PTFE Encapsulated O-Rings
A PTFE Encapsulated o-ring is a circular shaped seal with a round cross section consisting of two components, a PTFE jacket and an internal (core) energizer, which imparts memory to the seal. The encapsulated O-ring is intended to close off potential leak paths between mating surfaces in both static and dynamic applications.
Encapsulated O-rings are offered in two PTFE grades, FEP and PFA with a selection of three different energizers which give the user a choice depending on temperature and operating environment.
PTFE grades
FEP- The most versatile when considering overall corrosion resistance, sealing capability and temperature. Temperature range -450°F to +400°F (-267°C to 205°C).
PFA- A fluorocarbon copolymer similar to FEP but it also offers greatly improved mechanical and creep properties at elevated operating temperatures. Temperature range -450°F to + 500°F (-267°C to +260°C).
Features- When considering the encapsulated concept, one should take into account the many features which FEP and PFA.
PTFE Have to Offer:
| Corrosion resistance | No swelling | Broad temperature range |
| Abrasion resistance | Reusable | Good dialectic properties |
| Non-flammable | Permeation resistance | Flexibility |
| Good impact strength | Ultra low moisture absorption | Low coefficient of friction |
| Excellent resilience | Uniformity | Low cold flow |
| Lubricity |
The United States Federal Food and Drug Administration have published amendment 21 CFR 177.1550 which permits the use of FEP and PFA as articles or components of articles intended for use in contact with food. There is no general approval for use of these grades in medical applications.
CORE MATERIALS
The core material is the component which imparts “life’ or ‘memory’ to the encapsulated O-ring when it is subjected to compressive force.
VITON®
A fluoroelastomer compound with a combination of exceptional mechanical properties and compression set resistance. This particular energizer gives an O-ring excellent memory and the ability to recover rapidly from deformation. This core has a Shore A hardness of 75 with a suggested operating temperature range of -10°F to +300°F (-23°C to +150°C) in encapsulated applications.
SILICONE
This elastomer possesses mechanical properties similar to Viton®, with the exception of its slightly lower compression set resistance. It is more suitable for sensitive applications where lighter compressive forces are applied to energize the seal. This core has a Shore A hardness of 70 but it also offers a broader operating temperature range of -80°F to +500°F. (-62°C to +260°C).
ASTRA SEAL
The spring energizer, made from precision rolled stainless high strength steel gives a very high compression set resistance. The stainless spring core maintains its resilience during in long term exposure to cryogenic temperatures -420°F to +500°F (-250°C to +260°C). It offers superior sealing characteristics in face seal applications, especially in liquid oxygen and hydrogen service.
HOLLOW CORE
Hollow core O-rings provide effective sealing properties in applications where lower compressive forces may limit sealing ability of our standard O-rings. The combination of a hollow core insert with a slightly lower hardness offers a more flexible, easier to squeeze O-ring requiring less energy to activate its sealing capability.
Note: Hollow core energizers are available in a limited size range. Please contact Monroe Seals for specific details.
Encapsulated Materials Chart
| Comparison of Properties | FEP 160 | PFA |
| Excellent Resiliency | 1 | 1 |
| Corrosion Resistance | 1 | 1 |
| Mechanical Properties of Elevated Temp | 2 | 1 |
| Dielectric Properties | 1 | 1 |
| Flexibility | 1 | 1 |
| Low Moisture Absorption | 2 | 2 |
| Permeation Resistance | 2 | 2 |
| Cold Flow | 4 | 3 |
| Non-stick Characteristics | 1 | 1 |
| Low coefficient of friction | 1 | 1 |
| Abrasion Resistance | 3 | 3 |
| Operating Temperature Range | 2 | 1 |
| Impact Strength | 3 | 2 |
| Non-flammability | 1 | 1 |
| F.D.A. Approval | yes | yes |
| Shore Durometer (D) | 55 | 60 |
| Temperature High F | 400 | 500 |
| Temperature Low L | -400 | -400 |
1 = excellent 2 = good 3 = fair 4 = poor
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