07-10-2016, 03:53 PM
Wear Debris Analysis - A Meaningful Condition Monitoring Technique for Industrial Drives
[attachment=72678]
Abstract
Wear debris analysis has recently become a more widely applied technology in machinery health
monitoring. This paper describes what it is, where it's application is relevant and the kind of
successes that have been achieved in it's use.
1. Introduction
Wear is the primary mechanism by which industrial plant deteriorates. By observing the amount and
mechanism of wear periodically one is able to monitor the deterioration of plant. Traditionally this
has been done by SOAP (spectrometric) analysis of used oil. In industrial drives this has a major
deficiency, the most important size fraction, that is the particles above 10 microns are ignored. In a
"normal" industrial drive as shown in Fig. 1 the average particle size is 15-25 microns. In most
cases in a distress situation the size of these particles increases and traditional techniques have not
been able to effectively detect this. Wear debris analysis overcomes the particle size limitation and
gives additional information on the mechanism, location and extent of wear as well as the state of
the Lubricant and contaminant content.
To some extent wear debris analysis has taken over the major role of condition monitoring within
the mining industry within the UK even though it is a relatively newcomer on the condition
monitoring scene.
2. Wear Debris Analysis
The basic principle of operation is simple. A representative sample of oil is tested through the
following cycle.
1. Obtain an oil sample from a machine.
2. In the laboratory take a measured amount of the fluid and deposit into a clean
beaker. The sample is then diluted with a solvent
3. Draw the sample through a membrane filter or use a magnetic separation
technique such as the rotary particle depositor to separate the solids from the fluid.
4. The amount of ferrous wear is quantified by means of a debris analyser such as the
PQ2000 manufactured by Swansea Tribology Centre.
5. Visually analyse the debris at 100x magnification under a reflected light microscope
quantifying the following parameters:
Type of particle (relating to the mechanism of removal)
o Average particles size
o Maximum particle size
o Contamination index
These parameters are then trended in a custom designed software package and the diagnostician
awards the unit a Health Status. The health status is a single parameter which gives the unit a level
of threat. (Health status is a parameter between 1 -5 with 1 being a healthy machine and 5 being a
machine which is imminently threatened with failure.)
6. Repeat the procedure at a decided time interval.
Wear debris analysis is a relatively simple procedure not requiring a high skills level to perform.
Even so the results give a direct indication as to the level of threat and damage within industrial
drives absent from some of the more sophisticated techniques.
3. Visual and Microscopic Examination of the Debris Samples
Visual and microscopic examination of the sample is as important a source of information as the
regular testing of the debris samples.
Prior to filtering the sample, examination of the sample visually within the sample bottle gives useful
information. Water present within the oil sample can clearly be seen either in the form of
emulsification or as a distinct water layer. The general cleanliness level of the oil may also be
determined.
Once filtered the debris should be visually examined prior to microscopic examination. The
presence of water within the lubricant can be detected from the filter paper. This is seen in the form
of light circular areas on the filterpaper. Water also sometimes oxidises the ferrous material, and the
presence of rust indicates the ingress of water. Water effects the viscosity of the lubricant,
considerably reducing the effect of the lubricant, increasing wear rates and should be avoided.
Frequently gearboxes become contaminated with mineral particles such as silica, coal and shale.
These produce fine abrasive wear particles normally only observed under the microscope. The
unchecked presence of mineral particles specifically quartzite with it's high hardness should be
avoided. The mineral particles in suspension act as a grinding medium and produces excessive
bearing wear which leads to loss of gear and shaft location which further accelerates the wearing
process.
The various debris testers available do not respond to non magnetic materials such as:
Chromium Brass Coal
Tin Bronze Copper Minerals
Antimony Phosphor bronze Aluminium
Aluminium bronze Molybdenum disulphate
These are often clearly visible on the filter paper, and should be carefully looked for because even
though they may be present in quantities no indication would be given by the debris tester.
The sizing (both average, maximum particle size and the particle size distribution) is one of the
more important aspects of testing. In general the damage state of a gearbox is proportional to the
size of the particles. In it's simplist form of application four classes of size classification are used:
Fine less than 5 microns
Small less than 25 microns
Medium 25-60 microns
Large above 60 microns
As a general rule, which has exceptions, particles over 25 microns indicate a potentially dangerous
damage state for the unit.
The wear particle shape gives an indication as to the damage mechanism by which that particle
was removed. The wear shape characterisation being used is shown in Fig.2 and consists of:
Platelets two dimensional particles produced by metal to metal sliding.
Spherical produced by bearing fatigue or by lubrication failure resulting in local overheating.
Spirals similar in appearance to machining swarf, and are produced by a harder surface
abrading into a softer
Chunky produced by a fatigue mechanism
Fretting produced by an oxidation mechanism where small intense cyclic loads are present in the
presence, of oxygen in a close tolerance fit.
4. Wear Debris Analysis in South Africa:
The gearboxes in underground coal mining equipment have long been a maintenance problem.
Traditional techniques of failure analysis, quality assurance and control have only gone part of the
way to solving this problem. In 1986 Condition Monitoring Services was involved in suggesting a
predictive rather than a reactive maintenance philosophy for these units.
To date a number of wear debris analysis mini laboratories have been installed and have monitored
underground coal mining equipment with considerable success.
No other technique could have served this purpose due:
to the problems associated with taking conventional condition y monitoring tools into
fiery mines.
* thirdly to the logistical problems of monitoring large numbers of gearboxes within a very hostile
environment.
Since the early days of 1986 debris analysis has become a widespread and generally accepted
technique of condition monitoring. Examples of some of the successes achieved with debris
analysis are:
• failure prevention in diesel engines used in haul trucks.
• failure prevention in long wall mining and continuous miner gearboxes.
• failure prediction on a large selection of both surface and underground mining
equipment used in the gold mining industry.
• contamination control in surface gold mining process equipment.
• grease and oil selection through comparative lubricant trials.
• condition monitoring of critical coal milling gearboxes in the power
generation industry.
• failure investigations of critical bearings in ball mills used in the gold mining industry.
5. New Developments in Debris Analysis
There have been two innovative local developments of debris monitoring. These are
Contamination Control.
A simple technique for monitoring and reporting on levels of solid contamination within a system has
been developed. Previously monitoring of contamination to the accepted codes has either been
time consuming or required an expensive investment in equipment. Now users are able to set
contamination limits for their equipment and simply monitor whether they are within these limits.
Grease Analysis
A program for the routine monitoring of greases using debris analysis has been going on for over a
year now. Ale major problem concerning grease is separating the wear debris from the solids
occurring within the grease's additive assembly. As no generally accepted standard method existed,
this had to be developed and refined into a meaningful technique. There has now been a buildup of
data showing that not only can debris analysis be performed on greases but the technique is
sensitive to mechanical health.
6. Data Management Processing and Reporting
Today more and more importance is being placed on the collection, control and effective use of
information as a management tool. This is particularly appropriate in the field of maintenance
management where so much can be gained or lost through effective action at the appropriate point
in time. To facilitate using information as a powerful management resource, the CMS machinery
health monitoring system has been developed.
The system is designed to be as adaptable as possible so as to allow future expansion as the users
needs grow and also allow specific customised needs to be integrated as and when required.
[attachment=72678]
Abstract
Wear debris analysis has recently become a more widely applied technology in machinery health
monitoring. This paper describes what it is, where it's application is relevant and the kind of
successes that have been achieved in it's use.
1. Introduction
Wear is the primary mechanism by which industrial plant deteriorates. By observing the amount and
mechanism of wear periodically one is able to monitor the deterioration of plant. Traditionally this
has been done by SOAP (spectrometric) analysis of used oil. In industrial drives this has a major
deficiency, the most important size fraction, that is the particles above 10 microns are ignored. In a
"normal" industrial drive as shown in Fig. 1 the average particle size is 15-25 microns. In most
cases in a distress situation the size of these particles increases and traditional techniques have not
been able to effectively detect this. Wear debris analysis overcomes the particle size limitation and
gives additional information on the mechanism, location and extent of wear as well as the state of
the Lubricant and contaminant content.
To some extent wear debris analysis has taken over the major role of condition monitoring within
the mining industry within the UK even though it is a relatively newcomer on the condition
monitoring scene.
2. Wear Debris Analysis
The basic principle of operation is simple. A representative sample of oil is tested through the
following cycle.
1. Obtain an oil sample from a machine.
2. In the laboratory take a measured amount of the fluid and deposit into a clean
beaker. The sample is then diluted with a solvent
3. Draw the sample through a membrane filter or use a magnetic separation
technique such as the rotary particle depositor to separate the solids from the fluid.
4. The amount of ferrous wear is quantified by means of a debris analyser such as the
PQ2000 manufactured by Swansea Tribology Centre.
5. Visually analyse the debris at 100x magnification under a reflected light microscope
quantifying the following parameters:
Type of particle (relating to the mechanism of removal)
o Average particles size
o Maximum particle size
o Contamination index
These parameters are then trended in a custom designed software package and the diagnostician
awards the unit a Health Status. The health status is a single parameter which gives the unit a level
of threat. (Health status is a parameter between 1 -5 with 1 being a healthy machine and 5 being a
machine which is imminently threatened with failure.)
6. Repeat the procedure at a decided time interval.
Wear debris analysis is a relatively simple procedure not requiring a high skills level to perform.
Even so the results give a direct indication as to the level of threat and damage within industrial
drives absent from some of the more sophisticated techniques.
3. Visual and Microscopic Examination of the Debris Samples
Visual and microscopic examination of the sample is as important a source of information as the
regular testing of the debris samples.
Prior to filtering the sample, examination of the sample visually within the sample bottle gives useful
information. Water present within the oil sample can clearly be seen either in the form of
emulsification or as a distinct water layer. The general cleanliness level of the oil may also be
determined.
Once filtered the debris should be visually examined prior to microscopic examination. The
presence of water within the lubricant can be detected from the filter paper. This is seen in the form
of light circular areas on the filterpaper. Water also sometimes oxidises the ferrous material, and the
presence of rust indicates the ingress of water. Water effects the viscosity of the lubricant,
considerably reducing the effect of the lubricant, increasing wear rates and should be avoided.
Frequently gearboxes become contaminated with mineral particles such as silica, coal and shale.
These produce fine abrasive wear particles normally only observed under the microscope. The
unchecked presence of mineral particles specifically quartzite with it's high hardness should be
avoided. The mineral particles in suspension act as a grinding medium and produces excessive
bearing wear which leads to loss of gear and shaft location which further accelerates the wearing
process.
The various debris testers available do not respond to non magnetic materials such as:
Chromium Brass Coal
Tin Bronze Copper Minerals
Antimony Phosphor bronze Aluminium
Aluminium bronze Molybdenum disulphate
These are often clearly visible on the filter paper, and should be carefully looked for because even
though they may be present in quantities no indication would be given by the debris tester.
The sizing (both average, maximum particle size and the particle size distribution) is one of the
more important aspects of testing. In general the damage state of a gearbox is proportional to the
size of the particles. In it's simplist form of application four classes of size classification are used:
Fine less than 5 microns
Small less than 25 microns
Medium 25-60 microns
Large above 60 microns
As a general rule, which has exceptions, particles over 25 microns indicate a potentially dangerous
damage state for the unit.
The wear particle shape gives an indication as to the damage mechanism by which that particle
was removed. The wear shape characterisation being used is shown in Fig.2 and consists of:
Platelets two dimensional particles produced by metal to metal sliding.
Spherical produced by bearing fatigue or by lubrication failure resulting in local overheating.
Spirals similar in appearance to machining swarf, and are produced by a harder surface
abrading into a softer
Chunky produced by a fatigue mechanism
Fretting produced by an oxidation mechanism where small intense cyclic loads are present in the
presence, of oxygen in a close tolerance fit.
4. Wear Debris Analysis in South Africa:
The gearboxes in underground coal mining equipment have long been a maintenance problem.
Traditional techniques of failure analysis, quality assurance and control have only gone part of the
way to solving this problem. In 1986 Condition Monitoring Services was involved in suggesting a
predictive rather than a reactive maintenance philosophy for these units.
To date a number of wear debris analysis mini laboratories have been installed and have monitored
underground coal mining equipment with considerable success.
No other technique could have served this purpose due:
to the problems associated with taking conventional condition y monitoring tools into
fiery mines.
* thirdly to the logistical problems of monitoring large numbers of gearboxes within a very hostile
environment.
Since the early days of 1986 debris analysis has become a widespread and generally accepted
technique of condition monitoring. Examples of some of the successes achieved with debris
analysis are:
• failure prevention in diesel engines used in haul trucks.
• failure prevention in long wall mining and continuous miner gearboxes.
• failure prediction on a large selection of both surface and underground mining
equipment used in the gold mining industry.
• contamination control in surface gold mining process equipment.
• grease and oil selection through comparative lubricant trials.
• condition monitoring of critical coal milling gearboxes in the power
generation industry.
• failure investigations of critical bearings in ball mills used in the gold mining industry.
5. New Developments in Debris Analysis
There have been two innovative local developments of debris monitoring. These are
Contamination Control.
A simple technique for monitoring and reporting on levels of solid contamination within a system has
been developed. Previously monitoring of contamination to the accepted codes has either been
time consuming or required an expensive investment in equipment. Now users are able to set
contamination limits for their equipment and simply monitor whether they are within these limits.
Grease Analysis
A program for the routine monitoring of greases using debris analysis has been going on for over a
year now. Ale major problem concerning grease is separating the wear debris from the solids
occurring within the grease's additive assembly. As no generally accepted standard method existed,
this had to be developed and refined into a meaningful technique. There has now been a buildup of
data showing that not only can debris analysis be performed on greases but the technique is
sensitive to mechanical health.
6. Data Management Processing and Reporting
Today more and more importance is being placed on the collection, control and effective use of
information as a management tool. This is particularly appropriate in the field of maintenance
management where so much can be gained or lost through effective action at the appropriate point
in time. To facilitate using information as a powerful management resource, the CMS machinery
health monitoring system has been developed.
The system is designed to be as adaptable as possible so as to allow future expansion as the users
needs grow and also allow specific customised needs to be integrated as and when required.