Plasma cutter safey

[TomF]

Hello, Tom here, brand new.

I have limited knowledge of Plasma cutters. I was discussing them with someone and they claimed that when cutting steel with a plasma cutter, you can touch the cut edge with your bare hand in less than a minute. I understand that plasma cutters do cut faster than the standard cutters (oxygen/fuel?), but it surprised me that would be possible.

However I was under the impression that was dependent on the IPM. I can see where a CNC plasma cutter that cuts at say 400 ipm the metal might be safe to touch in under a minute since it was exposed to minimal heat build up. But we were talking about a video we were watching of a person operating a hand held plasma cutter where they cut a 24 inch diameter in a large steel pipe. A hole large enough for an adult to fit through. The operator's speed of moving the cutter seemed no faster than normal, meaning I will guess 8-10 ipm. Wouldn't the cut edge be just as hot with it being cut that slow?

[AndyA]

I'd say the cut pieces are just as hot as with O/A. I have the scars to prove it

Well... maybe it's not at *exactly* the same temperature, but it's above "ouch that hurts" and below glowing red.

[TomF]

Thank you Andy.

So am I understanding right that a plasma cutter's advantage in terms of the cut edge being safe to touch would only apply if it is executed with an increased IPM?

In my scenario of the video I provide in my earlier post, I was telling him that with it being a hand held plasma cutter operated by a person instead of a computer controlled machine (programming the IPM at high speeds), the line of cut is simply not performed fast enough, heat build up will occur just like a standard cutter. Or if there was any difference, it would be a matter of only a few seconds sooner that it would be safe to touch.

I said it would take several minutes before that 24 inch diameter edge would be safe to touch, he said it would be safe to touch in less than a minute.

Maybe he's trying to get me to burn my fingers by trying it? lol

[glock36]

A lot also depends on the thickness of the base material and also between material type ie aluminium or steal.


Good luck
God speed
Happy welding


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[tanglediver]

It depends. Thin sheet cuts quick on the bench, and you can grab it quick, no problema.

If you are gouging out some restricted bracketry under a fenderwell and you burn into it for 4 or 5 minutes straight, it will glow red.

[LarryO]

Ive found that after most cuts the metal is cool enough to put my tongue on it..........


....if you dont believe me, try it.

[Oscar]

hehe

you also have to have enough air pressure (assuming you have enough current) so that it blows ALL of the molten metal from the cut-line. If any lingers around on the underside, it will obviously transfer heat into the metal as it cools.

[TomF]

Thanks all, and Larry0 you're bad, haha.

Oscar. the fire sparks were certainly visible but are you saying if the proper air pressure is present, you would additionally see molten level spitting from the other side?

[farmersamm]

IIRC a plasma actually cuts at a higher temp than O/A.

I beleive the plasma stream can be as high as 30,000 degrees farenheit, whereas O/A puts out about around 3500 degrees.

The difference is the HAZ. Because the plasma has a small HAZ it cools faster, and distorts less.

You can burn yourself on any freshly cut piece of steel.

[rlitman]

Originally Posted by LarryO

Ive found that after most cuts the metal is cool enough to put my tongue on it..........


....if you dont believe me, try it.

Heh, heh. I like that one.

Originally Posted by farmersamm

IIRC a plasma actually cuts at a higher temp than O/A.

I beleive the plasma stream can be as high as 30,000 degrees farenheit, whereas O/A puts out about around 3500 degrees.

The difference is the HAZ. Because the plasma has a small HAZ it cools faster, and distorts less.

You can burn yourself on any freshly cut piece of steel.

Originally Posted by AndyA

I'd say the cut pieces are just as hot as with O/A. I have the scars to prove it

Well... maybe it's not at *exactly* the same temperature, but it's above "ouch that hurts" and below glowing red.

Plasma cuts at a much higher temperature than O/A. With a higher temperature, you can cut more, with less total heat input. That leaves a narrower HAZ, and less heat soaked into the metal, so you have a faster cool down time.

[TomF]

Thank you everyone for your answers. The video we watched was a movie scene from Aliens 1986. After cutting a 24 inch diameter in a large steel pipe, a character was touching the edges with her bare fingers about 45 seconds after making the cut.

I thought it would be too hot to touch, he said no that was enough time to cool off. Maybe it wouldn't have given her third degree burns, I don't know, but the very least I thought it would be hot enough, that it would make a person involuntarily coil back, maybe even cause blistering.

So I got the ammo I need thanks to you all for when I talk to him again.

[WeldingMachine]

Thank you everyone for your answers. The video we watched was a movie scene from Aliens 1986. After cutting a 24 inch diameter in a large steel pipe, a character was touching the edges with her bare fingers about 45 seconds after making the cut.

Just keep in mind: Those dudes in Aliens were pretty tough!

[TomF]

Lol, that's true, but I don't think they're fire proof.

[Oldiron2]

Originally Posted by TomF

Hello, Tom here, brand new.

I have limited knowledge of Plasma cutters. I was discussing them with someone and they claimed that when cutting steel with a plasma cutter, you can touch the cut edge with your bare hand in less than a minute. I understand that plasma cutters do cut faster than the standard cutters (oxygen/fuel?), but it surprised me that would be possible.

However I was under the impression that was dependent on the IPM. I can see where a CNC plasma cutter that cuts at say 400 ipm the metal might be safe to touch in under a minute since it was exposed to minimal heat build up. But we were talking about a video we were watching of a person operating a hand held plasma cutter where they cut a 24 inch diameter in a large steel pipe. A hole large enough for an adult to fit through. The operator's speed of moving the cutter seemed no faster than normal, meaning I will guess 8-10 ipm. Wouldn't the cut edge be just as hot with it being cut that slow?

Initially, an OA cutter needs to heat the metal up until it will oxidize when the Oxygen jet is turned on; not only the metal which will become the kerf, but the surrounding area too. As the cut proceeds, the burning produces heat which keeps the cut moving, but both it and the preheat still transfer a lot of heat to the surrounding metal.
A plasma torch, with the significantly hotter, more energy-concentrated plasma flame, starts without any preheat, instantly transferring its energy to the surface being cut, which is blown away as fast as it melts. The higher, more concentrated heat and thus faster melting both mean less time for conduction of heat into surrounding areas, and the shielding gas probably also has a bit of cooling effect on the kerf away from the plasma flame.

When the atomic bombs went off in Japan, 'shadows' of items were burned in relief into various objects like wooden walls; the objects, including people, shielded the surface beyond, but where not shielded, those surfaces were eroded in a fraction of a second due to the fantastic intensity of the heat.

[Broccoli1]

You assume they were using a Plasma Cutter, considering the fact that they used Pulse Rifles I doubt they still used technology from the 21st century to cut that hole.

[turbocad6]

yeah, that wasn't a plasma cutter it was an anti matter beam generator, you could touch it even seconds after the cut, it doesn't cut by heating the metal at all, it cuts by making the matter in it's stream into antimatter

[puddytat]

I've learned the hard way....don't touch it with the bare hands.......works every time.

Working without welding gloves around hot metal always means eventually you'll grab or touch something that is hot....happens too quick to get back from.
Ian..

[TomF]

Originally Posted by Broccoli1

You assume they were using a Plasma Cutter, considering the fact that they used Pulse Rifles I doubt they still used technology from the 21st century to cut that hole.

That's what I suggested at the very beginning, it was futuristic fictional cutting technology. But he argued it was a plasma cutter. Go figure.