Cutting aluminum diamond plate

[msc]

I have someone that wants me to cut some aluminum diamond plate into a decorative logo design. I know that I cannot cut aluminum over my water table. I think I have that figured out by building a cover and cutting rack to go over the water table. But is there anything else I need to know?

I have cut a little aluminum with my hand torch a while back and I think I remember it being sort of messy. Any advice would be appreciated.

Thanks, Mark

[Chris Linetty]

Mark, I'm new to plasma cutting. Why can't you cut aluminum over water? I actually did it recently and I can't say the cut was as smooth as steel, but it was of acceptable quality. other than that everything went fine. Let me know your thoughts. Thanks, Chris.

[Thor]

IIRC you're not supposed to cut submerged as the hydrogen can get trapped under sheet and than light. With most our water tables on air plasmas that you can cut submerged anyway, just keep the water below the sheet and you're good to go.

[SeanP]

Cut with the pattern facing down as well.

[msc]

Mark, I'm new to plasma cutting. Why can't you cut aluminum over water? I actually did it recently and I can't say the cut was as smooth as steel, but it was of acceptable quality. other than that everything went fine. Let me know your thoughts. Thanks, Chris.

I was told, apparently not completely accurate, that the gases created by the hot aluminum hitting the water created a toxic gas. From some of the responses here that is not completely correct.

[KIDTech]

Take this for what you will and in no way am I telling you to cut the aluminum. I can see there being an issue if say you left the metal in contact with the water over night and it created a pocket of hydrogen, you then come back in the morning flip on your machine, send a spark to it and you could cause a boom. There would have to be a lot of very specific issues occur though. I cut aluminum every now and then without worry but again this is me and I am not telling you it is right or wrong. All I can say is that if you are worried about it empty your pan and get yourself a nice respirator.

[jimcolt]

Here is my response that has been posted a few hundred times on various forums:

In regards to cutting aluminum over a water table, there generally is no concern of the possibility of hydrogen production and the ensuing explosion hazard. Aluminum cutting produces a by product of aluminum oxide, which sinks in the water and absorbs oxygen. When oxygen is removed from water (H20) it leaves hydrogen, which you will see rising to the surface (after cutting aluminum) as small bubbles.

Since the quantity is very small, and hydrogen is lighter than air, the small amount of hydrogen will dissipate in the ambient air.

Many water tables have a submerged chamber that is used (with compressed air) to rapidly raise and lower the water level in the table for small parts removal, cleaning, etc. If aluminum oxide is allowed to get into a closed chamber, hydrogen could be trapped and over time could form a large pocket, and with the event of a spark and some oxygen there could be an explosion. So if you have a raise lower type water table with an enclosed chamber (bladder) for storing water....and it was not designed specifically for aluminum cutting...then I would recommend against its use.

Most of the stories about aluminum and water tables causing explosions have no basis, although there have been a couple of issues over the 38 years I have been working for Hypertherm that involved minor explosions on large industrial machines. The ones that I am aware of were solved with aerators (no pump needed) that simply involved a couple of pipes with holes drilled in them in them...submerged in the water table. Low pressure compressed air was fed into the pipes to aerate the water, diluting the hydrogen.

On small tables without enclosed water chambers....simply allowing the material to have a slight gap (maybe 1/4" between material and water) is adequate to dissipate the very small amount of hydrogen produced. The hydrogen is not produced in any quantity by the actual cutting, rather, the aluminum oxide particles that sink to the bottom of the table will absorb oxygen (water is H2O, which is 2 molecules Hydrogen and 1 molecule Oxygen)....which leaves hydrogen. As the particles pull oxygen from water, the hydrogen rises in the form of small bubbles in very small quantity.....and will do it for hours after you are done cutting. If the hydrogen is trapped somewhere, like under an upward bowed plate...then it can form a pocket underneath the plate. So....when you are done cutting your aluminum on a water table...remove the plate, let the very small quantity of hydrogen rise and disipate in the air.

Cut all the aluminum you want on small water tables, just use common sense.

Jim Colt Hypertherm

Jim Colt Hypertherm

[msc]

Another great response. Thank you Jim. And thank you for being there and sharing your expertise with us.

Mark

[_Ogre]

we cut aluminum on a water table frequently without any issues
you will see very tiny bubbles for days after

Many water tables have a submerged chamber that is used (with compressed air) to rapidly raise and lower the water level in the table for small parts removal, cleaning, etc. If aluminum oxide is allowed to get into a closed chamber, hydrogen could be trapped and over time could form a large pocket, and with the event of a spark and some oxygen there could be an explosion. So if you have a raise lower type water table with an enclosed chamber (bladder) for storing water....and it was not designed specifically for aluminum cutting...then I would recommend against its use.

jim's reply does have me thinking though, we do have a bladder (two 55 gal barrels) under our table
chances of aluminum cuttings getting in there is slim, drain 2 or more ft from where we cut, but something i had not thought about before
we rarely drain into the barrels, more for adding water or level adjustments

[Gustav129]

I cut many many many sheets of aluminum. The last job I cut was 1" 6160. Plasma gas was liquid nitrogen, and water shielded. Water level was just at 2" under the material.

The hydrogen is formed by AL being submerged in the water. AL dross is more like a powder than molten metal like A36. So the dross has a much greater surface area, than lets say an AL part you just cut out. More hydrogen is created with dross. With the 1" 6160, a lot of dross was created because the kerf was over 1/4" wide. The table would be full and had to be cleaned every day. It looked like simmering oatmeal with all the hydrogen bubbling out of it.

The biggest concern is when the slats fill up with dross and create pockets of hydrogen that can't vent off to anywhere. If a sheet is left on the table over night, a much bigger pocket is created. Then when you pierce the material that pocket ignites. It can catch you off guard if you aren't expecting it.

[whiskeymike]

Is the OP's concern over toxic gas perhaps related to hearing about Galvanized steel? I know it's bad with welding, but not sure how much is released in cutting.

[Gustav129]

The OP was concerned about gasses given off with AL and water. When I was learning on a Torchmate in school, I was told I could not cut over a water table because the molten AL will "explode" on contact with water. When I landed a CNC job, during the interview, I clearly saw that that was absolutely false.

Galv?! Everybody in the shop will need respirators. It gives off fumes at 750 degrees.

[gamble]

90% of what I cut is aluminum. My water is generally 1/4" below (ish, I don't measure shit) the plate. No issues.