Before sintering and plating, NdFeB magnet material should be chamfered, degreased, pickled, ultrasonic cleaned and other processes that can get a stable and clean surface, in order to get a well-bonded, low porosity and long-lasting corrosion resistant plating.
Chamfering small parts chamfering can be used centrifugal finishing machine, larger parts can be used grinding wheel machine grinding over the edges and then chamfering with spiral vibration or centrifugal vortex finishing machine. Magnet manufacturers chamfering should be carried out in neutral or weakly alkaline media, do not use acidic or corrosive media chamfering.
Oil removal should be carried out in neutral and weakly alkaline degreasing agent, in order to avoid oxidation or hydrogen seepage, no anodic or cathodic electrolytic treatment . Acid washing with dilute nitric acid solution or weak organic acid for a short time, but should not be acid washing in strong halogen acid, do not acid washing in high concentration of strong acid, otherwise, the surface of the material is sharply coarsened and even pulverized.
The common sintering process for iron boron magnet materials is divided into two main steps:
1. Preparation of magnet powder
The preparation of iron-boron magnet materials requires the use of high-purity iron and boron mineral powders, which are mixed and ball-milled to form magnet powders. Among them, keeping the uniform size distribution of magnet particles is the key to ensure the quality.
2. Sintering manufacturing
After a series of treatment of magnet powder, the prepared powder is put into a hot press for sintering. The control of pressure and temperature are the key factors affecting the quality and shape of the sintered finished product. After sintering, the finished product can be formed by cutting or grinding, etc. The manufacturing process is roughly as follows:
1. Putting the mixed magnet powder into the mold;
2. Forming the powder by pressure;
3. Solid-state sintering: This is done at high temperatures (usually above 1000°C) and under a protective atmosphere to make the bonding between the powder particles tighter and form the magnet body;
4. Grinding or cutting: The magnet bodies are machined to make them into precise shapes and sizes.
The above steps are simple manufacturing processes, and the exact process conditions and parameters vary depending on the material and product requirements. Iron boron magnets have the disadvantages of not being easily machined after sintering and having a surface that is easily oxidized, requiring the selection of the correct hot press and processing.