Permanently Locking Threads 3

[paulcook]

I have two parts that need to be permanently threaded together.

One is cast aluminum with a 1/2-14 NPSM female thread.

The other is galvanized steel 1/2-14 NPSM nipple.

We currently use Loctite (the glue stick ones, primer green + high strength red) to keep these parts from rotating relative to each other.

Is there another way that we can thread these together so they never come apart/rotate relative to each other?

 

[DAVIDSTECKER]

If you're having a leakage issue, it may be that it is an issue with galling.
Years ago, I was at place where we used all aluminium pipe and had air getting into the hydraulic suction line.
Talking with the pipe supplier, he told me to use anti-seize instead of PTFE pipe dope.
Aluminium is a material that galls easily, and it locked up before the threads fully engaged, allowing air to get in.

 

[paulcook]

Thank you all for your suggestions and knowledge.

Re surface prep - this is a production environment, we can't really afford to have extensive/caustic/dirty prep requirements. The parts are of course cleaned before assembly.

Re staking threads - looked into that. The problem is that the threads that extend beyond the mating part I described must be serviceable (they thread into something else).

Re pressure - there is none. Pinning was considered, just not simple from an assembly / finishing perspective (aesthetics and keeping the anodizing intact is important).

Re alternate surface treatment.... maybe in the future.

As an update, I rebuilt the test piece using more Loctite and primer and it works within spec now. (Spec is "can a contractor accidentally break this connection if he's performing his job with a reasonable level of conscientiousness".)

In case someone unearths this thread in the future and wants to try these sticks:

Loctite SF7088 Primer (Green Stick)
Loctite 268 High Strength Threadlock (Red Stick)

 

[mfgenggear]

Paul
My opinion loctite or equivalent is the best method. Refer to their catalog for extra strength.
Keep in mind shelf life. Date it and replace after opening or stored for a length of time. It will degrade. In addition a slight peen a round the threads after assembly. Then allow for cure as recommended by the manufacturer.

 

[dvd]

People shrink fit steel pins into aluminum on a daily basis. If your highly proprietary gizmo is not subject to huge temperature swings, a shrink fit seems achievable. Aluminum has an expansion coefficient that is nicely larger than that of steel, so a huge warm-up for installation is not required. The devil is in the (proprietary) details.

[link

https://amesweb.info/fits-tolerances/ansi-limits-fits-calculator.aspx

]ANSI LIMITS, FITS AND TOLERANCES CALCULATOR[/url]

 

[paulcook]

@dvd - thanks for that reference. Always good to have another trick up the sleeve.