FW_Su2013_02

Uh, so if we want to talk about properties uh of stoichiometry, this is the fuel in the mixture from 0 to 100%. You'll find with most gases — acetylene, natural gas, hydrogen, propane — you'll go through a peak, and that's when you are at just the right ratio. If you're burning hydrogen you want to have H2O or something close to it. If you're burning acetylene you're going to have two CO2's and a — and one oxygen for an H2O, so you should have what, uh, 2 and a half uh oxygen molecules to burn, okay, for every acetylene molecule, so far as that goes. And if you have the proper ratio, you'll get a peak in temperature. The x is actually where stoichiometry is, um, and I can't remember — the zero is, um, oh, that's the neutral mixture, um, where uh essentially it's not oxidizing and not reducing. And that gets into your secondary flame.

If you actually look at the structure of a flame — actually I might have a nice color picture of this. Let's look it up in a good old welding... [Tom searches through a reference book.] uh, heat... well actually this one might have it but it won't be in color, let's see. I can't find it, I'll just draw it.

If you actually looked at a flame, like an oxyacetylene torch flame, you would find that it actually has structure to it. It's not just a ball of fire or a jet of fire sticking out. If you look carefully at it — [Tom draws on the board] — and this is your nozzle with the flame shooting out, you'll have what we call a primary flame and a secondary flame. Okay, so this is the primary combustion, and that's the hottest combustion. That's where you're going to get, for acetylene — if it's oxyacetylene torch you're going to get 3100 degrees centigrade in here. But in fact that's not burning to CO2 and H2O, that's burning to carbon monoxide and H2O. And out here, the carbon monoxide will combine with some of the oxygen in the air or leftover oxygen in the flame and give you carbon — carbon dioxide. Okay, so you have secondary combustion. It's a two-step process.

In fact the whole combustion process is extremely complex. Uh, if you take something simple like methane and you actually break down all the chemical steps and all the intermediaries, you actually — you have to break up uh the carbon and the hydrogen, and you'll get a uh something that only lasts for milliseconds or microseconds, uh that's a CH radical, it's not stable. But you have to break up the big molecule into little parts and then those react with other things. If you actually look at something simple like, I think it's methane, I can bring in the book if you want, but there's two pages of chemical formulas for something simple like CH4 going to carbon dioxide and water vapor, and there's carbon monoxide and there's all these other things, all these steps.

And those of you, you know, certainly on submarines and I think on surface ships — do you guys have Halon fire extinguishers now, still? No, not on surface ships but on subs? Not on submarines, not on subs? What — ever since the P. Smith thing they're starting to... Okay. So we used to use Halon. Did anyone ever do a demonstration with Halon to show you how it puts out a fire? Okay, what it does is — I mean I've seen it — they start a little candle over here and the guy just squirts a little Halon in the room, you know, like from here to, you know, he squirts it over here and over there. About 2 or 3 seconds later the flame will go out. Okay, and what it does is the chlorine or the bromine or whatever the halide is poisons these intermediate reactions and it stops the combustion process. It's very effective, it's just — it's not good for global warming and things like that. And so um it's a very effective extinguisher. I have an old Halon extinguisher in my kitchen. Um, don't tell the EPA, I'm sure I'll be a bust and they come in with a SWAT team to get my Halon from me. But um it's very effective. But it does poison the atmosphere.

So far as that goes, of course you poison the atmosphere every time you exhale, you realize that. You're putting out uh halo-hydrocar— you know, things like carbon tetrachloride is in your breath, okay. You produce it in your body, you have salt intake, you burn things in your body and you produce reaction products, some of which could blow out a fire — could put out a fire if they were higher concentration. Nonetheless, um, so we produce all kinds of things. Um, the Navy is sort of guilty, folks, of a number of environmental things. Anybody know about tributyl tin? Some of you. It was allowed in paint. Out with that on, you don't need to dry it, clean it, touch it. Absolutely, tributyl tin will keep all those barnacles off. Not only that, it kills every mollusk in the harbor — oysters, clams, you know, scallops, any mollusk in the harbor is dead meat, literally. I don't know where they found it out, but it was about 20, 25 years ago finally some people went to Congress and Congress told the Navy to quit using it. But economically it was great for the Navy, okay, and the Navy can always justify doing things, or the military can always justify doing things in national security. So, but Congress decided they'd rather have people scraping barnacles, right, than wiping out all the fishery industry in the harbor.

Uh, so in any case, I'm sure there's other things. If you go down to uh Aberdeen [Proving] Ground for the Army there's RDX everywhere in the ground, okay. This is the firing range. Used to be JP Morgan's private hunting reserve before the income tax. It's a $50,000 — I mean, there's deer running around and stuff, it's beautiful area at the top of the Chesapeake Bay. And to pay his tax when they came out with the income tax, JP Morgan decided to give away his hunting preserve, and it's now been a shooting range for the last 80 years or whatever. And uh as a result there's still deer and there's still shots going off, but they're not shooting at the deer — are protected — um, but there's RDX all over the soil. I mean, it's a huge environmental site, okay. But those aren't the big environmental sites.

But anyway, the secondary combustion uh — where I gave you some things — is talking about this outer flame rather than the inner flame. And you can change that inner-outer flame ratio by changing the amount of oxygen in the fuel-oxygen ratio. A neutral flame, you can get this... well that's what I was looking for in the welding handbook, there actually are pictures that kind of show you an oxidizing flame, um, a neutral flame, and a reducing flame. Okay, where you have, in the secondary flame, you either have excess oxygen or excess carbon. You can tell when you get a lot of excess carbon, 'cause all of a sudden your flame goes yellow rather than blue, okay, because now you have soot particles glowing red or yellow, uh carbon particles which give the flame the color. So when you see yellow flames it usually means that you're fuel rich, so far as that goes. Other questions? That answer your question? Okay, any other questions on this stuff?

Okay, so let's talk a little bit more about surface heating with flames. I actually found one of my overheads, if this one works. Um, the heat must diffuse across the gas boundary layer. Uh, the gas is coming out of some torch, hits the surface and diffuses to the side, and this essentially becomes a cold gas which has to be swept away. And the faster the gas is coming out, the thinner this boundary layer, you can sweep this away more effectively. But there's the laws of diminishing returns. And so we use — we talked about um diffuse flames where you have a very slow flame, uh, we talked about um premix flames like these, okay.

Um, got to turn it on again. [Tom turns on a torch.] Um, that's a premix flame. The mixing is done down in the ch— there's a little chamber in here and the air comes in and mixes with it. So you actually have a mixture, and if I unscrewed this thing uh you'd find a little piezoelectric thing just like on your gas stove at home, and creates a spark and it comes shooting out. If this is properly designed, which it is, uh the flame shoots out at a certain velocity and it might be several meters per second, is the flame velocity. If you had too big a uh a torch and not a big enough orifice, not enough gas, you could actually get flashback. Once it ignites, the gas could burn faster going into the torch than coming out. So you have to balance the speed out with the burning velocity of the gas going out. And the speed of that flame is determined by the thermal expansion of the gas as it burns. The hotter the flame, the hotter — the faster the velocity.

And if I run both of these, this being propane which burns at a lower temperature, you should hear a lower velocity. You can — should be able to hear the difference if I can... [Tom lights both torches.] Okay, that's a softer flame than this, right, because this is a higher temperature gas, and the higher temperature gas expands more — velocity, thinner boundary layers, better heat transfer. Okay, the maximum heat transfer from a burning gas is basically a jet burner, and we talked about jet burners. This is basically constant pressure burning, okay, it's one atmosphere, it's burning out in the atmosphere, one atmosphere. If I actually had a chamber around this and I ignited it inside a chamber with a little nozzle, that would be constant volume burning, and it would come shooting out with 10 times the velocity of this thing, okay. And that's a jet burner. Well, we have jet burners in jet engines. We burn them in the combustion chamber at constant volume and we shoot them out the back and it gives us a big reaction force. That's how rockets, that's how jet aircraft work, okay, so far as that goes.

You also have the question of, if you have inerts — if I go back to the summary thing — temperature of flames determined by the enthalpy of the reaction, of the delta-G of the reaction gas, the oxygen-fuel ratio, which has those kind of hump curves depending on fuel-oxygen ratio, and the presence of inerts. If I have an oxy-flame, whether it's oxyacetylene, oxy-propane, oxy-propylene, I will have about 10 times the velocity as that same fuel burning in air. All that nitrogen slows things down, drops the temperature by about a factor of two roughly, and then uh that drops the combustion velocity down by a factor of 10. Much less heat transfer. So that little — a little candle, a birthday candle, I can put my finger through there all I want. I can even do it fairly slowly, okay, like that, and not burn myself. If I did it with the MAP gas, even though it's burning in air, I got to do it pretty quick. I don't want to leave that thing in there for a second and a half or I'll end up with blistered skin, okay.

So heat intensity can be varied, but the maximum heat intensity I can get with even a jet burner is about 2,000 watts per square centimeter. It's much less than the electric arc. The electric — less than the electric arc can give me, 10,000. Now we actually do have applications of jet burners, okay. Um, they used to use them um to drill holes in rock. And with — if I have a — if I want to drill a hole in a rock, and this is my rock, and I come in here with a jet burner at 2,000 watts per square cm, because of the relatively low thermal conductivity of the rock compared to a metal, and the brittleness of the rock, I can heat this up and cause it to expand. As it wants to expand, it can't, and so it will buckle and crack, and with the high velocity of the jet burner I can blow the little shards of rock out of here, and I can with the flame burn right through, drill a hole right through that rock faster than any mechanical drill, by probably a factor of 3 to 5.

The only problem — the reason we quit using it about 25 years ago, it's sort of loud, like 180 dB, okay. I mean, which is really loud. Threshold of pain is like 130 dB, okay. It's a logarithmic scale, so you basically — all the neighbors, if you're drilling where there's a bunch of neighbors. But if you're at a mine site there's not a lot of neighbors except the bears and stuff, and they don't — the bears and stuff, and they don't complain that much. If they do, you'll know it. Um, in any case, they quit using it, but in the last 5 or 10 years they've actually gone back to using it and they're dealing with the noise problem, okay, because it is so much more productive at drilling holes through things like rock. So we do use jet burners for materials processing, not just for rocket engines.

Now what — anybody know in rocket engines, solid rocket — well, we have rocket engines where we just burn hydrogen and oxygen. And that was supposed to be the next space shuttle, the X-33 aerospace plane. It was going to — it had two hydrogen tanks and one oxygen tank, it was going to produce H2O, it was going to be clean burning, right. Uh, and the reason they did that is they wanted to keep the weight down, and what's lighter than hydrogen? Nothing, right. Um, so um they wanted to burn H2 as the rocket fuel. But you can get a hotter flame, much hotter flame. We can get about 3100 C with acetylene. You can get to 4,000 C with solid rocket boosters and stuff. Anybody know how we do that?

Same way as sparkler technology on the 4th of July, okay. You add metal powders, you add magnesium powder or aluminum powder, just like making a flare, okay. Now with the sparklers they're not trying to go for 4,000 degrees, 'cause people already burned themselves with sparklers. They actually add clay to the sparkler to drop the temperature. But in fact in a solid rocket motor they use aluminum and magnesium and then get 4,000 degree temperatures. And so that's the way to get uh really efficient uh burning temperatures for rockets and stuff.

There's a problem with solid rocket motors though. Once you turn them off — how do you turn them off? Turn them on, how do you turn them off? Well basically you don't, okay. You just burn out until the fuel's used up. Now people are developing solid rocket boosters that uh can be turned off, okay, and I don't know that much about them. But basically a solid rocket motor is just a mixture of oxidant and fuel and you have a controlled explosion going off, okay. It's hopefully just burning from one direction so it's a controlled explosion, okay, but it's burning very rapidly. In any case, we do know how to get higher temperatures uh for things if we need to, but in welding we don't usually need to. We usually make do with what we have.

Um, the main use of flames is not oxyacetylene welding anymore. Uh, oxyacetylene welding was very popular about 100 years ago. Um, acetylene was discovered in like 1836 by — who was it discovered by? Um... oh, by the way, there's a picture — this is the picture I was looking for in the welding handbook, actually this one's in the welding encyclopedia, for oxidizing flames, um, [Tom shows the book] this thing's not working, where's my — here we go. Um, for oxidizing flames, neutral flames, and reducing flames. And they have — you can't see it very well, it'd be better if it was in color — uh but you have secondary combustion. And the reducing flame with a lot of excess carbon has a bigger secondary flame, you want to see it there, okay. There's more secondary flame in the reducing flame because you have more carbon left over.

Um, so acetylene — Edmund Davy, who was Sir Humphrey Davy's brother I think, discovered acetylene in 1836. But it wasn't until 1862 that a guy named Wöhler determined that he could produce acetylene easily by just reacting water with calcium carbide. Uh, calcium carbide — if you happen to have some, if you pour water on it, just generates acetylene and uh calcium oxide. Um, and in fact if you go to a shipyard, that's typically how they do it. Anybody been to a shipyard where they might have a carbide shack? I remember someone telling me a story at Newport News. I was down there once, and uh one of the welding engineers — sitting in the office where the welding engineers sit, and he heard the alarm go off in the shipyard and the fire department was rushing to wherever it was, and another engineer came in and said, "well, they got a fire down at the carbide shack." And the welding engineer jumped out of there as fast as he could to beat the fire department to the carbide shack so they didn't douse it with water. 'Cause if you put water on the carbide you're just going to get a bigger flame, 'cause you're going to be generating acetylene. That's why they have a carbide shack. Because acetylene is a problem in storing acetylene.

And it was in the early 1900s that Thomas Wilson of Spray, North Carolina found an easy way to make calcium carbide. He was trying to synthesize metals — and Edison and Westinghouse had come along and you now had electricity — and he was running arc furnaces, and he put some carbon and some limestone in a furnace and tried to keep the air out so he could try to synthesize some chemical. And he ended up with this — I think it was a black powder — and he couldn't figure out anything to do with it, so threw it into the Neuse River in North Carolina, and something was around that ignited it, okay. And he thought, "that's strange, I've never seen water burn before." Um, and so he started studying it some more. He had synthesized calcium carbide. All you need to synthesize calcium carbide is an arc furnace, limestone, and carbon, okay. The electric energy breaks things down and you form calcium carbide.

Then if you take that calcium carbide in an acetylene generator on site — it's nothing more than a silo with calcium carbide, and you drop the calcium carbide powder into a hopper and you drip water on it, and acetylene comes off and you pipe the acetylene through the shipyard for flame cutting or whatever. Uh, that's because it's a pain in the neck to store acetylene. Acetylene tends to explode if you go above about 60 or 70 PSI, okay. It's explosive under pressure, okay, not a good thing. So you can't just compress it like a regular old compressed gas. What they learned — um and this was the beginning of the Prest-O-Lite division of Union Carbide, about uh 1904 — uh, this guy Avery, PC Avery from Indianapolis, got together with two famous automotive experts uh James Allison and Carl Fisher. Anybody ever heard of Fisher or Allison before? You ever heard of Detroit Diesel Allison? It's now Rolls-Royce. Uh, but basically Detroit Diesel Allison — Allison Diesel — Allison engines came out of Indianapolis. Anybody ever hear of Fisher Body in the old days? It's the division of General Motors that made all the automotive structures.

And Allison and Fisher set up shop right across from what they later built as the Indianapolis Speedway, okay. So these guys were kind of into automotive stuff. And they came up with a way to store acetylene. [Tom holds up an acetylene cylinder.] And this is a split acetylene cylinder. This is what's called a B cylinder. And the reason it's called a B cylinder is because B stands for bus, and this was the headlight — two of these would be the headlights on buses around 1910, okay. They just had a little flame shooting up the top uh off the acetylene cylinder. But you can't pressurize the acetylene, so what they learned is you could fill it up with acetone, and acetone will dissolve 400 times its volume in acetylene without creating a high pressure to cause the acetylene to go unstable. The problem is you don't want to just put a bunch of acetone in there sloshing around — it could leak out or something and then start its own fire. So over the years they used to put um sand or asbestos or whatever to try to keep the acetone uh from sloshing around.

In the early 50s they developed a calcium silicate binder uh which is 92% porous. So this has got a plastic sleeve over it but uh you can look at it at the top, it has a little felt — piece of felt to try to keep the ceramic powders in. Ceramic cement, it's extremely porous — 92% porous cement — and the rest of it filled with acetone. And that's why acetylene cylinders are so heavy if you've ever tried to move them around, they're heavy because they're full of liquid, okay. So transporting acetylene's a pain in the neck. You have to be careful uh because of uh not only the potentially explosive nature, but you also have to be careful that you not do any piping with pure uh copper. Everything has to be brass or nickel or stainless or whatever, usually it's brass. And the reason is, copper will react with acetylene to form copper acetylides, which are contact explosives.

And so uh — yeah, didn't eat, okay. So uh, you want to make a contact explosive — I wouldn't, you know, this is something you probably shouldn't do at home. Um, because if you don't know what you're doing, you may — it may go off before you want it to. Um, but for all you terrorists out there, I'm just telling you some ways to uh terrorize the neighborhood by um using contact explosives. I remember as an undergraduate here, the living group I was in, one guy got into mercury fulminate, which is a contact explosive. And he would put — he would take by his wooden desk, he put some straight pins, stand them up on the desk, he put um a grain of sugar on top, the head of the straight pin, he would put a drop of mercury fulminate on top of that to let it dry. And that made a contact explosive. And of course the sugar would attract the flies, this was during the summer. And this was his fly catcher. He would come, you know, fly would come up and he, boom, blow up the fly, okay. Um, so just a different approach to an MIT approach if you will to catching flies or fly catching.

Um, okay. So the highest heat intensity you can get is about 2,000 watts per square cm because we have this problem of heat transfer across the boundary layer. So why do we use electric arcs? Well electric arcs can actually give us a lot more heat transfer. Uh, even though the gas coming out of here from a jet burner is 3000 degrees centigrade, even if I increase the temperature of the gas to 10,000 centigrade, that is not going to do it. That might give me 500, but it's not going to give me 10,000. What happens with an electric arc is the electrons are not slowed down by the gas molecules, and I can have electrons punch their way right through this boundary layer. And it turns out, in an electric arc, 80 to 90% of the heat is carried by the electrons and not by the hot gases, okay.

So an electric arc — I like to think of it, and this is my own terminology, it's an electrically augmented flame, okay. It is essentially a flame with an electric current going through it. And when we talk about plasma arcs and things like that, you'll learn there's things called transferred plasma arcs. And a transferred plasma arc actually has electrons going to the workpiece, and it can have up to 20,000 watts per square centimeter on the surface. A non-transferred plasma arc, where essentially the current goes to a water-cooled copper tip here and no current goes to the workpiece, will only transfer about 2,000 watts per square cm. So you get a 90% of your heat in um transferred — non-transferred arcs is carried by the uh electrons.

So that's why an arc — you can think of an arc as an electrically augmented flame. And so now what I want to do is talk about arcs and the physics of arcs so we can understand how um arc welding works, because it is the most common form of welding, fusion welding. Um, I can say an arc is an electrically augmented flame, and typically you'll have an electrode, you'll have a workpiece. I've drawn this as a gas tungsten arc where the anode is the workpiece and the electrode is the cathode. Um, in here we're going to have a plasma jet. We're going to talk about that later. Uh, but the plasma jet is actually a wind going at about 500 uh miles an hour off the tip of that electrode created by electromagnetic forces. And if you've ever wondered why you can weld overhead, because the tip of that electrode's got a 500 mph wind blowing the drops up against gravity.

So there's some interesting physics going on in here. But I just told you that the electrons punch their way through the boundary layer. It turns out the electrode is relatively cold. If this is a tungsten electrode, it's at something like 2800 C. If this is the workpiece, it might even be molten, but even if it's water-cooled copper it's cold, at a couple of thousand degrees centigrade maximum in most cases. And so the electrons have a hard time getting out. The plasma doesn't ionize to be a conducting material until it gets away from this cool boundary layer at either electrode. And so we have, at both electrodes, if I plot the voltage as a function of distance across here — this is voltage this way — I have what we call the cathode fall voltage, for the electrons to punch their way through this un-ionized cold boundary layer takes a lot of voltage. They have to have enough energy to accelerate their way through an un-ionized vapor space.

Then they get into the plasma column, is what it's called, and that is ionized and it's a great conductor, and so I have a small voltage drop. It will be about 10 volts per centimeter — we'll talk about some of these things. Um, this cathode fall voltage is going to be on the order of 4, 5 volts over less than a millimeter, actually probably less than a quarter of a millimeter, okay. So it's a fairly steep voltage. And then we have the anode fall at the other end, where we have another boundary layer of cold gas, we have an anode fall voltage. And it turns out — we're going to talk about um how the heat is carried — but in the plasma column here, it is 10 volts per centimeter and 99% of the current is carried by the electrons in a high pressure arc. What do I mean by high pressure? For a physicist, anything above um half an atmosphere is high pressure, okay, in talking about arcs. And when we come back I'll explain why they define that as a high pressure arc.

Student: If you have an ionized gas — on the other side, how do you have an electrical — on the other side you said there's un-ionized gas at the tip of the electrode...

Oh, the electrons just, you know, they just have — they, if I don't want to say tunnel — they have enough energy, they blast their — they're ballistic, if you will. They shoot their way across that gap, okay. If you give them enough voltage gradient, they will puncture through the un-ionized gas because the electrons are very small, okay. If they do hit something they will bounce off like a billiard ball, but most of them will get through if you give them enough electric field to push them through. So that's the big voltage drop, is the big electric field that's accelerating across this un-ionized gap. But you're absolutely right, there is no conductive path across that gap. You're just giving them enough momentum to jump the gap, just like jumping over a river — running fast and jumping, right.

Student: Yep. The only experience I ever had welding was underwater for the first time. Can you — is that process exactly the same?

Yep, no — it's not going through water. When you strike that arc you vaporize the water. This plasma is at 10,000 degrees. Even if it's a water plasma, it's 10,000 degrees, that's vapor. In fact what happens in underwater welding, a certain fraction of your power is going to creating an air bubble — a plasma bubble — between the two electrodes. And there is no liquid water on either surface of either electrode, either the anode or cathode. So then you get the same efficiency essentially. You get a — you actually get a little bit better efficiency, because there's uh the outside walls, where right now in a regular, you know, arc in air, this is just radiating through the gas. But if you actually cool the outside of the plasma, because it's now a water sheath around it — it's just a plasma bubble surrounded by water — you actually constrict the arc. And so the plasma is narrower in underwater welding than it is in the air, because you've got the pressure of the air — the water — squeezing the little bubble of gas. That creates a higher current density through the plasma column. That creates greater heating, and so the underwater arc — the underwater welding arc is actually slightly hotter than the one in the air above on ground.

It turns out, since 90% of the heat's carried by the current, it really doesn't make a big difference. But it does make a measurable difference. You'll get a greater depth-to-width ratio for the same current underwater on a piece of carbon steel than you will up in the air, okay. You'll get different chemistry in the weld pool because you're at a higher pressure. And in fact the pressure that you can generate and maintain this bubble stable-wise, okay, with stability, is about 30 atmospheres, okay. If you go below 30 atmospheres, which is about 30 atmospheres — 450 PSI. So if you get to depths approaching that, like 400 feet, you can't do underwater welding below about 400 feet, because the water pressure will just swamp the whole thing out and shut the arc off, okay. You'll now, you know, I just have — running electric current through water, and that didn't do much, right. It won't be stable.

So if you actually go below about 400 feet you actually have to create um uh habitats, and you do dry welding at 900 feet down, right, or something, right. Did I do all those — that math right? You should know. Some for 450 — yeah, thousand feet. But in practice about 4 or 500 feet, all you really want to do, you start getting instabilities, and you can't maintain a stable bubble, okay. Not everything's symmetric, and if you have a wave of water come through and wash out your arc, that's not going to produce a good weld. So about 4 or 500 feet, it's the maximum that you can really do. In the laboratory you can go to 30 atmospheres, thousand feet um type of pressure depth. But I think usually once you get above — get once you get below about 4 or 500 feet, you start running into needing to have habitats. And if you're going to make a habitat you might as well make it a lower pressure in some cases, or you might do it at the higher pressure. But you actually run into problems above 30 atmospheres. The arc becomes unstable. It can't generate the gas and maintain a stable bubble if you will, of plasma, okay.

Why we take — okay. So I started telling you about arcs and how an arc's an electrically augmented flame, but before I go into further into arcs, I forgot, we got to talk about flame cutting. It's what I brought the samples for. Um, because they still do acetylene uh flame cutting. Uh, but we can also talk about whether acetylene or MAP gas is better for welding, 'cause there's been an open debate for 30 years in the welding community. People sell MAP gas, tell you it's safer. I told you all the problems with acetylene — it can explode under pressure, it can form copper acetylides and whatnot. MAP gas — C3H4 — or propylene, which is what people use now, is a liquid in a container, okay. And it doesn't explode under pressure, it doesn't have this triple bond that creates some of the problems and whatnot of stability. And so people say "oh you should use MAP." And other people say "oh no, acetylene works better," okay. Just like the plumbers who are doing soldering will tell you "oh no MAP works better than propane," okay. And they're right, because it's hotter, you can probably go twice as fast with MAP as you can with propane. And if you're a plumber, speed is important. If you're just a home plumber, you know, doing your own stuff, you don't care if you make the solder joint twice as fast. And it may be a little safer not to burn yourself, 'cause MAP you can burn yourself pretty badly pretty quickly because the higher heat intensity.

Um, but in any case — in fact we just had a — I actually represent the company that makes the cylinders, and we just had one uh — people do some interesting things with these uh cylinders. There was the guy, a plumber in Southern California who was lying on his stomach on the grass with a hole, where there was a copper pipe, and he wanted to sweat the copper elbow. And so he was — he had a cell phone in one hand, a cigar in his mouth, and he was starting to uh solder the copper pipe. But the elbow moved on him, so he started using the uh torch — the lit torch — as a hammer to get it back in place while he's talking on the phone, smoking a cigar, okay. Anything — actually he split the neck, and a woman was walking by with her granddaughter down the sidewalk and she saw this 8-foot flame just shoot out of the hole right in his face, okay. He wasn't happy.

Um, and then the one that settled just a month ago was — been going on for 3 years — this one guy in Southern California who uh he was smoking methamphetamines. People really like um MAP for smoking methamphetamines because it's got high heat intensity, that means you can vaporize it quickly — the methamphetamine — and you get a bigger high, I guess, okay. I don't know, but this is what I've learned, okay, by reading this stuff from these guys. Um, he claimed he wasn't. Um, but in fact it's not a good idea to throw these to the ground as hard as you can. Like, I estimate people have thrown these things at 45 miles an hour by looking at the fracture energy of the things and stuff. Um, so people do throw these things to the ground, and when they blow up — it turns out if I were to release all the gas in this, it's only 10 cubic feet if it was full of liquid, it's only 10 cubic feet. And the flammable limits are of MAP and acetylene are like um — uh you have to have like 2 or 3% by volume, okay, if I remember.

So this room would not fill up and explode. You might get a really intense fire over in that corner and burn down the corner. And they've done some tests out at Mount Shasta in California where they basically pull on these things to ignite them, and when the gas comes streaming out, it'll burn for 3, 4, 5 seconds. And as long as you're not standing in the middle of it, you're fine. But if you happen to be standing in the middle of it, you can get pretty severe burns, like 75% of your body, um. So it's not a good thing. Anyway, this guy — they started the trial, and it was a — didn't have a jury, we don't have to go through the reasons, but it was a federal case, and the judge heard the first two days of two weeks of testimony, and he was supposed to finish it up in May, and we were supposed to come in and talk about how this guy was really smoking um methamphetamines, and how we could prove that it didn't happen the way he said. But in fact he and his girlfriend — and we won't get into all of that, they were — he was in his 40s and she was um a grandmother in her 50s, um uh — but and we — it's probably not appropriate, certainly on tape, to talk about what they were doing while they were doing the drugs. But um they lied about everything.

Over — and it turns out we didn't have to put on our case, 'cause the judge threw it out. If you commit perjury, uh, the case can be thrown out just because you lied, okay. And the other side was prejudiced and there forth, that's what the judge did. He actually threw out the case halfway through, because what they said under oath at trial was not what they said under oath in their depositions, was not what they told the police the day it happened, was not what they told the halfway houses a couple of days later. You know, they kept on changing the story, okay, and eventually — but anyway. So people do some foolish things with these things like hammering on them with — while they're talking on this um cell phone and stuff, and they do fail every now and then, but usually because they're abused.

But people still debate for welding which you should use, acetylene or MAP gas. And so I did a little calculation once um to show that even though the temperature is only about 230 degrees centigrade difference for the oxy-fuel MAP or acetylene, it turns out, since the combustion intensity goes as the square of this — and you're really just talking about the temperatures above 1600 — uh, did I actually do that calculation for you here? Okay I don't think I did. But it's T-flame minus 1600 C is the melting temperature of steel, but you square that. It turns out you get 36% more heat even though it's like only a uh 2 or 3% difference in temperature. A small change in temperature makes a big difference in efficiency of heating the surface, okay, is the point. Um, so acetylene is better for welding. Uh, it's much better than propylene. I've never heard of anyone using propylene — losing another 100 degrees, you can just see how much slower it is.

But then we do use it for flame cutting, and flame cutting is an interesting process. Uh, you basically have some — you have a double set of tubes. This inner tube will have pure oxygen in it, and the outer tube, the annulus, will actually have your premixed flame. And you heat up the surface of your workpiece without turning the oxygen jet on yet. How many of you have done oxyacetylene cutting or watched it? So a couple of you done it. Actually has an extra lever. You light the torch, you hold the flame right up against the surface. I usually take that inner cone tip and just touch the inner cone tip — it's a couple millimeters long — um to the surface of the steel. And then you get it, and you kind of — I look for the oxide on the steel to kind of look like it's sparkling or bubbling on me, okay. That means I actually start to melt the iron oxide on the surface. And then you pull the oxygen torch, okay, and you inject pure oxygen into hot steel, and it will burn not at 10 to the 4 watts per square cm — I've estimated it's about 10 to the 5th watts per square cm — is about 10 times more intense than the heat of an arc. You're getting all the chemical heat of the pure oxygen burning with the iron.

And so it turns out for flame cutting, the way you get around the heat transfer problem of the boundary layer is you condense the boundary layer. The iron oxide becomes a liquid — this is your combustion product — and you don't have, if you have really pure oxygen — and really pure oxygen works best for flame cutting — you don't have a boundary layer. There's no inerts left over. And I'll talk about some inerts that are there that actually can slow you down. But there's no boundary layer formed, and you get about 10 to the 5 watts per square cm. You need, in theory, to have an iron — or an oxide of the metal, metal oxide, that melts slower than the melting temperature of the metal. So here's the metal — melting temperature of steel, 1536 C, iron oxide melts at 1380. Aluminum and magnesium cannot be flame cut because their oxide is a higher melting temperature than the uh than the metal. Chromium — stainless steels cannot be flame cut because they have a very refractory oxide and you can't melt it to blow it out of the way. Titanium in theory should not be able to be flame cut, but in fact it can be.

And what I have here — this is actually my first research project here at MIT back in the late 1970s on welding of titanium. [Tom hands samples around.] This is flame cut titanium — not flame cut, this is saw cut titanium, this is flame cut titanium. This only have a thinner piece, but you can flame cut it. Now a lot of smoke that comes off when you're flame cutting titanium turns out it's just titanium dioxide, which is basically in wall paint and stuff. And it's not particularly toxic, it's not toxic really at all, but a lot of smoke. And so one of my stories — back 25 years ago I didn't have the office I'm in right now, but the office I'm in right now is right — was right across from the welding lab, which is a little bit different then. But my technician was flame cutting some titanium and we had the vents on, but the vents weren't all that great and some smoke was getting out of the lab into the hall. And so the secretary to my — the my old thesis advisor — calls up the environmental police on me. And so they come by — this was when the environmental police were not quite so adamant about things — and the guy comes into the lab, he sees the technician, he says "what are you doing?" 'Cause there's smoke all around, and the guy says — my technician Bruce says "uh, flame cutting some titanium." He says — the guy says "what kind of lab is this?" He says "it's a welding lab." And I said, "well, what are you expecting to come out of a welding lab?" That was what the environmental guy said. They don't say those things now, this 20, 25 years later I probably would have been in handcuffs and up in the Cambridge police station. Um, but um it does generate a lot of smoke to flame cut titanium.

The reason it works is titanium will dissolve its oxide — start dissolving its own oxide at about 900 degrees centigrade. And so you get up to these higher temperatures in this protective titanium oxide coating, essentially dissolves away into the titanium, and you do expose fresh metal — fresh metal to pure oxygen and you get a very rapid reaction just like a flare, okay. It's a controlled flare, if you will, and it — there's no boundary layer that's formed, it burns right through there.

Student: Question on those — the samples — like magnesium and aluminum, the oxide layer is pretty thin, right? So why do you need to melt that oxide layer away because underneath...

Because the aluminum-magnesium have no solubility whatsoever for their oxide. They don't dissolve oxygen. Titanium does.

Student: I guess what I'm asking is, couldn't you melt the metal underneath through the...

Oh yeah, you can, and you'll end up with a very lousy looking cut, okay. I mean, you can melt through the stuff, but that's actually — if you do it in a controlled way, that's plasma cutting, and you can actually get a very good surface. I'm going to talk about that in a second, okay.

There are various qualities of plasma — of oxyacetylene cuts. Here's a plastic guide for good surfaces and bad surfaces. Sample 4 is the best surface. I didn't bring back my piece of HY-80 but that was done, and it was a sample 4 cut, okay. You can have really lousy cuts, you can have really great cuts with oxyacetylene cutting. I have seen in steel mills where they basically take an oxygen torch and cut through 3-foot-thick steel, okay. In fact when the steel comes off the continuous caster and it's already hot, you don't have to preheat it. They just take an oxygen lance and the guy goes and just cuts right through it. I mean just, you know, he can go several feet a minute. Just oxygen, no plan— yep, because it's already hot, okay. Just need the jet of oxygen to blow some of that uh surface oxide away.

Student: Yeah, so when we did it I think the torch was consumable — is that the same thing you're talking about, or...?

No, you're talking about carbon arc gouging.

Student: Okay, probably.

Were you gouging things to make uh prep for welding?

Student: Uh, they're just teaching us basics on dive school...

Okay, uh, oh, this is in dive school, okay. Well, that actually is a form of oxy-gouging, okay, where you have — strike an arc and you just have air blowing through a tube, double p— yeah. But you actually strike an arc — underwater you need to strike an arc. You have to have something to generate your bubble to start insulating everything from everything else, 'cause otherwise you'd quench the whole thing with water, okay. So in that case they take essentially what is a carbon arc gouging — you know, carbon tube, a graphite tube — and blow oxygen through the metal. But the outside, that carbon tube is actually striking an arc to create the bubble for the underwater, to exclude the water. And then you're exposing hot steel from the arc to the uh to the oxygen jet, and you're just burning through it. They call it burning of steel, and it really is burning of steel.

Student: Three metal shielded carbon tips, then we have the giant Broco torch, right? And then we also have the oxygen carry cable.

This — yeah, so you guys are talking about salvage operation with the great big stuff, okay. Just trying to cut great big things, okay. But it's pretty impressive to see this stuff cut through uh 3-foot-thick steel.

Student: We cut through big anchor chain.

Yeah, okay, so you can do some pretty impressive cutting. But you're using chemical heat, and you're getting around the gas boundary layer in most cases by forming a slag, a liquid slag, rather than having an inert gas that inhibits your oxygen coming in contact with the molten metal, okay. So you can get extremely high heat transfer rates, and you can cut titanium.

However, uh — well actually let me tell you what screws things up. Well, this is just another one — oxygen condenses as iron oxide, no boundary layer, combustion intensity reaches 10 to the 5 watts per square cm. And I told you the metal oxide should melt below the melting temperature of the metal, but that's not always true, like titanium. Um, there, you have a paper in there called "The Iron Oxygen Combustion Process" written by Alan Wells, who was — went on later to become director general of the Welding Institute. And this plot comes out of his paper on the iron oxygen combustion process. There are not a lot of papers on oxyacetylene welding. Most people don't consider it very scientific.

Um, and one of the things you need to understand is the difference between a scientist and an engineer. Um, and the quote I like comes from uh Theodore von Kármán. Does anybody know who Theodore von Kármán was? He was the founder of the Jet Propulsion Lab, okay. He was also sort of the person who explained why the Wright brothers were successful in flying, okay. Von Kármán was a professor — he was a Hungarian who was a professor at Caltech. Um, and he was into boundary layers and studying these types of things. And um around World War II he was one of the more prominent engineer-scientists in the country, and he did help found the Jet Propulsion Lab and all the combustion that goes along with that and whatnot. And Von Kármán had a quote that a scientist explains that which exists; an engineer creates that which never was, okay. And the reason I like the quote is the scientists think it's a wonderful quote — they explain what exists. And the um engineers think it's a great quote too, because they're creating things out of nothing, right. I mean you know — but they don't understand why it works a lot of times, but they just have to go out and solve the problem, okay. So engineers like the quote and scientists like the quote, which is why I think it's a great quote.

Now um, uh, you're taking some of your classes over near the Media Lab. Joel Moses, who used to be provost, number two guy at MIT, and was head of the electrical engineering department — he used to describe the Media Lab — he would take Von Kármán's quote and say, "and the Media Lab creates that which never will be," okay. The Media Lab is famous for doing simulations of what they want to build, okay. I mean I remember 15 years ago a student came in wearing a vest to talk to me about some material problem. He was an electrical engineering student in the Media Lab and he was trying to — he was building a wearable computer. So his jacket basically had wires and chips and stuff in it, so you could just put your jacket on and you would walk off with your computer, you know. As you're — now what happens when it rains, I don't know if your computer keeps working, but nonetheless. Uh, but that was one of the things. Now they did form One Laptop for a Child, and Media Lab's done um a number of interesting things, but mostly Nick Negroponte, the guy who started it — he's descended from um Italian royalty, and he still has that attitude of being a king, um, so far as that goes.

But anyway, um, this is — well, you don't have to read it necessarily — equivalent oxygen purity, and down here is oxygen purity, and up here it's talking about — this is the relative combustion rate, um with one being a low carbon steel um with 98% um purity here. This is 98% purity um of a low carbon steel — the oxygen purity. If you decrease the oxygen purity down to 90%, you'll have half the combustion rate. Now what they mean is, if you have some nitrogen — if you had 10% nitrogen in your oxygen jet, you're going to have a boundary layer, a 10% boundary layer, 'cause you have unburned nitrogen, and that slows down the process. Up here these are different types of steels. This is Armco iron, has almost no carbon. This is a razor steel — has about 1% carbon. A cast iron would be way down here. You can flame cut cast iron, but it'll be a very ragged edge. You have a very lousy looking cut because you have boundary layers that come and go and, you know, you don't have a nice consistent process of melting and burning through there.

So carbon contamination — higher carbon steels are more difficult to flame cut. Alloy steels that give off some vapors um — steels that have more chromium, such as HY-80s or HY steels, uh, will form chromium suboxides, okay, when you're burning them, and so they're harder to cut, they're slower to cut, and you can lose 10, 20% on your productivity um for oxyacetylene cut because of carbon in the steel, other alloying elements that form vapors, or um uh low purity oxygen.

Now the reason we're not as concerned about some of those things now is because we have plasma cutting. And plasma cutting uses an arc, 'cause you can get 10 times the heat intensity, and you can melt very nice edges. [Tom shows samples.] This is a piece of plasma cut — this is a laboratory sample from a plasma cutting company — and you have nice smooth edges, smoother than the oxygen cutting. This is a piece of stainless steel. The problem is you're using the heating of the metal to melt right through it and blow the metal out of the way. And when you get to corners and turn the corner, you'll see, we have problems at the corners. So we don't get nice square corners, and that has to do with your turning and changing your heat flow direction, right. So that's sort of an inherent problem. They just tried to cut a square of stainless steel and it's got round edges. This one actually shows — you have to burn — you can start in the middle by puncturing your way in. To cut this circle, they had to puncture here, start here, and then go around in the circle. And you can see they get a pretty smooth hole. So plasma cutting has replaced a lot of um oxyacetylene cutting, particularly in panel lines and stuff where you can have the big heavy plasma equipment.

And you don't, you know — oxyacetylene's still nice. I mean, I got an oxyacetylene outfit in the back of my garage that's not much bigger than your backpack here, okay. Oxygen torch and acetylene B cylinder, and I can go somewhere. I can go out in the woods and cut down a steel fence or something if I want. Go to the bank, cut through the vault — oh no I can't do that. Um, it's stainless steel. Um, but if I had a plasma torch I could do that, okay.

Uh, when they — when Dick Simmons, who's a graduate of MIT, who's worth about a billion dollars, um through Allegheny Ludlum Steel — they came to me. He was going to dedicate Simmons Hall, which is one of the undergraduate dorms, and they said um could they have him uh um weld his initials into the cornerstone, okay, for the dedication. I said, well, Dick probably hasn't welded for 40 years and he's going to be wearing a suit and I don't think that's such a good idea. What if we have him plasma cut a stainless steel ribbon? Oh, that's a great idea, okay. So they made a stainless steel ribbon, and I had a little plasma — the portable plasma unit — and I had to go over there and show Dick um in front of the whole — actually right before the whole MIT Corporation was there — for his dedication of this dormitory, that he had paid for most of it. But, and uh, he's wearing his nice suit, and I'm showing him how to — "okay Dick, all you have to do, here's the torch, uh, all you have to do is press this button, okay. I'll be here, okay, you press the button and just move it across and it'll melt through the thin stainless steel." And he did, it was fine, and everybody thought it was great. All the, you know, he — he was — he made all his money in stainless steel, and so he cut a piece of stainless steel to dedicate, you know, break the ribbon on his dorm.

And uh afterwards he came up to me, he was delighted too. He came up to me and started, said, "you know, I haven't done any cutting for years." I said, "I know, but it's not that hard to do plasma cutting." And it's not. Um, and he said, "but you got dirt on my uh on my suit." Now this is probably a $2,000 suit this man's wearing, right. And so I just kind of brushed it off as I said, "well it's just a little dust, or, you know, uh, smoke or cinders," or whatever. I brushed off, said "I'll buy you a new one, Dick." Um, but I didn't have to buy it. But in any case, um, plasma cutting is very easy to do, very good surface. Can cut uh stainless steel, aluminum, magnesium. It's limited — you can't cut 36 inches thick. In fact you have a hard time cutting more than about half an inch or an inch unless you have really big equipment. The limit is probably an inch and a half or 2 inches. But you know most of what people cut, it's not any thicker than that. So plasma cutting has been um the preferred method.

And what they do is they basically — in a panel line they'll do it over a water bath. And so the plasma cutting, all the smoke and drops and everything are going and quenched in the water. And so environmentally it's not that bad. However, yesterday I saw a request from the ship production committee — the Navy is soliciting um ideas for cold cutting of metals.

Student: Water?

Well yeah, you could do water jet with powders and stuff. But I mean, however, they just want to — they want to get away from plasma. And the reason is, uh, the Defense Department has environmental police, okay. And I'm sure the environmental police are looking at the amount of stainless steel that you cut, and they claim that you get hexavalent chrome. Now you don't, it turns out. And I met — I went over to the Pentagon once and gave a talk um about how it's not really hexavalent chrome. The fume, as it sits around afterwards, can turn to hexavalent chrome, but at a concentration that's, you know, so low that no one should worry about it.

But when it actually comes off, we proved thermodynamically the fume that comes off is not hexavalent chrome. It can't be. It's like one part in 10 to the 10th hexavalent chrome at uh the temperatures we're operating at. But as it sits around in the moisture and the air, and the fume gets corroded, if you will, by the moisture in the air, there will be an increase in the level of hexavalent. But most people don't pay attention to — they don't measure fresh fume, which is what a welder or an operator will breathe. They go and collect the fume, you know, wait a month to ship it to the lab, and then analyze it when it's been exposed for all this time, and so they get bad results. But anyway...

Student: From... yeah, they got a super-saw now so they don't have to burn whole cuts. They just cut.

Slow, isn't it?

Student: Very.

It's a lot slower than the — I don't know the saw type or...

Student: Put a clay to catch all the...

Yeah, I mean, I don't know what the —

Student: But they did use just a machine cutting — big, probably 2-foot saw.

Uh, it's...

Student: Like a circular...

There's a band saw, okay, big band saw, it's — I mean I got a band saw in my lab, and it's probably not a lot different. Mine's on a little table — they've sort of made this quote-unquote portable, but it's portable by someone having a chain fall, right, to bring the thing. It's not some guy just lifting it, is it?

Student: No, they set up rails.

Yeah, but I mean the blade's not moving very fast.

Student: Yeah I know.

Well, it's because partly because the HY steels are — you can't cut high strength steel that fast, because otherwise the friction — and that's why you need a bi-metal blade, right. If you cut it too fast, all you do is melt your tips, and then they're not very sharp at all after they melt.

Yeah, and I'm sure it's just the environmental police, I mean, they're changing a lot of the rules. And my example on changing the rules — um, I once had to investigate the explosion of a storage tank at a refinery in Oil City, Pennsylvania. And Oil City's just down the river from Titusville, where Edwin Drake drilled for oil in 1856 [1859], okay. Uh, so that was the beginning of the oil industry. And this plant had been built around 1900, and the tank that blew up and killed the welder and blew her across the river and stuff when it exploded uh was an old riveted 1920s tank, okay. And I remember the first day I got there, this was a Pennzoil facility, now it's closed. This was about 15 years ago, but at the time it was open. And these old riveted tanks, and small scale production compared to any other big refinery you'll have in Texas or the West Coast or even the East Coast.

And I thought — the first day you go out there in the tank farm area, and you dig down through the gravel about 1 foot, and you strike oil. They've been spilling oil there so long for, you know, that point, 80 years, that you go one foot down into the gravel and you strike oil, okay. So this is sort of — and I realized the second day the reason they hadn't closed it, because as soon as they closed it becomes an EPA site. As long as you're in operation you can keep polluting all you want — you can't pollute all you want, but you don't have to clean up the last 80 years, okay. But when you close it, they're going to come in and they're going to make you pay for the cleanup if they can identify who it is and stuff, which they could in this case anyway.

Um, what I learned is — you know how they transported the oil from Titusville down to Oil — from oil — from Titusville down to Oil City back around 1900? Just floated it on the river. Just poured it out on the river, and they had a little weir at the other end and skimmed it off the water. So the rules have changed, okay, over 100 years, okay. Now if they see Newton's rings out there — in fact that's what happened in my town. There's a — an old clay pit pond in front of the high school, um, and some high school student notices that there's some Newton's rings on the water, and so they start investigating. It's the elementary school up on the hill above it, about a third of a mile above it, that had a leak in the water — in the corrosion problem in some of the pipes for the number six bunker oil they burn to heat the school. And that cost the town $1.5 million dollars to repair that and stuff. So, but in the old days you just skim it, you know, put it on the water and skim it off, okay.

Yeah, well anyway, but there's lots of rules like that have changed over the years, and they're getting tighter, and it's increasing the cost. And so to a certain extent, what do we ship — the problems overseas, right. I mean, commercially all the ships were being decommissioned in Bangladesh. They just take the last trip, they'd end up — and they just run aground in Bangladesh. The ship aground in Bangladesh, just up on the beach, and then they come in with uh thousands of little um Bangladeshis with their acetylene torches, who are probably earning 50 cents a day. And they go in and they would cut the stuff up for scrap. There's asbestos and all. And the average life of one of these ship dismantlers was like 5 years, okay. But given the fact they would starve to death if they didn't have the job, and therefore starving to death is even quicker than 5 years, okay.

So anyway, there's lots of social issues. You know, but we don't um uh decommission — the Navy decommissions ships in the United States, right? Uh, although I've heard some ships in the Navy go other places. But at least you take the reactors out of them first, and you're probably still burying them in the Atlantic, right?

Student: Reactors? No, they're in Washington State.

Oh, you're burying them in Washington State. You used to bury them in the Atlantic Ocean, right off Norfolk. They Drove there? Yeah, okay, anyway.

Okay, question though on those samples you passed around — written on it either LPF or LPM or RPM, you know what that is? No, I got that from a company that makes plasma cutters, and they came out of their lab and they just kind of gave me some old samples. So, well, I will tell you, um, people have developed other cutting techniques with even better heat transfer than coming from a flame, a plasma flame. Uh, one company — who will I must, remain nameless, and I maybe shouldn't even describe this — they were trying to use jets of liquid copper. And they could cut through steel with a liquid copper jet at 10 times the speed of plasma cutting or oxyacetylene. Now the problem was, how do you generate a nice stable laminar flow jet of molten copper? Uh, and they did it in the laboratory and they could cut 10-foot lengths in the laboratory. But uh you're using fair— some fairly sophisticated ceramic materials, and their lifetime even so — because this was superheated — superheated copper — um was not very good. If you hit it with just straight copper, it could freeze. But if you had really superheated copper, I mean, you could, you know, you could zip through that stuff almost as fast as you can rip a sheet of paper, okay.

So I mean, people look at different things, and it's really just the fundamentals of heat transfer in that case. And a liquid metal can erode away a solid metal faster than anything else. You go through the heat transfer coefficients and the Peclet numbers and all these other things, and heat transfer, and yeah, liquid — a liquid metal will cut through another liquid metal faster than anything, okay.

Now there are some other things that people do. I remember 35 years ago as a young faculty member — might I finish with a story, just like I did yesterday — um, I get a phone call from a guy. And these crank phone calls always come to the junior faculty, right, they pass it down, you know, from headquarters to the junior faculty. And the guy says, uh, he had a problem, he needed to cut some aluminum. I said, "well, what kind of aluminum?" "Well, we're in a foundry, we just — you — we have some aluminum casting we do." I said, "well, um, well there's band saws." Uh he said, "well, I don't think band saw's going to work." I said, "uh, why not?" He said, "well, what we got's pretty big." I said, "well, how big is it?" He says, "about 2 feet thick." I said, "there's band saws that'll cut something that's 2 feet." "Well it's going to be hard to get in there." I said, "well, what do you have?" And it turns out he was in Alabama, and he had an aluminum foundry, and he had a melting pot of aluminum was about 2 feet deep, and they lost their electrical power for a day, and his pot froze on him. And it's down buried partway in the ground with all this ceramic around it and everything. So it's a little hard to get it in there. And I said, "well gee" — I was the young assistant professor, I didn't know how to do it — um, and I wasn't of much help to him.

But about 15 years later I was having dinner with a graduate of the department who was a senior executive vice president of Alcoa. And I said, "Peter, you guys at Alcoa, you must have aluminum pot lines freeze up every now and then where they make the molten aluminum, and they'd have about a 2-foot thick thing inside a big ceramic container." He said yeah. I said, "well, when it happens, how do you get it out of there? Because if that happens in carbon steel, it happens in steel mills all the time. I mean, people dump 300 tons of steel on the floor of the melt shop, and it'll solidify there, and they just send in people just like Bangladesh — they don't go get Bangladeshis, but they just set some people in with oxyacetylene torches, and they start cutting up this one or two-foot thick carbon steel with torches. It might take them a week to get in there and drill holes so they can — and put some bolts in there so they can sling these, you know, 5-ton pieces of steel out, essentially remelt them and stuff. But in a steel mill, you can — you have a breakout, and you have a big blob of steel, you can cut it up with oxyacetylene. And you couldn't cut it up with plasma, but oxyacetylene will do it. But aluminum you can't." And I said, "so how do you do it?"

He said, "well, there's this guy in Pittsburgh," okay. Now a lot of you are too young to remember — anybody know who Red Adair was? Okay, back in the 70s and '80s — that actually was a movie done about Red Adair. If you had an oil well blowout, Red Adair was the guy they would call, and he would fly in his Lear jet with his crews and stuff. And they basically come in with a crane and they would set off an explosive charge right next to the oil well, and had to make sure it didn't reignite, because some of the uh valves and piping was still a little hot from the fire that had been burning. But he was the expert in the world for putting out oil rigs that had gone, you know, had lit off and were gone wildcat, okay. And he actually — the undoing of Red Adair was the first Gulf War when Saddam Hussein set off all the oil — but they had other people, probably some of the military helping, learning from Red Adair. And when it was all done, Red Adair's secrets, you know, were out, okay, of how to do this.

Anyway, so this guy in Pittsburgh is the — was sort of the Red Adair of aluminum potline freeze-ups. And he would go in and he would drill some holes, and he'd put some charges in there, and he just light it off and blow it up. And I said, "well, doesn't it sometimes blow up the pot line?" He says, "yeah, but the pot — if you don't do it, the pot line's no good anyway. And sometimes it works and sometimes it doesn't. Just depends on how it breaks up that aluminum." Okay, but you just blow it apart, okay. So that's one approach.

Student: Okay, so that's like in the factory, right? This is like in the factory, right?

Yeah.

Student: Yeah, that's the movie. Yeah.

But anyway, so anyway um, cutting — there are various types of cutting problems that people run into, okay. And to uh Thursday we'll start talking a little bit more about arcs. But I finished up on flames unless you have other questions on flames. Okay.