Spring Loaded Seal
by Daniel Mays Daniel Mays No Comments

High-Performance Polymer Bearings: Materials, Advantages, and Use Cases

High-performance polymer bearings are replacing metal in increasingly demanding applications. The low-friction, dry-running capabilities, chemical resistance, and weight savings are just a few of the reasons why polymer bearings are gaining favor among engineers. This blog post focuses on three materials — PEEK, PPS, PAI, and PTFE — and their applicability to plane bearing applications.

Advantages of High-Performance Polymer Bearings

Bearing-grade engineering polymers such as PEEK, PPS, PAI, and PTFE are excellent options for bearing design. Compared to traditional metal bearings, these can run dry with minimal lubrication, generate less frictional heat, and experience less wear. They also offer corrosion resistance and are resistant to many problematic chemicals, along with significant weight savings. They also serve as natural electrical insulators and offer good vibration damping. High-performance polymer bearings are also compatible with clean environments (e.g., medical and semiconductor).

Understanding High-Performance Polymer Bearings

What makes a bearing material high-performance? First is low friction and natural lubricity, which reduces friction and the amount of heat generated by friction. Next is resistance: resistance to wear, resistance to chemicals, and resistance to absorbing moisture. Dimensional stability is also key, as well as the ability to maintain their load capacity under heat. Finally, PV limits serve as a benchmark for how suitable a high-performance polymer is for a particular application.

Material Profiles for High-Performance Polymer Bearings

1. PEEK (Polyetheretherketone)

PEEK is a semicrystalline, high-performance thermoplastic that is best known to engineers for its balance of strength, temperature resistance, and dimensional stability. It has excellent mechanical strength, with bearing grades able to withstand up to 6,00 psi. It also possesses excellent high-temperature performance up to 480°F continuous. In addition, PEEK has excellent chemical resistance that includes fuels, oils, solvents, and corrosive media. It also provides good creep resistance and dimensional stability even under thermal cycling.

Depending on the grade chosen, PEEK’s PV rating is 100,000 PV (Fluorolon 3015, PEEK BG) or 50,000 PV (Fluorolon 3010), with velocities up to 600 SFM and low friction (especially when graphite is used as a filler).

PEEK is often used with high-speed actuators, pumps, compressors, downhole and energy-sector applications, and aerospace mechanical linkages.

2. PPS (Polyphenylene Sulfide)

PPS is a rigid, aromatic polymer known for excellent chemical inertness and good dimensional stability, especially in corrosive environments. PPS is resistant to nearly all solvents, acids, bases, fuels, and process chemicals and has a continuous-use temperature of up to 400°F. It has naturally low friction and low moisture absorption, but is more brittle and less impact resistant than PEEK or PAI. 

PPS good PV ratings, depending on the grade used (i.e, 25,000 PV for Fluorolon 5065 and 11,000–12,000 PV  for Fluorolon 5025, 5010). It also possesses a load capacity of up to 2,000 psi, dependent on the grade chosen. 

PPS works very well in chemical processing equipment, automotive components exposed to aggressive chemicals, pumps and valves with moderate loads, and applications where chemical performance and corrosion resistance outweigh mechanical requirements.

3. PAI (Polyamide-Imide)

Torlon, or PAI, is the highest-strength thermoplastic available for bearing applications. Its imide backbone provides exceptional thermal, mechanical, and creep resistance. It has excellent compressive strength and fatigue resistance, with a continuous use temperature up to 500°F. It also has low friction in its graphite-filled grades, like Torlon 4301. 

PAI has good PV ratings, with 100,000 PV  for Torlon 4435 and  50,000 PV for Torlon 4301. Its velocity limit is 850–900 SFM, one of the highest speeds for non-metal bearings. And its load capacity is up to 1,000 psi. 

PAI bearings are commonly used for aerospace linkages and flap actuators, industrial machinery with extreme loads, robotic joints and linear motion systems, and high-temperature turbine or compressor environments. 

4. PTFE (Polytetrafluoroethylene, Filled and Unfilled)

PTFE is the lowest-friction engineering material available. It offers near-universal chemical resistance, but has lower strength and PV capability than PEEK or PAI. In fact, its ultra-low coefficient of friction makes it often used in dry-running or low-lubrication conditions. PTFE also has exceptional chemical resistance as it is inert to nearly all chemicals. High thermal resistance is another key property of PTFE: depending on the grade, it can be between
500°F–550°F depending on grade. However, it exhibits poor mechanical strength and creep resistance unless fillers are used.

Its PV rating depends heavily on fillers: 10,000 PV for filled PTFE grades like Rulon LR, J, W2, and only 1,000 PV  for unfilled PTFE: Fluorolon 1000. PTFE’s velocity limits are up to 400 SFM. For filled PTFE grades, the load capacity ranges from 750 to 1,000 psi.

PTFE bearings work best as low-load, low-to-moderate speed bearings. Common areas of application include chemical processing, where exposure to highly corrosive chemicals is expected, and semiconductor and cleanroom applications, where contamination is not acceptable.

Conclusion

High-performance polymer bearings made from PEEK, PPS, PAI, and PTFE offer significant advantages over traditional metal counterparts, including low friction, chemical resistance, and weight savings. And polymer bearings extend equipment life, improve reliability, and increase efficiency. 

If you’re evaluating materials for demanding bearing applications, our engineers can help you identify the best polymer solution for your requirements. Contact Advanced EMC today to discuss your design challenges and request a consultation.

Best Materials for Spring Energized Seals | Advanced EMC Technologies
by Daniel Mays Daniel Mays No Comments

Why Spring-Energized PTFE Seals Work in So Many Applications

Spring-energized PTFE seals work incredibly well. Engineers know that when designing equipment for truly hostile operational environments, whether facing cryogenic cold, aggressive media, or extreme pressure cycling, the reliability of the seal is absolutely critical. Traditional seals frequently fail under such harsh conditions, suffering from issues such as chemical attack, thermal degradation, or permanent deformation. The proven industrial solution for conquering these critical limitations lies in the PTFE spring-energized seal.

In this blog post, we discuss exactly why PTFE spring-energized seals work so well, including the use of PTFE and spring-energizers, along with a discussion of where these seals are used.

Where Spring-Energized Seals Conquer Extreme Conditions

Before discussing why these seals work so well, it would be wise to quickly review the many different industries and applications in which they have proven themselves. PTFE spring-energized seals have become indispensable across almost every challenging industrial sector because of their unique performance characteristics. Advanced EMC provides solutions for industries including Oil & Gas/Energy, Medical Devices, Aerospace & Defense, Automotive, and Food, Dairy, and Pharmaceutical.

In Oil & Gas and Energy, seals must handle extremely high pressures, sometimes up to 25 kpsi. They must also maintain integrity when exposed to chemically aggressive media such as sour gas and acid gases. In these applications, the PTFE jacket resists the chemicals while the energized springs help keep the seal in place.

For Aerospace & Defense, especially in cryogenic space applications, seals must survive conditions where temperatures drop below -250°C. Traditional elastomeric seals often shrink and lose sealing force at these cryogenic temperatures. PTFE spring-energized seals compensate for thermal contraction and are suitable for applications such as cryogenic fuel transfer and rocket engines. Virgin PTFE and high-purity filled PTFE variants also exhibit minimal outgassing, meeting NASA/ESA standards for use in a vacuum.

In the Medical Device and Pharmaceutical industries, reliability and purity are paramount. Virgin PTFE is both FDA- and USDA-approved. These seals are crucial in fluid management systems, surgical instruments, and diagnostic equipment. They withstand aggressive sterilization processes, including high-temperature Clean-In-Place (CIP) and Sanitize-In-Place (SIP) procedures, due to PTFE’s high thermal stability and chemical inertness. PTFE is also hydrophobic, repelling water and making it easier to clean complex geometries.

The Material Foundation: Why PTFE?

Polytetrafluoroethylene (PTFE), also know as Teflon®, is a synthetic fluoropolymer of tetrafluoroethylene. This material forms the resilient seal jacket, providing excellent chemical and thermal performance. Pure PTFE is almost completely chemically inert, meaning it resists attack from aggressive media such as acids, solvents, and reactive gases, minimizing the risk of degradation or swelling. It is also hydrophobic and non-wetting.

In addition, PTFE boasts an operating temperature range: it is thermally stable enough for continuous service up to 500°F, and certain specialized compounds can function reliably in cryogenic conditions as low as -450°F. PTFE also has the lowest coefficient of friction of any known solid and is naturally self-lubricating, which means it performs well in dry or non-lubricated applications. All of these are reasons to choose PTFE as the seal jacket in a spring-energized seal.

PTFE Spring-Energized Seals Work So Well

The core principle of a spring-energized seal lies in its architecture: a polymer seal jacket housing an internal metallic spring energizer. The spring’s primary job is to apply a continuous force against the sealing surface. This initial force ensures a consistent seal is maintained, especially at low system pressures.

The energizer’s constant force provides permanent resilience to the seal jacket, compensating for operational issues that would cause conventional seals to fail, including:

  • Jacket wear
  • Hardware misalignment and eccentricity
  • Dimensional changes due to thermal contraction or expansion
  • Misalignment

When system pressure increases, the pressure begins to supplement the spring force. This drives the seal lip against the mating surface, resulting in a tighter, highly efficient barrier. The spring design also ensures that the seal maintains force over time, eliminating the problem of permanent deformation or compression set seen in elastomers.

Engineers can select from various spring types to suit specific needs. The V spring (V ribbon spring energized seal) is an excellent candidate for cryogenic and vacuum applications, where coil springs (spiral pitch springs) work well, where low friction and high pressure are involved, typically in medium-speed applications. The helical flat spring is adapted to a wide range of pressures, from high pressure all the way down to vacuum conditions. An elastomeric O-ring energizer can be used when the use of metal must be avoided, and is adapted well to extreme pressures.

Conclusion

Robust, reliable sealing is absolutely necessary in mission-critical operations, regardless of the industry. Spring-energized PTFE seals provide a superior engineering solution. By combining the chemical inertness, wide temperature range, and low friction of PTFE with the persistent mechanical force of a metallic spring, these seals eliminate issues like compression set and loss of sealing force over time. They flex, adapt, and hold their seal integrity even when conditions shift fast.

For applications that demand unparalleled performance where failure is not an option, PTFE spring-energized seals work extremely well as they provide the durability, adaptability, and precision required. When specifying a PTFE spring-energized seal, never take for granted the finish of the mating surface. Advanced EMC Technologies offers expert polymer sealing solutions, leveraging more than 100 years of combined experience. Contact Advanced EMC today to learn how spring-energized seals can improve the reliability and lifespan of your system.