Testing of lubricants - Determination of flow pressure of lubricating greases according to Kesternich method - Part 2: Automatic method

Test Nozzle Filling

Apply the treated grease to the glass plate in a bubble-free manner within 10 minutes. Press the test nozzle several times to completely fill it and ensure that there are no bubbles.

Temperature Balance

The standard stipulates that temperature balance must be carried out for 2 hours ± 5 minutes before testing. The time requirements for reaching balance at different temperatures are shown in Table 1:

Pressure Increment Scheme

Use different pressure increment rates according to the expected result range:

Result Presentation and Accuracy Requirements

Test results are reported in hPa, without decimal places, and the test temperature is also indicated. Rounding is performed in accordance with DIN 1333.

Example: After 2 hours of temperature equilibration at -35°C, the measured flow pressure is 942hPa, which is reported as: Flow pressure -35°C according to DIN 51805-2: 942hPa

Method precision

Based on statistical studies in accordance with DIN EN ISO 4259, the repeatability (r) of the method is 10% and the reproducibility (R) is 30%.

Technical advantages and application value

The automated Kesternich method has significant advantages over manual methods: the test process is fully automated, eliminating human operating errors; the pressure increase and endpoint determination are automatically completed by the system, improving the repeatability and accuracy of the test results; and continuous testing at multiple temperature points can be achieved, greatly improving testing efficiency.

This method is particularly suitable for: evaluating the flow properties of greases in low-temperature environments, optimizing rheological properties in grease formulation development, and verifying consistency in quality control and incoming material inspection.

Implementation Recommendations and Precautions

Equipment Calibration

Pressure measuring devices should be calibrated regularly by comparing them to previously calibrated pressure gauges. For temperature measurement systems, it is recommended to use a DIN EN 60751 Class AA Pt100 resistance thermometer and perform regular comparison calibration.

Test Condition Control

Pay attention to temperature equilibration time; different equilibration times are required for different temperatures. Maintain a stable temperature during the test, within ±0.7K above 0°C and ±1K below 0°C.

Sample Processing Consistency

Ensure consistent sample pretreatment; different shear histories can significantly affect test results. It is recommended to strictly adhere to the standard's 60 double-stroke cycle for sample pretreatment.

Test Nozzle Maintenance

Clean the test nozzle regularly, using a suitable solvent to ensure that the nozzle material surface finish is not damaged. Check the elasticity of the O-ring, especially when using low-temperature elastic materials such as silicone for low-temperature testing.

Standard Development History and Outlook

The DIN 51805 series of standards has evolved from the initial manual Kesternich method to the current automated method, reflecting the trend of testing technology from manual operation to automation and intelligentization. The introduction of automated methods not only improves testing efficiency but, more importantly, enhances the comparability and repeatability of test results.

With the development of new materials and new lubrication technologies, more test methods for specialized greases (such as synthetic greases and bio-based greases) may be added in the future to supplement and improve the existing standard system.