Predictive maintenance by ferrography

Ferrography is a technique by which wear debris and contaminant particles are separated from a lubricant and analysed. The apparatus used and complementary investigational techniques are described. The use of Ferrography for machinery condition monitoring to prevent failure and to allow a safe change from expensive periodic dismantling of machinery for maintenance to the more economical predictive maintenance is outlined.     

铁谱技术在判断发动机磨损状态中的应用研究

发动机中各摩擦副的工作环境恶劣,磨拟状态复杂,很难精确描述。而发动机所处的磨损状态是判断其是否正常工作的重要标准,因此建立发动机磨损状态监测具有重大的经济和社会效益。笔者利用铁谱技术作为一种监测手段,通过磨粒分析来判断发动机的磨损状态。     

Application of ferrography to the study of wear and arthritis in human joints

Modifications in the ferrographic technique now permit its application to the analysis of synovial fluids. Studies of synovial fluid aspirated from artificial joint replacements have confirmed the usefulness of ferrography in the analysis of wear in prosthetic devices in situ. With natural joints, ferrography appears to be a highly sensitive monitor of the erosion of intraarticular surfaces. In addition, it holds promise as a diagnostic tool, with the potential to shed new light on the pathophysiology of various forms of arthritis.     

The interpretation of data from wear debris analysis, with particular reference to ferrography

A theoretical model of an oil lubrication system is presented. Wear particle generation and loss and lubricant usage are taken into account. The model can be used to reveal changes in the instantaneous wear rate from measurements of the wear debris concentration. The example of a diesel engine run-in is given. The model is also used to highlight the differences between oil analysis techniques which result from their differing sensitivities to particle sizes.     

An assessment of quantimet as an aid in the analysis of wear debris in ferrography

Wear debris extracted from oil samples taken from a twin-disc machine has been analysed using Quantimet to obtain data in terms of the number, size and distribution of wear particles in ferrograms. A correlation between wear and performance in the disc machine is achieved. From optical and stereoscan examination of the wear particles, the nature of the initial running-in wear behaviour of the discs is established.     

运用铁谱技术分析汽车磨损故障

掌握汽车运转情况,预防机械故障,消除安全隐患,实现对汽车故障的科学管理。在汽车修理厂现场抽取汽车有关部位油样,建立正常磨损工况、过度磨损工况、过热缺油工况和油液变质工况中粘着、滑动、切削、疲劳片状、球状、氧化磨粒的铁谱分析图形数据,经过不断完善、比较,建成模式识别基准;把采集的铁谱基片资料输入计算机,将其与巳有的识别基准进行比较,就可得到设备中各零件的磨损情况。实践证明,铁谱图形数据分析的故障和实际的故障是基本吻合的。对在役设备的润滑油或液压系统油中的各类磨损微粒进行微观分析,判断设备的早期故障。     

Study of grey relational grade identification for ferrography based on characteristic analysis of wear debris

Attention has been focused on how to achieve intelligent automation in ferrographic diagnosis in order to overcome the subjectivity of the diagnosis process. The present paper reports on a technique of characteristic measurement developed on the basis of the VC++ 6.0 programming platform, with characteristic parameters such as area, roundness, and aspect ratio being extracted from images of wear debris based on digital image analysis. However, the extraction of characteristic parameters from a ferrographic image is not the ultimate purpose of ferrographic diagnosis. The wear particles should be classified into several pre‐decision categories and their statistical distribution should also be calculated. The grey relational grade theory is introduced in this paper as a way to recognise wear debris and a new software system has been developed to deal with the problems occurring in the automation of ferrographic diagnosis. It is shown that the identification rules can be used to treat some real wear debris images with generally satisfactory results.     

Some quantitative aspects of ferrography

The principles and method of application of quantitative ferrography are outlined. The efficiency of particle precipitation and the repeatability of the apparatus are discussed and it is concluded that the technique is capable of detecting the onset of increased wear. Various severity-of-wear indices are considered, for both the analytical and the direct reading ferrograph, and their validity is illustrated by reference to their application to gas turbines, gearboxes and diesel engines.     

内燃机车铁谱分析中大磨粒浓度的定量分析与智能监测

在内燃机车油液监测过程中,对于不同的机车个体,润滑油中大磨粒浓度的正常与否所对应界值是不确定的。针对这种情况,结合一元线性回归的思想,本论文提出了利用Visual Basic语言进行了大磨粒浓度(DL)磨损状态自动判定系统的开发。对于某一个特定的机车个体,用户首先在该系统中输入一组列车正常运行的"走行公里(km)-浓度(ppm)"样本数据,该系统便可自动进行一元线性回归计算,并生成所对应的一元线性回归方程和标准判定方程,在这种前提条件下,用户只要输入待测的样本数据,并观察它和两条直线的位置关系,便可判定该状态点所对应的大磨粒浓度的正常与否,既提高了大磨粒浓度判定的效率和准确性,又提高了监测人员的工作。     

Quantitative estimation of wear amounts by real time measurement of wear debris in lubricating oil

A diagnostic technique that can estimate quantitatively wear amounts under lubricated condition was developed using our developed on-line particle counter. Wear tests were carried out by rubbing a bearing metal against a carbon steel in paraffin oil. The size and number of wear debris in the circulating oil could be measured in real time. The volume of each debris was calculated and, additionally, the total wear amount during a given duration was calculated by accumulating all debris volume. The wear amounts obtained by the quantitative estimation were fairly similar to the measured values of mass loss of the specimen.     

Intelligent identification of wear mechanism via on-line ferrograph images

Condition based maintenance（CBM） issues a new challenge of real-time monitoring for machine health maintenance. Wear state monitoring becomes the bottle-neck of CBM due to the lack of on-line information acquiring means. The wear mechanism judgment with characteristic wear debris has been widely adopted in off-line wear analysis; however, on-line wear mechanism characterization remains a big problem. In this paper, the wear mechanism identification via on-line ferrograph images is studied. To obtain isolated wear debris in an on-line ferrograph image, the deposition mechanism of wear debris in on-line ferrograph sensor is studied. The study result shows wear debris chain is the main morphology due to local magnetic field around the deposited wear debris. Accordingly, an improved sampling route for on-line wear debris deposition is designed with focus on the self-adjustment deposition time. As a result, isolated wear debris can be obtained in an on-line image, which facilitates the feature extraction of characteristic wear debris. By referring to the knowledge of analytical ferrograph, four dimensionless morphological features, including equivalent dimension, length-width ratio, shape factor, and contour fractal dimension of characteristic wear debris are extracted for distinguishing four typical wear mechanisms including normal, cutting, fatigue, and severe sliding wear. Furthermore, a feed-forward neural network is adopted to construct an automatic wear mechanism identification model. By training with the samples from analytical ferrograph, the model might identify some typical characteristic wear debris in an on-line ferrograph image. This paper performs a meaningful exploratory for on-line wear mechanism analysis, and the obtained results will provide a feasible way for on-line wear state monitoring.     

Developments in analytical ferrography

Recent work at the Foxboro Analytical ferrography laboratory on the recognition of non-ferrous metal particles, particles from lead-, tin- and Pb- Sn-based alloys, ferrous oxide particles and corrosive wear debris is described. An explanation of polarized light microscopy as it applies to ferrography is given. Ferrograms made from conductive substrates which can be used in a scanning electron microscope without requiring coating are discussed.     

3D measurement of crater wear by phase shifting method

In this paper, a new method of non-contact tool wear measurement is presented. It employs a phase shifting method using fringe patterns to measure crater wear by constructing a 3D map of the tool insert. Four fringe patterns with various phase-shifts are projected onto the rake face of the tool upon which four gray-level images are captured. By solving and then unwrapping the phase map with the four images, a 3D profile of the tool is obtained to provide the overall size of the crater wear land. Sample tool inserts with various crater wear surfaces have been evaluated with the method and the results demonstrate that the system is robust to ambient light and is accurate and applicable for use in real industrial environment to measure crater wear.     

Complex wear measurement on thin coatings by the cratering method

Ball cratering and rotating wheel tests are useful techniques for abrasive wear resistance evaluation of thin coatings. Nevertheless, such techniques involve significant experimental errors, coming from equipment deficiencies and changes in wear response depending on test parameters. In case of rotating wheel test, common instrumental errors are: geometry‐induced errors (curved or non‐horizontal sample surface), alignment errors (misalignment between ball/wheel rotation axis and sample stage) and optical measurement errors. In the present paper, errors due to crater dimension detection system (penetration depth or crater diameter) and equipment deficiencies (rotating axes misalignment and sample slope) were numerically analysed. A general expression for volume calculation was obtained, considering axes misalignment and sample slope, and experimentally validated by wear tests on Ti/TiN CAE‐PVD coatings and profilometer abraded volumes measurement. Results showed that axes misalignment and sample slope involve considerable errors in wear coefficient evaluation. However, errors can be corrected by the use of obtained expressions. Copyright © 2009 John Wiley & Sons, Ltd.     

The deleterious effect arising from preparation of ferrograms in ferrography and the consequences in subsequent analysis of wear particulates

The resolution of problems arising from the existing ferrography machine in the ferrographic deposition of wear particles is considered as a relevant prerequisite for the qualitative and quantitative analysis relating to the correct interpretation of the wear behaviour in lubricated systems.Crushing, shattering and polishing actions of wear particles generated from a lubricating system were confirmed to have occurred during preparation of Ferrograms when the existing ferrography machine was used because of the squeezing action of the peristaltic pump. Some polymer-like material, e.g. trichites, tubules and glassy flake materials, were entrapped inside the polytetrafluoroethylene (PTFE) tube where the PTFE tube was compressed by the pump. Severe cutting abrasive wear occurred on the inside wall of the PTFE tube as the wear particles passed through. The greater the tube diameter or wall thickness, the more the wear particles were reduced in size. The polishing action on the particles which accompanied this activity was also confirmed.     

微细电火花加工的微细电极在线检测

设计了微细电极在线检测系统。系统由卤素灯光源、变焦显微镜头、CCD摄像机和6自由度支架组成,具有1.61 μm的分辨率和113~729的放大率。在Linux平台下,基于V4L2 API开发了图像采集程序,使用mmap()内存映射方法获取图像数据。实现了IplImage数据结构和QImage类的转换,使图像既可以基于OpenCV进行处理,又可以基于Qt进行显示,通过Canny边缘检测算法提取了微细电极的边缘轮廓。实现了电极在线观测的G代码功能,进行了块状电极电火花磨削微细轴的实验。实验结果表明系统可以在线观察电极状态和在线测量电极尺寸,在线测量值与扫描电镜离线测量值的相对误差在5%以内, 解决了微细电火花加工的微细电极在线制造和检测等难题。     

An attempt to quantify the limits of failure detection by ferrography

An attempt is made to determine whether ferrography is likely to be able to detect the levels of damage that would lead to catastrophic failure in mining gear transmissions.

A level of maximum sustainable damage before catastrophic failure would occur is set. The level is necessarily very approximate, but it provides an estimate of the amount of wear debris that would be released into the oil. This amount is considered against the background level of wear debris likely in underground equipment to give the increases produced by failures.

The increases in the direct reading Ferrograph values produced by given increases in ferrous wear debris are derived from experimental data and are related back to the levels of maximum sustainable damage in mining gear boxes.

It is concluded that for some mining gear transmissions ferrography is unlikely to be able to detect maximum sustainable levels of damage.     

Non contact wear measurement on pneumatic seals

An experimental methodology aimed at the evaluation of wear in pneumatic seals is presented. New equipment was designed and manufactured in order to measure the radial thickness of worn material on the sealing edge both axially and circumferentially, by means of a laser sensor, as well as to avoid the necessity of disassembling the seals. The methodology is intended as an instrument for a quick comparison of seal prototypes and is proposed as an alternative to those methods that globally quantify the wear of samples by measuring their loss of weight or volume. Results obtained on a NBR commercial lip seal are presented.