Study On Non-linear Seepage Flow Law In Carbon Graphite And Impregnated Antimony Experimental Analysiys

Carbon-graphite possesses the advantages of good-lubricity, high-temperature tolerance, corrosion resistance and the elimination of oil lubricant, and thus has become the popular material for mechanical seal. However, there also exist voids in carbon-graphite, which lead to its poor air tightness and mechanical strength, so it is necessary to have the process of infiltration strengthening for carbon-graphite. There is a huge gap between China and foreign countries in carbon-graphite impregnation metals, therefore, our country exports low-end raw materials, whereas import high-end impregnation products. The reasons for this problems lie in our laggard technology in the impregnating metals and the scant fundamental research. This dissertation is designed to study the law of fluids flow within the porous medium of graphite, and is a basic theoretical study on the technology of infiltration strengthening of carbon-graphite.The objects of the study are 7 groups of carbon-graphite with different porosities. The results of the experiment of the seepage flow of single-phase water in the saturated carbon-graphite indicate that the flow of water deviates from Darcy's law, the flow curve is nonlinear, the fluid has starting pressure gradient in the osmotic process and that the permeability changes with the change of the pressure gradient. The high-precision nonlinear seepage equations are fitted and the physical meaning of the coefficient of the nonlinear term is discussed from the aspect of the mechanical properties of the boundary layer. Besides, the nonlinear seepage law of water is verified through Reynolds number criterion and FLUEN simulation, and it agrees well with the experimental phenomena.The antimony impregnation experiment of carbon-graphite is conducted, and it is found that the antimony flow is nonlinear in accordance with the Reynolds number. By comparison of the Reynolds number intervals and force analysis between the antonym flow and water flow, it can be concluded that the flow law of antonym in carbon-graphite is the same as that of water, and thus can be expressed as the nonlinear seepage equation of water. In addition, based on the analysis of the sample manifestation of carbon-graphite materials, some measures are put forward to solve the problems of corner-chipping, the adhesion of impregnate and the phenomenon of non-full impregnation, and it is pointed out that raising the impregnation pressure works better in improving the quality of impregnation materials than lengthening dwell time.The analysis of pressured-mercury test indicates that the major pore diameters of carbon-graphite is in the range of 1 ~3μmand displays normal distribution, impregnated antimony can fill most of the pores, and the volumes of those small pores which are not filled are larger than those of the bigger ones. In accordance with the statistics of the pressured-mercury test, the fractal dimensions are calculated, and it reveals the character of dual fractal of the carbon-graphite porous media, and the fractal inflection point is at the pointφ= 1μm. The reason of dual fractal is that the formation mechanisms of the big (φ> 1μm)and small (φ< 1μm)pores are different. The impregnation mainly takes place in the big pore interval (φ= 1~3μm), thus the properties of the big pore are the key factors affecting the quality of impregnation materials.The model of the relation between the porosity, permeability, fractal dimension and pore structure is established and verified by experiment. The friction and wear experiment on antimony impregnated graphite indicates that the lower the fractal dimension of antimony particle, the better the tribological properties are. Moreover, this dissertation gives the explanation on the nature of fractal dimension and concludes that the improvement of the homogeneity of the pores of impregnation materials is central to the enhancement of the quality of antimony impregnated graphite materials.Based on the flow law of antimony and in combination with the guidance of the size of impregnation materials and the betterment of the impregnation technique, the quality of antimony impregnated graphite metals can be improved by changing the blind impregnating in the production process.