The coating is used for protection. Neodymium can easily react with oxygen, and if it is not treated, it will be oxidized quickly. This is why all neodymium magnets are covered with a protective coating, which is very thin and will not affect the adhesion of magnets. In this paper, we will learn about some common coating types of neodymium magnets.
1. Epoxy resin (KTL) coating
Our epoxy coated magnet is cathode dip coating (KTL). Unlike our epoxy varnish technology and NiCu epoxy coating (also known as rubber-coated magnet), epoxy KTL coating has special stability in humid environment and in contact with weak acid, alkaline and saline solution. Due to these characteristics, it is strongly recommended to apply epoxy KTL coating to tidal power plants and offshore wind turbines.
In addition, KTL coating provides significantly better peeling performance for glue shear test. The black epoxy resin coating consists of three layers of nickel, copper and epoxy resin, which is exposed as the top layer. Very suitable for outdoor applications. However, black epoxy resin is not as wear-resistant as other plants. Under harsh conditions, the epoxy resin layer may be scraped off, exposing the underlying copper layer.
2. PTFE coating
The suggestion of Magnet Company successfully solved the problem that customers frequently change neodymium magnet in highly corrosive environment. In terms of cost, PTFE coated magnets cost more (twice as much as uncoated magnets), and the total cost is actually reduced by 50%. How come… By using PTFE coated magnets, our customers save the cost of frequent magnet replacement and regular inspection and maintenance of the machine.
3. Electroplating nickel (Ni-Cr alloy)
Galvanic nickel plating is a widely used method for sintering neodymium magnet coatings. The coating is applied to the magnet in three layers: one is an alkaline nickel layer, the other is a copper-nickel layer in the middle, and the last is a covering nickel layer. Considering the rigidity of surface, cost-effective production and excellent stability in humid environment and high temperature, nickel electroplating has advantages.
On the other hand, it is difficult to measure the thickness of the layer. In addition, this method leads to problematic adhesion and magnetic current loss caused by short circuit.
4. Nickel plating (Ni-Cr alloy)
This is the most common coating. Ni-Cu-Ni is a durable three-layer (nickel, copper and nickel coating). Very suitable for indoor use. If it is waterproof and moistureproof, it can be used outdoors. Good wear resistance.
This process is similar to the original nickel electroplating. Different from the original nickel surface coating, the final nickel layer is drawn by chemical method. This technology improves the anticorrosion performance, reduces the magnetic flux loss and enhances the adhesion performance under the sterilization condition.
5. Galvanized nickel-tin (NiCuSn) coating
The economical and efficient zinc-nickel-tin plating process is suitable for the application in humid environment where adhesion needs to be increased. Finally, the decrease of the hardness of the tin layer has an adverse effect. It especially intensifies the handling of magnetized articles.
6. Zinc plating (zinc) layer
Zinc coating of NdFeB magnets is a widely used technology. Generally, chromate coating is applied to galvanized parts in special tanks. Customers can choose blue and yellow chromate coatings.
The "yellow" coating rich in Cr+6 is no longer used in ROHS-compliant automobile production because its manufacturing process is harmful to health. Customers can use "blue", sometimes called "white", chromate coating. Compared with the performance of "yellow" coating, the anticorrosion performance of this coating is lower.
On the other hand, it excludes damage to human health and damage to the environment. Due to the mechanical stability of zinc coating, it is recommended to use it only when the temperature is as high as 80 C. The simple identification and good treatment of coating thickness make this technology very attractive. This process is most suitable for galvanized carrier materials.
7. Gold plating (Ni-Cu-Ni-Au) plating
The gold-plated layer has high corrosion resistance and conductivity. It is usually coated with a layer of nickel and copper to show the natural luster of gold. It works very well in water applications. The gold plating layer is very thin, but it still increases the cost of the magnet.
8. Chromium (Ni-Cu-Ni-Cr) coating
Chromium has better friction resistance and compression resistance. That’s why we use this coating to make spherical magnets. Its color is dark gray metallic.
9 copper (Ni-Cu) coating
Its color is shiny brown, red and golden yellow. Due to oxidation (darkening, spotting), the color may change with time. The copper-colored surface will be worn by frequent use (similar to a gold-plated magnet), so it is only suitable for decorative purposes.