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Formed-in-Place Gaskets vs. Conventional Compression Gaskets

Compression gaskets are pre-formed to a specific size, shape, and thickness. Formed-in-place (FIP) gaskets or liquid gaskets are liquids that cure after the parts are assembled. Both have their uses, and one may be more suitable than the other depending on the application.

Compression gaskets are made from a variety of materials including cork, rubber, and synthetic blends. Formed in Place or FIP gaskets are either anaerobic adhesives or room temperature vulcanizing silicone. Again, the choice between an anaerobic adhesive or an RTV silicone will depend on the application.

The use of pre-formed conventional compression gaskets is widespread and is normally the first port of call for a customer looking for an instant pressure seal.

Formed-in-place liquid gaskets are increasingly used to reduce inventory of various size and shape gaskets and to increase seal strength.
The advantages of formed-in-place gaskets over compression gaskets include:

  1. Improved reliability
    • If metal surfaces are damaged or scratched, adhesive will flow into the gap and prevent leakage
    • Allows true “metal to metal” designs
    • Reduces compression set and fastener loosening
    • Anaerobic adhesives add structural strength to the assembly
  2. Reduced costs
    • Machining tolerances can be relaxed
    • No need to store gaskets in all shapes and sizes – reduced inventory
    • Can be applied automatically so ideal on a production line
    • Eliminate bolt retorquing – lower servicing costs
  3. Easier Application
    • Single component – no mixing
    • Easy to automate
    • Rapid curing and certain products give instant low-pressure sealing before full cure
  4. Easier service
    • Formed-in-place gaskets allow easier disassembly and clean-up than compression gaskets
    • One package can be used in multiple flange size

Benefits of anaerobic gaskets over traditional sealing systems include:

  1. No gasket relaxation (so future retightening is not required, therefore reducing servicing costs)
  2. Non-shimming
  3. Structural strength
  4. Excess material remains liquid (so it can be easily cleaned or flushed through the system)
  5. The surface finish of metal components needn’t be “mirror finish,” scratches and imperfections are catered for
  6. No cure before assembly
  7. Reduced inventory costs
  8. Chemical compatibility
  9. Ideal for heavy-handed people that have problems handling pre-formed gaskets without damaging them!

Anaerobic adhesives do not offer gasketing solutions for all applications. Limitations include use on applications which require temperature resistance above 200°C. Anaerobic adhesives are also not recommended for applications in which large gap fill is required. For applications requiring temperature resistance over 200°C or where gap fill requirements are greater than 0.5mm, silicone gaskets may be preferred.

Benefits of Silicone formed-in-place liquid gaskets include:

  1. Ideal for sealing large gaps
  2. Highly flexible, so they flex with flange movement
  3. Can cope with scratched, damaged or pitted metal surfaces
  4. Reduced inventory costs, again there is no requirement to have a large stock of various shapes and sizes of pre-formed gasket
  5. Temperature range of between -70°C to 315°C for most; some achieve nearly 350°C!
  6. Good adhesion to a wide variety of metals

Limitation of Silicone “formed-in-place” liquid gaskets

  1. Poor resistance to fuel and aromatic solvents
  2. Not recommended for high-pressure applications due to their high elongation, low shear, and low tensile strength.
  3. Relatively slow cure speed

There is no single answer that is correct for all requirements or all applications. Understanding the limitations and benefits of each method allows the best selection for the application.

For further help and advice, please contact Permabond.