Loctite 242 threadlocker on degreased steel fastener - lubricant?

[JD]

Please consider a fastened joint in which Loctite 242 anaerobic threadlocker
has been applied to the associated degreased steel screw upon assembly.

Numerous sources describe the lubricating quality Locite 242. I have
Loctite-generated data tables with torque coefficients that reflect this as
being the case for 242 applied to steel fasteners with a slightly oily film
already on them (Kt=0.15); but per analogous tables for degreased steel
fasteners with the 242 applied, the torque coefficient is the same as that
of a dry steel fastener (Kt=0.20). Can this be true?

Wouldn't some Loctite 242 lubricating qualities prevail even on a degreased
fastener, thus justifying the application of lubed (vs dry) torque values in
applicable torque specs? Overtorquing with dry torque values could be very
damaging from an tensile strength standpoint if the joint is lubricated, yet
undertorquing with lubed values if not applicable might permit gapping.

Any input would be much appreciated. I realize that testing is the best
answer to this question, but I'd like to learn from the experiences of
others first.

Thanks.
JW

[Jeff Finlayson]

JD wrote:

> Please consider a fastened joint in which Loctite 242 anaerobic threadlocker
> has been applied to the associated degreased steel screw upon assembly.
>
> Numerous sources describe the lubricating quality Locite 242. I have
> Loctite-generated data tables with torque coefficients that reflect this as
> being the case for 242 applied to steel fasteners with a slightly oily film
> already on them (Kt=0.15); but per analogous tables for degreased steel
> fasteners with the 242 applied, the torque coefficient is the same as that
> of a dry steel fastener (Kt=0.20). Can this be true?

Friction factors (k) are higher for smaller fasteners. See App. B in
MIL-HDBK-60 for a formula for estimating the friction factor.

(MIL-HDBK-60 is at http://stinet.dtic.mil/str/dodiss4_fields.html)

> Wouldn't some Loctite 242 lubricating qualities prevail even on a degreased
> fastener, thus justifying the application of lubed (vs dry) torque values in
> applicable torque specs? Overtorquing with dry torque values could be very
> damaging from an tensile strength standpoint if the joint is lubricated, yet
> undertorquing with lubed values if not applicable might permit gapping.

I would consider it more like a plated fastener (k = 0.15). That's
in between lubed and dry conditions (k = 0.11 & 0.2). If you are
concerned with bolt strength, lubed condition is the most conservative.

FYI: http://euler9.tripod.com/fasteners/