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

The Benefits of Modified PTFE

Spring Energized PTFE Seal

Polytetrafluoroethylene (PTFE) is a chemically resilient fluoroplastic. An incredibly versatile material, PTFE is used (at least in some capacity) in nearly every industry imaginable. PTFE has its limitations, however.

What are the benefits of modified PTFE? Modified PTFE (or MPTFE) pushes the limits of regular PTFE, offering exciting new possibilities for a wide variety of applications. The reason behind such improvements? MPTFE, also known as TFM (trade name of Daikin) is a copolymer of tetrafluoroethylene and a small quantity of a perfluorinated modifier (perfluoropropyl vinyl ether, PPVE).

In other words, MTFM has added chemicals that make it stronger and more versatile than regular PTFE. And because of its strength and versatility, modified PTFE is used in a wide variety of industries. These include, but are not limited to, automotive, aerospace, medical device, LNG and more.

Modified PTFE is a Strong and Versatile Material

Modified PTFE has several advantages over regular PTFE. It has a substantially reduced deformation under load- 4% for Modified PTFE vs 10% for PTFE. This, as well as improved flexibility, make modified PTFE great for devices that need a little give but won’t break under pressure.

MPTFE also has lower porosity and permeability which helps reduce the amount of liquid absorption, making it perfect for products such as seals for wet environments. On top of that, modified PTFE has smoother surfaces, nonstick and dielectric properties, and a reduced cold flow. It has good metering properties, good electrical and mechanical properties. And with excellent fuel and additive resistance, MPTFE can replace conventional materials such as PTFE and make it easier to use more aggressive lubricants and seal designs.

In Conclusion

As you can see, MPTFE is an incredibly versatile and strong material to use. It can withstand more abuse than the average PTFE, giving it a clear advantage for a variety of applications. Use modified PTFE for your next project and let Advanced EMC Technologies help you create products that take full advantage of this wonderful material.

Contact us today to learn more!

by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

Why PTFE Rotary Shaft Seals Are a Great Choice for Food Processing Applications

While there are several options when it comes to approved polymeric or elastomeric seals for food processing applications, PTFE is one of the more popular choices–and that includes rotary shaft seals, as well.

Why are PTFE rotary shaft seals good for food processing applications? Rotary shaft seals for food processing equipment have to do more than an ordinary seal:  they also need to withstand aggressive cleaning and sanitation regimens that may involve corrosive chemicals, be approved for contact with food, and offer effective, reliable performance. 

How PTFE Rotary Shaft Seals are Used in Food Processing Applications

Food processing machines that make use of shaft seals include mixers, food portioning equipment, dry product filling systems, ice cream dispensers, milk dispensers, high-pressure homogenizers, water purification equipment, and distilled water pumps. They may be used with adhesives, flavorings, water, powders, preservatives, sauces, condiments, steam, and various fluids.

Operating Conditions

Rotary shaft seals for use in the food processing industry must be able to handle the standard operating conditions involved such as speed, temperature, and pressure. However, their operating environment can involve more than that: consideration has to be given to the type of media they will be exposed to (e.g., powders, extremely viscous fluids). 

PTFE is one of the polymers that have a proven track record with rotary shaft seals that have to function over a wide range of temperatures, pressures, and speeds, with various grades available that can offer more customized performance.

CIP/SIP

Rotary shaft seals must withstand the sterilization or cleaning procedures involved. CIP (Clean in Place), SIP (Sterilize in Place), and COP (Clean Out of Place) methods often require aggressive cleaning agents and/or superheated steam, powerful disinfectants, and potentially corrosive acids. 

PTFE is highly resistant to a wide range of aggressive chemicals, can handle repeated exposure to hot water and superheated steam, and will not react chemically to the powerful disinfectants and sanitizers that food processing equipment is exposed to.

Safe for Contact with Food

Any part of a rotary shaft seal that comes into contact with food must conform to the appropriate regulations, such as  FDA 21 CFR 177.1680, (EC) No. 1935/2004, and/or USP Class VI. Such approval is not easy to achieve: it takes into account whether the material releases any chemicals, tends to absorb moisture, goes through physical changes when exposed to high temperatures, reacts chemically to ingredients that are acidic, exhibits off-gassing, and more. 

PTFE comes in grades that are fully compliant with regulations regarding contact with food and FDA approved, making it a safe choice for rotary shaft seals for food processing equipment. In addition, it is the most chemically unreactive polymer on the market today.

Conclusion

Finally, PTFE rotary shaft seals have proven themselves to be highly reliable, which is why you will see them used in dangerous, mission-critical applications where safety and ruggedness are vital, such as those found in the oil and gas or aerospace industries. If you are looking for an FDA-approved rotary shaft seal for use in food processing applications, PTFE seals should be at the top of your list.

by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

PTFE Rotary Shaft Seals versus PTFE Spring-Energized Seals

PTFE is an excellent material for seals: it has extremely low friction, can operate in extreme temperatures, is dimensionally stable, available in FDA approved grades, and is compatible with a wide range of chemicals. When it comes to seals for rotating shafts, PTFE is often used with both standard rotary shaft seals as well as spring-energized seals.

Are rotary shaft seals the same as spring-energized seals? The short answer is no, they are not. While they serve many of the same purposes, the application for which you are using the seal will determine which type of PTFE seal you select.

Dynamic Seals

Dynamic seals, including those used in connection with rotating shafts, face far more challenges than static seals. If the shaft is misaligned, the seal lip can lose contact with the shaft surface during rotating, compromising the integrity of the seal. Shaft surfaces must be extremely smooth when rotation is taking place to minimize the wear on the seal lip and to make the seal more effective — and this is especially true when high speeds are involved. 

PTFE Rotary Shaft Seals

Rotary shaft seals are designed to provide a seal (and in some cases a wiping functionality) for circular shafts that are rotating or swiveling. Their job is to keep lubricants (either for the bearing or for the shaft itself) from leaking out while preventing the ingression of contaminants, which is why they are often called oil seals or grease seals. Many different designs are well adapted for specific sealing applications, such as mechanical pump seals, cryogenic temperatures, and harsh environments.

When designed and specified correctly, PTFE rotary shaft seals can provide excellent performance at relatively high speeds as long as the pressures are low (there are high-speed shaft seals that can handle higher speed levels, but again the pressure must remain low). In addition, the shaft must meet strict tolerances for surface finish and must be straight and correctly aligned. They are a cost-effective sealing solution for many designs

Spring Energized Teflon Seals

PTFE Spring-Energized Seals

PTFE spring-energized seals serve the same purpose as rotary shaft seals and can achieve all that rotary shaft seals can, with a few additions made possible by the spring energizer. For example, the presence of a spring-energizer enables the sealing lip to remain in contact with the surface of the shaft even when there is a significant pressure difference or the shaft is eccentric. The springer energizer also maintains seal integrity when there are significant changes in temperature that can affect the dimensions of the shaft size or the PTFE seal lip. The drawback for this enhanced performance, however, lies in the price: PTFE spring-energized seals are going to be more expensive than PTFE rotary shaft seals.

Polymer Spring Energized Teflon Seals

Conclusion

PTFE is an excellent material choice for many dynamic sealing applications, including those that involve high speeds, dry running capabilities, FDA approved materials, extremely high temperatures, or cryogenic temperatures. There are some dynamic applications where a PTFE rotary shaft seal simply cannot provide the necessary performance, and in those instances then a PTFE spring-energized seal should be considered.

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Factors Influencing Rotary Shaft Seal Performance: Pressure, Velocity, and Temperature


There are various factors that have a significant impact on the performance and behavior of a rotary shaft seal, including operating conditions (speed, pressure, temperature, environment), the mating shaft (hardness, surface finish, lead), and the choice of material for the seal itself.

In this blog post, we are going to review the operating conditions that must be considered for a successful rotary shaft seal.

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