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D4170-24 – Standard Test Method Technical Guide
📐 Test Equipment and Configuration
This test method evaluates the fretting wear protection provided by lubricating greases using a specialized tester equipped with two ball thrust bearings. The test grease is applied to lubricate the bearings, which are then subjected to controlled oscillatory motion to simulate fretting wear conditions. Fretting wear, as defined in Terminology D4175, is a form of attritive wear caused by vibratory or oscillatory motion of limited amplitude, characterized by the removal of finely-divided particles from rubbing surfaces. The discussion in the standard highlights that air can cause immediate local oxidation of the wear particles, and in ferrous metals, the oxidized debris is abrasive iron oxide (Fe₂O₃), leading to terms like fretting corrosion. This configuration is designed to measure the wear protection under small-amplitude vibrations, which is critical for bearing applications.
⚙️ Test Procedure and Conditions
The test procedure involves oscillating the bearings through an arc of 0.21 rad (12°) at a frequency of 30.0 Hz (1800 cpm). A consistent load of 2450 N (550 lbf) is applied for a duration of 22 hours at room temperature (Note 1). These parameters are factory-set to ensure reproducibility and should not be altered. The load spring constant may change over time, so periodic calibration is recommended. If necessary, a suitable shim should be fabricated to maintain correct load application. The tester operates with two ball thrust bearings lubricated with the test grease.
| 🟦 Parameter | 📏 Specified Value |
|---|---|
| Oscillation Arc | 0.21 rad (12°) |
| Frequency | 30.0 Hz (1800 cpm) |
| Applied Load | 2450 N (550 lbf) |
| Test Duration | 22 h |
| Temperature | Room temperature |
Note that the test is conducted at room temperature, and these conditions are critical for consistent results. The arc, frequency, and load are factory-set and should not be altered.
📊 Key Measured Properties
The primary measured property is the mass loss of the bearing races, which directly indicates the extent of fretting wear. This measurement provides a quantitative assessment of the grease’s protective capability. The wear debris produced is often oxidized, and in ferrous metals, it appears as abrasive iron oxide (Fe₂O₃), which can accelerate wear if not mitigated. A related phenomenon, false brinelling, is localized fretting wear that occurs when rolling elements of a bearing vibrate with small amplitude while pressed against the race. The mechanism proceeds in stages: asperities weld and tear, forming oxidized wear debris that accelerates wear due to limited escape. This test includes false brinelling in the determination of fretting wear.
⚠️ Safety Precautions: For specific warning statements, refer to sections 7.2 and 9.2 of the standard. Users must establish appropriate safety, health, and environmental practices.
💡 Technical Note: The spring