Calculations: VOC, HAP, Exempt Compounds

Calculating PERCENT WEIGHT SOLIDS FROM PERCENT VOLUME SOLIDS

Q. We are a Tier I automotive supplier and injection mold and paint exterior plastic parts.  Paint material is purchased by our suppliers in pounds and we receive the paint in drums measured in pounds.  If it falls within the specified range of lbs/gallon (55 gallon drum) then it's acceptable.  The more solids in the paint the more it weighs per gallon.

Our problem is that we purchase the paint material (including solvents) by the gallon and not by the pound.  We've been unable to get our suppliers to convert to selling it by the pound.  The cost detail that we receive is based on gallons, and the solids are given as a volume solids, as a percentage, and not in weight.

We need to ensure that the paint we actually receive is equal to what we pay for.  Since the price is based on % solids are we paying more per gallon than we actually receive?  How can we convert volume solids to weight solids, or how can we compare what we receive in lbs to what is quoted in volume?

A: In most cases the conversion is relatively easy.  From the MSDS you should have the approximate percent weights for each of the volatile ingredients.  By subtracting from 100 you can determine the approximate % weight solids.

If you want a precise measurement, your in-house QC lab can easily perform test ASTM D-2369 on the coatings you purchase.  If you don't have an in-house lab, then an outside lab can easily perform the test.

For your information I offer two- or three-day classes on calculations for the coatings industry.  If you are interested, please visit www.ronjoseph.com/calculations.htm for more information or upcoming locations.

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