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What is a Bloom? Steel Foundations

A bloom is a semi-finished product produced by continuous casting process (bloom caster) to be used in the production of heavy structural long products and rails. Blooms can have square or rectangular cross sections with sides typically ranging from 8 to 24 inches (200 to 600 mm).

The bloom 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 and 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. Bloom 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 in order to not melt from the heat of the molten steel. Mold powder is steadily applied at the top of the caster molds, which 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 blooms. The blooms are small enough to be handled by an overhead crane, rail cars, or mobile carriers to transport them to either a beam mill, rail mill, or a seamless pipe.

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