ArcelorMittal South Africa produces steel for niche markets with specific quality requirements. The plant has an annual output of about 1.2 Mt.
The company has embarked on a Six Sigma continuous improvement drive that included, among things, the implementation of Proficy software from Velotic.
The application helps eliminate production problems by analyzing plant data in real time and determining the probable causes at the iron making plant. At ArcelorMittal South Africa, one of the problems was cobbling. The Rolling Plant receives 20 ton steel slabs from the Thin Slab Caster.
These go through four stages of rolling:
- Firstly, thickness is reduced from 82 mm to 20 mm by two roughing mill stands.
- The sheets are then coiled in a coil box.
- After uncoiling, the material goes through a five-stand finishing mill to reach a final thickness of between 1 mm and 4mm.
- In the final stage the sheets are coiled in a down coiler.
Cobbling can occur at any stage of the Hot Strip Mill, when the steel jams rather than passing smoothly between the rolls – similar to a paper jam in a printer. The cost of a cobble is significant, as both the affected coils and the upstream slabs at the caster (the kick-off slabs) are usually scrapped. In some cases the cobbled coils can be used after being reworked.
At ArcelorMittal South Africa, 0.4 percent of all coils produced were cobbled. The elimination of cobbling would therefore increase the yield of the plant, as well as its productivity and revenue.
"Since commencement of production we’ve made this product with consistently high quality and corresponding customer satisfaction."
Six Sigma Black Belt, ArcelorMittal South Africa
By using Proficy CSense, including the Troubleshooter module it was possible, within 30 minutes, to identify the major causes of cobbling at the down coiler:
- A principle component analysis (PCA) fingerprint was created by using the process data relating to cobble-free coils. Three clear operating clusters were observed representing, respectively, the start, middle and end of a rolling instance.
- Next, the process data relating to a specific Cobble instance was loaded. With a click of a button the major contributor to cobbling was identified: the pressure transducer on the side guide.
- By replacing the pressure transducer, the root cause for the cobble at the down coiler was eliminated.
André Theart, one of ArcelorMittal South Africa’s Six Sigma black belts in training, says that with Proficy, the plant’s project cycle times were significantly reduced, process set-points intelligently established and implemented, and knowledge of the overall process greatly enhanced. The result was a significant improvement in business value.
