1. L. Del Fabbro, M. Campolo, A. Soldati 26 June, Milano, Italy Numerical evaluation of spray painting efficiency in industrial applications: the spray painting of glasses CIFI - Centro Interdipartimentale di Fluidodinamica e Idraulica And Department of Energy Technology Università degli Studi di Udine Trends in Surface Technology 08

2. Big ones … objects to be painted … … and small ones

3. Waste liquid gas solid Solvent Air Painted product How difficult is the process? A mass balance approach … Paint Transfer efficiency (T.E.) η=Q transferred / Q sprayed T.E. is as low as 8 ÷13 % for glasses !!!

4. Significant overspray  indoor air quality  VOC emissions Waste of raw materials  additional costs Improve the T.E.! … and consequences of inefficient spraying…

5. Increase in spray painting efficiency Savings Is it worth valued ?

6. Larger transfer efficiency Efficient use of raw materials Reduced emissions/low costs for end of pipe solution Same productivity/same quality Wastes Solvent Air Painted product Paint … the industrial optimum… A few point % increase in T.E. would be a good starting point …

7. 2006-2008: Research project to reduce the use of solvent in the spray painting of glasses (in cooperation with Safilo S.p.a.) 2006-2006: Feasibility analysis of research project to reduce the use of solvent in the spray painting of glasses (in cooperation with Safilo S.p.a.) 2000-2001: Characterization and evaluation of spray painting transfer efficiency in industrial installations (in cooperation with CATAS) Our previous experience in the field…

8. Present Case-Study: painting glasses Complex shapes Many different materials (metallic/non metalic) High quality standards …is there space left for process optimization? “Fashion and Luxury Eyewear/Sunglasses”

9. Step 0: Analyse the industrial process Evaluate T.E. on the field (T.E. = 8 ÷12 % for glasses) Step 1: Analysis of spray painting process for a spray gun Numerical simulation of transport/deposition of spray droplets Evaluation of spray painting efficiency Step2: Analysis of the industrial spray painting system (spray gun + hood) Objectives: identify control parameters to improve T.E. Steps of the analysis

10. The spray painting system Spray gun Spray hood

11. 1. Spray gun: flow field … DNS + Lagrangian tracking: 100 h CPU on super computer @ CINECA !!!

12. Small droplets Optimum size droplets Large droplets Low T.E. Large overspray Good T.E. Good surface quality Large T.E. Reduced overspray Surface defects 2. Transport/deposition of droplets

13. glasses Computational domain Head of spray gun Paint mix Atomizing air Air to squeeze the jet

14. 0.1 micron 10 micron Droplet trajectories

15. … and transfer efficiency … Optimum size droplets

16. Spray paint hood: flow field

17. 1 micron η = 13% Droplet trajectories Travel time distribution for paint droplets

18. Droplet size distribution is crucial  Use the best possible! Low T.E. High T.E. … hints for optimization …

19. Characterize Droplet Size Distribution (on line in industrial systems) spray 0.1µm to 2000µm misure on-line Particle size distribution dpdp % … and work in progress …