What is a Net Near Shape? Steel Foundations
A near-net shape is the semi-finished product produced by the continuous casting process (near-net-shape caster) used in the production of heavy structural beams, such as I-beams, or rounds for seamless tubes and pipes. The cross-sections can come in a variety of shapes and sizes that are designed to be nearly that of the final products, resulting in a reduction of subsequent processing steps and processing costs.
The near-net shape casting process begins with a ladle full of liquid steel suspended over a tundish. The tundish provides a buffer during ladle changes, which enables the casting process to be continuous. The tundish also provides the last opportunity for any inclusions (impurities) to float out of the steel into the slag prior to entering the solidification mold. The molten steel in the tundish flows to the nozzles suspended over the continuous casting molds. Near-net shape casters typically feed several molds and cast several strands of steel at the same time.
As the steel flows from the tundish into the caster molds, the molds oscillate up and down to “push” the liquid steel deeper into the mold. The copper-lined caster molds are water-cooled, so they do not melt from the heat of the molten steel. At the top of the caster molds, mold powder is steadily applied. The mold powder melts and lubricates the interface between the molten steel and the copper molds. While traveling through the oscillating molds, enough heat is removed to form a thin solidified shell on the surface of the strands, which allows them to stay intact as they exit the molds.
As the strands exit the molds and enter the spray chambers, most of the steel inside the strands is still molten. The spray chamber provides controlled cooling from water sprays to further solidify the steel within the strands, as they travel down through the caster. The point in the process where the strand is completely solidified is referred to as the metallurgical length of the caster, which can be almost to the end of the caster.
Eventually, the solidified strands are bent from vertical to horizontal and then cut by a gas torch system into individual pieces. The near-net shapes are small enough to be handled by an overhead crane, rail cars, or rubber-tired carriers to transport them to the next stages of production.
If beam blanks have been cast, the pieces are sent to the beam mill to be rolled into beams. If rounds are cast, they are typically sent to the pipe mill to be rolled and pierced into seamless pipe. Round bars can also be used for other applications such as bearing production.