Aluminium flange to steel sphere

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fpg
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Aluminium flange to steel sphere

Post by fpg »

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..
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Re: Aluminium flange to steel sphere

Post by Tyler Christensen »

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 »

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 »

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
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Re: Aluminium flange to steel sphere

Post by Brett »

It can be accomplished by spin welding, among other approaches, but that doesn't mean it's a good idea.
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Re: Aluminium flange to steel sphere

Post by morgoth31 »

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 »

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 »

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 »

The point of galvanising mild steel is to stop it rusting.
What would be the point of galvanising stainless steel?
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Doug Coulter
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Re: Aluminium flange to steel sphere

Post by Doug Coulter »

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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Re: Aluminium flange to steel sphere

Post by morgoth31 »

im talking about the sheet steel used in solar panels is made for the outdoors and is normally galvanized unless its high grade stainless.

i understand what yous saying.

stainless steel is not rustless steel it is rust resistant.

ss and aluminum can galvanically corrode

from all the charts ive seen it is dependent on the grade of steel mostly the magnetic stainless grades 300 and lower the non magnetic stainless doesnt corrode from everything ive found. and the aluminum is normally the less noble of the metals and is the one that corrodes. In the systems i work on there are massive magnetic fields so to keep from having hose clamps and such melt we use only non magnetic SS clamps. this is how i found out there is a big difference in SS grades and how they react to things. the cheap magnetic SS clamps actually rust quite easaly while the good non magnetic ones last alot longer.

just to make sure i wasnt absolutely wrong i did a search and found that SS and aluminum can and do galvanic corrode the level of this is dependent on the grade and composition of both metals. i know this because personnaly because i work on equipment that companies keep and use for 30 or more years on average an have seen even the best SS with rust and pitting on them.

yes i agree in this application there will most likely be little or none of this happening they are very dry and prolly no salt water near the system.

please look at this site picture and paragraph at bottom.

http://corrosion.ksc.nasa.gov/galcorr.htm

not much corrosion but you can see it happens

i dont doubt what you know i have seen too many alum to ss connections rotted and pitted personally normally the alum side. (since im the one who has to replace them and with more of the same but we use the good stuff so it good for many more years.)

thanks im sorry if this raised any trouble.
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Re: Aluminium flange to steel sphere

Post by morgoth31 »

and to add using a ss screws on alum is fine since the smaller amount of more noble ss decreases the rate of galv in reverse it would increase so using alum screws on ss plate would cause the alum to galv at a higher rate. which is why i was taught that you never use alum pop rivets on any type of sheet steel but ss rivets on alum is absolutely fine.

granted i didnt know exactly why till i just looked it up a bit ago and saw the volume of the more noble metal increases the effect.
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Doug Coulter
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Re: Aluminium flange to steel sphere

Post by Doug Coulter »

Well, I do live far from salt water, where even pure Al corrodes quick (Ask anyone who remembers TV antennas near the sea, made a ton of bucks once replacing them). But a 30+ year real life test on stuff I had to pay lots of money for (and therefore pay close attention to), proves that it's just not a problem.

And it is ridiculously irrelevant in a reducing atmosphere/vacuum that even will take quartz back to silicon metal. It's not the direction reactions "go" in there. In the pix of my tank on another thread here of my latest runs, you can see some Al coated over the SS by a runaway evap process I did while learning how to do it right -- see any corrosion? Flaking off? It's just not the right issue to worry about in this context. I have also noticed zero corrosion between the SS and the lead my tank is now covered in, there's just no reason to worry that unless I plan to put it in a swimming pool with acetic acid and salt or something similarly bizarre. This will all surely wear out before any corrosion will be a problem.

The PV panels were made by the way, by BP -- yeah, those guys who in astonishingly bad timing just shut down the factory in Md USA 3 months ago, because it wasn't making them much money -- they made them "too good" if the real life testing here shows anything - the only way to tell a new one from a 30 year old one is the label fades on the back, eventually. Before BP owned Solarex, it was Amoco, BTW, it's not like the oil companies don't know the music isn't going to stop, and want a chair to be in when it does. But you know what? As a result all existing BP panels in stock at warehouses just dropped in price like 30% and I'm buying another pallet of them....can't eat money, but I can cook with these. Get 'em while you can! Good investment for me, I'm all the way off the grid and have been going on 40 years now.

BTW, the BP panels, while aluminum frame, are mostly glass and plastic, and the Al is hard -anodized and you don't even get an electrical connection to it with a bolt unless you screw it in hard though to break through that - which isn't easy. No connection, no galvanic action, period.

If I was going to buy solar panels, either hot water, or PV (which is what I have) and they had *any* steel in them -- I'd not buy them. Someone got too cheap there, which means they probably did elsewhere too and that's too big an investment to screw up on. Many small solar outfits just choose to go out of business when it's time to honor guarantees. Had it happen.

Here's one pic of my larger system (which is larger now than then, the roof is now full).

http://www.coultersmithing.com

So I'm making fusion off solar power....and know whereof I speak on this. I'm getting 90 amps at 30 volt off them as I type.
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Carl Willis
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Re: Aluminium flange to steel sphere

Post by Carl Willis »

This thread has moved off into la-la land now...

Jerry's answer was the closest to being useful. Welding is out, but standard Al-to-stainless vacuum parts can be purchased from various vendors, e.g. http://atlasuhv.com/. The company I work for occasionally uses these to attach 304-SS CF components to large chambers that are made from aluminum for economic reasons. In other words, these kinds of transition fittings are routinely used. Galvanic corrosion is utterly a non-issue.

-Carl
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morgoth31
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Re: Aluminium flange to steel sphere

Post by morgoth31 »

i know and i said that in this case non issue im sorry if i over talked

btw nice set up in the pics and i love the using solar for fusion its a great twist.

yeah i worked for a place that did special electrical connections for the BP solar group these were for PV interconnections it was just a build and test shop but they were one of 50 sites that did it for BP.

again i apologise for getting to far off topic and will try to reign myself in.
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