Foams for Low Clamping Force Seals
by Phil Taylor, Vice President of Sales

Adding a gasket to seal a device, whether it is keeping out dust, air, water, or something else, seems like it would be an easy part of a design. However, there are a multitude of material options available for most applications, and choosing the right one may require some research. The focus for this newsletter’s Engineering Corner is on one large subset of gasket material options: foams for low clamping force seals.

Below is a brief introduction to some of the features and benefits of each category of foam. When you have a particular gasket application in mind, your Marian sales representative would be more than happy to help you narrow down your options and provide samples.

• Silicone Foam
  • Maintains its flexibility across a wide temperature range (-50°C to 200°C).
  • Superior flame resistance; low flame, smoke, and toxicity upon combustion.
  • Resists environmental extremes like UV and ozone.
  • Resilient to mechanical fatigue.
  • Superior resistance to compression set and creep.
    
    
• High Density Microcellular Urethane
  • Excellent compression set resistance, which enables durable and long-term performance for gasketing and sealing.
  • Low outgassing and non-fogging features. Good resistance to many chemicals. Material does not become brittle and is non-corrosive to metal.
  • Performs well over broad temperature ranges (-40ºC to 90 ºC).
  • Flame retardant without the use of additives. Many materials meet flammability requirements of UL HBF and MVSS 302.
  • Broad range of formulas and thicknesses.
  • Thickness limitation of up to .500″.
    
    
• Closed Cell EPDM Sponge
  • Non-crystalline material. Contains no plasticizers that can migrate and lead to premature membrane failure.
  • Can be formulated in a variety of combinations with other polymer modifiers.
  • Performs well in the -40ºF to 175°F temperature range.
  • Used in many applications that require water, UV, ozone, or indirect sunlight resistance (superior to neoprene in this regard).
  • Does not meet UL flame rating without additives and will not withstand oil and fuels.
    
    
• Closed Cell Neoprene Sponge
  • Resists light oil contact, ozone, alkalis and acids.
  • Generally serviceable from -40°F to 158°F continuous and can withstand 200°F intermittently.
  • Good choice for general enclosure door gaskets.
    
    
• Closed Cell Sponge Blend
  • Produced from a blend of neoprene, EPDM, and SBR.
  • Serviceable down to -70°F without cracking due to cold embrittlement.
  • Normally meets UL94HF-1 flammability requirements.
  • Oil resistance not as good as 100% neoprene sponge products.
  • Good choice for general purpose sponge gaskets.
    
    
• Light Density Polyester or Polyether Urethane Sponge or Foam
  • Wide range of flexibility and rigidity.
  • Often used for insulation.
  • Thermoplastic polyurethane is commonly used in medical devices.
  • Flexible polyurethane is sometimes used in automotive interiors.
    
    
• XLPE or Cross-linked polyethylene
  • Closed-cell, inert, stable, and lightweight.
  • Low outgassing if punctured and compressed (the gas given off is air).
  • Decent barrier qualities: thermal insulation and water permeation.
  • Does not promote the growth of bacteria or fungus.
  • Exposure of XLPE to salt water will have little effect on its properties.
  • Cost-effective solution to many cushioning and sealing needs.
    
    
• PVC (Vinyl) Foam
  • Closed cell structure seals out air, moisture, light and dust when compressed at least 30%.
  • UV resistant and resists most chemicals, acids, and solvents.
  • Service temperature range of -40°F to 200°F.
  • Inherently fire resistant.
    

These categories barely scratch the surface of the differences between the many different foam options for low clamping force seals. For more guidance in determining a sponge or foam for your application, please contact your Marian sales representative!