An example of a subsea AUV
by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

Polymer Bearings for Subsea Robotics: Surviving Pressure, Saltwater, and Zero-Maintenance Windows

The ocean floor remains one of the most unforgiving environments on Earth. Remotely operated vehicles (ROVs) and autonomous underwater vehicles (AUVs) descend thousands of meters to inspect pipelines, support offshore drilling, and conduct scientific surveys. And these ROVS do all of this in conditions that would destroy conventional mechanical components within hours, including bearings. For engineers designing subsea robotic systems, the question is never whether the environment will push the hardware to its limits. The question is whether the hardware is ready for it.

Bearings are among the most critical and vulnerable components in a subsea robot’s drivetrain, joint assemblies, and thruster systems. Make the wrong design choice here, and the entire mission fails. Make the right design choice, and you have a system that can run reliably at depth for extended deployments without ever surfacing for a service interval. Polymer bearings for subsea robotics are emerging as the answer for engineers who are finding that conventional metal bearings simply cannot provide the performance needed in the harsh environment beneath the ocean.

Pressure, Saltwater, and Maintenance-Free Operation

Subsea robotics engineers, whether they are designing robots for inspecting oil and gas pipelines or monitoring fish farms, face three specific challenges that conventional bearing materials are not designed to handle simultaneously: hydrostatic pressure, saltwater corrosion, and lubrication.

Hydrostatic pressure increases by roughly one atmosphere for every 10 meters (~32.8 ft) of depth. At 3,000 meters (~9840 ft), which is a routine working depth for deepwater inspection ROVs, the pressure exceeds 300 atmospheres. Metal bearings rely heavily on lubrication films and tight tolerances that can easily be compromised under such loads. Pressure-induced deformation, lubricant displacement, and housing distortion can all cause premature failure.

Saltwater corrosion is another relentless issue that must be addressed for successful bearing performance. Corrosion degrades surface finish, tightens clearances, and eventually seizes rotating assemblies entirely. Marine environments expose bearing surfaces to chloride ions, dissolved oxygen, and biological fouling. Steel bearings corrode; bronze bearings can undergo dezincification; and even stainless alloys remain vulnerable to crevice corrosion in low-oxygen zones.

Zero-maintenance windows may be the most operationally demanding constraint of all. A bearing on an offshore ROV working a deepwater site cannot be pulled, inspected, relubricated, or replaced on a daily basis. Many deployments run for weeks or months between topside recovery. Polymer bearings, such as those made from PEEK or PTFE composites, eliminate the need for periodic lubrication or adjustments, reducing operational costs and downtime, and ensuring continuous mission success because they are self-lubricating.

Polymer Bearings: Material Solutions for Subsea Demands

Bearing-grade polymer materials address all three of these challenges — pressure, saltwater, and maintenance-free operation — often simultaneously. Several proven engineering polymers stand out as solutions that can inspire confidence in subsea robotic applications.

PEEK (Polyether ether ketone) is the workhorse of high-performance polymer bearings in subsea use. It maintains exceptional dimensional stability even under hydrostatic loading, exhibits near-zero water absorption, and resists saltwater, hydraulic fluids, and most chemicals commonly encountered in offshore environments. Furthermore, PEEK bearings operate without external lubrication, drawing instead on the material’s inherently low friction coefficient. For ROV thruster assemblies and joint pivots, PEEK offers a compressive strength that approaches or exceeds many metal alloys while eliminating corrosion.

Filled PTFE successfully extends the lubrication-free advantage further. Unfilled PTFE is too soft for structural bearing applications, but glass-filled, carbon-filled, or bronze-filled PTFE delivers self-lubricating performance with meaningful load capacity and low friction. In slow-rotation or oscillating applications, such as the articulating arms of an inspection ROV, field PTfE bearings provide a smooth, stick-slip-free motion with no maintenance requirement and complete resistance to saltwater attack.

UHMWPE (Ultra-High Molecular Weight Polyethylene) brings outstanding impact resistance and surface toughness to applications where debris ingestion is a risk. Its extremely low coefficient of friction, combined with high chemical resistance and excellent fatigue life in wet environments, makes it well-suited for guide bearings and bushing applications in subsea manipulators and cable management systems.

Finally, Torlon (PAI, Polyamide-imide) is ideal for harsh, high-temperature, and high-load bearing applications where even PEEK approaches its limits. With excellent creep resistance and impressive compressive strength, Torlon-based bearings perform well in compact, high-load joint designs where space constraints are tight, and operating cycles are demanding.

Building Reliability Into Every Depth

The common thread across all of these materials is simple: each one removes a failure mode that metal bearings experience in the subsea environment. No corrosion, no lubrication intervals, dimensional stability under pressure, and compatibility with the full range of subsea fluids and cleaning agents are critical properties that high-performance polymers such as PEEK, filled PTFE, UHMWPE, and Torlon possess. 

For operators running extended deepwater missions, polymer bearings are not merely an alternative to metal bearings; they are the more reliable choice. Lower system weight, reduced drag on thruster assemblies, and the elimination of corrosion-driven maintenance costs all contribute to a lower total cost of ownership over the working life of AUVs and ROVs.

Ready to specify the right bearing material for your subsea robotic application? The bearing experts at Advanced EMC have strong expertise in bearing-grade polymers for even the most demanding marine and offshore environments. Contact Advanced EMC today to discuss your project requirements and get material recommendations backed by real engineering experience.

Polymer Bushings and Bearings
by Sara McCaslin, PhD Sara McCaslin, PhD 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.