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D5620-94 – Standard Test Method Technical Guide
📐 Scope and Application
This test method, ASTM D5620 – 94, covers the determination of the endurance (wear) life and load carrying capacity of thin film fluid lubricants. These lubricants are intended to operate after a single application, with excess material drained from the contact area of sliding metal surfaces, functioning in a drain and dry mode.
A thin film fluid lubricant is defined as a primary liquid with or without lubricating powder additives, but without binders or adhesives. It forms a film on the lubricated surfaces and performs its function after excess material has drained, without additional material being supplied. Values in SI units are regarded as the standard.
⚙️ Test Procedure and Load Mechanics
Using a Pin and Vee Block test machine (based on ASTM D 2625), the direct load is applied linearly, bisecting the angle of the vee block. The gage reading must be corrected to a standard curve referencing specific load ranges.
💡 Key Load Calculation: The direct load applied to the specimen is equivalent to the true load multiplied by the cosine of 42°. Calibration must be performed against the standard curve for either the 800 lbf (3550 N) or 3000 lbf (13300 N) gage reference.
| 🟦 Reference Parameter | 📏 SI Standard Values | 📐 Inch-Pound Values |
|---|---|---|
| 🎯 Low Range Gage Load Reference | 3550 N | 800 lbf |
| 🎯 High Range Gage Load Reference | 13300 N | 3000 lbf |
| ⚡ Load Correction Factor | True Load × cos 42° | |
📊 Measured Properties and Material Standards
The test method differentiates between Newtonian and non-Newtonian flow characteristics, which is critical for interpreting how a thin film lubricant behaves under shear stress. The primary output is the endurance (wear) life, measured in minutes until failure under a constant load. The standard specifies strict material and preparation requirements for the test specimens to ensure repeatability.
| 📄 Referenced Standard | ⚡ Specific Requirement for the Test |
|---|---|
| ASTM B 16 | Specification for Free-Cutting Brass Rod, Bar, and Shapes (specimen material) |
| ASTM D 2625 | Endurance (Wear) Life and Load-Carrying Capacity (Falex Method) (base procedure) |
| ASTM F 22 | Hydrophobic Surface Films by the Water Break Test (cleanliness verification) |
| Mil-P-16232 | Phosphate Coatings, Heavy, Manganese or Zinc Base (surface treatment) |
| TT-C-490 | Cleaning Methods for Ferrous Surfaces (specimen preparation) |
⚠️ Surface Preparation Compliance: The test results are heavily dependent on the surface condition of the test specimens. Strict adherence to the specimen material (B 16), phosphate coating (Mil-P-16232), and cleaning (TT-C-490) specifications is mandatory for a valid test of thin film fluid lubricants.
❓ Frequently Asked Questions
🔍 What is a “thin film fluid lubricant” as defined by D5620?
It is a fluid lubricant consisting of a primary liquid with or without lubricating powder additives, and without binders or adhesives. It forms a film on surfaces and performs its function after excess material has drained from the application area, operating without a continuous or intermittent supply.
💡 How is the “direct load” defined and calculated?
The direct load is the load applied linearly bisecting the angle of the vee block. It is corrected to either the 800-lbf (3550-N) or the 3000-lbf (13300-N) gage reference and is equivalent to the true load multiplied by the cos 42°.
⚡ How does the standard distinguish between Newtonian and non-Newtonian liquids?
A Newtonian liquid flows immediately on application of any force, with a flow rate directly proportional to the force. A non-Newtonian liquid has a viscosity dependent on the rate of shear and may require the force to exceed a yield point before it begins to flow.
📌 What is Endurance (Wear) Life and how is it measured?
Endurance (wear) life is the length of the test time before failure under a constant loaded condition. It is measured in minutes and represents the duration the applied thin film fluid lubricant performs its intended function.