ISO 21256-2:2020

INTERNATIONAL ISO
STANDARD 21256-2
First edition
2020-01
Fine bubble technology — Cleaning
applications —
Part 2:
Test method for cleaning machine-oil
stained surfaces of machined metal
parts
Reference number
ISO 21256-2:2020(E)
©
ISO 2020

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ISO 21256-2:2020(E)

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© ISO 2020
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ISO 21256-2:2020(E)

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 1
5 Reagents and materials . 2
6 Apparatus . 2
6.1 Test equipment . 2
6.2 Oil content meter . 3
7 Preparation of test pieces . 4
7.1 Test pieces . 4
7.2 Method for depositing oil stain on the test pieces . 4
8 Procedure. 4
8.1 Test procedure . 4
8.2 Conditions of cleaning test . 4
8.3 Measurement of test oil on the test piece . 5
9 Calculation of oil cleaning index of oil stain . 5
10 Test report . 6
Annex A (informative) Example of a method for depositing oil stain on the test pieces .7
Annex B (informative) Example of infrared spectrum of the test oil applied for oil content
meter .13
Bibliography .15
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ISO 21256-2:2020(E)

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
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organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
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
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/ patents).
Any trade name used in this document is information given for the convenience of users and does not
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expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www .iso .org/
iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 281, Fine bubble technology.
A list of all parts in the ISO 21256 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.
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ISO 21256-2:2020(E)

Introduction
Mineral oil is used in manufacturing processes of industrial products, for applications such as cutting,
lubrication and cooling. Oil remaining on the surface of products has to be cleaned during operation
and at the end of the process. The main cleaning solvent fluids used in these industries are solvent
based (e.g. hydrocarbon detergent liquids, bromine-containing detergents, and alkali detergents),
despite it being well known that such detergents can cause environmental pollution such as ozone layer
depletion, water pollution, etc.
As an ecological alternative, fine bubble technology, which does not use detergents, is becoming popular.
Use of fine bubble technology improves resource sustainability, energy saving and safety, as it uses less
water and no chemical substances.
This document is intended to provide a procedure that can help demonstrating the cleaning performance
of such technology, so that different methodologies can be compared.
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INTERNATIONAL STANDARD ISO 21256-2:2020(E)
Fine bubble technology — Cleaning applications —
Part 2:
Test method for cleaning machine-oil stained surfaces of
machined metal parts
1 Scope
This document specifies a test method for removal of machine oil stain from a noncorrosive metal
surface using fine bubble water. A test is provided to show the comparative cleaning advantage of
adding fine bubbles to the water.
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 3696, Water for analytical laboratory use — Specification and test methods
ISO 20480-1, Fine bubble technology — General principles for usage and measurement of fine bubbles —
Part 1: Terminology
ISO 20480-2, Fine bubble technology — General principles for usage and measurement of fine bubbles —
Part 2: Categorization of the attributes of fine bubbles
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 20480-1 and ISO 20480-2 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
oil cleaning index
number representing the residual oil removed from the test surface after cleaning
4 Principle
Evaluate the performance of test oil removal by fine bubble water by measuring the amount of residual
oil with fine bubble water applied and not applied. Evaluation of the performance is made by comparing
the oil cleaning index of test oil on the surface of the test piece with fine bubble water applied to a
control sample using ordinary water.
The residual oil is measured using an oil content meter based on infrared spectroscopy.
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ISO 21256-2:2020(E)

5 Reagents and materials
5.1 Water, which usually has been treated and conforms to grades of water given in ISO 3696.
5.2 Test oil. The test oil used to coat the test surface shall be triolein or an oil agreed between the
parties concerned. An example of infrared spectrum of the test oil applied for oil content meter is given
in Annex B.
5.3 Extraction solvent, containing 65 % to 75 % (mass fraction) of extracted chloro-tri-fluoro-ethylene
dimer (Cl(CF2CDCl)2Cl) and 25 % to 35 % (mass fraction) of extracted chloro-trifluoro-ethylene trimer
chloro-tri-fluoro-ethylene tetramer [Cl(CF CFCl) Cl]. See Reference [1].
2 3
6 Apparatus
6.1 Test equipment
Figure 1 shows a typical example of equipment, where the difference in result between the operation
with fine bubble generating system on and off can be compared. The dimensions of the cleaning tank
shall be as given in Figure 1.
a) The inside dimension of the cleaning tank shall be (280 ± 10) mm × (230 ± 10) mm × (340 ± 10) mm.
b) The inside diameter of the cleaning stream outlet shall (13 ± 0,1) mm.
c) The centre of the test piece shall be placed at (100 ± 10) mm distance from the cleaning stream
outlet, and (115 ± 10) mm distance from the side wall of the tank.
d) The centre of the test piece shall be placed on the axis of the outlet.
e) The position of the test piece shall be such that the cleaning stream hits normal to its surface.
f) The streamline at the outlet shall be parallel to the axis of the outlet.
g) The material of the tank shall be a transparent heat-resistance resin.
h) Test equipment and accessories shall be cleaned off residual oil after test for each test piece. Fresh
water shall be used for testing the subsequent test piece.
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ISO 21256-2:2020(E)

Dimension in millimetres
Key
1 fine bubble supply system
2 pump
3 filter
4 fine bubble generating system ON/OFF
5 flow rate of suction air
6 cleaning tank
7 cleaning stream outlet
8 test piece
9 cleaning water
10 flow rate of water
a
The fine bubble generator shall be able to turn ON/OFF.
b
The position of the test piece shall be such that the cleaning stream hits normal to its surface.
c
Quantity of water shall be 15 l.
Figure 1 — Test equipment
6.2 Oil content meter
Measuring instrument based on infrared spec
...