capacitors....................................................................................................... 614 7.2.3 Litz Wire and Cable...................................................................................... 614 7.2.4 Vacuum Tubes and Power Semiconductors.............................................. 614 7.2.4.1 SCR or Thyristor............................................................................ 614 7.2.4.2 Diode or Rectifier.......................................................................... 615 7.2.4.3 Transistors...................................................................................... 615 7.2.4.4 Vacuum Tube Oscillators............................................................. 618 7.2.4.5 Power–Frequency Application of Semiconductors.................. 618 7.3 Types of IH Power Supplies...................................................................................... 618 7.3.1 Rectifier or Converter Section..................................................................... 620 7.3.1.1 Full-Bridge Uncontrolled Rectifier.............................................. 620 7.3.1.2 Phase-Controlled Rectifier........................................................... 621 7.3.1.3 Uncontrolled Rectifier followed by Regulator.......................... 621 7.3.1.4 Active Three-Phase Rectifiers..................................................... 623

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7.3.2 7.3.3

7.4

7.5

7.6

Importance of Good Input Line Power Factor.......................................... 624 Input Line Harmonics and Their Reduction............................................ 624 7.3.3.1 Recommended Distortion Limits............................................... 625 7.3.3.2 Solutions to Power Factor and Harmonic Problems................ 626 7.3.4 Inverter Section............................................................................................. 627 7.3.4.1 Full-Bridge Inverter....................................................................... 627 7.3.4.2 Half-Bridge Inverter...................................................................... 628 7.3.4.3 Voltage-Fed Inverters with Simple Series Load........................ 628 7.3.4.4 Voltage-Fed Inverter with Series Connection to a Parallel Load (LC-LC)................................................................................. 631 7.3.4.5 Voltage-Fed Inverter with Series Inductor Connected to a Parallel Load (L–LC)............................................................. 632 7.3.4.6 Full-Bridge Current-Fed Inverters.............................................. 632 7.3.4.7 “E” Bridge Current-Fed Inverter................................................. 635 7.3.4.8 Single-Switch Inverter.................................................................. 636 7.3.5 Advances in Power Supply Control........................................................... 636 7.3.5.1 Circuit Boards................................................................................ 637 7.3.5.2 Fault Detection............................................................................... 637 7.3.5.3 Communication............................................................................. 638 7.3.6 Operational Considerations........................................................................ 638 7.3.6.1 Initial Cost...................................................................................... 638 7.3.6.2 Operating Cost............................................................................... 638 7.3.6.3 Reliability and Maintainability................................................... 639 7.3.6.4 Flexibility........................................................................................ 639 Load Matching........................................................................................................... 639 7.4.1 Prelude to the Discussion of Load Matching............................................ 639 7.4.2 Understanding Load Matching for IH.......................................................640 7.4.2.1 Basic Concept.................................................................................640 7.4.2.2 A Simple Example.........................................................................642 7.4.2.3 Parallel and Series Connected Load Circuits............................642 7.4.2.4 Load-Matching Procedures.........................................................643 7.4.2.5 Load-Matching Component Connections................................. 651 7.4.3 Summary........................................................................................................ 653 Medium- and High-Frequency Transformers for Heat Treating and Mass Heating........................................................................................................................ 653 7.5.1 AC/DC Reactors............................................................................................654 7.5.2 Instrumentation Transformers....................................................................654 7.5.3 Heat Station Transformers...........................................................................654 7.5.4 Ferrite-Core Transformers........................................................................... 655 7.5.5 Toroidal Transformers.................................................................................. 656 7.5.6 Integrated Magnetic Transformers............................................................. 657 7.5.7 Rectangular (C-Core) Transformers........................................................... 657 7.5.8 Narrow-Profile Transformers...................................................................... 658 7.5.9 Air-Core Radio Frequency Transformers.................................................. 658 7.5.10 Maintenance, Sizing, and Specification of Transformers........................ 659 Special Considerations for Power Supplies............................................................ 659 7.6.1 Duty Cycle..................................................................................................... 660 7.6.2 Rapid Cycling of Heat On and Off............................................................. 660

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7.6.3 Precise Control of Power and Time............................................................ 660 7.6.4 Minimum Utilization of Floor Space......................................................... 661 Special Considerations for Induction Brazing, Soldering, and Bonding........... 661 Special Considerations for IH Power Supplies in Mass Heating Applications.... 662 Special Considerations for IH Power Supplies in Strip Processing Applications................................................................................................................ 665 Simultaneous Dual-Frequency Power Supplies.................................................... 666 7.10.1 Dual Inverter................................................................................................. 666 7.10.2 Single Inverter............................................................................................... 667 7.10.3 Duty Ratio Inverter....................................................................................... 667 7.10.4 Dual Coupled Solenoid/C-Core.................................................................. 668 Inverters with Independent Frequency and Power Control................................ 668 Power Supply Cooling............................................................................................... 668 7.12.1 Water Quality................................................................................................ 669 7.12.2 Cooling Water Flow Rate............................................................................. 669 7.12.3 Cooling Water Recirculating Systems....................................................... 669 7.12.3.1 Pumps............................................................................................. 670 7.12.3.2 Heat Exchanger.............................................................................. 670 7.12.4 Common Water-Cooling Problems............................................................ 671 Process Control, Monitoring, and Quality Assurance......................................... 672 7.13.1 Prelude to Discussion of Process Control and Monitoring.................... 672 7.13.1.1 Specifics of Control and Monitoring of Induction Heat Treating........................................................................................... 673 7.13.1.2 Specifics of Control and Monitoring of Induction Mass Heating........................................................................................... 674 7.13.2 Meters and Meter Circuits........................................................................... 675 7.13.3 Features of Control/Monitoring Strategies for Induction Heat Treating versus Induction Mass Heating.................................................. 676 7.13.3.1 Induction Heat Treating............................................................... 676 7.13.3.2 Induction Mass Heating............................................................... 678 7.13.4 Basic Principles of Feedback and Control Algorithms............................680 7.13.4.1 Open-Loop Systems (Feedforward Control Systems).............. 680 7.13.4.2 Closed-Loop Systems (Feedback Control Systems).................. 681 7.13.4.3 ON–OFF Control Algorithms...................................................... 681 7.13.4.4 P, I, D, PI, and PID Control Algorithms...................................... 682 7.13.4.5 PLC Controller............................................................................... 683 7.13.4.6 Controller Tuning.......................................................................... 683 7.13.5 Energy Monitoring....................................................................................... 683 7.13.6 Profile/Signature Process Monitoring.......................................................684 7.13.7 Protective Devices and Safety Principles.................................................. 686 7.13.8 Final Remarks................................................................................................ 686

Epilogue........................................................................................................................................ 689 Appendix A: Periodic Table of the Elements........................................................................ 691 References.................................................................................................................................... 693 Index.............................................................................................................................................. 719

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Preface to the Second Edition of the Handbook of Induction Heating In the beginning there is PRICE, at the end there is COST. The difference is QUALITY. This quality insures the ability to avoid unpleasant surprises by utilizing past experience, engineering expertise, computer modeling capability and awareness of the latest advances in theoretical knowledge.

This second edition of the Handbook of Induction Heating, originally published in 2002, reflects a number of substantial advances that have taken place over the last decade in the practice and science of induction heating and heat treating, computer modeling, semiconductor power supplies, quality assurance, and process technology. This edition continues to be a synthesis of information, discoveries, and technical insights that have been accumulated at Inductoheat Inc., an Inductotherm Group company, and in industry and academia. Before beginning our work on the second edition, we were informed by CRC Press that the publication of the first edition of the Handbook of Induction Heating was an undisputable success. During the first 10 years, this book has continued to be on the publisher’s “bestseller” list. An overwhelming amount of letters and calls of appreciation regarding the publishing of the first edition have supported our belief that by writing the Handbook, we have succeeded with our effort to provide the industry and academia with a helpful engineering guide to modern induction heating and heat treating. Some materials presented in the first edition have been completely rewritten for the second edition. Several chapters have been expanded significantly, including but not limited to the following: • Metallurgical insights of induction hardening of steels, cast irons, and powder metallurgy components; effect of rapid heating on the kinetics of austenite formation; and specifics of induction hardening of different steel grades are examples of such. Also, the impact of prior microstructure, its heterogeneity, and the presence of the residual elements on the results of heat treatment are reviewed. • A number of innovations related to induction heat treating of various automotive components, including but not limited to induction surface hardening, were reviewed. Thanks to several innovative designs (patented and patent pending), important goals were achieved. For example, process flexibility in shaft scan hardening has been substantially enhanced thanks to a novel inverter design that allows controlling independently and instantly frequency and power during scanning. • Novel inductor designs have been developed. For example, in single-shot hardening of shaft-like components including output shafts, flanged shafts, yoke shafts, intermediate shafts, drive shafts, and others, a unique design inductor allows its life to be extended approximately ninefold compared to industry standard as xvii

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Preface to the Second Edition of the Handbook of Induction Heating

verified by the tool-room tags of the users. Other benefits of this remarkable technology include a measurable improvement in process robustness and dramatically reduced process sensitivity. Common misassumptions and misleading postulations associated with the theory and practice of electromagnetic induction heating are clarified in the second edition. The discussion of the causes for crack initiation and the propagation during fast heating and intense quenching and means to control or eliminate cracking has been greatly expanded. Problems associated with reaching excessive temperatures, occurrence of grain boundary liquation (incipient melting), grain coarsening, and other metallurgical factors are reviewed. A “fishbone” diagram of cracking and prevention is provided. Subtleties of induction tempering are reviewed and novel technologies are described. Advanced designs (patented and patent pending) focus on ensuring the metallurgical quality of heat-treated components and improving process robustness and machine flexibility. Intricacies and limitations of computer modeling of induction heating using commercially available codes (what managers and analysts should know) are discussed. Simple solutions for typical induction heating challenges when heat treating irregularly shaped parts are unveiled. Subtleties of quenching techniques applied to induction hardening are discussed. Several unique coil designs (patented and patent pending) are reviewed. The subject of induction contour hardening of complex geometry parts (including but not limited to gears and gear-like components, crankshafts, raceways, and other critical components) is also thoroughly discussed, describing inventions and innovations that have occurred in the last 3–5 years. Reduction of shape/size distortion of heat-treated components and elimination of the necessity of a subsequent straightening operation when hardening shaft-like components are examined. An introduction to the CamPro Technology is provided, and the achievement of an almost undetectable distortion when hardening camshafts is looked into. An appreciable amount of information is provided with respect to process annealing and stress relieving of tubular workpieces. An introduction to FluxManager Technology is provided. Aspects related to the failure analysis of hardening inductors and induction coils used in different applications and prevention of their premature failure are examined. Various design concepts and advanced process recipes/protocols were analyzed to help reduce the energy consumption of induction equipment. Novel semiconductor inverter technologies, including but not limited to simultaneous dualfrequency power supplies, and inverters with independent and instant frequency and power regulation (IFP-Technology) are studied. Essentials of induction heating of ferrous versus nonferrous metallic materials, as well as metallurgical specifics and process subtleties of induction heating billets

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and bars made of carbon steels versus microalloy steels versus stainless steels versus Ni-based superalloys, Al-based, Cu-based alloys, and so on, are reviewed. The modular design concept in induction heating for hot and warm forming is discussed with pictures of actual equipment and its description that provides ultimate system flexibility and true temperature control technology in induction billet heating. An introduction to InductoForge® Technology is provided. Best practices and recommendations related to equipment maintenance, Do’s and Dont’s items are discussed. The load-matching section was substantially updated, and engineering procedures assuring a proper “coil-to-power supply” load-matching characteristics are reviewed. Safety principles and recommendations are discussed. Special attention has been paid to modern requirements for quality assurance of components heated by means of electromagnetic induction as well as many other subjects.

This edition embarks on the next step, the design of practical, cost-effective, and energyefficient induction heating and heat-treating processes and equipment, providing numerous case studies, ready-to-use tables, diagrams, rules-of-thumb, simplified formulas, and graphs. Plots of electromagnetic fields, temperature profiles, and photographs of a variety of production installations are provided to show not only that the task has been previously accomplished but also why and how it has been done. An extensive list of references is provided here. In order to avoid an unreasonably large number of pages in the second edition, material related to metallographic sample preparation and review of basic temperature measurement techniques has been eliminated. Several excellent texts have been published exclusively covering those subjects. Therefore, we refer readers to review those texts, if required. We would also like to acknowledge the contribution of the employees of Inductoheat Inc. and Inductotherm Group Companies. Their professional attitude and commitment to quality have made them the benchmark in the induction heating and heat-treating industry and have made this work possible. We would like to acknowledge our sincere appreciation to Mr. Micah Black (Tucker Induction Systems, Inc.) for his work as coauthor of the first edition of this Handbook. Many thanks must go to the authors’ families. It goes without saying that a technical book of this magnitude requires many hours of meticulous work, hours that often have infringed upon or restricted planned family activities. We present this work in the hope that the second edition of the Handbook of Induction Heating will carry on the success of the first edition, providing an aid to practitioners, students, engineers, metallurgists, managers, and scientists revolving around induction heating technologies. Valery Rudnev, Don Loveless, and Raymond L. Cook

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Authors Valery Rudnev, FASM, is director of Science and Technology of Inductoheat, providing assistance in developing novel induction heating and heat-treating technologies for the entire Inductotherm Group of companies. Dr. Rudnev is considered by many as one of the leading global figures in the induction heating and heat-treating industry and is known within the American Society for Materials (ASM International) and among induction heating professionals worldwide as “Professor Induction.” In 2006, Dr. Rudnev was elected as a Fellow of the ASM International in recognition of his distinguished contributions to materials science and engineering. In 2013–2016, he was elected as the chairman of the Technical Committee of the Forging Industry Association (FIA) of North America. His credits include more than 50 patents and inventions and more than 200 publications. Dr. Rudnev contributed materials to 9 handbooks devoted to various aspects of induction heating, heat treating, materials science, and computer modeling. Don Loveless was group vice president of Technology (retired) at Inductoheat Inc. and continues as a consultant. He received his electrical engineering degree from Western Michigan University. His global responsibilities included development of 14 models of induction heating power supplies including IGBT and MOS FET inverters as well as medium- and high-frequency transformers for a wide variety of applications of induction heating and heat treating. Mr. Loveless joined Inductoheat in 1972. His credits include a great deal of “know-how,” technical reports, and research and engineering publications, including his contribution to several handbooks published in the United States and Europe. Mr. Loveless has been granted 20 US patents with 12 pending and has numerous related foreign patents. His inventions include system design and process innovations as well as power electronic components, circuits, and process control strategies. He is a life member of the IEEE Industrial Applications, Power Electronics, and Industrial Electronics Societies. Raymond L. Cook was vice president of Engineering (retired) at Inductoheat Inc. He is a registered professional engineer in the State of Michigan, with a B.S. degree from Western Michigan University and an M.B.A. from Wayne State University, Michigan. Mr. Cook’s credits include a great deal of “know-how,” and he has been involved in the pioneering designs of high-, medium-, and low-frequency solid-state inverters, load-matching equipment, machine and systems designs, process control, and monitoring systems for a wide variety of induction heating and heat-treating applications including hardening, annealing, tempering, stress relieving, shrink fitting, and many others. This includes the InductoScan Technology, which has become an acknowledged standard in modern induction scan hardening. Mr. Cook has been with Inductoheat for more than 36 years. He has written numerous technical publications including several chapters for various handbooks. xxi

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