Fluorinated polyethers are suitable lubricants for rolling-element bearings in cryogenic systems. Lubrication effectiveness is comparable to that of super-refined mineral oil lubricants operating at room temperature

Dietrich, M. W.

Townsend, D. P.

Zaretsky, E. V.

English

NASA Technical Reports Server

September 1970	 Brief 70-10347 
NASA TECH BRIEF	
441 
NASA Tech Briefs announce new technology derived from the U .S. space program. They are issued to encourage commercial 
application. Tech Briefs are available on a subscription basis from the Clearinghouse for Federal Scientific and Technical 
Information, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Division, NASA, Code UT, Washington, D.C. 20546. 
Liquid Cryogenic Lubricant 
Fluorinated polyethers have been shown to be 
suitable and effective lubricants for rolling-element 
bearings in cryogenic systems. Their lubrication effec-
tiveness is comparable to that of super-refined mineral 
oil lubricants operating at room temperature. 
There has always been a need for reliable bearings 
for short term use in cryogenic systems. Now the need 
exists for bearings that can operate for long periods 
of time. These systems include high-speed rocket 
turbopumps which run several minutes, as well as 
cooling-system pumps with moderate speeds and 
loads which run several hundred hours. Present 
cryogenic systems are lubricated by the transfer of a 
dry lubricant film from the ball-retainer (cage) pockets 
to the balls and subsequently to the races of the bear-
ing during operation. This "dry transfer-film" method 
of lubrication provides only boundary lubrication. 
Wear, therefore, occurs on the rolling elements as 
well as on the races of the bearing. This wear leads 
to early failure and relatively short bearing life. In 
addition, wear in the ball pockets of the retainer can 
be excessive, leading to premature retainer failure 
and thus catastrophic failure of the bearing. 
A study and test program were conducted using a 
different approach to the problem of lubrication in 
cryogenic systems. The new concept involved the use 
of liquid lubricants. To be an effective lubricant in a 
cryogenic system, a fluid must be a liquid in the cryo-
genic temperature range, capable of operating at the 
maximum system temperature without evaporating; 
it must be chemically inert, not susceptible to water 
absorption, and must have good heat-transfer proper-
ties; additionally, such a fluid must be able to form a 
fluid film in the high-pressure region of a rolling-
element contact.
The test lubricants evaluated in this effort were a 
family of fluorinated polyethers having the following 
general formula:
F(CFCF2O)nCHFCF3 
CF3 
Four fluids, each having a different viscosity, were 
evaluated in two phases: first, to compare the lubricat-
ing characteristics of fluorinated polyether fluids at 
outer-race temperatures of 160° to 410°R (89° to 
227°K) with those of a mineral oil at room tempera-
ture; and second, to determine the effect of fluid 
viscosity, maximum Hertz stress, and contact angle 
on the system temperature. Lubrication effectiveness 
was analyzed with respect to wear and the deforma-
tion of the ball running track and compared with the 
effectiveness of a super-refined mineral oil at room 
temperature. 
Rolling contact under these conditions results in 
an alteration of the rolling-element surfaces. This 
effect is usually indicated in three basic forms: (I) 
elastic deformation; (2) plastic deformation; and (3) 
wear. Deformation and wear were essentially the same 
for the specimens run in fluorinated polyethers at 
cryogenic temperatures as for those specimens run 
(under the same working viscosity) in super-refined 
mineral oil at room temperature or slightly higher. 
These results indicate that the fluorinated polyethers 
as lubricants in the range of 160° to 410°R (89° to 
227°K) are comparable to mineral oil lubricants at 
moderate temperature, i.e., 560° to 760°R (311° to 
478°K), and also verify the fact that the fluorinated 
(continued overleaf) 
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States 
Government nor any person acting on behalf of the United States
Government assumes any liability resulting from the use of the 
information contained in this document, or warrants that such use 
will be free from privately owned.rights.
https://ntrs.nasa.gov/search.jsp?R=19700000335 2020-03-17T00:41:54+00:00Z
polyether lubricants can form elastohydrodynamic 
films at the cryogenic temperatures tested. They show 
that the fluorinated polyethers could be used in many 
cryogenic applications,, providing longer life and 
higher reliability. 
Notes: 
1. These lubricants could prove valuable in gas Iiqui-
fication plants and frozen food processing indus-
tries. 
2. The following documentation may be obtained 
from:
Clearinghouse for Federal Scientific 
and Technical Information 
Springfield, Virginia 22151 
Single document price $3.00 
(or microfiche $0.65)
Reference: 
NASA-TN-D-5566(N70-1 1365), Rolling-
Element Lubrication with Fluorinated 
Polyether at Cryogenic Temperatures 
(1600
 to 410°R). 
3. Technical questions may be directed to: 
Technology Utilization Officer 
Lewis Research Center 
21000 Brookpark Road 
Cleveland, Ohio 44135 
Reference: B70-10347 
Patent status: 
No patent action is contemplated by NASA. 
Source: M. W. Dietrich, D. P. Townsend, and 
E. V. Zaretsky 
Lewis Research Center 
(LEW-1 1075) 
Brief 70-10347
	 Category 07


Liquid cryogenic lubricant

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