US3614604A - Method and apparatus for detecting workpiece surface defects and for fixing the location thereof using magnetic particles - Google Patents

Method and apparatus for detecting workpiece surface defects and for fixing the location thereof using magnetic particles Download PDF

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Publication number
US3614604A
US3614604A US873043A US3614604DA US3614604A US 3614604 A US3614604 A US 3614604A US 873043 A US873043 A US 873043A US 3614604D A US3614604D A US 3614604DA US 3614604 A US3614604 A US 3614604A
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United States
Prior art keywords
workpiece
powder
defect
ferritic
marking material
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Expired - Lifetime
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US873043A
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English (en)
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Kurt Reinshagen
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Elektrodenfabrik Oerlikon Buehrle AG
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Elektrodenfabrik Oerlikon Buehrle AG
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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

  • the workpiece is magnetized and a ferritic powder is sprayed over the surface thereof. Due to stray flux lines of the magnetic field occurring at the surface defects, the ferritic powder accumulates at such defects and effectively traces the same, rendering the defect visible.
  • the tracing ofthe defects is then fixed or preserved automatically so that the defects remain visible for subsequent corrective maintenance operations after the workpiece is demagnetized and the powder falls off.
  • the fixing" of the tracing occurs in that a colored marking material is applied or sprayed over the surrounding surface about the traced defects as well as over the ferritic powder which effects the tracing itself. The workpiece is then demagnetized and the ferritic powder and the colored marking material over the powder is removed.
  • the remainder of the surface remains dyed by the colored marking material thus outlining the surface defects and fixing or preserving the visible tracing thereof.
  • This technique is referred to herein as a so-called negative" process.
  • a positive" process is employed wherein the ferritic powder which traces the surface defects is permanently adhered to the surface by means of the application of heat. Subsequently, the workpiece is demagnetized leaving the permanently adhered ferritic powder at the defect location thus fixing the visible tracing.
  • This invention generally relates to workpiece surface defect detectors and particularly concerns a method and apparatus for rendering visible surface defects such as fissures, cracks, and the like on billets and other semifinished products.
  • the novel detection method and apparatus of the instant invention generally is of the type in which the workpieces or test samples are magnetized by the passage of an electric current therethrough.
  • stray flux lines of the magnetic field are produced at the defect locations, these stray flux lines attracting a ferritic powder which is applied to the workpiece surface by means of pneumatic streams and the like.
  • the stray flux lines of the magnetic field produced at surface defect locations on the workpiece are detected by a magnetic tape and these stray lines form signals thereon. These signals trigger the spraying of a colored stripe upon the general location of the surface defect.
  • this process has its disadvantages in that several fissures, cracks or other defects could conceivably be disposed under a single colored stripe and thus these defects would not individually be recognizable and the subsequent maintenance or repair personnel might repair only one defect rather than all defects under a colored stripe. Additionally, this known process suffers from the disadvantage that defects such as flakes or scales disposed at the surface of the workpiece are not readily indicated.
  • a powder for spraying which consists of agglomerated particles of both ferritic as well as nonferritic substances. Additionally, a powder having an even granular distribution can be utilized and, in this manner, an accurate image or reproduction of the defective location can be had.
  • the powder agglomerate which accumulates along the surface defects to thus designate the defective locations on the workpiece surface is actually fixed by means of the application of heat in a reaction chamber. In this case, a so-called positive image or reproduction of the defective location is obtained.
  • colored marking material is applied over the surface of the workpiece after the powder agglomerates have accumulated at the defect location.
  • the powder as well as the marking material thereon is then removed from the defect in a blowoff chamber whereas the remainder of the colored marking material over the workpiece surface is dried leaving an outline of the defect location. In this fashion, a so-called negative" indication of the defect location is obtained.
  • the powder removed from the workpiece surface can be reutilized.
  • Thenovel apparatus for carrying out the above-described process includes a magnetizing installation for effecting magnetization of the semifinished workpiece, the installation incorporating electrodes contacting the workpiece surface.
  • Spraying nozzles serving to spray ferritic particles onto the workpiece surface are disposed between the electrodes and, by means of the spray nozzles, the surface of the workpiece is evenly covered.
  • the novel apparatus further incorporates means for fixing or preserving the visible indication of the defect locations.
  • the means for fixing or preserving the visible indication of defect locations incorporate a colored material spraying device disposed in the magnetization path of the workpiece which serves to spray a colored substance over the surface of the workpiece upon which the ferritic powder has been applied.
  • a colored material spraying device disposed in the magnetization path of the workpiece which serves to spray a colored substance over the surface of the workpiece upon which the ferritic powder has been applied.
  • an orientation-or position-locating device is disposed in the area of the ferritic powder spraying installation and the colored marking material spraying installation and serves to actually detect the surface error location to thus selectively activate the colored substance spraying location such that the actual permanent marking of the surface defect is effected automatically.
  • the indicated surface error location is preserved or fixed by means of a reaction chamber disposed within the path of magnetization of the workpiece, this reaction chamber, as
  • the electrodes effecting the magnetization of the workpiece and particularly the electrodes contacting the discharge side of the workpiece comprise jaws disposed on an endless chain driven by a motor in synchronism with the feed speed of the workpiece itself. In th's fashion, the defective location indication is maintained in an unaltered condition for subsequent maintenance or repair operation.
  • FIG. 1 schematically depicts a first embodiment of an apparatus for carrying out the novel inventive method
  • FIG. 2 schematically depicts an alternative embodiment of an apparatus for realizing the novel inventive process
  • FIG. 3 schematically depicts a large scale plant for carrying out the process of the instant invention.
  • FIG. 4 schematically depicts portions of an overall apparatus, such portions specifically illustrating a spray chamber and a magnetization path.
  • the novel invention arises from the consideration that it is not sufficient to more or less inaccurately copy or trace surface defect locations initially rendered visible through the accumulation of ferritic powder particles in stray flux lines of the magnetic field and to subsequently utilize this tracing or copy for the repair of these defective locations.
  • the novel invention is based upon the consideration that an economical repair of the surface defects is only possible if the actual accumulation of the ferritic powder particles at the surface defect locations is itself made available for the subsequent repair or maintenance operation or, alternatively, if the true, accurate reproduction of such powder accumulation is so utilized since the workpiece, when the subsequent maintenance or repair operation is effected is no longer magnetized, some means must be provided by which the true image of the ferritic powder accumulation can be obtained and fixed. Of course, the actual fixation of this image must take place during magnetization of the workpiece, i.e., during the flow of electric current therethrough.
  • the workpiece l for example, is guided through the magnetization apparatus which, in this case, is stationarily disposed, the workpiece 1 having a given advance or feed speed.
  • the workpiece can be stationarily disposed and the magnetization installation could be caused to travel along the length of the workpiece. In both instances, however, the novel process of the instant invention takes place in a similar fashion.
  • the workpiece is evenly sprayed with a ferromagnetic powder by means of a powder-spraying installation 4.
  • This powder is carried upon the surface of the workpiece by means of a pneumatic air stream or current.
  • stray flux lines of the magnetic field occur at the defect locations such as surface fissures, cracks, flakes, or scales, and the ferromagnetic powder accumulates over and exactly traces the extent of the stray lines and thus of the surface defect location.
  • the workpiece l continues its feed movement and the accumulated powder reaches a location or position-finding device 5 serving to determine the existence of a defect location, this position-finding device 5 producing a signal actuating a colored marking or covering material spraying installation 6 which, after the workpiece has traveled further, sprays the detected defect location with a colored material substance. Thereafter, the defect location leaves the magnetization paths defined by the electrodes 2 and 3 and is demagnetized at which time the accumulated powder at the defect location at least substantially falls off.
  • the colored material which was subsequently sprayed over the accumulated powder by the spraying installation 6 also falls off such that a precise outline of the powder accumulation remains, which outline forms a clearly visible contrast with respect to the colored substance which remains on the remainder of the surface of the workpiece.
  • the workpiece is exposed to an air current which serves to dry the remaining colored substance and also serves to remove any possible ferritic powder residues. It has been found that the most accurate tracing or drawing of the defect locations can be obtained when the colored coating over the workpiece surface is light and extremely thin.
  • the process as above described can additionally be simplified in that the utilization of a location or position-finding device 5 can be eliminated. In this event, the entire surface of the workpiece would be completely sprayed with colored material. The removal of the accumulated ferritic powder upon passing out of the magnetization path and any possible subsequent treatment such as blowing with an air current would be carried out in the same fashion in the simplified process as above discussed. Yet, a larger quantity of colored material or substance must be utilized in this instance and this necessity is balanced against the economic savings achieved by dispensing with the utilization of a location or position finding device 5 and its control apparatus.
  • FIG. 2 an alternative embodiment of the novel invention is disclosed, this embodiment effecting a process which can be defined as a positive" process in contrast to the negative process associated with the description of FIG. I.
  • the workpiece again is designated by reference numeral 1 and is guided through a test installation device which, again, is assumed to be stationary. Electrodes 2 and 3 are provided which delimit the magnetization path. lnitially, the workpiece is sprayed inside the magnetization path with a ferromagnetic powder which, for example, can be applied to the workpiece surface by means of an air current.
  • a substance is additionally admixed to the ferromagnetic powder which substances serve to effect the adherance of the accumulated powder to the workpiece surface after the workpiece leaves the magnetization path.
  • workpiece 1 reaches a reaction chamber 7 in which the accumulated powder at the defect locations of the test piece 1 is fixed, this fixation being effected through the application of heat.
  • the defect location is thus marked by means of the fixed accumulated powder and such marked defect location will remain after the workpiece leaves the magnetization path and the magnetization of the workpiece is removed. This marking provides an indication of the defect location which must be removed to the subsequent maintenance or repair personnel.
  • the testing apparatus would be sprayed with not only one, but with several ferritic powder spraying devices such that the entire circumferential surface of the workpiece is covered in a single pass.
  • the marking and fixation of the defect location could also be carried out upon all sides of the workpiece, and, if a defect location or position finding device is provided, such device must be operative about the entire circumference of the workpiece and must supply corresponding signals for the activation of a colored material spraying installation which itself must be operative upon all workpiece sides.
  • defect position finding can take place by means of an infrared device which detects the radiation emanating from the accumulated ferritic powder which would previously have been heated so as to reach some given minimum response temperature.
  • radioactive error or defect position finding can be utilized and in this event, radioactive material would be admixed into the ferritic powder and the radiation given off by the accumulated powder would be detected.
  • the powder could be exposed to X-rays and the secondary radiation emanating from the accumulated powder at the defect locations would be detected.
  • the ferritic powder which is utilized In order to be able to accurately observe the size of the defect locations and analyze the same, the ferritic powder which is utilized must possess very specific properties. In known defect testing processes based upon the magnetization of the workpiece, the powder utilized normally has an undefined granule shape and size and, thus, it is possible that defect locations which are identical may show different images even though subjected to equal magnetization. This is the case since the respective granule composition and specifically the proportion of the respective granule components are variable. As the proportion of smaller granule particles in the powder increases, the ability of the powder to reproduce smaller fissures or other defects in the workpiece surface also increases in a variable though proportional fashion.
  • An additional advantage to such an agglomerate construction of the particles consists in the fact that the mineral additive can be dyed whereby, during the positive" technique above-described or during the partial colored substance spraying, a portrayal or image of the defect location having sharper contrast compared with the surrounding surface of the workpiece can be obtained.
  • FIG. 3 a schematic illustration of a large scale installation or plant for continuous testing of rolling billets is depicted.
  • a workpiece 1 is guided to an infeed station 9 via infeed roller bed or table 8.
  • the feed or advance speed of the workpiece is somewhat reduced such that a firm contact of the front surface of successively arriving workpieces can be obtained.
  • the actual testing station 10 incorporates the above-described components such as the magnetization path, the powder and spraying installations and devices, if desired, a position-finding device, as well as a color material spraying apparatus.
  • a blow off device can additionally be provided in installation 10 subsequent to the magnetization path as would be required if the above-described negative process were to be undertaken in which event, the color substance which had been sprayed and deposited on the workpiece would be dried and the remainder of the ferritic powder agglomerates which had not yet completely fallen off the workpiece could be removed.
  • a discharge roller bed or table 11 serves to guide the workpiece or billet to further transportation installations via which the billet would be led to the final repair or maintenance station.
  • the testing station or installation can also be constructed as a transverse or crosswise through passage installation instead of as a longitudinal through passage installation as depicted. With this modification, the workpiece or billet would be fed into the testing station via a crosswise transport system.
  • the testing station or installation could be constructed so as to be movable itself and travel along the test piece. Yet, the test station would operate in the same fashion as would be the case with a stationary installation and therefore, such test station would contain the same components. in such installations, all sides or surface of the billet can be examined for surface defects simultaneously. In the event of the provision of a test installation for testing single workpieces, or in the case of a subsequent retesting installation, it would be practical to utilize manual spray guns for the color material spray as well as for the application of the ferritic powder.
  • a spray chamber 11 incorporates a pair of rollers 12 and 13 which fonn one electrode delimiting the magnetization path.
  • spray nozzles 14 and 15 are arranged for lateral spraying of the workpiece l.
  • Nozzle rows are added to the spray nozzles 14 and 15 both above and below the workpiece I, so as to cover the entire surface thereof.
  • Nozzles l4 and 15 are coupled with the pneumatically loaded bearings of the rollers l2 and 13 and serve to move with the rollers such that the distance between the nozzle outlets and the surface of the workpiece would always be the same.
  • Reference numerals l6 and 17 serve to designate the discharge side contacting mechanism forming the second electrode delimiting the magnetization path. Contacting on the discharge side is carried out in such a manner that only a slight defacing of the test image occurs. In this respect, the contacting is effected via contact jaws 18 attached to a chain 19 driven by a nonillustrated motor in synchronism with the discharge roller bed or table.
  • the nonillustrated color material spraying installation would be disposed between the infeed rollers 12 and 13 and the discharge contacting elements 16 and 17.
  • blowoff device 20 which basically comprises a closed chamber having a plurality of compressed-air nozzles disposed on the inside thereof. These nozzles serve to complete the drying of the sprayed-on color material and further serve to blow off any possible ferritic powder residues, which residues are collected in the chamber and are subsequently reutilized in the process. Any powder residues which might have fallen off of the workpiece between the magnetization path and the blowoff device or installation 20 are also collected and reutilized.
  • the process in accordance with the instant invention contributes significantly to the improvement of the quality of rolled products.
  • the tracing of the various surface defect locations in semifinished products which tracing, up to now has been primarily carried out manually and which represents an exacting and tiresome workstep, is carried out mechanically herein whereby the highest possible degree of precision with respect to indication of the defect locations is achieved.
  • a process for rendering visible defects occurring at the surface of workpieces including the steps of magnetizing the workpiece by passing a direct electric current therethrough at a magnetization path whereby stray flux lines of the magnetic field are caused to develop at defect locations of the workpiece; applying a ferritic powder to at least a portion of the surface of the workpiece whereby the powder is attracted by the stray flux lines and accumulates at the region of the deflect locations thereby rendering such defect locations visible; covering the surface of the workpiece which has had applied thereto the owder and at least the immediately surroundlng regions 0 the workpiece with a marking ma enal,
  • An apparatus as defined in claim 6, further including means for establishing a feed velocity of the workpiece with respect to said apparatus, and wherein one of said pair of electrode units at the discharge end of said apparatus comprises workpiece contact means disposed on an endless chain driven in synchronism with the feed speed of the workpiece.

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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)
  • Analytical Chemistry (AREA)
  • Biochemistry (AREA)
  • General Health & Medical Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • Immunology (AREA)
  • Pathology (AREA)
  • Investigating Or Analyzing Materials By The Use Of Magnetic Means (AREA)
  • Investigating Materials By The Use Of Optical Means Adapted For Particular Applications (AREA)
  • Application Of Or Painting With Fluid Materials (AREA)
US873043A 1968-11-08 1969-10-31 Method and apparatus for detecting workpiece surface defects and for fixing the location thereof using magnetic particles Expired - Lifetime US3614604A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
CH1670968A CH526779A (de) 1968-11-08 1968-11-08 Verfahren und Vorrichtung zur bleibenden Sichtbarmachung von Fehlstellen, insbesondere Rissen, an der Oberfläche von Halbzeug

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US873043A Expired - Lifetime US3614604A (en) 1968-11-08 1969-10-31 Method and apparatus for detecting workpiece surface defects and for fixing the location thereof using magnetic particles

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US (1) US3614604A (de)
JP (1) JPS5211235B1 (de)
AT (1) AT301219B (de)
BE (1) BE741364A (de)
BR (1) BR6913562D0 (de)
CH (1) CH526779A (de)
CS (1) CS158656B2 (de)
DE (1) DE1953717C3 (de)
ES (2) ES373624A1 (de)
FR (1) FR2022867A1 (de)
GB (1) GB1289727A (de)
LU (1) LU59756A1 (de)
NL (1) NL6916879A (de)
PL (1) PL80328B1 (de)
RO (1) RO61659A (de)
SE (1) SE357829B (de)
SU (1) SU456433A3 (de)

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3763423A (en) * 1971-04-06 1973-10-02 F Forster Magnetic particle flaw detector including shield means to protect previously tested surfaces
US3845383A (en) * 1972-10-10 1974-10-29 Elkem Spigerverket As Method and apparatus for inspection of ferro-magnetic billets
US4130800A (en) * 1976-08-31 1978-12-19 Mecafina S.A. Magnetic particle test system using movable test piece clamping means movable jointly or independently
EP0090190A1 (de) * 1982-03-22 1983-10-05 Mecapec S.A. Verfahren und Einrichtung zur magnetischen Materialfehlerdetektion
US4694247A (en) * 1984-06-08 1987-09-15 Mecapec S.A. Method and apparatus including a cushion of pulverulent magnetic material for stray field magnetic testing of ferromagnetic parts
US5648720A (en) * 1993-03-25 1997-07-15 International Business Machines Corporation Apparatus and method for producing a magnetic image of a conductive pattern using eddy currents
US6373244B1 (en) * 1998-04-22 2002-04-16 Hilti Aktiengesellschaft Apparatus for marking a surface indicating elements located inwardly of the surface
US20040000105A1 (en) * 2002-04-04 2004-01-01 Brockman Thomas R. Selectively releasable and pivotable side curtain assembly
US8575923B1 (en) 2011-01-07 2013-11-05 OilPatch Technology Method and apparatus for special end area inspection
WO2020257915A1 (en) * 2019-06-28 2020-12-30 Solmax International Inc. Membrane inspection method based on magnetic field sensing

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4341997A (en) 1979-11-14 1982-07-27 Magnaflux Corporation Magnetic particle inspection process useable with simultaneous illumination by ultra-violet and white light
DE3132390A1 (de) * 1981-08-17 1983-03-03 Mecapec S.A., 8716 Schmerikon "verfahren und einrichtung zur magnetischen risspruefung"
GB2452769B (en) * 2007-09-17 2011-06-01 Motorola Inc Device and electrical contact mechanism therefor

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3073212A (en) * 1957-08-14 1963-01-15 Magnaflux Corp Optical apparatus for inspecting magnetic particle concentrations
DE1169696B (de) * 1957-04-13 1964-05-06 Daimler Benz Ag Vollautomatische Vorrichtung zum Ermitteln von Rissen in axialsymmetrischen Eisen- und Stahlteilen nach dem Magnetpulververfahren
US3249861A (en) * 1962-09-18 1966-05-03 Budd Co Method and apparatus for magnetic flaw detection by depositing magnetic particles ononly the area of the flaw
US3480855A (en) * 1967-04-10 1969-11-25 Magnaflux Corp Image dissector system having pattern rotation means

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE1169696B (de) * 1957-04-13 1964-05-06 Daimler Benz Ag Vollautomatische Vorrichtung zum Ermitteln von Rissen in axialsymmetrischen Eisen- und Stahlteilen nach dem Magnetpulververfahren
US3073212A (en) * 1957-08-14 1963-01-15 Magnaflux Corp Optical apparatus for inspecting magnetic particle concentrations
US3249861A (en) * 1962-09-18 1966-05-03 Budd Co Method and apparatus for magnetic flaw detection by depositing magnetic particles ononly the area of the flaw
US3480855A (en) * 1967-04-10 1969-11-25 Magnaflux Corp Image dissector system having pattern rotation means

Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3763423A (en) * 1971-04-06 1973-10-02 F Forster Magnetic particle flaw detector including shield means to protect previously tested surfaces
US3845383A (en) * 1972-10-10 1974-10-29 Elkem Spigerverket As Method and apparatus for inspection of ferro-magnetic billets
US4130800A (en) * 1976-08-31 1978-12-19 Mecafina S.A. Magnetic particle test system using movable test piece clamping means movable jointly or independently
EP0090190A1 (de) * 1982-03-22 1983-10-05 Mecapec S.A. Verfahren und Einrichtung zur magnetischen Materialfehlerdetektion
US4694247A (en) * 1984-06-08 1987-09-15 Mecapec S.A. Method and apparatus including a cushion of pulverulent magnetic material for stray field magnetic testing of ferromagnetic parts
US5648720A (en) * 1993-03-25 1997-07-15 International Business Machines Corporation Apparatus and method for producing a magnetic image of a conductive pattern using eddy currents
US6373244B1 (en) * 1998-04-22 2002-04-16 Hilti Aktiengesellschaft Apparatus for marking a surface indicating elements located inwardly of the surface
US20040000105A1 (en) * 2002-04-04 2004-01-01 Brockman Thomas R. Selectively releasable and pivotable side curtain assembly
US7254922B2 (en) * 2002-04-04 2007-08-14 Fairborn Usa, Inc. Selectively releasable and pivotable side curtain assembly
US8575923B1 (en) 2011-01-07 2013-11-05 OilPatch Technology Method and apparatus for special end area inspection
WO2020257915A1 (en) * 2019-06-28 2020-12-30 Solmax International Inc. Membrane inspection method based on magnetic field sensing
EP3990907A4 (de) * 2019-06-28 2023-01-18 Solmax International Inc. Membranprüfverfahren auf der basis von magnetfeldsensoren

Also Published As

Publication number Publication date
ES373624A1 (es) 1972-02-01
CH526779A (de) 1972-08-15
BE741364A (de) 1970-05-06
DE1953717A1 (de) 1970-12-10
SU456433A3 (ru) 1975-01-05
BR6913562D0 (pt) 1973-01-11
CS158656B2 (de) 1974-11-25
GB1289727A (de) 1972-09-20
RO61659A (de) 1977-02-15
DE1953717C3 (de) 1975-09-11
SE357829B (de) 1973-07-09
JPS5211235B1 (de) 1977-03-29
FR2022867A1 (de) 1970-08-07
DE1953717B2 (de) 1975-01-30
LU59756A1 (de) 1970-01-13
NL6916879A (de) 1970-05-12
AT301219B (de) 1972-08-25
PL80328B1 (de) 1975-08-30
ES373626A1 (es) 1972-02-01

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