by Denise Sullivan Denise Sullivan No Comments

Expanded PTFE vs. PTFE

expanded PTFE

Polytetrafluoroethylene (PTFE) is one of the most common materials used for seals. Expanded PTFE, or ePTFE, is a soft material with many of the same properties as PTFE. However, ePTFE is more flexible, making it a better choice for specific applications.

How does ePTFE compare to PFE? For better clarification, let’s look at some of the aspects of the two.

What is Expanded PTFE

Expanded Polytetrafluoroethylene (ePTFE) is a PTFE resin created through a unique processing method that includes stretching, making it flexible. Expanded PTFE has a mesh structure ideal for medical equipment, food processing, oil and gas, and any other industry requiring tight seals.

Like its counterpart PTFE, ePTFE is non-toxic, hygienic, and chemically inert. In addition, its flexible nature allows it to seal tightly over surfaces where traditional seals won’t work. 

Advantages of ePTFE 

Expanded PTFE has high sealability, especially at low stress. It can compensate for irregularities in the surface to create a steadfast seal. The ePTFE gasket sheets have superior resistance to creep and cold flow and adapt well to sealing surfaces.

Applications ePTFE 

The ePTFE gasket sheets have a porous nature making them ideal for use in medical devices. For example, it is found in dental implants and barrier membranes in medical equipment. It is also found in electronic insulators and high-performance filters.

The oil and gas industries use ePTFE sheets to even out bumps and ridges in chemical pipe flanges. Smoothing out the bumps helps to provide a tighter seal between the flanges for better leak control.

Other applications for ePTFE include:

  • Pumps
  • Glass-lined flanges, reactors
  • Heat exchangers
  • Apparatus constructions

Properties of ePTFE 

ePTFE is 100% multidirectional and is physiologically inert for all recommended applications. Other technical properties of ePTFE sheets include the following:

  • Chemical resistance in the entire pH range (except for molten alkali metals)
  • Temperature Range: -268°C to 270°C (-450°F to 518°F).
  • Density of 0.85g/cm3 +/- 0.10g/cm3 
  • Pressure range of vacuum up to 200bar (3000psi)

What is PTFE

Polytetrafluoroethylene (PTFE), also known by its trade name Teflon®, was discovered in the 1950s by Dupont Chemist Roy J. Plunkett. It is a non-wetting, high-density material that is resistant to high temperatures.

Because of its high melting point and insolubility in most solvents, PTFE is the ideal choice for most sealing applications. In addition, PTFE can be unfilled (virgin) or filled with various compounds, such as glass or carbon. 

Advantages of PTFE 

Using PTFE as a seal or gasket has many incredible advantages. These benefits make it the ideal choice for applications across many fields. Let’s take a look at some of those advantages. 

PTFE has a high-temperature resistance. PTFE can withstand temperatures of up to 500°F or 260°C. In addition, PTFE is chemically resistant to aggressive chemicals such as solvents, acids, and bases. 

Along with its temperature and chemical resistance, PTFE has non-corrosive properties and can be used as electrical and thermal insulation. This versatile material comes in a wide range of thicknesses, fillers, and compressed sheets.

Applications PTFE 

There are several applications in which PTFE is the ideal sealing solution. Industrial plants use PTFE as envelope gaskets to contain leakages of the substances being managed. The substance’s water resistance makes it suitable for industrial plants, the food industry, and medical laboratories.

PTFE is also used in construction because of its low frictional quality, which extends the life of the PTFE. The sheets are also used in industries where highly reactive substances because of the sheet’s resistance to acids. 

Properties of PTFE 

PTFE’s low coefficient of friction is not the only property that makes it ideal for many sealing applications. Other properties include:

  • A density of 2.10e3 – 2.2e3 kg/m3
  • Tensile strength is 2.07e7 – 3.45e7 Pa
  • Max Temperature 250°C to 271°C (482°F – 520°F)
  • Melting Temperature 215°C – 339°C ( 599°F to 642°F)
  • Chemical resistance to the entire pH range (except for molten alkali metals)

Conclusion

Both ePTFE and PTFE are suitable for most sealing applications. Determining which product is necessary depends on the application. Contact us today to learn more about our PTFE sealing options.

by Denise Sullivan Denise Sullivan No Comments

Introduction to PTFE Lip Seals

PFTE Lip seals

Radial shaft seals are often found in aggressive environments with high temperatures and pressures. Unfortunately, these environments are also frequently dry-running and unsuitable for traditional radial shaft seals. So, what are the options if traditional radial shaft seals won’t work? Using PTFE lip seals as rotary shaft seals can offer better protection and longer life than conventional radial shaft seals. Understanding these lip seals are essential to helping you make the right choice for your sealing needs.

What Are PTFE Lip Seals

PTFE (polytetrafluoroethylene) lip seals have a lip on the interior diameter (ID) that allows it to fasten to an outer diameter (OD) of a metal casing or shaft. The seal is completed with a gasket sandwiched between the sealing lips.

Not all lip seals are spring-energized. Therefore, the force from radial contact is lower. The lower pressure allows the seal to function at higher surface speeds of up to 10,000 sfpm. This type of seal is for high rates, making it the go-to choice for sealing rotating shafts.

PTFE Lip Seal Fillers

PTFE Lip seals can be enhanced by using fillers instead of virgin PTFE. Fillers can help the seal withstand sintering temperatures. Some of the filled compounds include:

  • Carbon-Graphite
  • Carbon Fiber
  • Aromatic Polyester
  • Molybdenum Disulfide and Fiberglass
  • Fiberglass
  • Graphite
  • Mineral
  • Stainless Steel

Each filler offers higher temperature resistance and lower creep rates than virgin PTFE. In addition, some offer lower abrasion or better corrosive protection depending on the filler type. Which type of filler you want will rely on the application where you use the lip seals. 

Applications That Use PTFE Lip Seals

PTFE lip seals are found in most applications where speed is concerned. However, they also are ideal for conditions where highly corrosive compounds or in dry, abrasive environments. 

Aerospace

The aerospace industry needs seals that can cope with extreme temperatures, surface velocities, and high pressures. External gearbox seals are just one place where PTFE lip seals are used in the aerospace industry.

Lip seals can handle the extremes and offer advanced fuel consumption efficiency. Better efficiency of burning about half-gallon of fuel per mile can save airlines an operating cost of $1.7 million per year. 

Other instances in which the aerospace industry uses lip seals include military applications such as:

  • Lift fans for vertical lift
  • Wing flap and slats actuator seals
  • Rotorhead
  • Equipment in arresting system to catch aircraft as it lands on aircraft carrier decks

Automotive

In the automotive industry, PTFE lip seals are employed in the drive shafts of the top-fuel blowers in NASCAR engines. Traditional crankshaft seals were burning out in these engines due to the high speeds and rapid pressure increases within five minutes at racing speeds.

They are also in e-drive and cooling systems in electric vehicles. Lip seals in electric cars can handle the shaft speeds seen in these automobiles. Electric vehicles can run at over 18,000 RPM, a higher rate than gas-powered cars. 

Conclusion

PTFE lip seals are ideal for rotary shafts operating at high speeds and temperatures, such as in the automotive or aerospace industries. Choosing suitable fillers can also help extend the seal’s life. Contact us today, and we can help you determine which PTFE lip seal options you want.