The terms that magnetic material professionals must know
1. The hysteresis loop curve of hard magnetic materials (such as neodymium iron boron strong magnetism) has two significant characteristics: one is that they can be strongly magnetized under the action of an external magnetic field, and the other is hysteresis, which means that the hard magnetic material still retains its magnetization state after the external magnetic field is removed. The following figure shows the relationship curve between the magnetic induction intensity B and the magnetization field intensity H of the hard magnetic material, which is called the hysteresis loop curve
2. When the magnetic field gradually changes from O to - Hc in reverse, the magnetic induction intensity B disappears, indicating that in order to eliminate remanence, a reverse magnetic field must be applied. Hc is called coercivity, and its magnitude reflects the ability of the magnetic material to maintain a remanent state. The purple line segment is called the demagnetization curve. 3. The intrinsic magnetic induction intensity generated by the magnetization of rectangular/square permanent magnet materials under an external magnetic field is called intrinsic magnetic induction intensity Bi, also known as magnetic polarization intensity J. The curve describing the relationship between the intrinsic magnetic induction intensity Bi (J) and the magnetic field intensity H is a curve that reflects the intrinsic magnetic properties of permanent magnet materials, known as the intrinsic demagnetization curve, abbreviated as the intrinsic curve. When the magnetic polarization intensity J on the intrinsic demagnetization curve is 0, the corresponding magnetic field intensity is called the intrinsic coercivity Hcj.
4. Surface treatment - Phosphating sintered neodymium iron boron exposed magnets will oxidize and corrode in the air. When neodymium iron boron magnets are circulated and stored for too long, and the subsequent surface treatment method is not clear, phosphating technology is generally used for simple anti-corrosion treatment. The process of phosphating treatment on the surface of the magnet is: degreasing → water washing → acid washing → water washing → surface conditioning → phosphating treatment → sealing and drying. The phosphating process is currently mainly produced using commercial phosphating solutions. After phosphating, the product has a uniform color and a clean surface. It can be vacuum sealed, which greatly extends the storage time and is better than previous oil immersed and oil coated storage methods. 5. Surface treatment - Electrophoretic coating is the process of immersing a component in a water-soluble electrophoresis bath, inserting both a positive electrode and a negative electrode into the bath, and reducing the direct current between the two poles to generate an electrochemical reaction. This results in the uniform deposition of water-soluble coating (usually polymer resin, such as epoxy resin) on the component, forming a corrosion-resistant coating composed of resin particles, or in other words, a polymer anti-corrosion layer. The electrophoretic coating not only has good adhesion with the surface of porous magnets, but also has excellent corrosion resistance to salt spray, acid, alkali, etc., with excellent anti-corrosion performance, but poor resistance to moisture and heat. 6. Surface Treatment - Parylene Parylene is a protective polymer material, also known as poly (p-xylene) in Chinese. It can be vapor deposited under vacuum, and the excellent penetration of Parylene active molecules can form a transparent insulation coating with no pinholes and uniform thickness inside, at the bottom, and around the components, providing a complete and high-quality protective coating to resist the damage of acid, alkali, salt spray, mold, and various corrosive gases. The unique preparation process and excellent performance of Parylene enable it to fully coat small and ultra small magnetic materials without weak points. The magnetic materials can be immersed in hydrochloric acid for more than 10 days without corrosion. Currently, many small and ultra small magnetic materials internationally use Parylene as insulation and protective coatings. 7. Dimensional tolerance, abbreviated as tolerance, refers to the allowable variation in the dimensions of a part during cutting. It is permissible for magnetic materials to have certain dimensional differences, and the absolute value of the difference between the maximum and minimum limit dimensions of the tolerance, or the difference between the allowable upper and lower deviations. 8. Geometric tolerance, also known as geometric tolerance, includes shape tolerance and position tolerance. Any component is composed of points, lines, and surfaces, which are called features. The actual elements of machined parts always have errors compared to ideal elements, including shape errors and position errors. Such errors affect the functionality of mechanical products, and corresponding tolerances should be specified in the design and marked on the drawings according to the specified standard symbols.
9. Neutral salt spray test (NSS) is an environmental test that mainly uses artificial simulated salt spray environmental conditions created by salt spray testing equipment to assess the corrosion resistance of products or metal materials. It is divided into two types: neutral salt spray and acidic salt spray, and the difference lies in the standards and testing methods they comply with, also known as "NSS" and "CASS" tests. Sintered Nd-Fe-B is subject to neutral salt spray test. According to the national standard, continuous spray test is adopted. The test conditions are: 35 ℃± 2 ℃, 5% ± 1% NaCl solution (mass fraction), and the pH of collected salt spray settling solution is between 6.5 and 7.2. The angle of sample placement has an impact on the test results. The tilt angle of sample surface placed in the salt spray box is 45 °± 5 °. 10. The wet heat test of sintered neodymium iron boron is a test method that evaluates the resistance of samples to wet heat deterioration in an accelerated manner. The samples are subjected to high unsaturated wet heat vapor pressure for a long period of time. The testing conditions are: temperature of 85 ℃± 2 ℃, relative humidity of 85% ± 5%, and humidification using distilled water or deionized water. The severity level is level 1, which is 168 hours. 11. High pressure accelerated aging test (PCT) is generally referred to as pressure cooker cooking test or saturated steam test. It mainly tests the high humidity resistance of the test sample by subjecting it to harsh temperature, saturated humidity, and pressure environments. The high-pressure accelerated aging test of sintered neodymium iron boron involves placing the sample in a high-pressure accelerated aging test equipment containing distilled water or deionized water with a resistivity greater than 1.0M Ω· cm. 12. Hardness and Strength Hardness refers to the ability of a material to resist local pressure from hard objects on its surface, and is an indicator for comparing the hardness of various materials. The higher the hardness, the stronger the metal's ability to resist plastic deformation. Strength refers to the maximum ability of a material to resist external destructive forces. Strength is divided into different forms of external force: tensile strength (tensile strength), which refers to the ultimate compressive strength under tension, the ultimate bending strength under pressure, and the ultimate strength when the external force is perpendicular to the material axis and causes the material to bend after being applied