PTFE Spring Energized Seals for Cryogenic Applications
by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

Designing Spring-Energized Seals for Cryogenic Hydrogen Systems

Cryogenic hydrogen systems are among the most challenging to specify reliable sealing solutions for, with issues ranging from the extremely low temperatures to hydrogen permeability and embrittlement. 

This blog post explores the challenges and proposes a proven solution: PTFE spring-energized seals. And discusses how Advanced EMC can help.

Challenges of Sealing in Cryogenic Hydrogen Systems

There are several key problems that arise when specifying a sealing solution for a cryogenic hydrogen application. Four of these are discussed below.

Extremely Low Temperatures

The first issue with sealing cryogenic hydrogen is the temperature. On average, hydrogen is stored and transported at about  253 °C. At such low temperatures, conventional elastomers will lose elasticity, shrink, and possibly crack. In addition, thermal contraction will cause the seal contact pressure to drop. And just because a seal is predicted to work at room temperature, it will fail disastrously when the temperatures drop to H2 storage temperature. 

Hydrogen Permeability and Leakage Risks

Hydrogen is extremely small, with diatomic hydrogen being the smallest molecule in the known universe. This small molecular size means that  H2 can diffuse through many different materials. The resulting permeability leads to serious risks of leakage or even explosive decompression during warm-up cycles. Resolution of these issues includes sealing solutions with exceptionally high tolerance, with a seal lip material that maintains integrity even at the molecular level.

Hydrogen Embrittlement

Hydrogen embrittlement is a problem for many materials. In short, hydrogen can diffuse into metal components and make them increasingly brittle over time. This embrittlement leads to cracked metal seal housings. 

Material Compatibility

Many conventional seal materials will become unsuitable when cryogenic temperatures are reached. Examples include thermal expansion mismatches between components and a loss of flexibility, which are among the top problems. Material selection quickly becomes limited to options such as PTFE and certain fluoroelastomers because only a handful of materials can retain their flexibility, dimensional stability, and roughness at the temperatures required for handling H2.

Spring Energized PTFE Seal

Spring-Energized Seals for Cryogenic Hydrogen Systems

Spring-energized seals are advanced solutions composed of a polymer seal jacket with an internal metallic spring energizer. Because of the spring energizer, a consistent sealing force can be achieved even in the presence of issues such as dimensional shifts and contraction. 

A properly designed spring-energized seal can effectively maintain a seal in liquid H2 environments. Such a seal can handle pressure cycling and dimensional changes, and reduces friction and wear compared to conventional seals.

Here’s a summary of how a spring-energized seal with a PTFE / filled PTFE jacket addresses the challenges described thus far:

ChallengeProblemPTFE Cryogenic Seal Advantage
Low TemperaturesElastomers shrink, crack, and lose sealing force at –253 °C.PTFE stays flexible and dimensionally stable with low thermal contraction.
Hydrogen PermeabilityH₂ diffuses through many materials, causing leakage or decompression.PTFE has low gas permeability; spring-energized lips maintain tight contact.
Hydrogen EmbrittlementMetals become brittle and crack under hydrogen exposure.PTFE is immune to embrittlement and protects surrounding components.
Material CompatibilityMost materials fail due to brittleness or expansion mismatch.PTFE retains flexibility, stability, and chemical resistance at cryogenic temperatures.

Advanced EMC Spring-Energized Seals

At Advanced EMC, we specialize in PTFE spring-energized seals. We offer cryogenic-rated PTFE jackets that use corrosion-resistant metal allows, such as Hastelloy or Inconel, for the enclosed energizers. Precision engineering and manufacturing mean optimized hacket profiles for containing H2 and machining as needed to achieve an extended service life. We have developed sealing solutions for various industries, and offer tailored spring force, geometry, and material properties for spring-energized solutions.

Conclusion

Sealing cryogenic liquid H2 involves major challenges. The extremely low temperatures, hydrogen permeability, hydrogen embrittlement, and material compatibility all lead to problems that conventional sealing solutions do not address well.  Spring-energized PTFE seals, however, address these issues and more for a robust, rugged, and reliable solution.

Advanced EMC’s expertise ensures seals that meet the unique demands of cryogenic hydrogen systems, enabling safe, efficient use of hydrogen in advanced energy applications. Contact us today to learn more!

Spring Loaded Seal
by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

Self-Lubricating Polymer Bearings in Maintenance-Free Design

Self-lubricating polymer bearings are an excellent alternative to traditional bearings when design engineers are looking to reduce the need for routine service, extend uptime, and improve the reliability of their products. These bearings may be naturally self-lubricating or include solid lubricants in the polymer to achieve low-friction motion without the need for oil or grease. 

In this blog post, we talk about how these bearings support maintenance-free designs, the advantages of using them, and the key considerations for their design.

The Cost of Downtime in Modern Equipment

Downtime is a significant problem in nearly every industry, from manufacturing to aerospace to robotics. Many of the outages experienced by equipment in these industries can be traced back to bearings, and further to lubrication issues, contamination, or lack of maintenance.

Traditional plane bearings rely on either manual greasing or centralized lubrication systems to maintain low friction and prevent wear. Such systems add complexity, require regular attention, and are susceptible to failures. However, in a maintenance-free design, these weak points can be eliminated through the use of self-lubricating polymer bearings. These bearings are inherently resistant to contamination, unaffected by lubrication schedule errors, and capable of operating for years without intervention.

How Self-Lubricating Polymer Bearings Support Maintenance-Free Design

The key to the self-lubricating performance of polymer bearings such as filled PTFE and PEEK lies in the material structure. Solid lubricants such as PTFE, graphite, or molybdenum disulfide (MoS₂) are dispersed uniformly throughout a polymer matrix. During operation, microscopic particles of these lubricants are transferred to the shaft or mating surface. This forms a continuous, low-friction film, reducing direct surface-to-surface contact, keeping operating torque low, minimizing wear, and eliminating the need for lubricants like oil or grease.

Unlike conventional lubrication, there is no dependence on things such as oil viscosity, pump function, or lubricant replenishment. Self-lubrication is self-sustaining. Lubrication is always present, even at startup, in stop-and-go motion, or during oscillating loads. This approach to lubrication makes it particularly valuable for high-speed equipment, equipment that runs 24/7, precision actuators, and\ enclosed systems where regular access for lubrication is difficult or impossible.

Advantages of Maintenance-Free Design with Self-Lubricating Bearings

Let us look at some of the advantages of maintenance-free design, especially as it applies to self-lubricating polymer bearings.

Reduced Maintenance Intervals

By eliminating the need for external lubrication, self-lubricating engineering polymers have the potential to significantly extend equipment service schedules. This, in turn, reduces the number of planned maintenance stops and minimizes the likelihood of lubrication-related failures. The result is more equipment with more consistent productivity and far less unplanned downtime. Furthermore, in remote or hazardous environments, such advantages can be critical. Gaining access for maintenance might be expensive, put technicians in danger, or be extremely difficult to achieve. Maintenance-free design can minimize or completely eliminate those challenges.

Improved Cleanliness

Leaks or aerosolized mists (which are often prevalent in high-speed applications) are a problem with traditional bearings. Small amounts of grease or oil lubrication can cause contamination, leading to a reduction in product quality or safety for areas such as food processing, medical devices, and electronics assembly.

Self-lubricating polymer bearings, however, avoid these issues entirely. When solid lubricants are embedded in the material, the polymer bearings are able to maintain smooth operation without producing or spreading liquid lubricants. This results in a cleaner, safer operating environment that meets strict regulatory and quality standards.

Corrosion Resistance

Metal bearings can experience rust, seizing, or surface degradation, but self-lubricating, polymer bearings maintain their performance over time. This corrosion resistance reduces the need for protective coatings, seals, or other corrosion-prevention measures, simplifying both design and maintenance.

Engineering polymers such as filled PTFE or PEEK exhibit excellent resistance to water, aggressive chemicals, and potentially corrosive agents. This chemical stability makes them an excellent choice for use in wet, chemically aggressive, or outdoor environments.

Consistent Performance

One of the performance benefits of self-lubricating polymer bearings is their ability to maintain stable friction coefficients across a range of operating temperatures. Self-lubricating bearings can deliver highly predictable torque and very smooth motion when under sustained high temperatures or cold running.

Such stability is maintained through repeated thermal cycles that often lead to the failure of metal bearings, including expansion and contraction or a change in the viscosity of the lubricants.

Considerations for Maintenance-Free Bearing Design

Here is a short summary of key design considerations when aiming for maintenance-free design using self-lubricating polymer designs..

Design FactorKey Details
Load and PV limitsEach polymer formulation has a defined pressure–velocity (PV) limit that must be respected to avoid premature wear. Virgin PTFE, for example, typically supports continuous PV ratings of 1,000–3,000 psi·ft/min, while filled PTFE can reach 4,000–10,000+ psi·ft/min.
Thermal expansion managementPolymers such as PTFE have a higher coefficient of thermal expansion than metals, which can impact bearing clearance. Designers should select an appropriate fit—press, interference, or adhesive bonding—based on expected thermal cycling and load conditions.
Shaft surface requirementsShaft finish directly affects transfer film formation. Experts usually recommend an Ra of 8–16 µin (0.2–0.4 µm) with a hardness of at least 55–60 HRC to prevent wear. 
Environmental factorsExposure to dust, moisture, chemicals, and temperature extremes should be considered when selecting polymer type and fillers. Hybrid formulations can combine multiple performance traits such as high load capacity, chemical resistance, and low wear.

Conclusion

Every maintenance task carries a cost that is not just in labor, but in production delays and lost opportunity. Self-lubricating polymer bearings support the goals of maintenance-free design by eliminating the need for lubrication and eliminating a major source of equipment failure. As industries continue to push for higher uptime and lower operating costs, integrating self-lubricating polymer bearings early in the design process can deliver significant benefits in reliability and performance.

If you are considering self-lubricating polymers for your next design, contact Advanced EMC today. Our team of experts can advise you on the best choices for your application and supply you with the bearing solutions you need.