Spring Energized PTFE Seal composite bushings
by Sara McCaslin Sara McCaslin No Comments

No Lubrication, No Problem: How Self-Lubricating Polymer Bearings Cut Maintenance Costs

Lubrication is widely considered an investment in your equipment. From keeping your bearings well lubricated, keeping the lubricant free from contamination, and dealing with design challenges when the use of a standard lubricant is not feasible, lubrication for bearings can quickly become expensive and time-consuming.

This article focuses on self-lubricating polymer bearings and includes how they work, how they can cut maintenance costs, and examples of their use.

How Self-Lubricating Polymer Bearings Work

Self-lubricating bearings are made from polymers that either have inherently low friction (virgin PTFE, UHMWPE, acetal, and nylon) or have achieved low friction through the use of internal lubricants (e.g., PTFE fibers, graphite, MoS2). In both situations, wear on the bearing creates an extremely low-friction transfer film on the mating surface. The transfer film serves as the lubricant, eliminating the need for a film or oil and grease.

Self-Lubricating Polymers

Inherently Low-Friction Polymers

  • PTFE (Polytetrafluoroethylene): PTFE (Teflon) has one of the lowest coefficients of friction of any solid material, and it can be used on its own or as a liner/filler in composite bearings. The primary drawback of unfilled PTFE is its low load capacity; this makes it common to see reinforced PTFE used for bearings.
  • UHMWPE (Ultra-High-Molecular-Weight Polyethylene): This polymer is extremely wear-resistant with good impact strength. Common in food processing and marine applications due to its chemical resistance and FDA compliance.
  • Acetal (POM/Delrin): This material is known for being stiff, dimensionally stable, and naturally slippery. Engineers have found it good for lightly loaded bearings and bushings in precision equipment. In addition, it is easy to machine into tight tolerances.

Engineering Polymers Used as Base Materials

  • Nylon (PA6, PA66): Nylon is actually a widely used bearing material. It offers good mechanical strength and moderate friction. You may find it oil-impregnated to boost its naturally self-lubricating performance. Nylon does, however, absorb some moisture, which can affect dimensional stability.
  • PEEK (Polyether Ether Ketone): PEEK is a high-performance option for extreme temperatures and aggressive chemical environments. And while it is expensive, it is also excellent in demanding aerospace, medical, and industrial applications.
  • PPS (Polyphenylene Sulfide): PPS offers good chemical and heat resistance. It is often used as a base material filled with PTFE or graphite for added lubricity.

Filled/Composite Polymer Blends

These are base polymers enhanced with solid lubricant fillers, and often the most practical choice for bearing applications.

  • PTFE-filled nylon or acetal: The addition of PTFE dramatically reduces friction and wear compared to unfilled versions.
  • Graphite-filled polymers: Graphite adds lubricity and helps in high-temperature or dry-running conditions.
  • Molybdenum disulfide (MoS₂)-filled polymers: The addition of MoS2 improves wear resistance, especially under heavy loads and low speeds.
  • Carbon fiber-reinforced PTFE: Carbon fiber adds both mechanical strength and overall load capacity while retaining PTFE’s extremely low friction.

How Self-Lubricating Polymer Bearings Cut Maintenance Costs 

Self-lubricating bearings reduce maintenance costs in several areas. 

First, they eliminate the time it takes to lubricate bearings because there are no scheduled grease/oil intervals, no technician time, and no specialized tools or fittings required. It also reduces expensive downtime because machines will not have to be taken offline for lubrication. The use of self-lubricating bearings also eliminates contamination-related failures involving oil or grease attracting dust or debris, or degrading over time. This also means fewer premature failures and the costs associated with them. 

Self-lubricating bearings also lower the total cost of ownership. Even though the unit cost for these bearings may be slightly higher upfront, savings do accumulate over the bearing’s service life. In addition, there are no environmental issues related to lubricants, such as oil disposal or the risk of lubricant leaks contaminating the product (relevant for food/pharmaceutical) or the environment.

Finally, self-lubricating bearings have predictable wear. This is due in part to the fact that polymer bearings often have more predictable wear curves, making replacement planning easier than reacting to lubrication failures.

Where Self-Lubricating Bearings are Used

As an example of plain bearings, PTFE-lined bushings are commonly used in pumps, conveyors, and hydraulic cylinders. Acetal or UHMWPE thrust washers work extremely well in linear actuators or rotating equipment, and olymer-flanged bearings are often used in packaging and printing machinery, where space is tight and frequent relubrication would interrupt production.

In agricultural equipment and outdoor machinery exposed to dust, dirt, and moisture, self-lubricating pillow block bearings have been found to be an excellent solution to such contamination. Pivot/oscillating bearings used in robotic arms, linkages, and hinges, where movement is intermittent rather than continuous (conditions where grease tends to get squeezed out), greatly benefit from the use of self-lubricating bearing solutions. Marine and outdoor equipment: bearings are available that are resistant to water washout, where grease would fail or wash away quickly.

Food and beverage processing uses FDA-compliant polymer bearings that eliminate the risk of grease contamination on production lines. Medical and laboratory equipment also utilizes clean-room compatible bearings for situations where any lubricant residue is unacceptable.

Self-lubricating bearings are commonly used as automotive and light vehicle components such as throttle bodies, pedal assemblies, and seat adjusters, where lifetime lubrication is a design requirement.  Finally, high-temperature industrial ovens and dryers face situations where polymer composites with graphite or MoS₂ fillers outperform designs where conventional grease would burn off or break down.

Conclusion

Self-lubricating bearings save cut maintenance costs in a number of ways, such as eliminating the labor costs associated with greasing, reducing downtime (both planned and unexpected), lowering the cost of ownership, and more. And there are several options available when it comes to self-lubricating bearings, including virgin or reinforced polymers. If you are looking for a self-lubricating bearing solution, contact the experts at Advanced EMC today.

Spring Energized PTFE Seal composite bushings
by Daniel Mays Daniel Mays No Comments

How Self-Lubricating Plain Polymer Bearings Keep Equipment Running Without Oil

Conventional bearings seize when oil runs out, but there are engineering polymer bearings that do not seize, nor do they experience stick-slip behavior. Where oil-free operation is required (e.g., food processing, pharma, wet/submerged environments), self-lubricating, high-performance polymers are the solution. This blog post discusses self-lubricating polymer plain bearings, including how they work, what the best naturally self-lubricating polymer options are, and how to select the right material.

The Problem with Conventional Lubrication

When the oil film fails at the contact surface, serious issues begin to develop for plain bearings, including adhesive wear, heat buildup, and seizure. The cost of failure of plain bearings is expensive and includes not only the cost of repairs but also unplanned downtime, contamination, and potential compliance risks. And while lubrication is necessary, there are some industries where adding lubrication to a bearing is simply impractical. These include food and beverage (NSF H1 and FDA), cleanrooms, and underwater applications. 

How Self-Lubricating Polymer Bearings Work

The core mechanism of self-lubricating bearings lies in the natural self-lubricating nature of the polymer (such as PTFE, UHMW-PE, and POM). There are two phases to the self-lubricating process: the run-in phase and the steady-state phase.

The Run-In (Break-In) Phase: When a new polymer bearing is installed, the metal shaft, no matter how highly polished it may be, has microscopic peaks and valleys called asperities. When the shaft begins to rotate against the bearing under a load, these asperities act like microscopic sandpaper. The asperities shear off a very thin layer of the polymer, and during this phase, the wear rate and friction are slightly higher. The image below shows an example of the asperities and their interaction with the lubricant film using PTFE as an example.

Steady-State Phase: The sheared polymer debris do not disappear. Rather, they get compacted into the valleys of the metal shaft’s surface. This process creates the transfer film. Once this film is fully established, the bearing is no longer rubbing against metal. Instead, it is rubbing against a thin layer of its own polymer material. Because polymer-on-polymer friction is exceptionally low, the wear rate drops dramatically, and the bearing can operate indefinitely without a need for external grease or oil, continuously replenishing the film as needed.

Key Polymer Materials (~150 words)

There are several polymers that have inherent self-lubricating properties due to their molecular structure, with no fillers or additives needed. Four of them are commonly used for plain bearings.

PTFE (Polytetrafluoroethylene)

PTFE has a fluorine-carbon backbone with extremely weak intermolecular forces, giving it one of the lowest coefficients of friction of any solid material (μ ≈ 0.04–0.10). The downside of PTFE for bearings tends to be its poor wear resistance, low load capacity, and tendency to creep in its pure form. However, it is available as a bearing-grade polymer that possesses additives to enhance the strength, stiffness, and wear of unfilled PTFE without sacrificing its low friction and natural lubricity. These fillers include carbon fiber, bronze, and graphite.

UHMWPE (Ultra-High Molecular Weight Polyethylene)

UHMWPE is heavily used in extreme bearing, wear pad, and sliding applications in its virgin, unfilled state. While cross-linked or oil-filled versions exist for specialty uses, its natural abrasion resistance is so remarkably high that it rarely needs compounding to function as a heavy-duty wear surface. Its low friction, excellent toughness, and good wear resistance make it an excellent choice for ebarings, and it is widely used in food processing and orthopedic implants.

Bearing-Grade POM (Acetal/Delrin)

Bearing-grade POM is naturally slippery because of its smooth, crystalline surface and low surface energy. While it is not as low-friction as PTFE, it does offer better dimensional stability and is load-capable without any additives. Virgin POM is hard, slick, and makes an excellent light-duty bearing, but at higher speeds or loads, it can generate excess heat or squeal (caused by slip-stick). The most common bearing-grade acetal has about 10-20% PTFE fibers as an additive. These fibers effectively smear across the contact surface during operation. This further lowers the coefficient of friction and increases the limiting PV  value associated with virgin acetal.

Real-World Payoff

Using a self-lubricating plain polymer bearing eliminates the need for re-lubrication intervals, which leads to significant labor and downtime savings. In addition, self-lubricating bearings pose no issues with lubricant contamination, having a direct impact on product quality as well as compliance benefits. In addition, these beatings result in an extended service life in wet, abrasive, or chemically aggressive environments where oil-lubricated bearings fail rapidly. In fact, as an example, consider a conveyor bushing in a food plant. The voice of a lubrication-free bearing means operation exceeds the service life of traditional greased bronze bearings by 3x.

Conclusion

Self-lubricated plain bearings are a proven engineering solution to bearing lubrication issues, not a compromise. The combination of the right material with correct design and proper run-in can provide you with reliable oil-free operation. Advanced EMC encourages you to evaluate your highest-maintenance lubrication points as retrofit candidates for replacement with self-lubricating solutions. For more information on self-lubricating bearings, contact us today!