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.

Semiconductor
by Daniel Mays Daniel Mays No Comments

Meeting SEMI Standards for Seal Purity, Outgassing, and Chemical Resistance

Semiconductor fabrication facilities are among the most demanding environments for seal materials on the planet because a single contamination event can scrap a wafer batch worth hundreds of thousands of dollars. And every polymer, lubricant, and elastomeric material contains residual volatiles. SEMI standards deal with how to take these residual volatiles into account when designing components, such as seals, for wafer fabrication environments. The purpose of this blog post is to discuss what SEMI standards actually require and how engineers select bearings to meet them.

The SEMI Standards Landscape

SEMI standards serve as the common language of the global semiconductor supply chain. For example, SEMI standards define fitness for use by establishing minimum thresholds (e.g., outgassing limits, contamination levels, chemical compatibility requirements) that a component must meet to be considered safe for use in semiconductor manufacturing environments. These standards also protect the wafer from contamination that can destroy device yield and make suppliers accountable. 

By referencing a SEMI standard in a procurement specification, a fabrication engineer can require documented, third-party-verifiable compliance rather than relying on a supplier’s marketing claims. These standards also enable global interoperability: tools, chemicals, and components built to SEMI standards can move across fabrications and geographies without extensive re-qualification. This serves as a major economic benefit in a highly globalized industry.

SEMI F-Series (Facilities and Materials)

The SEMI F-series serves as the most relevant category for seals. Standards like SEMI F57 govern polymeric components and wetted surface materials used in UHP (ultra-high purity) gas distribution systems, covering surface finish requirements, material qualification, and cleanliness protocols. SEMI F2 addresses test methods for metallic contamination on wetted surfaces. These are the specs a seal or bearing supplier is most likely to be asked to demonstrate compliance with.

SEMI C-Series (Chemicals)

The SEMI C-Series of standards defines purity grades and acceptable contamination levels for process chemicals such as acids, solvents, and oxidizers. While these standards primarily govern the chemicals themselves, they are also critically important for material selection. If your seal is sitting in a bath governed by a C-series chemical specification, that specification indirectly defines the chemical resistance your seal must demonstrate. Engineers selecting materials for wetted components need to understand what chemical grade they are designing for.

SEMI S2 (Safety Guidelines for Semiconductor Manufacturing Equipment)

S2 is a broad equipment safety standard with direct implications for materials selection. It addresses chemical containment, materials of construction for chemical-wetted components, ventilation requirements, and labeling. It’s often the standard a tool OEM must satisfy as a condition of fab entry, making it a gateway document that touches bearing and seal design.

Purity: Metallic Contamination and Ionic Cleanliness

When it comes to cleanliness in fabrication environments, the core concern when it comes to contamination is the presence of trace metals (Fe, Na, K, Ca) as killer defects in semiconductor devices. Both dynamic seals are going to shed particles, and this includes wear debris, surface oxides, and manufacturing residues. Among the key material considerations are the use of PTFE bearings and seals, while other options include ceramic bearings (Si₃N₄, ZrO₂) as the go-to for ultra-pure applications and surface treatments (e.g., electropolishing, passivation, and their limits).

Outgassing: The Invisible Contamination Problem

Through outgassing, volatile organic compounds (VOCs) deposit on wafer surfaces and disrupt lithography, deposition, and etch processes. Two standards commonly apply: SEMI F10 and NASA ASTM E595, serving as the benchmarks engineers reference. And there are two key metrics that matter: ML (Total Mass Loss) and CVCM (Collected Volatile Condensable Materials). The general targets used by engineers are TML < 1.0% and CVCM < 0.1%. And remember that a material can pass TML and fail CVCM. Bearings and seals must comply with both. However, CVCM is the one that matters most because it captures what actually re-deposits on a cooler surface.

In seal assemblies, the vast majority of problems come from lubricants and greases (silicone-based greases are particularly problematic in vacuum) and adhesives, polymer cage materials, and elastomeric seals. This includes nylon and acetal bearing cages and standard elastomeric seals with curative that can volatize under heat and vacuum. To avoid these issues, industry best practice is to use …

  • PFPE-based dry film lubricants
  • PTFE lip seals (which are known for their high purity and self-lubrication)
  • Perfluoroelastomers (FFKM)

Bake-Out Procedures

As already discussed, every polymer, lubricant, and elastomeric material contains residual volatiles that may include trapped solvents from manufacturing, absorbed moisture, unreacted monomers, and plasticizer fractions. At room temperature, these substances release slowly over weeks or months. Elevated temperature, however, drives that same process in hours, forcing the material to shed its residual volatiles before it is ever installed. This process is known as bake-out and must be accomplished for a material to be safe to use in a high-purity environment.

Chemical Resistance: Surviving the Process Chemistry

The process chemistry involved with semiconductor manufacturers includes chemicals such as HF, H₂SO₄, HCl, H₂O₂, IPA, NMP, ozone, and aggressive plasma environments. And although a material may be listed as chemically resistant on a data sheet, that does not account for critical variables such as concentration, temperature, and exposure time. Swell, extraction, and stress cracking are the failure modes that tables consistently miss.

The material compatibility hierarchy for seals is:

  • FFKM (Kalrez®, Perlast®): broadest chemical resistance, low extractables
  • PTFE: excellent passive resistance but poor dynamic sealing performance
  • EPDM / FKM (Viton®): acceptable in some applications, disqualified in others (HF is a hard no for FKM)

Conclusion

SEMI compliance is not just a checklist, but rather a systems-level engineering discipline. Material selection, outgassing qualification, and chemical resistance validation must work together to result in a fully SEMI-compliant seal. Engineers who treat these as a system rather than separate line items build better products. If you are looking for a SEMI-compliant sealing solution, contact the engineers at Advanced EMC today.