US2478772A

US2478772A - Method and apparatus for magnetic inspection

Info

Publication number: US2478772A
Application number: US559178A
Authority: US
Inventors: Morris L Mages; Herbert T Nordstrom
Original assignee: Magnaflux Corp
Current assignee: Magnaflux Corp
Priority date: 1944-10-18
Filing date: 1944-10-18
Publication date: 1949-08-09
Anticipated expiration: 1966-08-09

Description

1949- M. L. MAGES ET AL 2,473,772

METHOD AND APPARATUS FOR MAGNETIC INSPECTION Filed Oct. 18, 1944 3 Sheets-Sheet 1 Morris L. Mayes Herbert 7T [Vafdslram K i L-E 8- 9 1949- M. L. MAGES ET AL 2,478,772

METHOD AND APPARATUS FOR MAGNETIC INSPECTION Filed Oct. 18, 1944 3 Sheets-Sheet 2 ZNr/ENZ 5755 Morris L. Hayes Herbert TA/brdsifrom Aug. 9, 1949. MAGES ETAL 2,478,772

METHOD AND APPARATUS FOR MAGNETIC INSPECTION Filed Oct. 18, 1944 3 Sheets-Sheet 3 Morris L.Mayes He bert T/Vordsfrom Patented Aug. 9, 1949 METHOD AND APPARATUS FOR MAGNETIC INSPECTION Morris L. Mages and Herbert T. Nordstrom, Chicago, Ill., assignors to Magnailux Corporation, Chicago, 111., a corporation of Delaware Application October 18, 1944, Serial No. 559,178

, 23 Claims. (Cl. 175-483) This invention relates to a method and apparatus for magnetic inspection and more particularly to a novel method and apparatus for magnetizing a magnetizable object to be tested for flaws, cracks or other defects.

In the past, it has been determined that if a ferromagnetic object such as a steel part, is magnetized and finely divided ferromagnetic particles are distributed over the surface of the object either in the form of dry filings or in the form of a liquid suspension of such particles, the particles will become densely grouped or clustered over surface portions adjacent any minute crack or subsurface defect due to the intense leakage flux present adjacent such defect.

This phenomenon may be more easily understood by assuming that a bar magnet or other magnetized object having opposite poles at the ends thereof is broken in two. The broken surfaces would in effect become additional local poles of opposite polarity and as such would abruptly change the permeability of the flux path through the object giving rise to an intense leakage flux through the air between said broken surface, as distinguished from the former distribution of the flux before the bar had been broken which was almost entirely through the bar because of its enormously greater permeability than the surrounding air. Carrying this analysis a step further, if it is assumed that only small cracks or flaws instead of a complete break should occur in a solid magnetized body, the confronting surfaces of the flaw or crack portion would, in effect, constitute local poles, thereby causing an excessive amount of leakage fluxor' magnetic fringing at the surface of the body adjacent such defect. By thereafter spreading finely divided ferromagnetic particles over the surface of the magnetized body a visual indication of the presence and location of such defects is obtained due to the tendency of the particles to cluster in the vicinity of such defects thereby providing an easy method for checking each and every manufactured part to determine whether or not such part is defective.

The reliability of such tests depends primarily upon the establishment of a strong leakage flux around any defect. Such a flux is obtained if the article is placed in a magnetic held in such a manner that the lines of force intersect the longitudinal axis or plane of the crack. It has been found in practice that defects usually occur either with their longitudinal axis substantially parallel to, or substantially transverse to the longitudinal axis of the part being tested. It has been a common practice-in the past to test for longitudinal defects by passing a current axially along the part being tested while a coil externally of the part is employed to locate transverse defects. The method of passing current through the part for locating longitudinal defects is sometimes favored commercially over the coil system for the reason that the magnetic flux completes its path entirely through the metallic magnetized part, hence it is possible to produce a very intense magnetization of the part.

An outstanding disadvantage of this method is that it is not applicable to a wide variety of parts. For example, there is danger of burning the part at the contact points because of high currents used. Also, very small parts are difflcult to handle between contact heads, thus requiring a somewhat complicated mechanism to obtain proper handling faciilties and consuming considerable time for testing. For this reason a coil system is found to be advantageous particularly for locating longitudinal defects.

An object of the present invention is to provide a novel method and apparatus for testing for a longitudinal defects in a magnetizable metal part by subjecting the part solely to the influence of a magnetic field without passing current directly therethrough.

A further object of the present invention is to provide a novel method and apparatus for tramversely or circularly magnetizing a cylindrical. ferromagnetic part to be tested for flaws.

Another object of the present invention is to provide a novel yoke construction associated with magnetizing coils for magnetizing ferromagnetic parts.

A still further object of the present invention is to provide a novel method and apparatus for intermittently feeding and intermittently applying a magnetic field to magnetizable articles.

A still further object of the present invention is to provide a novel method and means for magnetizing uniformly shaped metal articles to be tested for defects to cause the magnetic flux to flow through the article in a manner to preclude coincidence between the line of entry or exit of the flux and the entire length of the defect.

A still further object of the present'invention is to provide a magnetizing yoke having novel laminated alternately staggered elemental pole faces.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and method of operation and manner of construction, together with further objects and advantages thereof, may best be understood by reference to the accompanying drawings, in which:

Figure 1 is a plan view of one embodiment of the present invention illustrating a feeding mechanism, a magnetizing yoke for magnetizing an article and a tank containing ferromagnetic particles in fluid suspension for detecting flaws in said article;

Figure 2 is a side view of the apparatus shown in Figure 1;

Figure 3 is an enlarged cross-sectional view taken along the line III-III of Figure 1;

Figure 4 is an enlarged cross-sectional view taken along the line IV-IV of Figure 2;

Figure 5 is an enlarged partial cross-sectional view taken along the line V-V of Figure 1;

Figure 6 is an enlarged view or one of the pole faces of the magnetizing yoke shown in Figures 1, 2 and 5;

Figure '7 is an end view taken along the line VII-VII of Figure 1;

Figure 8 is an enlarged cross-sectional view taken along the line VIII-VIII of Figure 5;

Figure 9 is a diagrammatic illustration of the staggered laminations of the magnetizing yoke as well as the body therebetween to be tested, illustrated in more detail in Figures 5 and 6; and

Fi ure 10 is a schematic illustration of an electrical circuit for magnetizing the magnetizing coils.

Referring more particularly to Figures 1 and 2, numeral I denotes an object to be tested for flaws such as, for example, a cylindrical roller bearing which is allowed to roll down an inclined plane 2 guided laterally by a pair of

guide rails

2 and 4. The roller surface of the inclined plane 2 is'covered with a sheet of varnished cambric or other suitable material clamped in position. The varnished cambric is thus easily replaceable after excessive wear takes place. The

guide rails

2 and 4 are adjusted transversely by means of a plurality of

screws

5, 6, 'l and 8, thereby making it possible to accommodate any particular size of roller bearing, for example, those from onehalf inch to about three inches in length. A motor 9 is provided which drives through suitable reduction gearing In to rotate a driven member or wheel ll. Wheel comprises two disks I2 and I: (see Fig. 8) clamped together. Each of the disks l2 and I2 has a V-shaped notch (see Figure 5), hence by rotatably displacing disks l2 and It the size of the V-shaped common opening may be changed as desired to accommodate different sized cylindrical objects. It is desirable that the V-shaped opening enclose slightly more than half of the roller hearing I. Set screw i5 is tightened so as to couple disk ii to the drive shaft l6. Set screw I1 is also tightened so as to firmly clamp disks l2 and I2 together. Notched disks H and I2 can be turned independently of motor 9 due to the presence of a clutch [4 in the motor drive. As will be observed in'Figure 3, clutch element l4 and drive shaft it are coupled by a. plurality of spring-pressed balls. A cam I8 is also rigidly secured to drive shaft l6, which cam actuates a micro-switch l9 as it rotates to close a circuit to allow energizing current to flow through

electromagnet coils

20 and 2| associated with a magnetizing yoke 22. Coil 20 is located above the top of table 2! whereas coil 2| is located below the table top.

Cores

24 and 25 associated with

coils

20 and 2| respectively are laminated and each lamination has a' V-shaped point which comes in close proximity to the surface of the roller hearing. The upper core 24 is supported so that the object I being tested will barely clear plate 29 of copper, or other suitable material, forming the yoke face. When

coils

20 and 2| are energized the spring action of the upper yoke support should allow the upper yoke face to actually make contact with the object I. Cam I8 should be adjusted so as to actuate micro-switch I9 at the proper time. That is, the current through the

magnetizing coils

20 and 2| should be turned on when the object almost reaches the center of the magnetizing coils, If the magnetizing coils are energized too soon object I may be shot past the coils with considerable force. If the current comes on too late, object I may roll past the magnetizing coils and then be attracted to the center of the coils.

Assuming object I is in alignment with the axes of

coils

20 and 2|, then by applying an energizing current for a period, for example, of a halfsecond or longer object I becomes magnetized. The magnetic field existing between the pointed pole faces of

cores

24 and 25 will extend transversely through object I and will divide substantially into two parallel, semi-circular paths as indicated more clearly in Figure 9 thereby applying substantially circular, or more accurately, semi-circular magnetization to object I. By application of such magnetization, that is, whereby the magnetic lines of flux are disposed substantially circularly, the best conditions are obtained for detecting longitudinal cracks or flaws at the surface or slightly thereunder whose planes are substantially radial. In other words, longitudinal defects, such as seams or grinding checks, will be at right angles to the magnetic flux path, hence will create a leakage field of maximum intensity in the air or other surrounding medium immediately adjacent such defect.

If the laminations of

cores

24 and 25 were arranged such that their respective points were in alignment thereby concentrating the magnetic flux path at the points of contact with the object in the form of a thin sheet of magnetic flux, the flux would separate essentially into two semicircular magnetic paths as described before and would magnetize the object so that surface defects at right angles to the semi-circular magnetic paths would be readily detectable by later applying finely divided ferromagnetic particles thereon. In the event, however, that the defect comprised a flaw whose plane coincided withsaid thin sheet of flux throughout the entire length of the flaw, the magnetic flux would go around both sides of the defect and would not cause an intense local leakage flux, hence such flaws would not be detectable. Such flaw positions are referred to as blind spots and necessitate the rotation of the object about 90 degrees and remagnetization in order to insure that no defects are present at the blind spots. Such rotation and remagnetization appreciably increases the time required for testing, hence is objectionable in large scale testing operations.

In accordance with our invention the lamina tions of

cores

24 and 25 are shaped as shown in Figure 9 and are reversed in the stacking operation so that the successive V-shaped points are staggered 'in the manner shown more clearly in Figures 6 and 9. By such staggering, alternately dissimilar magnetic paths on successive disc-like portions of object I are formed so that defects which are of greater length than the width of the lamination will not escape detection. In other words, if a portion of a defective crack, for example, should coincide with the small linear surface provided by a single lamination illustrated at the right of either pole in Figure 9 thereby causing no intense leakage flux, the magnetic path provided by the lamination illustrated at the left will intersect the portion of the flaw extending beyond the width of the right hand lamination thereby causing an intense leakage field which can be subsequently detected. A suitable width of laminations for magnetizing the roller bearings l is about one-fourth inchwith one-fourth inch spacing between the points of successive laminations. The V-shaped points may define angles of about 60 degrees. It should be understood, however, that the above dimensions are mentioned merely by way of example and are by no means limiting insofar as our novel laminated core structure is concerned.

After the object I is magnetized, coils 20 and 2| "are de-energized allowing object I to roll into a basket 30. Basket 30 is supported on the top of table 23 by arms 3! integrally secured to handle 32. Springs 33 secured to the supporting shaft 34, normally bias the handles into the position shown in full lines, namely above the surface of the inspection liquid contained in tank 35. The inspection liquid comprises finely divided ferromagnetic particles in liquid suspension. When tray 30 is filled with objects to be tested handles 32 may be pulled inwardly and the tray 30 lowered into tank 35 to the position shown in dotted lines in Figure 5, so as to submerge the objects in the testing liquid for a period of about two minutes or more to allow the ferromagnetic particles to cluster about defective portions that may be present in the objects. During this time another tray may be set into position to receive another load of objects to be tested by the liquid. The longer the time during which the objects are immersed, the more pronounced the indications will be. The inspection liquid is circulated in the path shown by arrows'in Figure 2 by means of circulating pump 36 which forces liquid through a plurality of nozzles 31 to effect agitation of the liquid and keep the ferromagnetic particles in liquid suspension.

Figure shows a suitable electrical system for energizing the

coils

20 and 2|. A 115 volt, 60 cycle, single phase supply line 40 may be used to energize the motor of circulating pump 33 and drive motor 9. Motor 9 is controlled by switch 4|. A line current of the order of 20 amps. may be drawing during energization of

coils

20 and 2! of the magnetizing yoke. A full wave rectifier comprising, for example, a pair of half-wave,

mercury vapor tubes

42 and 43, is used for converting the alternating current to direct current for the purpose of energizing coils 20 and 2i. The current passes through a four-pole main contactor 46. A red pilot light 45 indicates that the unit is connected to the line and a. green pilot light u indicates when'coils 20 and 2| are energized. A 10 mfd. condenser 41 and a pair of 20,000 ohms resistors 48 may be bridged across the contactor terminals as indicated.

It will be seen, therefore, that we have provided a novel and efiicient apparatus and method for energizing an object to be tested to avoid the occurrence of blind spots, thereby making a subsequent magnetic test reliable for the purpose of detecting the presence of fiaws and other imperfections in the object. Furthermore, we have provided an efiicient magnetizing yoke structure for insuring magnetization of a cylindrical article along substantially its entire peripheral surface. Furthermore, we have provided a. speedy method for mass scale magnetic testing of objects by which tests of about 1800 units per hour are readily realized. The expression "Ierromagnetic as used in the present speciflcation is intended in its broader sense, that is, including such metals as iron, steel, nickel, and cobalt and alloys and substantially all paramagnetic materials.

While we have shown 'a particular embodiment of our invention, it will, of course, be understood that we do not wish to be limited thereto, since many modifications may be made, and we, therefore, contemplate by the appended claims to cover all such modifications as fall within the true spirit and scope of our invention.

We claim as our invention:

1. The method of magnetizing a body which includes disposing it in a magnetic field and concentrating the lines of force of the magnetic field between a plurality of spaced offset points aligned in staggered relation on each of a pair of opposite surface portions of said body so that all portions of the body are magnetized.

2. The method of magnetizing a body which includes disposing it in a magnetic field and concentrating the lines of force of the magnetic field between two discontinuous alternately staggered surface areas each extending longitudinally of said body and transversely spaced from the other.

3. The method of magnetizing a. body which includes disposing it in a magnetic field, concentrating the lines of force of the magnetic field into a plurality of paths havin concentrated flux regions spaced longitudinally of said body between staggered lines on opposite sides of said body and directing said paths transversely of said body so that all portions of the body are magnetized.

4. The method of magnetizing a ferromagnetic body having a cylindrical surface which includes disposing it in a magnetic field, concentrating the ma netic fiux lines of said field between alternately staggered, closely spaced, points located at each of a pair of diametrically opposite surface portions of said body to effect magnetization of the body along staggered, semi-circular parallel paths.

5. The method of magnetizing a cylindrical body which includes directing a pencil-like, in-

tense sheet of magnetic fiux along diametrically.

opposite portions of an incremental disc-like portion of said body and simultaneously directing a separate pencil-like, intense sheet of magnetic flux along diametrically opposite portions of a second incremental disc-like portion adjoining the first, said flux sheets being directed in different radial planes with respect to said body so as to insure magnetization along the entire peripheral surface of said body.

6. Apparatus for the magnetic testing of ferrom'agnetic objects, including an electromagnet havin pointed pole faces in confronting relationship, each pole being formed of alternately laterally staggered V-shaped laminations whose points are arranged to substantially contact diametrically opposite longitudinal portions of a ferromagnetic object'along different discontinuous lines upon moving such an object into a position between said pole faces.

7. Apparatus for the magnetic testing of cylindrical ferromagnetic objects, including an electromagnet having a yoke including a pair of pole faces in confronting relationship arranged to substantially contact diametrically opposite longitudinal surface portions of an object, when such an object is disposed between said poles, each pole face comprising a plurality of'V-shaped laminations stacked with the points of the V's alternately laterally staggered so as to form pole faces in the form of two discontinuous lines parallel with the axis of said body and spaced from each other.

8. Apparatus for magnetic testing of ferromagnetic objects, including an electromagnet, means including a driven wheel having a notch at the surface thereof for feeding a plurality of objects, one by one, into position between oppositely disposed pole faces of said electromagnet, and electrical means including switching means synchronously operable with said driven wheel for intermittently energizing said electromagnet to effect magnetization of said bodies only during periods when one of said bodies is almost between said pole faces, whereby said bodies are magnetically drawn into position between said pole faces and magnetized.

9. Apparatus recited in claim 8 wherein said driven wheel comprises a pair of discs having V-shaped notches at the surface thereof, which discs are rotatably adjustable with respect to each other and adapted to be clamped together to form a V-shaped common opening of variable size.

10. The method of magnetizing a cylindrical body which includes establishing a plurality of spaced magnetic fields, one group of alternate fields being oriented in substantially one plane and the other group of alternate fields being oriented in substantially a second plane displaced angularly with respect to said first plane, whereby all portions of the body are magnetized.

11. The method of magnetizing a body which includes disposing it in a magnetic field, concentrating the lines of force of the magnetic field into a plurality of paths having concentrated fiux regions spaced longitudinally of said body and directing said paths transversely of said body, adjacent paths having angulariy difi'erent axes of orientation.

12. The method of magnetizing a body which includes disposing it in a magnetic field, concentrating the lines of force of the magnetic field into a plurality of paths having concentrated fiux regions spaced longitudinally of said body and directing said paths transversely of said body, certain of said paths having their magnetic axes angularly spaced from other paths in parallel transverse planes of the object.

13. A magnetizing device comprising a pair of magnetic poles whose pole faces are in confronting relationship, ea-ch pole face having a plurality of relatively separate sharply pointed pole tips, certain of said pole tips being disposed in one plane and the other of said pole tips being disposed in a second plane angularly disposed with respect to the first plane.

14. A magnetizing device comprising an electromagnet including a pair of laminated magnetic poles, the pole end of each lamination being tapered to form individual pole tips, the tips alternately lying in one of two planes extending between said poles, and one plane angularly disposed with respect to the other plane, thereby to insure magnetization along substantially the entire peripheral surface of a magnetizable body moved into a position between said poles.

15. In an apparatus for transversely magnetizing cylindrical objects which are subsequently to be simultaneously tested for flaws and other defects including a table having an inclined plane supported thereby for rolling a plurality of said objects into position, feeding means at the bottom of said inclined plane for providing a time interval between successive objects, an electrounagnet supported by said table having confronting pole faces, one of which is located above and the other below the surface of said table and between which said objects are adapted to roll, and means for intermittently energizing said electromagnet as a function of said time interval, said objects being temporarily held between said pole faces and restrained from further rolling during energization of said eiectromagnet.

16. A magnetizing device for magnetizing bodies comprising means for establishing a magnetic field and means each for concentrating the field between a plurality of spaced onset points aligned in staggered relation, one of said concentrating means being located in spaced opposition to another for receiving magnetizable bodies therebetween.

17. A magnetizing device comprising means for establishing a magnetic field and means each for concentrating the field between a staggered discontinuous surface area extending longitudinally of the concentrating means and spaced from the other.

18. A magnetizing device comprising means for establishing a magnetic field and means each for concentrating the field into a plurality of paths having concentrated flux regions spaced in staggered relation longitudinally of the paths. so that all portions of the body are magnetized.

19. A magnetizing device comprising means for establishing a magnetic field and means each for concentrating the field between alternately staggered, closely spaced points and in spaced opposed relation to the other for effecting magnetization of a cylindrical body along staggered, semi-circular parallel paths.

20. A magnetizing device comprising means for establishing a magnetic field and means each for concentrating the field into intense sheets of magnetic fiux along diametrically opposite portions of an incremental disk-like portion of a cylindrical body and simultaneously directing a separate pencil-like, intense sheet of magnetic flux along diametrically opposite portions of a second incremental disk-like portion adjoining the first, said flux sheets being concentrated in different radial planes with respect to said body so as to insure magnetization along the entire peripheral surface of said body.

21. A magnetizing device comprising means each for establishing a plurality of magnetic fields and means spacing said fields alternately in one of two planes, the two planes being displaced angularly with respect to each other, whereby all portions of a magnetizable body will be magnetized.

22. A magnetizing device comprising means for establishing a magnetic field and means for concentrating the lines of force of the magnetic field into a plurality of paths having concentrated flux regions spaced longitudinally of a body to be magnetized and directing said paths transversely 9 of said body, adjacent paths having angularly diiferent axes of orientation.

23. A magnetizing device comprising means for establishing a magnetic field and means each concentrating the lines of force of the magnetic field into a plurality of paths having concentrated flux regions spaced longitudinally of a body to be magnetized and directing said paths transversely of said body, certain of said paths having their magnetic axes angularly spaced from other paths in parallel transverse planes of the object.

MORRIS L. MAGES.

HERBERT T. NORDSTROM.

REFERENCES CITED Number Number 10 UNITED STATES PATENTS Name Date Switzer Nov. 2, 1909 Hess July 14, 1914 Messiter Dec. 22, 1914 Jobke Mar. 16, 1915 Osgood Feb. 6, 1917 Moore Dec. 4, 1934 Burt May 5, 1937 DeForest Oct. 15, 1940 Hansen et al. June 2, 1942 Arnold Dec. 22, 1942 Gaiser Sept. 5, 1944 Newman Dec. 16, 1947 FOREIGN PATENTS Country Date Switzerland Dec. 1, 1907 Sweden Feb. 10, 1938