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 Post subject: Mixing metals, Oxidation ect.
PostPosted: Wed Feb 19, 2003 8:35 am 
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I was planning on making a plate that will isolate the top of my case so that the power supply will be taking fresh air from the front, via 2 unused cd bays. I was just wondering, is it alright to use something like sheetmetal, will there be a reaction between the case metal and the sheetmetal? Oxidation, rusting ect. Is there a certain type of metal that i have to use, or do i have to put some kind of treatment on the metal?


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PostPosted: Wed Feb 19, 2003 9:05 am 
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Location: Worcester, UK
No, it should all be fine. Are you thinking of the problems people get when mixing copper and Alu in watercooling systems?

Why not make it out of card? Much easier and cheaper?

PS im doing something similar in mine - i have a 5V panaflo pushing air in at the front top and have taken the top two front drivebay covers out. Havent quite got round to making the divider yet tho hehe :roll:

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PostPosted: Wed Feb 19, 2003 9:25 am 
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Im making a harddrive decoupler out of sheetmetal anyways, because they cant easily be decoupled with the standard hard drive rack. So I was gonna cut the hardrive rack out and make my own. A 120mm case fan under the power supply will handle all the exhaust and the power supply will just have to keep itself cool.


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PostPosted: Wed Feb 19, 2003 9:44 am 
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Ah ok, i see. It should be fine regarding rusting etc as long as you keep it free from water :roll:

So you're making a 5.25" drive bay then?

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PostPosted: Wed Feb 19, 2003 12:53 pm 
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yea that way i can side sink the hardrive and still have room to suspend it. It may even be wider than 5.25" as I still have some extra space that it just wasted. Maybe I can fit in some bigger sidesinks on the hardrive.


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PostPosted: Thu Feb 20, 2003 2:44 pm 
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Hey Gaminggod, most computer cases are made out of...
  • satin-coat galvanized sheet steel - dull matte gray finish, good for painting up all pretty like
  • chromed sheet steel - shiny chome color, mostly on really cheap cases
  • aluminum - yup, needs no protective coating, paint optional / cosmetic except for marine environments
Unless your computer is in an unheated draughty space with high humidity, or a greenhouse, a boat, your bathroom, a swimming pool room, or a suana, you won't have any trouble no matter what you use. The zinc galvanizing is there specifically because it is far more reactive than the steel, so it corrodes first, turning a very dark dull gray like lead that has been outside a long time (think car battery terminals).

The other common types of sheet metal are...
  • regular galvanized - crystalline pattern, think funace ducts, good stuff but ugly and doesn't paint well
  • factory painted - metal roofing and siding, paint is not super hard so it scratches, white/brown for misc. flashing jobs is most common

If you ask at a sheet metal shop, they will likely sell you a peice cut to exactly the square dimensions you want, cut in a shear, which leaves the edges absolutely straight and clean and unwarped, like you will never get at home. Expect to pay from $1 to $2 per sq.ft..


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PostPosted: Thu Feb 20, 2003 7:23 pm 
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Location: United States, Mobile, AL
I worked at a sheetmetal place for a few weeks so Im pretty confident in my ability to make a simple little plate like im thinking. I just wish I had access to all the tooks presses, drills ect. that I had when I worked at the sheetmetal place, it would make it alot easier.


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 Post subject: Re: Mixing metals, Oxidation ect.
PostPosted: Fri Feb 21, 2003 11:23 am 
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Location: Los Angeles, CA USA
GamingGod wrote:
I was planning on making a plate that will isolate the top of my case so that the power supply will be taking fresh air from the front, via 2 unused cd bays. I was just wondering, is it alright to use something like sheetmetal, will there be a reaction between the case metal and the sheetmetal? Oxidation, rusting ect. Is there a certain type of metal that i have to use, or do i have to put some kind of treatment on the metal?

Hi GG,
I was thinking of making a very similar system. One mod I was planning to do to the PSU was to (decoupled) mount the fan on the outside of the PSU case on the side of PSU that faces the drive bays. I also thought about mounting two fans at 6v on this side.

This will do a couple things to reduce noise. It place the airflow impedience on the side of the fan where it creates less noise. It also burries the fan inside to case to further lessen audible sound.

Of course the internal design of the PSU must allow airflow in this direction. It actally should be easier to design for this unidirectional airflow but the ATX spec has the air flow making a 90 degree turn within the PSU.

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PostPosted: Fri Feb 21, 2003 12:45 pm 
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feel free to shoot this down entirely, but if you want to isolate the psu, then would it not be more simple to duct in some fresh air in to the psu? eg a tube running to a 80mm hole from the top of the case to the cpu intake. i ask more to find out the disadvantages of my suggestion than to offer a great tip, but you never know.


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PostPosted: Fri Feb 21, 2003 2:35 pm 
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Thats basically what im doing, but the whole top of the case will serve as tube. and 2 empty cdbays will serve as the intake. Actually I was planing on doing something like what you said, but i was thinking more about ducting the air from the bottom of the case as I think less noise would escape that way, and im going to filter the bottom of the case anyways, because all of my intakes will be coming in from the bottom.


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PostPosted: Fri Feb 21, 2003 3:14 pm 
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By having a junction of different materials you are creating a difference in electron potentials across the junction. Doing the calculation based on ground state potentials, it is safe to say that unless you have large amounts of exposed *pure* aluminum or tin, you are unlikely to have sensible degradation.

Aluminum and tin are extremely reactive metals. The reason why they do no seem to be, is that they quickly (order of minutes) form (atomically speaking) thick oxide layers. In the same vein, scratching of the pieces will not expose enough basal material to cause any problems.

But if you're looking for a good time, a fistful of ground rust and aluminum shavings with a magnesium fuse (thermite reaction) will melt a hole through a car engine, let alone your lovely new sonata. =)


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PostPosted: Fri Feb 21, 2003 4:07 pm 
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B wrote:
But if you're looking for a good time, a fistful of ground rust and aluminum shavings...


Sorry B, I believe that needs to be black iron oxide, which I think has one extra oxygen per molecule, instead of the normal orange/brown stuff we call rust. FeO3 instead of FeO2. I think that cutting torch slag might do the trick, but I'm not 100% sure.


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PostPosted: Tue Feb 25, 2003 4:23 am 
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crisspy wrote:
FeO3 instead of FeO2. I think that cutting torch slag might do the trick, but I'm not 100% sure.


Actually, right and wrong. Household rust is a mixture of FeO and Fe2O3 (I'm sure you just forgot the 2 after Fe). The thermite reaction will proceed with either iron, but stoichiometry may be off resulting in some residual Al.

Not that this thread was about chemistry or that the original poster or anyone is going to try this. =)


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