English to Portuguese Tech/Engineering Metallurgy / Casting Technical

Olá pessoa! Preciso de vocês. Não consigo encaixar bem "pig" com a palavra "zinc". Sei do que se trata, mas não consigo elaborar muito bem.

CONTEXTO:

When putting zinc pig, first make it dry and then slip it along the pot wall slightly to prevent the feed liquid from splashing. When maintaining the combustion machine, do not put diesel oil into the furnace chamber continuously when it is out of ignition.