Nylon lock nuts...OK to use underwater?

[paulyg]

I would like to suggest changing from a slotted type locknut to a "nylok" type because of extensive galling we have seen in some applications. Both the nut and threads were stainless steel. The application involves the chamber where the fastener is located being flooded with hot, dirty water, then drained on a periodic basis. The thread is a large size. I am concerned that the nylon may absorb water over time and the lock nut will lose tension. Does anyone have prior experience in this area.

 

[ZoltanT]

Nylons tend to absorb water and will swell slightly. I would be more concerned with the changes in temperature.

There are available lock nuts that have an embedded "circlip" where the nylon usually is in a "Nylok" nut. The circlip is flat but when installed, it is forced to take on a helical shape as it follows the valley of the thread. These can handle a wide variety of environments. I have seen them under the name of "Glenloch". A search for Glenloch on the net shows an Australian company (

http://www.jglen.com)

only. I've only seen these in stainless steel and a common use for them is automotive exhaust systems.

I would suggest talking to a fastener specialist and see if they can locate any for you.

 

[bcd]

Nylok nuts are extensively used on nuclear submarines. Proof positive that they are OK to use in water. Nylon will swell in humid air, and Nylok nuts are used outdoors as well without any related problems. Water and Nylon as used in locknuts will not be an issue.

Only problem I have encountered with Nylok type nuts is if they are reused too many times. Then their locking feature becomes ineffective.

bcd

 

[bmoorthy]

If your intention is to lock the fastener, why don't you try spring Washer rather than providing Lock Nut. Also you may try winding Ti wire above the first Nut so that locking action is given by Ti Wire. Dupont uses this technique in their internals fastening where constant fluid action is expected. I guess Ti is suitable in sea water service. You may try Ti nuts itself but first consult an expert regarding its galling properties.

 

[paulyg]

Thank you all for your informative posts.

 

[pauljohn]

I have often used a 3M product called '5200' in underwater situations and it has always worked great. It tends to lubricate threads on assembly and is a very aggresive adhesive but does not set hard but stays pliable. It also tends to seal the threads protecting them from the elements.

Problems encountered - it's a little messy on assembly and can be difficult to dissassemble. I am not sure what it's temperature limitations are.

I would be interested to know what anyone has to say about this method.