Spring Energized Teflon Seals
by Daniel Mays Daniel Mays No Comments

Inside PEEK Bearing Materials: High Load Capacity, Low Wear

Engineers are replacing metal bearings too often or are dealing with corrosion, weight, or lubrication failures. PEEK is a high-performance polymer alternative that is changing bearing design. In this article, we look at what PEEK is, why it performs well in many bearing applications, and where it genuinely makes sense to use it.

What Is PEEK and Why Does It Matter for Bearings?

PEEK (Polyether ether ketone) is a semi-crystalline thermoplastic that has proven an excellent solution to many bearing problems. It offers a high strength-to-weight ratio, excellent chemical resistance, a low coefficient of friction, and thermal stability up to 250°C continuous. This combination of properties leads to effective bearing performance, offering PEEK an advantage over both metal and many standard polymer solutions. 

High Load Capacity

The standard performance-bearing metric is the PV rating (pressure × velocity). If we look at the PV ratings of commonly used polymer bearing materials, we see that PTFE is severely limited despite its low friction, and nylon and acetal do not do much better. Unfilled PEEK has the best PV ratio, and when filled with carbon fiber, it has a significantly higher PV rating than other engineering polymers. This alone is an excellent reason to consider using PEEK in bearing applications. And note that filled PEEK grades are typically the main choice for demanding applications, while unfilled PEEK is more commonly used where chemical purity or machineability is the priority.

Low Wear Performance

One of the most interesting features of PEEK as a bearing material is its wear resistance, which is critical for many applications. PEEK’s molecular structure resists abrasion under dynamic loading, and it offers excellent performance in dry-running applications because it is self-lubricating, offering an excellent option when lubricants are discouraged or prohibited. Bearing-grade PEEK filled with carbon or graphite further enhances wear performance by significantly reducing wear rates. The low wear performance of PEEK bearings also leads to reduced downtime and longer maintenance intervals. 

Where PEEK Bearings Make Sense

PEEK has excellent properties, but they are not an ideal fit for all bearing applications. PEEK bearings are commonly used for applications such as the following:

  • Medical devices and surgical equipment, where biocompatibility and sterilization resistance prove critical
  • Food and beverage processing, where the self-lubricating property reduces contamination risks
  • Aerospace and defense, where the high strength-to-weight ratio leads to weight savings, reduced energy requirements, and SWaP-friendly designs
  • Chemical processing, where resistance to acids, solvents, and aggressive media exposure is necessary
  • Semiconductor and cleanroom environments, where PEEK exhibits no outgassing 

There are areas where PEEK is not recommended, however. It should not be used in ultra-high load static applications, where steel still dominates. In addition, it’s not well-suited to very high-temperature environments, which are likely beyond PEEK’s thermal ceiling. Finally, PEEK is not a good option for budget-sensitive, low-performance applications where cheaper plastics work well.

Conclusion

PEEK bearings are not a universal replacement for other materials, but rather a viable option for demanding operating environments where their unique properties justify the cost. If you are looking for a sealing solution that sounds like a great application for PEEK, contact the sealing experts here at Advanced EMC and put their knowledge to work for you.

Polymer Bushings and Bearings
by Daniel Mays Daniel Mays No Comments

Plain Polymer Bearings: When Simple Is a Design Advantage, Not a Compromise

Polymer plain bearings are often eliminated early in a design because it is easy equate complexity with performance. But that isn’t always true. While rolling-element bearings are the standard for a reason, the humble plain bearing, specifically when high-performance engineering polymers are used, offers a surprisingly robust alternative. Sometimes, eliminating moving parts is actually the biggest upgrade that can be made. 

This blog post explores what polymer plain bearings are, what their benefits are, and what their limitations are. 

Plain Polymer Bearings

A plain bearing (also known as a plane bearing) is the simplest design of a bearing, primarily because it has no rolling elements. These bearings come in several different forms, including cylindrical sleeves (the simplest), flanged (which can support axial loads), and thrust washers. As simple as their design is, however, there are many instances where they can outperform their rolling-element bearing counterparts. 

Plain Polymer Bearings vs Rolling-Element Bearings

What follows are some of the key benefits of simple plain bearing designs as compared to their rolling-element bearing counterparts. 

Superior Load Capacity and Shock Resistance: Plain bearings have a much larger surface-contact area than rolling element bearings possess. Because of this, plain bearings distribute loads much more effectively. Under shock loads, rolling-element bearings concentrate force into point loads that can cause fatigue or brinnelling. Plain bearings, however, can absorb shock and safely spread these impacts.

Predictable, Non-Catastrophic Failure: When a ball bearing fails, it seizes and can shatter and send problematic metal shrapnel into the system, a form of catastrophic failure that does serious damage beyond just the bearing itself. Plain bearings, on the other hand, experience wear at an even, predictable rate. This non-catastrophic failure mode is critical for applications in industries such as food processing and pharmaceutical applications, where contamination is a serious event.

Weight, Space, and Cost Savings: A typical plain bearing weighs less than half of a comparable needle-roller bearing, especially when a polymer bearing is used to replace a metal rolling-element bearing  (sometimes up to 14 times less than a deep-groove ball bearing). Their single-piece design eliminates the need for components such as snap rings and complex machined shoulders. This, in turn, enables engineers to shrink housing sizes and significantly reduce manufacturing costs.

Vibration Damping and Silence: Because they have no internal moving parts to rattle or slop around, plain bearings run quietly, and they naturally absorb a significant portion of mechanical vibration. This feature makes them extremely quiet when compared to rolling-element bearings.

Self-Lubrication: Perhaps the biggest advantage of plain engineering polymer bearings, such as PTFE and PEEK, is their maintenance-free nature. Instead of requiring continuous oil or grease, they rely on material transfer lubrication. As the shaft makes its first few rotations, the polymer smears a microscopic transfer film onto the mating metal shaft. This transfer film fills the microscopic recesses on the mating shaft, creating a dry-running, low-friction surface that prevents the messy buildup of debris common with greased bearings. 

When Polymer Plain Bearings are Not the Solution

Are plain bearings always the solution? No, and here’s a quick summary of where rolling-element bearings remain the recommended choice. For example, plain bearings are generally optimized for single-speed applications, but rolling-element bearings can tolerate a wider speed range, making them more suitable for applications with variable-speed drives. Start-stop cycles can also be a problem for plain bearings because it takes time for their lubricating transfer film to form, but rolling-element bearings are more efficient in such environments. In addition, high-precision applications work best with rolling-element bearings because polymer plain bearings require a radial clearance. Polymer bearings cannot handle the same level of edge loading as their equivalent rolling-element bearings. Finally, polymer plain bearings have much stricter mating shaft surface requirements.

Conclusion

Switching to plain bearings is not a solution for every design challenge. If you need extreme precision or are dealing with high-speed variability, rolling elements remain the best option. That said, the benefits of going simple are hard to ignore. Removing the risk of catastrophic seizure and reducing maintenance, polymer bearings solve the issues traditional rolling element metal bearings create. It comes down to knowing exactly what your application can tolerate.

If you are trying to decide between plain and rolling-element bearings, Advanced EMC can help. Contact us today and talk to one of our experienced bearing engineers.