by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

Wear and Friction in Polymer Bearings

When bearings fail, friction and wear are often the primary causes. Friction and wear in polymer bearings are critical factors in their design and performance. In fact, friction and wear influence everything from energy efficiency to service life. 

In this article, we examine the fundamentals of friction and wear, their impact on polymer bearing performance, and why understanding PV values is crucial for selecting the appropriate material. Whether you work in aerospace, medical devices, or industrial automation, this guide will help you make informed engineering decisions.

Understanding Friction

One way to define friction is the resistive force that occurs when two surfaces move against each other. In the context of polymer bearings, friction plays a key role in determining energy efficiency, heat generation, and overall wear behavior. 

Friction arises from surface interactions at the microscopic level. Even polished surfaces have asperities (tiny peaks and valleys) that cause mechanical interlocking and adhesion. In polymer bearings, friction behavior is influenced not only by surface roughness and contact pressure but also by factors such as lubrication, temperature, and material composition. The table below summarizes the main friction mechanisms at work in polymer bearings.

MechanismDescription
AdhesionIntermolecular bonding between polymer and counterface contributes to resistance.
Surface DeformationPolymer deforms under load during sliding, adding to frictional resistance.
Viscoelastic DissipationInternal energy loss from viscoelastic behavior increases the friction coefficient.
Transfer Film FormationA layer of polymer transfers to the counterface, altering friction over time.
Stick-Slip PhenomenonAlternating adhesion and sliding causes vibrations or unstable motion.
Surface Roughness/TextureMicrostructure of surfaces influences contact area and frictional behavior.

High friction in polymer bearings can lead to excessive heat buildup, accelerated wear, and energy loss in mechanical systems. However, polymers often offer lower coefficients of friction than metals, which makes them an excellent option for reducing drag and operating efficiently without the need for continuous lubrication. This is especially advantageous in applications where maintenance access is limited, the environment is cryogenic, or cleanliness and sanitation are critical.

Understanding Wear

Wear is the gradual removal or deformation of material at solid surfaces due to mechanical action. In polymer bearings, wear not only affects part longevity but can also significantly alter dimensions and negatively impact performance over time, potentially leading to even increased friction, misalignment, or failure.

Wear occurs through various mechanisms, including abrasion, adhesion, fatigue, and erosion. In polymer bearings, the dominant type of wear often depends on operating conditions such as load, speed, temperature, and the presence (or absence) of lubricants. The main wear types are summarized in the table below.

Wear TypeDescriptionCommon CausesRelevance to Polymers
Abrasive WearHard particles or rough surfaces wear away material.Contaminants, rough counterfaces, high contact stressCommon in dirty or poorly filtered environments.
Adhesive WearSurfaces bond at contact points and then tear apart during movement.High pressure, poor lubricationCan be minimized by using low-friction polymer grades.
Fatigue WearCracks form due to repeated cyclic loading, leading to material removal.Repeated loading/unloading cyclesImportant for dynamic applications (e.g., pumps).
Erosive WearMaterial is gradually removed by impact from particles or fluid flow.High-speed fluids with particulatesLess common, but relevant in slurry or fluid transport.

Polymers typically have a lower elastic modulus and can deform under load, which helps reduce localized stress and delay wear, provided the material is selected correctly and the PV value remains within limits.

Friction and Wear in Polymer Bearings

Polymer bearings behave differently than metal under friction and wear. Their unique tribological properties—including low friction coefficients, self-lubricating capabilities, and tolerance for misalignment—make them ideal for applications where conventional metal bearings would struggle to perform.

PV Value: What It Means and Why It Matters

A key metric used in evaluating polymer bearing performance is the PV value, which stands for Pressure × Velocity. It quantifies the combination of load (P, in psi or MPa) and surface speed (V, in ft/min or m/s) that a bearing can withstand before experiencing excessive wear or thermal failure. In general, higher PV values indicate that the bearing can withstand greater stress and speed. Exceeding the limiting PV can lead to thermal softening, deformation, or accelerated wear of the polymer material.

Every polymer material has a limiting PV, which is the maximum combination of pressure and velocity it can handle under steady conditions. Engineers must stay below this threshold when designing systems to prevent performance breakdowns. Factors that affect limiting PV include:

  • Material type (e.g., PTFE, PEEK, UHMW)
  • Lubrication conditions
  • Heat dissipation
  • Bearing geometry and clearance

Choosing a polymer with a suitable PV rating is essential when operating at high loads, high speeds, or both. Some high-performance polymers even incorporate fillers—such as glass, carbon, or graphite—to increase wear resistance and raise the limiting power-to-weight (PV) threshold. Typical values are in the table below.

MaterialCoefficient of FrictionWear ResistanceLimiting PVTypical Enhancements
PTFEVery Low (0.05–0.10)FairLowGlass, bronze, or carbon fillers
PEEKModerate (0.15–0.30)ExcellentHighCarbon fiber, PTFE, graphite
UHMW-PELow (0.10–0.20)GoodModerateUV stabilizers, glass fiber
Nylon (PA)Moderate (0.15–0.25)Good (in dry conditions)Moderate to High (with lube)Moly disulfide
Filled PTFEVery Low (0.04–0.09)GoodModerateGraphite, MoS₂, or glass fiber blends
Polymer Beads

Choosing the Right Polymer for Friction and Wear

Selecting the optimal polymer for a bearing application requires more than just knowing the coefficient of friction. It involves understanding how various operating conditions interact with the material’s tribological profile.

Here are the major factors engineers should consider:

Load and Speed (PV Value): The combined pressure and velocity—expressed as the PV value—should stay below the material’s limiting PV to prevent overheating, deformation, or rapid wear. For high-load, high-speed applications, advanced materials like PEEK or filled PTFE are often necessary.

Temperature Range: Thermal stability varies widely across polymers. PEEK and PTFE perform well in high-temperature environments, while materials like UHMW-PE or nylon may soften or creep under prolonged exposure to heat.

Lubrication Conditions: Some applications operate with continuous lubrication, while others require dry-running performance. PTFE and UHMW-PE offer excellent dry lubricity, making them ideal for maintenance-free or clean-room conditions.

Chemical Exposure: Exposure to aggressive chemicals or cleaners can cause degradation of many plastics. PTFE offers broad chemical resistance, while nylon and acetal may be more limited depending on the environment.

Wear Resistance and Service Life: If durability is a primary concern, choose polymers that exhibit low wear rates under dynamic conditions. Fillers such as carbon fiber, glass, and graphite can significantly improve wear resistance without sacrificing too much in terms of friction.

Cost and Availability: High-performance polymers, such as PEEK and specialty-filled PTFE blends, come at a cost, however. For less demanding applications, materials like nylon or acetal may offer a more cost-effective solution.

Conclusion

Friction and wear are critical in polymer bearing design and specification. These factors directly impact performance, efficiency, and service life. Understanding how such friction and wear operate, along with the impact of PV value, temperature, lubrication, and material composition on behavior, empowers engineers to make informed decisions. Whether the application requires high-speed, dry-running conditions or chemical resistance in a corrosive environment, selecting the right polymer is crucial. At Advanced EMC Technologies, we specialize in high-performance polymer solutions engineered for demanding tribological environments. Contact us today to find the right material for your next bearing application.

by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

When to Choose Auto Molding for PTFE Components

If efficiency, precision, and scalability are crucial for your design, auto molding for PTFE components can provide a distinct advantage over traditional molding methods. It is commonly used in industries where performance and consistency are non-negotiable, and this manufacturing process is ideal for producing high volumes of complex, tight-tolerance parts. 

In this article, we examine when auto molding is the optimal choice for producing PTFE components.

Understanding Auto Molding for PTFE

Auto molding, also known as automatic molding, is a high-efficiency process used to manufacture PTFE components at scale. Unlike the labor-intensive, low-volume traditional compression molding, auto molding supports automated, high-throughput production runs. This process leverages precision tooling and automated pressing systems to form consistent, repeatable components with minimal human intervention.

The method is particularly well-suited for producing a wide range of PTFE parts such as seals for medical devices, seats for aerospace systems, bushings for semiconductor manufacturing, and insulators for various applications—components that often require tight dimensional tolerances and uniform performance. Auto molding can accommodate a variety of PTFE-based materials, including filled and modified PTFE compounds, depending on the application’s mechanical, thermal, or chemical resistance requirements.

What sets modern auto molding apart is its integration with downstream operations such as automatic trimming, quality inspection, and packaging. Such features not only reduce cycle times but also improve part consistency across batches, making them ideal for demanding sectors such as medical devices, semiconductor manufacturing, and aerospace systems.

Basic Steps in the PTFE Auto Molding Process

  1. Create Molds
    Tool and die makers can fabricated the molds through various methods such as precision machining, die casting, or advanced techniques like 3D printing. The mold design must support tight tolerances and repeatability to ensure accurate and consistent product quality.
  2. Set Up the Machine
    Prepare the molding equipment by cleaning the molds, preheating as necessary, and configuring the press settings according to the material and part geometry.
  3. Prepare the Charge
    Select the appropriate PTFE material—virgin or filled—and measure the correct amount. Oversized charges can lead to flash formation, which may require post-processing.
  4. Insert the Charge
    Place the material charge at the center of the bottom mold cavity to ensure uniform compression.
  5. Compress the Part
    Close the mold and apply the necessary pressure, often in combination with heat, to shape the component. Heating improves material flow and reduces cycle time.
  6. Release the Part
    Once the part is fully formed and cooled, open the mold and remove the molded component.
  7. Clean and Finish
    Trim any excess flash and perform additional cleaning or finishing steps as required before assembly or quality inspection.

Key Advantages of Auto Molding

Auto molding offers several advantages for PTFE component production, particularly in high-volume environments:

  • Precision and Accuracy: The precision and repeatability of auto molding, made possible by automated control, instill confidence in consistently achieving part dimensions and tight tolerances across production runs. 
  • High-Volume Production: Auto molding has a high throughput, supporting rapid cycle times and is ideal for efficient mass production.
  • Strong Parts: Auto molded parts, free from issues like knitting lines and flow lines found within injection molding, ensure the quality and durability of the components.
  • Reduced Waste: Efficient material usage and automated trimming minimize scrap.
  • Lower Labor Costs: Minimal operator involvement leads to reduced labor overhead.
  • Automation Integration: Easily incorporated into fully automated production lines, including inspection and packaging.
  • Flexibility in Design: Parts and their molds can be designed using solid modeling tools, including CAD/CAM.

These benefits make auto molding an attractive option for applications where performance, consistency, and cost-efficiency are critical.

When Auto Molding Is the Right Choice

Auto molding is most effective when specific production and performance criteria are met. It is the preferred method for:

  • High-Volume Production: Auto molding excels in applications that require thousands or millions of identical PTFE parts, thereby reducing the per-unit cost.
  • Tight Dimensional Tolerances: Applications demanding precision, such as medical seals or semiconductor insulators, benefit from the process’s repeatability.
  • Complex Geometries: Components with detailed features or thin-walled structures are more reliably molded with precision and accuracy.
  • Consistency-Critical Industries: Regulatory-driven sectors, such as aerospace and healthcare, often require validated, uniform components that auto molding can deliver.
  • Automated Workflows: When production lines include robotic handling or in-line quality control, auto molding integrates seamlessly.

In these scenarios, the upfront investment in tooling and automation is offset by long-term gains in efficiency, reliability, and cost control.

Limitations and Considerations

While auto molding offers significant advantages, it is not suitable for every application. For example, the initial investment in precision molds and automation equipment can be high, making it less economical for short-run production. Additionally, auto molding exhibits limited flexibility, as design changes necessitate new tooling, which can delay production and increase costs. Some filled PTFE compounds may be challenging to process in auto molding equipment due to flow characteristics or filler content. And for R&D or low-volume custom parts, compression or isostatic molding remains a more practical option.

Conclusion

Auto molding for PTFE components provides a compelling solution for high-volume production environments where precision, repeatability, and cost efficiency are paramount. While not suitable for every project, it delivers clear advantages when the application demands tight tolerances, complex geometries, and consistent performance. For engineers and manufacturers seeking to optimize PTFE part production, auto molding is a strategic option worth serious consideration.

Contact Advanced EMC today to discuss how our auto molding capabilities can support your next high-performance PTFE application.