【作者】 刘颀；

【导师】 胡亚非；

【作者基本信息】 中国矿业大学 ， 流体力学， 2010， 博士

【摘要】 炭石墨具有良好的自润滑性、耐高温、耐腐蚀、不需要油(脂)类润滑剂等优点,成为机械密封行业的热门材料。但炭石墨存在孔隙,气密性差,机械强度差,必须经过浸渍金属填充孔隙的强化处理。我国浸渍金属炭石墨材料相比国外水平差距很大,存在出口低端、进口高端产品的现象,其原因主要在于浸渍金属工艺落后和基础研究薄弱。本文研究流体在石墨多孔介质中的流动规律,属于炭石墨浸渍强化工艺的基础理论研究。论文以7组不同孔隙率的炭石墨材料为研究对象,水的单相饱和渗流实验表明,水的流动偏离达西定律,渗流曲线呈现非线性,流体在渗流过程中存在启动压力梯度,而且渗透率随着压力梯度的变化而变化。论文拟合了水的高精度非线性渗流方程,并从边界层的力学特性角度阐述了非线性项系数的物理意义。对水的非线性渗流规律通过雷诺数判据与FLUENT模拟两种方法进行了验证,结果与实验现象比较吻合。论文进行了炭石墨材料浸锑实验,根据雷诺数计算结果判断锑流动处于非线性状态。通过锑与水在流动过程中的雷诺数区间、受力分析的比较,判断锑在炭石墨多孔介质中的流动规律与水相同,因此可用水的非线性渗流方程形式描述。分析了浸锑炭石墨材料试样表观状态,针对浸渍工艺中存在的崩角、浸渍剂粘附以及浸不透现象,提出了改进浸渍的措施,并指出提高浸渍压力比延长保压时间更能有效改善浸渍材料的质量。本文将分形理论引入炭石墨(浸锑)材料孔隙结构分析中。压汞实验结果表明:炭石墨材料的主要孔隙直径约在1 ~3μm之间,呈正态分布;锑浸渍能够充填绝大部分孔隙,未被充填的小孔隙体积要大于大孔隙。炭石墨多孔介质具有双重分形特征,分形拐点约在φ= 1μm处,双重分形的原因在于大孔隙(φ> 1μm)和小孔隙(φ< 1μm)形成的机理不同。浸渍主要发生在大孔隙区间,因此大孔隙的特性是影响浸渍材料质量的重要因素。原料配方是影响大孔隙的主要因素,也是提高浸渍产品质量首要保证。建立了炭石墨材料孔隙率、渗透率与分形维数及孔隙结构关系模型并进行了实验验证。浸锑材料的摩擦磨损性能实验表明,锑颗粒分形维数越小,摩擦学性能越好,并从分形维数本质上给出解释,认为提高炭石墨材料孔隙的均匀性是改善浸锑材料质量的重要手段。根据锑的流动规律、浸渍材料尺寸制定合适的浸渍工艺参数,可改变生产过程中的盲浸现状,提高炭石墨浸金属产品的质量。更多还原

【Abstract】 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.更多还原