Aluminum Threads - Preventing Damage
Aluminum Threads - Preventing Damage
(OP)
Hello,
I am new to the forum and I did search a little bit, but I couldn't find any answers on my own.
Pretty simple question - I currently have an aluminum housing with a threaded hole in the base (2 1.2-12 SAE). I have to build an adapter plate to screw into the hole, but I am unsure about what materials to use as to not damage the aluminum threads.
I have always worked with steel housings and it was simple to have items made out of aluminum. Now I need something even softer than aluminum.
Thanks for any help you can give me - other engineers have made the plates out of plastic to prevent damage, but I want something more durable since it will be use with hydraulic oils.
Thanks,
JF
I am new to the forum and I did search a little bit, but I couldn't find any answers on my own.
Pretty simple question - I currently have an aluminum housing with a threaded hole in the base (2 1.2-12 SAE). I have to build an adapter plate to screw into the hole, but I am unsure about what materials to use as to not damage the aluminum threads.
I have always worked with steel housings and it was simple to have items made out of aluminum. Now I need something even softer than aluminum.
Thanks for any help you can give me - other engineers have made the plates out of plastic to prevent damage, but I want something more durable since it will be use with hydraulic oils.
Thanks,
JF





RE: Aluminum Threads - Preventing Damage
RE: Aluminum Threads - Preventing Damage
RE: Aluminum Threads - Preventing Damage
Welcome to Eng-Tips.
Agree with TVP's response. What aluminum alloy & temper?
I don't understand your thread size -- is it 1/2"-12? But good news that the bolt screw can be significantly stronger than the plate before causing mechanical damage (due to greater area at root of female threads). Did a calculation a few years back using equations from Machinery's Handbook. For 3/8"-16, I recall the male threads must be > 2x as strong before being able to strip female threads. Do the calculation for your thread size..
For aluminum threaded holes, commonly used bolts/screws are aluminum (risk of galling), galvanized or zinc-plated (risk of zinc corrosion causing seizure) steel & 18/8 stainless (risk of aluminum corrosion causing seizure). Bare steel or copper alloys can cause severe galvanic corrosion of the aluminum; see thread338-137607 for effect of copper. Also, a case where steel bolts snapped off in an aluminum housing; my diagnosis is aluminum corrosion seized the threads: thread281-147765.
I suggest any of the 3 choices: Al 6061-T6, yellow chromated zinc-plated* steel or 18/8 stainless, but essential to use an anti-seize compound on the threads. Avoid any containing copper, silver or graphite, these cause galvanic corrosion of aluminum.
*Either electroplated or mechanically plated, as these are available chromated.
You can also use DACROMET®-coated steel fasteners; some are compounded with aluminum to avoid the galvanic problem. Can be used with a PLUS® Sealer for even better protection of the aluminum. http://www.dacromet.com/hcoat.htm
RE: Aluminum Threads - Preventing Damage
Interesting comments about galvanic corrosion.
I will agree threads in aluminum like to gall and corrode. We make some parts for an infrared camera where 32 tpi thread aluminum parts thread with stainless, aluminum, and 660 bronze. All must be assembled with nickel anti-seize or none will come apart.
I will ask if there is evidence of greater corrosion between the bronze parts and the stainless parts on older assemblies.
RE: Aluminum Threads - Preventing Damage
The operating pressure should be around 150 to 200 psi.
Thanks to everyone for the responses!
It does sound like my boss wants to go with bronze or brass, but I wanted to get other opinions.
RE: Aluminum Threads - Preventing Damage
Ed, same thing. A water-repellant gel is used on SS fasteners in aluminum for saltwater application. If the Ni anti-seize particles are embedded in a water-repellant matrix, OK. The Ni particles have an invisible oxide film from manufacturing which helps. Same priciple as Al-SS couples: both metals protected by an oxide film, so unless it's damaged, no galvanic reaction. But, I still want to warn against using any Cu alloy with Al. See the first link in my post above.
Ken
RE: Aluminum Threads - Preventing Damage
RE: Aluminum Threads - Preventing Damage
RE: Aluminum Threads - Preventing Damage
However, for Al-rich alloys on the Al-Cu side, there is a large difference in composition between constituent compositions & hence emf's. At a 300 oC equilibrium, a 2xxx alloy consists primarily of Al-0.2%Cu and CuAl2 (53.5 wt% Cu). The CuAl2 is more electropositive than the Al-rich matrix, so causes galvanic corrosion in the presence of electrolyte. But, even worse corrosion results because after some alloy dissolves, dissolved Cu in the electrolyte deposits onto the alloy, and there is a huge difference in emf between Cu & Al.
RE: Aluminum Threads - Preventing Damage
http://www.tef-gel.com/index.htm
I see this one used quite a bit too.
http://www.super-lube.com/