The roller hearth tunnel furnace is the critical link between the casting unit(s) and the rolling mill. The tunnel furnace has two primary functions. The first is to heat the incoming strip to rolling temperature and then equalize temperatures. The second function is to act as a buffer zone between the casting operation and the rolling operation.

The furnace length is determined by several factors mill productivity, slab heating time, maximum slab dimensions and buffer time requirements. Usually these furnaces are designed to hold three to four full length slabs.

Typically, a slab cut to length enters the furnace at casting speed and is heated for the appropriate time. It then is transferred at higher speed to the discharge zone where its temperature becomes very uniform. Finally, the slab is discharged at rolling speed into the first stand of the Hot Strip Mill.

If there is a delay at the Hot Strip Mill, a roll change for example, the slab is held in the discharge zone and oscillated until the mill is again ready to roll.

These furnaces have a high degree of computer control. The control must receive information from the casting operation and the mill operation and then adjust the furnace operation to provide a seamless match. This sophisticated control includes product tracking, level 2 thermal modeling and process simulation.