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IS0
I NTE R N AT1 O N A L ORGAN I Z AT I O N FOR STAND AR D I Z AT I O N
I S O R E C O M M E N D AT1 O N
R 293
PLASTICS
COMPRESSION MOULDING TEST SPECIMENS
OF THERMOPLASTIC MATERIALS
1st E D IT I ON
February 1963
COPYRIGHT RESERVED
The copyright of IS0 Recommendations and IS0 Standards belongs
to IS0 Member Bodies. Reproduction of these 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
Also issued in French and Russian. Copies to be obtained through the national standards organizations.
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BRIEF HISTORY
The IS0 Recommendation R 293, Plastics-Compression Moulding Test Specimens of
Thermoplastic Materials, was drawn up by Technical Committee ISO/TC 61, Plastics, the Secre-
tariat of which is held by the American Standards Association, Inc. (ASA).
Work on this question by the Technical Committee began in 1954 and led, in 1958, to the
adoption of a Draft IS0 Recommendation.
In October 1959, this Draft IS0 Recommendation (No. 318) was circulated to all the IS0
Member Bodies for enquiry. It was approved by the following Member Bodies:
Argentina Hungary Poland
Australia India Romania
Austria Israel Spain
Belgium Italy Sweden
Burma
Japan Switzerland
Chile Mexico United Kingdom
Czechoslovakia Netherlands U.S.A.
Germany Portugal U.S.S.R.
One Member Body opposed the approval of the Draft:
France.
The Draft IS0 Recommendation was then submitted by correspondence to the IS0 Council,
which decided, in February 1963, to accept it as an IS0 RECOMMENDATION.
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ISO/R 293 - 1963 (E)
IS0 Recommendation R 293 February 1963
PLASTICS
COMPRESSION MOULDING TEST SPECIMENS
OF THERMOPLASTIC MATERIALS
1. SCOPE
This IS0 Recommendation covers only the general principles to be followed when compression
moulding test specimens of thermoplastic materials. The exact conditions required to prepare
adequate specimens vary for each plastics material. These conditions are properly a part of the
specification for the material, or should be agreed upon by the seller and the purchaser.
NOTE. - It may be necessary to treat the moulding granules in some manner, prior to preparation of test speci-
mens. Preheating, drying, etc. are often required, particularly with those plastics which absorb moisture.
2. GENERAL
The principal stages in the compression moulding process for thermoplastics are the following:
(1) Raising of the temperature of the material to a level where application of pressure can cause
sufficient flow without thermal decomposition taking place,
(2) Application of pressure to the material, causing flow and assuming the shape of the mould
. in which it is contained,
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(3) Cooling of material to a temperature at which the moulding can be removed from the mould
without distortion taking place.
3. SUITABLE TYPES OF MOULDS
Types of moulds which have been found suitable for use when compression moulding thermo-
plastic materials are described below and shown schematically in Figures 1 to 4 (page 5).
3.1 A simple type of mould which is suitable for many thermoplastic materials is the three-
plate, frame type, examples of which are shown in Figures 1 and 1 A. In the interests of
combining simplicity with reproducibility of results between testing organizations, this
is the preferred type. However, other types, such as those described in clauses 3.2, 3.3 and
3.4 below, are not excluded.
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ISO/R 293 - 1963 (E)
3.2
A variation of the three-plate mould is the two-plate type, in which the center and lower
plates are combined. An example of this type of mould is shown in Figure 2.
3.3 A further variation of the two-plate mould is shown in Figure 3. In this case, the upper
plate has a plunger or force which fits into the cavity in the lower plate. This enables
materials of high bulk factor to be moulded.
All three moulds, described in clauses 3.1, 3.2 and 3.3, are heated indirectly by means of
heated platens.
3.4 Another type of mould, which is usually larger and more complicated than the three previous
types, is one which is fixed permanently in a press and which is cored to allow direct heating
and cooling of the mould. An example is shown in Figure 4.
While the simpler types of mould described in clause 3.1 are preferred, all four types of
The choice of mould type, and actual design
mould can give satisfactory test specimens.
and manufacture of the moulding device, depend on the material to be tested, the dimensions
of the test specimen to be moulded and other considerations of practical convenience.
The surfaces of the mould in immediate contact with the moulding material should be
anticorrosive.
4. PROCEDURE
4.1 Means of heating
A satisfactory and convenient method of heating is by means of high-pressure steam (see
Note below). This method combines the advantage of rapid heating with avoidance of
“hot spots”. Plates and fixed moulds should be cored or channeled to provide heating by
means of passing steam through them. The channels should be as large and as numerous
as possible in order to insure rapid and uniform heating and still maintain the required
strength and rigidity of the mould.
NOTE: Steam heating is inadequate for high heat resistant materials, such as fluoro-carbons.
Another convenient method of heating involves the use of electrical resistance heaters. This
method is slower than steam, but has the advantages of cleanliness and simplicity. Care
should be taken in the design and construction to provide maximum heat without the
occurrence of “hot spots” and to maintain rigidity of the plates.
Cooling is most conveniently accomplished by passing cold water through channels provided
for the purpose.
4.2 Temperature measurement
Temperature should be measured in both parts of the mould by means of thermocouples
or thermometers or other suitable means, at positions in the mould as near as possible to the
mould surface and/or at positions in the plates near the
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