Oxide restraint during co-casting of metals

Apparatus for casting a composite metal ingot, comprising:

• an open ended annular mold having a feed end, an exit end, a cooled mold wall between said feed end and said exit end, and a moveable bottom block adapted to fit within the exit end and movable in a direction along the axis of the annular mold, wherein the feed end of the mold is divided into at least two separate feed chambers, each feed chamber being adjacent at least one other feed chamber, and where adjacent pairs of feed chambers are separated by a divider;
• a feed device for delivering metal to each feed chamber to form a pool of molten metal in each feed chamber during casting, each pool having an upper surface maintained at a predetermined vertical height, and
• a surface oxide skimmer supported on said divider separating said adjacent pairs of feed chambers and extending into one of said feed chambers from above, said skimmer having a lower end positioned during casting at or below the predetermined vertical height of said upper surface of the pool of molten metal of said one of said feed chamber.