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D5621-24 – Standard Test Method Technical Guide
🧪 Test Overview and Scope
This test method, designated D5621‑24, covers the evaluation of the shear stability of hydraulic fluids in terms of the final viscosity that results from irradiating a sample of the hydraulic fluid in a sonic oscillator. The method uses millimetres squared per second (mm²/s) as the unit of viscosity, with the equivalent unit (cSt) shown in parentheses. Precision has been determined for hydraulic fluids with irradiated kinematic viscosities between 10 mm²/s and 50 mm²/s or percent viscosity loss between 5 % and 45 %, the ranges covered by the round robin samples. The standard does not purport to address all safety concerns, and it is the responsibility of the user to establish appropriate safety, health, and environmental practices.
⚙️ Test Procedure and Equipment
The apparatus required includes a sonic shear unit, fixed frequency oscillator, and sonic horn. A convenient volume of hydraulic fluid is irradiated for a period of time, and the viscosities before and after irradiation are determined by Test Method D445 and D7042. The conditions to obtain the data for the precision statement were: 30 mL sample, 12.5 min calibration, and 40 min sample irradiation at 0 °C jacket temperature. A standard reference fluid containing a readily sheared polymer is run frequently to ensure the equipment imparts a controlled amount of sonic energy to the sample.
| ⚡ Parameter | 📏 Value |
|---|---|
| Sample Volume | 30 mL |
| Calibration Time | 12.5 min |
| Sample Irradiation Time | 40 min |
| Jacket Temperature | 0 °C |
📊 Key Measured Properties
Viscosities before and after irradiation are determined using Test Method D445 for kinematic viscosity and D7042 for dynamic viscosity and density. The shear stability is evaluated based on the final viscosity or percent viscosity loss. The method has been found applicable to fluids containing both readily sheared and shear-resistant polymers. Correlation with performance in hydraulic applications has been established, with evidence showing a good correlation between sonic oscillation shear degradation and vane pump test results.
| 🟦 Property | 🎯 Range |
|---|---|
| Irradiated Kinematic Viscosity | 10 mm²/s to 50 mm²/s |
| Percent Viscosity Loss | 5 % to 45 % |
💡 Note: This test method permits evaluation of shear stability with minimum interference from thermal and oxidative factors that may be present in some applications. It is suitable for fluids with both readily sheared and shear-resistant polymers.
⚠️ Warning: Precision of the method has only been determined for hydraulic fluids with irradiated kinematic viscosities between 10 mm²/s and 50 mm²/s or percent viscosity loss between 5 % and 45 %. Users should establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
❓ Frequently Asked Questions
🔍 What is the purpose of ASTM D5621‑24?
This test method evaluates the shear stability of hydraulic fluids by measuring the final viscosity after sonic irradiation, providing insight into the fluid’s resistance to shear degradation under controlled conditions.
💡 What are the standard test conditions?
The precision conditions include a 30 mL sample, 12.5 minutes of calibration, 40 minutes of sample irradiation, and a jacket temperature of 0 °C.
⚡ Which viscosity test methods are referenced?
Test Method D445 for kinematic viscosity of transparent and opaque liquids and Test Method D7042 for dynamic viscosity and density are used to determine viscosities before and after irradiation.
📌 How is shear stability correlated with performance?
Evidence has shown a good correlation between shear degradation resulting from sonic oscillation and that obtained in vane pump test procedures, as referenced in the standard.