The Manufacture of High Permeability Mn-Zn Ferrites by Atmospherical Protect

For the manufacture of high permeability Mn-Zn ferrite cores, the zinc loss from the surface of sintering cores causes poor yield rate of final products. This experiment uses the atmospherical protection to reduce the evaporation of zinc. The control of the oxygen partial pressure and flow rate precisely can reduce the zinc loss about 20% to 35%, but it is not enough to get a good distribution of permeability of products, i.e. the distribution of initial permeability from 12000 to 15000 per products about 14% before atmospherical control and 25% after atmospherical control, respectively. Combination with precise control and zinc vapor compensation can increase the yield rate 9% to 15%. Another experiment to manufacture high permeability Mn-Zn ferrite cores for 15000f 30% in a batch type furnace(about 13 Kg 1 batch), is to use a new engineering neth hod to protect sintering core to avoid vaporizing zinc vapor, the yield rate can be rapidly increased from 25% to 75% and the effective capacity of furnace can be at least twofold. It is successful to manufacture homogeneous and high permeability of Mn-Zn ferrites both increasing the quality of products and decreasing the operating costs. Introduction: The high permeability Mn-Zn ferrites were developed for a long time by Dr. E Roess[l,2], but for mass production of Mn-Zn ferrites, the homogeneily of the products is not so easy to control. The one of the paramount llnportant reasons is the zinc loss from the outer surface of sintering cores which reduces the initial permeability , especially in the high permeability products. It is caused by the zinc vaporized of the surface of sintered cores in the reduced atmosphere, the lower oxygen partial pressure or longer annealing time, the more serious zinc vaporized[3]. It is more sensitive for smaller size high permeability Mn-Zn ferrites than for the variation of composition. So manufacturer must be dispensed extra source to eliminate failure products, and the cost upward. Experimental: Toroidal samples compounded with Fe2O3, MnCO?, ZnO were prepared by conventional powder metallurgy processes. Granulated powders were pressed into two size toroids, T4 X 2 X 3 (OD:~IIIIII, D:2mm, H:3mm) and T9 X 5 X 3 (OD:9mm, ID:51nm, H:3mm). Samples were fired in furnace, atmospheric conditions were controlled during cooling to maintain spinel phase equilibrium. In order to observe zinc vaporizing effect, T4 X 2 X 3 samples were placed on boat shape sagas. and put into a tube furnace there were ZnO-rich powder inside with different ratio of ZnOImatrix. Beside, we placed T4 " 2 X 3 cores into T 9 X 5 X 3 cores to coaxial sintering in the batch type furnace to compare the initial permeability distribution with the T4 X 2 X 3 cores sintering alone. Results and Discussion: It is well known that zinc vaporized from the outer surface of sintering cores will decrease the initial permeability[4,5]. We also discover the different position in the furnace when sintering Mn-Zn ferrite cores, the different level of zinc vaporized, so it is very difficulty to obtain homogeneous characteristics of Mn-Zn ferrites on the manufacture. 0.20 ) I 0 3 5 8 10 13 15 18 20 23 25 2110 powder ( g ) Figure I the relationship between the yield rate and the we~ght of ZnO powder Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jp4:1997116 C1-72 JOURNAL DE PHYSIQUE IV Figure 1 shows the relationship between the yield rate (/1 i = 15000*30% ) and the weight of ZnO powder in the tube furnace. Tlie actual effect of zinc loss is known, so the zinc vapor compensation were offered to reduce zinc vaporized. It is observable that zinc loss were repressed successfully by figure 1. But the yield rate increased from 30% to 47% diminutively, the reason is the bottom and surround of the cores contact with the boat shape saggars. Beside, by the restrictly of the sintering condition, the yield rate isn't increased when ZnO powder is beyond 18 gram. Figure 2(a,b) shows the permeability distribution of T4 X 2 X 3 cores sintering alone compared with that coaxial sintering with T9 X 5 X 3 cores. In figure 2a, the T4 X 2 X 3 cores were strewn on the sagas arbitrarily, the permeability distribution peak is smoothly. The cores were exposed in the reduction atmosphere and reaction with saggars are the cause of the random distribution.