Ask the Expert Question-and-Answer Archive

by Ron Joseph

November, 2003

Improving Efficiency of Automotive Paint Spray Operations

Q. We are two students doing our bachelor degree project where we are to improve the efficiency of a spray booth. The problem that the company is having is that there is heavy paint contamination on the booth walls, roof and the 8 robots due to overspray. This means that the operators and other personnel need to enter and clean the booth and its equipment after a certain amount of painted cars. Our goal is to minimize the contamination and increase the amount of painted cars before cleaning is needed.

To give you an idea of the spray booth, here is a short technical description.

The paint used is a solvent based paint which is sprayed with an electrostatic gun mounted on a robot (4 robots on each side of the line).

The booth ventilation system is a down draft with two fans on top of the booth and a filter carpet to obtain an equally distributed air flow. Beneath the floor there is a venturi water system which operates as a filter separating the paint from the air.

Average temperature in booth is 21°C (69°F) while the humidity value is 60%. The booth dimensions are L18m x H4m x W5m (L59ft x H13ft x W16ft).

The air velocity (measured 3 feet beneath the roof) is approximately 0,35m/s (69ft/min).

Cars are being transported on a rail through the booth with a speed of 6m/min (20ft/min) while being painted.

After exploring your website we have become aware of the many parameters affecting the result of a paintjob. What is your opinion in this case and which parameters do you think we should concentrate us on particularly.

A. Without seeing the spray booth operation it is difficult to give you much information. However, the most likely source of the contamination is from the spray guns. I have seen automotive robot operations that are extremely transfer efficient, and I have also seen very inefficient operations.

The most important parameters are in the spray gun setup. Does the company measure the resistivity of the coating to insure that they are getting the best possible wrap from the electrostatic spray guns? Are the guns of the conventional type or are they HVLP? Insure that the atomizing air and fluid (coating) pressures are as low as possible without slowing down the production line.

If you are able to maximize the paint automization and fine-tune the guns, you will see an immediate drop in paint overspray.

Another factor to consider is the turbulence of air inside the spray booth. Insure that the air is truly moving down toward the water trough and not moving horizontally in the booth. Often the air is so turbulent that the walls and ceiling are covered with overspray. It is not easy to measure for turbulence, but you can do so by using appropriate velometers.

If you can maximize the operation of the guns, and cut down on air turbulence in the booth you will save the company tens of thousands of dollars in paint usage and hazardous waste. I have been successful in doing this and was told by one customer that total savings came to over $500,000 per year. Not bad.