| Popis: |
Green pellet pressing is critical step in the preparation of oxide ceramic fuel that decides density, strength and microstructure of green pellets and pellets. The medium mode floating pressing properties of calcined alumina and Comeo alumina powder were compared, and the causes and solving measures of green pellets appearance defects were studied. The results show that the density of calcined alumina compact is much higher than that of Comeo alumina compact, but the strength of calcined alumina compact is much lower than that of Comeo alumina compact. The formability and compressibility of Comeo alumina and calcined alumina are opposite. With the increase of pressing pressure, the density and strength of Comeo alumina green pellets and calcined alumina green pellets gradually increase, but the influence of the properties of pressing powder on the density and strength is greater than the pressing parameters. The pressing curves of Comeo alumina green pellets and calcined alumina green pellets accord well with Huang Peiyun's double logarithm equation. Alumina is an inelastic compression in the pressing process, and there are work hardening and friction in the medium die. The density and strength of green pellets are related to powder strength, powder morphology and pressing pressure, but have nothing to do with pressing time, reducing time and demoulding pressure. With the increase of pressing pressure, the number of capping, blasting and crushing of calcined alumina green pellets decreases, and with the increase of demoulding maintenance pressure, the number of lid, blasting and crushing increases, and the degree of crushing deepens. Increasing the pressing pressure and decreasing the demoulding maintenance pressure are beneficial to reduce the defects such as lid dropping, head blasting and crushing, and when the pressure is 160 kN, macroscopic cracks appear on the surface of the green pellets. The low addition of zinc stearate makes the friction phenomenon of the medium die serious, resulting in side scratches and cracks. Zinc stearate plays the role of lubrication of the inner wall of the middle mold in the pressing stage. The sintering experiments show that the density of the pellet decreases gradually with the increase of zinc stearate addition, and the porosity of the pellet increases obviously. Zinc stearate acts as a pore-forming agent in the sintering stage. So when adding zinc stearatethe role of lubrication and pore-making should be considered at the same time. |
