Al-Ni-Co magnet has been widely used in various industrial and consumer products since its successful research and development in 1930s. This kind of magnet is composed of aluminum, nickel, cobalt, iron and other trace metal elements. Its high coercivity and high Curie temperature make it an ideal choice for motors, electric guitar pickups, microphones, sensors, speakers, traveling wave tubes and so on. But how much do you know about the production process of Al-Ni-Co magnets? This article will discuss this topic in depth.
There are two main methods to produce Al-Ni-Co magnets, one is sintering, and the other is casting. Compared with the magnets prepared by sintering method, the Al-Ni-Co magnets prepared by casting method have higher density and mass and better magnetic properties. However, the production of Al-Ni-Co magnets prepared by sintering method is more economical. The anisotropy and isotropy of Al-Ni-Co magnets can be controlled by both sintering and casting methods.
For large Al-Ni-Co magnets with a weight of tens of kilograms, casting method is usually adopted. For magnets weighing only a few grams, sintering method is generally used. If a large number of magnets are needed, the sintering process is usually selected.
Below, we will introduce these two steps of producing Al-Ni-Co magnets in detail:
Production steps of casting Al-Ni-Co magnet:
1. Casting furnace: Various grades of Al-Ni-Co have specific formulas in terms of the percentage of Al, Ni, Co and Fe used. A large number of single elements are put into an induction furnace and melted at a temperature above 1750 degrees Celsius. Since aluminum melts at a lower temperature, the amount of aluminum actually added is more than that needed to form the final magnet.
2. Casting: The molten material is poured into a shell mold or a larger wet sand mold. With the cooling of the molten metal, the shell mold starts to burn and disintegrates when the magnet cools.
3. Grinding: collect the newly cast magnets from the mold, and then grind them on the grinding wheel to remove the runner gate.
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Heat treatment: the magnet is heated to a high temperature, then placed in a magnetizer and cooled in a strong magnetic field. This process is called magnetization hardening. Then put the magnet in a large tempering furnace for a few days to stabilize the magnet.
5. Grinding: The magnet needs to be grounded to a strict tolerance. Due to the high hardness of the magnet, this process is completed by grinding.
6. Testing: You can use hysteresis curve tester, Gauss meter or fluxmeter to test Al-Ni-Co magnet.
7. Coating/painting: If special coating is needed, it should be done at the end of the process. The magnetic pole of the magnet may be polished to make it brighter.
8. Magnetization: The magnet is put into a coil or solenoid magnetizer, and the necessary magnetic field is generated in an instant by a powerful electric pulse to completely magnetize the magnet.
Preparation steps of sintered Al-Ni-Co magnet:
1. Pressing: Before producing sintered Al-Ni-Co magnets, raw materials need to be ground into powder. Then, the powdered magnetic material is pressed into a mold with a shape similar to that of a magnet.
2. Sintering: The pressed powder is sintered in a furnace in hydrogen atmosphere at a temperature higher than 1200 C.. This process fuses all the compressed particles together to form a magnet.
3. Cooling: Then, cool the hot material. In this process, if the material is cooled in the presence of external magnetic field, it will have anisotropic characteristics and preferred magnetic direction, making it stronger. If there is no external magnetic field, the formed magnet will be isotropic and have no preferential magnetic direction.
4. Coating: Generally speaking, sintered Al-Ni-Co magnets do not need further shape or processing, because the molds they are pressed into are very close to the required magnet shape. If a specific coating is needed, it can be done before magnetization.
5. Magnetization: Finally, the magnetic material is put into a coil or solenoid magnetizer, and a strong magnetic field is generated by an electric pulse in an instant to realize complete magnetization of the magnet.