ISO 27588:2012
(Main)Rubber, vulcanized or thermoplastic — Determination of dead-load hardness using the very low rubber hardness (VLRH) scale
Rubber, vulcanized or thermoplastic — Determination of dead-load hardness using the very low rubber hardness (VLRH) scale
Caoutchouc vulcanisé ou thermoplastique — Détermination de la dureté sous charge constante au moyen de l'échelle de très faible dureté (VLRH)
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Standards Content (Sample)
INTERNATIONAL ISO
STANDARD 27588
Second edition
2012-06-15
Rubber, vulcanized or thermoplastic —
Determination of dead-load hardness using
the very low rubber hardness (VLRH) scale
Caoutchouc vulcanisé ou thermoplastique — Détermination de la dureté
sous charge constante au moyen de l’échelle de très faible dureté (VLRH)
Reference number
©
ISO 2012
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ii © ISO 2012 – All rights reserved
Contents Page
Foreword .iv
Introduction . v
1 Scope . 1
2 Normative references . 1
3 Principle . 1
4 Apparatus . 1
5 Calibration . 2
6 Test pieces . 2
7 Time interval between forming the test pieces and testing . 2
8 Conditioning . 2
9 Temperature of test . 2
10 Procedure . 3
11 Test report . 3
Annex A (normative) Relationship between indentation depth and hardness, and derivation of the
VLRH scale . 4
Annex B (normative) Calibration schedule. 7
Bibliography . 9
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 committee has been
established has the right to be represented on that committee. International 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.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
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.
ISO 27588 was prepared by Technical Committee ISO/TC 45, Rubber and rubber products, Subcommittee
SC 2, Testing and analysis.
This second edition cancels and replaces the first edition (ISO 27588:2008), which has been revised to include
a calibration schedule for the apparatus used (see Annex B).
iv © ISO 2012 – All rights reserved
Introduction
The hardness test specified in this International Standard is intended as a more discriminating alternative to
the international rubber hardness degrees scale (ISO 48) for rubbers below 35 IRHD. A durometer method for
soft rubbers is described in ISO 7619-1 as the AO scale. Examples of applications are low-modulus bearings,
soft roller coverings and printing rubbers.
Figure 1 shows a comparison of the ranges of the IRHD N and IRHD L methods in ISO 48 with the VLRH scale
of this International Standard.
The methods differ primarily in the diameter of the indenting ball and the magnitude of the indenting force,
these being chosen to suit the particular application.
Figure 1 — Comparison of the ranges of hardness measurement methods for rubber
INTERNATIONAL STANDARD ISO 27588:2012(E)
Rubber, vulcanized or thermoplastic — Determination of dead-
load hardness using the very low rubber hardness (VLRH) scale
WARNING — Persons using this International Standard should be familiar with normal laboratory
practice. This standard does not purport to address all of the safety problems, if any, associated with
its use. It is the responsibility of the user to establish appropriate safety and health practices and to
ensure compliance with any national regulatory conditions.
1 Scope
This International Standard specifies a dead-load method for the determination of the hardness of very soft
vulcanized or thermoplastic rubbers using the very low rubber hardness (VLRH) scale.
The relation between the depth of penetration and the VLRH scale is linear.
2 Normative references
The following referenced documents are indispensable for the application 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 18898:2012, Rubber — Calibration and verification of hardness testers
ISO 18899, Rubber — Guide to the calibration of test equipment
ISO 23529, Rubber — General procedures for preparing and conditioning test pieces for physical test methods
3 Principle
The hardness test consists of measuring the difference between the depths of indentation of a ball into the
rubber under a small contact force and a large total force. From this difference, the hardness in “very low
rubber hardness degrees” (VLRH) is obtained using Table A.1 (see Annex A) or graphs based on this table
or a scale, reading directly in very low rubber hardness degrees, calculated from the tables and fitted to the
indentation-measuring instrument.
4 Apparatus
The essential parts of the apparatus are as follows, the appropriate dimensions and forces being shown in
Table 1. Detailed information can be found in References [1] and [2].
4.1 Vertically guided plunger, having a ball or spherical surface on the lower end, and means for supporting
the plunger so that the spherical tip is kept slightly above the surface of the annular foot prior to applying the
contact force.
4.2 Means for applying a contact force and an additional indenting force to the plunger, making
allowance for the mass of the plunger, including any fittings attached to it, and for the force of any spring acting
on it, so that the forces actually transmitted through the spherical end of the plunger are as specified.
4.3 Means for measuring the increase in depth of indentation of the plunger caused by the indenting
force, either in millimetres with a maximum uncertainty of 0,001 mm, or reading directly in VLRH with a resolution
such that a reading to at least 0,5 VLRH is possible.
4.4 Flat annular foot, normal to the axis of the plunger and having a central hole for the passage of the
plunger. The foot rests on the test piece and shall be rigidly connected to the indentation measurement device
so that a measurement is made of the movement of the plunger relative to the foot (i.e. the top surface of the
test piece), not relative to the surface supporting the test piece.
If it is required that measurements be made on test pieces with a curved surface, a calibration has to be carried
out. Tests need to be made on test pieces of the material with both flat and curved
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