Between "ferrogram" and "filtergram" makers is the multiple centrifiltergram maker: a new technique for solid debris separation

Transcription

1 Journal of Physics: Conference Series Between "ferrogram" and "filtergram" makers is the multiple centrifiltergram maker: a new technique for solid debris separation To cite this article: S Raadnui 2012 J. Phys.: Conf. Ser View the article online for updates and enhancements. Related content - Electrical pitting of grease-lubricated rolling and sliding bearings: a comparative study S Raadnui and S Kleesuwan - 25th International Congress on Condition Monitoring and Diagnostic Engineering (COMADEM 2012) Andrew Ball, Rakesh Mishra, Fengshou Gu et al. - The effect of external dynamic loads on the lifetime of rolling element bearings: accurate measurement of the bearing behaviour W Jacobs, R Boonen, P Sas et al. This content was downloaded from IP address on 21/01/2019 at 09:56

2 Between ferrogram and filtergram makers is the multiple centrifiltergram maker: a new technique for solid debris separation S Raadnui 1 Production Engineering Department, Faculty of Engineering, King Mongkut s University of Technology North Bangkok (KMUTNB),1518 Pibulsongkram Road, Bang-Sue, Postcode 10800, Bangkok, Thailand address: srr@kmutnb.ac.th, s_raadnui@yahoo.co.uk Abstract. Solid particle analysis (SPA) is one key to determining the root cause of machine problems. Debris found in lubricating oil sample is an excellent source of information for diagnosing machine contamination and wear problems. Analysing solid and wear debris morphology is very helpful in determining which machine component is being damaged and provides valuable information about the severity and rate of wear. The SPA process involves three steps: sample preparation, sample viewing and sample analysis. Sample preparation for SPA involves concentrating particles on a surface. Adequate magnification and lighting are required for viewing and analysis. Subsequently, findings must be characterized and recorded in a way that can be easily utilized by the maintenance department. To better perform the sample preparation step in the SPA, a Particle Separating Disk (PSD) is proposed in this particular paper. PSD is a new method for separating solid particles suspended within used lubricants i.e. lubricating oils, gear oils, hydraulic oils and greases. The PSD can be used to extract solid particles at all ranges (this includes solid particle sizes in range from a few microns to over 1 mm). A comparative study between the proposed technique and conventional solid debris separation methods such as Ferrography (Ferrogram Maker) and Micro Patch Analysis (Filtergram Maker) in various aspects is undertaken, and some preliminary results are presented. 1. Introduction The Particle Separating Disk (PSD) is designed to separate solid particles from used oil samples for viewing under a microscope [1 & 2]. A typical PSD is shown in Figure 1. A simple centrifuge unit, centrifuges the diluted sample through a set of filter patches and dries them quickly to allow for immediate examination. One oil sample provides multiple patches (large particles, medium size particles & small size solid particles). In addition multiple oil samples can be processed simultaneously. This is accomplished with the use of centrifugal force for solid particle separation. The Relative Centrifugal Force (RCF) can be calculated from the expression [3]: RCF = ω 2 r/g (1) 1 To whom any correspondence should be addressed. Published under licence by Ltd 1

3 Used lubricants Samples Figure 1. Typical PSD with used lubricants in places. Generally, it is inconvenient to measure the angular velocity (ω), and so it is more convenient to express the RCF in terms of revolutions per minute (rpm), N, and this gives the expression: RCF = 11.18r[N/1000] 2 (2) The centrifugal force is usually given in terms of g and is written as such or as xg. From equation (2), it can be seen that the centrifugal force acting on the particles is related to the square of the speed and hence doubling the speed increases the centrifugal force by a factor of four. The centrifugal force also increases with the distance from the axis of rotation (r). Hence particles in a homogeneous medium will accelerate as the radial distance increases. A typical procedure for the utilization of PSD in solid debris separation process is shown in Figures 2 and 3. Figure 2. PSD during solid debris separation process. 2

4 Smallest size solid debris Largest size solid debris Medium size solid debris Figure 3. PSD with filter patches after the separation process. 2. A proposed solid debris separation technique In this particular work, the opportunity is taken of evaluating conventional debris separation techniques with a new method such as PSD patch analysis and correlating their response with the observed solid debris characteristics. During the comparison and/or evaluation modes, selective used lubricants (heavily contaminated used hydraulic oil, used gear oil, used grease and used hydraulic oil samples from industry are taken and conventional ferrography, micro patch analysis techniques are applied to them along with the new method in parallel. This provides precise information for debris characteristics of the test methods and for interpreting the results obtained from different conventional methods, the PSD patch analysis technique is also utilized throughout the tests for the purpose of comparing the three main solid particle separation techniques. Throughout the test programme, the solid debris separation techniques are evaluated with respect to their ability and suitability for effective separation and wear debris evaluation of industrial lubricants. Each technique has a separating ability for varying sizes of solid particles in the lubricants. The main factor in assessing these techniques is their ability to detect the particles created during the various stages of wear modes and/or wear mechanisms during machinery operation, forewarning of any likelihood of breakdowns. Typical results from the parallel tests for used lubricants are shown in Figures 4 to 6 for used hydraulic oil, Figures 7 to 9 for used gear oil and Figures 10 to 12 for used grease respectively. 3

5 Figure 4. Severe sliding/cutting wear particle on Ferrogram slide (used hydraulic oil). Figure 5. Severe sliding and yellow metal cutting wear particles on Micro Patch (Filtergram). Figure 6. Severe sliding and yellow metal cutting wear particles on the PSD patches. 4

6 Figure 7. Rolling fatigue wear particle among a group of contaminants on Ferrogram slides. Figure 8. Gear fatigue wear particles on Micro Patches (Filtergram slides). Figure 9. Gear fatigue wear particles on PSD patches. 5

7 Figure 10. Rolling fatigue wear particles among a group of contaminants on ferrogram slides. Figure 11. Fatigue wear particles on Micro Patches (Filtergram slides). Figure 12. Fatigue wear particles on PSD patches. From Figures 4 to 12 above, irrespective of the method used to isolate the solid debris (ferrogram, filtergram and PSD patch) from the used lubricants (hydraulic oil, gear oil and grease), in this particular work, the appearance of the individual particles is generally the same. Hence, diagnostic features of the particles concerned can be preserved. The main difficulty in the application of debris 6

8 separation and debris morphological analysis techniques for lubricated machinery assessment is in discriminating between different failure modes/mechanisms. The initial results presented in this paper indicate that irrespective of the technique used to separate the solid debris from the used lubricant, the appearance of the individual particles is more or less the same. However, it should be noted that each technique will alter the bias of the types of solid debris found, depending on a number of different factors. These factors include whether the particles were separated magnetically, which will bias the results towards ferrous wear debris. Filtration separation will remove particle type bias, but the pore size of the micro patch used will bias the result towards particles larger than the pore size chosen. Hence, it is very important that these potential sources of bias are considered. 3. Conclusion For machine solid debris analysis, the tools of choice include ferrography, micro patch analysis (filtergram). Preferred tools also include various techniques for the analysis of all types of particles. However, high instrument acquisition costs, along with low sample throughput, make this a costly and impractical option for most solid debris analysis programs. Unfortunately, no single particle analysis technique is completely satisfactory in providing both qualitative and quantitative data. For example analytical ferrography and filtergram techniques, while powerful, are extremely time consuming, laboratory-based, high in initial cost and require highly skilled technicians for operation. In addition, filtergram analysis has proven useful for clean samples such as hydraulic fluids, but they can run into problems with dark oils, samples with free or emulsified water droplets, or in situations where particle concentrations are high, such as heavily loaded gears or grease samples. Because of these limitations of conventional analysis tools, there has always been a desire and need in any well-rounded solid debris analysis program for a method or analytical instrument that produces consistently objective data on solid debris separation and particle morphological analysis, at an affordable cost. The current introduction of the PSD seems to fulfill this need. Acknowledgement The work reported here is funded by the Thailand Research Fund (TRF). References [1] Raadnui S 2011 WIPO. International Publication number WO2011/ A1 [2] Raadnui S 2011 PCT. International Patent Application No.: PCT/TH2011/ [3] Leung W F 1998 Industrial centrifugation technology (London McGraw-Hill) 7