| The importance of the electromagnetic test methods used by FOERSTER was recognized as early as the thirties by the company founder, Friedrich Förster, and was corroborated scientifically and mathematically and incorporated time after time in industry-standard equipment in the fifties.
The term"electromagnetic
methods" covers the following areas:
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With the magneto-inductive method, it is
possible to investigate the core and surface selectively by varying the frequency. Excitation is either with one single frequency or with several frequencies (serial or simultaneous), depending on the testing task.
The hardened passenger-car crankshafts are supplied to the automatic tester after heat treatment. The MAGNATEST S detects inadmissible deviations from the required surface hardness by conducting a magneto inductive test. |
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Magneto-inductive methods
which cover the frequency band from a few Hz to approx.1,000 Hz conventionally with absolute coils and which are generally used to determine integral, technological material properties, such as grain structure, hardness, case-hardening depth and layer thickness.
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Semi-finished products, such as wires, bars and tubes, are tested for local flaws in the form of cracks and holes by encircling through-type coils.
The surface of semi-finished products or components is scanned with scanning probes. This allows maximum flaw resolution.
Example application: Valve spring wire is tested on a compact testing line with encircling, through-type coil (DEFECTOMAT) and rotating scanning probes (CIRCOGRAPH+ROTATING HEAD). The testing line also contains a demagnetization system and a flaw marking system.
Example application: Two scanning probes scan defined surface zones of a rotating brake disk.
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Eddy-current methods
methods which conventionally cover the frequency band up to approx. 10 MHz with differential coils and which are generally used for testing for surface flaws. |
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The high-energy, alternating-field, leakage-
flux method concentrates the magnetic flux at the material surface and is thus particularly suitable for detection of small surface flaws upwards of a depth of 0.1 mm.
Two rotating yokes generate the magnetic flux locally; the integrated magnetic field sensors detect the leakage flux emerging at the flaws.
CIRCOFLUX testing line at Aichi Steel Works, one of Japan's most important steel bar manufacturers.
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Magnetic leakage flux probe method
used with DC-field or AC-field magnetization preferably on tubes and steel bars with round cross-section and hot-rolled surfaces. |
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Object detection with ec (eddy current) method:
The active detection sensor of the eddy current technology is generating an electromagnetic field. This causes eddy currents in the object to be detected. These eddy currents generate a secondary electromagnetic field which is detected and evaluated by receiver sensor.
Magnetic field interferences caused by Fe objects and detection signals:
The sensor of the magnetometer technology is a passive sensor, this means no signal is generated by the sensor. The sensor measures field gradients, generated by ferromagnetic objects in the earths magnetic field. Dipole evaluation signals are the classical result.
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Metal detection using the eddy current principle which generates with one or two frequencies an electromagnetic field. This field is used for the detection of hidden metal objects, even objects with very low metal content. All metals can be detected. Object detection with ec (eddy current) method: The active detection sensor of the eddy current technology is generating an electromagnetic field. This causes eddy currents in the object to be detected. These eddy currents generate a secondary electromagnetic field which is detected and evaluated by the receiver sensor.
Magnetometer principle Which uses highly sensitive magnetic field sensors for the measurement of smallest magnetic fields and magnetic field gradients on earth and in space. Magnetic field interferences caused by Fe objects and detection signals: The sensor of the Magnetometer technology is a passive sensor, this means no signal is generated by the sensor. The sensor measures magnetic fields and magnetic field gradients, generated by ferromagnetic objects hidden in the earths magnetic field. Dipole evaluation signals are the classical results.
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