The Home Machinist!

Hi all, I was watching numerous videos of thermite welding rails together.. Once the stuff ignites, molten steel fills the gap between the two rails, and the excess flows off into a separate pan.. Why couldn't steel castings be made this way? Set up the crucible above the mold, and light it off??
Or am I missing something here?
John

You'll get nearly pure iron (not "cast iron", which has carbon in it) rather than steel, and it will have a lot of inclusions and voids. I have a 12" hemisphere of it as well as some smaller chunks. As cast it is not useful for anything but weight: it is soft and fractures easily. Hot working improves its properties tremendously but it still isn't steel.

Not to mention that you could buy the steel you need for the price of the aluminum alone.

What you should do is go to this site: http://www.alloyavenue.com/vb/forum.php

They delve into some exotic and dangerous practices, that could get a person injured.

For a Hobbyist, melting steel to cast, by any method, is extremely difficult.

If Harold ever gets his used Induction Furnace running, he may be able to do it.

Before anybody gets the wrong idea about how this works, Thermite welding just simply melts the steel rail ends and they blend together from the heat action. There is a considerable slag button that is useless at the end of the burn. Quite simply, the aluminum powder that provides the heat is also a strong reducing agent for iron, and sucks the oxides out of the weld when the joint is liquid, and acts as a strong flux. It melts the rail and its trace elements to be blended by natural agitation of the process. A weld. Metal casting is a very different path that is very old, and well known to it students.

We used small capsules of this material for bonding copper wire to steel for grounding light poles and other masted structures against lightning strikes and such problems.

At any rate, dont be fooled into thinking that the melted material is steel, It is a waste product of no value except for the heat the reaction produces, which is short and intense. Fun but dangerous stuff to play with. Akin to acids and other treatments, there be DRAGONS here, so know what you are playing with.

A thermite flare, or grenade as developed in WWII was developed to disable weapons by melting gears, gunsights, bearings and any sensative parts exposed to high heat to do away with their operation in just seconds. In the 50's My cousin ws assigned to an atomic cannon unit under the first armored division, and he always had access to such grenades to disable the breach should the gun be attacked. Similar to the civil war where the gun commander had spikes to block the touch hole and disable a gun before being abandoned.

History is such a wonder.

The melted material is iron (not steel, and not what is usually called "cast iron"), with aluminum oxide floating on top.

https://en.wikipedia.org/wiki/Exothermic_welding

According to https://en.wikipedia.org/wiki/Exothermi ... il_welding carbon steel pellets can be added so that the resulting filler material will be steel.