Aluminium flange to steel sphere

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fpg
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Aluminium flange to steel sphere

Post by fpg » Sat May 29, 2010 4:38 pm

Is it possible to weld an aluminium flange to a stainless steel hemisphere?

If so it will save me about 100 dollar for a new steel flange..

Tyler Christensen
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Re: Aluminium flange to steel sphere

Post by Tyler Christensen » Sat May 29, 2010 6:53 pm

No, welding them can't be done since they don't form an alloy. They can be soldered, although it would not be easy, and soldering flanges isn't recommended. Also, those two metals would act as an electrolytic cell and you would have corrosion of long periods of time.

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Re: Aluminium flange to steel sphere

Post by Jerry Biehler » Sat May 29, 2010 8:36 pm

There are bi-metalic junctions available out there. They are explosion welded together. They lay a sheet of aluminum on top of a sheet of steel with explosives over it. The force welds it together. They are often used for connecting aluminum heat exchangers to steel piping.

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Re: Aluminium flange to steel sphere

Post by robert_steinhaus » Tue Jun 01, 2010 7:54 am

Welding an aluminum flange to a stainless steel sphere is not practical. That is because of widely different melting temperatures, no mutual solubility in molten state, and because of differences in thermal conductivity and in thermal expansion that cause stresses and cracks. You would be far better off to pay the $100 and weld on a stainless steel flange with compatible metallurgy.

Rather exotic approaches for welding aluminum and stainless steel have been attempted. You might find some value in the following link if you are dead set on doing something that is intrinsically difficult.

http://www.welding-advisers.com/PRACTIC ... rNo26.html

Brett
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Re: Aluminium flange to steel sphere

Post by Brett » Tue Jun 01, 2010 10:28 am

It can be accomplished by spin welding, among other approaches, but that doesn't mean it's a good idea.

morgoth31
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Re: Aluminium flange to steel sphere

Post by morgoth31 » Sun Jun 27, 2010 1:59 pm

they would corrode placing disimular metals in contact can cause them to oxidize at an much higher rate. with how hot some of these get i wouldnt advise for alum myself because i think it could warp.

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Doug Coulter
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Re: Aluminium flange to steel sphere

Post by Doug Coulter » Sun Jun 27, 2010 2:25 pm

I think the main word here is that while it is possible (I've done explosive welding and cladding here -- fun!) it's just not a good idea to try it. I wouldn't sweat the corrosion, come on, this isn't going out in the rain after all,and Al and SS are bolted together in my solar systems without any obvious sign of corrosion in >3 decades of being out in the rain, anyway.

What kills this is the bond is necessarily weak compared to the strengths of the materials involved, and the tempco monster is going to take this thing apart in termperature cycling, crack or warp things.

I have run with Al and SS both involved, no big troubles there if there's some "give" someplace to make up for the tempco differences. In this case, I doubt you can arrange that. If you could find some magic glue that had the right "give" and could take the other conditions, it might work. I have found no such substance in quite a lot of looking for it. Viton type seals will handle this fine, though as the give is a built in feature of those -- but I don't think that solves anything in your case. Works well for sealing Al and quartz (about as different as it gets) though.
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Re: Aluminium flange to steel sphere

Post by morgoth31 » Sun Jun 27, 2010 2:56 pm

just an fyi since i work in the foundry world right now.

most SS is coated with galvanized or galvalum to make them corrosion resistant these coatings are either zinc or aluminum zinc coatings this lessens the dissimluar metal effects in metals used in the enviroment.

not saying uncoated SS wont survive they will dependent on the relative humidity or if your activly cooling disimular metals are worse in water cooling systems. i just worry about the aluminum oxide build up on the mating surfaces over time making them leaky.

but all in all yeah the thermal expansion and contraction rates will deff cause cracking of the aluminum over time.

i know doug knows that dissimular metals at the same temperature causes electron flow (ie thermocouple theory) and can plate one material to the other. it is slow with just contact but if you have water there it can be fast if kept dry this is very slow but wet it can go fast.

not trying to school anyone just thinking out loud.

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Re: Aluminium flange to steel sphere

Post by JohnCuthbert » Sun Jun 27, 2010 3:37 pm

The point of galvanising mild steel is to stop it rusting.
What would be the point of galvanising stainless steel?

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Re: Aluminium flange to steel sphere

Post by Doug Coulter » Sun Jun 27, 2010 4:04 pm

I doubt thermocouple effect in the small millivolts has any noticeable effect here on kilovolts, in a vacuum.

In 57 years I've NEVER seen SS coated with galvanize, never ever, not one time, and I own a machine shop for a lot of those years -- and still do, there might be a few thousand lbs of various SS alloy stock here, and none of it is coated -- why pay for the expensive Chromium content if it didn't work? Other things, sure, not stainless of any alloy I've ever encountered. That includes all the "normal" alloys as well as the more exotic ones used for gun barrels which is a whole nother world (I build benchrest rifles as a profitable hobby)

SS and Al are compatible underwater, as I mention, by actual decades-long weather testing on my solar array -- Al panels and racks, SS bolts, zero corrosion of either. It's why that entire industry does it that way, Al bolts are too expensive and too weak and too much tendency to seize so no one uses them.

Maybe *I* am going too far in schooling here, but these are just observed facts, after all which is the currency I try to always do deals in.
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