Parker O-Ring Handbook.pdf

Basic O-Ring Elastomers
2-2
Parker O-Ring Handbook
Basic O-Ring Elastomers
2.0 Elastomers
The basic core polymer of an elastomeric compound is
called a rubber, produced either as natural gum rubber in
the wild, on commercial rubber plantations or manufactured
synthetically by the chemical industry. Today, more than 32
synthetic rubbers are known, the most important ones are
listed in Table 2-1.
Modern elastomeric sealing compounds generally contain
50 to 60% base polymer and are often described simply as
“rubber.” The balance of an elastomer compound consists of
various fi llers, vulcanizing agents, accelerators, aging retardants
and other chemical additives which modify and improve
the basic physical properties of the base polymer to meet the
particular requirements of a specifi c application.
Elastomers used in producing seals, and particularly those
used in O-rings, will usually provide reliable, leak-free function
if fundamental design requirements are observed.
“Cross-linking” between the polymer chains is formed during
the vulcanization process, see Figure 2-1. Cross-linking of
the molecules changes the rubber from a plastic-like material
to an elastic material.
After vulcanization, including any required “post-cure,”
an elastomer compound attains the physical properties
required for a good sealing material. As with all chemical
reactions, temperature is responsible for the speed of reaction.
Only when the ideal process temperature is constant during
the entire vulcanization time, will the optimum degree of
curing be reached. For this reason, the conditions of vulcanization
are closely controlled and recorded as part of the
Parker quality assurance process.
2.1 Introduction to Elastomers
Before reviewing the available elastomers and their general
properties, it is necessary to fully understand the terms
“polymer,” “rubber,” “elastomer” and “compound” as they
are used in this handbook.
Elastomer
no cross-links
Elastomer
cross-linked
Figure 2-1: Schematic Representation of Polymer Chains
Before and After Vulcanization
2.1.1 Polymer
A polymer is the “result of a chemical linking of molecules
into a long chain-like structure.” Both plastics and elastomers
are classifi ed as polymers. In this handbook, polymer
generally refers to a basic class of elastomer, members
of which have similar chemical and physical properties.
O-rings are made from many polymers, but a few polymers
account for the majority of O-rings produced, namely Nitrile,
EPDM and Neoprene.
Synthetic Rubber
Abbreviation
DIN/ISO ASTM
Chemical Name
1629 D1418
M-Group (saturated carbon molecules in main macro-molecule chain):
Polyacrylate Rubber ACM ACM
Ethylene Acrylate — AEM
Chlorosulfonated Polyethylene Rubber CSM CSM
Ethylene Propylene Diene Rubber EPDM EPDM
Ethylene Propylene Rubber EPDM EPM
Fluorocarbon Rubber FPM FKM
Tetrafl uorethylene Propylene Copolymer FEPM FEPM
Perfl uorinated Elastomer — FFKM
O-Group (with oxygen molecules in the main macro-molecule chain):
Epichlorohydrin Rubber CO CO
Epichlorohydrin Copolymer Rubber ECO ECO
R-Group (unsaturated hydrogen carbon chain):
Butadiene Rubber BR BR
Chloroprene Rubber CR CR
Isobutene Isoprene Rubber (Butyl Rubber) IIR IIR
Chlorobutyl Rubber CIIR CIIR
Isoprene Rubber IR IR
Nitrile Butadiene Rubber NBR NBR
Styrene Butadiene Rubber SBR SBR
Hydrogenated Nitrile — HNBR
Carboxylated Nitrile XNBR XNBR
Q-Group (with Silicone in the main chain):
Fluorosilicone Rubber FMQ FVMQ
Methyl Phenyl Silicone Rubber PMQ PMQ
Methyl Phenyl Vinyl Silicone Rubber PMVQ PVMQ
Methyl Silicone Rubber MQ MQ
Methyl Vinyl Silicone Rubber VMQ VMQ
U-Group (with carbon, oxygen and nitrogen in the main chain):
Polyester Urethane AU AU
Polyether Urethane EU EU
Table 2-1: The Most Important Types of Synthetic Rubber, Their
Groupings and Abbreviations
Parker Hannifi n Corporation • O-Ring Division
2360 Palumbo Drive, Lexington, KY 40509
Phone: (859) 269-2351 Fax: (859) 335-5128
www.parkerorings.com