Plasma cutters are really useful shop tools. They can make quick work of steel, aluminum and stainless when they are correctly set up. This is especially true of modern machines. Some materials are safer to work with than others.
What are the hazards of cutting aluminum with plasma? It can be very dangerous to cut aluminum with a water table without the proper safety equipment. Aluminum releases hydrogen when plasma cut around water. Hydrogen can build up under large sheets and explode when being pierced.
That’s the short answer. In this post, I’ll go over exactly what conditions allow for this, as well as what you can do to prevent it if you do want to use a water table with aluminum. There are also some other hazards that can come up, depending on your setup and the grade of aluminum you’re working with.
Plasma Cutting Aluminium Hydrogen Explosion?
This is the main risk, but it’s really only a problem with water beds. No water = No problem.
Aluminum slag creates hydrogen bubbles, just like what you’ll get from a fresh carbonated drink. Since aluminum loves to react with oxygen, it’ll leave leftover hydrogen molecules. As you work the machine and the hot slag builds up at the bottom of the water tank, it produces more and more hydrogen. Gradually these hydrogen molecules will attract to each other and form bubbles.
Hydrogen is pretty volatile stuff. It’ll ignite at about 1000°F. Plasma can get up to over 20,000°F, which makes for a quick reaction.
The main concern is when you pierce a sheet. That’s when you’ll potentially hit a gas pocket that’s been accumulating, and it’ll most definitely ignite. The size of the explosion will be relative to how much hydrogen has been building up. Thin sheets especially are able to hold a lot of hydrogen, since they’re more flexible; they’ll cup the bubbles and prevent them from escaping.
Here’s the worst possible scenario for risk of hydrogen explosions:
The company has been cutting aluminum for a while without cleaning the slag out of the bottom of the tank. The operator loads up the next sheet, but there isn’t enough time to run it. He goes home for the weekend.
Monday morning he comes back and hits the green button. Boom.
Generally speaking, there’s a fairly low risk of this happening if you’re running small parts that can’t hold a lot of hydrogen. Or if you don’t give it enough time to accumulate; for example, you load the sheet and immediately start cutting. But if you wait before running it, you’re increasing the risk of a major safety writeup.
There are, however, some things that you can add to your tank to nearly eliminate this risk.
Ways to Reduce the Risk
There are actually a few ways to go about significantly reducing the risk of a hydrogen explosion. For example, if your tank has a control to raise and lower the water level, the operator can just use that function to allow the hydrogen to escape. The only issue with this is that you need to make sure it actually happens; you only need to forget once.
Install an aerator. This is basically just a few tubes with little holes drilled in them, hooked up to the shop air. When this is at the bottom of the tank, the air bubbles will rise up underneath the sheet. They’ll push the hydrogen bubbles out of the way and significantly reduce the risk of an explosion.
Install a bubble muffler. This is installed on the actual cutting torch. It uses compressed air to shield the plasma, using an inner nozzle. It also pumps water in high volume through an outer nozzle, which blasts anything away from the arc. Beyond blasting away the hydrogen, it has a few other perks.
For example, the high volume water works great for tanks that don’t submerge. It will also reduce the UV radiation and amount of light from the plasma eliminates almost all the fumes, as well as noticeably reduce the noise from cutting. Since the plates aren’t submerged, the hydrogen doesn’t build up. These are actually really great systems.
Install a filtration system. There are a few different types, but generally, these will consist of a high volume pump and a centrifuge. The water gets spun around inside the unit and this separates the hydrogen molecules before they form bubbles. This will also keep with water really clean since it’ll filter out aluminum particles and other contaminants.
This is really important to know!!!
Aluminum-lithium alloys are most commonly seen in aerospace applications, from airplanes to rockets. It’s got a phenomenal strength-to-weight ratio since lithium is so light.
It also is highly volatile when hot and around water. It’ll burst into flames and/or explode. Essentially, super dangerous.
If you need to cut an aluminum-lithium alloy, do it dry. Under no circumstances do you want water anywhere close to hot lithium.
Are There Dangerous Fumes When Plasma Cutting Aluminum?
This isn’t so much specific to aluminum as much as it is just a general safety concern. However, some sources do say that aluminum is especially nasty for fumes, and can potentially be associated with major health issues like Alzheimer’s disease.
Whenever you’re plasma cutting anything, and especially when you’re cutting aluminum, take practical measures to ensure a safe air quality. This means either a powerful fume collector or a proper breathing mask.
If you’re using a breathing mask, make sure that it’s appropriate for chemicals. It should say that right on the filter package. A lot of masks are only appropriate for dust particles, and won’t do a thing for fumes.
Is Plasma Cutting Effective for Aluminum?
This is a pretty common question. Given the additional safety concerns and historical complaints regarding plasma cutting, is this a practical tool to use?
Yes, on newer machines that are set up to handle it.
Previously, a lot of aluminum cutting machines only used compressed air to create the plasma arc. Compressed air doesn’t work so good on aluminum; the cuts are nasty, there’s a bunch of slag, you’ll get porosity, and the edges corrode.
To cleanly cut aluminum, a machine needs to be equipped to operate with an argon/helium mix, although other inert gases can work well too. This will properly shield the aluminum and make for a clean cut. This ain’t cheap stuff, though, and the machine needs to be designed to be compatible with this mix. The machine also needs to needs to be able to travel at high speeds to ensure good cut quality.
It’s not that you can’t cut aluminum with compressed air, but it just doesn’t work so well. Generally speaking, most shops find that a properly set up machine will be more cost-effective than a laser for aluminum over 1/4″ thick. The only caveat to that is part accuracy; lasers can typically hold +/-0.005″, whereas plasma cutting typically holds +/- 0.020″.
What are the best gases for cutting aluminum?
The best gas for cutting aluminum over 1/2″ thick is argon-helium with a nitrogen secondary. The machine needs to be set up to be able to safely deal with these gases. For aluminum under 1/2″ thick, use nitrogen with a compressed air secondary.
What are the settings for plasma cutting aluminum?
Actual settings will vary by plasma cutter. It’s best to consult your machine manual to get accurate settings for your machine. Many operators find that tip height is especially critical for aluminum.