Friction Factor

[barryodonnell]

Hi all,
Does anyone know the thread friction coefficient (average value) for an unlubricated waspaloy (i.e. nickel based superalloy) bolt mated with a waspaloy nut with silver coating?
In addition, the assembly will operate at elevated temperatures (approx. 600 deg. C). Can anyone suggest a reliable method for calculating the loss of preload due to temperature?
Thanks in advance

 

[PriamEngineering]

I don't know about the friction factor but you can calculate the loss of preload due to thermal expansion using the formula in ESDU 85021

 

[vonlueke]

Regarding the thread friction, per MIL-HDBK-60, 1990, p. 28, Table II, MIL-HDBK-60, 1990, Sect. 100.5.2, p. 26, Eq. 100.5.2, and Shigley, Mechanical Engineering Design, 1989, Eq. 8-19, p. 346, thread coefficient of friction is mu1 = 0.14 and torque coefficient (sometimes called "nut factor&quot is K = 0.185. Hope this helps.