How to find the principle of demagnetization?? What is the principle of demagnetization of ferromagn

Demagnetization is to place the workpiece in an alternating magnetic field to produce a hysteresis loop, and when the amplitude of the alternating magnetic field gradually decreases, the hysteresis loop.

The trajectory is also getting smaller and smaller, and when the magnetic field strength drops to zero, the residual remanent br in the workpiece is close to zero. When demagnetizing, the change in the direction and magnitude of the current and the magnetic field must be "commutated at the same time".

Demagnetization methods and demagnetization equipment.

AC demagnetization. a. Alternating current demagnetization method.

For the batch demagnetization of small and medium-sized workpieces, it is best to demagnetize the workpiece on a demagnetizing machine equipped with a track and a carriage, when demagnetizing, put the workpiece on the carriage and place it 30cm in front of the coil, when the coil is energized, slowly pass the workpiece along the track through the coil and at least 1m away from the coil to cut off the power.

For heavy or large workpieces that cannot be demagnetized on a demagnetizing machine, the coil can also be put on the workpiece, and the coil can be slowly passed through and away from the workpiece when the power is on, and the power is cut off at least 1m away.

b attenuation method. Due to the continuous commutation of the direction of the alternating current, the automatic attenuation demagnetizer or voltage regulator can be used to gradually reduce the current to zero for demagnetization, such as putting the workpiece in the first circle, sandwiching between the two magnetized chucks of the flaw detector, or reducing the current to zero for demagnetization after contacting the workpiece with a strut contact.

For welds of large pressure-bearing equipment, AC electromagnetic yokes can also be used for demagnetization. Connect the two poles of the electromagnetic yoke on both sides of the weld, turn on the power supply, let the electromagnetic yoke move slowly along the weld, and then turn off the power when it is 1m away from the weld, and demagnetize.

Direct current demagnetization.

The DC electromagnetized workpiece is demagnetized with DC electromagnetization, and can be automatically demagnetized by DC commutation attenuation or ultra-low frequency current.

aDC commutation attenuation demagnetization.

Demagnetization is carried out by continuously changing the direction of direct current (including three-phase full-wave rectification current) while decreasing the current through the workpiece to zero. The number of current attenuation should be as many as possible (generally more than 30 times), and the current amplitude of each attenuation should be as small as possible.

b. Automatic demagnetization of ultra-low frequency current.

Ultra-low frequency usually refers to the frequency that can be used to demagnetize a workpiece that is electromagnetized by three-phase full-wave rectification.

c. Demagnetization of heating workpiece.

Raising the temperature of the workpiece above the Curie point by heating is the most effective method of demagnetization, but it is not economical or practical.

Explanation of magnetization and demagnetization.

Demagnetization [tuì cí].

Demagnetization, also known as magnetic cleaning, demagnetization, etc., refers to the process of restoring the magnet to a magnetically neutral state. [1]

Chinese name. Demagnetization.

Foreign name. demagnetization

Alias. Magnetic cleaning.

Magnetically neutralized. Definition.

The process by which a magnet is restored to a magnetically neutral state.

Pinyin. tuì cí

Applied Disciplines. Metallurgical terminology.

Overview. Secondary residual magnetism is a disturbing factor in paleomagnetic research, because its magnetic stability is generally weaker than that of primary residual magnetism, so the unstable components can be removed by certain treatments. When treated with an external magnetic field (constant or alternating), it is called magnetic cleaning, or simply magnetic cleaning; When treated by heating or low temperature method, it is called thermal magnetic cleaning, referred to as thermal cleaning; When treated chemically, it is called chemical magnetic cleaning.

Magnetic cleaning is an important step in paleomagnetic work, which directly affects the reliability of the measurement results. Therefore, the improvement of magnetic cleaning technology is also one of the contents of paleomagnetic research. [2]

Demagnetization is the process by which a magnet returns to a magnetically neutral state, also known as magnetoneutrality. In industrial treatment, there are two methods of demagnetization: one is to heat the material above its Curie point, so that the spontaneous magnetization disappears, and then cool under the action of no magnetic field, and the direction of the magnetic moment of the formed magnetic domain is uniformly distributed, which is the most thorough magnetic neutralization method.

The other is to place the material in an alternating magnetic field that can saturate it, and then gradually reduce the strength of the magnetic field until it is equal to zero, and when this method is carried out once, the remanence in the material may not be completely depleted, and it can be repeated many times in order to achieve magnetic neutrality. [1]

Summary. Ferromagnetic material: A material that is not originally magnetic, but has a magnetic phenomenon due to the action of a magnetic field, which is called magnetization, and only ferromagnetic substances can be magnetized, and non-ferromagnetic substances cannot be magnetized.

The internal reason for the magnetization of ferromagnetic substances is that ferromagnetic substances are made up of many magnetic cells called magnetic domains. Each magnet is equivalent to a small magnet, and when there is no external magnetic field, the small magnetic domains are arranged in a disorderly manner, and the magnetism cancels each other out, and there is no magnetism to the outside. Under the action of the external magnetic field, the magnetic domains will be arranged in an orientation along the direction of the magnetic field, forming an additional magnetic field, which will significantly enhance the magnetic field.

Some ferromagnetic substances still maintain the same orientation and are still magnetic externally after removing the external magnetic field, which becomes a permanent magnet.

What is the principle of demagnetization of ferromagnetic materials?

Ferromagnetic material: A material that is not originally magnetic, but has a magnetic phenomenon due to the action of a magnetic field, which is called magnetization, and only ferromagnetic substances can be magnetized, and non-ferromagnetic substances cannot be magnetized. The internal reason for the magnetization of ferromagnetic substances is that ferromagnetic substances are made up of many magnetic cells called magnetic domains.

Each magnet is equivalent to a small magnet, and when there is no external magnetic field, the small magnetic domains are arranged in a disorderly manner, and the magnetism cancels each other out, and there is no magnetism to the outside. Under the action of the external magnetic field, the magnetic domains will be arranged in an orientation along the direction of the magnetic field, forming an additional magnetic field, which will significantly enhance the magnetic field. Some ferromagnetic substances still maintain the same orientation and are still magnetic externally after removing the external magnetic field, which becomes a permanent magnet.

As mentioned above, if you want to demagnetize a ferromagnetic substance (material), you need to disturb the consistency of its magnetic domain arrangement, and the methods are: 1. Fire: that is, at high temperatures, due to the violent movement of the molecules of the substance after heating.

Collisions and frictions occur in motion. The magnetic domains that were originally arranged in a certain order are changed and become disorganized. So as to achieve the purpose of demagnetization.

2. Hit and collide. It is also possible to demagnetize. The principle is similar to the above, because thermal and magnetic domain motion phenomena can also be generated.

3. Degaussing against the magnetic field. Add a reverse magnetic field to him and leave again, and then add and leave again after a while. This can also be degaussed by repeating it several times.

4.Degaussing using an alternating magnetic field is the same as above. The above should be noted in operation.

When leaving, leave gradually, not suddenly. In short, in order to demagnetize a ferromagnetic material, it is necessary to disrupt the direction of the magnetic domains. The arrangement of the magnetic domains is chaotic and does not show magnetism to the outside.

Demagnetizer is a kind of equipment used to eliminate remanence caused by machining, which generates magnetic field lines by electromagnetic coils, and directly or indirectly interferes with the magnetic properties of the original workpiece through magnetic field lines to achieve demagnetization of the workpiece.

The two most important conditions for demagnetization:

1. Magnetic pole overlap;

2. The strength of the magnetic field decreases.

Method of overlapping magnetic poles:

1. The magnetizing current adopts alternating current;

2. Change the direction of direct current alternately;

3. Change the direction of the specimen in the magnetic field.

The way of decreasing the strength of the magnetic field: the specimen fades away from the magnetic field or the magnetic field fades away from the specimen, and the current decay or step-down is controlled by the power supply.

1. The two most important conditions for demagnetization: the magnetic field strength of the overlapping poles of the magnetic quiet elimination pole decreases.

2. The method of overlapping magnetic poles: the magnetizing current adopts alternating current; Alternately change the direction of the direct current to change the direction of the specimen in the magnetic field.

3. Fang Qina method of decreasing magnetic field strength: the specimen gradually leaves the magnetic field or the magnetic field bridge fades away from the specimen, and the current attenuation or segmented step drop is controlled by the power supply.

The principle of the frame type Oak Mountain demagnetizer is to use the action of the alternating magnetic field to extract magnetic particles from the limited demagnetization gas in the demagnetization chamber, so that the north pole of the surface core excited by the motor is attracted to the reinforcing magnet. The polar pole of the magnet and the electromagnet are affected by the magnetic field almost at the same time, and the equilibrium geomagnetic field between the two poles of the magnet is strengthened to cancel out the alternating magnetic field excited by the motor, and the alternating magnetic field excited by the main motor is extracted from the north pole of the surface core, and the north pole of the surface core is reversed, so as to achieve demagnetization. The principle of frame demagnetizer is also valid for other electromagnetic systems, such as in converter technology, where it can be used to eliminate strong magnetic fields that can cause overload damage to the windings.

In addition, it can be used in power motors, frequency converters, and other magnetics to protect them from magnetic interference, thereby improving their efficiency and performance.