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The aerospace industry has some of the most exacting requirements for seals of any other industry.

In this blog post, we are going to take a closer look at the type of requirements for metal seals used in the aerospace industry, where they are used, and what types of materials are typically involved in metal seals used in the aerospace industry.

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Extreme Environments

Metal seals have proven their ability to perform in situations that involve extreme environmental conditions and safety critical applications. This includes temperatures ranging from cryogenic to extreme heat, either of which can destroy the majority of seals. Extreme pressure applicants, including vacuum conditions, are another type of situation where metal seals can outperform their counterparts. Special materials can be used when there will be exposure to aggressive or corrosive chemicals. This can include media that is notoriously hard to handle, such as:

  • air
  • steam
  • freons
  • certain oils and lubricants
  • fuel 

Besides the characteristics just discussed, there are other circumstances in aerospace applications where metal seals are preferred. For example, metal seals are well adapted to situations that involve absolutely no outgassing or extreme cleanliness where elastomers and polymers just will not work. They also work far better than polymers or elastomers in situations where there is a need for an extended shelf life – metal seals have a practically infinite shelf life. In general, they have a longer life in extreme conditions than comparable polymeric or elastomeric sealing solutions.  All of this combined is why we see metals seals preferred in many aerospace applications.

Aerospace Applications

Metal seals are found in many different aerospace applications. This includes:

  • probes and sensors
  • rocket fuel systems
  • hydraulic systems
  • MS standards

They are also used in connection with gas turbines, including the fuel systems and fuel nozzles, cooling air, bleed air, compressor sections, and turbine sections. The basic types of metal seals used in these types of applications include:

  • C-seals
  • E-seals
  • metallic lip seals
  • boss seals
  • face seals
  • custom designed seals
  • specialty seals

Other seals include brush seals, welded metal bellow seals, and circumferential segmented seals.

Seal Materials

Most high performance metal seals used in aerospace are made of superalloys such as Inconels, Hastelloys, or Waspaloy.  Materials such as these are preferred because of their resilience at extreme temperatures and extreme pressures, including fluctuations in both temperature and pressure.  Other materials include stainless steels, precipitation hardening steels, or titanium alloys. Seal surfaces may also be plated with materials such as lead, tin, indium, gold, silver or nickel.  

Conclusion

Metal seals are used in the aerospace industry for aggressive environments that polymeric and elastomeric seals simply cannot handle, such as extreme temperatures, extreme pressures (including vacuum pressures), cleanliness requirements, and no outgassing.  They also work well with difficult to handle fluids and gases including fuel, lubricants, and oils.  The most common types of seals used are C-seals, E-seals, and boss seals, as well as special purpose seals.  Materials typically include superalloys such as Inconel and Waspalloy, as well as some stainless steels and titanium alloys.

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