Performance Lubricants
PFPE Lubricants in Aerospace Applications
Krytox™ perfluoropolyether (PFPE) lubricants offer thermal stability and low vapor
pressure at very low molecular weights.

Whitepaper
This whitepaper is widely based on an article by James Anderton,
posted on Engineering.com, May 25, 2017

Aerospace applications have some of the most demanding
requirements when it comes to lubrication. Compared toautomotive applications, for example, the temperature
ranges where a single lubricant must perform areconsiderably broader. Military aerospace applications
can involve even greater extremes, in addition to otherrequirements, such as long storage life.
For example, consider an aircraft sitting on the runway
in Saudi Arabia, where the ambient temperature might
be 50 °C. When the plane reaches cruising altitude, thetemperature is about -55 °C. Applications close to engines
can reach >200 °C operational temperature, with potential
for another 50-100 °C soak-back.

Introduction to Krytox™ perfluoropolyether
lubricants (PFPEs)
Krytox™ perfluoropolyether (PFPE) lubricants werediscovered in 1959 and showed remarkable thermal andoxidative stability. Potential uses envisioned then included
lubricant for the MACH 3+ turbine engine, hydraulic oil,rocket gear box lubricant, and even gyroscope oil.
In 1963, Krytox™ oil was used in a GE engine test forthe supersonic transport aircraft. In 1964, new Krytox™
perfluoropolyether (PFPE)-based grease formulations weredeveloped jointly with the U.S. Navy and Air Force, resulting
in military specification MIL PRF-27617, which wasdeveloped specifically for Krytox™. The first commercial
sales of Krytox™ were for nonflammable lubricants for theApollo space program in 1965.

Chemours™

Krytox™

Performance Lubricants

PFPEF

CF3CO
CF3CF CF2F2n

PolyphenylEthersnEsters
Polyalphaolefins

H 3COROSi
CH 3CH3nO

HOOnPriceSilicone
Polylalkylene
Glycols

OO

HmO
RO

H

R'Compared to other lubricants, PFPEs are theleast common and most expensive. This isbecause the supply chain for PFPEs is much
more complex and capital-intensive comparedto other lubricants.

HC5 H11Petroleum Oil

3-6

VolumeKrytox™ oils are made from only fluorine, carbon, andKrytox™ performance lubricants have demonstrated

oxygen—a mixture of compounds collectively known

the broad applicability to replace hundreds of purposeby many names—including PFPE, perfluoroalkylether

formulated conventional oils and greases throughout the(PFAE), and perfluoropolyalkylether (PFPAE). Krytox™

aerospace industry. There are several key properties thatperfluorinated oils and greases deliver high performance,

make them well-suited to aerospace applications.

perform at wide temperature ranges, and provide superior
quality lubrication under extreme conditions in comparison
to hydrocarbon alternatives.

• They will not burn or support combustion, even in fullyliquid or gaseous oxygen.

• The various grades of Krytox™ lubricants cover awide temperature range, from -75 °C to +360 °C

With a global distribution network and world-classtechnical service, Krytox™ is the lubricant of choice forextreme conditions and performance. The use of Chemours

continuous, with spikes to temperatures greater than
400 °C.

• Krytox™ lubricants don’t degrade or break down inunique PTFE thickener provides superior chemical andthe presence of aggressive chemicals, and offer athermal stability to all Krytox™ grease product lines. Manylong lubricant life with no potential for carbonaceousgreases are also available with additional anti-wear andanti-corrosion additives to further boost performance in
critical operations.

Key properties of Krytox™ lubricants

deposits.

• Their high lubricant film thickness protects them underhigh loads and across a range of speeds.

• They are compatible with most elastomers, polymers
and a wide range of metals, in addition to being

Component failures in aerospace applications can benonhazardous, nontoxic, non-regulated and completely

catastrophic, not only in terms of the capital costs of thechemically inert.

parts themselves, but also because of the ancillary costs ofrepair and safety risks they engender.

Testing Krytox™ oils and greases
Krytox™ greases are tested using numerous industry

Volatility is especially important in space applications,standard procedures for evaluating the life of lubricating

since the lubricant must be able to operate in a vacuum.

greases, including ASTM D-3336 and SKF R0F+ testing

Many space applications require lubricants that canmethods.

function for the lifetime of the component, since there will
never be an opportunity to re-lubricate.

Krytox™

Performance Lubricants

The first procedure involves rotating
an SAE No. 204 bearing at 10,000
or 20,000 rpm at an elevated testtemperature. Using CRC-type spindles,a thrust load of 5-15 lbs (22-67 N) andISO 100 PFPE-K baseoil, PTFE thickener,
anti-corrosion additive,
rated -40°C to +200°C

24,820 hrs =2 years, 10 months

a radial load of 15 lbs (67 N) are applied
to the bearing.
5475 hrs =7.5 months

The test cycle is 20 hours on and4 hours off for the requisite test

2016 hrs =12 weeks

temperature. The test result is stated

336 hrs =2 weeksin terms of the number of cumulative
hours the bearing will run without
exceeding the motor overload setpoint, torque overload set point, or overtemperature limit.

Results of the ASTM D-3336 testing on a Krytox™ grease compared against standard electric motor
bearing greases. They are for a lightly loaded 6204 bearing at 10,000 rpm. The test cycle was
20 hours on and 4 hours off.

The SKF R0F+ bearing grease life
testing method involves runningfive groups of two bearings. Various
different bearing types and sizes canbe used at speeds between 5,000

PFPE-PTFE has 64x longer life
than conventional polyurea

PFPE-PTFE has 21x longer life
than shear-stable polyurea

and 25,000 rpm and from room
temperature up to a maximum of230 °C. The pneumatic loads on thesebearings can be set between 50-900 N

L10 = 101 hrs(= 4.2 days)

L10 = 310 hrs(= 1.8 weeks)

L10 = 6445 hrs(> 38 weeks)radially and 100–1100 N axially. Thebearings are run until failure, allowing
for Weibull statistical life distribution
after just one test.

ISO 100 PFPE-K baseoil, PTFE thickener,
anti-corrosion additive,
rated -40°C to +200°C

Results from SKF R0F+ bench bearing life test using 6204 bearings at 10,000 rpm at 177 °C.

Krytox™

Performance LubricantsCommon aerospace applications for Krytox™
lubricants
Perfluoropolyether lubricants have been used in a whole
host of aerospace applications, including:• Oxygen system couplings, valves, regulators and seals• Liquid fueled rocket engines and ground support••••••••systems
Instruments, gyroscopes and gimbals
Seals, valves and pneumatics
Bearings
Leadscrews and ballscrews
Electro-mechanical actuators
Engine ancillary gearbox spline couplings
Anti-friction mounts, engine oil tanks
Non-conducting lubricant for sealing of electricalconnectors• IR sensors and optics
There are also several specific examples of Krytox grease
applications:• Krytox™ 283AD grease is used for the engine starter
spline shaft in PW 400-series engines and is the only
product specified for this application. Krytox™ 250AD
grease is approved for hydraulic and fuel pump splines
on PW engines for the A330, A340 and A380 aircraft.
Chemours is also currently working with a major OEM
on next-generation grease-lubricated fuel pump splines.

• Krytox™ AGL683 grease was specifically developed

One of the most interesting applications for PFPE
lubricants is in the F-35 short take-off and vertical landingfor electro-mechanical actuator bearings, gears(STOVL) variant. In this case, Krytox™ extreme temperatureand ballscrews. It’s approved for devices in cabin air

lubricants are used for exhaust duct bearings, drive gearsconditioning and nitrogen generation systems. The light,and actuators, all of which routinely exceed 320 °C. The

semi-fluid grease is designed for lifetime lubrication

F-35 also offers an example of using PPFE lubricants

across a temperature range of -70 °C to +180 °C and

to improve performance for traditionally non-lubricatedis specifically formulated for low-temperature starting

materials, such as the Vespel variable vane brushes foundtorque with an additive package designed for anti-in the F-35 lift fan.

fretting and anti-corrosion.

• Krytox™ AGL829 grease was developed as a fire-proof
grease for thrust reverser drive units to eliminate theneed for external fire blankets. The light gearbox greaseis specifically designed to be a sealed-for-life lubricant
for low-temperature applications (-60 °C) that are
subject to high vibration and loads.

• The Krytox™ XHT-BD series of greases were developedfor extra-high temperature applications and are basedon triply fluorinated high-viscosity base oils with ahigh-adhesion, non-melting thickener. Krytox™ XHTBDX is specified for O-rings and flexible couplings inenvironmental control systems that are used to direct
hot engine air for wing and tail de-icing. Components inthis application regularly see temperatures of 315 °C.

F-35 cutaway. (Image courtesy of Charles R. Davis/USAF.)

Krytox™

Performance Lubricants

Krytox™ lubricants in aerospace

The combination of thermal stability, chemical inertness

Failure in aerospace applications is not an option,and the capacity for low vapor pressures at very low

especially since operating conditions in aerospace canmolecular weights makes Krytox™ lubricants ideal for abe severe. Inadequate lubrication or lubricants that dorange of civil and military applications. From engine mounts,

not perform as intended can lead to increased aircraft

to fuel tank valves, to fighter canopy slide rollers and seat

maintenance downtime and component failures.

adjuster mechanisms, Krytox™ is the only way to fly.

F-35 STOVL lifting off at Eglin Air Force Base. (Image courtesy of USAF/Samuel King Jr.)

Krytox™

Performance Lubricants

The information set forth herein is furnished free of charge and based on technical data that Chemours believes to be reliable. It is intended for use by persons having technical skill, at their own
discretion and risk. The handling precaution information contained herein is given with the understanding that those using it will satisfy themselves that their particular conditions of use present
no health or safety hazards. Because conditions of product use are outside our control, Chemours makes no warranties, express or implied, and assumes no liability in connection with any useof this information. As with any material, evaluation of any compound under end-use conditions prior to specification is essential. Nothing herein is to be taken as a license to operate under or arecommendation to infringe any patents.
NO PART OF THIS MATERIAL MAY BE REPRODUCED, STORED IN A RETRIEVAL SYSTEM OR TRANSMITTED IN ANY FORM OR BY ANY MEANS ELECTRONIC, MECHANICAL, PHOTOCOPYING, RECORDING OR
OTHERWISE WITHOUT THE PRIOR WRITTEN PERMISSION OF CHEMOURS.

For product information, industry applications, technical assistance, or global distributor contacts, visit krytox.com, call +49 (0) 6102 82233 2758 or send an e-mail toPerformance-lubricants-emea@chemours.com.
© 2018 The Chemours Company FC, LLC. Krytox™ and any associated logos are trademarks or copyrights of The Chemours Company FC, LLC. Chemours™ and theChemours Logo are trademarks of The Chemours Company.
C-11533 (8/2018)