ISO 21250-3:2020

INTERNATIONAL ISO
STANDARD 21250-3
First edition
2020-07
Rolling bearings — Noise testing of
rolling bearing greases —
Part 3:
Test and evaluation method MQ
Roulements — Essais de bruit de graisse pour roulement —
Partie 3: Méthode d’essai et interpretation MQ
Reference number
©
ISO 2020
© ISO 2020
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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
6 Test method MQ . 2
6.1 General information . 2
6.2 Measuring principle . 3
6.3 Testing procedure . 3
6.3.1 Reference measurement of preserved, ungreased bearings . 3
6.3.2 Comparison measurement of greased bearings . 4
7 Evaluation of results . 4
7.1 General information . 4
7.2 Description of results . 4
7.2.1 Preserved bearings . 4
7.2.2 Greased bearings . 4
7.3 Grease noise classes — Rating scale . 5
7.4 Accuracy of results . 5
7.5 Permissible results in specifications . 6
7.6 Plausibility of results . 6
Annex A (informative) Test machine, test setup, electronic system and test reports: examples .7
Annex B (normative) Preparation of test bearings and greasing .13
Annex C (normative) Plausibility of the results .15
Annex D (informative) Example of grease noise classes rating .18
Bibliography .19
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
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ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
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described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
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Attention is drawn to the possibility that some of the elements of this document may be the subject of
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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.
[11]
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 after this document allows the grease manufacturers to develop low-
noise lubricants with highest 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 MQ to
determine and assess the noise characteristics of rolling bearing grease jointly with ISO 21250-1,
ISO 21250-2 and ISO 21250-4.
INTERNATIONAL STANDARD ISO 21250-3:2020(E)
Rolling bearings — Noise testing of rolling bearing
greases —
Part 3:
Test and evaluation method MQ
1 Scope
This document specifies the testing and evaluation method of rolling bearing grease noise in accordance
with the method MQ.
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)].
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, the symbols and abbreviated terms contained in Table 1 and
subscripts contained in Table 2 apply.
Table 1 — Symbols and abbreviated terms
Symbol Unit Description
GD — Grease damping
a
H — High band, H-band (1 800 Hz to 10 000 Hz)
i — Consecutive number
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
−1
µm∙s Vibration velocity, twice smoothed to the counting point i
v
i
a
Can be used as subscript, too, where necessary.
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-symbol Description
MP Measuring point
MQ Method MQ according to ISO 21250-3
a
NL Noise level, average value (of vibration velocity)
a
NP Noise peak
pk Peak value
ref Reference, ungreased bearing
rms Root mean square
0-32 Starting interval 0 s to 32 s
0-64 Interval 0 s to 64 s
32-64 Operating interval 32 s to 64 s
a
SUN Start-up noise of the greased bearing
a −1 −1
Noise values with this subscript can be expressed in µm∙s or in % based on the reference value of 16,9 µm∙s .
5 Calculation method
The formulae for calculation of grease damping and peak values are shown in ISO 21250-1:2020, Table 4
and Table 5, respectively.
A sampling rate of 8 readings per second shall be used, i.e. within 32 s, 256 points are required.
6 Test method MQ
6.1 General information
The procedure of MQ requires test bearings to be greased manually. The dosed/balanced quantities
of grease shall be introduced in to the bearings by means of a manual grease dosing unit (feeder) or a
spatula. There are five pre-greased bearings to be measured for a period of 64 s (each one with a run-in
time), as shown in Figure 1.
2 © ISO 2020 – All rights reserved

NOTE Five doses of grease × 64 s = 320 s (including run-in-time) measurement: 4 096 measuring points
(MP) at 32,768 kHz ≙ 0,125 s, thus 512 MP/grease dose and in total 2 560 MP.
Figure 1 — Duration of measurement— Process MQ
The process for the manual pre-greasing is represented in B.2.
6.2 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 21250-1:2020,
Clause 7, applies. The peak detection algorithm for processing of the input signal is shown in
ISO 21250-1:2020, Table 5).
An example of a test machine, the test set-up, electronic system and test reports is given in Annex A.
6.3 Testing procedure
6.3.1 Reference measurement of preserved, ungreased bearings
The testing procedure shall include the following steps:
1) The noise tester shall be turned on and warmed up until a spindle temperature of 30 °C is reached
on the housing.
2) The MQ-test programme shall be started.
3) For five prepared (cleaned and newly preserved) test bea
...