Thread locker under the bolt head?

just_some_shmuck · Jul 16, 2018

Does anyone apply threadlocker under the head of the bolt?

Frequently, bolts are preloaded by measuring the torque used to tighten the bolt. Lubricants are frequently used on bolts to reduce the variability of the friction. When lubricating with oil, some people will recommend putting oil under the head of the bolt (assuming that the bolt is being rotated instead of the nut). Threadlockers reduce the friction (during installation) and reduce the variability of the friction - just like oil. Putting threadlocker under the bolt head would help just like oil under the head, but putting thread locker under the head feels weird to me. Is it common to put threadlocker under the bolt head?

hydtools · Jul 16, 2018

I think in most cases the thread locker gets wiped up the the and ends up under the head, anyway.

Ted

Screwman1 · Jul 17, 2018

Don't count on thread lockers to be a lubricant. We have tested some that reduced the nut factor and other brands increased the friction. I would not recommend doing it for either lubrication or locking- just increasing variability.

just_some_shmuck · Jul 17, 2018

Screwman1, I will be testing the nut factor. Thank you. That is good advice.

I've read in textbooks that threadlockers can act as lubricants, but some of the threadlocker datasheets made it sound like they would increase rather than decrease the friction (like you said). I was not sure if I was reading things correctly or not. Thank you for the insight.

racookpe1978 · Jul 23, 2018

Too much depends on the exact time between application of the thread locker on the joint, and the time delay until assembly, putting the nut on hand-tight, then pulling it to final torque value is complete. (Add temperature of the threadlock liquid and temperature of the parts, and temperature of the waiting area after torque is applied. )

IF (big "IF" there) you are always working in a perfect continuously operating assembly line with no breaks, it "might" work. But room air changes and startup and shutdown times will kill the first and last items assembled.

Also, forget about in-field repairs being done consistently to original spec's.

Use a lubricant.

dvd · Jul 24, 2018

Questions that I asked myself: How thick do you suppose the film of threadlocker under the bolt head is? Would the breakdown of the polymerized threadlocker, maybe related to cyclic loading, lead to a detrimental loss of tension in the bolt or clamped connection? What would govern the film thickness? Why is someone turning a bolt head without a washer?

Screwman1 · Jul 25, 2018

The film thickness under the head in the contact area is going to be negligible due to the contact pressure. I don't think that it would have any measurable effect on clamp retention. In the commercial world, there are millions of bolts installed and turned without the use of a washer- it is not good practice, but it gets done all the times in industrial applications.

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Thread locker under the bolt head?

just_some_shmuck

Mechanical

hydtools

Mechanical

Screwman1

Mechanical

just_some_shmuck

Mechanical

racookpe1978

Nuclear

dvd

Mechanical

Screwman1

Mechanical

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