chicago '93 eeic/icwa · chicago '93 eeic/icwa exposition rosemont convention center •...

PETITIONERS' EXHIBIT 1122 PAGE 1 OF 12

PROCEEDINGS: ELECTRICAL ELECTRONICS INSULATION CONFERENCE

AND ELECTRICAL MANUFACTURING & COIL

WINDING CONFERENCE

CHICAGO '93

EEIC/ICWA EXPOSITION

Rosemont Convention Center • Rosemont, Illinois October 4-7, 1993

INTERNATIONAL COIL WINDING

ASSOCIATION, INC.

~ Institute of Electrical We and Electronic Engineers

'u.~l) National Electrical Manufacturers Association

IEEE Catalog Number ISBN 0-7803-0846-8 ISBN 0-7803-0847-6 ISBN 0-7803-0848-4 Library of Congress ISSN: 1071-6270

93CH3219-3 (softbound) (caseboundl (microfiche) Number 76-641188

Additional copies may be obtained from :

ISBN:

IEEE Service Center 445 Hoes Lane Piscataway, NJ 08854

0-7803-0847-6 0-7803-0848-4

ICWA PO Box 278 Imperial Beach, CA 91933 Phone: 619-575-4191 Fax: 619-575-5009

Casebound Microfiche

IEEE Catalog Number: 93CH3219-3

Library of Congress Number: ISSN 1071-6270 Serial

Copyright and Reprint Permissions: Abstracting is permitted with credit to the source. Libraries are permitted to photocopy beyond the limits of U.S. copyright law for private use of patrons those articles in this volume that carry a code in the bottom of the first page, provided the percopy fee indicated in the code is paid through the Copyright Clearance Center, 29 Congress Street, Salem, MA 01970. Instructors are permitted to photocopy isolated articles for noncommercial classroom use without fee. For other copying , reprint , or republ ication permission, write to Director, Publishing Services, IEEE, 345 East 47th Street, New York, NY 10017. All rights reserved. Copyright © 1993 by The Institute of Electrical and Electronics Engineers, Inc.

PAGE 2 OF12

OF 12

Table of Contents

Epoxy Insulation

Tuesday, October 5, 1993, 8:30 AM

Session Director: John Bullivant - Consultant

The Effect of Electric Ageing on a Cast Epoxy 1 Insulation

Y. Li, J. Unsworth & B. Gao - University of Technology

Dynamic Mechanical Behaviours of Epoxy Insulating 7 Composites

Y. Li and J. Unsworth - University of Technology

Monitoring of Electrical Properties of Particulate 13 Filled Epoxy Resins Under Corrosive Stress

Bodo Brilhl and Lutz Niemeyer ASEA Brown Boveri Corporate Research Centre

Recent Progress in Computer Simulation Applied in 17 the Automatic Pressure Gelation (APG) Process For Epoxy Casting Systems

D. Konig, R. Reichert and I. O. Vlase - Technical University of Darmstadt, HV·Lab E. Hubler and U. MaBen - CIBA·GEIGY

Vacuum Sand - Casting System for Electric and Electronic Parts

E. Omori, M. Suzuki and K. Yasu· Hitachi Chemical

Motor Manufacturing


Session Director: Bill R. McCoy United Technologies Automotive

Current Technology in Stator Lacing Warren C. Brown - Link Engineering Company

New Trends in Stator Testing Donald R. Walter· Machine Products Corporation

Increasing the Efficiency of Induction Motors Dr. Michael Braun - PSW Industries

Noise Problems of Appliance Drain Pumps Ciineyt Oztiirk & Ahmet Balik~ioglu . Ar(:elik A. S.

PA46 Nylon - The Driving Material for E-Motors Jack Koenen, Lisa Krause and David Pomerantz

DSM Engineering Plastics, Inc.

25

29

33

41

45

53

ix

Coil & Transformer Manufacturing

Tuesday, October 5, 1993,9:00 AM

Session Director: James F. Lord Transformer Design & Manufacturing Consultant

Transformer Design Using Windows Paul K. Goethe and William D. Goethe

Optimized Program Service, Inc.

Multi-tasking Using Magnetic Design Analysis Software

Douglas Austin IT - Espey Mfg. & Electronics Corp.

Trickle Impregnated CoiIs Using Solvent Free, Single Part Epoxy

Steven B. Garbukas and Greg Palmer Copps Industries, Inc.

Low Pressure Encapsulation of Coils, Transformers and Electronic Assemblies with Thermosetting Liquid Molding Compound

Gene Segerson and Dr. Ronald Hunadi Thermoset Plastics, Inc.

Process Techniques

Tuesday, October 5, 1993,9:00 AM

Session Director: Francis P. Murphy· Consultant

57

65

71

73

Techniques and Thermoplastics for Encapsulating 81 High Performance Coils

James F. B. Patterson, J. Lang and M. Hozumi Du Pont Polymers

Tools for Commutator Turning 85 Dellburt Kitzel . E. C. Kitzel & Sons, Inc.

Considerations About the Influence of Different 91 Process Parameters During Vacuum Casting

Gerhard Karl Mais Wilhelm Hedrich Vakuumanlagen GmbH & Co. KG

Comparative Tracking Index of PSA Insulation for 97 Electrical Equipment Component Design Accounting to UL 1950

Leroy Herauf, Treasa Grasso and T. S. Kim 3M Electrical Specialties Div.

OF 12

EASA Day Technical Session


Session Directors: W. Brithinee - Brithinee Electric N. FIolo - The Flolo Corp .

Motor Repair Industry Response to the Energy Policy 105 Act of 1992: A Status Report

Thomas H. Bishop, P.E. - Longo Industries

One Multi-Location Network's Approach to 109 Environmental Stewardship In the 19905

G. H. Miller and V. V. Shearin - GE Apparatus Service

Practical Approaches to ISO 9000 for 115 Small-To-Midslze Company

Paul R. Vragel - Vragel & Associates, Inc. Mike Margitan - Active Industries

What is a Commutator? 121 George Strayer - Kirkwood Commutator

Rotating Electrical Equipment, Maintenance and Repair

Theo van Vliet - General Electric Canada Inc.

Magnet Wire - NEMA Tuesday, October 5, 1993, 9:30 AM

Session Director: Leon Molloy - ALCATEL

127

NEMA Magnet Wire Technical Committee Report 133 Ken Nair - Magnetek Lighting & Electronic Products

The New MW 1000 Standard 137 Thomas J. Cussen - Rea Magnet Wire Co., Inc.

International Winding Wire Standards 141 A Status Report

Steven Darling - Elektrisola, Inc.

Evaluation of A Carbonized Foam Electrode for D.C. 147 High Voltage Continuity Testing of Magnet Wire

Donald J. Barta and Christopher M. Weidman Phelps Dodge Magnet Wire Co.

A New Mathematical Modeling Approach to NEMA 153 Magnet Wire Dimensional Standards For Fine Sizes

David A. Metzler and Everett J. Scherrer Rea Magnet Wire Company, Inc.

x

Magnet Wire - General

Tuesday, October 5, 1993, 1:30 PM

Session Director: Dennis Paure - General Electric

Nonpolluting Solid Lubrication of EnameUed Wires 165 Gerhard Boockmann and F. Fichtner - Boockmann GmbH

The Relative Solvency and Viscosity Effects of 173 CresyUc Acid Isomers on High Solids Wire Enamel

Lynn M. Wells & M. Howard Strunk, Jr. - Merichem Co.

Development and Application of New Self-Bonding 179 Magnet Wires with Self-Lubricating Properties

Masuo Suzuki, Hideo Doshita, Masahiro Koyano and Makoto Tai - Optec Dai-Jchi Denko Co., Ltd.

Development of Laser Strlppable New Heat Resistant 185 Magnet Wire

T. Maezono, A. Higashiura, F. Sano and N. Nakamura Furukawa Electric Co., Ltd., Hiratsuka R&D Lab.

Insulating Material and Assessment Part 1


Session Director: WiUiam A. Nesgoda - General Electric

Overview of Our Heritage 191 W. Tillar Shugg - Shugg Enterprises, Inc.

Evaluation of Impregnates Designed for All-Film 195 Power Capacitors Engineering: Electric Conduction and Breakdown

Christian Brosseau - CERMO Universite Joseph Fourier

Thermal Aging Effects on the Electrical Properties of 201 FUm and Ceramic Capacitors

Eric Overton, Eric D. Baumann and Ira T. Myers - NASA Lewis Research Center and Ahmad N. Hammoud Sverdrup Technology, Inc. NASA Lewis

OF 12

A Fresh Look at Permanent Magnet Processing


Session Director: Earle S. Seely - Walker Scientific, Inc.

Permanent Magnets in Review 207 Roger Petrie - Tlwmas & Skinner, Inc.

Efficient Magnet Charging and Conditioning 211 Earle S. Seely - Walker Scientific Inc.

Jack M. Janicke - Magnetic Research, Inc.

Effective Magnetic Measurements . 215 Rollin J. Parker and Joseph C. Nowlan

Walker Scientific, Inc.

The Hysteresisgraph As a Quality Control Tool 221 Eric 1. Dennison - Walker Scientific Inc.

Permanent Magnet Motor Magnetizing 229 and Calibrating

James William Aydelott - Magnetic Instrwnentation Inc.

Multi-pole Magnetization of High Resolution 237 Magnetic Encoders

Yin-Jao Luo, E-Tuen Hwang and Shih-Ming Huang Servo Control Dept. - Mechanical Industry

Research Lab., Industrial Technology Research Institute

Coil Design, Winding & Assembly Considerations


Session Director: Joseph Pizzonia Coil Winding Equipment Co.

Toroidal con Winding Machines - Making , the Best Choice

Nadeem I. Mirza - CCW Industries

243

Precision Wire Stripping 251 John M. Cole P.E. and James C. Malloy

Kolene Corporation Jeff Riedel - Ford Motor Company

Miniature con Winding Techniques Provide 255 Reliability & Longevity to Disk Drive Components

Michael D. Branch - Storage Technology Corporation

Self-Supporting Coiis - Choosing the Best Procedures 259 Bernard F. Cecire - Spectra, Inc.

Mounting & Packaging Techniques for Toroidal 261 Devices

Harold Tischler - Torelco, Inc.

xi

High Volume Motor Manufacturing in the Automotive Sector



Metallurgical Aspects in High Volume 263 Copper Bonding

John G. Smeggil, Ph. D. and Elizabeth A. Rasley United Technologies Research Center

New Designs Aid Engineering Thermoplastics for 271 Small Motor Assemblies

J. J. Hanrahan, William J. Hassink and Warren E. Kenney DuPont Polymers

Epoxy Bonding of Magnets for Permanent 275 Magnet Motors

Todd Irion - Engineered Materials Systems Inc.

Commutator Turning: The Tool is Only the 281 Tip of the Solution

John N. Carter - Carter Diamond Tool, Corp.

Advanced Methods of Motor Testing 287 Jeff Jugan - Schenck Turner

Transformer Insulation

Wednesday, October 6, 1993, 8:30 AM

Session Director: Werner Heideman - EHV Weidmann

New U.L. Classification for Silicone Transformer Fluid

James L. Goudie and Sharon K. Mort Dow Coming Corporation

291

High Temperature Operating Capabilities of Silicone 297 Transformer Fluid

George A. Toskey - Dow Coming Corporation

Load Break Switching in Silicone Transformer Fluid 303 Sharon Mort and James Goudie - Dow Coming Corp.

Donald Ristuccia -ABB PowerT&D Co.

Corrosive and Non-Corrosive Sulfur in 309 Transformer Oils

T. V . Oommen - ABB Power T &D Company Inc.

New Cable for Advanced Power Transformer 313 Windings

Keith D. Bultemeier - Phelps Dodge Magnet Wire Co.

OF 12

Rotating Machinery - Insulation Systems

Wednesday, October 6, 1993,8:30 AM

Session Director: J. S. Edmonds - MCM Enterprise

Inorganic Bonded Mica Paper for Commutator and High-Temperature Applications

Arthur F. Doyle and Dennis Sklarski - Essex Group Inc.

New High Voltage Insulation with Increased Thermal Conductivity

A. Lutz and Dr. Rudolf BrUtsch - Von Roll Isola, The Swiss Insulating Works Ltd. G. Liptak: and R. Schuler - ABB Drives AG

Improved Mica Groundwall Insulation Via Grafted Polymers

James D. B. Smith and Rajendar K. Sadhir Westinghouse Science and Technology Center

Preliminary Evaluation of Motor Insulation for Variable Speed Application

Robert H. Rehder - General Electric Canada, Inc.

An Improved Sleevlng Insulation for Use of VPI Form-Wound Coils

L. Gerald Landry, James H. McGean and Fabian Nunez Essex Group

Electric Field Enhancement Studies on Stator Windings with Defect Sites Using Finite-Element Computation

S. E. CherukupaUi, G. L. Halldorson and H. E. Orton PowerTech Labs B. Huggins - B. C. Hydro

Magnetics in Transformers


Session Director: Carl R. Tufts - Consultant

317

323

329

333

337

345

Comparison of 9 Mil, 11 Mil, and 14 Mil 353 Ferro-resonant Transformer Design

Carl R. Tufts - Consultant

Trends of Power Applications - New Ferrite Materials 359 and Optimized Core Shapes

JOrgen Hess - Siemens Matsushita Components

Frequency Characteristics of Ferrite Core Inductors 369 Manikantan K. Jutty, Venkatramani Swaminathan and

Marian K. Kazirnierczuk - Wright State University

Alnico Permanent Magnets an Overview 373 Achuta S. Rao, Ph. D., Thomas & Skinner, Inc.

xii

Quality Considerations in Manufacturing Electrical Components


Session Director: Kent Robertson - Black & Decker, Inc.

World Class Manufacturing Sudershan K. Jetley - Bowling Green State University

Joseph Catalano - Marathon Special Products

High Quality, Low Cost Assembly Using the Injected Metal Assembly Process

Dave Wawrykow - Fishertech, Div. of Fisher Gauge Ltd.

Thermal Effect on the Torque-Speed Performance of a Brushless DC Motor

Barry K. Fussell - University of New Hampshire

Robotic Visual Servoing in a Flexible Manufacturing WorkceU

Todd E. Scaggs - Wright State University

Assembly Techniques in Manufacturing Motors


Session Director: Phil Kohlhaas 3M Electrical Specialties Division

385

397

403

413

Electrostatic Fluidized Bed - System Innovations and 419 Powder Advancements

Mark R. Strucaly - Electrostatic Technology, Inc.

Customer's Voice In Commutator Engineering 425 Manfred Hinderer - Kautt & Bux Manufacturing Co.

Reducing Motor Costs Through Chemistry 435 Charles H. Brickley - Polychem Corp.

Fundamental Process and Test Considerations in 439 Room Cure Trickle

Paul C. Dreier - Liquid Control Corporation

"Heatless Cure" - Coating of Electrical Windings 443 Thomas J. Weiss - Thomas & William Machinery Co.

OF 12

Magnet Wire - Testing


Session Director: Glen Clouse - Essex Group, Inc.

Origins of High Voltage Continuity Failures in Enamel Coated Copper Magnet Wire

Horace Pops and Julie Walker - Essex Group Inc.

Frequency Characteristic of Magnet Wires M. Hatada, S. Amano, T . Sawamoto and K. Ueda

Fujikura Ltd.

457

485

Moisture Resistance of Thin Film Electrical Insulation . 489 A Comp.arison of Test Methods

John C. Yodis and Scott K. Pearsall Schenectady International Inc.

SPC for Magnet Wire Tony Greene - Essex Group, Inc.

Magnet Wire - Freon Free Refrigerant Applications

Wednesday, October 6, 1993, 1:30 PM

Session Director: Kichizo Ito - Fujikura Ltd.

493

Responding to the CFC Challenge 495 Thomas W . Dekleva - ICI Klea

R. W. Yost ICI Americas, Inc.

Resistance of Electrical Insulating Varnish to 501 Environmentally Friendly Refrigerants

Robert A. Allen - Schenectady International Inc.

Polyester Insulation Materials, HFC Refrigerants 505 and Ester Lubricants

M. S. Sefton, S.V. Mortlock and M. A. Harding ICI Films and S. Corr and Gordon Tompsett ICI Chemicals & Polymers Ltd.

CompatibiUty of Non-Metallic Motor Components 507 with R22 & RS02 Replacement Refrigerants

S. Corr, T. W. Dekleva, P. Dowdle and Gordon Tompsett ICI Chemicals & Polymers Ltd. and John Allison, and Dr. RudolfBriltsch - Von Roll Isola

CompatibiUty of Alternative Refrigerants with Varnished Magnet Wire

Robert Doerr, Ph. D. and Stephen Kujak The Trane Company

513

xiii

Transformer Insulation


Session Director: Werner Heideman - EHV Weidmann

Comparison of Mechanical Strengths of Three Materiais Used as Pressure Plates in Oil-Filled Transformers

R. A. Kurz, Sr. - Custom Materials Inc.

Advantages of Corrugated Transformer Insulation James E. Vachris - Franklin Fibre-Lamitex Corp.

Development of New Insulation System for Use in Oil-Filled Transformers

Thomas M. Golner - Magnetek

Sensitivity of Identified Transfer Functions in Transformer Diagnosis

S. D. Mikkelsen, J . Bak-Jensen, B. Bak-Jensen and J. Tolstrup Sorensen - Aalborg University

Rotation Machines - Insulation Systems


Session Director: J . S. Edmonds - MCM Enterprise

519

525

529

533

Automated Digital Winding Test Analysis Methods 539 Stefan Schlichting - Baker Instrument Co.

Comparative Performance of Woven Glass and 545 Polyester Film Backed Micaceous Tapes for the Insulation of High Voltage A.C. Stator Windings of Rotating Electrical Machines

H. S. McNaughton GEC ALSTHOM Large Machines LId.

Verification oflnsulation Temperature Class Through 553 Weight Loss Measurements

James E. Ttmperley American Electric Power Service Corp.

Voltage Endurance Test Facility for Electric 557 Generator Stator Coils

F. T. Emery and R. F. Weddleton Westinghouse Electric Corp.

Experience Gained Performing Thermal Cycling Tests 563 Robert Rehder, Bernard Moore and Robert Draper

General Electric Canada, Inc.

OF 12

Wire and Cable Insulation

Wednesday, October 6, 1993, 1 :30 PM

Session Director: Robert Gear - US!

Repeated Failures and Water Treeing In Polyethylene 569 HV Cables

Dr. Tadeusz Czaszejko - Mcnash University

The Mechanism and Behaviour of Water Treeing In 573 Polymeric Materials

W. M. Al-Hasawi - College of Technological Studies Dr. A. A. Hossam-Eldin - Alexandria University A. J. Pearmain - Queen Marry College

Morphology and Chemical£omposition of Water 579 Trees In Mineral-Filled EPR Insulation .

James Xu and Andrew Garton - University of Connecticut Electrical Insulation Research Center

Commutator Fusing



A Systematic Approach to Process Control In Commutator Fusing

Federico Sba1chiero - Axis SpA Geoffrey pazzanese Axis USA

Commutator Fusing and Brazing Miniature Motors to Starter Motors

Edward D. Riordan - Joyal Products Inc.

An Overview of Commutator Fusing Technology William T. Egbert and Jon S. Wells - MicaJiI, Inc.

Efficient Fusing Using AC of DC Current Eric Kirker - Odawara Automation, Inc.

Verifying Armature Fusing Quality Allan Naegeli - Electronic Systems of Wisconsin

585

591

597

601

605

xiv

Armature Balancing: Process, Standards, and Trends


Session Director: Stephen Reimann - Vibratech Systems

Advantages and Applications for Two Station 613 Balancing Machines

Peter A. Ehlers - Schenck Trebel

Establishing Balance Tolerances For Armatures 619 G. Hines and M. Myers - Hines Industries, Inc.

Process and Product Considerations of Armatures by 627 Metal Removal

T. Jeff Franklin ill, American Hofmann Corporation

Standardization of Balancing Methodology In Motor 631 Manufacturing

Stephen J. Reimann - Vibratech Systems

Insulation Materials and Assessment Part 2

Thursday, October 7, 1993,8:30 AM

Session Director: William A. Nesgoda - General Electric

Precision Ovens for Thermal Endurance Evaluation of 635 Electrical Insulating Material

Rudolf R. Steinhaus - BASF Lacke + Farben AG

Evaluation of Electrical Material Properties: 639 Embedment Stress Testing on Electrical Encapsulation Resins

Diana Melick, D. Browning and K. Shelton Elf Atochem North America, Inc.

An Optical Technique to Detect the Degradation of 643 Electrical Insulation

S. S. Bamji, A. T. Bulinski and J. Shen National Research Council of Canada

Polymer Concrete High Voltage Insulation: A 649 Versatile Material for the 90's and Beyond

Muthian Gunasekaran - Sekar Enterprises

Evaluation of Surface Degradation of Polymer 655 insulating Materials Related to Lea~ge Current

H. Homma, T. Takahashi, T. Taniguchi .and K. Izumi Electrical Engineering Dept., Yolwsuka Research Laboratory

OF 12

Rotating Machines - Diagnostic Testing

Thursday, October 7, 1993, 8:30 AM

Session Director: James Timperley - AEP

Advantages of High Voltage DC Dielectric Tests 661 Compared with AC Tests

Alain Audoli and Jean-Louis Drorruni Electricite De France

New Technology for Partial Discharge Testing of 667 Operating Generators and Motors

Greg C. Stone - Iris Power Engineering and H. G. Sedding - Ontario Hydro

On-Line Monitoring of Partial Discharge in Rotating 673 Machine Windings & Auxiliaries Including the use of External Sensors

Y. Aksenov, M. Golovkov and V. Arsentiev - DIACS, Z. Berler, D. Kral and R. Sloss Northern States Power J. C. Bromley and W. McDermid - Manitoba Hydro

In-Service Monitoring of Stator Insulation Condition of a Large Thermal Generator

V. J. Green - FES International Ltd. A. G. Seidel Houston Lighting & Power

Advanced Methods for Continuous Insulation Condition Monitoring on Hydrogenerators

Greg C. Stone - Iris Power Engineering and James S. Edmonds - MCM Enterprise LTD.

Wire and Cable Insulation

Thursday, October 7, 1993,8:30 AM

Session Director: Robert Gear - USI

681

685

Moisture Cross-Linkable Insulation Compounds with 691 Flame-Retardant Properties

C. Mahabir and S. Haridoss - AT Plastics Inc.

The Effect of Interfacial Interaction on Charge 697 Storage in Clay Filled LDPE

Weijun Yin, John Tanaka and Dwight Damon University of Connecticut Electrical Insulation Research Center

Study on Life Estimation of Cable Insulation by Gas 703 Evolution and Oxygen Consumption During Radiation and Thermal Aging

T. Okuda, K. Kanemitsuya and K. Furukawa Mitsubishi Cable Industries, LTD., T. Yagi and T. Seguchi Japan Atomic Energy Research Institute

xv

Coil & Transformer Manufacturing


Session Director: James F. Lord Transformer Design & Manufacturing Consultant

Computer Design of AC and DC Inductors 707 Robert Kakalec - Energy Systems Technical Services, Inc.

Joseph Hubert - Independent Consultant Energy Systems

Transformer Design for Low Cost Battery Chargers 713 Richard M. Haas - Avex Electronics Inc.

Shielding and Magnetic Field Reduction for Small and 719 Medium Size Transformers and Reactors

Harold O'Connor Espey Manufacturing & Electronics Corp.

Coil Bobbin and Encapsulated Coil Plastics for the 725 1990's

S. B. Neher, M. Lana Sheer, Ph. D. and W. E. Garrison Du Pont Polymers

Applied Quality Functions in Electrical & Coil Winding Manufacturing


Session Director: Dr. John W. Sinn Center for Quality, Measurement & Automation, Bowling Green State University

Introduction and Overview of Statistical Process 729 Control

Dr. John W. Sinn - Bowling Green State University

Applying Machine Vision in Electrical Component 737 Manufacturing

David V. Gedeon and Topher D. Gedeon Bowling Green State University

Cause & Effect Analysis: Power Tool for Total Quality 751 J. E. Gibson - Black & Decker (U.S.) Inc.

Subject and Edition Index 755

OF 12

TECHNIQUES AND THERMOPLASTICS FOR ENCAPSULATING HIGH PERFORMANCE COILS

J. F. B. Patterson J. Lang

M. Hozumi

DuPont Polymers Wilmington, Delaware

ABSTRACT

The use of thermoplastic encapsulated transformers, sensors, solenoids, motor stators and other assemblies is soaring rapidly. This is due in part to the "electronic cars" of the 1990's with their numerous requirements for corrosion resistant sensors and solenoids, in part to the continuing trend to convert mechanical control systems to electromechanical controls, and in part to environmental pressures on volatile organic compound emissions (VOCs).

Thermoplastic encapsulation can also lead to part consolidation, a reduction in assembly operations compared with traditional potting methods, and enhanced physical support against vibration and mechanical shock.

This paper reviews recent developments in thermoplastic encapsulation materials, molding techniques, and mold design for encapsulating high performance coils. It also covers recently developed encapsulation systems for UL 1446 Class F (155 C) and Class H (180 C) applications.

Figure 1: 250 and 400 W choke transformers for lighting are encapsulated with PET polyester resin.

81

INTRODUCTION

At the 1990, 1991 and 1992 ICWA conferences, we reported on the encapsulation of transformers and small coils (1,2,3). We described the basic materials and processes used in the encapsulation of sensors, solenoids, contactors, motor stators, and transformers. This paper builds on the earlier presentations with new information about work with larger transformers, test procedures for encapsulation resins, delicate sensor encapsulations, and progress toward UL 1446 Class F (155 C) and Class H (180 C) recognition for encapsulation systems.

DISCUSSION

Thermoplastic encapsulation of transformers and small coils continues to grow very rapidly. Part of the growth is due to a rapid increase in the number of sensors for automotive electronic systems. These sensors need the durability that thermoplastic encapsulation provides. Other factors in the growth of encapsulation include environmental pressures on potting processes, general requirements for improved product reliability and safety, and the need to reduce part counts and simplify assembly.

This growth has created a need for modified resins and technology for more difficult encapsulations, including transformers larger than 500 VA, delicate electronic sensors, and coils/transformers requiring thermal cycling to temperatures in the 150-200 C range.

Transformers

The injection molding techniques and thermoplastic resins for encapsulating small transformers are well established. Smaller transformers in the range of 50 to 200 VA can be encapsulated on vertical clamp molding equipment while somewhat larger transformers can be accommodated on horizontal molding equipment with

shot sizes of up to 500 grams (see Figure 1).

For transformers in the 1 kVA or larger range, encapsulation with conventional injection molding equipment becomes difficun and expensive. Molds strong enough to support heavy 2-to-3-kVA transformers. for example, are themselves extremely expensive .

Another problem with encapsulating larger transformers is the tendency for cracks to occur in the encapsulation layer at the weld lines during thermal cycling in the 150 to 200 C range. This is attributed to the differences in the coefficients of linear thermal expansion between the encapsulation resin and the metal laminations of the transformers.

To avoid the problems of cost and weld line weakness,

we turned to compression molding with moldable composite sheet. We use paper-making technology to convert glass fibers and either nylon 6,6 or PET polyester fibers into a mat. The mat is cut into sections of the desired weight, dried and heated in a convection oven, and then compression molded around the transformerto encapsulate it . Figure 2 shows the process as compared to injection molding.

Using this technique, we have successfully encapsulated 3 kVA transformers whose encapsulation layers have successfully withstood repeated thermal cycling to 200 C.

Thermal cycling testing

Thermalcycling performance is an important indication

Process Comparison

INJECTION

Pellets Convey & Dry

RAW PREPARE FOR MATERIAL ~ MOLDING

COMPRESSION

Porous Sheet Cut & Stack

PAGE 11 OF 12

•

Figure 2

82

WiL7kkD1 Screw I Barrel Injection

'-_H_E_AT_ ..... I_-l~~ I. __ M_O_L_D

_ ...

Convection Heating

Compression

of performance in actual service for many encapsulations. To test the ability of resin compositions to withstand thermal cycling, we have developed a very simple test procedure that has found wide application in qualifying resins for encapsulating sensors and solenoids.

Forthe test, a steel ferrule is encapsulated with a 0.12-in. layerof the resin being evaluated. The ferrule is 1.3 in. long and 1.26 in. in diameter, and its shoulders are sharply machined. Figure 3 shows a ferrule and encapsulations ready for testing.

The encapsulated ferrule is tested for 7 cycles of 16 hours at 150 C followed by 8 hours at 40 C. Ahhough this test is not identical to standard thermal cycling tests , it has been used successfully to screen and compare the pertormance of a number of resins.

Pan suppon

It is essential to keep a component being encapsulated proper1y aligned in the molding tool. We have found that this can be done successfully with hydraulicallydriven pins that hold the component in place while resin is injected into the mold cavity. These pins retract just before the resin becomes solid, and continuing injection pressure from the molding machine supplies molten resin to fill voids that would result from the withdrawal of the pins .

When the mold is opened, the pins are extended to eject the finished part and stay in position to support the next component to be encapSUlated.

An alternative method uses fixed pins . The voids left in the part are filled using ultrasonic welding techniques.

Progress toward Classes F (155 C) and H (180 C)

Ahhough needs for most encapsulated transformers and coils can be met with a UL 1446 Class B (130 C) insulation system recognition, there is a trend toward requiring higher temperature classes. The industry is moving toward more compact components and assemblies that operate at higher temperatures than were common in the past.

Using the steel ferrule test described above and a resin

PAGE 12 OF 12 83

Figure 3: Steel ferrule (left) is encapsulated with thermoplastics for thermal cycle testing.

with a very low dissipation factor, we have been able to produce coils that have recently received provisional Class F and Class H recognitions.

SUMMARY

Starting lrom a relatively modest beginning, thermoplastic encapsulation is finding increasing use in sophisticated wound coil applications . Advances in design, molding technology, and resin composition have extended applicat ions lor e ncapsula! ion I ar beyond the initial expectations of many people in the industry. Driven by strong economic forces, encapsulation is a growth technology for the future .

References·

(I)J. F. B. Patterson and C. N. Johnson, "Thermoplastic encapsulation of coil forms,ff presented al the International Coil Winding Association Conference. Chicago, 111., October 1990.

(2) J. F. B. Patterson, ~Advances in thermoplastic coil encapsulation ," presented at the International Coil Winding Association Conference, Boston, .Mass., October 1991 . (3) G. D. Neal, J. F. B. Patterson, B. C . Golt and J. Deeble, "Advances in thermoplastic encapsulation of transformers and small wound coils,~ presented at the International Coil Winding Association Conference , Cincinatti, Oh., September 1992.

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