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Rubber O-Rings: “elastomers” would be a more appropriate definition

7 December 2020
Technics
Elastomer O-Ring

Definition and useful information

Have you ever wondered what material O-Rings are made of? Of course, the answers can be as different as the materials that give life to this important industrial component present in many products.

Here are some of the terms frequently mentioned in case you want to understand and further explore the technical issues related to industrial gaskets and O-Rings.

Elastomer, let’s get to know it better.

The word elastomer is formed by the combination of the words “elastic” and “polymer” and describes a solid material with elasticity as a fundamental property.

Rubber, and in general all elastomers, are chemically composed of polymers (i.e. macromolecules having a molecular weight of a few tens of thousands of atomic mass units); these macromolecules in resting conditions are folded on themselves, while when subjected to traction they are capable of stretching, and then resume their original configuration when the stress ceases.

In other words, we can say that an “elastic” material is a material that after having been subjected to a significant deformation under tensile stress, compression or stretching, quickly returns to its initial shape as soon as the set force is removed.

Rubber and degrees of crosslinking.

Unlike the macromolecules of thermoplastic polymers, the macromolecules that make up rubber have a certain degree of cross-linking, i.e. the macromolecules do not have a linear chain structure, but are more or less intertwined with each other (like a net); this binds the macromolecules to move around fixed points (the nodes of the net) and this restores the original configuration when the mechanical stress ceases.

In this way, the rubber can be elastic and return to its original shape. Thanks to this particular property, rubber has always found many fields of application.

 

How are the Elastomers classified?

According to the ASTM D 2000 standard, elastomers intended for technical applications can be divided into:

  • Types: based on resistance to ageing in hot air
  • Classes: based on resistance to swelling in oil

Other criteria refer to the resistance to particular fluids and environments such as ozone, water, etc.

The polymers are divided into groups, which are indicated with the last letter of the identification code indicated by ISO 1629 and ASTM D-1418 standards.

GroupDescription
MElastomers in this group contain saturated polyethylene polymer chains
OElastomers of this group contain oxygen atoms
QElastomers of this group contain oxygen and silicon atoms
RElastomers of this group contain unsaturated carbon
UElastomers of this group contain carbon, oxygen and nitrogen

Nomenclature of compounds for the production of O-Rings.

The following table summarises the nomenclatures regarding the most common compounds present on the market (the compounds used for our productions are highlighted in bold).

DescriptionISO 1629(1)ASTM D-1418(2)Group
SiliconeVMQVMQQ
FluorosiliconeFVMQFVMQQ
Etilene-Propilene-DieneEPDMEPDMM
PolyacrylateACMACMM
FluoroelastomerFPMFKMM
TFE/PFEPMFEPMM
PerfluoroelastomerFFPM(3)FFKMM
PolyurethaneAU / EUAU / EUU
Acrylonitrile ButadieneNBRNBRR
Hydriertes Acrylnitril-ButadienHNBR(3)HNBRR
PolychloropreneCRCRR
Styrene-ButadieneSBRSBRR
Natural RubberNRNRR
ButylIIRIIRR

+ PLUS +

Natural rubber is the only remaining material of natural origin. It is obtained from the extraction of latex from plants, for example, the one obtained through the coagulation process of latex extracted from Hevea brasiliensis.

Vulcanization, historically attributed to Charles Goodyear’s discovery, was the first chemical process to make natural rubber truly usable in practical applications.

It is said that the vulcanization process was discovered by chance after many attempts. While mixing liquefied rubber and sulphur, Goodyear accidentally spilt the cup on a very hot stove. After cooling down, the liquid substance turned out to be soft and elastic. Vulcanization had been discovered!

For more information and technical details, please contact us.

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