Elastomers are often the first choice for sealing and gasketing, but they’re not always the best. Silicone, neoprene, EPDM and Buna-N all have limitations that disqualify them from some applications. When that’s the case it may be time to consider PTFE seals.
Limitations of Elastomers
Elastomers are challenged by temperature extremes, aggressive chemicals and UV light. Some swell when in contact with oils, others outgas or give up molecules to the fluid being sealed against.
Food processing is a difficult environment. While it’s important to avoid product taint the materials must also endure aggressive cleaning regimens. Medical and pharmaceutical equipment presents similar challenges.
Many elastomeric materials harden in UV light, making them unsuitable for outdoor environments. Others will outgas, making them a bad choice for vacuum applications.
How PTFE Seals Score
PTFE is composed of carbon atoms bonded to fluorine. That makes it almost totally inert and a good choice for food, pharma and medical applications.
Less flexible than an elastomer, PTFE can nevertheless seal down to around -460°F. It’s also functional at temperatures as high as 570°F.
PTFE is unaffected by UV light, making it useful for outdoor applications or those involving UV sterilization. It has excellent electrical insulating properties and won’t swell when exposed to steam or oils. Another benefit from using PTFE seals in dynamic applications is a very low coefficient of friction.
PTFE Seals Limitations
Under load, especially at elevated temperatures, PTFE will creep. Joints should be designed to minimize the clamping forces applied directly to the material.
A second limitation is low strength. Some elastomers offer higher tensile strength combined with less elongation at breakage.
To address these issues PTFE formulators incorporate a range of fillers. Ranging from glass and carbon fiber to bronze and molybdenum disulfide, these can increase strength and hardness and reduce friction.
Seek specialist advice
When your sealing application challenges elastomeric materials it may be time to consider PTFE. However, with a large number of PTFE formulations available it’s difficult to know which is ideal. In such cases consult a materials specialist like those at Hennig Gasket.
