Method of and apparatus for direct casting of metal strip

In a method of direct casting crystalline metal sheet in a continuous strip, including

• providing a melt of the metal to be cast,
• providing a continuously driven metal chill surface, flowing a layer of the melt onto the moving metal chill surface and extracting heat from the layer of melt through the chill surface to solidify and temporarily bond the layer of melt to the chill surface and to shrink the solidified layer and cause it to be released from the chill surface, said layer having a width of at least 12 inches, and
• withdrawing the released solidified layer as a continuous metal strip having a thickness in the range of 0.015 to 0.080 inches, the improvement comprising,
• establishing a natural oxide interface between said layer of melt and said metal chill surface by permitting a natural oxide layer to develop on the surface of said metal chill surface as a result of exposure to heat from the melt and to the atmosphere, and
• maintaining said natural oxide interface in a smooth layer completely covering the area of said chill surface contacted by said melt by continuously engaging said natural oxide layer with a cylindrical rotary brush mounted for rotation about an axis spaced equal distant from the casting surface across the width of the strip, and
• driving said brush to polish the natural oxide interface following release of the metal strip, said polishing being accomplished in a manner to remove only the outer portion of natural oxide layer developed while leaving a smooth, continuous packed layer of natural oxide firmly adhering to the chill surface to provide said smooth natural oxide interface whereby abrasion of the metal chill surface is avoided, said layer of natural oxide being of substantially uniform thickness across the width of the chill surface and being maintained at said substantially uniform thickness substantially throughout the casting run.