浸渍石墨微观特征对机械密封润滑膜超声检测精度的影响

Influence of Micro Characteristics of Impregnated Graphite onUltrasonic Testing Accuracy of Lubricating Film of Mechanical Seal

针对机械密封润滑膜厚度的精准测量问题,研究浸渍石墨微观特征对超声膜厚检测精度的影响,采用石墨化度和气孔率对浸渍石墨的微观特征进行表征。以烧制温度和颗粒度为工艺变量制备具有不同石墨化度和气孔率的石墨试样,对石墨试样的声阻抗和润滑膜厚度进行超声测试。结果表明:声阻抗随着石墨化度的增大而增大,随着气孔率的增大而减小,表明石墨化度和气孔率对石墨声阻抗的影响规律性明显;石墨化度和气孔率对润滑膜厚度值的影响,并不像对声阻抗的影响一样是单调变化的,原因是样品的内部孔隙导致了测量误差的产生;当润滑膜厚度标定值为2μm时,润滑膜厚度的测量值均略小于标定值,这是因标定装置的最小刻度大于被测物表面的粗糙度导致的。在机械密封润滑膜厚度的测试中应对每次试验单独进行声阻抗的测试,以消除其对膜厚测量结果的影响。

In order to accurately measure the lubricating film thickness of mechanical seals,the influence of micro characteristics of impregnated graphite on the accuracy of ultrasonic film thickness measurement was studied.The microstructure of impregnated graphite was characterized by graphitization degree and porosity.Graphite samples with different graphitization degree and porosity were prepared with sintering temperature and particle size as process variables.The acoustic impedance and lubricating film thickness of graphite samples were measured by ultrasonic method.The results show that the acoustic impedance of graphite is increased with the increasing of graphitization degree and decreased with the increasing of porosity,indicating that the influence of graphitization degree and porosity on acoustic impedance of graphite is obvious.The influence of graphitization degree and porosity on lubricating film thickness is not monotonic as the influence on acoustic impedance,the reason is that the internal pores of the sample lead to the measurement error.When the film thickness is 2μm,the measured values of lubricating film thickness are slightly less than the calibration value,which is caused by that the minimum scale of the calibration device is greater than the roughness of the measured object surface.The acoustic impedance should be tested separately in each test so as to eliminate its influence on the measurement results of film thickness.