Antiseize changes the amount of clamping force produced by a set amount of applied torque.
AN6 (3/8-24) bolt tightened to 75% of bolt proof strength. Camping force: 5,788 pounds. Required torque:
- Cadmium plated and dry 28.9 lb Ft.
- Moly anti-seize 19.9 Lb Ft.
Caution should be exercised if you use thread lubricants other than what the manufacture specifies. Thread lubricants change the friction between the threads, and between the nut and bolt face and the flange. This results in the bolt being over-tightened if thread friction is lowered, and under-tightened if thread friction is increased. The chart shows how different types of thread lubricants change torque requirements.
In an investigation of a helicopter accident it was found that by applying anti-seize to the entire fastener instead of just to the threaded portion (as required) resulted in a 70% increase in fastener stress from 24,440 to 43,262 lbf. with the same torque applied! The increased stress resulted in the bolt breaking. It was also found that cleaning the bolt with MEK (methyl ethyl ketone) increased the stress from 24,440 to 25,706 lbf. A good reason to consult the manufacturer's torque recommendations.
source:
"Failure of bolts in helicopter main rotor drive plate assembly due to improper application of lubricant" by N. Eliaz, G. Gheorghiu, H. Sheinkopf, O. Levi, G. Shemesh, A. Mordecai, H. Artzi,
Published in Engineering-Failure-Analysis #10, 443-451, www.sciencedirect.com
Moly is a LUBRICANT and not an ANTISEIZE. If you lubricate a thread with molybdenum disulphide as an anti-seize you are asking for trouble. There are many proper anti-seize compounds available, that when used correctly keep the torque requirements within the manufacturer's tolerances.
ReplyDeleteNot according to the U.S. Department of Defense: MIL-T-8383B "This specification covers the general requirements of one type of antiseize thread compound, composed of molybenum disulfide-petrolatum"
ReplyDelete