Overview
ISO 21250-2:2020 specifies the BQ+ test and evaluation method for measuring noise of rolling bearing greases. It defines signal processing, measurement procedure, data acquisition and assessment criteria to characterise grease-induced bearing noise and grease damping ability. The method is intended to be used together with ISO 21250-1 and other parts of the ISO 21250 series.
Key topics and requirements
- Scope & references: Builds on ISO 21250-1 (test assembly and machine) and normative terms from ISO 5593 and ISO 15242-1.
- Signal processing: Time-domain vibration signals are converted to the frequency domain via FFT and analysed in frequency bands (M-band: 300–1 800 Hz; H-band: 1 800–10 000 Hz). Note: the L-band (50–300 Hz) is defined in the series but is not considered for grease noise testing in this method.
- Sampling and measurement: A sampling rate of 25.6 kHz over a measurement period of 3.2 s is specified. Peak detection is used to capture the highest vibration velocity peaks (µm·s).
- Test cycle & procedure: Typical cycle steps include blow-out (cleaning), grease dosing, running-in (default 10 s), peak reset, recording the peak (default 3.2 s), and repeating measurements. Standard routines: ~10 measurements per bearing, ~10 doses and multiple bearings (example: five bearings).
- Damping calculation: Damping ability (GD) is calculated per band (M and H) by comparing grease-lubricated noise level (NL) with a reference ungreased NL (as defined in the standard).
- Evaluation & GN scale: Results are classified on a Grease Noise (GN) scale (GN1…GN4) based on peak vibration velocity statistics (µm·s) and percentage thresholds (e.g., >95 % of values). GN classes indicate levels from very dirty/noisy to quiet/silent greases.
- Test equipment & automation: Recommendations cover test machine components (high-quality spindle, pneumatic loading, grease dosing unit), sensors, data acquisition electronics and software for automated test control, storage and evaluation. Annexes provide examples and calibration hints.
Applications and users
This standard is practical for:
- Grease manufacturers developing low-noise lubricants and improving damping properties.
- Rolling bearing manufacturers assessing lubricant compatibility and product noise performance.
- Test laboratories and QA teams performing routine acceptance, R&D benchmarking and comparative testing.
- End-users specifying low-noise greases for noise-sensitive applications (e.g., electric motors, appliances, precision machinery).
Related standards
Keywords: ISO 21250-2:2020, rolling bearing grease noise, BQ+ test, grease damping, GN scale, FFT vibration analysis, sampling rate 25.6 kHz, peak detection, test machine.
Open preview (PDF)Rolling bearings — Noise testing of rolling bearing greases — Part 2: Test and evaluation method BQ+
