Introduction to four manufacturing processes of bonded Nd-Fe-B
Bonded NdFeB, consisting of Nd2Fe14B, is a synthetic magnet. Bonded NdFeB magnets are made of fast-hardened NdFeB powder and binder mixed by “press molding” or “injection molding”. Bonded magnets have high dimensional accuracy and can be made into magnetic components with relatively complex shapes, and they are characterized by one-time molding and multi-pole orientation. NdFeB bonded magnets have high mechanical strength and can be molded with other components in a single process.
NdFeB bonded permanent magnet material is made of NdFeB magnetic powder with binder. Since the successful development of this material in 1988, its development has been quite rapid and its production has increased exponentially. As a high performance permanent magnet material, it meets the trend of short, small, light and thin development of contemporary electronic products.
The production and application of bonded NdFeB permanent magnet material is late, the application is not wide, the amount is small, mainly used in office automation equipment, electrical machinery, audio-visual equipment, instrumentation, small motors and measurement machinery, in cell phones, CD-ROM, DVD-ROM drive motor, hard disk spindle motor HDD, other micro DC motors and automation instrumentation and other fields are widely used. In recent years, the application ratio of bonded NdFeB permanent magnet material in China is 62% for computer, 7% for electronic industry, 8% for office automation equipment, 7% for automobile, 7% for apparatus and 9% for others.
The bonding process of bonded NdFeB magnets is an important part of magnet preparation, and there are 4 kinds of production methods.
1. Calendering
The magnetic powder and adhesive are mixed evenly in the ratio of 7:3 by volume, rolled into the required thickness and then manufactured into finished products after the solid word processing. Generally, surface treatment is not needed, and it is protected by film or decoration, and NdFeB requires nickel plating.
2. Injection molding
Mix magnetic powder with adhesive, mix by heating, early granulation, drying, then spiral guide rod to heating room heating, inject into the mold cavity molding, after cooling, that is the finished product. Generally use nylon 6, polyamide, polyester and pvc with the addition of 20%-30% (volume fraction), together with the shape of complex rigid bonded permanent magnets. After ferrite, samarium cobalt magnets and NdFeB magnets, surface treatment is not required.
3. Extrusion molding
It is basically the same as the injection molding method, the only difference is that the heated pellets are extruded through a cavity into the mold for continuous molding. The same nylon 6, polyamide, polyester and polyethylene are used to produce thin and thin-walled cylinders or rings of longer magnets, such as ferrite, samarium cobalt and NdFeB magnets, which are more difficult to achieve with other processes.
4. Compression Molding
The magnetic powder and adhesive are mixed in proportion, granulated and coupling agent is added, pressed and molded in the mold, cured at 120°~150°, and finally the finished product is obtained. Use solid epoxy type value or phenolic resin, add 1%~5%, can be bonded permanent magnets by larger size and simple shape generally use cathodic electrophoresis, spraying, vapor deposition and other methods for coating protection.
The molding process of bonded NdFeB magnets is basically divided into these four types, among which the most commonly used are injection molding and molding.
What is the difference between bonded NdFeB and sintered NdFeB?
Sintered NdFeB is a powder metallurgy process, generally called NdFeB, the material itself is very hard, hardness is about 560-580Hv, but it is quite brittle. The density is around 7.4-7.6g/cm3 with high resistance to demagnetization, but the temperature stability is average, depending on the performance level, the maximum working temperature is between 80-250 degrees Celsius, if not plated or coated, the corrosion resistance of the material is very poor and it is easy to oxidize. The resistivity of the material is about 160 micro-ohm cm, the remanent permeability is about 1.05μreo, the temperature coefficient of remanence is between -0.12~-0.1%/ degree Celsius, the temperature coefficient of endogenous coercivity is about -0.6%/ degree Celsius.
The price of bonded NdFeB is relatively cheap, on the one hand, it is less material and less process, the technology of sintered NdFeB is too bad, while the process of bonded NdFeB is simple, so the price difference is very big; bonded NdFeB magnet is made of fast quenching NdFeB powder and binder mixed by “press molding” or “injection molding”. Bonded NdFeB magnets are made by “press molding” or “injection molding”. Bonded magnets have high dimensional accuracy and can be made into magnetic components with relatively complex shapes, and have the characteristics of one-time molding and multi-pole orientation. The bonded NdFeB has high mechanical strength and can be molded in a single process with other components.
Source: China Permanent Magnet Manufacturer – www.rizinia.com
