Elastomer: the material for O-rings explained
Elastomers are the rubber-elastic materials behind nearly every O-ring. This article explains what defines an elastomer, how cross-linking and vulcanization work and how it differs from thermoplastics and thermosets.
- An elastomer is a rubber-elastic polymer that can be deformed and then returns to its original shape.
- This behaviour is based on cross-linked polymer chains. The cross-linking is created by vulcanization.
- Elastomers differ from thermoplastics and thermosets through their loose cross-linking and their elastic recovery.
- For O-rings, synthetic elastomers such as NBR, FKM, FFKM and EPDM are particularly relevant.
- Temperature, chemicals and UV radiation influence the properties, which is why material selection is crucial.
What is an elastomer?
An elastomer is a polymer that can be stretched or compressed under load and then returns almost completely to its original shape. Colloquially, this group of materials is simply called "rubber". It is precisely this rubber-elastic behaviour that makes elastomers the preferred material for O-rings and seals.
Elastomers consist of long polymer chains that are cross-linked with one another. When an elastomer is stretched, the chains extend. After the load is removed, they contract again and the component returns to its original shape. This property is called elasticity and distinguishes elastomers from many other materials such as metals or rigid polymers.
| Term | Meaning |
|---|---|
| Elastomer | Polymer material with rubber-elastic behaviour, returns to its original shape after deformation |
| Polymer chain | Long molecule made up of many building blocks (monomers) strung together |
| Cross-linking | Chemical bonds between the polymer chains, the basis of the restoring force |
| Vulcanization | Process that creates the cross-linking and improves strength as well as heat resistance |
Structure, cross-linking and vulcanization
The flexibility of elastomers results from their chemical structure. The polymer chains are cross-linked, that is, connected to one another by chemical bonds. This cross-linking allows the material to stretch and contract again without the chains permanently sliding apart.
The cross-linking is created by vulcanization. In this process, chemical bonds are formed between the polymer chains through heating. This step improves the elasticity as well as the strength and the heat resistance of the material. Vulcanization was developed in 1839 by Charles Goodyear and is regarded as a turning point in the industrial use of rubber.
From raw material to finished material
The manufacture of an elastomer takes place in several phases:
- Polymerization: Small molecules (monomers) are joined into long polymer chains.
- Mixing: Additives and fillers are added to set the desired properties.
- Shaping: The compound is brought into the desired shape, for example by pressing or extrusion.
- Vulcanization: Heating creates the cross-links between the chains.
Rubber-elastic behaviour
When an elastomer is stretched, the polymer chains extend. After the force is removed, the chains return to their original position. This behaviour is the basis for use in applications where flexibility and durability are required.
- Behaviour under load: Elastomers can be stretched to a certain degree without being damaged.
- Recovery after deformation: After the load is removed, they resume their original shape.
- Damping: They absorb vibrations and shocks.
Environmental factors and their effects
The properties of elastomers are influenced by the operating conditions. Temperature, chemicals and UV radiation act on elasticity and durability:
- Temperature: Strong cold or heat changes the elasticity.
- Chemical influences: Some media attack the material and weaken it.
- UV radiation: Prolonged exposure can lead to embrittlement.
That is why selecting the right elastomer for the respective installation situation is crucial. More on this in the O-ring basics.
Important elastomers for O-rings
A distinction is made between natural and synthetic elastomers. Natural elastomers such as latex are obtained from the sap of certain plants. Synthetic elastomers are produced chemically and usually offer improved properties for specific applications, such as oil or heat resistance.
For technical seals, synthetic elastomers are used above all. The most important materials for O-rings at a glance:
| Material | Brief profile |
|---|---|
| NBR | Standard material, good with mineral oils and fuels. See material comparison. |
| FKM | High temperature and media resistance, broad range of applications. Details at FKM O-rings. |
| FFKM | Highest chemical and thermal resistance. More at FFKM O-rings. |
| EPDM | Very good with water, steam and many polar media. |
Distinction from thermoplastics and thermosets
Elastomers are one of several groups of polymers. They can be distinguished from thermoplastics and thermosets by their behaviour under load and heating.
| Group | Behaviour |
|---|---|
| Elastomer | Loosely cross-linked, rubber-elastic, returns to its original shape after deformation, not meltable. |
| Thermoplastic | Not cross-linked, becomes soft and mouldable when heated, solid again on cooling. |
| Thermoset | Densely cross-linked, hard and rigid, not meltable and not elastic. |
The thermoplastic elastomers occupy a special position. They combine the easy processability of thermoplastics with the elastic behaviour of rubber and can therefore be melted and reshaped.
Frequently asked questions
What is an elastomer, simply explained?
What is the difference between natural and synthetic elastomer?
What is vulcanization?
How do elastomers differ from thermoplastics and thermosets?
How do environmental factors influence the properties of elastomers?
Which elastomers are suitable for O-rings?
