Neodymium iron boron has a fatal weakness: brittleness and susceptibility to rust. Bare magnets placed in humid air will develop white spots on the surface within a few days, and can pulverize and fall off after a few months. So neodymium iron boron is almost never shipped as a bare magnet and must be coated or coated. But the coating is not "thicker is better" or "more expensive is better". Choosing the wrong one can still cause rust, and the rust inside cannot be seen. After installation, the magnetic force suddenly drops.
First, let's talk about the conclusion: how to choose the four mainstream coatings
Comparison Table for Selection of Neodymium Iron Boron Mainstream Coating
Coating type
* Tip: The duration of salt spray testing is for reference only, and the actual lifespan is affected by environmental humidity, temperature, pH, and coating thickness (usually 10-25 μ m). Medical grade and industrial grade coating standards are different, and it is recommended to request third-party testing reports when selecting.
2. Nickel copper nickel: the most commonly used, but not universal
Three layer structure: bottom layer nickel (bottom layer) → middle copper (thickened/buffered) → surface layer nickel (bright anti-corrosion).
Advantages: Bright surface and good appearance; Wear resistant, not easily scratched during assembly; Salt spray for 24-72 hours (thickness and process determined); Moderate cost and fast delivery time.
Disadvantages: porosity exists, and long-term humid environments can cause water to enter through micropores; Cannot soak in water, cannot be exposed to outdoor rain; Salt spray environment (coastal factories) with reduced lifespan.
Suitable for: servo motor rotors, sensor magnetic columns, office equipment magnets, general industrial automation. Not suitable for: water pump motors, outdoor magnetic separators, food grade production lines.
3. Galvanization: cheap but don't expect it to carry weight
The galvanized layer is thin, the cost is low, and the appearance tends to be grayish white or rainbow colored.
Advantages: cheap, fastest delivery time; Suitable for large quantities of low-priced items. Disadvantages: Limited anti-corrosion ability, salt spray usually lasts for 12-24 hours; After knocking off the zinc layer, the substrate directly rusted; Not suitable for precision parts (difficult to control coating thickness).
Suitable for: occasions that are extremely cost sensitive, use in dry environments, and do not require a long lifespan. Hesheng suggests that unless explicitly requested by the customer, galvanizing for neodymium iron boron protection is generally not recommended proactively.
4. Epoxy resin: preferred for damp and water soaked scenarios
Epoxy coating is a spray or dip coating process with a thickness of 20-100 μ m, commonly black or gray.
Advantages: Good sealing and extremely low porosity; Water resistant, oil resistant, and resistant to weak acid and alkali; Salt spray can last for 96 to 500 hours (determined by formula and thickness); Can encapsulate irregular parts and multipole magnets.
Disadvantages: The surface is not shiny, and the appearance tends to be "industrial style"; The coating is hard but brittle, and may crack upon impact; High temperature (>150 ℃) will soften and degrade; The thickness of the coating affects the dimensional tolerance, and precision parts need to be calculated in advance.
Suitable for: magnetic separator magnetic rod, water pump magnetic rotor, outdoor iron remover, cleaning equipment magnet. Attention: If the epoxy coating is not fully cured, it will bubble and delaminate under high temperature and high humidity. The selection of suppliers depends on the curing process and salt spray report.
Fifth, Perrine: The Ceiling of Medical and Clean Environments
Parylene is a vapor deposition coating with uniform thickness, no dead corners, and no pores.Advantages:True zero porosity, with the strongest anti-corrosion ability;Good biocompatibility, suitable for medical grade use;Uniform thickness (even in complex shapes);It has better temperature resistance than epoxy and stronger chemical inertness.Disadvantages:Expensive, 3-5 times more expensive than nickel copper nickel;Equipment investment is large, not every factory can do it;The coating is thin (usually 5-25 μ m) and the wear resistance is average.Suitable for: medical implant/extracorporeal device magnets, food grade magnetic separation, semiconductor cleanroom magnetic components.