Understanding magnetic material knowledge

2022-01-11

1. Why are magnets magnetic?

Most matter is made up of molecules which are made up of atoms which in turn are made up of nuclei and electrons. Inside an atom, electrons spin and spin around the nucleus, both of which produce magnetism. But in most matter, the electrons move in all sorts of random directions, and the magnetic effects cancel each other out. Therefore, most substances do not exhibit magnetism under normal conditions.

Unlike ferromagnetic materials such as iron, cobalt, nickel or ferrite, the internal electron spins can spontaneously line up in small areas, forming a spontaneous magnetization region called a magnetic domain. When ferromagnetic materials are magnetized, their internal magnetic domains align neatly and in the same direction, strengthening the magnetism and forming magnets. The magnetization process of the magnet is the magnetization process of the iron. The magnetized iron and the magnet have different polarity attraction, and the iron is firmly "stuck" together with the magnet.

2. How to define the performance of a magnet?

There are mainly three performance parameters to determine the performance of the magnet:
Remanent Br: After the permanent magnet is magnetized to technical saturation and the external magnetic field is removed, the retained Br is called residual magnetic induction intensity.
Coercivity Hc: To reduce the B of the permanent magnet magnetized to technical saturation to zero, the reverse magnetic field intensity required is called magnetic coercivity, or coercivity for short.
Magnetic energy product BH: represents the magnetic energy density established by the magnet in the air gap space (the space between two magnetic poles of the magnet), namely, the static magnetic energy per unit volume of the air gap.

3. How to classify metal magnetic materials?

Metal magnetic materials are divided into permanent magnetic materials and soft magnetic materials. Usually, the material with intrinsic coercivity greater than 0.8kA/m is called permanent magnetic material, and the material with intrinsic coercivity less than 0.8kA/m is called soft magnetic material.

4. Comparison of magnetic force of several kinds of commonly used magnets

Magnetic force from large to small arrangement: Ndfeb magnet, samarium cobalt magnet, aluminum nickel cobalt magnet, ferrite magnet.

5. Sexual valence analogy of different magnetic materials?

Ferrite: low and medium performance, the lowest price, good temperature characteristics, corrosion resistance, good performance price ratio
Ndfeb: highest performance, medium price, good strength, not resistant to high temperature and corrosion
Samarium cobalt: high performance, highest price, brittle, excellent temperature characteristics, corrosion resistance
Aluminum nickel cobalt: low and medium performance, medium price, excellent temperature characteristics, corrosion resistance, poor interference resistance
Samarium cobalt, ferrite, Ndfeb can be made by sintering and bonding method. The sintering magnetic property is high, the forming is poor, and the bonding magnet is good and the performance is reduced a lot. AlNiCo can be manufactured by casting and sintering methods, casting magnets have higher properties and poor formability, and sintered magnets have lower properties and better formability.

6. Characteristics of Ndfeb magnet

Ndfeb permanent magnetic material is a permanent magnetic material based on intermetallic compound Nd2Fe14B. Ndfeb has a very high magnetic energy product and force, and the advantages of high energy density make ndFEB permanent magnet material widely used in modern industry and electronic technology, so that instruments, electroacoustic motors, magnetic separation magnetization equipment miniaturization, light weight, thin become possible.

Material characteristics: Ndfeb has the advantages of high cost performance, with good mechanical characteristics; The disadvantage is that the Curie temperature point is low, the temperature characteristic is poor, and it is easy to powdery corrosion, so it must be improved by adjusting its chemical composition and adopting surface treatment to meet the requirements of practical application.
Manufacturing process: The manufacture of Ndfeb using powder metallurgy process.
Process flow: batching → melting ingot making → powder making → pressing → sintering tempering → magnetic detection → grinding → pin cutting → electroplating → finished product.

7. What is a single-sided magnet?

Magnet has two poles, but in some job position need single pole magnets, so we need to use iron to a magnet encase, iron by the side of magnetic shielding, and through the refraction to the other side of the magnet plate, make the other side of the magnet magnetic strengthen, such magnets are collectively known as single magnetic or magnets. There is no such thing as a true one - sided magnet.
The material used for single-side magnet is generally arc iron sheet and Ndfeb strong magnet, the shape of the single-side magnet for ndFEB strong magnet is generally round shape.

8. What is the use of single-sided magnets?

(1) It is widely used in the printing industry. There are single-sided magnets in gift boxes, mobile phone boxes, tobacco and wine boxes, mobile phone boxes, MP3 boxes, moon cake boxes and other products.
(2) It is widely used in the leather goods industry. Bags, briefcases, travel bags, mobile phone cases, wallets and other leather goods all have the existence of single-sided magnets.
(3) It is widely used in the stationery industry. Single-side magnets exist in notebooks, whiteboard buttons, folders, magnetic nameplates and so on.

9. What should be paid attention to during the transportation of magnets?

Pay attention to indoor humidity, which must be maintained at a dry level. Do not exceed room temperature; Black block or blank state of the product storage can be properly coated with oil (general oil); Electroplating products should be vacuum-sealed or air-isolated storage, to ensure the corrosion resistance of coating; Magnetizing products should be sucked together and stored in boxes so as not to suck up other metal bodies; Magnetizing products should be stored away from magnetic disks, magnetic cards, magnetic tapes, computer monitors, watches and other sensitive objects. Magnet magnetization state should be shielded during transportation, especially air transportation must be completely shielded.

10. How to achieve magnetic isolation?

Only material that can be attached to a magnet can block the magnetic field, and the thicker the material, the better.

11. Which ferrite material conducts electricity?

Soft magnetic ferrite belongs to the magnetic conductivity material, specific high permeability, high resistivity, generally used at high frequency, mainly used in electronic communication. Like the computers and TVS we touch every day, there are applications in them.
Soft ferrite mainly includes manganese-zinc and nickel-zinc etc. Manganese-zinc ferrite magnetic conductivity is greater than that of nickel-zinc ferrite.
What is the Curie temperature of permanent magnet ferrite?
It is reported that the Curie temperature of ferrite is about 450℃, usually greater than or equal to 450℃. The hardness is about 480-580. The Curie temperature of Ndfeb magnet is basically between 350-370℃. But the use temperature of Ndfeb magnet can not reach the Curie temperature, the temperature is more than 180-200℃ magnetic property has attenuated a lot, magnetic loss is also very large, has lost the use value.

13. What are the effective parameters of the magnetic core?

Magnetic cores, especially ferrite materials, have a variety of geometric dimensions. In order to meet various design requirements, the size of the core is also calculated to suit the optimization requirements. These existing core parameters include physical parameters such as magnetic path, effective area and effective volume.

14. Why is corner radius important for winding?

The angular radius is important because if the edge of the core is too sharp, it can break the insulation of the wire during the precise winding process. Make sure the core edges are smooth. Ferrite cores are moulds with a standard roundness radius, and these cores are polished and deburred to reduce the sharpness of their edges. In addition, most cores are painted or covered not only to make their angles passivated, but also to make their winding surface smooth. The powder core has a pressure radius on one side and a deburring semi-circle on the other side. For ferrite materials, an additional edge cover is provided.

15. What type of magnetic core is suitable for making transformers?

To meet the needs of the transformer core should have a high magnetic induction intensity on the one hand, on the other hand to keep its temperature rise within a certain limit.
For inductance, the magnetic core should have a certain air gap to ensure that it has a certain level of permeability in the case of high DC or AC drive, ferrite and core can be air gap treatment, powder core has its own air gap.

16. What kind of magnetic core is best?

It should be said that there is no answer to the problem, because the choice of the magnetic core is determined on the basis of applications and application frequency, etc, any material choice and market factors to consider, for example, some material can ensure the temperature rise is small, but the price is expensive, so, when select material against high temperature, It is possible to choose a larger size but the material with a lower price to complete the work, so the choice of the best materials to application requirements for your first inductor or transformer, from this point, the operating frequency and the cost is the important factors, such as the optimal selection of different material is based on the switching frequency, temperature and magnetic flux density.

17. What is anti-interference magnetic ring?

Anti-interference magnetic ring is also called ferrite magnetic ring. Call source anti-interference magnetic ring, is that it can play a role of the anti-interference, for example, electronic products, by the outside disturbance signal, invasion of electronic products, electronic products received the outside disturbance signal interference, have not been able to run normally, and anti-interference magnetic ring, just can have this function, as long as the products and the anti-interference magnetic ring, it can prevent the outside disturbance signal into electronic products, It can make electronic products run normally and play an anti-interference effect, so it is called anti-interference magnetic ring.

Anti-interference magnetic ring is also known as ferrite magnetic ring, because ferrite magnetic ring it is made of iron oxide, nickel oxide, zinc oxide, copper oxide and other ferrite materials, because these materials contain ferrite components, and ferrite materials produced by the product like a ring, so over time it is called ferrite magnetic ring.

18. How to demagnetize the magnetic core?

The method is to apply an alternating current of 60Hz to the core so that the initial driving current is sufficient to saturate the positive and negative ends, and then gradually reduce the driving level, repeated several times until it drops to zero. And that's going to make it kind of revert back to its original state.
What is magnetoelasticity (magnetostriction)?
After the magnetic material is magnetized, a small change in geometry will occur. This change in size should be on the order of a few parts per million, which is called magnetostriction. For some applications, such as ultrasonic generators, the advantage of this property is taken to obtain mechanical deformation by magnetically excited magnetostriction. In others, a whistling noise occurs when working in the audible frequency range. Therefore, low magnetic shrinkage materials can be applied in this case.

20. What is a magnetic mismatch?

This phenomenon occurs in ferrites and is characterized by a decrease in permeability that occurs when the core is demagnetized. This demagnetization can occur when the operating temperature is higher than the Curie point temperature, and the application of alternating current or mechanical vibration gradually decreases.

In this phenomenon, the permeability first increases to its original level and then exponentially decreases rapidly. If no special conditions are expected by the application, the change in permeability will be small, as many changes will occur in the months following production. High temperatures accelerate this decline in permeability. Magnetic dissonance is repeated after each successful demagnetization and is therefore different from aging.


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