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by Ron Joseph
December, 2001
Paint Curing and VOC Emissions
Q.
I am trying to help
a client obtain an air emissions permit for a drying oven. Aerospace
components are spray coated in a paint booth and allowed to air dry to tack
free condition, usually around 30 minutes. Coated parts are then moved to
the drying oven. The air district (SCAQMD) requires that we quantify the
emissions from the drying oven. Your methodology works fine for quantifying
total facility emissions from coatings, but does not identify how much of
that comes from the oven. So my question is how much VOC is left in the
coating at various intervals after the part has been coated. Obviously most
of the VOC comes off during the initial drying period while the part is
still in the paint booth. Everyone agrees on that, but nobody has any
empirical data for how much VOC remains in the coating after a specific
amount of time. Any help you could provide in the way of hard numbers or
addition resources would be greatly appreciated.
A.
If I were required to get data on the emissions at various stages of drying I
would do the following:
- Perform a Method 24 analysis on the coating, but instead of curing the
coating in a laboaratory oven, cure them in the actual production oven at the
time and temperature that all the workpieces are cured. This test is very
easy to perform. I have done it in painting operations numerous times. DO
NOT USE MSDS DATA. ONLY USE THE ACTUAL MIXED COATING THAT IS BEING APPLIED
IN OTHER WORDS, TAKE IT OUT OF THE PRESSURE POT AT THE TIME OF PAINTING. DO
NOT MIX THE COATING YOURSELF IN A LAB.
The SCAQMD loves statistical data; therefore conduct the test on a sufficient
number of sample so that you can get a reasonably good mean and standard
deviation.
- Apply the coating to several metal panels in exactly the same manner that
the workpieces are coated. Insure that you use the same mixed paint, a
sample of which was earlier taken from the pressure pot.
- Remove a few of the panels at each stage of the curing process and
immediately transfer them to the oven. Determine the weight loss for each
set of panels. Calculate your statistics.
- If you do this right, you will know how much VOC is given off in the oven.
- If for any reason you get erroneous results, you might need to hone your
procedure some.
Again, I've performed these tests numerous times to determine the transfer
efficiency of a paint application, and I know that it works.
Good luck. |
