How to make a magnet? Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Ham Radio Technologies
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It is known that a noticeable effect of the magnetic field is noted only in iron-containing materials. But these materials also differ and are divided into soft magnetic and hard magnetic. Their main difference is the ability to maintain magnetization after the end of the magnetic field. In addition to iron and its alloys, ferrites made from iron dioxide powder with various additives (barium, cobalt, strontium, etc.) have magnetic properties by hot pressing under high pressure.
The cores of transformers and chokes are made from soft magnetic ferrites, while the hard magnetic ferrites are used to make permanent anisotropic magnets.
At home, you can make good permanent magnets from alloy steels. Without going into the intricacies of the range of steel grades, we can say that hardenable steels are suitable for manufacturing. There are always old needle files, files, hacksaw blades, etc. at hand. The selected material must first be "released", heated to red heat, and then slowly cooled. After manufacturing the magnet blank, it is hardened - heated to a light red heat and cooled sharply in cold water. The stronger the hardening, the better the magnet will be.
The magnetization process can be carried out on a simple installation consisting of an inductor and a fuse. The coil is wound on a frame of such a diameter that a magnet blank is placed inside. For example, to make a coil, I used a frame from imported solder (h=40 mm, D=50 mm, d=22 mm).
The coil is wound with PEV-2 wire 2 mm in diameter and contains about 500 turns. It is fixed on the base and connected to the mains via a fuse and a switch. The workpiece is placed inside the coil, a fuse is installed and the switch is closed. The fuse immediately burns out, but during this time the workpiece has time to magnetize.
For the fuse, you can use thin copper wire. For safety, it must be placed in a glass tube from a blown fuse and covered with clean quartz sand (for reliable discharge quenching).
The wire fuse blowout current Ipp can be approximately calculated using the empirical formula:
Ipp \u0,005d (d-0,2) / K where d is the wire diameter, mm (up to XNUMX mm);
K - constant coefficient (for copper K = 0,034). From this formula it follows that the wire diameter for the fuse
d \u0,005d K * Ipp + XNUMX.
Installation in the proposed version makes it possible to obtain permanent magnets with a strength of up to 200 mT, which is quite enough for use in structures containing microcircuits of magnetic field converters (MFCs).
The same setting can be used to demagnetize a radio assembly tool by turning on the coil through a step-down transformer with an output voltage of not more than 6 V. Power is supplied to the coil when it is located at a distance of at least 1 m from the demagnetized tool, it is taken in hand, brought to the tool and slowly removed, describing expanding circles.
When working with an induction coil when plugged in (220 V), follow the safety regulations.
Author: I.Semenov, Dubna, Moscow Region
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