1、SAE Technical Standards Board Rules provide that: “This report is published by SAE to advance the state of technical and engineering sciences. The use of this report is entirelyvoluntary, and its applicability and suitability for any particular use, including any patent infringement arising therefro
2、m, is the sole responsibility of the user.”SAE reviews each technical report at least every five years at which time it may be reaffirmed, revised, or cancelled. SAE invites your written comments and suggestions.QUESTIONS REGARDING THIS DOCUMENT: (724) 772-8512 FAX: (724) 776-0243TO PLACE A DOCUMENT
3、 ORDER; (724) 776-4970 FAX: (724) 776-0790SAE WEB ADDRESS http:/www.sae.orgCopyright 1991 Society of Automotive Engineers, Inc.All rights reserved. Printed in U.S.A.SURFACEVEHICLE400 Commonwealth Drive, Warrendale, PA 15096-0001INFORMATIONREPORTJ420REV.MAR91Issued 1952-06Revised 1991-03Superseding J
4、420 MAR81(R) MAGNETIC PARTICLE INSPECTION1. ScopeThe scope of this SAE Information Report is to provide general information relative to the nature anduse of magnetic particles for nondestructive testing. The document is not intended to provide detailedtechnical information, but will serve as an intr
5、oduction to the theory and capabilities of magnetic particletesting, and as a guide to more extensive references.2. References2.1 Related PublicationsThe following publications are provided for information purposes only and are not arequired part of this document.2.1.1 SAE PUBLICATIONAvailable from
6、SAE, 400 Commonwealth Drive, Warrendale, PA 15096-0001.AMS 2640Magnetic Particle Inspection, 1969.2.1.2 ASM PUBLICATIONSATTN: MSC/Book Order, ASM International, PO Box 473, Novelty, OH 44072-9901.Metals Handbook, Ninth Edition, Vol. 17, Nondestructive Evaluation and Quality Control, 1987. Metals Han
7、dbook, Eighth Edition, Vol. 11, 1976, pp. 4475. 2.1.3 ASTM PUBLICATIONSAvailable from ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959ASTM E 125Reference Photographs for Magnetic Particle Indications on Ferrous Castings ASTM E 269Standard Definitions for Terms Relating to Magnetic Parti
8、cle InspectionASTM E 709Recommended Practice for Magnetic Particle Examination 2.1.4 OTHER PULICATIONSNondestructive Testing Handbook, Vol. 6, Magnetic Particle Testing, 1989, American Society forNondestructive Testing, Columbus, OH 43228C. E. Betz, “Principles of Magnetic Particle Testing,“ Magnafl
9、ux Corp., Chicago, IL, 1985MIL-M-6867Magnetic Inspection Units, Department of DefenseMIL-STD-1949Inspection, Military Standard, Department of DefenseMIL-STD-410Qualification of Inspection Personnel, Department of DefenseProgrammed Instruction Handbook PI-4-3, Magnetic Particle Testing. Convair Div.,
10、 General DynamicsCorp., 1967SAE J420 Revised MAR91-2-SNT-TC-1A Nondestructive Testing and Certification, 1984, American Society for Nondestructive Testing,Columbus, OH 43228Tool and Manufacturing Engineers Handbook, Vol. 4, Quality Control and Assembly, 1987, Society ofManufacturing Engineers, Dearb
11、orn, MI 481213. GeneralMagnetic particle inspection is a nondestructive means of inspecting ferromagnetic materials suchas iron and steel for discontinuities (cracks, seams, near surface inclusions) by the detection of leakage fieldsthrough the use of magnetic particles.Magnetic particle inspection
12、is an aid to visual inspection of objects. Surface or near surface discontinuitiesthat might not be seen with the aid of optical magnification are regularly detected in manufacturing operationsor maintenance. The process is not applicable to nonmagnetic materials. The usual basic steps in magneticpa
13、rticle inspection of an object are: clean, magnetize, apply magnetic particles, inspect, and demagnetize.Post cleaning is frequently done. Magnetic particle inspection is a relatively simple procedure. It is mosteffective when the various factors, such as types of magnetization, current, particles,
14、equipment, and method,are properly selected for the application.4. PrincipleThe principle of magnetic particle inspection is the accumulation of particles due to magnetic fluxleakage at discontinuities in a magnetized test object. The material subjected to the inspection is magnetizedin a fashion wh
15、ich will produce north and south poles on opposite edges of a discontinuity. Finely dividedmagnetic particles are introduced into the flux leakage field between the poles, and are held there by themagnetic leakage flux. The visible accumulation of these particles is called an indication.5. Procedure
16、A magnetic field is induced in the part to be tested by the application of an electric currentthrough the part, or through a central conductor inserted through a hole in the part, or by means of a yoke,prods, or coil. The type of magnetization selected is determined primarily by the need to establis
17、h magneticflux lines perpendicular to the direction of anticipated surface imperfections. Any discontinuity at or near thesurface of the part will interrupt the magnetic flux induced in the part and a leakage field will be formed at thesurface of the part. Magnetic particles in the vicinity of this
18、leakage field will be attracted to it, forming a visibleindication which, to experienced interpreters, expresses the characteristics of the discontinuity. Following thecreation of the indication, the interpretation of the indication, and the evaluation of the discontinuity, the part issuitably demag
19、netized and, where required, cleaned.Adequate light must be provided for the quick and sure detection of the indications of discontinuities. Lightsshould be adjusted to give broad highlights on finished machine parts. If fluorescent lighting is used, the tubesshould be located transverse to the long
20、 axis of the parts being inspected. A nominal illumination level of108 1x (100 ft-c) of white light should be present on the part surface in the case of nonfluorescent inspection.Personnel should have eyesight, corrected or uncorrected, capable of distant vision of 20/30 in at least one eyeand shoul
21、d be able to read Jaeger Type No. 2 with both eyes at 305 mm (12 in).An adequate source of long wave ultraviolet light (approximate 3650 , colloquially known as black light) mustbe provided for inspection when using the flourescent magnetic particle inspection method. A filtered high-pressure mercur
22、y vapor source is generally recommended. The emitted light should have an intensity of 97 1x(90 ft-c) at a 380 mm (15 in) distance from the source, or no less than 140 mW cm2 (900 mW in2) on the partsurface. For detection of certain fine indications, illumination at the part surface may need to be a
23、s high as270 1x (250 ft-c). Personnel vision requirements are the same as for nonfluorescent inspection, but in addition,visual acuity in the green-yellow spectrum must be satisfactory.SAE J420 Revised MAR91-3-Demagnetization consists of removing objectionable residual magnetic fields from parts whi
24、ch have beensubjected to magnetic particle inspection. This must be done to prevent the deflection of adjacent sensitiveinstruments and to prevent the attraction of small magnetic chips, or the like, which could cause damage tocontacting surfaces. The most common type of demagnetization consists of
25、drawing the magnetized partthrough a high intensity alternating current solenoid. Another type, often used on heavier parts, consists ofpassing an alternating current or reversing direct current through the part or through a surrounding solenoid,and then gradually reducing the current value to near
26、zero. Demagnetization is sometimes effected insubsequent processing, such as heat treatment, or hot washing, of a part. Effectiveness of the demagnetizingis usually determined through use of inexpensive meters made for this purpose.Irons and steels exhibit magnetic characteristics which vary with ha
27、rdness and composition. Continuousmagnetization during particle application is used on relatively soft steels since they usually do not retainsufficient magnetism to allow the use of the residual method. These steels are processed for inspection byintroducing the magnetic particles into the leakage
28、fields created at the discontinuities while the magnetizingforce is present. Parts processed in this way are said to be processed by the continuous method. Use of thecontinuous method makes possible the successful inspection of irons and steels which do not retain sufficientmagnetism for processing
29、by the residual method. In addition to this, certain subsurface discontinuities areeasily detected in both hardened and unhardened parts by this method when direct current magnetization isemployed.The residual magnetization test method may be applied to hardened steels, and other highly retentivemat
30、erials, since they will retain magnetism after the force has been removed. These remaining magnetic fieldswill produce leakage fields adjacent to discontinuities strong enough to hold magnetic particles and produceindications. Parts processed through the use of these retained fields are said to be p
31、rocessed by the residualmethod. Use of the residual method often eliminates nonrelevant indications. It is especially useful for thedetection of surface discontinuities in hardened parts. An adequate level of magnetization is required.Wet particles used in suspension liquid usually consist of finely
32、 ground magnetic iron oxide. These particlesare coated so they can be easily dispersed in a liquid vehicle. They are generally available in powder formhaving red or black nonfluorescent colors. They are also available coated with a material which fluorescesunder long wave ultraviolet (black) light.
33、Wet particles are commonly used in maintenance, process, and finishinspection of machine and engine parts. The wet process offers the advantage of ease of application of theparticles, sensitivity in locating the finest discontinuities, and, especially with the fluorescent particle, rapidinspection r
34、ates.Dry particles consist of finely divided magnetic material in powder form. These particles are coated so as to beeasily conveyed by air to the part being inspected. They are generally available in many colors for maximumcontrast with the test object. Dry particles are commonly used for the maint
35、enance, process, and finishinspection of heavy weldments, heavy castings, and heavy forgings. Dry particles are superior for theinspection of very rough surfaces and for the location of subsurface discontinuities in rough castings, forgings,and weldments.Circular magnetization consists of inducing a
36、 circular magnetic field in a part so that the magnetic lines of forcetake the form of concentric rings about the axis of the current. This is accomplished by passing the currentdirectly through the part, or by passing the current through a conductor which passes through a hole in thepart, sometimes
37、 by use of prods. The circular method is used chiefly to indicate discontinuities radiating fromand parallel to the axis of the current flow.Longitudinal magnetization consists of inducing a longitudinal magnetic field in a part by making it the core of asolenoid, such as placing it in a coil or by
38、making it a link in a magnetic circuit through use of a yoke. In a partso magnetized, the lines of force will be parallel to the axis of the solenoid, and the part will exhibit theproperties of a bar magnet. The longitudinal method is used to indicate discontinuities transverse orcircumferential to
39、the long axis of a part.SAE J420 Revised MAR91-4-Moving field magnetization consists of inducing fields in a part in more than one direction almostsimultaneously. The fields induced may be a combination of circular and longitudinal or may be a combinationof either type. The moving field method may b
40、e used on many parts ordinarily requiring two or more distinctmagnetization and inspection operations. The moving field method, because of the rapidly changing fielddirections, makes possible the location of all detectable discontinuities after only one processing. This may, insome cases, eliminate
41、a great percentage of the time required for the inspection if the parts were processed bymore conventional methods.Alternating current magnetization is commonly used for moderately stressed parts in production and for thedetection of fatigue discontinuities due to service. Alternating current magnet
42、ization is always equal to, andoften superior to, direct current magnetization for the detection of surface discontinuities. Subsurfacediscontinuities are not revealed when alternating current is used. In moderately stressed parts, this greatlysimplifies inspection.Direct current magnetization is co
43、mmonly used for highly stressed parts. It is able to disclose certainsubsurface discontinuities in addition to surface discontinuities.Half-wave direct current is commonly used in the inspection of heavy weldments, heavy castings, and heavyforgings, in conjunction with dry magnetic particles. Half-w
44、ave direct current is essentially a pulsating directcurrent. The pulsations impart mobility to the magnetic particles, thereby assisting in aligning them in theweaker leakage fields produced by subsurface discontinuities. Subsurface discontinuities are best revealed bythe use of this type current.6.
45、 Notes6.1 Marginal IndiciaThe change bar (l) located in the left margin is for the convenience of the user in locatingareas where technical revisions have been made to the previous issue of the report. An (R) symbol to the leftof the document title indicates a complete revision of the report.PREPARE
46、D BY THE SAE IRON AND STEEL TECHNICAL COMMITTEE DIVISION 25NONDESTRUCTIVE TEST METHODS OF THE SAE IRON AND STEEL TECHNICAL COMMITTEESAE J420 Revised MAR91RationaleNot applicable.Relationship of SAE Standard to ISO StandardNot applicable.ApplicationThe scope of this SAE Information report is to provi
47、de general information relative to the natureand use of magnetic particles for nondestructive testing. The document is not intended to providedetailed technical information, but will serve as an introduction to the theory and capabilities of magneticparticle testing, and as a guide to more extensive
48、 references.Reference SectionNondestructive Testing Handbook, Vol. 6, Magnetic Particle Testing, 1989, American Society forNondestructive Testing, Columbus, OH 43228C. E. Betz, “Principles of Magnetic Particle Testing,“ Magnaflux Corp., Chicago, IL, 1985Metals Handbook, Ninth Edition, Vol. 17, Nonde
49、structive Evaluation and Quality Control, 1987, ASMInternational, Metals Park, OH 44073ASTM E 125, Reference Photographs for Magnetic Particle Indications on Ferrous Castings, AmericanSociety for Testing and Materials, Philadelphia, PA 19103ASTM E 269, Standard Definitions for Terms Relating to Magnetic Particle Inspection, American Societyfor Testing and Materials, Philadelphia, PA 19103ASTM E 709, Recommended Practice for Magnetic Particle Examination. American Society for Testingand Materials, Philadelphia, PA 19103MetalsHandbook, Eighth Edition, Vol. 11, 1976, pp.
