Classifications

• • 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
  • G01N27/90—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables for investigating the presence of flaws using eddy currents
  • G01N27/904—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables for investigating the presence of flaws using eddy currents with two or more sensors

Definitions

• This invention relates to a method and an apparatus for detecting discontinuities in materials.
• the invention relates to detecting, by electrical means, such discontinuities as cracks, slag inclusions and ' similar discontinuities in metallic materials, which chiefly exist in the form of a material web.
• the detection of discontinui ⁇ ties in materials is of great importance in the quality control of the materials.
• the materials are scanned by a proble which is sensitive to these discontinuities and reacts to discontinous changes or jumps in the properties of the material. Then the probe emits a signal.
• This signal can be processed in different ways, and can, for example, be presented on a display or by a recorder. The signal can also be analysed by a computer in order to make a closer investigation of the discontinuities.
• the problem is to in ⁇ vestigate metallic materials wherein these are scanned by means of a probe which is sensitive to discontinui- ties in the electromagnetic properties of the material.
• These electromagnetic discontinuities are produced by the discontinuities- of the material when for instance eddy currents are induced in the material or when a magnetic field is applied to the material.
• the invention is not limited to either metallic materials or to electromagnetic detection of the discontinuities.
• the invention can, as an example, also be applied for investigation of non-metallic materials by means of ultra-sound and a detector sensitive to ultra- sound, or by reflected laser light.
• the testing of the material is continuous in which case the material very often is continuously transport ⁇ ed as a web.
• the material is continuously scanned by one or more probes.
• the probe covers only a small area in each moment, and in order to cover a larger piece of material, the probe is moved.over the material.
• a large number of probes ca 'be used, but practical dif ⁇ ficulties limit this number.
• discontinuities are randomly distributed in the material and have no preferential direction, it is necessary to scan the material in at least two dif ⁇ ferent directions by means of two or more probes in order to detect safely all the discontinuities.
• One way of achieving this is to let two probes perform an oscillatory movement above the surface of the material perpendicularly to each other. Thus, above the web of the matrial , two probes could oscillate in two direc-
• the present invention avoids the above-mentioned disadvantages and provides an accurate scanning of the web of the material in two different directions in a simple and mecanically uncomplicated way. Also, this invention provides a higher capacity per probe regard ⁇ ing the scanned surface per time unit.
• the discontinuities of the material are detected by a probe sensitive to these, wherein the material is transported in the form of a web and at which at least two probes during the scanning, are moved above the web of the material in at least two circular paths, in a plane essentially parallel to the plane of the web of the material and having essentially equal radii and at least one first circular path is arranged in front of a second circular path and is dis ⁇ placed sideways in relation to the second one in such a way thet principally every part of the surface of the material web successively is covered by at least two circle paths with such an overlap that each half-circle segment successively is overlapped sideways by a con ⁇ secutive segment of a half-circle, all seen in the trav- el direction of the material web.
• the invention also relates to an apparatus for car ⁇ rying out the above-mentioned method and which is char ⁇ acterized in that the apparatus comprises at least two probes arranged to move above the material web in at least two circular paths, the geometrical planes of which are parallel to the geometrical plane of the ma- terial web and which have essentially equal radii.
• At least one first circular path is arranged in front of a second circular path and displaced sideways compared to the second one in such a way that essentially every part of the surface of the material web successively is covered by at least two circular paths with such an overlap that each half-circular segment successively is overlapped by a consecutive segment of a half-circle, all seen in the travel direction of the material web.
• the invention is illustrated more closely by the accompanying drawing which schematically shows a device according to the invention and also shows its function.
• part of a material web 1 is shown, which is moved in the direction of the arrow.
• the probes 2, 4 and 6 are arranged which are successively moved in the circular paths 3, 5 and 7.
• the probe 6 of circular path 7 will scan this point with a movement principally along the travel di- rection of the material web, while probe 2 or 4 of cir ⁇ cular path 3, respectively 5 will scan the same point at a travel direction principally perpendicular to the travel direction of the material path. It turns out that principally every point of the material path will be scanned in such a manner.
• OMPI other are not tangential to each other, a small area in the middle part will be scanned only by the probe 6 of circular path 7. This fact does not influence the use ⁇ fulness of the invention as long as the distance bet- ween the two circular paths 3 and 5 is small compared to the average size of the -discontinuities to be detec- ⁇ ted.
• a discontinuity situated in the narrow middle area which is not scanned by any of probes 2 and 4 of circu ⁇ lar paths 3 and 5, respectively, will then have a small length perpendicularly to the travel direction of the material web. This discontinuity will then be detected by probe 6 of circular path 7.
• the minimum velocity of the probes in their circular paths must be in a specific relationship to the travel speed of the material web. This relationship shall be such, that when a probe has made one complete revolution, the material web has been moved maximum the distance corresponding to the extension in the travel direction of the sensing part of the probe. If the trav ⁇ el speed is smaller some overlapping will occur, but at the same time the detecting capacity (covered surface area per time unit) will be reduced. Out of this also comes that the different probes should move with the same velocity in their circular paths.
• the radius of the circular paths is not very cri ⁇ tical but can be chosen from practical and equipment reasons. When a big radius is used, a larger area can be scanned with a probe but this can also lead to mecha- nical problems at higher rotational speeds. When using a small radius, higher rotational speeds can be achieved but at the same time the scanned surface area is reduced which means that more circular paths are necessary.
• the invention also comprises the possibility to arrange more than one probe in each circular path. These could preferably be evenly distributed along the peri-
• the smallest number of probes which can be used according to the invention is two. These are then ar ⁇ ranged each in one circular.path. These circular paths are arranged so that one is displaced forwardly with for example the double radius and sideways with about one radius, seen in the travel direction of the material web, and the width of the scanned web is maximally the radius of the circle.
• the displacement between the cir ⁇ cular paths in the travel direction of the material web is not very critical.
• the smallest displasement is best such that the circular paths do not touch each other, but in principle no upper limit exists for this dis ⁇ placement.
• the mecanical construction of an apparatus according to.the invention could be made by the use of already known components.
• the probes may be fitted into rotating discs or rings which together with suitable driving mechanisms, such as electrical motors, may be
• OMPI accomodated into suitable holding fixtures above the ma ⁇ terial web.
• a plurality of discs with probes could be accomo ⁇ dated into a bridge construction above the material web.
• the distance of the probes to the material web should be continously controlled in order to adapt it to different thicknesses of the material web and in order to give the desired sensitivity of the scanning procedure.
• the probes are connected in manner known per se to suitable devices for signal processing like ampli ⁇ bombs, recorders or picture displays or a computer for analysis and evaluation of the signals.
• the type of signal processing devices which will be used in each specific case is partly dependent on the actual princip- le of measurement, partly of the examined material etc. In the light of these factors, one skilled in the art can easily select the proper signal processing method.
• the present invention is mainly intended to be used to detect discontinuities in metallic materials and chief- ly those in the shape of a strip or web, such as plates or slabs or rolled material of steel, copper, aluminum or other metallic material.
• a strip or web such as plates or slabs or rolled material of steel, copper, aluminum or other metallic material.
• the scanned sur ⁇ face of the material is chiefly planar but also irregu ⁇ lar surfaces can be examined according to the invention.
• the invention is not limited only to the examination of metallic materials, but using suitable test principles, also other material types may be examined, such as plastics, paper., etc.
• test methods that are based upon ultra-sound, microwave technique or reflected laser light.
• the test principle according to the invention is always the same, only with slight modifications of the apparatus in order to suit the applied method of measurement. Probes to be used together with the different methods of measurements are by the expert and are in many cases available in the market.
• a simple method and a simple device is made available for detecting disconti- nuities in materials and at which it is guaranteed that essentially every point of the investigated material is scanned in two directions, whereby the discontinuities may be detected independently of their orientation.
• the invention may also be applied to very different kinds of materials and together with very different principles of measurements. This contributes to facilitate the qual ⁇ ity control of the material and make it faster, safer and less expensive.

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• Chemical & Material Sciences (AREA)
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• Physics & Mathematics (AREA)
• Chemical Kinetics & Catalysis (AREA)
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• Analytical Chemistry (AREA)
• Biochemistry (AREA)
• General Health & Medical Sciences (AREA)
• Electrochemistry (AREA)
• General Physics & Mathematics (AREA)
• Health & Medical Sciences (AREA)
• Investigating Or Analyzing Materials By The Use Of Magnetic Means (AREA)
• Investigating Or Analyzing Materials By The Use Of Ultrasonic Waves (AREA)
• Analysing Materials By The Use Of Radiation (AREA)
• Superconductors And Manufacturing Methods Therefor (AREA)
• Lubrication Of Internal Combustion Engines (AREA)
• Length Measuring Devices With Unspecified Measuring Means (AREA)
• Investigating Materials By The Use Of Optical Means Adapted For Particular Applications (AREA)
• Golf Clubs (AREA)

Applications Claiming Priority (2)

Publications (1)

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Cited By (3)

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Citations (1)

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• 1979
  • 1979-05-11 SE SE7904155A patent/SE435969B/sv not_active IP Right Cessation
• 1980
  • 1980-05-09 EP EP80850071A patent/EP0019604B2/en not_active Expired
  • 1980-05-09 JP JP50111580A patent/JPS56500509A/ja active Pending
  • 1980-05-09 US US06/229,585 patent/US4451787A/en not_active Expired - Lifetime
  • 1980-05-09 DE DE8080850071T patent/DE3067419D1/de not_active Expired
  • 1980-05-09 WO PCT/SE1980/000135 patent/WO1980002594A1/en not_active Ceased
  • 1980-05-09 AT AT80850071T patent/ATE7082T1/de not_active IP Right Cessation
  • 1980-05-09 AU AU59885/80A patent/AU542650B2/en not_active Ceased
• 1981
  • 1981-01-06 NO NO81810022A patent/NO154410C/no unknown

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