The Theory of Debris Group in Ferrographic Analysis

Abstract

Ferrography is now an accepted means of machine condition monitoring. The wear condition of machines should be determined by studying all the debris suspended in oil sample as a whole rather than focusing on debris individually, which is time consuming. In order to minimize the work of wear particle analysis, the theory of debris group in ferrographic analysis has been put forward. The basic concepts and principles of this theory have been introduced. The properties of debris group and their applications have been reported. And the method of debris group analysis using Mathematical Statistics and Fuzzy Mathematics also has been discussed. The theory of debris group plays as a bridge between wear particles and wear condition of wear system, which minimizes the work of wear particle analysis and makes the judgment of the wear system condition in a more objective and precise way. INTRODUCTION Ferrography is a technique to separate wear debris and contaminant particles from a lubricant and to arrange them on a transparent substrate for examination [1, 2]. It's widely used in the study of wear mechanisms, and as a device for the detection of the onset of abnormal wear as might occur in the course of a mechanical wear failure in a machine [3-5]. Wear debris is a strong indicator of tribological interactions under which it was formed. Careful examination of quantity, size, composition, and morphology of wear debris can yield specific information about the conditions of the moving surfaces. For many years, in maintenance, wear debris analysis has been a subject of practical and economical interest, since wear conditions in a machine can be monitored by the examination of debris without costly dismantlement of machinery. In wear debris analysis, wear modes are usually inferred by correlating wear debris with possible wear situations. For the past few decades, classified micrographs of wear particles from various wear conditions have been available in the wear particle atlas since the development of ferrography in the early 1970s. Examinations of wear debris have been carried out for the recognition of damage and its correct attribution to physical and chemical causes. And in recent years, in order to overcome the subjectivity of the debris morphology assessment, debris classification and status valuation of individual judgment, there have been many research efforts focused on the development of computer image processing and automated classification systems for the wear debris characterization and classification [6-10]. But no matter what means one uses, before attempting to analyze wear debris in each case, it is necessary to decide how many wear particles on the ferrogram or in the oil sample should be investigated to ensure that an accurate judgment of the wear system can be made, and then accordingly to select the most appropriate method for performing morphological analysis. However, no specific methodology which can efficiently explore the