ISO 21250-2:2020

Rolling bearings - Noise testing of rolling bearing greases - Part 2: Test and evaluation method BQ+

This document specifies the testing and evaluation method of rolling bearing grease noise in accordance with the method BQ+.

Roulements — Essais de bruit de graisse pour roulement — Partie 2: Méthode d’essai et interprétation BQ+

General Information

• Status: Published
• Publication Date: 02-Jul-2020
• ICS: 21.100.20 - Rolling bearings
• Technical Committee: ISO/TC 4 - Rolling bearings
• Drafting Committee: ISO/TC 4 - Rolling bearings
• Current Stage: 9060 - Close of review
• Completion Date: 04-Mar-2031

Relations

• Consolidated By: ISO 12623:2022 - Thermal insulating products for building equipment and industrial installations - Determination of short-term water absorption by partial immersion of preformed pipe insulation
• Effective Date: 06-Jun-2022

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

• ISO 21250-1:2020 - Basic principles, testing assembly and test machine
• ISO 21250-3, ISO 21250-4 - Other parts of the grease noise testing series
• ISO 15242-1 - Vibration measurement fundamentals
• ISO 5593 - Rolling bearings vocabulary

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.

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 21250-2
First edition
2020-07
Rolling bearings — Noise testing of
rolling bearing greases —
Part 2:
Test and evaluation method BQ+
Roulements — Essais de bruit de graisse pour roulement —
Partie 2: Méthode d’essai et interprétation BQ+
Reference number
©
ISO 2020
© ISO 2020
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
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CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii © ISO 2020 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols, abbreviated terms and subscripts . 1
5 Calculation method . 2
5.1 Signal processing. 2
5.2 Calculation of damping . 3
5.3 Calculation of peak values . 3
6 Test method BQ+ . 4
6.1 Measuring principle . 4
6.2 Testing procedure . 4
7 E valuation of results . 5
7.1 Rating scale . 5
7.2 Damping ability . 6
Annex A (informative) Test machine, test setup, electronic system and test reports: examples .7
Annex B (informative) Recommendation for inserting the amount of grease .12
Annex C (informative) Practical hints for calibration .15
Bibliography .17
Foreword
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electrotechnical standardization.
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iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 4, Rolling bearings.
This document is intended to be used in conjunction with ISO 21250-1.
A list of all parts in the ISO 21250 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
iv © ISO 2020 – All rights reserved

Introduction
The rolling bearing life theory emphasizes the use of pure and homogeneous lubricants as essential for
a long bearing service life. The lubrication of rolling bearings is described in several national standards.
[12]
The GfT worksheet 3 contains theoretical and practical knowledge of rolling bearing lubrication.
Grease lubrication is the most common type of rolling bearing lubrication. The purity grade of rolling
bearing grease is influenced by thickeners, base oils, additives and solid lubricant additives as well
as the manufacturing process and is reflected in the running noise. Therefore, noise testing of rolling
bearing greases is recommended.
In addition, grease noise testing in accordance with this document allows the grease manufacturers
to develop low-noise lubricants with better damping properties. This document can also support the
rolling bearing manufacturers and end-users in the selection of low noise grease with better damping
properties.
This document covers requirements for the testing assembly and the test machine of method BQ+
to determine and assess the noise characteristics of rolling bearing grease jointly with ISO 21250-1,
ISO 21250-3 and ISO 21250-4.
INTERNATIONAL STANDARD ISO 21250-2:2020(E)
Rolling bearings — Noise testing of rolling bearing
greases —
Part 2:
Test and evaluation method BQ+
1 Scope
This document specifies the testing and evaluation method of rolling bearing grease noise in accordance
with the method BQ+.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 5593, Rolling bearings — Vocabulary
ISO 15242-1, Rolling bearings — Measuring methods for vibration — Part 1: Fundamentals
ISO 21250-1:2020, Rolling bearings — Noise testing of rolling bearing greases — Part 1: Basic principles,
testing assembly and test machine
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 5593, ISO 15242-1, ISO 21250-1
and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
sampling rate
sample rate
frequency with which a continuous signal is sampled and converted into a time-
discrete signal
Note 1 to entry: The unit is hertz (Hz) or samples (readings) per second [samples per second (samples/s)].
3.2
peak reset
manual or automatic zeroizing of the peak detector
4 Symbols, abbreviated terms and subscripts
For the application of this document, the symbols, abbreviated terms and subscripts according to
ISO 21250-1:2020, Table 1 and Table 2, in addition to the symbols and abbreviated terms contained in
Table 1 and the subscripts contained in Table 2, apply.
Table 1 — Symbols and abbreviated terms
Symbol/abbreviated term Unit Description
f Hz Frequency
FFT — Fast Fourier transform
GD — Grease damping
a
H — High-band, H-band (1 800 Hz to 10 000 Hz)
b
L — Low-band, L-band (50 Hz to 300 Hz)
a
M — Medium-band, M-band (300 Hz to 1 800 Hz)
−1
v µm∙s Vibration velocity
a
Can be also used as subscript to indicate the related band.
b
The L-band is used in noise and vibration analysis in the ISO 15242 series. However, this document does not consider
this frequency range for grease noise testing and its analysis.
Table 2 — Subscripts
Subscript Description
BQ+ Method BQ+ according to this document
NL Noise level, average value (of vibration velocity)
ref Reference, ungreased bearing
rms Root mean square
5 Calculation method
5.1 Signal processing
The recorded time signal is transformed into a frequency signal via fast Fourier transform (FFT) and
is subjected to an analysis of the bands (L-, M- and H-band; effective value/rms-value), as shown in
Figure 1.
2 © ISO 2020 – All rights reserved

Key
a amplitude
f frequency
t time
FFT fast Fourier transform
H H-band
L L-band
M M-band
Figure 1 — Signal transformation
5.2 Calculation of damping
The damping ability is to be calculated according to Formulae (1) and (2).
M-band:
νν−
NL, M refNL, M
GD = (1)
MBQ+
ν
NL, M ref
H-band:
νν−
NL, H refNL, H
GD = (2)
HBQ+
ν
NL, H ref
5.3 Calculation of peak values
The peak detection algorithm for processing of the input signal is shown in ISO 21250-1:2020,
Figure 1 a).
The flow chart for determining the peak values is shown in Figure 2.
Figure 2 — Flow chart of grease noise assessing BQ+
The sampling rate of 25,6 kHz over a measurement period of 3,2 s shall be applied.
6 Test method BQ+
6.1 Measuring principle
For the application of this document, the measuring principle, test bearings and amount of grease, test
load, spindle speed, signal recording and display of measuring results according to ISO 2
...