how does smelting work

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I know that in order to smelt stuff, you need to heat it until it melts and then pour it into a form. But that oven and that form always need to have a higher melting point, right? So how do we create the oven at the top? How do we create stuff when nothing with a higher melting point exists to make an oven out of it?

Edit: I think I understand now, thank you again to the kind people in the replies who explained it to me 🙂

In: Technology
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The short answer is you make the crucible and oven out of higher melting point materials. These are usually ceramic. Ceramics generally have much higher melting points than metals. They also don’t need to be melted in order to be formed, which prevents the “well then how do you smelt the crucible” problem.

There are multiple avenues to answer this, but here’s a couple generic answers.

What you pour it into doesn’t have to be a true solid. It could, but doesn’t have to be. You can cast iron into sand, which is readily available and can form rough shapes, and it has the benefit of a higher melting temperature than iron.

You seem, though, to be getting at “If you keep casting things into things that can’t be melted by that liquid thing, and if you keep going up that chain, how do you cast that highest melting temperature thing.”

Melting is a physical change. You heat it up until it changes phase. You can shape that liquid into a form, cool it back into a solid, and you’re good. But there’s more ways to turn a not-solid thing into a solid thing. Chemical changes!

The most common one in this chain of thought is the production of ceramics. You can take clay, which is moldable at room temperature, and bake it at high temps. This forces out the water and the clay undergoes a transformation into a ceramic. This is a simple way of making molds that can withstand high temperatures without having to first mold the material the mold is made of (and further have a mold that can withstand *that* temperature, and so on).

Other people have addressed the crucible/casting form thing, but I want to address another misconception here:

Smelting isn’t just “heating things until they melt”. The thing you put into the smelter is an *ore* – not actually metal itself, but some sort of mineral with compounds that *contain* that metal. Iron oxide, iron sulfide, etc.

High temperature is important for making the metal at the end stage liquid so it can be poured off, but equally important to the smelting process is somehow making those other unwanted oxygen and sulfur and other atoms go away. For oxide ores especially, this means you need to add a *reductant* (aka *reducing agent*) to the ore in the smelter.

Carbon is historically the simplest and most ubiquitous metallurgic reductant, whether as charcoal or coke; it combines with the oxygen to form carbon dioxide that just escapes through the smokestack, leaving pure metal behind.

Just to add my two cents. What you pour molten metal into does not necessarily need to be of a higher melting point. It’s mass can be much larger, acting as a heat sink, requiring more heat to bring it up to melting point than is available in the molten metal.