Rubber -- Dimensional tolerances of solid moulded and extruded products

Caoutchouc -- Tolérances dimensionnelles des produits compacts moulés et extrudés

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ISO 3302:1976 - Rubber -- Dimensional tolerances of solid moulded and extruded products
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* Rubber - Dimensional tolerances of solid moulded and
extruded products
Caoutchouc - Tolérances dimensionnelles des produits compacts moulés et extrudés
First edition - 1976-08-15
Ref. No. IS0 3302-1976 (E)
UDC 678.44-48 : 531.7

Descripton : rubber, rubber products, mouldings, extruded products, dimensional tolerances.

2 - Price based on 7 pages
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IS0 (the International Organization for Standardization) is a worldwide federation

of national standards institutes (IS0 Member Bodies). The work of developing
International Standards is carried out through IS0 Technical Committees. Every
Member Body interested in a subject for which a Technical Committee has been set

up 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.

Draft International Standards adopted by the Technical Committees are circulated
to the Member Bodies for approval before their acceptance as International
Standards by the IS0 Council.
International Standard IS0 3302 was drawn UP by Technical Committee
SSO/TC 45, Rubber and rubber products, and was circulated to the Member Bodies
in May 1975.
It has been approved by the Member Bodies of the following countries
India Spain
Ireland Sri Lanka
Belgium Italy Sweden
Brazil Mexico Switzerland
Bulgaria Netherlands Turkey
New Zealand United Kingdom
Czechoslovakia Poland
Egypt, Arab Rep. of Portugal
France Romania
Germany South Africa, Rep. of
NO m mber Body expressed disapproval of the document.
O International Organization for Standardization, 1976
Printed in Switzerland
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IS0 3302-1976 (E)
Rubber - Dimensional tolerances of solid moulded and
extruded products
e O INTRODUCTION When particular physical properties are required in the
product, it may not always be possible to provide these in
a compound which is capable of extrusion to close
0.1 Section One : Mouldings
tolerances, and it is advisable, in these circumstances, that
The dimensional tolerances stated in this International
consultation should take place between the interested
Standard may be wider than those used in some other
parties. In general, the softer vulcanizates (i.e. of hardness
engineering practice. The following considerations apply :
below 50 IRHD) need greater tolerances than the harder
1) All rubber shows some shrinkage after moulding,
and allowance for this is made in the mould design. The
The tolerances chosen for use in any particular application
amount of shrinkage is dependent on the rubber and mix
should take into account the dimensional changes occurring
used, but also varies from batch to batch of the same
after extrusion and vulcanization; these will depend on the
mix. Products made from silicone rubbers, fluorocarbon
nature of the rubber arid mix used.
rubbers and polyacrylates are subject to large shrinkage;
In the case of certain synthetic rubbers, extrusion class El
therefore, classes MI and M2 tolerances (sub-clause 1.1)
tolerances (table 2) are not directly obtainable.
are very difficult to obtain.
The closer tolerance classes should not be demanded unless
2) Non-rubber parts bonded to the rubber will affect
the application requires it and should be restricted only to
the shrinkage and, therefore, the practicable tolerances.
those dimensions which are critical. The greater the degree
3) Moulds are made in various ways depending on the
of accuracy demanded, the closer the control which must
type of product and the accuracy demanded. In general,
be exercised during manufacture, and hence the dearer the
the product can be no more accurate than the mould,
product becomes.
and the greater the degree of accuracy demanded, the
more expensive become the moulds and their
4) Care should be taken in applying the standard
tolerances to products having wide sectional variations.
This International Standard specifies the dimensional
tolerances of solid moulded and extruded rubber products.
5) In cases where the rubber product is unavoidably
distorted during removal from the mould, the

dimensions of the products may be affected, and special 1.1 Section One : Mouldings

allowance may be needed.
1.1.1 Section One of this International Standard
establishes four classes of tolerance for fixed and closure
0.2 Section Two : Extrusions
dimensions (see 3.1 and 3.2) for products moulded in solid
rubber, namely :
Extruded rubber products require greater tolerances in
manufacture than those produced by moulding since, after

being forced through a die, swelling of the rubber takes Class MI for precision mouldings.

place, and during subsequent vulcanization shrinkage and
Such mouldings require precision moulds, fewer cavities per
deformation usually occur.
mould, close mix controls, etc., which result in high cost.

Deformation can be reduced by the use of supports during Optical comparators or other similar measuring devices may

vulcanization, the nature of the support depending on the be required to minimize distortion of the rubber by the

section being produced and the degree of control required. measuring instrument. This type of part requires expensive

control and inspection procedures and very frequently
These characteristics control the class of tolerance
applicable to given dimensions. some machining after moulding.
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IS0 3302-1976 (E) Class M2 for high quality mouldings involving Two classes of tolerance on outside dimensions

much of the close control required for class MI. (normally diameters) of surface-ground extrusions (tubing)

together with two classes of tolerance on wall thickness
of these extrusions :
1 .I .I .3 Class M3 for good quality mouldings.
EGI and EWI precision, Class M4 for mouldings where dimensional control
EG2 and EW2 good quality.
is non-critical.
1.1.2 It also prescribes the relevant conditions for the Three classes of tolerance for the cut length of
measurement of dimensions.
extrusions, and three classes of tolerance on the thickness
It does not apply to precision toroidal sealing rings.
of cut sections of extrusions :
LI and ECI precision,
1.2 Section Two : Extrusions
L2 and EC2 good quality,
1.2.1 Section Two of this International Standard
establishes eleven classes of tolerance for extrusions in solid
L3 and EC3 non-critical.
rubber, related to particular ranges of dimensions, namely : Three classes of tolerance on nominal cross-
1.2.2 It also prescribes the relevant conditions for the
sectional dimensions of unsupported extrusions :
measurement of dimensions.
El high quality,
E2 good quality,
E3 non-critical.
2 REFERENCES Three classes of tolerance on nominal cross-
ISO/R 471, Standard atmospheres for the conditioning
sectional dimensions of mandrel-supported extrusions :
and testing of rubber test pieces.
EM 1 precision,
IS0 2230, Vulcanized rubber - Guide to storage.
EM2 high quality,
Is0 4648, Rubber, vulcanized - Determination of
EM3 good quality. dimensions of test pieces and products.’
11 At present at the stage of draft.
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IS0 3302-1976 (E)
3 DEFINITIONS affected by deforming influences like flash thickness or
lateral displacement of different mould parts (upper and
In moulding of a rubber product, more rubber is used than
lower parts or cores). See the figure, dimensions W, x and y.
is required to fill the cavity, and the excess is flashed. This
flash tends to prevent the mould sections from fully closing
and thus affects the finished part dimensions.
3.2 closure dimensions (C) : Dimensions which can be
NOTE - For products moulded by transfer or injection, it is
altered by variation in the flash thickness or lateral
possible to regard all dimensions as fixed.
displacement of different mould parts. See the figure,
Two sets of tolerances, F and C, are given and are defined
dimensions s, t, U and z.
NOTE - The dimensions in 3.1 and 3.2 can only be toleranced in
so far as they are independent of each other.
3.1 fixed dimensions (FI : Dimensions which are not
Direction of pressure
Y LLower half of mould
FIGURE - Compression mould and moulded part
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IS0 3302-1976 (E)

The tolerances to apply shall be chosen from the four Measurements of dimensions shall not be made until 16 h

classes of tolerance described in clause 1, by agreement have elapsed after the moulding operation, this minimum

between the interested parties. time being extended to 72 h in case of dispute. Measure-

ments shall be completed within 3 months after the date
Standard tolerances are given in table 1. Fixed tolerances
of despatch to the purchaser or before the moulding
(F) are related by size to each dimension, but all closure
is put into use, whichever is the shorter time. Measurements
tolerances (Cl are determined by the largest closure
shall be made after conditioning at a temperature of 23 OC,
dimension (U).
in accordance with ISO/R 471, other than by specific
agreement between the interested parties. Care shall be
Closer tolerances than class MI can be agreed bet

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