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

Benefits of PTFE For Sealing Applications

PTFE (Polytetrafluoroethylene), also known by its trade name Teflon, is a polymer material commonly used in sealing applications that offers unparalleled stability and sealing characteristics across an extremely wide range of temperatures, from the extreme heat of a space shuttle engine to the cryogenically cold temperatures used to preserve

In this article, we will discuss how and why PTFE is one of the best materials to use for seals in a wide variety of applications.

Low Friction

PTFE has the highest melting point and lowest friction, and is the most inert of all the fluoropolymers. It has a continuous service temperature rating of 500 degrees Fahrenheit. Molding powders are excellent, fine cut granular resins, well suited for a variety of demanding chemical, mechanical, electrical and non-stick surface applications.

Such applications include:

  • Cookware
  • Outdoor Rain Gear
  • Medical Devices
  • And more!

Cryogenic Applications

Cryogenic seals are used with super-cooled media, like liquid hydrogen or compressed natural gas, at temperatures below -238°F and down to -460°F (absolute zero). Cold temperatures like this are rough on a seal because at these temperatures most materials begin to exhibit highly brittle behavior and lubricants typically cannot be used because they will freeze. PTFE seals, however, can handle temperatures all the way down to -450°F and are capable of dry running because of their extremely low friction. PTFE cryogenic seals are used in industries like oil & gas, pharmaceuticals, and aerospace.

High Temperature Applications

PTFE seals work well at the other end of the spectrum, too. They can continue to function in extreme temperatures up to 600°F, and continuous operating temperatures up to 600°F. Note that a filler may be required to enable the PTFE to dissipate heat more quickly. It’s not uncommon to see PTFE seals in petroleum or steam applications where temperatures greatly exceed 200°F.

PTFE is also non-flammable, making it ideal for use in applications such as jet propulsion engines. Where other materials would simply melt under the pressure of constant exposure to high temperature flames, PTFE is built to withstand even the hottest of environments.

The use of seals for high temperature applications include oil and gas industry and aerospace, to name a few.

Chemical Applications

The chemical resistance of PTFE is some of the best on the market. It is stable in most aggressive and corrosive media, including:

  • Acetone
  • Chloroform
  • Citric Acid
  • Hydrochloric Acid
  • Sulfuric Acid
  • Tallow
  • Sodium Peroxide
  • And more!

However, it should be pointed that that PTFE is not chemically resistive to liquid or dissolved alkali metals, fluorines and other extremely potent oxidizers, as well as fluorine gas and similar compounds. Outside of those, PTFE is an excellent choice for applications involving chemicals.

Oil and Gas Industry

Seals are critical for the safe and reliable operation of oil rigs across the globe. Not only do seals need to be able to withstand a wide variety of extreme temperatures, but they need to be able to handle extreme pressures as well. For well drilling, for example, seals need to handle pressures from 345 to 2070 bar (5000 to 30000 psi).

For those reasons, PTFE is an incredibly popular material to make oil and gas seals out of. Because of it’s resistance to heat, cold and high pressure, PTFE can withstand the rigors of oil and gas unlike any other material.

Spring-energized Seals

In order to retain sealing power under extreme temperatures, many engineers and designers go with spring-energized PTFE seals. The spring provides optimal sealing by forcing the lip of the seal against the mating surface and helps to account for dimensional changes as a result of temperature fluctuations.

A highly efficient seal is created as the system pressure increases enough to take over from the spring and engage the shaft or bore. The spring or energized seal assembly provides permanent resilience to the seal jacket and compensates for jacket wear, hardware misalignment and eccentricity. The jacket material is critical in design to assure proper seal performance.

Rotary Shaft Seals

Using PTFE in rotary shaft seals allows them to be able to run at higher pressures and velocities when compared to other materials. They are also able to have tighter sealing, often exceeding 35 BAR and can run at far more extreme temperatures ranging from -64 degrees Fahrenheit (-53 degrees Celsius) to 450 degrees Fahrenheit (232 degrees Celsius).

On top of that, they are:

  • Inert to most chemicals
  • Can withstand speeds up to 35 m/s
  • Compatible with most lubricants
  • Come in a wide range of sizes
  • And more!

Conclusion

PTFE is an ideal sealing material for both extremely high temperature applications and demanding cryogenic applications. It retains its key sealing properties: stiffness, strength, dimensional stability (may require spring energizer), low friction, and chemical compatibility- even in the most aggressive operating conditions.

Need PTFE sealing solutions? Advanced EMC Technologies is the leading provider of PTFE spring energized and rotary shaft seals in the US. Contact us today!

by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

Spring-Energized Seals for the Wind Industry

Spring-Energized Seals for the Wind Industry

There is little doubt that global interest in renewable energy sources remains high, and that includes wind-based energy sources. According to the World Wind Energy Association (WWEA), the overall capacity of wind turbines installed worldwide reached 650.8 gigawatts in 2019, representing a 10.1% increase from 2018. However, for increased growth in the wind industry, the design of wind turbines must become even more efficient and reliable — and wind turbine seals are one area where there is potential for improvement.

Wind Turbine Seals

Among over 5,000 components in a typical wind turbine, there are six places where you will always find seals:

  • Main bearing
  • Main gear
  • Pitch cylinder
  • Lock cylinder
  • Main and yaw brakes
  • Hydraulic accumulator

Another way of looking at wind turbine seals is by their location:

  • Rotor
  • Blades
  • Tower
  • Alternator
  • Gear Box

The importance of reliable seals in the wind industry cannot be overstated. They enhance the performance and efficiency of the wind turbines, extend their useful life, and minimize the costs and downtime associated with maintenance. Investing in the right type of seals for wind applications are critical, and traditional seals may not offer the sealing power and expected life that is needed.

Sealing Challenges in the Wind Industry

There are a host of challenges faced by engineers selecting seals for wind turbine applications beyond just vibration and high stresses caused by wind gusts and rotor speed variations. Because they are outdoors year-round, wind turbines are constantly exposed to UV and ozone which can cause seals to degrade more rapidly than normal. Then there are the extreme operating temperatures, from an icy  -40°F in Arctic regions to 140°F as a maximum standard operating temperature which can make it challenging to find a seal material that can maintain reliable performance. 

Then there are issues with abrasive substances such as sand, grit, and salt from seawater that can cause the lip of the seal to wear away. Then there are the inevitable changes in pressure that come from normal weather variations. The use of polymeric spring-energized seals, however, can address many of these challenges.

Spring-Energized Seals

In a spring-energized seal, a metal spring is used to maintain the seal lip in place to achieve a far more reliable seal for both keeping contaminants out and critical lubricants within. Spring-energized seals can maintain contact even in the presence of misalignments and uneven mating surfaces, dimensional changes resulting from temperature fluctuations or water absorption, premature wear from contact with abrasive substances, and vibration.

Various geometric configurations for the spring element are available, including coil, canted coil, helical, and cantilever springs. Each of these spring types has conditions for which they work best (e.g., cantilever springs work very well for static sealing). When the right spring geometry is coupled with an appropriate polymer, the result is a durable, rugged, reliable seal.

Arkansas Spring Energized Seal Company

Conclusion

One of the key aspects of wind turbine design involves selecting the right kind of seals — seals that will maintain consistent, secure contact even in the harshest of operating conditions. Spring-energized seals are an excellent way to contribute to efficient performance, reliability, and reduced maintenance requirements for modern wind turbines.

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Fluid Media and PTFE Spring-Energized Seal Performance


FLUID MEDIA AND PTFE SEALS:

You may not be aware of the fact that the fluid media has a significant effect on seal wear.  In this article, we are going to explore exactly how fluid media can affect the performance of your PTFE spring-energized seal.

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