Tribologische testen voor smeermiddelen : standaarden of

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

ddrees@falex.eu