An environmentally-friendly technology that uses water instead of hazardous acid to clean hot-rolled black steel coil is in use at a West Midlands steel processing plant. known asSCS
, the process was installed atServosteel's
main facility in Dudley last month(pictured below)
and has the capacity to process 200,000 tonnes of steel coil a year.
SCS differs from the traditional steel cleaning method, pickling, which uses an acid solution to clean steel before it is processed further. SCS uses only high-pressure water and specially-developed abrasive brushes. After cleaning, the steel is claimed to remain rust free under normal conditions without the need for any coating or covering with oil, which is required for pickled coil.
The system has proved effective in several commercial applications in the US, said its developers, Illinois-basedRed Bud Industries
. The company claims that three-year-old SCS-treated coil samples still show no signs of rust. This is because the brushing process removes the topmost layers of scale, leaving only a seven micron-thick layer of wustite — an iron oxide in its mineral form.
Wustite's chemistry differs from that of the top layers because there are fewer oxygen atoms in each molecule, which leaves the treated coil with a rust-inhibiting surface.
The process works not only when cleaning coil, but also flattening it. Steel, in its natural state, is not flat and a hot-rolled sheet coil will generally contain imperfections such as wavy edges and excessive crown. These must be removed to produce a flat steel sheet that will remain so during subsequent manufacturing operations such as laser, plasma and punch cutting.
SCS is able to do this with roller levellers, combined with the tension generated by the recoiler. This works on even poorly-shaped material with significant buckling or wavy edges, which enables the system to reclaim secondary coils.
It was after seeing samples of SCS-treated steel that Servosteel's managing director, Jim Spencer, decided to bring the SCS line to his company. Spencer said that after 50 years in the steel industry he has never seen steel with such an astonishingly smooth finish.
'With this process we have a very flat, very clean product that will not go rusty,' he said. 'At the same time it doesn't have oil, and that's a great assistance in many manufacturing processes like welding and lasering because you can weld quicker and get stronger joints.'
He also said that from a processing plant's perspective, SCS is much simpler than pickling methods. 'Pickling creates its own problems because you have this acid, which is around 80ºC. It has to be heated, and is very costly,' he said. 'Eventually the acid that will take up the mill scale has to be cleaned or disposed of — in itself an expensive process. SCS brushing is just a mechanical process, with water taking away the rust and mill scale.'
As an added environmental bonus, Spencer said the SCS system includes a sophisticated filtration system to recycle and re-use the water. The only by-product produced in the process is the remaining residue of metallic scale, which will be recycled with other steel scrap.
'Of course there are health benefits too for those working with SCS-treated steel,' said Spencer. 'There are no fumes coming off the wells or lasering, no oily clothing and no risk of dermatitis. It's an extraordinary thing where everybody wins — us, the manufacturers and the employees.'