In electric paint application, a rotating atomizer under voltage generates negatively charged paint droplets and accelerates them to several hundred kilometers per hour. The flight of the droplets is guided by a high-voltage field between the atomizer and the component. This allows the spray mist, which normally leads to losses of over 50 percent, to be reduced to 20 percent.
Basic research for better painting results
A team of researchers from the Fraunhofer Institute for Manufacturing Engineering and Automation IPA led by physicist Dr. Oliver Tiedje has now researched this process together with engineers from Esslingen University of Applied Sciences. In order to optimize it, they determined in a joint research project when, how and where the droplets pick up electrical charges.
In the first step, they determined how the conductivity of paint can be improved by adding additives. The speed and size of the droplets and the quantity of negative charges that arrived on the coated component were determined and evaluated.
Surprising findings
The result was surprising: contrary to the researchers' assumption, the number of registered charges did not increase when more paint was sprayed. It remained the same. The explanation was only provided by the simulation of the experiments: it showed that the charges emitted by the atomizer are located at the interface between the paint and the air. If more paint is applied, the paint film on the atomizer becomes thicker, but the surface remains the same. Therefore, the amount of charges does not change.
The computer model, which the teams worked on for two and a half years, takes into account all the phenomena of the electro-hydrodynamic painting process for the first time. Among other things, the viscosity and conductivity of the paint, the shape and rotational speed of the bell and the level of voltage applied were taken into account.
Optimized processes for efficient painting
In future, the simulations can help paint manufacturers to determine the optimum amount of additives for electrostatic painting processes. The digital models also support system manufacturers in testing new atomizer or bell designs or processes. Paint stores can use the simulations to virtually optimize the process parameters for different components. Time-consuming and material-intensive trial painting processes can thus be reduced to an absolute minimum.