'dirty' during the casting process. One of the main methods through which hot metal may become dirty is by oxidation, which occurs rapidly at molten metal temperatures (up to 1700 °C for steel); inclusions of gas, slag or undissolved alloys may also be present. To prevent oxidation, the metal is isolated from the atmosphere as much as possible. To achieve this, exposed liquid metal surfaces are covered – by the shrouds, or in the case of the ladle, tundish and mould, by synthetic slag. In the tundish, any inclusions that are less dense than the liquid metal – gas bubbles, other slag or oxides, or undissolved alloys – may also float to the surface and be trapped in the slag layer. While the tundish and mold fill for the first time at the start of a casting run, the liquid is badly contaminated with oxygen and the first items produced are typically quarantined or diverted to customers who do not require top-quality material. Upcasting solves this problem by forming a continuous product from a metal (e.g. copper or silver) seed (e.g. metal rod). Breakouts A major problem that may occur in continuous casting is breakout of the liquid metal: for whatever reason, the solid shell of the strand breaks and allows the still-molten metal contained within to spill out and foul the machine. In most industrial environments this event is very costly as it leads to a shutdown of the strand and typically requires an extended turnaround involving removal of the spilled material from within the strand equipment and/or replacement of damaged machinery. A breakout is usually due to the shell wall being too thin to support the liquid column above it, a condition which has several root causes often related to heat management. Improper cooling water flow to the mould or the strand cooling sprays may lead to inadequate heat removal from the solidifying metal, causing the solid shell to thicken too slowly. If the metal withdrawal rate is too fast, the shell may not have time to solidify to the required thickness even with enhanced cooling sprays. Similarly, the incoming liquid metal may be too hot and the final solidification may occur further down the strand at a later point than expected; if this point is below the straightening rolls, the shell may break from stresses applied during straightening. A breakout can also occur as a result of