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Dr. Ir. Dirk Drees, Dr. Ir. Emmanuel Georgiou, Michel De Bilde

Falex Tribology Belgium – Falex Application Center Tribology

A new test method to evaluate hydraulic fluids for vane pumps

Tribology is the science and technology related to friction, wear and lubrication

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Schedule of presentation

1. Objectives

2. Existing methodology and its limitations

3. Challenges

4. Alternative method

5. Pre-screening and evaluation tests

6. Other possibilities

7. Conclusions

8. Follow-up actions

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1. Objectives

• Establishing a new methodology to simulate vane pump

tests

• Efficient and accurate evaluation of friction and wear

• Matching in-field conditions to a lab tests

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1. Objectives

cost

time

correlation

after Czichos, ASM Metals Handbook Vol 18

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2. Existing methodology

& their limitationsConestoga Vickers Vane Pump: ASTM D7043 - DIN 51389 - ISO 20763

Pump assembly

Limitations:

• Time consuming tests (1 test takes 250 hrs)

• Large quantity of oil

• No data on friction

• Temperature of oil in not well controlled

Test Parameters

Speed (rpm) 1500

Load (lbf)

Time (h) 250

Loading rate (lbf/s)

Oil volume (L) 50

Flow rate (LPM)

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3. Challenges

• Simulate actual in-field conditions

• Accelerated wear to minimize testing time

• Accelerate wear without changing wear mechanisms

• In-situ monitoring of friction, wear of the tribosystem and

oil temperature near contact interface.

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4. Alternative method

Step 1: identifying wear mechanisms of actual components (Conestoga)

➢ Actual components (ring and vane) after testing

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4. Alternative method

Step 1: identifying wear mechanisms of actual components (Conestoga)

➢ Mild abrasion (smoothening) of vanes

➢ Mild abrasion and oxidative wear (oxide layer in contact)

➢ Formation of debris particles

Ring Vane

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4. Alternative method

Step 2: calculating centrifugal force

Where:

M : mass

ω : angular speed

r : radius

Centrifugal force of a vane in a pump is ≈ 65 – 75 N or 15 – 17 lbf

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4. Alternative method

Step 3: Multispecimen testing protocol

Test Parameters

Speed (rpm) 1500

Load (lbf) 800

Time (h) 25

Loading rate (lbf/s) 20-30

Oil volume (L) 3

Flow rate (LPM) 2

For more information on the procedure look into protocol developed by Falex US (April 8th 1997)

Starting point of updated protocol:

• Loading conditions are significantly higher than the ones met in actual

conditions → definine test conditions to have accelerated wear loss without

changing the wear mechanisms

* From our previous experience weight gain was observed. This does not

corresponds to reality

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4. Alternative method

Step 3: Multispecimen testing protocol

• Test samples (disks) were developed. Grooves simulate pressure variation.

• Three vanes are tested per experiment

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5. Pre-screening

& evaluation testsStep 4: accelerating wear and defining the working limits (failure map)

1500 rpm, 3 LPM, 2.5 L, 45 °C

Lo

ad

(lb

f)

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5. Pre-screening & evaluation tests

Step 4: accelerating wear and defining the working limits (failure map)

1500 rpm, 3 LPM, 2.5 L, 45 °C

Lo

ad

(lb

f)

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5. Pre-screening

& evaluation tests

➢ Heating up of hydraulic fluid

➢ Change in the lubrication regime (metal-metal contact)

Step 5: understanding failure (in-situ monitoring of COF & T at interface)

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5. Pre-screening

& evaluation testsStep 5: understanding failure (analysis of wear mechanisms)

At 400 lbf for 1 h:

At 200 lbf for 1 h:

Vane Disk

➢ Different wear mechanisms

➢ At 200 lbf wear mechanisms are closer to reality

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5. Pre-screening

& evaluation testsStep 6: optimization of testing conditions (defining working conditions)

➢ Mapping limits of contact pressure (calculated with Hertzwin software)

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5. Pre-screening

& evaluation tests

1500 rpm, 200 lbf, 2.5 L, 3 LPM 45 °C

➢ Wear is measurable

➢ Repeatable measurements

➢ Running-in period observed

➢ Weight loss is similar to the one obtained after Conestoga test (≈ 2 mg/h)

Step 7: matching Multispecimen with Conestoga tests

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5. Pre-screening

& evaluation tests

➢ Similar coefficient of friction at the steady state conditions

➢ Different running-in, possibly due to initial surface

➢ Increase of friction is accompanied by increase in temperature

➢ Lubrication regime confirmed

Step 7: matching Multispecimen with Conestoga tests

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5. Pre-screening

& evaluation testsStep 7: matching Multispecimen with Conestoga tests

Vane after Multispecimen testingat 200 lbf for 20 hrs

Vane after Conestoga vane pump testing for 250 hrs

➢ Similar wear mechanisms, namely mild abrasion and oxidative wear

(formation of a localized oxide tribo-layer)

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6. Other possibilities

Investigate the effect of T on the performance of hydraulic fluids

➢ No potential danger of overshooting temperature (≈ 10 °C) on friction

➢ Lubrication regime confirmed and compared

➢ In-situ monitor of evolution of COF and T near the contact

➢ Better comparison of performance of hydraulic fluids

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45 °C

55 °C

Investigate the effect of T on the performance of hydraulic fluids

6. Other possibilities

Vane Disk

Vane Disk

➢ Similar wear mechanisms on both vanes and disks

➢ Some difference in weight loss was observed →

Shorter tests allow to test repeatability

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7. Conclusions

➢ Conestoga Vickers Vane Pump tests can be simulated by

Multispecimen tester

➢ Similar wear mechanism as in Conestoga Vickers Vane Pump tests

for loads below 300 lbf

➢ Above 400 lbf severe abrasion of the disk and oxidative wear of the

vanes may occur

➢ Higher wear rate during first hour (running-in )

➢ Similar wear loss as in Conestoga Vickers Vane Pump tests

➢ In-situ monitoring of coefficient of friction and temperature allow for a

better understanding of occuring phenomena

➢ Possibility to change and regulate the contact conditions (speed,

load, acceleration etc.), temperature and hydraulic fluid flaw rate

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8. Follow-up actions

• Testing of various hydraulic oils that have been already

tested on the Conestoga

• Create a ranking based on friction and wear

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Thank you for your attention !