Ultrasonicators for ASTM D5621 Sonic Shear Stability of Hydraulic Fluids
The ASTM D5621 standard test method describes the sonic shear stability testing of hydraulic fluids and their viscosities at 40°C and 100°C, respectively. In order to test and determine the viscosity stability of hydraulic fluids under shear, a reliable testing method is required. The ASTM D5621 is a standardized protocol for the evaluation of shear stability of hydraulic fluids using ultra-sonic shear forces.
Ultrasonic Shear Stability Testing of Hydraulic Fluids using ASTM D5621
ASTM D5621 is a standarized protocol to determine viscosity loss of hydraulic fluids under sonic shear. Therefore, ultra-sonic shear forces are applied to samples of hydraulic fluid in order to evaluate the shear stability. Ideal for polymer containing hydraulic oils and engine oils.
Purpose: Hydraulic fluids (specific lubricants), engine oils, transmission fluids for cars, tractor fluids and other power transmission fluids are exposed to shear forces of varying degrees during usual operation, which can lead to changes in viscosity and a subsequent decrease in efficiency. In order to improve the viscosity index of hydraulic fluids, polymers (e.g. comb polymers) are added to such hydraulic fluids. The ASTM D5621 test examines viscosity changes in polymer-containing fluids exposed to ultrasound-generated shear forces, so-called sonic shear vibrations.
Application: It is goal of the ASTM D5621 standard protocol to determine the viscosity of the sample under shear stress. This test is relevant to hydraulic fluids since hydraulic fluids as power transmission fluids are exposed to shear. Their behaviour under certain shear conditions must be determined order to choose the suitable hydraulic fluid quality for the usage in specific machines and engines.
Procedure: The initial viscosity of the hydraulic fluid is determined. The sample is then placed in the test beaker, tempered to the test temperature and treated with an ultra-sonic vibrator (i.e., sonic shear device) for the test time specified. Afterwards, the viscosity of the sonicated sample is measured. The report lists the initial viscosity, the final viscosity and the percentage of viscosity change in centistokes.
Equipment for ASTM D5621 Standard Test Method for Sonic Shear Stability of Hydraulic Fluids
In order to perform the procedure described and standardized in the ASTM D5621 protocol, specified equipment is required.
- Ultra-Sonicator: a probe-type ultra-sonic shear device with a fixed frequency and ultra-sonic horn (also known as probe or sonotrode). A typical ultrasonic device used for ASTM D2603 testing is the UP400ST (24kHz, 400W) with ultrasonic probe (horn / sonotrode) S24d22.
- Water / ice bath: Cooling water bath or ice bath capable to maintain a jacket temperature of 0°C.
- Temperature sensor such as PT100 (included with the ultrasonic devices UP400ST)
- Griffin 50mL beaker, made from borosilicate glass.
- Sound enclosure (optional): A sound protection box (e.g., sound protection box SPB-L for UP400St) to enclose the ultra-sonic horn to reduce the noise level produced by the sonic shear device.
- Viscometer: Any viscometer and bath that meet the requirements of Test Method D445 are sufficient.
In order to facilitate uniform performance and repeatable results, the following auxiliary equipment is recommended:
Sonic Shear Test in Accordance to ASTM D6080
“The viscosity classification system for hydraulic fluids is defined in ASTM D6080. The D6080 classification system uses the ASTM D5621 Standard Test Method for Sonic Shear Stability of Hydraulic Fluid, referred subsequently as the sonic shear test, as the basis for defining the viscosity grade of multigrade hydraulic fluids (ASTM D5621). In the D5621 procedure, the polymer-containing oil is irradiated with a sonic oscillator for 40 min. Degradation of the polymer by the sonic method is the result of energetic void formation and collapse within the liquid, such as may occur under conditions of fluid cavitation. This method for determining permanent viscosity loss has been found to produce viscosity changes similar to those observed in vane, gear, and piston pump applications. Correlations with pump volumetric efficiency have also been reported. High-VI fluids that exhibited less permanent viscosity loss in the sonic shear test provided enhanced pump volumetric efficiency.” (Michael et al., 2018).
Michael et al. (2018) also found that for this particular investigation, sonic shear testing via the ASTM D5621 method correlated best with end of test viscosity measurements.
Why Hielscher Ultra-Sonicators for Shear Stability Tests in accordance to ASTM D5621?
Hielscher Ultrasonics supplies high-performance ultrasonic shear devices for shear stability tests in accordance with ASTM D5621 and ASTM D2603. With a fixed frequency, reliable ultrasonic shear power, Hielscher ultra-sonic shear devices are ideal for shear stability evaluation of hydraulic fluids. Hielscher ultrasonicators are equipped with smart software and settings, which allow for sophisticated testings according to ASTM standards. The menu is easily accessible via digital touch display or browser remote control. While the frequency is fixed, which is important for reliable sonication results and ASTM standards, the amplitude can be precisely set to a desired stroke impact.
Calibration of Hielscher ultrasonicators is simple and and can be rapidly and easy done via the sophisticated menu. All digital ultrasonicators are equipped with pluggable temperature sensor, which continuously records the sample temperature and transmits it back to the ultrasonic generator, where all important sonication data such as amplitude, sonication time and duration, temperature, and pressure (when pressure sensor is mounted) are recorded automatically on a built-in SD-card. These smart features allow for reliable and reproducible ultra-sonic shear tests and make the operation user-friendly and safe.
Hielscher Ultrasonics devices for shear stability tests are conform with both, ASTM D-5621 and ASTM D-2603 standards.
- fixed amplitude
- smart software
- digital, coloured touch-screen
- smart settings
- intuitive menu
- automatic data recording on SD-card
- integrated temperature sensor
- precise control
- easy to calibrate
- reproducible results
The UP400St has a fixed frequency of 24kHz and is thereby conform to ASTM D5621. A typical setup for ASTM D5621 test is the ultra-sonic shear system UP400ST with probe (horn / sonotrode) S24d22.
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Literature / References
- ASTM D5621-20, Standard Test Method for Sonic Shear Stability of Hydraulic Fluids, ASTM International, West Conshohocken, PA, 2020.
- ASTM D2603-20, Standard Test Method for Sonic Shear Stability of Polymer-Containing Oils, ASTM International, West Conshohocken, PA, 2020.
- Michael, Paul; Cheekolu, Mercy; Panwar, Pawan; Devlin, Mark; Davidson, Rob; Johnson, Duval; Martini, Ashlie (2018): Temporary and Permanent Viscosity Loss Correlated to Hydraulic System Performance. Tribology Transactions 61, 2018.
Facts Worth Knowing
Viscosity Properties of Hydraulic Fluids and Lubricants
The material characteristics of liquid and consistent lubricants are described by data, which are mostly determined via standardized test protocols.
There are two major control parameters for lubricants:
- Control value: With the examination of fresh lubricants, production and delivery processes can be controlled. A continuous monitoring of oil filling volumes during operation (testing used oils) allows for prompt action (oil change) before the deterioration of oil damages the machine (condemning limits).
- Suitability value: Suitability values rate the lubricants for their usage and compatibility with particular machines.
Definition of Lubricants and Hydraulic Oils
Lubricants are fluids, which can be used – in dependence of its nature – to eliminate heat and wear debris, supply additives into the contact, transmit power, protect, and / or to seal.
Hydraulic oils or hydraulic fluids are a major type of oils or lubricants (lubes), which are used in the industry as so-called industrial oils.
Hydraulic oil is a specific type of lubricant. This means that a hydraulic oil is not only a lubricant, a hydraulic oil is also the medium by which power is transferred throughout the hydraulic system. This means, it’s a lubricant and at the same time a power transfer medium. In order be an effective and reliable lubricant, hydraulic oils must exhibit various properties, which are comparable or similar to other lubricants. These material properties include: foaming resistance and degassing (air release) properties, stability against thermal, oxidative and hydrolytic degradation, anti-wear performance, filterability, the ability of de-emulsification, rust and corrosion inhibition, and certain viscosity properties regarding its influence on film thickness.
Hydraulic oils or hydraulic fluids are distinguished into:
- Hydraulic fluids based on mineral oil
- Synthetic pressure fluids
- Fire-resistant hydraulic fluids
Definition of CGS Unit Centistokes
Kinematic viscosity is often measured in the CGS unit centistokes (cSt), which is equivalent to 0.01 stokes (St). Stokes (symbol: St) and centiStokes (symbol: cSt) are CGS units. One centistokes (cSt) is equivalent to 0.01 stokes (St). One centiStoke is equivalent to one square centimetres per second (cm2/s–1). One stokes is equal to the viscosity in poise divided by the density of the fluid in grams per cubic centimetre (g/cm–3).