Metal Finishing Guide Book


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appendix b CALCULATION OF VOC IN COATINGS This appendix provides an overview of the most important calculations, which environmental engineers and paint facility staff need to perform on a regular basis. The calculations are actually quite easy to perform, and for each new concept one example is provided. CALCULATING THE VOC OF A SIMPLE COATING MIXTURE You wish to calculate the VOC content for a mixture comprising 1 gal of red alkyd enamel and 1/4 gal (0.25 gal) thinners. The respective VOC levels are 2.5 lb/gal for the enamel and 6.8 lb/gal for the thinners. To perform the calculation, set up a table where the first column lists the names of the components that you will be mixing together and the second contains the number of gallons to be added. In the third, you enter the VOC content as given to you by the paint manufacturer on the Material Safety Data Sheet (MSDS) and the last column is the total amount of solvent (or VOC) for each of the components. In this case, the table would appear as shown in Table I. Because the EPA assumes that all of the VOC (mostly the solvents) evaporates to cause emissions, the last column is headed "Emissions," instead of "VOC." Step 1: Multiply the number of gallons by the VOC content to arrive at the total amount of VOC (or Emissions) for each component. Step 2: After completing the last column, total the number of gallons in Column 2 as well as the lb of VOC (Emissions) in the mixture, Column 4. In this case the total number of gallons is 1.25 and the total Emissions 4.2 lb. Note that you do not need to total Column 3 as the result is meaningless. Step 3: The final step requires you to divide the number of gallons in the mixture into the total Emissions. Therefore, the VOC of one gallon of the mixed coating is: VOC = 4.2 lb/1.25 gal = 3.36 lb/gal In other words, if someone were to sample the coating you have just mixed, the VOC content would be 3.36 lb for one gallon of the mixture. If your state coating rule specifies a maximum VOC content of 3.5 lb/gal, your mixture is in compliance. CALCULATING THE VOC OF A TWO-COMPONENT COATING MIXTURE You wish to mix a two-component coating in the ratio four parts Component A and one part Component B. For the time being, you will not add any thinners. From the MSDS you get the following information: Component A = 3.6 lb/gal Component B = 2.2 lb/gal Set up the same table as before and insert the given information into columns 813

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