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Traction, compression and stretching: essential parameters of elastomers.

7 December 2020
Technics
Dynamic applications are defined as those where the seals act as dividers on the surfaces of two elements that move one against the other. We position dividing the dynamic applications of an O-Ring into alternating and rotating linear applications.

If it is true that we can consider as “elastic” a material that, after having been subjected to a considerable deformation under tensile, compression or stretching stress, quickly returns to its initial shape as soon as the set force is removed, we can consider these three stress parameters to be among the essential parameters of every rubber product, and therefore also of O-Rings.

However, what exactly are they? Let’s find out together.

Tensile stress

The tensile test carried out on an elastomer article determines the maximum elongation and the necessary force to be applied to the article until it breaks.

The tensile stress is the stress applied to the specimen during the tensile test. It is calculated as the force applied to a unit of the surface area of the cross-section.

The test result is measured in MPa (or N/mm2) or psi (pounds per square inch).

Stretching

An elastomer must be able to be stretched a lot and return to its original shape. Elastomers are characterised first of all by a low elastic modulus of stretching in the range 106-107 dyne/cm2.

There is a point of “no return” for each elastomer. It is defined as a yield point because the material starts to deform plastically, changing from a reversible elastic behaviour to a plastic behaviour characterised by the development of irreversible deformations.

Compression

An elastomer article is subjected to compression in order to exert a contrary force and to allow the seal. It is the elasticity of the rubber that guarantees the opposite thrust to that exerted by the surfaces on which the seal must be made. The higher the compression, the more elasticity the rubber will resist by exerting the seal.

Excessive compression can prematurely damage a seal. Poor compression can cause fluid loss.

These values are always given in the material data sheets in order to compare different compounds and assess their usability according to the different applications, whether static or dynamic and sealing environments. With the Compare tool, you can compare all the values present in the technical data sheets of our materials and evaluate which alternative is better to use for each different case. Try it out now!

If you need more information about the above-mentioned values, please get in touch with us, our technical staff will be able to offer the best answer to your questions. Think Big!

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