Demagnetising of large ferromagnetic work pieces - uses LF pulse groups of alternating polarity with alternately increasing and decreasing amplitude sequence

摘要

The demagnetising process is intended for large ferromagnetic workpieces which are exposed to a slowly decreasing magnetic A.C. field strength by decreasing the magnetising current and/or by increasing the distance between workpiece and magnetising coil, whose frequency is smaller than the mains frequency to achieve sufficient depth of penetration. The magnetising current is a low frequency pulse or gap current composed of pulse groups of alternating polarity, the intensity of which slowly and monotonously decreases, and where in each group the intensity of first increases and thereafter decreases and the envelope of which may be sinusoidal or triangular. The demagnetising of a large ferromagnetic workpiece is achieved by that the pulse groups of one polarity are suppressed.