by Brandon Pascual Brandon Pascual 2 Comments

When to Use PTFE Rotary Shaft Seals

When to Use PTFE Rotary Shaft Seals: Key Benefits and Industry Applications. Rotary shaft seals are critical in a wide range of industries, particularly in environments that require reliable sealing solutions in harsh conditions or adherence to strict regulatory standards like the FDA’s. Among the materials used for rotary shaft seals, PTFE (Polytetrafluoroethylene) stands out for its exceptional properties. But the question is, when should PTFE be the material of choice for rotary shaft seals?

In this blog, we’ll dive into the industries that rely on PTFE rotary shaft seals, explore the specific scenarios where PTFE seals shine, and look at the unique characteristics of PTFE that make it an essential material for high-performance applications.

Industries That Rely on PTFE Rotary Shaft Seals

PTFE rotary shaft seals are used in a variety of demanding industries. These industries require seals that can withstand harsh environments, high temperatures, aggressive chemicals, and strict regulatory requirements. Here are some of the key sectors that depend on PTFE seals:

  • Oil and Gas: The extreme temperatures and pressures in oil and gas drilling and refining make PTFE seals a critical component.
  • Transportation (including motorsports): High-speed applications and exposure to harsh conditions like heat and friction make PTFE essential in vehicles, especially in motorsports.
  • Semiconductor: In semiconductor manufacturing, where cleanliness and chemical resistance are key, PTFE’s non-reactive nature is indispensable.
  • Aerospace and Defense: PTFE seals are used in applications that must withstand extreme temperatures and low outgassing for high-altitude or space environments.
  • Medical Devices: In the medical field, where both chemical resistance and FDA compliance are critical, PTFE rotary shaft seals are widely used.
  • Food and Dairy: PTFE is valued for its compliance with strict health and safety regulations in food processing and dairy systems.
  • Fluid and Air Handling: PTFE’s resistance to various chemicals and ability to handle a wide range of temperatures makes it ideal for valves and pumps.
  • Manufacturing: Across different sectors of manufacturing, PTFE seals are used where aggressive media and high-speed rotary applications are involved.
  • Renewable Energy: Wind turbines, solar power systems, and other renewable energy technologies utilize PTFE for its low maintenance and durability in varying conditions.
  • Chemical Processing: PTFE’s unmatched chemical compatibility makes it a staple in industries handling corrosive substances.

In these industries, some key characteristics stand out: exposure to corrosive media, extreme temperatures, the need for low friction, reliability in dynamic movements, and strict compliance with regulations. PTFE excels in each of these areas, making it the go-to material for many rotary shaft seal applications.

When Should PTFE Rotary Shaft Seals Be Used?

Certain conditions make PTFE the superior choice for rotary shaft seals. Let’s take a look at the specific circumstances under which you should consider using PTFE:

1. When There’s Aggressive Media Involved

In industries such as chemical processing, oil and gas, and even food and beverage, seals are often exposed to harsh, corrosive media. PTFE is considered the most chemically compatible material available for seal lips, making it a perfect fit for aggressive environments. While rare compounds like certain alkali metals or fluorinated substances can affect PTFE, it is generally resistant to chemicals such as:

PTFE’s ability to withstand these harsh chemicals without degrading makes it a standout choice for applications where chemical exposure is a daily occurrence.

2. When Low Friction or Dry Running Is Needed

PTFE is one of the most low-friction materials in existence, with a coefficient of friction as low as 0.04 for virgin PTFE, making it unmatched in reducing friction. PTFE is also self-lubricating, eliminating the need for external lubricants in many applications. In rotary shaft seal applications, this property is especially beneficial in situations involving:

  • High-speed applications
  • Dynamic movements that generate friction
  • Seals where breakout torque must be minimized

Moreover, the lack of stick-slip behavior in PTFE rotary shaft seals helps to significantly reduce breakout torque, improving the overall efficiency of systems that rely on these seals.

3. When Applications Involve High Speeds

In high-speed applications, PTFE rotary shaft seals truly excel. They can handle shaft surface speeds of up to 35 m/s—much faster than many other seal materials. PTFE’s low friction and heat-resistance properties also make it ideal for seals exposed to high-speed rotation, where the interaction between the rotating shaft and seal lip could otherwise generate excessive heat and cause premature seal failure.

In motorsports, aerospace, and transportation industries, where high rotational speeds are common, PTFE is often the material of choice for seals.

4. When Thermal Stability Is Critical

PTFE’s thermal stability is one of its defining features. It can function in extreme temperatures, making it suitable for both high-heat and cryogenic applications.

  • High temperatures: PTFE can withstand temperatures of up to 500°F, making it a popular choice in the oil and gas industry, where thermal extremes are frequent.
  • Cryogenic conditions: At the other end of the spectrum, PTFE can also handle temperatures as low as -459°F, making it a suitable material for cryogenic applications where most other materials would fail.

Moreover, PTFE seals have a low coefficient of thermal expansion, meaning they maintain their dimensional stability even when exposed to significant temperature fluctuations. This is particularly useful in environments where seals must be able to adapt to both rapid heating and cooling without losing their shape or effectiveness.

5. When FDA/USDA Compliance Is Necessary

In industries like food and dairy or medical devices, where strict regulatory standards apply, PTFE is highly valued for its compliance with standards such as:

PTFE also stands up well to the rigorous cleaning and sanitation processes required in these industries, including exposure to steam, hot water, and aggressive cleaning chemicals. In addition, PTFE is hydrophilic, which means it resists moisture and prevents the buildup of water around the seal during cleaning.

Grades of PTFE Used in Rotary Shaft Seals

Several grades of PTFE are used in rotary shaft seals, each offering specific benefits:

  • Virgin PTFE: Ideal for slow, low-duty applications.
  • Glass-Filled PTFE: Enhanced strength and wear resistance; should only be used with high-hardness shafts.
  • Glass MoS2-Filled PTFE: Increases wear resistance and strength without the abrasiveness of standard glass-filled PTFE.
  • MoS2-Filled PTFE: Extends seal life and wear resistance, best suited for higher-duty applications.
  • Carbon-Filled PTFE: Adds wear resistance without significantly increasing the coefficient of friction.
  • Carbon and MoS2-Filled PTFE: Improves wear resistance, performance at high temperatures, and dry-running capabilities.

These different grades of PTFE allow engineers and manufacturers to select the perfect material for their specific rotary shaft sealing requirements.

Other Benefits of PTFE Rotary Shaft Seals

There are several other benefits to using PTFE for rotary shaft seals:

  • Wider Temperature Range: PTFE performs well in a broader temperature range compared to elastomeric seals.
  • Longer Lifespan: PTFE seals generally have a longer operational lifespan, reducing the need for frequent maintenance and replacements.
  • Low Outgassing: In applications like aerospace, where outgassing is a concern, PTFE is valued for its minimal emissions.
  • Inert to Most Chemicals: PTFE’s chemical inertness makes it compatible with most lubricants and aggressive fluids, and it is also self-lubricating, which improves longevity and reduces maintenance.

Why PTFE Rotary Shaft Seals Matter

The versatility, durability, and unique properties of PTFE make it an ideal choice for rotary shaft seals in a wide range of demanding applications. Whether it’s resisting harsh chemicals in the oil and gas industry, ensuring compliance with food safety regulations, or operating in high-speed motorsports environments, PTFE is a material that excels where others might fail.

If you’re considering PTFE rotary shaft seals for your application, contact Advanced EMC Technologies today. Our team of experts is ready to help you find the perfect sealing solution for your needs.

by Denise Sullivan Denise Sullivan No Comments

Rotary Shaft Mating Surfaces: What You Need to Know

 

rotary shaft mating surfaces

Rotary seals are essential to maintaining the life of the equipment. While choosing the appropriate rotary seal materials, the rotary shaft mating surfaces are equally important. 

Below, we will discuss rotary seals, materials used for seals, and rotary shaft properties.

Rotary Seals

Rotary seals work to help keep the system lubricated while excluding contaminates. A properly fitting seal can positively impact the life of the lubricant. Oil’s life span at 86°F (30°C) is 30 years. However, as the oil heats up, the life span diminishes rapidly to no more than a 30-day life span.

The addition of contaminants and water also limits the life of the oil and the ball bearings. For example, adding .002% water into the oil lubricant will reduce the ball bearing’s life by 50%. The cause of the ball-bearing integrity loss is called hydrogen embrittlement.

Common Materials Used for Rotary Seals

Rotary seals come in several different materials. The optimal choice is dependent on the environment in which it is used. The most common materials include nitrile rubber, polyacrylate rubber, fluoroelastomers (FKM), and PTFE.

While these materials are a good choice for rotary seals, conventional rubber seals are common in static applications where temperature and chemical compatibility are not a concern. PTFE is the solution in high-speed dynamic service requiring low friction seals or where exposure to severe temperature or chemicals exists. There are different types of PTFE used for rotary shaft seals.  Users can choose from 

  • Virgin PTFE
  • Molybdenum Disulfide Filled PTFE (MoS2)
  • Carbon Filled PTFE
  • Carbon and Graphite Filled PTFE
  • Carbon and MoS2  Filled PTFE
  • Glass Filled PTFE
  • Glass and MoS2  Filled PTFE
  • Polymide Filled PTFE

Properties of Rotary Shafts Mating Surfaces That Affect Sealing Performance

Most often, rotary shafts are metal. However, the rotary shaft mating surface could be made from plastics. No matter what material the shaft is made from, some properties will affect the sealing performance of the shaft.

The properties of the rotary shaft that affect sealing performance are the shaft harness and the shaft roughness. The sections below explain in greater detail how the hardness and roughness of the rotary shaft can affect the rotary shaft’s sealing performance. 

Rotary Shaft Hardness

The hardness of the rotary shaft is how deep an indenter can penetrate the surface of a shaft. The shaft’s hardness is measured in the Rockwell C scale. The higher the number, the more complex the surface. 

As a general rule, the rotary shaft should always be harder than the seal to ensure the seal wears out before the shaft. Additionally, if you choose a harder surface, there are more options for seal materials.

With a rotary shaft with a hardness exceeding 45 Rockwell C, the seal doesn’t have time to polish and “bed in.” That means that any roughness on the surface will cause issues with the seal, wearing it down quicker than average. A shaft with a hardness under 45 Rc requires a softer seal which doesn’t have as long of a life.

The choice of hardness depends on the environmental pressure and shaft speed. For example:

  • In environments of 1000 psi with rates up to 150 sfpm, a shaft with 70Rc or greater is necessary
  • Settings using shaft speed 2500 sfpm and 0 psi need a hardness of 60Rc or greater.
  • Rotary shaft speeds of up to 150 sfpm and 0 psi need a hardness of at least 35Rc, with lubrication, or 44, with no lubrication.

Rotary Shaft Mating Surface Roughness

The rotary shaft’s roughness refers to the shaft surface’s unevenness. To measure the roughness, measurements of high and low points of the shaft and taking the difference to determine the machined tolerance.

Ideally, a smoother surface will increase the seal life and offer outstanding performance. But on the other hand, when the surface is exceptionally smooth, there is no way for the oil to flow between the mating surface and the seal. As a result, the seal wears out quicker without lubricant between the seal and the mating surface.

Of course, a high roughness level can allow leaks through low points on the shaft. Therefore, the rotary shaft roughness needs to be relatively smooth but not so smooth that the seal cannot be lubricated.

Rotary shafts work with the rotary seals to keep lubrication from dirt and water. Understanding the properties of the rotary shaft mating surfaces helps determine the type of seal material chosen. Contact us today for your rotary seal and shaft mating needs.