Flexible Gasket Material Temperature Ranges. High Low and Fluctuating Temperatures.
Understanding the effect of operating temperature on flexible gasket materials.
If you have a technical question about the temperature ranges of gaskets or gasket materials, then please contact us for expert help and advice. What follows is offered as a general guide only. There is a huge range of operating temperatures that flat and flexible gaskets are required to perform within, which are as diverse as the different environments in which they are used. Whilst the temperature range of some materials is broad we can narrow down specific materials for different temperature environments.
This article covers:: An overview of gasket materials and average temperature ranges. | Which specific gasket materials are required for high temperature environments. | What happens when gaskets are exposed to extreme high and low temperatures. | How gasket materials are currently rated and tested for different temperatures. | Which sectors most commonly utilise which materials.
Many solid rubbers will work in a temperature of up to +120⁰C. Silicone and viton rubbers can be used up to +300⁰C. As the pressure increases then the CNAF (Compressed Non-Asbestos Fibre) materials will work well up to +450⁰C. Some flexible rubbers can function in continuous temperatures of up to +300⁰C such as a high temperature silicone, however higher temperatures will require ceramic, mica and clay based materials that can be used between +500⁰C and +1200⁰C.
Once you have reached a continuous upper temperature of approximately +500⁰C the flexible aspect of a gasket is compromised. The use of metals and compressible graphite are then used to create a seal using materials such as graphite sheeting (graphite can be used up to 800⁰C in a non-oxidising atmosphere) or spiral wound gaskets and ring type joints.
Selecting the right gasket material is critical for a reliable joint and effective operation.
Average Temperature Range Chart For Gasket Materials
The chart below will help you to determine which material has the best possible chance of sustaining your temperature range within your environment. Please also consider the chemicals and pressure that the material will be subject to when in use, as this is of equal importance to choosing the material for a reliable seal.
Average Temperature Ranges By Gasket Material Type*
|Material Type||Average Temperature Range|
|Cork||-25⁰C / +135⁰C|
|EPDM Rubber||-40⁰C / +120⁰C|
|EPDM Foam Rubber||-40⁰C / +70⁰C|
|Insertion Rubber||-20⁰C / +70⁰C|
|Natural Rubber||-60⁰C / +220⁰C|
|Styrene Butadiene (SBR)||-50⁰C / + 212⁰C|
|CNAF (Non-asbestos)||-100⁰C / +400⁰C|
|Neoprene Rubber||-30⁰C / + 120⁰C|
|Neoprene Foam Rubber||-40⁰C / + 85⁰C|
|Nitrile Rubber||-20⁰C / + 108⁰C|
|Gasket Paper||-20⁰C / +120⁰C|
|Plastic Shim||-70⁰C / +130⁰C|
|Silicone Rubber||-60⁰C / +300⁰C|
|Silicone Foam Rubber||-60⁰C / +300⁰C|
|Viton Rubber||-25⁰C / +250⁰C|
|Viton Foam Rubber||-25⁰C / +200⁰C|
|Mica (vermiculite)||Excess of +1000⁰C|
|Flexible Graphite||-240⁰C up to +1000⁰C (non-oxidised environment only).|
|PTFE||-73⁰C / + 204⁰C|
*Each material has many different grades and variants this is a general overview of the average temperature ranges of each material type.
What Happens When Gaskets Are Exposed To Extreme High And Low Temperatures?
Rubber properties are strongly temperature dependant.
Low Temperatures – When rubber is exposed to low temperatures the material changes from rubber-like entropy-elastic to stiff energy-elastic behaviour. This means that the rubber gets very brittle and can crack at low temperatures. Rubbers are generally used above a rigid glass state but the minimum temperature limit is not defined precisely. In the glass state the material cannot recover the elastic deformation required for a seal and the sealing capability is compromised: the gasket is highly susceptible to cracking and leaking. The datasheets of each individual material gives the upper and lower temperatures for each type of polymer.
High Temperatures when exposed to extreme high temperatures rubber gaskets are flammable and will ignite. In long term high heat rubber gaskets can shrink, melt, and de-form. You need to use a gasket suitable to your environment. If the heat is very high (above +500⁰C) a gasket that does not contain rubber such as a graphite or mica is the best option. You would have less compression using graphite or mica gaskets as they are rigid in nature (than a rubber or other compressible polymer). Other alternatives in high temperature (above +500⁰C) are spiral wound gaskets especially when combined with a high pressure environment. A spiral wound contains a spirally wound graphite/other filler within the spirally wound compression ring and a stainless or carbon steel outer ring to hold pressure within the flange, when the flange is tightened the graphite spirally wound section compresses creating a seal. Graphite can oxidise at temperatures of above +600⁰C, in this respect mica or thermiculite as the compressible filler within the spirally wound section is used. Thermiculite does not oxidise.
What Gasket Materials Are Required For High Temperature Environments? (Above 500⁰C)
Combustion environments, waste gas and engine environments are the most common high temperature environments, where temperatures are often in excess of 500⁰C.
Gasket Materials Most Resistant to High Temperatures
Gasket materials resistant to rapid thermal degradation are non-asbestos mica reinforced materials with a stainless steel insert. Aramid fibre with nitrile rubber binder with a tanged metallic insert, which is normally stainless or carbon steel. Thermiculite® is rated from cryogenic to 1000⁰C and unlike graphite it is free from oxidisation. Other materials to consider are Firefly (a clay based material), mica hi-temp and Thermiculite®. For more information, please contact RAM directly with your requirement and we can advise.
Which Gasket Material Has The Biggest Temperature Range
The gasket material with the biggest temperature range is Thermiculite. Thermiculite has the biggest overall range of any slightly flexible gasket material from below -150⁰C to + 1000⁰C. It is available in sheet form, within a Kammprofile, as the filler in a spiral wound and within a ring type joint. Applications for the highest temperature rated and tested gasket materials are most often used within the following sectors: aerospace, oil exploration, petro chemicals, industrial chemicals, fertilisers, oem and oil and gas, where process conditions are extreme.
How Are Gasket Materials Rated And Tested For Temperature And Fire Safety
Currently the main specific safety ratings for materials used for gaskets and seals in high temperature environments are in relation to flame retardency for consumer/environment safety. The main governing bodies and requested standards for related material are governed by:
ISO International Standards Organisation a European Group bringing together European standards. Incorporating the continuing and historical work of the BSI Group and Germanys VDMA the German Engineering Federation.
BSI Group – British Standard Institution -have since 1901 covered UK standards, initially within engineering the BSI group is now operating in 172 countries and manages standards and certification to ensure standard quality and manufacture of parts and products across many sectors.
JIS Japanese standards Japanese Industrial Standards specifies the standards used for industrial activities in Japan. Products are manufactured under a JIS mark which is the industrial Standardisation Law for manufacture in Japan. Formally JES since 2004 the law has been revised and now all Japanese products since October 2008 that are made by certified companies will bear the JIS mark.
ASTM American Society for Testing and Materials – an international standards organisation that develops and publishes voluntary consensus technical standards for a wide range of materials, products, systems and services.
UL Underwriters Laboratories – is an American worldwide safety consulting and certification company. Providing safety-related certification, validation, testing, inspection, auditing and advising.
Do Gaskets Have To Comply With Certain Specifications For Temperature?
Gaskets have to comply with specifications when the complete unit has to undergo testing. If the product you are making has to conform to certain legislation the test requirements will be stipulated under consumer/manufacturing law for the specific country. Most commonly this will be a UL rating if USA sales are expected. Many European and American products for consumer sale will be required to conform to certain safety testing. In this instance the use of specific UL rated materials will be required.
Heat ageing of the rubber is a precursor to many rubber tests, ASTM D573, ASTM D 1056, UL50, UL48, UL508 and UL 157 all have heat ageing requirements.
UL94 – The main flammability test for rubber materials is UL94. If you are producing consumer, residential and commercial products UL94 is the test rating required. UL94 consists of 6 different flame tests divided into 2 categories, vertical and horizontal. All methods involve the use of standard specimen size, a controlled heat source and a conditioning period prior to the test.
Other specific UL94 ratings we make bespoke Gaskets for include: UL 94V-0, UL94V-1, UL94HBF, UL94HF-1.
FAR 25.853 -is a flame test for aircraft interiors. Any areas of the interior compartments occupied by crew or passengers. Materials must be self-extinguishing under a vertical burn test.
We supply UL rated materials in the form of silicone, silicone foam, neoprene, neoprene foam and poron (urethane). Silicones with FAR 25.853 include HT-800 which is stocked as a foam and a solid, in sheet and strip form.
A List Of Gasket Materials That Are Most Commonly Used By Sector:
Oil and Gas Generally this industry will utilise spiral wounds, ring type joints, Kammprofile gaskets, non-asbestos material including brand names Klinger and Flexitallic (previously called Novus). Composite materials including mica and graphite, all these materials are utilised in high temperature, high pressure environments.
Automotive This industry will generally utilise silicone as a high temperature polymer that can be supplied in O-ring, sheet and liquid form. Nitrile and viton that are fuel and oil resistant are other often used polymers. EPDM is commonly used for door seals and plastic foams are used for seat fillers. Within the combustion areas of the engines, graphite and non-asbestos (including brand names Flexitallic and Klinger) materials will be used, these are resistant to fuels and oils combined with high temperatures (approx. +350⁰C). Finally, a cork composite material, often natural cork blended with nitrile can be used as a cheaper alternative to pure nitrile rubber. Classic cars now use a range of modern materials since asbestos is no longer allowed as a fibre within gasket formulations.
Aerospace This industry will utilise many different gasket materials. The certification requirements that need to be supplied along with the gaskets are often the most critical aspect within Aerospace. Products supplied in this area are supported by Certificates of Conformity, including batch and cure dates with full traceability. Supply chain, and specific standards like RR SABRE can be met by RAM when producing gaskets for the Aerospace industry.
Food Processing – Temperature limits in food production are also required to be taste and taint free. Silicone is most often utilised in this environment as a stable high-temperature polymer that also inhibits bacterial growth. For steam and high pressure environments non-asbestos material and graphite is required. EPDM is used in potable water applications which has great UV and environmental resistance over a number of years and seals effectively. PTFE with low co-efficient friction and excellent chemical resistance is used as an envelope to line flange gaskets made from rubber or non-asbestos.
Drinking Water/Water – Potable water in the UK often requires WRAS approval (Water Regulations Advisory Scheme). WRAS approved EPDM is stocked by RAM in the form of sheet, O-rings, and cord. Other weather seal materials that have very good UV resistance are EPDM, neoprene, non-asbestos and graphite will be used when steam is present along with higher pressures.
Electrical Enclosure gaskets require weather seals, UV resistance and general weather fluctuations and conditions mean an effective seal is required against weather elements. Neoprene, EPDM, nitrile foams and rubbers are used here. For conductive gasket materials and EMEI shielding products conductive foam can be used, wired silicone (solid/foam) and branded composite gasket materials can be supplied. Plastic shim is also used as a spacing and insulating material within the electrical industry. Gaskets can be selected to help meet IP tests. The test applies to the assembly not the gasket itself.
Petrochemical Flange Gaskets within this industry are often made with non-asbestos gasket material, including brands such as Flexitallic and Klinger. For higher pressure spiral wounds, Kammprofile, mica and graphite are used. Quality and safety in a volatile environment is paramount. Fuel, oil and corrosion resistant high grade rubbers such as nitrile, viton, silicone and PTFE in foam and solid form are also used. The quality of the rubber in high corrosion environments is very important. Correct supply of quality materials ensures an effective seal. PTFE as a low co-efficient friction material with excellent chemical resistance is supplied as envelopes for pipe flange gaskets, in sheet form or foamed to create a compressible material for sealing uneven flange faces.
Pharmaceutical Silicone rubber is often used within pharmaceutical environments. Platinum and peroxide curing of silicone for medical grade applications are often required. RAM can cut cured materials in a clean environment. For flange gaskets and equipment seals PTFE is used in the form of envelopes as a low bacterial growth, clean liner to pipe gaskets. Envelopes were developed as a cheaper alternative to solid PTFE for flange gaskets. Solid PTFE and foamed PTFE in the form of Softchem or other brand names are used when a compressible PTFE is required. Expanded PTFE is often used for sealing uneven flanges against very aggressive chemicals. Modified PTFEs are available for special environments that enhance the capabilities of PTFE.
Pumping Plastic shim is commonly used for pneumatic air compressors, boosters and vacuum pumps. Plastic shim provides good corrosion resistance and low co-efficient friction. EPDM and neoprene are used for pipe gaskets. When corrosive liquids are being used nitrile, viton, PTFE and Non-asbestos can also be used.
Rail For enclosures and components within internal public spaces a FAR 25.853 approval as discussed above may be required. Silicone, EPDM, nitrile can be supplied in solid or foam form. Manway gaskets in non-asbestos, viton and EPDM to seal against fuel, oil and water are most commonly utilised.