 Classification
of elastomers
Elastomers that
are intended for, but not limited to, use in automotive applications,
are designated by ASTM D2000 on the basis of type (heat resistance) and
class (oil resistance).
Resistance to
special fluids or environments (fuels, water, ozone, etc.) are also
classified in a similar manner. ASTM D1418 lists different polymers by
an abbreviated coding system (NBR, EPDM, ECO, SBR, FKM, etc.). By
utilizing this classification system, guidance is provided to the
engineer in the selection of practical, commercially available rubber
materials and to also provide a method for specifying these materials
by use of a simple "line call-out" designation.
Standard
compounds
Standard
compounds have been formulated to meet a number of laboratory and
industry standards for a wide range of applications.
Basic
characteristics of standard compounds are given in table 1.
Table 1:
Standard compounds - basic characteristics
| Code |
Polymer |
ASTM
D2000
Line Call-out |
Basic
characteristics |
| K6 |
NBR
70 |
M2 BG
714 B14 EA14 EF11 EF21 EO14 EO34 F15 |
Excellent
mechanical strength and resistance to wear, mineral oils, heat.
Poor resistance to fuels and out-door weathering. |
| C6 |
EPDM
70 |
M3 DA
710 A26 B36 C32 EA14 F19 G21 |
Good
resistance to water, steam, brake fluids, alkalies and diluted
acids.
Outstanding weather resistance. |
| M6 |
HNBR
70 |
M4 DH
716 A26 B36 C12 EO16 EO36 F17 |
Very
good mechanical characteristics.
Wear, ozone and high temperature ageing resistance.
Recommended for fuels and oils contact.
Low gas permeability.
Good for high and low temperatures. |
| F6 |
MVQ
70 |
M5 GE
706 A19 B37 EO16 EO36 F19 G11 |
Very
good heat and chemical resistance.
Recommended for food contact. Poor mechanical characteristics. |
| G6 |
FKM
75 |
M2 HK
710 A1-10 B38 EF31 EO78 Z1
Z1 Hardness 75 ±5 |
High
temperature resistance. Very good chemical resistance. Poor low
temperature flexibility. |
Physical
characteristics
Physical
characteristics of our standard compounds are listed to provide
assistance in selecting the proper compound.
A number of proprietary compounds with unique characteristics and
hardnesses are available along with additional information from our
Technical Sales and Services Department.
Chemical
resistance
Selection of
elastomers is normally the final result of a compromise between fluid
resistance and last, but not least, the cost of the product.
Chemical resistance of different elastomers are listed in standard
compounds - chemical resistance.
Tear
and wear resistance
Tear resistance
of elastomer (ASTM D624-B) is very important for those applications
where rubber parts are subject to strain and stresses, particularly when
surface cuts could cause tears and severely damage the effectiveness of
the seal.Wear resistance (ASTM D394) is very important for the correct
evaluation of any O-Ring in a dynamic sealing application.Critical
factors to be considered are: polymer type, hardness, surface finish,
lubrication, relative speed and environment.
Electrical
characteristics
Elastomers have
a large use in electric and electronic fields due to their dielectric
characteristics and versatility.
Typically, the attention of the project engineer is focused on the
electric insulation obtainable with rubber. On request, rubber can also
be supplied as an electric conductor or antistatic, by means of special
additives to the compound.
The most common standards regarding electric characteristics are ASTM
D257 and ASTM D991 (volume and surface resistivity), ASTM D149
(dielectric rigidity) and IEC Standards (International Electrical
Commission).
Special
compounds
GAPI
Compounding Division has the ability to meet the special compounding
requirements for a vast number of industries, offering materials
previously tested at a variety of temperature and media environments.
GAPI can also formulate compounds with specific characteristics, to
customer requirements, thus giving an invaluable service to our customers. The techincal data
and characteristics of some of those special compounds are listed in a
separate brochure.
Special
standards
A number of
governmental and independent regulatory agencies maintain standards
dealing with elastomers and the environments in which seals are expected
to perform. Listed are the agencies deeply involved in O-Ring approvals:
- WQC (Water Quality
Centre) of Great Britain dealing with elastomer gasketing in
contact with drinking water;
- DVGW of
Germany dealing with elastomer gasketing in contact with drinking
water;
- UL of USA,
which establishes standards and tests materials and products to
determine their hazards to life and property;
- NSF
International of USA provides standards in public health safety.
These
Organizations operate laboratories for examination and testing to
certify compounds and finished parts such as O-Rings.
GAPI has a
number of compounds certified by these Authorities.
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