Why does the extrusion screw and screw housing become contaminated with lead oxides and sulphides?
The hotter the liquid lead, the more oxygen, oxides and sulphides it will support within its melt, So when this hot lead is rapidly cooled within the screw housing it can no longer support the same quantity of oxides and sulphides. As the lead cools, it releases these contaminates and they become deposited on the surface of the extrusion screw and screw housing. It`s very similar to air and condensation, Hot air can support a lot of moisture but as soon as this air cools it can no longer maintain the same quantity, so disposes of the surplus in the form of condensation.
