Conventionally, movable molds are employed in continuous casting of thin metallic plates. Two types of such molds are known: one for drawing a casting in a generally horizontal direction, and the other for drawing a casting in a vertical direction. The former, as FIG. 29 illustrates, is a belt-type movable mold 103 positioned under a melt receiver 101 and endlessly trained around a pair of drive rollers 102A, 102B, front and rear, in a longitudinally inclined condition. Molten metal within the receiver 101 is drawn in the form of a thin plate-like casting sequentially as it is cooled and solidified on the surface of the belt-type mold 103. A movable mold of the latter type, as FIG. 30 shows, is a twin-roll type mold 113 wherein molten metal is drawn through a clearance defined between a pair of rolls 112A, 112B disposed under a melt receiver 111 and is then solidified in the form of a thin plate-like casting. Aforesaid melt receivers 101 and 111 are of a rectangular configuration, each including a pair of side walls 101a or 111a, as the case may be, disposed parallel to the path of casting withdrawal, and a rear wall 101b or front and rear walls 111b, 111b, as the case may be, disposed in rectangular relation to the withdrawal path.
Such conventional melt receiver is held stationary at a specified position and, therefore, it has a drawback that a casting drawn is often liable to break-out. The cause of such break-out may be explained as follows. A wall shell is formed at a corner portion defined between the movable mold and either one of the side walls or the front or rear wall, and it tends to grow. A grown wall shell adheres to a casting shell formed on the movable mold through solidification of molten metal and tends to pull the casting shell away from the direction of drawing, with the result that the casting shell is broken at a relatively thin portion thereof. Again, such wall shell adheres to the casting shell until such breaking occurs. This process of adhering and breaking is repeated again and again, with the result that the casting shell is not constant in thickness, being thus liable to break-out at its relatively thin and weak portions.