|
IS0
INTERN AT1 ON AL ORGAN I Z AT 1 ON FOR STA N DARD I2 AT1 O N
IS0 RECOMMENDATION
R 48
DETERMINATION OF HARDNESS
OF VULCANIZED NATURAL AND SYNTHETIC RUBBERS
lSf EDITION
July 1957
COPYRIGHT RESERVED
The copyright of IS0 Recommendations and IS0 Standards
IS0 Member Bodies. Reproduction of these
belongs to
documents, in any country, may be authorized therefore only
by the national standards organization of that country, being
a member of ISO.
For each individual country the only valid standard is the national standard of that country.
Printed in Switzerland
Copies to be obtained through the national standards organizations.
Also issued in French and Russian.
.
---------------------- Page: 1 ----------------------
BRIEF HISTORY
The IS0 Recommendation R 48, Determination of Hardness of Vulcanized
Natural and Synthetic Rubbers, was drawn up by the Technical Committee
ISO/TC 45, Rubber, the Secretariat of which is held by the British Standards
Institution (B.S. I.).
The draft proposal put forward by the Secretariat was considered and
amended at the meetings held in London (1948), the Hague (1949), Akron (1950),
Oxford (1951) and Paris (1953).
On 28 August 1954, the Draft IS0 Recommendation proposed by the
Technical Committee IS0 /TC 45 was submitted to all IS0 - Member Bodies.
In consideration of comments presented by the U.S.A. Member Body a
slight amendment was made to the formula relating log,, M to the hardness
in International Rubber Hardness Degrees and the Draft was approved, subject
to some editorial modifications, by the following 26 (out of a total of 34) Member
Bodies:
Austria *Ireland Spain
Belgium Israel Sweden
"Canada Italy Switzerland
Denmark Japan Union of South Africa
Finland Mexico United Kingdom
France Netherlands U.S.A.
Germany *New Zealand U.S.S.R.
Hungary Pakistan Yugoslavia
India Portugal
No Member Body opposed the Draft.
The Draft IS0 Recommendation was then submitted to the IS0 Council
which decided, at its meeting in July 1957, to accept it as an IS0 RECOM-
MENDATION.
* These Member Bodies stated that they had no objection to the Draft being approved.
-2-
---------------------- Page: 2 ----------------------
SOIR 48 - 1957 (E)
IS0 Recommendation R 48 July 1957
DETERMINATION OF HARDNESS
OF VULCANIZED NATURAL AND SYNTHETIC RUBBERS
FOREWORD
The standard hardness test is based on a measurement c the penetrailan c
a rigid ball into the rubber test piece under specified conditions. The measured
penetration is converted into International Rubber Hardness Degrees (IRH),
the scale of degrees being so chosen that O represents a material having an
elasticity modulus of zero and 100 represents a material of infinite elasticity
modulus, and so that the following conditions are fulfilled over most of the
normal range of hardness:
(a) one International Rubber Hardness Degree always represents approxi-
mately the same proportionate difference in Young’s modulus;
(b) readings in International Rubber Hardness Degrees are approximately
the same as those of the Shore durometer type “A”.
For substantially elastic isotropic materials like well-vulcanized natural rubbers,
the hardness in International Rubber Hardness Degrees bears a known relation
to Young’s modulus, although for markedly plastic or anisotropic rubbers the
relationship will be less precisely known.
1. SU MM ARY
The hardness test consists in measuring the difference between the depths
of penetration of the ball into the rubber under a small initial load and a
large final load. From this difference the hardness in International Rubber
Hardness Degrees is derived by using either Table 2, page 6, or the graph
based on this table, or a scale, reading directly in International Rubber
Hardness Degrees and derived from the table, fitted to the penetration-
measuring instrument.
-3-
.
---------------------- Page: 3 ----------------------
I
lSO/R 48 - 1957 (E)
The relation between the difference of penetration and the hardness expressed
in International Rubber Hardness Degrees is based on:
(1) the known relation, for a perfectly elastic isotropic material,
P (in hundredths of a millimetre)
between penetration
and Young’s modulus M (in kilogrammes-force per square centimetre),
namely
* F /M = 0.000 17 R 0.65 P
where F = indenting force (kgf)
R = radius of ball (cm)
(2) the use of a probit (integrated normal error) curve to relate log,, M
and the hardness in International Rubber Hardness Degrees, as
shown in the diagram on page 7, this curve being defined thus:
(a) value of log,, M corresponding to midpoint of curve
= either 1.37 (M expressed in kgf/cm2) or 2.52 (M expressed
in lb/in2), i.e. M = 23.3 kgf/cm2 or 330 Ib/in2
(b) maximum slope
= 57 International Rubber Hardness Degrees per unit increase
in log,,M
2. TEST PIECE
The test piece has its upper and lower surfaces flat, smooth and parallel
to one another, two pieces of rubber (but not more than two) may be super-
posed to obtain the necessary thickness.
The standard test piece is between 8 mm and 10 mm thick, the lateral dimen-
sions being such that no test is made at a distance from the edge of the
test piece less than the appropriate distance shown in Table 1 hereunder.
Non-standard fesf pieces may be thicker or thinner than the standard, but
2 mm thick. The lateral dimensions are such that no
in no case less than
TABLE 1
Minimum distance
Total thickness of test piece from point of impact
to edge of test piece
Millimetres 1 Inches I Millimetres inches
2.5 0.1 6.5 0.25
5 0.2 7.6 0.3
8 0.3 9.0 0.35
10 0.4 10.0 0.4
15 0.6 11.5 0.45
25 1.0 12.7 0.5
I I
Tests intended to be comparable must be made on test pie
...