A discharge control device is presented which includes a variable opening formed between two cylinders with parallel axes. The cylinders are mounted between two symmetrical support blocks having bores and are spaced at a distance equal to the sum of their radii. At least one of the cylinders has an external cut-out which, upon rotation of the two cylinders, defines the variable opening. The cylinders are in the form of discs with an axial thickness wherein the cut-out extends over the whole thickness. The discharge control device controls the flow of molten materials.