Guide to materials for technical seals: elastomers, technopolymers and metals

Material selection is one of the most important aspects in the design and selection of a technical seal. Correct geometry and a properly dimensioned groove or housing may not be sufficient if the material is not compatible with the fluid, temperature, pressure or actual operating conditions.

Elastomers, technopolymers and metals behave in very different ways. Elastomers are mainly valued for their elasticity and recovery capability; technopolymers offer chemical resistance, dimensional stability and specific mechanical performance; metals are used when the application requires resistance to particularly high pressures, temperatures or loads.

There is therefore no material that is universally suitable for every application. The choice must start from the function of the seal, the system in which it will be installed and the conditions it will have to withstand throughout its entire service life.

Why material affects seal performance

A seal must create and maintain sufficient contact pressure to prevent the passage of fluids or gases. To do this, the material must adapt to the groove or housing, compensate for tolerances and retain its properties over time.

Temperature, pressure and chemical compatibility are the first variables to consider, but they are not the only ones. Movement, friction, speed, exposure to weathering, sterilisation, washing cycles, contamination and expected service life also influence the selection.

A material may be perfectly compatible with a fluid at room temperature, but behave differently when the temperature increases. Likewise, a compound with high chemical resistance may not be the most suitable choice in the presence of continuous movement or strong mechanical stress.

Correct selection therefore requires an overall assessment of the following elements:

fluid or gas in contact with the seal, continuous and peak temperature, pressure, movement, friction and speed; groove or housing geometry, tolerances, surface finish, required service life and specific sector requirements.

Elastomers: elasticity and recovery capability

Elastomers are among the most widely used materials for technical seals. Their main characteristic is the ability to deform under compression and recover at least part of their original shape when the load is removed.

This property allows the seal to adapt to the mating surfaces, compensate for small dimensional deviations and maintain the contact pressure required for sealing.

The performance of an elastomer does not depend only on the base polymer. Compound formulation, hardness, additives, production process and vulcanisation conditions can significantly affect the behaviour of the component. Two seals made from the same elastomeric family may therefore deliver different performance.

NBR – Nitrile rubber

NBR is one of the most widely used elastomers in technical applications, thanks to its good balance between performance and cost. It generally offers good resistance to mineral oils, greases and various fuels, which is why it is often used in hydraulic systems, mechanical components and automotive applications.

Its main limitations concern resistance to ozone, weathering and higher temperatures. In moderate operating conditions, it often represents a suitable solution, while in more severe environments it may be necessary to evaluate materials with greater stability.

HNBR – Hydrogenated nitrile rubber

HNBR is derived from NBR through a hydrogenation process that improves resistance to heat, oxidation, ozone and ageing.

It is frequently used when good mechanical performance, wear resistance and greater stability than traditional NBR are required. It can represent an intermediate solution between NBR and FKM in automotive, hydraulic and dynamic applications.

ACM – Acrylic rubber

ACM is an acrylic rubber used mainly in applications involving contact with oils and relatively high temperatures. It is widely used in the automotive sector, particularly in lubrication and transmission systems.

Compared with other elastomers, it may have limitations at low temperatures and in the presence of certain fluids. The assessment must therefore consider the full temperature range of the application.

AEM – Ethylene acrylic rubber

AEM offers a good combination of heat resistance, oil resistance and ageing resistance. It is used in automotive and technical applications where high temperatures, lubricating fluids and mechanical stress are present.

Compared with ACM, it can provide more balanced behaviour in certain dynamic and thermal conditions, but compatibility must always be verified in relation to the specific fluid.

EPDM – Ethylene propylene diene rubber

EPDM is particularly suitable for applications involving water, steam, weathering and ozone. It is used in sanitary systems, food-related applications, heating systems and outdoor environments.

It is generally not suitable for contact with mineral oils, fuels and many petroleum-based fluids. Its selection is therefore closely linked to the nature of the fluid.

PU – Polyurethane

Polyurethane is selected when high wear resistance, good mechanical resistance and the ability to work in dynamic applications are required.

It is widely used in rod seals, piston seals, wipers and hydraulic components. Depending on the formulation, it can offer very different performance in terms of hardness, elasticity, thermal behaviour and chemical compatibility.

VMQ – Silicone rubber

VMQ, commonly referred to as silicone, maintains good elasticity across a wide temperature range and is used in applications requiring thermal stability, flexibility and specific application requirements.

It can be used in the food, medical and technical sectors when the formulation meets the required specifications. Mechanical and abrasion resistance are generally lower than those of other elastomers, which must be considered in dynamic applications.

FVMQ – Fluorosilicone

FVMQ combines some of the typical characteristics of silicone with improved resistance to oils, fuels and certain fluids.

It is evaluated in applications where low-temperature flexibility and compatibility with fuels or lubricants are required, such as in some automotive, aerospace and specialised technical systems.

FKM – Fluoroelastomer

FKM is used in applications requiring high thermal and chemical resistance. It is used in the automotive, gas, chemical and petrochemical sectors, as well as in systems exposed to oils, fuels and aggressive fluids.

Not all FKM compounds are equivalent: the formulation must be selected in relation to the fluid and operating environment. Low-temperature performance can also represent a critical factor.

FFKM – Perfluoroelastomer

FFKM is a high-performance elastomer intended for particularly critical applications. It offers very broad chemical resistance and can operate in severe thermal conditions, depending on the specific formulation.

It is used especially when a failure would have significant consequences or when more common materials do not provide sufficient compatibility. Its high cost makes an accurate application assessment necessary, avoiding its use where it is not truly required.

Technopolymers: stability, resistance and low friction

Technopolymers are used in sealing solutions when characteristics that are difficult to obtain with an elastomer are required: high chemical resistance, dimensional stability, low coefficient of friction, rigidity or the ability to work in demanding temperature and pressure conditions.

Unlike elastomers, many technopolymers have lower elastic recovery capability. For this reason, they can be used in combination with energising elements, springs or elastomeric components that help maintain contact pressure.

PTFE – Polytetrafluoroethylene

PTFE offers high chemical inertness, a very low coefficient of friction and a broad operating temperature range. It is used in seals, sealing rings, machined components and solutions for applications involving aggressive fluids.

Pure PTFE may show deformation under load and limited elasticity. To improve certain performance characteristics, filled compounds are used with materials that can increase wear resistance, dimensional stability or mechanical behaviour.

PCTFE – Polychlorotrifluoroethylene

PCTFE is characterised by good chemical resistance, dimensional stability and low gas permeability. These properties make it interesting for applications involving gases, cryogenic fluids and systems where permeability is a critical factor.

The choice compared with PTFE depends on temperature, fluid, pressure and the required mechanical characteristics.

PEEK – Polyether ether ketone

PEEK is a high-performance technopolymer with high mechanical, thermal and chemical resistance. It is used for structural components, anti-extrusion rings, guide elements and applications requiring rigidity and dimensional stability.

It can work in severe conditions, but must be selected by considering loads, temperature, processing and interaction with the other components of the system.

Metals: sealing in severe conditions

Metallic materials are used when elastomers and technopolymers are not sufficient, or when the application requires resistance to very high temperatures, pressures and loads.

Metal gaskets work through controlled deformation and contact between surfaces. For this reason, surface finish, tightening force, geometry and flange material play a particularly important role.

Copper

Copper is used to produce washers and sealing components thanks to its deformability, thermal conductivity and ability to adapt to metal surfaces.

Copper washers are used in fittings, automotive systems, circuits and applications where tightening must generate sufficient deformation to ensure sealing.

Bronze

Bronze offers good mechanical properties, wear resistance and favourable behaviour in applications subject to friction.

It can be used for bushings, guide elements and technical components that interact with sealing systems. The choice of alloy depends on loads, operating environment and required characteristics.

Spiral-wound gaskets

Spiral-wound gaskets are made from alternating metallic elements and filler materials. They are used mainly on flanges and process plants subject to high pressures and temperatures.

Their performance depends on the correct combination of metallic material, filler, flange class, tightening and operating conditions. They should therefore not be considered interchangeable products based on dimensions alone.

General comparison between the main families

The three main families of materials used in technical seals respond to different application requirements.

Elastomers are selected mainly when elasticity, adaptability to the groove or housing and recovery capability over time are required. For this reason, it is essential to evaluate compatibility with fluids, temperature, compression set and ageing resistance.

Technopolymers are used when the application requires greater chemical resistance, dimensional stability, low friction or specific mechanical performance. In this case, it is important to consider deformation under load, wear, applied loads and, where necessary, the possible presence of energising elements.

Metals are used in the most severe applications, where mechanical resistance, stability at high temperatures and the ability to work with high pressures are required. Their performance depends significantly on tightening, surface quality, controlled deformability and correct component geometry.

This distinction helps guide the selection process, but it is not sufficient on its own to identify the most suitable material. Within the same family, there are compounds, grades and alloys with very different behaviours. The choice must therefore always be connected to the actual operating conditions and to the function the seal must perform within the system.

Material and geometry must be evaluated together

One of the most frequent critical issues is analysing the material separately from the seal geometry. In reality, material, profile and groove or housing form a single system.

A high-performance elastomer may not work if the compression level is incorrect. A PTFE component may wear quickly if the surface finish is not suitable. A metal gasket may leak if tightening does not generate the correct deformation.

Movement also changes the selection criteria. A static seal, a piston seal, a wiper and a component for rotary movement require different materials and geometries.

For this reason, the question should not only be “which material resists this fluid?”, but “which combination of material, profile and groove or housing can maintain performance under the real operating conditions of the application?”.

When to evaluate a special material

The use of a high-performance material is justified when operating conditions exceed the limits of more common materials or when the cost of failure is particularly high.

However, automatically using FKM, FFKM, PEEK or other advanced materials does not guarantee a better solution. A more expensive material can introduce mechanical, installation or low-temperature behaviour issues.

Selection must therefore be proportionate to the application. In many cases, a correctly selected compound and a well-designed groove or housing provide better results than an oversized material used without a complete analysis.

Tecnonext’s approach to material selection

Tecnonext supports companies, technical departments and purchasing managers in selecting materials for seals and technical components.

The analysis starts from the actual operating conditions: fluid, temperature, pressure, movement, friction, groove or housing geometry, tolerances, required service life and sector requirements. This makes it possible to assess not only the theoretical compatibility of the material, but also its behaviour within the application.

Knowledge of elastomers, technopolymers and metallic materials makes it possible to identify solutions that are consistent with the required performance, avoiding both insufficient materials and excessively oversized choices.

For a technical discussion, an application assessment or to schedule a visit, contact

Tecnonext:

035 059 0010 

info@tecnonext.it 

Via Rudello, 11, 24067 Sarnico BG

FAQ – Materials for technical seals

What is the best material for a technical seal?

There is no single best material. The choice depends on fluid, temperature, pressure, movement, service life and application geometry.

When is it preferable to use an elastomer?

Elastomers are generally suitable when elasticity, adaptability to the groove or housing and the ability to maintain contact pressure are required.

When are PTFE or PEEK used?

PTFE and PEEK are evaluated when chemical resistance, dimensional stability, low friction or higher mechanical performance than elastomers are required.

When is a metal gasket necessary?

Metal gaskets are used mainly in applications with high pressures and temperatures, where elastomers and technopolymers may not be sufficient.