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Aluminum screw(bolt) in steel thread?

teachme

Aluminum
Joined
Apr 13, 2020
Anyone have experience with this?
We're working with large amounts of steel that are expensive to replace.
Bushing aren't an option, so we tap directly into our parts.

We're looking into aluminum screws, and replace them every few months.

Is galling an issue and will it affect the threads?
Are we better off using steel screws?

The screws will be torqued and removed ~10 times/day.
 
What is the function of the screws? Are they under load or just to hold two static pieces together? What is the worst case scenario in a catastrophic failure of the screw/bolt? If aluminum works, why not brass?

What exactly are you trying to accomplish?
 
Application is joining two plates of steel 1" & 3/4" thick (without nuts). Function is simply holding the parts in place.
Torque no more than 35 Nm./screw.
The conditions don't involve heavy loads, vibrations, extreme temps, etc.
This is for a CNC

Just realized your name xD
 
The screws are 1/4". I think nylon would snap right off at 35 nm. I've never used nylon screws, but seems possible
don't assume, ask the vendor.

BTW You've got qty (2) threads running on the same question.

see if you can delete one.
 
Stainless steel is a far better choice.

It is smoother than many other steel fasteners so there will be less wear on the threads.

For frequent use such as yours I would look into spraying the screws with dry lube at a minimum, moly or other slick coating preferred.
 
Engineer says, disposable must be softer than remainder. Screw or bolt thus simplest steel you can find, rolled if possible, not cut

Aluminium is an instant oxygenizer. When you scratch its surface, it oxygenises right behind the scratching tool, but you won’t see it. The layer of Al[SUB]2[/SUB]O[SUB]3[/SUB] is quite thin, only about a hundredth of a millimeter. Al[SUB]2[/SUB]O[SUB]3[/SUB] is corundum, harder than steel. By the time the female threads will be worn from the hard alum oxide.

Rust on steel is also hard, it’s actually a grinding compound, polishing red, but your bolts won’t oxidise that fast.
 
You do know that glass filled nylon can be made stronger than some of the lower grades of aluminum, right?

Then there are the fundamental issues of using aluminum fasteners, especially "removing them ~10 times a day" because of the galling concern. Galling doesn't get better, only ever worse. 35 N·m on a 1/4" fastener would concern me to begin with (if only for the brazen disregard for consistent units of measure!). When the aluminum surface welds itself, you are going to be in the fast lane on the one-way road to bolt extraction city.
 
How about hardened studs in the lower piece with low strength loctite. Plain steel nuts on top. Replace the nuts when they wear out.
 
If the load isn't a big issue, then galvanic corrosion is the only real problem. Using a decent anti-corrosion grease should extend the life of the connection considerably.
 
where do the 35 nm come from? thats about the max for a m8 12.9 screw. i see 9 ft.lbs. for a grade 8 1/4" screw.
 
where do the 35 nm come from? thats about the max for a m8 12.9 screw. i see 9 ft.lbs. for a grade 8 1/4" screw.

Exactly.
No need to "ask the vendor" if 1/4" nylon bolts can be torqued to 35Nm!
That works same way as Nasa Mars orbiter :D (possibly for similar reasons too..)

Good 1/4" UNF grade 8 bolt with large head might just about survive torquing to 35Nm. Assuming its dry, large head, and it friction welds itself to underlying steel part..
 
and the last is another good point, because the friction between aluminum and steel is unknown in most cases (as far as i can see). example: take an ls1 water pump screw and torque it to that specs into a steel nut. you will be beyond yield point.
 








 
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