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NdFeB Magnet Coating

 

COATINGS

 

NdFeB magnets (Neodymium) require a protective coating / surface finish to prevent corrosion of the magnet.

Moisture in the atmosphere is potentially enough to cause an uncoated NdFeB magnet to show signs of corrosion. Marine environments are particularly effective at making NdFeB magnets corrode. The process of corrosion is similar to rusting – the structure of the NdFeB magnets changes permanently resulting in a progressive loss in magnetic performance (the magnet will weaken; the magnet also breaks down into a powder during the corrosion process). Total magnetic failure is possible due to corrosion. To prevent this, the magnet is given a coating / surface finish.

There is a variety of surface finishes available. The application sometimes affects the choice of coating (e.g. gold plating is a noble element and is therefore chemically inert and ideal for many medical applications, rubber coating provides additional friction, etc).

The standard coating for NdFeb Magnet is a triple layer plating of Nickel-Copper-Nickel (Ni-Cu-Ni). Unless requested otherwise, this Ni-Cu-Ni coating is always applied to the magnets. It should be noted that the level of protection given by any coating depends on the environment the magnet will be subjected to and how the coating is looked after. If the coating is scratched or broken, it will not offer protection from moisture.

If moisture is sealed within the coating during the time of coating, the magnet may corrode from the inside out with little obvious signs of corrosion. The plating process is carried out on magnets that have been thoroughly cleaned and dried. Ideally the coatings should give a hermetic seal but the coating type may not make this possible. Not all coatings are hermetic i.e. some coatings may absorb water / let water through over long time period. In some circumstances, it may be beneficial to combine coatings to maximise corrosion protection (e.g. rubber coated zinc plating is used to assist magnet performance in marine environments).

Follwos are the widely used coatings for NdFeB magnets and the properties

 

Coating Type

Thickness

Color

Working Max Temp

PCT>

SST>

Characteristics

Ni,  Ni-Ni-Ni,     Ni-Cu-Ni (Electroplating)

10-30um

Silver

250

48hrs

72hrs

Excellent environmental suitability, application for cleanroom.

Ni-Sn (Electroplating)

10-30um

Semi bright silver

160

48hrs

72hrs

Excellent environmental suitability with fine conductivity, application for electronic equipment.

Zn (Electroplating)

8-15um

Silver      White-blue     Rainbow

160

_

24hrs

Excellent environmental suitability for most cases, Rainbow Zinc is the best one in Zinc electroplating.

Au (Electroplating)

10-20um

Golden

250

48hrs

192hrs

Application for electronic equipment and accessories

Ag (Electroplating)

8-15um

Silver

250

48hrs

192hrs

Application for electronic equipment and accessories.

IVD Al

10-30um

Silver

400

48hrs

192hrs

Excellent enviromental suitability and with fine adhesion.

Epoxy

8-15um

Dark grey

120

24hrs

72hrs

Salt spray and humidity resistance.

Phosphating

_

Light grey

_

_

_

Short term anti-corrosion, transportation and storage.

 

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