Method and apparatus using magnetic flux scanning to test grain structure of magnetic sheet material
AssigneeAllegheny Ludlum Corporation
InventorsLayton D. Crytzer, Leroy R. Balmer
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Abstract
The grain structure of electrical steel strip is tested by inducing a magnetic flux field into the strip by pole pieces at opposite sides of a permanent magnet. A magnetic detector head between the pole pieces responds to the leakage of flux as the steel strip and/or magnetic detection undergoes relative movement. A recorder is used to identify banding and mixed grain structures which cause a smaller flux leakage amplitude than larger desired grains.
Claims19
Apparatus for continuously testing the grain structure which can adversely affect the magnetic quality of an electrically conductive steel strip, said apparatus including the combination of:
- means for inducing only a direct current magnetic flux field on one side of said steel strip to a detection site at that side of said steel strip without contacting the strip;
- means for advancing said steel strip relative to said means for inducing a magnetic flux field, which field is parallel to the direction of strip advancement to allow continuous examination of the grain structure at diverse detection sites;
- means for moving transversely across the width of said steel strip, said means for inducing a magnetic flux field;
- and
- means responsive to flux leakage at grain boundaries in the steel strip which leakage results from the relative advancing and transverse movement between said strip and responsive means for deriving an electrical signal indicative of the grain structure of the steel strip at selected detection sites established by the flux field without contacting the strip, said means responsive includes a magnetic pickup head oriented to define a pickup area having a length equal to or larger than a nominal grain size of the strip, the length oriented in a direction of strip movement.
A method for identifying banding and mixed grains in a grain oriented silicon steel strip, said method including the steps of:
- inducing only a direct current magnetic flux field in said magnetic steel strip from one side of said steel strip without contacting the strip,
- causing relative movement between said magnetic flux field and the grain structure of the steel strip to allow continuous examination of the grain structure at diverse sites, said relative movement includes advancing said steel strip lengthwise relative to said flux field and transversing said flux field across the width of said steel strip,
- deriving an electrical signal corresponding in magnitude to flux leakage at grain boundaries from the same side of said steel strip without contacting the strip;
- arranging a magnetic pickup head above said steel strip and orientating said magnetic pickup head so as to define a pickup area having a length equal to or greater than the nominal grain size of the strip, the length oriented in a direction of strip movement;
- and
- comparing the magnitude of the electrical signal represented by the flux leakage within areas of the steel strip having large grains as compared within areas of the steel strip having small grains to determine areas of banding and mixed grain structure.
Dependencies are inferred from the claim text.