My entirely speculative impression on the repeated phrasing here is that there’s a bit of a legal disclaimer built in: to wit, “once you kick this off, you can’t stop it, so best not mess with it, eh there guv?” No sense having a sound technician spending several minutes extracting, copying, and laying down a phrase on the soundtrack when you can have host dude say it in three or four seconds.
Geez, we debunked this at MIT ca.1978! (and I’m sure we weren’t the first) The problem isn’t the thermite, which is certainly capable of the job. it’s the cooling. Molten metal won’t “weld” anything in place, and it would take several minutes for the “weld” to cool to any appreciable mechanical strength, by which time, the unwitting trolley would be well on its way to its next stop , with maybe a flat spot on its rim. Even if the wheels lined up just right, it would be highly unlikely that the trolley would weld at it’s next stop, because it would likely have cooled against the rail in its travels, and even a splash of molten metal against a cool (heavy heatsink) rail would not form any appreciable bond
(We didn’t research the construction/composition of MBTA/MTA trolley cars through history. When the ub-doy (“D’oh!” in our day) realization hit, we lost interest in the problem.)
More to the point: what moron would perform such a test on an expensive piece of rolling stock, amidst innocent bystanders, on a section of track that was vital to the daily lives of so many MIT students? Succeed or fail, that bit of vandalism would get you in deep trouble with every authority that could find an excuse to claim jurisdiction.
Yup I call “Those wacky college kids” shenanigans. (BTW, the place to look would in MBTA records and the newspapers. Paralyzing the Mass Ave trolley would be noticed!
Use fine sand with some clay. Most of my sand casting is done in a sand/clay mix.
Dunno; you might be right, but to me it seems just like excessive editing and thrifty re-use of material.
There’s a difference between stopping a train, and preventing one from starting. From what I’ve heard, a penny jammed in front of and behind the drive wheels of a railroad locomotive will keep it at a standstill, even though a train that’s already moving will flatten a penny without even noticing. Granted, a streetcar is probably lighter than a loco, but it’s probably also considerably less powerful. So it’s conceivable that our hypothetical pranksters could have stopped the car via some other means for long enough for the weld to set, or even that they used only those other means, and just told folks they used thermite.
Still, the lack of mention in any newspaper is probably pretty definitive, especially considering that nobody can remember exactly who did it or when.
The first time that I was up close and personal with thermite was in high school chemistry. Teacher put a few spoonfulls into an iron cup on a stand and lit it off.
The aluminum oxide sprayed up and out in a pyrotechnic fountain, big shower of sparks. Everything nearby was spattered with little grains of the stuff. The molten iron melted through the cup and poured straight down in one glug.
As far as the “irreversible thermite reaction” I think that’s pretty accurate - once it starts I don’t think that there’s much you can do to stop it (thermite produces its own oxygen so you can’t put it out very easily; throwing water on it can result in an impressive steam explosion - happened one year at college). Reminds me of what I read about primercord (nylon rope with a plastic explosive center, used to detonate explosive charges simultaneously) - since the fuse “burns” at ~25,000 feet per second you’d better be damn sure that you want to light it because you can’t stamp it out…
Nein! Nein! Nein! Speaking as someone who worked in a foundry that did both types of casting, I can tell you that lost wax casting is a different animal than sand casting. The ceramic/plaster molds must be heated before the metal is poured into them, otherwise, they’ll shatter. (Even when they’re hot, they can still break.) Having molten metal spray around is not a fun time for anyone. (Been there, got the third degree burns to prove it.) We used a stuff called “Gray Matter” and you should be able to find it, or something like it at any ceramic’s supply house.
Also, Mangetout, I suggest reading some of the books from these fine folks before playing around with molten metal. It’s a lot of fun, but if you’re not careful, you can lose a limb quite easily. Drop me an email, and I’ll send you a bunch of links on metal casting that I’ve got on my other PC this weekend, if you’re interested.
Thanks. The risks of injury etc are actually part of the reason that thermite seems an attractive option - if it’s properly set up, I don’t have to be anywhere near the thing when the molten metal is poured. In all likelihood, this will just be another interesting project that I dream about and never fulfil, but for certain I’m not going to take it lightly if I ever do start it.
This Youtube video is pretty interesting: apparently shows a cool way of getting a momentary thermite reaction.
Could the MIT students have used just a small amount of thermite? Wedge it against the wheel, set it off, local area melts, but then being a small amount it quickly cools.
Mangetout, start with pewter, you can melt it on the stove top or with a brulee torch in a steel ladle. You can do lost wax casting, or else the ever-fun two-cuttlebones method, great fun. I’ve made replica medieval buckles, and a friend does medieval jewelery using silicone molds. I think he’s been eyeing website articles about melting bronze in the microwave, too.
Actually, that’s not a bad idea - I have easy access to large cuttlebones on nearby beaches. I did lots of sand casting with lead in my early teenage years.
Thermite seems just a bit uncontrollable.
thwap your right, I typed without thinking thru the whole question. sigh
I tend to use a plaster coating built up over the wax, then melt the wax out and bury it in the sand (for lower temp metals) Not something I would try with molten steel.
or maybe would, if I could find a way or pouring it from a good distance 
Thanks for the correction, I went scatterbrained and gave out false information.
Osip
Errr. I’m not saying I’ve ever done thermite. That would be a very unsafe thing to try. But if I had done it, I would probably tell you that it is a bitch to ignite. And I would (if I ever did it, which I didn’t of course) have access to both powdered iron oxide and powdered aluminum.
I’m not sure I buy this… Got a cite? Or how about just a cite giving me the torque imparted by a locomotive at the wheel, the coefficient of static friction for steel on steel, the radius of the wheel, and the mass of the locomotive… Do I need anything else?
No sweat. Foundry work in this country is rapidly becoming a lost art. IME, other than the higher levels of heat, pouring steel is easier than pouring aluminum. Aluminum tends to be a bit “syrupy” while steel is more like water.
Unfortunately, the only cite I have is the word of my uncle, who used to hang around railyards a lot in his irresponsible youth. But even if a penny won’t do the trick, any MIT student ought to be able to figure out something he can throw in front of the wheels to temporarily stop a streetcar.
Certainly the thickness of a penny, probably also the compressive strength of copper, and maybe the coefficient of dynamic friction. If the problem is still standing as of tomorrow afternoon, I’ll have a go at it, too.
I think pennies are often copper plated steel nowadays…
Zinc, actually.
You’re right. They are steel here - you can pick them up with a magnet, but copper plated zinc in the USA.
(As usual, the term ‘penny’, actually meaning ‘cent’, threw me)