Sintered NdFeB permanent magnets are manufactured by powder metallurgy process. The process is as follows:
Processing of raw materials→ mixing→melting→milling→magnetic orientation and compression→Sintering Densification→ tempering aging→machining and surface treatment→ detection.
From the technological process, it can be seen that the whole process is a systematic engineering, especially the high performance NdFeB permanent magnetic material. Each process of its production process has "the right to decide" and "the right of negation" for the product performance.
In order to produce high performance NdFeB permanent magnetic material, the organization and manager of the enterprise should pay attention to every link of the production process and guide the staff to pay attention to every detail in the process. This is the "Four preventions" of "Anti - oxidation, anti confusion, anti impurity and damp proof".
In order to ensure the quality of the sintered NdFeB permanent magnetic materials, our daily basic work should be carried out around the "four prevention" work, namely, emphasizing the prevention of oxidation, anti confusion, anti impurity and damp proof.
So how to prevent oxidation?
NdFeB is a rare earth permanent magnet material, which contains a large proportion of rare earth elements. The characteristic of the rare earth element is that the chemical property is very active, it is easy to react with the oxygen in the air to produce the rare earth oxide, such as the reaction of neodymium and oxygen to produce neodymium oxide. After the oxidation of rare earth, the magnetic properties of the products will be greatly reduced. Therefore, during the production process of Nd-Fe-B materials, how to do the "anti oxidation" work well is an important quality link.
First of all, when we purchase raw materials, we must ensure the purity of rare earth metals and reduce oxygen content. When the material is stored, the material should be sealed with plastic bags and put in the bucket to avoid contact with the air. The material with high quality is filled with nitrogen to protect and bind the mouth of the bag when the ingredients are finished. Do not take small pieces of metal neodymium and other rare earth materials excessively because they will be oxidized aftera while, such as metal neodymium fracture turning red, metal praseodymium turning white and so on.
Secondly, in the process of melting, we should ensure the atmosphere of the furnace. The new mold, the new furnace and the remedial furnace must be dried before putting into use. The valve and connection parts of the smelting furnace should be ensured to be normal, so that no air, water and oil will escape. And the vacuum pump (mechanical pump, roots pump and diffusion pump) must work well. It should be repaired and maintained in time. The vacuum hygiene should be cleaned regularly according to the technical regulations. Only by doing the above points can the vacuum degree in the furnace be guaranteed and a good product be made.
The coarse crushing, medium crushing, airflow grinding and stirring of the milling process must be protected by nitrogen. Checking and supplementing the nitrogen pressure of the stainless steel barrel (plastic bag) at any time. Check whether there is leakage of the stainless steel barrel valve or plastic bag before use. If it does, then it should be replaced in time or covered with a new bag .If the powder is found to be hot during processing, cooling measures such as nitrogen charging should be adopted to prevent oxidation.
During molding process, we should pay full attention to the oxygen content of the powder box and nitrogen protection box to ensure that thefigure of the process is lower than the prescribed one so as to prevent the oxidation of magnetic powder. Staff have to hurry up to strip oil and send these materials into furnace. Products of high performance are particularly important and must be operated in nitrogen protection boxes in terms of process requirements in order to prevent products’ diamond angle and edge angle from oxidation.
In addition, we should always pay attention to the purity of argon used, and solve that the abnormal situations in time. The cooling water temperature should be observed frequently. The cooling time should be explicit. Finally, the product can not come out below 80 ℃ because the it will be oxidized at high temperature.
Therefore, "anti oxidation" is an indispensable part of our work on the quality work of NdFeB permanent magnet materials. We should start from the actual work and make unremitting efforts.