US3876932A - Omnidirectional magnetic particle flaw detecting apparatus - Google Patents

Omnidirectional magnetic particle flaw detecting apparatus Download PDF

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Publication number
US3876932A
US3876932A US379336A US37933673A US3876932A US 3876932 A US3876932 A US 3876932A US 379336 A US379336 A US 379336A US 37933673 A US37933673 A US 37933673A US 3876932 A US3876932 A US 3876932A
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United States
Prior art keywords
coils
coil
composite
magnetizing
intersection
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Expired - Lifetime
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US379336A
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English (en)
Inventor
Hitoshi Domon
Takaharu Yasuda
Katsuhiro Kawashima
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Nippon Steel Corp
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Nippon Steel Corp
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Priority claimed from JP7271672A external-priority patent/JPS5223757B2/ja
Priority claimed from JP47092970A external-priority patent/JPS4864349A/ja
Priority claimed from JP6668073A external-priority patent/JPS5321669B2/ja
Application filed by Nippon Steel Corp filed Critical Nippon Steel Corp
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/72—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables
    • G01N27/82—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables for investigating the presence of flaws
    • G01N27/83—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables for investigating the presence of flaws by investigating stray magnetic fields
    • G01N27/84—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables for investigating the presence of flaws by investigating stray magnetic fields by applying magnetic powder or magnetic ink

Definitions

  • ABSTRACT An omnidirectional magnetic particle flaw detecting [30] Foreign Application Priority.
  • the apparatus includes two sets July 20. 1972 Ja an 47-72716 of magnetizing coils crossed Such a manner that an Aug. 8, 1972 Ja an 47-92970 elliptical rotating magnetic held y be formed With June 13. 1973 Ja an 48-66680 its major axis running along the Width direetieh of test material at the center of the crossed coils at the time 52 us. c1 324/38; 324/37 when Said eehe ere eh-eeted, end e eheulet rotating 1511 1m. 01.
  • the present invention relates to amagnetic particle testing apparatus for flaw detectionof magnetizied articles and, more particularly, to an omnidirectional magnetic particle flaw detecting apparatus which is able to detect flaws regardless of their directionrelative-to the device so that flaws in a test material lying in a direction perpendicular to the, direction of travel of the test material can be detected with the same level ofdetecting sensitivity as flaws lying along the direction of travel of test material.
  • This system utilizes current with phases'different by' 1205' ina three-phase current source.
  • this system to say nothing of the conventional apparatus, has not been; successful in solving the problem ?of detecting flaws lying in various directions, all in thesame level of detecting sensitivity.
  • vAnother objectof the present invention is to provide a magnetic particle flawdetecting apparatuswhich can detect flaws at any position on-the surface away from the intersection of coils: that is,, which can perform omnidirectional detection.
  • a further object of the present invention is to provide a magnetic particle flaw detecting apparatus which is so efficient that it can detect flaws at the, same time all over the entire width of wide, plain materials, such as slab or thick plate, in all directions, without contacting flaws.
  • the magne tic field produced on the test material in the lengthwise direction extends to a much greater extent than that in the widthwise direction, as the material itself has been magnetized. This results in the reduction of the magnetic field produced in the widthwise direction relative t o'the lengthwise direction,
  • FIG. 1 is a perspective view of magnetizing coils of the flaw detecting apparatus according to the present invention.
  • FIG. 2 shows a circuit for the connection of the electric source with the coils of FIG. 1.
  • FIG. 3 shows the relationship between coil turn ratio and the major axis-minor axis ratio of the elliptical rotating-magnetic field formed at'the center of the coils, when these coils are air-cored.
  • FIG. 4 shows the relationship between the angles formed by crossing magnetizing coils and the major axis-minor axis ratios of the elliptical rotating magnetic field formed at the center of the coils, when these coils are air-cored.
  • FIG. 5 shows the result of flaw detection achieved by the flaw detecting apparatus of the present invention.
  • FIG. 6 shows the slit flaws in billets used for the test .of FIG. 5.
  • FIG. 7 is a front view of a billet as it is inserted into a magnetizing coil.
  • FIG. 8 shows the result of flaw detection carried out by a prior art flaw detecting apparatus.
  • FIG. 9 is a perspective view of the apparatus of the present invention having two sets of crossing magnetizing coils.
  • FIG. 10 is a schematic illustration of a device for switching the electric source between coils for use in the apparatus of FIG. 9.
  • FIG..11 is a perspective view of magnetizing coils .used in the embodiments of the present invention.
  • FIG. 12 is a perspective view of a magnetizing com- ,posite coil made of the magnetizing coils of FIG. 11.
  • FIG. 13 shows an electric power circuit connected with the magnetizing composite coil of FIG. 12.
  • a magnetizing coil 1 is constructed with a first composite coil 2 and a second composite coil 3.
  • Thefirst composite coil 2 has a rectangular shape, and has an outer coil 4 and an inner coil 5.
  • the outer coil 4 and inner coil 5 are wound on the same reel, but have different numbers of turns.
  • the second composite coil 3 is constructed in the same manner as the first composite coil 2.
  • the two composite coils 2 and 3 are arranged to cross each other at the centers respectively of their corresponding horizontal parts, thus forming the magnetizing coil 1.
  • FIG. 2 shows the connection between the electric sources respectively for the first composite coil 2 and the second composite coil 3.
  • numerals 8 and 9 denote terminals of the outer coil 4 of the first composite coil 2 for the connectionof an electric source
  • numerals 10 and 11 denote terminals of the inner coil 5 for the connection of the electric source
  • numerals l2 and 13 denote terminals of the outer coil 6 of the second coil composite 3 for the connection of the electric source
  • numerals 1 4 and 15 denote terminals of the inner coil 7 for the connection of the electric source.
  • Letters u, v, and w of three-phase current source 17 denote phases for the output terminals on the secondary side of the transformer which is subjected to V wire connection in the three-phase electric source.
  • Alternating current is supplied to the outer coil 4 of the first composite coil 2 from the terminals 8 and 9, connected with the alternating current source 17; and an alternating current with a certain phase difference, in this case 120 from the phase of the current supplied to saidouter coil 4, is supplied to the inner coil 5 in the reverse direction to that to the outer coil 4.
  • an alternating current with a certain phase difference in this case 120 from the phase of the current supplied to saidouter coil 4 is supplied to the inner coil 5 in the reverse direction to that to the outer coil 4.
  • the coil turn ratio between the outer and the inner coils of respective composite coils is determined by considering the shape of the test material, the phase difference between alternating current supplied to the coils and other factors, so that a nearly circular rotating magnetic field may be formed on the surface of the test material during the flaw detecting process.
  • the crossing angle 0 between the composite coils 2 and 3, defined in the region through which the test materials travel, is so determined that a circular rotating magnetic field may be formed on the surface of the test material.
  • the shape of the composite coils is not limited to a rectangle, but may vary appropriately according to the sectional form of test materials, and in each composite coil the two coils may be placed side by side instead of the above-mentioned superposition of one coil over the other. 7 i
  • alternating current having a phase difference of 120 relative to each other is supplied to the coils 4 and 5 of the first composite coil 2.
  • the same thing applies to the coils 6 and 7 of the second composite coil 3.
  • the relation between the first composite coil 2 and the second composite coil 3 is maintained through their connection with the electric sources.
  • the coil turn ratio between the outer coil 4 and the inner coil 5 of the first composite coil 2 is preferably between 1.5 and 2.5. The same ratio also applies to the second composite coil 3. Outer coils 4 and 6 and inner coils 5 and 7 have, respectively, the same number of turns.
  • the major axisminor axis ratio of an elliptical rotating magnetic field will greatly increase, but this is not practical, since this requires a large amount of power to attain the required detecting sensitivity.
  • the coil turn ratio is more than 2.5, the major axis-minor axis ratio will approach ⁇ / 3 which situation will appear as if the major axis and the minor axis of the elliptical rotating magnetic field were reversed in comparison with the air-cored arrangement when the material is in the flaw detecting test, thereby causing a difference in detecting sensitivity between tests in the width and in the length of the test material, which does not meet the purpose of the present invention.
  • FIG. 3 shows the relationship between the abovementioned coil turn ratio and the ratio between the major axis and the minor axis of the elliptical rotating magnetic field at the center when the coils are aircored; if the coil turn ratio is less than 1.5, the major axis-minor axis ratio will gradually approach infinity as the ratio approaches 1; and as the coil turn ratio becomes greater, the major axis-minor axis ratio gradually approachesv 3.
  • the desired rotating magnetic field can be obtained by determining the appropriate coil turn ratio according to the present invention. Further, for readily adjusting the ratio between the major axis and the minor axis of the elliptical rotating magnetic field to the desired value, the composite coils having the above-mentioned coil turn ratio, are made to cross each other, but it is then necessary to make the crossing angle 0 acute. In case this angle 0 is an obtuse angle, that is, more than it will be impossible to obtain an elliptical rotating magnetic field having its major axis running along the width of the test material when the coils are air-cored.
  • an angle 0 of less than 60 is effective to obtain an optimum elliptical rotating magnetic field; if the angle 0 is too small, the effective width of the passage of material will be narrowed, making it necessary to increase the size of the magnetizing coils.
  • FIG. 4 shows the relationship between the crossing angle of coils on one hand and the ratio between the major axis and the minor axis of the elliptical rotating magnetic field at the center of the coils on the other hand. It is apparent that the optimum major axis-minor axis ratio can be obtained from a crossing angle between 60 and 30. Detection signals generated by the magnetic flaw detecting apparatus of the present invention are processed in a known circuit and are output as flaw detecting signals.
  • Magnetic flaw detection (the determination of leakage flux) was conducted with a flaw detecting apparatus constructed with magnetic coils, each having a coil turn ratio of 4 :'2 obtained by making the number of actual turns of the outer coil and of the inner coil, respectively,"4 and 2. The composite coils are then crossed,
  • FIG. 5 The results of the measurement of leakage flux, for quantitative confirmation of the efficacy of the subject invention, are shown in FIG. 5.
  • all the slits a, b, and c were detected as flaws with nearly the same detecting sensitivity even though slit a was perpendicular to the direction of travel A of the billet of rolling billets; slit b was at 45. to this direction and slit was parallel with said; direction. This clearly establishes that all slits can'beldetected with nearly the same detecting sensitivity.
  • FIG. 8 shows the result of a flaw detection test which was made on a material of the same kind and size as mentioned above, that. is, a square steel billet, with a prior art apparatus constructed with two coils, each coil having six turns and crossed at right angles.
  • the apparatus does not overcome the prior art difficulties specified in the instant application and achieves poor results compared with the test obtained with the subject invention. More.particularly, the level of detecting sensitivity foraslit lying perpendicular to and 'parallelwith the direction of progress is reversedbetween FIG. 8 and FIG. so far as the detecting position is in the vicinity of the center of the in tersection of the magnetizing coils.
  • the apparatus ofthe present invention is efficient; it works with, nearly the same level of detecting sensitivity regardless of the directions of slits (flaws) made on the apparatus may work with low detecting sensitivity.
  • FIG. 9 is a, perspective view of a magnetic particle flaw detecting apparatus designed toobviate this disadvantage.
  • Magnetizing coil 21 consists of composite coils 23 and 24, constructedas detailed above, and is superposed with similarly constructed magnetizing coil 22 consisting of composite coils 26 and 27.
  • the device may be coupled to a power source in a manner similar .to that detailed above.
  • the coils are positioned such that an imaginary lineconnectingthe' points of intersection 25 of the composite coils 23, 24 and an imaginary line connecting the points of intersection 28 of the "composite coils 26, 27 cross each other at right angles .and at the. respective center of the imaginary lines.
  • the apparatus of the present invention is constructed as mentioned above, and shall be operated as follows:
  • a test material such as a square steel billet, is introvucked into the structure built as shown in FIG. 9 in the direction of the arrow
  • current should not be supplied simultaneously to the magnetizing coils 21 and 22; this introduction would create a mixture of rotating magnetic fields formed by the respective coils 21 and 22 which effects the range of the flaw detection.
  • the apparatus of the present invention is so operated that the current supply is alternated at a high rate between the coils 21 and 22, so that they alternately and singly operate for a limited time. This method of current supply will not cause mixing of the elliptical rotating magnetic fields produced by respective coils,- making it possible to carry out flaw detection on amulti-face basis.
  • FIG. 10 shows an embodiment of a device for switching the power sourcefor the above-mentioned purpose.
  • This device is so constructed that a thyristor 32 and a step-down transformer 33 are connected in series, thereby alternating the current from the source be tween the coils 21 and 22. If the rate of travel of the test materials is assumedto be 60 m/min. (l in/sec.) and an alternating current of 60 Hz is switched every 2 cycles (1/30 sec.), the material will progress 6.7 cm during ,present invention, to supply a small amount of current,
  • flaw detection of squarebillets over the entire surface area can be made in one pass through the apparatus of the present invention with constancy in every direction and with a high level of detecting sensitivity.
  • the magnetic particleflaw detecting apparatus for testing broad articles like plate, is explained, as follows: In tliis case, the composite f'coils made of two sets of magnetizing coils are not suff cient to cover the breadth of such material. Thereforefa magnetizing coil series made of more than two sets of magnetizing coils connected in series at the intersections thereof are used.
  • the crossed coils shown in FIG. 12 may be used to solve the above-mentioned problem.
  • FIGQll shows a magnetizing element coil 41,'which isniadefby' crossing two coils 42 and 43 and forminga certain crossing angle Obetween their respective top parts 44 and 47' and also between their respective bottorn partsj45' and 48.
  • Numerals 46 and 49 indicate sides, respectively, of the coils 42 and 43.
  • the crossing angle 0 and the current phase difference between the c'oils42 and 43 are left to choice in view of the above disclosure.
  • Tabs 73, 74, and 76 indicate terminals for connecting the coils with an electric power source. According to the present invention, more than two of such unit magnetizing element coils, as shown in FIG. 12, may be connected in series into two conjunctive magnetizing coil series.
  • Two such series 51 and 52 may be superposed so that the intersection 56 of the magnetizing element coils of the second conjunctive magnetizing coil series 52 is placed at the center of the opening 55 between the connecting parts 53 and 54 of the magnetizing element coils of the first conjunctive magnetizing coil series 51.
  • conjunctive magnetizing composite coils are formed having chain-like intersections at the top and thebottom parts.
  • Superposition can be made in any ent invention. Also, according to the present invention,
  • the number of. magnetizing element coils may be adjustedin accordance with the width of the test materials.
  • the intersection 56 of the second conjunctive magnetizing coil series needs not be strictly the center of the opening 55 between the intersection 57 of the first conjunctive magnetizing coil series, but may be in the vicinity of the center.
  • the magnetizing coils are serially coupled at their top and bottom portions, respectively.
  • Numerals 61,62, 63, 64, and 65 and 66 indicate terminals of respective conjunctive magnetizing coil series for the connection with their electric power source. Each of these numerals is used for two 7 terminals in order to point out the connection positions 'to ,t he current source output terminals shown in FIG. .13, q
  • the magnetic particle flaw detecting apparatus of the present invention which is constructed as mentioned above, is operated in the following manner.
  • a plate-like magnetic article such as thick steel plate, is charged into the space formed by the conjunctive magneticcoil series 51 and 52 along the direction line A, and when it is in the air-core of the conjunctive magnetic composite coil for flaw detection, if it is so devised as to have.
  • the magnetic field produced on the surface of the test material form a circular rotating magnetic field, an omnidirectional magnetic field will periodically travel over the full width of the test material, making.
  • the crossing angle 0 of magnetizing element coils is preferably between 120 and FIG. 13 shows a circuit for connecting flaw detection coils 51 and 52 of the apparatus of the, present invention to the current source.
  • numerals 67, 68 and 69 indicate periodical current switches, such as 32 in FIG. 10. In the up position of the switches, only conjunctive series 51 is energized. In the down position, only conjunctive series 52 is energized.
  • Numerals 70 and 71 denote respective transformers having V-connection with the three-phase current source. Letters U, V, W, u, v and w denote, respectively: the primary and the secondary phases of the terminals of the transformer. Letters R, S and T denote the phases of lines of the three-phase current source.
  • the inventors of the present invention were successful in omnidirectional flaw detection over the entire surface of thick steel plate test materials by using the magnetic particle flaw detecting apparatus constructed with the connection of magnetizing element coils inter 'secting at right angles, as shown in FIG. 12, and by using a three-phase alternating current having a phase difference of n This being the achievement of the apparatus of the present invention, it is now possible to subject broad plate-shaped magnetic articles to flaw detection on an omnidirectional basis over the whole surface area without contacting materials at high accuracy and efficiency.
  • An omnidirectional magnetic particle flaw detecting apparatus comprising a first set of magnetizing coils consisting of a first planar composite coil and a second planar composite coil the planes positioned to intersect each other, each said composite coil being composed of two coils sharing one coil reel but having different numbers of coil turns, the coil turn ratio between the two coils of each coil composite being so determined as to produce 'a nearly circular rotating magnetic field on the surface of a test material when the test material is inserted into the magnetizing coils, and an alternating current source means coupled to the two coils of each of said composite coils and supplying alternating current respectively differing in phase. relative to the two coils, whereby surface flaws can be detected with the same sensitivity independent of the flaw direction.
  • the device of claim 1 further comprising a second set of magnetizing coils consisting of a third planar composite coil and a fourth planar composite coil, the planes of said third and' fourth composite coils being positioned to intersect each other and being positioned concentrically with said first and second composite coils such that an imaginary line connecting points of intersection of said first and second composite coils and an imaginary line connecting points of intersection of said third and fourth composite coil are at right angles and intersect at their respective centers, said third and fourth composite coils each consisting of two coils sharing one coil reel but having different numbers of coil turns, the coil turn ratio therebetween being such as to form a nearly circular rotating magnetic field on the surface part of test materials when the test material is inserted into the magnetizing coils, and said third and fourth composite coils being coupled to said alternating current source means.
  • angles respectively formed by the intersection of the planes of the first and second composite coils and the third and fourth composite coils in the direction in which the test material is inserted are acute.

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Physics & Mathematics (AREA)
  • Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
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  • Investigating Or Analyzing Materials By The Use Of Magnetic Means (AREA)
US379336A 1972-07-20 1973-07-16 Omnidirectional magnetic particle flaw detecting apparatus Expired - Lifetime US3876932A (en)

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Application Number Priority Date Filing Date Title
JP7271672A JPS5223757B2 (de) 1972-07-20 1972-07-20
JP47092970A JPS4864349A (de) 1971-12-06 1972-09-18
JP6668073A JPS5321669B2 (de) 1973-06-13 1973-06-13

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Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5404101A (en) * 1992-02-27 1995-04-04 Logue; Delmar L. Rotary sensing device utilizing a rotating magnetic field within a hollow toroid core
US5754043A (en) * 1993-10-29 1998-05-19 Logue; Delmar L. Driving cores for polar coordinates sensors
EP1515137A1 (de) * 2003-09-12 2005-03-16 General Electric Company Omnidirektionale Wirbelstromsonde
WO2009103938A1 (en) * 2008-02-22 2009-08-27 University Of Exeter Controllable magnetic systems
WO2009123847A1 (en) * 2008-03-29 2009-10-08 Illinois Tool Works Inc. Apparatus and method for non-destructive testing of ferromagnetic workpieces
US20100085045A1 (en) * 2008-10-07 2010-04-08 General Electric Company Omnidirectional Eddy Current Array Probes and Methods of Use
CN101393168B (zh) * 2008-11-10 2011-09-28 盐城东车科技有限公司 一种磁粉探伤装置
US20110273170A1 (en) * 2010-04-28 2011-11-10 Nemak Dillingen Gmbh Method and Apparatus for a Non Contact Metal Sensing Device
CN105067700A (zh) * 2015-07-27 2015-11-18 洛阳轴研科技股份有限公司 一种压下轴承的磁粉探伤方法
EP2955514A1 (de) * 2014-06-12 2015-12-16 Helling GmbH Vorrichtung zur zerstörungsfreien Prüfung metallischer Werkstücke

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5134367A (en) * 1991-03-19 1992-07-28 The Babcock & Wilcox Company Rotating eddy current roller head for inspecting and profiling tubing having two separate cross wound coils
FR2780510B1 (fr) * 1998-06-25 2002-05-03 Minh Quang Le Dispositif electromagnetique de controle non destructif permettant la creation des champs magnetiques et des courants de foucault dirigeables

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US1129584A (en) * 1914-07-17 1915-02-23 James P B Duffy Magnetic testing device.
US2338793A (en) * 1942-05-07 1944-01-11 Magnetic Analysis Corp Testing apparatus
US3354385A (en) * 1964-04-29 1967-11-21 American Mach & Foundry Electromagnetic inspection system utilizing search coils nested within one another
US3495166A (en) * 1967-04-10 1970-02-10 Magnaflux Corp Eddy current crack detector systems using crossed coils

Patent Citations (4)

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Publication number Priority date Publication date Assignee Title
US1129584A (en) * 1914-07-17 1915-02-23 James P B Duffy Magnetic testing device.
US2338793A (en) * 1942-05-07 1944-01-11 Magnetic Analysis Corp Testing apparatus
US3354385A (en) * 1964-04-29 1967-11-21 American Mach & Foundry Electromagnetic inspection system utilizing search coils nested within one another
US3495166A (en) * 1967-04-10 1970-02-10 Magnaflux Corp Eddy current crack detector systems using crossed coils

Cited By (17)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5404101A (en) * 1992-02-27 1995-04-04 Logue; Delmar L. Rotary sensing device utilizing a rotating magnetic field within a hollow toroid core
US5754043A (en) * 1993-10-29 1998-05-19 Logue; Delmar L. Driving cores for polar coordinates sensors
EP1515137A1 (de) * 2003-09-12 2005-03-16 General Electric Company Omnidirektionale Wirbelstromsonde
US6888347B2 (en) 2003-09-12 2005-05-03 General Electric Company Omnidirectional eddy current probes, array probes, and inspection systems
WO2009103938A1 (en) * 2008-02-22 2009-08-27 University Of Exeter Controllable magnetic systems
US8405477B2 (en) 2008-02-22 2013-03-26 University Of Exeter Controllable magnetic systems
US20110052393A1 (en) * 2008-02-22 2011-03-03 University Of Exeter Controllable magnetic systems
WO2009123847A1 (en) * 2008-03-29 2009-10-08 Illinois Tool Works Inc. Apparatus and method for non-destructive testing of ferromagnetic workpieces
US7948233B2 (en) 2008-10-07 2011-05-24 General Electric Company Omnidirectional eddy current array probes and methods of use
US20100085045A1 (en) * 2008-10-07 2010-04-08 General Electric Company Omnidirectional Eddy Current Array Probes and Methods of Use
CN101393168B (zh) * 2008-11-10 2011-09-28 盐城东车科技有限公司 一种磁粉探伤装置
US20110273170A1 (en) * 2010-04-28 2011-11-10 Nemak Dillingen Gmbh Method and Apparatus for a Non Contact Metal Sensing Device
US8901930B2 (en) * 2010-04-28 2014-12-02 Nemak Dillingen Gmbh Method and apparatus for a non contact metal sensing device
EP2955514A1 (de) * 2014-06-12 2015-12-16 Helling GmbH Vorrichtung zur zerstörungsfreien Prüfung metallischer Werkstücke
WO2015188892A1 (de) * 2014-06-12 2015-12-17 Helling Gmbh Vorrichtung zur zerstörungsfreien prüfung metallischer werkstücke
CN105067700A (zh) * 2015-07-27 2015-11-18 洛阳轴研科技股份有限公司 一种压下轴承的磁粉探伤方法
CN105067700B (zh) * 2015-07-27 2018-06-22 洛阳轴承研究所有限公司 一种压下轴承的磁粉探伤方法

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SE401406B (sv) 1978-05-02
DE2336677B2 (de) 1979-07-19
DE2336677A1 (de) 1974-01-31
DE2336677C3 (de) 1980-04-17

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