by Denise Sullivan Denise Sullivan No Comments

Advanced Properties and Applications of PTFE in Sealing Technology

PTFE has a unique combination of properties that make it ideal for use in sealing technology. One of its most notable characteristics is its ability to withstand extremely high and low temperatures. PTFE can operate in temperatures ranging from as low as -200°C to as high as 260°C, making it an excellent choice for applications where sealing performance needs to be maintained at extreme temperatures.

PTFE

Another significant advantage of PTFE is its chemical resistance. It is highly resistant to various chemicals, including acids, alkalis, and organic solvents. This makes it an excellent choice for use in chemical processing plants or other facilities where exposure to harsh chemicals is common.

PTFE also has excellent non-stick properties, which make it ideal for use in applications where adhesion could compromise the effectiveness of the seal. Its low coefficient of friction means that even under heavy loads or with repeated cycles of movement, PTFE will not experience significant wear or degradation.

In addition to these properties, it has outstanding electrical insulation characteristics and acts as a barrier against moisture and dust.

Manufacturing PFE Gaskets

Pure PTFE gaskets are produced by molding directly from suspended material or cutting (turning) from PTFE sheets (rods). Molding plates have uneven density and poor flexibility while turning plates have a relatively uniform density. Still, their material is curved due to the influence of the processing technology, which is not conducive to installation and use.

Modified PTFE gaskets add a certain proportion of functional materials, such as glass fiber or graphite powder, during production. The resulting gasket provides improved strength and durability compared with pure PTFE gaskets while maintaining this advanced material’s desirable properties.

Despite its many advantages, however, some limitations are associated with using PTFE in sealing applications. For example:

  • It can be difficult to achieve consistent compression when using pure PTFE gaskets due to their poor flexibility
  • PTFE can be prone to creep under sustained pressure, which can result in a loss of sealing performance over time
  • PTFE is unsuitable for high-pressure applications as it has low tensile strength and may deform or fail under high loads.

Applications for PTFE 

Despite these limitations, PTFE remains one of the most advanced materials available in sealing technology. Its unique combination of properties makes it ideal for use in various applications where reliable sealing is essential.

One potential application area where PTFE could increase use is the automotive industry. As electric vehicles become more prevalent, there will be an increased demand for seals that withstand harsh operating conditions. Its excellent temperature resistance, chemical resistance, and non-stick properties make it an ideal choice for use in battery enclosures and other critical components.

Another potential application area is within the food processing industry. Many food products are highly acidic or alkaline, which can cause traditional seals to degrade over time. PTFE’s chemical resistance makes it an excellent choice for acidic or alkaline foods. At the same time, its non-stick properties mean that any residue left on the seal after cleaning can easily be removed.

In conclusion, Polytetrafluoroethylene (PTFE) has many advanced properties that make it ideal for use in sealing technology. Its ability to withstand extreme temperatures while maintaining effective sealing performance sets it apart from other materials commonly used in this field. While some limitations are associated with using the material in certain applications, such as those involving high-pressure loads, its unique combination of properties means it remains one of the most important materials currently available. Over time, we may see even greater advances made with this remarkable material with continued research and development into new formulations and manufacturing techniques.

by Denise Sullivan Denise Sullivan No Comments

The Effect Surface Finish Has on PTFE Seals

Surface finish plays an essential role in the effectiveness of PTFE seals. The different finishes provide different degrees of contact between the two components, which affects the seal’s strength and reliability. In this paper, we will discuss the effect of surface finish on PTFE seal performance and suggest ways to improve seal quality.

Surface finish on PTFE

The Influences of Surface Finish on Friction

The surface finish is critical for polymer-based seals. Despite being considered a soft plastic, PTFE is significantly harder than traditional o-ring materials. Because of this, if the mating surface is designed for other materials, it can cause the PTFE seals to leak.

As you can see in the graph below, the improvement in the surface finish has a favorable effect on the frictional force required.

The following specifications were used in the force test that resulted in the above data.

  • Stroke Speed: 4 in/min (102 mm/min)
  • Shaft Diameter: 0.1875in. (4.762mm)
  • Ambient Temperature: 73°F (23°C)
  • Mating Surface Material: 17 -4 PH S.S.
  • Mating Surface Hardness: -40 Rc

Surface Finish Influences on Wear

The finish of the mating surface is one of the main factors in the PTFE seal wear. Wear on the seal is generally proportional to frictional force. In other words, less friction reduces the wear on the seal. 

The following graph shows how a smoother surface finish reduces the PTFE seal wear rate.

To calculate the wear rate in microinches RMS, we used the formula IN3 -MIN/LB-FT-HR -10-9. For microinches Ra, we used the formula CM3 -MIN/KG-M-HR -10-9.

We used the following test parameters during our testing to ensure accuracy for each test.

  • Surface Speed: 55 fpm (17 m/min)
  • Loading Stress: 55 lb./in2 (4 bar)
  • Wear Rate in Air: @ PV 3025 lb./in2 x ft/min (7.5 N/mm x m/min)
  • Mating Surface Hardness: Rc 42
  • Matin Surface Maerial 17 -4 PH Stainless steal
  • Mating Surface Finish: 1.6 to 111.1 microinches RMS (1.4 to 100 microinches RA)
  • Ambient Temperature: 70°F (21°C)
  • Ambient Relative Humidity 75% RH
  • Duration 5 Hours
  • Seal material FP

Influences on Sealing Ability

Finally, we looked at how the surface finish affected PTFE’s sealing ability. In general, the sealing ability of PTFE is proportional to the fluid’s viscosity. If a media, like gas, has a reduced viscosity, it is more difficult to seal. In these situations, having a smoother finish on the mating surface can help ensure fewer leaks.

We’ve found that different mediums require not only different finish ranges between them but also different finish ranges when considering if the surface is dynamic or static. You can see our suggested finish in the table below.

MediaDynamic Surface Static Surface 
Gases and Liquids at Cryogenic Temperatures2 to 4 microinches RMS
(1.8 to 3.6 Microinches Ra)		4 to 8 Microinches RMS
(3.6 to 7.2 Microinches Ra)
Gas at Non-Cryogenic Temperatures6 to 12 Microinches RMS
(5.4 to 10.8 Microinches Ra)		12 to 32 Microinches RMS
(10.8 to 28.8 Microinches Ra)
Liquids8 to 16 Microinches RMS
(7.2 to 14.4 Microinches Ra)		16 to 32 Microinches RMS
(14.4 to 28.8 Microinches Ra)

As you can see, the mating surface finishes can profoundly affect PTFE seals. Because of this, if the mating surface is designed for other materials, it can cause the PTFE seals to leak. Finally, we examined how this affected PTFE’s sealing ability. In general, the sealing ability of PTFE is proportional to the fluid’s viscosity.