Rubber -- Dimensional tolerances for use with products

Caoutchouc -- Tolérances dimensionnelles à utiliser pour les produits

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ISO 3302:1990 - Rubber -- Dimensional tolerances for use with products
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Second edition
1990-04-0 1
Rubber - Dimensional tolerances for use with
Caoutchouc - Tolérances dimensionnelles a utiliser pour les produits
Reference number
IS0 3302: 1990( E)
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IS0 (the International Organization for Standardization) is a worldwide
federation of national standards bodies (IS0 member bodies). The work
of preparing International Standards is normally carried out through IS0
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, govern-
mental and non-governmental, in liaison with ISO, also take pari in the
work. IS0 collaborates closely with the International Electrotechnical
Commission (IEC) on all matters of electrotechnical standardization.
Drafl International Standards adopted by the technical committees are
circulated to the member bodies for voting. Publication as an Interna-
tional Standard requires approval by at least 75 % of the member bodies
casting a vote.
International Standard IS0 3302 was prepared by Technical Committee
ISO/TC 45, Rubber and rubber products.
This second edition cancels and replaces the first edition (IS0
3302:1976), of which it constitutes a technical revision including, in par-
ticular, the addition of a new clause (clause 7) dealing with calendered
O is0 1990

All rights reserved. No part of thls publication may be reproduced or utilized In any form

or by any means, electronic or mechanical, including photocopylng and mlcrofilm, without

permission In writing from the publisher.
International Organlzatlon for Standardization
Case Postale 56 CH-1211 Genève 20 Switzerland
Printed In Switzerland
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IS0 33021990(E)
Rubber products are subject to changes in their dimensions after proc-
essing and vulcanization. This may be due to a variety of factors, such
as mould shrinkage or relaxation of die swell.
These changes should be determined and allowed for when designing
such items as moulds and dies used in the manufacture of a given
The closer tolerance classes outlined in this specification should not be
demanded unless required by the final application and should be re-
stricted to those dimensions deemed to be critical. The greater the de-
gree of accuracy demanded, the closer the control which must be
exercised during manufacture, and hence the higher the costs.
When particular physical properties are required in the product, it may
not always be possible to provide them in a mix which is capable of
fabrication to close tolerances. It is advisable, in these circumstances,
that consultation should take place between the interested parties. In
general, softer vulcanizates (i.e. those of hardness below 50 IRHD -
see IS0 48) need greater tolerances than harder ones.
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Rubber - Dimensional tolerances for use with products
1 Scope 3 Measurement of dimensions
This International Standard specifies classes of di-
3.1 General
mensional tolerances, and their values, for moulded,
0 extruded and calendered solid rubber products. The
For solid products, measurements of dimensions
relevant test methods necessary for the establish-
shall not be made until 16 h have elapsed after
ment of compliance with this International Standard
vulcanization, this minimum time being extended to
are also specified.
72 h in cases of dispute. Measurements shall be
completed within 3 months after the date of des-
The tolerances are primarily intended for use with
patch to the purchaser or before the product is put
vulcanized rubber but may also be suitable for pro-
into use, whichever is the shorter time. Measure-
ducts made of thermoplastic rubbers.
ments shall be made at standard temperature, after
conditioning (see IS0 471). Care shall be taken to
This standard does not apply to precision toroidal
ensure that the products are not subjected to ad-
sealing rings or to calendered composite products
verse storage conditions (see IS0 2230) and that
such as rubber-coated fabrics or products where a
they are not distorted during measurement.
rubber coating is applied by the process of topping
or skim coating.
3.2 Test instruments
3.2.1 Depending on the circumstances, measure-
2 Normative references
ments shall be made using one or more of the fol-
lowing types of instrument:
The following standards contain provisions which,
through reference in this text, constitute provisions For solid products, a micrometer dial
of this International Standard. At the time of publi-
gauge, the foot of which shall exert a pressure of
cation, the editions indicated were valid. All stand-
22 kPa f 5 kPa for rubber of hardness equal to or
ards are subject to revision, and parties to
greater than 35 IRHD or of 10 kPa f 2kPa for rub-
agreements based on this International Standard
ber of hardness less than 35 IRHD (see IS0 4648 and
are encouraged to investigate the possibility of ap-
IS0 48).
plying the most recent editions of the standards in-
dicated below. Members of IEC and IS0 maintain A suitable optical measuring instrument.
registers of currently valid International Standards. Fixed gauges, for upper and lower limits
IS0 48:1979, Vulcanized rubbers - Determination of
appropriate to the dimensions being measured.
hardness (Hardness between 30 and 85 IRHD). Other devices, including tape measures
IS0 471:1983, Rubber - Standard temperatures, hu-
(with or without vernier), sliding calipers and micro-
midities and fimes for the conditioning and testing
meter calipers.
of test pieces.
3.2.2 All instruments shall be capable of measuring
IS0 2230:1973, Vulcanized rubber - Guide to
the dimension with an error within the tolerances
st orage.
IS0 4648:1978, Rubber, vulcanized - Determination
3.2.3 In all measurements intended to be compar-
of dimensions of fest pieces and products for test
ative, the same measuring device shall be used.
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IS0 3302:1990(E)
d) Care shall be taken in applying the standard tol-
4 Tolerances
erances to products having wide sectional vari-
For the purposes of this International Standard,
nominal dimensions and tolerances are based on
e) In cases where the rubber product is unavoidably
the R 5 and R 10 series of preferred numbers re-
distorted during removal from the mould, the di-
mensions of the products may be affected, and
special allowance may be needed.
The dimensions of certain parameters of a particular
product may not all require the application of the
same class of tolerance. Dimensions of different
parameters of the product on the same drawing may
5.2 Classification
have different class tolerances applied to them.
When drawings do not indicate a required class tol-
This clause establishes four classes of tolerance for
erance, the largest tolerance given in the related
fixed and closure dimensions (see 5.3) for products
table shall be applied.
moulded in solid rubber, namely:
a) Class M1 for precision mouldings. Such

1 Tolerances that are specified in this International mouldings require precision moulds, fewer cavi-

Standard in terms of a positive value and an equal nega-
ties per mould, close mix controls, etc., which
tive value (e.g. & 0,35) may also be expressed in terms
results in high cost. Optical comparators or
of unequal positive and negative values, providing the
other, similar, measuring devices may be re-
difference between the two values remains the same. For
quired to minimize distortion of the rubber by the
exaryle, I0,35 may also be expressed as ?:;: or To.’
measuring instrument. This type of part requires
Or -0,7! etc.
expensive control and inspection procedures.
2 Special consideration of tolerances will be necessary
for a vulcanizate with a low hardness and a high tensile
b) Class M2 for high-quality mouldings involving
strength (e.g. natural rubber gum vulcanizate).
much of the close control required for class M1.
c) Class M3 for good-quality mouldings.
5 Mouldings
d) Class M4 for mouldings where dimensional con-
trol is non-critical.
5.1 General
5.3 Fixed dimensions and closure dimensions
The dimensional tolerances stated in this Interna-
tional Standard may be wider than those used in
In moulding a rubber product, more rubber is used
some other engineering practice. The following
than is required to fill the cavity, and the excess is
considerat ions apply:
flashed. This flash tends to prevent the mould
sections from fully closing and thus affects the
a) All rubber shows some shrinkage when cooled
finished-part dimensions.
after moulding, and allowance for this is made in
the mould design. The amount of shrinkage is
NOTE 3 For products moulded by transfer or injection,
dependent on the rubber type and the mix used,
it is possible to regard all dimensions as fixed.
but also varies from batch to batch of the same
mix. Products made from some silicone rubbers,
Two sets of tolerances, F and C, are given and are
fluorocarbon elastomers and other special-
defined below.

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