NEMA MW 820-2016 Conductor Softness Testing Methods.pdf

1、NEMA Standards PublicationNational Electrical Manufacturers AssociationNEMA MW 820-2016Conductor Softness Testing MethodsNEMA MW 820-2016 Conductor Softness Testing Methods Published by: National Electrical Manufacturers Association 1300 North 17th Street, Suite 900 Rosslyn, Virginia 22209 Approved:

2、 March 17, 2016 www.nema.org 2016 National Electrical Manufacturers Association. All rights, including translation into other languages, reserved under the Universal Copyright Convention, the Berne Convention for the Protection of Literary and Artistic Works, and the International and Pan American c

3、opyright conventions. NOTICE AND DISCLAIMER The information in this publication was considered technically sound by the consensus of persons engaged in the development and approval of the document at the time it was developed. Consensus does not necessarily mean that there is unanimous agreement amo

4、ng every person participating in the development of this document. ANSI standards, of which the document contained herein is one, are developed through a voluntary consensus standards development process. This process brings together volunteers and/or seeks out the views of persons who have an inter

5、est in the topic covered by this publication. As Secretary of the ANSI Accredited Standards Committee, NEMA administers the process in accordance with the procedures of the American National Standards Institute to promote fairness in the development of consensus. As a publisher of this document, NEM

6、A does not write the document and it does not independently test, evaluate or verify the accuracy or completeness of any information or the soundness of any judgments contained in its standards and guideline publications. NEMA disclaims liability for any personal injury, property or other damages of

7、 any nature whatsoever, whether special, indirect, consequential or compensatory, directly or indirectly resulting from the publication, use of, application, or reliance on this document. NEMA disclaims and makes no guaranty or warranty, express or implied, as to the accuracy or completeness of any

8、information published herein, and disclaims and makes no warranty that the information in this document will fulfill any of your particular purposes or needs. NEMA does not undertake to guarantee the performance of any individual manufacturers or sellers products or services by virtue of this standa

9、rd or guide. In publishing and making this document available, NEMA is not undertaking to render professional or other services for or on behalf of any person or entity. Nor is NEMA undertaking to perform any duty owed by any person or entity to someone else. Anyone using this document should rely o

10、n his or her own independent judgment or, as appropriate, seek the advice of a competent professional in determining the exercise of reasonable care in any given circumstances. Information and other standards on the topic covered by this publication may be available from other sources, which the use

11、r may wish to consult for additional views or information not covered by this publication. NEMA has no power, nor does it undertake to police or enforce compliance with the contents of this document. NEMA does not certify, test or inspect products, designs or installations for safety or health purpo

12、ses. Any certification or other statement of compliance with any health- or safety-related information in this document shall not be attributable to NEMA and is solely the responsibility of the certifier or maker of the statement. NEMA MW 820-2016 Page i 2016 National Electrical Manufacturers Associ

13、ation TABLE OF CONTENTS Foreword . ii Introduction . iii Significance and use iv Section 1 General 1 1.1 Scope 1 1.2 References 1 1.3 Definitions 1 Section 2 Test Methods 3 2.1 Stress/Strain Testing . 3 2.1.1 Summary of the Test Method . 3 2.1.2 Significance and Use 3 2.1.3 Apparatus . 3 2.1.4 Test

14、Specimen Preparation 3 2.1.5 Procedure . 3 2.1.6 Stress/Strain Curve Interpretation 4 2.1.7 Calculations 4 2.2 Low-Stress Elongation (LSE) . 4 NEMA 820-2016 Page ii 2016 National Electrical Manufacturers Association FOREWORD This publication is periodically reviewed by the NEMA Magnet Wire Section f

15、or revisions considered to be necessary to keep it up to date with changes in technology and regulations. Proposed or recommended revisions should be submitted to: Senior Technical Director, Operations National Electrical Manufacturers Association 1300 North 17th Street, Suite 900 Rosslyn, Virginia

16、22209 MW 820 was developed by the Magnet Wire Section of NEMA. At the time this edition was approved, the Magnet Wire Section had the following members: Condumex Inc. Mxico, D.F., Mxico Elektrisola Inc. Boscawen, NH Essex Group Inc. Fort Wayne, IN Magnekn San Nicolas, NL, Mxico MWS Wire Industries W

17、estlake Village, CA Rea Magnet Wire Company Inc. Fort Wayne, IN NEMA MW 820-2016 Page iii 2016 National Electrical Manufacturers Association INTRODUCTION The testing of conductor “softness” incorporates different metallurgical principles such as ductility, malleability, and surface hardness characte

18、ristics. The purpose of MW 820 is to present different wire testing methodologies used by magnet wire manufacturers and users to characterize the “softness of the conductor” in order to predict how well the magnet wire will wind and be formed into its final desired shape and position. NEMA 820-2016

19、Page iv 2016 National Electrical Manufacturers Association SIGNIFICANCE AND USE NEMA MW 1000 describes two different conductor softness test methods. Total percent elongation and springback test methods and specifications are described in NEMA MW 1000, part 3, section 3.4, Elongation, and section 3.

20、7, Springback. The intent is not to duplicate these test methods, but it is important to recognize and reference them in this publication. Other test methods for conductor malleability and formability need to be described. Maximum formability is desirable because it facilitates winding magnet wire m

21、ore compactly, yields coils that will retain their shape best after removal from the winding forms, and permits the most rapid possible winding with minimum force, minimum wire breakage, and reduced abrasive effects. Each of these test methods provides a more significant measure of formability than

22、do tests for hardness, tensile strength, or total percentage of elongation. These test methods do not necessarily cover identical zones of the total stress-strain region. The springback method employs mild bending, hence a combination of elongation and compression. The low-stress elongation method e

23、mploys very slight elongation, and the elastic ratio method employs the greatest elongation. Both the low-stress elongation and springback methods allow the deformed film-insulated magnet wire to return partially or entirely to the unstressed condition, while the elastic ratio method does not. NEMA

24、MW 820-2016 Page 1 Section 1 General 1.1 Scope This publication describes ultimate tensile, yield strength, elastic ratio, low-stress elongation (LSE), and Rockwell hardness test methods and the equipment that may be used to determine these measurements. 1.2 References The following references are t

25、o the current revision of each of the standards listed below: The Aluminum Association, Inc. 1525 Wilson Blvd. Suite 600 Arlington, VA 22209 ANSI: H35.1 American National Standard Alloy and Temper Designation Systems for Aluminum American Society for Testing Materials 100 Barr Harbor Drive West Cons

26、hohocken, PA 19428-2959 ASTM B152 Standard Specification for Copper Sheet, Strip and Rolled Bar ASTM B233 Standard Specification for Aluminum 1350 Drawing Stock for Electrical Purposes ASTM B279 Standard Test Method for Stiffness of Bare Soft Square and Rectangular Copper and Aluminum Wire for Magne

27、t Wire Fabrication ASTM D1676 Standard Test Methods for Film Insulated Magnet Wire ASTM E18 Standard Test Methods for Rockwell Hardness of Metallic Materials National Electrical Manufacturers Association 1300 N. 17th Street, Suite 900 Rosslyn, Virginia 22209 NEMA MW 1000 Magnet Wire 1.3 Definitions

28、elongation (of magnet wire): maximum percent that a magnet wire can be stretched before it ruptures or breaks, also referred to as its breaking point elastic ratio/modulus (of magnet wire): ratio of load at 5 percent elongation divided by load at break, expressed as a percentage value formability (o

29、f magnet wire): characteristic that permits the magnet wire conductor to maintain the shape into which it has been formed hardness/indentation hardness: depth of penetration of an indenter under a large load compared to the penetration made by a preload low-stress elongation (LSE) (of magnet wire):

30、amount of permanent deformation caused by short-time application of a force near the yield strength, expressed as a percentage of elongation of the magnet wire malleability (of magnet wire): characteristic of the magnet wire conductor that allows it to be stretched and formed into shape NEMA 820-201

31、6 Page 2 2016 National Electrical Manufacturers Association modulus/elastic modulus/modulus of elasticity/Youngs modulus: calculation obtained by dividing tensile stress by extensional strain in the elastic (initial, linear) portion of the stressstrain curve; the elastic modulus of an object is defi

32、ned as the slope of its stressstrain curve in the elastic deformation region strain: ratio of the change in some length parameter caused by the deformation to the original value of the length parameter stress: force causing a deformation divided by the area to which the force is applied tensile stre

33、ngth/ultimate tensile strength (UTS) (of magnet wire): applied force required to elongate a magnet wire to its breaking point divided by the cross sectional area of the conductor windability (of magnet wire): characteristic that allows film-insulated magnet wire to be manufactured into a coil with a

34、 minimum of physical and electrical damage and the maximum of formability and compaction. work hardening (of magnet wire): loss of malleability and formability resulting from the bending or stretching of magnet wire yield strength (of magnet wire): force required to begin deformation of the magnet w

35、ire, usually described when the magnet wire is elongated 0.2 percent; also referred to as the 0.2 percent offset yield strength divided by the cross-sectional area of the conductor NEMA MW 820-2016 Page 3 2016 National Electrical Manufacturers Association Section 2 Test Methods 2.1 Stress/Strain Tes

36、ting 2.1.1 Summary of the Test Method The conductor is slowly elongated to break, and a stress-strain diagram is recorded by the elongating instrument. 2.1.2 Significance and Use This test method is applicable to all sizes and shapes of copper and aluminum film-insulated magnet wire. The material, f

37、ilm build, and cure of insulation on the conductor has only minor influences on the testing results, since the majority of the cross-sectional area is due to the conductor. These tests are not typically performed on magnet wire where the insulation is fiberglass, polyester/fiberglass, or polyimide t

38、ape wrapped, as these insulation coverings may influence the test results. 2.1.3 Apparatus Use a tensile testing machine that is capable of recording or indicating load (stress) and elongation (strain) simultaneously with a full scale bias of within 0.5 percent in each range. The range of the instru

39、ment used in this test method shall be chosen that load values and elongation percentages can be read on the recording with a precision of 1.0 percent. The jaws shall be designed to preclude slippage or breaking at the jaw. Select an appropriate load cell so the stress level will be within the cente

40、r of the range. 2.1.4 Test Specimen Preparation Cut a magnet wire specimen with an effective gage length of 10 0.1 in. (250 2.5 mm). Extra length is necessary to place in the jaws of the stress/strain tester. Handle it carefully so that no bending occurs except for straightening with a minimum amoun

41、t of work hardening prior to insertion in the jaws. No elongation of the specimen shall be performed prior to the test. Determine the dimensions of the film-insulated magnet wire. Determine the dimensions of the magnet wire conductor after using a suitable means of removing the insulation and not de

42、forming the conductor cross-sectional area. Microscopic measurement of a properly mounted specimen may also be used. The dimensions of the conductor are used in all of the calculations. 2.1.5 Procedure After insertion of the specimen in the jaws, eliminate any noticeable curvature or slack in the wi

43、re specimen. The initial specimen length after removing the slack in the specimen shall be considered the gage length. Elongate the specimen at a rate of elongation not to exceed 10 in./min. (250 mm/min.). Test a minimum of three specimens. NEMA 820-2016 Page 4 2016 National Electrical Manufacturers

44、 Association 2.1.6 Stress/Strain Curve Interpretation A = Cross-sectional area F = Force I = Initial sample length L = Final sample length E = Elastic ratioslope = F/A = strain = I/L elongation or stress 1: True elastic limit 2: Proportionality limit 3: Elastic limit 4: Offset yield strength Figure

45、1 Typical yield behavior for non-ferrous alloys 2.1.7 Calculations Elongation: (Final length (cross head displacement) original gage length / original gage length) x 100 Tensile: Ultimate tensile strength is the maximum engineering stress (applied load divided by the original conductor cross-section

46、al area of the specimen) in a uniaxial stress-strain test: UTS = max force / conductor cross sectional area (A) Yield strength: The point in the stress-strain curve at which the curve levels off and plastic deformation begins to occur. When a yield point is not easily defined based on the shape of t

47、he stress-strain curve, an offset yield point is arbitrarily defined. The value for this is commonly set at 0.1 or 0.2 percent strain. An 0.2 percent offset yield is the force at 0.2 percent elongation divided by the original conductor cross sectional area: 0.2 percent yield = Force 0.2 percent elon

48、gation (using the slope of the elastic ratio) / A Elastic ratio: Divide the load obtained at 5 percent elongation, under stress, by the load at break; this quotient, multiplied by 100, is the elastic ratio. Modulus, elastic modulus, modulus of elasticity, Youngs modulus, n: calculated by dividing th

49、e tensile stress by the extensional strain in the elastic (initial, linear) portion of the stressstrain curve. The elastic modulus of an object is defined as the slope of its stressstrain curve in the elastic deformation region represented by “E” in the attached stress/strain curve. 2.2 Low-Stress Elongation 2.2.1 Summary of Test Method The specimen is elongated to a specified low-level stress per unit cross-sectional area. The permanent elongation resulting from this short-term low-level stress exposure is taken as a measure of formability/mal