Various combinations of stainless steel, mild steel, and aluminum bolt-nut couples are tightened to 60 lb-ft in partial vacuum and in air. Results are given for tests with and without two lubricants /a fluorosilicone and a sodium silicate bonded dry-film/

Demorest, K. E.

English

NASA Technical Reports Server

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MLF5in Vacuum 
D MLF5in Air 
FS 1281 in Air 
EQ No Lubricant in Air 
September 1970	 Brief 70-1039 
NASA TECH BRIEF 
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I -_	
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I - -_ 01- _10AMMOMid;_ 
NASA Tech Briefs announce new technology derived from the U .S. space program. They are issued to encourage comrnerIdl 
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. 
Comparison of Release Torques of Tightened Bolts in Vacuum and Air 
SM	 SA	 SS	 MS	 MA	 MM
Average Release Torques for Six Couples 
Release torques were determined in air and in par-
tial vacuum (10-6 to 10 torr) for 0.5-in. NC-2 bolts 
tightened to 60 lb-ft. The bolt-nut couples were as 
follows: stainless-steel bolts in nuts of stainless steel 
(SS), mild steel (SM), and aluminum (SA); and mild-
steel bolts in nuts of stainless steel (MS), mild steel 
(MM), and aluminum (MA). All couples were tested 
ss ith and vithout two lubricants: FS-1291. a fluoro-
silicone; and MLF-5, a sodium silicate bonded dry-
film lubricant containing MoS,, graphite, and gold 
powder. 
Without lubrication and in air the release torque 
was highest with SM and MS couples; in vacuum, 
only SA showed significantly higher torque, but all 
couples except MM suffered some galling of threads. 
In air, application of FS-1281 made all release torques 
FtI Cued oerIeaI) 
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=19700000381 2020-03-17T00:43:41+00:00Z
more constant, yet the average torque remained high—
within 7 or 8 lb-ft of the tightening torque. The danger 
of contamination of the (vacuum) ion pumps prevented 
tests with the grease under vacuum. 
In air, application of MLF-5 to the bolt threads 
significantly reduced all release torques. In vacuum 
the same lubrication reduced dramatically the overall-
average release torque to roughly 50% of the tightening 
torque; both SA and MA couples showed release 
torques about 70% higher than those for pairings of 
the harder metals. 
It is concluded that release torque is a function of 
material, lubricant, and environment. Without lubri-
cation the torque varies little between air and vacuum, 
but galling is more probable in vacuum. Grease FS-
1281 reduces torques only slightly but makes them 
more constant. With all couples MLF-5 greatly re-
duces release torques in air and especially in vacuum; 
such lubrication is more effective between two hard 
surfaces than between a hard and a soft surface.
Note: 
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-TM-X-53936 (N70-17607) Bolt 
Torque Tests in Vacuum 
Patent status: 
No patent action is contemplated by NASA. 
Source: K. E. Demorest 
Marshall Space Flight Center 
(MFS-20773) 
Brief 70-10395	 Category 06


Comparison of release torques of tightened bolts in vacuum and air

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