Powder metallurgy
Powder metallurgy method (also called sintering process) is the mostly applied processing method of neodymium magnet. And the resultant of this processing method is sintered neodymium magnet. This processing method is a little bit complex because it involves large number of sub steps. However, the main steps of this method are relatively concise, which are shown here (Also see figure 1): First, raw material of neodymium magnet was prepared and treated preliminarily. After that, accessory ingredients with specific quantity were added into the raw material that has been treated. Then, both accessory ingredients and raw material that has been treated were melted, followed by mixing two kinds of substances up (Denote the mixture as substance 1). Subsequently, substance 1 was crushed, followed by fine grinding (Here, the resultant is denoted as substance 2). Next, other new accessory ingredients were added into substance 2 to produce substance 3. And then, substance 3 was pressed, following by sintering to get substance 4. After that, heat treatment was applied to substance 4, followed by machining to obtain substance 5. Then, electroplating method was performed, followed by magnetizing. This time, substance 6 (which is the semi-manufactured goods of neodymium magnet product) is produced. Subsequently, this semi-manufactured good was checked, followed by packing. If its quality reaches required standard, one specific neodymium magnet product is produced[1].
Figure 1: Sintering process[1]
Compression moulding
Compression molding method is also one optional processing method of neodymium magnet. Especially for bonded Nd-Fe-B magnets, the application of this processing method provides relatively high packing density of magnetic powder. It implies that higher magnetic energy product is available. What’s more, this processing method has relatively low cost and has less requirement to the equipment at the same time. All these benefits make compression molding method becomes remarkable in all the processing methods of bonded Nd-Fe-B magnets. The concise procedure of this processing method is also a highlight. The main steps with their corresponding cautions are shown here: First, the magnetic powder was chosen. The report said that there have five main kinds of magnetic powder, which involve magnetic powder of rapid quenching，HDDR magnetic powder，Two-phase Nano-coupling magnetic powder，MA magnetic powder and atomization magnetic powder. Different magnetic powder have different characteristic, which implies that the strategy of selection of magnetic powder should satisfy the application of bonded Nd-Fe-B magnets. After that, coupling reagent was applied to the surface treatment of magnetic powder since the characteristic of the surface of magnetic powder will change because of the application of coupling reagent. Such change is able to strengthen the conjunction between magnetic powder and agglomerant, this strengthen will increase the resistance to oxidation also the resistance to corrosion of magnetic powder. What’s more, the mechanical property and magnetic performance will be modified if suitable coupling reagent is chosen. After these previous two steps, denote the resultant as substance 1. Then, agglomerant with powder form was added into substance 1, followed by uniformly mixing agglomerant and substance 1 up to produce substance 2. Subsequently, substance 2 was experienced prilling process, followed by pressing, which is the most important step in all procedure. The pressure that used for pressing need to be controlled to maintain the most positive magnetic performance. Too lower pressure will lead to low density of magnet. It represents low magnetic performance. Similarly, too large pressure will cause damage to magnetic powder. It is another factor about magnetic performance decreasing. What’s more, shape of magnetic powder, size distribution and apparent density also need to be considered since they can influence magnetic performance as well. Now the resultant is denoted as substance 3. Next, substance 3 was heated to accomplish solidification. The operating temperature depends on agglomerant. And then, cathode electrophoresis was applied to resultant to accomplish the surface treatment, followed by magnetism. After these eight process, bonded Nd-Fe-B magnets is produced[2].
Dentures
Tiny neodymium magnets can be used for attachments in corrective devices or for holding together replacement dentures where several teeth are missing. Because of their strength, even tiny neodymium magnets can be effective and when coated they have an increased resistance to corrosion[4].
Motors and Generators
Electric motors rely upon a combination of an electromagnet and a permanent magnet, usually a neodymium magnet to convert electric energy into mechanical energy. A generator is the reverse, it converts mechanical energy into electric energy by moving a conductor through a magnetic field[3].
Hard disk drives
A hard disk drive records data by magnetising and demagnetising a thin film of ferromagnetic material on a disk. Each disk is separated into many tracks and sectors and each sector has many tiny individual magnetic cells which are magnetised by the drives read/write head when data is written to the drive. Hard drive heads are made from ferrite wrapped in a fine wire coil. When writing, the coil is energised, a strong magnetic field forms, and the recording surface adjacent to the gap is magnetised. Strong magnets are also used in the actuator that moves the read/write head into position[4].
Lifting machinery
Permanent magnets are essential in the heavy engineering and manufacturing industries, used for lifting large ferrous items. Switchable release magnets using super-strong neodymium magnets are commonly used as they are supplied with a quick-release switching mechanism[4].
MRI scanners
MRI scanners produce a large magnetic field which aligns the protons in a human body in the direction of the magnetic field. Radio frequency waves are then directed at the body producing detailed internal images. Many ‘open’ MRI machines used in hospitals use large
neodymium magnets, they literally help save lives[4].
Reference
[1] Hu Wenyan.Properties and Research Progress of NdFeB Permanent Magnet Materials[J].Modern Electronic Technology, 2012,35(02): 151-152+155.
[2] Bai Shuxin, Zhang Hong, Lu Li. High-performance magnetic composites - bonded NdFeB magnets [J]. Magnetic materials and devices, 2002 (04): 24-27.
[3]] Wang Fang. (2018). Development of Nd-Fe-B permanent magnetic materials. Gansu Science and Technology Vertical and Transverse, v.47; No. 278 (08), 50-53
[4] First 4 Magnets. A Division of Magnet Expert. Retrieved from: