- Email: [email protected]
‘Comparison of spectrographic and ferrographic analysis of crankcase oils from the High Speed Train’
Judder predicted
to other machinery such as manipulator arms or the rotating and slewing mechanisms of cranes.
Gear driven rotating mechanisms judder when the dynamic conditions cause the drive system to switch from drive to overrun or from driving to braking. A recently announced computer program allows the probability ofjudder occurring to be predicted at the design stage. Following work undertaken over several years on the assessment of designs for tank and gun turrets for the UK Ministry of Defence, Frazer-Nash has evolved a suite of programs called TROJAN (Turret Rocking and Judder Analysis). It is claimed that it can be widely applied
The program assesses both the static and dynamic forces bearing on a slewing mechanism and enables the designer to explore combinations of layout and the limits of operational modes to determine the extremes of forces and the couples acting, the drive force requirements and the likelihood ofjudder. It allows for the independent movement of subsystems and for inclinations and movement of the whole structure as well as for the forces and moments generated, for example, by the load suspended from the jib of the crane. According to Frazer-Nash, these capabilities ensure
that all possible combinations of design parameters and operating conditions can be identified, explored and analysed. All the elements of the suite are modular and structured to enable data to be stored and drawn from a library of components. Thus a design configuration can be assembled partly from original data and partly from library descriptions; this enables a designer to minimise his input time and effort and also permits rapid, inexpensive analysis of modifications and alternative design. Frazer-Nash (Consultancy) Ltd, River Cottage, 2 Lower Teddington Road, Hampton Wick, Kingstonupon-Thames, Surrey, UK, KT1 4ER
'Comparison of spectrographic and ferrographic analysis of crankcase oils from the High Speed Train" - G.R. Morley, Tribology I nternational, Ju ne 1981, 14(3), 159--165 In this paper the author has published some very interesting data and information obtained from condition monitoring, by a spectrographic oil analysis programme and by ferrography, of diesel engines of the High Speed Train and has effectively demonstrated that regular examination by the former method of oil samples from these units as undertaken by the Scientific Services Branch of British Rail results in more efficient operation and in considerable savings in repair costs. The comments with regard to the results obtained by ferrography, however, when comparing the two methods, apparently indicate some inadequacy in their interpretation. As some of the criticisms regarding the usefulness of ferrography for condition monitoring of diesel engines were considered to be rather severe, it was decided to present the following observations which might be of interest to others concerned with condition monitoring of equipment involving inter-alia the detection and estimation of metallic wear debris. 1. In the first varagraph in 'Comments' (page 164 of the paper) the statement is made that of the seven
364
engines monitored regularly prior to works overhaul 'spectrographic analysis gave abnormal results on only one engine but on two occasions' and 'in neither case did direct read ferrography indicate anything abnormal'. These comments presumably refer to the data on 43041 Engine No 207 (Table 7) and it can be seen that for samples dated 9.8.80 and 10.8.80 a distinct increase in D L and D s readings had occurred. This alone was therefore cause to recommend examination of the engine or at least to prepare an analytical ferrogram. It cannot be fairly stated in this case that direct read ferrography did not detect anything abnormal. 1.1 With regard to the statement concerning ferrography used in the analytical mode on samples of oil from this engine no such results are given in Table 7, and therefore no evidence quoted to substantiate this remark about analytical ferrography. 2. In the second paragraph related to 'the three specific cases when
TRIBOLOGY international December 1981
abnormal spectrographic results were causing concern' the two engines requiring 'Stop and Examine' recommendations were presumably 43022, Engine No 40 and 43111, Engine No 51. 2.1 Admittedly, the direct read ferrography results on samples from 43022 (Table 8) were decreasing but the analytical ferrogram showed cutting wear particles to be present, a definite abnormality and therefore good reason to 'Stop and Examine'. The clear numerical difference between D L and D S readings (ie of large and small particles) would be a guide to the necessity for performance of analytical ferrography. 2.2 It is generally accepted that when condition monitoring of large units is being carried out by direct read ferrography this is best employed in detecting distinct changes in wear trends by examination of several samples taken consecutively. Therefore, for 431 l 1 (Table 10) it was hardly reasonable to state that the D L and D S readings
3.2 The results from samples from 43029 Engine No 100 (Table 5) definitely indicated some distress. There were variable D L and DS readings with distinct differences between D L and D S and the 25.5.80 and 2.6.80 samples showed clear increases in, as well as differences between, the values of DL and D S. Analytical ferrography showed an increase in particles from cutting wear.
(carried out on a single sample) were normal; in fact, when compared with similar results from samples from other faulty units eg 43041 (Table 7) and 43029 (Table 5)4311 l could have been suspected to have an abnormality. 3. Considering the three power cars 43028, 43029 and 43040 (third paragraph), the attainment of DL and D S values which are broadly equal to each other is a general indication that the unit is experiencing normal wear processes.
There was surely need for concern and for 'Stop and Examine' procedure. The observations from the works overhaul on this unit confirmed this. In fact, the statement relating to this engine that it would have been prematurely examined is unfair. Ferrography demonstrated that there was real cause for concern and it is more realistic to consider that this was missed by spectrographic analysis. This is a good example of ferrography detecting the larger wear particles which are missed spectrographically.
In the instance of 43028 Engine No 73 (Table 4), the change in D E and D S indicated that the overall proportion of wear debris had increased (possibly, as the analytical ferrogram showed, due to the presence of dust), but that the nature of this wear was probably normal. A more extensive background of ferrographic experience with samples from several of these units and subsequent examination of components could establish that results of this nature should be regarded as indicative of generally increased wear, but that a 'Stop and Examine' position had not been reached. This particular unit (43028) might, however, have benefited from an oil change; any potentially abrasive debris which might have been present would then have been removed.
4. The fourth (and last) paragraph in 'Comments' relating to 43031 Engine No 101 (Table 9) states that spectrographic data were required to indicate an aluminium trend which direct read ferrography had not shown, but no results from direct read ferrography are given. In any event this was an unfair criticism of ferrography because it is indicated in the table (under 'Comments') that action to leave in service was taken and this was as a result of information provided by analytical ferrography.
3.1 A similar explanation applies to 43040 Engine No 17S (Table 6) and in fact it is stated in the table (see column headed 'Comments'), 'Overall ferrogram satisfactory'.
In the field of condition monitoring of diesel engines there is general agreement that the most effective technique for routine monitoring both for cost and detection success has been, and will continue to be, spectrographic oil analysis. It is however of relevance from British Rail experience on the HST monitoring programme that during the last eighteen months spectroscopy has detected 157 potential failures; of these, 109 were due to coolant leaks as detected by the presence of sodium in the oil sample. The application of a technique such as ferrography which is effective on ferrous and ferrous associated wear
debris to the routine monitoring of the HST programme would therefore not be expected to be considered the most efficient detection technique of impending failure. The following comments may be considered of relevance when considering effectiveness of ferrography on diesel engine oil analysis.
(i)
The Paxman Valenta engine (2250 hp) used in the HST programme has chromium plated cylinder liners and the level of ferrous debris of this engine would depend on the wear of its piston
It should also be noted that 'reduction in spectrographic data' had confirmed that no action needed to be taken when in fact from the figures quoted the reduction (to 8 ppm A1 on 30.12.79 sample) was followed by an increase (to 11 ppm A1 on 31.12.79 sample). 5. Suitably interpreted, therefore, the data given in this paper indicated that with sufficient background development (such as has already been carried out for the spectrographic analysis programme) ferrography alone could provide beneficial condition monitoring of diesel engines and that if not the primary monitor, in conjunction with some other technique for wear metal determination (not necessarily direct emission spectrography) it would give important and valuable additional information on which decisions regarding remedial action, in instances of incipient failure, could be taken and thus provide even greater financial advantage. Far from being (as stated by Mr Morley) 'of no benefit whatsoever in its application to condition monitoring of diesel engines in the HST and therefore likely to be of little use in other diesel engines' the employment of direct read ferrography (coupled with analytical ferrography) in this application could be assessed as being potentially, at least, as useful as a spectrographic oil analysis programme. The techniques are indeed complementary and used together would provide the fullest information. D. McNaught, Fuels and Lubricants Section, London Transport Research Laboratory
rings and crankshaft. The damage in the cases quoted in this paper have had non ferrous association ie aluminium piston damage, coolant leaks etc with the level of iron rarely exceeding 50 ppm. Evaluation of these techniques would therefore be more beneficial for engines generating higher levels of ferrous debris such as engines fitted with cast iron liners. Detection of impending failure would then be dependent on the failure mechanism generating debris at a level in excess of the background noise of the overall system. A number of European
TRIBOLOGY international December 1981
365
and American engine manufacturers are at present testing ferrography as an analysis technique for both marine and railroad application on such engines. (ii) Sampling procedures are particularly critical when using ferrography. Particles detected range in size from 1-250/am; particle settling out is then of importance as also is the filter which would extract, in general, particles larger than 25/am. In spectrophotomerry, particles smaller than 2/am are analysed, so even if the oil sample is extracted from the sump after the engine has cooled analysis would be expected to give consistent readings.
(iii) In research and development, ferrography has already been used successfully on diesel engine programmes to investigate, for example, the effects of lubricants and lubricant additives, cylinder liner surface finish, filter efficiency and running in. This is attributable to not only the size of particles detectable but also that the technique measures rate of wear debris generation, whereas spectroscopy measures the accumulation of wear debris.
than ferrography in its present mode. On-line ferrography, a continuous monitoring system, is at present being evaluated for railroad application in North America and a report of this work will obviously be of interest. Ferrography has already proved of benefit as an additional analytical tool for wear debris analysis in research and development areas and as such Should be considered in conjunction with other techniques and can only be of mutual benefit to the investigator.
In conclusion it is considered a fair comment that spectrographic oil analysis is both a quicker and more cost ef(ective method o f r o u t i n e condition monitoring of diesel engines
M.H. Jones Department of Mechanical Engineering, University College of Swansea, Singleton Park, Swansea, UK, SA2 8PP
Surface Roughness Effects in Hydrodynamic and Mixed Lubrication Edited by S.M. Rohde and H.S. Cheng Many engineering components work under conditions where the surface roughness is comparable with the thickness of the lubricant film as deduced from hydrodynamic theory assuming perfectly smooth surfaces. This is a mode of operation which is imperfectly understood and one in which the boundary between successful operation and failure is often narrower than expected. Therefore the subject of this slim volume is of some importance in current tribological research and development. This is a collection of eight papers presented during the Winter Meeting of ASME at Chicago in November 1980. They range from exclusively theoretical treatments of hydrodynamic lubrication of random rough surfaces to a severely practical investigation of the influence of surface roughness of cylinders' bores on engine oil economy. The balance of work presented here is tilted towards Pubfished by the American Society o f Mechanical Engineers, 345 East 4 7th Street, New York, N Y 10017, USA at US$30.00 [or $15. O0 for A SME members) Book Number GO0193
366
the theoretical side. In my view this is rather a pity. In the future some of these theoretical treatments may be found useful; however the current need is for experimental work which links these theories (and presently available refined computer-based techniques for surface analysis) to some hard experimental evidence related to engineering practice. In the Foreword to this volume the Editors acknowledge the existence of this gap. They remark " . . . m a n y new models have appeared and none have been fully substantiated by careful experimental evidence,.., even
among analytical models the correlations have not been entirely satisfactory". This volume should therefore be on the shelves of all organisations interested in this growing and important subject. In particular it is to be hoped that this volume, and other research publications which have appeared in this field, will encourage researchers and perhaps, more importantly, their sponsors, to attempt more vigorously to span this gap between theory and practice.
J.F. A rchard
Basic Lubrication Theory (3rd Edition) A. Cameron No universally accepted standard textbook covering modern lubrication theory has yet emerged. This one by Professor Cameron having reached its third edition ten years after its launch in 1971 is clearly one of the Published by Ellis Horwood Ltd, Cooper Street, Chiehester, Sussex, UK at £12.50. ISBN 0 853 121 77 Paperback: £9.50
TRIBOLOGY international December 1981
contenders. For this edition, the text has been completely reset and the author, in conjunction with his colleague, Dr Ettles, has rewritten parts of two of the chapters, where rapid changes are occurring, and added tw3 completely new chapters on wear and numerical methods. It is written in a lively style with the main part of the book devoted to
to other machinery such as manipulator arms or the rotating and slewing mechanisms of cranes.
Gear driven rotating mechanisms judder when the dynamic conditions cause the drive system to switch from drive to overrun or from driving to braking. A recently announced computer program allows the probability ofjudder occurring to be predicted at the design stage. Following work undertaken over several years on the assessment of designs for tank and gun turrets for the UK Ministry of Defence, Frazer-Nash has evolved a suite of programs called TROJAN (Turret Rocking and Judder Analysis). It is claimed that it can be widely applied
The program assesses both the static and dynamic forces bearing on a slewing mechanism and enables the designer to explore combinations of layout and the limits of operational modes to determine the extremes of forces and the couples acting, the drive force requirements and the likelihood ofjudder. It allows for the independent movement of subsystems and for inclinations and movement of the whole structure as well as for the forces and moments generated, for example, by the load suspended from the jib of the crane. According to Frazer-Nash, these capabilities ensure
that all possible combinations of design parameters and operating conditions can be identified, explored and analysed. All the elements of the suite are modular and structured to enable data to be stored and drawn from a library of components. Thus a design configuration can be assembled partly from original data and partly from library descriptions; this enables a designer to minimise his input time and effort and also permits rapid, inexpensive analysis of modifications and alternative design. Frazer-Nash (Consultancy) Ltd, River Cottage, 2 Lower Teddington Road, Hampton Wick, Kingstonupon-Thames, Surrey, UK, KT1 4ER
'Comparison of spectrographic and ferrographic analysis of crankcase oils from the High Speed Train" - G.R. Morley, Tribology I nternational, Ju ne 1981, 14(3), 159--165 In this paper the author has published some very interesting data and information obtained from condition monitoring, by a spectrographic oil analysis programme and by ferrography, of diesel engines of the High Speed Train and has effectively demonstrated that regular examination by the former method of oil samples from these units as undertaken by the Scientific Services Branch of British Rail results in more efficient operation and in considerable savings in repair costs. The comments with regard to the results obtained by ferrography, however, when comparing the two methods, apparently indicate some inadequacy in their interpretation. As some of the criticisms regarding the usefulness of ferrography for condition monitoring of diesel engines were considered to be rather severe, it was decided to present the following observations which might be of interest to others concerned with condition monitoring of equipment involving inter-alia the detection and estimation of metallic wear debris. 1. In the first varagraph in 'Comments' (page 164 of the paper) the statement is made that of the seven
364
engines monitored regularly prior to works overhaul 'spectrographic analysis gave abnormal results on only one engine but on two occasions' and 'in neither case did direct read ferrography indicate anything abnormal'. These comments presumably refer to the data on 43041 Engine No 207 (Table 7) and it can be seen that for samples dated 9.8.80 and 10.8.80 a distinct increase in D L and D s readings had occurred. This alone was therefore cause to recommend examination of the engine or at least to prepare an analytical ferrogram. It cannot be fairly stated in this case that direct read ferrography did not detect anything abnormal. 1.1 With regard to the statement concerning ferrography used in the analytical mode on samples of oil from this engine no such results are given in Table 7, and therefore no evidence quoted to substantiate this remark about analytical ferrography. 2. In the second paragraph related to 'the three specific cases when
TRIBOLOGY international December 1981
abnormal spectrographic results were causing concern' the two engines requiring 'Stop and Examine' recommendations were presumably 43022, Engine No 40 and 43111, Engine No 51. 2.1 Admittedly, the direct read ferrography results on samples from 43022 (Table 8) were decreasing but the analytical ferrogram showed cutting wear particles to be present, a definite abnormality and therefore good reason to 'Stop and Examine'. The clear numerical difference between D L and D S readings (ie of large and small particles) would be a guide to the necessity for performance of analytical ferrography. 2.2 It is generally accepted that when condition monitoring of large units is being carried out by direct read ferrography this is best employed in detecting distinct changes in wear trends by examination of several samples taken consecutively. Therefore, for 431 l 1 (Table 10) it was hardly reasonable to state that the D L and D S readings
3.2 The results from samples from 43029 Engine No 100 (Table 5) definitely indicated some distress. There were variable D L and DS readings with distinct differences between D L and D S and the 25.5.80 and 2.6.80 samples showed clear increases in, as well as differences between, the values of DL and D S. Analytical ferrography showed an increase in particles from cutting wear.
(carried out on a single sample) were normal; in fact, when compared with similar results from samples from other faulty units eg 43041 (Table 7) and 43029 (Table 5)4311 l could have been suspected to have an abnormality. 3. Considering the three power cars 43028, 43029 and 43040 (third paragraph), the attainment of DL and D S values which are broadly equal to each other is a general indication that the unit is experiencing normal wear processes.
There was surely need for concern and for 'Stop and Examine' procedure. The observations from the works overhaul on this unit confirmed this. In fact, the statement relating to this engine that it would have been prematurely examined is unfair. Ferrography demonstrated that there was real cause for concern and it is more realistic to consider that this was missed by spectrographic analysis. This is a good example of ferrography detecting the larger wear particles which are missed spectrographically.
In the instance of 43028 Engine No 73 (Table 4), the change in D E and D S indicated that the overall proportion of wear debris had increased (possibly, as the analytical ferrogram showed, due to the presence of dust), but that the nature of this wear was probably normal. A more extensive background of ferrographic experience with samples from several of these units and subsequent examination of components could establish that results of this nature should be regarded as indicative of generally increased wear, but that a 'Stop and Examine' position had not been reached. This particular unit (43028) might, however, have benefited from an oil change; any potentially abrasive debris which might have been present would then have been removed.
4. The fourth (and last) paragraph in 'Comments' relating to 43031 Engine No 101 (Table 9) states that spectrographic data were required to indicate an aluminium trend which direct read ferrography had not shown, but no results from direct read ferrography are given. In any event this was an unfair criticism of ferrography because it is indicated in the table (under 'Comments') that action to leave in service was taken and this was as a result of information provided by analytical ferrography.
3.1 A similar explanation applies to 43040 Engine No 17S (Table 6) and in fact it is stated in the table (see column headed 'Comments'), 'Overall ferrogram satisfactory'.
In the field of condition monitoring of diesel engines there is general agreement that the most effective technique for routine monitoring both for cost and detection success has been, and will continue to be, spectrographic oil analysis. It is however of relevance from British Rail experience on the HST monitoring programme that during the last eighteen months spectroscopy has detected 157 potential failures; of these, 109 were due to coolant leaks as detected by the presence of sodium in the oil sample. The application of a technique such as ferrography which is effective on ferrous and ferrous associated wear
debris to the routine monitoring of the HST programme would therefore not be expected to be considered the most efficient detection technique of impending failure. The following comments may be considered of relevance when considering effectiveness of ferrography on diesel engine oil analysis.
(i)
The Paxman Valenta engine (2250 hp) used in the HST programme has chromium plated cylinder liners and the level of ferrous debris of this engine would depend on the wear of its piston
It should also be noted that 'reduction in spectrographic data' had confirmed that no action needed to be taken when in fact from the figures quoted the reduction (to 8 ppm A1 on 30.12.79 sample) was followed by an increase (to 11 ppm A1 on 31.12.79 sample). 5. Suitably interpreted, therefore, the data given in this paper indicated that with sufficient background development (such as has already been carried out for the spectrographic analysis programme) ferrography alone could provide beneficial condition monitoring of diesel engines and that if not the primary monitor, in conjunction with some other technique for wear metal determination (not necessarily direct emission spectrography) it would give important and valuable additional information on which decisions regarding remedial action, in instances of incipient failure, could be taken and thus provide even greater financial advantage. Far from being (as stated by Mr Morley) 'of no benefit whatsoever in its application to condition monitoring of diesel engines in the HST and therefore likely to be of little use in other diesel engines' the employment of direct read ferrography (coupled with analytical ferrography) in this application could be assessed as being potentially, at least, as useful as a spectrographic oil analysis programme. The techniques are indeed complementary and used together would provide the fullest information. D. McNaught, Fuels and Lubricants Section, London Transport Research Laboratory
rings and crankshaft. The damage in the cases quoted in this paper have had non ferrous association ie aluminium piston damage, coolant leaks etc with the level of iron rarely exceeding 50 ppm. Evaluation of these techniques would therefore be more beneficial for engines generating higher levels of ferrous debris such as engines fitted with cast iron liners. Detection of impending failure would then be dependent on the failure mechanism generating debris at a level in excess of the background noise of the overall system. A number of European
TRIBOLOGY international December 1981
365
and American engine manufacturers are at present testing ferrography as an analysis technique for both marine and railroad application on such engines. (ii) Sampling procedures are particularly critical when using ferrography. Particles detected range in size from 1-250/am; particle settling out is then of importance as also is the filter which would extract, in general, particles larger than 25/am. In spectrophotomerry, particles smaller than 2/am are analysed, so even if the oil sample is extracted from the sump after the engine has cooled analysis would be expected to give consistent readings.
(iii) In research and development, ferrography has already been used successfully on diesel engine programmes to investigate, for example, the effects of lubricants and lubricant additives, cylinder liner surface finish, filter efficiency and running in. This is attributable to not only the size of particles detectable but also that the technique measures rate of wear debris generation, whereas spectroscopy measures the accumulation of wear debris.
than ferrography in its present mode. On-line ferrography, a continuous monitoring system, is at present being evaluated for railroad application in North America and a report of this work will obviously be of interest. Ferrography has already proved of benefit as an additional analytical tool for wear debris analysis in research and development areas and as such Should be considered in conjunction with other techniques and can only be of mutual benefit to the investigator.
In conclusion it is considered a fair comment that spectrographic oil analysis is both a quicker and more cost ef(ective method o f r o u t i n e condition monitoring of diesel engines
M.H. Jones Department of Mechanical Engineering, University College of Swansea, Singleton Park, Swansea, UK, SA2 8PP
Surface Roughness Effects in Hydrodynamic and Mixed Lubrication Edited by S.M. Rohde and H.S. Cheng Many engineering components work under conditions where the surface roughness is comparable with the thickness of the lubricant film as deduced from hydrodynamic theory assuming perfectly smooth surfaces. This is a mode of operation which is imperfectly understood and one in which the boundary between successful operation and failure is often narrower than expected. Therefore the subject of this slim volume is of some importance in current tribological research and development. This is a collection of eight papers presented during the Winter Meeting of ASME at Chicago in November 1980. They range from exclusively theoretical treatments of hydrodynamic lubrication of random rough surfaces to a severely practical investigation of the influence of surface roughness of cylinders' bores on engine oil economy. The balance of work presented here is tilted towards Pubfished by the American Society o f Mechanical Engineers, 345 East 4 7th Street, New York, N Y 10017, USA at US$30.00 [or $15. O0 for A SME members) Book Number GO0193
366
the theoretical side. In my view this is rather a pity. In the future some of these theoretical treatments may be found useful; however the current need is for experimental work which links these theories (and presently available refined computer-based techniques for surface analysis) to some hard experimental evidence related to engineering practice. In the Foreword to this volume the Editors acknowledge the existence of this gap. They remark " . . . m a n y new models have appeared and none have been fully substantiated by careful experimental evidence,.., even
among analytical models the correlations have not been entirely satisfactory". This volume should therefore be on the shelves of all organisations interested in this growing and important subject. In particular it is to be hoped that this volume, and other research publications which have appeared in this field, will encourage researchers and perhaps, more importantly, their sponsors, to attempt more vigorously to span this gap between theory and practice.
J.F. A rchard
Basic Lubrication Theory (3rd Edition) A. Cameron No universally accepted standard textbook covering modern lubrication theory has yet emerged. This one by Professor Cameron having reached its third edition ten years after its launch in 1971 is clearly one of the Published by Ellis Horwood Ltd, Cooper Street, Chiehester, Sussex, UK at £12.50. ISBN 0 853 121 77 Paperback: £9.50
TRIBOLOGY international December 1981
contenders. For this edition, the text has been completely reset and the author, in conjunction with his colleague, Dr Ettles, has rewritten parts of two of the chapters, where rapid changes are occurring, and added tw3 completely new chapters on wear and numerical methods. It is written in a lively style with the main part of the book devoted to