Strong magnetism refers to a kind of strong magnet, and its professional name is rare earth strong magnetism, NdFeB. This kind of magnet has high performance and is widely used in toys, packaging boxes, lamps, handicrafts, speakers, medical machinery, health products, electronic products, hardware tools and other products. In general, N33, N35 and N38 are suitable. These three are the most common properties of NdFeB's strong magnetism. In general, if the requirements are not very high,
High performance above N40: This performance is generally used in mobile phones, precision instruments, aerospace, cutting-edge scientific research and other fields, and it is divided into N40, N42, N45, N48, N50 and N52. The temperature resistance of the above nine properties is ≤80℃, and once it exceeds this temperature, it will demagnetize.
(2) Brand of magnet materials
1. Brand of magnet material
In order to distinguish permanent magnets made of different materials and make it easy for people to know, most factories use fixed letters to represent different magnets, such as N35 magnets, where N stands for NdFeB and Y stands for permanent magnet ferrite. If it is PCx, such as PC40, it is soft ferrite with high permeability.
2. Sintered NdFeB brand
The brand of sintered NdFeB permanent magnet consists of three parts: the main name and two magnetic characteristics. The first part is the main name, which is simplified from the chemical symbol Nd of neodymium to N. The second part is the nominal value of the maximum magnetic energy product (BH)max of the material (in KA/m3), and the letters in the third part indicate the highest working temperature of the magnet. Example of brand: N35H stands for sintered NdFeB permanent magnet, with a maximum BH of about 35MGOe (280 KA/m3) and a maximum working temperature of 120℃.
The brands of NdFeB magnetic materials are: N30 ~ N5230h ~ 50h30sh ~ 50sh28uh ~ 40uh30eh ~ 35eh, etc.
3. Working temperatures corresponding to different brands
The maximum working temperature corresponding to different brands is basically the same for each manufacturer:
1) There is no letter after the data. For example, the temperature resistance of N35 is generally ≤80℃
2) The data ends with m, for example, the temperature resistance of N50M is generally ≤ 100℃.
3) The data ends with h, for example, the temperature resistance of N48M is generally ≤ 120℃.
4) The data ends with SH, for example, the temperature resistance of N45SH is generally ≤ 150℃.
5) The data ends with UH, for example, the temperature resistance of N35UH is generally ≤ 180℃.
6) The data ends with EH. For example, the temperature resistance of N50M is generally ≤200℃.
7) The data ends with EH. For example, the temperature resistance of N50M is generally ≤220℃.
The last five properties are all high temperature resistant. If this temperature is exceeded, the magnet will demagnetize.
A magnet with high temperature resistance, such as 38SH, has a temperature resistance of 150 degrees, and its magnetic force at room temperature is equivalent to N38. It should be mentioned here that at the same temperature of 70 degrees, the working performance of 38SH is much better than that of N38. Of course, the temperature of 90 degrees is self-evident, exceeding 100 degrees. Neodymium magnet is the most taboo, and the highest temperature of N brand magnet is 80 degrees.
(3) remanence
Short for remanence, symbol Br. Remanence Br: The permanent magnet is magnetized to technical saturation, and the retained Br is called remanence induction intensity after the external magnetic field is removed.
(4) the introduction of coercive force
The unit of coercivity is Oster (Oe) or Ampere/Meter (A/m), 1 A/m= 79.6 Oe. Coercive force is divided into magnetic coercivity (Hcb) and intrinsic coercivity (Hcj).
1. magnetic coercivity
When the magnet is magnetized reversely, the reverse magnetic field intensity required to reduce the magnetic induction intensity to zero is called magnetic induction coercivity. But at this time, the magnetization of the magnet is not zero, but the applied reverse magnetic field and the magnetization of the magnet cancel each other. The external magnetic induction intensity is zero. At this time, if the external magnetic field is removed, the magnet still has certain magnetism.
2. Intrinsic coercivity
The reverse magnetic field strength required to reduce the magnetization of a magnet to zero is called intrinsic coercivity. Intrinsic coercivity is a physical quantity to measure the demagnetization resistance of a magnet, which means that the magnetization m in the material returns to zero. In the use of magnets, the higher the coercivity of magnets, the better the temperature stability.
(5) Maximum magnetic energy product
The maximum magnetic energy product represents the magnetic energy density established by the magnet in the air gap space (the space between the poles of the magnet), that is, the static magnetic energy per unit volume of the air gap. Because this energy is equal to the product of Bm and Hm of the magnet, it is called magnetic energy product.
(6) Working temperature
The brands of magnets range from N35 to the highest N52 according to their magnetic properties. Some manufacturers have N44 grade, some have N45 grade directly, and other grades are basically the same. N series maximum 80 degrees; M series maximum 100 degrees; H max 120 degrees; SH max 150 degrees; UH max 180 degrees; Uh, Max. 200 degrees; Ah, the maximum is 220 degrees.
(7) Surface treatment (electroplating)
Neodymium magnet coating: nickel, copper, chromium, gold, black zinc, epoxy resin. Its surface plating is different, its color and storage time are different, and each has its own advantages and disadvantages.
1. Galvanizing
The surface looks silvery white, and salt spray of 12-48 hours can be used. It can be bonded with some glue (such as AB glue), and it can be preserved for two to five years after electroplating. Its advantage is that the price is relatively low.
Step 2: Nickel plating
It looks like stainless steel, which is not easy to oxidize when placed in air, with beautiful appearance and good gloss. Electroplating can pass the salt spray test of 12-72 hours. Its disadvantage is that it can't be bonded with some glue, which will make the coating fall off. In order to accelerate the oxidation speed, nickel-copper-nickel electroplating 120-200 hours is commonly used in the market, but its electroplating cost is relatively high.
3. Copper plating
Most of them appear in the hardware industry, NdFeB industry is rarely used, and its appearance is yellow.
Step 4: Chrome plating
Chromium plating industry is also rare, and its electroplating cost is very high, which is unacceptable to ordinary companies. But it has strong corrosion resistance and is not easy to react with other substances. Mainly used in places with strong pH value, the domestic product price is relatively low, so few people choose it.
5. Black zinc plating
According to customer requirements, the product surface treatment is black. Electroplating process is to add a layer of black protective film through chemical treatment on the basis of zinc plating. This film can also protect the product, increase the salt spray time and prolong the oxidation time. However, its surface is easily scratched and loses its protective effect. Few people use it now, and most of them are replaced by resin.
6. Gold plating
This industry is very popular now. Most of the gold jewelry we saw in some stalls on the street was gold-plated or copper. Gold plating makes the product look like gold and very beautiful. Generally used in jewelry industry, magnet products can also be gold-plated for magnetic jewelry.
7. Epoxy resin electroplating
After nickel plating, the product is coated with a layer of resin paint. This industry only entered the market in the past two years and developed rapidly. Many people are using various electroplating products now, and its greatest advantage is that it can achieve the color you want.
(8) What is the relationship between the magnetic force of a magnet and remanence, apparent magnetic force, magnetic energy product and performance grade?
The remanence is proportional to the surface magnetism. To improve the magnetic force, it is necessary to improve the remanence, which is to improve the number of rows. The higher the brand, the higher the remanence and the higher the magnetic energy product.