Computer Systems and Software


Fig. 2. Analyses of data collected before and after reveal the impact of improvements to the calibration procedure for the laying head at the Laverton Rod Mill. The more accurate true temperature estimates help the mill ensure that the levels of scale on its rods are within acceptable boundaries.


result to determine the potential savings accrued through reduced variation and scale weights. Pareto analysis determined which rod grades caused delays


on the wire drawing machines. Changing the characteristics of the feed used to create the steel rods at the Laverton Rod Mill was not an option, so the team looked for other ways to reduce the percentage of rod scale and increase the wire mill’s yield. They ran experiments to test the cooling processes used at the rod mill, the descaling and drawing practices used at the wire mill, and operational parameters at both mills. First, they ran a test to evaluate the effects of cooling


conveyer parameters on the amount of scale. They also measured the temperatures of the wire drawing block and the laying head at the rod mill. Minitab analysis revealed a significant difference when the reform temperature on the cooling conveyer was reduced by 30 per cent. Next, they tested the effects of drawing methods on yield.


For the control run and the test run, the team set up production lines with new dies, new lubricant for each die, new brushes in the descaler unit, and kept the run speed consistent. The run using their trial parameters resulted in lower


temperatures, cleaner product, lower die wear, and less visible scale. A strength test showed no statistical difference between the quality of the trial product and the control product. They measured die wear on the wire drawing machine


and found the new parameters also dramatically affected the life of the drawing dies. In one test, the diameter of wire from a die was 6.22mm at


the start of the run. After running 15tonnes of wire using the control rod, the die had reached a diameter of nearly 6.32mm. Die wear for the line that used the trial rod was significantly less - after 15tonnes, the diameter was below 6.24mm. After implementing various improvements, the team used Minitab to analyse scale weight and laying head temperature for a recent rolling of 7mm wire. Minitab’s analysis confirmed that the rod mill could produce rods suitable for mechanical descaling, with a much lower yield loss than in the past. Using Minitab, the team created control charts to clearly


show the effect of trials undertaken at the mill and effectively communicate their results.


Results


Team efforts have improved the cooling process at the Laverton Rod Mill. Operators can better control laying head temperature, and Minitab analysis has confirmed that the improved cooling process significantly reduced scale weight. The Minitab histograms show how improvements to the


rod mill’s calibration procedure reduced the gap between the estimated true temperature and the temperature reported by the laying head. This reduced real laying temperatures compared to previous rollings, and lower laying temperatures reduce yield loss due to mill scale for rod mill customers. The new rod from Laverton is a much cleaner, visibly


superior product for the Geelong Wire Mill. By reducing the amount of scale, increasing yield, and realizing savings in labour and consumables, OneSteel anticipates saving approximately $275 000 annually. The reduction in scale also offers additional downstream processing benefits. With the improvements confirmed, OneSteel’s project


team entered the Control phase of their DMAIC process. They used Minitab’s control charts to lock in the changes they made to procedures and maintenance activities. That made it easy to sustain the improvements and ensure that the savings continue in future years. l


Fig. 3. When One Steel’s project team measured scale on rods from the Laverton mill and analysed their data in Minitab, they found 62 per cent of the samples they tested had unacceptably high scale levels.


Enter 27 or ✔ at www.engineerlive.com/asia


Eston Martz is with Minitab Inc, State College, PA, USA. www.minitab.com


www.engineerlive.com 27


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