Pre-burning effect of permanent ferrite magnet2018-08-01
The main effects of pre-burning are as follows:
(1) Reduce chemical inhomogeneity
The billet after calcination has been partially ferrite, which meets the chemical composition requirements of the formulation while retaining certain chemical activity. When the unreacted portion undergoes a solid phase reaction again, a structure in which the complete ferrite magnet is magnetized can be obtained, and the chemical unevenness of the sintered product is lowered.
(2) Reduce the shrinkage rate of the fired product and reduce the possibility of product deformation
The calcination process is a solid phase reaction process, the ferrite structure begins to form and volume shrinkage occurs, which is advantageous for increasing the density and mechanical strength of the blank, thereby reducing the possibility of deformation of the product, and further, the reduction of the shrinkage rate is also given to the molding die. Design and manufacture bring convenience.
(3) Easy to granulate and form
The un-fired mixed oxide has a fine particle size and a wide particle size distribution, which is disadvantageous for granulation and molding. The ferrite powder after pre-baking and secondary ball milling can meet the requirements of granulation, molding particle size and particle size distribution.
(4) Increase the density of ferrite magnet products
During calcination, the salt raw material decomposes, and the gas escapes (for example, SrC03 is decomposed into vaporized helium and carbon dioxide), and the secondary pores do not cause pores due to gas evolution. In addition, after the secondary ball milling, the portion that has not been ferrite-formed may be newly exposed to the powder particles, and the reaction is contacted again during sintering to further ferrite, thereby increasing the product density.
(5) Improve the consistency of product performance
The difference in chemical activity of raw materials often leads to inconsistency in product performance. Controlling the calcination process can reduce the difference in chemical activity of raw materials and improve the consistency of product performance.