1. What does it mean to control coating weight? Bob Wilhelm Objective Control Ltd.

2. What does it mean to control coating weight? What a strange question! What is it meant to imply? Because coating weight is a stochastic property distributed over two sides of a two-dimensional strip, there is no such thing as “ the ” coating weight of the strip. Simultaneously meeting product specifications and producing product economically has deep implications for the control strategy.

3. Scanning Measurement

4. One scan of coating weight What do these variations represent? Cross- strip, along-strip, both, or neither? How should this information be used for purposes of coating weight control? 020040060080010001200 120 130 140 150 160 170 Cross-Direction Position (mm) Coating Weight (gsm)

5. Weight Distribution over a Coil

6. Weight Distribution as a Color Map

7. Visualizing profile stability

8. Separating Coating Weight Components : CD, MD, Residual Coating weight seen as a time series from the scanning measurement. 1000105011001150120012501300 120 140 160 180 200 220 Coating Weight (gsm) Distance from head of coil (m)

9. Complete Removal of CD

10. Power Spectrum of CD & MD 00.20.40.60.811.21.41.61.82 0 1000 2000 3000 4000 Power Spectral Density frequency (m -1 ) weight weight with cross-direction removed

11. Removal of Estimated CD 020040060080010001200 130 140 150 160 170 180 190 200 Coating Weight (gsm) Strip Distance (m) measured weight weight with average profile removed

12. Edge-Induced Bias Inclusion of edges can bias skew and crossbow computations. Skew and crossbow control control based on these results can make things worse. Virtual “ edge trim ” provides a simple solution.

13. Three Consecutive Coils with Coating Weight Transitions

14. Two-Sided Target Management

15. Constraint Scenarios a) Total weight minimized. Equal coatings maintained.

16. Constraint Scenarios a) Total weight minimized. Equal coatings maintained. b) Total weight and one side minimized with deviation from equal coating.

17. Constraint Scenarios a) Total weight minimized. Equal coatings maintained. b) Total weight and one side minimized with deviation from equal coating. c) Both sides minimized with deviation from equal coating.

18. Constraint Scenarios a) Total weight minimized. Equal coatings maintained. b) Total weight and one side minimized with deviation from equal coating. c) Both sides minimized with deviation from equal coating. d) One side minimized with side-to-side ratio constrained.

19. Two-Sided Target Management Nominal coating weight target Optimized coating weight target Total weight triple spot minimum spec Total weight single spot minimum spec Single side triple spot minimum spec

20. Target Management Dynamics Throughout a Coil 0100020003000400050006000700080009000 200 250 300 350 400 450 500 Coil C total Coating Weight Location in Coil weight nominal wt target weight setpoint scan average single spot min single spot max triple spot min triple spot max setpoint min setpoint max

21. Target Management Results CoilChange in Target (gsm) % Change in Target C-3.76-1.32 D-7.88-2.17 E-6.98-2.43 F-3.68-1.28 G-3.95-1.38 H-6.16-2.15 I-5.99-2.09

22. Conclusions (1) There is no such thing as “ the ” coating weight of a real strip. Controlling average coating weight across the strip is a practical and appropriate technique from a control viewpoint, but is, by itself, inadequate to guarantee either product quality or zinc savings.

23. Conclusions (2) Coating weight control requires that various coating characteristics be individually identified and dealt with: Cross direction Strip direction Residual Control intended to address one problem must be carefully designed to ignore variations caused by the others.

24. Conclusions (3) Active automatic target management is needed to maximize profit while guaranteeing quality. Automatic target management addresses the all-important “ residual ” variation. It is time to reexamine industry standard coating weight specifications in light of today ’ s production and control capabilities.

25. Thank you.