Upload
others
View
1
Download
0
Embed Size (px)
Citation preview
Tribologische testen voor smeermiddelen : standaarden of innovatie ?
(partly in English)
Falex Tribology nv
dr. ir. Dirk Drees
Tribology is the science and technology related to friction, wear and lubrication
Recent History of Falex Tribology
• From sales point to test service organisation • Outsourcing trend • Limits on capital equipment • Short term investment/problem solving
in industry • Loss of experience/know-how in industry
• 2000 2 staff, focus sales
• 2002 3 staff, sales and test work
• 2004 4 staff, sales, testing and development EU projects
• 2008-2016 5 staff, sales, testing and development Financial and industrial crisis accelerated outsourcing trend !
34%
25%
28%
13%
Sales 2005
Equipment Specimens Testing Other
20%
20%51%
9%
Sales 2015
EEN PROVOCATIEVE TITEL ?
Introduction
Een provocatieve titel ?
Het zou ook ‘Standaarden en innovatie’ kunnen zijn...
• Wat zijn standaarden
• Waarom standaarden
• Nut van standaarden
• Problemen met standaarden
• Waarom géén standaarden
• Wat dan wel...
Een provocatieve titel ?
• Standaarden voor tribologische testen ...
• Smering, wrijving, (anti-)slijtage, extreme pressure
• JASO (Japan) – CEC, ILSAC, ACEA (Europe) – API, SAE (USA)
• ‘specificaties’
• Gebruik maken van standaard testen om een minimale product kwaliteit vast te leggen
• Collectie van ‘requirements’ : meetresultaat van standaarden als criteria
Wat is een standaard
• ASTM : industry consensus
• DIN : workgroup consensus
• CEC : committee result
• ASTM most open to participation. Driven by industrial users of products
• Membership = active participation allowed
• End user, test manufacturer, product manufacturer...
• ASTM most tribology related standards
• But tribology related : minority in all material testing standards !
• Lubricants = volumes 5.01 to 5.05
• Mostly physical and chemical tests
ASTM Voluntary Industry consensus standard
• Definition of a standard procedure/method to test something
• Property of material
• Property of a product, machine, building, agriculture, mines, ...
• Scope of a standard defined
• What is it for ?
• Significance or use
• Bias, or Precision statement defined
• Bias : relation to reality?
• Precision statements
ASTM Voluntary Industry consensus standard
• Consensus on how to test something under conditions that will be the same world-wide, and all information required to assure the best reproducibility of the conditions :
• Test materials
• Test equipment that has participated in precision determination
• Round robin
• Procedure – as detailed as possible ...
ASTM Voluntary Industry consensus standard
• Why ?
• some organizations choose to use or specify standard test methods for the usual reasons: (a) ability to compare new results with other results done under the same conditions, (b) product quality assurance, (c) customer confidence, (d) industry preference, (e) within lab consistency, (f) database development, (g) compare company products to competitors’ products under formalized conditions, and more.
(P. Blau, Co-ed. Wear, )
• No mention of ‘simulate components or application’ !
10
• Difficulty : a tribological test is not a tensile test…
11
Tribological properties must be described in terms of a system.
Coefficient of friction, wear rates, extreme pressure and abrasion resistance are only meaningful when reported along with all test conditions.
Changing any test condition can affect different tribological results.
Criticisms and problems with standards
Concept related
• The standard does not correlate to my field experience
• The standard has poor repeatability/reproducibility
• The standard gives the wrong results (see first criticism)
Execution related
• Procedure correctly executed ?
• Operator training
• Test equipment maintenance and calibration
• Correct materials used
• Correct parameters used
Criticisms and problems with standards
Illustration popularity vs. relevance
• The Four Ball test machine / Vierkugelapparatus VKA / 4billes...
• Remembering Mr. Plint’s lecture 2014 : Sliding Hertzian point contacts in reality ?
Criticisms and problems
Conclusion :
If the standard is not properly performed or for the wrong reasons, then it has no value.
If it is properly performed and relevant for the application, the repeatabiliy may not be sufficient to record small improvements
Then what about research and innovation ???
Standard <-> Innovation ?
‘The test does not correlate to my conditions’
Simulating the conditions ? Is it ever possible in a test ?
HOW TO SELECT A TEST METHOD ?
Test method selection for ‘innovation’
16
correlation
Czichos, ASM Metals Handbook Vol. 18
Mang,Bobzin, Batles, Industrial Tribology, Wiley 2011
Test method selection
cost
time
17
• Difficulty : a tribological test is not a tensile test…
Test method selection
18
Tribological properties must be described in terms of a system.
Coefficient of friction, wear rates, extreme pressure and abrasion resistance are only meaningful when reported along with all test conditions.
Changing any test condition can affect different tribological results.
Test method selection
19
• Description of
• structural components of the tribosystem
• material pair 1 & 2
• lubricant 3 and environment 4
• operational parameters of the tribosystem
• interaction parameters of the tribosystem
• tribometric characteristics
in what follows, the methodology of
the ASM Metals Handbook, Vol. 18 is
used as illustration
Test method selection
20
• material pair properties
• chemical : composition
• physical : thermal conductivity, electrical...
• mechanical :E-modulus, hardness, toughness...
• geometric : dimensions, surface topography
• microstructural : grain size distrib., phases, ...
• lubricant & environment properties
• chemical : composition, acidity, humidity...
• physical : density, thermal conductivity, ...
• mechanical : viscosity, viscosity index, ...
Test method selection
21
Test method selection
22
• operational parameters
• type of motion : sliding, rolling, spinning, oscillating...
• load : forces, frequency of load
• velocity : relative motion of triboelements
• temperature : initial, friction induced
• time depence of parameters : cyclic, continuous...
• duration : of operation, test, lifetime
Test method selection
24
• interaction parameters
• contact mode : elastic, plastic, stresses
• lubrication regime : boundary, hydrodynamic
Test method selection
25
• tribometric characteristics : what needs to be measured ?
• friction : frictional force, frictional work/energy
• wear : wear volume, wear rate, ...
• heating
• Others
• Wear mechanism conformity !
Test method selection
26
Tribological Aspect Number (T.A.N.)
• A systematic approach to corresponding a field application with a test setup
• Evaluate the operational parameters
• Motion type
• Contact area evolution
• Contact pressure evolution
• Entry angle (lubrication)
• Match operational parameters with laboratory test machine
• Standard test equipment
• Custom test equipment
• Special testers
27
TAN Motion
28
TAN Geometry
29
TAN Contact pressure
30
TAN Entry angle
31
Tribological Aspect Number (T.A.N.)
32
1. IDENTIFY FIELD PROBLEM
TAN CODE
XXXX
2. BENCH TEST 2. BENCH TEST
TAN CODE TAN CODE
XXXX YYYY
3. SELECT 3. SELECT
PRESSURE/LOAD PROCEDURAL COMPROMISERUBBING SPEED ADJUSTMENT
MATERIALS PRESSURE/LOADLUBRICANT RUBBING SPEED
MATERIALSLUBRICANT
4. SET 4. SET
TIME AND TEMPERATURE TIME AND TEMPERATURE
SIMULATION RANKING
TAN Method
33
After the T.A.N. code …
• Measure what ? • Friction • Wear evolution • Temperature • Vibrations • Acoustic • Chemical/electrochemical data • Other…
• Challenges in measurements • Precision • Accelerated testing • Realistic wear and pressures • Wear evolution
34
1. Analysis of field contact : TAN
2. Determination of metrics : what to measure ?
3. Feasibility of lab/bench testing
4. First selection of test parameters : correlation (wear mechanism, wear rate, friction, general behaviour)
5. Recursive optimisation of lab/bench testing
6. Correlation with field
(‘75% of all investment in time and cost’)
7. Statistical testing of new solutions (Routine testing)
Typical steps towards a new lab test procedure
35
Many options, choose the right one
• T.A.N. simulation
• Parameters of the real environment
• Precision
• Efficiency
• Test specimens
• COST …
With permission of Phoenix Tribology UK - www.phoenix-tribology.com
OVERCOME THE CHALLENGES
Innovation in lab testing
37
1. The ‘Standard’ test challenge • For some reason, a standard isn’t suitable
• Cost, correlation, precision, …
‘make’ a new test : better, or just more precision ?
2. Contact pressure challenge • Typical components in operation : 1-200 MPa pressure
• Typical pressure in standard lab tests : 1 GPa (ball on flat)
Simulations with lower contact pressures
3. Wear rate challenge • Typical machine component lifetime : > 2000 hr
Wear rate = 2000nm/2000hr = 1 nm/hour
• Typical standard test : 1-10 hr create 1 µm wear
Wear rate = 1000 nm/10 hr = 100 nm/hour
• Wear evolution
Challenges and limitations to lab testing
38
• Wear measurement precision and false results • misleading results
• Example : Four Ball Wear ASTM D4172 test results
Optical :
446 µm
Optical :
405 µm
3-D
Confocal
:
444 µm
3-D
Confocal
:
270 µm
Case : precision of standard methods
39
• Wear measurement precision • ASTM G133 test method used on plastic wear
• Flat-on-flat contact – weight loss
• ‘life simulation’ = 432 km
• Each lab test = < 8 km (22 hours)
Note on precision of standard methods
40
Matching contact pressure in lab scale testing with in-field
conditions
Lab testing strategy – contact pressure analysis
20 N on a line contact of
10 x 10 mm cylinder
results in same realistic
contact pressure as 0.5 N
on a 5 mm radius ball !
ASTM G133 test with cylinder-on-flat
100 N load (220 MPa)
Two speeds: 2 Hz and 20 Hz (0.04 and 0.4 m/s)
Case : piston simulation and friction modifier additives
0 500 1000 1500 2000 2500 3000
0.06
0.08
0.10
0.12
0.14
0.16
120 °C 80 °C 20 °C
RM
S C
oF
Test duration (s)
At 2 Hz test frequency
GMO PGMO
Friction additive in engine oil – 3 temperatures
0 500 1000 1500 2000 2500 3000
0.06
0.08
0.10
0.12
0.14
0.16
120 °C 80 °C 20 °C
RM
S c
oeff
icie
nt
of
fric
tio
n
Test duration (s)
At 20 Hz test frequency
GMO PGMOA A
Individual differences between GMO and additive A visible
BUT : Run-in behaviour and noisy signal : statistical evaluation needed
Ball-on-flat, AISI E 52100 steel, 25 mm x 8 mm disk, 3.175 mm Ø ball
50 mN load (240 MPa), 2 mm stroke length,
0.5 mm/s speed, and 50 reciprocating cycles
Repeatable test samples !
Friction additive in engine oil – precision
High precision friction measurement
0 10 20 30 40 50
0,05
0,10
0,15
0,20
0,25
+GMO +B +C
+D Base oil +F
Avera
ge c
oeff
icie
nt
of
fric
tio
n
Number of cycles
0 10 20 30 40 50
0,05
0,10
0,15
0,20
0,25
Avera
ge c
oeff
icie
nt
of
fric
tio
n
Number of cycles
REPEAT MEASUREMENT
+GMO +B +C
+D Base oil +F
High precision friction measurements
0,05
0,10
0,15
0,20
0,25
0,30
10W40
+GMO
+B
+C
+D
Base oil
+F
Avera
ge c
oeff
icie
nt
of
fric
tio
n
0,05
0,10
0,15
0,20
0,25
0,30
Avera
ge c
oeff
icie
nt
of
fric
tio
n
10W40
+GMO
+B
+C
+D
Base oil
+F
High precision friction measurements new (more) information from the contact
‘Triboscopy’
High precision friction measurements new (more) information from the contact
48
• Accelerated testing • Increase speed ? • Increase pressure ?
• Thermal input • Change of wear mechanism • Elastic plastic deformation of materials • PV limit for polymers / Transformations in metals
• Continuous versus intermittent ? • Changes lubrication mechanism (hydrodynamic-boundary) • Start-stop cycling • Exposed materials : chemical / electrochemical reactions
• Increase temperature ? • Changes lubricant properties
Acceleration must be verified with a correlation study !
Multistation testing a better alternative than accelerating ?
Challenges and limitations to lab testing
49
• Wear evolution and low wear • Run-in wear vs. Long term wear ?
• Long term wear determines lifetime
• Run-in wear determines subsequent evolution
• Wear evolution measurement
0 50 100 150 200 250 300
0,0
0,2
0,4
0,6
0,8
1,0
Evolution of wear volume in POE-0
in CO2 (10 bar)
in air
We
ar
vo
lum
e (
mm
3)
test time (min)
W
(log)t
Run-in
Wear rate
50
Fn.d V
285 0,251
570 0,822
855 0,909
1140 1,381
1710 2,438
570 0,922
1140 1,223
1710 2,383
2280 3,088
3420 4,405
855 0,776
1710 2,133
2565 3,533
3420 4,857
5130 8,414
0 1000 2000 3000 4000 5000 6000
0
2
4
6
8
1099% confidence; 15 points
99% confidence; 4 points
We
ar
Vo
lum
e
Load x distance (N.m)
Fn.d V
285 0,251
570 0,822
855 0,909
1140 1,381
1710 2,438
570 0,922
1140 1,223
1710 2,383
2280 3,088
3420 4,405
855 0,776
1710 2,133
2565 3,533
3420 4,857
5130 8,414
0 1000 2000 3000 4000 5000 6000
0
2
4
6
8
10W
ea
r V
olu
me
Load x distance (N.m)
Wear rate and statistics
50 station wear tester
Case Example: Aircraft component
Aim: wear resistance of polymer composites under lubricating sliding with and without contaminating particles
Case Example: Aircraft component
Result : 50 data points, average values, effect of particle contamination in the contact
Economics : 250 Euro per data point 40 km sliding distance <-> 2400 Euro per data point 8 km distance in single station test
Meters sliding distance
Case Example: Grease comparison
Aim: anti wear of greases in a slow moving contact
Case Example: Grease comparison
Result : 20 data points, 10 greases (‘duplicate tests’) Economics : 200 Euro per data point 3.3 km distance <-> 2400 Euro per data point of 4.3 km distance in single station test
58
0
5
10
15
20
25
30
35
0 0,5 1 1,5 2 2,5 3
k f
acto
r (1
0-1
5 m
3/N
.m)
Cycles Miljoenen
Uncoated
0
5
10
15
20
25
30
35
0 0,5 1 1,5 2 2,5 3
k f
acto
r (1
0-1
5 m
3/N
.m)
Cycles Miljoenen
PVD DLC 1
26 individual tests, 4 coating categories, wear evolution and total wear after 2.5 M cycles Duration project : 24 days = more than one result per day despite 24 day wear test !
Case Example: Vacuum DLC
Aim: wear evaluation of PTFE vs DLC coatings
59
0
5
10
15
20
25
30
35
0 0,5 1 1,5 2 2,5 3
k f
acto
r (1
0-1
5 m
3/N
.m)
Cycles Miljoenen
PVD DLC 2
0
5
10
15
20
25
30
35
0 0,5 1 1,5 2 2,5 3k f
acto
r (1
0-1
5 m
3/N
.m)
Cycles Miljoenen
IBAD DLC
Case Example: Vacuum DLC
26 individual tests, 4 coating categories, wear evolution and total wear after 2.5 M cycles Duration project : 24 days = more than one result per day despite 24 day wear test !
Aim: wear evaluation of PTFE vs DLC coatings
60
Case Example: Vacuum DLC
Aim: wear evaluation of PTFE vs DLC coatings
NEW METHODS
Innovation in lab testing
62
Grease tackiness
Existing challenges:
Fast method to pre-screen in an efficient and accurate way the tackiness
of industrial greases
Need for precision measurements to differenciate between similar greases
Need for an objective method...
63
State of the art
Subjective, speed dependent
64
Objective force measurement with precision tester
Sample preparation
A repeatable grease film of 200 µm thickness was applied by filling the rectangular gap between two pieces of 200µm thick adhesive film
65
Indentation – retraction with copper ball
Slow retraction speed
High retraction speed
Retraction speed variation
effect of retraction speed
0.05 mm/s 0.5 mm/s
1 mm/s 5 mm/s
effect of retraction speed (at 20mN)
0.05 mm/s 0.5 mm/s 1 mm/s 2 mm/s 5 mm/s
0
10
20
30
40
50
Pull-
off forc
e (
mN
) 0.05 mm/s
0.5 mm/s
1 mm/s
2 mm/s
5 mm/s
5. Comparison
Existing comparison
Grease 1 Grease 2 Grease 3
Strongly depends on user, quantity of grease, speed etc.
Objective differences
What if Stribeck curves existed for Greases ?
Grease 1 Grease 2 Grease 3 Invers
e o
f th
readin
g t
endency
SAMENVATTING
Standards or Innovation
Samenvatting
• Standaarden of innovatie ?
• Er is ruimte voor de 2 : Standaarden én innovatie
• Standaard = correct uitvoeren + voor de juiste reden
• Standaard voldoet niet innovatie
• Innovatie in test werk
• Hogere precisie in metingen : frictie, slijtage beter onderscheid voor ontwikkeling
• Aangepaste methode aan werkelijkheid correlatie met praktijk
• Correcte contactdrukken
• Realistische slijtage snelheden
• Parallelle testen winnen tijd/geld
• Statistisch waardevolle data
• Snellere besluitvorming mogelijk
• Levensduur inschattingen
• Nieuwe test methoden nodig ?
• Bv. Grease tackiness objectief meten
Meer vragen dan antwoorden ? Wij zijn er voor u...
www.falex.eu