Jump to content
I Forge Iron

Thermite welding

Recommended Posts

Hey everyone !

I don;t know if this is the best place for this thread. . but it has the most people on it at any one time. ..soo

Does anyone know anything about welding with Thermite?
( as far as I know that's how they weld sections of RailRoad together seamlessly and it sounds like it could have applications in repairing badly damaged anvils. .and even reattach horns)

Has anyone tried it?

How do you make it and use it?

Link to comment
Share on other sites

I can verify that railroads do themite weld rail sections together (at least the one I work for does). We have boxes of it at work. :D There is a chapter im my 1942 edition of Machinerys Handbook labeled "Thermite Welding" but I haven't actually read it, I just noted its existance and since it is at work right now I can't reference it.

I guess if you have any other questions that are left unanswered in this post come Tuesday I can talk to some people at work who do it and get specific answers.

Link to comment
Share on other sites

That makes me wonder if it could be used to weld a new faceplate on... Say you had one with a badly cracked original plate, or wanted to add a new plate to a cheap cast iron body.

Maybe something as simple as piling a generous layer between the anvil and a new faceplate, both preheated, and igniting it.

If it were, indeed, more or less "that easy", that'd be a good way to patch up heavily damaged anvils, or improve some of the cheap import ASOs. Maybe a plate milled from S7 and quenched almost immediately after welding?


Link to comment
Share on other sites

some thoughts on thermite:

1 the process is not controllable, once started it can not be stopped until the mixture is consumed. the heat generated is so intense that it will separate the hydrogen and oxygen in water causing an explosion. In Jr High school I had a teacher who was trying to use thermite as a heat source to roast gold from some ore that he had collected. He was surprised by the size of the reaction and tried to stop it by poring water over it. The resulting explosion knocked him out the open door of his garage. and flash burned his exposed skin.

2 In railroad usage the thermite weld would be more correctly called a casting. The thermite a mixture aluminum and iron rust, is used to raise the temperature of the iron to a point that it melts through the bottom of a fire cement crucible, into a mold that forms around the track. The molten iron is hot enough to melt and liquefy several inches of the parent track forming the weld. Here is a pdf file of rail welding: http://www.ameco.net/pdf/Thermite_Welding.pdf

3. I have seen a military demonstration of the use of a thermite grenade used to declassify a metal and concrete fire proof safe. A thermite canister weighing about 1/2 lb was placed on the top of a 5' safe filled with news papers. The reaction was over in less than one minute and it took about 10 min for the smoke to clear. A hole about 6 inches in diameter was burned in the top of the safe and became larger as it passed through each shelf. It burned through the "Fire Proof" bottom of the safe and through a 4 inch concrete slab into the dirt below. The news papers were reduced to unreadable ash.

4 The reaction is very fast. I have read of very large thermite reactions (in the tens of tons) and that the initial reaction was done in the mater of a few minutes. The gases emitted from the burn are aluminum oxide vapor and the reaction is violent in nature, with sparks flying every where. Fire is a danger.

5. the Iron produced is low carbon Iron any carbon in the steel will be burned and the heat from any weld will affect the carbon content of the base metal unless a molding method is used

6. Be safe thermite will not burn skin it will VAPORIZE IT! It will not stop burning until IT is done. Aluminum/iron oxide was used to seal the skin of the Hindenburg and is suspected in the fire that brought down the World Trade Center. (Burning fuel oxidized steel beams combined with the molten aluminum of the aircraft starting the thermite reaction...) Thermite was used in the fire bombing of Dresden Germany, and Tokyo Japan in World War II. leveling those cites in the fire storms.

Link to comment
Share on other sites

Before I get slammed by others with more knowledge than myself on the subject of thermite, let me state, that I did not say that thermite could not be used to weld an anvil. I believe that it would be difficult to do and that you might destroy several in the learning process. Second Thermite in the destruction of the WTC/911 is a hotly debated subject, and one that I personally find hard to believe. I do know that thermite can be used as bloom/foundry for metal casting and that copper oxides can replace iron oxides in the reaction for copper casting. I would also wonder about the cost/benefit of using thermite in the process. Also understand that under our post 911 legal system the mere ownership of thermite maybe hazardous to your personal freedom. Your mileage may very.....

Link to comment
Share on other sites

Department of Energy Richland Operations Office
Lessons Learned Issued in 2001
Fireball from Aluminum Grinding Dust

Date: September 21, 2001
Identifier: 2001-RL-HNF-0036

Lessons Learned Statement:
Aluminum grinding dust can create a serious explosive fire hazard when it is mixed with steel or iron grinding dust.

Discussion of Activities:
A safety coordinator at the Esso Oil Company plant in Longford, Australia, was using a belt grinder in his home workshop to smooth the edge of a hacksaw cut on a 2" length of 1.5" angle iron. He had been grinding for about 1.5 to 2 minutes when there was a loud "THUMP" accompanied by an approximately 2-foot diameter brilliant yellow orange fireball. The fireball lasted no more than 1 second and then completely extinguished itself. It completely enveloped the machine, his hands to half way up his forearms, and the front of his torso.

Injuries included deep second-degree burns to about 60% of the victim's left hand and 50% of his right hand and first degree burns to his neck, chin, cheeks, lips, and the end of his nose. The right cuff of his shirt was smoldering, his face felt a burning sensation, and he could hear the front of his hair sizzling. Nothing on the bench was burning. A few streaks of white powder were deposited on the bench top and on a few items lying on the bench. The workshop was filled with dense white smoke with very little odor. His fingers and the ends of his thumbs escaped relatively unscathed as they were protected from the heat flash. He was wearing glasses, which protected his eyes. He also lost half his moustache, one of his eyebrows, and about 1 inch off the front of his hair. His eyelashes were curled by the heat but not singed. The burns to his face were caused solely by radiant heat, as the fireball did not come that high.

A few days before the event, the man's son had ground the heads off about twelve aluminum pop rivets. Finely divided aluminum mixed with finely divided ferrous oxide (the black powder residue from grinding steel) produced a compound called thermite. Thermite is used to fill incendiary bombs and is used commercially to weld large steel items. It burns at approximately 3500C (6300F), hence the extensive burns from such a short exposure time.

Recommended actions:
The victim recommended that the manufacturer of the grinding wheel should include a very strong warning about the dangers posed by grinding steel after having ground aluminum. That warning should include precautions to thoroughly clean the grinding machine of all aluminum dust before grinding iron or steel.

Estimated Savings/Cost Avoidance: N/A

Priority Descriptor: YELLOW/Caution

Work / Function: Machining and Fabrication

Hanford-Defined Category: N/A

Hazard(s): Fire / Smoke

ISM Core Function(s): Analyze Hazards; Develop/Implement Controls

Originator: Bruce Robinson, Longford Plant Safety Coordinator; Longford Ext. 6348; Fax (03)5149 6496.
Introduced into the DOE LL system by Fluor Hanford, Inc.

Contact: Project Hanford Lessons Learned Coordinator; (509) 373-7664; FAX 376-6112; e-mail: PHMC_Lessons_Learned@rl.gov

Authorized Derivative Classifier: Not required

Reviewing Official: John Bickford

Keywords: grinder, thermite, aluminum dust

References: Bechtel Australia Alert 01, Grinder work with Aluminium
Link to comment
Share on other sites

Personally, I think the idea has potential. And I say that as a guy that's already burned up a lot of rod and a full tank of argon trying to fix what might have been a fatally-cracked-anyway anvil. :D

Yes, I agree it'll take some experimenting- unfortunately probably by someone with more time and money than I have. You don't need to experiment on anvils either, just scrap steel, or maybe old train rails or something.

The "Grinder explosion" was eventually determined to probably have been closer to a dust explosion (but using the same components) than an actual thermite style reaction. The point is the same, though- don't grind both steel and aluminum on the same machine. :D

Next, without trying to get too political, thermite had nothing to do with the WTC collapse. Neither the steel girders nor the aluminum aircraft were finely powdered, and while the aluminum burned (like a soda can in a campfire) the steel didn't. The entire thermite theory comes from a single report where someone analyzed the air around the collapse site, and detected elevated numbers of a daughter compound gas (isopropane or something, as I recall.)

The conspiracy theorists did a Google search, and found that chemical was used in one manufacturers' relatively new thermite formulations, added two plus two and came up with "green cheese", and declared that thermite bombs had been emplanted to bring down the towers.

Except that the chemical is consumed when the thermite burns, leaving little or none to detect; to get the levels detected would have required something like sixteen tons of thermite; and, most importantly, that daughter compound is easily and commonly the result of burning any one of several types of plastics- of which there were, of course, many tons of in the WTC.

Stepping back off my soapbox, yes, the reaction is not controllable, but that just means you have to have a proper setup first. It'd be nice if it were as simple as a small clay or firebrick dam, pouring about a quarter-inch of thermite on the anvil, setting the new faceplate on top, and lighting it off. I don't think it'll be quite that easy, but I think it might prove to be easier and quicker than forge-welding on a new plate, or building it back up with electric welding rod.

As for the soft iron alloy, again, I don't see a problem; Peter Wrights, Mouseholes and a handful of other well-respected brands are solid wrought iron, with a hard plate welded to it.

If I can find a legal supplier of the stuff, or better yet somebody with some experience with it, I might give it a try (with some scrap, first, of course.)


Link to comment
Share on other sites

The small thermite ignitions I have seen looked a lot like a decent sized pile of smokeless powder was being burned. Flame and smoke trailed up rather high. The difference, was that molten iron came pouring out from underneath it. I do not think it would be at all easy to weld a new face onto an anvil this way. My understanding of how they weld with it, is they dam up an area for the liquid iron to pour into, and the two (or more) ends of the metal to be welded meet in this reservoir. Thermite is ignited above it, and the result is allowed to flow into the the reservoir.

It does burn hot, as noted above, and once started can not be stopped. The demo was put on for us as a warning to be careful about grinding aluminum in a steel shop. I can't imagine they could ever treat thermite as a controlled substance (like nitrogen based fertilizer), there is just too much steel and aluminum out there.. Security is really only a state of mind.

Link to comment
Share on other sites

I do not think it would be at all easy to weld a new face onto an anvil this way. My understanding of how they weld with it, is they dam up an area for the liquid iron to pour into, and the two (or more) ends of the metal to be welded meet in this reservoir. Thermite is ignited above it, and the result is allowed to flow into the the reservoir.

-Yep. The references to train rail welding show pretty much exactly that; molds are placed around the rail, and a ceramic "bucket" full of thermite is placed on the top and ignited. After it's had a chance to react a bit, it burns through the base of the "bucket" and fills the mold.

However, that's not an impossible technique to duplicate for a one-off project like this. Some fireclay, some fire brick, a few buckets of dry sand, lay the anvil on it's side so the metal can fill a void between the new faceplate and the body...

Link to comment
Share on other sites

  • 13 years later...



I'm not a welder but a science teacher in the UK. We demonstrate the thermite reaction regularly and it is a very easy safe reaction to do.

You just need to ensure that you have properly heat resistant materials around where the reaction will proceed; we use sand.

If you wanted to make a clay or sand mold of some type that would absolutely contain a reaction large enough to produce about 4cm^2 of iron (presumably enough to weld a small joint).


I would add that it helps to add some oxygen supply such as barium oxide to ensure complete use of reactants.

Link to comment
Share on other sites

There is a railway behind our company, and one day, when I was taking a walk, they performed a thermite weld on the track.  I decided I needed a long break and stayed to watch.  Anybody interested in more details can ask, but I had a couple of interesting observations.  First, most of the time taken for the weld was used to preheat the track.  They used a huge gasoline engine blown torch and got it good and hot.  I think they were running it for at least half an hour.  The gasoline engine ran a compressor which aspirated the burner.  Second, the thermite burn was very controlled.  I have seen thermite demonstrations, and the rail welding was nothing like it.  There were essentially no sparks or flashes, and just a thin wisp of smoke emanating from the reaction vessel.  This was surprising to me, and they must have been using a mixture with some sort of moderator in it.  Third, I walked by after they were done and looked at the discards.  The sprue was huge.  This is apparently necessary so that the junk stratifies at the top.  The top of the sprue was ragged and porous.  They used a magnesia thimble which was very robust.  Still it was cracked.  I could salvage a few pieces, but I didn't know what to do with them.  They probably would have been better than firebricks for cast iron welds.  The crew spent a lot of time grinding.  They used huge conical wheels and a gasoline powered grinder.  When the wheels were used up, they would throw it on the side of the tracks and chuck up another one.

I have no doubt that this process would work for welding together a makeshift anvil, but may be too involved for any but the most dedicated tinkerers.


Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...