Silicone is a very versatile elastomer that is used in numerous industries due to its superior physical and chemical properties, such as: excellent thermal resistance, higher longevity in hostile environment and flame retardancy [1]. These properties make silicone a desirable material for fuel systems, which unfortunately is not possible due to silicone’s limited fuel and oil resistance. However, this problem can be solved by substituting a small number of methyl groups in silicone (VMQ) with trifluorpropyl substituents, which results in fluorosilicone (FVMQ)[1].

The trifluoropropyl substituents enhance silicone’s chemical resistance to non-polar solvents, hydrocarbon fuels, oil, acids, and alkaline chemicals, making it a more ideal material for sealing in applications requiring resistance to hot fuels, oils and diesel based lubricants[2],[3]. This makes fluorosilicone a preferred material for static sealing and cushioning applications in aerospace, automotive and aviation industries [2].

 

Fluorosilicone is a Problem-Solving Material for Aviation Industry

Figure 1: Fluorosilicone is a Problem-Solving Material for Aviation Industry

 

Whilst it offers similar properties to silicone, there are several differences as shown in table below:

Unit Silicone[1] Fluorosilicone[4]
Hardness Range Shore A 3-90 30-85
Operating Temperature ℃ -50 to +250 -55 to +180
Tensile Strength N/mm2 5-12 8
Elongation at Break % 100-1,100 200%

 

As seen above, standard compound fluorosilicone has an operating temperature of up to 180℃. Due to this limitation, fluorosilicone is primarily used in fuel systems at temperatures up to 177℃[5]. However, there exists high-performance fluorosilicone that has a temperature range of -55℃ to 230℃[2]. It also has been reported that fluorosilicone could remain serviceable from -68℃ to 232℃, making it a fuel-resistant elastomer that is superior compared to fluorocarbon (FKM, such as Viton and Tecnoflon, poor low-temperature flexibility) and nitrile (NBR, heat resistance only up to 120℃)[2].

It is important to note that fluorosilicone is generally recommended for static applications only due to its relatively low tear strength, limited abrasion resistance and fair flex-cracking resistance [3],[5].

Fluorosilicone is usually used in the form of O-rings, gaskets, washers, diaphragms, and seals in fuel line connections, fuel control devices, electrical connectors, hydraulic line connectors, and fuel system access panels[6].

For more information and to keep updated with our research and development of fluorosilicone products, please do not hesitate to contact us.

 

References

  1. Wacker Chemie AG, ‘Solid and Liquid Silicone Rubber: Material and Processing Guidelines’. Wacker Chemie AG, n.d.
  2. Stockwell Elastomerics, ‘Fluorosilicone / Fluorosilicone Rubber’, Stockwell Elastomerics, Inc., n.d. https://www.stockwell.com/fluorosilicone/ accessed 11th September 2019
  3. Polymerdatabase, ‘ FVMQ – Fluorosilicone Rubber(Fluorovinylmethulsiloxane Rubber’. Polymer Properties Database, 2015. http://polymerdatabase.com/Elastomers/FVMQ.html, accessed 10th September 2019
  4. Infinity Seal, ‘Fluorsilicone [FVQM]’ Infinity Seal, 2015. https://infinityseal.com/wp-content/uploads/2015/05/fsilicone.pdf accessed 10th September 2019
  5. Eriks, ‘FVMQ’ https://o-ring.info/en/materials/fluorsilicone-fvmq/ accessed 10th September 2019.
  6. Bhuvaneswari, et. al., ‘Evaluation of Fluorosilicone – Silicone Elastomer Blend for Aeronautical Fuel System’. 2014 http://www.polymerjournals.com/pdfdownload/1204301.pdf accessed 11th September 2019