When a fast-moving billet or bar fails to enter the next set of rolls correctly, it buckles and folds over itself at high speed. This creates a massive, glowing pile of scrap metal on the mill floor that halts production. Clearing it requires shutting down the line and cutting the twisted mass apart with torches.
Heard on the job
Hit the emergency stop, we just had a massive cobble on stand four and there's red-hot bar snaking everywhere.
Insider tip
A cobble on a high-speed wire rod mill can shoot hot steel out like a whip, making it one of the most dangerous events in a rolling plant.