What is a magnetic tile?

What is a magnetic tile?

Magnetic tile is a kind of permanent magnet, which is mainly used in permanent magnet motor.

Classification of magnetic tiles:

There are three main categories of magnetic tile according to the different raw materials:

• 1. Ferrite magnetic tile
• 2. NdFeB magnetic tile
• 3. Aluminum nickel cobalt magnetic tile

The use of magnetic tile:

Magnetic tile is mainly used in permanent magnet DC motor. Different from electromagnetic motor which generates magnetic potential source through excitation coil, permanent magnet motor generates constant magnetic potential source with permanent magnet material. Permanent magnet magnetic tile instead of electric excitation has many advantages, can make the motor structure is simple, convenient maintenance, light weight, small volume, reliable use, less copper, copper consumption is low, small energy consumption, etc.. The influence of the performance of magnetic tile on the motor:

• (1) High residual magnetic induction intensity Br. Because BR is high, the motor can have high speed, large output torque and large power. The motor will have higher efficiency.
• (2) High HCB. Because HCB is high, the required electromotive force output of the motor can be ensured, so that the working point of the motor is close to the maximum magnetic energy product, and the capacity of the magnet can be fully utilized.
• (3) High HCJ. HCJ high can ensure that the motor has a strong anti-overload demagnetization and anti-aging, anti-low temperature ability.
• (4) High (BH) Max. The higher (BH) Max is, the better the actual operating coefficient of permanent magnet ferrite in the motor is.
• (5) Magnetic energy Φ the bigger the better, this will greatly improve the work efficiency of the machine.
• (6) The better the rectangular degree of demagnetization curve, the smaller the dynamic loss of the motor.
• (7) The higher the resistivity of permanent magnet ferrite, the smaller the eddy current loss.
• (8) The temperature coefficient of permanent magnet ferrite is small, so it has good temperature stability at high temperature.

A brief history of the development of magnetic tiles

The development of magnetic tile is changing according to the demand of permanent magnet motor itself.
1) Permanent magnet motor is divided into permanent magnet DC motor and permanent magnet AC motor.
Permanent magnet AC motor refers to the multi-phase synchronous motor with permanent magnet rotor, previously mainly used ferrite and aluminum nickel-cobalt magnetic tile, with the power requirements are more and more high, ferrite and aluminum nickel-cobalt because of the low magnetic energy product can not meet the requirements, now NdFeB magnetic tile is widely used in the field of high-power synchronous motor and generator. Of course, NdFeB magnetic tile, because of rare earth resources, the price of raw materials doubled, its manufacturing costs and production prices will continue to rise in the future, affecting its extensive use in some low-end fields. The negative temperature coefficient of NdFeB permanent magnet itself and low Curie temperature also limit its application in high temperature occasions.
Permanent magnet DC motor is divided into brushless motor and general DC motor with commutator, from the shape of the magnet, the number of poles to judge its application
In the ordinary DC motor, with 2 and 4 poles in the majority, and the magnetic tile is basically used as the motor stator, micro DC motor most of the use of ferrite magnetic tile, mainly used in the field of toys, home appliances, automobiles. Brushless motor with magnetic tile as stator, generally more than 6 poles, so its central Angle is far less than the ordinary DC motor with the magnetic tile. But the magnetic tile as a brushless motor rotor, there can be 4, 6 more than the number of poles, for 4 poles, the rotor is the outer surface of magnetization, and because to assemble into a circle, its central Angle is close to 90°, which can be different from the ordinary DC motor.
2) Magnetic tile according to different application fields, have different requirements for performance and magnetic field wave form, as the rotor field, its outer surface table field requirement is high, the basic requirements for sine wave waveform, the stator, then according to the requirements of the motor output, select the requirement of the spark and noise, as the stator magnetic tile, tile arc high table field, because of magnetic tile itself shape and nature of production, the main waveform as saddle, the waveform output is big, but the spark noise, no-load current. In order to improve the vibration noise, reversing spark, reduce no-load current, the shape and size of the magnetic steel, mold design and so on should be carefully designed, among which the unequal thickness magnetic tile has been widely used, its principle is to make the magnetic tile arc air gap magnetic field waveform tends to flat top wave.
Production technology of magnetic tile
According to different materials and types, the technology of magnetic tile varies greatly.

The ferrite tile is mainly sintered ferrite, and the NdFeB tile is divided into sintering and bonding

• 1. The production process of sintered ferrite tile is mainly divided into wet pressure anisotropy, dry pressure isotropy and dry pressure anisotropy. The difference between anisotropy and isotropy is whether there is orientation magnetic field during press forming. This paper mainly introduces the process of wet compaction. The process flow of wet compaction is as follows: raw material – pre sintering – coarse grinding (primary ball milling) – proportioning – secondary ball milling (wet grinding) – magnetic field forming – sintering – grinding – Cleaning – magnetization. Because the slurry contains water, the particles are easy to turn in the magnetic field, so the orientation degree is higher than that of dry compaction, and the performance is also higher.
• 2. Sintered Nd-Fe-B magnetic tile: proportioning – smelting – crushing – pulverizing – magnetic field forming – isostatic pressing – vacuum sintering and tempering – wire cutting and other processing – electroplating – magnetization

There are three common magnetization methods:

• 1. The magnetic tile is magnetized separately, then installed into the casing, and then assembled as a whole;
• 2. The magnetic tile is installed into the casing (glued) and then magnetized, and then assembled as a whole;
• 3. The magnetic tile is installed into the casing (glued), and then the finished product is assembled, and finally the whole is magnetized.

The influence of different ways on magnetization of magnetic tile is as follows:

• 1. The surface remanence of the first magnetization method is about 10% lower than that of the second and third magnetization methods;
• 2. The first way of magnetization is very convenient, some factories use solenoid tunnel magnetization, the production efficiency is very high;
• 3. In some cases, it is very convenient to use the second way of magnetization;
• 4. The third way is magnetization. Many small motors (mostly with three slots) use this way. When installing the rotor, because there is no magnetic force, it is very easy to assemble, but it is not convenient to check whether the magnetic field is fully charged.
• 5. The first magnetization method belongs to open circuit magnetization. Because there is no external magnetic circuit and no closed circuit during magnetization, magnetization is not easy to be saturated, which has an impact on the magnetic flux density of magnetic tile, which is generally lower than that of closed circuit magnetization;
• 6. The second way of magnetization is the most commonly used, which belongs to closed-circuit magnetization. The magnetic flux density after magnetization is also the highest, and the waveform of air gap flux density can be adjusted by the shape of the magnetizing head to meet the requirements of different motor performance. However, when assembling the motor, special tooling is needed, otherwise the rotor may be damaged or the magnetic tile may be damaged due to magnetic attraction Magnetic fragmentation;
• 7. The third magnetization method also belongs to closed-circuit magnetization (because the rotor lamination is a good magnetic conductive material). The magnetic flux density of magnetized tile is generally between the first and the second. Note: when using the whole machine, it is better to keep the carbon brush and rotor winding in an open circuit state, otherwise, there may be sparking on the contact surface between the carbon brush and the commutator.

Source: China Arc Magnet Manufacturer – www.rizinia.com