For decades or even centuries, finding effective seals against dynamic surfaces has been a significant challenge that has grown in complexity since the early introduction and advancement of automobiles, airplanes and complex machinery.
Thermoplastics such as polytetrafluoroethylene (PTFE) lip seals, also known as rotary shaft seals, are relied upon more and more frequently today.
This article will take a closer look at the life of the mighty PTFE rotary lip seal and its evolution through the years.
The Origin of PTFE Rotary Lip Seals: The Rise of a Sealing “Superhero”
Every “superhero” has an origin story. The same can be said for PTFE lip seals. Early pioneers used rope, rawhide, or leather straps with fat on wheel axles as some of the first seals or sealing elements. However, these seals were prone to leakage and needed regular upkeep. Many of the elastomeric seal companies of today once operated as tanneries.
During the late 1920s, the first radial lip seal was created from leather and a metal fastener case. In the late 1940s, synthetic rubber began to take the place of leather. 40 years later, a number of manufacturers began to reassess the entire sealing system and often built sealing surfaces into seal assembly and incorporated multiple lips with vertical and horizontal contact points.
The Fluorocarbon Company was one such manufacturer. In 1982, the Fluorocarbon Company bought SealComp, which was at the time a small, family-owned lip seal business based in Michigan. After its purchase, the Fluorocarbon Company relocated SealComp to a plant in South Carolina that produced metallic seals for nuclear and petrochemical markets.
This new lip seal business focused on high-pressure hydraulic pumps and motors, military alternators, and other commercial products including aftermarket diesel truck crankshafts seals and thermostats.
In the mid-1990s, The Fluorocarbon Company changed its name to Furon, and was acquired by Saint-Gobain Seals in 2001. This added Furon to Saint-Gobain’s already robust spring-energized seals business that was founded in 1955.
In 1995, an elastomer band was added to Saint-Gobain Seals' lip seal outer diameter. This was done to eliminate the metal-to-metal press fit and to ensure tight sealing between the seal and the customer’s housing gland. Additional features were later added for seal removal and positive stops to position the seal and stop incorrect installation.
The Unique Anatomy of PTFE Lip Seals: Their “Super Powers” and Strengths
There are many similarities between elastomer rubber lip seals and OmniSeal® PTFE lip seal products, as well as a number of differences.
In their construction, both seals are very similar in that they use metal casing for structure, a press fit into a stationary housing gland, and a wear lip material to rub on the rotating shaft. They also use a similar amount of space when in use.
It is the elastomer lip seals that are the most common shaft seal product on the market, which are directly molded to a metal casing that provides the necessary rigidity. The majority of elastomer rubber lip seals use an extension spring for the loading mechanism for tight sealing. Typically, the spring is found directly above the seal to shaft interface contact point, giving the necessary loads to pinch off the oil film.
OmniSeal® PTFE lip seals do not use extension springs for sealing in the majority of cases. Instead, these seals respond on any loads applied to the stretching of the sealing lip and bend radius produced by the metal casings. When compared to elastomer lip seals, PTFE lip seals use a far wider lip to shaft contact pattern. PTFE lip seals also make use of a lighter unit loading, but a wider footprint. Their design has taken this direction to address the wear rate, and these changes were made to lower the unit loading, which is also known as PV.
The specific application for PTFE lip seals is found in sealing rotating shafts, in particular those with high speed. They offer an excellent alternative to elastomer rubber lip seals if the conditions are challenging and exceed their capabilities.
Essentially, PTFE lip seals were designed to bridge the gap between conventional elastomer lip seals and mechanical carbon face seals. As they can operate at higher pressures and velocities when compared to most elastomer lip seals, they are an excellent alternative.
Their performance is not adversely affected in hostile environments with extreme temperatures, aggressive media, high surface speeds, high pressure, or lack of lubrication. A good example of PTFE’s superior functionality is in industrial air compressors, where they are configured to provide in excess of 40,000 hours of maintenance-free service.
The fabrication of PTFE lip seals is subject to some misconceptions. Elastomer rubber lip seals mold rubber directly to a metal casing. This metal casing offers the necessary rigidity while the elastomer takes on the working portion of the seal.
In contrast, PTFE lip seals cannot be molded directly onto metal casings. PTFE materials do not transition into a liquid state or a state that allows the material to flow; as a result, PTFE lip seals are created by machining the sealing members that are then assembled into a metal casing, followed by mechanical clamping.
Important factors including shaft speed, surface velocity, operating temperatures, the media being sealed, and system pressures should all be carefully considered when selecting your precise fit sealing solution for a rotary application. Your decision should also be informed by a number of other operating conditions, but the conditions noted above are of primary concern.
PTFE Lip Seals to Your Rescue: Going Against “Archenemies” and Challenges
With great power comes great responsibility. Over time, Saint-Gobain Seals' focus has moved to applications asking more of PTFE lip seals. The seal's ability to cope with challenging industrial, automotive, and aerospace applications are one of their key benefits.
They are able to run at higher pressures and velocities on rotating shafts when compared to elastomer lip seals, and their advantages don’t stop there. Other benefits of PTFE lip seals include:
- Tight sealing, even under high pressure in excess of 35 BAR
- Ability to run at temperatures far above or below elastomer rubber lip seals (with typical temperature ranges from -53 °C to 232 °C)
- Elastomer coatings on the seal’s outer diameter make for easy installation without damaging mating hardware
- Available in custom designs and a wide range of sizes and materials
- Inert to most chemicals
- Withstands high speed in excess of 35 m/s
- Low friction and ability to address rotating equipment and vibration for longer life
- Compatible with most lubricants and able to run in dry or abrasive media.
PTFE Lip Seals Unite: OmniSeal® and DynaLip® Sealing Solutions
Two of Saint-Gobain Seals’ common types of lip seals are OmniSeal® PTFE metal-cased rotary lip seals and DynaLip® polymer seals, both of which are interchangeable. The main differences between the two are seen in their construction. Metal-cased seals use sheet metal to form seal casings, where the sealing lips are then assembled for the seal to be mechanically clamped.
Created in the early 1970s, OmniSeal® rotary lip seals are able to withstand hostile environments with temperature ranges from -53 °C to 232 °C, demanding chemical environments, and dry and abrasive media. Dynamic rotary sealing applications for PTFE seals include:
- Turbine engines
- Diesel engines
- Pharmaceutical processing
- Food processing
DynaLip® seals came around a decade after OmniSeal® rotary lip seals. Their creation became a necessity when Saint-Gobain Seals began working on a military application for blending and mixing highly explosive materials. Metal-cased lip seals were deemed categorically unsuitable for this purpose due to the chance of them coming into contact with rotating shafts mixing explosives. As a result, Saint-Gobain Seals’ design engineers conceptualized a lip seal without metal that still retained its key benefits.
With DynaLip® seals, the need for metal components was eliminated entirely as the whole seal was machined from the same polymer material. In most cases, an elastomer O-ring is used between the seal outer diameter and the mating housing bore. The O-ring provides tight static sealing and anti-rotation. In contrast, OmniSeal® lip seals can be made of over three different materials encased in metal casing.
Today, the original DynaLip® seals have triggered a number of different versions that are also ideal for field installation as they do not require specialized tools for installation, and also for applications that require the seal to be removed for cleaning. These seals are often more cost-effective due to their simple design.
How are OmniSeal® PTFE lip seals, DynaLip® polymer seals and other lip seals from Saint-Gobain Seals making THE difference in our daily lives?
When You Need Speed
PTFE lip seals can offer brilliant sealing capabilities and low friction in dry or abrasive media. They are often suitable for challenging applications where speed is necessary.
A great example of where PTFE lip seals replace elastomer and carbon face seals is in the air compressor market. Saint-Gobain Seals began working with most major air compressor companies in the mid-1980s, where they replaced rubber lip and carbon face seals that were prone to leaking.
The original designs were based on conventional, high pressure lip seals and, over time, as demands increased and better performance was needed, seals were required to have zero leakage and extended seal life.
New technologies were developed to more than triple the lifespan of the seals while always maintaining tight leak control. Due to this, Saint-Gobain Seals PTFE lip seals are considered the industry standard with the ability to offer over 40,000 hours of maintenance-free service.
In Screw Compressors
PTFE lip seals offer excellent leak control and the ability to run at 1,000 to 6,000 RPM with a huge range of lubricants and over extended periods of time (15,000 hours) so as to reduce warranty claims. Saint-Gobain Seals offer shaft seals ranging from 0.500 inch to 6.000 inch diameters (13 mm to 150 mm) for the screw compression industry.
Mixers are another area in which seal customization is common in this industry. Saint-Gobain Seals’ customers in this industry need seals to handle shaft deflection and wobble of up to 0.300 inches (7.62 mm), which is a huge dynamic shaft runout. To handle this along with the operating rotational speed, Saint-Gobain Seals offers a patented, floating lip seal design.
In Freon Recovery Pumps
OmniSeal® lip seals are easy to install, address strict EPA leakage requirements and are also compatible with oil and refrigerants and for use in small spaces for the entire lifespan of the pump.
Additionally, Saint-Gobain Seals’ lip seals address dynamic sealing environments, extreme speeds, pressures, and temperatures present in vacuum pumps, along with blowers, chemical pumps, encoders, alternators, drilling and tapping spindles, hydraulic motors and pumps, and air conditioning recovery pumps, among many more applications.
Their seals are also used on equipment that requires FDA-approved materials used in the following machinery:
- Hygienic motors seals
- Pharmaceutical mixers
- Pharmaceutical pill compactors
- Food processing equipment
- Food saws
- Mixing equipment.
All of these are demanding applications and require very low seal frictional drag to keep temperatures down. As well as being FDA compliant, seals must be free of cavities that may allow materials being sealed to become trapped, as well as be compatible with acids, bases and cleaners. They are also required to handle high-pressure wash-down and pass IP69K testing.
Saint-Gobain Seals’ lip seals are used in auxiliary power units (APUs), turbine engines, starters, alternators and generators, fuel pumps, Ram Air Turbines (RATs) and flap actuators, which is one of the largest markets for lip seals.
The APU was deployed on US Airways Flight 1549 (Miracle on the Hudson), and provided electrical power to help land the plane safely. Saint-Gobain Seals’ lip and spring-energized seals were installed in the core system of this plane, which is considered critical for flight and has to work 100 percent of the time when deployed.
There are a number of reasons why aerospace manufacturers depend on lip seals such as these. Custom-designed OmniSeal® lip seals provide tighter seals and enhanced performance over their elastomer counterparts. They also require less space than mechanical carbon face seals in turbine shafts and external gearboxes.
They can cope with temperatures ranging from -65 °F to 350 °F (-53 °C to 177 °C) and pressures up to 25 PSI (0 to 1.7 BAR) with a typical surface velocity of 2,000 to 4,000 ft. per minute (10 to 20 m/s). Some of the Saint-Gobain Seals solutions in this area can run at speeds of over 20,000 feet per minute, which is equivalent to 102 meters per second.
Another big market is found in aircraft engine seals where lip seals are used in external gearbox seals for major aircraft engine builders. Saint-Gobain Seals’ lip seals are also used in geared turbofan jet engines. This type of engine sports a gear system that separates the engine fan from the low-pressure compressor and turbine, allowing each module to operate at optimal speeds.
As a result, they can offer advanced efficiency. Around a half-gallon of fuel burnt per mile in a typical airliner, this more efficient engine is expected to save an average of $1.7 million in operating costs per airliner per year.
Along with supporting commercial industries, PTFE lip seals also find application in the military, in particular in the Department of Defence. This includes uses in fighter jets, aircraft carriers, and helicopters.
PTFE lip seals are used on a wide range of military aircraft; for instance, in lift fans for vertical lift, helicopter gearbox engine seals with their spring-energized seals also being used in the rotorhead, and wing flap and slats actuator seals, as well as in critical equipment in arresting systems to catch the aircraft as it lands on the deck. It is incredibly important that the equipment used for these applications does not fail.
Saint-Gobain Seals’ lip seals are put to work in some of the most challenging applications in crankshafts, distributors, fuel pumps and cam seals, which are used in the racing industry where naturally, engines are frequently pushed to their limits.
The majority of NASCAR teams and Indianapolis car engines make use of Saint-Gobain Seals lip seals. In fact, every top qualifier and finisher at Indianapolis in 2019 used lip seals in at least the front and rear crank shaft. Saint-Gobain Seals also has a patented design created specifically for NASCAR to rectify common problems causing PTFE split seals to fail.
When crankshaft seals in restrictor plate engines were being burned out at high speeds and rapid pressures at a recent race at Daytona Super Speedway, a top NASCAR engine builder turned to Saint-Gobain Seals lip seals. The result was a win-win for everyone as Brad Keselowski and the #2 Penske Ford won the race while using Saint-Gobain Seals’ lip seals. To add to this successful event even futher, four of the top five finishers drove cars with this top builder’s engines that benefited from these lip seals too.
Yet another use for Saint-Gobain Seals' lip seals in racing is in top-fuel blowers. There are extreme conditions in these engines, with every element bending, shaking, and twisting, causing parts to come into contact with each other that usually shouldn’t. As such, the average lifespan of a top-fuel blower is less than five minutes when used at racing speeds.
Saint-Gobain Seals' lip seals are used on the drive shaft of the blowers. They can cope with temperatures from -40 °F to 350 °F (-40 °C to 177 °C), pressures from vacuum to unknown high-pressure spikes, and shaft speeds of 4,000 to 14,000 RPM.
In turbochargers, OmniSeal® lip seals run at high speeds of 4,000 to 36,000 RPM and can cope with extreme temperature ranges from -40 °F to 350 °F (-40 °C to 177 °C), with limited lubrication over an extended seal life.
E-drive and cooling systems in electric vehicles also make use of Saint-Gobain Seals' lip seals. The shaft seals are required to run at much higher speeds than on gas driven engines, with the majority of engines running at over 18,000 RPM.
The PTFE Lip Seal Story Doesn’t End There
While all of the above examples are just some of the main areas in which PTFE have found applications, they are also relied on in demanding applications in the life sciences, with piston cup seals for oxygen concentrators to improve patients’ breathing and mobility. These particular piston cup seals use unique spin forming technologies to minimize seal friction drag, which extends the time the unit can be used without needing to be recharged. Custom blended materials help to maximize performance for this application.
Saint-Gobain Seals’ lip seals are also making an impact in rescue applications. They are used to propel fluids in pump systems as fire fighters spray foam retardant. When compared to PTFE seals, most elastomer rubber lip seals would not survive the chemicals used in these systems.
Extensive Experience for Every Need
Whatever your needs, Saint-Gobain Seals draws on extensive experience in designing quality, innovative sealing solutions to address and improve performance in specific applications. Through a co-engineering approach, Saint-Gobain Seals engage with their customers’ engineers from the very beginning of a project to develop and meet specific requirements, from optimal sealing jacket material formulations, sealing jacket design configurations, to optimal spring energizer configurations, to arrive at the best result.
Saint-Gobain Seals are always looking for ways to improve the design and manufacture of their seal products. Upper limits in speed, pressure, and temperature of their products are found through rigorous testing and they continually aim to go beyond the perceived limits of seals.
Today, Saint-Gobain Seals' rotary lip seals on the main turbine shaft of turbine engines are easily able to run at speeds and temperatures nobody thought was possible just a few years ago. Saint-Gobain Seals also focuses on designing features that offer multiple benefits, from shipping mandrels to help keep sealing lips formed, and customized mandrel design for use as a multi-purpose installation tool.
This information has been sourced, reviewed and adapted from materials provided by Saint-Gobain Seals.
For more information on this source, please visit Saint-Gobain Seals.