How does electrostatic spray painting work?

diudiu

1. The problem statement, all variables and given/known data

Why must the object that is undergoing electrostatic spray painting be earthed/grounded?

2. The attempt at a solution

I understand that during electrostatic spray painting, the paint droplets are positively charged and they are attracted to the negatively charged surface of the object. however, why must the object be earthed during the process?

sgstudent

It is for safety. In the metal body, you will have the side facing the spray to be negative while the other side is positive. So if its not grounded, once the spray's positive and the negative metal are neutralized, there is still a positive metal side which would redistribute itself VIA movement of electrons. So now if you touch the metal body, you will be electrocuted! Electrons will flow through you to the car and hence electrocutes you. But if it is grounded, electrons will flow up immediately, neutralizing the positive charges on the car body. Hope this helps

diudiu

hmm actually, the question in my paper to be exact was: 'why does the coat of paint on the object become very patchy with some areas being missed out when there is no earth connection at the metal object?'

sgstudent

Because of the positive ions that is left behind! The positive spray wouldn't want to go near those areas with positive as they are repelled by each other. So as a result, it leaves those patches and missed out.