Cutting Aluminum

[02Diesel]

I'm new to cutting aluminum and have some questions about cutting it with a plasma table. I'm trying to see if cutting our aluminum with the table will be a cost savings over the shearing it so I'm trying to a little homework. We have a HPR260, Burny 10 plus lcd, on a C&G systems machine, with a down draft table using a Donaldson Torent filter system.

One of my Questions is this: We primarily cut mild steel and some 316 and 304 stainless, will there be a problem mixing aluminum with the steel in the dust collection barrel and the table bed? Or should both be cleaned before cutting aluminum and cleaned again before switching back to steel? I've heard some stories of barrels starting on fire or getting really hot when the two are mixed.

I did a small test cut on some 1/2" 6061 today at 260 amp nitrogen/air cut set to all the specs in the book. It was much nicer cut than I had expected it to be. These parts need to be welded after cutting and I was wondering if using, I think it's H35 (been a long week) would leave a better cut for welding with less clean up?

Thanks for your suggestions,
Steve

[hooked]

nitrogen and air is best bet! i cut alum. in the shop as the normal day! but for the lil amount of steel we do i clean the section of the table out! dreams of my younger days of trying to put the fire out of the timesaver when we didnt swap the barrels between alum. and steel pop back into my head as the fire truck shows up to foam the collection barrels!!! just not going to ever take that kinda chance again!! our welders either wire brush or file the plasma edge and it works great!!!

[jimcolt]

Best bet for cut quality on aluminum with your 260 is to follow the cut parameter charts for aluminum exactly as the operators manual suggests. The best cuts on aluminum are usually with air or nitrogen.....I do not belive there are cut charts for H35 cutting of aluminum.

As far as the fume collection barrel...potential for fire...you should run that by the manufacturer of your fume system for suggestions.

Jim Colt Hypertherm

[DaFischQC]

Jumping in here..are you saying cutting aluminum with my plasma table in the garage\shop would potentially cause fire in any way, shape, or form? Always wanted to try and finally have a nice thin sheet to test on. Just use a normal squirrel cage vented to a window opening. Don't know anything about fumes, etc. Just know I have to turn up the amps to cut aluminum..or maybe even I'm wrong there. Sorry to hijack..just asking. Thanks!

[jimcolt]

Aluminum cutting will not produce a fire in your shop. If you are using a water table that can trap small amounts of hydrogen that is created by sunken aluminum oxide particles...or if you are blowing aluminum oxide particles into an enclosed filter device...then you could potentially have a problem. Cutting over a water tray...and exhausting fumes outside will not cause any issues like this. Of course we all have to watch sparks as with any metal cutting, welding, grinding operations to ensure they do not start a fire.

Jim Colt Hypertherm

Jumping in here..are you saying cutting aluminum with my plasma table in the garage\shop would potentially cause fire in any way, shape, or form? Always wanted to try and finally have a nice thin sheet to test on. Just use a normal squirrel cage vented to a window opening. Don't know anything about fumes, etc. Just know I have to turn up the amps to cut aluminum..or maybe even I'm wrong there. Sorry to hijack..just asking. Thanks!

[Gamelord]

I have a downdraft system (no water table) and cut aluminum all the time with no issues at all. It isn't really any different than steel other than your settings are slightly different. It cuts pretty easy and no fire issues.

I don't understand the fire & barrel issues, something is obviously not right.

If you have a water table, just run the water about 1/2" below the plate and you should never have an issue. The reason is to allow for hydrogen to escape. With the water up to the plate (or slightly above) the problem that "could" occur is that the plate could warp a small amount, creating a dome shaped which could accumulate hydrogen under the plate. Then when you pierce through it ignites and boom. If you are doing small pieces of aluminum and not full 10' (or larger) plates you would probably never have an issue.

Also, if you have water basins under your table for water storage that are sealed, hydrogen could get caught/trapped in there which could create an issue.

All of these issues are quite rare and usually only a concern when doing tons of production runs with aluminum.

[02Diesel]

I did some research on why mixing aluminum and steel can cause a potential fire. According to Wikipedia when aluminum oxide and iron oxide are mixed it creates an exothermic reaction, basically it creates Thermite. Some of the most common early types of iron oxide used were mill scale and red iron (rust). When mixed with aluminum oxide it creates Thermite. The mix is ignited by large amounts of heat, in this case the heat generated by the plasma cutting process. The reason it is very difficult to put out as mentioned by "hooked" in his post is because the mixture generates its own oxygen and basically burns until the reaction is over. It's my understanding that this a very rare occurrence and the mix of aluminum oxide and iron oxide has to be just right for the reaction to occur but to be safe ... I'm cleaning the table before and after. That?s just my 2 cents and maybe I misunderstood the Wikipedia entry, it has been few years since science class. Here?s the Wikipedia link for you guys to decide.

http://en.wikipedia.org/wiki/Thermite

Jim,
The reason I was asking about using H35 plasma was because it?s the only other 260 amp aluminum option in our book. H35 is more expensive so I?m not leaning that way but I just thought I?d ask about it. We should probably be using it for cutting our stainless instead of using our mild steel O2 settings so it would have given me another to reason to recommend we add it to the shop.

[Marty]

my expierence with cutting up to 1/4 inch aluminum is similiar to Gamelord's

I just ventilate the area completely so no gas can accumulate in pockets under the cut material

30 inch fan at one end of the shop and another at the opposite end with all shop doors open, so there is good strong cross vent.Same routine for spraying clear coat, but with a 3M mask....

i have a feeling that routine is not really necessary but then i do buy the occasional lottery ticket once a year "just in case"

[BorstMetalWorks]

I can vouch that hydrogen explosions do happen. it was the first cut after the weekend. I cut alot of aluminum the week before and the water table was bubbling like a glass of 7 up when i went in monday morning. I was just a few feet into the first cut of the week and "KA-BOOM". it picked up a 96 x 240" sheet of 5/16" aluminum up about 10 inches and scared the heck out of me and my brother. Thank goodness it was a brand new full sheet or else it my have shot a already cut small piece somewhere.

Just saying,

Be careful. I run the water a little lower now and sometimes put a fan so that it blows under the sheet on top of the water.

[Stout]

If you have a water table and are concerned about a possible hydrogen explosion then I have this solution on my table. Run a lawn soaker hose under your slats down the middle of the table and pressurize it with air. The air bleeds out under the material you are cutting and mixes with and displaces any accumulated hydrogen gas. It just pushes the hydrogen out around the plate before it builds up.