Magnetic marker and manufacturing method therefor

A manufacturing method for a magnetic marker, comprising:

• forming a magnetically switchable wire having a diameter of 70 μm to 110 μm by an in-gas melt spinning method such that at least one magnetic material having a dendrite structure and, selected from alloys including an alloy consisting mainly of Fe and containing 3 to 5% of Si and 1 to 3% of Ni, an alloy consisting mainly of Fe and containing 3 to 6% of Si and 1 to 4% of Mo, and an alloy consisting mainly of Fe and containing 3 to 5% of Si and 1 to 3% of Co, is melted, and the resulting molten alloy is cooled and coagulated in a cooling gas while being ejected from a nozzle;
• wherein said magnetically switchable wire has primary arms of dendrite which are oriented at an angle of 10° or less to the axis of said wire;
• and
• cutting said wire to a length of 40 mm or less, thereby obtaining a magnetic marker adapted to undergo occurrence of magnetic inversion or major Barkhausen discontinuity or generation of pulses when an alternating field of intensity higher than the coercive force of said wire is applied thereto.

A manufacturing method for a magnetic marker, which manufactures a magnetically switchable wire for the magnetic marker by using:

• alloy melting mechanism for melting at least one magnetic material having a dendrite structure and selected from alloys including an alloys consisting mainly of Fe and containing 3 to 5% of Si and 1 to 3% of Ni, an alloy consisting mainly of Fe and containing 3 to 6% of Si and 1 to 4% of Mo, and alloy consisting mainly of Fe and containing 3 to 5% of Si and 1 to 3% of Co;
• wherein said magnetically switchable wire has primary arms of dendrite which are oriented at an angle of 10° or less to the axis of said wire;
• a spinning nozzle capable of forming a molten metal jet by downwardly ejecting said molten alloy in a manner such that the molten alloy falls;
• a gas flow cylinder located so as to surround a fall path for said molten metal jet;
• cooling gas introducing mechanism for introducing a cooling gas for coagulating said molten metal jet into said gas flow cylinder;
• and
• a discharge portion through which the wire obtained as said molten metal jet is coagulated is discharged from said gas flow cylinder to the outside.

A magnetic marker comprising:

• a magnetically switchable wire formed of a magnetic material and adapted to undergo occurrence of sharp magnetic inversion when an alternating field of intensity higher than the coercive force thereof is applied thereto;
• and
• a magnetic casing formed of a magnetically hard or semihard magnetic material, covering magnetically switchable wire, and capable of generating a bias magnetic field to prevent magnetic inversion of said magnetically switchable wire,
• said magnetic casing having heat-treated portions partially differentiated in magnetic properties by heat treatment in the longitudinal direction thereof.