l. del fabbro, m. campolo, a. soldati 26 june, milano, italy numerical evaluation of spray painting...
TRANSCRIPT
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 TechnologyUniversità degli Studi di Udine
Trends in Surface Technology 08
Big ones
… objects to be painted …
… and small ones
Waste
liquid gas solid
Solvent
Air
Painted product
How difficult is the process? A mass balance approach …
Paint
Transfer efficiency (T.E.)
η=Qtransferred / Qsprayed
T.E. is as low as 8 ÷13 % for glasses !!!
• Significant overspray
indoor air quality
VOC emissions
• Waste of raw materials
additional costs
Improve the T.E.!
… and consequences of inefficient spraying…
60
70
80
90
100
8% 9% 10% 11% 12%
Spray Painting Transfer Efficiency
Pai
nti
ng
Co
st
Increase in spray painting efficiency
Savings
Is it worth valued ?
Larger transfer efficiency
Efficient use of raw materials
Reduced emissions/low costs for end of pipe solution
Same productivity/same quality
WastesSolvent
Air
Painted product
Paint
… the industrial optimum…
A few point % increase in T.E. would be a good starting point …
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…
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”
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
The spray painting system
Spray gun
Spray hood
1. Spray gun: flow field …
DNS + Lagrangian tracking:100 h CPU on super computer @ CINECA !!!
Small droplets
Optimum size droplets
Large droplets
Low T.E.Large overspray
Good T.E.Good surface quality
Large T.E.Reduced overspraySurface defects
2. Transport/deposition of droplets
glasses
Computational domain
Head of spray gun
Paint mix
Atomizing air
Air to squeeze the jet
0.1 micron
10 micron
Droplet trajectories
Transfer efficiency
0102030405060708090
100
0.01 0.05 0.1 0.5 1 5 10 20 30 40
Droplet size [micron]
%… and transfer efficiency …
Optimum size droplets
Spray paint hood: flow field
1 micron
η = 13%
Droplet trajectories
Travel time distribution for paint droplets
0102030405060708090
100
0.01 0.05 0.1 0.5 1 5 10 20 30 40
Droplet size [micron]
%
Droplet size distribution is crucial Use the best possible!
Low T.E.
High T.E.
… hints for optimization …
Characterize Droplet Size Distribution
(on line in industrial systems)
•spray0.1µm to 2000µm misure on-line
Particle size distribution
dp
%
… and work in progress …