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.

Challenges of Rotary Shaft Seals in the Food Industry | Advanced EMC Technologies
by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

Challenges Faced When Specifying Rotary Shaft Seals for the Food Industry

A good seal should be reliable, experience minimal wear, be easy to install, and enhance equipment performance–but the rotary shaft seals on equipment for food preparation and handling involves much more.

The wrong rotary shaft seal for a food industry application can lead to expensive downtime, costly material waste, damaged equipment, problematic production delays, and even lawsuits. That is why it is critical that the rotary shaft seals that are used in the food industry be carefully specified–which involves several challenges.

Where Are Rotary Shaft Seals Found?

Dynamic rotary shaft seals are a key component for equipment such as …

  • High pressure homogenizers
  • Water purification equipment
  • Meat blenders
  • Distilled water pumps
  • Milk dispensers
  • Ice cream dispensers
  • Food portioning systems
  • Mixers
  • Screw conveyors
  • Milling rice, wheat, and flower
  • Holding tanks
  • Hoppers
  • Crushers
  • Dry product filling systems

Reliable rotary shaft seals are critical for food preparation and handling that includes chocolate manufacturing, baking, beverage manufacturing, bulk material handling, material and poultry processing, feed and grain processing, and dairy processing.

Exposure to Media

Seals in the food industry can be exposed to various types of media, including water, oils, acids, adhesives, powders, semisolids, suspensions, slurrys, and more. Some forms of media, such as acids and slurries, can accelerate the rate of wear experienced by a rotary shaft seal and lead to premature failure if the wrong material is selected. The choice of a material that is compatible both chemically and with the form of media is critical.

Sterilization and Sanitation

Many times rotary shaft seals will be subjected to sterilization procedures for CIP (Clean in Place), SIP (Sterilize in Place) and COP (Clean Out of Place). These methods may require aggressive cleaning agents or disinfectants, superheated steam, and potentially corrosive acids. Finding a suitable rotary shaft seal material that can handle the sanitation and sterilization methods in place for the target equipment can be challenging but not impossible.  

Another potential issue with regard to cleaning involves potential need for seals that can be disassembled and cleaned daily. The ability to spend minimal time in disassembly/assembly can have a significant effect on the cleaning process in terms of time, effort, and the quality of sanitation or sterilization achieved.

Temperatures

As just alluded to, seals may be periodically exposed to extremely high temperatures for cleaning or may simply operate in a high-temperature environment. However, not all temperature concerns relate to high temperatures: some applications involve sub-zero temperatures. The seal and material behavior at the extreme operating temperatures must be considered when specifying seal geometry and material.

Contamination

The food industry can be quite demanding when it comes to rotary shaft seals. Because food is involved, there are a myriad of concerns regarding contamination, with potential sources including lubricants for the seals, contamination from seals that have begun to leak, and contamination from the seals themselves. 

Compliance with Applicable Standards

Any part of a rotary shaft seal that comes into contact with food must conform to regulations such as …

  • USP Class VI
  • FDA 21 CFR 177.1680, 177.1550, and CFR 177.2600
  • (EU) 1935/2004
  • 3-A sanitary standards 18-03 and 20-27
  • NSF/ANSI standard 61 for drinking water systems
  • WRAS BS 6920
  • 3-A Sanitary Standards
  • (EC) No. 1935/2004

And compliance involves more than just the contamination concerns just discussed. The standards and regulations also look at answers to questions such as …

  • Does the material release any chemicals?
  • Does it exhibit outgassing?
  • Does it tend to absorb moisture?
  • Does it react chemically to acidic food ingredients?
  • Can the material be detected or traced?

Conclusion

Issues such as media type, sterilization and sanitation procedures, temperatures, contamination, and regulatory compliance are all challenges faced in the food industry, and that includes dynamic seals for equipment such as mixers and dispensers. Failure to address these issues leads to the premature failure of seals, which in turn leads to material waste, downtime, and production delays as well as the loss of customer confidence and even lawsuits. 

At Advanced-EMC, we understand the challenges involved with specifying rotary shaft seals for the food industry. Our team has the knowledge and experience to assist you in finding the right rotary shaft seal for all your food industry applications. We will work with you to choose a sealing solution that will provide excellent reliability, easy maintenance, and outstanding performance, all while complying with all applicable standards.