Design and Wear Performance of Sliding Bearing of Stirring Device of Mixer-Settler

Mixer-settler is the key equipment of liquid-liquid extraction in spent fuel reprocessing plant. The mixer-settler of the spent fuel reprocessing plant has long-distance power transmission, and the lower end of the stirring device is supported by two sets of sliding bearing, and no addition of lubricating grease is allowed during operation. The working environment of mixer-settler has nitric acid vapor corrosion and radioactive radiation. According to operating experience, sliding bearing failure is one of the key factors restricting the long-term reliable operation of the mixer-settler. In this study, through the design of self-lubricating composites, the design of sliding bearing structure and the selection of lubrication mode, the maintenance free and long service life of sliding bearing of mixer-settler was realized. According to the design principle of self-lubricating composite, a kind of cermet composite material and a kind of self-lubricating composite were provided, an embedded lubricating sliding bearing assembly was designed. The metal-ceramic composite material (WN20) developed in this study had excellent mechanical properties. Titanium carbide and tungsten carbide particles were used as the ceramic phase of the cermet composite material, and vanadium carbide was the inhibitor of abnormal grain growth. Due to the requirements of the service conditions (i.e. the use of cobalt and copper was avoided), nickel as the main metal binder phase, and chromium and molybdenum as the minor metal binder phase are used instead. The spark plasma sintering technology was selected for the preparation process of the cermet composite material. The density, hardness, compressive strength, bending strength, fracture toughness, impact toughness and linear expansion coefficient were 13 g/cm³, 81 HRA, 3 052 MPa, 730 MPa, 17.1 MPa·m^1/2, 2.04 J/cm² and 6.1×10⁻⁶ ℃⁻¹, respectively. The spark plasma sintering technology was selected for the preparation process of the cermet composite material. The metal-based self-lubricating composite (FC13), which was composed of Fe, Ni, Cr, C (graphite) and MoS₂, was self-lubricating with excellent anti-wear performance under dry friction. FC13 was prepared by medium frequency induction hot pressing sintering process. Its density, hardness and compressive strength were 5.4 g/cm³, 110 HB and 283 MPa, respectively. FC13 had excellent corrosion resistance and was suitable for the mixer-settler for acidic media. The sample size of the bearing bush was Φ23 to Φ19~20. The diameter of BL type solid lubricant embedding hole was 2 mm, the number of the hole was 90, and the embedding hole area accounted for 24% of the whole wear area. The friction test parameters were a load of 196 N, a rotation speed of 600 r/min in air at room temperature. The wear depth was calculated using a micrometer to measure the inner diameter of the bearing and the outer diameter of the shaft before and after the experiment, and the average value of the multiple measurements was taken. Using composite solid lubricant embedded lubrication, the sliding bearing made of FC13 and WN20 showed excellent anti-wear performance. A Falex friction tester was used to test the wear performance of the sliding bearing. In the 250 h wear test, the friction coefficient and bearing temperature did not change significantly, the average friction coefficient was 0.08, and the average bearing temperature was 44 ℃. The wear depth of the bearing bush in 250 h was 3.8 μm, and the wear of the shaft was too small to measure. The structure, material and lubrication method of the sliding bearing assembly in this study met the design and use requirements of sliding bearings of mixer-settler.