by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

Why PTFE Keeps Winning: The Material Science Behind High-Reliability Seal Solutions

Some materials survive extreme environments while others redefine what “extreme” means. From cryogenic hydrogen at -459°F to continuous operating temperatures of 500°F, from high-speed rotary shafts approaching 100,000 RPM to chemically aggressive process media, modern sealing applications demand more than incremental improvement. They demand stability, predictability, and performance under conditions where traditional elastomers begin to fail.

PTFE seals occupy that space.

This article examines why PTFE continues to be specified in aerospace, chemical processing, food and pharmaceutical systems, and high-speed rotary equipment. This article explores its extreme temperature stability, low-friction tribological behavior, chemical inertness, high-speed capability, long-term reliability, and the ability to tailor performance through fillers and spring energization. The goal is not simply to list advantages, but to understand how those properties translate into measurable engineering performance.

Extreme Temperature Stability

One of the properties that sets PTFE seals apart is their ability to maintain mechanical integrity across a wide range of temperatures, from -459°F (-273°C) to +500°F (+260°C). In addition, they resist melting and degradation at continuous operating temperatures of 500°F, including spikes up to 600°F. High temperatures are not the only area where PTFE excels. PTFE seals remain flexible and retain sealing force even in the presence of cryogenic fluids (e.g., liquid hydrogen, deep space). They successfully prevent the embrittlement problems that are so common in traditional elastomeric seal solutions. In addition, PTFE has a very low coefficient of thermal expansion that supports dimensional stability even during rapid temperature cycling.

Superior Tribological Properties

PTFE also offers an extremely low coefficient of friction, as low as 0.04. This property reduces torque requirements and power loss. PTFE also deposits a microscopic film on the mating surface, creating a PTFE-on-PTFE interface that minimizes wear and enables dry running. Dry running is an extremely useful feature of PTFE, meaning it can run without external lubrication and eliminate stick-slip even after long periods of inactivity. 

Chemical and Environmental Resistance

PTFE is one of the most chemically non-reactive polymers. It is non-reactive with almost all industrial chemicals, including aggressive acids (hydrochloric and sulfuric), solvents, and hydrocarbon fuels. Furthermore, it does not become brittle, swell, or degrade when it is exposed to corrosive media. Virgin PTFE grades are FDA, USDA, and 3-A Sanitary approved for food, dairy, and pharmaceutical use. PTFE is hydrophobic: it repels water and resists moisture buildup, making cleaning and sterilization much easier. Finally, PTFE is ideal for aerospace and high-vacuum environments because of its minimal outgassing, which prevents the contamination of sensitive optics or electronics.

High-Speed and Pressure Performance

PTFE rotary shaft seals can handle shaft surface speeds around 6,900 rpm and rotational speeds on the order of 100,000 RPM, which exceeds the limits seen in traditional elastomeric seals. They can also handle pressures up to 100-150 psi, and when BUR or sprig-energized options are used,, they can withstand significantly higher pressures. 

Operational Longevity and Reliability

PTFE seals have an unlimited shelf life, unlike traditional rubber seals, which age and degrade during storage. In addition, the self-lubrication and wear resistance of PTFE seals reduce unexpected downtime and maintenance downtime.  In addition, non-abrasive grades of PTFE can protect mating shafts from grooving and other surface damage that compromise seal performance. Finally, the low friction of PTFE reduces energy consumption. 

Customizability via Fillers and Design

Another key benefit of PTFE is that it can be compounded with fillers to target specific material properties. 

  • Glass Fiber: Increases wear resistance and compressive strength
  • Carbon/Graphite: Improves thermal conductivity and allows for use in steam/water, and is safer for softer shafts
  • Molybdenum Disulfide (MoS₂): Increases hardness and lubricity for high-pressure dry running
  • Polyimide: Ultra-low friction for use against soft mating surfaces like aluminum

In addition, metal springs can be added to provide a constant sealing force and compensate for seal wear, hardware misalignment, or thermal contraction.

Conclusion

In high-performance applications, failure rarely stems from a single variable. It emerges when materials, load, temperature, motion, and environment are not aligned. PTFE provides the stability needed to bring those variables into balance.

To learn more about PTFE options for sealing solutions, contact the PTFE seal experts here at Advanced EMC. We are here to help you from the initial design stages through to testing and implementation.

Small Diameter Spring Energized Seals
by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

How Spring Selection Defines Spring-Energized Seal Performance

Most failures blamed on PTFE actually originate in the spring. This blog post discusses the load-management system and key features of spring-energized seals for canted coil springs, V springs, cantilever springs, helical springs, and coil springs.

Canted Coil Springs (Slant Coil Springs)

Canted Coil Springs and Slant Coil Springs from Advanced EMC Technologies

These springs are wound so that individual coils are set at an angle to the longitudinal axis. They are highly versatile and often used for dynamic sealing applications. Their key feature of canted coil springs is the flat load curve they provide. These spring energizers generate a nearly constant force across a wide deflection range. The constant force allows precise control over friction and torque, making these spring energizers ideal for applications where these factors are critical. Canted coil springs are also unlikely to experience compression set.

Canted coil spring energizers work best in moderate to high-speed rotary applications. Beyond sealing, their unique design allows them to serve as mechanical connectors (latching/locking), EMI/RF shields, and multi-point electrical conductors.

V Springs (V Ribbon Springs)

The V spring is a general-purpose, cantilever-type energizer. They offer an excellent balance of performance and cost-effectiveness. In addition, V springs provide a moderate load over a wide deflection range. They function well in both static and dynamic applications, including those involving rotary or reciprocating motion.

V springs are frequently recommended for severe service conditions, including vacuum pressures and cryogenic temperatures. V spring energizers are often a preferred choice for harsh operating environments.

Cantilever Springs (Finger Springs)

Often referred to as finger springs, these spring energizers feature a V-shaped cross-section and are distinguished by a linear load curve, meaning the force increases linearly with deflection.

The load is concentrated at the very front edge of the seal lip, which provides positive wiping action and makes them particularly effective for exclusion and scraping applications. They also generate extremely low friction.

Cantilever spring energizers are well-suited for sealing viscous media. They are typically found in low to medium-speed applications, such as hydraulic cylinders, pumps, compressors, and shocks.

Helical Springs (Helical Flat / Compression Springs)

Helical springs consist of a wound ribbon of metal and are characterized by a high load-versus-displacement curve. Because they produce a very high unit load with a small deflection range, helical springs provide tight, reliable sealing. They are well-adapted for sealing light gases and liquids.

Helical springs are generally limited to static, slow-dynamic, or intermittently dynamic applications because friction and wear are less of a concern than seal reliability. These spring energizers are often used in pipe flanges and crush jackets where the seal must embed into surface irregularities. Experts highly recommend helical configurations for cryogenic applications.

Coil Springs (Spiral Pitch Springs)

When many people visualize a spring-energized seal, they picture this wire coil type. These spring-energizers actually perform best in high-pressure, medium-speed applications and are known for their low friction. 

Spring Materials

The performance of spring-energizers is also dependent on the material selection. The material selection is primarily determined by the chemical and thermal environments involved. At Advanced EMC, we recommend one of the following spring materials: 

  • Stainless Steel (300 Series, 17-7 PH, 301/304): Common for general-purpose and cryogenic applications
  • Hastelloy: Recommended for highly corrosive media
  • Elgiloy: Used for high heat, corrosive environments, and salt water
  • Inconel: Used in severe environments and cryogenic applications

Conclusion

When spring-energized seals fail, the problem is often not the jacket, but the spring. Knowing about load consistency, deflection behavior, and how that force is delivered over time is key to deflection, friction, wear, and whether a seal actually survives its operating environment.

At Advanced EMC, spring-energized seals are engineered as complete systems, not just components. Our team will assist you from spring selection to geometry and material pairing, aligning the seal design with real-world conditions. If you are troubleshooting a failure or designing for demanding service, contact Advanced EMC today.