US 4,792,755 AGranted

Process and apparatus for the non-destructive examination of ferromagnetic bodies having sections of surface adjoining each other along edges and/or at corners

AssigneeNukem GmbH

InventorsGerhard H/u/ schelrath, Ekkehard Rehfus

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Abstract

This invention relates to a process and an apparatus for the non-distructive examination of ferromagnetic bodies having sections of their surface adjoining along edges. The bodies or body parts are examined for structural faults or disturbances, including the regions along the edges and/or at the corners. A magnetic field is produced in the given body or body section. This field is stationary with respect to magnetic field sensors provided for measuring the stray fields on the surface. In a first measuring phase, measurements obtained for stray flux which are characteristic for the various positions of the magnetic field sensors along the surface of the body or body section are stored as reference values. In a second measuring phase, the reference values allocated to the various positions are subtracted from the stray flux values measured at these positions. The differences are then compared with predetermined threshold values.

Claims11

Dependent claims

A method for non-destructively examining at least corners or edges or radially symmetric ferromagnetic bodies rotatable about an axis of symmetry thereof, said corners or edges contoured along the axial direction of said body, comprising the steps of:

producing a static magnetic field in said body;
measuring in a first measuring phase, to obtain first measured stray flux values, magnetic stray fields extending outside said body along the axial direction of said body on or over at least a section of a contoured edge or corner surface of said body and also situated at a location so that other sections of said edge or corner surface of said body can be measured as a result of changes in relative position between said body and said location;
storing first measured values of said stray flux measurements as compensation values with reference to said location at which said measurements arise along said section of said surface;
rotating said body so that said other sections of said contoured edge or corner surface are successively positioned at said location;
measuring in a second measuring phase a plurality of stray fluxes of said other sections of said edge or corner surface of said body to obtain second measured stray flux values;
subtracting said second measured stray flux values measured at said other sections of said edge or corner surface from said compensation value allocated to said location to obtain difference values;
comparing said difference values with predetermined threshold values;
and
indicating a structural fault exists when said difference values are of greater magnitude than said predetermined threshold values, wherein stray fields due to edge or corner contours are compensated.

6 more elements

An apparatus for non-destructively examining at least corners or edges of radially symmetric ferromagnetic bodies rotatable about an axis of symmetry thereof, said corners or edges being contoured along the axial direction of said body, comprising:

means for generating a static magnetic field so that stray fields of said static magnetic field extend outside said body;
magnetic field sensing means for measuring stray flux values of said stray fields positioned at a location to follow contours of a first section of the surface of said body along the axial direction thereof at least along edges or corners at a slight and constant distance therefrom in a plane passing through an axis of symmetry of said body;
means for rotating said body about said axis of symmetry so that other sections of said edge or corner surface of said body are succesively positioned at said location;
memory means for storing compensation values obtained by and associated with said magnetic field sensing means with respect to said first section;
means for subtracting stray flux values measured at each successive section of said body surface by said magnetic field sensing means from said compensation values associated with said magnetic field sensing means to obtain a difference signal for each section of body surface measured;
and
means for threshold discrimination of said difference signals of a magnitude greater than a predetermined threshold to determine if a structural fault exists, wherein stray fields due to edge or corner contours are compensated.

4 more elements

Dependencies are inferred from the claim text.