Molten metal is poured into a crucible ‘tundish’ furnace. For the creation of wrought copper alloys to be successful, this process happens within a controlled environment or atmosphere.
This ‘tundish’ maintains a large reservoir of molten bronze at controlled temperatures. It has to be positioned above a water cooled graphite die. Any doss that enters this dish quickly floats to the top of a metal bath. And from this metal bath any film or residue can be removed.
An ‘entrainment of slag’ in cast bars cannot happen. There must be no solid inclusions and no porosity from gas or shrinkage must occur. Further than that, the bronze will enter a freezing zone. This will be at a temperature that provides sufficient excess of liquids. This ensures that any shrinkage pores from previous cast materials can be filled. All this can be achieved in very much less than a second. All this happens before rapid freezing must begin.
As a result, a severe segregation of alloying elements can be avoided. Specially patented techniques now in use further help the cause of reducing segregation. This greatly improves casting strength. A fine grain structure is thus generated. The newly frozen layer of the metal shrinks away quite quickly as a result. It gets removed from the graphite die by way of set electrically driven pinch rolls. So, while the newly solidified casting portion leaves its freezing zone, die in gravity is filled with its molten metal straight from the tundish.
And so begins a solidification process all over again. Finally, once a casting has achieved its desired length it will be cut off with a flying saw that’s positioned just below the pinch rolls. And that, readers, is how cast bronze is prepared.Continue reading