The steel story: magic of the hot strip mill

Journalist Glen Humphries and photographer Sylvia Liber pull back the steel curtain and take you deep inside BlueScope's Port Kembla steelworks.

Illawarra Mercury
May 9, 2016

What they do to steel at the hot strip mill just doesn’t seem possible.

Having seen and touched those long thick steel slabs it’s really hard to imagine them being stretched into something almost paper thin.

And yet, that’s the sort of magic they do at the hot strip mill.

The mill takes a slab of steel of around 12 metres long and roughly 25 centimetres thick and turn it into something that could be almost a kilometre long and as slim as 1.5 millimetres.

Sure, there’s science - and brute force of machines behind it - but watching that slab get stretched out is a sight to behold.

The process starts at the far end of the 800-odd metre-long hot strip mill, where slabs arrive from the slab yard and are loaded one at a time in the furnace.

Depending on what the end requirements are, the slabs will be heated (by the use of gas from the coke ovens) to between 1150 and 1250 degrees Celsius.

Once inside they slowly move through the furnace until they come out the other side three hours later. And they’re very, very hot.

Once out of the furnace the slab is hit with a spray of water to remove the scale (a protective coating that naturally forms on the slab) before being sent down a long conveyor belt stretching several hundred metres to the roughing mill.

A crane prepares to pick up two slabs and deliver them to the hot strip mill furnace to heat them up before rolling them flat.
A red-hot slab of steel moves between two work rolls, which will flatten the slab.
After the steel has been rolled flat it is sprayed with water to keep it at the right temperature for the finishing procedure.

To break it down, the roughing mill is basically two large rollers in between which the hot steel passes.

Depending on the thickness required, it will make either five, seven or nine passes.

And, at each pass, a computer will bring the two rollers closer together to squash and stretch the slab.

Once you see this happen it’s easy to understand why the conveyor is several hundred metres long and while the building is about a kilometre long - they need that length to fit the long, flattened strip of steel.

During the lengthening, water is used to keep the steel at the desired temperature.

With 3000 litres of water used to make each tonne of steel, it’s easy to see why BlueScope recycles the water, avoiding the need to use mains water.

After the roughing mill, the long strip of steel is rolled into a coil to retain its heat before being unrolled again and delivered on the conveyor to the finishing mill.

This is the section where the fine-tuning happens.

The roughing mill is where the brute force is applied in flattening the steel.

The finishing mill is where the subtle actions are taken to get the steel to the exact thinness required.

After that, the strips are coiled up and passed underneath the road to the nearby coil processing area, where they’re stored untilt the next stage in journey – which could be out the gates or to another part of BlueScope.

Steel slabs roll out of the furnace and onto a conveyor line, which will take them to the roughing mill where they will be flattened and stretched.
A steel slab enters the roughing mill to get rolled flat. It will move back and forwards several times as it is flattened to the required thickness.
Shift leader Mick Grogan.
Hot strip mill operations manager Milco Stojanoski.
The hot strip mill offices, opened in 1955 by Prime Minister Sir Robert Menzies, is nicknamed "the Taj". It's short for "Taj Mahal" and a reflection of how grand the building looked when it first opened.
Next week we look at coil processing.