by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

Designing Polymer Seals for Dynamic Applications: Balancing Wear, Friction, and Thermal Expansion

Designing polymer seals for dynamic applications can be a challenging task. Polymer seals have proven vital in dynamic applications such as rotary shafts, reciprocating pistons, and oscillating systems. However, dynamic conditions can introduce challenges that are not found in static conditions. These challenges include continuous motion, heat buildup, wear mechanisms, and variable pressures.

This blog post examines three key challenges involved in dynamic sealing: wear, friction, and thermal expansion.

The Role of Polymers in Dynamic Seals

Engineering polymers such as PTFE and PEEK offer several advantages over both traditional metals and elastomeric seals in dynamic systems. Such benefits include outstanding performance even in operating environments that include extreme temperatures and require excellent chemical compatibility and extremely low friction. And engineers can further enhance the most desirable features of these polymers through the use of fillers and blends (e.g., graphite, carbon, bronze, glass, and even PTFE).  Polymer seals are also lightweight and ideal for compact systems where space is limited.

Balancing Wear Resistance

One of the most limiting factors in dynamic seal applications is wear. The three most common wear mechanisms involved are adhesion, abrasion, and fatigue. 

  • Adhesive wear happens when the seal momentarily sticks to the counterface, thus tearing material away from the surface and resulting in material transfer or scoring.
  • Abrasive wear occurs when hard (abrasive) particles or rough surfaces cut into the polymer, creating grooves and accelerating material loss.
  • Fatigue wear takes place when the seal is subject to repeated cyclic stresses that form micro-cracks, eventually leading to surface flaking or spalling.

Polymers can effectively address wear issues. PTFE effectively combines extremely low dynamic friction and excellent self-lubrication. This combination makes it well-suited for high-wear dynamic applications such as piston rings in gas compressors. Another example is the use of PEEK seals in aerospace actuators, where its high resistance and ability to maintain mechanical strength at high temperatures make it an excellent choice for applications involving cycling under high loads.

One of the most effective ways to further improve the wear resistance of PTFE and PEEK dynamic seals would be the use of filled composites, the use of appropriate surface finishes on countersurfaces, and wise design choices that minimize localized stresses.

Managing Friction

Friction is particularly problematic in dynamic seals, as it leads to heat generation, energy loss, and accelerated degradation. This problem leads to a trade-off between achieving an effective sealing force and maintaining low friction. 

PTFE is an excellent example of how low-friction engineering polymers can help achieve this balance. PTFE has the lowest coefficient of friction of any engineering polymer, and is far less than that of metal or elastomers. Its self-lubricating nature keeps friction very low at the shaft-seal interface, which will minimize heat buildup and lost energy. In fact, it can even reduce energy loss during dry running conditions. The strength and modulus of elasticity of PTFE can be modified through the use of fillers and hybrids.

Spring-energized seals, which use a metallic energizer to keep the seal lip in contact with the sealing surface and generate a predictable, consistent load to compensate for problems such as wear, thermal expansion, and pressure changes. As the load is kept within a predictable range, the friction is also kept at consistent levels over a well-distributed sealing force.

Thermal Expansion Considerations

Polymers indeed possess a higher coefficient of thermal expansion when compared to metals and most elastomers. Changes in dimensions can impact clearance, sealing performance, and contact pressure in dynamic sealing applications. In aerospace and automotive applications, for example,  there can be an abundance of extreme temperature cycling, which is going to be especially problematic in rotary shaft seal designs. 

There are several approaches to minimizing the impact of thermal expansion, starting with customized PTFE or PEEK polymer blends with materials that will lower the coefficient of thermal expansion without compromising wear resistance or friction.

The use of spring-energized seals allows the polymeric sealing lip to remain in contact with the sealing surface despite changes in geometry or alignment, whether they are due to wear, thermal expansion, or thermal contraction in the presence of extreme temperature cycling. 

Note that both of these approaches can be further enhanced through predictive modeling of how the seal will deform under thermal stress.

Polymer Seals for Dynamic Applications: Design Best Practices

Here are some straightforward design best practices related to dynamic sealing challenges:

  • Always match the seal geometry to motion type (i.e., rotary vs reciprocating).
  • Carefully consider the allowable surface roughness and hardness of mating surfaces.
  • Respect the PV limit (pressure × velocity) when selecting a polymer.
  • Remember the importance of predictive modeling (finite element analysis for thermal and tribological performance).
  • Always test under real-world operating conditions before full-scale deployment.

Conclusion

Dynamic sealing requires balancing wear, friction, and thermal expansion, with no single solution that fits all. Fortunately, advances in polymer science and composites make it possible to design seals that meet increasingly demanding requirements. However, engineers must still carefully match polymer formulations, energizers, and geometries to the unique conditions of each application.

If you need a dynamic seal for an application, contact the experts at Advanced EMC. Our engineers are very experienced and highly knowledgeable, able to take you all the way from seal design and material selection to testing.

Medical application for polymer medical technology parts
by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

Canted Coil Springs in the Medical Industry: Precision, Reliability, and Biocompatibility

Canted coil springs in the medical industry find a wide variety of applications, whether they are providing controlled force, stable electrical contact, or dependable sealing. Canted coil springs, also called slant coil springs, look deceptively simple. In reality, they are finely engineered components that offer something engineers in the medical field can’t do without: predictable performance in tiny spaces where failure is not an option.

In this blog post, we discuss the role of canted coil springs in medical devices, highlighting the features that make them stand out to engineers, their applications, and the design considerations involved in selecting the right type.

The Role of Canted Coil Springs in Medical the Medical Industry

Canted coil springs are angled, or canted, in such a way that they produce nearly constant force across a wide range of deflection. For medical devices, consistent force is often a necessity for reliability. Additionally, pacemakers, robotic surgical tools, and infusion pumps all rely on highly repeatable and dependable performance. The compact shape of these springs also makes them a good fit for miniaturized systems. This includes implantables, where every cubic millimeter counts. 

In fact, canted coil springs play a critical role across a wide range of medical technologies. In implantable devices (e.g., pacemakers, defibrillators, and cochlear implants), they ensure long-term, stable connectivity that patients can rely on. Surgical robotics benefit from connectors that incorporate canted coil springs to endure thousands of mating cycles without performance loss, making them easier to service and highly dependable in the operating room. In drug delivery systems such as infusion pumps or implantable reservoirs, spring-energized seals provide a consistent sealing force that enables precise, controlled dosing. Even advanced imaging equipment, including MRI and CT scanners, depends on these springs for EMI/RFI shielding and stable electrical interfaces, which preserve signal quality and reliability.

Why Engineers Rely on Canted Coil Springs in the Medical Industry

There are several key reasons why engineers rely on canted coil springs in medical applications.

Force Deflection Control

Canted coil springs are well known for their highly predictable load-deflection curves. In implantable devices, for example, stability over millions of cycles is essential. A spring that holds its force profile year after year helps reduce fatigue risks and mechanical drift, ensuring the device works as intended throughout its lifespan.

Sealing Performance

In spring-energized seals, canted coil springs are often paired with PTFE or other polymers. The result is a gas-tight, liquid-tight barrier that maintains its performance even in the presence of repeated sterilization cycles, aggressive fluids, and pressure changes. Engineers rely on this type of sealing solution for surgical instruments and drug delivery systems; leakage is simply not acceptable.

Electrical Conductivity

The angled coils on a canted coil spring allow it to be used as a highly reliable multi-contact electrical connectors. Instead of one or two contact points, they create multiple low-resistance electrical paths. These paths remain stable even under extremely harsh conditions that may involve vibration, thermal cycling, and repeated connections. This type of performance leads to lower insertion force, less wear, and added benefits like EMI and RFI shielding. For imaging systems, neuromodulation devices, and implantable electronics, these advantages lead to reliable signal integrity and longer service life.

Most Common Questions about Canted Coil Springs } Advanced EMC Technologies

Design Considerations for Engineers

Designing with canted coil springs can be complicated. Engineers need to tune load and deflection characteristics for the specific application, keeping stress within limits to extend fatigue life. This is made possible through the development of customized cant coil spring geometries.

As devices continue to shrink, tolerance control becomes critical. Finite element analysis is often used to predict performance under repeated load, while integration with polymers such as PTFE will enable hybrid solutions that balance mechanical, chemical, and biocompatibility needs.

Material choice is also vital, as it is where performance meets safety. Engineers typically work with stainless steel (316L), MP35N, Elgiloy, or Inconel due to factors such as corrosion resistance, fatigue life, and compliance with biocompatibility standards, including ISO 10993. For connectors, precious metal coatings like gold or platinum can further improve conductivity while resisting corrosion inside the body. Meeting these material and testing requirements is what makes it possible for springs to go from concept to regulatory approval.

Looking Ahead at Canted Coil Springs in the Medical Industry

As wearable and implantable medical electronics continue to grow, so does the demand for components that are smaller, lighter, and more efficient. Canted coil springs are well-positioned to meet that demand. Ongoing work with additive manufacturing and smart materials may add new features, such as adaptive force profiles or embedded sensors, that further expand their role in next-generation medical systems.

Conclusion

The ability of canted coil springs to maintain precise force, reinforce seals, and ensure electrical reliability makes them indispensable for a wide range of applications, from surgical robots to implantable devices. For engineers tasked with designing systems that must be both safe and dependable, these springs are a proven solution.

If you would like guidance on selecting or customizing canted coil springs for your next medical application, contact Advanced EMC. Our engineering team specializes in matching spring technology to the unique challenges of medical design. Give us a call today.