Smelting facilities (smelters) use ore from asteroid mines to turn into metal. Their metal production is comparably higher than their ore consumption, so there is usually some ore that doesn't go into the production cycle. This is what's expected, since many buildings and upgrade require ore. Smelters are usually found around asteroid fields with asteroid mines on them. They are also said to be a good source of income to have when high leveled. A smelting facility is a mid lvel building.