Elastomeric materials

In order to understand the O-rings, In addition, it is necessary to talk about the elastomeric materials used to manufacture them. 

In this blog entry we will bring you up to date about the characteristics of the different materials and their functionality - let's get started!

Imperfections

When considering a seal between two surfaces, it is absolutely essential to take into account the level of imperfections it has. Even on the flattest surface there is a degree of unevenness.

For this reason, it is difficult to generate a seal directly between two surfaces, unless a large force is applied that crushes one face against the other.

The filling of surface imperfections is effectively achieved through the use of seals made from elastomeric materials.

Other possibilities

In addition to elastomers, there are also other gasketing materials. These are presented below:

• Compressed fibers which are popularly known as “cartons” and require considerably more clamping force than elastomers.

• Materials combining fibers, graphite, Teflon, etc. and other reinforcing materials.

• All-metal materials which, under extreme conditions, show the necessary elasticity for the sealing of two surfaces.

Elastic memory of elastomeric materials

Elastomer seals always act by virtue of their elasticity. They deform under a load or force and recover their shape when the force ceases.

To understand how they achieve this, one must imagine a skein of wool with a particularity: the various threads that make up the ball are linked together by springs. So that when the ball is tightened, it deforms and when the load that deforms it disappears, then the springs “intervene” and recover the separation between strands. Hence the term “elastic memory”.

It must be taken into account that all elastomers lose this so-called elastic memory with time and use. As with everything else, they also wear out.

Types of rubber

• Acrylonitrile Butadiene Rubber

Also known as Nitrile or NBR. Excellent for use with mineral oils and general uses.

• Fluorinated rubber

Known as Viton, or FKM or FPM. It has high chemical and temperature resistance to up to 200 degrees. Therefore, it is often used in applications where other rubbers would have problems with high temperatures.

• Ethylene Propylene Rubber

EPDM. Able to withstand hot water and steam better than other elastomers. It does not work well with mineral oils or greases. 

• Silicone Rubber, or VMQ

This type of rubber has a wide temperature range but limited chemical and mechanical resistance. It is suitable for food applications.

• Perfluoroelastomer rubber

Known as FFKM or FFPM with virtually universal chemical resistance. 

• Hydrogenated Nitrile or HNBR

This elastomer improves the temperature resistance of NBR and has a high wear resistance.

• Chloroprene rubber

Also known as neoprene or CR. Well-known for being one of the first synthetic rubbers. It has a very good resistance to weathering and withstands mineral oils. 

• FEPM

Aflas® or FEPM, is a registered trademark for a compound very similar to FPM, but has improved chemical vapor resistance and to some chemical products.

• NR

The NR it has good elastic qualities and is used in mechanical applications as in anti-vibration mounts. It is not a material widely used in sealing.

• Polyurethane 

Polyurethane is a thermoplastic, but has a high elasticity and capacity for deformation and elastic memory. It is suitable for working with mineral oils, but not with water, much less with hot water. Due to its wear resistance, it is used in high-pressure hydraulic seals.

Characteristics that an elastomeric material must have

In order to consider a material suitable for use in O-ring seals it must have several qualities that make it suitable for this purpose. These include temperature, chemical resistance and hardness.

Temperature

The operating temperature limits for elastomeric materials are as follows much more limited than those for metal parts, It is therefore important to take them into account. 

Elastomeric materials have limits both above and below. At the top, are usually around 100 to 120 degrees Celsius., although there are compounds that can reach up to 300. As for subzero temperatures, The usual range is around minus 30 to 40 degrees Celsius. 

Chemical resistance

Chemical resistance is another factor to be taken into account. This one, can vary greatly from one elastomer to another. 

Hardness

The hardness of elastomeric materials is usually measured on the following scale Shore-A. For sponge rubbers the following scales are used Shore-0 y Shore-00, while the hardest plastics are measured on the scale Shore D. 

Shelf life

Elastomeric materials have a limited life. Consult our table and you will see the shelf life for each type of elastomeric material. 

We hope this article has been of interest to you. If you need more information about our custom bellows manufacturing service or technical advice, consult our team of experts.