Sealing Materials, and Elastomers: An Overview
|
|
Elastomers as sealing materials constitute various materials for specific seals and applications in sealing technology. Elastomers are dimensionally stable and elastically deformable plastics. A prime example is rubber bands. They are dimensionally stable yet possess elastic properties and tensile stress with an entropic effect (entropy elasticity). Similar to thermosets, elastomers are interconnected through covalent bonds between individual molecular chains (macromolecules). This rubber elasticity occurs as the tangled polymer chains respond to tensile stress by stretching or untangling. Also see our materials for seals and gaskets.
Seals are an indispensable part of our lives. Without them, there would be no running water, no power plants, and no cars. Given the diverse possible applications for seals, there are numerous materials for seals, each coming with many advantages and some disadvantages. Therefore, at Kofler - Dichtungen, we also offer special seals and custom-made seals and gaskets. As a manufacturer of seals, you will find in our section an overview of the most important sealing materials, their advantages and disadvantages, and their optimal applications.
Working materials - What are the advantages of different sealing materials?
The possible areas of application and requirement profiles for seals and their different materials or sealing materials are numerous:
flat gaskets and seals for aqueous goods to be transported, oils or gases; profile seals made of silicone, for example, must withstand many deformations elastically every day in door frames, dynamic seals in hydraulic cylinder systems (e.g. piston seals, rod seals) must withstand high pressures, temperatures, and the various hydraulic media. (Also read – What are hydraulic seals?)
That is why many different materials are used as sealing material. Thus, the optimal material can be advantageously used for practically every field of application, while the disadvantages are not significant.
Elastomer - The most important sealing materials at a glance
Today, there are numerous materials (Wikipedia - elastomer, elastomers) that can be used as sealing material. Thanks to modern manufacturing processes, the properties can even be fine-tuned within a material class.
Now we will show you the advantages and disadvantages of these materials and where they can be used.
NBR Gaskets and Seals - Acrylonitrile Butadiene Rubber
NBR stands for Nitrile Butadiene Rubber. It is synthesized through a chemical reaction between acrylonitrile and butadiene, followed by either thermal or chemical vulcanization.
NBR seals and gaskets exhibit exceptional mechanical resistance. Depending on the content of nitrile, NBR is compatible to a good or very good degree with low-aromatic hydrocarbons, oils, and fats. This makes it an ideal choice for fuel lines and seals that come into contact with oil, such as hydraulic seals, radial shaft seals, and Simmerring seals.
NBR has moderate stability against hot acids and bases.
Viton® seals, FKM, FPM
Unfortunately, there are often uncertainties with fluoroelastomers, as the names have changed. FKM is the designation for fluoroelastomers according to the US standard ASTM. The abbreviation FPM was used in DIN/ISO. Viton® is the trade name of a fluoroelastomer from DuPont. Generally, FKM is produced from fluorocarbons with subsequent crosslinking (similar to vulcanization).
FKM is very resistant to aggressive chemicals, mineral oil, gasoline, diesel, alcohol, and withstands high temperatures. FKM has a significantly higher density than other elastomer materials.
EPDM Seals and Gasket - Ethylene Propylene Diene Rubber
The abbreviation EPDM stands for ethylene propylene diene monomer rubber. In general, a distinction is made between natural rubber and synthetic rubber. EPDM is a synthetic rubber, i.e. an artificial rubber. This rubber technology is produced by the chemical reaction of three components, with subsequent vulcanization. Additives such as carbon, calcium carbonate or pigments are used in the production to ensure the fine adjustment of the material properties and the colour.
Due to its chemical nature, EPDM is very stable to polar substances such as water or alcohols such as glycol, acid, alkali, heat, UV radiation and remains soft and elastic up to -40°C (-40°F). EPDM is poorly compatible with non-polar substances such as mineral oil, petrol, diesel, kerosene and halogen-containing solvents.
Silicone seals: WMD/VMQ
Silicone rubber, colloquially known as "silicone," is created through crosslinking reactions from specific silicone oils, a process very similar to vulcanization. There are various manufacturing methods classified according to the number of components and the application temperature.
The most well-known technique involves one-component crosslinking at room temperature, commonly used in standard household silicone sealants. For sealing technology, especially for applications such as O-rings, high-performance materials are often produced using a more complex process with multiple components at elevated temperatures.
Silicone seals are particularly utilized where performance at low or high temperatures (under -50°C up to 200°C or -58°F up to 392°F) is needed, including excellent electrical insulation properties, ozone resistance, and UV radiation resistance. Additionally, silicone as a material is physiologically safe, making it suitable for medical applications and food processing.
However, silicone is incompatible with acids, alkalis, oils, and fuels. It is also not suitable for mechanical stresses
FFKM Seals and Gasket – Perfluoroelastomer
FFKM seals and gaskets consist of perfluoroelastomers, which have an even higher fluorine content than FKM. It is made from at least three raw materials: tetrafluoroethylene (raw material for PTFE (Teflon)production), a perfluoro ether (improves elasticity) and a cross-linkable component that allows final vulcanization. FFKM is therefore like elastic Teflon.
FFKM is an absolute high-performance material that can fully exploit its advantages in extreme conditions. It can withstand aggressive chemicals and oxygen plasma and is suitable for continuous use above 300°C (572°F). The production of seals and gaskets from FFKM is expensive, so this material is only used in high-tech systems, or if a seal defect would be associated with very high costs and damage.
PTFE: Polytetrafluoroethylene, Teflon
Polytetrafluoroethylene, widely known as "Teflon," is an extremely versatile material. Its unique chemical composition makes it a distinctive type of plastic.
Teflon is utilized specifically when high self-lubrication and chemical resistance are demanded. It lacks any adhesive qualities and boasts very low friction values. Another notable feature is that static and dynamic friction are equal, allowing it to start moving or stop without jerking.
Its chemical resistance spans almost all chemicals, including hydraulic fluids, acids, alkalis, and hot water, and it is non-flammable. PTFE is particularly prevalent in the food industry due to its inert nature, ensuring it does not transfer to the processed goods
However, Teflon is relatively sensitive to mechanical stresses such as lateral forces and compression.
|
|
|
|
