loctite,oil or anti-seize ? 4

[motomartin]

Don't know if this has been asked before, but here goes....

We make a highly dynamic and vibratory rotating machine that is subject to large and irregular loads.
It has various types of bolted joint connections in the form of flanges, collars, rings etc etc.

Previous designers have dictated that all bolts should be lightly oiled and be torqued to a value that puts the bolt into its elastic range.

Very occasionally we get a bolt come loose.

I argue that the bolt should be degreased and loctited - with no lock washer, and that if the bolt 'galls' when tightening that anti-seize should be lightly applied to the bolt body and under the head - but clear of the threads.

There are discussions about this method compared to the current way of working.

What is the accepted method of bolt locking in this environment ?

 

[MintJulep]

Moto,

Did you mean to say that you tighted the bolts past the elastic range and to yield?

The light oiling is probably an attempt to reduce the scatter associated with torque control. However, oil is not really very good for that. Anti-sieze would be better for reducing scatter.

Anti-sieze and loctite do not mix. Regardless of how careful the shop is the will eventually contaminate a portion of the thread.

Have you considered Nylock type nuts, or nylon inserts in the bolts?

 

[desertfox]

Hi motomartin

I did a contract at a company where they made aircraft valves which were subject to high vibration. There method was after tightening the bolts down they wirelocked all the bolt heads together.

regards desertfox

 

[IRstuff]

One would think that for certain applications where safety might be involved, a positive mechanical locking mechanism, such as wiring or cotter pinning would be the prefered method.

As far as I know, all the cars I've ever owned used cotter pins to ensure that the wheel nut didn't come off.

TTFN

 

[arto]

How about:
Neverseez & tighten it to that the bolts are preloaded above what they'll see in service [ref. ASME PCC-1, "Guidelines for Pressure Boundary Bolted Flange Joint Assembly"; MIL-HDBK-60, "Threaded Fasreners - Tightening to Proper Tension"] & lockwire per MS33540 "General Practices for Safety Wiring & Cotter Pinning"

Also see NASA Ref. Pub. 1228 "Fastener Design Manual" for good info on locking.

 

[CoryPad]

The best solution is to develop sufficient preload to avoid loosening. The best "additional" step is to use thread adhesive.

Safety wire does not prevent loosening - it only prevents complete fastener loss and joint separation. Likewise, cotter pins on automobile drive shafts or tapered ball studs do not prevent loosening. They are passive safety devices, in that one can be assured that the joint is seated if the hole is open and can have the pin inserted.

The following previous threads provide some good information:

thread725-340

thread725-57042

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[Pulpboy]

If you want to stop a bolt from loosening I would use loctite. All the others, lock washers, wire, welds, lock nuts do not prevent loosening in extreme cases. Get in contact with your loctite rep and they can tell you what type to use.

The only other option that you might want to try is a torque indicating bolt. Some you can look at and see if they are still in a proper stress range and some you have to hook up a probe to. Then if you don't want to use loctite you can monitor the bolts and whenever one is loosening you can retighten it. Suggestions are maxibolts or try

http://www.smartbolts.com

 

[solidworkswell]

if you are concerned about the bolt coming loose cause of vibrations and irregular loads. i would consider a fine thread which do well in vibrating conditions. But there is a disadvantage to this as they do not high loads.

Pre-loading the bolt shoud work well.

 

[unclesyd]

Take a look at this thread form.

Go to “profile” then “applications” there is quite a few articles/papers on the use of the Spiralock Thread Form to mitigate problems with vibration.

http://www.spiralock.com/

 

[johnchrc]

If you are having problems with galling during assembly, you need to use anti-seize or anti-galling paste on threads. Alternatively you could coat the bolts with anti-galling coating. You could use the loc-tite then.

Would jam nut be an option?

 

[sbi]

all very good ideas, till you let your foundry crew work on the shakout table, i have always used loctites copper antisize to help torque bolts down. bt on our shaker we found a little hot melt glue helps aka spot weld with a wire welder, nuts do not come loose down side need a good supply of 5" chop saw blades to cut top of nut off


SBI
Central Ne.,USA

 

[unclesyd]

What ever you do, do it right.

http://www.msha.gov/FATALS/2002/FTL02M18.HTM