×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Material choice for 1.25" threaded fastening

Material choice for 1.25" threaded fastening

Material choice for 1.25" threaded fastening

(OP)
Hiya,
I'm designing a fitting which will have the male half of a 1.25" screw thread fastening on one end. The female half is being made by another company, and is anodised aluminium. The whole fastening is going to be regularly done and undone by hand - the part I'm designing is kind of an optional add-on.

I know aluminium-aluminium threads have a serious problem with seizing. It's my understanding that anodized aluminium threads  also tend to seize, although I'm assuming this is for different reasons.

My material choices are:
Stainless steel (303, probably)
Brass
Anodized aluminium.

Does anyone have any experience of this sort of situation? Anyone recommemnd any particular material? Weight is also a consideration, so the lighter the better.

Ta

Matt Freeman,
Design Engineer,
UK

RE: Material choice for 1.25" threaded fastening

You say that the parts will be put on by hand. I've never had any trouble with two anodized pieces of aluminum being assembled hand tight.

I've had good luck with using a hard anodize per MIL-A-8625 Type III. Might want to give that a look.

RE: Material choice for 1.25" threaded fastening

Loads?

RE: Material choice for 1.25" threaded fastening

Does it have to be a metal?

If it does, could it have a threaded non-metal liner?

cheers

RE: Material choice for 1.25" threaded fastening

(OP)
[MintJulep] and [CorblimeyLimey]: by way of answering more than one question at a time, although it is supposed to be only hand-tight, it's going out to customers as part of a measuring system and I wouldn't put it past customers to 'hand tighten' it with a pipe wrench. On that basis, and because it's likely to be screwed and unscrewed maybe twice a day for its entire design life, I've so far ruled out polymers... unless you guys know better... smile

Matt Freeman,
Design Engineer,
UK

RE: Material choice for 1.25" threaded fastening

You can keep the metal-to-metal joint, you just need to apply a lubricant to the threads.  Your choices include PTFE masking (also known as Teflon tape), anti-seize (Loctite has a range of products), or a molybdenum disulfide lubricant (Dow Corning offers a few).

Regards,

Cory

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

RE: Material choice for 1.25" threaded fastening

OK, but you didn't answer MJs question of the loads involved.

Is the part being used to lock/clamp something in place or for positioning?

Is the thread fine or coarse?

Can a lubricant be used?

cheers

RE: Material choice for 1.25" threaded fastening

(OP)
Sorry, I'll try again:

I don't think lubricant can really be used - it's an often handled part, so we can't guarantee the state the customers will keep it in, so it's best to assume it's unlubricated. Sure, you could use something pre-impregnated, but I think that's overkill.

The drawing specifies a 1.25" -20 UN thread. I'm a metric boy myself, but I think that's a coarse thread.

As to the loads - to be honest, I don't have any figures I can give you right now, it's all a bit back-of-fag-packet. I'll try and post some figures before the end of the day.

Matt Freeman,
Design Engineer,
UK

RE: Material choice for 1.25" threaded fastening

Stainless or Corosion resistant steel can be problematic with Aluminium from a corrosion point of view if you have anything aproching a harsh environment.

As suggested above hard annodized will probably be better than standard for this application.

KENAT, probably the least qualified checker you'll ever meet...

RE: Material choice for 1.25" threaded fastening

I'd go with Brass, cause it wont sieze/gall and I dont (offhand) think that it will make a bad glavanic couple with the Al. (The anodizing is likely to get broken through/worn away.)

Also the brass is going to be easy to produce, will thread easy, and be a completely different color, that way when the guy in the field drops it he can find it again.

Nick
I love materials science!

RE: Material choice for 1.25" threaded fastening

If feasable, I would suggest you look into using a threaded insert for the female piece. This is based on my own experience, where mating aluminum parts were stripped because of reasons you've already stated (over torque or lack of lubricant).

RE: Material choice for 1.25" threaded fastening

We use a dry film lube of Al-Al threads per MIL-PRF-46010. It is cured on the threads, and does not come off from handling or installation of threads. Might do the trick for you.

Sample callout:
APPLY EVERLUBE 9002 IAW MIL-PRF-46010 TO THE THREADS, .0003 TO .0005 THICK. CURE AT 400 DEG F +/- 15 DEG F FOR 120-140 MINUTES.

RE: Material choice for 1.25" threaded fastening

(OP)
That's great, thanks all for your help!

Matt Freeman,
Design Engineer,
UK

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources