Magnets of the production process of the key processes introduced(4)

- Nov 20, 2017 -

5. The production process of the key processes introduced

⑦ surface treatment

As the NdFeB permanent magnets Nd and Fe are relatively easy to corrosion and oxidation, making the sintered NdFeB permanent magnet corrosion resistance and poor oxidation, so how to improve its anti-oxidation and corrosion performance, its surface protection has become the production and Important issues in use. To this end, many researchers conducted their research on oxidation and corrosion behavior and their surface protection. As a result, the corrosion resistance of sintered NdFeB can be improved by adding elements, but the Br and (BH) max decrease. Therefore, surface anti-corrosion technology is usually used to reduce the oxidation and corrosion of NdFeB permanent magnets. Currently used for sintering NdFeB permanent magnet anti-corrosion coating can be divided into three categories: (1) metal coating; (2) electrophoretic coating; (3) vapor deposition coating. The following table lists the coating technology and types of sintered NdFeB permanent magnet materials.

Surface coating material

Coating method

Coating thickness (μm)

Coating color

Coating Features Description

nickel

plating

≥ 5

Light yellow

Corrosion resistance, with outstanding resistance to high temperature, high humidity capacity

Zinc

plating

≥ 5

silver white

Has strong corrosion resistance, salt spray test ability

tin

plating

≥ 5

Silver

Has excellent corrosion resistance, ductility and solderability

silver

plating≥ 5SilverHas enhanced corrosion resistance, increased conductivity

gold

plating≥ 5GoldenHas outstanding high temperature capability, corrosion resistance, good resistance to discoloration

copper


plating≥ 5yellowHas good electrical conductivity, thermal conductivity and mechanical ductility. Can also be used for partial carburizing

Nickel - copper - nickel

plating15-30SilverNickel coating longer than the protection and service life

Epoxy resin


Electrophoresis15-20black, greyCorrosion resistance, outstanding salt spray resistance, strong resistance to high temperature, high humidity capacity

⑧ magnetizing, testing, packaging

The machined magnet needs to be magnetized, then tested for performance, and finally packaged for shipping. The purpose of magnetization is to magnetize the magnetic substance or to increase the magnetism of the magnetism-deficient magnet. Magnetizing the following two instruments and working principle:

First, constant current magnetizer:

How it works: In the coil through the constant current DC, the coil to produce a constant magnetic field. Suitable for magnetization of low coercivity permanent magnet materials.

Second, pulse magnetizing machine

How it works: In the coil through the instantaneous pulse of large current, so that the coil produces a super-short magnetic field. Suitable for high coercivity permanent magnetic materials or complex multi-polar magnetizing occasions. Magnetizing, as long as the excitation current, the moment can be completed. The picture below shows the commonly used magnetizer pictures.

Magnetizing according to the different needs of customers, the need for magnetization in different directions, the following figure shows the magnetization direction of several commonly used magnets.

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Article from NdFeB Industry Network

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