Which nut and bolt to use that will avoid cold welding and corrosion
Which nut and bolt to use that will avoid cold welding and corrosion
(OP)
Im designing a solar tracking frame that needs to be corrosion resistant for installations in coastal areas and UV resistant.
I am using 6061-T6 aluminum for the frame members.
There is an EPDM gasket between members to avoid crevice corrosion
I am securing the frame members together with 18-8 Stainless steel bolts through plastic sleeves to insulate the ss from the aluminum.
there is neoprene backed ss washers under the bolt head and nut.
We were using nylon insert ss nuts on the bolts but because of cold-welding, this inn't working.
Im considering using the "ultra corrosion-resistant coated" bolts from McMaster Carr and keeping the ss nuts. I am hoping that this could solve the cold-welding issue and maybe i wont need to use plastic sleeves to insulate the bolts from the aluminum.
Ideas?, Suggestions?
I am using 6061-T6 aluminum for the frame members.
There is an EPDM gasket between members to avoid crevice corrosion
I am securing the frame members together with 18-8 Stainless steel bolts through plastic sleeves to insulate the ss from the aluminum.
there is neoprene backed ss washers under the bolt head and nut.
We were using nylon insert ss nuts on the bolts but because of cold-welding, this inn't working.
Im considering using the "ultra corrosion-resistant coated" bolts from McMaster Carr and keeping the ss nuts. I am hoping that this could solve the cold-welding issue and maybe i wont need to use plastic sleeves to insulate the bolts from the aluminum.
Ideas?, Suggestions?





RE: Which nut and bolt to use that will avoid cold welding and corrosion
Bolts: Alloy 2024-T4 according to ASTM F 468
Nuts: Alloy 6061-T6 according to ASTM F 467
Washers: Alloy 2024-T4 according to ASTM B 209
Fastenal will be a better supplier of these parts than McMaster-Carr.
RE: Which nut and bolt to use that will avoid cold welding and corrosion
The other option would be to use marine grade Cu alloy hardware. Bronze and brass.
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Plymouth Tube
RE: Which nut and bolt to use that will avoid cold welding and corrosion
RE: Which nut and bolt to use that will avoid cold welding and corrosion
There are other Aluminum alloys available for your application. I would give someone like Aluminum Fasteners a call about your requirements
http://www.aluminumfastener.com/index.html
RE: Which nut and bolt to use that will avoid cold welding and corrosion
If 6061-T6 bolts and washers are available to you, use them instead. Just be sure to specify the ASTM standards (same ones above) so that you get parts with guaranteed properties.
RE: Which nut and bolt to use that will avoid cold welding and corrosion
I'm assuming that the aluminum frame has some sort of corrosion protection such as anodize or prime/paint. If so, then using 18-8 fasteners on that surface would be galvanically isolated.
Galling of your 18-8 threads can be prevented by applying a dry film lube like MoS2 to one of the threaded parts. Also, if using 18-8 parts in a marine environment, make sure they're passivated.
Hope that helps.
Terry
RE: Which nut and bolt to use that will avoid cold welding and corrosion
Use course treaded 300 SST (non 303) fasteners. Wet install fasteners head and shank with proseal polysulfide sealant, P/N 823E508 PRC Desoto. Changing nuts to a different hardness of the bolt will prevent galling. Fasteners not frequently removed: Anti-seize should used or consider a thin fluorocarbon fastener coating system.
Fasteners through heavy aluminum foundations, the aluminum should be sleeved with a SS bushing.