Bell heaters for the annealing mill. Each one fits over a single stack of ribbon coils.

Steel is delivered to the site in ribbon coils, from a steel furnace. You can see one of the coils, in fairly poor shape, next to my friend in the shot below. The first stage is to remove the oxidation, that’s where the pickling line comes in. The ribbons are fed through acid tanks to remove the oxidation layer, and then recoiled. In the gallery below, there is a shot of the pickling tanks, though there isn’t much to see.

Coil of Steel Ribbon (with friend for scale)

The ribbons are then fed into the temper mill, which hardens the steel. From there, the tandem mill produces whatever thickness the customer desires in the steel ribbons. I wasn’t able to get any decent shots of the tandem mill, as it was shrouded by tarps to keep it warm, or the temper mill, because the shot I took didn’t turn out very well.

An unfortunate side effect of the cold mills is that the steel loses some of its workability, and is more difficult to stamp or press. In order to counter this effect, an annealing mill carefully heats the steel to its re-crystallization temperature, allowing the crystals to re-align, and then it is slowly cooled back to room temperature for delivery. Annealing is carried out in several different ways. In the photos below you can see pillars of corrugated metal. These pillars cover a stack of three or four coils, and help control the heating and cooling rates. These pillars can be heated individually with a heating bell, or in groups of three via a heating box. I’m not sure of the benefits/drawbacks of the two techniques, but you can see that both are in use interspersed in the same facility below.

You can view these photos in a flickr set.