Ask the Expert Question-and-Answer Archive

by Ron Joseph

November, 2003

Booth Oven Splilt in Automotive Painting Operation

Q. We are looking at installing a paint line to coat engines and have a question on the Paint Booth versus Cure Oven Split.

Background:
Engines enter the first paint booth following a wash booth (engines are warm). The first coat is applied in the first booth that has a residence time of 4 minutes. It then moves to a flash off enclosure for 4 minutes. It then enters the second paint booth where a second coat of the same paint is applied. It takes 4 minutes to apply this second coat and then moves to a flash off enclosure where it remains for 4 minutes. Each application has a dry film thickness of approximately 2 mils. It then enters a long cure oven.

The paint contains 4.3 lbs/gal VOC, 61.9% by weight solids, has a air cure time 45-60 minutes. The main solvents are methyl propylketone (16% wt), aromatic light naphtha (6%), and toluene 3%.

Air flow rate at the booth is downflow at 80 feet per min. There is a 10 foot vestibule with 5000cfm each at the entrance and exit of the booths.

In your proffessional judgement and based on your knowledge of the industry, what do you think the VOC split would be between the paint booths and the cure oven? I look forward to hearing from you soon.

A. Thanks for the question and the details. I wish I could give you an educated guess, but I simply can't. There are too many factors that influence the booth/oven split. I recently visited an automotive assembly plant to perform a paint operation audit, and the folks there told me that they do not measure this value. Instead, they have come to an agreement with their air quality agency that they will simply assume an 80/20 split, with 80% being emitted in the spray booth. I asked them if they have verified this, and they told me that it was more than they wanted to do. They simply based their emissions calculations on the agreed-upon assumption.

Having seen several automotive assembly plant painting operations I think that the 80/20 ratio seems to be reasonable. Of-course, you can perform stack tests and come up with some other ratio, but even that will change from one day to the next.

What are your reasons for wanting to know this ratio? Is it to calculate your emissions? If so can you simply come to an agreement with your permitting agency? Please get back to me.