Smelting e esteira transportadora: o que têm em comum

1. Passo 1. Smelting — utiliza — Carvão vegetal. Before coke, metal was smelted with charcoal.
2. Passo 2. Carvão vegetal — é material para — Gunpowder. Gunpowder is a mix of saltpetre, sulphur and charcoal.
3. Passo 3. Gunpowder — evoluiu para — Dinamite. A replacement for gunpowder in mining.
4. Passo 4. Dinamite — funciona como — Tunnelling shield. Two ways of driving tunnels — mechanical and explosive.
5. Passo 5. Tunnelling shield — evoluiu para — Tunnel boring machine. A development of the tunnelling shield.
6. Passo 6. Tunnel boring machine — tem como parte — Esteira transportadora. Spoil is removed by a conveyor.

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