by Jackie Johnson Jackie Johnson No Comments

Using PEEK for Bearings

NTRODUCTION:

The first bearings recorded in history were likely made of wood or bronze, but modern engineers can choose from a variety of materials ranging from classical choices such as stainless steel to various types of polymers.  One modern (and fascinating) bearing material is PEEK.  In this article, we will look at five specific characteristics of PEEK that have allowed it to evolve as a popular material for bearings.

What is PEEK?

PEEK (polyetheretherketone) is semicrystalline thermoplastic known for retaining its functionality at high temperatures and in challenging environments. This includes aspects such as strength, wear resistance, dimensional and structural stability, and chemical inertness.  These factors alone have convinced many engineers to switch from traditional bearing materials to PEEK.

PEEK was invented in November of 1978 by UK based company Victrex PLC, and received a US patent in 1982 after being introduced to the US by then Imperial Chemical Industries (ICI). The processing conditions implemented to mold the material influence its crystallinity, or structure, and this results in the superb mechanical and chemical resistance properties of PEEK.

PEEK Efficiency

PEEK is lightweight and strong, giving it a high strength-to-weight ratio.  This means that a metal bearing would weigh significantly more than its equivalent PEEK counterpart.  This not only reduces overall weight, but also the inertia of the system, which in turn can increase efficiency.

A Durable Material

By reinforcing PEEK with carbon fibers, its load bearing capacity and dimensional stability are increased.  The carbon fibers will increase PEEK’s ability to dissipate heat, reducing the chances of thermal expansion.  Such characteristics are vital for bearings in high performance applications, where a slight change in bearing geometry could result in a system failure.

By using PEEK, bearings are better able to withstand high temperatures and corrosion, making it well suited for applications in extreme environments. In fact, PEEK can withstand temperatures up to 662°F!

Plain PEEK has a low coefficient of friction. By adding graphite and PTFE filler, friction can be further reduced.  The ability to add such fillers to PEEK can result in self-lubricating bearings with increased wear resistance.

Manufacture

PEEK is compatible with various manufacturing processes, with bearings typically produced using machining and injection molding.  Both modern CNC machining and injection molding support the efficient manufacture of high precision, complex parts such as bearings.

Evolution of Bearing Materials

Bearing materials have evolved far beyond wood and bronze.  Characteristics such as the potential strength, reduced weight, reinforcement, self-lubrication, and easy manufacture of materials like PEEK continue make them a competitive choice for bearing material design.

Take the next step in bearing design, specific material compatibility should be checked on each application.  Advanced EMC provides a free white paper on Advanced Polymer Bearing Design.

by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

Rotary Shaft Seals in Wind Energy Applications

Wind turbines are becoming an increasingly common sight in many parts of the world, including both on-shore and off-shore wind farms. Each of these wind turbines includes complex electrical and mechanical systems that convert wind energy into electrical power. A key aspect of achieving this conversion in a reliable, consistent manner is the numerous seals involved–including rotary shaft seals. This post will discuss the use of rotary shaft seals in wind energy applications.

Global Look at Installed Wind Energy Capacity

According to data from Statista, the global installed wind energy capacity continues to grow, reaching a record 743 GW in 2020. Furthermore, the cumulative capacity of wind energy is expected to reach 840.9 GW by 2022. To be able to provide energy efficiency and predictability, every aspect of generation and transfer must be designed for reliability, from the massive propeller blades to the energy transfer systems. 

Wind Turbines and Seals

When propellers are often 120 ft long, it is extremely important that the rotors function effectively. Of particular interest are rotary shaft seals which are usually tasked with keeping lubricants in and contamination outside. In a wind turbine, there are two specific areas where rotary shaft seals are critical: the main shaft bearings and gearbox shafts. These seals are directly involved with the main turbine shaft, and a failure in these rotary shaft seals means the wind turbine is quickly rendered useless. 

Challenges of Seals for the Wind Energy Market

Rotary shaft seals for wind turbines are not only critical to the functionality of a wind turbine but also face some of the most difficult operating environments. 

All rotary shaft seals for wind turbines must deal with high speeds. While the tip of the propeller may seem to move slowly, the length of these propellers means that the shaft speeds are incredibly high. Extremely high speeds mean that friction between the shaft and the seals can lead to significant heat generation, which means energy losses. These high speeds also lead to faster wear. Low friction and excellent wear resistance are extremely important.

There are also extreme temperature changes involved which can drop to cryogenic levels. The seal material used must be dimensionally stable despite these temperature changes and maintain performance at extremes (e.g., not becoming brittle when temperatures drop below freezing). Temperatures can also impact the type of lubricant that can be used with the seal.

Another challenge faced by the rotary shaft seals for the main shaft bearings is UV exposure, which can cause certain materials to rapidly degrade. Add to that potential exposure to water, ice, snow, rain, sand, dust, and winds and the choice of a good seal material becomes even more critical. In addition, exposure to moisture can also cause problems for wind turbine seals. Some materials will absorb water which will deform their shape.

The fact that these turbines are often located in remote locations and that changing out the seals is not a simple task means that repair costs just for labor are expensive. Because many of the seals are large in diameter and are considered custom seal designs means that the seals themselves are far from inexpensive. 

Turbines for off-shore wind farms face an extra set of challenges with exposure to saltwater and extreme weather events such as tropical storms and hurricanes. In addition, they are usually even more remote than their on-shore counterparts, making maintenance and repair much more challenging and expensive.

PTFE Rotary Shaft Seals in Wind Energy Applications

The type and geometry of rotary shaft seals are extremely important when selecting a seal for a wind turbine, but so is the seal lip material. One of the materials that are extremely well-adapted for facing the challenges just outlined is PTFE, polytetrafluoroethylene.

PTFE has the lowest coefficient of friction of any polymer. Furthermore, with a wise choice of additives, it can exhibit excellent wear resistance. Because of its low friction, self-lubrication, dry running capabilities, and very low breakout friction, PTFE works extremely well in high-speed applications.

PTFE also has an extensive operating temperature range of -328°F and 500°F with a melting point of  620°F. This allows it to maintain performance at the high speeds involved with wind turbines as well as the extreme temperatures involved with their operating environment. In addition, PTFE has a low coefficient of thermal expansion compared to many other polymers which means it changes geometry very little when temperature changes occur.

PTFE also has very good UV resistance, which means that it maintains its properties even during extended exposure to sunlight. In addition, PTFE performs well even in the presence of saltwater and other potential environmental issues. Saltwater can, of course, lead to problems but PTFE is not significantly affected in terms of wear and friction. In addition, PTFE also has a very low moisture absorption rate which means that it can remain dimensionally stable in the presence of water.

Conclusion

Rotary shaft seals for wind turbines, whether installed on the main shaft bearings or the gearbox shafts, must be able to function in extremely adverse conditions. One of the best materials for wind energy seal applications, both onshore and offshore, is PTFE. If you are looking for a reliable, robust wind energy sealing solution, contact the experts here at Advanced EMC. Our sealing team can recommend the best PTFE blend, seal type, and seal geometry for your rotary shaft seal needs.

by Jackie Johnson Jackie Johnson No Comments

U.S. Plastics Pact and the Plastics Industry

In September of 2020, the United States launched the US Plastics Pact, a consortium of industry leaders whose goal is to work collectively towards a circular economy for plastics in the United States. Around 100 companies, including big brand names such as Coca-Cola and Target, as well as organizations geared towards sustainability such as the Ocean Conservancy, have agreed to be a part of the program, with the end goal being all plastic packaging be recyclable by 2025. In June of this year, the U.S. Plastics Pact released their roadmap, providing their plan for hitting the ambitious 2025 target.

The goals set in the road-map seem lofty, and not everyone in the plastics industry agrees with the timeline and language used.

In this week’s blog post, we will go over the goals set by the U.S. Plastics Pact Roadmap, the industry leaders who are on board, and the ones who are not.

Roadmap to Sustainability

On June 15th, the US Plastics Pact, with the help of WRAP UK, released a 36-page road-map detailing their plan to make plastic waste a thing of the past. The plan targeted four specific areas to address said plastic waste, through, according to their website, “specific actions, responsibilities, and interim timeframes in order to realize meaningful, target outcomes for a circular economy for plastic packaging.”

These target areas are:

  • Defining a list of packaging to be designated as problematic or unnecessary by 2021.
  • Ensuring 100% of new plastic packaging is reusable, recyclable or compostable by 2025.
  • Undertaking actions to effectively recycle or compost 50% of plastic packing (including PET and PP thermoformed and injected molded containers) by 2025.
  • Ensuring the average recycled content or responsibly sourced bio-based content in plastic packaging (such as PE films) is at 30% by 2025.

The roadmap also calls to boost recycling rate of packaging made from PET, polypropylene and high-density polyethylene to 70% by 2025.

It’s goal by the end of 2022 is for all of its members to make public commitments to use recycled content in most of their packaging.

Lofty goals, but goals they say are obtainable. Not everyone agrees, however.

Realistic Goals or Pipe Dream?

The American Chemistry Council, the trade association for chemical companies and plastics manufacturers, says it welcomes the goals of the pact. In fact, many plastic firms have also signed on to the pact, including Amcor, Eastman Chemical and the National Association for PET Container Resources.

The issue, according to the ACC, is the timeline, and the language regarding phasing out “problematic plastic products”. In a statement issued by Joshua Baca, ACC’s vice president of plastics, said they want the Pact to be “transparent, data-driven and make recommendations based on science and engineering, rather than ideology” and to have “an inclusive and open process” that will “generate more informed and reliable outcomes and minimize risks of unintended consequences that can result from material substitution.”

The ACC had announced its own plans to create a circular plastics economy in 2018. Their plan was slightly less aggressive, with goal of 100% recyclable plastic packaging by 2030, and 100% of plastic packaging being either re-used, recycled or recovered by 2040. In 2020, the ACC announced their own “Roadmap to Reuse”, which outlined the ACC’s vision to achieve the previously listed goals.

Some in the plastics industry agree with the Pact.

Many plastic firms and trade groups have also signed on to the pact, including Amcor, Eastman Chemical and the National Association for PET Container Resources.

Amcor’s VP of Sustainability, David Clark, went on record saying “…we are proud to support the rollout of the US Plastics Pact Roadmap – which shows how cooperation across the value chain can help us solve the problem of waste in the environment.”

The National Association for PET Container Resources, or NAPCOR, even worked with the Pact to help launch the Roadmap, with NAPCOR Executive Director Darrel Collier saying that the U.S. Plastics Pact recycling goal of 50% is “ambitious, but not impossible.”

In Conclusion

While not everyone is keen on the US Plastics Pact Roadmap’s ambitious plans to create a circular plastics economy and reduce waste, many companies are more on board.

With more and more manufacturing companies agreeing to do their part to reduce plastic waste, The US Plastics Pact believes it can pave the way forward to a more sustainable plastics industry. The ACC also believes their plan can achieve those goals, while giving a more realistic timeline.

The important thing is, according to Collier, to do something.

“The timeframe is short, and the workload is immense, but if we choose to do nothing, the visions of a circular economy across the U.S. will give way to the status quo.”

With help from plastics manufacturers, companies can help make sure plastics remain both in the US economy, but out of the environment, for years to come.

by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

Types of PTFE Used in Rotary Shaft Seals

Rotary shaft seal applications, ranging from wind energy to automotive seals, require reliable performance in often challenging environments. To meet the challenges, filled-PTFE is often the material of choice for the seal lip. But which type of PTFE will work best for your application?

In this week’s blog post, we will go over the various types of PTFE used in rotary shaft seals, their pros and cons, and what type of PTFE is best for you.

Pros and Cons of Virgin PTFE

Looking at the pros and cons of virgin PTFE reveals where there is a need for filler materials when used in rotary shaft seals.

Benefits of virgin PTFE:

  • Extremely low friction
  • Low breakout friction
  • Generates very little torque
  • Dry running and no stick-slip behavior
  • FDA and USDA approved
  • Excellent chemical compatibility
  • Can handle pressures up to 500 psi
  • Excellent performance in the presence of extreme temperatures
  • Works well for large diameter seals

Virgin PTFE contains no additives or fillers and is ideal for food, dairy, and pharmaceutical applications as long the pressure is extremely low. It works extremely well in cryogenic environments but is otherwise limited to light-duty, slow rotary applications. It is recommended for use in applications that involve soft shaft surfaces. 

There are also areas where virgin PTFE can be improved for use as a rotary shaft seal. It has very limited wear resistance, stiffness, and compressive strength. In addition, it does not last long when used in conjunction with hard surfaces. The answer to these limitations for PTFE rotary shaft seals is the addition of fillers.

Fillers Available for Use with PTFE

PTFE is available with different fillers that can enhance its natural properties. In the context of rotary shaft seals, these are the most commonly used fillers:

  • MoS2-Filled PTFE
  • Carbon-filled PTFE
  • Carbon and Graphite-filled PTFE
  • Carbon and MoS2-filled PTFE
  • Glass-Filled PTFE
  • Glass and MoS2-filled PTFE
  • Polyimide-filled PTFE
Molybdenum Disulfide-Filled PTFE

MoS2-filled (Molybdenum Disulfide) is a mineral that is only added in small quantities and usually in conjunction with materials such as carbon or glass (although it can also work as a stand-alone filler).

MoS2 makes for a harder, slippery material. Because it acts as a lubricant, it can be used to increase the wear resistance, surface hardness, and compressive strength of PTFE without significantly increasing the coefficient of friction as much as, say, carbon or glass filler.  

Carbon-Filled PTFE

There are two different forms that carbon filler can take ( powder and fiber) and the carbon can be either natural or synthetic. Sometimes the term graphite is used synonymously with carbon, and while both are made from carbon, graphite is actually an allotrope of carbon in an extremely stable form. In addition, carbon comes in the form of short fibers or powder while graphite takes the form of flakes when used as a filler.

Because carbon serves as a natural lubricant (as does graphite), it increases the wear resistance of a PTFE rotary shaft seal without serious impact on the low coefficient of friction exhibited by PTFE. In addition, carbon is extremely neutral in a chemical sense and can handle extreme environments.  As a filler, carbon also contributes to the compressive strength of PTFE, enhances its thermal conductivity, and aids in the dissipation of static electricity (because of its natural conductivity).

In short, carbon-filled PTFE rotary shaft seals work well in aggressive environments that may involve extreme temperatures, high pressures, corrosive chemicals, and exposure to steam. Because carbon is not nearly as abrasive as glass fibers, carbon-filled PTFE works on a wider range of shaft surfaces.

Carbon and Graphite-Filled PTFE

Usually provided in a mixture of 23% carbon and 2% graphite (by volume), this particular grade of PTFE is a good choice for general-purpose rotary shaft seal applications. The combination of carbon and graphite also makes it ideal for situations where extrusion and deformation are problematic because of the additional stiffness provided by both carbon and graphite. The addition of graphite also increases the lubricity of the carbon-filled PTFE and provides self-lubricating properties that may be lost due to the use of carbon, which allows it to work well on softer shaft surfaces.

Carbon and Molybdenum Disulfide-Filled PTFE

There are also PTFE grades that combine carbon and MoS2. The result is increased wear resistance and better high-temperature performance while still maintains the capability of dry running.

Glass-Filled PTFE

Glass, usually in the form of glass fibers (i.e., fiberglass) and added at  25% (by volume), is very effective at enhancing both the wear resistance and strength of PTFE. It also provides additional stiffness, does not compromise the chemical neutrality of PTFE, is lightweight, and can contribute to the high-temperature performance of PTFE. Because of its abrasiveness, however, it should only be used on shafts with a high hardness value (surface hardness greater than 62 Rockwell C).

Note that the milled glass fibers are extremely small, with an average nominal diameter of 13µm and a length of about 0.8 mm. E glass, also known as electrical glass because of its insulating properties, is the only type of glass used for reinforcing PTFE and composite materials in general.

Glass and Molybdenum Disulfide-filled PTFE

To reduce the abrasiveness of glass without losing the benefit of the added strength, stiffness, and wear resistance, one option is to combine glass with MoS2. The typical percentages, by volume, are 15% glass and 5% MoS2. This particular grade works well in high-speed rotary applications, vacuum pressures, or when used with inert gases.

Polyimide-Filled PTFE

The final filler under discussion is Polyimide (PI), a synthetic resin known for extremely low friction (the lowest of all PTFE-fillers discussed) and non-abrasive behavior. It works well when used with very soft shaft materials such as aluminum or other plastics. PI-filled PTFE is also capable of dry running and works extremely well in start-stop applications.

Conclusion

PTFE is available with various fillers to enhance critical properties such as compressive strength, stiffness, and wear resistance. This has made it a common choice for many rotary shaft applications where it has been found to perform reliably.

If you are considering the use of a PTFE rotary shaft seal, contact the sealing group here at Advanced EMC. They will be able to help you select not just the correct type of seal but the ideal material for your design.

by Jackie Johnson Jackie Johnson No Comments

Why Geckos Can’t Cling to PTFE

It may come as a surprise to some but geckos are not, in fact sticky! Gecko’s can cling to glass and climb up walls, but geckos are not inherently adhesive. In fact, there are certain surfaces geckos can not cling to at all- mainly PTFE.

In this week’s blog post we will go over exactly how the gecko gets its Spiderman like abilities, and why exactly they can not seem to climb on PTFE.

A Sticky Situation

With certain types of geckos, their feet contain thousands of tiny, hair-like, hierarchical fibrils called setae, that end in even more, microscopic hair-like structures, so tiny they are not much larger than the wavelength of visible light.

These setae are also ultra-flexible, so when a gecko jumps to another surface, they are able to absorb an incredible amount of energy and redirect it, allowing the gecko to quickly cling from surface to surface.

There are two prevailing theories as to how this process works. One is known as van der Waals forces, or molecular attractions that operate over very small distances. The other, proposed by Yale research Hadi Izadi is that geckos use static electricity which allows them to cling to most surfaces.

Most surfaces except, it seems, Teflon.

Teflon – The Bane of Geckos?

Did you know that PTFE was engineering specifically to resist adhesion by van der Waals forces?  PTFE is composed of carbon and fluorine atoms.  Of all the elements known to date, fluorine has the highest electronegativity.  This causes PTFE to repel other atoms that come near it.  More specifically, it works against van der Waals forces.

Furthermore, the molecular structure of Teflon is such that the fluorine atoms surround the carbon atoms.  It repels any atoms that try to come near the carbon atoms, giving PTFE its outstanding chemical inertness.

Researchers at the University of Akron, in an effort to further understand, and hopefully replicate, gecko stickability, decided to see what kind of surfaces geckos can cling to, and Teflon was one of the materials tested.

The answer?

Because of its ability to resist adhesion by van der Waals forces- geckos, who potentially use van der Waal forces to cling to other materials, cannot cling to dry PTFE surfaces.

In Conclusion

So, it would seem that the very mechanisms that prevent geckos from walking up dry PTFE provide its most attractive characteristics: extremely low friction and high chemical resistivity.  So, when you are looking for a low-friction option for a bearing or seal, don’t forget the bane of gecko’s everywhere: PTFE.

by Jackie Johnson Jackie Johnson No Comments

A Win for Recycled PET (rPET)

A project conducted by the Natural Resources Institute at London’s University of Greenwich has resulted in the development of invisible UV-fluorescent markers used on the labels that, once placed on food-grade PET packaging, can be used to sort food from non-food. This would allow for easier sorting and greater use of rPET (recycled PET) among food packaging.

Chemical recycling of plastics is an alternative to traditional recycling, in that it converts plastics into either random or regular hydrocarbon fragments, after which it reforms and purifies these fragments into feedstock for repolymerization, which is the process of turning microbeads into solid polymers.

Traditionally, it has been very hard to separate waste from the plastic, a fact that made much of the plastic used in the food packaging industry unrecyclable.

In this week’s blog post, we will go over several different examples of manufacturers using this new tech

UK Company Goes Green

According to Greiner Packaging, one of the UK’s leading manufacturers in plastic food packaging, the need to include recycled content in their packaging has been on the top of their mind for several years now. In fact, Greinier was one of the founding members of the UK Plastic Pact, which set four overarching objectives to create a circular economy for plastics, of which one goal was to increase the rate of recycled content to 30%. Thanks to the new technology allowing recycled PET (rPET) and PP (rPP), they are closer than ever to achieve their goal.

As one of the larger producers of plastic packaging, Greinier saw it as a responsibility to be part of the solution. As media and consumers continue to post negative comments about plastics, they felt strongly that it is only those who work in the supply chain who can create meaningful change.

New FDA Approved Methods

Recycled Food Packaging

Back in the United States, the FDA has recently given the go ahead for Indorama Ventures, the world’s largest PET producer, to begin manufacturing recycled PET for use in food and drink packaging. The organization issued a letter which stated that Indorama Ventures glycolysis process can produce RPET for use with all food types.

According to the letter:

“Based on the description of the glycolysis you submitted for our review, we have determined that your process is similar to the glycolysis we have previously reviewed and found to be effective in cleaning and producing recycled PET of a purity suitable for food contact”

A Better Way to Ship

The FDA also approved the company SeaCap Plastic Packaging’s initiative to recycle PP into 100% recycled content corrugated cartons for shipping produce and seafood. These cartons could be exposed to a variety of temperatures ranging from room temp all the way down to freezing, as long as the food was not heated it remained safe.

According to the letter:

“Because of strict source control, there is little likelihood of unacceptable contaminant levels in the recycled PP material.”

Bottle-to-Bottle Recycling

Finally, the FDA also approved for the company Polymetrix to use a special HDPE recycling process, which, according to them is a “super clean” process that can recycle HDPE beverage containers into PCR for molding into 100% recycled-content bottles for milk, water and juices. These bottles could then be exposed to room temperature and refrigerated temperatures, making them safe and effective.

Austrian Company Expands Recycling System

The Austrian company PET-to-PET significantly increased it’s capacities for food grade recycled PET with the installation of another Starlinger bottle-to-bottle recycling system.

PET-to-PET recycled around 1.13 billion PET bottles into rPET in 2020.

The recoSTAR PET 165 HC iV+ bottle-to-bottle recycling system is the second line from Starlinger in operation at PET to PET. It has a throughput of 1,800 kg/h and achieves excellent decontamination results. The produced regranulate can replace virgin PET at a rate of 100%.

The company was able to increase throughput by 7.3% despite the COVID-19 pandemic with subsequent lockdowns

In Conclusion

Thanks to a new method of removing food waste from plastic packaging, the plastics industry, particularly plastic packaging manufacturers such as Greiner and SeaCap, are able to achieve greater sustainability. Also, plastic recyclers, such as PET-to-PET, are able to recycle even more content, and as such are growing their businesses even more.

Together, the plastics industry is one step closer to a solution to end plastic waste.

by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

When to Use a PTFE Rotary Shaft Seal

Rotary shaft seals are used in a host of applications, including many that involve harsh environments or strict compliance with FDA standards. But when should PTFE be used?

Industries Where Rotary Shaft Seals Are Used

A good place to start would be looking at some of the industries that depend on the reliable performance of PTFE rotary shaft seals:

Certain characteristics become apparent from this list, such as exposure to corrosive and aggressive chemicals, low friction, reliability, extreme temperatures, and high purity. 

When to Consider a PTFE Rotary Shaft Seal

There are certain circumstances under which PTFE is the material of choice for a rotary shaft seal:

  • When there is aggressive media involved
  • When low friction or dry running is needed
  • When applications involve high speeds
  • When thermal stability is critical
  • When FDA/USDA compliance is necessary
  • When high temperatures are involved
When there is aggressive media involved

PTFE is the most chemically compatible seal lip material on the market, with the main exceptions being rare fluorinated compounds and certain alkali metals. In addition, some halogenated and organic solvents can be absorbed by PTFE and cause temporary (and minor) changes in dimension. On the other hand, it is compatible with chemicals such as acetone, hydrochloric acid, sulfuric acid, citric acid, tallow, and sodium peroxide.

When low friction or dry running is needed

The coefficient of friction for PTFE ranges from 0.04 for virgin PTFE(the lowest for any material currently in existence) to 0.19 for 15% Glass / 5% MoS2. In addition, PTFE is self-lubrication, low coefficient of friction, and lack of stick-slip behavior results in significantly reduced breakout torque.

When applications involve high speeds

PTFE rotary shaft seals perform extremely well in high-speed applications with shaft surface speeds up to 35 m/s. PTFE also has the lowest coefficient of friction of both polymers and elastomers, making it perfect for seals that must have an extremely low coefficient of friction. This can be a critical factor in high-speed rotary shaft seal applications where significant heat can be generated between the rotating shaft and the seal lip. 

When thermal stability is critical

The maximum service temperature for PTFE is around 500°F and it has the highest melting point of all fluoropolymers, which is why it is used extensively in the oil and gas industry. However, it is often a material of choice for cryogenic applications down to -64°F because of its ability to maintain both its strength and elasticity at low temperatures.

PTFE also possesses a low coefficient of thermal expansion, ranging from 3.8×105 for 25% glass-reinforced PTFE to 5.5×105 for virgin PTFE. Because of this, seals made from PTFE are able to maintain their dimensional stability in operating conditions that can involve significant temperature changes.

When FDA/USDA compliance is necessary

PTFE is available in several different grades that are compliant with strict standards related to food, dairy, and water:

  • FDA 21 CFR 177.1550 for fluoropolymers
  • (EU) 1935/2004
  • 3-A sanitary standards 18-03 and 20-27
  • NSF/ANSI standard 61 for drinking water systems

PTFE also holds up extremely well to the intense cleaning and sanitation procedures that such seals may undergo, including hot water, steam, and aggressive cleaning compounds. In addition, PTFE is also hydrophilic, which can prevent water and moisture from being trapped around the seal during cleaning.

PTFE Grades for Rotary Shaft Seals

The most common PTFE grades used for rotary shaft seal applications are:

  • Virgin, which works well for slow rotary light duty
  • Glass-filled, which enhances strength and wear resistance but should only be used on shafts with high hardness 
  • Glass MoS2-filled, which increases wear resistance and strength without the abrasiveness of glass-filled
  • MoS2-filled, which increases wear resistance and life but should not be used on shafts with low hardness
  • Carbon-filled, which will increase wear resistance with less impact on the coefficient of friction
  • Carbon and MoS2-filled, which increases wear resistance, enhances high-temperature performance, and maintains the capability of dry running

Other Benefits of PTFE Rotary Shaft Seals

There are other benefits to using PTFE for rotary shaft seals, such as their wider temperature ranges and longer life span when compared to elastomeric seals. They also have low outgassing, good electrical insulation properties,  They are also inert to most chemicals and not only compatible with most lubricants but also self-lubricating).

If you are considering a PTFE rotary shaft seal, contact Advanced EMC today. Our team of experienced seal experts will work with you to determine is PTFE is the right material for your application.

by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

Underlip Temperatures and Rotary Shaft Seals

Many engineers do not realize the impact that underlip temperatures can have on seal performance and service life, especially when elastomeric materials are used. Learn why underlip temperature is so important and what you can do to reduce its impact.

What is Underlip Temperature?

Before we can define underlip temperature, we should start out with sump temperature, which refers to the temperature of the oil/lubricant. The lip of an oil seal moves across a very thin meniscus of oil. Some friction exists between the seal lip and the shaft which can generate enough heat to increase the temperature under the lip of the seal. This temperature at the point where the seal lip and shaft make contact is referred to as the underlip temperature and it can be higher than the sump temperature, especially for higher shaft speeds.

Why Underlip Temperature is Important

If the seal lip material does not possess good thermal conductivity, the heat generated can raise the underlip temperature high enough to exceed the operating temperature limits of the seal. This will result in accelerated wear and eventual seal failure. Signs of such a problem might be a seal lip that is …

  • Cracked
  • Blistered
  • Hardened

That is why it is important to use the estimated underlip temperature, as opposed to the sump temperature, as the expected operating temperature for a seal.

Estimating the Underlip Temperature

The underlip temperature is related to the friction between the seal and the shaft as well as the shaft speed. One way to estimate the increase in underlip temperature (in degrees Fahrenheit) based on shaft speed is to take the square root of the shaft seal speed in feet per minute.

Change in Underlip Formula | Advanced EMC Technologies

Before we look at an example, remember that …

Example 1

Suppose you need to estimate the increase in underlip temperature for a shaft rotating at 2500 fpm. The associated increase in underlip temperature would be ….

Example 2

If a 3” shaft is rotating at 2500 rpm and the sump temperature is 150°F, what would the underlip temperature be?

If the sump temperature is 150°F, then the underlip temperature is the sump temperature + the change in underlip temperature …

150°F + 44°F = 194°F

Faster Estimate

There is a faster way to estimate the underlip temperature, but it is not nearly as accurate: add 20°F for every 1000 rpm of shaft speed. However, the applicability of this estimate is limited to sump temperatures less than 210°F.

What Influences an Increased Underlip Temperatures

The underlip temperature is a function of several different characteristics. These include …

  • Shaft speed
  • Shaft size
  • Surface condition of the shaft
  • Friction between the shaft and seal
  • Thermal conductivity of the seal lip material
  • Oil level

In the chart below, you can see how the underlip temperature increases as the rotational shaft speed increase for a 1” diameter shaft. Even for a relatively small shaft, the increase in underlip temperature is significant.

Sump Temperatures vs Underlip Temperatures | Advanced EMC Technologies

In this next chart, it is evident how the change in underlip temperatures varies significantly as a function of shaft speed and diameter. In particular, notice that the upper limit for a 5-inch shaft rotating at 5000 rpm can lead to a 90°F increase in underlip temperature.

Change in Underlip Temperatures

When specifying a seal for a specific application, the engineer has control over the surface condition of the shaft, the friction between the shaft and the seal, and the thermal conductivity of the seal lip material. 

Reducing the Change in Underlip Temperatures

A smoother shaft combined with a low-friction seal lip material reduces the amount of heat generated at the point of contact, which can help reduce the increase in underlip temperature. 

Furthermore, a material with high thermal conductivity will be more likely to conduct generated heat away from the seal lip, further reducing the increase in underlip temperature.

Conclusion

Polymer seal lip materials such as PTFE and PEEK provide reduced friction, higher thermal conductivity, and better performance at high temperatures than their elastomeric counterparts when used in rotary shaft seals. When elastomeric seals are exhibiting signs of failure due to high underlip temperatures (i.e., cracking, blistering, hardening), then it may be time to consider a change in seal lip material.

At Advanced EMC, our rotary shaft seal experts can help you troubleshoot the cause of premature seal failure and advise you on the best choice of material for your application. Contact us today for more information.

 

by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

Rotary Shaft Seals for Automobiles

Even the simplest automobile requires a wide variety of seals, including rotary shaft seals. In this blog post, you will learn the basics of these seals within the context of the automotive industry, including the materials commonly used and why PTFE is so often recommended.

Rotary Shaft Seals

The goal of a rotary shaft seal is to prevent the leakage of oil, grease, and other fluids (e.g., transmission fluid, brake fluid, air conditioning refrigerant) while also keeping environmental contaminants out. These seals, sometimes called oil or grease seals, are used with bearings to keep lubricants within the bearing and environmental contamination out (i.e., lubrication retention). The term rotary refers to their ability to perform in the presence of both rotary and swiveling movements.

Where Rotary Shaft Seals Are Used in the Automotive Industry

Rotary shaft seals are a necessary part of many components and systems within cars, trucks, buses, high performance vehicles, and motorsports. And seals are needed for EVs (electric vehicles) and HEV (Hybrid Electric Vehicles) as well. These seals are also used with ATV (All Terrain Vehicles).  Some of the most common areas of application in automotive transportation are:

  • Air conditioning compressors
  • Braking systems
  • Pumps
  • Gearboxes
  • Power transmissions
  • Steering wheels

In most of these applications, the failure of a seal can lead to serious repercussions that include bodily injury, damage to the vehicle, and danger to those around the vehicle. Because of this, finding the right high quality seal for your application is extremely important.

Automotive Seal Operating Conditions

While the conditions for automotive rotary shaft seals do vary depending on their specific applications, the most common operating environments include …

  • Extreme temperatures
  • Environmental elements
  • Vibration and shock loadings
  • High contamination exposure
  • Chemical compatibility
  • Low friction
  • Wear resistance
  • Compliance with automotive standards

Environmental elements include exposure to sunlight, ozone, UV, and oxidation, all of which can accelerate the degradation of a seal. Contamination can include water, dirt, grease, and other debris, while the seals are likely to be exposed to materials such as diesel, hydraulic fluid, brake fluids, coolants, and chemical solvents. 

Materials Used in Rotary Shaft Seals

The basic components of a spring energized seal include a flexible inner seal lip that is bonded to a rigid outer component. In addition, some of these seals may include a spring energizer to keep the lip in contact with the sealing surface (note that spring-energized seals are most commonly used for oil retention as opposed to grease retention). Furthermore, some applications may require a seal with two lips where one serves as a wiper seal or dust lip to further prevent the ingression of contaminants.

The outer material for a rotary shaft seal is responsible for seal positioning and retention in the seal housing. This part of the seal is typically made from stainless steel, aluminum, or a rigid non-metallic composite material. 

The seal lip itself is made from either an elastomer or a polymer, with high performance PTFE being one of the most commonly used polymers. PTFE meets all the requirements for an effective, dependable seal lip, including the ability to handle high pressures, wide ranging chemical compatibility, extremely low friction, and excellent wear resistance. PTFE can also include additives such as carbon or MoS2 that can enhance properties such as strength, stiffness, wear resistance, and low friction.

Nitrile rubber (NBR, Buna-N) and polyacrylate rubber (ACM) are both widely used elastomeric materials for automotive rotary shaft seals. Another often used elastomer category is fluoroelastomers commonly referred to as FKM, Viton, and FPM. These offer superior performance compared to nitrile and polyacrylate, but they do cost more. 

PTFE Rotary Shaft Seals

At Advanced-EMC, we highly recommend the use of PTFE rotary shaft seals in the automotive industry where possible. They provide excellent performance in the harsh conditions often involved and are the most chemically compatible and low friction polymer on the market today. They can outperform elastomeric materials and are quickly replacing their use in many applications.

There are several grades of PTFE to choose from, including …

  • Virgin PTFE: light-duty service with slow speeds
  • 25% Glass-filled PTFE: wear and extrusion resistant but abrasive to shafts with a hardness less than 62C
  • 23% Carbon / 2% Graphite-filled PTFE: general purpose service where extrusion and deformation resistance are necessary
  • 15% Glass / 5% MoS2 filled PTFE: excellent wear resistance makes it well adapted to higher speed applications
  • Polyimide-filled PTFE: because of its low abrasion, works well with soft materials such as 300 SS and Aluminum
  • Modified PTFE: higher mechanical strength and better wear resistance

Conclusion

Rotary shaft seals can be found everywhere from the air conditioning to the power transmission system on a vehicle. Finding the right sealing solution that can handle the extremely harsh operating conditions and high temperature environments can be challenging, but PTFE has become one of the most popular choices for the seal lip material. 

If you are interested in an effective, reliable sealing solution for your automotive application, contact the knowledgeable team at Advanced-EMC today. Our engineers can work with you to find the right seal, made from the right materials, for even your most challenging designs.

 

by Jackie Johnson Jackie Johnson No Comments

How to Design and Select Seals for Oil and Gas

As competition for natural resources increases, petrochemical companies have begun to look to new locations that pose new challenges from arctic operations with low ambient temperatures to subsea equipment with high pressures and extreme temperatures.

In addition, companies face higher demands for safety, reliability, and environmentally-friendly designs and processes.  There is also the challenge of reducing the footprint of structures and equipment for exploration and production of oil and gas.  All of these factors combined have driven up the costs involved in exploration and production, and made the design of oil and gas systems far more complex.

The design and selection of appropriate seals is key to many of these issues…

When seals malfunction, unpleasant things result:

  • personal safety hazards,
  • explosions and fires,
  • damage to local ecosystems,
  • downtime,
  • and repair costs.

The selection of seals that are effective and reliable is vital.  Many engineers are turning to PTFE spring-energized seals for oil and gas operations.  In this post, we are going to take a look at why based on the three key factors for seal selection: temperature, pressure, and media.

Extreme Temperatures

Temperature is one of the key aspects of selecting a seal in the oil and gas industry.  High temperature steam can cause a seal to become brittle and crack.  Temperatures below the glass transition temperature of a seal can cause a seal to behave as a brittle material, resulting in unexpected failure.

Polytetrafluoroethylene PTFE (Teflon) behaves differently from other plastics when it comes to its behavior at extremely high and cryogenically low temperatures.  There is still considerable debate over what its glass transition temperature is, but researchers agree that it can hold its strength at higher temperatures than most polymers, and still behave in a ductile manner at lower temperatures.

There are several different types of PTFE polymer seal jackets are available for spring-energized seals.  They cover a range of temperatures; for example, polyimide filled PTFE can function in temperatures down to -450° F while glass/PTFE can operate in temperatures up to 500° F.

Pressure Issues 

Pressures between 1,500 psi and 15,000 psi are becoming commonplace, buy in some applications pressures are up to 25,000 psi. PTFE seals offer excellent performance at both low pressures – where the spring energized seals support sealing even at low temperatures – and high pressures.

Pressure specifications for a seal are not just limited to the sealing capabilities, but can affect other properties as well.  For example, pressure can affect the glass transition temperature of a polymer: high pressures can drive down the glass transition temperature of a polymer, causing it to exhibit unexpected brittle behavior.  This is especially critical in sub-sea environments.

Another issue with pressure is extrusion.  There are certain types of filled PTFE that offer extremely high resistance to extrusion:  Moly-Filled PTFE, Glass-Moly PTFE, and Polyimide-Filled PTFE.

Aggressive Media

Seals in the oil and gas industry are obviously are going to be exposed to chemically aggressive media.  Sour gas and acid gas are some of the most chemically aggressive materials encountered in this industry, but PTFE is resistant to their attacks.  When media such as this are combined with high pressures and extreme temperatures, PTFE still performs well.

Conclusion

Oil and gas companies are faced with increasingly complex challenges, and to meet those challenges they need cutting edge equipment with reliable components.  Spring energized PTFE seals are one of those components, providing a leak-tight seal, excellent performance over a wide range of temperatures, and compatibility with many corrosive chemicals encountered.