Solution for a global economical smooth pot roll rotation B. HÜBNER – Bimetals, Liège, Belgium

1. Solution for a global economical smooth pot roll rotation B. HÜBNER – Bimetals, Liège, Belgium

2. Content Introduction Importance of the pot rolls rotation at the HDG process Constraints for the best Zn coating quality and appearance Correct design and materials choices Constant development

3. Pot Rolls, an Old problem Fig. 1: sketch of the First CGL Fig. 2 : Zn squeeging rolls position initially undriven rolls finally driven rolls • From the beginning with the first Sendzimir CGL process built in 1931 • N²+ H² reducing atmosphere for the strip surface preparation prior the Zn coating • Original mechanics and problems to be solved with the liquid Zn +Pb at 450°C effects • Original materials adopted for immersed rolls and arms

4. Some Old designs The First Generation • Problems with the mechanics at the first European CGL at Maubeuge (France) in 1935 • First development for a better rotation and longer life time of the immersed equipment • Housing and bearing approach with the Armco steel advantages in the liquid Zn Fig. 4 : original gap adjusting systems Fig.5 Supporting plates on bushing in Arms Fig. 3 : weld coated shaft

5. Some Old designs: bush-system The 2nd Generation • Bushes and shafts evolution according harder Co base materials • Progress of the assembling and narrow mechanical tolerances • Right combination for corrosion and erosion resistance for the bearing’ tribological components Fig8 Design for Roll Shaft made of solid Co Based superalloy Fig 7 Welded coating directly on roll shaft TABLE 1 – POS 3

6. Some Old designs: segment-system • Importance of the components’ lifetime for high speed process • Industrial targets and costs reduction using adequate bushing components • Components ’reconditioning and recycling possibilities respecting the environment Fig9 Full Co Base bearing after usage, male and female Fig 10 b female part of bearing after acid pickling

7. A Quick Summary of FormerSolutions

8. Some present solutions and Maintenance recommendations • Perfect rolls straightness and geometry for a smooth rotation • Necessary strict procedures and tolerances for the global hard ware • Assembling stand and maintenance • Optimized tribological couple considering the working surfaces’ HRc+Ra • Gaps’ adjustment values (G-g) Fig 11 Different system for Corrector and stabiliser rolls a. stable position Fig 12 Pot roll design used "2 rolls" 3 rolls" b. hollow open c. hollow closed

9. Some present solutions • Chronological improvements • Best compromises considering costs-materials availability-maintenance-lifetime and strip quality all along the campaign • See Table 1 Fig 13 Various Bearing designs a b c d

10. The Case of Roller bearing • Usage of Roller bearing was a Dream for the Zn hostile environment (T°-corrosion-expansion) • Experiments revealed it was an Inadequate solution • Industrial trials 1995-2002 • Different designs and materials used for the tried assembling • Costs and unsolved problems Fig. 14 : Bi-metallic roller bearing

11. The Latest Solutions • The best compromise for costs and lifetime • Important objectives and compromises for the best design • Brain storming for the necessary improvements to minimize the hard working conditions ‘effects • Plug and use concept for the components • See Table 2 for the existing solutions and the possible comparisons Fig.15 a Fig. 15 b Bushing system Complete housing

12. The Total Cost Approach Yearly costs Costs and wear according production with “a 3 rolls design” for a modern CGLine Costs /T in 2011 for a “60 days campaign” assembly components lifetime Wear values to be considered and scraped materials recycling possibilities Include reconditioning

13. The Total Cost Approach

14. Conclusion 80 years history of Continuous HDGLine technical development Possible progress for the submerged hardware thanks cooperation in engineering No universal solution: each case requires detailed analyses for a judicious solution