Practical Notes for SRV® Users

Fretting wear evaluation of lubricating oils using the SRV® test system

This note focuses on fretting wear phenomena for different lubricating oils. Typical challenges associated with fretting include:

High-frequency vibrations
Very small relative movement amplitudes

The well-established ASTM D7594-24 standard describes a Test Method for Determining Fretting Wear Resistance of Lubricating Greases under High Hertzian Contact Pressures Using a High-Frequency, Linear-Oscillation (SRV®) Test Machine.

Fretting protection is also crucial for many lubricating oils and fluids. This topic has been discussed among SRV® users. Liquids are evaluated under comparable fretting conditions (0.3 mm stroke, 50 Hz frequency and 4-hour duration) using an oil bath.

Fretting Tests Performed at Optimol Instruments

Fretting tests based on the conditions of ASTM D7594 were carried out on six different oils with varying viscosities and formulations. All tests were performed using an oil bath at 50 °C and 80 °C. Each test was repeated once to evaluate repeatability.

Tested oils:

Nr.	Type	Base oil	Viscosity @ 40°C in cSt
Oil 1	Gear oil	Synthetic	68
Oil 2	Gear oil	Mineral	51
Oil 3	Base oil	Synthetic	47
Oil 4	Industry oil	Mineral	30
Oil 5	Industry oil	Mixed	24,5
Oil 6	Hydraulic oil	Mixed	46

Results and Observations

Coefficient of Friction (CoF)

Figure 1 shows the highly repeatable results obtained for Oil 1 at 50 °C, which demonstrate good fretting protection. Both measures achieved CoF values of approximately 0.155

Figure 2 illustrates Oil 5 at 50 °C with no fretting protection. Adhesive failure occurs from the beginning of the test due to high CoF values and fluctuation in stroke

Using the oil bath ensured repeatability of all test results at both temperatures.

Wear Scar Analysis

In addition to the friction curves, the wear scars on the ball and disk after testing provide further insight into the fretting protection performance of the tested fluids. This allows a clear differentiation between the oils.

Figure 3 shows exemplary the 3D-microscope analysis of the wear scars for Oil 6. This oil exhibited good fretting protection.

Wear Data Comparison

Figure 4 shows a bar chart comparing the measured and calculated wear volumes of the ball and disk, and the total wear volumes of all the oils tested at 50°C.

The results confirm:

Very good test repeatability.
Clear differences in fretting wear protection among the oils and enable a good ranking between the fluids.
The same results and ranking for tests were performed at 80 °C.

Summary

We hope these insights from our internal project are helpful for all SRV® users. The results demonstrate that using oil bath by testing under ASTM-based fretting conditions (ASTM D7594-24) provides reliable and reproducible data for evaluating fretting wear protection of fluids.

Comments and questions are most welcome.
Please feel free to contact me at:
ameneh.schneider@optimol-instruments.de

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